Breakthrough Discoveries

In celebration of the 60th Anniversary of the ISN, the ISN Research Working Group (RWG), under the leadership of Chair, Adeera Levin, and Deputy Chair, Masaomi Nangaku, publishes a monthly series, “Breakthrough Discoveries”.

This series highlights 60 + 1 historical discoveries of significant impact to the nephrology community. So that the selection of discoveries was globally representative, the leadership of the ten ISN Regional Boards were asked to provide references from their respective regions. Subsequently, Leon Fine, Pierre Ronco, and John Feehally were advisors and the RWG leadership and the ISN Executive Committee reviewed and voted for the final selection.

Every month in 2020, the ISN RWG, supported by the ISN Young Nephrologist Committee, highlights and discusses five breakthrough discoveries.

This series frames the year of celebratory activities, and highlights ISN’s commitment to research, collaboration, and global community, as well as the achievements ISN has made through its members and supporters.

By Sabine Karam MD

The Italian anatomist Marcello Malpighi (1628–1694), often referred to as the founder of microscopical anatomy, is credited for the first microscopic description of the glomeruli. He described them as dark, vascular structures resembling fruit suspended from a branch (… quae sanguineis vasis atro liquore turgidis in speciolae arbori formam productis, velut poma appenduntur). He demonstrated their continuity with the renal vasculature in ‘De renibus,’ a section of ‘De Viscerum Structura Exercitatio Anatomica’, originally published in Bologna, Italy, in 1666 and then in London, in 1669(1). In 1782, Alexander Schlumlanski (1758-1795) described ‘de Structura renum’ in his dissertation as a connection between the circulation and the uriniferous tubules, deduced by experimenting on pig kidneys(2). However, it was the surgeon and anatomist William Bowman (1816-1892) who elucidated the capillary architecture of the glomerulus and the continuity between its surrounding capsule and the proximal tubule in detail (see Discovery #3 by Lili Zhou). He presented his findings in the paper “On the Structure and Use of the Malpighian Bodies of the Kidney”(3). Nonetheless, the term glomerulus would come into usage only a few years later in the mid-nineteenth century. It seems to be derived from the Latin word ‘glomus’, which means ‘ball of thread’(4).

References

  1. M. M. De Viscerum Structura Exercitatio Anatomica. Londini: Typis T.R. Impensis Jo.Martyn;(London). MDCLXIX1669. p. 83–4.
  2. A. S. Dissertatio inauguralis anatomica De Structura Renum MDCCLXXXII. : Argentorati (Strasbourg): Typis Lorenzii & Schuleri;; 1782.
  3. Todd Bentley R BW. The physiological anatomy and physiology of man. West Strand,London:John W Parker and sons. 1859;2:482-507.
  4. Merriam Webster Dictionary. Glomerulus.

By Yosuke Hirakawa
The University of Tokyo Hospital

The symptoms of kidney disease are non-specific; therefore, diagnosis of kidney disease without laboratory testing is difficult. This was especially the case in the early 19th century. Surprisingly, the first identification of kidney disease was made by Richard Bright in 1827 before the identification of creatinine and routine measurement of urea. He extensively examined patients with proteinuria, anasarca, and uremia by checking urinary albumin and renal morbid anatomy in his work as a physician at Guy’s Hospital in London (1, 2). Today, some of his cases would be diagnosed as having nephrotic syndrome caused by glomerulonephritis. (3). Identification of what became known as “Bright’s disease” made a huge contribution to medicine. The most important aspect is the distinction Bright made between patients with kidney diseases and patients with cardiac diseases. After this differentiation, the characteristics of kidney disease patients started to be eagerly examined, and it was followed by increased urea and creatinine levels being identified shortly afterwards as major hallmarks of kidney disease.

References

  1. Boss J. Richard Bright’s Reports of Medical Cases (1827): A sesquicentennial note. Bristol Med Chir J. 1978;93:5-6, 18.
  2. Cameron JS. Bright’s Disease Today: The Pathogenesis and Treatment of Glomerulonephritis – I. Br Med J. 1972;4:87-90
  3. Weller RO, Nester B. Histological reassessment of Three Kidneys Originally Described by Richard Bright in 1827-36. Br Med J. 1972 Jun 24;2:761-3.

By Lili Zhou
Nanfang Hospital, Southern Medical University

The kidney is the most important organ in the human body to excrete urine and maintain the balance of water and electrolytes. These processes take place through the subtle mechanisms of the nephron, a tiny unit of workforce within the kidney. In 1842, after two years of exploration, Dr. William Bowman, a famous English surgeon and anatomist, discovered the nephron’s true nature. Through repeated injections from the arteries, tubes, and veins in multiple species’ kidneys, he found the real structure of the Malpighian bodies, as well as their connecting tubes and circulation. The Malpighian bodies, called glomerulus today, originate and gradually subdivide from the afferent artery terminal twigs to become two rounded capillary vessels tufts. These vessels ultimately converge to become one efferent channel (smaller in size than the afferent) to enter the capillary plexus surrounding the uriniferous tubes (proximal convoluted tubules, loop of Henle, and distal convoluted tubules). The interconnected capillary plexus surrounding the tubes serves as the portal system in contact with the tubes’ basement membrane to renal veins. The tubes are the extension of Malpighian bodies’ capsules (Bowman’s capsule) and expand tortuously near the Malpighian bodies but straighten when proceeding toward the excretory channel (collecting duct). All these features retard blood flow and delay the excretion of nutrients into urine to maintain the balance of water, sugar, and electrolyte assimilation and excretion. This revolutionary discovery opened a new era in physiological and pathological research in kidneys.

References

  1. W. Bowman. On the Structure and Use of the Malpighian Bodies of the Kidney, with Observations on the Circulation through That Gland. Philosophical Transactions of the Royal Society of London Vol. 132 (1842), pp. 57-80.

Rolando Claure
Universidad Mayor de San Simon School of Medicine, Cochabamba, Bolivia.

Urinary sediment has been used as a diagnostic tool since the 17th century(1) and Pierre Rayer occupies a special place in the history of nephrology for his attempt to classify various diseases using this important diagnostic tool. Alongside his intern, Eugene Napoleon Vigla, Rayer revolutionized the study of kidney diseases by using microscopy to analyze urinary sediments, describing crystals, cells, casts, and yeasts(2, 3).

At the Hôpital de la Charité, a microscope became available in 1835 and Rayer promptly set up a program to investigate urinary sediment findings in various forms of kidney diseases. His proposed classification was based on clinical findings, urinary microscopy, and gross specimens whenever possible. Renal diseases were divided into acute nephritis with many red blood cells and too much albumin in the urine, and chronic albuminuric nephritis corresponding to what is now known as nephrotic syndrome. There was also mention of suppurative forms of nephritis, with pus cells in the urine, the result of either blood-borne or ascending infection of the kidneys(4).

After this first description, routine chemical analysis of urine and microscopic examination of the sediment were introduced during the first half of the 19th century. After a first wave of interest, the use of urinary sediment has progressively decreased(5); urinary microscopy analysis is now performed mostly in central laboratories and is infrequently performed by nephrologists who have lost the expertise to identify some types of casts and/or cells in order to perform clinical correlations(6). Nephrologists should reclaim this noninvasive test, since combining it with a comprehensive clinical evaluation and new biomarkers would provide new insights into renal diseases(7).

References

  1. Armstrong JA. Urinalysis in Western culture: a brief history. Kidney Int. 2007;71(5):384-7.
  2. Fogazzi GB, Cameron JS. The introduction of urine microscopy into clinical practice. Nephrol Dial Transplant. 1995;10(3):410-3.
  3. Fogazzi GB, Cameron JS. Urinary microscopy from the seventeenth century to the present day. Kidney Int. 1996;50(3):1058-68.
  4. Richet G. From Bright’s disease to modern nephrology: Pierre Rayer’s innovative method of clinical investigation. Kidney Int. 1991;39(4):787-92.
  5. Eknoyan G. Looking at the urine: the renaissance of an unbroken tradition. Am J Kidney Dis. 2007;49(6):865-72.
  6. Fogazzi GB, Garigali G. The clinical art and science of urine microscopy. Curr Opin Nephrol Hypertens. 2003;12(6):625-32.
  7. Claure-Del Granado R, Macedo E, Mehta RL. Urine microscopy in acute kidney injury: time for a change. Am J Kidney Dis. 2011;57(5):657-60.

By Yosuke Hirakawa
The University of Tokyo Hospital

Routine measurement of urea and creatinine, sensitive indicators of renal function, forms the present-day basis of clinical nephrology. Around 1850, two important events related to measurement of urea and creatinine occurred.

The word “creatinine” was probably first used by Justus von Liebig in 1847 (1). He found the ingredient creatinine in beef tea. Beef tea was a traditional English remedy, made using only beef and salt, not tea leaves. It had previously been known that creatine, the precursor of creatinine, was abundant in animal muscle. Liebig, who established the Justus von Liebig’s Extract of Meat Company, found that the addition of hydrochloric acid to creatine resulted in the production of creatinine. Around this time, creatinine was not used as an indicator of renal function; researchers focused on urea as an indicator of renal function, with Joseph Picard having established the reproducible and sensitive method of urea measurement in 1856. He later found that urea concentration in the renal vein fell from that in the renal artery (3). Around the same time, toxic mechanism came to be accepted as the etiology of uremic syndrome; therefore, the establishment of the urea measurement technique and the discovery of the urea fall in the renal vein led to the concept that urea was the causative substance of uremic syndrome. However, a brave study of urea loading in human patients performed in 1972 revealed that urea itself is not a uremic toxin (4).

References

  1. Pierre Delanaye (2012). “Serum Creatinine: An Old and Modern Marker of Renal Function” in Pierre Delanaye (ed.) Nephrology and Clinical Chemistry: The Essential Link pp9-20.
  2. Kramer H, Rosas SE, Matsushita K. Beef Tea, Vitality, Creatinine, and the Estimated GFR. Am J Kidney Dis. 2016;67:169-72.
  3. Gabriel Richet. Early history of uremia. Kidney Int 1988;33:1013-5
  4. Johnson WJ, Hagge WW, Wagoner RD, Dinapoli RP, Rosevear JW. Effects of urea loading in patients with far-advanced renal failure. Mayo Clin Proc 1972;47:21-29

By Yosuke Hirakawa
Division of Nephrology and Endocrinology, the University of Tokyo Hospital

In 1862, anatomist Jacob Henle presented the existence of nephron loops, widely known today as the loop of Henle. (1). He provided a morphological description; the importance of electrolyte reabsorption had not yet been determined and the existence of tubular reabsorption was only proved in the 1920s by Alfred Newton Richards. Henle is famous for his description of epithelial tissue: large sheets of cells free from blood vessels, blood components, and nerve endings. Henle described first epithelial tissue in the digestive tract followed by glandular and tubular organs, including the kidney (2). In renal medulla, Henle found two tubular subtypes: one type was a papillary collecting duct with a diameter of 0.05-0.06 mm; the other type had a much smaller diameter of approximately 0.02-0.03 mm, running parallel to the collecting ducts but returning in a narrow hairpin curve toward the surface. The latter is the well-known loop of Henle. As an anatomist, Henle examined other epithelial tissues also: Henle’s gland in the eyelids and Henle’s layer in the hair follicle (3).

References

  1. Morel F. The loop of Henle, a turning-point in the history of kidney physiology. Nephrol Dial Transplant. 1999;14:2510-5
  2. Kinne-Saffran E, Kinne RK. Jacob Henle: the kidney and beyond. Am J Nephrol. 1994;14:355-60.
  3. Weyers W. Jacob Henle–a pioneer of dermatopathology. Am J Dermatopathol. 2009;31:6-12

By Yosuke Hirakawa
The University of Tokyo Hospital

It is now common knowledge that urine is produced by glomerular filtrate and tubular reabsorption of substances such as electrolytes and glucose. This phenomenon was initially understood by Alfred Newton Richards and his colleagues in the 1920s. At that time, many researchers had tried to observe glomerular circulation but did not have the capacity or methods to do so. Richards was the pioneer who decided to observe frog kidneys, which are thin and flat.(1). He investigated the effect of adrenaline on glomerular circulation with a micropipette introduced into glomerular space with the help of a micromanipulator. In the process, he obtained enough glomerular fluid for quantitative tests. He found that glomerular filtrate contained both chloride and sugar, detectable in blood but undetectable in bladder urine, leading to the conclusion that there must be 2 different processes: glomerular filtration and tubular reabsorption respectively. This description is thought to be one of the most important contributions in our understanding of renal physiology (2) on which subsequent understandings of glomerular filtration rate (GFR) and solute transport have been built. Richards’ achievements are widely known and the ISN ensures that his outstanding and fundamental contribution to basic research is honored through the Alfred Newton Richards Award for basic science.

References

  1. Schmidt CF. Alfred Newton Richards 1876-1966. Ann Intern Med. 1969: Suppl 8:15-27.
  2. Sands JM. Micropuncture: unlocking the secrets of renal function. Am J Physiol Renal Physiol. 2004; 287:F866-7.

By Sabine Karam MD
Saint George Hospital University Medical Center, Beirut, Lebanon

Homer W. Smith (1895-1962), physiologist and medical writer, was a pioneer in renal physiology. He recognized the clinical importance of renal clearance methods, a concept initially introduced by Donald Van Slyke in 1928 (1). He introduced them as a tool for the precise measurement of renal function in medical practice and elaborated on the concepts of glomerular filtration, effective renal plasma flow, and intrarenal resistance(2). Smith also played an essential role in elucidating tubular transport capacity, the reabsorption and secretion of various substances such as urea and creatinine, as well as providing novel insights into the mechanisms of the excretion of water and electrolytes(3). Finally, he was instrumental in setting the perfect example of collaboration between basic scientists and clinicians, a model which has since been followed worldwide(2). Dr. Smith’s studies of the kidney culminated in 1951 with the authoritative summary, “The Kidney, Structure and Function in Health and Disease“. He also had a remarkable career in philosophy and literature, as illustrated by the reflective essay, “From Fish to Philosopher,” describing the evolutionary role of the kidney in enabling survival in both water and on land(4). Today, his legacy endures through the Homer W. Smith annual award in renal physiology established by the American Society of Nephrology in 1964.

References

  1. SE B. Clearance concept in renal physiology. In: GOTrSCHALK CW BR, GIEBISCH GH, editor. Renal Physiology, People and Ideas. Bethesda: American Physiological society; 1987.
  2. Baldwin DS, Neugarten J. Homer Smith: his contribution to the practice of nephrology. J Am Soc Nephrol. 1995;5(12):1993-9.
  3. Giebisch G. Homer W. Smith’s contribution to renal physiology. J Nephrol. 2004;17(1):159-65.
  4. Fishman AP. Homer W. SMITH (1895-1962). Circulation. 1962;26:984-5.

By Nikolay Bulanov
Sechenov First Moscow State Medical University

In 1886, Max Jaffe (1841 – 1911), a German physician and chemist, observed that creatinine produced an intensive red color in alkaline picrate solution and detected needle-formed crystals under the microscope which he reported in his landmark paper (1).

However, the quantitative analytical method used to assess creatinine concentration was developed in the first decade of the twentieth century by an outstanding Swedish-born American biochemist Otto Folin (1867 – 1934), who called it the “Jaffe method” (2). Even over a century after its introduction into clinical practice, this procedure is still widely used to measure creatinine levels due to its simplicity and low-cost. However, several organic compounds called pseudochromogens (e.g. acetone, glucose) that were first recognized by Jaffe can also react with alkaline picrate and lead to an analytical bias.

In 1957, Alfred Free (1913 – 2000) and his co-authors working at the Ames Corporation published a paper describing a new colorimetric test for urinary protein (3). The first dipstick was a yellow paper strip, impregnated with a citrate buffer and tetrabromphenol blue, which turns green in the presence of protein. Free et al tested their new method obtaining approximately 5000 turbid urine samples from patients and healthy subjects and demonstrated its adequate sensitivity and specificity. Today, urinary dipstick test is one of the most common screening techniques for early detection of kidney diseases.

In 1945, Bowling Barnes, David Richardson, John Berry, and Robert Hood introduced flame photometer to measure the low concentration of sodium and potassium in a solution (4). Flame photometer measures the intensity of emitted light when a metal is introduced into the flame, giving information about the amount of the element present in the sample. This technology allows for cheap and simple measurements of electrolytes in serum and urine.

References

  1. Jaffe M. Ueber den Niederschlag welchen Pikrinsäure in normalen Harn erzeugt und über eine neue reaction des Kreatinins. Z Physiol Chem. 1886;10:391–400.
  2. Shaffer PA. Otto Folin 1867-1934. Washington, DC: National academy of sciences;1952:47–82
  3. Free AH, Rupe CO, Metzler I. Studies with a new colorimetric test for proteinuria. Clin Chem. 1957;3:716–727.
  4. Barnes RB, Richardson D, Berry JW, Hood RL. Flame photometry; A rapid analytical procedure. Ind Eng Chem Anal Ed. 1945;17:605-11.

By Nikolay Bulanov
Sechenov First Moscow State Medical University

In 1886, Max Jaffe (1841 – 1911), a German physician and chemist, observed that creatinine produced an intensive red color in alkaline picrate solution and detected needle-formed crystals under the microscope which he reported in his landmark paper (1).

However, the quantitative analytical method used to assess creatinine concentration was developed in the first decade of the twentieth century by an outstanding Swedish-born American biochemist Otto Folin (1867 – 1934), who called it the “Jaffe method” (2). Even over a century after its introduction into clinical practice, this procedure is still widely used to measure creatinine levels due to its simplicity and low-cost. However, several organic compounds called pseudochromogens (e.g. acetone, glucose) that were first recognized by Jaffe can also react with alkaline picrate and lead to an analytical bias.

In 1957, Alfred Free (1913 – 2000) and his co-authors working at the Ames Corporation published a paper describing a new colorimetric test for urinary protein (3). The first dipstick was a yellow paper strip, impregnated with a citrate buffer and tetrabromphenol blue, which turns green in the presence of protein. Free et al tested their new method obtaining approximately 5000 turbid urine samples from patients and healthy subjects and demonstrated its adequate sensitivity and specificity. Today, urinary dipstick test is one of the most common screening techniques for early detection of kidney diseases.

In 1945, Bowling Barnes, David Richardson, John Berry, and Robert Hood introduced flame photometer to measure the low concentration of sodium and potassium in a solution (4). Flame photometer measures the intensity of emitted light when a metal is introduced into the flame, giving information about the amount of the element present in the sample. This technology allows for cheap and simple measurements of electrolytes in serum and urine.

References

  1. Jaffe M. Ueber den Niederschlag welchen Pikrinsäure in normalen Harn erzeugt und über eine neue reaction des Kreatinins. Z Physiol Chem. 1886;10:391–400.
  2. Shaffer PA. Otto Folin 1867-1934. Washington, DC: National academy of sciences;1952:47–82
  3. Free AH, Rupe CO, Metzler I. Studies with a new colorimetric test for proteinuria. Clin Chem. 1957;3:716–727.
  4. Barnes RB, Richardson D, Berry JW, Hood RL. Flame photometry; A rapid analytical procedure. Ind Eng Chem Anal Ed. 1945;17:605-11.

By Yosuke Hirakawa
Division of Nephrology and Endocrinology, the University of Tokyo Hospital

In 1914, Franz Volhard, a clinician, and Theodor Fahr, a pathologist, published the textbook, Die Brightsche Nierenkrankheit. Klinik, Pathologie und Atlas (Bright’s disease. Clinical aspects, Pathology and illustrations) (1)(2). This is one of the most important textbooks because for the first time several pathological entities were described. ‘Bright’s disease’ was categorized into nephrosis (nephrotic syndrome), nephritis, and arteriosclerotic renal disease; now recognized as focal segmental glomerulonephritis, crescentic glomerulonephritis, and membranoproliferative glomerulonephritis (3). The original classification described by Volhard and Fahr formed the basis of current renal pathology constructs. This specific textbook is also notable as one of the last to be hand-illustrated in color. The beautiful drawings can be seen in the Nephrol Dial Transplant article from 1998 (cited as #1).

References

  1. Fogazzi GB, Ritz E. Novel classification of glomerulonephritis in the monograph of Franz Volhard and Theodor Fahr. Nephrol Dial Transplant. 1998;13:2965-7.
  2. Luft FC, Dietz R. Franz Volhard in historical perspective. Hypertension. 1993;22:253-6.
  3. J Stewart Cameron. “Glomerular Disease – Before 1950” in John Feehally, Christopher McIntyre, J. Stewart Cameron (ed.). Landmark Papers in Nephrology (English Edition) 1st Edition. pp102-3.

By Caner Alparslan
Diyarbakır Gazi Yaşargil Training and Research Hospital, Turkey

The use of percutaneous kidney biopsy technique has become one of the most important tools in nephrology practice. In conjunction with the introduction of immunofluorescence and electron microscopy, the technique of percutaneous kidney biopsy has contributed to an improved understanding of kidney diseases. Nill Alwall performed the first percutaneous kidney biopsy in 1944. One year later, he presented preliminary results in Lund, Sweden. However, he stopped performing percutaneous kidney biopsies after one patient developed a hemorrhagic complication (1-2). Nonetheless, Antonio Perez-ara in Cuba (in 1948), and Paul Iverson and Claus Brun in Copenhagen (in 1949), unaware of each other’s work (3-4), began to perform percutaneous kidney biopsies. A liver biopsy aspiration needle was used by Iverson and Brun, whereas Perez-ara used a Vim-Silverman needle to perform the procedure. In following years, Robert M. Kark and Robert C. Muehrcke further developed the prone position percutaneous kidney biopsy technique which was subsequently adopted by many countries (5). In children, the first documented attempts were made in 1955 in Cuba and 1957 in Europe (1).

Localizing the kidney is an important component of obtaining a sample(s) and, in part, reducing biopsy related complications. Until 1961, fluoroscopy and intravenous pyelography were used to localize the kidney. G.M. Berlyne suggested the use of ultrasound to localize kidneys, which subsequently became the standard in percutaneous kidney biopsy technique (1).

Today, with advances in technology and tools, disposable automatic biopsy needles and higher resolution in imaging aid in the performance of safe and useful percutaneous kidney biopsies to yield tissue samples. This tissue remains the ultimate tool to aid in diagnosis, management, and identification of new therapeutic targets in both pediatric and adult nephrology practice.

References

  1. Cameron JS, Hicks J. The introduction of renal biopsy into nephrology from 1901 to 1961: a paradigm of the forming of nephrology by technology. Am J Nephrol 1997;17:347-358.
  2. Alwall N. Aspiration biopsy of the kidney, including report of a case of amyloidosis diagnosed in 1944 and investigated autopsy. Acta Med Scand 1952;143:430-435.
  3. Iversen P, Brun C. Aspiration biopsy of the kidney. Am J Med 1951;11:324-330.
  4. Perez-Ara A. La biopsia-punctural del rinon no megalico-consideraciones generales y aportacion de un nuevo metodo. Bol Liga Cubana Contra Cancer 1950;25:121-147.
  5. Muehrcke RC, Kark RM, Pirani CL. Biopsy of the kidney in the diagnosis and management of renal disease. NEJM 1955;253:537-546.

By Shankar Prasad Yadav
B.P. Koirala Institute of Health Sciences, Nepal

The use of immunofluorescence techniques to detect specific tissue antigens using fluorescein-labeled antibody was first described in the 1940s by Albert Hewett Coons and colleagues. The antibody, coupled with fluorescein (immunochemical reagent), reacts with tissue containing antigen and produces a light emission visible through a fluorescence microscope. Coons used fluorescein to detect pneumococcal antigen in Aschoff nodules, a pathognomonic marker of rheumatic fever (1,2).

It was not until the 1950s, however, that the use of this principle in kidney biopsy was demonstrated by R.C. Mellors. The technique was modified to localize the antibody in kidney tissue. In this landmark study (3), fifteen healthy rabbits were injected with bovine gamma globulin, while four rabbits were used as a control group: this led to the description of different patterns of acute glomerulonephritis among twelve of the experimental animals. In the second part of the experiment, antibody was prepared from the globulin fraction of chicken anti-serum and rat immunoglobulin, which was coupled with fluorescence thiocyanate to generate fluorochrome reagent. The application of this reagent to kidney tissue, with subsequent fluorescent microscopy, demonstrated that there was increased intensity of immunofluorescence in the glomerulus of affected rabbits in comparison to tubules, or unaffected, or control group. These findings helped to conceptualize the antigen-antibody reaction as central in the pathogenesis of human glomerulonephritis.

Current use of immunofluorescence in diagnosing glomerulonephritis including IgA nephropathy, C3 glomerulonephritis, lupus nephritis, or detection of C4d in humoral anti-graft reactions are based on the fundamental principles elucidated by Mellors more than 60 years ago.

References

  1. Coons AH, Creech H J & Jones R N. Immunological properties of an antibody containing a fluorescent group.  Soc. Expt. Biol. Med.47, 200–202 (1941).
  2. Coons AH., Creech HJ., Jones RN. & Berliner E. The demonstration of pneumococcal antigen in tissues by the use of fluorescent antibody.  Immunol.45, 159–170 (1942).
  3. Mellors RC, Arias-Stella J, Siegei M, & Pressman D. Analytic Pathology II. Histopathologic demonstration of glomerular·localizing antibodies in experimental glomerulonephritis. Am. J. Path., In Press, 1955.

By Nikolay Bulanov
Sechenov First Moscow State Medical University, Russia

In 1957, American scientists Marilyn Farquhar, Robert Vernier, and Robert Good published the first paper describing the implications of a new technique of electron microscopy to study glomerular pathology (1). They explored ultrastructural changes in the glomeruli of sixteen patients with ‘nephrosis’, seven patients with glomerulonephritis, and three patients with systemic lupus erythematosus. Electron microscopy revealed the effacement of podocyte foot processes in ‘nephrosis,’ and the glomerular basement membrane thickening in glomerulonephritis and lupus nephritis. Since then, electron microscopy is widely employed in clinical practice and has contributed to the discovery of several renal diseases, e.g. fibrillary glomerulonephritis. Today, electron microscopy is considered essential for definite diagnosis of glomerular diseases associated with mutations in type IV collagen genes, minimal change disease, and renal lesions associated with monoclonal gammopathy, etc. This technique reveals changes in cell structure, glomerular basement membrane, and localization of immune deposits that can’t be visualized by light microscopy or immunofluorescence microscopy. However, electron microscopy requires special processing of tissue samples and is therefore relatively expensive, time-consuming, and not universally available in some countries.

References

  1. Farquhar MG, Vernier RL, Good RA. An electron microscope study of the glomerulus in nephrosis, glomerulonephritis, and lupus erythematosus. J Exp Med. 1957;106(5):649–660.

By Lili Zhou
Division of Nephrology, Nanfang Hospital, Southern Medical University, China

Glomerular capillary tufts are responsible for filtration. However, the structure and function of the different cell types within the glomerular capillary tufts were not well described until 1987. Described endothelial cells (ECs), as highly attenuated and fenestrated cells, could not be demonstrated to modulate blood flow. In 1987, Dr. Kriz Wilhelm discovered that mesangial cells (MCs) are important components that influence filtration dynamics. Filled with microtubules and intermediate filaments, these stellate-like MCs could contract and easily regulate the area size of mesangium. They also protrude tongue-like cell processes that extend to the mesangial angle (i.e. the sites where glomerular basement membrane (GBM) deviates from its pericapillary course and covers the mesangium). These processes can change the width of the GBM channel to permit the constriction and relaxation of capillaries and then modulate the intraglomerular blood flow and filtration. In addition to mesangial cells, he described podocytes, which sit outside the GBM. In 1995, Wilhelm summarized the podocyte structure-function relationships and those of other cell types. Through his work, a variety of cell types (MC, EC, podocytes) were described, and their structural relationship to the slit diaphragms and GBM with functional implications in the perfusion and filtration functions of the kidneys were subsequently elucidated.

References

  1. Sakai T, Kriz W. The structural relationship between mesangial cells and basement membrane of the renal glomerulus. Anat Embryol (Berl) 176 (3), 373-86. 1987.
  2. Mundel P, Kriz W. Structure and function of podocytes: an update. Anat Embryol (Berl) 192 (5), 385-97. Nov 1995.
  3. Kriz W. Maintenance and breakdown of glomerular tuft architecture. J Am Soc Nephrol 29 (4), 1075-1077. Apr 2018.
  4. Kriz W. The inability of podocytes to proliferate: cause consequences and origin. Anat Rec (Hoboken) 2019 Oct 12 [Online ahead of print].

By Mirna Aleckovic-Halilovic and Mirha Pjanic
University Clinical Center Tuzla, Bosnia and Herzegovina

Fully understanding renal aspects of acid-base regulation has always been a challenge. A landmark paper that paved the way to current knowledge on acid excretion in different renal diseases and became a citation classic in 1979 was written by Oliver Wrong and H.E.F. Davies and published in 1959 (1).

At the time, knowledge on acid excretion variation in different renal diseases was limited and there was a clear need for the development of a clinically useful test to detect impairment of kidney acid elimination. The authors devised a test, still widely used today, using ammonium chloride as an external acidification stimulus. They tested 10 subjects with normal renal function and 58 patients with different renal conditions. The cut-off point of pH 5.3 became the accepted criterion for defining a defect in renal acid excretion.

Contrary to accepted belief, they found that renal ability to acidify urine was not impaired in subjects with renal failure, and that systemic acidosis was, in fact, the result of greatly

reduced excretion of ammonium and, to a lesser extent, reduced excretion of buffer and therefore reduced excretion of titratable acid, all due to reduced renal mass and nephron number.

On the other hand, they found that renal ability to acidify urine in renal tubular acidosis (RTA) was greatly impaired, and although buffer excretion was reduced, reflecting the reduced hydrogen ion secretion, urinary ammonium excretion was relatively well-preserved; this gave an explanation as to why many patients with RTA were not acidotic and had what the authors named “incomplete RTA”.

The authors further recognized that the form of RTA associated with features of renal Fanconi syndrome was different from the classical form, known today as distal RTA, and suggested an abnormality of proximal nephron function (2).

This first major work by Oliver Wrong, (1) as well as his very last paper, (3) was on RTA, a clinical disorder he returned to throughout his life. He was rightly named a ‘salt and water’ physician and a prize for innovative research in nephrology at the University College of London is named in his honor.

References

  1. Wrong O, Davies HE. The excretion of acid in renal disease. Q J Med. 1959;28(110):259-313.
  2. Unwin, RJ (2012). “Back to the future: renal tubular acidosis then and now”. QJM. 105 (9): 915–916. doi:10.1093/qjmed/hcs134PMID 22855286.
  3. Khositseth S, Bruce LJ, Walsh SB, Bawazir WM, Ogle GD, Unwin RJ, et al. Tropical distal renal tubular acidosis: clinical and epidemiological studies in 78 patients. Q J Med 2012;105:861–77.

By Nikolay Bulanov
Sechenov First Moscow State Medical University

Investigation of renal physiology is impossible without studying the function of different parts of the nephron. The first experiments on isolated tubules were described in 1924 by Wearn et al. who performed renal tubule micropuncture in vivo (1). However, this technique was complicated and only able to assess surface tubule segments. In the 1950s, Maurice B. Burg began to consider the possibility of perfusing single renal tubules in vitro. After several years of hard work in the Laboratory of Kidney and Electrolyte Metabolism, Burg et al. published a paper describing the dissection of different tubule segments in single rabbit nephrons and their electrolyte and water composition (2). They demonstrated that proximal tubules maintained transcellular gradients for sodium, potassium, and chloride ions. To assess transcellular transport, the authors measured the volume and composition of the effluent perfusion fluid. Decades later, Maurice Burg recalled that this experiment required considerable time, collaboration, and effort, including the development of special concentric perfusing micropipettes, and the application of a wide range of microdissection and analytical techniques (3). This study contributed to a better understanding of cellular structure and function of both normal and diseased kidneys.

References

  1. Wearn JT, Richards AN. Observations on the composition of glomerular urine with particular reference to the problem of reabsorption in the renal tubules. Am J Physiol. 1924; 71:209–227.
  2. Burg M, Grantham J, Abramow M, Orloff J. Preparation and study of fragments of single rabbit nephrons. Am J Physiol. 1966; 210:1293–1298.
  3. Burg M. Introduction: Background and development of microperfusion technique. Kidney Int. 1982; 22:417–424.

By Sabine Karam MD
Saint George Hospital University Medical Center, Beirut, Lebanon

Rolf Kinne from the Max Planck Institute of Molecular Physiology and Heini Murer from the University of Zurich made significant contributions to the understanding of transport mechanisms in human epithelial cells and, most notably, in the proximal tubular cells. They used the membrane-molecular approach (1, 2) to isolate intestinal and renal brush-border-membrane vesicles in order to study their transport properties in vitro. Intestinal and renal brush-border membranes were found to contain an Na/H antiport system that catalyzes an electroneutral exchange of Na+ against protons and can subsequently produce a proton gradient in the presence of a concentration difference for Na+. They concluded that there was an active proton secretion in the small intestine and the proximal tubule of the kidney (3). This technique allowed to localize transport elements situated in the two opposite sides of the cell (luminal and basolateral); and to characterize the driving forces, molecular properties, and regulatory influence of these transport elements. They summarized their findings in a seminal paper published in 1980 (4).

References

  1. Kinne R, Schwartz IL. Isolated membrane vesicles in the evaluation of the nature, localization, and regulation of renal transport processes. Kidney Int. 1978;14(6):547-56. Epub 1978/12/01. doi: 10.1038/ki.1978.163. PubMed PMID: 219287.
  2. Kinne R. Membrane-Cellular aspects of tubular transport. In: K.Thureau, editor. MTP International Review of Sciences Kidney and Urinary Tract Physiology, Vol11. London: Butterworths, Baltimore: University Park Press; 1976. p. 169-210.
  3. Murer H, Hopfer U, Kinne R. Sodium/proton antiport in brush-border-membrane vesicles isolated from rat small intestine and kidney. Biochem J. 1976;154(3):597-604. Epub 1976/03/15. PubMed PMID: 942389; PubMed Central PMCID: PMCPMC1172760.
  4. Murer H, Kinne R. The use of isolated membrane vesicles to study epithelial transport processes. J Membr Biol. 1980;55(2):81-95. Epub 1980/07/15. doi: 10.1007/bf01871151. PubMed PMID: 6997489.

By Rolando Claure-Del Granado
Hospital Obrero #2 – CNS, Universidad Mayor de San Simón

Total body water content is largely determined by the total amount of salt in the body, and the kidneys ultimately control the salt and water concentration. Despite wide fluctuations in the intake of salt and water, the renal mechanisms maintain the serum sodium chloride concentration within a very narrow range. The kidneys can perform this critically important regulatory role by virtue of being the target organ of various stimuli regulating salt and water homeostasis. Our understanding of the mechanisms by which the kidney can generate both dilute and concentrated urine was made possible by a description of how the operation of the countercurrent multiplication system works.

Wirtz et al. initially developed the general architecture of the renal countercurrent multiplication system in 1951(1). Since that initial description, several alternate models of countercurrent multiplication systems were proposed; however, most of these models were advanced by theoretic arguments without experimental basis.

In 1972, Kokko and Rector (2) proposed a completely new model of the countercurrent multiplication system. The fundamental difference between this and previous models was that the new model removed the necessity of postulating active transport processes in the thin ascending limb. This model was therefore consistent with experimental results and satisfied the mathematical formulations simultaneously developed by Stephenson(3). The model developed by Kokko and Rector stressed the importance of urea recirculation and allowed for an understanding of the pathophysiology behind many of the clinical states associated with a deranged balance of sodium and water.

References

  1. Kokko JP. The role of the renal concentrating mechanisms in the regulation of serum sodium concentration. Am J Med. 1977;62(2):165-9.
  2. Kokko JP, Rector FC, Jr. Countercurrent multiplication system without active transport in inner medulla. Kidney Int. 1972;2(4):214-23.
  3. Stephenson JL. Concentration of urine in a central core model of the renal counterflow system. Kidney Int. 1972;2(2):85-94.

By Fumiaki Ando
Tokyo Medical and Dental University, Tokyo, Japan

Water and sodium homeostasis are closely interrelated and precisely regulated by the kidneys. The disruption of homeostatic balance is a common problem encountered in clinical practice. Water channels and amiloride-sensitive epithelial Na+ channel (ENaC) are representative molecules to determine body fluid-electrolyte parameters in blood and urine.

The first water channel, aquaporin-1 (AQP1), was identified as a 28-kDa membrane protein (CHIP28) in erythrocytes by Peter Agre and coworkers (1). Agre was awarded the 2003 Nobel Prize in Chemistry for this discovery. AQP1 is a constitutively open water channel present at the luminal membrane of the proximal tubule cells and the descending thin limbs of the loop of Henle in the kidney. AQP2 is another important aquaporin localized in the renal collecting ducts (CD) that is critical in regulating urine volume (2). In contrast to AQP1, AQP2 is dynamically regulated and is translocated from intracellular vesicles to the apical plasma membrane in response to dehydration leading to water reabsorption from urine via the luminal AQP2. Loss-of-function mutations in the AQP2 cause congenital nephrogenic diabetes insipidus.

ENaC is a plasma membrane protein localized primarily in the renal CD that plays a fundamental role in sodium reabsorption and regulates body sodium content and blood pressure. Canessa et al. found the first ENaC subunit (α), cloned from the colon of salt-deprived rats, in 1993 (3). Two other subunits (β and γ) were identified by functional complementation of the α subunit (4). Liddle syndrome is caused by gain-of-function mutations in the ENaC that induce impairment of its degradation by the ubiquitin-proteasome system and a subsequent increase in ENaC expression.

References

  1. Preston GM, Carroll TP, Guggino WB, Agre P. Appearance of water channels in Xenopus oocytes expressing red cell CHIP28 protein. Science. 1992;256(5055):385-7.
  2. Fushimi K, Uchida S, Hara Y, Hirata Y, Marumo F, Sasaki S. Cloning and expression of apical membrane water channel of rat kidney collecting tubule. Nature. 1993;361(6412):549-52.
  3. Canessa CM, Horisberger JD, Rossier BC. Epithelial sodium channel related to proteins involved in neurodegeneration. Nature. 1993;361(6411):467-70.
  4. Canessa CM, Schild L, Buell G, Thorens B, Gautschi I, Horisberger JD, Rossier BC. Amiloride-sensitive epithelial Na+ channel is made of three homologous subunits. Nature. 1994;367(6462):463-7.

By Shankar Prasad Yadav
B.P. Koirala Institute of Health Sciences, Nepal

The identification and description of each component of the clinical entity known as “nephrotic syndrome” have developed over centuries. Severe edema in children was described by Cornelius as far back as 1484, but he did not identify it as a kidney-related issue.1 Much later, in 1722, Theodore Zwinger postulated that this edema was related to pathological changes in the kidney.2 However, it was R. Bright (1827) and his contemporaries who demonstrated the presence of proteinuria and then proposed the triad of edema, diseased kidney, and proteinuria as defining the clinical syndrome. 3 Subsequently, the presence of elevated lipids in the blood of such patients was discovered by R. Christison.4

In 1905, the term “nephrosis”, coined by Friedrich Muller, was used to describe the pathological lesion of such patient as degenerative rather than inflammatory and hence replaced “nephritis”.5 In addition, Fritz Munk (1920) demonstrated lipid in the urine of such patients and reportedly used the term “lipoid nephrosis” to describe such conditions.6 During this period, in kidney specimens observed through optical microscopy in patients with nephrosis, the gross appearance of glomeruli seemed almost normal; therefore, the idea of “pure nephrosis”, or minimal change, emerged and it was conceded that the proteinuria resulted from tubular defect. The term “Nephrotic Syndrome” was gradually popularized in 1948.7

References

  1. Chadwick J, Mann WN. The medical works of Hippocrates. London: Oxford University Press, 1950: 228 (Section 2, No 136), 240 (Section 13, No 266), 244 (Section 7, No 34).
  2. Roelans C. Liber de aegritudinibus infantium. (c 1484). Reproduced in: Sudhoff KFJ. Erstlingeder padiatrischen Literatur. Munchen: Monchner Drucke, 1925: cxciii-cxciiii.
  3. Bright R. Reports of medical cases selected with a view of illustrating the symptoms and cure of diseases by reference to morbid anatomy. London: Longman Green, 1827. Vol 1.
  4. Christison R. On the cause of the milky and whey-like appearance sometimes observed in the blood. Edin Med Surg J 1830; 33: 274-280.
  5. Muller F. Morbus Brightii. Verhandl Deutsch Path Gesellsch 1905; 9: 64-99.
  6. Munk F. Klinische Diagnostik der degenerativen Nierenerkrankungen. Z Klin Med 1913; 78:1.52.
  7. Bradley SE, Tyson CJ. The ‘nephrotic syndrome’. N Engl J Med 1948; 238: 223-227, 260-266.

By Eishin Yaoita
Niigata University Graduate School of Medical and Dental Sciences, Niigata, Japan

Cultured cells that reproduce phenotypes in vivo are essential elements in the study of biology and pathophysiology. The most important step for glomerular cell culture was the isolation of glomeruli. In 1950, S.A. Greenspon and C.A. Krakower first isolated large numbers of glomeruli by a sieving method using a stainless-steel screen (1). In 1970, L. Quadracci and G.E. Striker applied glomeruli that had been isolated using a modified sieving method to cell-culture and reported three cell types in the culture (2). Which cells came from podocytes remains controversial. P. Mundel et al. considered cobblestone-like polygonal cells to be dedifferentiated podocytes (3) and established podocyte cell lines using conditionally immortalized mice (4), which has had a great impact on podocyte research. In parallel, it has been suggested that polygonal cells originate from the parietal epithelial cells of Bowman’s capsule as represented by J.O. Nørgaard’s paper (5). Few polygonal cells have actually been seen in outgrowths from glomeruli isolated by the innovative method invented by M. Takemoto et al., in which almost all glomeruli are decapsulated (6). In addition, phenotypes very close to podocytes in vivo have been successfully restored using the outgrowths from glomeruli isolated by Takemoto’s method (7), whereas phenotypes from polygonal cells from glomeruli isolated by the sieving method have not.

References

  1. Greenspon SA, Krakower CA. Direct evidence for the antigenicity of the glomeruli in the production of nephrotoxic serums. AMA Arch Pathol. 1950; 49:291-7.
  2. Quadracci L, Striker GE. Growth and maintenance of glomerular cells in vitro. Proc Soc Exp Biol Med. 1970; 135:947-50.
  3. Mundel P, Reiser J, Kriz W. Induction of differentiation in cultured rat and human podocytes. J Am Soc Nephrol. 1997; 8:697-705.
  4. Mundel P, Reiser J, Zúñiga Mejía Borja A, Pavenstädt H, Davidson GR, Kriz W, Zeller R. Rearrangements of the cytoskeleton and cell contacts induce process formation during differentiation of conditionally immortalized mouse podocyte cell lines. Exp Cell Res. 1997; 236:248-58.
  5. Nørgaard JO. Rat glomerular epithelial cells in culture. Parietal or visceral epithelial origin? Lab Invest. 1987; 57:277-90.
  6. Takemoto M, Asker N, Gerhardt H, Lundkvist A, Johansson BR, Saito Y, Betsholtz C. A new method for large scale isolation of kidney glomeruli from mice. Am J Pathol. 2002; 161:799-805.
  7. Yaoita E, Yoshida Y, Nameta M, Takimoto H, Fujinaka H. Induction of interdigitating cell processes in podocyte culture. Kidney Int. 2018; 93:519-24.

By Sabine Karam MD
Saint George Hospital University Medical Center, Beirut, Lebanon

Up until the late 1970s, it was thought that all forms of immune-complex glomerulonephritis were due to circulating immune complexes passively trapped in glomeruli. This theory was challenged by works done by W.G. Couser and B.J. Van Damme on Heymann nephritis, a rat model of experimental membranous nephropathy (MN) that showed that deposits in experimental MN formed in situ when circulating immunoglobulin G (IgG) antibodies bound to an unknown glomerular antigen located in the subepithelial space (1-3). This hypothesis was only confirmed in a human model several years later when, in 2002, H.G. Debiec et al. described a case of neonatal MN in which transplacental passage of antineutral endopeptidase (NEP) antibodies from a pre-sensitized NEP-deficient mother bound to NEP on the baby’s podocytes(4). The pathogenesis of primary MN was finally elucidated in 2009 when D.J. Salant et al. found that the M-type phospholipase A2 receptor (PLA2R) expressed in podocytes of normal human glomeruli colocalized with IgG4 in immune deposits in the glomeruli of the majority of patients with idiopathic MN(5) and therefore constituted a major antigen in this disease. Salant had worked with Couser earlier in his career. Furthermore, this mechanism of adaptive immunity was found to have a genetic basis through the finding that the HLA-DQA1 allele on chromosome 6p21 was closely associated with idiopathic membranous nephropathy and could facilitate an autoimmune response against targets such as variants of PLA2R1(6).

Not only is the discovery seminal, but it’s also notable that Dr. Couser was President of the ISN from 2005-2007 and won the 2020 Hamburger Award.

References

  1. Couser WG, Steinmuller DR, Stilmant MM, Salant DJ, Lowenstein LM. Experimental glomerulonephritis in the isolated perfused rat kidney. J Clin Invest. 1978;62(6):1275-87. Epub 1978/12/01. doi: 10.1172/JCI109248. PubMed PMID: 372233; PubMed Central PMCID: PMCPMC371893.
  2. Van Damme BJ, Fleuren GJ, Bakker WW, Vernier RL, Hoedemaeker PJ. Experimental glomerulonephritis in the rat induced by antibodies directed against tubular antigens. V. Fixed glomerular antigens in the pathogenesis of heterologous immune complex glomerulonephritis. Lab Invest. 1978;38(4):502-10. Epub 1978/04/01. PubMed PMID: 147961.
  3. Couser WG, Salant DJ. In situ immune complex formation and glomerular injury. Kidney Int. 1980;17(1):1-13. Epub 1980/01/01. doi: 10.1038/ki.1980.1. PubMed PMID: 6990087.
  4. Debiec H, Guigonis V, Mougenot B, Decobert F, Haymann JP, Bensman A, et al. Antenatal membranous glomerulonephritis due to anti-neutral endopeptidase antibodies. N Engl J Med. 2002;346(26):2053-60. Epub 2002/06/28. doi: 10.1056/NEJMoa012895. PubMed PMID: 12087141.
  5. Beck LH, Jr., Bonegio RG, Lambeau G, Beck DM, Powell DW, Cummins TD, et al. M-type phospholipase A2 receptor as target antigen in idiopathic membranous nephropathy. N Engl J Med. 2009;361(1):11-21. Epub 2009/07/03. doi: 10.1056/NEJMoa0810457. PubMed PMID: 19571279; PubMed Central PMCID: PMCPMC2762083.
  6. Stanescu HC, Arcos-Burgos M, Medlar A, Bockenhauer D, Kottgen A, Dragomirescu L, et al. Risk HLA-DQA1 and PLA(2)R1 alleles in idiopathic membranous nephropathy. N Engl J Med. 2011;364(7):616-26. Epub 2011/02/18. doi: 10.1056/NEJMoa1009742. PubMed PMID: 21323541.

By Mirna Aleckovic-Halilovic and Mirha Pjanic

University Clinical Center Tuzla, Bosnia and Herzegovina,
Clinic for Internal Diseases,
Department for Nephrology, Dialysis and Renal Transplantation

Jean Berger was the renal pathologist who first characterized IgA nephropathy alongside Nicole Hinglais in 1968, and then in 1969 (1, 2), although P. Galle and Berger had described “intercapillary fibrinoid deposits” earlier, in 1962 (3). This distinct clinicopathological entity with predominant mesangial IgA deposits was soon realized to be the most prevalent primary chronic glomerular disease and an important cause of kidney failure worldwide. Until this breakthrough (1), laboratories using immunofluorescence mostly used only anti-IgG reagents, as IgG was thought to be the predominant immunoglobulin class involved in the immunopathogenesis of nephritis (4).

Ever since the publication of this seminal paper, the presence of IgA nephropathy is established only by kidney biopsy. Furthermore, the immunofluorescence findings are the pathologic hallmark of this disease. The light microscopic features of IgA nephropathy may vary greatly among patients and within individual biopsy samples.

Enormous efforts were put into research to identify the etiology and pathogenesis of IgA nephropathy. While they are still poorly understood, recent studies shed some light on the pathogenesis (see the narrative: “IgA hinge glycosylation in IgA nephropathy and IgA vasculitis”). Some studies have shown the efficacy of steroids and inhibition of the renin-angiotensin system, but there is no single therapeutic strategy shown to be effective against this disease.

The current state of knowledge regarding pathogenesis is that an initiating event is likely and that the main feature defining this glomerulonephritis is dominant or codominant mesangial deposits of IgA. Hence, Berger and his associates were the first to describe IgA nephropathy, and their work remains the backbone of diagnostics and today’s understanding of it.

While we are striving, in all areas of medicine, to move away from eponyms in naming diseases in pursuit of a better understanding of the underlying mechanisms, we acknowledge that, for many, IgA nephropathy will remain Berger’s disease.

References

  1. Berger J, Hinglais N. Les dépôts intercapillaires d’IgA-IgG. J Urol Nephrol 1968; 74: 694–695.
  2. Berger J. IgA glomerular deposits in renal disease. Transplant Proc 1969; 1: 939–944.
  3. GALLE P, BERGER J: Depots fibrinoides intercapillaires. J Urol Nephrol (Paris) 68:123—127, 1962.
  4. Jean Berger (1930–2011) Feehally, John et al. Kidney International, Volume 80, Issue 5, 437 – 438.

By Nikolay Bulanov
Sechenov First Moscow State Medical University, Russia

Immunoglobulin A (IgA) deposits in the glomeruli – the hallmark feature of IgA nephropathy – were first described in 1968 by Jean Berger and Nicole Hinglais (1). However, the underlying mechanisms of mesangial IgA deposition in the glomeruli couldn’t be explained until the mid-90s. In 1995, Alice C. Allen et al. studied serum IgA1, IgG, and C1 inhibitor glycosylation in several patients with biopsy-proven IgA nephropathy (IgAN) and healthy controls. IgAl from patients with IgAN showed significantly higher binding than controls to lectins specific for O-linked N-acetyl galactosamine that indicated reduced terminal galactosylation of the hinge region O-linked moieties (2). In 1998, Allen et al. found a similar increase in IgA1 lectin binding in both adults and children with Henoch-Schönlein purpura (currently known as IgA vasculitis) with kidney involvement compared to other forms of glomerulonephritis and controls (3). In 1999, Milan Tomana et al. showed that circulating immune complexes (CICs) isolated from sera of patients with IgAN consisted of undergalactosylated polymeric IgA1 and IgG antibodies specific for N-acetyl galactosamine residues in O-linked glycans of the hinge region of IgA1 heavy chains (4). These studies provided insights into immunological abnormalities resulting in the formation of CICs containing aberrantly glycosylated IgA1 that escape removal through the reticuloendothelial system and form mesangial deposits in IgAN and IgA vasculitis.

References

  1. Berger J, Hinglais N. Les depots intercapillaires d’IgA-IgG. J Urol Nephrol. 1968; 74:694–95.
  2. Allen AC, Harper SJ, Feehally J. Galactosylation of N- and O-linked carbohydrate moieties of IgA1 and IgG in IgA nephropathy. Clin Exp Immunol. 1995; 100:470–474.
  3. Allen AC, Willis FR, Beattie TJ, Feehally J. Abnormal IgA glycosylation in Henoch-Schönlein purpura restricted to patients with clinical nephritis. Nephrol Dialysis Transplant. 1998; 13:930–934.
  4. Tomana M, Novak J, Julian BA, et al. Circulating immune complexes in IgA nephropathy consist of IgA with galactose-deficient hinge region and antiglycan antibodies. J Clin Invest. 1999; 104:73–81.

Bry Dr. Rhys D. R. Evans
Department of Renal Medicine, University College London, UK

Measurement of blood pressure is an integral part of the assessment of a patient with kidney disease due to the recognition of hypertension as a key clinical manifestation of impaired renal function. Richard Bright (1789-1858),provided the earliest descriptions of kidney disease in a series of patients with ‘dropsy’ (oedema) in 18271. The triad of dropsy, albuminuria, and kidney disease became known as “Bright’s Disease”. However, it was another English Physician, Frederick Henry Horatio Akbar Mahomed (1849-1884), who is thought to have been the first to make the link between hypertension and kidney disease. After developing techniques to measure blood pressure as a medical student,in 1874,he published his observations of hypertension being an early clinical feature of acute and chronic kidney (Bright’s) disease2

One of hisearliest observations with the sphygmograph wasthatthepulseofacuteBright’sdiseasecloselyresembles that which had previously been described as occurring in chronic Bright’s disease, or, more strictly speaking, with cirrhosis of the kidneyHe found that both conditions were accompanied by a pulse of high tension.

He went on to note: “that previous to the commencement of any kidney change, or to the appearance of albumin in the urine, the first condition observable is high tension in the arterial system”. 

Hence the link between hypertension and kidney disease had been made. 

References

  1. Dr. Bright’s Reports of Medical Cases in Guy’s Hospital. Medico-Chir. Rev.8, 90–103 (1828).
  2. Mahomed, F. A. The Etiology of Bright’s Disease and the Prealbuminuric Stage. Medico-Chir. Trans.57, 197–228 (1874).

By Abduzhappar Gaipov 
Nazarbayev University School of Medicine, Nur-Sultan, Kazakhstan

In the early 1900s, several authors tried to demonstrate the renal cause of hypertension.However, most of the studies were controversial (1). In 1934,  Harry Goldblatt(18911977), professor of experimental pathology at the Case‐Western Reserve University School of Medicine, Cleveland, established a successful experimental model of hypertension (2)From careful examination of autopsy specimens, Dr. Goldblatt noted the narrowing of the renal arteries and enlargement of the heart in patients who died from hypertension and renal failure. He suggested that a decrease in blood flow in the kidneys, and consequently reduced oxygen supply to the kidneys (ischemia), might be the cause of hypertension (3)Goldblatt performed experimental studies on dogs and demonstrated renal ischemia-induced hypertension by constricting both renal arteries with a self-styled adjustable silver clamp, which resulted in an elevation of blood pressure (2, 4). The clamping of other arteries (splenic or femoral) did not result in hypertension, which showed the specific role of kidneys in hypertension. Further, this experimental model became the basis for identifying the role of the renin-angiotensin system in the regulation of blood pressure (5, 6).

References 

  1. Goldblatt H. Experimental Hypertension Induced by Renal Ischemia: Harvey Lecture, May 19, 1938. Bull N Y Acad Med. 1938;14(9):523-53.
  2. Goldblatt H, Lynch J, Hanzal RF, Summerville WW. Studies on Experimental Hypertension: I. The Production of Persistent Elevation of Systolic Blood Pressure by Means of Renal Ischemia. J Exp Med. 1934;59(3):347-79.
  3. Van Epps HL. Harry Goldblatt and the discovery of renin. J Exp Med. 2005;201(9):1351.
  4. Gerbi C, Rubenstein BB, Goldblatt H. Studies on Experimental Hypertension: X. The Oxygen Consumption of the Ischemic Kidney. J Exp Med. 1940;71(1):71-6.
  5. Katz YJ, Goldblatt H. Studies on Experimental Hypertension: Xxi. The Purification of Renin. J Exp Med. 1943;78(1):67-74.
  6. Goldblatt H, Katz YJ, Lewis HA, Richardson E. Studies on Experimental Hypertension: Xx. The Bioassay of Renin. J Exp Med. 1943;77(4):309-13.

By Daisuke Nakano 
Department of Pharmacology, Kagawa University, Japan

In 1889, Golgi (1) initially reported that Henle’s loop regularly returns to its originating glomerulus and makes close anatomical contact with the vascular pole. At the site of contact, 5–15 cells are packed more closely to each other than at adjacent sections of the distal tubule. In 1933, Karl Zimmermann (2) named this portion of epithelium with prominent nuclei “macula densa.” Today, macula densa cells are well known as the tubular component of juxtaglomerular apparatusand control tubuloglomerular feedback (TGF). In the 1930s, given the observation of the closeanatomical contact, it was hypothesized that juxtaglomerular apparatus, including macula densa, affects tonus of afferent/efferent arterioles (3). In 1964, K. Thurau and J. Schnermann (4) demonstrated the function of macula densa using a micropuncture technique. They observed thatan increase in luminal Na+ concentration at the tubules near macula densa reduced GFR in a renin-dependent manner, accounting for the term TGF. Thus, over a period of 70 years, the role of the macula densa, in a variety of important functions, was described.

References 

  1. Golgi C. Annotazioni intorno all’ Istologia dei reni dell’ uomo e dialtri mammiferi e sull’ Istogenesi dei canalicoli oriniferi. Atti R.Accad Lincei Rend.1889; 5: 334-342.
  2. Zimmermann K. Ueber den Bau des Glomerulus der Saeugerniere: Weittere Mitteilunger. Ztschr Mikrosk Anat Forsch. 1933;32:176-278.
  3. Goormaghtigh N. L’appareil neuro-myo-artériel juxtaglomérulaire du rein: ses réactions en pathologie et ses rapports avec le tube urinifère, Compt Rend Soc Biol, 1937;129:293-296.
  4. Thurau K und Schermann J. Die Natriumkonzentration an den Macula densa-Zellen als regulierender Faktor für das Glomerulumfiltrat (Mikropunctionsversuche). Klinische Wochenschrift. 1964;43:410-413.

By Lili Zhou
Division of Nephrology, Nanfang Hospital, Southern Medical University, China

As the vasoactivehormone effector of the reninangiotensinaldosterone system (RAAS), angiotensin II (AngII) was first found to induce vasoconstriction of the glomerular capillaries in 1972, suggesting the potential existence of its receptors in glomerular mesangiumHowever, the specific AngII receptors in isolated glomeruliwerenot well characterized until 1974 (2).The AngII receptorsturned out to localize on themesangial cells and induce a contractile response (3)There are two subtypes of AngII receptors, AT1 and AT2. In 1992,using antagonist-inhibited 125I-AngII binding, D. Chansel et al. found that AT1 primarily mediates the vasoconstrictive properties of AngII on mesangial cells throughincreases in intracellular calcium concentration (4).In 1993the localization of AT1 in mesangium was directly visualized by in situ hybridization (5). Subsequently, the more widespread distribution of Ang II receptors,possibly including in podocytes, was hypothesizedby W. Kriz et al.(6)based on data from Yamada et al. (7). The presence of both AT1 and AT2 receptorsin podocytes was subsequentlyverified by Sharma et al. in 1998 (8). AT1 was found to be more abundant (~75%) than AT2 inpodocytes (9)and responsible for structural podocyte damage and cell stress induced by AngII (10). The discovery of AT1 and its function inmesangial cells and podocytes over the last 30 years has led to rationale as to the importance of AngII on glomerular microcirculation and ultrafiltration originally described in 1976 (11). Since then, additionalfunctions of AT1 and AT2 have been elucidated, and the elegant contribution to the coordination and regulation of glomerular functions described

References: 

  1. Hornych H, Beaufils M, Richet G.The effect of exogenous angiotensin on superficial and deep glomeruli in the rat kidney.Kidney Int. 1972 Dec;2(6):336-43.
  2. Sraer JD, Sraer J, Ardaillou R, Mimoune O.Evidence for renal glomerular receptors for angiotensin II.Kidney Int. 1974 Oct;6(4):241-6.
  3. Foidart J, Sraer J, Delarue F, Mahieu P, Ardaillou R.Evidence for mesangial glomerular receptors for angiotensin II linked to mesangial cell contractility.FEBS Lett. 1980 Dec 1;121(2):333-9.
  4. Chansel D, Czekalski S, Pham P, Ardaillou R.Characterization of angiotensin II receptor subtypes in human glomeruli and mesangial cells.Am J Physiol. 1992 Mar;262(3 Pt 2):F432-41.
  5. Kakinuma Y, Fogo A, Inagami T, Ichikawa I.Intrarenal localization of angiotensin II type 1 receptor mRNA in the rat.Kidney Int. 1993 Jun;43(6):1229-35.
  6. Kriz W, Hackenthal E, Nobiling R, Sakai T, Elger M, Hähnel B.A role for podocytes to counteract capillary wall distension.Kidney Int. 1994 Feb;45(2):369-76.
  7. Yamada H, Sexton PM, Chai SY, Adam WR, Mendelsohn FA.Angiotensin II receptors in the kidney. Localization and physiological significance.Am J Hypertens. 1990 Mar;3(3):250-5.
  8. Sharma M, Sharma R, Greene AS, McCarthy ET, Savin VJ.Documentation of angiotensin II receptors in glomerular epithelial cells.Am J Physiol. 1998 Mar;274(3 Pt 2):F623-7.
  9. Wang L, Flannery PJ, Spurney RF.Characterization of angiotensin II-receptor subtypes in podocytes.J Lab Clin Med. 2003 Nov;142(5):313-21.
  10. Hoffmann S, Podlich D, Hähnel B, Kriz W, Gretz N.Angiotensin II type 1 receptor overexpression in podocytes induces glomerulosclerosis in transgenic rats.J Am Soc Nephrol. 2004 Jun;15(6):1475-87.
  11. Blantz RC, Konnen KS, Tucker BJ.Angiotensin II effects upon the glomerular microcirculation and ultrafiltration coefficient of the rat.J Clin Invest. 1976 Feb;57(2):419-34.

By Shankar Prasad Yadav
B.P.Koirala Institute of Health SciencesDharan, Nepal

Current knowledge and understanding ofthe Renin-Angiotensin-Aldosterone System (RAAS) and its effects on organ systems are based on the discoveryof renin made by Robert Tigerstedtin the 1890s.Tigerstedtprofessor of physiology, alongside his student P.G. Bergman,conducted experiments to prove the hypothesis that kidneys contributeto hypertension.1

Firstly, tissue extracts were methodically prepared from rabbit kidneys and subsequently injected intothe jugular veins of rabbits.A rise in blood pressure followed each injectionOther important findings included theobservation that the extract from the cortex led to a rise in blood pressure, while an extract from the medullary portion didnot. This observationbased on a simple experiment, allowed the conclusion that the substance causing hypertension originated from the cortex. Tigerstedt and Bergman also demonstrated that in a nephrectomized rabbit, blood injected from the renal arteriesincreased the blood pressure, leading to the conclusion that the substances causing hypertension are secreted into the bloodstreamInterestingly,during the experiment,it was noted that there was no altered activity in the heart and that this pressure effect was not neurallymediated. These conclusions were based on the observation that the pressure increased despite the high cervical section or crushing of the spinal cord. Since the substance and the effect werepredominantly related to the kidney (renal), the term “renin” was coined.1,2  

It was not until 1939 when reninwas found to be an enzyme rather an effectorand responsible for the production of angiotensin II,that the actual vasoconstrictor responsible for hypertension was properly understood.3

References:

  1. Tigerstedt R, Bergman PG. Niere und KreislaufSkand Arch Physiol. 1898(8):223–271
  2. Philips M.I, Schmidt-Ott KM. The discovery of renin 100 years ago. News Phsiol. Sci 1999(14). 271-274
  3. Braun-Menendez E, and I. H. Page. Suggested revision of nomenclature: angiotensin. Science 1958:127: 242

By Yosuke Hirakawa
Division of Nephrology and Endocrinology, the University of Tokyo Hospital, Japan

Alport syndrome, characterized by progressive renal failure, hearing impairment, and ocular changes, is a representative genetic kidney disease interpreted nowadays as a glomerular disease arising from genetic mutations in Col4A3Col4A4, or Col4A5. Alport syndrome has a long history, dating back to 1927 when Arthur Cecil Alport, a South African physician, identified this disease in a British family (1). Cases of familial nephritis, however, were reported even earlier; William Howship Dickinson was an English physician who published several case reports of kidney diseases at that time (2). He described familial cases of albuminuria as early as 1875. Dr. Dickinson was “a well-rounded physician,” and because of his involvement in a children’s hospital, he described hereditary albuminuria in four generations of a single family (3). His observations on familial albuminuria highlighted genetic cases of kidney diseases and contributed to the discovery of Alport’s disease.

References

  1. Alport Cecil A. Hereditary Familial Congenital Haemorrhagic Nephritis, Br Med J. 1927; 1(3454): 504–506.
  2. Dickinson W. H. Notes of four cases of intermittent haematuria. Lancet 1865;1: 568-9.
  3. Obituary. William Howship Dickenson, M.D.Cantab., F.R.C.P.Lond. Br Med J 1913;1:141

By Yosuke Hirakawa
Division of Nephrology and Endocrinology, the University of Tokyo Hospital

In 1924, Arthur Cecil Alport reviewed the family history of a 14-year-old boy he was examining. He found that almost all children in three generations of this family had hematuria, nephritis, and deafness. He re-examined a family previously reported by Guthrie in 1902, and Hurst in 1915, to have familial nephritis. In 1927, Alport published his study on what earlier physicians had called “hereditary familial congenital haemorrhagic nephritis,” reporting a familial case of nephritis and deafness. He described that (i) affected members originated from one deaf female over four generations, (ii) deafness was a marked feature, and (iii) affected male members developed nephritis and deafness and died before they reached adulthood (1). At that time, they could not determine whether this disease was congenital or not, and the researchers focused on the possibility of a bacterial contribution. Approximately 60 years later, it was demonstrated that a Col4A5 mutation causes X-linked Alport syndrome, and a Col4A3 or Col4A4 mutation causes autosomal dominant Alport syndrome (2, 3). In “thin basement membrane nephropathy,” the family history may test positive for hematuria, but kidney failure and deafness are typically absent or occur relatively late in life. Some experts consider this to be a variant of Alport syndrome. Despite the long history of describing this condition, effective treatment for Alport syndrome has not been established. While promising molecules are under investigation, researchers continue to look for novel pharmaceutical or genetic treatments (4, 5).

References

  1. Alport AC. HEREDITARY FAMILIAL CONGENITAL HAEMORRHAGIC NEPHRITIS. Br Med J. 1927;1:504-6
  2. Barker DF, Hostikka SL, Zhou J, et al. Identification of mutations in the COL4A5 collagen gene in Alport syndrome. Science 248:1224-1227,1990
  3. Mochizuki T, Lemmink HH, Mariyama M, et al. Identification of mutations in the alpha 3(IV) and alpha 4(IV) collagen genes in autosomal recessive Alport syndrome. Nat Genet 8:77-81, 1994
  4. Briggs JP and Hostetter TH. Editorial Note: From Both Sides Now. J Am Soc Nephrol. 2018;29:355-356.
  5. Yamamura T, Horinouchi T, Adachi T, et al. Development of an exon skipping therapy for X-linked Alport syndrome with truncating variants in COL4A5. Nat Commun 2020;11:2777.

By Muzamil Olamide Hassan
Renal Unit, Department of Medicine, Obafemi Awolowo University Teaching Hospital, Nigeria

To date, there have been relatively few actionable discoveries in genomics and nephrology. APOL1 risk variants are among the most powerful common risk variants identified as increasing the risk for chronic kidney disease. In 2010, two coding sequence variants in the APOL1 gene on chromosome 22 (identified in the 1000 Genomes Project) demonstrated by far the strongest association with chronic kidney disease. The first variant is two amino acid substitutions (S342G and I384M) near the C terminus that almost always occur together. Referred to as G1 and G2, the latter is a 6 base-pair deletion resulting in the loss of two amino acid residues, N388 and Y389. These two single nucleotide polymorphisms together confer resistance to Trypanosoma brucei infections and are common in West African populations. The G1 and G2 variants greatly increase the risk of human immunodeficiency virus-associated nephropathy, focal segmental glomerulosclerosis, chronic kidney disease attributed to hypertension, and non-diabetic kidney disease. Given the recent advances in understanding the role of APOL1 and its genetic variants in human kidney disease, it is believed that these discoveries will lead to important changes in clinical care, ultimately reducing the burden of kidney disease in patients of African descent.

References

  1. Kopp JB, Smith MW, Nelson GW, Johnson RC, Freedman BI, et al. MYH9 is a major-effect risk gene for focal segmental glomerulosclerosis. Nat. Genet. 2008,40:1175–84
  2. Kao WH, Klag MJ, Meoni LA, Reich D, Berthier-Schaad Y, et al. MYH9 is associated with nondiabetic end-stage renal disease in African Americans. Nat.Genet.2008, 40:1185–92
  3. Genovese G, Friedman DJ, Ross MD, Lecordier L, Uzureau P, et al. Association of trypanolytic ApoL1 variants with kidney disease in African Americans. Science 2010, 329:841–45
  4. Tzur S, Rosset S, Shemer R, Yudkovsky G, Selig S, et al. Missense mutations in the APOL1 gene are highly associated with end stage kidney disease risk previously attributed to the MYH9 gene. Hum. Genet. 2010, 128:345–50.
  5. Friedman DJ, Pollak MR. APOL1 and Kidney Disease: From Genetics to Biology. Annu.Rev.Physiol.2020.82:323–42

By Fabian Braun
University Medical Center Hamburg-Eppendorf, Germany

One ever-evolving field of research is the functional study of the glomerular filtration barrier. While electron microscopy analyses in the early days delineated the three major components – fenestrated endothelium, glomerular basement membrane, and podocyte foot processes – the molecular basis for the retainment of large macromolecules was poorly understood for many years. Karl Tryggvason and his group changed this when they successfully cloned a gene, NPHS1, encoding a glomerular transmembrane protein of the immunoglobin superfamily they termed “nephrin”1. In the same study, they identified mutations altering the transcription of nephrin to be the basis for congenital nephrotic syndrome of the Finnish type. In a follow-up investigation, they were able to determine the localization of nephrin to the podocytes and specifically to the slit diaphragm (SD)2. Tryggvason’s group has thus shaped our understanding of the interaction between SD proteins and podocyte ultrastructure, and thereby how we appreciate the development of proteinuria. The meticulous analyses, which identified additional slit diaphragm proteins, deepened our understanding of the precise structure of the glomerular filtration barrier.

References

  1. Kestilä M. et al. Positionally Cloned Gene for a Novel Glomerular Protein—Nephrin—Is Mutated in Congenital Nephrotic Syndrome. Mol Cell 1, 575–582 (1998).
  2. Ruotsalainen V. et al. Nephrin is specifically located at the slit diaphragm of glomerular podocytes. Proceedings of the National Academy of Sciences of the United States of America 96, 7962–7967 (1999).

By Sabine Karam
Saint George Hospital University Medical Center, Beirut, Lebanon

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common monogenic disorders in humans, affecting 1 in 1000 individuals. Mutations in the PKD1 gene located on chromosome 16 are the most common cause of ADPKD. The PKD1 sequence was first described in 1995, after obtaining the genomic sequence of the PKD1 locus and ascertaining the assembly of a PKD1 transcript from the sequence of 46 exons (1). The 14.5 kb PKD1 transcript was found to encode a 4304 amino acid protein that was identified as polycystin 1, an integral membrane protein involved in cell-cell/matrix interactions (2). The second gene, PKD2, that accounts for 15% of affected families, was localized on chromosome 4q21-23 (3, 4). Truncating mutations were identified in 1996 (5), leading to the discovery of polycystin 2. Both polycystins were found to have a role in the regulation of intracellular calcium (6, 7) and, as a result, affect the concentration of adenosine-3′,5′-cyclic monophosphate (cAMP) which plays a major role in cystogenesis (8, 9). These insights accelerated a broader understanding of the disease and moved the field toward directed therapeutic clinical trials for ADPKD. In 2004, the first therapeutic agent was identified. Known then as the vasopressin V2 receptor (VPV2R) antagonist OPC31260, the molecule was shown in a mouse model of ADPKD to reduce renal cyclic AMP (cAMP) levels with marked inhibition of cystogenesis (10). Shortly afterward, a randomized placebo-controlled trial was launched – the Tolvaptan Efficacy and Safety in Management of Autosomal Dominant Polycystic Kidney Disease and Its Outcomes (TEMPO) 3:4. This study was completed in 2012 and demonstrated that the modification of ADPKD progression was achievable following twice-daily oral dosing with tolvaptan, an oral selective vasopressin V2-receptor antagonist (11).

References

  1. Polycystic kidney disease: the complete structure of the PKD1 gene and its protein. The International Polycystic Kidney Disease Consortium. Cell. 1995;81(2):289-98. Epub 1995/04/21. doi: 10.1016/0092-8674(95)90339-9. PubMed PMID: 7736581.
  2. Hughes J, Ward CJ, Peral B, Aspinwall R, Clark K, San Millan JL, et al. The polycystic kidney disease 1 (PKD1) gene encodes a novel protein with multiple cell recognition domains. Nat Genet. 1995;10(2):151-60. Epub 1995/06/01. doi: 10.1038/ng0695-151. PubMed PMID: 7663510.
  3. Kimberling WJ, Kumar S, Gabow PA, Kenyon JB, Connolly CJ, Somlo S. Autosomal dominant polycystic kidney disease: localization of the second gene to chromosome 4q13-q23. Genomics. 1993;18(3):467-72. Epub 1993/12/01. doi: 10.1016/s0888-7543(11)80001-7. PubMed PMID: 8307555.
  4. Peters DJ, Spruit L, Saris JJ, Ravine D, Sandkuijl LA, Fossdal R, et al. Chromosome 4 localization of a second gene for autosomal dominant polycystic kidney disease. Nat Genet. 1993;5(4):359-62. Epub 1993/12/01. doi: 10.1038/ng1293-359. PubMed PMID: 8298643.
  5. Mochizuki T, Wu G, Hayashi T, Xenophontos SL, Veldhuisen B, Saris JJ, et al. PKD2, a gene for polycystic kidney disease that encodes an integral membrane protein. Science. 1996;272(5266):1339-42. Epub 1996/05/31. doi: 10.1126/science.272.5266.1339. PubMed PMID: 8650545.
  6. Koulen P, Cai Y, Geng L, Maeda Y, Nishimura S, Witzgall R, et al. Polycystin-2 is an intracellular calcium release channel. Nat Cell Biol. 2002;4(3):191-7. Epub 2002/02/21. doi: 10.1038/ncb754. PubMed PMID: 11854751.
  7. Nauli SM, Alenghat FJ, Luo Y, Williams E, Vassilev P, Li X, et al. Polycystins 1 and 2 mediate mechanosensation in the primary cilium of kidney cells. Nat Genet. 2003;33(2):129-37. Epub 2003/01/07. doi: 10.1038/ng1076. PubMed PMID: 12514735.
  8. Yamaguchi T, Pelling JC, Ramaswamy NT, Eppler JW, Wallace DP, Nagao S, et al. cAMP stimulates the in vitro proliferation of renal cyst epithelial cells by activating the extracellular signal-regulated kinase pathway. Kidney Int. 2000;57(4):1460-71. Epub 2000/04/12. doi: 10.1046/j.1523-1755.2000.00991.x. PubMed PMID: 10760082.
  9. Hanaoka K, Guggino WB. cAMP regulates cell proliferation and cyst formation in autosomal polycystic kidney disease cells. J Am Soc Nephrol. 2000;11(7):1179-87. Epub 2000/06/23. PubMed PMID: 10864573.
  10. Torres VE, Wang X, Qian Q, Somlo S, Harris PC, Gattone VH, 2nd. Effective treatment of an orthologous model of autosomal dominant polycystic kidney disease. Nat Med. 2004;10(4):363-4. Epub 2004/03/03. doi: 10.1038/nm1004. PubMed PMID: 14991049.
  11. Torres VE, Chapman AB, Devuyst O, Gansevoort RT, Grantham JJ, Higashihara E, et al. Tolvaptan in patients with autosomal dominant polycystic kidney disease. N Engl J Med. 2012;367(25):2407-18. Epub 2012/11/06. doi: 10.1056/NEJMoa1205511. PubMed PMID: 23121377; PubMed Central PMCID: PMCPMC3760207.