Frank A. Carone

Identification and Localization of Polycystin, the PKD1 Gene Product

Polycystin, the product of autosomal dominant polycystic kidney disease (ADPKD) 1 gene (PKD1) is the cardinal member of a novel class of proteins. As a first step towards elucidating the function of polycystin and the pathogenesis of ADPKD, three types of information were collected in the current study: the subcellular localization of polycystin, the spatial and temporal distribution of the protein within normal tissues and the effects of ADPKD mutations on the pattern of expression in affected tissues. Antisera directed against a synthetic peptide and two recombinant proteins of different domains of polycystin revealed the presence of an approximately 400-kD protein (polycystin) in the membrane fractions of normal fetal, adult, and ADPKD kidneys. Immunohistological studies localized polycystin to renal tubular epithelia, hepatic bile ductules, and pancreatic ducts, all sites of cystic changes in ADPKD, as well as in tissues such as skin that are not known to be affected in ADPKD. By electron microscopy, polycystin was predominantly associated with plasma membranes. Polycystin was significantly less abundant in adult than in fetal epithelia. In contrast, polycystin was overexpressed in most, but not all, cysts in ADPKD kidneys.

CHANGES IN RENAL CONCENTRATING ABILITY PRODUCED BY PARATHYROID EXTRACT

Polyuria is a frequent symptom of hyperparathyroidism. Impairment of renal concentrating ability, often out of proportion to other signs of renal insufficiency, has been noted in patients with hyperparathyroidism (1-3) as well as in patients and animals with hypercalcemia due to other causes (4-6). In many patients with hyperparathyroidism, extensive deposits of calcium in the renal parenchyma, secondary fibrosis, superimposed pyelonephritis and vascular disease have combined to destroy considerable amounts of renal substance. The mechanism of the reported decrease in renal concentrating ability in such patients is not clear, since fixation of urinary specific gravity is a well-known accompaniment of the simple ablation of renal tissue (7). In the present experiments, renal concentrating capacity was found to be depressed in dogs in which hypercalcemia had been induced for only 24 hours by injecting parathyroid extract. This functional defect was associated with morphologic changes in the distal portions of nephrons and the collecting ducts.

Nephrogenic diabetes insipidus caused by amyloid disease: Evidence in man of the role of the collecting ducts in concentrating urine

Abstract A patient with renal amyloidosis was found to have marked impairment of renal concentrating ability, with polyuria and hyposthenuria unresponsive to vasopressin therapy. Postmortem microdissection studies revealed that the deposits of amyloid were localized chiefly in cuffs surrounding the medullary collecting ducts. These findings underline the role of the collecting ducts in the production of a concentrated urine in man.

Renal tubular necrosis induced by compounds structurally related to d-serine

Abstract d -serine is nephrotoxic in rats causing acute tubular necrosis of the straight segment of the proximal tubule. In an effort to determine the mechanism of this injury, the nephrotoxic effect of eighteen compounds structurally related to d -serine was investigated. Necrosis of the proximal straight tubules of rat kidneys was not observed with compounds wherein the hydroxyl or amino group of d -serine was blocked or eliminated, a methyl group was on the same carbon atom as the hydroxyl or amino group, the hydroxyl and amino groups were reversed, or the carbon chain lengthened. Only dl -2,3-diaminopropionic acid, other than d -serine itself, consistently induced proximal straight tubular necrosis. The l -isomer was without effect. Our results suggest that the nephrotoxicity observed with d -serine and dl -diaminopropionic acid is related to their selective absorption, based, within narrow limits, upon functional groups, size, and configuration of the molecule.

The treatment of the hemolytic-uremic syndrome with inhibitors of platelet function

In four patients with clinical and laboratory manifestations of the hemolytic-uremic syndrome, the administration of aspirin and dipyridamole was associated with a dramatic and rapid increase in the platelet count. In three of the four patients there was also improvement in neurologic or renal function. No subject experienced bleeding or other untoward effects. We conclude that a trial of aspirin and dipyridamole therapy is warranted early in the course of the hemolytic-uremic syndrome.

Recent advances in the understanding of polycystic kidney disease

Polycystic kidney disease is characterized by localized autonomous cellular proliferation, compartmentalized fluid accumulation within the cysts, and intraparenchymal fibrosis of the kidney. The clinical features include renal failure, liver cysts, and vascular and cardiac valve abnormalities. Recent developments have extended our understanding of cyst formation, fluid secretion, and the genetics of polycystic kidney disease. Two causal genes for polycystic kidney disease, PKD1 and PKD2, that are responsible for greater than 95% of cases of autosomal dominant polycystic kidney disease, have been identified and sequenced. The mechanisms of cystogenesis are being uncovered and the phenotypic features of cystic epithelial cells are being discovered. This review describes recent advances made in the molecular biology of the genetic causes of polycystic kidney disease. The mechanistic details of cystogenesis are discussed and contrasted with the paradigms that guide current experimental approaches.

The Pathogenesis of Polycystic Kidney Disease

Polycystic kidney disease (PKD) is a genetic or acquired disorder characterized by progressive distention of multiple tubular segments and manifested by fluid accumulation, growth of non-neoplastic epithelial cells and remodeling of the extracellular matrix resulting ultimately in some degree of renal functional impairment, with the potential for regression following removal of the inductive agent(s). It is due to an aberration of one or more factors regulating tubular morphogenesis. Human PKD can pursue a rapid course with renal failure occurring perinatally (infantile PKD) or an indolent course without renal failure developing during the life of the individual (adult PKD). Human acquired PKD develops in atrophic and scarred end-stage kidneys with non-cystic forms of renal disease. Cell proliferation, fluid secretion, impaired cell-cell and cell-matrix interaction, defective function of the Golgi apparatus, cell undifferentiation, and an abnormal matrix have been implicated in the pathogenesis of PKD based on clinical and experimental studies. Under normal conditions, the dynamic turnover of tubular epithelia and matrices are tightly regulated to maintain tubular morphology. The basic defect in PKD is tubular dysmorphogenesis. Our finding indicates that the principal phenotypic features of autosomal dominant PKD (ADPKD) are altered structure and function of the Golgi complex, altered structure and composition of the matrix and cell undifferentiation, all of which are probably interrelated. If the gene product of the ADPKD 1 gene results in a defective matrix, the abnormal Golgi function and cell differentiation may be due to faulty matrix-cell communication.

Compounds protective against renal tubular necrosis induced by d-serine and d-2,3-diaminopropionic acid in the rat☆

Abstract d -Serine and d -2,3-diaminopropionic acid ( d -DAPA) induce necrosis of the epithelial cells of the proximal straight tubules of the rat kidney. Nineteen compounds with chemical structures and/or functional groups similar to d -serine or d -DAPA were tested for their protective effect against the induction of this injury. The acute tubular necrosis inducible by d -serine and d -DAPA was prevented by d -alanine, d -threonine, d -homoserine, dl -α-methyl serine, β-hydroxy- dl -leucine, and α-aminoisobutyric acid. In addition, protection from necrosis due to d -DAPA, but not that due to d -serine, was found with l -threonine, l -serine, l -2,3-diaminopropionic acid, and 3-hydroxypropionic acid. Little or no protective effect against d -serine of d -DAPA was afforded by l -alanine, β-alanine, dl -isoserine, dl -3-hydroxybutyric acid, l- or dl -lactic acid, 2-amino-2-methyl-1-propanol, taurine, and isethionic acid. The compounds that protected against d -serine-induced necrosis had in common the d -configuration (except for aminoisobutyric acid), the α-amino group, and the carboxyl group. The structural characteristics and chirality of the protective agents against d -DAPA were more varied and less definable than for d -serine. d -Alanine, dl -α-methyl serine, and α-aminoisobutyric acid protected on a mole-for-mole basis against d -serine-induced necrosis. d -Alanine was protective against d -serine even when given 30 min after d -serine administration. These results suggest that protection may be due to competition with d -serine or d -DAPA for a cellular or transport binding site.

Diverse aspects of metanephric development

Mammalian nephrogenesis constitutes a series of complex developmental processes in which there is a differentiation and rapid proliferation of pluripotent cells leading to the formation of a defined sculpted tissue mass, and this is followed by a continuum of cell replication and terminal differentiation. Metanephrogenesis ensues with the intercalation of epithelial ureteric bud into loosely organized metanephric mesenchyme. Such an interaction is reciprocal, such that the intercalating ureteric bud induces the conversion of metanephric mesenchyme into an epithelial phenotype, while the mesenchyme stimulates the iterations of the ureteric bud. The induced mesenchyme then undergoes a series of developmental stages to form a mature glomerulus and tubular segments of the kidney. Coincidental with the formation of these nephric elements, the developing kidney is vascularized by the process of vasculogenesis and angiogenesis. Thus, the process of metanephric development is quite complex, and it involves a diverse group of molecules whos biological activities are inter‐linked with one another and they regulate, in a concerted manner, the differentiation and maturation of the mammalian kidney. This diverse group of molecules include extracellular matrix (ECM) proteins and their receptors, ECM‐degrading enzymes and their inhibitors, growth factors and their receptors, proto‐oncogenes and transcription factors. A large body of literature data are available, which suggest a critical role of these molecules in metanephric development, and this review summarizes the recent developments that relate to metanephrogenesis. Microsc. Res. Tech. 39:261–284, 1997.

ROLE OF THE MATRIX IN AUTOSOMAL DOMINANT POLYCYSTIC KIDNEY DISEASE

At present, even though we have accumulated a wealth of knowledge regarding structural, and molecular changes in ADPKD, the primary cause of the disease remains unknown. Obviously the gap in our understanding of the nature of the disease has been narrowed substantially over the past decade. With current techniques and efforts, the ultimate mystery of ADPKD should be resolved during the next decade.