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Biomedical subjects

E D Avner

Publications and source records attributed to E D Avner.

At least 73 records · Page 4Linked to original sources
PubMed1993

Epithelial polarity and differentiation in polycystic kidney disease.

Renal cysts are central pathological features in a number of human congenital and acquired diseases, and produce significant morbidity and mortality. This review describes our laboratory's efforts to identify specific alterations in epithelial cell polarity and differentiation associated with renal tubular cyst formation and progressive enlargement. Studies in a murine model of human autosomal recessive polycystic kidney disease, the C57BL/6J cpk/cpk (CPK) mouse have demonstrated quantitative (increased activity) and qualitative (apical membrane distribution) alterations in Na+,K(+)-adenosine triphosphatase activity that mediate tubular cyst formation. Proximal tubular cyst formation in CPK kidneys is characterized by increased activity of a basolateral Na+,K(+)-ATPase, which drives organic anion secretion and consequent tubular fluid secretion. In contrast, collecting tubule cyst formation is characterized by increased apical membrane Na+,K(+)-ATPase expression, which may be a marker of the relatively undifferentiated phenotype of cyst lining cells. If such apically expressed enzyme is active, it may have pathogenic import in collecting tubule cyst formation and enlargement by mediating net basal to apical vectorial solute and fluid transport.

Animals↗
PubMed1993

A new murine model of autosomal recessive polycystic kidney disease.

We describe the renal cystic disease occurring in a new inbred strain of mice which developed as a spontaneous mutation in otherwise healthy Balb/c mice. The disease displays characteristics of an autosomal recessive polycystic kidney disease. Affected animals develop massive cystic enlargement of the kidneys and die of renal failure at the age of 4 weeks. During postnatal development, there is a gradual shift in site of the lesions. At birth, cystic dilations are localized almost exclusively in proximal tubular segments, whereas in the terminal stages of the disease, 80% of the cysts are localized in collecting tubular segments as defined by segment specific lectin binding. The composition of the basement membrane of the cystic tubular walls during postnatal development as analyzed by immunocytochemistry is essentially normal during the earliest stage of cyst formation. However, with disease progression, the cystic tubular basement membrane demonstrates a decreased immunoreactivity to anti-laminin and anti-entactin antibodies. This indicates a shift in cyst localization during disease progression in this model, and suggests that basement membrane abnormalities are not a primary feature of the early cyst formation and progressive enlargement.

Animals↗
PubMed1992

Abnormal sodium pump distribution during renal tubulogenesis in congenital murine polycystic kidney disease.

Congenital polycystic kidney disease is characterized by the formation of large fluid-filled cysts in kidney tubules. It has been postulated that increased epithelial cell proliferation and altered transtubular fluid transport are necessary for cyst formation. To address the latter problem, we have studied the plasma membrane distribution of the alpha 1 and beta 1 subunits of Na+/K(+)-ATPase during progressive stages of proximal and collecting tubular cyst formation in the CPK mouse, a murine model of autosomal recessive polycystic kidney disease. In both control and cystic proximal tubules, Na+/K(+)-ATPase distribution was restricted to the basal-lateral membrane of cells. However, in newborn through day 5 kidney tissue, 16% of control vs. 47% of cystic outer cortical, 6% of control vs. 46% of cystic inner cortical, and 2% of control vs. 63% of cystic medullary collecting tubules demonstrated apical and lateral membrane distribution of Na+/K(+)-ATPase. In all nephrogenic zones, the percentage of control or cystic collecting tubules demonstrating apical membrane distribution of Na+/K(+)-ATPase decreased over time, but the percentage of cystic collecting tubules with apical membrane Na+/K(+)-ATPase remained significantly greater than in developmentally matched controls. No alterations in the normal distributions of other apical or basal-lateral membrane marker proteins were noted at any stage of control or cystic proximal or collecting tubule development. We conclude that apical-lateral membrane Na+/K(+)-ATPase expression is a normal transient feature of early collecting tubule development. However, apical membrane Na+/K(+)-ATPase persists in cystic kidneys, suggesting that such expression may be a manifestation of the relatively undifferentiated phenotype of epithelial cells lining collecting tubule cysts. The persistence of apical membrane Na+/K(+)-ATPase, if the enzyme is functional, may have pathogenic important in abnormal transtubular fluid transport in polycystic kidney disease.

Aging↗
PubMed1992

The case against screening urinalyses for asymptomatic bacteriuria in children.

Screening children for asymptomatic bacteriuria to prevent pyelonephritis and renal scarring is widely recommended, but its cost-effectiveness has not been established. We reviewed published studies to determine the costs and benefits of screening toilet-trained, asymptomatic children for bacteriuria. Given the sensitivity and specificity of current screening methods (approximately 80% each) and the prevalence of bacteriuria in asymptomatic children (approximately 1% in girls and 0.03% in boys), screening 100,000 children would result in 19,897 (20%) false-positive tests; initial screening and two urine cultures to confirm the diagnosis of asymptomatic bacteriuria would miss 28% of 515 children with true bacteriuria, and cost nearly $2.9 million. There is no evidence that detection and treatment of children with asymptomatic bacteriuria prevents subsequent pyelonephritis or renal scarring. Screening for bacteriuria in asymptomatic children is costly, fails to prevent pyelonephritis or renal scarring, and should be discontinued as a part of routine well-child care.

Bacteriuria↗
PubMed1991

Localization of arginine biosynthetic enzymes in renal proximal tubules and abundance of mRNA during development.

Argininosuccinate synthetase and argininosuccinate lyase catalyze the conversion of citrulline to arginine in kidney. Immunohistochemical staining of mouse kidney sections with antibodies to these two enzymes, compared with the staining patterns of known markers for proximal tubules, demonstrated that these enzymes are localized within the proximal tubules. The relative abundance of mRNA encoding argininosuccinate synthetase and argininosuccinate lyase during fetal and postnatal development of mouse kidney was also determined. Changes in relative abundance of these mRNA in kidney are coordinate during development, paralleling the developmental profile of phosphoenolpyruvate carboxykinase mRNA, which is also expressed in proximal tubules. Although relative abundances of the mRNA are comparable in liver and kidney of adult mice, the profiles of mRNA abundance during development of these two organs are distinct. The results indicate that these enzymes and their corresponding mRNA can serve as useful markers for examining the differentiation and development of renal proximal tubules in vivo and in cultured explants.

Animals↗
PubMed1990

Polypeptide growth factors and the kidney: a developmental perspective.

A variety of polypeptides with stimulatory or inhibitory effects on cell proliferation have been identified. In addition to stimulating or inhibiting the proliferation of cells and maintaining their viability, polypeptide growth factors play significant roles in embryogenesis and differentiation. The current review focuses on five specific polypeptide growth factor families (epidermal growth factor, insulin-like growth factors, transforming growth factors, platelet-derived growth factor, and fibroblast growth factors) and discusses their possible relationship to normal renal physiology, abnormal renal pathophysiology, and renal organogenesis. On the basis of current data, it is clear that polypeptide growth factors are multifunctional agents with important effects on renal function and renal organogenesis.

Growth Substances↗
PubMed1990

Polypeptide growth factors in metanephric growth and segmental nephron differentiation.

Although the developing nephron expresses receptors for various polypeptide growth factors, the specific roles of such factors in renal organogenesis are unknown. Therefore, the effects of epidermal growth factor (EGF) (8.2 x 10(-11) M-1.6 x 10(-8) M), multiplication stimulating activity (MSA) (6.6 x 10(-10) M-1.3 x 10(-8) M) and transforming growth factor beta (TGF-beta) (1 x 10(-12) M-1 x 10(-9) M) on organotypic renal growth and segmental nephron differentiation were studied in a serum-free hormone-supplemented, murine metanephric organ culture system. Following culture in control or growth-factor-supplemented medium, explant growth was assessed, and explant growth and differentiation were determined morphometrically in four defined neprhon segments which were identified morphologically or immunohistologically with segment-specific antibodies and/or lectins: glomeruli, proximal tubules, thick ascending limb-early distal tubules, and collecting tubules. Results showed that EGF increased overall renal growth and specific differentiation of distal elements, but retarded differentiation of glomeruli and proximal tubules. EGF also induced hyperplastic cystic malformation in proximal tubules. MSA stimulated explant growth and promoted segmental differentiation of all tubular segments. TGF-beta globally retarded in vitro nephrogenesis. Such data demonstrate that polypeptide growth factors have multiple and often disparate effects on overall renal growth in relation to differentiation of discrete nephron segments and provide insight into the factors which may regulate normal and abnormal renal embryogenesis.

Animals↗
PubMed1989

Abundance of mRNAs encoding urea cycle enzymes in fetal and neonatal mouse liver.

The relative abundances of mRNAs encoding the five urea cycle enzymes during development of mouse liver have been determined and compared with those of mRNAs encoding four other liver-specific proteins (phosphoenolpyruvate carboxykinase, tyrosine aminotransferase, alpha-fetoprotein, and albumin). Urea cycle enzyme mRNAs in fetal liver are expressed at 2-14% of the abundance in adult liver as early as 6 days before birth. Expression of the urea cycle enzyme mRNAs is not coordinate during the fetal and neonatal period. However, profiles of three urea cycle enzyme mRNAs are quite similar to that of alpha-fetoprotein mRNA, suggesting the possibility of a common response to regulatory signals during fetal development. With the exception of ornithine transcarbamylase mRNA, the urea cycle enzyme mRNAs have been shown previously to be inducible by cAMP and glucocorticoids. However, only argininosuccinate lyase mRNA exhibits any significant change in abundance at birth, resembling postnatal expression of tyrosine aminotransferase mRNA. The results indicate that the urea cycle enzyme mRNAs are potentially useful markers for elucidating various features of hepatocyte differentiation in mammals.

Albumins↗
PubMed1989

Choice of urine sample predictive of microalbuminuria in patients with insulin-dependent diabetes mellitus.

Twenty-four-hour, four-hour (8 to 12 am), and overnight urine collections were examined for their ability to detect microalbuminuria in 292 patients with insulin-dependent diabetes mellitus (IDDM). Albumin excretion rate (AER) was measured and also estimated from the product of the urinary albumin/creatinine ratio (A/C) and the calculated 24-hour creatinine excretion. The fractional excretion of albumin (FEA) was also determined in aliquots from each urine sample. The correlation coefficients between measured 24-hour AER and estimated AER were 0.940 and 0.956 for four-hour and overnight collections, respectively (significance of each correlation, P less than 0.001). There was no advantage in using the FEA over the A/C ratio in predicting measured AER. Urinary A/C ratios (mg/mg) between 0.03 and 0.31 in the four-hour collections were highly predictive of microalbuminuria and of measured AER in the 24-hour collections: AER24-h (microgram/min/1.73 m2) = 2.74 + 0.870 x A/C4-h (all log10 values). In a subgroup of 175 patients having all three collections validated, 34 (20%) had microalbuminuria defined as AER 20 to 200 micrograms/min/1.73 m2 in at least two of the three samples and 44 (25%) had overt nephropathy (greater than 200 micrograms/min/1.73 m2). The ability of the AER in one urine collection to predict microalbuminuria in at least one of the other two collections was assessed in these 175 patients. Compared with the overnight urine collection, the four-hour collection had greater sensitivity while affording similar specificity and positive predictive value. Based on these data, the A/C ratio from a morning urine sample following initial AM voiding would seem adequate for the detection and monitoring of microalbuminuria in patients with IDDM.

Adult↗
PubMed1989

In vitro modulation of tubular cyst regression in murine polycystic kidney disease.

Recent studies in a murine model of genetically-determined polycystic kidney disease, the CPK mouse, have suggested that alterations in renal Na-K ATPase activity in concert with tubular epithelial hyperplasia have pathogenic import in proximal tubular cyst formation. In the current study, we therefore studied the relative roles of Na-K ATPase activity, tubular epithelial hyperplasia, and basal lamina alterations during in vitro modulation of proximal tubular cyst regression during serum-free organ culture of newborn CPK kidneys. Under basal in vitro conditions, regression of CPK proximal tubular cysts was demonstrated in association with progressive decreases in Na-K ATPase activity and tubular epithelial hyperplasia. The pattern of proximal tubular cyst regression was modified by: a) Na-K ATPase activity induction with triiodothyronine, which promoted proximal tubular cystogenesis; and b) Na-K ATPase activity inhibition with ouabain, which blocked the effects of T3 on the process of cyst formation. Modulation of proximal tubular cystogenesis by Na-K ATPase induction and inhibition were accomplished without significant changes in proximal tubular epithelial hyperplasia or expression of basal lamina components. We conclude that increased Na pump activity may have a significant role in proximal tubular cyst formation and progressive enlargement in the CPK mouse.

Animals↗
PubMed1988

Congenital murine polycystic kidney disease. II. Pathogenesis of tubular cyst formation.

In the current study, the pathogenesis of proximal tubular cyst formation was studied in an animal model of polycystic kidney disease, the CPK mouse. The specific roles of (a) sodium-potassium adenosine triphosphatase (Na-K ATPase) activity, determined by an enzyme-linked kinetic microassay, (b) proximal tubular epithelial hyperplasia, determined by calculation of mitotic indices, and (c) altered proximal tubular basal lamina formation, determined by immunohistological localization of basal lamina glycoproteins, were investigated at progressive developmental stages of CPK proximal tubular cyst formation. Increases in renal Na-K ATPase were present at the earliest fetal stages of proximal tubular cyst formation, and subsequently paralleled the course of proximal tubular cyst progression. Proximal tubular epithelial hyperplasia, although not present at the earliest stages of cyst formation, was a consistent feature of progressive proximal tubular cystic enlargement. Abnormalities in basal lamina glycoprotein expression were not present at any stage of proximal tubular cyst development. We conclude that increased Na-K ATPase and tubular epithelial hyperplasia are significant features of proximal tubular cyst formation in the CPK mouse.

Age Factors↗
PubMed1988

Renal epithelial development in organotypic culture.

An in vitro model system for the experimental study of renal epithelial differentiation is described. Fetal murine metanephric tissue consisting of nephrogenic blastema and branched ureteric bud is isolated following 24-36 h of natural embryonic inductive interaction (13 +/- 0.4 days gestation) and cultured as an intact organ in a Trowell-type assembly. During 120 h of organ culture incubation in completely defined serum-free medium, advanced organotypic proximal tubular and glomerular epithelial differentiation proceed in the absence of vascularization, perfusion, and urine production. The system thus experimentally separates the processes of three-dimensional organ growth and post-induction renal epithelial differentiation from glomerular filtration, flow-related phenomena, endothelial or mesangial cell interactions, and the effects of growth factors or transport substrates present in mammalian serum or urine. Studies to date in the model system have defined the growth factor requirements of epithelial growth and differentiation and have demonstrated that specific hormonally induced alterations in tubular epithelial cell metabolism and function may lead to specific patterns of tubular maldevelopment. Whole organ metanephric organ culture is thus a valuable in vitro model system for future investigations into the complex processes of normal and abnormal renal epithelial differentiation.

Animals↗
PubMed1988

Regulation of glucocorticoid receptors and Na-K ATPase activity by hydrocortisone in proximal tubular epithelial cells.

The effect of hydrocortisone (HC) in modulating glucocorticoid receptors (GR) and sodium-potassium adenosine triphosphatase (Na-K ATPase) activity was studied in primary cultures of immunoisolated murine proximal tubular epithelial cells (PTEC). Utilizing monoclonal antibody against stage-specific embryonic antigen-1, a homogeneous population of PTEC was obtained in high yield. The cells were cultured to confluence and further treated for 48 h in serum-free growth medium containing no HC (control); 50 nM HC; or 50 nM HC plus 20 nM of the antiglucocorticoid, RU 38486. PTEC treated with 50 nM HC had 56% of GR binding and 160% Na-K ATPase activity as compared to controls (P less than 0.01). GR binding was abolished by incubation in RU 38486 whereas Na-K ATPase fell below control values (P less than 0.05). Brief incubations of HC-treated PTEC with 0.5 mM ouabain resulted in a fall in GR binding without a change in Na-K ATPase activity. These data indicate that in PTEC, HC regulates GR binding and they suggest that stimulation of Na-K ATPase activity is a direct biological response to this receptor-hormone interaction. Thus, primary cultures of immunoaffinity-isolated PTEC offer a good model system for investigating the molecular basis underlying the regulation of GR binding and postreceptor events influenced by glucocorticoids.

Animals↗
PubMed1988

Immunocytochemical localization of gamma-glutamyltranspeptidase during fetal development of mouse kidney.

In the fully developed kidney, gamma-glutamyltranspeptidase is localized predominantly to the apical plasma membrane of the proximal tubules. The appearance of this activity during murine fetal nephrogenesis was quantitated using a sensitive fluorometric assay, and development of membrane polarity was assessed by immunocytochemistry. Specific activity of the transpeptidase in 13-day fetal kidney was approximately 1 mU/mg protein. Between 13-21 days of gestation, total transpeptidase activity increased 7500-fold, whereas specific activity increased 50-fold. At 13 days of gestation, gamma-glutamyltranspeptidase immunoreactivity is localized to the apical surfaces of developing renal vesicles and the proximal segment of the S-shaped tubules. The organized cell structures have tight tubular junctions but lack a well-defined brush-border membrane. By 15 days of gestation, immunostaining of the apical surface of developing proximal segments is more prominent, and slight reactivity of the basolateral membrane is evident. By 17 days of gestation, the kidney is organized into discrete zones. The large increase in gamma-glutamyltranspeptidase activity correlates with the appearance of increased immunostaining of the developing brush-border membranes of the proximal tubules contained in the inner cortex. A very similar although somewhat delayed pattern of appearance of transpeptidase activity and immunostaining was observed in metanephric organ culture. Induction of proximal tubular cyst formation had no effect on the increase in transpeptidase activity that occurred during organotypic nephrogenesis.

Animals↗