REGULATION OF NORMAL AND CYSTIC RENAL TUBULOGENESIS

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Developmental abnormalities in renal tubule morphogenesis and function are characteristic of polycystic kidney disease, a major genetic disorder in humans that affects over 500,000 people in the United Stats. The cause of the disease is unknown, but it has been postulated that increased cell proliferation and altered transtubular fluid transport are important. Our long term objectives are to understand the morphoregulatory mechanisms involved in the development of normal renal tubule epithelia organization, and to determine whether these mechanisms are altered during development of polycystic kidney disease. We have established in vitro methods to analyze renal epithelial cell development (Transfilter Cultures), and the role of candidate morphogenetic factors in tubulogenesis that will be extended to analyze cells from cystic tubule epithelia of cpk mice, a murine model of polycystic kidney disease. Our preliminary studies show that in early development Na/K-ATPase is transiently localized to the apical membrane domain of normal cells, but is continuously expressed on the apical membrane in cystic epithelial cells. Our previous results indicate that the normal distribution of Na/K-ATPase at the basal-lateral membrane is generated by cell-cell contact and interactions with the membrane- cytoskeleton and membrane lipids. We will test the hypothesize that abnormal regulation of soluble factors that induce tubulogenesis in development could lead to increased cell proliferation of tubular epithelia and, combined with the retention of active Na/K-ATPase on the apical membrane, the formation of cystic tubules: 1. Define the temporal and spatial regulation of Na/K-ATPase distribution following mesenchyme induction and conversion to epithelial cells during normal development. Patterns of expression and distribution of Na/K- ATPase, membrane-cytoskeleton, and membrane lipids will be determined. 2. Modulate the timing of E-cadherin-induced cell-cell interactions during mesenchyme conversion and epithelial cell differentiation. Effects of inhibiting cell-cell contacts on cell differentiation and tubulogenesis during metanephrogenic mesenchyme induction and conversion in culture will be analyzed. 3. Investigate mesenchyme induction and epithelial cell differentiation in transfilter cultures from metanephroi of CPK mice. Patterns of expression and distribution of Na/K-ATPase, membrane-cytoskeleton, and membrane lipids will be determined and compared temporally and spatially to those in normal development. 4. Analyze the expression and function of soluble factors, that regulate tubulogenesis in vitro, on normal and cystic epithelial cell differentiation and tubulogenesis. Expression and function of Scatter Factor/Hepatocyte Growth Factor (SC/HGF), a potent inducer of tubulogenesis in renal epithelial cells in vitro, will be examined in cultures of developing renal tubules from normal and cystic metanephroi, and in purified populations of normal and cystic epithelial cells induced to form branching tubular networks in vitro.