GLOMERULAR LAMININS--STRUCTURE AND FUNCTION

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Cell-matrix interactions are critically important to cellular adhesion, proliferation, differentiation and regulation of matrix synthesis. Specificity of these interactions is determined by the subset of extracellular matrix (ECM) proteins expressed in a particular compartment and the subset of ECM protein receptors expressed by individual cells. Family members of collagen IV and laminin (LM) that are present within glomeruli are relatively unique and have limited distribution in other renal and non-renal ECMs. In renal diseases associated with glomerulosclerosis, the sclerotic lesions contain ECM proteins normally present as well as newly expressed ones. In preliminary studies of diabetic nephropathy and mesangial cells (MC) in culture, we have shown-that the mesangium contains unique isoforms of LM and that insulin and angiotensin II regulate their synthesis and accumulation. Based on these data, we hypothesize that normal MC secrete two classes of LM heterotrimers, a class that contains B2 and entactin and influences ECM assembly. A second class contains unique MC LMs that lack entactin, are concentrated on the cell surface and have unique functions within the glomerulus. Insulin and angiotensin II regulate the rate of synthesis of individual LM chains. In disease states where levels of these hormones are elevated for significant periods of time, their effects lead to progressive increases in LM isoforms normally present in low abundance. These changes lead to alterations in the structure and function of the mesangium, alter feedback regulation of ECM synthesis and ultimately contribute to loss of renal function. These hypotheses will be examined by the following specific aims: 1. Two new LM chains unique to the MC will be cloned, sequenced, and the heterotrimeric composition of MC LMs determined. 2. The mechanisms of insulin and angiotensin II-mediated changes in synthes of individual LM chains will be determined. Feedback regulation by B1 monom and its control by insulin and angiotensin II will be defined. 3. The function of unique MC LMs will be assessed by their ability to induc phenotypic changes and gene activation. The relationship to glomerular innervation, tile neurotrophins, and wound healing/scarring will be examine 4. The relevance of insulin and angiotensin II-mediated alterations in LM isoform expression to the development of glomerulosclerosis in diabetes and aging will be examined using in vivo models of these diseases. These studies will contribute basic information on structure and function o unique glomerular LMs and establish the role of insulin and angiotensin II regulation of LM synthesis and accumulation in glomerular disease.