A defect in prorenin processing which may be intimately related to the nephropathy and hypertension of diabetes mellitus will be the focus of this collaborative investigation. The objective of this investigation is to define specific molecular and cellular defects in prorenin processing in diabetes and to determine whether this defect can be normalized by antihypertensive treatment which may retard the progression of nephropathy. This will be accomplished by the following goals: (1) Determine the structure of human recombinant prorenin by x-ray crystallographic analysis. This will allow us to identify specific sites in the prorenin molecule involved in (a) activation of renin, (b) interaction with the processing enzyme, or (c) regulation of intracellular sorting. (2) Use cultured AtT- 20 cells transfected with the human renin gene as a model system of constitutive and regulated secretion of prorenin and renin, respectively. We will determine how specific blocks in the regulated pathway affect constitutive secretion. (3) Evaluate structural or biochemical lesions in the diabetic kidney which could lead to increased prorenin production. Electron microscopy (EM) immunohistochemistry and measurement of prorenin processing activity will be performed on renal biopsy specimens from patients with and without diabetes mellitus and compared to results in AtT- 20 cells. (4) Determine the effect of antihypertensive treatment on diabetic nephropathy and plasma prorenin levels. We will assess the relationships between prorenin, albumin excretion, renal hemodynamics, and postaglandins and lipoxygenase products before and after therapy with inhibitors of the renin system. The knowledge of prorenin structure (Aim 1) will support identification of prorenin processing defects in an in vitro system (Aim 2) and in vivo (Aim 3). Application of these data to diabetics with nephropathy and hypertension may lead to a rational new approach to treatment (Aim 4).
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