Experimental diabetic neuropathy exhibits a variety of well characterized biochemical and functional abnormalities. These include impaired peripheral nerve conduction velocity, reduced myo-inositol content, diminished Na+, K+-ATPase activity and decreased axonal transport. However, the pathogenesis of this disorder remains poorly understood. Recently, we have demonstrated that the turnover of phosphatidylinositol-4,5-bisphosphate (PIP2) and the phosphorylation of several myelin proteins is enhanced in nerves from both streptozotocin-induced diabetic rats and Wistar fatty diabetic rats. The overall goal of this project is to strengthen the hypothesis that these metabolic alterations are intimately involved in the development of peripheral nerve dysfunction. To accomplish this, four specific aims will be pursued. (1) We will extend the correlation between altered lipid and protein phosphorylation and other biochemical, morphological and functional abnormalities to several additional spontaneously diabetic rodent models, specifically the Biobreeding (BB-Wor) rat, the nonobest diabetic mouse and to Wisar fatty diabetic animals that have been hyperglycemic for up to 18 months. (2) We will investigate whether the metabolic alterations are manifested in nerves from normal rats maintained in an O2-poor environment known to produce endoneurial hypoxia and are prevented or reversed in diabetic rats placed in an 02-supplemented atmosphere. (3) Our findings suggest that protein kinase C (PKC) mediates increased myelin protein phosphorylation in diabetic nerve. Stimulated turnover of polyphosphoinositides in diabetic nerve could elevate 1,2-diacylglycerol levels, thereby enhancing activity of protein kinase C in-causing increased phosphorylation of accessible, possibly novel, sites on affected myelin proteins. To test this proposition, we will (a) firmly establish that PKC is responsible for enhanced protein phosphorylation through use of activators and inhibitors of this enzyme; (b) compare the levels of PKC activity and its distribution between myelin and cytosol in normal and diabetic nerve; (c) measure the content, fatty acid composition and molecular species profile of 1,2-diacylglycerol in normal and diabetic nerve; (d) assess whether the distribution of incorporated radioactive phosphorate groups at sites in the myelin glycoprotein, Po is altered in diabetic as compared to normal nerve. (4) We will determine the content at the ultrastructural level of elemental Na, K, P, Cl and Ca in axoplasm, axonal mitochondria, myelin and Schwann cell cytoplasm in the internode and at the node of Ranvier of normal, diabetic and hypoxic nerve by X-ray microanalysis. The high resolution analytical technique will enable us to ascertain whether and at what locations elemental (and by inference, ionic) composition and distribution is perturbed in diabetic nerve. This investigation should provide new information bearing on the etiology of experimental diabetic neuropathy and may have relevance to the pathogenesis of the human disease.
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