Selective loss of pericytes is an early pathological change in diabetic retinopathy. The loss of pericytes may impair the integrity of the retinal microvasculature, leading to breakdown of the blood-ocular barrier. We have previously found that high glucose reduces pericyte viability and also decreases phosphatidylinositol bisphosphate (PIP2) levels. We hypothesize that the reduction in pericyte viability by high glucose is mediated through the inositol phospholipid-signal transduction process. In this application we propose to study the biochemical mechanisms by which this occurs. Activated sorbitol pathway and decreased myo-inositol content induced by high glucose may alter cell signal transduction through reduced PIP2 levels. We propose to study pericyte metabolism under high glucose conditions to determine what leads to the decrease in PIP2. Gp, a member of the family of GTP-binding proteins, couples external signal receptors to the enzyme phosphoinositidase (PIase) which catalyzes PIP2 hydrolysis. Therefore, Gp levels and PIase activities will be determined. The products of PIP2 hydrolysis and other signal messengers (IP3, DG, cAMP, intracellular Ca+2 and Protein kinase C and A) will also be measured. The incorporation of tritium-labelled thymidine, an index of cell proliferation, will be used to correlate components of the inositol phospholipid signal system with pericyte viability. In the proposed studies, the supplementation of myoinositol, insulin or aldose reductase inhibitors to pericytes grown in high glucose medium will be used as in vitro """"""""therapy"""""""" to attempt to correct the reduced rate of pericyte proliferation. The results of these investigations may lead to a better understanding of the pathogenesis of diabetic retinopathy.
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