We proposed that many of the retinal, renal and cardiovascular pathologies in diabetes are due to the activation of diacylglycerol (DAG) and protein kinase C (PKC), especially ?1/2 and d isoform pathways induced by hyperglycemia (HG). A large body of evidence in cultured vascular cells and vascular tissues (retinal, renal, glomeruli, arteries and myocardium) from diabetic animals and patients have shown that DAG/ PKC pathways are activated and associated with increases in cytokine expression or activities (VEGF, ET-1, PDGF ? orTGF ?, ICAM's), capillary permeability, matrix protein production, changes in signaling molecules (MAP kinases and AKT) and elevation of oxidative stress via NADPH oxidase activation. Clinical studies have shown that PKC ? isoform selective inhibitor ruboxistaurin (RBX) preserved visual acuity, renal function and endothelial functions in the presence of hyperglycemia. However, for diabetic retinopathy (DR), treatment with RBX did not prevent the progression to proliferative retinopathy, but accelerated the resolution of macular edema. Both basic and clinical results suggest that PKC ? isoform activation may selectively affect endothelial functions. We have provided preliminary data to show that hyperglycemia enhanced pericyte apoptosis, which parallels with PKC d isoform and p38 MAPK activation, remained elevated even after the cells were returned to normal glycemic condition. Thus, these results suggest that the pericyte cell model could be a model of """"""""Metabolic Memory"""""""" as observed in clinical studies. Thus, we are proposing that the differential activation of PKC ? 1/2 and d isoforms induced by hyperglycemia, are causing different and specific cellular changes in retinal endothelial cells and pericytes, respectively. Thus, to prevent the progression of DR, both PKC ? 1/2 and d isoforms may need to be normalized. To test this new hypothesis, we will: (1) identify the specific signaling mechanisms by which PKC ? 1/2 and d isoforms are mediating their different effects in retinal endothelial cells (activation of ERK1/2 MAPK-occludin and others) and pericytes (p38 MAPK, NADPH oxidases) ? and others;(2) define the isoform selective roles of PKC ? 1/2 and d isoforms on the various changes in biochemical, hemodynamic and pathological parameters observed in the endothelial cells and pericytes by using control and diabetic PKC ?-/- and d-/- mice and endothelial cell targeted overexpression of PKCP2 in C57/BL6 mice. Finally, the idea of dual activation of PKC ? / d isoforms are needed to induce DR will be tested by treating diabetic PKC d-/- mice with PKC ? specific inhibitor RBX to determine whether most of the retinal pathologies in diabetes can be prevented.
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