Vasomotor Dysfunction of Retinal Arterioles in Diabetes
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abstract
Retinopathy is a major complication of diabetes mellitus and a leading cause of blindness in American adults. Hyperglycemia is associated with reduced retinal blood flow in early diabetes, suggesting that dysfunction of arterioles may contribute to retinal damage. Interestingly, noninvasive imaging of retinal blood flow is being regarded as providing a ''window'' into the health of the heart. Although diabetes can impair coronary blood flow and promote cardiomyopathy, it is possible that underlying mechanisms, which remain unclear, contributing to coronary and retinal arteriolar dysfunction are different. Also, development of a diabetes animal model relevant to human microcirculation for mechanistic study of vasomotor dysfunction of arterioles from the retina and heart is lacking. To address these clinically important issues, we developed streptozocin-induced type 1 diabetes in the pig, an animal model that we have shown resembles human in retinal vasomotor regulation/dysregulation. Our preliminary data show that within 2 wk of diabetes, endothelium-dependent nitric oxide (NO)-mediated dilation of retinal and coronary arterioles is specifically impaired. Endothelial dysfunction correlates with oxidative stress and enhanced Rho kinase (ROCK) expression, and can be prevented and restored in coronary arterioles but only prevented in retinal arterioles by antioxidants and arginase blockade. It appears that signaling events leading to their vasomotor dysfunction in short-term diabetes are different. Mechanistic differences in vasodilator dysfunction under acute (3 hr) vs. prolonged (2 to 12 wk) hyperglycemia suggest that temporal control of arginase II and SIRT1, two regulatory enzymes for NO bioavailability, may mediate this pathophysiology in retinal arterioles, whereas continuous activation of c-Jun N-terminal kinase (JNK) and arginase I contributes to coronary dysfunction. However, the exact role and signaling sequence for specific ROCK isoform activation linking to oxidative stress and arginase have not been defined. Herein, we will test thehypothesis that early diabetes activates endothelial ROCK-dependent JNK-interacting protein-1 (JIP1)/JNK signaling, which enhances downstream NAD(P)H oxidase and p38-dependent proteasome activities in retinal arterioles and xanthine oxidase activity in coronary arterioles. Oxidative stress leads to temporal control of arginase II and SIRT1 with subsequent reduction of NO-mediated dilation in retinal arterioles, whereas prolonged elevation of arginase I sustains coronary dysfunction. We will pursue 3 specific aims: (1) Determine whether enhanced ROCK-dependent phosphorylation of JIP1 contributes to diabetes-induced dysfunction of retinal and coronary arterioles by increasing oxidative stress. (2) Determine whether enhanced JNK-dependent oxidase signaling contributes to diabetes-induced dysfunction of retinal and coronary arterioles. (3) Determine whether enhanced arginase activity and p38-induced activation of proteasomes contribute to temporal control of diabetes-induced dysfunction of retinal and coronary arterioles. Outcomes will identify novel targets involved in retinal and coronary arteriolar dysfunction during early diabetes.
