The Retinal Microenvironment in Diabetic Retinopathy

DESCRIPTION (provided by applicant): Diabetic retinopathy is one of the most common causes of retinal disease in adults. Many molecular and histological changes have been demonstrated, and it is now recognized that neural as well as vascular problems exist. The most important contributor to vascular dysfunction is the elevation of vascular endothelial growth factor (VEGF), which causes vascular leakage and angiogenesis. Unfortunately, we still do not know what underlies the increase in VEGF. Hypoxia and acidosis are both known regulators of VEGF, but the magnitude and time course of changes in retinal oxygen and pH are not known in diabetes. More information about these parameters will allow a better understanding of disease progression, and ultimately may lead to an understanding of pathways that can be targeted before VEGF causes damage. We will make intraretinal recordings of PO2 and pH in rats with streptozotocin (STZ)-induced diabetes, and in rats with acidosis in the absence of diabetes. To place these changes in the context of other events, we will also measure important vascular parameters (blood flow, leakage, molecular signals). SPECIFIC AIM 1: Oxygen in diabetic retinopathy. Retinal tissue hypoxia has been implicated in the increased VEGF that is found in both the background and proliferative phases of retinopathy. There is considerable indirect support for the existence of hypoxia in diabetic retinopathy, but very limited direct evidence. We will characterize intraretinal oxygenation in rats with up to 1 year of diabetes. Our hypothesis is that inner retinal PO2 will decrease over this time. We will also investigate changes in the regulation of retinal oxygen in diabetics. Our hypothesis is that changes in regulation of PO2 will be a more sensitive indicator of changes in the microenvironment and occur earlier than changes in baseline PO2. We found increased PO2 in the retina in an earlier study at 12 weeks of diabetes. Our hypothesis is that this was due to increased blood flow, which we will now investigate. SPECIFIC AIM 2: Acidosis in diabetic retinopathy. VEGF is regulated by acidosis in some tissues but the role of pH in controlling VEGF in the adult retina is unknown. We will characterize retinal pH in rats with up to 1 year of diabetes. Our hypothesis is that the inner retina will be more acidic than normal for at least a few months. We also hypothesize that molecular mechanisms come into play to reduce acidosis, such as increased carbonic anhydrase and acid removal mechanisms. These will be evaluated with mRNA and protein measurements. SPECIFIC AIM 3: Is retinal acidosis sufficient to upregulate VEGF? Finding that the diabetic retina is acidotic will open the possibility that it is one of the factors that regulates VEGF, but will not tell us whether it is important. Consequently, we will produce acidosis in the absence of diabetes, via carbonic anhydrase inhibition. We will first establish a treatment protocol that yields intraretinal pH values similar to diabetes, and then evaluate changes in VEGF and leakage. Our hypothesis is that acidosis alone will be sufficient to increase VEGF, produce molecular changes that underlie leakage, and cause leakage itself. PUBLIC HEALTH RELEVANCE: This project will provide information about retinal metabolic processes that are impaired in diabetic retinopathy, a major blinding complication of diabetes. This work will be done by measuring oxygen and pH locally in the retina of rats with or without experimental diabetes. We hope to clarify how the disease progresses, and test hypo