Diabetes is a growing epidemic. It results from buildup of excess glucose caused by the body's inability to produce or regulate insulin. While there is a significant amount of research being conducted on insulin signaling in various organs, very little of that research has involved insulin regulation in the eye as it may relate to diabetic retinopathy. Diabetic retinopathy is the leading cause of vision loss in people of working age in the United States. During the onset of diabetes there is a loss of sympathetic nerve activity that takes place in different regions of the body, leading to dysfunction of the kidneys, heart, and peripheral vasculature. Since it has been postulated that sympathetic nerves are compromised with the onset of diabetes, this also could mean that they play a role in the eye. A further look into sympathetic innervation and its role in the eye has indicated that sympathetic nerves are playing a role in histological and functional changes that are similar to those occurring in diabetic retinopathy. One cell type in the retina that may be susceptible to changes in sympathetic neurotransmission is the Muller cell. Muller cells serve as structural support cells for the retina, and span the entire thickness of the retina. Since Muller become activated and express increased GFAP levels, this suggests that Muller cells are being compromised and may also alter their regulation of inflammatory markers, glucose transport, oxidative stress, growth factors, and finally cell survival. For the work in this proposa, rat Muller cells (rMC-1) will be cultured in DMEM medium grown in high glucose (25mM) or low glucose (5mM) conditions, and treated with 10uM isoproterenol followed by various analyses of insulin signaling and apoptosis. Preliminary data suggest that insulin receptor signaling is decreased in Muller cells cultured in high glucose conditions. To further delineate the role of insulin signaling, experiments will be done using siRNA against the insulin receptor to further identify roles in the regulation of apoptosis by beta-adrenergic receptors and cross-talk between beta-adrenergic receptors and insulin signaling. In addition to the work on cells in culture, we will also use beta-1-adrenergic receptor knockout mice and their littermates to more specifically define the role of beta-1-adrenergic receptor signaling on insulin signaling and apoptosis in vivo. The relevance to public health from this proposal will be in determining the interactions of beta-adrenergic receptors and insulin signaling in the diabetic retina. Since diabetic patients often require insulin treatment, it is critical to determine the regulation of cellular events in the retina following insulin and other treatments.
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