Glut1 and the microvascular complications of diabetes

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The goal of this proposal is to determine whether systemic reduction of the facilitative glucose transporter, Glut1 (Slc2a1), prevents the major microvascular complications of diabetes: diabetic retinopathy (DR), diabetic kidney disease (DKD) and diabetic peripheral neuropathy (DPN) and/or augments the current standard of care for Type 2 diabetes. Each microvascular complication is mitigated by tight glycemic control, but efforts to maintain euglycemia in diabetic patients has been elusive. Here, we will investigate whether the systemic reduction of Glut1 using a genetic approach prevents DR, DKD and DPN phenotypes in mouse models of both Type 1 and Type 2 diabetes for the following reasons: (1) Glut1 is highly expressed in the retina and the cells that comprise the inner and outer blood retinal barriers, throughout the nephron and tubules of the kidney and in the paranodal region of the peripheral nerves as well as the Schwann cells that surround the nerves. (2) Reduction of Glut1 in the eye via pharmacology, siRNA or genetic approaches reduces hallmarks of DR and reduction of Glut1 in mesangial cells of the nephron prevents DKD phenotypes in mouse models of Type 1 diabetes. (3) Inhibition of the sodium-glucose cotransporter-2 (Sglt2) is insufficient to fully prevent DR, DKD and DPN phenotypes. (4) Small nucleotide polymorphisms in Glut1 are associated with increased risk of both DR and DKD. (5) Intensive insulin therapy, which lowers prevalence of DR, DKD and DPN can regulate Glut1 at both transcription and post- translational levels. Because Glut1 is elevated in the diabetic retina and kidney, reduced Slc2a1/Glut1 expression and increased Glut1 turnover may contribute to the mechanism by which intensive insulin therapy reduces DR, DKD and DPN. These observations form the premise for our hypothesis that reduction of Glut1 will prevent the microvascular complications of diabetes, augment the current standard of care for Type 2 diabetes, and contributes to the mechanism by which intensive insulin therapy confers protection against DR, DKD and DPN. We will test this hypothesis with the following specific aims. In Aim 1 we will utilize the Glut1+/- mouse which harbors a hemizygous Glut1 deletion to determine if systemic reduction of Glut1 prevents DR, DKD and DPN in a STZ-induced mouse model of Type 1 diabetes or in the Leprdb/dbeNOS-/- mouse model of progressive Type 2 diabetes. We will further determine if the addition of systemic Glut1 reduction to the current standard of care for Type 2 diabetes, treatment of hyperglycemia (metformin), hypertension (ramipril) and inhibition of Sglt2 (empaglifozin), augments protection from diabetic phenotypes. In Aim 2 we will test the hypothesis that intensive insulin therapy regulates Glut1 by utilizing the STZ-induced mouse model of Type 1 diabetes. Activation of the Forkhead Box O transcription factor, FOXO1, downstream signal transduction molecules, and Slc2a1 mRNA levels will be measured in each microvascular tissue to determine if Glut1 can be regulated by insulin transcriptionally. Activation of the ubiquitin-proteasome pathway and Glut1 protein levels will additionally be measured to interrogate post-translational control of Glut1 by insulin. These experiments will reveal whether Glut1 contributes to the development of DR, DKD and DPN in Type 1 and/or Type 2 diabetes and if targeted reduction of Glut1 can be considered for the future development of novel therapeutics for the treatment of these pathologies. Nearly 25% of veterans are affected by diabetes, making the care and treatment of DR, DKD and DPN of great significance for the VHA.