Pathways of Insulin Transport across the Blood-Brain Barrier



 DESCRIPTION (provided by applicant): Insulin resistance is highly correlated with cardiovascular disease, vascular dysfunction, and neurodegenerative disorders (17,21,48). While the bulk of research regarding insulin resistance has focused on its manifestations in liver, muscle, and adipose, the brain is becoming an increasingly important focal point. Unlike muscle and adipose, the brain does not require insulin to facilitate glucose uptake. Instead, insulin in te brain appears to have a neuroregulatory role as a satiety signal (27) and regulator of body weight (8). Additionally, administration of intranasal insulin to individuals with Alzheimer's disease improves cognitive function (15). While there are many roles for insulin action in the brain, there is little understanding as to how insulin crosses the highly-restrictive endothelium o the blood-brain barrier (BBB). Limited research investigating insulin transport into the brain sampled from the cerebrospinal fluid (CSF) as a surrogate for brain interstitial fluid (BISF) and detected very low insulin concentrations (3,54); however, recent novel findings have demonstrated that the CSF is a different pool than the BISF that surrounds neurons (32). Nevertheless, the gradient between plasma and CSF insulin is greater in obese than in lean individuals (33), suggesting decreased transendothelial transport (TET) of insulin during obesity. This phenomenon is also observed in peripheral insulin TET (56), where vasculature is considerably more fenestrated than the BBB. Insulin TET across the brain microvasculature has not been examined. Previous work in our laboratory has demonstrated insulin's TET in muscle vasculature is dependent on insulin receptor (IR) signaling, mediated by nitric oxide, and facilitated by activation of caveolin-1 (Cav1), the main protein component of caveolae. The goal of this project is to determine whether insulin transport by the BBB vasculature is dependent on IR signaling, mediated by Cav1, and whether this is modified during insulin resistance. My first aim will employ primary rat brain microvascular endothelial cells (RBMVECs) to determine mechanistic relationships between IR, IR signaling, and Cav1 to determine their role in insulin uptake, signaling, and trans endothelial transport. My second aim will use the high-fat diet (HFD) fed rat model to determine the effect of insulin resistance on insulin transport into the brain, with continued focus on function and regulation of IR and Cav1 signaling pathways in freshly-isolated brain endothelial cells and in fixed brain slices. Taken together, these experiments will elucidate the pathway(s) through which insulin is transported across the BBB to exert its actions on neurons in the brain. Ultimately, this will provide novel pharmacologic target for the treatment of insulin resistance.