Abstract TMP33: Obesity And Hyperinsulinemia Impair Insulin Receptor Transport In The Brain Microvascular Endothelium

Abstract

Introduction: Obesity afflicts over 650 million individuals worldwide and is a strong risk factor for both stroke and dementia. Hyperinsulinemia-induced insulin resistance, a finding commonly seen in obesity, is linked to brain insulin deficiency. As insulin is neuroprotective, impaired transport from the peripheral circulation into the brain may underlie the enhanced risk of vascular cognitive impairment in obese individuals. Thus, the focus of this study is to understand the role of aberrant insulin receptor endocytosis in impaired brain insulin transport associated with diet-induced obesity. Methods: C57Bl/6J mice were placed on a control or high fat diet beginning at 6 weeks of age for 24 weeks (n=3-5) and hippocampi collected to image microvascular receptor transport. To isolate the effects of insulin resistance, primary murine brain microvascular endothelial cells (MBEC) were exposed to hyperinsulinemia (HI; 20nM insulin for 12 hours). Naïve and HI cells were stimulated for 15 minutes with 20nM insulin and processed for immunoblotting, microscopy, and flow cytometry (n=3-12). Results: High fat diet fed mice exhibited reduced internalization of insulin receptor-positive vesicles in the vascular endothelium as compared to controls (0.27+/-0.04 v. 0.37+/-0.02). Correspondingly, HI MBECs displayed reduced insulin receptor internalization, disrupted actin architecture, and a decreased abundance of early endosomes as compared to naïve cells (0.90+/-0.12 v. 2.07+/-0.29). HI cells further demonstrated a shift towards increased endocytic vesicle formation and swelling relative to naïve cells (1.90+/-0.21 v. 1.04+/-0.08), the result of which may be due to an observed increase in endoplasmic reticulum stress and impaired nitric oxide synthase capacity. Conclusion: Diet-induced obesity impairs insulin receptor endocytosis into the brain vascular endothelium. These data suggest that hyperinsulinemia induces a compensatory shift in endocytic machinery, with receptors potentially becoming trapped within endocytic buds as opposed to trafficking into the cell. By uncovering the mechanisms linking obesity to cognitive decline, this study will help identify novel therapeutic targets for vascular cognitive impairment and dementia.