Physics of inter-organ glucose flux in glucose intolerance

Vanderbilt University, Nashville TN

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Abstract

Project Summary/Abstract Disposition index (DI) is a sensitive predictor of progression to type 2 diabetes (T2D). DI is a composite measure of glucose uptake by insulin-sensitive tissues (primarily skeletal muscle) and glucose-stimulated insulin release by beta cells. Previous investigations concerning DI have focused on its cellular and biochemical determinants. However, this framing often neglects that glucose and insulin must first arrive in skeletal muscle before insulin- stimulated glucose uptake can proceed, and glucose must first arrive in the pancreatic islets to trigger insulin release. Meanwhile, there is mounting evidence of microvascular dysfunction and extracellular matrix (ECM) remodeling in both organs during T2D pathophysiology. Both effects would be expected to slow the delivery of glucose and insulin, but the physics of inter-organ glucose flux remain poorly understood. This proposal seeks to test the hypothesis that systemic microvascular and ECM barriers to glucose/insulin delivery play a causal role in glucose intolerance. This proposal includes two specific aims to establish the sufficiency/insufficiency of microvascular and ECM barriers to glucose/insulin delivery in creating glucose intolerance. The hypotheses of these aims are: 1) muscle insulin resistance results from microvascular and ECM barriers to glucose/insulin delivery, and 2) impaired insulin secretion results from impaired glucose delivery to pancreatic islets. I have developed innovative techniques for direct in vivo measurements of microvascular perfusion and glucose delivery and have inherited a method recently developed in our lab for direct in vivo measurements of insulin delivery. These techniques will be applied in genetically modified mice lacking VEGF (and thus displaying reduced vascular supply) in each organ to assess the impacts of microvascular barriers to glucose/insulin delivery. These techniques will also be applied in lean and obese C57Bl/6J mice, with or without PEGPH20 treatment to reduce interstitial HA accumulation with obesity, to assess the impacts of ECM barriers on glucose delivery. Relevance to glucose uptake and insulin secretion will be confirmed using radiolabeled glucose tracers and serum insulin following an intravenous glucose challenge, respectively. These studies will serve to determine whether physical impediments to glucose and insulin delivery can limit insulin-stimulated glucose uptake and glucose-stimulated insulin secretion, and as a result, contribute to impaired DI and T2D progression. The results from the proposed experiments hold the potential to illuminate an as-of-yet undiscovered category of potential T2D therapies harnessing the physics of inter-organ glucose flux.