Role and Regulation of Skeletal Muscle Mitochondrial Dynamics in Type 2 Diabetes

ABSTRACT The traditional view of mitochondria as isolated, spherical, energy producing organelles has undergone a revolutionary transformation. It is now established that mitochondria form dynamic networks that are regulated by cycles of fission, fusion, and biogenesis. However, the impact of mitochondrial dynamics on metabolic function in human health and disease remains unclear. During the previous cycle, we demonstrated that DRP1-mediated mitochondrial fission contributes to the onset of insulin resistance and progression to type 2 diabetes by mediating mitochondrial calcium flux and bioenergetic function. We provide preliminary data that links RHOT1, a mitochondrial outer membrane protein involved in quality control and motility, to glucose homeostasis and type 2 diabetes. We will build on our prior research and test the central hypothesis that RHOT1-mediated mitochondrial trafficking contributes to the maintenance of glucose homeostasis. In Aim 1 we will establish skeletal muscle RHOT1 aggregation as a pathophysiological signature of lipid-induced insulin resistance by comparing age-, sex-, and weight-matched patients with and without type 2 diabetes followed by a hyperinsulinemic-euglycemic clamp with tracers to evaluate lipid and glucose kinetics. In Aim 2, we will test whether insulin mass action is sufficient to relieve RHOT1 aggregation in vivo by infusing insulin into patients with difficult-to-treat type 2 diabetes with intent to normalize glucose homeostasis. Skeletal muscle biopsies will be obtained in Aims 1 and 2 to evaluate mitochondrial protein expression, network dynamics, ultrastructure, and bioenergetic function. In Aim 3, we will determine the molecular mechanism whereby RHOT1 mediates glucose homeostasis. Genetic and pharmacologic tools will be employed to establish gain- and loss-of-function models of RHOT1 expression in primary human skeletal muscle cells. The proposed research will provide a comprehensive clinical-translational assessment of skeletal muscle mitochondrial dynamics in patients with type 2 diabetes while establishing RHOT1 as a novel mediator of insulin sensitivity and cellular glucose homeostasis. The experimental approach harnesses innovative molecular and cellular tools, interfaced with physiologically significant human studies to obtain clinically meaningful data on glucose homeostasis in patients with type 2 diabetes. These studies have the potential to establish a knowledge base that will lead to new therapies for future generations of patients with type 2 diabetes.