Protecting the Diabetic Skeletal Muscle by Nampt Activation

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Project Summary Diabetes is a leading cause of death in the US and worldwide with deleterious consequences to the musculoskeletal system. Regardless of glycemic control, diabetes in skeletal muscle manifests with altered metabolism leading to progressive skeletal muscle loss, functional decline, fast-type myofiber atrophy, increased susceptibility to injury and impaired regeneration. The proposal we develop understanding for the direct causal phenomenon associated with altered metabolism and increased risk to skeletal muscle in diabetes. We have identified that diabetes causes significant elevation in muscle NADH levels along with depleted NAD+ reserves. This phenomenon directly associates with decreased muscle function and damage. Based on our preliminary studies and expertise in the area of pyridine nucleotides and metabolic regulation, we hypothesize that decreased NAD/NADH ratio in the diabetic skeletal muscle leads to decline in muscle function, and activation of nicotinamide phosphoribosyl transferase (Nampt) is protective. The major objective is to develop Nampt activators to protect skeletal muscles from diabetes and other metabolic-related syndromes. For this, we propose two specific aims. Under Specific Aim 1A, we will rescue insulin resistance in diabetic skeletal muscle with P7C3. We will utilize diabetic mouse model to identify decreased muscle activity and strength and the relevance of Nampt, NAD/NADH ratio for improvement of function. The experimental approach will include functional, biochemical and molecular measurements. These experiments will establish the fundamental role of NAD/NADH in diabetic skeletal muscle. Specific Aim 1B will develop the innovative skeletal muscle targeting P7C3 nano particle drug delivery system. The Carnitine-P7C3 particle will allow higher therapeutic efficacy for in vivo and in vitro delivery. Under Specific Aim 2A we will investigate the mechanistic basis of P7C3 against diabetic complications in skeletal muscle. The signaling pathway involving Nampt-HNF1β-PPARα will be elucidated using muscle specific knock out mouse models for HNF1βflox along with HSAcre mice to evaluate the chief role of hepatocyte nuclear factor 1-β (HNF1β) as a new functional metabolic modulator in skeletal muscles. Finally, in Sub aim 2B we will investigate the molecular pharmacology of Nampt and its specificity for targeting and identification of SIRT1, HNF1β along with lipid signaling mediators involved in muscle protection. Overall, completion of the project will determine the causal role of Nampt in diabetic skeletal muscle and unravel novel mechanisms with new targets HNF1β that co- orchestrate with Nampt to optimally regulate metabolism in skeletal muscle.