Key Facilitator Proteins that Mediate Sarcolemma Membrane Repair have Potential as Therapeutics for Muscle Disease and Injury

Abstract

A common aspect of many diseases and traumatic injuries affecting skeletal muscle is the necrotic death of muscle fibers. Necrotic death of muscle fibers involves the breakdown of the sarcolemmal membrane that can be exacerbated by increased fragility of the membrane or by compromised endogenous sarcolemmal membrane repair processes. Increasing these repair mechanisms could act as a therapeutic approach for a number of muscle diseases and injuries. Duchenne muscular dystrophy (DMD) is a fatal X‐linked inherited neuromuscular disorder caused by mutations in the dystrophin gene that provides a model for muscle injury and the effects of membrane repair. The dystrophin protein normally serves as a shock absorber for mechanical stress and as a signaling platform protein in muscle fibers. When dystrophin is lacking, patients experience an accumulation of membrane damage that muscle fibers cannot adequately repair. As a result, there is an increase in fiber necrosis that exceeds the regenerative capacity of the muscle. This causes DMD patients to develop striated muscle deterioration that leads to eventual death in the third decade of life. There is currently no cure for DMD and treatments that stimulate the membrane repair process in muscle fibers have been greatly overlooked and underutilized as a potential therapeutic approach. This project investigates a novel membrane repair signaling cascade in skeletal muscle that utilizes glucose storage vesicles (GSVs) and their key regulators Akt Substrate 160 kDa (AS160) and rab G proteins as a means to close membrane wounds. Based on our preliminary data, we hypothesize that AS160 phosphorylation and activation of associating rab G proteins facilitate the translocation of intracellular GSVs to disruption sites in the sarcolemma membrane for wound closure. Thus, modulating the function of these proteins may stimulate repair and have therapeutic benefits for DMD. Through the use of mutant plasmids and live cell imaging, we have observed that GSVs containing the glucose transport protein GLUT4, as well as affiliated rabs, translocate to injury cites in C2C12 myoblasts and isolated mouse muscle fibers. We have also identified that AS160 phosphorylation from the phosphoinositide‐3 kinase (PI3K)/Akt1 signaling axis regulates membrane repair in cultured muscle cells. Importantly, we have screened GSV associating rab G proteins and have found that specific rab proteins are involved in sarcolemma membrane repair in vivo, and that activating rab10 significantly improves membrane resealing in vivo in the muscle of a Duchenne muscular dystrophy mouse model (MDX). This project explores a novel signaling cascade controlling membrane repair that could be leveraged to develop new therapies for muscle disease and injury.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.