The Role of the Regenerating Protein Family on Skeletal Muscle Regeneration

Abstract

Skeletal muscle regeneration is dependent upon the influences of intrinsic and extrinsic factors that stimulate satellite cells. Regenerating proteins are upregulated at the onset of trauma or inflammation in the pancreas, gastrointestinal tract, liver, neural cells and other tissues. Studies have shown that Reg proteins have a mitogenic, anti-apoptotic and anti-inflammatory function in damaged tissues and is necessary for normal progression of regeneration. As skeletal muscle is also able to regenerate itself at a rapid rate, it seems highly likely that Reg proteins function to promote myogenesis in skeletal muscle regeneration. Therefore, the goal of our research was to characterize the expression of the Reg proteins and receptor in regenerating skeletal muscle and satellite cells, investigate the effect of exogenous Reg protein on myogenesis, and to examine direct Reg protein effect on satellite cell activity. To determine whether Reg proteins participate in skeletal muscle regeneration, mice were injected with marcaine in their tibialis anterior muscles to induce skeletal muscle damage. The gene expression analysis of undamaged and marcaine-damaged tibialis anterior muscles and mice satellite cells showed that Reg I, II, IIIα, IIIγ, IV and EXTL3 genes are present during skeletal muscle regeneration and satellite cells significantly express Reg I, IIIα, IIIγ and EXTL3. As Reg I and IIIα are most prevalent in vivo and in vitro respectively, we advocate these isoforms as the predominant candidates in skeletal muscle regeneration. To determine the effect of exogenous Reg protein on myogenesis, we performed gene expression and muscle morphometry analysis of Reg IIIα or PBS injected tibialis anterior muscles. Interestingly, our results indicate that the addition of Reg IIIα to damaged muscles inhibited myogenesis. To determine the direct effect of Reg protein on myogenic stem cell activity, Reg proteins were added to mice satellite cells and C2C12 cells. Results from these studies were inconclusive due to the failure of known positive and negative controls. Overall, our studies suggest that Reg proteins contribute to skeletal muscle regeneration; however, as an overabundance of Reg IIIα in regenerating tissues may have inhibited myogenesis, it is imperative that other isoforms or lower concentrations be investigated.