Identifying Extracellular Matrix Protein Dynamics in Skeletal Muscle Hypertrophy for Regenerative Therapies

Skeletal muscle regeneration is hindered in severe injuries and degenerative diseases, including volumetric muscle loss (VML), due to the failure of current treatments to induce functional tissue growth. Various biological functions in skeletal muscle are supported by the extracellular matrix (ECM), a collection of proteins and glycosaminoglycans. In vivo studies on murine plantaris muscle hypertrophy indicate that ECM remodeling facilitates muscle growth, but a global analysis of ECM protein dynamics during skeletal muscle hypertrophy and repair are unknown. Understanding this influence of the ECM can establish instructive cues for regenerative therapies. Here, we define global proteomic changes throughout stages of plantaris muscle hypertrophy, with an emphasis on characterizing ECM proteins. Synergistic ablation of the gastrocnemius and soleus muscles induced a compensatory hypertrophic effect causing a 40% mass increase in the plantaris muscle 28 days post injury. Liquid chromatography-tandem mass spectrometry revealed the differential abundance of 1233 proteins, including 99 ECM proteins, across five time points. After two days of injury, a significant increase of ECM glycoproteins was observed although the overall collagen abundance decreased. Throughout the duration of injury, the relative abundance of type I collagen decreased while there was an increase of proteins associated with type I collagen fibrillogenesis (types III and V) and basement membrane (types IV and VI). Collectively, these results provide a better understanding of ECM dynamics throughout skeletal muscle hypertrophy. Future studies will evaluate protein synthesis by using non-canonical amino acids to identify newly synthesized proteins. Temporal analysis of protein dynamics symbolic to injury and tissue growth will provide tissue engineers with precise information to develop successful regenerative therapies to restore functional muscle in VML.