Project Summary/Abstract Distorted expression of isoforms of the skeletal muscle myosin heavy chain (MHC) protein, which collectively determine the MHC proteome, is a hallmark of altered proteome in muscle of humans with obesity. The most striking feature of this is a characteristic reduction in the content of the slow MHC-I isoform, which is responsible for determining the content of Type I muscle fibers. Type I muscle fibers are characterized by increased capacity for glucose uptake, and in contrast to Type II fibers, maintain their sensitivity to insulin within the adverse metabolic environment associated with obesity. Increased content of Type I fibers in skeletal muscle, and thus favorable metabolic effects in muscle, require increased expression of MHC-I in muscle. Importantly, the slow MHC-I gene drives the molecular mechanisms that determine the overall MHC proteome and fiber type phenotype in skeletal muscle. We seek to determine the underlying biology that sustains distorted MHC proteome in skeletal muscle of humans with obesity. We will evaluate overall protein turnover in skeletal muscle of humans with obesity and lean controls, and focus specifically on that of MHC isoforms. We will determine gene expression of the MHC isoforms and associated molecular factors implicated in activating Type I muscle fiber programing to obtain a deeper insight into the biology that sustains the unfavorable MHC proteome/muscle fiber phenotype in muscle of humans with obesity. We will employ acute aerobic exercise and increase in plasma amino acids as experimental tools to target biological processes of transcription and translation related to MHC genes expression in skeletal muscle. Ultimately, our findings will provide an understanding of mechanisms responsible for unfavorable MHC proteome and fiber type phenotype in skeletal muscle of humans with obesity. These findings will advantage our knowledge about molecular targets that can favorably remodel the muscle proteome and improve metabolism in muscle of humans with obesity.