The LHCN-M2 cells were derived using the platform for immortalization of human cells from the Myology Institute in Paris. Author Contributions: The overall study was designed by P.R.K. contributing to increased morbidity and mortality (6). Skeletal muscle loss occurs as a result of an imbalance between protein synthesis and breakdown, with similar signaling pathways being implicated. For example, increased growth differentiation factor (GDF)-15 and reduced insulin-like growth factor-1 have been reported in both critical illness Fructose and COPD (7C10). In addition to occurring as a consequence of muscle loss, decreased function also results from a reduction in the muscles capacity to generate ATP, associated with a reduction in the activity of mitochondrial protein complexes, notably complexes I, III, and IV (11C13). These complexes contain proteins encoded by mitochondrial DNA that require translation by mitochondrial ribosomes. Although muscle mass and oxidative capacity are primarily thought to be controlled by separate processes (protein and mitochondrial turnover), they are to some extent interdependent, because increasing oxidative capacity requires protein synthesis and increasing protein synthesis requires energy. Similarly, reducing oxidative capacity requires protein breakdown and autophagy, processes that operate during muscle breakdown. It is perhaps therefore not surprising that the loss of muscle mass and oxidative capacity often occur together (14) raising the possibility that there are common regulatory mechanisms or factors. Understanding such factors is important in identifying novel therapeutic approaches to treating muscle dysfunction. MicroRNAs (miRNAs) are small RNAs that control the translation and degradation of sets of mRNAs, modulating biologic responses and cell phenotype by regulating the levels of key proteins in multiple biologic pathways. For example, miRNA-1 (miR-1) is elevated during muscle differentiation and regeneration (15), contributing to myogenesis both by suppressing the expression of HDAC4 (an inhibitor of several myogenic transcription factors) and by entering mitochondria and increasing mitochondrial translation (16). Consistent with Rabbit polyclonal to TP73 this, we and others have previously reported reduced expression of miR-1 is associated with muscle wasting in COPD (17), renal failure (18), and ICU-acquired weakness (ICUAW) (7), although there is some discrepancy in the COPD literature (10). We have also identified a miRNA pattern associated with muscle mass in patients with COPD that is distinct from that in Fructose healthy Fructose individuals (19). The miRNAs identified were associated with pluripotency and regeneration, indicating that patients who lost the most muscle were unable to respond sufficiently to the physiologic stress imposed by disease. This observation suggests that some patients are more susceptible to muscle atrophy in the presence of disease but does not identify factors associated with disease that drive the loss of muscle, nor did the miRNA pattern identified associate with the loss of oxidative capacity. Consequently, we hypothesized that there would be changes in miRNA expression in the quadriceps of patients with COPD that promoted atrophy and a loss of oxidative capacity. In this study, we therefore reanalyzed our screen to identify miRNAs associated with COPD that were predicted to target pathways controlling protein turnover and energy balance; miR-542-3p and -5p fulfilled these criteria (mitochondrial translation and transforming growth factor [TGF]- signaling, respectively). However analysis of the expression of these miRNAs in patients with established ICUAW showed that they were more markedly increased in those patients than in patients with COPD, consistent with the more rapid muscle atrophy that these patients undergo. We confirmed the ability of these miRNAs to target the appropriate biochemical pathways both and and showed that expression of the miRNA could cause muscle wasting and Animal Experiments Targets of miR-542-3p/5p were identified by Ago-2 pull down. The effects of the miRNAs on gene and protein expression, and on mitochondrial function and TGF- signaling were determined in LHCN-M2 cells, a human skeletal muscle cell line. Overexpression of the miRNA in mouse muscle was.