Article révisé par les pairs
Résumé : Ethanol causes dysregulated muscle protein homeostasis while simultaneously causing hepatocyte injury. Since hepatocytes are the primary site for physiological disposal of ammonia, a cytotoxic cellular metabolite generated during a number of metabolic processes, we determined if hyperammonemia aggravates ethanol-induced muscle loss. Differentiated murine C2C12 myotubes, skeletal muscle from pair-fed or ethanol-treated mice and human patients with alcoholic cirrhosis and healthy controls were used to quantify protein synthesis, mTORC1 signaling and autophagy makers. Alcohol metabolizing enzyme expression and activity in mouse muscle and myotubes and ureagenesis in hepatocytes were quantified. Expression and regulation of the ammonia transporters, RhBG and RhCG, were quantified by real time PCR, immunoblots, reporter assays, biotin tagged promoter pulldown with proteomics, and loss of function studies. Alcohol and aldehyde dehydrogenases were expressed and active in myotubes. Ethanol exposure impaired hepatocyte ureagenesis, induced muscle RhBG expression and elevated muscle ammonia concentrations. Simultaneous ethanol and ammonia treatment impaired protein synthesis and mTORC1 signaling and increased autophagy with consequent decreased myotube diameter to a greater extent than either treatment alone. Ethanol treatment and withdrawal followed by ammonia exposure resulted in greater impairment in muscle signaling and protein synthesis than ammonia treatment in ethanol-naïve myotubes. Of the 3 transcription factors that were bound to the RhBG promoter in response to ethanol and ammonia, DR1/NC2 indirectly regulated transcription of RhBG during ethanol and ammonia treatment. Direct effects of ethanol was synergistic with increased ammonia uptake in causing dysregulated skeletal muscle proteostasis and signaling perturbations with a more severe sarcopenic phenotype.

Documents en relation

DI-fusion