Metabolic basis of sarcopenia in alcohol-related liver disease

About This Grant

ABSTRACT The prevalence of and mortality related to alcohol related liver disease (ALD) continues to increase with limited therapies. Sarcopenia or loss of muscle mass is a frequent and consistent clinical consequence of ALD. Sarcopenia is an independent contributor to mortality, morbidity, and adverse post-liver transplant outcomes in patient with liver disease including ALD. Despite extensive clinical studies that are primarily observational, there is limited understanding of the mechanistic basis of sarcopenia in ALD. Most studies have focused on targeted molecular and specific subcellular organelle dysfunction that contribute to impaired protein synthesis, increased autophagy, and consequent sarcopenia. In preliminary studies, using multiomics analyses of untargeted datasets, we have identified the global landscape of skeletal muscle perturbations in ALD. We and others have reported impaired muscle mitochondrial oxidative function with changes in redox status (NAD+/NADH ratio) and changes in global metabolomics in ALD. Targeted metabolite analyses showed decreased skeletal muscle tricarboxylic acid (TCA) cycle intermediates including alpha-ketoglutarate (KG) in preclinical models and human skeletal muscle from patients with ALD. Alpha ketoglutarate (KG) is a critical intermediary metabolite that regulates diverse cellular functions including protein synthesis, stress responses, and senescence. However, the mechanism(s) of reduced KG in skeletal muscle in ALD is not known. Reduction in KG may be due to either cataplerosis (loss of TCA cycle intermediates) or less anaplerosis (gain of TCA cycle intermediates). Tracer studies have been used extensively to dissect the mechanisms of metabolite alterations in cellular and in vivo models. The use of 13C- and 15N-labeled molecules allows for tracing the metabolic fate of molecules and can help determine the mechanisms for reduced skeletal muscle TCA cycle intermediates in ALD. Based on our published and preliminary data, we will test the hypothesis that during ALD, cataplerosis of KG to glutamate, to enhance ammonia disposal and restore redox homeostasis, causes reduced TCA cycle intermediates in skeletal muscle. This hypothesis will be tested by 2 aims. In AIM 1 we will trace the metabolic fate of KG in murine and human induced pluripotent stem cell derived myotubes using 13C-labeled glucose and 13C/15N glutamine and glutamate. We will quantify isotopomers of TCA cycle intermediates, glutamate, and its derivative amino acids in response to ethanol treatment by gas/liquid chromatography mass spectrometry. In AIM 2 we will establish the in vivo relevance of these studies in the skeletal muscle from a mouse model of ALD with sarcopenia. Intraperitoneal injection of 13C6 glucose will be followed by isotopomer analyses of TCA cycle intermediates and amino acids. We anticipate increased cataplerosis of KG that generates glutamate (for ammonia disposal) and subsequently proline as a redox restoring process. These studies will allow the PI to generate pilot data for future studies and lay the foundation for potential metabolite targeted therapeutics.