US EPA

7439372 

Journal Article 

The Pathogenesis of Physical Frailty and Sarcopenia 

Dasarathy, S; , 

2020 

Springer International Publishing 

Cham 

Frailty and Sarcopenia in Cirrhosis 

33-53 

10.1007/978-3-030-26226-6_4 

http://link.springer.com/10.1007/978-3-030-26226-6_4
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Disordered energy metabolism in cirrhosis contributes to skeletal muscle proteolysis and impaired protein synthesis with dysregulated protein homeostasis (proteostasis) and resultant sarcopenia. Circulating abnormalities including hyperammonemia, hypogonadism, decreased branched chain amino acids, and endotoxemia are potential mediators of the liver-muscle axis. Etiology of liver disease including ethanol and fatty acids also directly affects muscle proteostasis. Transcriptional upregulation of myostatin via ammonia-induced activation of p65NFKB impairs signaling by the protein homeostasis regulatory molecule, mammalian target of rapamycin complex 1 (mTORC1). The recently described hyperammonemic stress response (HASR) is characterized by activation of an amino acid sensor, general control non-derepressible 2 (GCN2) with persistent phosphorylation of eIF2α with reduction in protein synthesis. Hyperammonemia of cirrhosis also increases autophagic proteolysis and mitochondrial dysfunction with cataplerosis. Targeting mediators of the liver-muscle axis, the signaling perturbations in the muscle, and strategies to restore metabolic homeostasis with ammonia-lowering, anaplerotic agents and myostatin antagonists have the potential to be novel and effective therapies to reverse sarcopenia in cirrhosis.