Dysregulated cellular redox status during hyperammonemia causes mitochondrial dysfunction by inhibiting sirtuin mediated deacetylation

Perturbed metabolism of ammonia, an endogenous cytotoxic molecule, causes mitochondrial dysfunction with decreased nicotinamide adenine dinucleotide (NAD+) in skeletal muscle. Consistent with our previous report of enrichment of NAD metabolism and sirtuin pathways during hyperammonemia, NAD+-dependent Sirtuin3 (Sirt3) expression and deacetylase activity weredecreased with increased muscle protein acetylation in murine and human skeletal muscle/myotubes. Acetylomics and cell fractions showed hyperammonemia-induced hyperacetylation of critical mitochondrial and signaling molecules. Overexpression of mitochondrial targeted Lactobacillus brevis NADH oxidase (MitoLbNOX) reversed ammonia-induced oxidative dysfunction, electron transport chain (ETC) supercomplex disassembly, lower ATP content, NAD+, and redox ratio (NAD+/NADH). Protein hyperacetylation, post-mitotic senescence and lower mitochondrial sirtuin (Sirt3) expressionduring hyperammonemia were also reversed by MitoLbNOX. Sirt3 overexpression alone did not reverse ammonia-induced redox or mitochondrial dysfunction but reversed hyperacetylation and senescence. These data show that targeting redox ratio, rather than Sirt3, more consistently restores mitochondrial homeostasis and protein acetylation during hyperammonemia.