6 - Differential Redox Changes in Liver Mitochondrial Proteomes from Phenotypically Distinct Mouse Models of Glutathione Deficiency

Abstract

Intrahepatocyte generation of free radicals and depletion of glutathione (GSH) are believed to be key mediators involved in the cellular pathogenic events underlying fatty liver disease (FLD). As the most abundant intracellular non-protein thiol, GSH has an important biochemical role in electrophile detoxification and oxidant elimination. Additionally, changes in GSH/GSSG (its oxidized form) redox couple may modify protein functions via redox post-translational modification. We have developed two unique transgenic mouse models in which hepatic GSH synthesis is repressed by abolishing the expression of the catalytic (GCLC) or the modifier (GCLM) subunit of glutamate-cysteine ligase, the rate-limiting enzyme in GSH biosynthesis. Our previous studies show that these mice have GSH deficiencies at different levels but exhibit either resistance to steatosis (GCLM knockout mice) or develop spontaneous liver pathologies featuring all clinical stages of FLD (liver-specific GCLC knockout mice). Importantly our studies show that functional integrity of the mitochondria is a key determinant of the hepatic phenotype under conditions of chronic GSH deficiency. The purpose of the current study is to investigate the hypothesis that GSH plays an important regulatory role in mitochondrial redox signaling network. We performed redox proteomics analysis of liver mitochondrial proteomes derived from two phenotypically distinct mouse models. Cellular redox buffering couples (GSH-GSSG, NADH-NAD and NADPH-NADP) were measured in parallel. The proteomics analysis revealed phenotype-associated Cysteine redox profiles of mitochondrial proteins that are involved in oxidative phosphorylation, lipid metabolism, xenobiotic metabolism, and cellular stress response. Biochemically, decreased NAD/NADH ratio appears to correlate with a protective phenotype. In conclusion, our preliminary data suggest a redox-based role of GSH in modulating mitochondrial pathways that are mechanistically linked to the pathogenesis of FLD.