Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States
David G McFadden
Department of Biochemistry, University of Texas Southwestern Medical Center, Dallas, United States; Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, United States
Janaka Wansapura
Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, United States
Ralph J DeBerardinis
Children's Medical Center Research Institute, University of Texas Southwestern Medical Center, Dallas, United States; Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, United States; Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, United States; Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, United States
Children's Medical Center Research Institute, University of Texas Southwestern Medical Center, Dallas, United States; Harold C. Simmons Comprehensive Cancer Center, University of Texas Southwestern Medical Center, Dallas, United States; Department of Pediatrics, University of Texas Southwestern Medical Center, Dallas, United States
Mitochondrial electron transport chain (ETC) dysfunction due to mutations in the nuclear or mitochondrial genome is a common cause of metabolic disease in humans and displays striking tissue specificity depending on the affected gene. The mechanisms underlying tissue-specific phenotypes are not understood. Complex I (cI) is classically considered the entry point for electrons into the ETC, and in vitro experiments indicate that cI is required for basal respiration and maintenance of the NAD+/NADH ratio, an indicator of cellular redox status. This finding has largely not been tested in vivo. Here, we report that mitochondrial complex I is dispensable for homeostasis of the adult mouse liver; animals with hepatocyte-specific loss of cI function display no overt phenotypes or signs of liver damage, and maintain liver function, redox and oxygen status. Further analysis of cI-deficient livers did not reveal significant proteomic or metabolic changes, indicating little to no compensation is required in the setting of complex I loss. In contrast, complex IV (cIV) dysfunction in adult hepatocytes results in decreased liver function, impaired oxygen handling, steatosis, and liver damage, accompanied by significant metabolomic and proteomic perturbations. Our results support a model whereby complex I loss is tolerated in the mouse liver because hepatocytes use alternative electron donors to fuel the mitochondrial ETC.
