Differential requirements for mitochondrial electron transport chain components in the adult murine liver

Abstract

Mitochondrial electron transport chain (ETC) dysfunction is a common cause of metabolic disease in humans, but 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 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 (cI) 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 and redox 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, steatosis, and liver damage, accompanied by significant metabolomic and proteomic perturbations. Correspondingly, we find that complex I-deficient livers are reliant on an alternative pathway, whereby electrons are donated to the ETC via dihydroorotate dehydrogenase, to maintain redox status. Our results support a model whereby complex I loss is tolerated in the mouse liver because hepatocytes make use of alternative electron donors to fuel the mitochondrial ETC.

Mitochondrial metabolism in primary and metastatic human kidney cancers

“…Oxygen consumption rates (OCR) were measured using a Seahorse XFe96 Analyzer (Agilent Technologies) as previously described 36,67 . Fresh kidney and tumour samples were homogenized with 40 strokes of a Dounce homogenizer in mitochondrial isolation buffer (HEPES [5 mM], sucrose [70 mM], mannitol [220 mM], MgCl2 [5 mM], KH2PO4 [10 mM], and EGTA [1 mM], pH 7.2) and isolated via differential centrifugation at 4 °C.…”

“…Oxygen consumption rates (OCR) were measured using a Seahorse XFe96 Analyzer (Agilent Technologies) as previously described 36,67 . Fresh kidney and tumour…”