The mitochondrial calcium uniporter mediates mitochondrial Fe²⁺ uptake and hepatotoxicity after acetaminophen

Acetaminophen (APAP) overdose disrupts hepatocellular lysosomes, which release ferrous iron (Fe²⁺) that translocates into mitochondria putatively via the mitochondrial calcium uniporter (MCU) to induce oxidative/nitrative stress, the mitochondrial permeability transition (MPT), and hepatotoxicity. To investigate how MCU deficiency affects mitochondrial Fe²⁺ uptake and hepatotoxicity after APAP overdose, global MCU knockout (KO), hepatocyte specific (hs) MCU KO, and wildtype (WT) mice were treated with an overdose of APAP both in vivo and in vitro. Compared to strain-specific WT mice, serum ALT decreased by 88 and 56%, respectively, in global and hsMCU KO mice at 24 h after APAP (300 mg/kg). Hepatic necrosis also decreased by 84 and 56%. By contrast, when MCU was knocked out in Kupffer cells, ALT release and necrosis were unchanged after overdose APAP. Intravital multiphoton microscopy confirmed loss of viability and mitochondrial depolarization in pericentral hepatocytes of WT mice, which was decreased in MCU KO mice. CYP2E1 expression, hepatic APAP-protein adduct formation, and JNK activation revealed that APAP metabolism was equivalent between WT and MCU KO mice. In cultured hepatocytes after APAP, loss of cell viability decreased in hsMCU KO compared to WT hepatocytes. Using fructose plus glycine to prevent cell killing, mitochondrial Fe²⁺ increased progressively after APAP, as revealed with mitoferrofluor (MFF), a mitochondrial Fe²⁺ indicator. By contrast in hsMCU KO hepatocytes, mitochondrial Fe²⁺ uptake after APAP was suppressed. Rhod-2 measurements showed that Ca²⁺ did not increase in mitochondria after APAP in either WT or KO hepatocytes. In conclusion, MCU mediates uptake of Fe²⁺ into mitochondria after APAP and plays a central role in mitochondrial depolarization and cell death during APAP-induced hepatotoxicity.