NEK7 couples SDHB to orchestrate respiratory chain electron transport homeostasis that impedes liver fibrosis.

The mode of electron transport in mitochondrial respiratory chain determines whether it generates energy or more reactive oxygen species (ROS), a key for cellular adaptation to diverse oxygen environments. However, the understanding of the mechanisms remains incomplete. Here, we find that NIMA-related kinase 7 (NEK7), targeted to mitochondria by its signal peptides, binds to succinate dehydrogenase complex iron sulfur subunit B (SDHB), stabilizing the spatial conformation of complex II and promoting forward electron transport. Deficiency of NEK7 in hepatocytes induces reverse electron transport (RET) and inhibits mitochondrial respiration, thereby promoting ROS generation, triggering spontaneous liver fibrosis and aggravating CCl4-induced liver fibrosis, which can be attenuated by RET inhibitors. More importantly, NEK7 overexpression effectively alleviates CCl4- and choline-deficient, high-fat diet-induced liver fibrosis. Overall, these findings highlight the pivotal role of NEK7 in orchestrating complex II and electron transport, providing new insights into the regulation of mitochondrial homeostasis and potential fibrosis treatments.