Loss of TMEM65 in mice causes mitochondrial disease mediated by mitochondrial Ca2.

Transmembrane protein 65 (TMEM65) depletion in a patient caused severe mitochondrial encephalomyopathy, highlighting its clinical importance. Recent studies show TMEM65 acts as a mitochondrial Na+/Ca2+ exchanger in vitro. Here, we generated conditional Tmem65 knockout mice to define its role in neuromuscular tissues in vivo. Both whole-body and nervous system-specific Tmem65 knockouts exhibited severe growth retardation and seizure-associated sudden death at ~3 weeks, establishing TMEM65 as indispensable for neuronal function. Additionally, skeletal muscle-specific knockout produced adult-onset myopathy preceded by elevated mitochondrial Ca2+. Consistently, TMEM65 ablation caused loss of Na+-dependent mitochondrial Ca2+ export. Notably, blocking mitochondrial Ca2+ entry by mitochondrial calcium uniporter (MCU) knockout rescued the early lethality of whole-body Tmem65 ablation, extending lifespan from ~3 weeks to >1 year. These data reveal an essential physiological role for TMEM65 and suggest that modulating mitochondrial Ca2+ may offer therapeutic value for TMEM65 misexpression and other mitochondrial diseases associated with Ca2+ overload.