LSMEM2, Localized at the Neuromuscular Junction, Modulates Mitochondrial Integration in Skeletal Muscles

In addition to the canonical metabolism-regulating function, Adenosine monophosphate-activated protein kinase (AMPK) has noncanonical functions, in which AMPK spatiotemporally phosphorylates specific sets of substrates. Recently, we identified LSMEM2, a novel substrate of AMPK in the heart. LSMEM2 is a membrane protein localized at the intercalated disc (ICD), whose function is currently under investigation. Interestingly, LSMEM2 is also expressed in the skeletal muscles. As skeletal muscles lack a homophilic intercellular junction corresponding to the ICD in the heart, predicting the role of LSMEM2 in skeletal muscles is difficult. In this study, we identified that LSMEM2 is expressed in skeletal muscles, specifically at the neuromuscular junction (NMJ). LSMEM2-knockout mice showed no histological abnormalities, suggesting that LSMEM2 is not essential for skeletal muscle development. The overexpression of full-length wild-type or C-del mutant of LSMEM2 led to the tubular aggregate formation with functional abnormality in male mice. RNA sequence analysis revealed that the gene sets of mitochondrial oxidative phosphorylation and vesicle-mediated transport are enriched in LSMEM2 overexpression. Furthermore, histological analysis demonstrated the accumulation of swollen subsarcolemmal mitochondria in LSMEM2-overexpressing skeletal muscles. The study findings suggest that LSMEM2 may play a role in the pathogenesis of skeletal muscle diseases.