Reduced muscle mitochondrial enzyme activity in MuSK-immunized mice

Aim: Muscle specific kinase (MuSK) antibody-positive myasthenia gravis (MG) patients might present with clinical and electrophysiological signs of muscle atrophy. In this study, we investigated the potential contribution of mitochondrial dysfunction to muscle atrophy induced by MuSK immunity. Methods: Mitochondrial enzyme expression was investigated in muscle samples of MuSK-immunized, acetylcholine receptor (AChR)-immunized, and complete Freund's adjuvant (CFA)-immunized C57BL/6 (B6) mice using histochemical methods. Mitochondrial enzyme activity was also investigated in MuSK- and CFA-immunized mice. Results: Histochemical analysis showed normal muscle fiber activity on succinate dehydrogenase (SDH) and cytochrome oxidase (COX) stains in all immunization groups. However, MuSK-immunized mice had more ragged-red fibers on modified Gomori-trichrome (MGT) stain and more pronounced type 1 muscle fiber atrophy. MuSK-immunized mice also showed reduced citrate synthase, SDH, and NADH-cytochrome c-reductase activity. Discussion: Our results suggest that MuSK-immunity might induce muscle atrophy through mitochondrial dysfunction.