Calsequestrin-1 Deficiency Induced Malignant Hyperthermia-Like Skeletal Injury through Mitochondrial Disorder

Calsequestrin-1 (CASQ1) is a candidate gene defect for malignant hyperthermia (MH) with significant skeletal muscle symptoms and injury, in which mitochondrial dysfunction may play an important role. However, the mechanisms underlying the mitochondrial changes are unknown. In this study we aimed to investigate the possible mechanisms for mitochondrial disorder using calseguestrin-1 knockout (Casq1-KO) mice. Casq1-KO mouse skeletal muscle injury was detected by the measurement of grip strength, and hematoxylin-eosin (H&E) and Gomori immune-staining. Mitochondrial function was evaluated by assessments of membrane potential (MMP), ATP production, and mitochondrial Ca²⁺ level. Western blot and malondialdehyde (MDA) assays were used to evaluate mitochondrial oxidative stress. AAV9-carrying CMV-Casq1 gene transfection was applied to confirm the effect of Casq1 deficiency on the skeletal muscle. The results showed that Casq1-KO mice exhibited obvious skeletal muscle dysfunction, structural change, and promotions of reactive oxygen species (ROS) production and its signal pathway activation. Significant decreases in ATP production and MMP, and an increase in mitochondrial Ca²⁺ level were observed in Casq1-KO skeletal mitochondria compared with those of WT. Interestingly, the expression of mitochondrial Ca²⁺ channel (MICU1), an important mitochondrial Ca²⁺ regulatory protein, was remarkably reduced in Casq1-KO skeletal mitochondria. Transduction of AAV9-CMV-Casq1 into Casq1-KO skeletal muscle recovered the Casq1 and MICU1 expression, mitochondrial Ca²⁺ level, MMP, and ATP production, with significant mitigation of skeletal oxidative stress and injuries. In conclusion, Casq1 deficiency or dysfunction could induce skeletal muscle injuries directly. Depressed MICU1 expression with an increased mitochondrial Ca²⁺ and ROS production may contribute significantly to the skeletal myopathy in malignant hyperthermia-like skeletal syndrome.