Mitigation of muscular dystrophy in mice by SERCA overexpression in skeletal muscle

Muscular dystrophies (MDs) comprise a group of degenerative muscle disorders characterized by progressive muscle wasting and often premature death. The primary defect common to most MDs involves disruption of the dystrophin-glycoprotein complex (DGC). This leads to sarcolemmal instability and Ca²⁺ influx, inducing cellular necrosis. Here we have shown that the dystrophic phenotype observed in δ-sarcoglycan-null (Sgcd^-/-) mice and dystrophin mutant mdx mice is dramatically improved by skeletal muscle-specific overexpression of sarcoplasmic reticulum Ca²⁺ ATPase 1 (SERCA1). Rates of myofiber central nucleation, tissue fibrosis, and serum creatine kinase levels were dramatically reduced in Sgcd^-/- and mdx mice with the SERCA1 transgene, which also rescued the loss of exercise capacity in Sgcd^-/- mice. Adeno-associated virus-SERCA2a (AAV-SERCA2a) gene therapy in the gastrocnemius muscle of Sgcd^-/- mice mitigated dystrophic disease. SERCA1 overexpression reversed a defect in sarcoplasmic reticulum Ca²⁺ reuptake that characterizes dystrophic myofibers and reduced total cytosolic Ca²⁺. Further, SERCA1 overexpression almost completely rescued the dystrophic phenotype in a mouse model of MD driven solely by Ca²⁺ influx. Mitochondria isolated from the muscle of SERCA1-Sgcd^-/- mice were no longer swollen and calpain activation was reduced, suggesting protection from Ca²⁺-driven necrosis. Our results suggest a novel therapeutic approach using SERCA1 to abrogate the altered intracellular Ca²⁺ levels that underlie most forms of MD.