Redox-sensitive eccentric contraction-induced force loss in a muscle-specific Actb knockout myopathy model

Eccentric contraction (ECC)-induced force loss is one of the most robust and reproducible phenotypes of the dystrophin-deficient mdx mouse, which is the most widely studied model of Duchenne muscular dystrophy. Despite its utility as a quantitative assessment of therapeutic efficacy in preclinical trials, the mechanism of ECC force loss in mdx skeletal muscle remains incompletely understood. We have previously shown that dystrophin directly interacts with non-muscle cytoplasmic actin isoforms in structures called “costameres” and that oxidative stress and altered redox metabolism contribute to ECC force loss in mdx muscle. Key methods include physiological measurement of skeletal muscle isometric and eccentric force (in vitro) and torque (in vivo), DCF fluorescence, and histopathological and biochemical assessment of skeletal muscle. Here we demonstrate that extensor digitorum longus (EDL) muscles from muscle-specific, cytoplasmic β-actin knockout (ms- Actb KO) mice also present with significant ECC force loss, but the phenotype progresses more slowly and is of lower magnitude compared to mdx EDL muscles. We further demonstrate that muscle-specific transgenic overexpression of cytoplasmic β-actin protects ms- Actb KO muscles from ECC force loss. Consistent with our previous results in mdx mice, treatment of ms- Actb KO EDL muscles with the redox modulators N -acetylcysteine or the H 2 S donor sodium hydrogen sulfide prevents ECC force loss to a similar extent as transgenic cytoplasmic β-actin replacement. Different from mdx , however, ms- Actb KO ECC force loss occurs in the absence of a concomitant increase in ECC-induced reactive oxygen species production. Our results implicate oxidative stress and altered redox metabolism as critical regulators of ECC force loss in two independent models of myopathy. Together, the data presented here enhance the understanding of ECC force loss in both dystrophin-deficient and cytoplasmic β-actin-deficient forms of myopathy, specifically expanding on a unifying, redox-based mechanism of ECC force loss to include a non-dystrophin-deficient model of myopathy.