Overexpression of SERCA1a in the mdx diaphragm reduces susceptibility to contraction-induced damage

Abstract

Although the precise pathophysiological mechanism of muscle damage in dystrophin-deficient muscle remains disputed, calcium appears to be a critical mediator of the dystrophic process. Duchenne muscular dystrophy patients and mouse models of dystrophin deficiency exhibit extensive abnormalities of calcium homeostasis, which we hypothesized would be mitigated by increased expression of the sarcoplasmic reticulum calcium pump. Neonatal adeno-associated virus gene transfer of sarcoplasmic reticulum ATPase 1a to the mdx diaphragm decreased centrally located nuclei and resulted in reduced susceptibility to eccentric contraction-induced damage at 6 months of age. As the diaphragm is the mouse muscle most representative of human disease, these results provide impetus for further investigation of therapeutic strategies aimed at enhanced cytosolic calcium removal.

FIG. 1.

Overexpression of SERCA1a in the mdx diaphragm protects from eccentric contraction–induced loss of force production. (a) Immunoblotting of diaphragm homogenates demonstrated 69% less SERCA1a in the mdx diaphragm (red column) in comparison with C57 Bl/6 controls (navy column). AAV-mediated gene transfer increased SERCA1a content in mdx/SERCA1a diaphragm (green column) to 52% of control. (b) The muscle fiber size distribution was unaffected by SERCA1a overexpression. (c) An increase in the proportion of type IIA fibers and a decrease in the proportion of type IIX fibers were observed in the mdx/SERCA1a group. (d) The percentage of centrally nucleated fibers (CNFs) was reduced from 25% in the mdx diaphragm to 13% in the mdx/SERCA1a diaphragm. (e) Force production was measured following a series of eccentric contractions (ECC). Beginning at the second contraction, there was a significant attenuation of the force loss in mdx/SERCA1a diaphragm in comparison with the untreated mdx diaphragm. Data represent means ± SD. *P < 0.05, mdx vs. C57/Bl6. ^#P < 0.05, mdx vs. mdx/SERCA1a. Color images available online at www.liebertonline.com/hum.