Sarcospan integration into laminin-binding adhesion complexes that ameliorate muscular dystrophy requires utrophin and ?7 integrin.

ABSTRACT: Duchenne muscular dystrophy (DMD) is caused by mutations in the dystrophin gene that result in loss of the dystrophin-glycoprotein complex, a laminin receptor that connects the myofiber to its surrounding extracellular matrix. Utrophin, a dystrophin ortholog that is normally localized to the neuromuscular junction, is naturally upregulated in DMD muscle, which partially compensates for the loss of dystrophin. Transgenic overexpression of utrophin causes broad sarcolemma localization of utrophin, restoration of laminin binding and amelioration of disease in the mdx mouse model of DMD. We previously demonstrated that overexpression of sarcospan, a dystrophin- and utrophin-binding protein, ameliorates mdx muscular dystrophy. Sarcospan boosts levels of utrophin to therapeutic levels at the sarcolemma, where attachment to laminin is restored. However, understanding the compensatory mechanism is complicated by concomitant upregulation of ?7?1 integrin, which also binds laminin. Similar to the effects of utrophin, transgenic overexpression of ?7 integrin prevents DMD disease in mice and is accompanied by increased abundance of utrophin around the extra-synaptic sarcolemma. In order to investigate the mechanisms underlying sarcospan 'rescue' of muscular dystrophy, we created double-knockout mice to test the contributions of utrophin or ?7 integrin. We show that sarcospan-mediated amelioration of muscular dystrophy in DMD mice is dependent on the presence of both utrophin and ?7?1 integrin, even when they are individually expressed at therapeutic levels. Furthermore, we found that association of sarcospan into laminin-binding complexes is dependent on utrophin and ?7?1 integrin.

SUBMITTER: Marshall JL 

PROVIDER: S-EPMC4355028 | biostudies-literature | 2015 Apr

REPOSITORIES: biostudies-literature