P.1.16 Sarcospan amelioration of muscular dystrophy restores laminin binding and is dependent on α7β1 integrin and utrophin

• DOI: 10.1016/j.nmd.2013.06.400
• Publication Date: 2013-08-28T20:42:59Z
• Authors: J.M. Marshall; J. Oh; E. Chou; J. Lee; K. Allan; J. Holmberg; D.J. Burkin; R.H. Crosbie-Watson
• Keywords: Utrophin; Sarcolemma; Dystroglycan; ITGA7

Duchenne muscular dystrophy is a progressive muscle wasting disorder caused by loss of the predominant adhesion complex at the muscle membrane, the dystrophin–glycoprotein complex. Over-expression of compensatory adhesion complexes, α 7 β 1 integrin or the utrophin–glycoprotein complex, rescues dystrophic pathology in the mdx mouse model of Duchenne muscular dystrophy. The utrophin–glycoprotein complex is normally localized to the neuromuscular junction and is comprised of utrophin, dystroglycan, and the sarcoglycan–sarcospan subcomplex. We have recently demonstrated that sarcospan amelioration of mdx muscular dystrophy increases protein abundance of the utrophin–glycoprotein complex and α 7 β 1 integrin around the extra-synaptic membrane; however, the mechanism of sarcospan-mediated rescue is unknown. Here, we show that the rescue effect is dependent on both α 7 integrin and utrophin, which in turn determine muscle cell binding to laminin in the extracellular matrix. Since sarcospan over-expression stabilizes the utrophin–glycoprotein complex and α 7 β 1 integrin at the sarcolemma, we investigated the possibility that sarcospan acts synergistically between both complexes. We biochemically isolated a macromolecular complex containing α 7 β 1 integrin and the utrophin–glycoprotein complex. Using several double- and triple-knockout mice, we discovered that integrin and sarcospan synergistically contribute to utrophin-glycoprotein complex function by promoting interactions between α - and β -dystroglycan, thereby disturbing laminin connections. Our data highlights the importance of both α 7 β 1 integrin and utrophin for sarcospan rescue of mdx dystrophic pathology.