Absence of alpha 7 integrin in dystrophin-deficient mice causes a myopathy similar to Duchenne muscular dystrophy

Both the dystrophin-glycoprotein complex and alpha 7 beta 1 integrin have critical roles in the maintenance of muscle integrity via the provision of mechanical links between muscle fibres and the basement membrane. Absence of either dystrophin or alpha 7 integrin results in a muscular dystrophy. To clarify the role of alpha 7 integrin and dystrophin in muscle development and function, we generated integrin alpha 7/dystrophin double-mutant knockout (DKO) mice. Surprisingly, DKO mice survived post-natally and were indistinguishable from wild-type, integrin alpha 7-deficient and mdx mice at birth, but died within 24-28 days. Histological analysis revealed a severe muscular dystrophy in DKO mice with endomysial fibrosis and ectopic calcification. Weight loss was correlated with the loss of muscle fibres, indicating that progressive muscle wasting in the double mutant was most likely due to inadequate muscle regeneration. The data further support that premature death of DKO mice is due to cardiac and/or respiratory failure. The integrin alpha 7/dystrophin-deficient mouse model, therefore, resembles the pathological changes seen in Duchenne muscular dystrophy and suggests that the different clinical severity of dystrophin deficiency in human and mouse may be due to a fine-tuned difference in expression of dystrophin and integrin alpha 7 in both species. Together, these findings indicate an essential role for integrin alpha 7 in the maintenance of dystrophin-deficient muscles.