Bone tissue and muscle dystrophin deficiency in mdx mice.

Duchenne muscular dystrophy is a neuromuscular disease caused by the lack of dystrophin that affects skeletal muscles, causing degeneration of muscle fibers and replacing them with fibrous and adipose tissue, events that gradually lead to functional loss. Patients with Duchenne muscular dystrophy have shown that bones become more fragile with age and with advancement of the disease. Muscle weakness and reduced mobility have been suggested to be the factors that promote bone deterioration. However, it seems that this does not occur in mdx mice. It has been identified in mdx mice the existence of a factor related or not to the lack of dystrophin that also participates in the impairment of bone quality. Mdx mice also exhibit muscle degeneration, but unlike human, it is compensated by muscle regeneration. In consequence, there is an increase in the muscle mass, but not necessarily of muscle contractile strength. The accommodation of this increased muscle mass promotes bone formation at specific sites, such as at tendo-osseous junctions. In addition, the inflammatory response to muscle injury may be responsible for the increase in angiogenesis and regeneration observed in mdx mice, inducing the release of cytokines and chemokines that play an important role in the recruitment of leukocytes and macrophages. Then, mdx mice may possess compensatory mechanisms in bone in response to a genetic defect.