Blocking the activity of the protein myostatin could be an attractive therapeutic strategy for the treatment of muscle degeneration diseases, indicates research in the 28 November issue of Nature. Khurana and colleagues found that blocking myostatin activity in the mdx mouse model of Duchenne muscular dystrophy causes a significant increase in muscle size and improves muscle function. Such blockade could be beneficial for a variety of primary and secondary myopathies, including the muscular dystrophies (MD), and muscle loss for other reasons.

Duchenne MD is an X-linked muscle disease caused by an absence of the protein dystrophin. Dystrophin and a similar protein, utrophin, are structural proteins in skeletal and cardiac muscle cells. Affected boys show signs of disease early in life, stop walking at the beginning of the second decade, and usually die by 20 years of age. Mutations in genes encoding members of the dystrophin-associated glycoprotein complex lead to different MDs. There is no cure for these diseases, but corticosteroids, including prednisone and a related compound, deflazacort, can delay the loss of muscle strength and function in Duchenne MD patients. Experimental approaches include gene therapy, cell transplantation and upregulation of alternative therapeutic proteins.

Myostatin is a negative regulator of muscle mass — a mutation in the myostatin gene is responsible for the enormous musculature in 'double-muscled' Belgian blue cattle. After injecting month-old mdx mice with myostatin-blocking antibodies for three months, the authors found that the levels of utrophin in the muscle were not elevated, suggesting that blockade ameliorated the dystrophic phenoptype via a utrophin-independent mechanism. Elevated serum creatine kinase (CK) concentration is a sign of dystrophin deficiency in mdx mice; however, after three months of myostatin blockade the serum CK concentration was almost normal. Not all dystrophic changes in mdx mice were reversed by blocking myostatin; the mice were still susceptible to muscle-fibre damage by lengthening contractions. However, the authors suggest that this might not be the case if the treatment was started at birth, rather than a month later.

The pharmacological intervention of injecting antibodies to myostatin would obviate a number of practical difficulties associated with other experimental approaches to MDs. Interestingly, myostatin has also been implicated in the development of obesity and insulin resistance. This protein could represent a target for the design of small-molecule inhibitors.