Myostatin (formerly known as Growth and Differentiation Factor 8) is a growth factor that limits muscle tissue growth, i.e. higher concentrations of myostatin in the body cause the individual to have less developed muscles. The myostatin protein is produced in muscle cells, circulates in the blood and acts on muscle tissue, apparently by slowing down the development of muscle stem cells. The precise mechanism remains unknown.
Myostatin and the associated gene were discovered in 1997 by geneticists McPherron and Se-Jin Lee, who also produced a strain of mutant mice that lack the gene and are about twice as strong as normal mice. The gene has been sequenced in humans, mice, zebrafish and several other animals, showing few differences among species. Lee found in 1997 that the strong Belgian Blue and Piedmontese cattle strains have a defective myostatin gene; these strains have been produced through breeding.
In 2001, Lee created mice with intact myostatin gene and large muscle mass by inserting mutations that boosted the production of various myostatin blocking substances.
In 2004, a German boy was diagnosed with a mutation in both copies of the myostatin-producing gene, making him considerably stronger than his peers. His mother, a former sprinter, has a mutation in one copy of the gene.
Further research into myostatin and the myostatin gene may lead to therapies for muscular dystrophy. The idea is to introduce substances that block myostatin. In 2002, researchers at the University of Pennsylvania showed that an antibody specific to myostatin improves the condition of mice with muscular dystrophy. It remains unclear whether long term treatment with myostatin inhibitors is beneficial: the depletion of muscle stem cells could worsen the disease later on.
As of 2005, no myostatin inhibiting drugs for humans are on the market, but an antibody genetically engineered to neutralize myostatin was developed by New Jersey pharmaceutical company Wyeth and currently undergoes human testing. Some athletes, eager to get their hands on such drugs, turn to the internet, where fake "myostatin blockers" are being sold.
Myostatin is a member of the TGF-beta superfamily of proteins. Human Myostatin consists of two identical subunits, each containing 110 amino acid residues. Its total molecular weight is 25.0 kDa. It can be produced in genetically engineered E. coli and is available for sale. Johns Hopkins University owns the patents on myostatin.