Overproduction of follistatin in mice along with the absence of myostatin, previously known to make mice put on muscle, doubled the increase.

A second protein, follistatin, when overproduced in mice lacking myostatin doubles the muscle-building effect of the absence of myostatin alone, according to Se-Jin Lee, M.D., Ph.D., a professor of molecular biology and genetics at Johns Hopkins. Dr. Lee previously discovered that the absence of the protein myostatin leads to oversized muscles in mice and men.

Dr. Lee believes that this added muscle increase could boost research efforts to beef up livestock or promote muscle growth in patients with muscular dystrophy and other wasting diseases.

Dr. Lee first discovered that follistatin was capable of blocking myostatin activity in muscle cells grown under lab conditions. When he gave it to normal mice, the rodents bulked up, just as would happen if the myostatin gene in these animals was turned off. He then genetically engineered a mouse that both lacked myostatin and made extra follistatin.

If follistatin was increasing muscle growth solely by blocking myostatin, then Dr. Lee surmised that follistatin would have no added effect in the absence of myostatin. “To my surprise and delight, there was an additive effect,” remarks Dr. Lee. The mice reportedly averaged a 117% increase in muscle fiber size and a 73% increase in total muscle fibers compared to normal mice.

The study appears online on August 29 in PLoS ONE.

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