Scientists from Ohio State University and the Center for Gene Therapy at Ohio’s Nationwide Children’s Hospital have successfully demonstrated the genetic enhancement of muscle growth in monkeys (Kota et al. 2009).
In brief, the researchers used a viral vector (AAV1, adeno-associated virus 1) containing the human gene for follistatin, a glycoprotein which encourages muscle growth (by blocking myostatin). Researchers injected this vector into the right quadriceps muscle of macaque monkeys, thereby permanently genetically modifying that muscle to produce more follistatin.
As expected, muscle size and strength increased over a 3 month period after treatment, and was maintained at that enhanced level for a year (the effects of the enhancement likely would have lasted for the rest of the monkeys’ lives, but the monkeys were killed after a year for autopsy). Quadriceps circumference increased from around 16-17cm to about 21cm. In addition, twitch strength (force produced by rapid muscle contraction) increased by about 25% and tetanic strength (force produced by sustained contraction) by 12.5%. This increase was not correlated with any change to other organs or hormones.
As always, there are a few caveats. Firstly, drugs were used to suppress the immune systems of the monkeys for two weeks prior to the injections, in order to increase the efficiency of the viral vector and to avoid immune reactions (the immune system attacks viruses, even relatively harmless ones like AAV).
Second, mystatin inhibition can reduce the elasticity of tendons (Mendias et al, 2007), increasing risk of injury. My solution was to limit the modifications of myostatin to myocytes (muscle cells), rather than tenocytes (tendon cells). This most recent study attempted to do just that, by using a muscle creatine kinase promoter to control expression of the inserted follistatin trangene (therefore, only cells that also express creatine kinase would express the follistatin insert, and I assume tenocytes don’t express much creatine kinase). With this extra limitation, however, the researchers did not see as dramatic increases in muscle growth as those I presented above (which were from a vector that would be expressed in any cell).
Nonetheless, this study shows a successful localised insertion of a transgene in monkeys and a permanent increase in muscle size and overall strength, without any changes to other organs or levels of testosterone (or other hormones). I’m sure a good workout at the gym has some benefits to health (specifically cardiac health) that wouldn’t be mimicked by changes to follistatin or myostatin, but regardless this is another step towards super-strength and other enhancements.