Modulation of myostatin expression during modified muscle use

Previous findings have provided strong evidence that myostatin functions as a negative regulator of muscle mass during development and growth. In the present study , we test the hypothesis that myostatin may serve a similar function in fully differentiated muscle experiencing modified loading. Our findings show that the myostatin expression can be modulated in fully differentiated, non-pathologicalskeletal muscle in a manner that is inversely related to changes in muscle mass. Atrophy of rat hind limb muscles induce by 10 days of unloading resulted in in a 165 decrease in plantaris mass, a 110% increase in myostatin mRNA, and a 37% increase in myostatin protein. Immunohistochemical observations showed that a detectable increase in myostatin concentration at myotendinous junctions during muscle unloading. The concentration of myostatin mRNA and protein returned to values not significantly different from ambulatory controls after 4 days of reloading, during which time plantaris mass also returned to control values. However the results also show that of 30min of daily muscle loading during the unloading period were sufficient to prevent significant losses of muscle mass caused by muscle unloading, although muscle mass loos during unloading is accompanied by increases in myostatin.