In vivo evaluation of changes in body composition of transgenic mice expressing the myostatin pro domain using dual energy X-ray absorptiometry.

Over expression of the pro domain of myostatin (MLC-pro) interferes with myostatin function, thus promoting muscle growth. The purpose of this study was to use dual energy X-ray absorptiometry (DXA) to monitor, in vivo, the course of changes in body composition of control and MLC-pro transgenic (TG) mice between 10 and 91 days of age. MLC-pro TG (n = 32) and littermate control (n = 28) mice were produced by mating G-3 male TG mice with non-TG females. At days 10, 20 and weekly thereafter to day 62, and finally at day 91, the mice were anesthetized and scanned by DXA. By day 34, the body weight of the male TG mice was more than that of the control mice and was accompanied by a larger lean mass (LM) and a lower percentage of fat (%F) (P < 0.05). At day 91, the male TG mice had 15.6% greater body weight, 19.4% more LM, 22.4% lower %F, 11.5% more bone mineral, and 4.4% higher bone density (P < 0.05). The lower %F in the TG mice was due mainly to an increase in LM, rather than reduced FM. Measurements of the TG female mice were not different (P > 0.05) from those of control female mice. A region-of-interest analysis was used to provide a separate measure of the hind limb. By using DXA, this study determined the onset and degree of differences in body composition of MLC-pro TG and littermate control mice.