The Effect of Myostatin SNP on Muscle Fiber Properties in Thoroughbred Horses during Training Period

Abstract

PURPOSE: Variants of the myostatin gene (MSTN) have been shown to have an influence on muscle hypertrophy phenotypes in a wide ranges of mammalian species. Recently, a thoroughbred horse with a C-Allele at the g.66493737C/T single nucleotide polymorphism (SNP) has been reported to be suited to short distance racing. In this study, we examined the effect of the MSTN SNP on muscle fiber properties in young horses during a training period. METHODS: To investigate the effect of the MSTN SNP on muscle fiber before training, several mRNA expressions were relatively quantified in biopsy samples from the middle gluteal muscle of 24 untrained male thoroughbred horses (1.5-year old, C/C: n = 8, C/T: n = 8, T/T: n = 8) using real-time RT-PCR analysis. Furthermore, the remaining muscle samples were used for immunohistochemical analysis to determine the number of satellite cells (SC), as well as the population and area of each fiber type. All measurements were revaluated in biopsy samples of the same horses after a 5-month period of conventional training. RESULTS: As compared to values before training, although there were not significant differences, cross sectional areas of all muscle fiber types increased (12-17%) in all SNP groups after training. Although the expressions of MSTN mRNA decreased in all SNP groups, a significant decrease was found in only the C/C group after training. However, the expressions of mRNA related to SCs activation and proliferation (HGF, Pax7, MyoD, and Myogenin) were identical among all SNP groups after training. While, expression of VEGFa, PGC1α, and SDHa mRNAs, which relate to the biogenesis of mitochondria and capillaries, was significantly higher (54-82%) in the T/T group than the C/C group after training. CONCLUSION: It is suggested that hypertrophy of muscle fiber is directly associated with a decrease in MSTN mRNA expression in the C/C group, and that increased expressions of VEGFa, PGC1α, and SDHa in the T/T group might be indirectly caused by the MSTN SNP. These results indicate that the C/C and T/T groups with the MSTN SNP have an advantage in short and long distance races, respectively.