ACTN3 R577X Genotype Is Associated with ACTN3 Protein Expression Levels and Myosin Heavy Chain Composition in Japanese College-Level Male Sprinters

Abstract

Alpha-actinin (ACTN) 3 R577X polymorphisms have three genotypes: RR, RX and XX. Only RR and RX genotypes express ACTN3 protein in type II fibers. The purpose of this study was to clarify whether there are differences in ACTN3 protein expression levels and myosin heavy chain (MyHC) composition between RR and RX genotypes in Japanese college-level male sprinters. Materials and Methods: Forty-three Japanese college-level male sprinters participated in this study. Subjects were genotyped for ACTN3 R577X using a real-time polymerase chain reaction assay. Furthermore, muscle biopsies from the vastus lateralis muscle were obtained from a subset of subjects who had R allele and gave their consent (4 RR and 9 RX). ACTN3 protein expression levels were assessed by western blotting. MyHC composition was determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Results: There was no difference in 100-m sprint performance among RR, RX and XX genotypes in all 43 subjects. In 13 biopsysampled subjects, there was also no difference in 100-m sprint performance between RR and RX and ACTN3 protein expression levels tended to be higher in RR genotype than in RX genotype. Although there were no differences in the proportion of type I and II MyHC isoforms between both genotypes, RR genotype had a significantly higher proportion of type IIx MyHC isoform and a significantly lower proportion of type IIa MyHC isoform than RX genotype. Conclusions: ACTN3 protein expression levels and the proportion of type IIx MyHC isoform are higher in RR genotype compared with RX genotype in Japanese college-level male sprinters.