Altered gene and protein expressions of vitamin D receptor in skeletal muscle in sarcopenic patients who sustained distal radius fractures

Abstract

Despite the presence of vitamin D receptor (VDR) in skeletal muscle cells, the relationship between VDR expressions and muscle mass or function has not been well studied. The purpose of this study was to compare VDR gene and protein expression in the forearm muscle between sarcopenic and non-sarcopenic individuals who have sustained distal radius fractures. Twenty samples of muscle tissue from sarcopenic patients (mean age 63.4 +/- 8.1 years) and 20 age- and sex-matched control tissues (62.1 +/- 7.9 years) were acquired from the edge of dissected pronator quadratus muscle during surgery for distal radius fractures. The mRNA expression levels of VDR as well as the myokines of interest that may be associated with muscle mass change (myogenin and myostatin) were analyzed with real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). In addition, Western blot assay and immunohistochemistry for VDR were performed. Sarcopenic patients showed a significantly lower level of gene expression for VDR and myogenin, but a greater level of gene expression for myostatin than the controls according to qRT-PCR analysis. The density of VDR protein expressions was 2.1 times greater, while that of myostatin was 2.6 times lower, in the control group than in the sarcopenic group according to Western blot analysis. On immunohistochemical analysis, the density of the cells expressing VDR was significantly decreased in the sarcopenic patients. Sarcopenic patients who sustained distal radius fractures presented lower vitamin D receptor gene and protein expression in skeletal muscles compared to non-sarcopenic individuals.