Toth Michael J, Tchernof André
Department of Medicine, University of Vermont, Burlington, VT 05405, USA.
Exp Gerontol. 2006 Nov;41(11):1195-200. doi: 10.1016/j.exger.2006.08.005. Epub 2006 Oct 6.
Age-related changes in myosin heavy chain (MHC) phenotype impact both the quantity and functional character of skeletal muscle. The present study was undertaken to examine the hypothesis that age-related changes in MHC mRNA abundance underlie alterations in protein synthesis rates and content. We measured the abundance of mRNA for MHC isoforms (MHC I, MHC IIa, IIx) and actin by RT-PCR in 6 young (mean +/- SE; 29 +/- 3) and 12 elderly (73 +/- 1 yr; P<0.01) volunteers and examined their association to MHC protein synthesis rates and their respective protein products. We found no differences between young and elderly volunteers in MHC isoform or actin transcript levels. Because of the absence of age effects, data were pooled for correlation analyses. Although total MHC mRNA levels were not related to MHC fractional synthesis rates, the relative abundance of MHC I and MHC IIa mRNA were positively (r = 0.450; P = 0.06) and negatively (r = -0.493; P<0.05) associated with MHC protein synthesis rates, respectively. MHC mRNA levels were positively correlated to their respective protein products (range of r-values: 0.551-0.727; P<0.05 to P<0.01), but were not related to skeletal muscle IGF-I mRNA abundance, circulating IGF-I or markers of immune activation. Our results argue against the notion that changes in MHC protein synthesis rates with age are related to altered MHC mRNA abundance, although our findings do suggest that possibility that individual variability in MHC protein synthesis rates is related to the relative abundance of MHC I versus MHC IIa transcripts.
肌球蛋白重链（MHC）表型的年龄相关变化会影响骨骼肌的数量和功能特性。本研究旨在检验以下假设：MHC mRNA丰度的年龄相关变化是蛋白质合成速率和含量改变的基础。我们通过逆转录聚合酶链反应（RT-PCR）测量了6名年轻志愿者（平均±标准误；29±3岁）和12名老年志愿者（73±1岁；P<0.01）中MHC亚型（MHC I、MHC IIa、IIx）和肌动蛋白的mRNA丰度，并研究了它们与MHC蛋白质合成速率及其各自蛋白质产物的关联。我们发现年轻和老年志愿者在MHC亚型或肌动蛋白转录水平上没有差异。由于不存在年龄效应，将数据合并进行相关性分析。尽管总MHC mRNA水平与MHC分数合成速率无关，但MHC I和MHC IIa mRNA的相对丰度分别与MHC蛋白质合成速率呈正相关（r = 0.450；P = 0.06）和负相关（r = -0.493；P<0.05）。MHC mRNA水平与其各自的蛋白质产物呈正相关（r值范围：0.551 - 0.727；P<0.05至P<0.01），但与骨骼肌胰岛素样生长因子-I（IGF-I）mRNA丰度、循环IGF-I或免疫激活标志物无关。我们的结果反驳了随着年龄增长MHC蛋白质合成速率的变化与MHC mRNA丰度改变有关的观点，尽管我们的发现确实表明MHC蛋白质合成速率的个体差异可能与MHC I与MHC IIa转录本的相对丰度有关。
