McCarthy John J, Esser Karyn A, Andrade Francisco H
Dept. of Physiology, University of Kentucky Medical Center, 800 Rose St., Lexington, KY 40536-0298, USA.
Am J Physiol Cell Physiol. 2007 Jul;293(1):C451-7. doi: 10.1152/ajpcell.00077.2007. Epub 2007 Apr 25.
MicroRNAs are highly conserved, noncoding RNAs involved in posttranscriptional gene silencing. MicroRNAs have been shown to be involved in a range of biological processes, including myogenesis and muscle regeneration. The objective of this study was to test the hypothesis that microRNA expression is altered in dystrophic muscle, with the greatest change occurring, of the muscles examined, in the diaphragm. The expression of the muscle-enriched microRNAs was determined in the soleus, plantaris, and diaphragm muscles of control and dystrophin-deficient (mdx) mice by semiquantitative PCR. In the soleus and plantaris, expression of the mature microRNA 133a (miR-133a) and miR-206, respectively, was decreased by approximately 25%, whereas in the diaphragm, miR-206 expression increased by 4.5-fold relative to control. The increased expression of miR-206 in the mdx diaphragm was paralleled by a 4.4-fold increase in primary miRNA-206 (pri-miRNA-206) transcript level. Expression of Myod1 was elevated 2.7-fold only in the mdx diaphragm, consistent with an earlier finding demonstrating Myod1 can activate pri-miRNA-206 transcription. Transcript levels of Drosha and Dicer, major components of microRNA biogenesis pathway, were unchanged in mdx muscle, suggesting the pathway is not altered under dystrophic conditions. Previous in vitro analysis found miR-206 was capable of repressing utrophin expression; however, under dystrophic conditions, both utrophin transcript and protein levels were significantly increased by 69% and 3.9-fold, respectively, a finding inconsistent with microRNA regulation. These results are the first to report alterations in expression of muscle-enriched microRNAs in skeletal muscle of the mdx mouse, suggesting microRNAs may have a role in the pathophysiology of muscular dystrophy.
微小RNA是高度保守的非编码RNA，参与转录后基因沉默。微小RNA已被证明参与一系列生物学过程，包括肌发生和肌肉再生。本研究的目的是检验以下假设：在营养不良性肌肉中，微小RNA表达会发生改变，在所检查的肌肉中，膈肌的变化最大。通过半定量PCR测定对照小鼠和抗肌萎缩蛋白缺陷（mdx）小鼠的比目鱼肌、跖肌和膈肌中肌肉富集的微小RNA的表达。在比目鱼肌和跖肌中，成熟微小RNA 133a（miR - 133a）和miR - 206的表达分别降低了约25%，而在膈肌中，miR - 206的表达相对于对照增加了4.5倍。mdx膈肌中miR - 206表达的增加与初级微小RNA - 206（pri - miRNA - 206）转录水平增加4.4倍相平行。Myod1的表达仅在mdx膈肌中升高了2.7倍，这与早期发现一致，即Myod1可以激活pri - miRNA - 206转录。微小RNA生物合成途径的主要成分Drosha和Dicer的转录水平在mdx肌肉中未发生变化，表明该途径在营养不良条件下未改变。先前的体外分析发现miR - 206能够抑制抗肌萎缩蛋白的表达；然而，在营养不良条件下，抗肌萎缩蛋白的转录本和蛋白水平分别显著增加了69%和3.9倍，这一发现与微小RNA调节不一致。这些结果首次报道了mdx小鼠骨骼肌中肌肉富集的微小RNA表达的改变，表明微小RNA可能在肌肉营养不良的病理生理学中起作用。
