Submitted on February 27, 2009
Revised on August 14, 2009
Accepted on August 14, 2009
Evidence of MyomiR network regulation of 
-myosin heavy chain gene expression during skeletal muscle atrophy
John J. McCarthy1*, Karyn A. Esser1, Charlotte A. Peterson1, and Esther E. Dupont-Versteegden1
1 University of Kentucky
* To whom correspondence should be addressed. E-mail: jjmcca2{at}uky.edu.
There is a growing recognition that non-coding RNAs (ncRNA) play an important role in the regulation of gene expression. A class of small (19-22 nt) ncRNAs, known as microRNAs (miRs), have received a great deal of attention lately because of their ability to repress gene expression through a unique post-transcriptional 3'-UTR mechanism. The objectives of the current study were to identify miRs expressed in the rat soleus muscle and determine if their expression was changed in response to hindlimb suspension. Comprehensive profiling revealed 151 miRs were expressed in the soleus muscle and expression of 18 miRs were significantly (p < 0.01) changed after two and/or seven days of hindlimb suspension. The significant decrease (16%) in expression of muscle-specific miR-499 in response to hindlimb suspension was confirmed by RT-PCR and suggested activation of the recently proposed MyomiR network during atrophy. Further analysis of soleus muscle subjected to hindlimb suspension for 28 days provided evidence consistent with MyomiR network repression of 
-myosin heavy chain gene (-MHC) expression. The significant down-regulation network components miR-499 and miR-208b by 40% and 60%, respectively, was associated with increased expression of Sox6 (2.2-fold) and Pur,(23%), predicted target genes of miR-499 and known repressors of -MHC expression. A Sox6 3'-UTR reporter gene confirmed Sox6 is a target gene of miR-499. These results further expand the role of miRs in adult skeletal muscle and are consistent with a model in which the MyomiR network regulates slow myosin expression during muscle atrophy.
