Study Explores miRNAs in Inflammatory Muscle Pain

August 14, 2007

A generation ago, when most biology students heard the acronym RNA, they thought of the messenger RNA that our cells process into tens of thousands of different proteins.  When today’s biology students hear the term, they might ask, “Which type of RNA?”  Researchers over the last fifteen years have delved more deeply into other types of RNA that are present in our cells and, in some cases, have discovered entirely new classes of RNA.  Of these new discoveries, perhaps the most interesting is microRNA, or miRNAs.  Scientists have identified hundreds of these short RNA sequences in plants, animals, and viruses.  They also have determined that these small molecules serve to downregulate gene expression by pairing with a specific region of the messenger RNA and blocking its subsequent translation into protein, especially during development. 

For pain researchers, this discovery is interesting because microRNAs also have been detected in mature neurons.  In the June issue of the journal Molecular Pain, a team of NIDCR supported scientists and colleagues now provide a possible explanation.  The scientists demonstrate for the first time that certain microRNAs are selectively expressed in neurons within the peripheral nervous system after inducing inflammatory muscle pain.  “Most importantly,” the scientists noted, “we observed that several miRNA molecules, likely in the mature form, are regulated by an inflammatory irritant and their changes are correlated with the development of allodynia,” an over-reaction to non noxious stimuli.  This suggests that as allodynia occurs and microRNAs are downregulated, more messenger RNA in the peripheral neurons can be translated into proteins that take part in the inflammatory process.  “Whether this miRNA downregulation is mechanistically involved in inflammatory pain cannnot be addressed in the present study,” the authors wrote.  “How miRNA participates in inflammatory pain relies, at least in part, on the elucidation of their target mRNAs and/or on the impact of manipulated levels of specific miRNA on nocipception.”  The authors added that more comprehensive studies will be needed to begin answer these questions.