Aging-associated genes and let-7 microRNAs: a contribution to myogenic program dysregulation in oculopharyngeal muscular dystrophy

Oculopharyngeal muscular dystrophy (OPMD) is a late-onset muscle disease caused by an abnormal (GCN) triplet expansion within the polyadenylate-binding protein nuclear 1 gene and consequent mRNA processing impairment and myogenic defects. Because a reduced cell proliferation potential and the consequent regeneration failure of aging muscle have been shown to be governed by lethal-7 ( let-7) microRNA-mediated mechanisms, in the present study, we evaluated the role of let-7 in the pathogenesis of OPMD. By a multidisciplinary approach, including confocal microscopy, Western blot, and quantitative PCR analyses on muscle biopsies from patients and unaffected individuals, we found a significant increase in let-7 expression in OPMD muscles associated with an unusual high percentage of paired box 7-positive satellite cells. Furthermore, IL-6, a cytokine involved in the regulation of satellite cell proliferation and differentiation and a potential target of let-7, was found strongly down-regulated in OPMD compared with control muscles. The decrease in IL-6 transcript levels and protein content was also confirmed in vitro during differentiation of patients' and controls' muscle cells. Overall, our data suggest a key role of let-7 in the regeneration and degeneration process in OPMD muscle and pointed to IL-6 as a potential target molecule for new therapeutic approaches for this disorder.-Cappelletti, C., Galbardi, B., Bruttini, M., Salerno, F., Canioni, E., Pasanisi, M. B., Rodolico, C., Brizzi, T., Mora, M., Renieri, A., Maggi, L., Bernasconi, P., Mantegazza, R. Aging-associated genes and let-7 microRNAs: a contribution to myogenic program dysregulation in oculopharyngeal muscular dystrophy.