The role of microRNAs in X-Linked Myotubular Myopathy

X-linked myotubular myopathy (XLMTM) is a congenital neuromuscular disorder characterized by profound hypotonia and severe skeletal muscle weakness in the affected newborn males. The pathology is associated with mutations in the MTM1 gene leading to loss of function of the resulting encoded protein, myotubularin. Myotubularin is a phosphoinositol lipid phosphases known to be involved in endosome trafficking and membrane remodeling, however, the molecular mechanisms underlying myotubular myopathy are not yet clear. MicroRNAs (miRNAs) are post transcriptional modulators of gene expression and play an important role in many developmental processes and diseases. To identify functional miRNA-protein networks that may be dysregulated in myotubular myopathy, we performed miRNA as well as mRNA expression profiling of skeletal muscle of Mtm1 knockout mice. Bioinformatic analysis and real-time RTPCR validation resulted in identification of 12 miRNAs that showed significantly differential expression in Mtm1 mice. The functional targets of these miRNAs in myotubular myopathy were identified by a combinatorial approach in which computationally predicted targets genes of these 12 miRNAs were matched with statistically altered genes obtained by mRNA profiling of skeletal muscle tissues from Mtm1 mice. Ontological classification of target genes revealed genes primarily belonging to skeletal muscle development and maintenance, regulation of cell cycle and differentiation of muscle fibers. Expression analyses of miRNA-target genes identified from this study were also performed during earlier developmental time points (2 and 4 weeks) in Mtm1 mice for a better comprehensive insight of miRNA-mRNAs in the progression of the disease. We observed that an increase in the severity of XLMTM is associated with an increase in the fold change of several miRNAs and their target genes, suggesting their crucial role in pathology of myotubular myopathy. We hope understanding the molecular pathways involving these miRNA-mRNA networks, which are disrupted in myotubular myopathy, will contribute to uncovering the mechanisms of muscle development and maintenance and the development of new therapies for myotubular myopathy.