Dysregulation of MicroRNA Expression in Myotonic Dystrophies

Myotonic dystrophies (DM) are dominantly inherited multisystemic disorders affecting skeletal muscle, heart, eye, and the endocrine system. Myotonic dystrophy type-1 (DM1) is caused by expansion of a CTG repeat in the 3\u2019UTR of DMPK gene, while myotonic dystrophy type-2 (DM2) is caused by expansion of a CCTG repeat in the intron 1 of ZNF9 gene. Both amplifications lead to the production of mutant mRNA transcripts which interfere with alternative splicing of other genes. However, other molecular mechanisms may be involved in DM pathogenesis. MicroRNAs (miRNAs) are short non-coding RNAs regulating gene expression at post-trascriptional level. Recently, dysregulation of miRNAs expression has been correlated with several muscle diseases. However, miRNAs levels have not been studied in DM. We measured the expression of 24 miRNAs in muscle biopsies of DM1 (n 15), DM2 (n 9) and control (n 10) subjects. Upregulation of miR1 and miR335 and downregulation of miR29b, miR29c, miR33 and miR223 was observed in DM1 biopsies. In DM2 biopsies, upregulation of miR34c was identified. Moreover tissue distribution of selected miRNAs was determined by in situ hybridization. This initial screening shows that miRNAs are differentially expressed in DM, suggesting their potential role in DM pathogenesis

Dysregulated expression of micrornas in myotonic dystrophy type 1

Myotonic dystrophy type 1(DM1) is a dominantly inherited multisystemic disorder affecting skeletal muscle, heart, eye, and the endocrine system. DM1 is caused by expansion of a CTG repeat in the 3\u2019UTR of DMPK gene. This genetic lesion leads to the accumulation of the expanded CUG transcripts into discrete nuclear RNA foci which interfere with alternative splicing of other genes. However, other molecular mechanisms may be involved in DM1 pathogenesis. MicroRNAs (miRNAs) are short non-coding RNAs that regulate the stability and/or the translational efficiency of target messenger RNAs. Recently, several studies have demonstrated that microRNA expression is disrupted in several myopathies such as Duchenne, Becker, facioscapulohumeral muscular dystrophies and DM1. The aim of this study is to assay whether levels and cellular localization of a group of candidate miRNAs is altered in DM1 patients, potentially contributing to DM1 pathogenetic mechanisms. We have analysed the expression of 24 specific miRNAs by TaqMan Real Time PCR (qPCR) method on muscle biopsies from DM1 (n=15) and control (n=10) subjects. We found that miR-1 and miR-335 are up-regulated, whereas miR-29b and c, and miR-33 are downregulated in DM1 biopsies compared to controls. In order to assess whether miRNA deregulation is functionally relevant, we have examined the impact of the identified miRNAs deregulation on the expression of their potential target genes in DM1 patients. Potential targets analysis by qPCR shows that both miR-29 and miR-1 targets are significantly up-regulated. Moreover the cellular localization of the identified miRNAs has been assayed by in situ hybridization on cryostat muscle sections derived from 5 DM1 and control biopsies. The cellular distribution of muscle specific miR-1, miR-133b and miR-206 appears to be severely altered in DM1 skeletal muscles. Our results indicate that the observed miRNA dysregulations and myslocalizations may contribute to DM1 pathogenetic mechanisms