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MEF2A regulates the Gtl2-Dio3 microRNA mega-cluster to modulate WNT signaling in skeletal muscle regeneration.

ABSTRACT: Understanding the molecular mechanisms of skeletal muscle regeneration is crucial to exploiting this pathway for use in tissue repair. Our data demonstrate that the MEF2A transcription factor plays an essential role in skeletal muscle regeneration in adult mice. Injured Mef2a knockout mice display widespread necrosis and impaired myofiber formation. MEF2A controls this process through its direct regulation of the largest known mammalian microRNA (miRNA) cluster, the Gtl2-Dio3 locus. A subset of the Gtl2-Dio3 miRNAs represses secreted Frizzled-related proteins (sFRPs), inhibitors of WNT signaling. Consistent with these data, Gtl2-Dio3-encoded miRNAs are downregulated in regenerating Mef2a knockout muscle, resulting in upregulated sFRP expression and attenuated WNT activity. Furthermore, myogenic differentiation in Mef2a-deficient myoblasts is rescued by overexpression of miR-410 and miR-433, two miRNAs in the Gtl2-Dio3 locus that repress sFRP2, or by treatment with recombinant WNT3A and WNT5A. Thus, miRNA-mediated modulation of WNT signaling by MEF2A is a requisite step for proper muscle regeneration, and represents an attractive pathway for enhancing regeneration of diseased muscle.

SUBMITTER: Snyder CM

PROVIDER: S-EPMC3513991 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BACKGROUND:MicroRNAs (miRNAs) are a class of small non-coding RNAs that have recently emerged as important regulators of gene expression. They negatively regulate gene expression post-transcriptionally by translational repression and target mRNA degradation. miRNAs have been shown to play crucial roles in muscle development and in regulation of muscle cell proliferation and differentiation. METHODOLOGY/PRINCIPAL FINDINGS:By comparing miRNA expression profiling of proliferating myoblasts versus differentiated myotubes, a number of modulated miRNAs, not previously implicated in regulation of myogenic differentiation, were identified. Among these, miR-221 and miR-222 were strongly down-regulated upon differentiation of both primary and established myogenic cells. Conversely, miR-221 and miR-222 expression was restored in post-mitotic, terminally differentiated myotubes subjected to Src tyrosine kinase activation. By the use of specific inhibitors we provide evidence that expression of miR-221 and miR-222 is under the control of the Ras-MAPK pathway. Both in myoblasts and in myotubes, levels of the cell cycle inhibitor p27 inversely correlated with miR-221 and miR-222 expression, and indeed we show that p27 mRNA is a direct target of these miRNAs in myogenic cells. Ectopic expression of miR-221 and miR-222 in myoblasts undergoing differentiation induced a delay in withdrawal from the cell cycle and in myogenin expression, followed by inhibition of sarcomeric protein accumulation. When miR-221 and miR-222 were expressed in myotubes undergoing maturation, a profound alteration of myofibrillar organization was observed. CONCLUSIONS/SIGNIFICANCE:miR-221 and miR-222 have been found to be modulated during myogenesis and to play a role both in the progression from myoblasts to myocytes and in the achievement of the fully differentiated phenotype. Identification of miRNAs modulating muscle gene expression is crucial for the understanding of the circuits controlling skeletal muscle differentiation and maintenance.

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MEF2A regulates the Gtl2-Dio3 microRNA mega-cluster to modulate WNT signaling in skeletal muscle regeneration.

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