Activation of the myogenin gene expression is required for the differentiation of skeletal muscle cells and also causes neurogenic muscle atrophy. Researchers now identified a novel long non-coding RNA (lncRNA) that is essential for skeletal muscle differentiation and neurogenic muscle atrophy through the activation of myogenin gene expression. The researchers presume that their discovery broadens our understanding of the biological role of lncRNAs and may provide a new therapeutic strategy for neurogenic atrophy in humans such as spinal cord injury, amyotrophic lateral sclerosis (ALS), Huntington's disease, and spinal muscular atrophy (SMA). The research is published in EMBO Reports.

Skeletal muscle is the largest organ in our body and is important not only for exercise but also for maintenance of whole body homeostasis. Skeletal muscle tissue is formed by differentiated skeletal myoblasts and the formation of skeletal muscle, called myogenesis, has been studied as a good model of cell differentiation systems. For proper myogenesis, spatiotemporal activation of myogenin gene expression, coding a myogenic transcriptional factor, is essential. However, the mechanisms inducing high-level myogenin expression in skeletal muscle cells have not been elucidated.

Recent findings indicate that antisense lncRNAs expressed from the promoter region of protein-coding genes regulate the expression of neighboring protein-coding genes. In their work at Fujita Health University, Japan, the research group of Prof. Kunihiro Tsuchida and other laboratories have uncovered that a new lncRNA, named Myoparr (myogenin promoter-associated myogenic regulatory antisense lncRNA), is essential for maximum activation of myogenin gene expression both in vitro and in vivo. In addition to the essential role of Myoparr in myogenic differentiation, Tsuchida and colleagues also found that inhibition of Myoparr expression in mice is a promising therapeutic strategy for neurogenic muscle atrophy caused by denervation.

The researchers first observed that an unidentified transcript, termed Myoparr, was expressed from the promoter region of myogenin gene using chromatin immunoprecipitation sequencing (ChIP-seq) analysis and reverse transcription polymerase chain reaction (RT-PCR)-based cloning. Further investigation showed that Myoparr was coexpressed with myogenin during myogenesis in mouse and human and was essential for the activation of myogenin gene expression in an epigenetic manner. “Our study indicates that Myoparr is a novel activator of myogenin expression and is also essential for myogenesis. Thus, identification of Myoparr uncovered a molecular mechanism required for high-level myogenin expression”, explains Tsuchida.

Moreover, the researchers found that Myoparr was also an essential activator for the expression of myogenic microRNAs, which control cell cycle withdrawal of myoblasts, in a myogenin-independent manner. This finding indicates that lncRNA expressed from the promoter region of protein-coding genes does not merely regulate neighboring protein-coding gene expression but may also affect gene expression at distal loci in a neighboring gene-independent manner. Mechanistically, the researchers found that Myoparr interacts with Ddx17, a transcriptional coactivator of MyoD, and promotes the association between Ddx17 and the histone acetyltransferase PCAF, indicating that Myoparr may regulate the expression of downstream genes, myogenin and myogenic microRNAs, by controlling the amount of the Ddx17-PCAF transcriptional activator complex at the target loci.

Besides myogenesis, the researchers investigated the role of Myoparr in neurogenic muscle atrophy using denervated mice. Sciatic nerve transection induced Myoparr as well as myogenin expression in mice tibialis anterior muscles. They showed that inhibition of Myoparr expression using Myoparr-specific shRNA sequences substantially repressed the myogenin expression induced by denervation and rescued muscle wasting in mice. “Induced myogenin expression has been reported in mouse models of neurogenic atrophy, such as spinal cord injury, amyotrophic lateral sclerosis (ALS), Huntington's disease, and spinal muscular atrophy (SMA). We also succeeded in identification of human Myoparr from human skeletal muscle cells. Although more research in humans is needed, we hope that Myoparr inhibition may be a useful therapeutic strategy for neurogenic atrophy in humans,” says Tsuchida.

Myogenin promoter-associated lncRNA Myoparr is essential for myogenic differentiation

Keisuke Hitachi, Masashi Nakatani, Akihiko Takasaki, Yuya Ouchi, Akiyoshi Uezumi, Hiroshi Ageta, Hidehito Inagaki, Hiroki Kurahashi, and Kunihiro Tsuchida

DOI: 10.15252/embr.201847468

Read the article:
http://embor.embopress.org/content/early/2019/01/03/embr.201847468