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Nogo maintains muscle integrity and regulates muscle regeneration via modulating Nogo-A expression

ABSTRACT: Nogo, also called RTN4, functions through three isoforms including Nogo-A, -B, and -C. Although Nogo-A is a well-known CNS inhibitor and the level of Nogo-A is increased in muscles of ALS patients, its role in the regulation of skeletal muscle homeostasis and regeneration is still vague. In this study, we analyzed various pathological muscle condition of human and mouse model, and discovered significant increase of Nogo-A and myogenic factors. To understand the role of Nogo in skeletal muscle, muscle transcripts from Nogo+/+ and Nogo-/- mouse were analyzed and observed intensified gene expression involved in adipocyte differentiation and lipid metabolism, and reduced gene expression related to muscle differentiation and structure organization suggesting muscle disorder from muscle replacement with fat deposition. Skeletal muscle structure from Nogo null mice displayed dystrophic phenotypes including impaired myofiber structure and immune cell infiltrations, and dysregulated homeostatic features such as higher level of MyoD, procaspase 3, CHOP, and AKT compared to wild-type muscle. Notexin-injured Nogo deficient muscle resulted higher level of immune cell infiltration but defective in IL-6 production, a well-known myokine from immune cells, and abnormally upregulated regenerative muscle fibers than normal muscle. Therefore we hypothesized that increased Nogo-A in pathological conditions may regulate muscle regeneration. Then differentiating C2C12 cells and induced myogenic stem cells(iMSC) showed upregulated Nogo-A and Myogenin, and Nogo-A silencing in C2C12 cells abrogated the capability to differentiate into myotubes. In conclusion, Nogo functions to maintain muscle homeostasis and integrity, and altered Nogo-A expression in pathological muscle condition mediates muscle regeneration. These understanding suggests Nogo-A as a novel differentiation target for the treatment of myopathies at clinical set.

ORGANISM(S): Mus musculus

PROVIDER: GSE131955 | GEO | 2019/05/31

REPOSITORIES: GEO

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Project description:Wnt/M-NM-2-catenin signaling is involved in various aspects of skeletal muscle development and regeneration. In addition, Wnt3a and M-NM-2-catenin are required for muscle-specific gene transcription in embryonic carcinoma cells and satellite-cell proliferation during adult skeletal muscle regeneration. Downstream targets of canonical Wnt signaling are cyclin D1 and c-myc. However, both target genes are suppressed during differentiation of mouse myoblast cells, C2C12. Underlying molecular mechanisms of M-NM-2-catenin signaling during myogenic differentiation remain unknown. Using C2C12 cells, we examined intracellular signaling and gene transcription during myoblast proliferation and differentiation. We confirmed that several Wnt signaling components, including Wnt9a, Sfrp2 and porcupine, were consistently upregulated in differentiating C2C12 cells. Troponin T-positive myotubes were decreased by Wnt3a overexpression, but not Wnt4. TOP/FOP reporter assays revealed that co-expression with Wnt4 reduced Wnt3a-induced luciferase activity, suggesting that Wnt4 signaling counteracted Wnt3a signaling in myoblasts. FH535, a small-molecule inhibitor of M-NM-2-catenin/Tcf complex formation, reduced basal M-NM-2-catenin in cytoplasm and decreased myoblast proliferation. K252a, a protein kinase inhibitor, increased membrane-bound M-NM-2-catenin and enhanced myoblast fusion. Treatments with K252a or Wnt4 resulted in increased cytoplasmic vesicles containing phosphorylated M-NM-2-catenin (Tyr654) during myogenic differentiation. These results suggest that various Wnt ligands control subcellular M-NM-2-catenin localization, which regulate myoblast proliferation and myotube formation. Wnt signaling via M-NM-2-catenin likely acts as a molecular switch that regulates the transition from cell proliferation to myogenic differentiation. Control cells (day 0) prior to differentiation induction with n=4; differentiated for two days with n=3; differentiated for four days with n=3.

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Nogo maintains muscle integrity and regulates muscle regeneration via modulating Nogo-A expression

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