title: Role of the mTORC1 complex in satellite cell activation by RNA-induced mitochondrial restoration: dual control of cyclin D1 through microRNAs.
abstract: During myogenesis, satellite stem cells (SCs) are induced to proliferate and differentiate to myogenic precursors. The role of energy sensors such as the AMP-activated protein kinase (AMPK) and the mammalian Target of Rapamycin (mTOR) in SC activation is unclear. We previously observed that upregulation of ATP through RNA-mediated mitochondrial restoration (MR) accelerates SC activation following skeletal muscle injury. We show here that during regeneration, the AMPK-CRTC2-CREB and Raptor-mTORC-4EBP1 pathways were rapidly activated. The phosho-CRTC2-CREB complex was essential for myogenesis and activated transcription of the critical cell cycle regulator cyclin D1 (Ccnd1). Knockdown (KD) of either mTORC or its subunit Raptor delayed SC activation without influencing the differentiation program. KD of 4EBP1 had no effect on SC activation but enhanced myofiber size. mTORC1 positively regulated Ccnd1 translation but destabilized Ccnd1 mRNA. These antithetical effects of mTORC1 were mediated by two microRNAs (miRs) targeted to the 3' untranslated region (UTR) of Ccnd1 mRNA: miR-1 was downregulated in mTORC-KD muscle, and depletion of miR-1 resulted in increased levels of mRNA without any effect on Ccnd1 protein. In contrast, miR-26a was upregulated upon mTORC depletion, while anti-miR-26a oligonucleotide specifically stimulated Ccnd1 protein expression. Thus, mTORC may act as a timer of satellite cell proliferation during myogenesis.
authors.affiliation: Genetic Engineering Laboratory, CSIR-Indian Institute of Chemical Biology, Calcutta, India.
authors.forename: Sukanta
authors.initials: S
authors.lastname: Jash
authors.affiliation: Genetic Engineering Laboratory, CSIR-Indian Institute of Chemical Biology, Calcutta, India.
authors.forename: Gunjan
authors.initials: G
authors.lastname: Dhar
authors.affiliation: Genetic Engineering Laboratory, CSIR-Indian Institute of Chemical Biology, Calcutta, India.
authors.forename: Utpalendu
authors.initials: U
authors.lastname: Ghosh
authors.affiliation: Genetic Engineering Laboratory, CSIR-Indian Institute of Chemical Biology, Calcutta, India nilugrandson@gmail.com.
authors.forename: Samit
authors.initials: S
authors.lastname: Adhya
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000378:metabolism; D000818:Animals; D049109:Cell Proliferation; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D019938:Cyclin D1 / Q000235:genetics* / Q000378:metabolism*; D005786:Gene Expression Regulation; D055785:Gene Knockdown Techniques; D006801:Humans; D008297:Male; D035683:MicroRNAs / Q000235:genetics*; D024510:Muscle Development; D018482:Muscle, Skeletal / Q000293:injuries*; D012313:RNA / Q000378:metabolism; D020871:RNA Stability; D000077278:RNA, Mitochondrial; D051381:Rats; D017207:Rats, Sprague-Dawley; D032496:Satellite Cells, Skeletal Muscle / Q000502:physiology*; D013234:Stem Cells / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D015534:Trans-Activators / Q000378:metabolism
chemical_list: C545700:CRTC2 protein, rat; D017362:Cyclic AMP Response Element-Binding Protein; C542191:MIRN1 microRNA, rat; C556274:MIRN26 microRNA, rat; D035683:MicroRNAs; D000077278:RNA, Mitochondrial; D015534:Trans-Activators; D019938:Cyclin D1; D012313:RNA; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases