title: Celastrol overcomes HSP72 gene silencing-mediated muscle atrophy and induces myofiber preservation.
abstract: To elucidate a potential anabolic role of heat shock proteins (HSPs) in myofiber preservation, we assessed the effect of HSP70 gene silencing versus its overexpression on skeletal muscle atrophy or rescue. HSP72 gene expression was silenced by pre-treatment with HSP72 siRNA in cultured rat L6 myotubes, and the pro-anabolic effect of HSPs was examined in the absence or presence of the HSP inducer celastrol (CEL). Compared to the negative control (NC), both nuclear accumulation and phosphorylation of heat shock transcription factor 1 remained high under the 6-h treatment of CEL. The HSP72 siRNA treatment significantly decreased HSP72 mRNA and protein expression and myotube diameter. CEL treatment, however, markedly increased the HSP72 expression and rendered the myotube size recovered to the NC level even in the siRNA-treated cells. Moreover, the HSP72 siRNA upregulated forkhead box O3 (FoxO3) expression in the nucleus while CEL increased p-FoxO3 exclusively in the cytoplasm, thus leaving the p-FoxO3/FoxO3 balanced to the NC level by siRNA + CEL treatment. The atrophic effect of HSP72 siRNA was consistent with the upregulation of atrogin-1 and proteasome activity but CEL treatment abrogated such effect by activation of Akt1, ribosomal S6 kinase (S6K) and extracellular signal-regulated kinase 1/2 (ERK1/2), irrespective of HSP72 silencing. These results suggest that CEL-mediated overexpression of HSP72 overcomes the atrophic effect of HSP72 gene silencing via both enhancement of FoxO3 phosphorylation and activation of Akt1-ERK1/2 signaling pathway.
authors.affiliation: Division of Biological Science and Technology, College of Science and Technology, Yonsei University, Wonju, Gangwon-Do, Republic of Korea. ichoi@yonsei.ac.kr.
authors.forename: T
authors.initials: T
authors.lastname: Gwag
authors.forename: K
authors.initials: K
authors.lastname: Park
authors.forename: J
authors.initials: J
authors.lastname: Park
authors.forename: J-H
authors.initials: JH
authors.lastname: Lee
authors.forename: T
authors.initials: T
authors.lastname: Nikawa
authors.forename: I
authors.initials: I
authors.lastname: Choi
mesh_terms: D000818:Animals; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000235:genetics; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors / Q000235:genetics; D020868:Gene Silencing / Q000187:drug effects*; D050884:HSP72 Heat-Shock Proteins / Q000235:genetics*; D000076249:Heat Shock Transcription Factors; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000235:genetics; D018485:Muscle Fibers, Skeletal / Q000187:drug effects*; D009124:Muscle Proteins / Q000235:genetics; D018482:Muscle, Skeletal / Q000187:drug effects; D009133:Muscular Atrophy / Q000188:drug therapy* / Q000235:genetics; D053978:Pentacyclic Triterpenes; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000235:genetics; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D044843:SKP Cullin F-Box Protein Ligases / Q000235:genetics; D014157:Transcription Factors / Q000235:genetics; D014315:Triterpenes / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; C499515:FOXO3 protein, rat; D000071316:Forkhead Box Protein O3; D051858:Forkhead Transcription Factors; D050884:HSP72 Heat-Shock Proteins; D000076249:Heat Shock Transcription Factors; C000619709:Hsf1 protein, rat; D009124:Muscle Proteins; D053978:Pentacyclic Triterpenes; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D014157:Transcription Factors; D014315:Triterpenes; C486692:Fbxo32 protein, rat; D044843:SKP Cullin F-Box Protein Ligases; D051057:Proto-Oncogene Proteins c-akt; D046988:Proteasome Endopeptidase Complex; C050414:celastrol