title: The Impact of Hyperthermia on Receptor-Mediated Interleukin-6 Regulation in Mouse Skeletal Muscle.
abstract: In inflammatory cells, hyperthermia inhibits lipopolysaccharide (LPS)-induced interleukin-6 (IL-6) gene expression and protein secretion. Since hyperthermia alone stimulates IL-6 in skeletal muscle, we hypothesized that it would amplify responses to other receptor-mediated stimuli. IL-6 regulation was tested in C2C12 myotubes and in soleus during treatment with epinephrine (EPI) or LPS. In EPI-treated myotubes (100 ng/ml), 1 h exposure at 40.5°C-42°C transiently increased IL-6 mRNA compared to EPI treatment alone at 37°C. In LPS-treated myotubes (1 μg/ml), exposure to 41°C-42°C also increased IL-6 mRNA. In isolated mouse soleus, similar amplifications of IL-6 gene expression were observed in 41°C, during both low (1 ng/ml) and high dose (100 ng/ml) EPI, but only in high dose LPS (1 μg/ml). In myotubes, heat increased IL-6 secretion during EPI exposure but had no effect or inhibited secretion with LPS. In soleus there were no effects of heat on IL-6 secretion during either EPI or LPS treatment. Mechanisms for the effects of heat on IL-6 mRNA were explored using a luciferase-reporter in C2C12 myotubes. Overexpression of heat shock factor-1 (HSF-1) had no impact on IL-6 promoter activity during EPI stimulation, but elevated IL-6 promoter activity during LPS stimulation. In contrast, when the activator protein-1 (AP-1) element was mutated, responses to both LPS and EPI were suppressed in heat. Using siRNA against activating transcription factor-3 (ATF-3), a heat-stress-induced inhibitor of IL-6, no ATF-3-dependent effects were observed. The results demonstrate that, unlike inflammatory cells, hyperthermia in muscle fibers amplifies IL-6 gene expression to EPI and LPS. The effect appears to reflect differential engagement of HSF-1 and AP-1 sensitive elements on the IL-6 gene, with no evidence for involvement of ATF-3. The functional significance of increased IL-6 mRNA expression during heat may serve to overcome the well-known suppression of protein synthetic pathways occurring during heat shock.
authors.affiliation: University of Florida, Department of Applied Physiology & Kinesiology, College of Health and Human Performance, Gainesville, FL, United States of America.
authors.forename: Steven S
authors.initials: SS
authors.lastname: Welc
authors.affiliation: University of Florida, Department of Applied Physiology & Kinesiology, College of Health and Human Performance, Gainesville, FL, United States of America.
authors.forename: Deborah A
authors.initials: DA
authors.lastname: Morse
authors.affiliation: University of Florida, Department of Applied Physiology & Kinesiology, College of Health and Human Performance, Gainesville, FL, United States of America.
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Mattingly
authors.affiliation: University of Florida, Department of Applied Physiology & Kinesiology, College of Health and Human Performance, Gainesville, FL, United States of America.|Federal University of Vale do São Francisco, Physical Education School, Petrolina, Brazil.
authors.forename: Orlando
authors.initials: O
authors.lastname: Laitano
authors.affiliation: University of Florida, Department of Applied Physiology & Kinesiology, College of Health and Human Performance, Gainesville, FL, United States of America.
authors.forename: Michelle A
authors.initials: MA
authors.lastname: King
authors.affiliation: University of Florida, Department of Applied Physiology & Kinesiology, College of Health and Human Performance, Gainesville, FL, United States of America.
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Clanton
mesh_terms: D000818:Animals; D002460:Cell Line; D004837:Epinephrine / Q000378:metabolism*; D005334:Fever / Q000235:genetics* / Q000378:metabolism; D015850:Interleukin-6 / Q000235:genetics* / Q000378:metabolism; D008070:Lipopolysaccharides / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018482:Muscle, Skeletal / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D018808:Transcription Factor AP-1 / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D015850:Interleukin-6; D008070:Lipopolysaccharides; D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D004837:Epinephrine