title: Endogenous HMGB1 contributes to ischemia-reperfusion-induced myocardial apoptosis by potentiating the effect of TNF-&alpha;/JNK.
abstract: High-mobility group box 1 (HMGB1) is a nuclear protein that has been implicated in the myocardial inflammation and injury induced by ischemia-reperfusion (I/R). The purpose of the present study was to assess the role of HMGB1 in myocardial apoptosis induced by I/R. In vivo, myocardial I/R induced an increase in myocardial HMGB1 expression and apoptosis. Inhibition of HMGB1 (A-box) ameliorated the I/R-induced myocardial apoptosis. In vitro, isolated cardiac myocytes were challenged with anoxia-reoxygenation (A/R; in vitro correlate to I/R). A/R-challenged myocytes also generated HMGB1 and underwent apoptosis. Inhibition of HMGB1 attenuated the A/R-induced myocyte apoptosis. Exogenous HMGB1 had no effect on myocyte apoptosis. However, inhibition of HMGB1 attenuated myocyte TNF-α production after the A/R was challenged; surprisingly, HMGB1 itself did not induce myocyte TNF-α production. Exogenous TNF-α induced a moderate proapoptotic effect on the myocytes, an effect substantially potentiated by coadministration of HMGB1. It is generally accepted that apoptosis induced by TNF-α is regulated by the balance of activation of c-Jun NH(2)-terminal kinase (JNK) and NF-κB. Indeed, in the present study, TNF-α increased the phosphorylation status of JNK and p65, a subunit of NF-κB; HMGB1 greatly potentiated TNF-α-induced JNK phosphorylation. Furthermore, inhibition of JNK (SP-600125) prevented the myocyte apoptosis induced by a TNF-α/HMGB1 cocktail. Finally, A/R increased HMGB1 production in both wild-type and toll-like receptor 4-deficient myocytes; however, deficiency in toll-like receptor 4 diminished A/R-induced myocyte apoptosis, TNF-α, and JNK activation. Our results indicate that myocyte-derived HMGB1 and TNF-α work in concert to promote I/R-induced myocardial apoptosis through JNK activation.
authors.affiliation: Critical Illness Research, Lawson Health Research Institute, 800 Commissioners Road E, VRL Rm A6-138, London, Ontario, Canada.
authors.forename: Hu
authors.initials: H
authors.lastname: Xu
authors.forename: Yongwei
authors.initials: Y
authors.lastname: Yao
authors.forename: Zhaoliang
authors.initials: Z
authors.lastname: Su
authors.forename: Yunbo
authors.initials: Y
authors.lastname: Yang
authors.forename: Raymond
authors.initials: R
authors.lastname: Kao
authors.forename: Claudio M
authors.initials: CM
authors.lastname: Martin
authors.forename: Tao
authors.initials: T
authors.lastname: Rui
mesh_terms: D000818:Animals; D017209:Apoptosis; D024243:HMGB1 Protein / Q000378:metabolism*; D006335:Heart Injuries / Q000378:metabolism* / Q000473:pathology; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009203:Myocardial Infarction / Q000378:metabolism* / Q000473:pathology; D015428:Myocardial Reperfusion Injury / Q000378:metabolism* / Q000473:pathology; D032383:Myocytes, Cardiac / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation; D051197:Toll-Like Receptor 4 / Q000172:deficiency / Q000235:genetics; D051996:Transcription Factor RelA / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
chemical_list: D024243:HMGB1 Protein; C498144:Rela protein, mouse; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha; D048031:JNK Mitogen-Activated Protein Kinases