title: Hypoxia inducible factor-1 modulates hemin-induced IL-8 secretion in microvascular endothelium.
abstract: Ischemia/Reperfusion injury and hemolysis are characterized by erythrocyte lysis and release of free heme into the microcirculation. Following substantial erythrocyte lysis, heme overwhelms circulatory heme-binding protein networks rapidly forming hemin, the oxidized form of iron protoporphyrin IX. Hemin's role in modulating inflammatory responses in microvascular endothelium (MVEC) remains ill-defined. We studied the impact of hemin exposure on human MVEC interleukin-8 (IL-8) expression. Hemin significantly up-regulated MVEC IL-8 secretion and was associated with cellular iron loading. Hemin-induced IL-8 up-regulation was significantly attenuated by increasing environmental serum concentrations. As well, hemin-induced IL-8 secretion was significantly reduced in a concentration-dependent fashion following pyrrolidine dithiocarbamate exposure, suggesting that induction occurred via an oxidant-sensitive mechanism. Interestingly, transfection studies revealed that oxidant-driven transcription factors NF-kappaB and AP-1 played no role in hemin-induced IL-8 transcription. In studies employing actinomycin D, hemin was found to dramatically lengthen IL-8 mRNA half-life. Of major importance in the current report was the finding that hypoxia inducible factor-1 (HIF-1), a powerful transcription factor mediating tissue responses to hypoxia, potently regulated hemin-induced IL-8 secretion in human MVEC. Activation of HIF-1 via the prolyl hydroxylase inhibitor dimethyloxalylglycine attenuated hemin-induced IL-8 secretion. These studies were confirmed via DNA-directed siRNA silencing of HIF-1alpha. In conclusion, hemin induces a serum protein-sensitive pro-inflammatory phenotype in MVEC via an oxidant-sensitive mechanism that is powerfully regulated by HIF-1.
authors.affiliation: Division of Pulmonary Disease and Critical Care Medicine, Department of Internal Medicine, Virginia Commonwealth University Medical Center, Box 980050, Richmond, VA 23298, USA.
authors.forename: Ramesh
authors.initials: R
authors.lastname: Natarajan
authors.forename: Bernard J
authors.initials: BJ
authors.lastname: Fisher
authors.forename: Alpha A
authors.initials: AA
authors.lastname: Fowler
mesh_terms: D000600:Amino Acids, Dicarboxylic / Q000494:pharmacology; D000975:Antioxidants / Q000494:pharmacology; D002470:Cell Survival; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D042783:Endothelial Cells / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006427:Hemin / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D007249:Inflammation / Q000235:genetics / Q000378:metabolism*; D016209:Interleukin-8 / Q000235:genetics / Q000378:metabolism*; D007501:Iron / Q000378:metabolism; D008833:Microcirculation / Q000378:metabolism; D011393:Procollagen-Proline Dioxygenase / Q000037:antagonists & inhibitors / Q000378:metabolism; D011759:Pyrrolidines / Q000494:pharmacology; D020871:RNA Stability; D012333:RNA, Messenger / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D044967:Serum / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013859:Thiocarbamates / Q000494:pharmacology; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D000600:Amino Acids, Dicarboxylic; D000975:Antioxidants; D004791:Enzyme Inhibitors; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D016209:Interleukin-8; D011759:Pyrrolidines; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D013859:Thiocarbamates; C020972:pyrrolidine dithiocarbamic acid; D006427:Hemin; D007501:Iron; D011393:Procollagen-Proline Dioxygenase; C040947:oxalylglycine