title: Long-term HIF-1α transcriptional activation is essential for heat-acclimation-mediated cross tolerance: mitochondrial target genes.
abstract: An important adaptive feature of heat acclimation (HA) is the induction of cross tolerance against novel stressors (HACT) Reprogramming of gene expression leading to enhanced innate cytoprotective features by attenuating damage and/or enhancing the response of "help" signals plays a pivotal role. Hypoxia-inducible factor-1α (HIF-1α), constitutively upregulated by HA (1 mo, 34°C), is a crucial transcription factor in this program, although its specific role is as yet unknown. By using a rat HA model, we studied the impact of disrupting HIF-1α transcriptional activation [HIF-1α:HIF-1β dimerization blockade by intraperitoneal acriflavine (4 mg/kg)] on its mitochondrial gene targets [phosphoinositide-dependent kinase-1 (PDK1), LON, and cyclooxygenase 4 (COX4) isoforms] in the HA rat heart. Physiological measures of cardiac HACT were infarct size after ischemia-reperfusion and time to rigor contracture during hypoxia in cardiomyocytes. We show that HACT requires transcriptional activation of HIF-1α throughout the course of HA and that this activation is accompanied by two metabolic switches:1) profound upregulation of PDK1, which reduces pyruvate entry into the mitochondria, consequently increasing glycolytic lactate production;2) remodeling of the COX4 isoform ratio, inducing hypoxic-tolerant COX4.2 dominance, and optimizing electron transfer and possibly ATP production during the ischemic and hypoxic insults. LON and COX4.2 transcript upregulation accompanied this shift. Loss of HACT despite elevated expression of the cytoprotective protein heat shock protein-72 concomitantly with disrupted HIF-1α dimerization suggests that HIF-1α is essential for HACT. The role of a PDK1 metabolic switch is well known in hypoxia acclimation but not in the HA model and its ischemic setting. Remodeling of COX4 isoforms by environmental acclimation is a novel finding.
authors.affiliation: Laboratory of Environmental Physiology, Faculty of Dental Medicine, The Hebrew University, Jerusalem, Israel.
authors.forename: Rivka
authors.initials: R
authors.lastname: Alexander-Shani
authors.affiliation: Laboratory of Environmental Physiology, Faculty of Dental Medicine, The Hebrew University, Jerusalem, Israel.
authors.forename: Ahmad
authors.initials: A
authors.lastname: Mreisat
authors.affiliation: Laboratory of Environmental Physiology, Faculty of Dental Medicine, The Hebrew University, Jerusalem, Israel.
authors.forename: Elia
authors.initials: E
authors.lastname: Smeir
authors.affiliation: Cardiology, Johns Hopkins Hospital, Baltimore, Maryland; and.
authors.forename: Gary
authors.initials: G
authors.lastname: Gerstenblith
authors.affiliation: Gerontology Research Center, National Institute on Aging, Baltimore, Maryland.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Stern
authors.affiliation: Laboratory of Environmental Physiology, Faculty of Dental Medicine, The Hebrew University, Jerusalem, Israel; m.horowitz@mail.huji.ac.il.
authors.forename: Michal
authors.initials: M
authors.lastname: Horowitz
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D006360:Heat-Shock Proteins / Q000378:metabolism*; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000096:biosynthesis*; D008297:Male; D008929:Mitochondria, Heart / Q000502:physiology*; D024101:Mitochondrial Proteins / Q000378:metabolism; D032383:Myocytes, Cardiac / Q000502:physiology*; D051381:Rats; D000071436:Thermotolerance / Q000502:physiology*; D015533:Transcriptional Activation / Q000502:physiology*; D059467:Transcriptome
chemical_list: D006360:Heat-Shock Proteins; C497444:Hif1a protein, rat; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D024101:Mitochondrial Proteins
keywords: COX4 isoforms; HIF-1α; PDK1; acriflavine; heart; heat acclimation-mediated cross tolerance