Hypoxia-inducible factor (HIF) 1alpha accumulation and HIF target gene expression are impaired after induction of endotoxin tolerance.
The oxygen-sensitive transcription factor hypoxia-inducible factor 1 (HIF-1) is known as the key regulator of hypoxia-induced gene expression. In addition to hypoxia, endotoxins such as bacterial LPS as well as proinflammatory cytokines have been shown to induce HIF-1, suggesting an integrative role for HIF-1 in conditions of hypoxia and inflammation. Cells can become tolerant to endotoxins by repetitive exposure to LPS. Herein, we studied the effect of endotoxin tolerance on HIF-1alpha accumulation and expression of HIF target genes in human monocytic cells and primary mouse peritoneal macrophages. Tolerant cells had reduced levels of HIF-1alpha under hypoxia, which was due to lowered levels of HIF-1alpha mRNA. HIF-1alpha expression is under control of NF-kappaB and increased DNA binding of the p52 subunit of NF-kappaB was found in tolerant cells. Knock down of p52 abolished the effects of endotoxin tolerance on HIF-1alpha expression, which suggest a negative regulatory role of p52 on HIF-1alpha transcription during endotoxin tolerance. Endotoxin tolerant cells showed diminished expression of the HIF target genes phosphoglycerate kinase 1 and adrenomedullin and reduced viability under hypoxic conditions, as well as a significantly reduced invasion. Peritoneal macrophages from endotoxin-tolerant mice made showed significantly reduced HIF-1alpha protein accumulation and subsequent HIF target gene expression. We conclude that endotoxin tolerance impairs HIF-1alpha induction which reduces the ability of monocytic cells to survive and function under hypoxic conditions.
Frede
Stilla
S
Institut für Physiologie, Universität Duisburg-Essen, Essen, Germany.
Stockmann
Christian
C
Winning
Sandra
S
Freitag
Patricia
P
Fandrey
Joachim
J
D000818:Animals; D015153:Blotting, Western; D015687:Cell Hypoxia / Q000276:immunology*; D002460:Cell Line; D002470:Cell Survival; D004731:Endotoxins / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay; D015870:Gene Expression / Q000276:immunology*; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000276:immunology* / Q000378:metabolism; D007108:Immune Tolerance / Q000276:immunology*; D017737:Macrophages, Peritoneal / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D009000:Monocytes / Q000276:immunology* / Q000378:metabolism; D052003:NF-kappa B p52 Subunit / Q000276:immunology / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction
D004731:Endotoxins; C497442:HIF1A protein, human; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D052003:NF-kappa B p52 Subunit