title: Hypoxia affects dendritic cell survival: role of the hypoxia-inducible factor-1α and lipopolysaccharide.
abstract: Dendritic cells (DC) are the most potent antigen-presenting cells and during their life cycle they are exposed to different oxygen tensions. Similarly to inflamed and tumor tissues, lymphoid organs are characterized by a hypoxic microenvironment; thus, the modality by which hypoxia may affect DC is important for regulating both the quality and the intensity of the immune response. Here, we show that human monocyte-derived DC, exposed to hypoxia, expressed high levels of the hypoxia-inducible factor (HIF)-1α, associated with upregulation of BNIP3 and BAX expression. This was paralleled with downregulation of the anti-apoptotic molecule Bcl-2, enhanced caspase-3 activity and poly (ADP-ribose) polymerase cleavage, along with cell death. Transfection of HIF-1α siRNA protected DC from the effects of hypoxia. Of interest, when hypoxic DC were maturated with lipopolysaccharide (LPS), we did not observe an increased cell death, while HIF-1α accumulation and BNIP3 expression were still significantly upregulated. In contrast with immature DC, mature DC expressed higher levels of Bcl-2, and, more importantly, of phosphorylated Akt. Transfection of HIF-1α siRNA to mature DC resulted in a significant upregulation of Akt phosphorylation as well. Moreover, inhibition of PI3K/Akt pathway resulted in an increased cell death of hypoxic mature DC. We may conclude that a prolonged exposure to hypoxia induces a cell death program which could be prevented by HIF-1α inhibition and/or LPS maturation. Our results may contribute to further understand the physiology of DC and the molecular mechanisms involved in the survival of DC, with important implications in the regulation of the immune response.
authors: Unit of Neuroimmunophysiology, Department of Physiology, University of Siena, Siena, Italy. naldini@unisi.it
authors: Antonella
authors: A
authors: Naldini
authors: Emilia
authors: E
authors: Morena
authors: Annalisa
authors: A
authors: Pucci
authors: Diego
authors: D
authors: Miglietta
authors: Elena
authors: E
authors: Riboldi
authors: Silvano
authors: S
authors: Sozzani
authors: Fabio
authors: F
authors: Carraro
mesh_terms: D016923:Cell Death; D002470:Cell Survival; D003713:Dendritic Cells / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D006801:Humans; D000860:Hypoxia; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000633:toxicity*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D010100:Oxygen / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008070:Lipopolysaccharides; D008565:Membrane Proteins; D010100:Oxygen; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; C090121:BNIP3 protein, human; C497442:HIF1A protein, human