Hypoxia-inducible factors 1 and 2 are important transcriptional effectors in primary macrophages experiencing hypoxia (original) (raw)
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Hypoxia Regulates Macrophage Functions in Inflammation
The Journal of Immunology, 2005
The presence of areas of hypoxia is a prominent feature of various inflamed, diseased tissues, including malignant tumors, atherosclerotic plaques, myocardial infarcts, the synovia of joints with rheumatoid arthritis, healing wounds, and sites of bacterial infection. These areas form when the blood supply is occluded and/or unable to keep pace with the growth and/or infiltration of inflammatory cells in a given area. Macrophages are present in all tissues of the body where they normally assist in guarding against invading pathogens and regulate normal cell turnover and tissue remodeling. However, they are also known to accumulate in large numbers in such ischemic/hypoxic sites. Recent studies show that macrophages then respond rapidly to the hypoxia present by altering their expression of a wide array of genes. In the present study, we outline and compare the phenotypic responses of macrophages to hypoxia in different diseased states and the implications of these for their progression and treatment.
Inflammatory mediators are perpetuated in macrophages resistant to apoptosis induced by hypoxia
Proceedings of the National Academy of Sciences, 1997
A hypoxic͞anoxic microenvironment has been proposed to exist within a vascular lesion due to intimal or medial cell proliferation in vascular diseases. Here, we examined whether hypoxia alters macrophage function by exposing murine macrophage-like RAW 264.7 (RAW) cells to hypoxia (2% O 2 ). When cells were exposed to hypoxia, a significant number of RAW cells underwent apoptosis. Additionally, small subpopulations of RAW cells were resistant to hypoxia-induced apoptosis. Through repeated cycles of hypoxia exposure, hypoxia-induced apoptosis-resistant macrophages (HARMs) were selected; HARM cells demonstrate >70% resistance to hypoxia-induced apoptosis, as compared with the parental RAW cells. When heat shock protein (HSP) expression was examined after hypoxia, we observed a significant decrease in constitutive heat shock protein 70 (HSC 70) in RAW cells, but not in HARMs, as compared with the control normoxic condition (21% O 2 ). In contrast, the expression level of glucose-regulated protein 78 (GRP 78) in RAW and HARM cells after hypoxia treatment was not altered, suggesting that HSC 70 and not GRP 78 may play a role in protection against hypoxia-induced apoptosis. When tumor necrosis factor ␣ (TNF-␣) production was examined after hypoxic treatment, a significant increase in TNF-␣ production in HARM but decrease in RAW was observed, as compared with cells cultured in normoxic conditions. HARM cells also exhibit a much lower level of modified-LDL uptake than do RAW cells, suggesting that HARMs may not transform into foam cells. These results suggest that a selective population of macrophages may adapt to potentially pathological hypoxic conditions by overcoming the apoptotic signal.
PLoS ONE, 2012
In chronic inflammatory lesions there are increased numbers of macrophages with a possible contribution of enhanced survival/proliferation due, for example, to cytokine action; such lesions are often hypoxic. Prior studies have found that culture in low oxygen can promote monocyte/macrophage survival. We show here, using pharmacologic inhibitors, that the hypoxia-induced pro-survival response of macrophages exhibits a dependence on PI3-kinase and mTOR activities but surprisingly is suppressed by Akt and p38 MAPK activities. It was also found that in hypoxia at CSF-1 concentrations, which under normoxic conditions are suboptimal for macrophage proliferation, macrophages can proliferate more strongly with no evidence for alteration in CSF-1 receptor degradation kinetics. TNF promoted macrophage survival in normoxic conditions with an additive effect in hypoxia. The enhanced hypoxia-dependent survival and/or proliferation of macrophages in the presence of CSF-1 or TNF may contribute to their elevated numbers at a site of chronic inflammation. Citation: Hamilton JA, Lacey DC, Turner A, de Kok B, Huynh J, et al. (2012) Hypoxia Enhances the Proliferative Response of Macrophages to CSF-1 and Their Pro-Survival Response to TNF. PLoS ONE 7(9): e45853.
Macrophages (MΦ) often accumulate in hypoxic areas, where they significantly influence disease progression. Anti-inflammatory cytokines, such as IL-10, generate alternatively activated macrophages that support tumor growth. To understand how alternative activation affects the transcriptional profile of hypoxic macrophages, we globally mapped binding sites of hypoxia-inducible factor (HIF)-1α and HIF-2α in primary human monocyte-derived macrophages prestimulated with IL-10. 713 HIF-1 and 795 HIF-2 binding sites were identified under hypoxia. Pretreatment with IL-10 altered the binding pattern, with 120 new HIF-1 and 188 new HIF-2 binding sites emerging. HIF-1 binding was most prominent in promoters, while HIF-2 binding was more abundant in enhancer regions. Comparison of ChIP-seq data obtained in other cells revealed a highly cell type specific binding of HIF. In MΦ HIF binding occurred preferentially in already active enhancers or promoters. To assess the roles of HIF on gene expression, primary human macrophages were treated with siRNA against HIF-1α or HIF-2α, followed by genome-wide gene expression analysis. Comparing mRNA expression to the HIF binding profile revealed a significant enrichment of hypoxia-inducible genes previously identified by ChIP-seq. Analysis of gene expression under hypoxia alone and hypoxia/IL-10 showed the enhanced induction of a set of genes including PLOD2 and SLC2A3, while another group including KDM3A and ADM remained unaffected or was reduced by IL-10. Taken together IL-10 influences the DNA binding pattern of HIF and the level of gene induction
Hypoxia selectively inhibits monocyte chemoattractant protein-1 production by macrophages
The Journal of …, 2004
Hypoxia, a local decrease in oxygen tension occurring in inflammatory and tumor lesions, modulates gene expression in macrophages. Because macrophages are important chemokine producers, we investigated the regulatory effects of hypoxia on macrophage-derived chemokines. We demonstrated that hypoxia inhibits the production of the macrophage and T lymphocyte chemotactic and activating factor, monocyte chemoattractant protein-1 (MCP-1). Exposure of mouse macrophages to low oxygen tension resulted in the down-regulation of constitutive MCP-1 mRNA expression and protein secretion. Hypoxia inhibitory effects were selective for MCP-1 because the chemokines macrophage inflammatory protein-1 (MIP-1), RANTES, IFN-␥-inducible protein-10, and MIP-2 were not affected, and MIP-1␣ was induced. Hypoxia also inhibited, in a time-dependent fashion, MCP-1 upregulation by IFN-␥ and LPS. Moreover, the inhibitory action of hypoxia was exerted on human monocytic cells. MCP-1 downregulation was associated with inhibition of gene transcription and mRNA destabilization, suggesting a dual molecular mechanism of control. Finally, we found that the triptophan catabolite picolinic acid and the iron chelator desferrioxamine, which mimic hypoxia in the induction of gene expression, differentially regulated the expression of MCP-1. This study characterizes a novel property of hypoxia as a selective inhibitor of MCP-1 production induced by different stimuli in macrophages and demonstrates that down-regulation of gene expression by hypoxia can be controlled at both transcriptional and posttranscriptional levels. Inhibition of MCP-1 may represent a negative regulatory mechanism to control macrophage-mediated leukocyte recruitment in pathological tissues.
Journal of Leukocyte Biology, 2007
Hypoxia, a condition of low oxygen tension, occurring in many pathological processes, modifies the mononuclear phagocyte transcriptional profile. Here, we demonstrate hypoxic up-regulation of the CCL20 chemokine in primary human monocytes (Mn) and macrophages. mRNA induction was paralleled by protein secretion and dependent on gene transcription activation. Functional studies of the CCL20 promoter using a series of 5-deleted and mutated reporter constructs demonstrated the requirement for the NF-B-binding site located at position -92/-82 for gene transactivation by hypoxia, as transcription was abrogated by a 3-bp mutation of the NF-B motif; three copies of the wild-type NF-B-binding site conferred hypoxia responsiveness to a minimal heterologous promoter; and hypoxia increased specific NF-B binding to this sequence. Furthermore, we provide evidence of the specific role of a single NF-B family member, p50, in mediating CCL20 gene transcription in hypoxic Mn. p50 homodimers were the only detectable NF-B complexes binding the cognate B site on the CCL20 promoter upon hypoxia exposure, and NF-Bp50 knockdown by lentiviral-mediated short hairpin RNA interference resulted in complete binding inhibition. NF-Bp50 overexpression in transient cotransfection studies promoted CCL20 gene transactivation, which was abrogated by mutation of the -92/-82 B site. Moreover, nuclear expression of the other NF-B family members was inhibited in hypoxic Mn. In conclusion, this study characterizes a previously unrecognized role for hypoxia as a transcriptional inducer of CCL20 in human mononuclear phagocytes and highlights the importance of the NF-B pathway in mediating this response, with potential implications for inflammatory disease and cancer pathogenesis. J. Leukoc. Biol. 83: 000 -000; 2008.
Journal of Leukocyte Biology, 2008
Hypoxia, a condition of low oxygen tension, occurring in many pathological processes, modifies the mononuclear phagocyte transcriptional profile. Here, we demonstrate hypoxic up-regulation of the CCL20 chemokine in primary human monocytes (Mn) and macrophages. mRNA induction was paralleled by protein secretion and dependent on gene transcription activation. Functional studies of the CCL20 promoter using a series of 5-deleted and mutated reporter constructs demonstrated the requirement for the NF-B-binding site located at position -92/-82 for gene transactivation by hypoxia, as transcription was abrogated by a 3-bp mutation of the NF-B motif; three copies of the wild-type NF-B-binding site conferred hypoxia responsiveness to a minimal heterologous promoter; and hypoxia increased specific NF-B binding to this sequence. Furthermore, we provide evidence of the specific role of a single NF-B family member, p50, in mediating CCL20 gene transcription in hypoxic Mn. p50 homodimers were the only detectable NF-B complexes binding the cognate B site on the CCL20 promoter upon hypoxia exposure, and NF-Bp50 knockdown by lentiviral-mediated short hairpin RNA interference resulted in complete binding inhibition. NF-Bp50 overexpression in transient cotransfection studies promoted CCL20 gene transactivation, which was abrogated by mutation of the -92/-82 B site. Moreover, nuclear expression of the other NF-B family members was inhibited in hypoxic Mn. In conclusion, this study characterizes a previously unrecognized role for hypoxia as a transcriptional inducer of CCL20 in human mononuclear phagocytes and highlights the importance of the NF-B pathway in mediating this response, with potential implications for inflammatory disease and cancer pathogenesis. J. Leukoc. Biol. 83: 000 -000; 2008.