Dendritic cells (DCs) serve as a bridge between innate and adaptive immunity and help to maintain intestinal homeostasis. Inflammatory bowel disease (IBD) is associated with dysregulation of the mucosal immune response. The concomitant hypoxic inflammation in IBD will activate the transcription factor hypoxia-inducible factor-1 (HIF-1) to also drive gene expression in DCs. Recent studies have described a protective role for epithelial HIF-1 in mouse models of IBD. We investigated the role of HIF-1 in DC function in a dextran sodium sulfate (DSS)-induced model of murine colitis. Wild-type and dendritic cell-specific HIF-1α knockout mice were treated with 3% DSS for 7 days. Knockout of HIF-1α in DCs led to a significantly larger loss of body weight in mice with DSS-induced colitis than in control mice. Knockout mice exhibited more severe intestinal inflammation with increased levels of proinflammatory cytokines and enhanced production of mucin. Induction of regulatory T cells (Tregs) was impaired, and the number of forkhead box P3 (Foxp3) Tregs was diminished by dendritic HIF-1α knockout. Our findings demonstrate that in DCs HIF-1α is necessary for the induction of sufficient numbers of Tregs to control intestinal inflammation.

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Background: Because the nuclear factor-κB (NF-κB) coupled pathway is believed to amplify inflammation prevailing in sepsis, the authors tested the hypotheses that the insertiondeletion polymorphism (−94ins/delATTG) (1) alters nuclear translocation of nuclear factor-κB and activator protein-1 (NF-κB1) in monocytes after lipopolysaccharide stimulation; (2) affects lipopolysaccharide-induced NF-κB1 messenger RNA expression, tumor necrosis factor α concentrations, and tissue factor activity; and (3) may be associated with increased 30-day mortality in patients with sepsis. Methods: Nuclear translocation of NF-κB1 in monocytes after lipopolysaccharide stimulation from healthy blood donors was performed with immunofluorescence staining (n = 5 each). Lipopolysaccharide-induced NF-κB1 messenger RNA expression was measured with real-time polymerase chain reaction (PCR; n = 60), tumor necrosis factor α concentrations with a multiplexing system kit (n = 60), and tissue factor activity with thromboelastometry (n = 105). In a prospective study, multivariate proportional hazard analysis tested 30-day mortality in patients with sepsis (n = 143). Methods and Results:The homozygous deletion genotype compared with the homozygous insertion genotype was associated with a nearly twofold increase in nuclear translocation of NF-κB1 (P = 0.001), a threefold difference in NF-κB1 What We Already Know about This Topic• The nuclear factor-κB and activator protein-1-coupled signaling pathway of the innate immune system is known to amplify and perpetuate inflammatory and coagulatory mechanisms in sepsis• Genetic variations that alter nuclear factor-κB gene expression could affect pathophysiologic mechanisms and thereby influence mortality in severe sepsis What This Article Tells Us That Is New• A functional insertion-deletion polymorphism in the promoter of nuclear factor-κB and activator protein-1 affected expression and regulation of mediators of inflammation and coagulation in vitro • Expression of the same polymorphism was associated with increased 30-day mortality in patients with severe sepsis Downloaded from anesthesiology.pubs.asahq.org by guest on 06/07/2019

Background: Hypoxia-inducible factor-1 (HIF-1) is a molecular key player in response to hypoxemic/inflammatory conditions prevailing in sepsis. In a prospective observational study, we tested the hypotheses that sepsis affects HIF-1α messenger ribonucleic acid (mRNA) expression (primary hypothesis) and also (secondary hypotheses) the expression of the HIF-1α target genes adrenomedullin and β 2 -integrins. Furthermore, we tested that lipopolysaccharide administration increases HIF-1α mRNA and protein in naive and endotoxin-tolerant monocytes. Methods: In 99 patients with sepsis and 48 healthy volunteers, leukocyte HIF-1α mRNA expression (real-time polymerase chain reaction), cytokine concentrations (enzymelinked immunosorbent assay), and intracellular distribution of HIF-1α protein (immunofluorescence staining) were assessed. In vitro, HIF-1α mRNA expression and protein were measured in naive or endotoxin-tolerant (48 h; 0.05 ng/ml lipopolysaccharide) monocytes, with/without additional lipopolysaccharide (6 h; 1 μg/ml). Results: In comparison to healthy volunteers, HIF-1α mRNA expression (−67%; P = 0.0001) and HIF-1α protein positive cells (−66.7%; P = 0.01) were decreased in sepsis. mRNA expression of adrenomedullin (−75%), CD11a (−85%), and CD11b (−86%; all P = 0.0001) was also decreased. In contrast, interleukin 6 (P = 0.0001), interleukin 10 (P = 0.0001), and tumor necrosis factor-α (P = 0.0002) concentrations were increased. Of note, HIF-1α mRNA expression was inversely associated with illness severity (Simplified Acute Physiology Score II; r = −0.29; P = 0.0001). In vitro, acute lipopolysaccharide administration of naive monocytic cells increased HIF-1α mRNA expression, whereas HIF-1α mRNA and protein (−60%; P = 0.001) were decreased in endotoxin-tolerant cells, which still up regulated cytokines. Conclusions: In sepsis, HIF-1α mRNA expression was suppressed and inversely associated with illness severity. Hypoxia-inducible Factor and Target Gene Expression What We Already Know about This Topic• Sepsis is a leading cause of perioperative morbidity and mortality • Hypoxia-inducible factor-1α is a marker of cellular hypoxia What This Article Tells Us That Is New• In monocytes of patients with sepsis, hypoxia-inducible factor-1α was decreased compared to monocytes of healthy control patients, and the decrease in expression was inversely related to the severity of sepsis • Disease severity may be linked to an impaired response to hypoxia ◇

Dendritic cells (DCs) are an important link between innate and adaptive immunity. DCs get activated in inflamed tissues where oxygen tension is usually low, which requires the transcription factor hypoxia inducible factor (HIF)-1 for cellular adaptation. To investigate whether the HIF-1 transcriptional complex plays a pivotal role in the function of DCs, we compared the effects of exogenous inflammatory stimuli and hypoxia on HIF-1α in bone marrow-derived DCs from wild type and myeloid-specific HIF-1α knock-out mice. We showed that the Toll-like receptor ligands lipopolysaccharides and cytosine-phosphatidyl-guanines significantly induce HIF-1α mRNA and protein, leading to elevated HIF-1 target gene expression of vascular endothelial growth factor. In contrast, polyinosinic:polycytidylic acid did not show comparable effects. Furthermore the potential to up-regulate inflammatory cytokines critically influences DC function. Our data demonstrate that HIF-1α protein is needed for adequate production of interferon-α and -β. In co-cultures of DCs and cytotoxic T cells, we observed that DCs lacking active HIF-1α protein induce significantly less CD278 and granzyme B mRNA in T cells. We conclude that HIF-1α plays a crucial role in DC interferon production and T cell activation, linking the innate and adaptive immune system.

Material Supplementary 4.DC1http://www.jimmunol.org/content/suppl/2010/06/23/jimmunol.090324

Inflammation and hypoxia are hallmarks of inflammatory bowel disease. Low oxygen levels activate hypoxia-inducible factors as central transcriptional regulators of cellular responses to hypoxia, particularly in myeloid cells where hypoxia-inducible factors control immune cell function and survival. Still, the role of myeloid hypoxia-inducible factor-1 during inflammatory bowel disease remains poorly defined. We therefore investigated the role of hypoxia-inducible factor-1 for myeloid cell function and immune response during colitis. Experimental colitis was induced by administration of 2.5% dextran sulfate sodium to mice with a conditional knockout of hypoxia-inducible factor-1α in myeloid cells and their wild type siblings. Murine colon tissue was examined by histologic analysis, immunohistochemistry, and quantitative polymerase chain reaction. Induction of experimental colitis increased levels of hypoxia and accumulation of hypoxia-inducible factor-1α positive cells in colon tissue of both treated groups. Myeloid hypoxia-inducible factor-1α knockout reduced weight loss and disease activity index when compared to wild type mice. Knockout mice displayed less infiltration of macrophages into intestinal mucosa and reduced mRNA expression of markers for dendritic cells and interleukin-17 secreting T helper cells. Expression of inflammatory and anti-inflammatory cytokines also showed a reduced and delayed induction in myeloid hypoxia-inducible factor-1α knockout mice. Our results show a disease promoting role of myeloid hypoxia-inducible factor-1 during intestinal inflammation. This might result from a hypoxia-inducible factor-1 dependent increase in pro-inflammatory interleukin-17 secreting T helper cells in the absence of obvious changes in regulatory T cells. In contrast, knockout mice appear to shift the balance to anti-inflammatory signals and cells resulting in milder intestinal inflammation.

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-1α accumulation and expression of HIF target genes in human monocytic cells and primary mouse peritoneal macrophages. Tolerant cells had reduced levels of HIF-1α under hypoxia, which was due to lowered levels of HIF-1α mRNA. HIF-1α expression is under control of NF-κB and increased DNA binding of the p52 subunit of NF-κB was found in tolerant cells. Knock down of p52 abolished the effects of endotoxin tolerance on HIF-1α expression, which suggest a negative regulatory role of p52 on HIF-1α 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-1α protein accumulation and subsequent HIF target gene expression. We conclude that endotoxin tolerance impairs HIF-1α induction which reduces the ability of monocytic cells to survive and function under hypoxic conditions.