Loss of the Oxygen Sensor PHD3 Enhances the Innate Immune Response to Abdominal Sepsis

Abstract

Hypoxia and HIFs (HIF-1α and HIF-2α) modulate innate immune responses in the setting of systemic inflammatory responses and sepsis. The HIF prolyl hydroxylase enzymes PHD1, PHD2 and PHD3 regulate the mammalian adaptive response to hypoxia; however, their significance in the innate immune response has not been elucidated. We demonstrate in this study that deficiency of PHD3 (PHD3−/−) specifically shortens the survival of mice subjected to various models of abdominal sepsis because of an overwhelming innate immune response, leading to premature organ dysfunction. By contrast, this phenotype was absent in mice deficient for PHD1 (PHD1−/−) or PHD2 (PHD2+/−). In vivo, plasma levels of proinflammatory cytokines were enhanced, and recruitment of macrophages to internal organs was increased in septic PHD3-deficient mice. Reciprocal bone marrow transplantation in sublethally irradiated mice revealed that enhanced susceptibility of PHD3-deficient mice to sepsis-related lethality was specifically caused by loss of PHD3 in myeloid cells. Several in vitro assays revealed enhanced cytokine production, migration, phagocytic capacity, and proinflammatory activation of PHD3-deficient macrophages. Increased proinflammatory activity of PHD3-deficient macrophages occurred concomitantly with enhanced HIF-1α protein stabilization and increased NF-κB activity, and interference with the expression of HIF-1α or the canonical NF-κB pathway blunted their proinflammatory phenotype. It is concluded that impairment of PHD3 enzyme function aggravates the clinical course of abdominal sepsis via HIF-1α– and NF-κB–mediated enhancement of the innate immune response.

Hypoxia-dependent regulation of inflammatory pathways in immune cells

“…While our understanding of the role of HIF hydroxylases in the regulation of immune cell function is far from complete, recent studies investigating individual HIF hydroxylase isoforms in discreet immune and epithelial cell subtypes have identified isoform-specific roles (80)(81)(82)(83)(84)(85)(86)(87)(88)(89). Notably, these phenotypes are not fully accounted for by downstream HIF-dependent effects, further supporting the existence of alternative hydroxylase-regulated pathways such as NF-κB in immune cells.…”

“…In macrophages, PHD2 loss or haplodeficiency alters M1/ M2 cell differentiation in an NF-κB-dependent manner (80,81), whereas PHD3 loss alters apoptosis and proinflammatory activity (82,83). In neutrophils, PHD3 regulates apoptosis, although this effect appears to be NF-κB independent (84).…”

Hypoxic regulation of neutrophil function and consequences for Staphylococcus aureus infection

“…Interestingly, under hypoxia PHD3 deficiency only impacted on neutrophil apoptosis, with other effector functions, such as phagocytosis, chemotaxis and the respiratory burst, being unaffected. Specific roles of the other PHD enzymes in neutrophils still require elucidation but, given the distinct functions for PHD3 observed in macrophages [39], may well be of interest. PHD enzymes belong to a wider family of 2-oxoglutarate-dependent oxygenases including the Jumonji histone demethylases.…”

“…Secondly, PHD3 is upregulated by hypoxia and prolongs neutrophil survival independent of HIF1a by suppression of the pro-apoptotic factor Siva-1. The impact of hypoxia-mediated neutrophil survival is context dependent; PHD3-deficient mice exhibited accelerated neutrophil apoptosis and enhanced resolution of sterile inflammation (ALI and colitis models) [38], but displayed increased mortality (thought to reflect aberrant macrophage function) when challenged with abdominal sepsis [39].…”

Prolyl Hydroxylase 3 Attenuates MCL-1–Mediated ATP Production to Suppress the Metastatic Potential of Colorectal Cancer Cells

“…Mouse embryonic fibroblasts (MEF) were isolated from PHD3 À/À mice (13 days postcoitum) and MEFs lacking MCL-1 protein (Mcl-1 D/null ) as described previously (15,16). Carcasses were minced and suspended in trypsin-EDTA with DNase.…”