Prolyl hydroxylase 3 (PHD3) is essential for hypoxic regulation of neutrophilic inflammation in humans and mice

Abstract

The regulation of neutrophil lifespan by induction of apoptosis is critical for maintaining an effective host response and preventing excessive inflammation. The hypoxia-inducible factor (HIF) oxygen-sensing pathway has a major effect on the susceptibility of neutrophils to apoptosis, with a marked delay in cell death observed under hypoxic conditions. HIF expression and transcriptional activity are regulated by the oxygen-sensitive prolyl hydroxylases (PHD1-3), but the role of PHDs in neutrophil survival is unclear. We examined PHD expression in human neutrophils and found that PHD3 was strongly induced in response to hypoxia and inflammatory stimuli in vitro and in vivo. Using neutrophils from mice deficient in Phd3, we demonstrated a unique role for Phd3 in prolonging neutrophil survival during hypoxia, distinct from other hypoxia-associated changes in neutrophil function and metabolic activity. Moreover, this selective defect in neutrophil survival occurred in the presence of preserved HIF transcriptional activity but was associated with upregulation of the proapoptotic mediator Siva1 and loss of its binding target Bcl-x L . In vivo, using an acute lung injury model, we observed increased levels of neutrophil apoptosis and clearance in Phd3-deficient mice compared with WT controls. We also observed reduced neutrophilic inflammation in an acute mouse model of colitis. These data support what we believe to be a novel function for PHD3 in regulating neutrophil survival in hypoxia and may enable the development of new therapeutics for inflammatory disease.

Hypoxic regulation of neutrophil function and consequences for Staphylococcus aureus infection

“…HIF-1a target genes in hypoxic neutrophils but is necessary for cell survival in hypoxic conditions, suggesting that these pro-survival effects are mediated independent of HIF-1a in neutrophils [38]. Interestingly, under hypoxia PHD3 deficiency only impacted on neutrophil apoptosis, with other effector functions, such as phagocytosis, chemotaxis and the respiratory burst, being unaffected.…”

“…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].…”

Hydroxylases as therapeutic targets in inflammatory bowel disease

“…73 Neutrophil infiltration and the formation of colonic crypt abscesses is a hallmark of IBD and the regulation of neutrophil lifespan is consequently a key event in determining the extent and duration of inflammation. Hypoxia-dependent pathways have been previously demonstrated to have an important role in the regulation of neutrophil apoptosis.…”

“…PHD3 loss results in decreased-neutrophil survival under hypoxic conditions. 73 Furthermore, in mice which are homozygous deficient in PHD3, there is a reduction in neutrophilic inflammation in DSS-induced colitis. 73 Therefore, enhanced neutrophil apoptosis is another mechanism by which pharmacologic hydroxylase inhibition may be protective in murine models of colitis.…”

Multifaceted functions of Siva-1: more than an Indian God of Destruction

“…Moreover, Siva-1 gene expression is also upregulated in response to DNA damage signals and hypoxia conditions (Daoud et al, 2003;Walmsley et al, 2011). Ectopic expression of a metastasis suppressor Tip30/CC3 activates Siva-1 transcription in small cell lung carcinoma (Xiao et al, 2000).…”