IL4Rα signaling abrogates hypoxic neutrophil survival and limits acute lung injury responses <i>in vivo</i>

Rationale: Acute respiratory distress syndrome is defined by the presence of systemic hypoxia and consequent on disordered neutrophilic inflammation. Local mechanisms limiting the duration and magnitude of this neutrophilic response remain poorly understood.  Objectives: To test the hypothesis that during acute lung inflammation tissue production of proresolution type 2 cytokines (IL-4 and IL-13) dampens the proinflammatory effects of hypoxia through suppression of HIF-1a (hypoxia-inducible factor-1a)mediated neutrophil adaptation, resulting in resolution of lung injury.  Methods: Neutrophil activation of IL4Ra (IL-4 receptor a) signaling pathways was explored ex vivo in human acute respiratory distress syndrome patient samples, in vitro after the culture of human peripheral blood neutrophils with recombinant IL-4 under conditions of hypoxia, and in vivo through the study of IL4Ra-deficient neutrophils in competitive chimera models and wild-type mice treated with IL-4.  Measurements and Main Results: IL-4 was elevated in human BAL from patients with acute respiratory distress syndrome, and its receptor was identified on patient blood neutrophils. Treatment of human neutrophils with IL-4 suppressed HIF-1a-dependent hypoxic survival and limited proinflammatory transcriptional responses. Increased neutrophil apoptosis in hypoxia, also observed with IL-13, required active STAT signaling, and was dependent on expression of the oxygen-sensing prolyl hydroxylase PHD2. In vivo, IL-4Ra-deficient neutrophils had a survival advantage within a hypoxic inflamed niche; in contrast, inflamed lung treatment with IL-4 accelerated resolution through increased neutrophil apoptosis.  Conclusions: We describe an important interaction whereby IL4Ra-dependent type 2 cytokine signaling can directly inhibit hypoxic neutrophil survival in tissues and promote resolution of neutrophil-mediated acute lung injury

Prolyl hydroxylase 2 inactivation enhances glycogen storage and promotes excessive neutrophilic responses.

Fully activated innate immune cells are required for effective responses to infection, but their prompt deactivation and removal are essential for limiting tissue damage. Here, we have identified a critical role for the prolyl hydroxylase enzyme Phd2 in maintaining the balance between appropriate, predominantly neutrophil-mediated pathogen clearance and resolution of the innate immune response. We demonstrate that myeloid-specific loss of Phd2 resulted in an exaggerated inflammatory response to Streptococcus pneumonia, with increases in neutrophil motility, functional capacity, and survival. These enhanced neutrophil responses were dependent upon increases in glycolytic flux and glycogen stores. Systemic administration of a HIF-prolyl hydroxylase inhibitor replicated the Phd2-deficient phenotype of delayed inflammation resolution. Together, these data identify Phd2 as the dominant HIF-hydroxylase in neutrophils under normoxic conditions and link intrinsic regulation of glycolysis and glycogen stores to the resolution of neutrophil-mediated inflammatory responses. These results demonstrate the therapeutic potential of targeting metabolic pathways in the treatment of inflammatory disease.This work was principally supported by a Wellcome Trust Senior Clinical Fellowship award (098516 to SRW), Medical Research Council (MRC) Clinical Training Fellowship awards (G0802255 to AART; MR/K023845/1 to RSD), an Academy of Medical Sciences (AMS) starter grant (to AART), a Wellcome Trust Senior Clinical Fellowship award (076945 to DHD), British Lung Foundation Fellowship (F05/7 to HMM), and a Engineering and Physical Sciences Research Council and Medical Research Council grant (EP/L016559/1, JAW). The MRC /University of Edinburgh Centre for Inflammation Research is supported by an MRC Centre Grant. The work of PC is supported by long-term structural funding-Methusalem funding from the Flemish Government. CJS thanks the Wellcome Trust and Cancer Research UK for support