Introduction: Macrophages can have pro-inflammatory or anti-inflammatory effects, which changes in response to the surrounding milieu, including hypoxia, with cellular metabolic switch.Hypoxia-inducible factor (HIF) is central to adaptation to hypoxia and plays an essential role in modulating macrophage characteristics, including their effects on inflammation and promoted glycolysis.Prolyl hydroxylase domaincontaining proteins (PHDs) are decisive molecules in down-regulating HIF under normoxia.In the clinical settings, PHD (HIF-PH) inhibitors have been used for anemia with chronic kidney disease (CKD).However, the role of PHDs in macrophage-mediated inflammation remains unclear.Methods: We generated conditional knockout mice (cKO), in which Phd1, 2 and 3 were specifically deficient in macrophages (Phd1fl/fl; Phd2fl/fl; Phd3fl/fl; LysMCre/+).Their littermates (Phd1fl/fl; Phd2 fl/fl; Phd3 fl/fl; LysM+/+) were used as the control.Mice were treated with lipopolysaccharide (LPS) as a model of systemic inflammation.To examine the macrophages in vitro, RAW264.7 cells treated with a PHD inhibitor and bone marrow-derived macrophages (BMDMs) from cKO mice were exposed to LPS.Furthermore, liver macrophages from mice with and without LPS treatment were isolated with FACS as CD45+ CD3e-CD19-CD49b-Ly6G-CD11b+ Tim4+ F4/80+ cells and their transcriptomes were comprehensively analyzed with microarray.Results: In a model of LPS-induced systemic inflammation, the survival of cKO was remarkably and significantly ameliorated compared to the control, which was accompanied by a decrease in the serum IL-1 and the expression of pro-inflammatory cytokines (IL-1b, IL-6, IL-12b and IL-18) in the multiple organs.Consistently, in RAW cells, treatment with a PHD inhibitor mitigated the LPS-induced expressions of proinflammatory cytokines, including IL-1b, IL-6, IL-12b, and IL-18, and chemokines such as Ccl2 and Cxcl2.Furthermore, LPS-treated BMDMs from cKO mice showed decreased expressions of these pro-inflammatory mediators.In liver macrophages from cKO mice at baseline, the expressions of multiple HIF-target genes including glycolysis genes were increased, which indicates the activation of HIF with Phd knockout, and an increase in the expressions of anti-inflammatory genes were also found.Moreover, a decrease in pro-inflammatory gene expressions including Tnf-a, IL12b, IL-18, Ccl2, and Ccl8 and an increase in anti-inflammatory genes including Arg1, Tgf-b3 were observed in macrophages of LPS-treated cKO mice, compared to the LPS-treated control mice.Conclusion: PHD knockout in macrophages suppressed the expression of pro-inflammatory genes and contributed to the suppression of systemic inflammation.PHD (HIF-PH) inhibitors can have anti-inflammatory effects via macrophages, which might improve their therapeutic effects on anemia with CKD.I have no potential conflict of interest to disclose.I did not use generative AI and AI-assisted technologies in the writing process.
Iwasaki et al. (Wed,) studied this question.