Stressed erythrophagocytosis induces immunosuppression during sepsis through heme-mediated STAT1 dysregulation
Tolani F. Olonisakin, … , Prabir Ray, Janet S. Lee
Tolani F. Olonisakin, … , Prabir Ray, Janet S. Lee
Published September 17, 2020
Citation Information: J Clin Invest. 2021;131(1):e137468. https://doi.org/10.1172/JCI137468.
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Research Article Infectious disease Pulmonology

Stressed erythrophagocytosis induces immunosuppression during sepsis through heme-mediated STAT1 dysregulation

Abstract

Macrophages are main effectors of heme metabolism, increasing transiently in the liver during heightened disposal of damaged or senescent RBCs (sRBCs). Macrophages are also essential in defense against microbial threats, but pathological states of heme excess may be immunosuppressive. Herein, we uncovered a mechanism whereby an acute rise in sRBC disposal by macrophages led to an immunosuppressive phenotype after intrapulmonary Klebsiella pneumoniae infection characterized by increased extrapulmonary bacterial proliferation and reduced survival from sepsis in mice. The impaired immunity to K. pneumoniae during heightened sRBC disposal was independent of iron acquisition by bacterial siderophores, in that K. pneumoniae mutants lacking siderophore function recapitulated the findings observed with the WT strain. Rather, sRBC disposal induced a liver transcriptomic profile notable for suppression of Stat1 and IFN-related responses during K. pneumoniae sepsis. Excess heme handling by macrophages recapitulated STAT1 suppression during infection that required synergistic NRF1 and NRF2 activation but was independent of heme oxygenase-1 induction. Whereas iron was dispensable, the porphyrin moiety of heme was sufficient to mediate suppression of STAT1-dependent responses in human and mouse macrophages and promoted liver dissemination of K. pneumoniae in vivo. Thus, cellular heme metabolism dysfunction negatively regulated the STAT1 pathway, with implications in severe infection.

Authors

Tolani F. Olonisakin, Tomeka Suber, Shekina Gonzalez-Ferrer, Zeyu Xiong, Hernán F. Peñaloza, Rick van der Geest, Yuting Xiong, David O. Osei-Hwedieh, Jesús Tejero, Matthew R. Rosengart, Wendy M. Mars, Daria Van Tyne, Andreas Perlegas, Samuel Brashears, Daniel B. Kim-Shapiro, Mark T. Gladwin, Michael A. Bachman, Eldad A. Hod, Claudette St. Croix, Yulia Y. Tyurina, Valerian E. Kagan, Rama K. Mallampalli, Anuradha Ray, Prabir Ray, Janet S. Lee

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Figure 7

The porphyrin moiety of heme is necessary and sufficient for NRF1/NRF2 activation and STAT1 suppression.

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The porphyrin moiety of heme is necessary and sufficient for NRF1/NRF2 a...
(A) STAT1 immunoblot in BMDMs challenged with KP (MOI 10:1), KP + hemin (25 μM), KP + hemin + DFX (300 μM), or KP + hemin + DFO (300 μM) for 4 hours. All groups contained vehicle (DMSO, ~1%). Blot is representative of 2 independent experiments. (B) CXCL10 was measured in cell culture supernatant by ELISA 4 hours after infection. (C) Chemical structures of hemin (iron protoporphyrin IX, FePPIX), cobalt protoporphyrin IX (CoPPIX), and protoporphyrin IX (PPIX). (D) Mt1 and (E) Nqo1 expression, (F) Hmox1, and (G) Stat1 gene expression, (H) CXCL10 secretion in BMDMs challenged with KP, KP + FePPIX (50 μM), KP + CoPPIX (50 μM), or KP + PPIX (50 μM) for 4 hours. (D–G) Fold change relative to PBS-treated BMDMs. (B and F–H) n = 3 technical replicates per group. **P < 0.01, ***P < 0.001, ****P < 0.0001 by 1-way ANOVA with Tukey’s multiple comparisons test. (I) BACH1, HO-1, p-STAT1, and total STAT1 immunoblot in BMDMs challenged with KP and increasing concentrations of PPIX. (J) IRF1 immunoblot in human monocyte–derived macrophages (HMDMs) challenged with vehicle (PBS), KP, KP + FePPIX (25 μM), or KP + PPIX (25 μM) for 4 hours. (K) CXCL10 and (L) TNF-α secretion from HMDMs in J. n = 3 donors. ****P < 0.0001 by 2-way ANOVA with Tukey’s multiple comparisons test. KP was instilled intratracheally into C57BL/6 mice and followed by i.p. challenge with vehicle (2.5% DMSO) or CoPPIX (5 mg/kg, 25 mg/kg) 1 hour after KP instillation. Bacterial burden was obtained from (M) lung, (N) spleen, (O) liver tissue homogenates, and (P) blood of mice 24 hours after KP infection and reported as CFU/mL. Each point indicates individual mice, n = 10–11 mice per group combined from 2 independent studies. Line indicates median. *P < 0.05, **P < 0.01 by Kruskal-Wallis test with Dunn’s multiple comparisons test.