The polarization of macrophages is regulated by transcription factors such as nuclear factor kappa B (NF-κB) and activator protein 1 (AP-1). In this manuscript, we delineated the role of the transcription factor Fos-related antigen 1 (Fra-1) during macrophage activation and development of arthritis. Network level interaction analysis of microarray data derived from Fra-1- or Fra-2-deficient macrophages revealed a central role of Fra-1, but not of Fra-2 in orchestrating the expression of genes related to wound response, toll-like receptor activation and interleukin signaling. Chromatin-immunoprecipitation (ChIP)-sequencing and standard ChIP analyses of macrophages identified arginase 1 (Arg1) as a target of Fra-1. Luciferase reporter assays revealed that Fra-1 down-regulated Arg1 expression by direct binding to the promoter region. Using macrophage-specific Fra-1- or Fra-2- deficient mice, we observed an enhanced expression and activity of Arg1 and a reduction of arthritis in the absence of Fra-1, but not of Fra-2. This phenotype was reversed by treatment with the arginase inhibitor Nω-hydroxy-nor-L-arginine, while ʟ-arginine supplementation increased arginase activity and alleviated arthritis, supporting the notion that reduced arthritis in macrophage-specific Fra-1-deficient mice resulted from enhanced Arg1 expression and activity. Moreover, patients with active RA showed increased Fra-1 expression in the peripheral blood and elevated Fra-1 protein in synovial macrophages compared to RA patients in remission. In addition, the Fra-1/ARG1 ratio in synovial macrophages was related to RA disease activity. In conclusion, these data suggest that Fra-1 orchestrates the inflammatory state of macrophages by inhibition of Arg1 expression and thereby impedes the resolution of inflammation.
Nicole Hannemann, Shan Cao, Daniel Eriksson, Anne Schnelzer, Jutta Jordan, Martin Eberhardt, Ulrike Schleicher, Jürgen Rech, Andreas Ramming, Steffen Uebe, Arif Ekici, Juan D. Cañete, Xiaoxiang Chen, Tobias Bäuerle, Julio Vera, Christian Bogdan, Georg Schett, Aline Bozec
Neuromyelitis optica (NMO) is an autoimmune CNS disorder mediated by pathogenic aquaporin-4 (AQP4) water channel autoantibodies (AQP4-IgG). Although AQP4-IgG–driven complement-dependent cytotoxicity (CDC) is critical for the formation of NMO lesions, the molecular mechanisms governing optimal classical pathway activation are unknown. We investigated the molecular determinants driving CDC in NMO using recombinant AQP4–specific autoantibodies (AQP4 rAbs) derived from affected patients. We identified a group of AQP4 rAbs targeting a distinct extracellular loop C epitope that demonstrated enhanced CDC on target cells. Targeted mutations of AQP4 rAb Fc domains that enhance or diminish C1q binding or antibody Fc-Fc interactions showed that optimal CDC was driven by the assembly of multimeric rAb platforms that increase multivalent C1q binding and facilitate C1q activation. A peptide that blocks antibody Fc-Fc interaction inhibited CDC induced by AQP4 rAbs and polyclonal NMO patient sera. Super-resolution microscopy revealed that AQP4 rAbs with enhanced CDC preferentially formed organized clusters on supramolecular AQP4 orthogonal arrays, linking epitope-dependent multimeric assembly with enhanced C1q binding and activation. The resulting model of AQP4-IgG CDC provides a framework for understanding classical complement activation in human autoantibody–mediated disorders and identifies a potential new therapeutic avenue for treating NMO.
John Soltys, Yiting Liu, Alanna Ritchie, Scott Wemlinger, Kristin Schaller, Hannah Schumann, Gregory P. Owens, Jeffrey L. Bennett
Retinoic acid–related orphan receptor α (RORα) is considered a key regulator of polarization in liver macrophages that is closely related to nonalcoholic steatohepatitis (NASH) pathogenesis. However, hepatic microenvironments that support the function of RORα as a polarity regulator were largely unknown. Here, we identified maresin 1 (MaR1), a docosahexaenoic acid (DHA) metabolite with a function of specialized proresolving mediator, as an endogenous ligand of RORα. MaR1 enhanced the expression and transcriptional activity of RORα and thereby increased the M2 polarity of liver macrophages. Administration of MaR1 protected mice from high-fat diet–induced NASH in a RORα-dependent manner. Surprisingly, RORα increased the level of MaR1 through transcriptional induction of 12-lipoxygenase (12-LOX), a key enzyme in MaR1 biosynthesis. Furthermore, we demonstrated that modulation of 12-LOX activity enhanced the protective function of DHA against NASH. Together, these results suggest that the MaR1/RORα/12-LOX autoregulatory circuit could offer potential therapeutic strategies for curing NASH.
Yong-Hyun Han, Kyong-Oh Shin, Ju-Yeon Kim, Daulat B. Khadka, Hyeon-Ji Kim, Yong-Moon Lee, Won-Jea Cho, Ji-Young Cha, Bong-Jin Lee, Mi-Ock Lee
In contrast to microbially triggered inflammation, mechanisms promoting sterile inflammation remain poorly understood. Damage-associated molecular patterns (DAMPs) are considered key inducers of sterile inflammation following cell death, but the relative contribution of specific DAMPs, including high–mobility group box 1 (HMGB1), is ill defined. Due to the postnatal lethality of Hmgb1-knockout mice, the role of HMGB1 in sterile inflammation and disease processes in vivo remains controversial. Here, using conditional ablation strategies, we have demonstrated that epithelial, but not bone marrow–derived, HMGB1 is required for sterile inflammation following injury. Epithelial HMGB1, through its receptor RAGE, triggered recruitment of neutrophils, but not macrophages, toward necrosis. In clinically relevant models of necrosis, HMGB1/RAGE-induced neutrophil recruitment mediated subsequent amplification of injury, depending on the presence of neutrophil elastase. Notably, hepatocyte-specific HMGB1 ablation resulted in 100% survival following lethal acetaminophen intoxication. In contrast to necrosis, HMGB1 ablation did not alter inflammation or mortality in response to TNF- or FAS-mediated apoptosis. In LPS-induced shock, in which HMGB1 was considered a key mediator, HMGB1 ablation did not ameliorate inflammation or lethality, despite efficient reduction of HMGB1 serum levels. Our study establishes HMGB1 as a bona fide and targetable DAMP that selectively triggers a neutrophil-mediated injury amplification loop in the setting of necrosis.
Peter Huebener, Jean-Philippe Pradere, Celine Hernandez, Geum-Youn Gwak, Jorge Matias Caviglia, Xueru Mu, John D. Loike, Robert F. Schwabe
Non-apoptotic forms of cell death can trigger sterile inflammation through the release of danger-associated molecular patterns, which are recognized by innate immune receptors. However, despite years of investigation the mechanisms which initiate inflammatory responses after heart transplantation remain elusive. Here, we demonstrate that ferrostatin-1 (Fer-1), a specific inhibitor of ferroptosis, decreases the level of pro-ferroptotic hydroperoxy-arachidonoyl-phosphatidylethanolamine, reduces cardiomyocyte cell death and blocks neutrophil recruitment following heart transplantation. Inhibition of necroptosis had no effect on neutrophil trafficking in cardiac grafts. We extend these observations to a model of coronary artery ligation-induced myocardial ischemia reperfusion injury where inhibition of ferroptosis resulted in reduced infarct size, improved left ventricular systolic function, and reduced left ventricular remodeling. Using intravital imaging of cardiac transplants, we uncover that ferroptosis orchestrates neutrophil recruitment to injured myocardium by promoting adhesion of neutrophils to coronary vascular endothelial cells through a TLR4/TRIF/type I IFN signaling pathway. Thus, we have discovered that inflammatory responses after cardiac transplantation are initiated through ferroptotic cell death and TLR4/Trif-dependent signaling in graft endothelial cells. These findings provide a platform for the development of therapeutic strategies for heart transplant recipients and patients, who are vulnerable to ischemia reperfusion injury following restoration of coronary blood flow.
Wenjun Li, Guoshuai Feng, Jason M. Gauthier, Inessa Lokshina, Ryuji Higashikubo, Sarah Evans, Xinping Liu, Adil Hassan, Satona Tanaka, Markus Cicka, Hsi-Min Hsiao, Daniel Ruiz-Perez, Andrea Bredemeyer, Richard W. Gross, Douglas L. Mann, Yulia Y. Tyurina, Andrew E. Gelman, Valerian E. Kagan, Andreas Linkermann, Kory J. Lavine, Daniel Kreisel
Persistent, unresolved inflammation in adipose tissue is a major contributor to obesity-associated metabolic complications. However, the molecular links between lipid-overloaded adipocytes and inflammatory immune cells in obese adipose tissues remain elusive. Here we identified adipocyte-secreted microRNA-34a (miR-34a) as a key mediator through its paracrine actions on adipose-resident macrophages. The expression of miR-34a in adipose tissues was progressively increased with the development of dietary obesity. Adipose-selective or adipocyte-specific miR-34a–KO mice were resistant to obesity-induced glucose intolerance, insulin resistance, and systemic inflammation, and this was accompanied by a significant shift in polarization of adipose-resident macrophages from proinflammatory M1 to antiinflammatory M2 phenotype. Mechanistically, mature adipocyte-secreted exosomes transported miR-34a into macrophages, thereby suppressing M2 polarization by repressing the expression of Krüppel-like factor 4 (Klf4). The suppressive effects of miR-34a on M2 polarization and its stimulation of inflammatory responses were reversed by ectopic expression of Klf4 in both bone marrow–derived macrophages and adipose depots of obese mice. Furthermore, increased miR-34a expression in visceral fat of overweight/obese subjects correlated negatively with reduced Klf4 expression, but positively with the parameters of insulin resistance and metabolic inflammation. In summary, miR-34a was a key component of adipocyte-secreted exosomal vesicles that transmitted the signal of nutrient overload to the adipose-resident macrophages for exacerbation of obesity-induced systemic inflammation and metabolic dysregulation.
Yong Pan, Xiaoyan Hui, Ruby Lai Chong Hoo, Dewei Ye, Cyrus Yuk Cheung Chan, Tianshi Feng, Yu Wang, Karen Siu Ling Lam, Aimin Xu
Goblet cell metaplasia, a disabling hallmark of chronic lung disease, lacks curative treatments at present. To identify novel therapeutic targets for goblet cell metaplasia, we studied the transcriptional response profile of IL-13–exposed primary human airway epithelia in vitro and asthmatic airway epithelia in vivo. A perturbation-response profile connectivity approach identified geldanamycin, an inhibitor of heat shock protein 90 (HSP90) as a candidate therapeutic target. Our experiments confirmed that geldanamycin and other HSP90 inhibitors prevented IL-13–induced goblet cell metaplasia in vitro and in vivo. Geldanamycin also reverted established goblet cell metaplasia. Geldanamycin did not induce goblet cell death, nor did it solely block mucin synthesis or IL-13 receptor–proximal signaling. Geldanamycin affected the transcriptome of airway cells when exposed to IL-13, but not when exposed to vehicle. We hypothesized that the mechanism of action probably involves TGF-β, ERBB, or EHF, which would predict that geldanamycin would also revert IL-17–induced goblet cell metaplasia, a prediction confirmed by our experiments. Our findings suggest that persistent airway goblet cell metaplasia requires HSP90 activity and that HSP90 inhibitors will revert goblet cell metaplasia, despite active upstream inflammatory signaling. Moreover, HSP90 inhibitors may be a therapeutic option for airway diseases with goblet cell metaplasia of an unknown mechanism of action.
Alejandro A. Pezzulo, Rosarie A. Tudas, Carley G. Stewart, Luis G. Vargas Buonfiglio, Brian D. Lindsay, Peter J. Taft, Nicholas D. Gansemer, Joseph Zabner
Neutrophil (PMN) infiltration of the intestinal mucosa is a hallmark of tissue injury associated with inflammatory bowel diseases (IBDs). The pathological effects of PMNs are largely attributed to the release of soluble mediators and reactive oxygen species (ROS). We identified what we believe is a new, ROS-independent mechanism whereby activated tissue-infiltrating PMNs release microparticles armed with proinflammatory microRNAs (miR-23a and miR-155). Using IBD clinical samples, and in vitro and in vivo injury models, we show that PMN-derived miR-23a and miR-155 promote accumulation of double-strand breaks (DSBs) by inducing lamin B1–dependent replication fork collapse and inhibition of homologous recombination (HR) by targeting HR-regulator RAD51. DSB accumulation in injured epithelium led to impaired colonic healing and genomic instability. Targeted inhibition of miR-23a and miR-155 in cultured intestinal epithelial cells and in acutely injured mucosa decreased the detrimental effects of PMNs and enhanced tissue healing responses, suggesting that this approach can be used in therapies aimed at resolution of inflammation, in wound healing, and potentially to prevent neoplasia.
Veronika Butin-Israeli, Triet M. Bui, Hannah L. Wiesolek, Lorraine Mascarenhas, Joseph J. Lee, Lindsey C. Mehl, Kaitlyn R. Knutson, Stephen A. Adam, Robert D. Goldman, Arthur Beyder, Lisa Wiesmuller, Stephen B. Hanauer, Ronen Sumagin
In response to viral pathogens, the host upregulates antiviral genes that suppress translation of viral mRNAs. However, induction of such antiviral responses may not be exclusive to viruses, as the pathways lie at the intersection of broad inflammatory networks that can also be induced by bacterial pathogens. Using a model of Gram-negative sepsis, we show that propagation of kidney damage initiated by a bacterial origin ultimately involves antiviral responses that result in host translation shutdown. We determined that activation of the eukaryotic translation initiation factor 2-α kinase 2/eukaryotic translation initiation factor 2α (Eif2ak2/Eif2α) axis is the key mediator of translation initiation block in late-phase sepsis. Reversal of this axis mitigated kidney injury. Furthermore, temporal profiling of the kidney translatome revealed that multiple genes involved in formation of the initiation complex were translationally altered during bacterial sepsis. Collectively, our findings imply that translation shutdown is indifferent to the specific initiating pathogen and is an important determinant of tissue injury in sepsis.
Takashi Hato, Bernhard Maier, Farooq Syed, Jered Myslinski, Amy Zollman, Zoya Plotkin, Michael T. Eadon, Pierre C. Dagher
Pyrin is an inflammasome sensor that promotes caspase-1–mediated pyroptotic cell death and maturation of proinflammatory cytokines IL-1β and IL-18. Familial Mediterranean fever (FMF), an autoinflammatory disorder, is associated with mutations in the gene encoding pyrin (MEFV). FMF-knockin (FMF-KI) mice that express chimeric pyrin protein with FMF mutation (MefvV726A/V726A) exhibit an autoinflammatory disorder mediated by autoactivation of the pyrin inflammasome. Increase in the levels of TNF are observed in FMF-KI mice, and many features of FMF overlap with the autoinflammatory disorder associated with TNF receptor signaling. In this study, we assessed the contribution of TNF signaling to pyrin inflammasome activation and its consequent role in distinct FMF pathologies. TNF signaling promoted the expression of pyrin in response to multiple stimuli and was required for inflammasome activation in response to canonical pyrin stimuli and in myeloid cells from FMF-KI mice. TNF signaling promoted systemic wasting, anemia, and neutrophilia in the FMF-KI mice. Further, TNF-induced pathology was induced specifically through the TNFR1 receptor, while TNFR2-mediated signaling was distinctly protective in colitis and ankle joint inflammation. Overall, our data show that TNF is a critical modulator of pyrin expression, inflammasome activation, and pyrin-inflammasomopathy. Further, specific blockade of TNFR1 or activation of TNFR2 could provide substantial protection against FMF pathologies.
Deepika Sharma, Ankit Malik, Clifford Guy, Peter Vogel, Thirumala-Devi Kanneganti
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