Succinate is a signaling metabolite sensed extracellularly by succinate receptor 1 (SUNCR1). The accumulation of succinate in macrophages is known to activate a pro-inflammatory program; however, the ...contribution of SUCNR1 to macrophage phenotype and function has remained unclear. Here we found that activation of SUCNR1 had a critical role in the anti-inflammatory responses in macrophages. Myeloid-specific deficiency in SUCNR1 promoted a local pro-inflammatory phenotype, disrupted glucose homeostasis in mice fed a normal chow diet, exacerbated the metabolic consequences of diet-induced obesity and impaired adipose-tissue browning in response to cold exposure. Activation of SUCNR1 promoted an anti-inflammatory phenotype in macrophages and boosted the response of these cells to type 2 cytokines, including interleukin-4. Succinate decreased the expression of inflammatory markers in adipose tissue from lean human subjects but not that from obese subjects, who had lower expression of SUCNR1 in adipose-tissue-resident macrophages. Our findings highlight the importance of succinate-SUCNR1 signaling in determining macrophage polarization and assign a role to succinate in limiting inflammation.
Macrophage phenotypic and functional heterogeneity derives from tissue-specific transcriptional signatures shaped by the local microenvironment. Most studies addressing the molecular basis for ...macrophage heterogeneity have focused on murine cells, whereas the factors controlling the functional specialization of human macrophages are less known. M-CSF drives the generation of human monocyte-derived macrophages with a potent anti-inflammatory activity upon stimulation. We now report that knockdown of MAFB impairs the acquisition of the anti-inflammatory profile of human macrophages, identify the MAFB-dependent gene signature in human macrophages and illustrate the coexpression of MAFB and MAFB-target genes in CD163
tissue-resident and tumor-associated macrophages. The contribution of MAFB to the homeostatic/anti-inflammatory macrophage profile is further supported by the skewed polarization of monocyte-derived macrophages from multicentric carpotarsal osteolysis (Online Mendelian Inheritance in Man #166300), a pathology caused by mutations in the
gene. Our results demonstrate that MAFB critically determines the acquisition of the anti-inflammatory transcriptional and functional profiles of human macrophages.
Macrophages regulate essential aspects of innate immunity against pathogens. In response to microbial components, macrophages activate primary and secondary inflammatory gene programs crucial for ...host defense. The liver X receptors (LXRα, LXRβ) are ligand‐dependent nuclear receptors that direct gene expression important for cholesterol metabolism and inflammation, but little is known about the individual roles of LXRα and LXRβ in antimicrobial responses. Here, the results demonstrate that induction of LXRα transcription by prolonged exposure to lipopolysaccharide (LPS) supports inflammatory gene expression in macrophages. LXRα transcription is induced by NF‐κB and type‐I interferon downstream of TLR4 activation. Moreover, LPS triggers a reprogramming of the LXRα cistrome that promotes cytokine and chemokine gene expression through direct LXRα binding to DNA consensus sequences within cis‐regulatory regions including enhancers. LXRα‐deficient macrophages present fewer binding of p65 NF‐κB and reduced histone H3K27 acetylation at enhancers of secondary inflammatory response genes. Mice lacking LXRα in the hematopoietic compartment show impaired responses to bacterial endotoxin in peritonitis models, exhibiting reduced neutrophil infiltration and decreased expansion and inflammatory activation of recruited F4/80lo‐MHC‐IIhi peritoneal macrophages. Together, these results uncover a previously unrecognized function for LXRα‐dependent transcriptional cis‐activation of secondary inflammatory gene expression in macrophages and the host response to microbial ligands.
The inflammatory response is a defense mechanism of the innate immune system against infections and other injuries. In response to microbial components, macrophages activate primary and secondary inflammatory gene programs crucial for host defense. De la Rosa et al. provide evidence that inflammation triggers a reprogramming of the transcription factor liver X receptor α (LXRα), that sustains cytokine and chemokine gene expression through direct binding to DNA consensus sequences and collaboration with NF‐κB at enhancers of secondary inflammatory response genes. This novel TLR4‐LXRα‐NF‐κB axis supports macrophage inflammatory gene expression and in vivo immune‐cell recruitment during inflammatory responses to microbial ligands, positioning LXRα as a key factor in the transcriptional regulation in the late stages of inflammation.
Summary
Cyclic AMP regulatory element binding protein and signal transducer and activator of transcription 3 (STAT3) may control inflammation by several mechanisms, one of the best characterized is ...the induction of the expression of the anti‐inflammatory cytokine interleukin‐10 (IL‐10). STAT3 also down‐regulates the production of pro‐inflammatory cytokines induced by immunoreceptor tyrosine‐based activation motif (ITAM)‐coupled receptors, a mechanism termed cross‐inhibition. Because signalling via ITAM‐dependent mechanisms is a hallmark of fungal pattern receptors, STAT3 activation might be involved in the cross‐inhibition associated with invasive fungal infections. The fungal surrogate zymosan produced the phosphorylation of Y705‐STAT3 and the expression of Ifnb1 and Socs3, but did not induce the interferon (IFN)‐signature cytokines Cxcl9 and Cxcl10 in bone marrow‐derived dendritic cells. Unlike lipopolysaccharide (LPS), zymosan induced IL‐10 and phosphorylated Y705‐STAT3 to a similar extent in Irf3 and Ifnar1 knockout and wild‐type mice. Human dendritic cells showed similar results, although the induction of IFNB1 was less prominent. These results indicate that LPS and zymosan activate STAT3 through different routes. Whereas type I IFN is the main effector of LPS effect, the mechanism involved in Y705‐STAT3 phosphorylation by zymosan is more complex, cannot be associated with type I IFN, IL‐6 or granulocyte–macrophage colony‐stimulating factor, and seems dependent on several factors given that it was partially inhibited by the platelet‐activating factor antagonist WEB2086 and high concentrations of COX inhibitors, p38 mitogen‐activate protein kinase inhibitors, and blockade of tumour necrosis factor‐α function. Altogether, these results indicate that fungal pattern receptors share with other ITAM‐coupled receptors the capacity to produce cross‐inhibition through a mechanism involving STAT3 and induction of SOCS3 and IL‐10, but that cannot be explained through type I IFN signalling.
LPS and the fungal surrogate zymosan activate STAT3. Type I IFN are the mediators of LPS effect, but the mechanism of Y705‐STAT3 phosphorylation by zymosan is more complex. Zymosan produced the phosphorylation of Y705‐STAT3 and the expression of IFNB1 and SOCS3, but did not induce IFN‐signature cytokines. This study shows: (i) the activation of STAT3 by zymosan through a mechanism independent of type I IFN, (ii) the lack of involvement of the JAK/STAT3 system on the production of IL‐10 elicited by zymosan, (iii) a cross‐inhibitory effect of zymosan receptors on type I IFN responses.
Oncogene-immortalized bone marrow-derived macrophages are considered to be a good model for the study of immune cell functions, but the factors required for their survival and proliferation are still ...unknown. Although the effect of the thyroid hormones on global metabolic and transcriptional responses in macrophages has not yet been examined, there is increasing evidence that they could modulate macrophage functions. We show here that the thyroid hormone T3 is an absolute requirement for the growth of immortal macrophages. The hormone regulates the activity of the main signaling pathways required for proliferation and anabolic processes, including the phosphorylation of ERK and p38 MAPKs, AKT, ribosomal S6 protein, AMPK and Sirtuin-1. T3 also alters the levels of metabolites controlling transcriptional and post-transcriptional actions in macrophages, and causes widespread transcriptomic changes, up-regulating genes needed for protein synthesis and cell proliferation, while down-regulating genes involved in immune responses and endocytosis, among others. This is not observed in primary bone marrow-derived macrophages, where only p38 and AMPK activation is regulated by T3 and in which the metabolic and transcriptomic effects of the hormone are much weaker. However, the response to IFN-γ is reduced by T3 similarly in immortalized macrophages and in the primary cells, confirming previous results showing that the thyroid hormones can antagonize JAK/STAT-mediated signaling. These results provide new perspectives on the relevant pathways involved in proliferation and survival of macrophage cell culture models and on the crosstalk between the thyroid hormones and the immune system.
Liver X Receptors (LXR) control cholesterol metabolism and exert anti-inflammatory actions but their contribution to human macrophage polarization remains unclear. The LXR pathway is enriched in ...pro-inflammatory macrophages from rheumatoid arthritis as well as in tumors-associated macrophages from human tumors. We now report that LXR activation inhibits the anti-inflammatory gene and functional profile of M-CSF-dependent human macrophages, and prompts the acquisition of a pro-inflammatory gene signature, with both effects being blocked by an LXR inverse agonist. Mechanistically, the LXR-stimulated macrophage polarization shift correlates with diminished expression of MAFB and MAF, which govern the macrophage anti-inflammatory profile, and with enhanced release of activin A. Indeed, LXR activation impaired macrophage polarization in response to tumor-derived ascitic fluids, as well as the expression of MAF- and MAFB-dependent genes. Our results demonstrate that LXR activation limits the anti-inflammatory human macrophage polarization and prompts the acquisition of an inflammatory transcriptional and functional profile.
Preclinical and clinical studies suggest that hypothyroidism might cause hepatic endocrine and metabolic disturbances with features that mimic deficiencies of testosterone and/or GH. The absence of ...physiological interactions between testosterone and GH can be linked to male differentiated liver diseases. Testosterone plays relevant physiological effects on somatotropic-liver axis and liver composition and the liver is a primary organ of interactions between testosterone and GH. However, testosterone exerts many effects on liver through complex and poorly understood mechanisms. Testosterone impacts liver functions by binding to the Androgen Receptor, and, indirectly, through its conversion to estradiol, and cooperation with GH. However, the role of testosterone, and its interaction with GH, in the hypothyroid liver, remains unclear. In the present work, the effects of testosterone, and how they impact on GH-regulated whole transcriptome and lipid composition in the liver, were studied in the context of adult hypothyroid-orchiectomized rats. Testosterone replacement positively modulated somatotropic-liver axis and impacted liver transcriptome involved in lipid and glucose metabolism. In addition, testosterone enhanced the effects of GH on the transcriptome linked to lipid biosynthesis, oxidation-reduction, and metabolism of unsaturated and long-chain fatty acids (FA). However, testosterone decreased the hepatic content of cholesterol esters and triacylglycerols and increased fatty acids whereas GH increased neutral lipids and decreased polar lipids. Biological network analysis of the effects of testosterone on GH-regulated transcriptome confirmed a close connection with crucial proteins involved in steroid and fatty acid metabolism. Taken together, this comprehensive analysis of gene expression and lipid profiling in hypothyroid male liver reveals a functional interplay between testosterone and pulsed GH administration.
In recent years, the central role of cell bioenergetics in regulating immune cell function and fate has been recognized, giving rise to the interest in immunometabolism, an area of research focused ...on the interaction between metabolic regulation and immune function. Thus, early metabolic changes associated with the polarization of macrophages into pro-inflammatory or pro-resolving cells under different stimuli have been characterized. Tumor-associated macrophages are among the most abundant cells in the tumor microenvironment; however, it exists an unmet need to study the effect of chemotherapeutics on macrophage immunometabolism. Here, we use a systems biology approach that integrates transcriptomics and metabolomics to unveil the immunometabolic effects of trabectedin (TRB) and lurbinectedin (LUR), two DNA-binding agents with proven antitumor activity. Our results show that TRB and LUR activate human macrophages toward a pro-inflammatory phenotype by inducing a specific metabolic rewiring program that includes ROS production, changes in the mitochondrial inner membrane potential, increased pentose phosphate pathway, lactate release, tricarboxylic acids (TCA) cycle, serine and methylglyoxal pathways in human macrophages. Glutamine, aspartate, histidine, and proline intracellular levels are also decreased, whereas oxygen consumption is reduced. The observed immunometabolic changes explain additional antitumor activities of these compounds and open new avenues to design therapeutic interventions that specifically target the immunometabolic landscape in the treatment of cancer.
The liver X receptors α and β (LXRα and LXRβ) are oxysterol-activated transcription factors that coordinately regulate gene expression that is important for cholesterol and fatty acid metabolism. In ...addition to their roles in lipid metabolism, LXRs participate in the transcriptional regulation of macrophage activation and are considered potent regulators of inflammation. LXRs are highly similar, and despite notable exceptions, most of their reported functions are substantially overlapping. However, their individual genomic distribution and transcriptional capacities have not been characterized. Here, we report a macrophage cellular model expressing equivalent levels of tagged LXRs. Analysis of data from chromatin immunoprecipitation coupled with deep sequencing revealed that LXRα and LXRβ occupy both overlapping and exclusive genomic regulatory sites of target genes and also control the transcription of a receptor-exclusive set of genes. Analysis of genomic H3K27 acetylation and mRNA transcriptional changes in response to synthetic agonist or antagonist treatments revealed a putative mode of pharmacologically independent regulation of transcription. Integration of microarray and sequencing data enabled the description of three possible mechanisms of LXR transcriptional activation. Together, these results contribute to our understanding of the common and differential genomic actions of LXRs and their impact on biological processes in macrophages.
To evaluate the role of liver X receptor (LXR) nuclear receptors on irradiation-induced cell death and polarization of macrophages and the potential implications in the context of radiation therapy ...treatment of cancer.
Primary and immortalized murine bone marrow-derived macrophages (BMDMs) from wild type or LXR double knock-out mice were exposed to gamma irradiation. Subsequently, analysis of LXR signaling on cell proliferation and cytotoxicity induced by ionizing radiation was determined by time-lapse photomicroscopy. Genotoxic cell damage was evaluated by Western blot of γ-H2AX and p53. Pyroptosis was analyzed through cell viability assay, lactate dehydrogenase release assay, and Western blot of caspase-1 active protein. Expression of inflammatory markers was measured by real-time quantitative polymerase chain reaction.
Genetic and pharmacologic inactivation of LXR induced radiosensitivity of macrophages. LXR deficiency decreased cell proliferation and enhanced cytotoxicity induced by ionizing radiation in both immortalized and primary BMDMs. Protein levels of γ-H2AX and p53, both involved in response to cell damage, were exacerbated in LXR-deficient macrophages exposed to irradiation. Cell membrane damage was augmented and cell viability was decreased in LXR-deficient macrophages compared with LXR wild type macrophages in response to irradiation. In addition, LXR deficiency enhanced both caspase-1 activation and lactate dehydrogenase release in BMDM exposed inflammasome activators. LXR inactivation or deficiency markedly increased the expression of proinflammatory markers IL-1β, IL-6, and inducible nitric oxide synthase in irradiated macrophages.
The present work identifies LXR transcription factors as potential therapeutic targets to enhance the suppressive effects of radiation therapy on tumor growth through induction of macrophage cell death and activation of the inflammatory cascade.
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