Regulation of alternative macrophage activation by chromatin remodeling

NF-κB: Governing Macrophages in Cancer

Tumor-associated macrophages (TAMs) are the major component of the tumor microenvironment (TME), where they sustain tumor progression and or-tumor immunity. Due to their plasticity, macrophages can exhibit anti- or pro-tumor functions through the expression of different gene sets leading to distinct macrophage phenotypes: M1-like or pro-inflammatory and M2-like or anti-inflammatory. NF-κB transcription factors are central regulators of TAMs in cancers, where they often drive macrophage polarization toward an M2-like phenotype. Therefore, the NF-κB pathway is an attractive therapeutic target for cancer immunotherapy in a wide range of human tumors. Hence, targeting NF-κB pathway in the myeloid compartment is a potential clinical strategy to overcome microenvironment-induced immunosuppression and increase anti-tumor immunity. In this review, we discuss the role of NF-κB as a key driver of macrophage functions in tumors as well as the principal strategies to overcome tumor immunosuppression by targeting the NF-κB pathway.

Human-specific CHRFAM7A primes macrophages for a heightened pro-inflammatory response at the earlier stage of inflammation

α7-Nicotinic acetylcholine receptor (α7-nAChR) is the key effector molecule of the cholinergic anti-inflammatory pathway. Evolution has evolved a uniquely human α7-nAChR encoded by CHRFAM7A. It has been demonstrated that CHRFAM7A dominant negatively regulates the functions of α7-nAChR. However, its role in inflammation remains to be fully characterized. CHRFAM7A transgenic (Tg) mice were phenotypically normal and their peritoneal macrophages exhibited decreased ligand-binding capability and, importantly, an activated gene expression profile of pro-inflammatory cytokines. Surprisingly, when challenged with sepsis, the Tg mice showed no survival disadvantage relative to their wild-type (Wt) counterparts. Further analysis showed that the complete blood count and serum levels of pro-inflammatory cytokines were comparable at resting state, but the degrees of leukocyte mobilization and the increase of pro-inflammatory cytokines were significantly higher in Tg than Wt mice at the early stage of sepsis. In vitro, peritoneal macrophages of the Tg mice exhibited an exaggerated response to lipopolysaccharides (LPSs), especially at the earlier time points and at lower dosages of LPS. Remarkably, monocytes from CHRFAM7A-carrier showed similar dynamic changes of the pro-inflammatory cytokines to that observed in the Tg mice upon LPS challenge. Our results suggest that CHRFAM7A increases the mobilization of leukocytes and primes macrophages that confer an enhanced immune response at the early stage of inflammation, which may lead to prompt pathogen clearance, an evolutionary advantage in less severe inflammatory conditions.

NOTCH4 potentiates the IL-13 induced genetic program in M2 alternative macrophages through the AP1 and IRF4-JMJD3 axis

IL-13 signaling polarizes macrophages to an M2 alternatively activated phenotype, which regulates tissue repair and anti-inflammatory responses. However, an excessive activation of this pathway leads to severe pathologies, such as allergic airway inflammation and asthma. In this work, we identified NOTCH4 receptor as an important modulator of M2 macrophage activation. We show that the expression of NOTCH4 is induced by IL-13, mediated by Janus kinases and AP1 activity, probably mediated by the IL-13Rα1 and IL-13Rα2 signaling pathway. Furthermore, we demonstrate an important role for NOTCH4 signaling in the IL-13 induced gene expression program in macrophages, including various genes that contribute to pathogenesis of the airways in asthma, such as ARG1, YM1, CCL24, IL-10, or CD-163. We also demonstrate that NOTCH4 signaling modulates IL-13-induced gene expression by increasing IRF4 activity, mediated, at least in part, by the expression of the histone H3K27me3 demethylase JMJD3, and by increasing AP1-dependent transcription. In summary, our results provide evidence for an important role of NOTCH4 signaling in alternative activation of macrophages by IL-13 and suggest that NOTCH4 may contribute to the increased severity of lesions in M2 inflammatory responses, such as allergic asthma, which points to NOTCH4 as a potential new target for the treatment of these pathologies.

Ezh2 emerges as an epigenetic checkpoint regulator during monocyte differentiation limiting cardiac dysfunction post-MI

Epigenetic regulation of histone H3K27 methylation has recently emerged as a key step during alternative immunoregulatory M2-like macrophage polarization; known to impact cardiac repair after Myocardial Infarction (MI). We hypothesized that EZH2, responsible for H3K27 methylation, could act as an epigenetic checkpoint regulator during this process. We demonstrate for the first time an ectopic EZH2, and putative, cytoplasmic inactive localization of the epigenetic enzyme, during monocyte differentiation into M2 macrophages in vitro as well as in immunomodulatory cardiac macrophages in vivo in the post-MI acute inflammatory phase. Moreover, we show that pharmacological EZH2 inhibition, with GSK-343, resolves H3K27 methylation of bivalent gene promoters, thus enhancing their expression to promote human monocyte repair functions. In line with this protective effect, GSK-343 treatment accelerated cardiac inflammatory resolution preventing infarct expansion and subsequent cardiac dysfunction in female mice post-MI in vivo. In conclusion, our study reveals that pharmacological epigenetic modulation of cardiac-infiltrating immune cells may hold promise to limit adverse cardiac remodeling after MI.

Trichinella spiralis co-infection exacerbates Plasmodium berghei malaria-induced hepatopathy

Background

Although Plasmodium parasites and intestinal helminths share common endemic areas, the mechanisms of these co-infections on the host immune response remain not fully understood. Liver involvement in severe Plasmodium falciparum infections is a significant cause of morbidity and mortality. However, the effect of pre-existing Trichinella spiralis infection on the immune response and liver immune-pathogenesis in P. berghei ANKA (PbANKA)-infected mice needs to be elucidated.

Methods

Outbred Kunming mice were infected with T. spiralis and 9 days later were challenged with P. berghei ANKA (PbANKA), and the investigation occurred at 13 days after co-infection.

Results

Compared with PbANKA-mono-infected mice, T. spiralis + PbANKA-co-infected mice had similar survival rate but lower PbANKA parasitaemia; however, there were more severe hepatosplenomegaly, increased liver and spleen indexes, and increased liver pathology observed by hematoxylin and eosin staining; higher expression levels of galectin (Gal)-1, Gal-3, CD68⁺ macrophages, and elastase-positive neutrophils measured by immunohistochemical staining; upregulated mRNA expression levels of Gal-1, Gal-3, cytokines (interferon-gamma (IFNγ) and interleukin (IL)-6), and M1 macrophage polarization marker (inducible nitric oxide synthase (iNOS)) in the liver, and increased expression levels of Gal-1, IFNγ, IL-6, eosinophil cationic protein, eosinophil protein X, and M1 (IL-1β and iNOS) and M2 (Ym1) macrophage polarization markers in the spleen of co-infected mice detected by using quantitative real-time reverse transcription polymerase chain reaction (qRT-PCR). In vitro study showed that compared with PbANKA-mono-infected mice, there were significantly increased expression levels of Gal-1, Gal-3, IL-6, IL-1β, and iNOS in the peritoneal macrophage isolated from co-infected mice detected by using qRT-PCR. Correlation analysis revealed significant positive correlations between Gal-3 and IL-1β in the peritoneal macrophages isolated from PbANKA-mono-infected mice, between Gal-3 and IFNγ in the spleen of co-infected mice, and between Gal-1 and Ym1 in the peritoneal macrophages isolated from co-infected mice.

Conclusions

Our data indicate that pre-existing infection of T. spiralis may suppress P. berghei parasitaemia and aggravate malaria-induced liver pathology through stimulating Gal-1 and Gal-3 expression, activating macrophages, neutrophils, and eosinophils, and promoting mediator release and cytokine production.

Adoptive transfer of Trichinella spiralis-activated macrophages can ameliorate both Th1- and Th2-activated inflammation in murine models

Trichinella spiralis is a zoonotic nematode and food borne parasite and infection with T. spiralis leads to suppression of the host immune response and other immunopathologies. Alternative activated macrophages (M2) as well as T_reg cells, a target for immunomodulation by the helminth parasite, play a critical role in initiating and modulating the host immune response to parasite. The precise mechanism by which helminths modulate host immune response is not fully understood. To determine the functions of parasite-induced M2 macrophages, we compared the effects of M1 and M2 macrophages obtained from Trichinella spiralis-infected mice with those of T. spiralis excretory/secretory (ES) protein-treated macrophages on experimental intestinal inflammation and allergic airway inflammation. T. spiralis infection induced M2 macrophage polarization by increasing the expression of CD206, ARG1, and Fizz2. In a single application, we introduced macrophages obtained from T. spiralis-infected mice and T. spiralis ES protein-treated macrophages into mice tail veins before the induction of dextran sulfate sodium (DSS)-induced colitis, ovalbumin (OVA)-alum sensitization, and OVA challenge. Colitis severity was assessed by determining the severity of colitis symptoms, colon length, histopathologic parameters, and Th1-related inflammatory cytokine levels. Compared with the DSS-colitis group, T. spiralis-infected mice and T. spiralis ES protein-treated macrophages showed significantly lower disease activity index (DAI) at sacrifice and smaller reductions of body weight and proinflammatory cytokine level. The severity of allergic airway inflammation was assessed by determining the severity of symptoms of inflammation, airway hyperresponsiveness (AHR), differential cell counts, histopathologic parameters, and levels of Th2-related inflammatory cytokines. Severe allergic airway inflammation was induced after OVA-alum sensitization and OVA challenge, which significantly increased Th2-related cytokine levels, eosinophil infiltration, and goblet cell hyperplasia in the lung. However, these severe allergic symptoms were significantly decreased in T. spiralis-infected mice and T. spiralis ES protein-treated macrophages. Helminth infection and helminth ES proteins induce M2 macrophages. Adoptive transfer of macrophages obtained from helminth-infected mice and helminth ES protein-activated macrophages is an effective treatment for preventing and treating airway allergy in mice and is promising as a therapeutic for treating inflammatory diseases.

Epigenetic and transcriptional regulation of IL4-induced CCL17 production in human monocytes and murine macrophages

Interleukin 4 (IL4) is generally viewed as a Th2 cytokine capable of polarizing macrophages into an anti-inflammatory phenotype, whereas granulocyte macrophage-colony-stimulating factor (GM-CSF) is often viewed as a proinflammatory cytokine with part of this function due to its action on monocytes/macrophages. Paradoxically, these two cytokines act additively to enhance the in vitro differentiation of dendritic cells from precursors such as monocytes. One up-regulated marker of an IL4-polarized M2 macrophage is the chemokine (C-C motif) ligand 17 (CCL17), which we have recently reported to be induced by GM-CSF in monocytes/macrophages in an interferon regulatory factor 4 (IRF4)-dependent manner. In this study, we report that IL4 also induces CCL17 production by acting through IRF4 in human monocytes and murine macrophages. Furthermore, evidence is presented that IL4 up-regulates IRF4 expression at the epigenetic level by enhancing the expression and activity of jumonji domain-containing protein 3 (JMJD3) demethylase. Intriguingly, silencing the signal transducer and activator of transcription 6 (STAT6) gene led to a decrease in not only CCL17 formation, but also in that of its upstream regulators, JMJD3 and IRF4. Moreover, IL4 treatment of human monocytes resulted in an increased association of STAT6 to the promoter regions of the CCL17, IRF4, and JMJD3 genes. Thus, despite their vastly different functions, IL4 and GM-CSF appear to share elements of a common signaling pathway in regulating CCL17 production in human monocytes and murine macrophages.

NOX2-dependent ATM kinase activation dictates pro-inflammatory macrophage phenotype and improves effectiveness to radiation therapy

Although tumor-associated macrophages have been extensively studied in the control of response to radiotherapy, the molecular mechanisms involved in the ionizing radiation-mediated activation of macrophages remain elusive. Here we show that ionizing radiation induces the expression of interferon regulatory factor 5 (IRF5) promoting thus macrophage activation toward a pro-inflammatory phenotype. We reveal that the activation of the ataxia telangiectasia mutated (ATM) kinase is required for ionizing radiation-elicited macrophage activation, but also for macrophage reprogramming after treatments with γ-interferon, lipopolysaccharide or chemotherapeutic agent (such as cisplatin), underscoring the fact that the kinase ATM plays a central role during macrophage phenotypic switching toward a pro-inflammatory phenotype through the regulation of mRNA level and post-translational modifications of IRF5. We further demonstrate that NADPH oxidase 2 (NOX2)-dependent ROS production is upstream to ATM activation and is essential during this process. We also report that the inhibition of any component of this signaling pathway (NOX2, ROS and ATM) impairs pro-inflammatory activation of macrophages and predicts a poor tumor response to preoperative radiotherapy in locally advanced rectal cancer. Altogether, our results identify a novel signaling pathway involved in macrophage activation that may enhance the effectiveness of radiotherapy through the reprogramming of tumor-infiltrating macrophages.

IFN-γ Priming Effects on the Maintenance of Effector Memory CD4(+) T Cells and on Phagocyte Function: Evidences from Infectious Diseases

Although it has been established that effector memory CD4⁺ T cells play an important role in the protective immunity against chronic infections, little is known about the exact mechanisms responsible for their functioning and maintenance, as well as their effects on innate immune cells. Here we review recent data on the role of IFN-γ priming as a mechanism affecting both innate immune cells and effector memory CD4⁺ T cells. Suboptimal concentrations of IFN-γ are seemingly crucial for the optimization of innate immune cell functions (including phagocytosis and destruction of reminiscent pathogens), as well as for the survival and functioning of effector memory CD4⁺ T cells. Thus, IFN-γ priming can thus be considered an important bridge between innate and adaptive immunity.

Redefining the transcriptional regulatory dynamics of classically and alternatively activated macrophages by deepCAGE transcriptomics

Classically or alternatively activated macrophages (M1 and M2, respectively) play distinct and important roles for microbiocidal activity, regulation of inflammation and tissue homeostasis. Despite this, their transcriptional regulatory dynamics are poorly understood. Using promoter-level expression profiling by non-biased deepCAGE we have studied the transcriptional dynamics of classically and alternatively activated macrophages. Transcription factor (TF) binding motif activity analysis revealed four motifs, NFKB1_REL_RELA, IRF1,2, IRF7 and TBP that are commonly activated but have distinct activity dynamics in M1 and M2 activation. We observe matching changes in the expression profiles of the corresponding TFs and show that only a restricted set of TFs change expression. There is an overall drastic and transient up-regulation in M1 and a weaker and more sustainable up-regulation in M2. Novel TFs, such as Thap6, Maff, (M1) and Hivep1, Nfil3, Prdm1, (M2) among others, were suggested to be involved in the activation processes. Additionally, 52 (M1) and 67 (M2) novel differentially expressed genes and, for the first time, several differentially expressed long non-coding RNA (lncRNA) transcriptome markers were identified. In conclusion, the finding of novel motifs, TFs and protein-coding and lncRNA genes is an important step forward to fully understand the transcriptional machinery of macrophage activation.

Ex vivo and in vitro effect of serum amyloid a in the induction of macrophage M2 markers and efferocytosis of apoptotic neutrophils

Macrophages affect the magnitude and duration of inflammatory response in a functionally heterogeneous manner. The phenotype of macrophages is maintained through a reversible homeostatic mechanism. A number of determinants that modulate macrophage plasticity have been identified, although the precise mechanisms are not fully understood. In this study, we report that stimulation of isolated human blood monocytes and mouse bone marrow-derived macrophages with human serum amyloid A (SAA), a major acute-phase protein, leads to induced expression of macrophage M2 markers, including IL-10, Ym1, Fizz-1, MRC1, IL-1Rn, and CCL17. The same effect was observed with macrophages exposed to SAA in peritoneal cavity. SAA also increases arginase 1 activity and enhances macrophage efferocytosis of apoptotic neutrophils in mouse macrophages. The induction of M2 markers requires MyD88 and the activation of multiple signaling pathways, but it is independent of Stat6. SAA induces IFN regulatory factor (IRF)4 expression and increases its DNA-binding activity. Silencing IRF4 by small interfering RNA abrogates SAA-induced expression of the M2 markers. These results suggest a potential role for SAA to alter macrophage phenotype and modulate macrophage functions through an MyD88-dependent mechanism that involves IRF4-mediated transcription.

IFN-γ primes macrophage activation by increasing phosphatase and tensin homolog via downregulation of miR-3473b

The classical activation of macrophages, one of major innate effector cells, requires IFN-γ pretreatment (priming) and subsequent TLR stimuli (triggering). The priming effect of IFN-γ can promote macrophages to secrete higher level of proinflammatory cytokines but lower level of the anti-inflammatory cytokines, enhancing microbicidal and tumoricidal activity of macrophages. However, the underlying molecular mechanisms for IFN-γ-priming effect on macrophage activation remain to be fully understood. microRNAs (miRNAs) are now emerging as important regulators in immune response, including signaling transduction in immune cell function. In this study, we explored the effect of IFN-γ on miRNA expression profiling in macrophages and tried to identify the definite miRNA involved in the priming effect of IFN-γ. We discovered that miR-3473b, which was significantly downregulated after IFN-γ priming, could attenuate the priming effect of IFN-γ. miR-3473b promoted Akt/glycogen synthase kinase 3 signaling and IL-10 production through directly targeting phosphatase and tensin homolog (PTEN) to suppress activation of macrophages and inflammatory response. Our data indicate that IFN-γ beefs up macrophage innate response and cytotoxicity by downregulating miR-3473b to release PTEN from suppression, and then the increase of PTEN contributes to the full activation of IFN-γ-primed macrophages. Our results provide mechanistic insight to priming effect of IFN-γ on macrophage classical activation by identifying an IFN-γ/miR-3473b/PTEN regulatory loop in the regulation of macrophage function.

The M1 and M2 paradigm of macrophage activation: time for reassessment

Macrophages are endowed with a variety of receptors for lineage-determining growth factors, T helper (Th) cell cytokines, and B cell, host, and microbial products. In tissues, macrophages mature and are activated in a dynamic response to combinations of these stimuli to acquire specialized functional phenotypes. As for the lymphocyte system, a dichotomy has been proposed for macrophage activation: classic vs. alternative, also M1 and M2, respectively. In view of recent research about macrophage functions and the increasing number of immune-relevant ligands, a revision of the model is needed. Here, we assess how cytokines and pathogen signals influence their functional phenotypes and the evidence for M1 and M2 functions and revisit a paradigm initially based on the role of a restricted set of selected ligands in the immune response.

Diagnostic biomarkers are hidden in the infected host's epigenome

The success of our immune system depends on its ability to react efficiently, which in turn is supported by a large degree of plasticity as well as memory. Some aspects of this plasticity and memory are now known to be under epigenetic control - determined both by default, during differentiation, and by responses to environmental factors, including infectious agents. Thus, epigenetic marks in the immune system can occur as predetermined or as responsive marks and as such can potentially serve as diagnostic markers for disease susceptibility and disease progression or treatment response. Here, the authors review some examples of epigenetic control and epigenetic marks during the differentiation process of the immune system and memory formation, followed by some examples of epigenetic marks in the immune system subsequent to infection. These are used to illustrate the potential use of epigenetic marks as diagnostic markers in adverse immune system conditions and treatment thereof.

Association between inflammatory infiltrates and isolated monosomy 22/del(22q) in meningiomas

Meningiomas contain highly variable levels of infiltrating tissue macrophages (TiMa) and other immune cells. In this study we investigated the potential association between the number and immunophenotype of inflammatory and other immune cells infiltrating the tumor as evaluated by multiparameter flow cytometry, and the clinico-biological, cytogenetic and gene expression profile (GEP) of 75 meningioma patients. Overall, our results showed a close association between the amount and cellular composition of the inflammatory and other immune cell infiltrates and the cytogenetic profile of the tumors. Notably, tumors with isolated monosomy 22/del(22q) showed greater numbers of TiMa, NK cells and (recently)-activated CD69(+) lymphocytes versus meningiomas with diploid and complex karyotypes. In addition, in the former cytogenetic subgroup of meningiomas, tumor-infiltrating TiMa also showed a more activated and functionally mature phenotype, as reflected by a greater fraction of CD69(+), CD63(+), CD16(+) and CD33(+) cells. GEP at the mRNA level showed a unique GEP among meningiomas with an isolated monosomy 22/del(22q) versus all other cases, which consisted of increased expression of genes involved in inflammatory/immune response, associated with an M1 TiMa phenotype. Altogether, these results suggest that loss of expression of specific genes coded in chromosome 22 (e.g. MIF) is closely associated with an increased homing and potentially also anti-tumoral effect of TiMa, which could contribute to explain the better outcome of this specific good-prognosis cytogenetic subgroup of meningiomas.