Differential expression patterns of MafB and c-Maf in macrophages in vivo and in vitro

Bone Marrow Myeloid-Lymphatic Progenitors Expand Tumor Lymphatic Vasculature Through Cell Fusion

Background: Bone marrow (BM)-derived myeloid-lymphatic endothelial cell progenitors (M-LECPs) promote formation of tumor lymphatics that are responsible for metastasis to lymph nodes. The regenerative capacity of BM progenitors to other lineages is mediated through cell fusion, a process that delivers a pro-mitotic message directly to division-restricted cells. This suggested that M-LECPs might use a similar mechanism to induce division of lymphatic endothelial cells (LECs).

METHODS

To test this hypothesis, we determined expression of fusogenic markers in M-LECP produced in vitro and recruited to human or mouse tumors in vivo as well as quantified their fusion with LECs in both settings. Fusion in vivo was determined in female chimera mice grafted with male BM that have been implanted with MDA-MB-231 or EMT6 breast tumors. Co-staining for Y-chromosome and LEC-specific markers allowed us to quantify tumor lymphatic vessels fused with BM progenitors.

RESULTS

We found that both tumor-recruited and in-vitro-produced M-LECPs expressed multiple fusogenic regulators and possessed a significant fusogenic activity towards cultured and vessel-lining LECs. Y-chromosomes, a marker of fusion, were detected in nearly half of tumor lymphatics and were associated with mitotic division, vessel formation, and node metastasis. Both in vitro and in vivo assays showed dependency of fusion on Th2 and Toll-like receptor-4 (TLR4) pathways.

CONCLUSIONS

This novel mechanism of tumor lymphatic formation triggered by fusion with BM myeloid-lymphatic progenitors suggests a variety of new targets for inhibition of metastatic spread.

MAFB in macrophages regulates cold-induced neuronal density in brown adipose tissue

Transcription factor MAFB regulates various homeostatic functions of macrophages. This study explores the role of MAFB in brown adipose tissue (BAT) thermogenesis using macrophage-specific Mafb-deficient (Mafbf/f::LysM-Cre) mice. We find that Mafb deficiency in macrophages reduces thermogenesis, energy expenditure, and sympathetic neuron (SN) density in BAT under cold conditions. This phenotype features a proinflammatory environment that is characterized by macrophage/granulocyte accumulation, increases in interleukin-6 (IL-6) production, and IL-6 trans-signaling, which lead to decreases in nerve growth factor (NGF) expression and reduction in SN density in BAT. We confirm MAFB regulation of IL-6 expression using luciferase readout driven by IL-6 promoter in RAW-264.7 macrophage cell lines. Immunohistochemistry shows clustered organization of NGF-producing cells in BAT, which are primarily TRPV1+ vascular smooth muscle cells, as additionally shown using single-cell RNA sequencing and RT-qPCR of the stromal vascular fraction. Treating Mafbf/f::LysM-Cre mice with anti-IL-6 receptor antibody rescues SN density, body temperature, and energy expenditure.

Tumor microenvironment restricts IL-10 induced multipotent progenitors to myeloid-lymphatic phenotype

Lymphangiogenesis is induced by local pro-lymphatic growth factors and bone marrow (BM)-derived myeloid-lymphatic endothelial cell progenitors (M-LECP). We previously showed that M-LECP play a significant role in lymphangiogenesis and lymph node metastasis in clinical breast cancer (BC) and experimental BC models. We also showed that differentiation of mouse and human M-LECP can be induced through sequential activation of colony stimulating factor-1 (CSF-1) and Toll-like receptor-4 (TLR4) pathways. This treatment activates the autocrine interleukin-10 (IL-10) pathway that, in turn, induces myeloid immunosuppressive M2 phenotype along with lymphatic-specific proteins. Because IL-10 is implicated in differentiation of numerous lineages, we sought to determine whether this pathway specifically promotes the lymphatic phenotype or multipotent progenitors that can give rise to M-LECP among other lineages. Analyses of BM cells activated either by CSF-1/TLR4 ligands in vitro or orthotopic breast tumors in vivo showed expansion of stem/progenitor population and coincident upregulation of markers for at least four lineages including M2-macrophage, lymphatic endothelial, erythroid, and T-cells. Induction of cell plasticity and multipotency was IL-10 dependent as indicated by significant reduction of stem cell markers and those for multiple lineages in differentiated cells treated with anti-IL-10 receptor (IL-10R) antibody or derived from IL-10R knockout mice. However, multipotent CD11b+/Lyve-1+/Ter-119+/CD3e+ progenitors detected in BM appeared to split into a predominant myeloid-lymphatic fraction and minor subsets expressing erythroid and T-cell markers upon establishing tumor residence. Each sub-population was detected at a distinct intratumoral site. This study provides direct evidence for differences in maturation status between the BM progenitors and those reaching tumor destination. The study results suggest preferential tumor bias towards expansion of myeloid-lymphatic cells while underscoring the role of IL-10 in early BM production of multipotent progenitors that give rise to both hematopoietic and endothelial lineages.

Selective oxidative protection leads to tissue topological changes orchestrated by macrophage during ulcerative colitis

Ulcerative colitis is a chronic inflammatory bowel disorder with cellular heterogeneity. To understand the composition and spatial changes of the ulcerative colitis ecosystem, here we use imaging mass cytometry and single-cell RNA sequencing to depict the single-cell landscape of the human colon ecosystem. We find tissue topological changes featured with macrophage disappearance reaction in the ulcerative colitis region, occurring only for tissue-resident macrophages. Reactive oxygen species levels are higher in the ulcerative colitis region, but reactive oxygen species scavenging enzyme SOD2 is barely detected in resident macrophages, resulting in distinct reactive oxygen species vulnerability for inflammatory macrophages and resident macrophages. Inflammatory macrophages replace resident macrophages and cause a spatial shift of TNF production during ulcerative colitis via a cytokine production network formed with T and B cells. Our study suggests components of a mechanism for the observed macrophage disappearance reaction of resident macrophages, providing mechanistic hints for macrophage disappearance reaction in other inflammation or infection situations.

Biologic Mechanisms of Macrophage Phenotypes Responding to Infection and the Novel Therapies to Moderate Inflammation

Pro-inflammatory and anti-inflammatory types are the main phenotypes of the macrophage, which are commonly notified as M1 and M2, respectively. The alteration of macrophage phenotypes and the progression of inflammation are intimately associated; both phenotypes usually coexist throughout the whole inflammation stage, involving the transduction of intracellular signals and the secretion of extracellular cytokines. This paper aims to address the interaction of macrophages and surrounding cells and tissues with inflammation-related diseases and clarify the crosstalk of signal pathways relevant to the phenotypic metamorphosis of macrophages. On these bases, some novel therapeutic methods are proposed for regulating inflammation through monitoring the transition of macrophage phenotypes so as to prevent the negative effects of antibiotic drugs utilized in the long term in the clinic. This information will be quite beneficial for the diagnosis and treatment of inflammation-related diseases like pneumonia and other disorders involving macrophages.

Case report: Mafb promoter activity may define the alveolar macrophage dichotomy

Cre-LoxP system has been widely used to induce recombination of floxed genes of interest. Currently available macrophage promoter-specific Cre recombinase mice strains have various limitations that warrants the testing of additional Cre strains. V-maf musculoaponeurotic fibrosarcoma oncogene family, protein b -Cre (Mafb-Cre) mice label macrophages in most organs such as spleen, small intestine, lung, bone marrow, and peritoneal cavity. However, whether Mafb-Cre recombinase targets the gene recombination in alveolar macrophage remains untested. Here, we utilized Mafb^Cre/WTR26^mTmG/WT strain that expresses mTOM protein in all the cells of mouse body except for those that express Mafb-Cre-regulated mEGFP. We performed fluorescent microscopy and flow cytometry to analyze mTOM and mEGFP expression in alveolar macrophages from Mafb^Cre/WTR26^mTmG/WT mice. Our analyses revealed that the Mafb-Cre is active in only ~40% of the alveolar macrophages in an age-independent manner. While Mafb- (mTOM+/mEGFP-) and Mafb+ (mEGFP+) alveolar macrophages exhibit comparable expression of CD11b and CD11c surface markers, the surface expression of MHCII is elevated in the Mafb+ (mEGFP+) macrophages. The bone marrow-derived macrophages from Mafb^Cre/WTR26^mTmG/WT mice are highly amenable to Cre-LoxP recombination in vitro. The bone marrow depletion and reconstitution experiment revealed that ~98% of alveolar macrophages from Mafb^Cre/WTR26^mTmG/WT → WT chimera are amenable to the Mafb-Cre-mediated recombination. Finally, the Th2 stimulation and ozone exposure to the Mafb^Cre/WTR26^mTmG/WT mice promote the Mafb-Cre-mediated recombination in alveolar macrophages. In conclusion, while the Mafb-/Mafb+ dichotomy thwarts the use of Mafb-Cre for the induction of floxed alleles in the entire alveolar macrophage population, this strain provides a unique tool to induce gene deletion in alveolar macrophages that encounter Th2 microenvironment in the lung airspaces.

c-MAF coordinates enterocyte zonation and nutrient uptake transcriptional programs

Small intestinal villi are structural and functional units present in higher vertebrates and uniquely adapted to nutrient absorption. Villus enterocytes are organized in transcriptional "zones" dedicated to specialized tasks such as absorption of specific nutrients. We report that the transcription factor c-MAF is expressed in differentiated lower and mid-villus enterocytes and is a target of BMP signaling. Maf inactivation perturbed the villus zonation program by increasing carbohydrate-related transcripts while suppressing transcripts linked to amino-acid and lipid absorption. The formation of cytoplasmic lipid droplets, shuttling dietary fat to chylomicrons, was impaired upon Maf loss indicating its role in dietary lipid handling. Maf inactivation under homeostatic conditions expanded tuft cells and led to compensatory gut lengthening, preventing weight loss. However, delayed Maf-/- enterocyte maturation impaired weight recovery after acute intestinal injury, resulting in reduced survival. Our results identify c-MAF as a regulator of the intestinal villus zonation program, while highlighting the importance of coordination between stem/progenitor and differentiation programs for intestinal regeneration.

Single-cell transcriptome analysis of tumor immune microenvironment characteristics in colorectal cancer liver metastasis

BACKGROUND

Liver metastasis is the leading cause of death in colorectal cancer (CRC) patients, and the precise mechanisms remain unclear. In this study, single-cell RNA sequencing (scRNA-seq) was used to analyze the cellular and molecular heterogeneity between CRC primary lesion and corresponding liver metastasis, and to clarify the characteristics of the tumor microenvironment (TME) in synchronous liver metastasis of CRC.

METHODS

A case of microsatellite stable (MSS) sigmoid carcinoma with synchronous liver metastasis was selected, and tissues from the primary tumor and the liver metastasis were collected for scRNA-seq. The EdgeR package software was used to identify the differentially expressed genes between cells. Gene Set Enrichment Analysis (GSEA) was performed and the clusterProfiler R package was used for Gene Ontology (GO) enrichment analysis. The SCENIC and CellphoneDB packages were used to reconstruct the transcriptional regulatory networks and to analyze the intercellular interaction network, respectively.

RESULTS

Compared to the primary tumor, the proportion of myeloid cells in the metastatic tumor was significantly increased, while B cells and plasma cells were decreased. In the metastatic tumor, the myeloid-derived suppressor cell (MDSC) characteristic gene, mannose receptor C-type 1 (MRC1) and tumor associated macrophage 2 (TAM2)-related gene, were highly expressed. Furthermore, angiogenesis, oxidative phosphorylation, and endothelial mesenchymal transition (EMT) of myeloid cells were also significantly enhanced. There were less myeloid cells in primary tumors, and these were mainly monocytes and TAM1; while the number of TAM2 was significantly upregulated in the metastatic samples. In liver metastasis, the T cell population was exhausted, and this was accompanied by a significant increase in the number of CD4+ T cells and a decrease in the number of CD8+ T cells. Furthermore, some immune checkpoint molecules were highly expressed. Interactions between myeloid cells and other cell populations appeared to be strong.

CONCLUSIONS

The TME of CRC liver metastasis is significantly immunosuppressed. Interactions between myeloid cells and other cell populations in the TME contribute to the establishment of a pro-metastatic niche that promotes colonization and growth of CRC cells in the liver. TAMs may be a potential immunotherapeutic target for MSS CRC.

Transcription Factor MAFB as a Prognostic Biomarker for the Lung Adenocarcinoma

MAFB is a basic leucine zipper (bZIP) transcription factor specifically expressed in macrophages. We have previously identified MAFB as a candidate marker for tumor-associated macrophages (TAMs) in human and mouse models. Here, we analyzed single-cell sequencing data of patients with lung adenocarcinoma obtained from the GEO database (GSE131907). Analyzed data showed that general macrophage marker CD68 and macrophage scavenger receptor 1 (CD204) were expressed in TAM and lung tissue macrophage clusters, while transcription factor MAFB was expressed specifically in TAM clusters. Clinical records of 120 patients with lung adenocarcinoma stage I (n = 57), II (n = 21), and III (n = 42) were retrieved from Tsukuba Human Tissue Biobank Center (THB) in the University of Tsukuba Hospital, Japan. Tumor tissues from these patients were extracted and stained with anti-human MAFB antibody, and then MAFB-positive cells relative to the tissue area (MAFB+ cells/tissue area) were morphometrically quantified. Our results indicated that higher numbers of MAFB+ cells significantly correlated to increased local lymph node metastasis (nodal involvement), high recurrence rate, poor pathological stage, increased lymphatic permeation, higher vascular invasion, and pleural infiltration. Moreover, increased amounts of MAFB+ cells were related to poor overall survival and disease-free survival, especially in smokers. These data indicate that MAFB may be a suitable prognostic biomarker for smoker lung cancer patients.

Macrophage-Specific, Mafb-Deficient Mice Showed Delayed Skin Wound Healing

Macrophages play essential roles throughout the wound repair process. Nevertheless, mechanisms regulating the process are poorly understood. MAFB is specifically expressed in the macrophages in hematopoietic tissue and is vital to homeostatic function. Comparison of the skin wound repair rates in macrophage-specific, MAFB-deficient mice (Mafbf/f::LysM-Cre) and control mice (Mafbf/f) showed that wound healing was significantly delayed in the former. For wounded GFP knock-in mice with GFP inserts in the Mafb locus, flow cytometry revealed that their GFP-positive cells expressed macrophage markers. Thus, macrophages express Mafb at wound sites. Immunohistochemical (IHC) staining, proteome analysis, and RT-qPCR of the wound tissue showed relative downregulation of Arg1, Ccl12, and Ccl2 in Mafbf/f::LysM-Cre mice. The aforementioned genes were also downregulated in the bone marrow-derived, M2-type macrophages of Mafbf/f::LysM-Cre mice. Published single-cell RNA-Seq analyses showed that Arg1, Ccl2, Ccl12, and Il-10 were expressed in distinct populations of MAFB-expressing cells. Hence, the MAFB-expressing macrophage population is heterogeneous. MAFB plays the vital role of regulating multiple genes implicated in wound healing, which suggests that MAFB is a potential therapeutic target in wound healing.

Susceptibility genes of hyperuricemia and gout

Gout is a chronic metabolic disease that seriously affects human health. It is also a major challenge facing the world, which has brought a heavy burden to patients and society. Hyperuricemia (HUA) is the most important risk factor for gout. In recent years, with the improvement of living standards and the change of dietary habits, the incidence of gout in the world has increased dramatically, and gradually tends to be younger. An increasing number of studies have shown that gene mutations may play an important role in the development of HUA and gout. Therefore, we reviewed the existing literature and summarized the susceptibility genes and research status of HUA and gout, in order to provide reference for the early diagnosis, individualized treatment and the development of new targeted drugs of HUA and gout.

Proximal and Distal Regions of Pathogenic Th17 Related Chromatin Loci Are Sequentially Accessible During Pathogenicity of Th17

Pathogenic Th17, featured by their production of pro-inflammatory cytokines, are considered as a key player in most autoimmune diseases. The transcriptome of them is obviously distinct from that of conventional regulatory Th17. However, chromatin accessibility of the two Th17 groups have not been comprehensively compared yet. Here, we found that their chromatin-accessible regions(ChARs) significantly correlated with the expression of related genes, indicating that they might engage in the regulation of these genes. Indeed, pathogenic Th17 specific ChARs (patho-ChARs) exhibited a significant distribution preference in TSS-proximal region. We further filtered the patho-ChARs based on their conservation among mammalians or their concordance with the expression of their related genes. In either situation, the filtered patho-ChARs also showed a preference for TSS-proximal region. Enrichment of expression concordant patho-ChARs related genes suggested that they might involve in the pathogenicity of Th17. Thus, we also examined all ChARs of patho-ChARs related genes, and defined an opening ChAR set according to their changes in the Th17 to Th1 conversion. Interestingly, these opening ChARs displayed a sequential accessibility change from TSS-proximal region to TSS-distal region. Meanwhile, a group of patho-TFs (transcription factors) were identified based on the appearance of their binding motifs in the opening ChARs. Consistently, some of them also displayed a similar preference for binding the TSS-proximal region. Single-cell transcriptome analysis further confirmed that these patho-TFs were involved in the generation of pathogenic Th17. Therefore, our results shed light on a new regulatory mechanism underlying the generation of pathogenic Th17, which is worth to be considered for autoimmune disease therapy.

Single-cell atlas of peripheral blood mononuclear cells from pregnant women

Background

During pregnancy, mother–child interactions trigger a variety of subtle changes in the maternal body, which may be reflected in the status of peripheral blood mononuclear cells (PBMCs). Although these cells are easy to access and monitor, a PBMC atlas for pregnant women has not yet been constructed.

Methods

We applied single‐cell RNA sequencing (scRNA‐seq) to profile 198,356 PBMCs derived from 136 pregnant women (gestation weeks 6 to 40) and a control cohort. We also used scRNA‐seq data to establish a transcriptomic clock and thereby predicted the gestational age of normal pregnancy.

Results

We identified reconfiguration of the peripheral immune cell phenotype during pregnancy, including interferon‐stimulated gene upregulation, activation of RNA splicing‐related pathways and immune activity of cell subpopulations. We also developed a cell‐type‐specific model to predict gestational age of normal pregnancy.

Conclusions

We constructed a single‐cell atlas of PBMCs in pregnant women spanning the entire gestation period, which should help improve our understanding of PBMC composition turnover in pregnant women.

Association of Ligamentum Flavum Hypertrophy with Adolescent Idiopathic Scoliosis Progression-Comparative Microarray Gene Expression Analysis

The role of the ligamentum flavum (LF) in the pathogenesis of adolescent idiopathic scoliosis (AIS) is not well understood. Using magnetic resonance imaging (MRI), we investigated the degrees of LF hypertrophy in 18 patients without scoliosis and on the convex and concave sides of the apex of the curvature in 22 patients with AIS. Next, gene expression was compared among neutral vertebral LF and LF on the convex and concave sides of the apex of the curvature in patients with AIS. Histological and microarray analyses of the LF were compared among neutral vertebrae (control) and the LF on the apex of the curvatures. The mean area of LF in the without scoliosis, apical concave, and convex with scoliosis groups was 10.5, 13.5, and 20.3 mm2, respectively. There were significant differences among the three groups (p < 0.05). Histological analysis showed that the ratio of fibers (Collagen/Elastic) was significantly increased on the convex side compared to the concave side (p < 0.05). Microarray analysis showed that ERC2 and MAFB showed significantly increased gene expression on the convex side compared with those of the concave side and the neutral vertebral LF cells. These genes were significantly associated with increased expression of collagen by LF cells (p < 0.05). LF hypertrophy was identified in scoliosis patients, and the convex side was significantly more hypertrophic than that of the concave side. ERC2 and MAFB genes were associated with LF hypertrophy in patients with AIS. These phenomena are likely to be associated with the progression of scoliosis.

Radiation inducible MafB gene is required for thymic regeneration

The thymus facilitates mature T cell production by providing a suitable stromal microenvironment. This microenvironment is impaired by radiation and aging which lead to immune system disturbances known as thymic involution. Young adult thymus shows thymic recovery after such involution. Although various genes have been reported for thymocytes and thymic epithelial cells in such processes, the roles of stromal transcription factors in these remain incompletely understood. MafB (v-maf musculoaponeurotic fibrosarcoma oncogene homolog B) is a transcription factor expressed in thymic stroma and its expression was induced a day after radiation exposure. Hence, the roles of mesenchymal MafB in the process of thymic regeneration offers an intriguing research topic also for radiation biology. The current study investigated whether MafB plays roles in the adult thymus. MafB/green fluorescent protein knock-in mutant (MafB^+/GFP) mice showed impaired thymic regeneration after the sublethal irradiation, judged by reduced thymus size, total thymocyte number and medullary complexity. Furthermore, IL4 was induced after irradiation and such induction was reduced in mutant mice. The mutants also displayed signs of accelerated age-related thymic involution. Altogether, these results suggest possible functions of MafB in the processes of thymic recovery after irradiation, and maintenance during aging.

How Macrophages Become Transcriptionally Dysregulated: A Hidden Impact of Antitumor Therapy

Tumor-associated macrophages (TAMs) are the essential components of the tumor microenvironment. TAMs originate from blood monocytes and undergo pro- or anti-inflammatory polarization during their life span within the tumor. The balance between macrophage functional populations and the efficacy of their antitumor activities rely on the transcription factors such as STAT1, NF-κB, IRF, and others. These molecular tools are of primary importance, as they contribute to the tumor adaptations and resistance to radio- and chemotherapy and can become important biomarkers for theranostics. Herein, we describe the major transcriptional mechanisms specific for TAM, as well as how radio- and chemotherapy can impact gene transcription and functionality of macrophages, and what are the consequences of the TAM-tumor cooperation.

Identification and characterization of a novel adiponectin receptor agonist adipo anti-inflammation agonist and its anti-inflammatory effects in vitro and in vivo

BACKGROUND AND PURPOSE

Adiponectin (APN) is an adipokine secreted from adipocytes that binds to APN receptors AdipoR1 and AdipoR2 and exerts an anti-inflammatory response through mechanisms not fully understood. There is a need to develop small molecules that activate AdipoR1 and AdipoR2 and to be used to inhibit the inflammatory response in lipopolysaccharide (LPS)-induced endotoxemia and other inflammatory disorders.

EXPERIMENTAL APPROACH

We designed 10 new structural analogues of an AdipoR agonist, AdipoRon (APR), and assessed their anti-inflammatory properties. Bone marrow-derived macrophages (BMMs) and peritoneal macrophages (PEMs) were isolated from mice. Levels of pro-inflammatory cytokines were measured by reverse transcription and real-time quantitative polymerase chain reaction (qRT-PCR), enzyme-linked immunosorbent assay (ELISA) and microarray in LPS-induced endotoxemia mice and diet-induced obesity (DIO) mice in which systemic inflammation prevails. Western blotting, immunohistochemistry (IHC), siRNA interference and immunoprecipitation were used to detect signalling pathways.

KEY RESULTS

A novel APN receptor agonist named adipo anti-inflammation agonist (AdipoAI) strongly suppresses inflammation in DIO and endotoxemia mice, as well as in cultured macrophages. We also found that AdipoAI attenuated the association of AdipoR1 and APPL1 via myeloid differentiation marker 88 (MyD88) signalling, thus inhibiting activation of nuclear factor kappa B (NF-κB), mitogen-activated protein kinase (MAPK) and c-Maf pathways and limiting the production of pro-inflammatory cytokines in LPS-induced macrophages.

CONCLUSION AND IMPLICATIONS

AdipoAI is a promising alternative therapeutic approach to APN and APR to suppress inflammation in LPS-induced endotoxemia and other inflammatory disorders via distinct signalling pathways.

Transcriptional, Epigenetic and Metabolic Programming of Tumor-Associated Macrophages

Macrophages are key innate immune cells in the tumor microenvironment (TME) that regulate primary tumor growth, vascularization, metastatic spread and tumor response to various types of therapies. The present review highlights the mechanisms of macrophage programming in tumor microenvironments that act on the transcriptional, epigenetic and metabolic levels. We summarize the latest knowledge on the types of transcriptional factors and epigenetic enzymes that control the direction of macrophage functional polarization and their pro- and anti-tumor activities. We also focus on the major types of metabolic programs of macrophages (glycolysis and fatty acid oxidation), and their interaction with cancer cells and complex TME. We have discussed how the regulation of macrophage polarization on the transcriptional, epigenetic and metabolic levels can be used for the efficient therapeutic manipulation of macrophage functions in cancer.

Transcription factor c-Maf is a checkpoint that programs macrophages in lung cancer

Macrophages have been linked to tumor initiation, progression, metastasis, and treatment resistance. However, the transcriptional regulation of macrophages driving the protumor function remains elusive. Here, we demonstrate that the transcription factor c-Maf is a critical controller for immunosuppressive macrophage polarization and function in cancer. c-Maf controls many M2-related genes and has direct binding sites within a conserved noncoding sequence of the Csf-1r gene and promotes M2-like macrophage-mediated T cell suppression and tumor progression. c-Maf also serves as a metabolic checkpoint regulating the TCA cycle and UDP-GlcNAc biosynthesis, thus promoting M2-like macrophage polarization and activation. Additionally, c-Maf is highly expressed in tumor-associated macrophages (TAMs) and regulates TAM immunosuppressive function. Deletion of c-Maf specifically in myeloid cells results in reduced tumor burden with enhanced antitumor T cell immunity. Inhibition of c-Maf partly overcomes resistance to anti-PD-1 therapy in a subcutaneous LLC tumor model. Similarly, c-Maf is expressed in human M2 and tumor-infiltrating macrophages/monocytes as well as circulating monocytes of human non-small cell lung carcinoma (NSCLC) patients and critically regulates their immunosuppressive activity. The natural compound β-glucan downregulates c-Maf expression on macrophages, leading to enhanced antitumor immunity in mice. These findings establish a paradigm for immunosuppressive macrophage polarization and transcriptional regulation by c-Maf and suggest that c-Maf is a potential target for effective tumor immunotherapy.

Transcription factor MafB is a marker of tumor-associated macrophages in both mouse and humans

The transcription factor MafB is specifically expressed in macrophages. We have recently demonstrated that MafB is expressed in anti-inflammatory alternatively activated M2 macrophages in vitro. Tumor-associated macrophages (TAMs) are a subset of M2 type macrophages that can promote immunosuppressive activity, induce angiogenesis, and promote tumor cell proliferation. To examine whether MafB express in TAMs, we analyzed green fluorescent protein (GFP) expression in Lewis lung carcinoma tumors of MafB-GFP knock-in heterozygous mice. FACS analysis demonstrated GFP fluorescence in cells positive for macrophage-markers (F4/80, CD11b, CD68, and CD204). Moreover, quantitative RT-PCR analysis with F4/80⁺GFP⁺ and F4/80⁺GFP^- sorted cells showed that the GFP-positive macrophages express IL-10, Arg-1, and TNF-α, which were known to be expressed in TAMs. These results indicate that MafB is expressed in TAMs. Furthermore, immunostaining analysis using an anti-MAFB antibody revealed that MAFB is expressed in CD204-and CD68-positive macrophages in human lung cancer samples. In conclusion, MafB can be a suitable marker of TAMs in both mouse and human tumor tissues.

Role of MafB in macrophages

The transcription factor MafB regulates macrophage differentiation. However, studies on the phenotype of Mafb-deficient macrophages are still limited. Recently, it was shown that the specific expression of MafB permits macrophages to be distinguished from dendritic cells. In addition, MafB has been reported to be involved in various diseases related to macrophages. Studies using macrophage-specific Mafb-deficient mice show that MafB is linked to atherosclerosis, autoimmunity, obesity, and ischemic stroke, all of which exhibit macrophage abnormality. Therefore, MafB is hypothesized to be indispensable for the regulation of macrophages to maintain systemic homeostasis and may serve as an innovative target for treating macrophage-related diseases.

Maf expression in human macrophages and lymph node sinus macrophages in patients with esophageal cancer

The large Maf transcription factors are expressed in immune cells including macrophages and lymphocytes. To investigate the distribution of Maf expression in human organs, immunostaining for Maf was performed using sections of several human organs. High Maf expression was seen in the nucleus of macrophages in the gastrointestinal tract and lymph node sinus macrophages (LySMs). Then, we assessed whether Maf expression in LySMs was correlated with CD169 expression and the clinical prognosis in patients with esophageal cancer. Maf expression was associated with CD169 expression, but Maf expression in LySMs was not associated with the clinical course in patients with esophageal cancer. We determined which cytokines stimulate Maf expression using cultured macrophages. Immunocytochemistry showed that Maf expression was significantly elevated by interferon-γ. These results are the first report of Maf expression in human samples. Maf expression may be a marker for the macrophage population in humans.

Loss of MafA and MafB expression promotes islet inflammation

Maf transcription factors are critical regulators of beta-cell function. We have previously shown that reduced MafA expression in human and mouse islets is associated with a pro-inflammatory gene signature. Here, we investigate if the loss of Maf transcription factors induced autoimmune processes in the pancreas. Transcriptomics analysis showed expression of pro-inflammatory as well as immune cell marker genes. However, clusters of CD4+ T and B220+ B cells were associated primarily with adult MafA^−/−MafB^+/−, but not MafA^−/− islets. MafA expression was detected in the thymus, lymph nodes and bone marrow suggesting a novel role of MafA in regulating immune-cell function. Analysis of pancreatic lymph node cells showed activation of CD4+ T cells, but lack of CD8+ T cell activation which also coincided with an enrichment of naïve CD8+ T cells. Further analysis of T cell marker genes revealed a reduction of T cell receptor signaling gene expression in CD8, but not in CD4+ T cells, which was accompanied with a defect in early T cell receptor signaling in mutant CD8+ T cells. These results suggest that loss of MafA impairs both beta- and T cell function affecting the balance of peripheral immune responses against islet autoantigens, resulting in local inflammation in pancreatic islets.

Functional Urate-Associated Genetic Variants Influence Expression of lincRNAs LINC01229 and MAFTRR

Genetic variation in the genomic regulatory landscape likely plays a crucial role in the pathology of disease. Non-coding variants associated with disease can influence the expression of long intergenic non-coding RNAs (lincRNAs), which in turn function in the control of protein-coding gene expression. Here, we investigate the function of two independent serum urate-associated signals (SUA1 and SUA2) in close proximity to lincRNAs and an enhancer that reside ∼60 kb and ∼300 kb upstream of MAF, respectively. Variants within SUA1 are expression quantitative trait loci (eQTL) for LINC01229 and MAFTRR, both co-expressed with MAF. We have also identified that variants within SUA1 are trans-eQTL for genes that are active in kidney- and serum urate-relevant pathways. Serum urate-associated variants rs4077450 and rs4077451 within SUA2 lie within an enhancer that recruits the transcription factor HNF4α and forms long range interactions with LINC01229 and MAFTRR. The urate-raising alleles of rs4077450 and rs4077451 increase enhancer activity and associate with increased expression of LINC01229. We show that the SUA2 enhancer region drives expression in the zebrafish pronephros, recapitulating endogenous MAF expression. Depletion of MAFTRR and LINC01229 in HEK293 cells in turn lead to increased MAF expression. Collectively, our results are consistent with serum urate variants mediating long-range transcriptional regulation of the lincRNAs LINC01229 and MAFTRR and urate relevant genes (e.g., SLC5A8 and EHHADH) in trans.

Macrophages Switch Their Phenotype by Regulating Maf Expression during Different Phases of Inflammation

Macrophages manifest distinct phenotype according to the organs in which they reside. In addition, they flexibly switch their character in adaptation to the changing environment. However, the molecular basis that explains the conversion of the macrophage phenotype has so far been unexplored. We find that CD169⁺ macrophages change their phenotype by regulating the level of a transcription factor Maf both in vitro and in vivo in C57BL/6J mice. When CD169⁺ macrophages were exposed to bacterial components, they expressed an array of acute inflammatory response genes in Maf-dependent manner and simultaneously start to downregulate Maf. This Maf suppression is dependent on accelerated degradation through proteasome pathway and microRNA-mediated silencing. The downregulation of Maf unlocks the NF-E2-related factor 2-dominant, cytoprotective/antioxidative program in the same macrophages. The present study provides new insights into the previously unanswered question of how macrophages initiate proinflammatory responses while retaining their capacity to repair injured tissues during inflammation.

The transcription factor cMaf is targeted by mTOR, and regulates the inflammatory response via the TLR4 signaling pathway

cMaf is a leucine-zipper transcription factor that is involved in cell differentiation, oncogenic transformation, and human diseases; however, the functions of cMaf in inflammatory responses in macrophages are still not fully understood. Western blot analysis showed that cMaf expression was induced by lipopolysaccharide (LPS) stimulation in mouse macrophages. An enzyme-linked immunosorbent assay was performed to detect the level of expression of inflammatory cytokines after knockdown of cMaf expression in macrophages using a small interfering RNA (siRNA). Signaling pathway inhibitor analyses indicated that extracellular signal-related kinase and phosphoinositide 3-kinase contribute to mammalian target of rapamycin phosphorylation (mTOR), which controls cMaf expression at the translational level by regulating the expression of eIF4E-binding protein 1 and S6 ribosomal kinase 1 in response to Toll-like receptor 4 signaling. Histopathological findings of the lung and a survival analysis showed that mice transplanted with cMaf-knockdown macrophages were more susceptible to LPS challenge. Taken together, our study revealed that the control of cMaf expression at the translational level by mTOR regulated the expression of inflammatory genes in response to LPS challenge. Moreover, cMaf protected mice from septic shock indicating that cMaf may improve host fitness, thereby enabling the survival of certain infectious diseases.

Transcriptional mechanisms that control expression of the macrophage colony-stimulating factor receptor locus

The proliferation, differentiation, and survival of cells of the macrophage lineage depends upon signals from the macrophage colony-stimulating factor (CSF) receptor (CSF1R). CSF1R is expressed by embryonic macrophages and induced early in adult hematopoiesis, upon commitment of multipotent progenitors to the myeloid lineage. Transcriptional activation of CSF1R requires interaction between members of the E26 transformation-specific family of transcription factors (Ets) (notably PU.1), C/EBP, RUNX, AP-1/ATF, interferon regulatory factor (IRF), STAT, KLF, REL, FUS/TLS (fused in sarcoma/ranslocated in liposarcoma) families, and conserved regulatory elements within the mouse and human CSF1R locus. One element, the Fms-intronic regulatory element (FIRE), within intron 2, is conserved functionally across all the amniotes. Lineage commitment in multipotent progenitors also requires down-regulation of specific transcription factors such as MYB, FLI1, basic leucine zipper transcriptional factor ATF-like (BATF3), GATA-1, and PAX5 that contribute to differentiation of alternative lineages and repress CSF1R transcription. Many of these transcription factors regulate each other, interact at the protein level, and are themselves downstream targets of CSF1R signaling. Control of CSF1R transcription involves feed–forward and feedback signaling in which CSF1R is both a target and a participant; and dysregulation of CSF1R expression and/or function is associated with numerous pathological conditions. In this review, we describe the regulatory network behind CSF1R expression during differentiation and development of cells of the mononuclear phagocyte system.