Autocrine VEGF-B signaling maintains lipid synthesis and mitochondrial fitness to support T cell immune responses.

T cells rewire their metabolic activities to meet the demand of immune responses, but how to coordinate the immune response by metabolic regulators in activated T cells is unknown. Here, we identified autocrine VEGF-B as a metabolic regulator to control lipid synthesis and maintain the integrity of the mitochondrial inner membrane for the survival of activated T cells. Disruption of autocrine VEGF-B signaling in T cells reduced cardiolipin mass, resulting in mitochondrial damage, with increased apoptosis and reduced memory development. The addition of cardiolipin or modulating VEGF-B signaling improved T cell mitochondrial fitness and survival. Autocrine VEGF-B signaling through GA-binding protein α (GABPα) induced sentrin/SUMO-specific protease 2 (SENP2) expression, which further de-SUMOylated PPARγ and enhanced phospholipid synthesis, leading to a cardiolipin increase in activated T cells. These data suggest that autocrine VEGF-B mediates a signal to coordinate lipid synthesis and mitochondrial fitness with T cell activation for survival and immune response. Moreover, autocrine VEGF-B signaling in T cells provides a therapeutic target against infection and tumors as well as an avenue for the treatment of autoimmune diseases.

Influenza virus causes lung immunopathology through down-regulating PPARγ activity in macrophages.

Fatal influenza (flu) virus infection often activates excessive inflammatory signals, leading to multi-organ failure and death, also referred to as cytokine storm. PPARγ (Peroxisome proliferator-activated receptor gamma) agonists are well-known candidates for cytokine storm modulation. The present study identified that influenza infection reduced PPARγ expression and decreased PPARγ transcription activity in human alveolar macrophages (AMs) from different donors. Treatment with PPARγ agonist Troglitazone ameliorated virus-induced proinflammatory cytokine secretion but did not interfere with the IFN-induced antiviral pathway in human AMs. In contrast, PPARγ antagonist and knockdown of PPARγ in human AMs further enhanced virus-stimulated proinflammatory response. In a mouse model of influenza infection, flu virus dose-dependently reduced PPARγ transcriptional activity and decreased expression of PPARγ. Moreover, PPARγ agonist troglitazone significantly reduced high doses of influenza infection-induced lung pathology. In addition, flu infection reduced PPARγ expression in all mouse macrophages, including AMs, interstitial macrophages, and bone-marrow-derived macrophages but not in alveolar epithelial cells. Our results indicate that the influenza virus specifically targets the PPARγ pathway in macrophages to cause acute injury to the lung.

Interaction between proteins of the PPARγ and NFκB immune response pathways and rotavirus non-structural proteins.

Cells infected with MA104 rotavirus and/or transfected with plasmids expressing NSP proteins, were analyzed for expression of cellular proteins related to NFκB and PPARγ pathways and evaluated through the ELISA, luminescence, flow cytometry and Western blot techniques. The association between cellular and viral (NSPs) proteins was examined by ELISA, epifluorescence and confocal microscopy techniques. It was observed that NSP1 protein interacts with RXR, NSP1, and NSP3 with PPARγ, NSP2 with p-IKKα/ß and NSP5 with NFκB proteins. We have found that phosphorylated PPARγ is localized in cytoplasm and transcriptional activity of PPRE is diminished. These results lead to the conclusion, that RRV activates the proinflammatory pathway, increasing the expression of NFκB and possibly by PPARγ phosphorylation, its translocation to the nucleus is impeded, thus inactivating the proinflammatory pathway. Keywords: rotavirus; PPARγ; NFκB; NSPs; RRV.

Macrophages activated by hepatitis B virus have distinct metabolic profiles and suppress the virus via IL-1ß to downregulate PPARα and FOXO3.

Macrophages display phenotypic plasticity and can be induced by hepatitis B virus (HBV) to undergo either M1-like pro-inflammatory or M2-like anti-inflammatory polarization. Here, we report that M1-like macrophages stimulated by HBV exhibit a strong HBV-suppressive effect, which is diminished in M2-like macrophages. Transcriptomic analysis reveals that HBV induces the expression of interleukin-1ß (IL-1ß) in M1-like macrophages, which display a high oxidative phosphorylation (OXPHOS) activity distinct from that of conventional M1-like macrophages. Further analysis indicates that OXPHOS attenuates the expression of IL-1ß, which suppresses the expression of peroxisome proliferator-activated receptor α (PPARα) and forkhead box O3 (FOXO3) in hepatocytes to suppress HBV gene expression and replication. Moreover, multiple HBV proteins can induce the expression of IL-1ß in macrophages. Our results thus indicate that macrophages can respond to HBV by producing IL-1ß to suppress HBV replication. However, HBV can also metabolically reprogram macrophages to enhance OXPHOS to minimize this host antiviral response.

Bioinformatics and in-silico findings reveal medical features and pharmacological targets of biochanin A against colorectal cancer and COVID-19.

Severe mortality due to the COVID-19 pandemic resulted from the lack of effective treatment. Although COVID-19 vaccines are available, their side effects have become a challenge for clinical use in patients with chronic diseases, especially cancer patients. In the current report, we applied network pharmacology and systematic bioinformatics to explore the use of biochanin A in patients with colorectal cancer (CRC) and COVID-19 infection. Using the network pharmacology approach, we identified two clusters of genes involved in immune response (IL1A, IL2, and IL6R) and cell proliferation (CCND1, PPARG, and EGFR) mediated by biochanin A in CRC/COVID-19 condition. The functional analysis of these two gene clusters further illustrated the effects of biochanin A on interleukin-6 production and cytokine-cytokine receptor interaction in CRC/COVID-19 pathology. In addition, pathway analysis demonstrated the control of PI3K-Akt and JAK-STAT signaling pathways by biochanin A in the treatment of CRC/COVID-19. The findings of this study provide a therapeutic option for combination therapy against COVID-19 infection in CRC patients.

Emerging perspectives on mitochondrial dysfunctioning and inflammation in epileptogenesis.

INTRODUCTION: Mitochondrial dysfunction is a common denominator of neuroinflammation recognized by neuronal oxidative stress-mediated apoptosis that is well recognized by common intracellular molecular pathway-interlinked neuroinflammation and mitochondrial oxidative stress, a feature of epileptogenesis. In addition, the neuronal damage in the epileptic brain corroborated the concept of brain injury-mediated neuroinflammation, further providing an interlink between inflammation, mitochondrial dysfunction, and oxidative stress in epilepsy. MATERIALS AND METHODS: A systematic literature review of Bentham, Scopus, PubMed, Medline, and EMBASE (Elsevier) databases was carried out to provide evidence of preclinical and clinically used drugs targeting such nuclear, cytosolic, and mitochondrial proteins suggesting that the correlation of mechanisms linked to neuroinflammation has been elucidated in the current review. Despite that, the evidence of elevated levels of inflammatory mediators and pro-apoptotic protein levels can provide the correlation of inflammatory responses often concerned with hyperexcitability attributing to the fact that mitochondrial redox mechanisms and higher susceptibilities to neuroinflammation result from repetitive recurring epileptic seizures. Therefore, providing an understanding of seizure-induced pathological changes read by activating neuroinflammatory cascades like NF-kB, RIPK, MAPK, ERK, JNK, and JAK-STAT signaling further related to mitochondrial damage promoting hyperexcitability. CONCLUSION: The current review highlights the further opportunity for establishing therapeutic interventions underlying the apparent correlation of neuroinflammation mediated mitochondrial oxidative stress might contribute to common intracellular mechanisms underlying a future prospective of drug treatment targeting mitochondrial dysfunction linked to the neuroinflammation in epilepsy.

PPARG-mediated ferroptosis in dendritic cells limits antitumor immunity.

Dendritic cells (DCs) are antigen-presenting cells of the immune system, which play a key role in antitumor immunity by activating cytotoxic T cells. Here, we report that elevated ferroptosis, a lipid peroxidation-mediated cell death, impairs the maturation of DCs and their function in tumor suppression. Ferroptosis is selectively induced in DCs by the GXP4 inhibitor RSL3, but not the SLC7A11 inhibitor erastin. Ferroptotic DCs lose their ability to secrete pro-inflammatory cytokines (TNF and IL6) and express MHC class I in response to the maturation signal of lipopolysaccharide. Moreover, ferroptotic DCs fail to induce CD8+ T cells to produce IFNG/IFNγ. Mechanistically, PPARG/PPARγ, a nuclear receptor involved in the regulation of lipid metabolism, is responsible for RSL3-induced ferroptosis in DCs. Consequently, the genetic depletion of PPARG restores the maturation and function of DCs. Using immunogenic cell death-based DC vaccine models, we further demonstrate that PPARG-mediated ferroptosis of DCs limits antitumor immunity in mice. Together, these findings demonstrate a novel role of ferroptotic DCs in driving an immunosuppressive tumor microenvironment.

A2E-induced inflammation and angiogenesis in RPE cells in vitro are modulated by PPAR-α, -ß/δ, -γ, and RXR antagonists and by norbixin.

N-retinylidene-N-retinylethanolamine (A2E) plays a central role in age-related macular degeneration (AMD) by inducing angiogenesis and inflammation. A2E effects are mediated at least partly via the retinoic acid receptor (RAR)-α. Here we show that A2E binds and transactivates also peroxisome proliferator-activated receptors (PPAR) and retinoid X receptors (RXR). 9'-cis-norbixin, a di-apocarotenoid is also a ligand of these nuclear receptors (NR). Norbixin inhibits PPAR and RXR transactivation induced by A2E. Moreover, norbixin reduces protein kinase B (AKT) phosphorylation, NF-κB and AP-1 transactivation and mRNA expression of the inflammatory interleukins (IL) -6 and -8 and of vascular endothelial growth factor (VEGF) enhanced by A2E. By contrast, norbixin increases matrix metalloproteinase 9 (MMP9) and C-C motif chemokine ligand 2 (CCL2) mRNA expression in response to A2E. Selective PPAR-α, -ß/δ and -γ antagonists inhibit the expression of IL-6 and IL-8 while only the antagonist of PPAR-γ inhibits the transactivation of NF-κB following A2E exposure. In addition, a cocktail of all three PPARs antagonists and also HX531, an antagonist of RXR reproduce norbixin effects on inflammation. Altogether, A2E's deleterious biological effects could be inhibited through PPAR and RXR regulation. Moreover, the modulation of these NR by norbixin may open new avenues for the treatment of AMD.

Anti-inflammatory effects of oleic acid and the anthocyanin keracyanin alone and in combination: effects on monocyte and macrophage responses and the NF-κB pathway.

Monocyte recruitment and activation of macrophages are essential for homeostasis but are also related to the development and progression of cardiometabolic diseases. The management of inflammation with dietary components has been widely investigated. Two components that may influence inflammation are unsaturated fatty acids such as oleic acid (OA; 18:1cis-9) and antioxidant compounds like anthocyanins. Molecular and metabolic effects of such bioactive compounds are usually investigated in isolation, whereas they may be present in combination in foods or the diet. Considering this, we aimed to analyze the effects of OA and the anthocyanin keracyanin (AC) alone and in combination on toll-like receptor-mediated inflammatory responses in monocytes and macrophages. For this, THP-1-derived macrophages and monocytes were exposed to 3 treatments: OA, AC, or the combination (OAAC) and then stimulated with lipopolysaccharide. Inflammation-related gene expression and protein concentrations of IL-1ß, TNF-α, IL-6, MCP-1, and IL-10 were assessed. Also, NFκBp65, IκBα, and PPAR-γ protein expression were determined. OA, AC, and OAAC decreased pNFκBp65, PPARγ, IκBα, TNF-α, IL-1ß, IL-6, and MCP-1 and increased IL-10. MCP-1 protein expression was lower with OAAC than with either OA and AC alone. Compared to control, OAAC decreased mRNA for TLR4, IκKα, IκBα, NFκB1, MCP-1, TNF-α, IL-6, and IL-1ß more than OA or AC did alone. Also, IL-10 mRNA was increased by OAAC compared with control, OA, and AC. In summary, OA and AC have anti-inflammatory effects individually but their combination (OAAC) exerts a greater effect.

PPARγ is essential for the development of bone marrow erythroblastic island macrophages and splenic red pulp macrophages.

Tissue-resident macrophages play a crucial role in maintaining homeostasis. Macrophage progenitors migrate to tissues perinatally, where environmental cues shape their identity and unique functions. Here, we show that the absence of PPARγ affects neonatal development and VCAM-1 expression of splenic iron-recycling red pulp macrophages (RPMs) and bone marrow erythroblastic island macrophages (EIMs). Transcriptome analysis of the few remaining Pparg-deficient RPM-like and EIM-like cells suggests that PPARγ is required for RPM and EIM identity, cell cycling, migration, and localization, but not function in mature RPMs. Notably, Spi-C, another transcription factor implicated in RPM development, was not essential for neonatal expansion of RPMs, even though the transcriptome of Spic-deficient RPMs was strongly affected and indicated a loss of identity. Similarities shared by Pparg- and Spic-deficient RPM-like cells allowed us to identify pathways that rely on both factors. PPARγ and Spi-C collaborate in inducing transcriptional changes, including VCAM-1 and integrin αD expression, which could be required for progenitor retention in the tissue, allowing access to niche-related signals that finalize differentiation.

Cardiolipin-mediated PPARγ S112 phosphorylation impairs IL-10 production and inflammation resolution during bacterial pneumonia.

Bacterial pneumonia is a global healthcare burden, and unwarranted inflammation is suggested as an important cause of mortality. Optimum levels of the anti-inflammatory cytokine IL-10 are essential to reduce inflammation and improve survival in pneumonia. Elevated levels of the mitochondrial-DAMP cardiolipin (CL), reported in tracheal aspirates of pneumonia patients, have been shown to block IL-10 production from lung MDSCs. Although CL-mediated K107 SUMOylation of PPARγ has been suggested to impair this IL-10 production, the mechanism remains elusive. We identify PIAS2 to be the specific E3-SUMOligase responsible for this SUMOylation. Moreover, we identify a concomitant CL-mediated PPARγ S112 phosphorylation, mediated by JNK-MAPK, to be essential for PIAS2 recruitment. Furthermore, using a clinically tested peptide inhibitor targeting JNK-MAPK, we blocked these post-translational modifications (PTMs) of PPARγ and rescued IL-10 expression, improving survival in murine pneumonia models. Thus, we explore the mechanism of mito-DAMP-mediated impaired lung inflammation resolution and propose a therapeutic strategy targeting PPARγ PTMs.

The phase changes of M1/M2 phenotype of microglia/macrophage following oxygen-induced retinopathy in mice.

OBJECTIVE: Microglia/macrophage activation is previously reported to be involved in various ocular diseases. However, the separate role of M1/M2 phenotype microglia/macrophage in the pathological process of oxygen-induced retinopathy (OIR) remains unknown. In this research, we explored the role and regulatory mechanism of M1/M2 microglia/macrophage in OIR in C57BL/6J mice. Furthermore, we demonstrated the time phase of M1/M2 shifting of microglia/macrophage during the natural process of OIR, which is very essential for further investigations. MATERIALS AND METHODS: C57BL/6j pups were exposed to hyperoxia environment from postnatal 7(P7) to P12 then returned to normoxia. The mice were then euthanized, and the eyes were harvested at a series of time points for further investigation. The M1/M2 phenotype microglia/macrophage activity was presented by immunofluorescent staining and real-time quantitative polymerase chain reaction (qPCR). The NF-κb-STAT3 signaling and IL-4-STAT6-PPAR-γ signaling pathway activity was examined by western blot analysis. RESULTS: The microglia/macrophage were activated when the OIR model was set up after P12. The M1 microglia/macrophage activation was found in neovascularization (NV) tufts in both central and peripheral retina, which started from P12 when the mice were returned to normoxia environment and peaked at P17. During this period of time, the NF-κb-STAT3 signaling pathway was activated, resulting in the upregulated M1 phenotype microglia/macrophage polarization, along with the enhanced inflammatory cytokine expression including tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and IL-1ß. Consequently, the NV tufts were observed from P12 and the volume continued to increase until P17. However, the M2 phenotype microglia/macrophage activity took over during the late phase of OIR started from P17. The IL-4-STAT6-PPAR-γ signaling activity was upregulated from P17 and peaked at P20, inducing M2 phenotype microglia polarization, which consequently led to the inhibition of inflammatory cytokines and spontaneous regression of NV tufts. CONCLUSIONS: Microglia/macrophage participate actively in the natural process of OIR in mice, and two phenotypes exert different functions. Treatment modulating microglia/macrophage polarize toward M2 phenotype might be a novel and promising method for ocular neovascular diseases such as retinopathy of prematurity (ROP), wet age-related macular degeneration (wAMD), and diabetic retinopathy (DR).

Bifidobacterium pseudocatenulatum Ameliorates DSS-Induced Colitis by Maintaining Intestinal Mechanical Barrier, Blocking Proinflammatory Cytokines, Inhibiting TLR4/NF-κB Signaling, and Altering Gut Microbiota.

This study was designed to explore the effects and discrepancy of different CLA-producing Bifidobacterium pseudocatenulatum on relieving colitis and to investigate the potential mechanisms. B. pseudocatenulatum MY40C and CCFM680 were administered to mice with DSS-induced colitis. The content of tight junction proteins and mucin2 was significantly upregulated. TNF-α and IL-6 were downregulated, while IL-10 and PPAR-γ were upregulated. TLR4/NF-κB pathway activation was significantly inhibited. Moreover, each treated strain increased Allobaculum and decreased Sutterella, Bacteroides, and Oscillospira. The colonic conjugated linoleic acid (CLA) concentrations were significantly and positively correlated with the effectiveness of strain in relieving colitis. In conclusion, MY40C and CCFM680 supplementation alleviated DSS-induced colitis by protecting intestinal mechanical barrier, modulating gut microbiota, blocking proinflammatory cytokines, and inhibiting TLR4/NF-κB pathway. These results are conducive to promote clinical trials and product development of probiotics for colitis.

Increased lipid metabolism impairs NK cell function and mediates adaptation to the lymphoma environment.

Natural killer (NK) cells play critical roles in protection against hematological malignancies but can acquire a dysfunctional state, which limits antitumor immunity. However, the underlying reasons for this impaired NK cell function remain to be uncovered. We found that NK cells in aggressive B-cell lymphoma underwent substantial transcriptional reprogramming associated with increased lipid metabolism, including elevated expression of the transcriptional regulator peroxisome activator receptor-γ (PPAR-γ). Exposure to fatty acids in the lymphoma environment potently suppressed NK cell effector response and cellular metabolism. NK cells from both diffuse large B-cell lymphoma patients and Eµ-myc B-cell lymphoma-bearing mice displayed reduced interferon-γ (IFN-γ) production. Activation of PPAR-γ partially restored mitochondrial membrane potential and IFN-γ production. Overall, our data indicate that increased lipid metabolism, while impairing their function, is a functional adaptation of NK cells to the fatty-acid rich lymphoma environment.

PPARγ as an E3 Ubiquitin-Ligase Impedes Phosphate-Stat6 Stability and Promotes Prostaglandins E2-Mediated Inhibition of IgE Production in Asthma.

Increased serum IgE level is one of the features of allergic asthma. It is reported that IgE production can be enhanced by E-prostanoid 2 (EP2) receptor of prostaglandin E2 (PGE2); however, whether E-prostanoid 4 (EP4) receptor (encoded by Ptger4) has a unique or redundant role is still unclear. Here, we demonstrated the mice with B cell-specific deletion of the EP4 receptor (Ptger4fl/flMb1cre+/-) showed their serum levels of IgE were markedly increased. A much more severe airway allergic inflammation was observed in the absence of EP4 signal using the OVA-induced asthma model. Mechanistic studies demonstrated that the transcription levels of AID, GLTε, and PSTε in EP4-deficient B cells were found to be significantly increased, implying an enhanced IgE class switch. In addition, we saw higher levels of phosphorylated STAT6, a vital factor for IgE class switch. Biochemical analyses indicated that inhibitory effect of EP4 signal on IgE depended on the activation of the PI3K-AKT pathway. Further downstream, PPARγ expression was up-regulated. Independent of its activity as a transcription factor, PPARγ here primarily functioned as an E3 ubiquitin-ligase, which bound the phosphorylated STAT6 to initiate its degradation. In support of PPARγ as a key mediator downstream of the EP4 signal, PPARγ agonist induced the down-regulation of phospho-STAT6, whereas its antagonist was able to rescue the EP4-mediated inhibition of STAT6 activation and IgE production. Thus, our findings highlight a role for the PGE2-EP4-AKT-PPARγ-STAT6 signaling in IgE response, highlighting the therapeutic potential of combined application of EP4 and PPARγ agonists in asthma.

Activation of PPAR-γ induces macrophage polarization and reduces neutrophil migration mediated by heme oxygenase 1.

Natural or synthetic ligands for peroxisome proliferator-activated receptor gamma (PPAR-γ) represent an interesting tool for pharmacological interventions to treat inflammatory conditions. In particular, PPAR-γ activation prevents pain and inflammation in the temporomandibular joint (TMJ) by decreasing cytokine release and stimulating the synthesis of endogenous opioids. The goal of this study was to clarify whether PPAR-γ activation induces macrophage polarization, inhibiting inflammatory cytokine release and leukocyte recruitment. In addition, we investigated the involvement of heme oxygenase 1 (HO-1) in downstream events after PPAR-γ activation. Our results demonstrate that PPAR-γ activation ablates cytokine release by Bone Marrow-Derived Macrophages (BMDM) in vitro. 15d-PGJ2 induces the PPAR-γ heterodimer activation from rat macrophages, with macrophage polarization from M1-like cells toward M2-like cells. This response is mediated through HO-1. PPAR-γ activation diminished neutrophil migration induced by carrageenan, which was also HO-1 dependent. Ca2+/calmodulin expression did not change after PPAR-γ activation indicating that is not required for the activation of the intracellular L-arginine/NO/cGMP/K+ATP channel pathway. In summary, the anti-inflammatory actions induced by PPAR-γ activation involve macrophage polarization. HO-1 expression is increased and HO-1 activity is required for the suppression of neutrophil migration.

Lipid-Droplet Formation Drives Pathogenic Group 2 Innate Lymphoid Cells in Airway Inflammation.

Innate lymphoid cells (ILCs) play an important role in the control and maintenance of barrier immunity. However, chronic activation of ILCs results in immune-mediated pathology. Here, we show that tissue-resident type 2 ILCs (ILC2s) display a distinct metabolic signature upon chronic activation. In the context of allergen-driven airway inflammation, ILC2s increase their uptake of both external lipids and glucose. Externally acquired fatty acids are transiently stored in lipid droplets and converted into phospholipids to promote the proliferation of ILC2s. This metabolic program is imprinted by interleukin-33 (IL-33) and regulated by the genes Pparg and Dgat1, which are both controlled by glucose availability and mTOR signaling. Restricting dietary glucose by feeding mice a ketogenic diet largely ablated ILC2-mediated airway inflammation by impairing fatty acid metabolism and the formation of lipid droplets. Together, these results reveal that pathogenic ILC2 responses require lipid metabolism and identify ketogenic diet as a potent intervention strategy to treat airway inflammation.

Macrophage immunophenotype but not anti-inflammatory profile is modulated by peroxisome proliferator-activated receptor gamma (PPARγ) in exercised obese mice.

Moderate aerobic training may be therapeutic for chronic low-grade inflammatory diseases due to the associated anti-inflammatory response that is mediated by immune cells. The peroxisome proliferator-activated receptor gamma (PPARγ) regulates the M1 (pro-inflammatory) and M2 (anti-inflammatory) polarization, as well as the immunometabolic response of macrophages. Against this background, the present study seeks to clarify whether the conditional deletion of PPARγ in macrophages would have any effect on the anti-inflammatory role of moderate aerobic training. To test this hypothesis, two mice strains were used: PPARγ LyzCre+/+ (KO) and littermates control animals (WT). Each genotype was divided into 1) sedentary high-fat diet (HF) and 2) high-fat diet and moderate aerobic training (HFT) (n = 5-8 per group). The experimental protocol lasted for 12 weeks, comprising 4 weeks of HF diet only and 8 weeks of HF diet and aerobic training (5 times/week, 50-60 minutes/day at 60% of maximum speed). Metabolic analyses were carried out on the serum glucose homeostase, adipose tissue morphology and cytokine content, and macrophage cytokine production.Immunophenotyping and gene expression were also performed. KO male mice were more prone to hypertrophy in the subcutaneous adipose tissue, though only the IL-1ß (p = 0.0049) was higher compared to the values observed in WT animals. Peritoneal macrophages from KO animals exhibited a marked inflammatory environment with an increase in TNF-α (p = 0.0008), IL- 1ß (p = 0.0017), and IL-6 (p < 0.0001) after lipopolysaccharide stimulation. The moderate aerobic training protected both genotypes from weight gain and reduced the caloric intake in the KO animals. Despite the attenuation of the M2 marker CD206 (p < 0.001) in the absence of PPAR-γ, the aerobic training modulated cytokine production in LPS stimulated peritoneal macrophages from both genotypes, reducing proinflammatory cytokines such as TNF-α (p = 0.0002) and IL-6 (p < 0.0001). Overall, our findings demonstrate the essential role of PPARγ in macrophage immunophenotypes. However, the deletion of PPARγ did not inhibit the exercise-mediated anti-inflammatory effect, underscoring the important role of exercise in modulating inflammation.

N6-methyladenosine demethylase FTO promotes M1 and M2 macrophage activation.

Macrophage polarization is the driving force of various inflammatory diseases, especially those involved in M1/M2 imbalance. N6-methyladenosine (m6A) is the most prevalent internal mRNA modification in eukaryotes that affects multiple biological processes, including those involved developmental arrest and immune response. However, the role of m6A in macrophage polarization remains unclear. This study found that FTO silencing significantly suppressed both M1 and M2 polarization. FTO depletion decreased the phosphorylation levels of IKKα/ß, IκBα and p65 in the NF-κB signaling pathway. The expression of STAT1 was downregulated in M1-polarized macrophages while the expression of STAT6 and PPAR-γ decreased in M2 polarization after FTO knockdown. The actinomycin D experiments showed that FTO knockdown accelerated mRNA decay of STAT1 and PPAR-γ. Furthermore, the stability and expression of STAT1 and PPAR-γ mRNAs increased when the m6A reader YTHDF2 was silenced. In conclusion, our results suggest that FTO knockdown inhibits the NF-κB signaling pathway and reduces the mRNA stability of STAT1 and PPAR-γ via YTHDF2 involvement, thereby impeding macrophage activation. These findings indicated a previously unrecognized link between FTO and macrophage polarization and might open new avenues for research into the molecular mechanisms of macrophage polarization-related diseases.

Suppressive role of PPARγ in the IgE-dependent activation of mast cells.

Mast cells (MCs) play a central role in IgE-dependent immune responses. PPARγ is a nuclear receptor that is essential for adipocyte differentiation and insulin sensitivity. Although PPARγ is expressed in activated MCs, the effect of PPARγ suppression in IgE-mediated activation of MCs is largely unknown. In the current study, we evaluated the effect of PPARγ knockdown on the function of IgE plus antigen (Ag)-stimulated MCs using siRNA-transfected bone marrow-derived MCs (BMMCs). We found that the mRNA expression level of cytokines in IgE/Ag-stimulated BMMCs was significantly increased in PPARγ knockdown BMMCs, and IgE/Ag-mediated degranulation and the protein production level of TNF-α was moderately increased by PPARγ knockdown, whereas the cell surface expression level of FcεRI was not affected by PPARγ knockdown. Oral administration of pioglitazone (PPARγ agonist) significantly suppressed body temperature change of mice in passive systemic anaphylaxis, supporting the inhibitory functions of PPARγ in IgE/Ag-dependent activation of MCs in vivo. IgE-mediated up-regulation of mRNA levels of Ptgs2 (encoding COX-2) was drastically enhanced in PPARγ knockdown BMMCs. Although several prostaglandin (PG) derivatives are known to be ligands for PPARγ, treatment with a COX inhibitor, acetyl salicylic acid, up-regulated the IgE-mediated increase of Il13, Tnf and Ptgs2 mRNA levels in a synergistic manner with PPARγ siRNA. Knockdown of COX-1 and/or COX-2 by siRNA showed that suppression of IgE/Ag-mediated activation was mainly dependent on COX-1. Taken together, these results indicate that PPARγ suppresses IgE/Ag-induced transactivation of cytokine genes and the Ptgs2 gene in MCs in a manner distinguishable from that of PGs.