IFN-γ Drives Human Monocyte Differentiation into Highly Proinflammatory Macrophages That Resemble a Phenotype Relevant to Psoriasis.

As key cells of the immune system, macrophages coordinate the activation and regulation of the immune response. Macrophages present a complex phenotype that can vary from homeostatic, proinflammatory, and profibrotic to anti-inflammatory phenotypes. The factors that drive the differentiation from monocyte to macrophage largely define the resultant phenotype, as has been shown by the differences found in M-CSF- and GM-CSF-derived macrophages. We explored alternative inflammatory mediators that could be used for in vitro differentiation of human monocytes into macrophages. IFN-γ is a potent inflammatory mediator produced by lymphocytes in disease and infections. We used IFN-γ to differentiate human monocytes into macrophages and characterized the cells at a functional and proteomic level. IFN-γ alone was sufficient to generate macrophages (IFN-γ Mϕ) that were phagocytic and responsive to polarization. We demonstrate that IFN-γ Mϕ are potent activators of T lymphocytes that produce IL-17 and IFN-γ. We identified potential markers (GBP-1, IP-10, IL-12p70, and IL-23) of IFN-γ Mϕ and demonstrate that these markers are enriched in the skin of patients with inflamed psoriasis. Collectively, we show that IFN-γ can drive human monocyte to macrophage differentiation, leading to bona fide macrophages with inflammatory characteristics.

Targeting epigenetics as atherosclerosis treatment: an updated view.

PURPOSE OF REVIEW: This review discusses the current developments on epigenetic inhibition as treatment for atherosclerosis. RECENT FINDINGS: The first phase III clinical trial targeting epigenetics in cardiovascular disease (CVD), BETonMACE, using the bromodomain inhibitor apabetalone (RVX-208) showed no significant effect on major adverse cardiovascular events (MACE) in patients with type II diabetes, low HDL-c and a recent acute coronary artery event compared with its placebo arm. SUMMARY: Preclinical and clinical studies suggest that targeting epigenetics in atherosclerosis is a promising novel therapeutic strategy against CVD. Interfering with histone acetylation by targeting histone deacetylates (HDACs) and bromodomain and extraterminal domain (BET) proteins demonstrated encouraging results in modulating disease progression in model systems. Although the first phase III clinical trial targeting BET in CVD showed no effect on MACE, we suggest that there is sufficient potential for future clinical usage based on the outcomes in specific subgroups and the fact that the study was slightly underpowered. Lastly, we propose that there is future window for targeting repressive histone modifications in atherosclerosis.

PCSK9 monoclonal antibodies reverse the pro-inflammatory profile of monocytes in familial hypercholesterolaemia.

AIMS: Migration of monocytes into the arterial wall contributes to arterial inflammation and atherosclerosis progression. Since elevated low-density lipoprotein cholesterol (LDL-C) levels have been associated with activation of plasma monocytes, intensive LDL-C lowering may reverse these pro-inflammatory changes. Using proprotein convertase subtilisin/kexin type 9 (PCSK9) monoclonal antibodies (mAbs) which selectively reduce LDL-C, we studied the impact of LDL-C lowering on monocyte phenotype and function in patients with familial hypercholesterolaemia (FH) not using statins due to statin-associated muscle symptoms. METHODS AND RESULTS: We assessed monocyte phenotype and function using flow cytometry and a trans-endothelial migration assay in FH patients (n = 22: LDL 6.8 ± 1.9 mmol/L) and healthy controls (n = 18, LDL 2.9 ± 0.8 mmol/L). Monocyte chemokine receptor (CCR) 2 expression was approximaterly three-fold higher in FH patients compared with controls. C-C chemokine receptor type 2 (CCR2) expression correlated significantly with plasma LDL-C levels (r = 0.709) and was positively associated with intracellular lipid accumulation. Monocytes from FH patients also displayed enhanced migratory capacity ex vivo. After 24 weeks of PCSK9 mAb treatment (n = 17), plasma LDL-C was reduced by 49%, which coincided with reduced intracellular lipid accumulation and reduced CCR2 expression. Functional relevance was substantiated by the reversal of enhanced migratory capacity of monocytes following PCSK9 mAb therapy. CONCLUSIONS: Monocytes of FH patients have a pro-inflammatory phenotype, which is dampened by LDL-C lowering by PCSK9 mAb therapy. LDL-C lowering was paralleled by reduced intracellular lipid accumulation, suggesting that LDL-C lowering itself is associated with anti-inflammatory effects on circulating monocytes.

IFN-γ priming of macrophages represses a part of the inflammatory program and attenuates neutrophil recruitment.

Macrophages form a heterogeneous population of immune cells, which is critical for both the initiation and resolution of inflammation. They can be skewed to a proinflammatory subtype by the Th1 cytokine IFN-γ and further activated with TLR triggers, such as LPS. In this work, we investigated the effects of IFN-γ priming on LPS-induced gene expression in primary mouse macrophages. Surprisingly, we found that IFN-γ priming represses a subset of LPS-induced genes, particularly genes involved in cellular movement and leukocyte recruitment. We found STAT1-binding motifs enriched in the promoters of these repressed genes. Furthermore, in the absence of STAT1, affected genes are derepressed. We also observed epigenetic remodeling by IFN-γ priming on enhancer or promoter sites of repressed genes, which resulted in less NF-κB p65 recruitment to these sites without effects on global NF-κB activation. Finally, the epigenetic and transcriptional changes induced by IFN-γ priming reduce neutrophil recruitment in vitro and in vivo. Our data show that IFN-γ priming changes the inflammatory repertoire of macrophages, leading to a change in neutrophil recruitment to inflammatory sites.

Interferon-ß promotes macrophage foam cell formation by altering both cholesterol influx and efflux mechanisms.

Foam cell formation is a crucial event in atherogenesis. While interferon-ß (IFNß) is known to promote atherosclerosis in mice, studies on the role of IFNß on foam cell formation are minimal and conflicting. We therefore extended these studies using both in vitro and in vivo approaches and examined IFNß's function in macrophage foam cell formation. To do so, murine bone marrow-derived macrophages (BMDMs) and human monocyte-derived macrophages were loaded with acLDL overnight, followed by 6h IFNß co-treatment. This increased lipid content as measured by Oil red O staining. We next analyzed the lipid uptake pathways of IFNß-stimulated BMDMs and observed increased endocytosis of DiI-acLDL as compared to controls. These effects were mediated via SR-A, as its gene expression was increased and inhibition of SR-A with Poly(I) blocked the IFNß-induced increase in Oil red O staining and DiI-acLDL endocytosis. The IFNß-induced increase in lipid content was also associated with decreased ApoA1-mediated cholesterol efflux, in response to decreased ABCA1 protein and gene expression. To validate our findings in vivo, LDLR(-/-) mice were put on chow or a high cholesterol diet for 10weeks. 24 and 8h before sacrifice mice were injected with IFNß or PBS, after which thioglycollate-elicited peritoneal macrophages were collected and analyzed. In accordance with the in vitro data, IFNß increased lipid accumulation. In conclusion, our experimental data support the pro-atherogenic role of IFNß, as we show that IFNß promotes macrophage foam cell formation by increasing SR-A-mediated cholesterol influx and decreasing ABCA1-mediated efflux mechanisms.

Macrophage polarization: the epigenetic point of view.

PURPOSE OF REVIEW: The first functions of macrophages to be identified by Metchnikoff were phagocytosis and microbial killing. Although these are important features, macrophages are functionally very complex and involved in virtually all aspects of life, from immunity and host defense, to homeostasis, tissue repair and development. To accommodate for this, macrophages adopt a plethora of polarization states. Understanding their transcriptional regulation and phenotypic heterogeneity is vital because macrophages are critical in many diseases and have emerged as attractive targets for therapy. Here, we review how epigenetic mechanisms control macrophage polarization. RECENT FINDINGS: It is becoming increasingly clear that chromatin remodelling governs multiple aspects of macrophage differentiation, activation and polarization. In recent years, independent research groups highlighted the importance of epigenetic mechanisms to regulate enhancer activity. Moreover, distinct histone-modifying enzymes were identified that control macrophage activation and polarization. SUMMARY: We recap epigenetic features of distinct enhancers and describe the role of Jumonji domain-containing protein 3 (Jmjd3) and Hdac3 as crucial mediators of macrophage differentiation, activation and polarization. We hypothesize that epigenetic enzymes could serve as the link between environment, cellular metabolism and macrophage phenotype. To conclude, we propose epigenetic intervention as a future pharmacological target to modulate macrophage polarization and to treat inflammatory diseases such as atherosclerosis.

Inhibiting epigenetic enzymes to improve atherogenic macrophage functions.

Macrophages determine the outcome of atherosclerosis by propagating inflammatory responses, foam cell formation and eventually necrotic core development. Yet, the pathways that regulate their atherogenic functions remain ill-defined. It is now apparent that chromatin remodeling chromatin modifying enzymes (CME) governs immune responses but it remains unclear to what extent they control atherogenic macrophage functions. We hypothesized that epigenetic mechanisms regulate atherogenic macrophage functions, thereby determining the outcome of atherosclerosis. Therefore, we designed a quantitative semi-high-throughput screening platform and studied whether the inhibition of CME can be applied to improve atherogenic macrophage activities. We found that broad spectrum inhibition of histone deacetylases (HDACs) and histone methyltransferases (HMT) has both pro- and anti-inflammatory effects. The inhibition of HDACs increased histone acetylation and gene expression of the cholesterol efflux regulators ATP-binding cassette transporters ABCA1 and ABCG1, but left foam cell formation unaffected. HDAC inhibition altered macrophage metabolism towards enhanced glycolysis and oxidative phosphorylation and resulted in protection against apoptosis. Finally, we applied inhibitors against specific HDACs and found that HDAC3 inhibition phenocopies the atheroprotective effects of pan-HDAC inhibitors. Based on our data, we propose the inhibition of HDACs, and in particular HDAC3, in macrophages as a novel potential target to treat atherosclerosis.

Cardiovascular risk in ANCA-associated vasculitis: Monocyte phenotyping reveals distinctive signatures between serological subsets.

BACKGROUND AND AIMS: Anti-neutrophil cytoplasmic antibodies (ANCA)-associated vasculitides (AAV) is associated with an increased cardiovascular risk, particularly the myeloperoxidase AAV serotype (MPO-AAV). Distinct alterations in monocyte phenotypes may cause accelerated atherosclerotic disease in AAV. METHODS: A cohort including 43 AAV patients and 19 healthy controls was included for downstream analyses. Extensive phenotyping of monocytes and monocyte-derived macrophages was performed using bulk RNA-sequencing and flow cytometry. An in vitro transendothelial migration assay reflecting intrinsic adhesive and migratory capacities of monocytes was employed. Subsequent sub-analyses were performed to investigate differences between serological subtypes. RESULTS: Monocyte subset analysis showed increased classical monocytes during active disease, whereas non-classical monocytes were decreased compared to healthy controls (HC). RNA-sequencing revealed upregulation of distinct inflammatory pathways and lipid metabolism-related markers in monocytes of active AAV patients. No differences were detected in the intrinsic monocyte adhesion and migration capacity. Compared to proteinase-3(PR3)-AAV, monocytes of MPO-AAV patients in remission expressed genes related to inflammation, coagulation, platelet-binding and interferon signalling, whereas the expression of chemokine receptors indicative of acute inflammation and monocyte extravasation (i.e., CCR2 and CCR5) was increased in monocytes of PR3-AAV patients. During active disease, PR3-AAV was linked with elevated serum CRP and increased platelet counts compared to MPO-AAV. CONCLUSIONS: These findings highlight changes in monocyte subset composition and activation, but not in the intrinsic migration capacity of AAV monocytes. MPO-AAV monocytes are associated with sustained upregulation of inflammatory genes, whereas PR3-AAV monocytes exhibit chemokine receptor upregulation. These molecular changes may play a role in elevating cardiovascular risk as well as in the underlying pathophysiology of AAV.

Targeting the ACOD1-itaconate axis stabilizes atherosclerotic plaques.

Inflammatory macrophages are key drivers of atherosclerosis that can induce rupture-prone vulnerable plaques. Skewing the plaque macrophage population towards a more protective phenotype and reducing the occurrence of clinical events is thought to be a promising method of treating atherosclerotic patients. In the current study, we investigate the immunomodulatory properties of itaconate, an immunometabolite derived from the TCA cycle intermediate cis-aconitate and synthesised by the enzyme Aconitate Decarboxylase 1 (ACOD1, also known as IRG1), in the context of atherosclerosis. Ldlr-/- atherogenic mice transplanted with Acod1-/- bone marrow displayed a more stable plaque phenotype with smaller necrotic cores and showed increased recruitment of monocytes to the vessel intima. Macrophages from Acod1-/- mice contained more lipids whilst also displaying reduced induction of apoptosis. Using multi-omics approaches, we identify a metabolic shift towards purine metabolism, in addition to an altered glycolytic flux towards production of glycerol for triglyceride synthesis. Overall, our data highlight the potential of therapeutically blocking ACOD1 with the aim of stabilizing atherosclerotic plaques.

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.

Hematopoietic Somatic Mosaicism Is Associated With an Increased Risk of Postoperative Atrial Fibrillation.

BACKGROUND: On-pump cardiac surgery triggers sterile inflammation and postoperative complications such as postoperative atrial fibrillation (POAF). Hematopoietic somatic mosaicism (HSM) is a recently identified risk factor for cardiovascular diseases and results in a shift toward a chronic proinflammatory monocyte transcriptome and phenotype. OBJECTIVES: The aim of this study was to assess the prevalence, characteristics, and impact of HSM on preoperative blood and myocardial myeloid cells as well as on outcomes after cardiac surgery. METHODS: Blood DNA from 104 patients referred for surgical aortic valve replacement (AVR) was genotyped using the HemePACT panel (576 genes). Four screening methods were applied to assess HSM, and postoperative outcomes were explored. In-depth blood and myocardial leukocyte phenotyping was performed in selected patients using mass cytometry and preoperative and postoperative RNA sequencing analysis of classical monocytes. RESULTS: The prevalence of HSM in the patient cohort ranged from 29%, when considering the conventional HSM panel (97 genes) with variant allelic frequencies ≥2%, to 60% when considering the full HemePACT panel and variant allelic frequencies ≥1%. Three of 4 explored HSM definitions were significantly associated with higher risk for POAF. On the basis of the most inclusive definition, HSM carriers exhibited a 3.5-fold higher risk for POAF (age-adjusted OR: 3.5; 95% CI: 1.52-8.03; P = 0.003) and an exaggerated inflammatory response following AVR. HSM carriers presented higher levels of activated CD64+CD14+CD16- circulating monocytes and inflammatory monocyte-derived macrophages in presurgery myocardium. CONCLUSIONS: HSM is frequent in candidates for AVR, is associated with an enrichment of proinflammatory cardiac monocyte-derived macrophages, and predisposes to a higher incidence of POAF. HSM assessment may be useful in the personalized management of patients in the perioperative period. (Post-Operative Myocardial Incident & Atrial Fibrillation [POMI-AF]; NCT03376165).

Monocyte and Macrophage Lipid Accumulation Results in Down-Regulated Type-I Interferon Responses.

Macrophages are critical components of atherosclerotic lesions and their pro- and anti-inflammatory responses influence atherogenesis. Type-I interferons (IFNs) are cytokines that play an essential role in antiviral responses and inflammatory activation and have been shown to promote atherosclerosis. Although the impact of type-I IFNs on macrophage foam cell formation is well-documented, the effect of lipid accumulation in monocytes and macrophages on type-I IFN responses remains unknown. Here we examined IFN stimulated (ISG) and non-ISG inflammatory gene expression in mouse and human macrophages that were loaded with acetylated LDL (acLDL), as a model for foam cell formation. We found that acLDL loading in mouse and human macrophages specifically suppressed expression of ISGs and IFN-ß secretion, but not other pro-inflammatory genes. The down regulation of ISGs could be rescued by exogenous IFN-ß supplementation. Activation of the cholesterol-sensing nuclear liver X receptor (LXR) recapitulated the cholesterol-initiated type-I IFN suppression. Additional analyses of murine in vitro and in vivo generated foam cells confirmed the suppressed IFN signaling pathways and suggest that this phenotype is mediated via down regulation of interferon regulatory factor binding at gene promoters. Finally, RNA-seq analysis of monocytes of familial hypercholesterolemia (FH) patients also showed type-I IFN suppression which was restored by lipid-lowering therapy and not present in monocytes of healthy donors. Taken together, we define type-I IFN suppression as an athero-protective characteristic of foamy macrophages. These data provide new insights into the mechanisms that control inflammatory responses in hyperlipidaemic settings and can support future therapeutic approaches focusing on reprogramming of macrophages to reduce atherosclerotic plaque progression and improve stability.

DOT1L regulates lipid biosynthesis and inflammatory responses in macrophages and promotes atherosclerotic plaque stability.

Macrophages are critical immune cells in inflammatory diseases, and their differentiation and function are tightly regulated by histone modifications. H3K79 methylation is a histone modification associated with active gene expression, and DOT1L is the only histone methyltransferase for H3K79. Here we determine the role of DOT1L in macrophages by applying a selective DOT1L inhibitor in mouse and human macrophages and using myeloid-specific Dot1l-deficient mice. We found that DOT1L directly regulates macrophage function by controlling lipid biosynthesis gene programs including central lipid regulators like sterol regulatory element-binding proteins SREBP1 and SREBP2. DOT1L inhibition also leads to macrophage hyperactivation, which is associated with disrupted SREBP pathways. In vivo, myeloid Dot1l deficiency reduces atherosclerotic plaque stability and increases the activation of inflammatory plaque macrophages. Our data show that DOT1L is a crucial regulator of macrophage inflammatory responses and lipid regulatory pathways and suggest a high relevance of H3K79 methylation in inflammatory disease.

High titers and low fucosylation of early human anti-SARS-CoV-2 IgG promote inflammation by alveolar macrophages.

Patients diagnosed with coronavirus disease 2019 (COVID-19) become critically ill primarily around the time of activation of the adaptive immune response. Here, we provide evidence that antibodies play a role in the worsening of disease at the time of seroconversion. We show that early-phase severe acute respiratory distress syndrome coronavirus 2 (SARS-CoV-2) spike protein-specific immunoglobulin G (IgG) in serum of critically ill COVID-19 patients induces excessive inflammatory responses by human alveolar macrophages. We identified that this excessive inflammatory response is dependent on two antibody features that are specific for patients with severe COVID-19. First, inflammation is driven by high titers of anti-spike IgG, a hallmark of severe disease. Second, we found that anti-spike IgG from patients with severe COVID-19 is intrinsically more proinflammatory because of different glycosylation, particularly low fucosylation, of the antibody Fc tail. Low fucosylation of anti-spike IgG was normalized in a few weeks after initial infection with SARS-CoV-2, indicating that the increased antibody-dependent inflammation mainly occurs at the time of seroconversion. We identified Fcγ receptor (FcγR) IIa and FcγRIII as the two primary IgG receptors that are responsible for the induction of key COVID-19-associated cytokines such as interleukin-6 and tumor necrosis factor. In addition, we show that anti-spike IgG-activated human macrophages can subsequently break pulmonary endothelial barrier integrity and induce microvascular thrombosis in vitro. Last, we demonstrate that the inflammatory response induced by anti-spike IgG can be specifically counteracted by fostamatinib, an FDA- and EMA-approved therapeutic small-molecule inhibitor of Syk kinase.

Myeloid Ezh2 Deficiency Limits Atherosclerosis Development.

Macrophages define a key component of immune cells present in atherosclerotic lesions and are central regulators of the disease. Since epigenetic processes are important in controlling macrophage function, interfering with epigenetic pathways in macrophages might be a novel approach to combat atherosclerosis. Histone H3K27 trimethylation is a repressive histone mark catalyzed by polycomb repressive complex with EZH2 as the catalytic subunit. EZH2 is described to increase macrophage inflammatory responses by supressing the suppressor of cytokine signaling, Socs3. We previously showed that myeloid deletion of Kdm6b, an enzymes that in contrast to EZH2 removes repressive histone H3K27me3 marks, results in advanced atherosclerosis. Because of its opposing function and importance of EZH2 in macrophage inflammatory responses, we here studied the role of myeloid EZH2 in atherosclerosis. A myeloid-specific Ezh2 deficient mouse strain (Ezh2del) was generated (LysM-cre+ x Ezh2fl/fl) and bone marrow from Ezh2del or Ezh2wt mice was transplanted to Ldlr-/- mice which were fed a high fat diet for 9 weeks to study atherosclerosis. Atherosclerotic lesion size was significantly decreased in Ezh2del transplanted mice compared to control. The percentage of macrophages in the atherosclerotic lesion was similar, however neutrophil numbers were lower in Ezh2del transplanted mice. Correspondingly, the migratory capacity of neutrophils was decreased in Ezh2del mice. Moreover, peritoneal Ezh2del foam cells showed a reduction in the inflammatory response with reduced production of nitric oxide, IL-6 and IL-12. In Conclusion, myeloid Ezh2 deficiency impairs neutrophil migration and reduces macrophage foam cell inflammatory responses, both contributing to reduced atherosclerosis.

Macrophage ATP citrate lyase deficiency stabilizes atherosclerotic plaques.

Macrophages represent a major immune cell population in atherosclerotic plaques and play central role in the progression of this lipid-driven chronic inflammatory disease. Targeting immunometabolism is proposed as a strategy to revert aberrant macrophage activation to improve disease outcome. Here, we show ATP citrate lyase (Acly) to be activated in inflammatory macrophages and human atherosclerotic plaques. We demonstrate that myeloid Acly deficiency induces a stable plaque phenotype characterized by increased collagen deposition and fibrous cap thickness, along with a smaller necrotic core. In-depth functional, lipidomic, and transcriptional characterization indicate deregulated fatty acid and cholesterol biosynthesis and reduced liver X receptor activation within the macrophages in vitro. This results in macrophages that are more prone to undergo apoptosis, whilst maintaining their capacity to phagocytose apoptotic cells. Together, our results indicate that targeting macrophage metabolism improves atherosclerosis outcome and we reveal Acly as a promising therapeutic target to stabilize atherosclerotic plaques.

Human monocyte-to-macrophage differentiation involves highly localized gain and loss of DNA methylation at transcription factor binding sites.

BACKGROUND: Macrophages and their precursors monocytes play a key role in inflammation and chronic inflammatory disorders. Monocyte-to-macrophage differentiation and activation programs are accompanied by significant epigenetic remodeling where DNA methylation associates with cell identity. Here we show that DNA methylation changes characteristic for monocyte-to-macrophage differentiation occur at transcription factor binding sites, and, in contrast to what was previously described, are generally highly localized and encompass both losses and gains of DNA methylation. RESULTS: We compared genome-wide DNA methylation across 440,292 CpG sites between human monocytes, naïve macrophages and macrophages further activated toward a pro-inflammatory state (using LPS/IFNγ), an anti-inflammatory state (IL-4) or foam cells (oxLDL and acLDL). Moreover, we integrated these data with public whole-genome sequencing data on monocytes and macrophages to demarcate differentially methylated regions. Our analysis showed that differential DNA methylation was most pronounced during monocyte-to-macrophage differentiation, was typically restricted to single CpGs or very short regions, and co-localized with lineage-specific enhancers irrespective of whether it concerns gain or loss of methylation. Furthermore, differentially methylated CpGs were located at sites characterized by increased binding of transcription factors known to be involved in monocyte-to-macrophage differentiation including C/EBP and ETS for gain and AP-1 for loss of methylation. CONCLUSION: Our study highlights the involvement of subtle, yet highly localized remodeling of DNA methylation at regulatory regions in cell differentiation.

Peritoneal macrophages have an impaired immune response in obesity which can be reversed by subsequent weight loss.

Introduction: Obesity is recognized as a risk factor for various microbial infections. The immune system, which is affected by obesity, plays an important role in the pathophysiology of these infections and other obesity-related comorbidities. Weight loss is considered the most obvious treatment for obesity. However, multiple studies suggest that the comorbidities of obesity may persist after weight loss. Deregulation of immune cells including adipose tissue macrophages of obese individuals has been extensively studied, but how obesity and subsequent weight loss affect immune cell function outside adipose tissue is not well defined. Research design and methods: Here we investigated the phenotype of non-adipose tissue macrophages by transcriptional characterization of thioglycollate-elicited peritoneal macrophages (PM) from mice with diet-induced obesity and type 2 diabetes (T2D). Subsequently, we defined the characteristics of PMs after weight loss and mimicked a bacterial infection by exposing PMs to lipopolysaccharide. Results and conclusions: In contrast to the proinflammatory phenotype of adipose tissue macrophages in obesity and T2D, we found a deactivated state of PMs in obesity and T2D. Weight loss could reverse this deactivated macrophage phenotype. Anti-inflammatory characteristics of these non-adipose macrophages may explain why patients with obesity and T2D have an impaired immune response against pathogens. Our data also suggest that losing weight restores macrophage function and thus contributes to the reduction of immune-related comorbidities in patients.

Salt increases monocyte CCR2 expression and inflammatory responses in humans.

Inflammation may play a role in the link between high salt intake and its deleterious consequences. However, it is unknown whether salt can induce proinflammatory priming of monocytes and macrophages in humans. We investigated the effects of salt on monocytes and macrophages in vitro and in vivo by performing a randomized crossover trial in which 11 healthy human subjects adhered to a 2-week low-salt and high-salt diet. We demonstrate that salt increases monocyte expression of CCR2, a chemokine receptor that mediates monocyte infiltration in inflammatory diseases. In line with this, we show a salt-induced increase of plasma MCP-1, transendothelial migration of monocytes, and skin macrophage density after high-salt diet. Macrophages demonstrate signs of an increased proinflammatory phenotype after salt exposure, as represented by boosted LPS-induced cytokine secretion of IL-6, TNF, and IL-10 in vitro, and by increased HLA-DR expression and decreased CD206 expression on skin macrophages after high-salt diet. Taken together, our data open up the possibility for inflammatory monocyte and macrophage responses as potential contributors to the deleterious effects of high salt intake.

Targeting Histone Deacetylases in Myeloid Cells Inhibits Their Maturation and Inflammatory Function With Limited Effects on Atherosclerosis.

Monocytes and macrophages are key drivers in the pathogenesis of inflammatory diseases. Epigenetic targets have been shown to control the transcriptional profile and phenotype of these cells. Since histone deacetylase protein inhibitors demonstrate profound anti-inflammatory activity, we wanted to test whether HDAC inhibition within monocytes and macrophages could be applied to suppress inflammation in vivo. ESM technology conjugates an esterase-sensitive motif (ESM) onto small molecules to allow targeting of cells that express carboxylesterase 1 (CES1), such as mononuclear myeloid cells. This study utilized an ESM-HDAC inhibitor to target monocytes and macrophages in mice in both an acute response model and an atherosclerosis model. We demonstrate that the molecule blocks the maturation of peritoneal macrophages and inhibits pro-inflammatory cytokine production in both models but to a lesser extent in the atherosclerosis model. Despite regulating the inflammatory response, ESM-HDAC528 did not significantly affect plaque size or phenotype, although histological classification of the plaques demonstrated a significant shift to a less severe phenotype. We hereby show that HDAC inhibition in myeloid cells impairs the maturation and activation of peritoneal macrophages but shows limited efficacy in a model of atherosclerosis.