Niche-Specific Reprogramming of Epigenetic Landscapes Drives Myeloid Cell Diversity in Nonalcoholic Steatohepatitis.

Tissue-resident and recruited macrophages contribute to both host defense and pathology. Multiple macrophage phenotypes are represented in diseased tissues, but we lack deep understanding of mechanisms controlling diversification. Here, we investigate origins and epigenetic trajectories of hepatic macrophages during diet-induced non-alcoholic steatohepatitis (NASH). The NASH diet induced significant changes in Kupffer cell enhancers and gene expression, resulting in partial loss of Kupffer cell identity, induction of Trem2 and Cd9 expression, and cell death. Kupffer cell loss was compensated by gain of adjacent monocyte-derived macrophages that exhibited convergent epigenomes, transcriptomes, and functions. NASH-induced changes in Kupffer cell enhancers were driven by AP-1 and EGR that reprogrammed LXR functions required for Kupffer cell identity and survival to instead drive a scar-associated macrophage phenotype. These findings reveal mechanisms by which disease-associated environmental signals instruct resident and recruited macrophages to acquire distinct gene expression programs and corresponding functions.

Signaling is the pathway to macrophage function.

Tissue and inflammatory contexts are well appreciated to shape macrophage function to promote health or disease. However, there has been minimal progress towards understanding how these contexts modify signaling-to-transcription networks. Integration of mechanistic modeling and data-driven approaches will be crucial for investigating how cell state impacts macrophage decision-making.

CD301b(+) Mononuclear Phagocytes Maintain Positive Energy Balance through Secretion of Resistin-like Molecule Alpha.

Mononuclear phagocytes (MNPs) are a highly heterogeneous group of cells that play important roles in maintaining the body's homeostasis. Here, we found CD301b (also known as MGL2), a lectin commonly used as a marker for alternatively activated macrophages, was selectively expressed by a subset of CD11b(+)CD11c(+)MHCII(+) MNPs in multiple organs including adipose tissues. Depleting CD301b(+) MNPs in vivo led to a significant weight loss with increased insulin sensitivity and a marked reduction in serum Resistin-like molecule (RELM) α, a multifunctional cytokine produced by MNPs. Reconstituting RELMα in CD301b(+) MNP-depleted animals restored body weight and normoglycemia. Thus, CD301b(+) MNPs play crucial roles in maintaining glucose metabolism and net energy balance.

Intraperitoneal transfer of wild-type bone marrow repopulates tissue macrophages in the Csf1r knockout rat without contributing to monocytopoiesis.

Homozygous null mutation of the Csf1r gene (Csf1rko) in rats leads to the loss of most tissue macrophage populations and pleiotropic impacts on postnatal growth and organ maturation, leading to early mortality. The phenotype can be reversed by intraperitoneal transfer of WT BM cells (BMT) at weaning. Here, we used a Csf1r-mApple transgenic reporter to track the fate of donor-derived cells. Following BMT into Csf1rko recipients, mApple+ve cells restored IBA1+ tissue macrophage populations in every tissue. However, monocytes, neutrophils, and B cells in the BM, blood, and lymphoid tissues remained of recipient (mApple-ve ) origin. An mApple+ve cell population expanded in the peritoneal cavity and invaded locally in the mesentery, fat pads, omentum, and diaphragm. One week after BMT, distal organs contained foci of mApple+ve , IBA1-ve immature progenitors that appeared to proliferate, migrate, and differentiate locally. We conclude that rat BM contains progenitor cells that are able to restore, replace, and maintain all tissue macrophage populations in a Csf1rko rat directly without contributing to the BM progenitor or blood monocyte populations.

Moderate l-lactate administration suppresses adipose tissue macrophage M1 polarization to alleviate obesity-associated insulin resistance.

As a crucial metabolic intermediate, l-lactate is involved in redox balance, energy balance, and acid-base balance in organisms. Moderate exercise training transiently elevates plasma l-lactate levels and ameliorates obesity-associated type 2 diabetes. However, whether moderate l-lactate administration improves obesity-associated insulin resistance remains unclear. In this study, we defined 800 mg/kg/day as the dose of moderate l-lactate administration. In mice fed with a high-fat diet (HFD), moderate l-lactate administration for 12 weeks was shown to alleviate weight gain, fat accumulation, and insulin resistance. Along with the phenotype alterations, white adipose tissue thermogenesis was also found to be elevated in HFD-fed mice. Meanwhile, moderate l-lactate administration suppressed the infiltration and proinflammatory M1 polarization of adipose tissue macrophages (ATMs) in HFD-fed mice. Furthermore, l-lactate treatment suppressed the lipopolysaccharide-induced M1 polarization of bone marrow-derived macrophages (BMDMs). l-lactate can bind to the surface receptor GPR132, which typically drives the downstream cAMP-PKA signaling. As a nutrient sensor, AMP-activated protein kinase (AMPK) critically controls macrophage inflammatory signaling and phenotype. Thus, utilizing inhibitors of the kinases PKA and AMPK as well as siRNA against GPR132, we demonstrated that GPR132-PKA-AMPKα1 signaling mediated the suppression caused by l-lactate treatment on BMDM M1 polarization. Finally, l-lactate addition remarkably resisted the impairment of lipopolysaccharide-treated BMDM conditional media on adipocyte insulin sensitivity. In summary, moderate l-lactate administration suppresses ATM proinflammatory M1 polarization through activation of the GPR132-PKA-AMPKα1 signaling pathway to improve insulin resistance in HFD-fed mice, suggesting a new therapeutic and interventional approach to obesity-associated type 2 diabetes.

The GDF3-ALK7 signaling axis in adipose tissue: a possible therapeutic target for obesity and associated diabetes?

ALK7, a type I receptor for the transforming growth factor-ß superfamily, is known to be predominantly expressed in adipocytes in both mice and humans. The present review describes recent findings suggesting that ALK7 plays a major role in regulating lipid metabolism and fat mass. Furthermore, the ligands and upstream regulators that activate ALK7 signaling are discussed. The focus is on findings in mice and their derivative tissues and cells that harbor the mutations of ALK7 and related molecules. Particular attention is paid to the contradictory nature of the current literature about the loss-of-function phenotypes and the relationship with insulin secretion and sensitivity. Additional attention is paid to the ALK7 gene variants found in humans and their associated traits. The goal is to seek a parsimonious, and preferably singular and unified, description of the underlying mechanism. This review also introduces recent promising findings about ALK7 neutralizing treatment to obese mice.

Fetuin-A regulates adipose tissue macrophage content and activation in insulin resistant mice through MCP-1 and iNOS: involvement of IFNγ-JAK2-STAT1 pathway.

In the context of obesity-induced adipose tissue (AT) inflammation, migration of macrophages and their polarization from predominantly anti-inflammatory to proinflammatory subtype is considered a pivotal event in the loss of adipose insulin sensitivity. Two major chemoattractants, monocyte chemoattractant protein-1 (MCP-1) and Fetuin-A (FetA), have been reported to stimulate macrophage migration into inflamed AT instigating inflammation. Moreover, FetA could notably modulate macrophage polarization, yet the mechanism(s) is unknown. The present study was undertaken to elucidate the mechanistic pathway involved in the actions of FetA and MCP-1 in obese AT. We found that FetA knockdown in high fat diet (HFD) fed mice could significantly subdue the augmented MCP-1 expression and reduce adipose tissue macrophage (ATM) content thereby indicating that MCP-1 is being regulated by FetA. Additionally, knockdown of FetA in HFD mice impeded the expression of inducible nitric oxide synthase (iNOS) reverting macrophage activation from mostly proinflammatory to anti-inflammatory state. It was observed that the stimulating effect of FetA on MCP-1 and iNOS was mediated through interferon γ (IFNγ) induced activation of JAK2-STAT1-NOX4 pathway. Furthermore, we detected that the enhanced IFNγ expression was accounted by the stimulatory effect of FetA upon the activities of both cJun and JNK. Taken together, our findings revealed that obesity-induced FetA acts as a master upstream regulator of AT inflammation by regulating MCP-1 and iNOS expression through JNK-cJun-IFNγ-JAK2-STAT1 signaling pathway. This study opened a new horizon in understanding the regulation of ATM content and activation in conditions of obesity-induced insulin resistance.

GABA-stimulated adipose-derived stem cells suppress subcutaneous adipose inflammation in obesity.

Accumulating evidence suggests that subcutaneous and visceral adipose tissues are differentially associated with metabolic disorders. In obesity, subcutaneous adipose tissue is beneficial for metabolic homeostasis because of repressed inflammation. However, the underlying mechanism remains unclear. Here, we demonstrate that γ-aminobutyric acid (GABA) sensitivity is crucial in determining fat depot-selective adipose tissue macrophage (ATM) infiltration in obesity. In diet-induced obesity, GABA reduced monocyte migration in subcutaneous inguinal adipose tissue (IAT), but not in visceral epididymal adipose tissue (EAT). Pharmacological modulation of the GABAB receptor affected the levels of ATM infiltration and adipose tissue inflammation in IAT, but not in EAT, and GABA administration ameliorated systemic insulin resistance and enhanced insulin-dependent glucose uptake in IAT, accompanied by lower inflammatory responses. Intriguingly, compared with adipose-derived stem cells (ADSCs) from EAT, IAT-ADSCs played key roles in mediating GABA responses that repressed ATM infiltration in high-fat diet-fed mice. These data suggest that selective GABA responses in IAT contribute to fat depot-selective suppression of inflammatory responses and protection from insulin resistance in obesity.

An Iron Refractory Phenotype in Obese Adipose Tissue Macrophages Leads to Adipocyte Iron Overload.

Adipocyte iron overload is a maladaptation associated with obesity and insulin resistance. The objective of the current study was to determine whether and how adipose tissue macrophages (ATMs) regulate adipocyte iron concentrations and whether this is impacted by obesity. Using bone marrow-derived macrophages (BMDMs) polarized to M0, M1, M2, or metabolically activated (MMe) phenotypes, we showed that MMe BMDMs and ATMs from obese mice have reduced expression of several iron-related proteins. Furthermore, the bioenergetic response to iron in obese ATMs was hampered. ATMs from iron-injected lean mice increased their glycolytic and respiratory capacities, thus maintaining metabolic flexibility, while ATMs from obese mice did not. Using an isotope-based system, we found that iron exchange between BMDMs and adipocytes was regulated by macrophage phenotype. At the end of the co-culture, MMe macrophages transferred and received more iron from adipocytes than M0, M1, and M2 macrophages. This culminated in a decrease in total iron in MMe macrophages and an increase in total iron in adipocytes compared with M2 macrophages. Taken together, in the MMe condition, the redistribution of iron is biased toward macrophage iron deficiency and simultaneous adipocyte iron overload. These data suggest that obesity changes the communication of iron between adipocytes and macrophages and that rectifying this iron communication channel may be a novel therapeutic target to alleviate insulin resistance.

C-C motif chemokine receptor 9 regulates obesity-induced insulin resistance via inflammation of the small intestine in mice.

AIMS/HYPOTHESIS: Accumulation of adipose tissue macrophages is considered pivotal in the development of obesity-associated inflammation and insulin resistance. In addition, recent studies suggest an involvement of the intestine as the primary organ in inducing hyperglycaemia and insulin resistance. We have reported that the C-C motif chemokine receptor (CCR) CCR9 is associated with intestinal immunity and has a pathogenic role in various liver diseases. However, its contribution to type 2 diabetes is unknown. In the current study, we aimed to clarify the involvement of CCR9 in the pathology of type 2 diabetes and the potential underlying mechanisms. METHODS: To elucidate how CCR9 affects the development of metabolic phenotypes, we examined the impact of CCR9 deficiency on the pathogenesis of type 2 diabetes using male C57BL/6J (wild-type [WT]) and CCR9-deficient (CCR9 knockout [KO]) mice fed a 60% high-fat diet (HFD) for 12 weeks. RESULTS: WT and Ccr9KO mice fed an HFD exhibited a comparable weight gain; however, glucose tolerance and insulin resistance were significantly improved in Ccr9KO mice. Moreover, visceral adipose tissue (VAT) and the liver of Ccr9KO mice presented with less inflammation and increased expression of glucose metabolism-related genes than WT mice. Ccr9 and Ccl25 expression were specifically higher in the small intestine but was not altered by HFD feeding and type 2 diabetes development. Accumulation of IFN-γ-producing CD4+ T lymphocytes and increased intestinal permeability in the small intestine was observed in WT mice following HFD feeding, but these changes were suppressed in HFD-fed Ccr9KO mice. Adoptive transfer of gut-tropic CCR9-expressing T lymphocytes partially reversed the favourable glucose tolerance found in Ccr9KO mice via exacerbated inflammation in the small intestine and VAT. CONCLUSIONS/INTERPRETATION: CCR9 plays a central role in the pathogenesis of type 2 diabetes by inducing an inflammatory shift in the small intestine. Our findings support CCR9 as a new therapeutic target for type 2 diabetes via the gut-VAT-liver axis.

Adipose tissue macrophage burden, systemic inflammation, and insulin resistance.

Adipose tissue inflammation, as defined by macrophage accumulation, is proposed to cause insulin resistance and systemic inflammation. Because the strength of this relationship for humans is unclear, we tested whether adipose tissue macrophage (ATM) burden is correlated with these health indicators. Using immunohistochemistry, we measured abdominal subcutaneous CD68+ (total ATM), CD14+ (proinflammatory/M1), and CD206+ (anti-inflammatory/M2) ATM in 97 volunteers (BMI 20-38 kg/m2, in addition to body composition, adipocyte size, homeostasis model assessment of insulin resistance, ADIPO-IR, adipose tissue insulin resistance measured by palmitate, plasma lipids, TNF, and IL-6 concentrations. There were several significant univariate correlations between metabolic parameters to IL-6 and ATM per 100 adipocytes, but not ATM per gram tissue; adipocyte size was a confounding variable. We used matching strategies and multivariate regression analyses to investigate the relationships between ATM and inflammatory/metabolic parameters independent of adipocyte size. Matching approaches revealed that the groups discordant for CD206 but concordant for adipocyte size had significantly different fasting insulin and IL-6 concentrations. However, groups discordant for adipocyte size but concordent for ATM differeded in that visceral fat, plasma triglyceride, glucose, and TNF concentrations were greater in those with large adipocytes. Multivariate regression analysis indicated that indexes of insulin resistance and fasting triglycerides were predicted by body composition; the predictive value of ATM per 100 adipocytes or per gram tissue was variable between males and females. We conclude that the relationship between ATM burden and metabolic/inflammatory variables is confounded by adipocyte size/body composition and that ATM do not predict insulin resistance, systemic inflammation, or dyslipidemia. ATM may primarily play a role in tissue remodeling rather than in metabolic pathology.

Perilipin 1 (Plin1) deficiency promotes inflammatory responses in lean adipose tissue through lipid dysregulation.

Lipid droplets are specialized cellular organelles that contain neutral lipid metabolites and play dynamic roles in energy homeostasis. Perilipin 1 (Plin1), one of the major lipid droplet-binding proteins, is highly expressed in adipocytes. In mice, Plin1 deficiency impairs peripheral insulin sensitivity, accompanied with reduced fat mass. However, the mechanisms underlying insulin resistance in lean Plin1 knockout (Plin1-/-) mice are largely unknown. The current study demonstrates that Plin1 deficiency promotes inflammatory responses and lipolysis in adipose tissue, resulting in insulin resistance. M1-type adipose tissue macrophages (ATMs) were higher in Plin1-/- than in Plin1+/+ mice on normal chow diet. Moreover, using lipidomics analysis, we discovered that Plin1-/- adipocytes promoted secretion of pro-inflammatory lipid metabolites such as prostaglandins, which potentiated monocyte migration. In lean Plin1-/- mice, insulin resistance was relieved by macrophage depletion with clodronate, implying that elevated pro-inflammatory ATMs might be attributable for insulin resistance under Plin1 deficiency. Together, these data suggest that Plin1 is required to restrain fat loss and pro-inflammatory responses in adipose tissue by reducing futile lipolysis to maintain metabolic homeostasis.

Macrophages and cellular immunity in Drosophila melanogaster.

The invertebrate Drosophila melanogaster has been a powerful model for understanding blood cell development and immunity. Drosophila is a holometabolous insect, which transitions through a series of life stages from embryo, larva and pupa to adulthood. In spite of this, remarkable parallels exist between Drosophila and vertebrate macrophages, both in terms of development and function. More than 90% of Drosophila blood cells (hemocytes) are macrophages (plasmatocytes), making this highly tractable genetic system attractive for studying a variety of questions in macrophage biology. In vertebrates, recent findings revealed that macrophages have two independent origins: self-renewing macrophages, which reside and proliferate in local microenvironments in a variety of tissues, and macrophages of the monocyte lineage, which derive from hematopoietic stem or progenitor cells. Like vertebrates, Drosophila possesses two macrophage lineages with a conserved dual ontogeny. These parallels allow us to take advantage of the Drosophila model when investigating macrophage lineage specification, maintenance and amplification, and the induction of macrophages and their progenitors by local microenvironments and systemic cues. Beyond macrophage development, Drosophila further serves as a paradigm for understanding the mechanisms underlying macrophage function and cellular immunity in infection, tissue homeostasis and cancer, throughout development and adult life.

Scutellaria baicalensis Alleviates Insulin Resistance in Diet-Induced Obese Mice by Modulating Inflammation.

Insulin resistance is strongly associated with the metabolic syndrome, and chronic inflammation is known to be a major mechanism of insulin resistance and is a therapeutic target. This study was designed to evaluate the effect of Scutellaria baicalensis (SB) in high-fat diet (HFD)-induced insulin-resistant mice and to investigate its mechanism based on inflammatory responses. Mice were fed a HFD to induce insulin resistance and then administered SB for nine weeks. Body weight, glucose, lipid, insulin, epididymal fat pad and liver weights, and histologic characteristics were evaluated to determine the effect on insulin resistance. In order to evaluate the effects on the inflammatory process, we analyzed the proportions of macrophages in liver and epididymal fat and measured inflammatory gene expression. Fasting and postprandial glucose, fasting insulin, HOMA-IR, triglycerides, and low density lipoprotein cholesterol levels were significantly decreased by SB administration. The epididymal fat and liver showed significant weight decreases and histological improvements. Total adipose tissue macrophages (ATMs) decreased (27.71 ± 3.47% vs. 45.26 ± 7.26%, p < 0.05), M2 ATMs increased (47.02 ± 6.63% vs. 24.28 ± 8.00%, p < 0.05), and CD11b⁺ Kupffer cells decreased. The expression levels of tumor necrosis factor alpha and F4/80 in the liver were significantly decreased (12.03 ± 1.47% vs. 25.88 ± 4.57%, p < 0.05) compared to HFD group. These results suggest that SB improved insulin resistance through inhibition of macrophage-mediated inflammation.

Muscularis macrophages: Key players in intestinal homeostasis and disease.

Macrophages residing in the muscularis externa of the gastrointestinal tract are highly specialized cells that are essential for tissue homeostasis during steady-state conditions as well as during disease. They are characterized by their unique protective functional phenotype that is undoubtedly a consequence of the reciprocal interaction with their environment, including the enteric nervous system. This muscularis macrophage-neuron interaction dictates intestinal motility and promotes tissue-protection during injury and infection, but can also contribute to tissue damage in gastrointestinal disorders such as post-operative ileus and gastroparesis. Although the importance of muscularis macrophages is clearly recognized, different aspects of these cells remain largely unexplored such their origin, longevity and instructive signals that determine their function and phenotype. In this review, we will discuss the phenotype, functions and origin of muscularis macrophages during steady-state and disease conditions. We will highlight the bidirectional crosstalk with neurons and potential therapeutic strategies that target and manipulate muscularis macrophages to restore their protective signature as a treatment for disease.

Short communication: Effects of body fat mobilization on macrophage infiltration in adipose tissue of early lactation dairy cows.

Intense lipolysis triggers an inflammatory response within adipose tissue characterized by adipose tissue macrophage (ATM) infiltration; however, the mechanisms triggering this process are poorly characterized in transition dairy cows. The aim of this study was to determine the association between ATM infiltration and body fat mobilization in the transition period, markers of excessive lipolysis, and adipose tissue expression of genes related to chemotactic and inflammatory responses. Subcutaneous adipose tissue samples were taken from the tailhead of 9 multiparous Holstein cows, 27 ± 2.2 d (far-off) and 10 ± 1.5 d (close-up) before and 9 ± 0.3 d after calving (fresh). Blood samples were collected by coccygeal venipuncture 2 h before adipose sample collections. Body condition score (BCS) was assessed independently by 3 experienced technicians at every time point. Based on BCS loss intensity between the close-up and fresh period, cows were divided into 2 groups: low BCS loss (LBCSL, change in BCS <0.25 units, n = 5) and high BCS loss (HBCSL, change in BCS >0.25 units, n = 4). Although none of the LBCSL cows had a health event, all cows in the HBCSL group suffered from one or more clinical disorder (retained placenta, milk fever, or ketosis) in the transition period. The number of ATM was determined by immunohistochemistry, and expression of selected chemotactic and inflammatory genes was determined by reverse-transcription quantitative real-time PCR in subcutaneous adipose tissue samples. The proportion of ATM in subcutaneous adipose tissue increased in HBCSL during the postpartum period. The proportion of ATM was not associated with serum ß-hydroxybutyrate or free fatty acid concentrations on the day of adipose tissue collection. The ATM infiltration in the fresh period was associated with local expression of the chemotactic genes, C-C motif chemokine ligand 22 (CCL22), osteopontin (SPP1), and the receptor for SPP1, cluster of differentiation 44 (CD44). This supports a potential chemotactic role of CCL22 and SPP1 for ATM in bovine adipose tissue. None of the genes encoding pro- or anti-inflammatory mediators, tumor necrosis factor (TNF), IL6, and IL10 were associated with the proportion of ATM. Our results indicate that ATM infiltration of subcutaneous adipose tissue is associated with body fat mobilization in early-lactation dairy cows and supports a role for ATM in the adaptation of adipose tissues to the metabolic challenges of the transition period.

Influence of adipocyte size and adipose depot on the number of adipose tissue macrophages and the expression of adipokines in dairy cows at the end of pregnancy.

The aim of this study was to determine the number of adipose tissue macrophages (ATM) and the mRNA expression of adipokines [adiponectin (ADIPOQ), leptin (LEP), interleukin 6 (IL6), tumor necrosis factor (TNF), and interleukin 10 (IL10)] in different adipose depots from cows with a variable body condition score (BCS) at the end of the dry period. We hypothesized that the number of ATM and the expression of these adipokines depend on adipocyte size and the anatomical location of the adipose depot. Subcutaneous, omental, mesenteric, perirenal, and intrapelvic adipose tissue samples were taken immediately after euthanasia of 10 Holstein Friesian dairy cows (upcoming parity 2 to 5, age 3.9 ± 1.4 yr; mean ± standard deviation) at the end of pregnancy (actual days of pregnancy at the moment of euthanasia: 269 ± 5 d). During the dry period, all animals received similar diets to meet but not exceed requirements. Five animals were considered to have a normal BCS (2.5-3.5) and 5 animals were considered to be over-conditioned (BCS = 3.75-5). Body weight of the animals at the moment of euthanasia was 717 ± 77 kg. Expression of the different genes was determined by reverse transcription quantitative real-time PCR. Adipocyte size was determined by measuring the area of 100 adipocytes on histological sections. Average adipocyte area was 10,475 ± 1,019, 8,500 ± 780, 10,383 ± 1,227, 11,466 ± 1,039, and 11,087 ± 1,632 µm2 for the subcutaneous, mesenteric, omental, intrapelvic, and perirenal adipose depot, respectively. Immunohistochemistry using anti-bovine CD172a antibodies was performed to determine the proportion of ATM (the number of CD172a-positive cells per 100 adipocytes, given as a percentage). Expression of LEP, IL6, and TNF was positively associated with adipocyte size, whereas no association could be detected between ADIPOQ and IL10 with the size of the adipocytes. The omental adipose depot was especially infiltrated with ATM (1.92 ± 0.55, 1.10 ± 0.33, and 8.28 ± 2.24% for the subcutaneous, mesenteric, and omental adipose depot, respectively). The proportion of ATM was positively associated with the size of the adipocytes in the omental and mesenteric adipose depot. Expression of ADIPOQ, LEP, IL6, TNF, and IL10 differed among depots, which suggests differences in inflammatory characteristics depending on the anatomical location of depots. In conclusion, the results of the present study confirm the adipose tissue as a potential source of inflammatory mediators and demonstrate ATM infiltration, especially in the omental adipose depot.

New "programmers" in tissue macrophage activation.

Tissue macrophages and monocyte-derived macrophages are under continuous influence from environmental signals that define their activation status. Along these lines, macrophages integrate tissue and stress signals and are specifically programmed by these signals towards a spectrum of functions necessary to fulfill their duty within their particular microenvironment, be it homeostatic tissue function, response to inflammatory pathophysiology, or even resolution of an inflammation. Recent years have seen tremendous progress in our understanding how macrophages at different sites are transcriptionally and epigenetically programmed to execute their diverse tasks throughout the body. The identification of transcription factors guiding these reprogramming activities is currently a major topic in macrophage research. We summarize the most recent findings within the last 18 months concerning the identification of novel transcription factors associated with particular macrophage location or function. Furthermore, we extend the view of cellular programming of macrophages to additional levels of regulation, for example, by long non-coding RNAs. Clearly, in addition to transcription factors, there are many more "programmers" shaping the versatile functionality of these exciting innate immune cells.

Luteolin reduces obesity-associated insulin resistance in mice by activating AMPKα1 signalling in adipose tissue macrophages.

AIMS/HYPOTHESIS: Inflammatory polarisation of adipose tissue macrophages (ATMs) plays a critical role in the development of obesity-associated metabolic diseases such as insulin resistance and diabetes. Our previous study indicated that dietary luteolin (LU) could prevent the establishment of insulin resistance in mice fed a high-fat diet (HFD). Here, we further investigated the effects of LU, which is a natural flavonoid, on pre-established insulin resistance and obesity-associated ATM polarisation in mice. METHODS: Five-week-old C57/BL6 mice were fed on a low-fat diet or HFD for 20 weeks, with some mice receiving supplementation with 0.01% LU from weeks 1 or 10 of the HFD to assess the actions of LU on insulin resistance and ATM polarisation. Furthermore, the role of LU in metabolic-dysfunction-associated macrophage phenotypes was investigated in vitro. RESULTS: Dietary LU supplementation, either for 20 weeks or from weeks 10 to 20 of an HFD, significantly improved insulin resistance in HFD-fed mice. In addition, inflammatory macrophage infiltration and polarisation were suppressed in mouse epididymal adipose tissues. Furthermore, LU treatment directly reversed lipopolysaccharide-stimulated and metabolism-regulated molecules, and induced inflammatory polarisation in mouse RAW264.7 cells and peritoneal cavity resident macrophages. Finally, using the selective AMP-activated protein kinase (AMPK) inhibitor compound C and Ampkα1 (also known as Prkaa1) silencing with siRNA, we found that LU activated AMPKα1 in macrophages to inhibit their inflammatory polarisation and enhanced insulin signals in adipocytes that were stimulated with macrophage-conditioned media. CONCLUSIONS/INTERPRETATION: Dietary LU ameliorated insulin resistance in diet-induced obese mice by promoting AMPKα1 signalling in ATMs.

Alcohol withdrawal alleviates adipose tissue inflammation in patients with alcoholic liver disease.

BACKGROUND & AIMS: Patients with alcoholic liver disease (ALD) display inflammation of the subcutaneous adipose tissue (SAT) which correlates with liver lesions. We examined macrophage markers and polarization in the SAT of alcoholic patients and adipokine expression according to liver inflammation; we studied the consequences of alcohol withdrawal. PATIENTS AND METHODS: Forty-seven patients with ALD were prospectively included. SAT and blood samples were collected at inclusion and after 1 week of alcohol withdrawal. Pro-inflammatory cytokines/chemokines, inflammasome components and products, adipokine expression levels, macrophage markers and polarization in liver and SAT samples were assessed by RT-PCR arrays. RESULTS: mRNA expression level of chemokines (IL8, semaphorin 7A) correlated with hepatic steatosis in both liver and SAT. Liver expression of inflammasome components (IL1ß, IL18, caspase-1) and SAT IL6 and CCL2 correlated with liver damage. In patients with mild ALD, 1 week of alcohol withdrawal was sufficient to decrease expression level of total macrophage markers in the adipose tissue, to orient adipose tissue macrophages (ATM) towards an anti-inflammatory M2 phenotype and to decrease the mRNA expression of cytokines/chemokines (IL18, CCL2, osteopontin, semaphorin 7A). In patients with severe ALD, 1 week of abstinence was also associated with an increase in CCL18 expression. CONCLUSIONS: In alcoholic patients, upregulation of chemotactic factors in the liver and SAT is an early event that begins as early as the steatosis stage. The inflammasome pathway is upregulated in the liver of patients with ALD. One week of alcohol withdrawal alleviates macrophage infiltration in SAT and orients ATM towards a M2 anti-inflammatory phenotype; this implicates alcohol in adipose tissue inflammation (ClinicalTrials.gov NCT00388323).