Gland Macrophages: Reciprocal Control and Function within Their Niche.

The human body contains dozens of endocrine and exocrine glands, which regulate physiological processes by secreting hormones and other factors. Glands can be subdivided into contiguous tissue modules, each consisting of an interdependent network of cells that together perform particular tissue functions. Among those cells are macrophages, a diverse type of immune cells endowed with trophic functions. In this review, we discuss recent findings on how resident macrophages support tissue modules within glands via the creation of mutually beneficial cell-cell circuits. A better comprehension of gland macrophage function and local control within their niche is essential to achieve a refined understanding of gland physiology in homeostasis and disease.

The endothelial function biomarker soluble E-selectin is associated with nonalcoholic fatty liver disease.

BACKGROUND & AIMS: Plasma soluble E-selectin (sE-selectin) is a frequently used biomarker of systemic endothelial dysfunction. The present study explored the relationship between nonalcoholic fatty liver disease (NAFLD) and plasma sE-selectin levels. METHODS: Expression of E-selectin in liver, visceral adipose tissue (VAT) and muscle was studied in relation to plasma sE-selectin in severely obese individuals (n = 74). The course of hepatic E-selectin expression in relation to hepatic steatosis and inflammation was examined in C57BL/6J LDLR-/- mice on a Western-type diet. The relationship between biomarkers of NAFLD, that is, plasma aminotransferase (ALT) and NAFLD susceptibility genes (rs738409 [PNPLA3] and rs1260326 [GCKR]), and plasma sE-selectin was studied in the combined CODAM (n = 571) and Hoorn (n = 694) studies. RESULTS: E-selectin expression in liver, not VAT or muscle, was associated with plasma sE-selectin in severely obese individuals (ß = 0.26; 95% CI: 0.05-0.47). NAFLD severity was associated with hepatic E-selectin expression (P = .02) and plasma sE-selectin (P = .003). LDLR-/- mice on a Western-type diet displayed increased hepatic E-selectin expression that followed the same course as hepatic inflammation, but not steatosis. In the CODAM study, plasma ALT was associated with plasma sE-selectin, independent of potential confounders (ß = 0.25; 95% CI: 0.16-0.34). Both rs738409 and rs1260326 were associated with higher plasma sE-selectin in the combined CODAM and Hoorn studies (P = .01 and P = .004 respectively). CONCLUSIONS: NAFLD and related markers are associated with higher expression of hepatic E-selectin and higher levels of plasma sE-selectin. Further studies are required to investigate the role of E-selectin in the pathogenesis of NAFLD and the applicability of sE-selectin as a plasma biomarker of NAFLD/NASH.

CD11c-MHC2low Macrophages Are a New Inflammatory and Dynamic Subset in Murine Adipose Tissue.

BACKGROUND: The prevalence of obesity is rising and leads to increased morbidity and mortality. Adipose tissue inflammation, due to accumulation and activation of adipose tissue macrophages (ATMs), is a key driver of this phenomenon. Macrophages are heterogeneous cells, adapting quickly to the microenvironment, resulting in so-called M1 or M2 macrophages. In this study, we describe the dynamics and inflammatory properties of a newly identified ATM subset in obese mice. METHODS: LDLR-/- mice received a high fat diet (HFD) for 5 weeks or 16 weeks to induce obesity. Adipose tissues were isolated and immune cell subsets were analyzed with flow cytometry or microarray analysis. Bone marrow transplantation (BMT) using CD45.1 and CD45.2 LDLR-/- mice was performed to determine ATM origin. RESULTS: Upon HFD, there is a massive increase of ATM subsets in the adipose tissue. CD11c-M2 ATMs could be subdivided based on their MHC2 expression into CD11c-MHC2high ATMs and previously unidentified CD11c-MHC2low ATMs. CD11c-MHC2low ATMs accumulated very rapidly after 10 days of HFD, after which they increased even further with prolonged HFD. Microarray data showed that CD11c-MHC2low ATMs resembled CD11c-MHC2high ATMs in the steady state, but became more inflammatory during development of obesity. In vitro stimulation of bone marrow-derived macrophages with palmitate, abundantly present in HFD, resulted in the induction of the CD11c-MHC2low phenotype. CONCLUSIONS: Among M2 macrophages, a novel pro-inflammatory subset of macrophages was found based on their low level of MHC2 expression. This subset may play a role in the development of adipose tissue inflammation.

Hepatic Fat Content and Liver Enzymes Are Associated with Circulating Free and Protein-Bound Advanced Glycation End Products, Which Are Associated with Low-Grade Inflammation: The CODAM Study.

Advanced glycation end products (AGEs) accumulate in fatty livers and may contribute to low-grade inflammation (LGI), potentially via their receptor, RAGE. It is unknown if the AGE accumulation in fatty livers results in elevated circulating AGEs. In a cohort study, we investigated the association of liver fat and hepatocellular damage with circulating AGEs and soluble RAGE (sRAGE) and subsequently the association of circulating AGEs and sRAGE with LGI. Cross-sectional associations of liver fat percentage (eLF%; ln-transformed) and liver enzymes (LE score; standardized) with circulating AGEs (free CML, CEL, and MG-H1 in nM and protein-bound CML, CEL, and pentosidine in nmol/mmol lysine; ln-transformed) and sRAGE (pg/ml, ln-transformed) and additionally of AGEs and sRAGE with LGI (standardized) were determined by multiple linear regression. eLF% was positively associated with circulating free CEL (ß = 0.090; 95% CI 0.041; 0.139) but inversely with protein-bound CML (ß = -0.071; 95% CI -0.108; -0.034). Similarly, the LE score was positively associated with free CML (ß = 0.044; 95% CI 0.012; 0.076) and CEL (ß = 0.040; 95% CI 0.009; 0.072) but inversely with protein-bound CML (ß = -0.037; 95% CI -0.060; -0.013). Free CML (ß = 0.297; 95% CI 0.049; 0.545) was positively associated with LGI, while protein-bound CML (ß = -0.547; 95% CI -0.888; -0.207) was inversely associated, although this association was absent after adjustment for BMI. eLF% and LE score were not associated with sRAGE and sRAGE not with LGI after adjustment for BMI. Liver fat and enzymes were positively associated with circulating free AGEs, which were associated with LGI. In contrast, inverse relations were observed of liver fat and enzymes with circulating protein-bound AGEs and of protein-bound AGEs with LGI. These data suggest that hepatic steatosis and inflammation affect the formation and degradation of hepatic protein-bound AGEs resulting in elevated circulating free AGE levels. These alterations in AGE levels might influence LGI, but this is likely independent of RAGE.

Adipose tissue macrophages do not affect atherosclerosis development in mice.

BACKGROUND AND AIMS: Obese individuals have a higher risk of developing atherosclerosis, possibly driven by adipose tissue (AT) inflammation. We recently showed that AT macrophages (ATMs), which accumulate in the expanding obese AT, produce mediators causing immune cell recruitment from the bone marrow. In the current study, we evaluated whether ATMs are directly involved in atherosclerotic plaque development. METHODS: Lean ldlr-/- acceptor mice received visceral AT (vAT) from lean, obese, or ATM-depleted obese ldlr-/- mice. Acceptor mice were fed high cholesterol diet (HCD) for 4 weeks before and 8 weeks after AT transplantation to induce atherosclerosis. Atherosclerotic plaque development was studied 8 weeks after transplantation. RESULTS: Transplanting donor vAT from obese mice increased circulating triglycerides and B-cells, but decreased Ly6c- monocytes. Plasma cholesterol, Ly6c+ monocytes, T-cells, NK-cells and eosinophils were unaffected. Depleting ATMs from obese AT using clodronate liposomes prior to vAT transplantation prevented the increase in triglycerides and B-cells and decrease in Ly6c- monocytes, but did increase eosinophils. Circulating Cxcl1 was reduced by obese AT transplantation and Ifn-γ tended to be increased while Tnf and Il-1ß were unaffected. ATM-depleted obese AT transplantation also reduced Cxcl1, but increased circulating Tnf levels. However, obese AT transplantation with or without depletion of ATMs did not influence atherosclerotic plaque size, phenotype, or stability. CONCLUSIONS: ATMs from obese vAT do not affect atherosclerotic plaque development or phenotype.

RAGE deficiency does not affect non-alcoholic steatohepatitis and atherosclerosis in Western type diet-fed Ldlr-/- mice.

Non-alcoholic fatty liver disease is a spectrum of liver diseases ranging from steatosis only to non-alcoholic steatohepatitis (NASH). The latter is characterized by hepatic inflammation, which increases the risk of cardiovascular disease. It is poorly understood which factors contribute to the onset of hepatic inflammation characterizing the progression from steatosis to NASH. Previously, we demonstrated increased advanced glycation endproducts (AGEs) in the livers of NASH patients. We hypothesise that AGEs play a key role in NASH development by activating their proinflammatory receptor, RAGE. RAGE-deficient mice and wildtype littermates, both on Ldlr-/- background, were fed a Western type diet (WTD) for 3 or 12 weeks. Flow cytometry, histology, gene expression and AGE measurements were performed to evaluate the effects of RAGE deficiency. RAGE-deficient mice displayed reduced weight gain and visceral fat expansion compared to control mice. No difference in adipose tissue inflammation was observed between groups. RAGE deficiency did not affect WTD-induced monocytosis, circulating lipids or hepatic steatosis. WTD-induced hepatic neutrophil and macrophage accumulation and atherosclerotic plaque development was comparable between control and RAGE-deficient mice. No difference in AGE levels was observed. RAGE does not seem to play a major role in the development of NASH or atherosclerosis in a hyperlipidemic mouse model.

Characterization of Immune Cells in Human Adipose Tissue by Using Flow Cytometry.

Infiltration of immune cells in the subcutaneous and visceral adipose tissue (AT) deposits leads to a low-grade inflammation contributing to the development of obesity-associated complications such as type 2 diabetes. To quantitatively and qualitatively investigate the immune cell subsets in human AT deposits, we have developed a flow cytometry approach. The stromal vascular fraction (SVF), containing the immune cells, is isolated from subcutaneous and visceral AT biopsies by collagenase digestion. Adipocytes are removed after centrifugation. The SVF cells are stained for multiple membrane-bound markers selected to differentiate between immune cell subsets and analyzed using flow cytometry. As a result of this approach, pro- and anti-inflammatory macrophage subsets, dendritic cells (DCs), B-cells, CD4+ and CD8+ T-cells, and NK cells can be detected and quantified. This method gives detailed information about immune cells in AT and the amount of each specific subset. Since there are numerous fluorescent antibodies available, our flow cytometry approach can be adjusted to measure various other cellular and intracellular markers of interest.

MicroRNA-221/222 Family Counteracts Myocardial Fibrosis in Pressure Overload-Induced Heart Failure.

Pressure overload causes cardiac fibroblast activation and transdifferentiation, leading to increased interstitial fibrosis formation and subsequently myocardial stiffness, diastolic and systolic dysfunction, and eventually heart failure. A better understanding of the molecular mechanisms underlying pressure overload-induced cardiac remodeling and fibrosis will have implications for heart failure treatment strategies. The microRNA (miRNA)-221/222 family, consisting of miR-221-3p and miR-222-3p, is differentially regulated in mouse and human cardiac pathology and inversely associated with kidney and liver fibrosis. We investigated the role of this miRNA family during pressure overload-induced cardiac remodeling. In myocardial biopsies of patients with severe fibrosis and dilated cardiomyopathy or aortic stenosis, we found significantly lower miRNA-221/222 levels as compared to matched patients with nonsevere fibrosis. In addition, miRNA-221/222 levels in aortic stenosis patients correlated negatively with the extent of myocardial fibrosis and with left ventricular stiffness. Inhibition of both miRNAs during AngII (angiotensin II)-mediated pressure overload in mice led to increased fibrosis and aggravated left ventricular dilation and dysfunction. In rat cardiac fibroblasts, inhibition of miRNA-221/222 derepressed TGF-ß (transforming growth factor-ß)-mediated profibrotic SMAD2 (mothers against decapentaplegic homolog 2) signaling and downstream gene expression, whereas overexpression of both miRNAs blunted TGF-ß-induced profibrotic signaling. We found that the miRNA-221/222 family may target several genes involved in TGF-ß signaling, including JNK1 (c-Jun N-terminal kinase 1), TGF-ß receptor 1 and TGF-ß receptor 2, and ETS-1 (ETS proto-oncogene 1). Our findings show that heart failure-associated downregulation of the miRNA-221/222 family enables profibrotic signaling in the pressure-overloaded heart.

Adipose tissue macrophages induce hepatic neutrophil recruitment and macrophage accumulation in mice.

OBJECTIVE: Obesity is a risk factor for non-alcoholic steatohepatitis (NASH). This risk has been attributed to visceral adipose tissue (vAT) expansion associated with increased proinflammatory mediators. Accumulation of CD11c+ proinflammatory adipose tissue macrophages (ATM) is an important driver of vAT inflammation. We investigated the role of ATMs in hepatic inflammation during NASH development. DESIGN: vAT isolated from lean, obese or ATM-depleted (using clodronate liposomes) obese mice was transplanted to lean ldlr-/- acceptor mice. Systemic and hepatic inflammation was assessed either after 2 weeks on standard chow or after 8 weeks on high cholesterol diet (HCD) to induce NASH. RESULTS: Transplanting donor vAT from obese mice increased HCD-induced hepatic macrophage content compared with lean-transplanted mice, worsening liver damage. ATM depletion prior to vAT transplantation reduced this increased hepatic macrophage accumulation. On chow, vAT transplantation induced a more pronounced increase in circulating and hepatic neutrophil numbers in obese-transplanted than lean-transplanted mice, while ATM depletion prior to vAT transplantation reversed this effect. Microarray analysis of fluorescence-activated cell sorting of CD11c+ and CD11c- macrophages isolated from donor adipose tissue showed that obesity resulted in enhanced expression of neutrophil chemotaxis genes specifically in CD11c+ ATMs. Involvement of the neutrophil chemotaxis proteins, CXCL14 and CXCL16, was confirmed by culturing vAT. In humans, CD11c expression in vAT of obese individuals correlated with vAT expression of neutrophil chemotactic genes and with hepatic expression of neutrophil and macrophage marker genes. CONCLUSION: ATMs from obese vAT induce hepatic macrophage accumulation during NASH development, possibly by enhancing neutrophil recruitment.

Circulating classical monocytes are associated with CD11c+ macrophages in human visceral adipose tissue.

Immune cell accumulation in adipose tissue (AT) is associated with the development of AT inflammation, resulting in metabolic dysfunction. Circulating immune cell patterns may reflect immune cell accumulation in expanding AT. However, data linking human leukocytes in blood and AT is lacking. We investigated whether blood immune cell populations are associated with their counterparts in subcutaneous (scAT) or visceral AT (vAT). Flow cytometry was performed on blood, scAT and vAT from 16 lean and 29 obese men. Circulating natural killer (NK)-cells, classical monocytes and nonclassical monocytes were higher in obese individuals. vAT, but not scAT, of obese individuals contained more inflammatory CD11c+ "M1" macrophages and NK cells compared to lean individuals. Blood classical monocytes were associated with CD11c+ macrophages in vAT but not scAT. This association was unrelated to expression of the adhesion molecules CD11b and CD11c or of the chemokine receptor CX3CR1 on these monocytes. Other AT immune cells were not associated with their respective counterparts in blood. Finally, CD11c+ macrophages and CD4+ T-cells in vAT were associated with their counterparts in scAT. In conclusion, blood classical monocytes reflect CD11c+ macrophages in vAT.