Notch signaling regulates macrophage-mediated inflammation in metabolic dysfunction-associated steatotic liver disease.

The liver macrophage population comprises resident Kupffer cells (KCs) and monocyte-derived macrophages with distinct pro- or anti-inflammatory properties that affect the severity and course of liver diseases. The mechanisms underlying macrophage differentiation and functions in metabolic dysfunction-associated steatotic liver disease and/or steatohepatitis (MASLD/MASH) remain mostly unknown. Using single-cell RNA sequencing (scRNA-seq) and fate mapping of hepatic macrophage subpopulations, we unraveled the temporal and spatial dynamics of distinct monocyte and monocyte-derived macrophage subsets in MASH. We revealed a crucial role for the Notch-Recombination signal binding protein for immunoglobulin kappa J region (RBPJ) signaling pathway in controlling the monocyte-to-macrophage transition, with Rbpj deficiency blunting inflammatory macrophages and monocyte-derived KC differentiation and conversely promoting the emergence of protective Ly6Clo monocytes. Mechanistically, Rbpj deficiency promoted lipid uptake driven by elevated CD36 expression in Ly6Clo monocytes, enhancing their protective interactions with endothelial cells. Our findings uncover the crucial role of Notch-RBPJ signaling in monocyte-to-macrophage transition and will aid in the design of therapeutic strategies for MASH treatment.

A subset of Kupffer cells regulates metabolism through the expression of CD36.

Tissue macrophages are immune cells whose phenotypes and functions are dictated by origin and niches. However, tissues are complex environments, and macrophage heterogeneity within the same organ has been overlooked so far. Here, we used high-dimensional approaches to characterize macrophage populations in the murine liver. We identified two distinct populations among embryonically derived Kupffer cells (KCs) sharing a core signature while differentially expressing numerous genes and proteins: a major CD206loESAM- population (KC1) and a minor CD206hiESAM+ population (KC2). KC2 expressed genes involved in metabolic processes, including fatty acid metabolism both in steady-state and in diet-induced obesity and hepatic steatosis. Functional characterization by depletion of KC2 or targeted silencing of the fatty acid transporter Cd36 highlighted a crucial contribution of KC2 in the liver oxidative stress associated with obesity. In summary, our study reveals that KCs are more heterogeneous than anticipated, notably describing a subpopulation wired with metabolic functions.

The corepressors GPS2 and SMRT control enhancer and silencer remodeling via eRNA transcription during inflammatory activation of macrophages.

While the role of transcription factors and coactivators in controlling enhancer activity and chromatin structure linked to gene expression is well established, the involvement of corepressors is not. Using inflammatory macrophage activation as a model, we investigate here a corepressor complex containing GPS2 and SMRT both genome-wide and at the Ccl2 locus, encoding the chemokine CCL2 (MCP-1). We report that corepressors co-occupy candidate enhancers along with the coactivators CBP (H3K27 acetylase) and MED1 (mediator) but act antagonistically by repressing eRNA transcription-coupled H3K27 acetylation. Genome editing, transcriptional interference, and cistrome analysis reveals that apparently related enhancer and silencer elements control Ccl2 transcription in opposite ways. 4C-seq indicates that corepressor depletion or inflammatory signaling functions mechanistically similarly to trigger enhancer activation. In ob/ob mice, adipose tissue macrophage-selective depletion of the Ccl2 enhancer-transcribed eRNA reduces metaflammation. Thus, the identified corepressor-eRNA-chemokine pathway operates in vivo and suggests therapeutic opportunities by targeting eRNAs in immuno-metabolic diseases.

Inflammatory and immune etiology of type 2 diabetes.

Type 2 diabetes (T2D) represents a global threat affecting millions of patients worldwide. However, its causes remain incompletely dissected and we lack the tools to predict which individuals will develop T2D. Although there is a clear proven clinical association of T2D with metabolic disorders such as obesity and nonalcoholic fatty liver disease (NAFLD), the existence of a significant number of nondiabetic obese subjects suggests yet-uncovered features of such relationships. Here, we propose that a significant proportion of individuals may harbor an immune profile that renders them susceptible to developing T2D. We note the heterogeneity of circulating monocytes and tissue macrophages in organs that are key to metabolic disorders such as liver, white adipose tissue (WAT), and endocrine pancreas, as well as their contribution to T2D genesis.

Blood Monocyte Phenotype Is A Marker of Cardiovascular Risk in Type 2 Diabetes.

BACKGROUND: Diabetes is a major risk factor for atherosclerotic cardiovascular diseases with a 2-fold higher risk of cardiovascular events in people with diabetes compared with those without. Circulating monocytes are inflammatory effector cells involved in both type 2 diabetes (T2D) and atherogenesis. METHODS: We investigated the relationship between circulating monocytes and cardiovascular risk progression in people with T2D, using phenotypic, transcriptomic, and metabolomic analyses. cardiovascular risk progression was estimated with coronary artery calcium score in a cohort of 672 people with T2D. RESULTS: Coronary artery calcium score was positively correlated with blood monocyte count and frequency of the classical monocyte subtype. Unsupervised k-means clustering based on monocyte subtype profiles revealed 3 main endotypes of people with T2D at varying risk of cardiovascular events. These observations were confirmed in a validation cohort of 279 T2D participants. The predictive association between monocyte count and major adverse cardiovascular events was validated through an independent prospective cohort of 757 patients with T2D. Integration of monocyte transcriptome analyses and plasma metabolomes showed a disruption of mitochondrial pathways (tricarboxylic acid cycle, oxidative phosphorylation pathway) that underlined a proatherogenic phenotype. CONCLUSIONS: In this study, we provide evidence that frequency and monocyte phenotypic profile are closely linked to cardiovascular risk in patients with T2D. The assessment of monocyte frequency and count is a valuable predictive marker for risk of cardiovascular events in patients with T2D. REGISTRATION: URL: https://www.clinicaltrials.gov; Unique identifier: NCT04353869.

Fully automated epicardial adipose tissue volume quantification with deep learning and relationship with CAC score and micro/macrovascular complications in people living with type 2 diabetes: the multicenter EPIDIAB study.

BACKGROUND: The aim of this study (EPIDIAB) was to assess the relationship between epicardial adipose tissue (EAT) and the micro and macrovascular complications (MVC) of type 2 diabetes (T2D). METHODS: EPIDIAB is a post hoc analysis from the AngioSafe T2D study, which is a multicentric study aimed at determining the safety of antihyperglycemic drugs on retina and including patients with T2D screened for diabetic retinopathy (DR) (n = 7200) and deeply phenotyped for MVC. Patients included who had undergone cardiac CT for CAC (Coronary Artery Calcium) scoring after inclusion (n = 1253) were tested with a validated deep learning segmentation pipeline for EAT volume quantification. RESULTS: Median age of the study population was 61 [54;67], with a majority of men (57%) a median duration of the disease 11 years [5;18] and a mean HbA1c of7.8 ± 1.4%. EAT was significantly associated with all traditional CV risk factors. EAT volume significantly increased with chronic kidney disease (CKD vs no CKD: 87.8 [63.5;118.6] vs 82.7 mL [58.8;110.8], p = 0.008), coronary artery disease (CAD vs no CAD: 112.2 [82.7;133.3] vs 83.8 mL [59.4;112.1], p = 0.0004, peripheral arterial disease (PAD vs no PAD: 107 [76.2;141] vs 84.6 mL[59.2; 114], p = 0.0005 and elevated CAC score (> 100 vs < 100 AU: 96.8 mL [69.1;130] vs 77.9 mL [53.8;107.7], p < 0.0001). By contrast, EAT volume was neither associated with DR, nor with peripheral neuropathy. We further evidenced a subgroup of patients with high EAT volume and a null CAC score. Interestingly, this group were more likely to be composed of young women with a high BMI, a lower duration of T2D, a lower prevalence of microvascular complications, and a higher inflammatory profile. CONCLUSIONS: Fully-automated EAT volume quantification could provide useful information about the risk of both renal and macrovascular complications in T2D patients.

Genetic variants of interferon-response factor 5 are associated with the incidence of chronic kidney disease: the D.E.S.I.R. study.

Inflammation has been associated with renal diseases. The Interferon Regulatory Factor (IRF)-5 is a key transcription factor in the pro-inflammatory polarization of M1-like macrophages. GWAS have reported that the IRF5 locus is associated with autoimmune diseases and with the estimated glomerular filtration rate (eGFR). We study whether allelic variations in IRF5 are associated with the incidence of chronic kidney disease (CKD) in a general population. We genotyped eleven IRF5 SNPs in the French D.E.S.I.R. cohort from the general population (n = 4820). Associations of SNPs with baseline renal parameters were assessed. Data were analyzed for three endpoints during a 9-year follow-up, incidence of:at least stage 3 CKD, the KDIGO criterion "certain drop in eGFR", and incidence of micro/macro albuminuria. In the cross-sectional analysis, rs10954213 and rs10954214 were associated with eGFR and rs1874328 with urinary albumin/creatinine ratio (ACR). Rs3807306, rs11761199, rs78658945, rs1874328, rs10954213 and rs11770589 were associated with the incidence of stage 3 CKD in multi-adjusted models. Rs4731532, rs3807306, and rs11761199 were associated with the incidence of CKD defined by the KDIGO. Rs4731532, rs3807306, rs11761199 and rs79288514 were associated with the incidence of micro/macro albuminuria. Our results support the hypothesis of the importance of IRF5 mediated macrophage polarization in the etiology of CKD.

Understanding the heterogeneity and functions of metabolic tissue macrophages.

Growing evidence places tissue-resident macrophages as essential gatekeepers of metabolic organ homeostasis, including the adipose tissue and the pancreatic islets. Therein, macrophages may adopt specific phenotypes and ensure local functions. Recent advances in single cell genomic analyses provide a comprehensive map of adipose tissue macrophage subsets and their potential roles are now better apprehended. Whether they are beneficial or detrimental, macrophages overall contribute to the proper adipose tissue expansion under steady state and during obesity. By contrast, macrophages residing inside pancreatic islets, which may exert fundamental functions to fine tune insulin secretion, have only started to attract attention and their cellular heterogeneity remains to be established. The present review will focus on the latest findings exploring the phenotype and the properties of macrophages in adipose tissue and pancreatic islets, questioning early beliefs and future perspectives in the field of immunometabolism.

Untargeted Multiomics Approach Coupling Lipidomics and Metabolomics Profiling Reveals New Insights in Diabetic Retinopathy.

Diabetic retinopathy (DR) is a microvascular complication of diabetes mellitus (DM) which is the main cause of vision loss in the working-age population. Currently known risk factors such as age, disease duration, and hemoglobin A1c lack sufficient efficiency to distinguish patients with early stages of DR. A total of 194 plasma samples were collected from patients with type 2 DM and DR (moderate to proliferative (PDR) or control (no or mild DR) matched for age, gender, diabetes duration, HbA1c, and hypertension. Untargeted lipidomic and metabolomic approaches were performed. Partial-least square methods were used to analyze the datasets. Levels of 69 metabolites and 85 lipid species were found to be significantly different in the plasma of DR patients versus controls. Metabolite set enrichment analysis indicated that pathways such as metabolism of branched-chain amino acids (methylglutaryl carnitine p = 0.004), the kynurenine pathway (tryptophan p < 0.001), and microbiota metabolism (p-Cresol sulfate p = 0.004) were among the most enriched deregulated pathways in the DR group. Moreover, Glucose-6-phosphate (p = 0.001) and N-methyl-glutamate (p < 0.001) were upregulated in DR. Subgroup analyses identified a specific signature associated with PDR, macular oedema, and DR associated with chronic kidney disease. Phosphatidylcholines (PCs) were dysregulated, with an increase of alkyl-PCs (PC O-42:5 p < 0.001) in DR, while non-ether PCs (PC 14:0-16:1, p < 0.001; PC 18:2-14:0, p < 0.001) were decreased in the DR group. Through an unbiased multiomics approach, we identified metabolites and lipid species that interestingly discriminate patients with or without DR. These features could be a research basis to identify new potential plasma biomarkers to promote 3P medicine.

Body-weight variability and risk of cardiovascular outcomes in patients with type 1 diabetes: a retrospective observational analysis of data from the DCCT/EDIC population.

BACKGROUND: Cardiovascular risk and body-weight management are both emerging challenges of type 1 diabetes care. We evaluated the association between intraindividual variability of body-weight and risk of cardiovascular events in people with type 1 diabetes. METHODS: We analyzed 1,398 participants from the DCCT/EDIC studies. Five indices of intraindividual variability of body-weight were calculated for each participant taking into account body-weight measures obtained during the DCCT follow-up (average 6 ± 2 years). The Average Successive Variability (ASV) index, the main variable of interest, was defined as the average absolute difference between successive body-weight measures. The primary outcome was a composite of major adverse cardiovascular events (MACE: nonfatal myocardial infarction or stroke, or cardiovascular death) occurring during the subsequent EDIC follow-up (20 ± 3 years). All-cause death was a secondary outcome. Risk of outcomes were assessed by Cox proportional hazards regression analyses, adjusted for traditional cardiovascular risks factors, including BMI. RESULTS: The cumulative incidence of MACE and all-cause death during follow-up were 5.6% (n = 79) and 6.8% (n = 95), respectively. The adjusted Hazard Ratio (HR) for MACE by every increase of 1 standard deviation (SD) of ASV was 1.34 (95% CI, 1.06-1.66), p = 0.01. For all-cause death, the adjusted HR for 1 SD increase of ASV was 1.25 (1.03-1.50), p = 0.03. Similar results were observed when considering the other indices of intraindividual variability of body-weight. CONCLUSIONS: High body-weight variability (body-weight cycling) is associated with increased risk of MACE and all-cause death in people with type 1 diabetes, independently of the BMI and traditional cardiovascular risk factors.

Leukocyte telomere length, allelic variations in related genes and risk of coronary heart disease in people with long-standing type 1 diabetes.

BACKGROUND: Type 1 diabetes is associated with accelerated vascular aging and advanced atherosclerosis resulting in increased rates of cardiovascular disease and premature death. We evaluated associations between Leukocyte telomere length (LTL), allelic variations (SNPs) in LTL-related genes and the incidence of coronary heart disease (CHD) in adults with long-standing type 1 diabetes. METHODS: We assessed associations of LTL, measured at baseline by RT-PCR, and of SNPs in 11 LTL-related genes with the risk of coronary heart disease (CHD: myocardial infarction or coronary revascularization) and all-cause death during follow-up in two multicenter French-Belgian prospective cohorts of people with long-standing type 1 diabetes. RESULTS: In logistic and Cox analyses, the lowest tertile of LTL distribution (short telomeres) at baseline was associated with the prevalence of myocardial infarction at baseline and with increased risk of CHD (Hazard ratio 3.14 (1.39-7.70), p = 0.005, for shorter vs longer tertile of LTL) and all-cause death (Hazard ratio 1.63 (95% CI 1.04-2.55), p = 0.03, for shorter vs combined intermediate and longer tertiles of LTL) during follow-up. Allelic variations in six genes related to telomere biology (TERC, NAF1, TERT, TNKS, MEN1 and BICD1) were also associated with the incidence of CHD during follow-up. The associations were independent of sex, age, duration of diabetes, and a range of relevant confounding factors at baseline. CONCLUSIONS: Our results suggest that short LTL is an independent risk factor for CHD in people with type 1 diabetes.

Plasma total adiponectin and changes in renal function in a cohort from the community: the prospective Data from an Epidemiological Study on the Insulin Resistance Syndrome study.

BACKGROUND: High adiponectin levels are associated with diabetic nephropathy. Nevertheless, it is not known whether plasma adiponectin is associated with renal function decline in the general population. We evaluated whether adiponectin concentrations were associated with changes in renal function in a community cohort, the Data from an Epidemiological Study on the Insulin Resistance Syndrome (DESIR) study. METHODS: Plasma adiponectin concentrations were measured in a random sample of 3284 people from the DESIR study, a 9-year prospective cohort from the general population. Data were analysed for three endpoints during follow-up: incidence of Stage 3 chronic kidney disease (CKD); the Kidney Disease: Improving Global Outcomes (KDIGO) criterion 'certain drop in eGFR' and rapid kidney function decline [estimated glomerular filtration rate (eGFR) slope steeper than -3 mL/min/1.73 m2/year]. RESULTS: After exclusion of participants with an eGFR <60 mL/min/1.73 m2 at baseline and those with type 2 diabetes or impaired fasting glycaemia at any time during follow-up (remaining n = 2174), there was a 113% higher risk for a rapid decline in kidney function in participants with adiponectin above the third tertile (T3) versus below the first tertile (T1) (Ptrend = 0.004) and a 53% higher risk for kidney function decline as defined by the KDIGO criterion (Ptrend = 0.04). In a cross-sectional analysis, adiponectin was positively associated with urinary albumin:creatinine ratio at baseline (P = 0.009). CONCLUSIONS: In a healthy cohort from the general population, higher levels of plasma adiponectin were associated with decreased renal function at baseline and at follow-up. This result is similar to what is observed in people with diabetic nephropathy, in contrast with animal models of nephropathy.

Gout and pseudo-gout-related crystals promote GLUT1-mediated glycolysis that governs NLRP3 and interleukin-1ß activation on macrophages.

OBJECTIVE: Macrophage activation by monosodium urate (MSU) and calcium pyrophosphate (CPP) crystals mediates an interleukin (IL)-1ß-dependent inflammation during gout and pseudo-gout flare, respectively. Since metabolic reprogramming of macrophages goes along with inflammatory responses dependently on stimuli and tissue environment, we aimed to decipher the role of glycolysis and oxidative phosphorylation in the IL-1ß-induced microcrystal response. METHODS: Briefly, an in vitro study (metabolomics and real-time extracellular flux analysis) on MSU and CPP crystal-stimulated macrophages was performed to demonstrate the metabolic phenotype of macrophages. Then, the role of aerobic glycolysis in IL-1ß production was evaluated, as well in vitro as in vivo using 18F-fluorodeoxyglucose positron emission tomography imaging and glucose uptake assay, and molecular approach of glucose transporter 1 (GLUT1) inhibition. RESULTS: We observed that MSU and CPP crystals led to a metabolic rewiring toward the aerobic glycolysis pathway explained by an increase in GLUT1 plasma membrane expression and glucose uptake on macrophages. Also, neutrophils isolated from human synovial fluid during gout flare expressed GLUT1 at their plasma membrane more frequently than neutrophils isolated from bloodstream. Both glucose deprivation and treatment with either 2-deoxyglucose or GLUT1 inhibitor suppressed crystal-induced NLRP3 activation and IL-1ß production, and microcrystal inflammation in vivo. CONCLUSION: In conclusion, we demonstrated that GLUT1-mediated glucose uptake is instrumental during the inflammatory IL-1ß response induced by MSU and CPP crystals. These findings open new therapeutic paths to modulate crystal-related inflammation.

Functional and phenotypical analysis of IL-6-secreting CD4+ T cells in human adipose tissue.

Emerging evidence indicates that a dynamic interplay between the immune system and adipocytes contributes to the disturbed homeostasis in adipose tissue of obese subjects. Recently, we observed IL-6-secretion by CD4+ T cells from the stromal vascular fraction (SVF) of the infrapatellar fat pad (IFP) of knee osteoarthritis patients directly ex vivo. Here we show that human IL-6+ CD4+ T cells from SVF display a more activated phenotype than the IL-6- T cells, as evidenced by the expression of the activation marker CD69. Analysis of cytokines secretion, as well as expression of chemokine receptors and transcription factors associated with different Th subsets (Treg, Th1, Th2, Th17 and Tfh) revealed that IL-6-secreting CD4+ T cells cannot be assigned to a conventional Th subset. TCRß gene analysis revealed that IL-6+ and IL-6- CD4+ T cells appear clonally unrelated to each other, suggesting a different specificity of these cells. In line with these observations, adipocytes are capable of enhancing IL-6 production by CD4+ T cells. Thus, IL-6+ CD4+ T cells are TCRαß T cells expressing an activated phenotype potentially resulting from an interplay with adipocytes that could be involved in the inflammatory processes in the OA joint.

Lipid environment induces ER stress, TXNIP expression and inflammation in immune cells of individuals with type 2 diabetes.

AIMS/HYPOTHESIS: Obesity and type 2 diabetes are concomitant with low-grade inflammation affecting insulin sensitivity and insulin secretion. Recently, the thioredoxin interacting protein (TXNIP) has been implicated in the activation process of the NOD-like receptor family, pyrin domain containing 3 (NLRP3) inflammasome. In this study, we aim to determine whether the expression of TXNIP is altered in the circulating immune cells of individuals with type 2 vs type 1 diabetes and whether this can be related to specific causes and consequences of inflammation. METHODS: The expression of TXNIP, inflammatory markers, markers of the unfolded protein response (UPR) to endoplasmic reticulum (ER) stress and enzymes involved in sphingolipid metabolism was quantified by quantitative reverse transcription real-time PCR (qRT-PCR) in peripheral blood mononuclear cells (PBMCs) of 13 non-diabetic individuals, 23 individuals with type 1 diabetes and 81 with type 2 diabetes. A lipidomic analysis on the plasma of 13 non-diabetic individuals, 35 individuals with type 1 diabetes and 94 with type 2 diabetes was performed. The effects of ER stress or of specific lipids on TXNIP and inflammatory marker expression were analysed in human monocyte-derived macrophages (HMDMs) and THP-1 cells. RESULTS: The expression of TXNIP and inflammatory and UPR markers was increased in the PBMCs of individuals with type 2 diabetes when compared with non-diabetic individuals or individuals with type 1 diabetes. TXNIP expression was significantly correlated with plasma fasting glucose, plasma triacylglycerol concentrations and specific UPR markers. Induction of ER stress in THP-1 cells or cultured HMDMs led to increased expression of UPR markers, TXNIP, NLRP3 and IL-1ß. Conversely, a chemical chaperone reduced the expression of UPR markers and TXNIP in PBMCs of individuals with type 2 diabetes. The lipidomic plasma analysis revealed an increased concentration of saturated dihydroceramide and sphingomyelin in individuals with type 2 diabetes when compared with non-diabetic individuals and individuals with type 1 diabetes. In addition, the expression of specific enzymes of sphingolipid metabolism, dihydroceramide desaturase 1 and sphingomyelin synthase 1, was increased in the PBMCs of individuals with type 2 diabetes. Palmitate or C2 ceramide induced ER stress in macrophages as well as increased expression of TXNIP, NLRP3 and IL-1ß. CONCLUSIONS/INTERPRETATION: In individuals with type 2 diabetes, circulating immune cells display an inflammatory phenotype that can be linked to ER stress and TXNIP expression. Immune cell ER stress can in turn be linked to the specific exogenous and endogenous lipid environment found in type 2 diabetes.

GPS2-dependent corepressor/SUMO pathways govern anti-inflammatory actions of LRH-1 and LXRbeta in the hepatic acute phase response.

The orphan receptor LRH-1 and the oxysterol receptors LXRalpha and LXRbeta are established transcriptional regulators of lipid metabolism that appear to control inflammatory processes. Here, we investigate the anti-inflammatory actions of these nuclear receptors in the hepatic acute phase response (APR). We report that selective synthetic agonists induce SUMOylation-dependent recruitment of either LRH-1 or LXR to hepatic APR promoters and prevent the clearance of the N-CoR corepressor complex upon cytokine stimulation. Investigations of the APR in vivo, using LXR knockout mice, indicate that the anti-inflammatory actions of LXR agonists are triggered selectively by the LXRbeta subtype. We further find that hepatic APR responses in small ubiquitin-like modifier-1 (SUMO-1) knockout mice are increased, which is due in part to diminished LRH-1 action at APR promoters. Finally, we provide evidence that the metabolically important coregulator GPS2 functions as a hitherto unrecognized transrepression mediator of interactions between SUMOylated nuclear receptors and the N-CoR corepressor complex. Our study extends the knowledge of anti-inflammatory mechanisms and pathways directed by metabolic nuclear receptor-corepressor networks to the control of the hepatic APR, and implies alternative pharmacological strategies for the treatment of human metabolic diseases associated with inflammation.

GPS2 is required for cholesterol efflux by triggering histone demethylation, LXR recruitment, and coregulator assembly at the ABCG1 locus.

Transcriptional coregulators, rather than ligand signals, are suspected to confer context and pathway specificity to nuclear receptor signaling, but the identity of such specifying coregulators and the underlying molecular mechanisms remain largely enigmatic. Here we address this issue in metabolic oxysterol receptor LXR pathways and describe the selective requirement of GPS2 for ABCG1 cholesterol transporter gene transcription and cholesterol efflux from macrophages. We implicate GPS2 in facilitating LXR recruitment to an ABCG1-specific promoter/enhancer unit upon ligand activation and identify functional links to histone H3K9 demethylation. We further describe fundamental differences between ABCG1 and ABCA1 with regard to GPS2 in relation to other coregulators, which are likely to apply to additional LXR-regulated genes. Our work identifies a coregulator-dependent epigenetic mechanism governing the access of a nuclear receptor to communicating regulatory regions in the genome. The pathway and coregulator selectivity of this mechanism implies pharmacological possibilities for the development of selective LXR agonists.

Human epicardial adipose tissue induces fibrosis of the atrial myocardium through the secretion of adipo-fibrokines.

AIMS: Recent studies have reported a relationship between the abundance of epicardial adipose tissue (EAT) and the risk of cardiovascular diseases including atrial fibrillation (AF). However, the underlying mechanisms are unknown. The aim of this study was to examine the effects of the secretome of human EAT on the histological properties of the myocardium. METHODS AND RESULTS: Samples of EAT and subcutaneous adipose (SAT), obtained from 39 patients undergoing coronary bypass surgery, were analysed and tested in an organo-culture model of rat atria to evaluate the fibrotic properties of human fat depots. The EAT secretome induced global fibrosis (interstitial and peripheral) of rat atria in organo-culture conditions. Activin A was highly expressed in EAT compared with SAT and promoted atrial fibrosis, an effect blocked using neutralizing antibody. In addition, Activin A levels were enhanced in patients with low left-ventricular function. In sections of human atrial and ventricular myocardium, adipose and myocardial tissues were in close contact, together with fibrosis. CONCLUSION: This study provides the first evidence that the secretome from EAT promotes myocardial fibrosis through the secretion of adipo-fibrokines such as Activin A.

Liver X receptor: from metabolism to cancer.

Cholesterol plays an indispensable role in regulating the properties of cell membranes in mammalian cells. Accumulation of cholesterol and its intermediates, such as oxysterols, lead to activation of the nuclear receptors LXRs (liver X receptors). LXR is an important regulator of cholesterol homoeostasis by controlling its transport and its neo-synthesis. Accumulating evidence indicates that the endogenous ligands of LXRs, oxysterols, play an active and important role in regulating the fate and function of immune cells. Indeed, LXRs are negative regu-lators of innate immunity by interfering with macrophage activation. Recent advances have highlighted a controversial role for LXR in cancer. In this issue of the Biochemical Journal, Wang et al. propose that LXR agonist directly controls IFN-γ (interferon-γ) expression, which limits tumour growth. This protective effect mediated by LXR appears to be dependent on IFN-γ. Thus, despite accumulation of endogenous ligand of LXR in cancer, activation of LXR seems protective. This novel evidence provides a new perspective for targeting LXR in cancer, although controversial studies can be also found in the literature. In order to avoid side effects associated with LXR agonists, molecular and cellular studies are required to decipher this unexpected action of LXRs.

Cathepsin S inhibition lowers blood glucose levels in mice.

AIMS/HYPOTHESIS: Cathepsin S (CatS) belongs to a family of proteases that have been implicated in several disease processes. We previously identified CatS as a protein that is markedly overexpressed in adipose tissue of obese individuals and downregulated after weight loss and amelioration of glycaemic status induced by gastric bypass surgery. This prompted us to test whether the protease contributes to the pathogenesis of type 2 diabetes using mouse models with CatS inactivation. METHODS: CatS knockout mice and wild-type mice treated with orally active small-molecule CatS inhibitors were fed chow or high-fat diets and explored for change in glycaemic status. RESULTS: CatS deletion induced a robust reduction in blood glucose, which was preserved in diet-induced obesity and with ageing and was recapitulated with CatS inhibition in obese mice. In vivo testing of glucose tolerance, insulin sensitivity and glycaemic response to gluconeogenic substrates revealed that CatS suppression reduced hepatic glucose production despite there being no improvement in insulin sensitivity. This phenotype relied on downregulation of gluconeogenic gene expression in liver and a lower rate of hepatocellular respiration. Mechanistically, we found that the protein 'regulated in development and DNA damage response 1' (REDD1), a factor potentially implicated in reduction of respiratory chain activity, was overexpressed in the liver of mice with CatS deficiency. CONCLUSIONS/INTERPRETATION: Our results revealed an unexpected metabolic effect of CatS in promoting pro-diabetic alterations in the liver. CatS inhibitors currently proposed for treatment of autoimmune diseases could help to lower hepatic glucose output in obese individuals at risk for type 2 diabetes.