Postprandial macrophage-derived IL-1ß stimulates insulin, and both synergistically promote glucose disposal and inflammation.

The deleterious effect of chronic activation of the IL-1ß system on type 2 diabetes and other metabolic diseases is well documented. However, a possible physiological role for IL-1ß in glucose metabolism has remained unexplored. Here we found that feeding induced a physiological increase in the number of peritoneal macrophages that secreted IL-1ß, in a glucose-dependent manner. Subsequently, IL-1ß contributed to the postprandial stimulation of insulin secretion. Accordingly, lack of endogenous IL-1ß signaling in mice during refeeding and obesity diminished the concentration of insulin in plasma. IL-1ß and insulin increased the uptake of glucose into macrophages, and insulin reinforced a pro-inflammatory pattern via the insulin receptor, glucose metabolism, production of reactive oxygen species, and secretion of IL-1ß mediated by the NLRP3 inflammasome. Postprandial inflammation might be limited by normalization of glycemia, since it was prevented by inhibition of the sodium-glucose cotransporter SGLT2. Our findings identify a physiological role for IL-1ß and insulin in the regulation of both metabolism and immunity.

IL-33 Deals with the Gray Matter.

The central nervous system undergoes extensive postnatal synapse remodeling that is critical for the formation of mature neural circuits. In a recent issue of Science, Vainchtein et al. (2018) describe an additional role for astrocyte-derived interleukin-33 (IL-33) in promoting synapse refinement by microglia in the developing brain.

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.

Interleukin-33-Activated Islet-Resident Innate Lymphoid Cells Promote Insulin Secretion through Myeloid Cell Retinoic Acid Production.

Pancreatic-islet inflammation contributes to the failure of ß cell insulin secretion during obesity and type 2 diabetes. However, little is known about the nature and function of resident immune cells in this context or in homeostasis. Here we show that interleukin (IL)-33 was produced by islet mesenchymal cells and enhanced by a diabetes milieu (glucose, IL-1ß, and palmitate). IL-33 promoted ß cell function through islet-resident group 2 innate lymphoid cells (ILC2s) that elicited retinoic acid (RA)-producing capacities in macrophages and dendritic cells via the secretion of IL-13 and colony-stimulating factor 2. In turn, local RA signaled to the ß cells to increase insulin secretion. This IL-33-ILC2 axis was activated after acute ß cell stress but was defective during chronic obesity. Accordingly, IL-33 injections rescued islet function in obese mice. Our findings provide evidence that an immunometabolic crosstalk between islet-derived IL-33, ILC2s, and myeloid cells fosters insulin secretion.

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.

Islet Inflammation and ß Cell Dysfunction in Type 2 Diabetes.

Pancreatic islets are the body's central rheostat that regulates glucose homeostasis through the production of different hormones, including ß cell-derived insulin. During obesity-induced type 2 diabetes (T2D), islet ß cells become dysfunctional and inadequate insulin secretion no longer ensures glycemic control. T2D is associated with a chronic low-grade inflammation that manifests in several metabolic organs including the pancreatic islets. Growing evidence suggests that components of the innate immune system, and especially macrophages, play a crucial role in regulating islet homeostasis. Yet, the phenotypes and functions of islet macrophages in physiology and during T2D have only started to attract attention and remain unclear. In this review, the current knowledge about islet inflammation and macrophages will be summarized in humans and rodent models. Recent findings on the cellular and molecular mechanisms involved in islet remodeling and ß cell function during obesity and T2D will be discussed.

Glucose-Dependent Insulinotropic Peptide Stimulates Glucagon-Like Peptide 1 Production by Pancreatic Islets via Interleukin 6, Produced by α Cells.

BACKGROUND & AIMS: Glucose-dependent insulinotropic peptide (GIP) induces production of interleukin 6 (IL6) by adipocytes. IL6 increases production of glucagon-like peptide (GLP)-1 by L cells and α cells, leading to secretion of insulin from ß cells. We investigated whether GIP regulates GLP1 and glycemia via IL6. METHODS: We obtained samples of human pancreatic islets and isolated islets from mice; human α cells and ß cells were sorted by flow cytometry and incubated with GIP. Islets were analyzed by quantitative polymerase chain reaction and immunohistochemistry. BKS.Cg-Dock7m+/+ Leprdb/J db/db mice (diabetic mice) and db/+ mice, as well as C57BL/6J IL6-knockout mice (IL6-KO) and C57BL/6J mice with the full-length Il6 gene (controls), were fed a chow or a high-fat diet; some mice were given injections of recombinant GIP, IL6, GLP, a neutralizing antibody against IL6 (anti-IL6), lipopolysaccharide, and/or IL1B. Mice were given a glucose challenge and blood samples were collected and analyzed. RESULTS: Incubation of mouse and human pancreatic α cells with GIP induced their production of IL6, leading to production of GLP1 and insulin secretion from pancreatic islets. This did not occur in islets from IL6-KO mice or in islets incubated with anti-IL6. Incubation of islets with IL1B resulted in IL6 production but directly reduced GLP1 production. Incubation of mouse islets with the sodium glucose transporter 2 inhibitor dapagliflozin induced production of GLP1 and IL6. Injection of control mice with GIP increased plasma levels of GLP1, insulin, and glucose tolerance; these effects were amplified in mice given lipopolysaccharide but reduced in IL6-KO mice or in mice given anti-IL6. Islets from diabetic mice had increased levels of IL1B and IL6, compared with db/+ mice, but injection of GIP did not lead to production of GLP1 or reduce glycemia. CONCLUSIONS: In studies of pancreatic islets from human beings and mice, we found that GIP induces production of IL6 by α cells, leading to islet production of GLP1 and insulin. This process is regulated by inflammation, via IL1B, and by sodium glucose transporter 2. In diabetic mice, increased islet levels of IL6 and IL1B might increase or reduce the production of GLP1 and affect glycemia.

Adipose tissue adaptive response to trans-10,cis-12-conjugated linoleic acid engages alternatively activated M2 macrophages.

In mice, nutritional supplementation with the trans-10,cis-12 isomer of linoleic acid (t10,c12-CLA) promotes lipoatrophy, hyperinsulinemia, and macrophage infiltration in white adipose tissue (WAT). We explored the dynamics of these interrelated responses over 2 consecutive 7 d periods of t10,c12-CLA administration and withdrawal. t10,c12-CLA down-regulated lipogenic and lipolytic gene expression and increased collagen deposition, but with no evidence of cross-linking. An abundant CD45(+) cell infiltrate, comprising prominently CD206(+)CD11c(-) macrophages, was found in WAT in association with an anti-inflammatory gene signature. Infiltration of natural killer (NK) and dendritic cells contributed to WAT's innate immune response to t10,c12-CLA. Less abundant adaptive immune cells colonized WAT, including B, NK T, γδ T, and αß T cells. By contrast, T-regulatory cell abundance was not affected. Interruption of treatment allowed recovery of WAT mass and normalization of insulinemia, coincident with regain of WAT homeostasis owing to a coordinated reversion of genic, structural, and immune deregulations. These data revealed a striking resilience of WAT after a short-term metabolic injury induced by t10,c12-CLA, which relies on alternatively activated M2 macrophage engagement. In addition, the temporal links between variations in WAT alterations and insulinemia upon t10,c12-CLA manipulation strengthen the view that WAT dysfunctional status is critically involved in altered glucose homeostasis.

Defining macrophage phenotype and function in adipose tissue.

In obesity, chronic low-grade inflammation is thought to mediate the effects of increased adipose tissue mass on metabolic comorbidity. Of the different cell types that contribute to obesity-induced inflammation in adipose tissue, this review focuses on macrophages and their monocytes precursors. Mechanisms for monocyte recruitment to adipose tissue, and how both monocytes and macrophages are phenotypically modified in this environment in response to increasing fat mass, are considered. The versatile phenotype of adipose tissue macrophages might contribute not only to inflammatory and metabolic alterations, but could also help to maintain adipose tissue homeostasis in the setting of obesity.

mTOR inhibition suppresses salinomycin-induced ferroptosis in breast cancer stem cells by ironing out mitochondrial dysfunctions.

Ferroptosis constitutes a promising therapeutic strategy against cancer by efficiently targeting the highly tumorigenic and treatment-resistant cancer stem cells (CSCs). We previously showed that the lysosomal iron-targeting drug Salinomycin (Sal) was able to eliminate CSCs by triggering ferroptosis. Here, in a well-established breast CSCs model (human mammary epithelial HMLER CD24low/CD44high), we identified that pharmacological inhibition of the mechanistic target of rapamycin (mTOR), suppresses Sal-induced ferroptosis. Mechanistically, mTOR inhibition modulates iron cellular flux and thereby limits iron-mediated oxidative stress. Furthermore, integration of multi-omics data identified mitochondria as a key target of Sal action, leading to profound functional and structural alteration prevented by mTOR inhibition. On top of that, we found that Sal-induced metabolic plasticity is mainly dependent on the mTOR pathway. Overall, our findings provide experimental evidence for the mechanisms of mTOR as a crucial effector of Sal-induced ferroptosis pointing not only that metabolic reprogramming regulates ferroptosis, but also providing proof-of-concept that careful evaluation of such combination therapy (here mTOR and ferroptosis co-targeting) is required in the development of an effective treatment.

CD14dimCD16+ and CD14+CD16+ monocytes in obesity and during weight loss: relationships with fat mass and subclinical atherosclerosis.

OBJECTIVE: Studies suggest the implication of CD16(+) subpopulations (CD14(+)CD16(+), CD14(dim)CD16(+)) in inflammatory diseases. We aimed to determine the frequency of these subpopulations during weight loss in obesity and diabetes, conditions associated with changes in systemic inflammation, and we tested the link with subclinical atherosclerosis. METHODS AND RESULTS: CD14(dim)CD16(+) and CD14(+)CD16(+) frequencies were measured by flow cytometry in lean subjects, obese subjects before and after a hypocaloric diet or gastric surgery, and obese diabetic subjects before and after gastric surgery. Both monocyte subsets were increased in obese subjects, with a significant enrichment of the CD14(dim)CD16(+) subpopulation in obese diabetic patients. Multivariate analysis demonstrated a link between the percentages of CD14(dim)CD16(+) monocytes and glycemia, independent of fat mass. Drastic weight loss led to a sharp decrease of this subset, the variations of which were strongly related to fat mass changes. A reduction of at least 5% of fat mass was sufficient to observe a significant decrease of CD14(dim)CD16(+) monocytes. A diminution of the CD14(+)CD16(+) subset was also observed during weight loss and was associated with a decrease in intima-media thickness. CONCLUSIONS: This work demonstrates a major impact of fat mass variations on CD14(dim)CD16(+) monocyte subsets and that the decrease in the CD14(+)CD16(+) subpopulation is linked to a reduction of subclinical atherosclerosis. CLINICAL TRIAL REGISTRATION: URL: http://clinicaltrials.gov. Unique identifier: NCT00476658.

Targeting colonic macrophages improves glycemic control in high-fat diet-induced obesity.

The obesity epidemic continues to worsen worldwide. However, the mechanisms initiating glucose dysregulation in obesity remain poorly understood. We assessed the role that colonic macrophage subpopulations play in glucose homeostasis in mice fed a high-fat diet (HFD). Concurrent with glucose intolerance, pro-inflammatory/monocyte-derived colonic macrophages increased in mice fed a HFD. A link between macrophage numbers and glycemia was established by pharmacological dose-dependent ablation of macrophages. In particular, colon-specific macrophage depletion by intrarectal clodronate liposomes improved glucose tolerance, insulin sensitivity, and insulin secretion capacity. Colonic macrophage activation upon HFD was characterized by an interferon response and a change in mitochondrial metabolism, which converged in mTOR as a common regulator. Colon-specific mTOR inhibition reduced pro-inflammatory macrophages and ameliorated insulin secretion capacity, similar to colon-specific macrophage depletion, but did not affect insulin sensitivity. Thus, pharmacological targeting of colonic macrophages could become a potential therapy in obesity to improve glycemic control.

[Adipose tissue, a new playground for immune cells]. / Le tissu adipeux - Un nouveau terrain de jeu pour les cellules immunitaires.

Adipose tissue has been under focus in the last decade and pivotal concepts have emerged from the studies of its complex biology. Low-grade inflammation both at the systemic level and in adipose tissue itself characterizes obesity. Among the different cell types contributing to inflammation, this review focuses on the mechanisms and consequences of macrophage accumulation in obese adipose tissue. Mechanisms for monocyte recruitment to adipose tissue, and how macrophages' phenotypes are modified in this environment in response to increasing fat mass, are considered. We review recent studies addressing the complex and versatile phenotype of adipose tissue macrophages that contribute to inflammatory and metabolic alterations, but could also help to maintain adipose tissue homeostasis in the setting of obesity both in mouse and human situations. A newly discovered consequence of adipose tissue inflammation is fibrosis. Whether macrophages and/or other immune cells exert a pro-fibrotic effect in adipose tissue is still unclear. This wealth of new information will hopefully help to design new ways to control adipose tissue inflammation and its deleterious sequels.

Mechanisms of Macrophage Polarization in Insulin Signaling and Sensitivity.

Type-2 diabetes (T2D) is a disease of two etiologies: metabolic and inflammatory. At the cross-section of these etiologies lays the phenomenon of metabolic inflammation. Whilst metabolic inflammation is characterized as systemic, a common starting point is the tissue-resident macrophage, who's successful physiological or aberrant pathological adaptation to its microenvironment determines disease course and severity. This review will highlight the key mechanisms in macrophage polarization, inflammatory and non-inflammatory signaling that dictates the development and progression of insulin resistance and T2D. We first describe the known homeostatic functions of tissue macrophages in insulin secreting and major insulin sensitive tissues. Importantly we highlight the known mechanisms of aberrant macrophage activation in these tissues and the ways in which this leads to impairment of insulin sensitivity/secretion and the development of T2D. We next describe the cellular mechanisms that are known to dictate macrophage polarization. We review recent progress in macrophage bio-energetics, an emerging field of research that places cellular metabolism at the center of immune-effector function. Importantly, following the advent of the metabolically-activated macrophage, we cover the known transcriptional and epigenetic factors that canonically and non-canonically dictate macrophage differentiation and inflammatory polarization. In closing perspectives, we discuss emerging research themes and highlight novel non-inflammatory or non-immune roles that tissue macrophages have in maintaining microenvironmental and systemic homeostasis.

Adipocyte Reprogramming by the Transcriptional Coregulator GPS2 Impacts Beta Cell Insulin Secretion.

Glucose homeostasis is maintained through organ crosstalk that regulates secretion of insulin to keep blood glucose levels within a physiological range. In type 2 diabetes, this coordinated response is altered, leading to a deregulation of beta cell function and inadequate insulin secretion. Reprogramming of white adipose tissue has a central role in this deregulation, but the critical regulatory components remain unclear. Here, we demonstrate that expression of the transcriptional coregulator GPS2 in white adipose tissue is correlated with insulin secretion rate in humans. The causality of this relationship is confirmed using adipocyte-specific GPS2 knockout mice, in which inappropriate secretion of insulin promotes glucose intolerance. This phenotype is driven by adipose-tissue-secreted factors, which cause increased pancreatic islet inflammation and impaired beta cell function. Thus, our study suggests that, in mice and in humans, GPS2 controls the reprogramming of white adipocytes to influence pancreatic islet function and insulin secretion.

Monocytopenia, monocyte morphological anomalies and hyperinflammation characterise severe COVID-19 in type 2 diabetes.

Early in the COVID-19 pandemic, type 2 diabetes (T2D) was marked as a risk factor for severe disease and mortality. Inflammation is central to the aetiology of both conditions where variations in immune responses can mitigate or aggravate disease course. Identifying at-risk groups based on immunoinflammatory signatures is valuable in directing personalised care and developing potential targets for precision therapy. This observational study characterised immunophenotypic variation associated with COVID-19 severity in T2D. Broad-spectrum immunophenotyping quantified 15 leucocyte populations in peripheral circulation from a cohort of 45 hospitalised COVID-19 patients with and without T2D. Lymphocytopenia and specific loss of cytotoxic CD8+ lymphocytes were associated with severe COVID-19 and requirement for intensive care in both non-diabetic and T2D patients. A morphological anomaly of increased monocyte size and monocytopenia restricted to classical CD14Hi CD16- monocytes was specifically associated with severe COVID-19 in patients with T2D requiring intensive care. Increased expression of inflammatory markers reminiscent of the type 1 interferon pathway (IL6, IL8, CCL2, INFB1) underlaid the immunophenotype associated with T2D. These immunophenotypic and hyperinflammatory changes may contribute to increased voracity of COVID-19 in T2D. These findings allow precise identification of T2D patients with severe COVID-19 as well as provide evidence that the type 1 interferon pathway may be an actionable therapeutic target for future studies.

Inhibition of IL-1beta improves Glycaemia in a Mouse Model for Gestational Diabetes.

Gestational diabetes mellitus (GDM) is one of the most common diseases associated with pregnancy, however, the underlying mechanisms remain unclear. Based on the well documented role of inflammation in type 2 diabetes, the aim was to investigate the role of inflammation in GDM. We established a mouse model for GDM on the basis of its two major risk factors, obesity and aging. In these GDM mice, we observed increased Interleukin-1ß (IL-1ß) expression in the uterus and the placenta along with elevated circulating IL-1ß concentrations compared to normoglycemic pregnant mice. Treatment with an anti-IL-1ß antibody improved glucose-tolerance of GDM mice without apparent deleterious effects for the fetus. Finally, IL-1ß antagonism showed a tendency for reduced plasma corticosterone concentrations, possibly explaining the metabolic improvement. We conclude that IL-1ß is a causal driver of impaired glucose tolerance in GDM.

Innate immune priming of insulin secretion.

Increasing evidence suggests a role for the immune system to finely tune metabolic homeostasis. The possibility that the immune system can likewise regulate islet endocrine function has only commenced drawing attention. Islet beta cells are the main producers of insulin and have to dynamically respond to fluctuating insulin demands of the body. While inflammation has long been considered as an important pathogenic feature of diabetes development, pioneer studies have shown that immune cells reside inside pancreatic islets under steady state and that components of the immune system can promote beta cell insulin production. The present review will thus highlight the recent research on specific immune pathways regulating beta cell function discussing the beneficial influence of innate immune cells.

Role of innate immune cells in metabolism: from physiology to type 2 diabetes.

Growing evidence suggests that components of the innate immune system play a crucial role in regulating metabolic homeostasis. Macrophages were the primary immune cells to be described in both the white adipose tissue and the pancreatic islets. Therein, their functions, beneficial or detrimental, are extending under steady state and in the context of obesity-induced type 2 diabetes. Other populations, including innate lymphoid cells, are emerging as key sentinels of metabolic tissues and privileged partners of macrophages. The present review will thus explore the phenotype and the role of innate immune cells in metabolic physiology and dysfunction. Discussion will tackle pending questions and future perspectives in the field of immunometabolism.

ß Cell-Specific Deletion of the IL-1 Receptor Antagonist Impairs ß Cell Proliferation and Insulin Secretion.

Interleukin-1 receptor antagonist (IL-1Ra) is elevated in the circulation during obesity and type 2 diabetes (T2D) but is decreased in islets from patients with T2D. The protective role of local IL-1Ra was investigated in pancreatic islet ß cell (ßIL-1Ra)-specific versus myeloid-cell (myeloIL-1Ra)-specific IL-1Ra knockout (KO) mice. Deletion of IL-1Ra in ß cells, but not in myeloid cells, resulted in diminished islet IL-1Ra expression. Myeloid cells were not the main source of circulating IL-1Ra in obesity. ßIL-1Ra KO mice had impaired insulin secretion, reduced ß cell proliferation, and decreased expression of islet proliferation genes, along with impaired glucose tolerance. The key cell-cycle regulator E2F1 partly reversed IL-1ß-mediated inhibition of potassium channel Kir6.2 expression and rescued impaired insulin secretion in IL-1Ra knockout islets. Our findings provide evidence for the importance of ß cell-derived IL-1Ra for the local defense of ß cells to maintain normal function and proliferation.