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.

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.

Insulin receptor plays a central role in skin carcinogenesis by regulating cytoskeleton assembly.

Diabetes mellitus prevalence is increasing rapidly and is a major cause of mortality and morbidity worldwide. In addition to the known severe complications associated with the disease, in recent years diabetes has been recognized as a major risk factor for cancer. Patients with diabetes experience significantly higher incidence of and higher mortality rates from many types of cancer. However, to date there are no conclusive data on the pathophysiology underlying the association between these two diseases. We previously reported that insulin regulates skin proliferation and differentiation, while IGF1 had different sometimes contrasting effects to those of insulin, suggesting direct involvement of insulin in transformation. To this end, we developed an epidermal skin-specific insulin receptor knockout (SIRKO) mouse, in which the insulin receptor (IR) is inactivated only in skin, with no other metabolic consequences. We found that IR inactivation by itself resulted in a marked decrease in skin tumorigenesis. In the control group 100% of the mice developed tumors, but in the SIRKO group tumor incidence was over 60% lower, and 25% of the SIRKO mice did not develop tumors at all, and the tumors that did develop were smaller and benign in their appearance. Furthermore, IR inactivation in vitro not only prevented cell transformation but also reversed the keratinocyte-transformed phenotype. We found that IR inactivation led to a striking abnormality in the major keratin cytoskeleton filaments structure in both in vivo and in vitro, a change that we were able to link to the decreased transformation potential in IR-null cells. In summary, we identified a unique pathway in which IR regulates cytoskeletal assembly, thus affecting skin transformation, opening a new potential target for cancer treatment and prevention.-Weingarten, G., Ben Yaakov, A., Dror, E., Russ, J., Magin, T. M., Kahn, C. R., Wertheimer, E. Insulin receptor plays a central role in skin carcinogenesis by regulating cytoskeleton assembly.

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.

IL-1ß promotes adipogenesis by directly targeting adipocyte precursors.

Postprandial IL-1ß surges are predominant in the white adipose tissue (WAT), but its consequences are unknown. Here, we investigate the role of IL-1ß in WAT energy storage and show that adipocyte-specific deletion of IL-1 receptor 1 (IL1R1) has no metabolic consequences, whereas ubiquitous lack of IL1R1 reduces body weight, WAT mass, and adipocyte formation in mice. Among all major WAT-resident cell types, progenitors express the highest IL1R1 levels. In vitro, IL-1ß potently promotes adipogenesis in murine and human adipose-derived stem cells. This effect is exclusive to early-differentiation-stage cells, in which the adipogenic transcription factors C/EBPδ and C/EBPß are rapidly upregulated by IL-1ß and enriched near important adipogenic genes. The pro-adipogenic, but not pro-inflammatory effect of IL-1ß is potentiated by acute treatment and blocked by chronic exposure. Thus, we propose that transient postprandial IL-1ß surges regulate WAT remodeling by promoting adipogenesis, whereas chronically elevated IL-1ß levels in obesity blunts this physiological function.

Developmental priming of cancer susceptibility.

DNA mutations are necessary drivers of cancer, yet only a small subset of mutated cells go on to cause the disease. To date, the mechanisms that determine which rare subset of cells transform and initiate tumorigenesis remain unclear. Here, we take advantage of a unique model of intrinsic developmental heterogeneity (Trim28+/D9) and demonstrate that stochastic early life epigenetic variation can trigger distinct cancer-susceptibility 'states' in adulthood. We show that these developmentally primed states are characterized by differential methylation patterns at typically silenced heterochromatin, and that these epigenetic signatures are detectable as early as 10 days of age. The differentially methylated loci are enriched for genes with known oncogenic potential. These same genes are frequently mutated in human cancers, and their dysregulation correlates with poor prognosis. These results provide proof-of-concept that intrinsic developmental heterogeneity can prime individual, life-long cancer risk.

A rapid microglial metabolic response controls metabolism and improves memory.

Chronic high-fat feeding triggers widespread metabolic dysfunction including obesity, insulin resistance, and diabetes. While these ultimate pathological states are relatively well understood, we have a limited understanding of how high-fat intake first triggers physiological changes. Here, we identify an acute microglial metabolic response that rapidly translates intake of high-fat diet (HFD) to a surprisingly beneficial effect on spatial and learning memory. Acute high-fat intake increases palmitate levels in cerebrospinal fluid and triggers a wave of microglial metabolic activation characterized by mitochondrial membrane activation, fission and metabolic skewing towards aerobic glycolysis. These effects are generalized, detectable in the hypothalamus, hippocampus, and cortex all within 1-3 days of HFD exposure. In vivo microglial ablation and conditional DRP1 deletion experiments show that the microglial metabolic response is necessary for the acute effects of HFD. 13C-tracing experiments reveal that in addition to processing via ß-oxidation, microglia shunt a substantial fraction of palmitate towards anaplerosis and re-release of bioenergetic carbons into the extracellular milieu in the form of lactate, glutamate, succinate, and intriguingly, the neuro-protective metabolite itaconate. Together, these data identify microglial cells as a critical nutrient regulatory node in the brain, metabolizing away harmful fatty acids and liberating the same carbons instead as alternate bioenergetic and protective substrates. The data identify a surprisingly beneficial effect of short-term HFD on learning and memory.

Epigenetic dosage identifies two major and functionally distinct ß cell subtypes.

The mechanisms that specify and stabilize cell subtypes remain poorly understood. Here, we identify two major subtypes of pancreatic ß cells based on histone mark heterogeneity (ßHI and ßLO). ßHI cells exhibit ∼4-fold higher levels of H3K27me3, distinct chromatin organization and compaction, and a specific transcriptional pattern. ßHI and ßLO cells also differ in size, morphology, cytosolic and nuclear ultrastructure, epigenomes, cell surface marker expression, and function, and can be FACS separated into CD24+ and CD24- fractions. Functionally, ßHI cells have increased mitochondrial mass, activity, and insulin secretion in vivo and ex vivo. Partial loss of function indicates that H3K27me3 dosage regulates ßHI/ßLO ratio in vivo, suggesting that control of ß cell subtype identity and ratio is at least partially uncoupled. Both subtypes are conserved in humans, with ßHI cells enriched in humans with type 2 diabetes. Thus, epigenetic dosage is a novel regulator of cell subtype specification and identifies two functionally distinct ß cell subtypes.

The cephalic phase of insulin release is modulated by IL-1ß.

The initial cephalic phase of insulin secretion is mediated through the vagus nerve and is not due to glycemic stimulation of pancreatic ß cells. Recently, IL-1ß was shown to stimulate postprandial insulin secretion. Here, we describe that this incretin-like effect of IL-1ß involves neuronal transmission. Furthermore, we found that cephalic phase insulin release was mediated by IL-1ß originating from microglia. Moreover, IL-1ß activated the vagus nerve to induce insulin secretion and regulated the activity of the hypothalamus in response to cephalic stimulation. Notably, cephalic phase insulin release was impaired in obesity, in both mice and humans, and in mice, this was due to dysregulated IL-1ß signaling. Our findings attribute a regulatory role to IL-1ß in the integration of nutrient-derived sensory information, subsequent neuronally mediated insulin secretion, and the dysregulation of autonomic cephalic phase responses in obesity.

Independent phenotypic plasticity axes define distinct obesity sub-types.

Studies in genetically 'identical' individuals indicate that as much as 50% of complex trait variation cannot be traced to genetics or to the environment. The mechanisms that generate this 'unexplained' phenotypic variation (UPV) remain largely unknown. Here, we identify neuronatin (NNAT) as a conserved factor that buffers against UPV. We find that Nnat deficiency in isogenic mice triggers the emergence of a bi-stable polyphenism, where littermates emerge into adulthood either 'normal' or 'overgrown'. Mechanistically, this is mediated by an insulin-dependent overgrowth that arises from histone deacetylase (HDAC)-dependent ß-cell hyperproliferation. A multi-dimensional analysis of monozygotic twin discordance reveals the existence of two patterns of human UPV, one of which (Type B) phenocopies the NNAT-buffered polyphenism identified in mice. Specifically, Type-B monozygotic co-twins exhibit coordinated increases in fat and lean mass across the body; decreased NNAT expression; increased HDAC-responsive gene signatures; and clinical outcomes linked to insulinemia. Critically, the Type-B UPV signature stratifies both childhood and adult cohorts into four metabolic states, including two phenotypically and molecularly distinct types of obesity.

Distinct Transcriptional Responses across Tissue-Resident Macrophages to Short-Term and Long-Term Metabolic Challenge.

The innate immune system safeguards the organism from both pathogenic and environmental stressors. Also, physiologic levels of nutrients affect organismal and intra-cellular metabolism and challenge the immune system. In the long term, over-nutrition leads to low-grade systemic inflammation. Here, we investigate tissue-resident components of the innate immune system (macrophages) and their response to short- and long-term nutritional challenges. We analyze the transcriptomes of six tissue-resident macrophage populations upon acute feeding and identify adipose tissue macrophages and the IL-1 pathway as early sensors of metabolic changes. Furthermore, by comparing functional responses between macrophage subtypes, we propose a regulatory, anti-inflammatory role of heat shock proteins of the HSP70 family in response to long- and short-term metabolic challenges. Our data provide a resource for assessing the impact of nutrition and over-nutrition on the spectrum of macrophages across tissues with a potential for identification of systemic responses.

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.

Over-expression of a retinol dehydrogenase (SRP35/DHRS7C) in skeletal muscle activates mTORC2, enhances glucose metabolism and muscle performance.

SRP-35 is a short-chain dehydrogenase/reductase belonging to the DHRS7C dehydrogenase/ reductase family 7. Here we show that its over-expression in mouse skeletal muscles induces enhanced muscle performance in vivo, which is not related to alterations in excitation-contraction coupling but rather linked to enhanced glucose metabolism. Over-expression of SRP-35 causes increased phosphorylation of AktS473, triggering plasmalemmal targeting of GLUT4 and higher glucose uptake into muscles. SRP-35 signaling involves RARα and RARγ (non-genomic effect), PI3K and mTORC2. We also demonstrate that all-trans retinoic acid, a downstream product of the enzymatic activity of SRP-35, mimics the effect of SRP-35 in skeletal muscle, inducing a synergistic effect with insulin on AKTS473 phosphorylation. These results indicate that SRP-35 affects skeletal muscle metabolism and may represent an important target for the treatment of metabolic diseases.

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.

The Polycomb-Dependent Epigenome Controls ß Cell Dysfunction, Dedifferentiation, and Diabetes.

To date, it remains largely unclear to what extent chromatin machinery contributes to the susceptibility and progression of complex diseases. Here, we combine deep epigenome mapping with single-cell transcriptomics to mine for evidence of chromatin dysregulation in type 2 diabetes. We find two chromatin-state signatures that track ß cell dysfunction in mice and humans: ectopic activation of bivalent Polycomb-silenced domains and loss of expression at an epigenomically unique class of lineage-defining genes. ß cell-specific Polycomb (Eed/PRC2) loss of function in mice triggers diabetes-mimicking transcriptional signatures and highly penetrant, hyperglycemia-independent dedifferentiation, indicating that PRC2 dysregulation contributes to disease. The work provides novel resources for exploring ß cell transcriptional regulation and identifies PRC2 as necessary for long-term maintenance of ß cell identity. Importantly, the data suggest a two-hit (chromatin and hyperglycemia) model for loss of ß cell identity in diabetes.

The Role of Inflammation in ß-cell Dedifferentiation.

Chronic inflammation impairs insulin secretion and sensitivity. ß-cell dedifferentiation has recently been proposed as a mechanism underlying ß-cell failure in T2D. Yet the effect of inflammation on ß-cell identity in T2D has not been studied. Therefore, we investigated whether pro-inflammatory cytokines induce ß-cell dedifferentiation and whether anti-inflammatory treatments improve insulin secretion via ß-cell redifferentiation. We observed that IL-1ß, IL-6 and TNFα promote ß-cell dedifferentiation in cultured human and mouse islets, with IL-1ß being the most potent one of them. In particular, ß-cell identity maintaining transcription factor Foxo1 was downregulated upon IL-1ß exposure. In vivo, anti-IL-1ß, anti-TNFα or NF-kB inhibiting sodium salicylate treatment improved insulin secretion of isolated islets. However, only TNFα antagonism partially prevented the loss of ß-cell identity gene expression. Finally, the combination of IL-1ß and TNFα antagonism improved insulin secretion of ex vivo isolated islets in a synergistic manner. Thus, while inflammation triggered ß-cell dedifferentiation and dysfunction in vitro, this mechanism seems to be only partly responsible for the observed in vivo improvements in insulin secretion.

Pancreatic α Cell-Derived Glucagon-Related Peptides Are Required for ß Cell Adaptation and Glucose Homeostasis.

Pancreatic α cells may process proglucagon not only to glucagon but also to glucagon-like peptide-1 (GLP-1). However, the biological relevance of paracrine GLP-1 for ß cell function remains unclear. We studied effects of locally derived insulin secretagogues on ß cell function and glucose homeostasis using mice with α cell ablation and with α cell-specific GLP-1 deficiency. Normally, intestinal GLP-1 compensates for the lack of α cell-derived GLP-1. However, upon aging and metabolic stress, glucose tolerance is impaired. This was partly rescued with the DPP-4 inhibitor sitagliptin, but not with glucagon administration. In isolated islets from these mice, glucose-stimulated insulin secretion was heavily impaired and exogenous GLP-1 or glucagon rescued insulin secretion. These data highlight the importance of α cell-derived GLP-1 for glucose homeostasis during metabolic stress and may impact on the clinical use of systemic GLP-1 agonists versus stabilizing local α cell-derived GLP-1 by DPP-4 inhibitors in type 2 diabetes.

Angiotensin II induces interleukin-1ß-mediated islet inflammation and ß-cell dysfunction independently of vasoconstrictive effects.

Pathological activation of the renin-angiotensin system (RAS) is associated with the metabolic syndrome, and the new onset of type 2 diabetes can be delayed by RAS inhibition. In animal models of type 2 diabetes, inhibition of the RAS improves insulin secretion. However, the direct effects of angiotensin II on islet function and underlying mechanisms independent of changes in blood pressure remain unclear. Here we show that exposure of human and mouse islets to angiotensin II induces interleukin (IL)-1-dependent expression of IL-6 and MCP-1, enhances ß-cell apoptosis, and impairs mitochondrial function and insulin secretion. In vivo, mice fed a high-fat diet and treated with angiotensin II and the vasodilator hydralazine to prevent hypertension showed defective glucose-stimulated insulin secretion and deteriorated glucose tolerance. Application of an anti-IL-1ß antibody reduced the deleterious effects of angiotensin II on islet inflammation, restored insulin secretion, and improved glycemia. We conclude that angiotensin II leads to islet dysfunction via induction of inflammation and independent of vasoconstriction. Our findings reveal a novel role for the RAS and an additional rationale for the treatment of type 2 diabetic patients with an IL-1ß antagonist.