Prohormone convertase 1/3 deficiency causes obesity due to impaired proinsulin processing

Defective insulin processing is associated with obesity and diabetes. Prohormone convertase 1/3 (PC1/3) is an endopeptidase required for the processing of neurotransmitters and hormones. PC1/3 deficiency and genome-wide association studies relate PC1/3 with early onset obesity. Here, we find that deletion of PC1/3 in obesity-related neuronal cells expressing proopiomelanocortin mildly and transiently change body weight and fail to produce a phenotype when targeted to Agouti-related peptide- or nestin-expressing tissues. In contrast, pancreatic β cell-specific PC1/3 ablation induces hyperphagia with consecutive obesity despite uncontrolled diabetes with glucosuria. Obesity develops not due to impaired pro-islet amyloid polypeptide processing but due to impaired insulin maturation. Proinsulin crosses the blood-brain-barrier but does not induce central satiety. Accordingly, insulin therapy prevents hyperphagia. Further, islet PC1/3 expression levels negatively correlate with body mass index in humans. In this work, we show that impaired PC1/3-mediated proinsulin processing, as observed in human prediabetes, promotes hyperphagic obesity

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-1β (IL-1β) expression in the uterus and the placenta along with elevated circulating IL-1β concentrations compared to normoglycemic pregnant mice. Treatment with an anti-IL-1β antibody improved glucose-tolerance of GDM mice without apparent deleterious effects for the fetus. Finally, IL-1β antagonism showed a tendency for reduced plasma corticosterone concentrations, possibly explaining the metabolic improvement. We conclude that IL-1β is a causal driver of impaired glucose tolerance in GDM

The Role of Inflammation in β-cell Dedifferentiation

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

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

The deleterious effect of chronic activation of the IL-1β system on type 2 diabetes and other metabolic diseases is well documented. However, a possible physiological role for IL-1β in glucose metabolism has remained unexplored. Here we found that feeding induced a physiological increase in the number of peritoneal macrophages that secreted IL-1β, in a glucose-dependent manner. Subsequently, IL-1β contributed to the postprandial stimulation of insulin secretion. Accordingly, lack of endogenous IL-1β signaling in mice during refeeding and obesity diminished the concentration of insulin in plasma. IL-1β 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-1β 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-1β and insulin in the regulation of both metabolism and immunity

β Cell-Specific Deletion of the IL-1 Receptor Antagonist Impairs β 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 β cell (βIL-1Ra)-specific versus myeloid-cell (myeloIL-1Ra)-specific IL-1Ra knockout (KO) mice. Deletion of IL-1Ra in β 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. βIL-1Ra KO mice had impaired insulin secretion, reduced β cell proliferation, and decreased expression of islet proliferation genes, along with impaired glucose tolerance. The key cell-cycle regulator E2F1 partly reversed IL-1β-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 β cell-derived IL-1Ra for the local defense of β cells to maintain normal function and proliferation

Pancreatic α Cell-Derived Glucagon-Related Peptides Are Required for β 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 β cell function remains unclear. We studied effects of locally derived insulin secretagogues on β 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