TonEBP/NFAT5 haploinsufficiency attenuates hippocampal inflammation in high-fat diet/streptozotocin-induced diabetic mice

Recent studies have shown that overexpression of tonicity-responsive enhancer binding protein (TonEBP) is associated with many inflammatory diseases, including diabetes mellitus, which causes neuroinflammation in the hippocampus as well as hepatic steatosis. However, the exact mechanism in diabetic neuroinflammation is unknown. We report that haploinsufficiency of TonEBP inhibits hepatic and hippocampal high-mobility group box-1 (HMGB1) expression in diabetic mice. Here, mice were fed a high-fat diet (HFD) for 16 weeks and received an intraperitoneal injection of 100 mg/kg streptozotocin (STZ) and followed by continued HFD feeding for an additional 4 weeks to induce hyperglycemia and hepatic steatosis. Compared with wild-type diabetic mice, diabetic TonEBP(+/-) mice showed decreased body weight, fat mass, hepatic steatosis, and macrophage infiltration. We also found that adipogenesis and HMGB1 expression in the liver and hippocampus were lower in diabetic TonEBP(+/-) mice compared with the wild type. Furthermore, iba-1 immunoreactivity in the hippocampus was decreased in diabetic TonEBP(+/-) mice compared with that in the wild type. Our findings suggest that TonEBP haploinsufficiency suppresses diabetes-associated hepatic steatosis and neuroinflammation

Beta-cell specific Insr deletion promotes insulin hypersecretion and improves glucose tolerance prior to global insulin resistance

Insulin receptor (Insr) protein is present at higher levels in pancreatic β-cells than in most other tissues, but the consequences of β-cell insulin resistance remain enigmatic. Here, we use an Ins1 knock-in allele to delete Insr specifically in β-cells of both female and male mice. We compare experimental mice to Ins1 -containing littermate controls at multiple ages and on multiple diets. RNA-seq of purified recombined β-cells reveals transcriptomic consequences of Insr loss, which differ between female and male mice. Action potential and calcium oscillation frequencies are increased in Insr knockout β-cells from female, but not male mice, whereas only male βInsr islets have reduced ATP-coupled oxygen consumption rate and reduced expression of genes involved in ATP synthesis. Female βInsr and βInsr mice exhibit elevated insulin release in ex vivo perifusion experiments, during hyperglycemic clamps, and following i.p. glucose challenge. Deletion of Insr does not alter β-cell area up to 9 months of age, nor does it impair hyperglycemia-induced proliferation. Based on our data, we adapt a mathematical model to include β-cell insulin resistance, which predicts that β-cell Insr knockout improves glucose tolerance depending on the degree of whole-body insulin resistance. Indeed, glucose tolerance is significantly improved in female βInsr and βInsr mice compared to controls at 9, 21 and 39 weeks, and also in insulin-sensitive 4-week old males. We observe no improved glucose tolerance in older male mice or in high fat diet-fed mice, corroborating the prediction that global insulin resistance obscures the effects of β-cell specific insulin resistance. The propensity for hyperinsulinemia is associated with mildly reduced fasting glucose and increased body weight. We further validate our main in vivo findings using an Ins1-CreERT transgenic line and find that male mice have improved glucose tolerance 4 weeks after tamoxifen-mediated Insr deletion. Collectively, our data show that β-cell insulin resistance in the form of reduced β-cell Insr contributes to hyperinsulinemia in the context of glucose stimulation, thereby improving glucose homeostasis in otherwise insulin sensitive sex, dietary and age contexts

High-fat diet combined with low-dose streptozotocin injections induces metabolic syndrome in Macaca mulatta

Metabolic syndrome (MetS) is associated with abdominal obesity, hyperlipidemia, insulin resistance, and type 2 diabetes mellitus, and increases the risk of cardiovascular disease. Given the complex multifactorial pathogenesis of MetS, qualified animal models are currently seriously limited for researchers. The aim of our study was to develop a MetS model in juvenile rhesus monkeys (Macaca mulatta). Rhesus monkeys (1-year-old) fed a high-fat diet (15 % fat, 2 % cholesterol) were used as the HF group (n = 6), and those on a normal diet (5 % fat) were used as the control group (n = 4). After being fed a high-fat diet for approximately 12 months, 2 monkeys (HF + STZ group) were injected with low-dose streptozotocin (STZ, 25 mg/kg) twice, with a 7 days interval, and were then fed the same diet continuously for another 24 months. After 36 months of treatment, the high-fat diet monkeys, including the HF and HF + STZ groups, had acquired increased body weights, abnormal serum lipids, and impaired glucose tolerance compared to the control group. In addition, much more marked metabolic changes were observed in the two monkeys of the HF + STZ group, particularly in terms of high-blood glucose level and insulin resistance. Morphological observation of biopsies of liver and pancreatic tissues showed decreased islet number and mass and decreased insulin staining in the monkeys of the HF + STZ group. In addition, Oil red O staining suggested remarkable accumulation of lipid droplets in the hepatocytes. Our study suggested that a long-term high-fat diet followed with a low-dose STZ was able to induce MetS in juvenile rhesus monkeys with faster pathophysiological progress compared with high-fat diet induction alone. Our primary data showed that this method may have potentials to develop MetS animal model in non-human primates