Neurogenin3-driven deletion of tuberous sclerosis complex 1 (Tsc1) activated mechanistic target of rapamycin complex 1 (mTORC1) measured by the upregulation of mTOR and S6 phosphorylation in islet cells. Neurogenin3-Tsc1−/− mice demonstrated a significant increase in average islet size and mean area of individual islet cell. Insulin mRNA and plasma insulin levels increased significantly after weaning. Glucagon mRNA and plasma levels increased in neonate followed by modest reduction in adult. Somatostatin mRNA and plasma levels markedly increased. Neurogenin3-Tsc1−/− mice fed standard chow demonstrated a significant improvement in glucose tolerance and no alteration in insulin sensitivity. In Neurogenin3-Tsc1−/− mice fed 45% high-fat diets, both glucose tolerance and insulin sensitivity were significantly impaired. Rapamycin reversed the activation of mTORC1, attenuated β cells hypertrophy and abolished the improvement of glucose tolerance. TSC1-mTORC1 signaling plays an important role in the development of pancreatic endocrine cells and in the regulation of glucose metabolism.
Li Ding, Yue Yin, Lingling Han, Yin Li, Jing Zhao and Weizhen Zhang
Yunshuang Yue, Yi Wang, Dan Li, Zhigang Song, Hongchao Jiao and Hai Lin
Bacterial lipopolysaccharide (LPS), also known as endotoxin, induces profound anorexia. However, the LPS-provoked pro-inflammatory signaling cascades and the neural mechanisms underlying the development of anorexia are not clear. Mammalian target of rapamycin (mTOR) is a key regulator of metabolism, cell growth, and protein synthesis. This study aimed to determine whether the mTOR pathway is involved in LPS-induced anorexia. Effects of LPS on hypothalamic gene/protein expression in mice were measured by RT-PCR or western blotting analysis. To determine whether inhibition of mTOR signaling could attenuate LPS-induced anorexia, we administered an i.c.v. injection of rapamycin, an mTOR inhibitor, on LPS-treated male mice. In this study, we showed that LPS stimulates the mTOR signaling pathway through the enhanced phosphorylation of mTORSer2448 and p70S6KThr389. We also showed that LPS administration increased the phosphorylation of FOXO1Ser256, the p65 subunit of nuclear factor kappa B (P<0.05), and FOXO1/3aThr 24 / 32 (P<0.01). Blocking the mTOR pathway significantly attenuated the LPS-induced anorexia by decreasing the phosphorylation of p70S6KThr389, FOXO1Ser256, and FOXO1/3aThr 24 / 32. These results suggest promising approaches for the prevention and treatment of LPS-induced anorexia.
Can Liu, Mian Zhang, Meng-yue Hu, Hai-fang Guo, Jia Li, Yun-li Yu, Shi Jin, Xin-ting Wang, Li Liu and Xiao-dong Liu
Panax ginseng is one of the most popular herbal remedies. Ginsenosides, major bioactive constituents in P. ginseng, have shown good antidiabetic action, but the precise mechanism was not fully understood. Glucagon-like peptide-1 (GLP1) is considered to be an important incretin that can regulate glucose homeostasis in the gastrointestinal tract after meals. The aim of this study was to investigate whether ginseng total saponins (GTS) exerts its antidiabetic effects via modulating GLP1 release. Ginsenoside Rb1 (Rb1), the most abundant constituent in GTS, was selected to further explore the underlying mechanisms in cultured NCI-H716 cells. Diabetic rats were developed by a combination of high-fat diet and low-dose streptozotocin injection. The diabetic rats orally received GTS (150 or 300 mg/kg) daily for 4 weeks. It was found that GTS treatment significantly ameliorated hyperglycemia and dyslipidemia, accompanied by a significant increase in glucose-induced GLP1 secretion and upregulation of proglucagon gene expression. Data from NCI-H716 cells showed that both GTS and Rb1 promoted GLP1 secretion. It was observed that Rb1 increased the ratio of intracellular ATP to ADP concentration and intracellular Ca2 + concentration. The metabolic inhibitor azide (3 mM), the KATP channel opener diazoxide (340 μM), and the Ca2 + channel blocker nifedipine (20 μM) significantly reversed Rb1-mediated GLP1 secretion. All these results drew a conclusion that ginsenosides stimulated GLP1 secretion both in vivo and in vitro. The antidiabetic effects of ginsenosides may be a result of enhanced GLP1 secretion.
Dang-Dang Li, Ying-Jie Gao, Xue-Chao Tian, Zhan-Qing Yang, Hang Cao, Qiao-Ling Zhang, Bin Guo and Zhan-Peng Yue
Tryptophan 2,3-dioxygenase (T do 2) is a rate-limiting enzyme which directs the conversion of tryptophan to kynurenine. The aim of this study was to examine the expression and regulation of T do 2 in mouse uterus during decidualization. T do 2 mRNA was mainly expressed in the decidua on days 6–8 of pregnancy. By real-time PCR, a high level of T do 2 expression was observed in the uteri from days 6 to 8 of pregnancy, although T do 2 expression was observed on days 1–8. Simultaneously, T do 2 mRNA was also detected under in vivo and in vitro artificial decidualization. Estrogen, progesterone, and 8-bromoadenosine-cAMP could induce the expression of T do 2 in the ovariectomized mouse uterus and uterine stromal cells. T do 2 could regulate cell proliferation and stimulate the expression of decidual marker Dtprp in the uterine stromal cells and decidual cells. Overexpression of T do 2 could upregulate the expression of Ahr, Cox2, and Vegf genes in uterine stromal cells, while T do 2 inhibitor 680C91 could downregulate the expression of Cox2 and Vegf genes in uterine decidual cells. These data indicate that T do 2 may play an important role during mouse decidualization and be regulated by estrogen, progesterone, and cAMP.
Jiali Liu, Yue Li, Xiaoyan Zhou, Xi Zhang, Hao Meng, Sanyuan Liu, Lei Zhang, Juntao He, Qian He and Yan Geng
High-fat diet (HFD) not only induces insulin resistance in liver, but also causes autophagic imbalance and metabolic disorders, increases chronic inflammatory response and induces mitochondrial dysfunction. Calcium/calmodulin-dependent protein kinase IV (CaMKIV) has recently emerged as an important regulator of glucose metabolism and skeletal muscle insulin action. Its activation has been involved in the improvement of hepatic and adipose insulin action. But the underlying mechanism is not fully understood. In the present study, we aimed to address the direct effects of CaMKIV in vivo and to evaluate the potential interaction of impaired insulin sensitivity and autophagic disorders in hepatic insulin resistance. Our results indicated obese mice receiving CaMKIV showed decreased blood glucose and serum insulin and improved insulin sensitivity as well as increased glucose tolerance compared with vehicle injection. Meanwhile, defective hepatic autophagy activity, impaired insulin signaling, increased inflammatory response and mitochondrial dysfunction in liver tissues which are induced by high-fat diet were also effectively alleviated by injection of CaMKIV. Consistent with these results, the addition of CaMKIV to the culture medium of BNL cl.2 hepatocytes markedly restored palmitate-induced hepatic insulin resistance and autophagic imbalance. These effects were nullified by blockade of cyclic AMP response element-binding protein (CREB), indicating the causative role of CREB in action of CaMKIV. Our findings suggested that CaMKIV restores hepatic autophagic imbalance and improves impaired insulin sensitivity via phosphorylated CREB signaling pathway, which may offer novel opportunities for treatment of obesity and diabetes.