Liraglutide, a human glucagon-like peptide-1 analogue, stimulates AKT-dependent survival signalling and inhibits pancreatic β-cell apoptosis.

Liraglutide, a human long-lasting GLP-1 analogue, is currently regarded as a powerful treatment option for type 2 diabetes. Apart from glucoregulatory and insulinotropic actions, liraglutide increases β-cell mass through stimulation of β-cell proliferation and islet neogenesis, as well as inhibition of β-cell apoptosis. However, the underline molecular mechanisms have not been fully characterized. In this study, we investigated the mechanism by which liraglutide preserves islet β-cells in an animal model of overt diabetes, the obese db/db mice, and protects a mouse pancreatic β-cell line (βTC-6 cells) against apoptosis. Treatment of 12-week-old diabetic mice with liraglutide for 2 weeks had no appreciable effects on blood non-fasting glucose concentration, islet insulin content and body weight. However, morphological and biochemical examination of diabetic mouse pancreatic islets demonstrated that liraglutide restores islet size, reduces islet β-cell apoptosis and improves nephrin expression, a protein involved in β-cell survival signalling. Our results indicated that liraglutide protects βTC-6 cells from serum withdrawal-induced apoptosis through inhibition of caspase-3 activation. The molecular mechanism of the anti-apoptotic action of liraglutide in βTC-6-cells comprises stimulation of PI3-kinase-dependent AKT phosphorylation leading to the phosphorylation, hence inactivation of the pro-apoptotic protein BAD and inhibition of FoxO1 transcription factor. In conclusion, we provided evidence that the GLP-1 analogue liraglutide exerts important beneficial effects on pancreatic islet architecture and β-cell survival by protecting cells against apoptosis. These findings extend our understanding of the actions of liraglutide and further support the use of GLP-1R agonists in the treatment of patients with type 2 diabetes.

Kapodistria K ，Tsilibary EP ，Kotsopoulou E ，Moustardas P ，Kitsiou P ... -  《-》

Nephrin, a transmembrane protein, is involved in pancreatic beta-cell survival signaling.

Nephrin, a cell surface signaling receptor, regulates podocyte function in health and disease. We study the role of nephrin in β-cell survival signaling. We report that in mouse islet β-cells and the mouse pancreatic beta-cell line (βTC-6 cells) nephrin is associated and partly co-localized with PI3-kinase. Incubation of cells with functional anti-nephrin antibodies induced nephrin clustering at the plasma membrane, nephrin phosphorylation and recruitment of PI3-kinase to nephrin thus resulting in increased PI3K-dependent Akt phosphorylation and augmented phosphorylation/inhibition of pro-apoptotic Bad and FoxO. Nephrin silencing abolished Akt activation and increased susceptibility of cells to apoptosis. High glucose impaired nephrin signaling, increased nephrin internalization and up-regulated PKCα expression. Interestingly, a marked decrease in nephrin expression and phosphorylated Akt was observed in pancreatic islets of db/db lepr-/- diabetic mice. Our findings revealed that nephrin is involved in β-cell survival and suggest that glucose-induced changes in nephrin signaling may contribute to gradual pancreatic β-cell loss in type 2 diabetes.

Kapodistria K ，Tsilibary EP ，Politis P ，Moustardas P ，Charonis A ，Kitsiou P ... -  《-》

Protective action of liraglutide in beta cells under lipotoxic stress via PI3K/Akt/FoxO1 pathway.

Liraglutide, a modified form of glucagon-like peptide-1 (GLP-1), has been found to improve beta cell function in type 2 diabetes (T2DM). However, the effect of liraglutide on beta cell function under lipotoxic stress and the underlying molecular mechanisms remain unclear. In the present study, we investigated the role of PI3K/Akt/FoxO1 signaling in liraglutide-involved beta cell protection in high free fatty acids (FFAs) condition. The apoptosis, proliferation, and insulin secretion capability of MIN6 cells and islets from C57BL/6J mice were evaluated when exposed to FFAs with/without liraglutide. The expression of effectors involved in PI3K/Akt/FoxO1signalling pathway was detected by real-time PCR and western blotting in MIN6 cells and islets from C57BL/6J mice. Liraglutide substantially inhibited the lipoapoptosis and improved the proliferation and insulin secretion of beta cells in high FFAs condition. Western blot revealed that the phosphorylation of Akt and FoxO1 was markedly decreased under lipid stress but was elevated when treated with liraglutide. Moreover, FFAs could up-regulate the expression levels of p27, Bax, Cidea but down-regulate the expression levels of Pdx-1, MafA, and NeuroD in beta cells, which was canceled by the addition of liraglutide. Moreover, LY294002, a PI3K inhibitor, could significantly abrogate all the protective actions of liraglutide against lipotoxicity. We concluded that liraglutide markedly improved beta cell function under lipid stress and that the protective action of liraglutide was mediated by activation of PI3K/Akt, which resulted in inactivation of FoxO1 along with the down-regulation of p27, Bax, Cidea and up-regulation of Pdx-1, MafA, and NeuroD expressions.

Shao S ，Nie M ，Chen C ，Chen X ，Zhang M ，Yuan G ，Yu X ，Yang Y ... -  《-》

Positive effects of GLP-1 receptor activation with liraglutide on pancreatic islet morphology and metabolic control in C57BL/KsJ db/db mice with degenerative diabetes.

Stable glucagon-like peptide-1 (GLP-1) mimetics, such as the GLP-1 analogue liraglutide, are approved for treatment of type 2 diabetes. GLP-1 has a spectrum of anti-diabetic effects that are of possible utility in the treatment of more severe forms of diabetes. The present study has evaluated the effect of once daily liraglutide injection (25 nmol/kg bw) for 15 days on metabolic control, islet architecture, and islet morphology in C57BL/KsJ db/db mice. Liraglutide had no appreciable effects on body weight, food intake, and non-fasting glucose and insulin concentrations. However, HbA1c was significantly (p < 0.001) decreased, and oral glucose tolerance improved in liraglutide treated db/db mice. Pancreatic insulin content was increased (p < 0.05) compared with saline controls, and the ratio of pancreatic insulin to glucagon in liraglutide mice was similar to lean mice. Although liraglutide did not alter islet number or area, the proportion of beta cells per islet was significantly increased (p < 0.05) and alpha cells decreased (p < 0.05), with normalization of islet architecture. In harmony with this, cell proliferation was significantly (p < 0.001) augmented and apoptosis reduced (p < 0.001) in liraglutide treated mice. Expression of pancreatic islet glucose-dependent insulinotropic polypeptide immunoreactivity was observed in lean control and, particularly, liraglutide treated db/db mice, whereas control db/db mice exhibited little glucose-dependent insulinotropic polypeptide staining. These data reveal that stable GLP-1 analogues exert important beneficial effects on pancreatic islet architecture and beta-cell turnover, indicating that they may be useful in the treatment of severe forms of diabetes with islet degeneration.

Moffett RC ，Patterson S ，Irwin N ，Flatt PR ... -  《-》

Activation of glucagon-like peptide-1 receptor inhibits tumourigenicity and metastasis of human pancreatic cancer cells via PI3K/Akt pathway.

It has been reported that glucagon-like peptide-1 (GLP-1) agents are associated with an increased risk of pancreatic cancer in patients with type 2 diabetes. Reports have indicated that GLP-1 promotes pancreatic metaplasia and premalignant lesions. The aims of this study were to determine the effects of GLP-1-based therapy on pancreatic cancer cells. Immunohistochemistry was used to investigate GLP-1 receptor (GLP-1R) expression in 30 human pancreatic cancer tissues. We also analysed associated clinicopathological data and each patient's prognosis. Two human pancreatic cancer cell lines were used to evaluate the in vitro effects of the GLP-1R agonist liraglutide on cell growth, migration and invasion. Mouse xenograft models of human pancreatic cancer were established to evaluate the effects of liraglutide in vivo. Human pancreatic cancer tissues showed lower levels or a lack of GLP-1R expression when compared with levels in the tumour-adjacent pancreatic tissues. Negative GLP-1R expression occurred more frequently in advanced tumours with larger diameters and lymphatic metastasis, and was associated with a poor prognosis. GLP-1R activation with liraglutide inhibited tumourigenicity and metastasis of human pancreatic cancer cells in vitro and in vivo. Akt activation was dose-dependently inhibited by liraglutide, and the PI3K inhibitors, LY294002 and wortmannin, displayed similar suppressive effects to liraglutide in human pancreatic cancer cells. GLP-1R activation has an antitumour effect on human pancreatic cancers via inhibition of the PI3K/Akt pathway. This finding suggests that GLP-1-based therapies may be beneficial, rather than harmful, in treating type 2 diabetic patients with pancreatic cancer.

Zhao H ，Wang L ，Wei R ，Xiu D ，Tao M ，Ke J ，Liu Y ，Yang J ，Hong T ... -  《-》