Saturated fatty acids entrap PDX1 in stress granules and impede islet beta cell function.

AIMS/HYPOTHESIS: Failure of pancreatic and duodenal homeobox factor 1 (PDX1) to localise in the nucleus of islet beta cells under high-fat diet (HFD) conditions may be an early functional defect that contributes to beta cell failure in type 2 diabetes; however, the mechanism of PDX1 intracellular mislocalisation is unclear. Stress granules (SGs) are membrane-less cytoplasmic structures formed under stress that impair nucleocytoplasmic transport by sequestering nucleocytoplasmic transport factors and components of the nuclear pore complex. In this study, we investigated the stimulators that trigger SG formation in islet beta cells and the effects of SGs on PDX1 localisation and beta cell function. METHODS: The effect of palmitic acid (PA) on nucleocytoplasmic transport was investigated by using two reporters, S-tdTomato and S-GFP. SG assembly in rat insulinoma cell line INS1 cells, human islets under PA stress, and the pancreas of diet-induced obese mice was analysed using immunofluorescence and immunoblotting. SG protein components were identified through mass spectrometry. SG formation was blocked by specific inhibitors or genetic deletion of essential SG proteins, and then PDX1 localisation and beta cell function were investigated in vitro and in vivo. RESULTS: We showed that saturated fatty acids (SFAs) are endogenous stressors that disrupted nucleocytoplasmic transport and stimulated SG formation in pancreatic beta cells. Using mass spectrometry approaches, we revealed that several nucleocytoplasmic transport factors and PDX1 were localised to SGs after SFA treatment, which inhibited glucose-induced insulin secretion. Furthermore, we found that SFAs induced SG formation in a phosphoinositide 3-kinase (PI3K)/eukaryotic translation initiation factor 2α (EIF2α) dependent manner. Disruption of SG assembly by PI3K/EIF2α inhibitors or genetic deletion of T cell restricted intracellular antigen 1 (TIA1) in pancreatic beta cells effectively suppressed PA-induced PDX1 mislocalisation and ameliorated HFD-mediated beta cell dysfunction. CONCLUSIONS/INTERPRETATION: Our findings suggest a link between SG formation and beta cell dysfunction in the presence of SFAs. Preventing SG formation may be a potential therapeutic strategy for treating obesity and type 2 diabetes.

Suppression of free fatty acid receptor 1 expression in pancreatic ß-cells in obese type 2 diabetic db/db mice: a potential role of pancreatic and duodenal homeobox factor 1.

It is known that long-chain fatty acids bind to free fatty acid receptor 1 (Ffar1), also known as G protein-coupled receptor 40 (GPR40), and amplify glucose-stimulated insulin secretion (GSIS) from pancreatic ß-cells and that Ffar1 agonists facilitates insulin secretion and ameliorates glycemic control. On the other hands, pancreatic and duodenal homeobox factor 1 (Pdx1) is an important transcription factor for various ß-cell-related genes including insulin gene and thereby contributes to the maintenance of mature ß-cell function. The aim of this study was to evaluate how Ffar1 expression in ß-cells is altered under diabetic conditions. In this study, we used male obese type 2 diabetic mice and control mice. We evaluated Ffar1 and Pdx1 mRNA and protein expression levels in both mice. In addition, we examined whether Pdx1 is a possible regulator of Ffar1 expression using small interfering RNA for Pdx1 (siPdx1) in ß-cell-derived cell line. As the results, Ffar1 mRNA and protein expression in ß-cells were significantly lower in obese type 2 diabetic db/db mice compared to control mice which was accompanied by the decreased expression of Pdx1. In addition, down-regulation of Pdx1 expression using siPdx1 suppressed Ffar1 expression. Furthermore, adenoviral Pdx1 overexpression significantly increased Ffar1 expression. In conclusion, Ffar1 expression is markedly down-regulated under diabetic conditions which is accompanied by decreased expression of Pdx1. Furthermore, it is likely that Pdx1 is a regulator of Ffar1 expression in ß-cells.

Generation of insulin-producing cells from PDX1 and NKX6.1 gene-modified bone marrow mesenchymal stem cells / 中国病理生理杂志

AIM:To differentiate bone marrow mesenchymal stem cells(BMSCs) into functional insulin-producing cells to produce sufficient pancreatic islet cells for transplantation.METHODS:Recombinant adenovirus vectors carrying PDX1 and NKX6.1 genes were constructed and the bone marrow mesenchymal stem cells were infected by the recombinant adenovirus combined with several cytokines for differentiation.The expressions of PDX1,NKX6.1 and insulin and C-peptide in the differentiated bone marrow mesenchymal stem cells were detected by RT-PCR and Western blotting.After the differentiated bone marrow mesenchymal stem cells were transplanted into subrenal capsule of diabetic mice,cell morphology of the grafts as well as their secretion of insulin and C-peptide were detected.Besides,regulating capacities of grafts on the blood glucose level of the diabetic mice were also detected.RESULTS:BMSCs induced by recombinant adenovirus(pAdxsi-CMV-PDX1/CMV-NKX6.1) and several cytokines showed positive dithizone staining and the expressions of ?-cell related molecule such as insulin and glucose transporter 2 were detected by RT-PCR,which showed a sustaining and stable expression.The similar results were showed by Western blotting,immunohistochemical staining and indirect immunofluorescence.The insulin secretions in the cells stimulated with glucose at concentrations of 5.5 and 25 mmol/L in the experimental group were(1 240.4?109.3) mU/L and(3 539.8?245.1) mU/L,respectively,and were significantly higher than those in control group.Moreover,transplantation of the cells to STZ mice in treatment group made serum glucose recover to normal level.CONCLUSION:PDX1 and NKX6.1 gene-modified bone marrow mesenchymal stem cells differentiate into insulin-producing cells in vitro.When these cells transplanted into STZ induced diabetic mice,their serum glucose could return to the normal level and they could live well.Thus this is a promising method for diabetes treatment.