Expression Of Ndrg2 In Pancreatic β Cells And Preliminary Study On Its Function

ObjectiveN-myc downstream regulated gene 2 (NDRG2), together with NDRG1, NDRG3 and NDRG4, constitute the NDRG family. Although NDRG family is possibly related to cell proliferation and differentiation, the exactly biological function has not yet been completely elucidated. Human NDRG2 was discovered and reported firstly by our research group, which share 95% identity with mouse NDRG2. Our previous findings have suggested that NDRG2 is highly expressed in pancreatic islet. Furthermore, it has been reported that Akt mediates insulin-stimulated phosphorylation of Ndrg2. Bioinformatics analysis revealed that there exsit binding sites of pancreatic specific transcription factors Pax6 and INSM1 in the promoter region of NDRG2. Therefore, further investigation on the localization and biological function of Ndrg2 in pancreas will be helpful to elucidate the physiological and pathological roles of Ndrg2.Methods①Immunohistochemistry and Immunofluorescence were used to detect the distribution and localization of Ndrg2 in the pancreatic endocrine cells;②Clinical pathological samples from pancreatic patients were applied to analyze the distribution of Ndrg2 and insulin by immunohistochemistry. Western blot was used to analyze the expression level of Ndrg2 in the normal pancreas and the pancreas of the patients with islet cell hyperplasia;③The biological functions of Ndrg2 in pancreatic endocrine cells were observed by upregulating and downregulating the expression of Ndrg2 in pancreatic endocrine cells;④The variations in biological functions and related signal pathway of the pancreatic endocrine cells were observed by exposure to high glucose and free fatty acids concentration.Results①Ndrg2 immunoreactivity could be seen in pancreatic islet, which is present in insulin-containing islet cells, but not in glucagon-containing islet cells or somatostatin-containing or pancreatic polypeptide-containing islet cells;②Clinical pathological samples from patients with pancreatic disease revealed that Ndrg2 immunoreactivity mainly distributed in pancreatic islet, which is similar to the distribution and localization of insulin immunoreactivity. In the pancreas of the patients with islet cell hyperplasia, the amount and volume of pancreatic islets increased, companying with the upregulation of Ndrg2;③When Ndrg2 was overexpressed inβTC3 cells, the mRNA and protein levels of Insulin I was down-regulated. While Ndrg2 was knocked down inβTC3 cells by RNAi, the insulin content is higher than control group;④When Akt is constitutively activated, the Ndrg2 phosphorylation was increased. WhenβTC3 cells were exposed chronically to high glucose and free fatty acids concentration, the GSIS ofβTC3 cells was weaken and the phosphorylation level of Akt at ser473 decreased. WhenβTC3 cells were exposed chronically to high free fatty acids concentration, the GSIS ofβTC3 cells was weaken, and the protein level of PTEN increased, the phosphorylation level of Akt at ser473 decreased, the phosphorylation level of Ndrg2 at ser332 and thr348 decreased too.Conclusions①Ndrg2 is mainly expressed in pancreaticβcells. Among the several mouse cell lines, Ndrg2 expression is high in pancreaticβcell lineβTC3. The above results suggest that Ndrg2 may play important roles in pancreaticβcells;②The clinical pathological samples from pancreatic patients have revealed that the distribution and localization of Ndrg2 are remarkably similar to those of insulin. In the pancreas of the patients with islet cell hyperplasia, the expression of Ndrg2 increased as the results of pancreaticβcells hyperplasia;③There exists negative correlation between Ndrg2 and insulin inβTC3 cells, suggesting Ndrg2 is possibly involved in regulation of INSULIN gene transcription;④Ndrg2 is the substrate of protein kinase Akt. High glucose and free fatty acids concentration will lead to glucotoxicity and lipotoxicity inβTC3 cells, accompanyed with the variety of PTEN-Akt-Ndrg2 signal pathway.