آموزش تحصیلات تکمیلی علوم پایه دانشکده  

[1]  SH2 domain containing inositol 5-phosphatase

Abstract

Dyslipidemia is one of the key risk factors for cardiovascular disease in type 2 diabetes (T2D). The dyslipidemia is characterized by increased plasma concentration of triglycerides (TG), reduced concentration of high density lipoprotein cholesterol (HDL-C) and an increased concentration of small dense low density lipoprotein (LDL) cholesterol. Evidence from both animal and human studies suggests that insulin resistance (in adipose and liver tissues) is an important underlying cause of hypertriglyceridemia in subjects with metabolic syndrome and T2D. Hepatic de-novo lipogenesis and production of triglyceride rich VLDL is regulated via the phosphoinositide 3-kinase cascade, however, the role of a negative regulator of this pathway, the SH2 domain containing inositol 5-phosphatase (SHIP2) in this process, remains unknown. In the present study, we studied the molecular mechanisms linking SHIP2 expression to metabolic dyslipidemia using overexpression or suppression of SHIP2 gene in HepG2 cells exposed to oleate (0.5 mM) and high glucose (33mM). The results showed that overexpression of the wild type SHIP2 gene (SHIP2-WT) led to a higher total lipid content (28%) compared to control, whereas overexpression of the dominant negative SHIP2 gene (SHIP2-DN) reduced total lipid content in oleate treated cells by 40%. Overexpression of SHIP2-WT also led to a significant increase in both secretion of apoB100 containing lipoproteins and de-novo lipogenesis, as demonstrated by an enhance in both secreted apoB100 and MTP expression, increased intra and extracellular triglyceride levels and enhanced the expression of lipogenic genes such as SREBP1c, FAS and ACC. On the other hand, overexpression of the SHIP2-DN gene prevented oleate-induced de-novo lipogenesis and the secretion of apoB100 containing lipoproteins in HepG2 cells. Interestingly, treatment of HepG2 cells with high glucose (33 mM) showed an induction of  SHIP2 mRNA and protein levels. Overexpression of the dominant negative mutant SHIP2 (SHIP2-DN) ameliorated high glucose-induced de-novo lipogenesis and the secretion of apoB100 containing lipoprotein in HepG2 cells, as demonstrated by a reduction in both secreted apoB100 and MTP expression, and decreased triglyceride levels and the expression of lipogenic genes such as SREBP1c, FAS and ACC. Overexpression of the SHIP2-DN decreased high glucose-induced apoB100 containing lipoproteins secretion via reduction in ROS generation, JNK phosphorylation and Akt activation. Furthermore, using the specific inhibitor and activator, it was found that the AMPK/mTOR/SREBP1 is the signaling pathway that mediates the effects of SHIP2 modulation on hepatic de-novo lipogenesis. Taken together, these findings suggest that SHIP2 expression level is an important determinant of hepatic lipogenesis and lipoprotein secretion in insulin resistance state, and its inhibition can potentially be a target in treatment of dyslipidemia in diabetic patients.