Normalization of Prandial Blood Glucose and Improvement of Glucose Tolerance by Liver-Specific Inhibition of SH2 Domain–Containing Inositol Phosphatase 2 (SHIP2) in Diabetic KKAy Mice

Abstract

Type 2 diabetes is characterized by a progressive resistance of peripheral tissues to insulin. Recent data have established the lipid phosphatase SH2 domain-containing inositol phosphatase 2 (SHIP2) as a critical negative regulator of insulin signal transduction. Mutations in the SHIP2 gene are associated with type 2 diabetes. Here, we used hyperglycemic and hyperinsulinemic KKA y mice to gain insight into the signaling events and metabolic changes triggered by SHIP2 inhibition in vivo. Liver-specific expression of a dominant-negative SHIP2 mutant in KKA y mice increased basal and insulin-stimulated Akt phosphorylation. Protein levels of glucose-6-phosphatase and phosphoenolpyruvate carboxykinase were significantly reduced, and consequently the liver produced less glucose through gluconeogenesis. Furthermore, SHIP2 inhibition improved hepatic glycogen metabolism by modulating the phosphorylation states of glycogen phosphorylase and glycogen synthase, which ultimately increased hepatic glycogen content. Enhanced glucokinase and reduced pyruvate dehydrogenase kinase 4 expression, together with increased plasma triglycerides, indicate improved glycolysis. As a consequence of the insulin-mimetic effects on glycogen metabolism, gluconeogenesis, and glycolysis, the liverspecific inhibition of SHIP2 improved glucose tolerance and markedly reduced prandial blood glucose levels in KKA y mice. These results support the attractiveness of a specific inhibition of SHIP2 for the prevention and/or treatment of type 2 diabetes. Diabetes 56:2235-2241, 2007 A key event in insulin signal transduction is the increase in phosphatidylinositol-3,4,5-trisphosphate [PI(3,4,5)P 3 ], which recruits and activates downstream effectors at the plasma membrane (1). The lipid phosphatase SH2 domain-containing inositol phosphatase 2 (SHIP2) is expressed in insulin target tissues and dephosphorylates PI(3,4,5)P 3 at the D5 position (2,3). Activating mutations in the SHIP2 gene contribute to the genetic susceptibility to type 2 diabetes in humans (4). Mice lacking the SHIP2 gene (Inppl1 Ϫ/Ϫ mice) are viable and have normal glucose and insulin levels with normal insulin and glucose tolerances. However, Inppl1Ϫ/Ϫ mice are protected from diet-induced obesity, hyperglycemia, and insulin resistance (5). The function of SHIP2 in differentiated L6 myotubes and 3T3-L1 adipocytes was extensively studied by inhibition of the endogenous SHIP2 via overexpression of a dominantnegative SHIP2 mutant (dnSHIP2). SHIP2 inhibition increases phosphorylation of Akt (also known as protein kinase B) and glycogen synthesis in both cell lines (6,7). The liver-specific overexpression of dnSHIP2 in db/db mice results in dramatically decreased fasting glucose levels due to the reduced expression of the gluconeogenic genes glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) (8). However, the strong reduction in fasting blood glucose concentration confounds the interpretation of an improved glucose tolerance test in this model. Furthermore, an effect o...

SH2 domain-containing inositol 5-phosphatase (SHIP2) regulates de-novo lipogenesis and secretion of apoB100 containing lipoproteins in HepG2 cells

“…Regarding the PTEN, it was reported that the deletion of PTEN in liver resulted in steatohepatitis along with enhanced liver insulin action with improved systemic glucose tolerance (17,18). Later studies supported this notion, as the loss of PTEN activity increased lipid substrate availability in the face of reduced hepatic lipoprotein production capacity leading to hepatosteatosis and fatty liver (19). These studies have shown a role for PTEN in regulating lipogenesis in liver cells; however, less information is available on the role of another lipid phosphatase, SHIP2, in liver lipid and lipoprotein metabolism.…”

“…SHIP2 overexpression leads to inhibition of insulininduced Akt activation, glucose uptake, and glycogen synthesis in 3T3-L1 adipocytes, L6 myotubes [18] and tissues of animal models [19,20]. In addition, liver-specific down regulation or inhibition of SHIP2 improves the insulin signaling in mice [19,21]. Furthermore, the heterozygous knockout mice of SHIP2 gene were resistant against high-fat diet-induced obesity and insulin resistance [15].…”

“…An increased expression of SHIP2 gene has been reported from the skeletal muscle and adipose tissues of db/db mice [16,17]. SHIP2 overexpression leads to inhibition of insulininduced Akt activation, glucose uptake, and glycogen synthesis in 3T3-L1 adipocytes, L6 myotubes [18] and tissues of animal models [19,20]. In addition, liver-specific down regulation or inhibition of SHIP2 improves the insulin signaling in mice [19,21].…”

Endothelial SHIP2 Suppresses Nox2 NADPH Oxidase–Dependent Vascular Oxidative Stress, Endothelial Dysfunction, and Systemic Insulin Resistance

“…SHIP2 modulation on insulin sensitivity in models of type 2 diabetes. Adenoviral expression of a dominant-negative mutant SHIP2 in the liver of obese hyperglycemic mice restored insulin sensitivity and Akt phosphorylation (22), whereas the expression of wild-type SHIP2 blunted these (23). In humans, SHIP2 (Inppl1) polymorphisms are associated with obesity, type 2 diabetes, and the metabolic syndrome (24,25).…”

Lipid phosphatase SHIP2 downregulates insulin signalling in podocytes

“…Lipid phosphatase SHIP2 downregulates PI3K mediated signalling, induced by insulin and other growth factors, by hydrolyzing PI(3,4,5,)P 3 to PI(3,4)P 2 (Blero et al 2001. SHIP2 overexpression in mice has a negative effect on glucose tolerance (Kagawa et al 2008,Fukui et al 2005 and SHIP2 knockout mice appear resistant to high fat diet-induced obesity and insulin resistance (Sleeman et al 2005), and in addition, inhibition of SHIP2 in the liver has been shown to improve glucose tolerance in diabetic mice (Grempler et al 2007). Taken together, SHIP2 is a downregulator of PI3K mediated insulin signalling, that is known to function in liver, muscle and adipose cells, but its role in the kidney has not been studied previously.…”