Reduction of Low Molecular Weight Protein-tyrosine Phosphatase Expression Improves Hyperglycemia and Insulin Sensitivity in Obese Mice

Abstract

To investigate the role of low molecular weight proteintyrosine phosphatase (LMW-PTP) in glucose metabolism and insulin action, a specific antisense oligonucleotide (ASO) was used to reduce its expression both in vitro and in vivo. Reduction of LMW-PTP expression with the ASO in cultured mouse hepatocytes and in liver and fat tissues of diet-induced obese (DIO) mice and ob/ob mice led to increased phosphorylation and activity of key insulin signaling intermediates, including insulin receptor-␤ subunit, phosphatidylinositol 3-kinase, and Akt in response to insulin stimulation. The ASO-treated DIO and ob/ob animals showed improved insulin sensitivity, which was reflected by a lowering of both plasma insulin and glucose levels and improved glucose and insulin tolerance in DIO mice. The treatment did not decrease body weight or increase metabolic rate. These data demonstrate that LMW-PTP is a key negative regulator of insulin action and a potential novel target for the treatment of insulin resistance and type 2 diabetes.The incidence of diabetes has been steadily increasing and has become a major public health concern. Over 85% of diabetic patients have type 2 diabetes. Obesity, which can result from a sedentary life style and high calorie diet, is a major risk factor for the development of this disorder (1). A hallmark of type 2 diabetes is insulin resistance, characterized by a decreased insulin response in a variety of tissues (2), including liver, fat, and muscle. Therefore, increasing insulin sensitivity is a practical strategy for the treatment of type 2 diabetes.Insulin initiates its physiological response by binding to its membrane-bound receptor (IR, a ␣ 2 ␤ 2 -heterotetramer protein), 2 which causes autophosphorylation of the ␤-subunit and receptor activation, resulting in subsequent phosphorylation of its two major downstream substrates, IRS-1 and IRS-2 (3-5). Phosphorylated IRS-1 and -2 interact with and activate other SH2 domain-containing adapter molecules such as NCK2, Grb2, Shc, Syp (4 -8), and the regulatory subunit (p85) of phosphatidylinositol 3-kinase (PI3-K) (9, 10). Activated PI3-K stimulates Akt (or protein kinase B) that in turn phosphorylates and inactivates glycogen synthase kinase-3 (11), resulting in activation of glycogen synthase (12), thereby increasing the utilization of glucose for glycogen synthesis. In fat and muscle, activation of this pathway also causes transfer of GLUT4 from the cytoplasm to the cell membrane, resulting in increased glucose uptake (13). Therefore, IR-IRS-1/2-PI3-K-Akt signaling cascade is a key pathway in mediating the effects of insulin action on blood glucose levels. A number of studies have established a role for intracellular phosphatases in the negative regulation of insulin signaling (14 -16) such as protein-tyrosine phosphatase (PTP) 1B that negatively regulates insulin action through dephosphorylating tyrosine-phosphorylated IR (15, 16). Insulin sensitivity was enhanced in PTP1B knock-out mice, in which increased tyrosine phosphorylation of IR was found...

Reduced adiposity and improved insulin sensitivity in obese mice with antisense suppression of 4E-BP2 expression

“…Pharmacokinetic studies have found that antisense oligonucleotides (ASOs) are active in a variety of tissues in vivo, including liver and adipose tissue, but are not active in muscle and brain when administered systemically (8,21,36). Data from this study indicate that ASO treatment dramatically reduced 4E-BP2 levels in both liver and fat, which caused decreased body weight and adiposity, improved liver steatosis, and improved insulin sensitivity.…”

Alteration of Hepatic but Not Renal Transporter Expression in Diet-Induced Obese Mice

“…For example, renal 25-hydroxyvitamin D 3 -24-hydroxylase (CYP24) mRNA synthesis also is markedly elevated in ob/ob and db/db mice, and administration of leptin attenuates this effect (Matsunuma and Horiuchi, 2007;Tsuji et al, 2010). Second, the ob/ob and db/db models typically exhibit higher levels of insulin and glucagon compared with those in DIO mice, and insulin is known to interact with various nuclear hormone receptor-activated pathways (Pandey et al, 2007;Davis et al, 2010).…”

Age at the Onset of Type 2 Diabetes Correlates with Phenotype of Low Molecular Weight Protein Tyrosine Phosphatase

“…Protein Tyrosine Phosphatase in glucose metabolism is suggested by several lines of evidence: Insulin receptors and Band 3 Protein (B3P) are hydrolyzed by cLMWPTP [1]; diabetic subjects with low enzymatic activity have low glycemic level [2,3]; lowering enzyme activity by a specific antisense oligonucleotide improves insulin sensitivity and decrease blood glucose level in obese mice [4]. On these basis cLMWPTP could be considered a candidate gene for Type 2 Diabetes.…”