Increased Energy Expenditure, Decreased Adiposity, and Tissue-Specific Insulin Sensitivity in Protein-Tyrosine Phosphatase 1B-Deficient Mice

Abstract

Protein-tyrosine phosphatase 1B (PTP-1B) is a major protein-tyrosine phosphatase that has been implicated in the regulation of insulin action, as well as in other signal transduction pathways. To investigate the role of PTP-1B in vivo, we generated homozygotic PTP-1B-null mice by targeted gene disruption. PTP-1B-deficient mice have remarkably low adiposity and are protected from diet-induced obesity. Decreased adiposity is due to a marked reduction in fat cell mass without a decrease in adipocyte number. Leanness in PTP-1B-deficient mice is accompanied by increased basal metabolic rate and total energy expenditure, without marked alteration of uncoupling protein mRNA expression. In addition, insulin-stimulated whole-body glucose disposal is enhanced significantly in PTP-1B-deficient animals, as shown by hyperinsulinemic-euglycemic clamp studies. Remarkably, increased insulin sensitivity in PTP-1B-deficient mice is tissue specific, as insulin-stimulated glucose uptake is elevated in skeletal muscle, whereas adipose tissue is unaffected. Our results identify PTP-1B as a major regulator of energy balance, insulin sensitivity, and body fat stores in vivo.Obesity and diabetes mellitus represent major public health problems. Type 2 diabetes is a polygenic disease affecting over 100 million people worldwide. The risk of developing type 2 diabetes is increased in populations that lead a sedentary lifestyle and consume a typical western diet, in which more than 50% of the calories are derived from fat (34, 37). A high-fat diet and low energy expenditure predispose to obesity, a condition characterized by increased insulin resistance in insulinresponsive tissues, such as skeletal muscle, liver, and white adipose tissue (9, 42). Body weight also is subject to polygenic regulation (18). Many of the key genes that regulate body mass and glucose homeostasis remain to be identified (27).Insulin plays a critical role in regulating glucose homeostasis, lipid metabolism, and energy balance. Insulin signaling is initiated by binding of insulin to the insulin receptor (IR), a receptor tyrosine kinase. Insulin binding evokes a cascade of phosphorylation events, beginning with the autophosphorylation of the IR on multiple tyrosyl residues. Autophosphorylation enhances IR kinase activity and triggers downstream signaling events. These include tyrosyl phosphorylation of IR substrate (IRS) proteins (IRS-1 to -4) and other adapter molecules (e.g., Grb2 and Shc), whose combined actions mediate the biological effects of insulin (reviewed in references 24, 43, 54, and 69).

Protein Tyrosine Phosphatase 1B (PTP1B) Deficiency Accelerates Hepatic Regeneration in Mice

“…19,20,53 In this study, we show protection against the development of hepatic steatosis together with improved regenerative responses in PTP1B Ϫ/Ϫ mice fed an HFD before PH. In addition to the protection against insulin resistance and obesity, 20,54 an additional benefit of PTP1B deficiency may be the improvement of liver regeneration under conditions of increased lipid intake, as demonstrated herein by accelerated or increased induction of S-phase markers and an increased hepatosomal index compared with wild-type controls. In clinical situations, obese patients with fatty livers, who frequently develop insulin resistance, tend to have poor outcomes after resection or liver transplantation.…”

“…18 Extensive analysis of the PTP1B-deficient (PTP1B Ϫ/Ϫ ) mice has confirmed that the IR is a key physiological target of PTP1B. 19,20 In fact, PTP1B inhibition is actually being assayed as a potential therapy for type 2 diabetes mellitus. Despite the negative modulation of activation of receptors of the tyrosine kinase superfamily by PTP1B, PTP1B Ϫ/Ϫ mice lack any obvious signs of increased activity of these receptors, such as susceptibility to tumor development through life.…”

Aryl Vinyl Sulfonates and Sulfones as Active Site-Directed and Mechanism-Based Probes for Protein Tyrosine Phosphatases

“…Total cell lysates were treated with the azide tagged PVSN probe (20 µM) for 30 min at room temperature and pH 6.0, and exposed to 0.125 mM of the alkyne-labeled biotin, 1.25 mM tris(2-carboxyethyl)phosphine (TCEP), 0.127 mM tris(benzyltriazolylmethyl)amine (TBTA), and 1.25 mM CuSO 4 for 1 hr to conjugate the PVSN-adducted HePTP with biotin for subsequent visualization. As shown in Figure 7, Western-blot analysis of the reaction mixture with anti-biotin and anti-(His) 6 antibodies showed robust labeling of HePTP, while little background labeling was observed for the entire non-PTP proteome under these conditions. This level of labeling specificity indicates that the PVSN/PVS scaffolds can be employed as activity-based probes to profile PTP activity in complex proteome.…”

“…With these reagents in hand, we assessed the compatibility of the PTP labeling strategy in a well-defined system, namely E. coli, which has no PTPs in its proteome. The specificity of the PVSN-based probe for targeted PTP analysis was evaluated in total cell lysates from both control E. coli and E. coli expressing recombinant (His) 6 -tagged HePTP. Total cell lysates were treated with the azide tagged PVSN probe (20 µM) for 30 min at room temperature and pH 6.0, and exposed to 0.125 mM of the alkyne-labeled biotin, 1.25 mM tris(2-carboxyethyl)phosphine (TCEP), 0.127 mM tris(benzyltriazolylmethyl)amine (TBTA), and 1.25 mM CuSO 4 for 1 hr to conjugate the PVSN-adducted HePTP with biotin for subsequent visualization.…”

“…Labeling of HePTP in complex proteome by azide tagged PVSN probe and alkyne labeled biotin. Total cell lysates with or without (His) 6 -tagged HePTP were treated with the azide tagged PVSN probe (20 µM) for 30 min at room temperature and pH 6.0, and exposed to 0.125 mM of the alkyne-labeled biotin, 1.25 mM TCEP, 0.127 mM TBTA, and 1.25 mM CuSO 4 for 1 hr to conjugate the PVSN-adducted HePTP with biotin. The identity of the (His) 6 -HePTP was revealed by its reactivity to anti-(His) 6 antibody.…”