Mice lacking the protein-tyrosine phosphatase PTP1B are hypersensitive to insulin and resistant to obesity. However, the molecular basis for resistance to obesity has been unclear. Here we show that PTP1B regulates leptin signaling. In transfection studies, PTP1B dephosphorylates the leptin receptor-associated kinase, Jak2. PTP1B is expressed in hypothalamic regions harboring leptin-responsive neurons. Compared to wild-type littermates, PTP1B(-/-) mice have decreased leptin/body fat ratios, leptin hypersensitivity, and enhanced leptin-induced hypothalamic Stat3 tyrosyl phosphorylation. Gold thioglucose treatment, which ablates leptin-responsive hypothalamic neurons, partially overcomes resistance to obesity in PTP1B(-/-) mice. Our data indicate that PTP1B regulates leptin signaling in vivo, likely by targeting Jak2. PTP1B may be a novel target to treat leptin resistance in obesity.
Obesity is a major health problem and a risk factor for type 2 diabetes. Leptin, an adipocyte-secreted hormone, acts on the hypothalamus to inhibit food intake and increase energy expenditure. Most obese individuals develop hyperleptinemia and leptin resistance, limiting the therapeutic efficacy of exogenously administered leptin. Mice lacking the tyrosine phosphatase PTP1B are protected from diet-induced obesity and are hypersensitive to leptin, but the site and mechanism for these effects remain controversial. We generated tissue-specific PTP1B knockout (Ptpn1(-/-)) mice. Neuronal Ptpn1(-/-) mice have reduced weight and adiposity, and increased activity and energy expenditure. In contrast, adipose PTP1B deficiency increases body weight, whereas PTP1B deletion in muscle or liver does not affect weight. Neuronal Ptpn1(-/-) mice are hypersensitive to leptin, despite paradoxically elevated leptin levels, and show improved glucose homeostasis. Thus, PTP1B regulates body mass and adiposity primarily through actions in the brain. Furthermore, neuronal PTP1B regulates adipocyte leptin production and probably is essential for the development of leptin resistance.
SUMMARY The primary task of white adipose tissue (WAT) is the storage of lipids. However, ‘beige’ adipocytes also exist in WAT. Beige adipocytes burn fat and dissipate the energy as heat, but their abundance is diminished in obesity. Stimulating beige adipocyte development, or WAT browning, increases energy expenditure and holds potential for combating metabolic disease and obesity. Here we report that insulin and leptin act together on hypothalamic neurons to promote WAT browning and weight loss. Deletion of the phosphatases PTP1B and TCPTP enhanced insulin and leptin signaling in proopiomelanocortin neurons and prevented diet-induced obesity by increasing WAT browning and energy expenditure. The co-infusion of insulin plus leptin into the CNS or the activation of proopiomelanocortin neurons also increased WAT browning and decreased adiposity. Our findings identify a homeostatic mechanism for coordinating the status of energy stores, as relayed by insulin and leptin, with the central control of WAT browning.
OBJECTIVE-The protein tyrosine phosphatase PTP1B is a negative regulator of insulin signaling; consequently, mice deficient in PTP1B are hypersensitive to insulin. Because PTP1B Ϫ/Ϫ mice have diminished fat stores, the extent to which PTP1B directly regulates glucose homeostasis is unclear. Previously, we showed that brain-specific PTP1B Ϫ/Ϫ mice are protected against high-fat diet-induced obesity and glucose intolerance, whereas muscle-specific PTP1B Ϫ/Ϫ mice have increased insulin sensitivity independent of changes in adiposity. Here we studied the role of liver PTP1B in glucose homeostasis and lipid metabolism. RESEARCH DESIGN AND METHODS-We analyzed body mass/adiposity, insulin sensitivity, glucose tolerance, and lipid metabolism in liver-specific PTP1B Ϫ/Ϫ and PTP1Bfl/fl control mice, fed a chow or high-fat diet. RESULTS-Compared with normal littermates, liver-specific PTP1BϪ/Ϫ mice exhibit improved glucose homeostasis and lipid profiles, independent of changes in adiposity. Liver-specific PTP1B Ϫ/Ϫ mice have increased hepatic insulin signaling, decreased expression of gluconeogenic genes PEPCK and G-6-Pase, enhanced insulin-induced suppression of hepatic glucose production, and improved glucose tolerance. Liver-specific PTP1B Ϫ/Ϫ mice exhibit decreased triglyceride and cholesterol levels and diminished expression of lipogenic genes SREBPs, FAS, and ACC. Liver-specific PTP1B deletion also protects against high-fat diet-induced endoplasmic reticulum stress response in vivo, as evidenced by decreased phosphorylation of p38MAPK, JNK, PERK, and eIF2␣ and lower expression of the transcription factors C/EBP homologous protein and spliced X box-binding protein 1. CONCLUSIONS-Liver
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