Background-Obesity causes hypertension and sympathoactivation, a process proposed to be mediated by leptin. Protein tyrosine phosphatase 1B (PTP1B), a major new pharmaceutical target in the treatment of obesity and type II diabetes mellitus, constrains the metabolic actions of leptin, but the extent to which PTP1B regulates its cardiovascular effects is unclear. This study examined the hypothesis that PTP1B is a negative regulator of the cardiovascular effects of leptin. Methods and Results-PTP1B knockout mice had lower body fat but higher mean arterial pressure (116Ϯ5 versus 105Ϯ5 mm Hg, PϽ0.05) than controls. Leptin infusion produced a greater anorexic effect in PTP1B knockout mice and a marked increase in mean arterial pressure (135Ϯ5 mm Hg) in PTP1B knockout mice only. The decrease in mean arterial pressure in response to ganglionic blockade was higher in PTP1B knockout mice (Ϫ38Ϯ3% versus Ϫ29Ϯ3%, PϽ0.05), which suggests increased sympathetic tone. PTP1B deletion blunted mean arterial pressure responses to phenylephrine injection (55Ϯ10% versus 93Ϯ7%, PϽ0.05). Phenylephrine-induced aortic contraction was reduced in PTP1B knockout mice (57.7Ϯ9% versus 96.3Ϯ12% of KCl, PϽ0.05), consistent with desensitization to chronically elevated sympathetic tone. Furthermore, PTP1B deletion significantly reduced gene expression of 3 ␣ 1 -adrenergic receptor subtypes, consistent with blunted constriction to phenylephrine. Conclusions-These data indicate that PTP1B is a key regulator of the cardiovascular effects of leptin and that reduced vascular adrenergic reactivity provides a compensatory limit to the effects of leptin on mean arterial pressure.

ObjectiveTo investigate the role played by leptin in thermoregulation, we studied the effects of physiological leptin replacement in leptin-deficient ob/ob mice on determinants of energy balance, thermogenesis and heat retention under 3 different ambient temperatures.MethodsThe effects of housing at 14 °C, 22 °C or 30 °C on core temperature (telemetry), energy expenditure (respirometry), thermal conductance, body composition, energy intake, and locomotor activity (beam breaks) were measured in ob/ob mice implanted subcutaneously with osmotic minipumps at a dose designed to deliver a physiological replacement dose of leptin or its vehicle-control.ResultsAs expected, the hypothermic phenotype of ob/ob mice was partially rescued by administration of leptin at a dose that restores plasma levels into the physiological range. This effect of leptin was not due to increased energy expenditure, as cold exposure markedly and equivalently stimulated energy expenditure and induced activation of brown adipose tissue irrespective of leptin treatment. Instead, the effect of physiological leptin replacement to raise core body temperature of cold-exposed ob/ob mice was associated with reduced thermal conductance, implying a physiological role for leptin in heat conservation. Finally, both leptin- and vehicle-treated ob/ob mice failed to match energy intake to expenditure during cold exposure, resulting in weight loss.ConclusionsThe physiological effect of leptin to reduce thermal conductance contributes to maintenance of core body temperature under sub-thermoneutral conditions.

Rationale: Obesity is a risk factor for cardiovascular dysfunction, yet the underlying factors driving this impaired function remain poorly understood. Insulin resistance is a common pathology in obese patients and has been shown to impair vascular function. Whether insulin resistance or obesity, itself, is causal remains unclear. Objective: The present study tested the hypothesis that insulin resistance is the underlying mediator for impaired NO-mediated dilation in obesity by genetic deletion of the insulin-desensitizing enzyme protein tyrosine phosphatase (PTP)1B in db/db mice. Methods and Results: The db/db mouse is morbidly obese, insulin-resistant, and has tissue-specific elevation in PTP1B expression compared to lean controls. In db/db mice, PTP1B deletion improved glucose clearance, dyslipidemia, and insulin receptor signaling in muscle and fat. Hepatic insulin signaling in db/db mice was not improved by deletion of PTP1B, indicating specific amelioration of peripheral insulin resistance. Additionally, obese mice demonstrate an impaired endothelium dependent and independent vasodilation to acetylcholine and sodium nitroprusside, respectively. This impairment, which correlated with increased superoxide in the db/db mice, was corrected by superoxide scavenging. Increased superoxide production was associated with increased expression of NAD(P)H oxidase 1 and its molecular regulators, Noxo1 and Noxa1. Conclusions: Deletion of PTP1B improved both endothelium dependent and independent NO-mediated dilation and reduced superoxide generation in db/db mice. PTP1B deletion did not affect any vascular function in lean mice. Taken T he prevalence of obesity and its cardiovascular complications represents a significant health concern in Western societies, 1,2 but the root causes of cardiovascular dysfunction in obese individuals remain unclear. Metabolic dysfunction, notably insulin resistance, is evident in obesity. 3,4 It has been speculated that insulin resistance, rather than other aspects of obesity, is the underlying cause of cardiovascular injury in obese patients. [5][6][7][8][9] This hypothesis has been difficult to test because insulin-sensitizing drugs have off-target effects 4,10 and nonobese models of insulin resistance do not evaluate the relative importance of obesity versus insulin resistance. [11][12][13][14][15][16][17] The insulin receptor is a classic receptor tyrosine kinase 18 and, as such, is deactivated by protein tyrosine phosphatases, notably protein tyrosine phosphatase (PTP)1B. 19 -21 Deletion of PTP1B improves insulin sensitivity in mouse models of obesity, 22 and putative PTP1B antagonists have been used pharmacologically to improve glucose tolerance. [23][24][25] Increases in the activity and/or expression of PTP1B correlate with blunted insulin signaling in a variety of tissue types. 26 -28 Whether PTP1B deletion and amelioration of insulin resistance improves cardiovascular dysfunction associated with obesity remains unknown.The present study tested the hypothesis that PTP1B deleti...

Dynamic adjustment of insulin secretion to compensate for changes of insulin sensitivity that result from alteration of nutritional or metabolic status is a fundamental aspect of glucose homeostasis. To investigate the role of the brain in this coupling process, we used cold exposure as an experimental paradigm because the sympathetic nervous system (SNS) helps to coordinate the major shifts of tissue glucose utilization needed to ensure that increased thermogenic needs are met. We found that glucose-induced insulin secretion declined by 50% in rats housed at 5°C for 28 h, and yet, glucose tolerance did not change, owing to a doubling of insulin sensitivity. These potent effects on insulin secretion and sensitivity were fully reversed by returning animals to room temperature (22°C) for 4 h or by intravenous infusion of the α-adrenergic receptor antagonist phentolamine for only 30 min. By comparison, insulin clearance was not affected by cold exposure or phentolamine infusion. These findings offer direct evidence of a key role for the brain, acting via the SNS, in the rapid, highly coordinated, and reciprocal changes of insulin secretion and insulin sensitivity that preserve glucose homeostasis in the setting of cold exposure.

In rodent models of type 2 diabetes (T2D), sustained remission of hyperglycemia can be induced by a single intracerebroventricular (icv) injection of fibroblast growth factor 1 (FGF1), and the mediobasal hypothalamus (MBH) was recently implicated as the brain area responsible for this effect. To better understand the cellular response to FGF1 in the MBH, we sequenced >79,000 single-cell transcriptomes from the hypothalamus of diabetic Lepob/ob mice obtained on Days 1 and 5 after icv injection of either FGF1 or vehicle. A wide range of transcriptional responses to FGF1 was observed across diverse hypothalamic cell types, with glial cell types responding much more robustly than neurons at both time points. Tanycytes and ependymal cells were the most FGF1-responsive cell type at Day 1, but astrocytes and oligodendrocyte lineage cells subsequently became more responsive. Based on histochemical and ultrastructural evidence of enhanced cell-cell interactions between astrocytes and Agrp neurons (key components of the melanocortin system), we performed a series of studies showing that intact melanocortin signaling is required for the sustained antidiabetic action of FGF1. These data collectively suggest that hypothalamic glial cells are leading targets for the effects of FGF1 and that sustained diabetes remission is dependent on intact melanocortin signaling.