CCR5 antagonist treatment inhibits vascular injury by regulating NADPH oxidase 1

BACKGROUND

Chemokine (C- Cmotif) ligand 5 (CCL5) and its receptor C-C motif chemokine receptor 5 (CCR5), have been broadly studied in conjunction with infectious pathogens, however, their involvement in cardiovascular disease is not completely understood. NADPH oxidases (Noxs) are the major source of reactive oxygen species (ROS) in the vasculature. Whether the activation of Noxs is CCL5/CCR5 sensitive and whether such interaction initiates vascular injury is unknown. We investigated whether CCL5/CCR5 leads to vascular damage by activating Noxs.

MATERIAL AND METHODS

We used rat aortic smooth muscle cells (RASMC) to investigate the molecular mechanisms by which CCL5 leads to vascular damage and carotid ligation (CL) to analyze the effects of blocking CCR5 on vascular injury.

RESULTS

CCL5 induced Nox1 expression in concentration and time-dependent manners, with no changes in Nox2 or Nox4. Maraviroc pre-treatment (CCR5 antagonist, 40uM) blunted CCL5-induced Nox1 expression. Furthermore, CCL5 incubation led to ROS production and activation of Erk1/2 and NFkB, followed by increased vascular cell migration, proliferation, and inflammatory markers. Notably, Nox1 inhibition (GKT771, 10uM) blocked CCL5-dependent effects. In vivo, CL induced pathological vascular remodeling and inflammatory genes and increased Nox1 and CCR5 expression. Maraviroc treatment (25 mg/Kg/day) reduced pathological vascular growth and Nox1 expression.

CONCLUSIONS

Our findings suggest that CCL5 activates Nox1 in the vasculature, leading to vascular injury likely via NFkB and Erk1/2. Herein, we place CCR5 antagonists and/or Nox1 inhibitors might be preeminent antiproliferative compounds to reduce the cardiovascular risk associated with medical procedures (e.g. angioplasty) and vascular diseases associated with vascular hyperproliferation.

Recent advances in understanding lipodystrophy: a focus on lipodystrophy-associated cardiovascular disease and potential effects of leptin therapy on cardiovascular function

Lipodystrophy is a disease characterized by a partial or total absence of adipose tissue leading to severe metabolic derangements including marked insulin resistance, type 2 diabetes, hypertriglyceridemia, and steatohepatitis. Lipodystrophy is also a source of major cardiovascular disorders which, in addition to hepatic failure and infection, contribute to a significant reduction in life expectancy. Metreleptin, the synthetic analog of the adipocyte-derived hormone leptin and current therapy of choice for patients with lipodystrophy, successfully improves metabolic function. However, while leptin has been associated with hypertension, vascular diseases, and inflammation in the context of obesity, it remains unknown whether its daily administration could further impair cardiovascular function in patients with lipodystrophy. The goal of this short review is to describe the cardiovascular phenotype of patients with lipodystrophy, speculate on the etiology of the disorders, and discuss how the use of murine models of lipodystrophy could be beneficial to address the question of the contribution of leptin to lipodystrophy-associated cardiovascular disease.

Abstract 007: Endothelial Mineralocorticoid Receptors are Increased by Pregnancy in Mice and Mediate Obesity-Associated, Leptin-Induced Endothelial Dysfunction in Pregnancy

Obesity is a risk factor for endothelial dysfunction and hypertension in pregnancy. Our lab has demonstrated that obesity-associated hypertension in female animal models develops via leptin-mediated, aldosterone-induced endothelial dysfunction (ED). We also showed that female mice are more sensitive to leptin-induced aldosterone activation of endothelial mineralocorticoid receptors (ECMR) due to an endogenous sex-specific upregulation of ECMR in females. Our previous data demonstrates that endothelial progesterone receptor activation increases ECMR expression and that ECMR deletion protects female mice from obesity-associated, leptin-mediated ED. However, whether ECMR play a role in ED in pregnancy is unknown. Therefore, we hypothesized that high progesterone levels increase ECMR expression in pregnant mice and that ECMR deletion protects pregnant mice from obesity-associated, leptin-mediated ED. Endothelial cells were isolated from aorta of timed-pregnant Balb/C mice (gestation day (GD) 17) and assessed for ECMR expression via RT-PCR. ECMR mRNA expression increased 9.2±0.2-fold (*P<0.05) in pregnant compared to nonpregnant mice in association with high plasma progesterone levels (24±6 ng/ml pregnant vs 2±2 nonpregnant, *P<0.05). Endothelial function was experimentally measured by wire myography concentration response curves to acetylcholine in mouse aorta analyzed by 2-way ANOVA of curves with repeated measures. No changes in endothelial-independent sodium nitroprusside responses were observed. Chronic leptin infusion in mid-pregnancy (GD11-17) induced ED in pregnant mice that was impaired both compared to sham-treated pregnant (*P<0.05) and non-pregnant leptin-infused females (*P<0.05), indicating that increased ECMR expression in pregnancy increases sensitivity to leptin-induced ED. Further evidence for this notion is provided in that ECMR deletion in pregnant mice protected them from leptin-mediated ED (*P<0.05). Collectively, these data indicate a role for ECMR in the pathogenesis of obesity-associated ED in pregnancy and indicate a potential role for MR antagonists for the treatment of hypertensive pregnancies such as preeclampsia.

Abstract 121: Leptin Restores Endothelial Function, Diminishes Vascular Adrenergic Contractility, but Does Not Alter Arterial Stiffness and Blood Pressure, in a Mouse Model of Congenital Generalized Lipodystrophy

Leptin which has been associated with cardiovascular disease in the context of obesity, is the current treatment for the metabolic disorders associated with congenital generalized lipodystrophy (CGL). However, the effects of chronic leptin infusion on vascular function and arterial pressure remain unknown in CGL. Here, we hypothesized that deletion in leptin will alter while leptin infusion will restore cardiovascular function via direct vascular mechanisms in CGL in male Berardinelli-Seip 2 gene deficient mice (gBscl2-/-), a mouse model of CGL. CGL mice exhibited reduced adipose mass and leptin levels (gBscl2+/+: 4.03 ± 0.3 vs gBscl2-/-: 0.38 ± 0.1*, ng/dL *P<0.05), as well as evidence of cardiovascular dysfunction including impaired endothelium-dependent relaxation, increased vascular contractility for phenylephrine (gBscl2+/+: 55.3 ± 1 vs gBscl2-/-: 106.2 ± 2.7*, Emax *P<0.05), augmented pulse wave velocity (PWV) (gBscl2+/+: 259.6 ± 20.4 vs gBscl2-/-: 412.4 ± 2.7*, cm/s *P<0.05), vascular fibrosis and elevated mean arterial pressure (MAP) (gBscl2+/+: 100.7 ± 1.4 vs gBscl2-/-: 109.5 ± 2*, mmHg *P<0.05). Blood vessels from CGL mice exhibit increased Nox1 expression gene expression (3 fold) and reactive oxygen species production. Nox1 inhibition (GKT771 10 -5 M) or PPARγ activator (Pioglitazone 10 -5 M) restored endothelial function. Remarkably, chronic (0.3mg/day/7 days) and acute leptin supplementation restored endothelial function and decreased Nox1 expression and ROS production. Selective genetic ablation of leptin receptors in endothelial cells promoted endothelial dysfunction, via Nox-1 dependent mechanisms. Furthermore, leptin reduced vascular adrenergic contractility, but did not reduce MAP, nor PWV or vascular fibrosis in CGL. In conclusion, leptin restores endothelial function via PPARγ-dependent decreases in Nox1, reduces vascular adrenergic contractility, but does not affect the blood pressure and vascular structure, in gBscl2-/- mice. These data reveal a new direct role of leptin receptors in the control of vascular homeostasis and present leptin as a potential therapy for the treatment of vascular disease associated with low leptin levels.

Atorvastatin inhibits pro-inflammatory actions of aldosterone in vascular smooth muscle cells by reducing oxidative stress

Vascular inflammatory responses play an important role in several cardiovascular diseases. Of the many pro-inflammatory vasoactive factors implicated in this process, is aldosterone, an important mediator of vascular oxidative stress. Statins, such as atorvastatin, are cholesterol-lowering drugs that have pleiotropic actions, including anti-oxidant properties independently of their cholesterol-lowering effect. This study investigated whether atorvastatin prevents aldosterone-induced VSMC inflammation by reducing reactive oxygen species (ROS) production. Vascular smooth muscle cells (VSMC) from WKY rats were treated with 1 μM atorvastatin for 60 min or for 72 h prior to aldosterone (10-7 mol/L) stimulation. Atorvastatin inhibited Rac1/2 and p47phox translocation from the cytosol to the membrane, as well as reduced aldosterone-induced ROS production. Atorvastatin also attenuated aldosterone-induced vascular inflammation and macrophage adhesion to VSMC. Similarly EHT1864, a Rac1/2 inhibitor, and tiron, ROS scavenger, reduced macrophage adhesion. Through its inhibitory effects on Rac1/2 activation and ROS production, atorvastatin reduces vascular ROS generation and inhibits VSMC inflammation. Our data suggest that in conditions associated with aldosterone-induced vascular damage, statins may have vasoprotective effects by inhibiting oxidative stress and inflammation.

Identification of novel macropinocytosis inhibitors using a rational screen of Food and Drug Administration-approved drugs

BACKGROUND AND PURPOSE

Macropinocytosis is involved in many pathologies, including cardiovascular disorders, cancer, allergic diseases, viral and bacterial infections. Unfortunately, the currently available pharmacological inhibitors of macropinocytosis interrupt other endocytic processes and have non-specific endocytosis-independent effects. Here we have sought to identify new, clinically relevant inhibitors of macropinocytosis, using an FDA-approved drug library.

EXPERIMENTAL APPROACH

In the present study, 640 FDA-approved compounds were tested for their ability to inhibit macropinocytosis. A series of secondary assays were performed to confirm inhibitory activity, determine IC50 values and investigate cell toxicity. The ability of identified hits to inhibit phagocytosis and clathrin-mediated and caveolin-mediated endocytosis was also investigated. Scanning electron microscopy and molecular biology techniques were utilized to examine the mechanisms by which selected compounds inhibit macropinocytosis.

KEY RESULTS

The primary screen identified 14 compounds that at ~10 μM concentration inhibit >95% of macropinocytotic solute internalization. Three compounds - imipramine, phenoxybenzamine and vinblastine - potently inhibited (IC50  ≤ 131 nM) macropinocytosis without exerting cytotoxic effects or inhibiting other endocytic pathways. Scanning electron microscopy imaging indicated that imipramine inhibits membrane ruffle formation, a critical early step leading to initiation of macropinocytosis. Finally, imipramine has been shown to inhibit macropinocytosis in several cell types, including cancer cells, dendritic cells and macrophages.

CONCLUSIONS AND IMPLICATIONS

Our results identify imipramine as a new pharmacological tool to study macropinocytosis in cellular and biological systems. This study also suggests that imipramine could be a good candidate for repurposing as a therapeutic agent in pathological processes involving macropinocytosis.

Abstract 100: High-throughput Screening of FDA-approved Drugs Identifies Novel Inhibitors of Macropinocytosis

Aims: Macropinocytosis has been implicated in atherosclerosis, cancer, allergic disorders, and other pathologies. Unfortunately, most currently available pharmacological inhibitors of macropinocytosis interrupt other endocytic processes and have non-specific endocytosis-independent effects. The goal of the present study was to perform a high-throughput screen (HTS) of FDA-approved drugs to identify new, clinically relevant inhibitors of macropinocytosis.

Methods: In the present study, 640 FDA-approved compounds were tested for their ability to inhibit macropinocytosis. A series of secondary assays were performed to confirm inhibitory activity, determine IC 50 values, and investigate cell toxicity. The ability of identified hits to inhibit phagocytosis, clathrin- and caveolin-mediated endocytosis was also investigated. Scanning electron microscopy and molecular biology techniques were utilized to investigate the mechanisms by which selected compounds inhibit macropinocytosis.

Results: The HTS campaign identified 14 compounds that at ~10 μM concentration inhibit >95% of macropinocytotic solute internalization. Our results demonstrated that three lead compounds, namely imipramine, phenoxybenzamine, and vinblastine, potently inhibit (IC 50 ≤ 130 nM) macropinocytosis without exerting cytotoxic effects or inhibiting other endocytic pathways. Mechanistically, we found that imipramine inhibits translocation of ADP-ribosylation factor 6 to the plasma membrane and prevents membrane ruffle formation, a critical early step leading to macropinocytosis. Imipramine inhibited macropinocytosis in multiple cell types, including cancer cells, dendritic cells, and macrophages. Finally, incubation of macrophages with imipramine inhibited nLDL macropinocytosis and foam cell formation in vitro .

Innovation and Conclusion: The identified macropinocytosis inhibitors may prove useful as new pharmacological tools to more fully discern the role of macropinocytosis in pathological processes and as therapeutic agents in various disorders involving macropinocytosis.

Abstract P153: Mineralocorticoid Receptor Inhibition Abolishes Sex-specific, Renin Angiotensin Aldosterone System-associated Salt Sensitivity in Female Mice

Up to half of essential hypertension cases in women are associated with salt sensitive blood pressure (BP) increases, however, the sex-specific mechanisms of salt sensitivity in women are unknown. Our lab has shown that female mice are more sensitive to the hypertensive effects of aldosterone than male mice but it is unknown if aldosterone plays a role in salt sensitivity in female mice. We hypothesized that increasing dietary sodium via a high salt diet would increase blood pressure in female mice which would be abrogated by mineralocorticoid receptor (MR) antagonism. To determine salt sensitivity male and female Balb/C mice were implanted with radiotelemeters for continuous recording of BP. BP was recorded during baseline (7 days) and throughout the administration of a high salt (4% NaCl, HS) diet for 7 days with or without concurrent eplerenone supplementation (daily 200 mg/kg/day). Plasma and kidneys were then harvested. Systolic (SBP) and diastolic (DBP) BP were increased in female mice, but not in males, on HS (7.8±3.3 SBP and 7.8±4.0 DBP Δ change in mmHg in female (P<0.05) vs -3.7±3.1 SBP and 3.1±2.1 DBP in male, respectively, n=7-8). Plasma aldosterone levels were decreased in HS male mice compared to control (224±57 vs 151±19 pg/ml, n=3-5), however, increased modestly in HS females (254±56 vs 394±158 pg/ml, n=3-6). Preliminary data indicated that MR antagonism with eplerenone ablated increases in SBP and DBP in HS female mice, while having no effect on blood pressure in HS males (-22.8 SBP and -23.9 DBP Δ change in mmHg in female vs 1.0 SBP and -1.5 DBP in male, n=2). In addition, and in association with an absence of aldosterone suppression with HS, renal mRNA expression of renin (1.4±0.1-fold, P<0.05, n=5), angiotensinogen (4.4±0.2-fold, P<0.05, n=5), AT1 receptor (52.9±0.9-fold, P<0.05, n=5), MR (1.6±0.2-fold, P<0.05, n=5) and α-ENAC (1.3±0.0-fold, P<0.05, n=5) were increased in HS female mice compared to control females. These data indicate that BP increases in HS female mice are associated with unexpected increases in plasma aldosterone as well as mRNA expression of proteins associated with renin angiotensin aldosterone system activation, which may be novel mechanisms via which females have increased risk for salt sensitive hypertension.

Abstract 128: Leptin: A Regulator of Aldosterone Synthase Expression & Aldosterone Secretion in Visceral Adipocytes, in Mice

Obesity is associated with inappropriately high aldosterone levels, which contribute to the development of metabolic and cardiovascular disorders. The origin of these high aldosterone levels is incompletely understood. We recently demonstrated that the adipocyte-derived hormone leptin regulates aldosterone synthase (CYP11B2) expression and stimulates aldosterone release from adrenal zona glomerulosa cells. Recent studies demonstrate that adipocytes express CYP11B2 and secrete aldosterone. However, the mechanisms regulating aldosterone release from adipocytes remain unclear. Likewise, whether visceral (Visc) and subcutaneous (SubQ) adipose tissue contribute to a similar extent to aldosterone production is unknown. We tested the hypothesis that leptin increases adipocyte CYP11B2 expression and aldosterone production and investigated whether Visc and SubQ adipose tissues respond similarly to leptin. Immunostaining of mouse adipose tissue cross-sections and isolated mature adipocytes revealed that Visc and SubQ adipose tissue express leptin receptors. Treatment of mouse freshly isolated mature adipocytes, non-differenciated (stromal fraction) and differentiated adipocytes revealed that leptin dose-dependently increased CYP11B2 expression and aldosterone production in Visc adipose tissue only. Although leptin receptor and CYP11B2 levels were similar in SubQ and Visc adipocytes, SubQ adipocytes were unresponsive to leptin. The physiological relevance of these in vitro data was tested by measuring plasma aldosterone levels in mice deprived of adipose tissue (lipodystrophic mice) treated with leptin. Absence of adipose tissue in lipodystrophic mice blunted leptin-induced increases in aldosterone levels (WT-vehicle: 471±82 vs. WT-Leptin: 1699±396, p<0.05; KO-vehicle: 539±71 vs. KO+leptin: 787±156, NS). The human relevance of these data was determined by reporting that CYP11B2 expression gradually increased with body mass index in human mediastinal and omental fat depots. In summary these data strongly suggest that leptin regulates CYP11B2 levels and aldosterone release in visceral adipose tissue and that leptin-induced, adipocyte-derived aldosterone may contribute to obesity-associated hyperaldosteronism.

Abstract 096: Leptin and High Salt Diet Induce Greater Increases in Blood Pressure in Female than Male Mice

Recent studies by our group demonstrated that leptin is a direct regulator of aldosterone secretion and increases blood pressure via sex-specific mechanisms involving leptin-mediated activation of the aldosterone-mineralocorticoid receptor signaling pathway in females and sympatho-activation in males. Although it is well accepted that females secrete more leptin and aldosterone than males, it is unknown whether leptin infusion raises blood pressure similarly in male and female mice and whether higher aldosterone levels sensitize females to salt-induced hypertension. We hypothesized that female mice would be more sensitive to leptin than males and also have a potentiated blood pressure rise in response to high salt diet compared to males. Male and female Balb/C mice were implanted with radiotelemeters for continuous measurement of mean arterial pressure (MAP) at 10 weeks of age. MAP was measured for seven days prior to feeding with a high-salt diet (HS, 4%NaCl) for seven days. Following a recovery period, animals were then implanted with osmotic minipumps containing leptin (0.9mg/kg/day) recorded for seven days. Baseline MAP was similar between males and females (101.3±2.9 vs 99.3±3.7 mmHg, n=4 and 5, respectively), however, HS diet resulted in a greater MAP increase in females (15.0±2.6 mmHg) compared to males (3.1±4.5 mmHg, P<0.05). MAP with leptin treatment was increased with leptin in females moreso than in males, however, this did not reach significance (6.8±5.8 vs 1.8±5.9 mmHg, respectively). This potential sex difference in blood pressure responses to leptin was not associated with changes in body weight (0.07±0.44 vs -0.22±0.2 g, respectively) nor changes in blood glucose (-19.67±15.06 vs -15.4±11.4 mg/dl, respectively) in males and females in response to leptin. In summary, female mice are more sensitive to HS diet-induced blood pressure increases than males. Females may be more sensitive to leptin-mediated blood pressure increases than males. Further investigation is needed to determine whether these sex differences in blood pressure responses to HS diet and leptin are mediated by aldosterone or other mechanisms.

Abstract 429: PTP1B, a Link Between Endoplasmic Reticulum Stress and Endothelial Dysfunction

Endothelial dysfunction is a common feature of diabetes and a major contributor to diabetic vascular complications. Despite aggressive diabetes management strategies, preventing diabetes-induced endothelial dysfunction remains a difficult challenge. Endothelium insulin resistance and endoplasmic reticulum (ER) stress have been reported to contribute to endothelial dysfunction. Protein tyrosine phosphatase 1B (PTP1B) is a phosphatase bound to the ER known to regulate insulin sensitivity and ER stress. We hypothesize that diabetes alters PTP1B regulation of endothelial cell function and that inhibiting PTP1B may allow a strategy to prevent diabetes-induced endothelial dysfunction. Using immuno-histochemistry we showed that PTP1B is expressed in the endothelial cells of human saphenous vein, and in human primary aortic endothelial cells. Western-blot and quantitative real-time PCR analysis revealed that diabetes increased PTP1B and ER stress markers expression (CHOP: 1.4±0.2, GRP78: 1.5±0.2, XBP1spliced: 2.1±0.3, XBP1: 1.4±0.2 fold changes), in human saphenous veins. Deletion of PTP1B in obese diabetic mice (db/db) significantly reduced the level of expression (mRNA) of ER stress markers in mouse aorta. Incubation of mouse aortic rings with tunicamycin (tunica) or thapsigargin (thapsi), two ER stress inducers, increased the level of expression of ER stress markers (mRNA) and significantly reduced endothelium-dependent relaxation. (Tunica: -17±5%, thapsi: -30±6%, vs. DMSO). NO synthase inhibition with LNAME completely abolished endothelium-dependent relaxation in vehicle and tunica-treated rings. Neither the reactive oxygen species (ROS) scavenger tempol, nor catalase restored endothelial function, in tunica-treated rings. This suggests that ER stress induces a reduction in NO bioavailability independent of ROS. Aortic rings from PTP1B KO mice were protected against ER stress-induced endothelial dysfunction and exhibited a modest increase in ER stress markers compared to control rings, in response to tunica. All together these data demonstrate that PTP1B deletion prevents ER stress-induced endothelial dysfunction and that targeting PTP1B might be a beneficial approach to restore diabetic endothelial dysfunction.

Vascular effects of deletion of melanocortin-4 receptors in rats

Obesity is a major cause of hypertension, but links between the obese and hypertensive states remain incompletely understood. A major component of cardiovascular function in obese individuals is a state of sympathoactivation. A postulated mechanism of this sympathoactivation is the activation of specific classes of neurons commonly associated with metabolic control, which also affect sympathetic outflow to cardiovascular targets. One class of neurons is characterized by expression of melanocortin-4 receptors (MC4R) which are activated by metabolic signals such as leptin and insulin. In this study, we examined the effects of deletion of MC4R in a novel rat model. MC4R knockout (KO) rats are obese and profoundly insulin resistant without frank diabetes. Despite these conditions, MC4R KO rats are normotensive. Moderate bradycardia and significant increases in peripheral resistance were evident in MC4R KO rats. To determine if the dissociation between hypertension and obesity was associated with changes in vascular function, in vitro reactivity to vasoactive agents and in vivo reactivity to sympathetic blockade were examined. Vasodilator function was not affected by obesity in MC4R KO rats. Reactivity to phenylephrine was reduced, suggesting desensitization of adrenergic signaling. In response to ganglionic blockade with mecamylamine, blood pressure and hindlimb resistance fell more in MC4R KO rats, suggesting that sympathoactivation of the vascular was still evident, despite the absence of hypertension. These findings suggest that obesity causes sympathoactivation of the vasculature despite the absence of MC4R. Dissociation of obesity from hypertension in this model may reflect more renal mechanisms of blood pressure control.

Abstract 23: Increasing Leptin Sensitivity in Proopiomelanocortin Neurons Does not Sensitize the Cardiovascular System to Leptin

Leptin-mediated control of metabolic function requires activation of the proopiomelanocortin (POMC) neurons in the hypothalamus. Whether POMC neurons also control the cardiovascular effects of leptin still remain to be determined. In order to test the hypothesis that POMC neurons regulate leptin-mediated cardiovascular control, protein tyrosine phosphatase 1B (PTP1B), the molecular restrain of the leptin signaling pathway was deleted in the whole animal (PTP1BKO/WT) or specifically in POMC neurons (PTP1BPOMC/flox) of mice on the C57Bl/6 background using the Cre-Lox technique. PTP1B deletion in POMC neurons recapitulates the protective effects of the total KO on the control of body weight and insulin sensitivity. Conscious blood pressure (BP) measurements (telemetry) revealed that neither baseline (PTP1BWT: 103±4 vs. PTP1BKO: 104±7, PTP1Bflox: 112±3 vs. PTP1BPOMC: 117±6 mmHg) nor BP response to chronic leptin infusion (PTP1BWT: 105±6 vs. PTP1BKO: 107±5, PTP1Bflox: 119±3 vs. PTP1BPOMC: 118±3 mmHg) or cage switch stress were affected by the deletion of PTP1B in PTP1BKO and PTP1BPOMC. Sympathetic tone, assessed by measuring the drop in BP in response to ganglionic blockade was increased in PTP1BKO but not in PTP1BPOMC. Vascular adrenergic tone, an index of chronic sympatho-activation inversely correlated to the level of sympathetic activity was measured in isolated aortic rings via wire myography. Aortic rings from PTP1BKO mice exhibited a reduced adrenergic tone (PTP1BWT: 95±7 vs. PTP1BKO: 46±6% of KCl, p<0.05), whereas PTP1BPOMC presented an increased vascular constriction (PTP1Bflox: 85±79 vs. PTP1BPOMC: 112±13% of KCl, p<0.05) non-specific to the adrenergic response. However, the reduction in vascular adrenergic tone induced by chronic leptin infusion was preserved in PTP1BPOMC mice. These data suggest that POMC neurons do not regulate basal sympathetic tone towards the vasculature. These data also highlight the key role of POMC neurons in the control of metabolic function but minimalize their role in the regulation of cardiovascular effects of leptin.

Deletion of protein tyrosine phosphatase 1b improves peripheral insulin resistance and vascular function in obese, leptin-resistant mice via reduced oxidant tone

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 together, these data reveal a role for peripheral insulin resistance as the mediator of vascular dysfunction in obesity.