Summary Dominant negative mutations in the nuclear hormone receptor peroxisome proliferator-activated receptor-γ (PPARγ) cause hypertension by an unknown mechanism. Hypertension and vascular dysfunction are recapitulated by expression of dominant negative PPARγ specifically in vascular smooth muscle of transgenic mice. Dominant negative PPARγ increases RhoA and Rho-kinase activity, and inhibition of Rho-kinase restores normal reactivity and reduces arterial pressure. RhoBTB1, a component of the Cullin-3 RING E3 ubiquitin ligase complex, is a PPARγ target gene. Decreased RhoBTB1, Cullin-3 and neddylated Cullin-3 correlated with increased levels of the Cullin-3 substrate RhoA. Knockdown of Cullin-3 or inhibition of cullin-RING ligase activity in aortic smooth muscle cells increased RhoA. Cullin-RING ligase inhibition enhanced agonist-mediated contraction in aortic rings from normal mice by a Rho-kinase-dependent mechanism, and increased arterial pressure in vivo. We conclude that Cullin-3 regulates vascular function and arterial pressure thus providing a mechanistic link between mutations in Cullin-3 and hypertension in humans.

Rationale Activation of peroxisome proliferator-activated receptor-γ (PPARγ) by thiazolidinediones lowers blood pressure, whereas PPARγ mutations cause hypertension. Previous studies suggest these effects may be mediated through the vasculature, but the underlying mechanisms remain unclear. Objective To identify PPARγ mechanisms and transcriptional targets in vascular smooth muscle and their role in regulating resistance artery tone. Methods and Results We studied mesenteric artery (MA) from transgenic mice expressing dominant negative (DN) mutant PPARγ driven by a smooth muscle cell (SMC)-specific promoter. MA from transgenic mice exhibited a robust increase in myogenic tone. Patch clamp analysis revealed a reduced large conductance Ca2+-activated K+ (BKCa) current in freshly dissociated SMC from transgenic MA. Inhibition of protein kinase C (PKC) corrected both enhanced myogenic constriction and impaired BKCa channel function. Gene expression profiling revealed a marked loss of the regulator of G protein signaling 5 (RGS5) mRNA in transgenic MA, which was accompanied by a substantial increase in angiotensin II-induced constriction in MA. RGS5 siRNA caused augmented myogenic tone in intact mesenteric arteries and increased activation of PKC in SMC cultures. PPARγ and PPARδ each bind to a PPAR response element close to the RGS5 promoter. RGS5 expression in non-transgenic MA was induced following activation of either PPARγ or PPARδ, an effect that was markedly blunted by DN PPARγ. Conclusions We conclude that RGS5 in smooth muscle is a PPARγ and PPARδ target, which when activated blunts angiotensin-II-mediated activation of PKC, preserves BKCa channel activity, thus providing tight control of myogenic tone in the microcirculation.

Peroxisome proliferator-activated receptor-␥ (PPAR␥) is a ligand-activated transcription factor of the nuclear hormone receptor superfamily. Increasing evidence suggests that PPAR␥ is involved in the regulation of vascular function and blood pressure in addition to its well recognized role in metabolism. Thiazolidinediones, PPAR␥ agonists, lower blood pressure and have protective vascular effects through largely unknown mechanisms. In contrast, loss-of-function dominant-negative mutations in human PPAR␥ cause insulin resistance and severe early onset hypertension. Recent studies using genetically manipulated mouse models have begun to specifically address the importance of PPAR␥ in the vasculature. In this minireview, evidence for a protective role of PPAR␥ in the endothelium and vascular smooth muscle, derived largely from studies of genetically manipulated mice, will be discussed.

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...

An indispensable role for the brain renin-angiotensin system (RAS) has been documented in most experimental animal models of hypertension. To identify the specific efferent pathway activated by the brain RAS that mediates hypertension, we examined the hypothesis that elevated arginine vasopressin (AVP) release is necessary for hypertension in a double-transgenic model of brain-specific RAS hyperactivity (the "sRA" mouse model). sRA mice experience elevated brain RAS activity due to human angiotensinogen expression plus neuron-specific human renin expression. Total daily loss of the 4-kDa AVP prosegment (copeptin) into urine was grossly elevated (≥8-fold). Immunohistochemical staining for AVP was increased in the supraoptic nucleus of sRA mice (~2-fold), but no quantitative difference in the paraventricular nucleus was observed. Chronic subcutaneous infusion of a nonselective AVP receptor antagonist conivaptan (YM-087, Vaprisol, 22 ng/h) or the V(2)-selective antagonist tolvaptan (OPC-41061, 22 ng/h) resulted in normalization of the baseline (~15 mmHg) hypertension in sRA mice. Abdominal aortas and second-order mesenteric arteries displayed AVP-specific desensitization, with minor or no changes in responses to phenylephrine and endothelin-1. Mesenteric arteries exhibited substantial reductions in V(1A) receptor mRNA, but no significant changes in V(2) receptor expression in kidney were observed. Chronic tolvaptan infusion also normalized the (5 mmol/l) hyponatremia of sRA mice. Together, these data support a major role for vasopressin in the hypertension of mice with brain-specific hyperactivity of the RAS and suggest a primary role of V(2) receptors.