Peroxisome proliferator-activated receptor gamma (PPARgamma) is a ligand-activated transcription factor that plays a critical role in metabolism. Thiazolidinediones, high-affinity PPARgamma ligands used clinically to treat type II diabetes, have been reported to lower blood pressure and provide other cardiovascular benefits. Some mutations in PPARgamma (PPARG) cause type II diabetes and severe hypertension. Here we tested the hypothesis that PPARgamma in vascular muscle plays a role in the regulation of vascular tone and blood pressure. Transgenic mice expressing dominant-negative mutations in PPARgamma under the control of a smooth-muscle-specific promoter exhibit a loss of responsiveness to nitric oxide and striking alterations in contractility in the aorta, hypertrophy and inward remodeling in the cerebral microcirculation, and systolic hypertension. These results identify PPARgamma as pivotal in vascular muscle as a regulator of vascular structure, vascular function, and blood pressure, potentially explaining some of the cardioprotective effects of thiazolidinediones.

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.

Abstract-The ligand-activated transcription factor peroxisome proliferator activated receptor gamma (PPAR␥) is expressed in vascular endothelium where it exerts anti-inflammatory and antioxidant effects. However, its role in regulating vascular function remains undefined. We examined endothelial function in transgenic mice expressing dominant-negative mutants of PPAR␥ under the control of an endothelial-specific promoter to test the hypothesis that endothelial PPAR␥ plays a protective role in the vasculature. Under baseline conditions, responses to the endotheliumdependent agonist acetylcholine were not affected in either aorta or the basilar artery in vitro. In response to feeding a high-fat diet for 12 weeks, acetylcholine produced dilation that was markedly impaired in the basilar artery of mice expressing dominant-negative mutants, but not in mice expressing wild-type PPAR␥ controlled by the same promoter. Unlike basilar artery, 12 weeks of a high-fat diet was not sufficient to cause endothelial dysfunction in the aorta of mice expressing dominant-negative PPAR␥, although aortic dysfunction became evident after 25 weeks. The responses to acetylcholine in basilar artery were restored to normal after treatment with a scavenger of superoxide. Baseline blood pressure was only slightly elevated in the transgenic mice, but the pressor response to angiotensin II was augmented. Thus, interference with PPAR␥ in the endothelium produces endothelial dysfunction in the cerebral circulation through a mechanism involving oxidative stress. Consistent with its role as a fatty acid sensor, these findings provide genetic evidence that endothelial PPAR␥ plays a critical role in protecting blood vessels in response to a high-fat diet. Key Words: endothelium Ⅲ oxidative stress Ⅲ transcription Ⅲ transgenic animals Ⅲ vascular P eroxisome proliferator activated receptor gamma (PPAR␥) is a ligand-activated transcription factor targeted by the thiazolidinedione (TZD) class of antidiabetes medications. Activation of PPAR␥ by TZDs improves insulin sensitivity and lowers blood pressure in type II diabetes, whereas individuals with dominant-negative mutations in PPAR␥ present with severe insulin resistance, type II diabetes, and early-onset hypertension. 1 Studies in humans and animals suggest that TZDs are generally cardioprotective, although their clinical safety has been recently challenged. 2 That TZDs can lower blood pressure in the face of weight gain and water and salt retention by the kidneys suggests that the antihypertensive effects may be particularly profound.Heterozygous mice carrying one normal PPAR␥ allele and one dominant-negative allele (L/ϩ mice) exhibit a moderate increase in blood pressure. 3,4 We have recently reported that L/ϩ mice exhibit endothelial dysfunction and hypertrophy and inward remodeling in the cerebral vasculature. 4 Oxidative stress was the basis of endothelial dysfunction in the model as superoxide was increased and vascular function was restored to normal by a free radical scavenger. These data prov...

Abstract-The transcription factor PPAR␥ is expressed in endothelium and vascular muscle where it may exert antiinflammatory and antioxidant effects. We tested the hypothesis that PPAR␥ plays a protective role in the vasculature by examining vascular structure and function in heterozygous knockin mice expressing the P465L dominant negative mutation in PPAR␥ (L/ϩ). In L/ϩ aorta, responses to the endothelium-dependent agonist acetylcholine (ACh) were not affected, but there was an increase in contraction to serotonin, PGF 2␣ , and endothelin-1. In cerebral blood vessels both in vitro and in vivo, ACh produced dilation that was markedly impaired in L/ϩ mice. Superoxide levels were elevated in cerebral arterioles from L/ϩ mice and responses to ACh were restored to normal with a scavenger of superoxide. Diameter of maximally dilated cerebral arterioles was less, whereas wall thickness and cross-sectional area was greater in L/ϩ mice, indicating cerebral arterioles underwent hypertrophy and remodeling. Thus, interference with PPAR␥ signaling produces endothelial dysfunction via a mechanism involving oxidative stress and causes vascular hypertrophy and inward remodeling. These findings indicate that PPAR␥ has vascular effects which are particularly profound in the cerebral circulation and provide genetic evidence that PPAR␥ plays a critical role in protecting blood vessels. (Hypertension. 2008;51:867-871.)Key Words: endothelial function Ⅲ dominant negative Ⅲ hypertension Ⅲ remodeling Ⅲ hypertrophy T he peroxisome proliferator-activated receptor gamma (PPAR␥) is a ligand-activated transcription factor which has gained prominence because of its involvement in complex diseases such as diabetes, obesity, atherosclerosis, and hypertension. Recent interest in the role of PPAR␥ in the vasculature has substantially increased because of the antiinflammatory and antioxidant effects reported for PPAR␥ agonists (reviewed by Schiffrin et al 1 ). Naturally occurring mutations in humans, resulting in either constitutive activation or impairment of PPAR␥ function, strongly support its physiological importance and illustrate the severe consequences for cardiovascular related events when PPAR␥ signaling is altered. 2 Individuals with dominant negative mutations in PPAR␥ present with early onset hypertension and elements of the metabolic syndrome. 2 Although the importance of PPAR␥ in adipose tissue is now well documented, its role in the cardiovascular system has only begun to emerge. PPAR␥ is the molecular target of the thiazolidinediones (TZDs) class of antidiabetes drugs. These drugs increase insulin sensitivity but also lower blood pressure in patients with type 2 diabetes 3 and in animal models of hypertension. 4 TZDs also improve endothelial function and reduce blood pressure in nondiabetic models of hypertension, underscoring the potential protective effects of PPAR␥ in the vessel wall. 5 PPAR␥ is expressed in endothelium and vascular muscle and there is growing evidence that PPAR␥ may have direct effects in the vasculature. 6 ...

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All components of the renin angiotensin system necessary for ANG II generation and action have been reported to be present in renal proximal convoluted tubules. Given the close relationship between renal sodium handling and blood pressure regulation, we hypothesized that modulating the action of ANG II specifically in the renal proximal tubules would alter the chronic level of blood pressure. To test this, we used a proximal tubule-specific, androgen-dependent, promoter construct (KAP2) to generate mice with either overexpression of a constitutively active angiotensin type 1A receptor transgene or depletion of endogenous angiotensin type 1A receptors. Androgen administration to female transgenic mice caused a robust induction of the transgene in the kidney and increased baseline blood pressure. In the receptor-depleted mice, androgen administration to females resulted in a Cre recombinase-mediated deletion of angiotensin type 1A receptors in the proximal tubule and reduced blood pressure. In contrast to the changes observed at baseline, there was no difference in the blood pressure response to a pressor dose of ANG II in either experimental model. These data, from two separate mouse models, provide evidence that ANG II signaling via the type 1A receptor in the renal proximal tubule is a regulator of systemic blood pressure under baseline conditions.

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.

describing a role for AVP in the potential diagnosis and therapeutic treatment of preeclampsia. Ongoing research by MKS, DAS, and JLG developing diagnostic tests for preeclampsia that involve measurements of the AVP system are supported in part by a seed grant from Carmentix Pte Ltd/Esco Ventures.