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Low-salt diet is beneficial in salt-sensitive hypertension but may provoke cardiovascular risk in patients with heart failure, diabetes mellitus, or other cardiovascular abnormalities because of endogenous renin-angiotensin system activation. PPAR (peroxisome proliferator-activated receptor)-γ is a transcription factor which promotes an antioxidant pathway in the endothelium. We studied transgenic mice expressing a dominant-negative mutation in PPAR-γ selectively in the endothelium (E-V290M) to test the hypothesis that endothelial PPAR-γ plays a protective role in response to low salt-mediated renin-angiotensin system activation. Plasma renin and Ang II (angiotensin II) were significantly and equally increased in all mice fed low salt for 6 weeks. Vasorelaxation to acetylcholine was not affected in basilar artery from E-V290M at baseline but was significantly and selectively impaired in E-V290M after low salt. Unlike basilar artery, low salt was not sufficient to induce vascular dysfunction in carotid artery or aorta. Endothelial dysfunction in the basilar artery from E-V290M mice fed low salt was attenuated by scavengers of superoxide, inhibitors of NADPH oxidase, or blockade of the Ang II AT1 (angiotensin type-1) receptor. Simultaneous AT1 and AT2 receptor blockade revealed that the restoration of endothelial function after AT1 receptor blockade was not a consequence of AT2 receptor activation. We conclude that interference with PPAR-γ in the endothelium produces endothelial dysfunction in the cerebral circulation in response to low salt-mediated activation of the endogenous renin-angiotensin system, mediated at least in part, through AT1 receptor activation and perturbed redox homeostasis. Moreover, our data suggest that the cerebral circulation may be particularly sensitive to inhibition of PPAR-γ activity and renin-angiotensin system activation. [ABSTRACT FROM AUTHOR]

Pharmacological activation of PPAR-γ (peroxisome proliferator-activated receptor-γ) protects the vasculature. Much less is known on the cell-specific impact of PPAR-γ when driven by endogenous ligands. Recently, we found that endothelial PPAR-γ protects against angiotensin II-induced endothelial dysfunction. Here, we explored that concept further examining whether effects were sex dependent along with underlying mechanisms. We studied mice expressing a human dominant-negative mutation in PPAR-γ driven by the endothelial-specific vascular cadherin promoter (E-V290M), using nontransgenic littermates as controls. Acetylcholine (an endothelium-dependent agonist) produced similar relaxation of carotid arteries from nontransgenic and E-V290M mice. Incubation of isolated arteries with angiotensin II (1 nmol/L) overnight had no effect in nontransgenic, but reduced responses to acetylcholine by about 50% in male and female E-V290M mice (P<0.05). Endothelial function in E-V290M mice was restored to normal by inhibitors of superoxide (tempol), NADPH oxidase (VAS-2870), Rho kinase (Y-27632), ROCK2 (SLX-2119), NF-κB (nuclear factor-kappa B essential modulator-binding domain peptide), or interleukin-6 (neutralizing antibody). In addition, we hypothesized that PPAR-γ may influence the angiotensin 1-7 arm of the renin-angiotensin system. In the basilar artery, dilation to angiotensin 1-7 was selectively reduced in E-V290M mice by >50% (P<0.05), an effect reversed by Y-27632. Thus, effects of angiotensin II are augmented by interference with endothelial PPAR-γ through sex-independent mechanisms, involving oxidant-inflammatory signaling and ROCK2 (Rho kinase). The study also provides the first evidence that endothelial PPAR-γ interacts with angiotensin 1-7 responses. These critical roles for endothelial PPAR-γ have implications for pathophysiology and therapeutic approaches for vascular disease. [ABSTRACT FROM AUTHOR]

Studies were designed to determine the effects of increases of renal perfusion pressure on the production of hydrogen peroxide (H(2)O(2)) and NO(2)(-)+NO(3)(-) within the renal outer medulla. Sprague-Dawley rats were studied with either the renal capsule intact or removed to ascertain the contribution of changes of medullary blood flow and renal interstitial hydrostatic pressure on H(2)O(2) and NO(2)(-)+NO(3)(-) production. Responses to three 30-minute step changes of renal perfusion pressure (from approximately 85 to approximately 115 to approximately 145 mm Hg) were studied using adjustable aortic occluders proximal and distal to the left renal artery. Medullary interstitial H(2)O(2) determined by microdialysis increased at each level of renal perfusion pressure from 640 to 874 to 1593 nmol/L, as did H(2)O(2) urinary excretion rates, and these responses were significantly attenuated by decapsulation. Medullary interstitial NO(2)(-)+NO(3)(-) increased from 9.2 to 13.8 to 16.1 mumol/L, with parallel changes in urine NO(2)(-)+NO(3)(-), but decapsulation did not significantly blunt these responses. Over the range of renal perfusion pressure, medullary blood flow (laser-Doppler flowmetry) rose approximately 30% and renal interstitial hydrostatic pressure rose from 7.8 to 19.7 cm H(2)O. Renal interstitial hydrostatic pressure and the natriuretic and diuretic responses were significantly attenuated with decapsulation, but medullary blood flow was not affected. The data indicate that pressure-induced increases of H(2)O(2) emanated largely from increased tubular flow rates to the medullary thick-ascending limbs of Henle and NO largely from increased medullary blood flow to the vasa recta. The parallel pressure-induced increases of H(2)O(2) and NO indicate a participation in shaping the "normal" pressure-natriuresis relationship and explain why an imbalance in either would affect the blood pressure salt sensitivity. [ABSTRACT FROM AUTHOR]

Peroxisome proliferator-activated receptor gamma (PPARG), a ligand-activated transcription factor, plays a protective role in the endothelium through mechanisms that remain unclear. RBP7 is an intracellular retinoid binding protein belonging to the family of fatty acid-binding proteins (FABP) and is a PPARG target. RBP7 expression was increased 2.6-fold by rosiglitazone (RZ), a PPARG agonist in mouse lung endothelial cells, which was blocked by GW9662, a PPARG antagonist. We hypothesized that the protective effects of PPARG on the endothelium are mediated by RBP7. Studies were performed in: 20-week HFD-fed RBP7-deficient (KO) and wild type (WT) and age-matched chow-fed KO and WT mice. HFD increased fasting glucose in both WT and KO mice compared to chow-fed groups, and caused similar hepatic steatosis. HFD-fed mice were more glucose-intolerant and insulin-resistant compared with chow-fed mice, but there were no differences comparing KO with WT mice. Weight gain in response to HFD was also similar in KO and WT mice. Thus KO and WT mice exhibited similar HFD-induced metabolic dysfunction. Endothelium-dependent relaxation to acetylcholine (Ach) was normal in chow-fed KO mice, but was impaired in carotid artery of HFD-fed KO mice (49±6% KO vs 70±4% WT, p<0.05, 30μM Ach). Endothelial-independent relaxation was similar in all groups. Superoxide production in carotid artery (DHE-fluorescence) was elevated 1.5-fold in HFD-fed KO mice compared with the other 3 groups. Normal relaxation to Ach was restored by anti-oxidant treatment, suggesting HFD causes oxidative stress in the absence of RBP7. Systolic blood pressure was similar in HFD-fed KO and WT mice (110±4 mmHg in KO vs 105±0 mmHg in WT). Because other members of the FABP family facilitate steroid hormone receptor function, we hypothesized that RBP7 may facilitate PPARG function. To initially test this, we examined the cellular localization of an RBP7-GFP fusion protein. In vehicle treated COS7 cells, RBP7 was distributed both in cytoplasm and nucleus. RZ treatment resulted in a robust shift of RBP7 into the nucleus. In conclusion, RBP7 protects the endothelium from HFD-induced oxidative and vascular dysfunction, independent of changes to systemic metabolism. [ABSTRACT FROM AUTHOR]

PPARG, a ligand-activated transcription factor, in the endothelium regulates vascular function and blood pressure, through mechanisms that remain poorly defined. Endothelial-specific expression of dominant negative (DN) PPARG (E-V290M) caused endothelial dysfunction when combined with a high fat diet (HFD). RBP7 is an intracellular retinoid binding protein belonging to the family of fatty acid-binding proteins and a PPARG target gene. RBP7 expression in aorta is induced by rosiglitazone and repressed by DN PPARG, and its level of expression is highly correlated with PPARG in other tissues. RBP7 is also expressed in endothelium. We hypothesize that RBP7 may mediate some vascular protective effects of PPARG during HFD. We examined vascular responses in basilar artery (BA, pressurized myograph) and carotid artery (CA, wire myograph) of RBP7-deficient (KO), heterozygous (HZ), and wild type (WT) mice fed normal chow diet (ND) or HFD for 8 or 20 wks. Weight gain was similar in all three HFD-fed groups and was higher than ND-fed mice. There was no difference in the endothelium-dependent, acetylcholine (ACh)-induced relaxation in either BA or CA of any group under ND. Following 8 wks HFD, BA from KO mice exhibited impaired relaxation to ACh compared to control mice (at 100μM: 33±7% KO vs 73±7% HZ vs 83±10% WT, p<0.05). A normal response was observed to the nitric oxide donor, nitroprusside (SNP). An impaired ACh-, but not SNP- or papaverine-induced relaxation was observed in CA of KO mice after 20 wks of HFD (ACh 30μM: 49±6% KO vs 61±3% HZ vs 70±4% WT, p<0.05). No differences were found in phenylephrine- and endothelin-1-induced contractions in CA in any group. Pre-incubation of BA for 30 minutes with the superoxide scavengers tempol (1mM) or PEG-superoxide dismutase (PEG-SOD, 100 U/ml) completely restored ACh-induced relaxation to normal (ACh at 100μM: 79±7% Tempol-KO; 75±12% PEG-SOD-KO; 81±11% WT). This phenotype was very similar to that observed in HFD fed E-V290M mice. We conclude that loss of RBP7 causes endothelial dysfunction in response to a HFD through a mechanism involving oxidative stress. These findings provide the first evidence that RBP7 plays a protective role in the endothelium, which might be related to the endothelial protective effects of PPARG. [ABSTRACT FROM AUTHOR]