Treatment with Ligilactobacillus murinus lowers blood pressure and intestinal permeability in spontaneously hypertensive rats

One feature of hypertension is a microbial imbalance with increased intestinal permeability. In this study, we examined whether an alteration in the microbiota affects blood pressure and intestinal permeability in spontaneously hypertensive rats (SHRs). We performed a 16S metagenome analysis of feces from 10- to 15-week-old SHRs using a synthetic long-read sequencing approach, and found a candidate for the microbiome treatment, Ligilactobacillus murinus (L. murinus), that was robustly decreased. Oral administration of L. murinus to SHRs for 2 weeks significantly inhibited blood pressure elevation and improved endothelium-dependent vasodilation but did not attenuate enhanced vascular contraction in SHR mesenteric arteries. The proximal colon of SHRs exhibited increased intestinal permeability with decreased levels of the tight junction protein claudin 4, morphological changes such as decreased intestinal crypts and elevated TNF-α levels, which was reversed by treatment with L. murinus. Consistent with these intestinal phenotypes, plasma lipopolysaccharides levels were elevated in SHR but decreased following L. murinus administration. We concluded that oral administration of L. murinus to SHRs exerts protective effects on intestinal permeability via restoration of claudin 4 expression and reversal of morphologic disorder, which may improve low-grade endotoxemia and thus reduce development of hypertension via recovery of endothelial vasodilating functions.

Hypertension is linked to enhanced lymphatic contractile response via RGS16/RhoA/ROCK pathway

Lymph capillary network can be expected to alter blood pressure via regulating interstitial electrolyte and volume balance. However, the pathophysiology of lymphatic vessel in hypertension is poorly understood. In this study, we examined lymph vessel function focusing on contractile response in hypertensive rats. It was found that thoracic ducts isolated from adult (10-14 wk old) spontaneously hypertensive rats (SHRs) exhibited increased agonist-mediated contraction compared with age-matched Wistar-Kyoto (WKY) rats, whereas lymphatic contractions in younger (4 wk old) SHRs, exhibiting normal blood pressure, were no different compared with age-matched control rats. Tight regulation of blood pressure with antihypertensive drugs (hydrochlorothiazide/hydralazine) did not prevent the augmented lymphatic contraction in adult SHRs; however, treatment of SHRs with angiotensin II (ANG II) type 1 receptor blocker (losartan) for 6 wk abolished the augmentation of lymphatic contractions. In addition, ANG II infusion in Wistar rat caused augmented lymphatic contractile responses in the thoracic duct. The augmented contractions in adult SHRs were diminished by a ROCK inhibitor (Y-27632). Consistently, the thoracic ducts in SHRs showed significantly higher phosphorylation of myosin phosphatase targeting protein-1 than WKY rats. Furthermore, gene expression profiling of adult SHR lymphatics showed marked loss of regulator of G-protein signaling 16 (RGS16) mRNA, which was confirmed by the real-time PCR. Treatment with the RGS inhibitor CCG-63808 enhanced contractions in thoracic ducts from Wistar rats, which were abolished by the ROCK inhibitor. It is concluded that lymphatic contractile function was enhanced in hypertensive model rats, which could be mediated by dysregulation of the ROCK pathway possibly through RGS16.NEW & NOTEWORTHY Lymph capillary controls interstitial electrolyte and volume balance, which may blunt increased blood pressure. However, the function of lymphatic vessel in hypertension is poorly understood. Our study showed that the lymphatic smooth muscle contractility is hyperreactive in two different hypertensive models. The lymphatic dysfunction could be mediated by dysregulation of ROCK pathway possibly through RGS16. The present finding supports a new concept showing the functional relationship between lymphatic contractile activity and hypertension.

Abstract 003: Treatment With Ligilactobacillus Improves Gut Permeability And Hypertension In Spontaneously Hypertensive Rats

Emerging evidence provide that a microbial imbalance (dysbiosis) is linked to several diseases including cardiovascular diseases. One of the features in hypertension is increased gut permeability. Supporting this, plasma endotoxin level is increased in hypertension and our previous study indicated that the plasma level of exotoxin from Streptococcus was increased in spontaneously hypertensive rats (SHR). Thus, we hypothesized that improvement of gut permeability in hypertension might be expected to prevent development of hypertension. In this study, we performed a 16S metagenome analysis using a synthetic long read sequencing approach by LoopSeq in feces from 10- to 15-week old SHR and Wistar-Kyoto rat (WKY). The analysis revealed that two difference species of anti-inflammatory microbiome were strongly decreased in SHR compared with WKY (n=4). We focus on the decreased Ligilactobacillus sp. (LAB) in SHR and oral administration of LAB to SHR for 2 weeks. SHR (10-15-week-old) exhibited increased gut permeability in proximal colon (P<0.05, n=4), which was improved by treatment with LAB for 2 weeks (P<0.05, n=4). The expression level of tight junction protein Claudin4 was decreased in SHR proximal colon (SHR vs WKY, 1.0±0.1 vs 1.7±0.2-fold increase to SHR, P<0.05, n=8), which was significantly increased by LAB treatment (SHR vs SHR+LAB, 1.0±0.1 vs 2.8±0.5-fold increase to SHR, P<0.05, n=10). Proximal colon in SHR increased the expression level of TNF-α mRNA (1.0±0.2 vs 0.2±0.1, P<0.05, n=8), which was reversed by LAB (1.0±0.2 vs 0.3±0.1, P<0.05, n=10). The level of mucin 2 was lower in SHR proximal colon (1.0±0.2 vs 4.3±0.8, P<0.05, n=8), which was not reversed by LAB (1.0±0.1 vs 0.8±0.3, n=10). We observed that high blood pressure in SHR was attenuated by treatment with LAB for 2 weeks (194.0±5.9 vs 149.7±4.8 mmHg, P<0.05, n=10). LAB also improved decrease in acetylcholine-induced relaxation in SHR mesenteric artery (P<0.05, n=5-8). We conclude that treatment of SHR with the decreased anti-inflammatory microbiota, LAB improves gut permeability in proximal colon possibly through inhibition of inflammation, resulting in lowering blood pressure. These results suggest that anti-inflammatory microbiome might be a new therapeutic target for hypertension.

Abstract P125: Long-term Exposure Of Angiotensin II Enhanced Vascular Contraction Via Activation Of Protein Kinase C Beta

Protein kinase C (PKC) β is linked to lymphoma and diabetes complications including diabetic retinopathy, nephropathy and neuropathy. Also, recent studies revealed that PKCβ activation also accelerates atherosclerotic plaque formation in diabetes. These findings strongly indicate that PKCβ is a potential target for the treatment of diabetic vascular complications. Although PKCβ is associated with diabetic vascular dysfunction, role of PKCβ in hypertension remains unclear. Since hypertension is one of most important risk factor for vascular diseases including atherosclerosis, we here examined whether PKCβ is involved in angiotensin II-induced vascular dysfunction. Treatment with angiotensin II (100 nM) for 30 min strongly increased phosphorylation at the PKCβ activation site at S660 in aorta from Wistar rat (n=4). Treatment of rat aorta with angiotensin II (100 nM) for 24 hr increased contractile responses to serotonin (5-HT, Maximum contraction, control vs. Angiotensin II, 92.2±20.0 vs 142.1±20.5%, P<0.05, n=6) or endothelin-1 (ET-1, 157.4±30.6 vs 214.1±24.3%, P<0.05, n=8). In contrast, angiotensin II did not affect vascular contractile response to noradrenaline (n=4). The enhanced contraction induced by angiotensin II was blocked by CGP53353 (1 μM), a PKCβ inhibitor (5-HT, Angiotensin II vs. CGP53353+Angiotensin II,197.8±27.8 vs. 167.4±17.6%, P<0.05, n=4-5). Pretreatment with LY333531 (1 μM), another PKCβ inhibitor, also prevented angiotensin II-induced vascular dysfunction (P<0.05, n=3-4). Next, we generated PKCβ knockout rat using rGONAD. Consistent with the results using PKCβ inhibitors, angiotensin II-induced enhanced contractile responses to 5-HT (122.6±15.6 vs 111.0±16.3%, n=4) and ET-1 (137.9±39.9 vs 139.2±30.1%, n=4) were dismissed in PKCβ knockout rat. We also confirmed that phorbol12-myristate13-acetate (0.05-5 μg/ml), a PKC activator, enhanced vascular contractile responses to 5-HT and ET-1 in dose-dependent manner (P<0.05, n=4). We conclude that long exposure of angiotensin II (24 hr) causes increase in vascular contractile responses to 5-HT and ET-1 and the augmented contraction are due to activation of PKCβ. Our result suggests that PKCβ might be associated with angiotensin II-related vascular dysfunction.

[Gut microflora and metabolic syndrome: new insight into the pathogenesis of hypertension]

Emerging evidences indicate that a microbial imbalance (dysbiosis) is linked to several diseases including metabolic cardiovascular diseases. A fecal microbiota transplantation from hypertensive human donor to germ-free mice caused blood pressure elevation. In addition, there is a report demonstrating that angiotensin II-induced hypertension and vascular dysfunction were attenuated in germ-free mice, suggesting that gut microbiome may mediate development of hypertension. Although detailed mechanism by which the dysbiosis induces an increased blood pressure remains unknown, changes in microbiome may modify host immune systems and induce inflammatory dysfunction in cardiovascular system, resulting in dysregulation of blood pressure. Some cohort studies demonstrated an association between a higher abundance of Streptococcaceae spp. and blood pressure. One recent report demonstrated that an increasing number of gram-positive Streptococcus was found in the feces of adult spontaneously hypertensive rats with an increased intestinal permeability. We hypothesized that increased bacterial toxin levels derived from gut Streptococcus may be a factor inducing blood pressure dysregulation. In this review, we discuss the possible role of microbiome in cardiovascular disease, especially hypertension.

Streptococcal Exotoxin Streptolysin O Causes Vascular Endothelial Dysfunction Through PKCβ Activation

Streptolysin O (SLO) is produced by common hemolytic streptococci that cause a wide range of diseases from pharyngitis to life-threatening necrotizing fasciitis and toxic shock syndrome. While the importance of SLO in invasive hemolytic streptococcus infection has been well demonstrated, the role of circulating SLO in non-invasive infection remains unclear. The aim of this study was to characterize the pharmacological effect of SLO on vascular functions, focusing on cellular signaling pathways. In control Wistar rats, SLO treatment (1-1000 ng/mL) impaired acetylcholine-induced endothelial-dependent relaxation in the aorta and second-order mesenteric artery in a dose-dependent manner, without any effects on sodium nitroprusside-induced endothelium-independent relaxation or agonist-induced contractions. SLO also increased phosphorylation of the endothelial NO synthase (eNOS) inhibitory site at Thr495 in the aorta. Pharmacological analysis indicated that either endothelial dysfunction or eNOS phosphorylation was mediated by protein kinase Cβ (PKCβ), but not by the p38 mitogen-activated protein kinase (MAPK) pathway. Consistent with this, SLO increased phosphorylation levels of PKC substrates in the aorta. In vivo study of control Wistar rats indicated that intravenous administration of SLO did not change basal blood pressure, but significantly counteracted the acetylcholine-induced decrease in blood pressure. Interestingly, plasma anti-SLO IgG levels were significantly higher in 10- to 15-week-old spontaneously hypertensive rats compared to age-matched control rats (P<0.05). These findings demonstrated that SLO causes vascular endothelial dysfunction, which is mediated by PKCβ-induced phosphorylation of the eNOS inhibitory site. Significance Statement This study showed for the first time, that in vitro exposure of vascular tissues to SLO impairs endothelial function, an effect that is mediated by PKCb-induced phosphorylation of the eNOS inhibitory site. Intravenous administration of SLO in control and hypertensive rats blunted the ACh-induced decrease in blood pressure, providing evidence for a possible role of SLO in dysregulation of blood pressure.

Failure to vasodilate in response to salt loading blunts renal blood flow and causes salt-sensitive hypertension

AIMS

Salt-sensitive (SS) hypertension is accompanied by impaired vasodilation in the systemic and renal circulation. However, the causal relationship between vascular dysfunction and salt-induced hypertension remains controversial. We sought to determine whether primary vascular dysfunction, characterized by a failure to vasodilate during salt loading, plays a causal role in the pathogenesis of SS hypertension.

METHODS AND RESULTS

Mice selectively expressing a peroxisome proliferator-activated receptor γ dominant-negative mutation in vascular smooth muscle (S-P467L) exhibited progressive SS hypertension during a 4 week high salt diet (HSD). This was associated with severely impaired vasodilation in systemic and renal vessels. Salt-induced impairment of vasodilation occurred as early as 3 days after HSD, which preceded the onset of SS hypertension. Notably, the overt salt-induced hypertension in S-P467L mice was not driven by higher cardiac output, implying elevations in peripheral vascular resistance. In keeping with this, HSD-fed S-P467L mice exhibited decreased smooth muscle responsiveness to nitric oxide (NO) in systemic vessels. HSD-fed S-P467L mice also exhibited elevated albuminuria and a blunted increase in urinary NO metabolites which was associated with blunted renal blood flow and increased sodium retention mediated by a lack of HSD-induced suppression of NKCC2. Blocking NKCC2 function prevented the salt-induced increase in blood pressure in S-P467L mice.

CONCLUSION

We conclude that failure to vasodilate in response to salt loading causes SS hypertension by restricting renal perfusion and reducing renal NO through a mechanism involving NKCC2 in a mouse model of vascular peroxisome proliferator-activated receptor γ impairment.

Anti-inflammatory mechanisms of the vascular smooth muscle PPARγ

This review highlights molecular mechanisms of anti-inflammatory and protective effects of the nuclear transcription factor, peroxisome proliferator-activated receptor γ (PPARγ) in vascular tissue. PPARγ is an ubiquitously expressed nuclear factor, and well-studied in adipose tissue and inflammatory cells. Additionally, beneficial effects of vascular PPARγ’s on atherosclerosis and vascular remodeling/dysfunction have been reported although the detailed mechanism remains to be completely elucidated. Clinical and basic studies have shown that the synthetic PPARγ ligands, thiazolidinediones (TZDs), have protective effects against cardiovascular diseases such as atherosclerosis. Recent studies utilizing genetic tools suggested that those protective effects of TZDs on cardiovascular diseases are not due to a consequence of improvement of insulin resistance, but may be due to a direct effect on PPARγ’s in vascular endothelial and smooth muscle cells. In this review, we discuss proposed mechanisms by which the vascular PPARγ regulates vascular inflammation and remodeling/dysfunction especially in smooth muscle cells.

Abstract P079: Lymphatic Contraction Was Enhanced In Spontaneously Hypertensive Rats

Because lymph capillary network regulates interstitial electrolyte and volume balance, this system may function as regulating blood pressure (BP). Thus, changes in lymphatic activity can be expected to alter systemic BP. We recently reported that increasing BP caused lymphatic endothelial dysfunction via oxidative stress in hypertension. In this study, we examined lymphatic contractile function in thoracic duct from 10-14-week-old Wister-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). No distinct morphological difference was observed in thoracic duct isolated from WKY and SHR (n=4). Thoracic duct from SHR exhibited enhanced contractile response to serotonin (5-HT) or endothelin-1 (ET-1) compared to age-matched WKY (5-HT: 127.8±19.7% vs 53.6±10.3% of KCl-induced maximum contraction, p<0.05, n=5). The augmented contraction in SHR was diminished by fasudil, ROCK inhibitor (p<0.05, n=4-5). Consistent with this, increased phosphorylation of myosin phosphatase targeting protein (MYPT) was observed in SHR thoracic duct. Expression of ROCK1 or ROCK2 was not changed in SHR thoracic duct. Next we examined lymphatic contractile function in 4-week-old SHR showing normal BP. Contractile response to 5-HT or ET-1 was not enhanced in young SHR compared to age-matched WKY (n=4). To examine if lymphatic dysfunction was associated with increased BP, we treated 4-week-old SHR with antihypertensive drugs (hydrochlorothiazide and hydralazine) for 6 weeks. This treatment completely blocked elevation of systolic BP (SBP) in SHR (p<0.05, n=5), but did not prevent the augmentation of lymphatic contraction (5-HT: 99.0±7.2% vs 98.1±14.5%, n=5). Interestingly, treatment of young SHR with losartan (Angiotensin II type 1 receptor [AT1R] blocker) for 6 weeks ameliorated the augmented contraction (5-HT: 137.4±12.7% vs 77.9±8.8%, p<0.05, n=5), while this treatment scarcely diminished the increase in SBP (152.0±8.7 mmHg vs. 177.2±10.9 mmHg, p<0.05, n=5). We conclude that lymphatic contractile function was significantly enhanced in adult hypertensive SHR, which is mediated by RhoA/ROCK pathway thorough activation of AT1R. The increase in lymphatic constriction may be involved in increased BP in hypertension through decreased lymphatic compliance.

Increased Blood Pressure Causes Lymphatic Endothelial Dysfunction via Oxidative Stress in Spontaneously Hypertensive Rats

The lymphatic system is involved in the pathogenesis of edema, inflammation, and cancer metastasis. Because lymph vessels control fluid electrolytes and volume balance, changes in lymphatic activity can be expected to alter systemic blood pressure. This study examined possible changes in lymphatic contractile properties in spontaneously hypertensive rats (SHR). Thoracic ducts isolated from 10- to 12-week-old SHR exhibited either decreased acetylcholine-induced endothelium-dependent relaxation or sodium nitroprusside-induced endothelium-independent relaxation compared with age-matched Wister-Kyoto rats. The impairment in acetylcholine responsiveness was more pronounced than sodium nitroprusside responsiveness. N-Nitro-L-arginine methyl ester, a nitric oxide synthase inhibitor blunted acetylcholine-induced relaxation in Wister-Kyoto rats, indicating an involvement of endothelial nitric oxide production. Endothelial dysfunction in lymph vessels of SHR was attenuated by tempol (a superoxide dismutase mimetic), apocynin, or VAS-2870 (NADPH oxidase inhibitors). Consistent with these observations, nitrotyrosine levels were significantly elevated in SHR, indicative of increased oxidative stress. In addition, protein expression of NADPH oxidase 2 and phosphorylation of p47^phox (Ser345) were significantly increased in SHR. Further, SB203580 (a p38 MAPK inhibitor) restored the acetylcholine-induced relaxation in SHR. It is notable that 4-week-old SHR, which exhibited normal blood pressure, did not show any decreased activity of acetylcholine- or sodium nitroprusside-induced relaxation. Additionally, antihypertensive treatment of 4-week-old SHR with hydrochlorothiazide and reserpine or hydrochlorothiazide and hydralazine for 6 weeks completely restored lymphatic endothelial dysfunction. We conclude that contractile activity of lymphatic vessels is functionally impaired with the development of increasing blood pressure, which is mediated through increased oxidative stress via the p38 MAPK/NADPH oxidase 2 pathway.

Abstract 065: Endothelial CULLIN3 Mutation Causes Vascular Dysfunction, Arterial Stiffening, and Hypertension

Mutations in CULLIN3 gene (causing in-frame deletion of exon 9) cause human hypertension (HT), which is likely to be driven by a combination of renal tubular and vascular mechanisms. We have recently shown that smooth muscle expression of Cul3Δ9 mutant causes vascular dysfunction and HT via augmented RhoA/Rho-kinase signaling, strongly supporting a vascular role of Cul3 in BP regulation. To test the importance of endothelial Cul3 in vivo , we bred the conditionally activatable Cul3Δ9 mice with tamoxifen-inducible Tie2-CRE ERT2 mice. The resultant mice (E-Cul3Δ9) developed nocturnal hypertension (Night time peak systolic BP, E-Cul3Δ9: 138±3 vs Control: 121±4 mmHg, p<0.01) and arterial stiffening (pulse wave velocity, 3.7±0.3 vs 2.7±0.1 m/s, p<0.01). No difference was seen in daytime BP. Nitric oxide synthase (NOS) inhibitor L-NAME induced smaller increases in nocturnal peak SBP and DBP in E-Cul3Δ9 mice (15±1 vs 27±3 mmHg, p<0.01), suggesting their NOS activity is low. Of note, E-Cul3Δ9 mice exhibited impaired endothelial-dependent relaxation in carotid artery (Max ACh relaxation: 69% vs 84%, p<0.05) and cerebral resistance basilar artery (41% vs 77%, p<0.01). No difference in smooth muscle function was observed. To determine the molecular mechanisms, we isolated primary aortic endothelial cells from mice carrying the inducible Cul3Δ9 construct and induced Cul3Δ9 expression in vitro using adenovirus carrying Cre recombinase gene. Expression of Cul3Δ9 resulted in marked decreases in wild type Cul3 protein, phosphorylated eNOS, and nitric oxide production. Because protein phosphatase 2A (PP2A) is a known Cul3 substrate which dephosphorylates eNOS, we determined whether impaired eNOS activity was attributable to PP2A. Cul3Δ9-induced impairment of eNOS activity was rescued by a selective PP2A inhibitor Okadaic Acid (4 nM), but not by a Protein Phosphatase 1 inhibitor Tautomycetin (4 nM). These data define a novel regulatory pathway involving Cullin3/PP2A/phospho-eNOS in the endothelium. Selective endothelial expression of Cul3Δ9 partially phenocopies the hypertension observed in Cul3Δ9 patients, suggesting that mutations in Cullin-3 cause human hypertension in part through a vascular mechanism characterized by endothelial dysfunction.

Abstract 120: Protective Role of Vascular Smooth Muscle Rho-Related BTB Domain Containing Protein 1 in Hypertension and Arterial Stiffness

Rho-related BTB domain containing protein 1 (RhoBTB1) is an atypical GTPase associated with human hypertension. RhoBTB1 was decreased in aorta from mice expressing a hypertension (HT)-causing PPARγ mutation (P467L) specifically in vascular smooth muscle (VSM, S-P467L mice). Restoration of VSM RhoBTB1 improved vasodilation, reversed arterial stiffness and HT by suppressing phosphodiesterase 5 (PDE5) activity. Here we sought to reveal the molecular function of RhoBTB1 and study its protective role in Angiotensin II (Ang II) induced hypertension. PDE5 and RhoBTB1 reciprocally co-immunoprecipitated in HEK293 cells; and notably, endogenous Cullin3 from HEK293 cells was also present in RhoBTB1/PDE5 immunoprecipitant. Whereas, RhoBTB1 was not sufficient to inhibit PDE5 activity in vitro (1.9±0.2 vs 1.7 ±0.2 nmol/min/mg, n=3), it was required for PDE5 ubiquitination in HEK293 cells. RhoBTB1-mediated PDE5 ubiquitination was blunted by pan-Cullin inhibitor MLN4924 treatment, and MLN4924 increased PDE5 activity in aorta. Thus, RhoBTB1 serves as a substrate adaptor for Cullin3-Ring ubiquitin ligase (CRL3) complex. Like mutation in PPARγ, Ang II infusion also reduced aortic RhoBTB1 expression. We generated mice with VSM specific, tamoxifen inducible RhoBTB1 (S-RhoBTB1) expression. Activation of RhoBTB1 expression with tamoxifen partially prevented Ang II induced HT and vascular dysfunction. However, activation of the RhoBTB1 transgene after 2-week of Ang II infusion did not reverse established Ang II HT and failed to reverse impaired vasodilation to acetylcholine and sodium nitroprusside in aorta and carotid artery. Remarkably however, arterial stiffness as measured by aortic Pulse Wave Velocity was decreased in S-RhoBTB1 compared to non-transgenic mice receiving Ang II infusion (4.6±0.4 vs 3.2±0.3 mm/ms, p<0.05, n=5-7). In conclusion, RhoBTB1 serves as CRL3 substrate adaptor and promotes PDE5 ubiquitination. Pretreatment with RhoBTB1 partially prevents Ang II HT, while restoration of VSM RhoBTB1 was not sufficient to reverse Ang II mediated HT but showed a potential in reducing arterial stiffness.

[Role of PPARγ, a transcription factor in cardiovascular disease]

Peroxisome proliferator-activated receptor γ (PPARγ) is a ligand activated transcription factor known to regulate fatty acid metabolism. Thiazolidinediones (TZDs), PPARγ synthetic agonists, currently used to treat patients with type 2 diabetes, have been shown to lower the blood pressure and protect against vascular diseases such as atherosclerosis. In line with these findings, it has been reported that individuals with loss-of-function mutations of PPARγ developed sever early-onset hypertension in addition to metabolic abnormalities. Accumulating evidences suggest PPARγ in the vasculature has protective effects on cardiovascular disease despite unclear mechanism. Because of ubiquitous expression of PPARγ, TZDs are well-known to be associated with serious side effects such as weight gain, fluid retention, and bone fractures. Thus identification of mechanisms on tissue-specific PPARγ activity may lead to the development of targeted treatment which is characterized by no deleterious effects. This review discusses role of PPARγ in cardiovascular disease.

Endothelial PPARγ (Peroxisome Proliferator-Activated Receptor-γ) Protects From Angiotensin II-Induced Endothelial Dysfunction in Adult Offspring Born From Pregnancies Complicated by Hypertension

Preeclampsia is a hypertensive disorder of pregnancy associated with vascular dysfunction and cardiovascular risk to offspring. We hypothesize that endothelial PPARγ (peroxisome proliferator-activated receptor-γ) provides cardiovascular protection in offspring from pregnancies complicated by hypertension. C57BL/6J dams were bred with E-V290M sires, which express a dominant-negative allele of PPARγ selectively in the endothelium. Arginine vasopressin was infused throughout gestation. Vasopressin elevated maternal blood pressure at gestational day 14 to 15 and urinary protein at day 17 consistent. Systolic blood pressure and vasodilation responses to acetylcholine were similar in vasopressin-exposed offspring compared to offspring from control pregnancies. We treated offspring with a subpressor dose of angiotensin II to test if hypertension during pregnancy predisposes offspring to hypertension. Male and female angiotensin II-treated E-V290M offspring from vasopressin-exposed but not control pregnancy exhibited significant impairment in acetylcholine-induced relaxation in carotid artery. Endothelial dysfunction in angiotensin II-treated E-V290M vasopressin-exposed offspring was attenuated by tempol, an effect which was more prominent in male offspring. Nrf2 (nuclear factor-E2-related factor) protein levels were significantly elevated in aorta from male E-V290M offspring, but not female offspring compared to controls. Blockade of ROCK (Rho-kinase) signaling and incubation with a ROCK2-specific inhibitor improved endothelial function in both male and female E-V290M offspring from vasopressin-exposed pregnancy. Our data suggest that interference with endothelial PPARγ in offspring from vasopressin-exposed pregnancies increases the risk for endothelial dysfunction on exposure to a cardiovascular stressor in adulthood. This implies that endothelial PPARγ provides protection to cardiovascular stressors in offspring of a pregnancy complicated by hypertension and perhaps in preeclampsia.

Interference With Endothelial PPAR (Peroxisome Proliferator-Activated Receptor)-γ Causes Accelerated Cerebral Vascular Dysfunction in Response to Endogenous Renin-Angiotensin System Activation

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.

RhoBTB1 protects against hypertension and arterial stiffness by restraining phosphodiesterase 5 activity

Mice selectively expressing PPARγ dominant negative mutation in vascular smooth muscle exhibit RhoBTB1-deficiency and hypertension. Our rationale was to employ genetic complementation to uncover the mechanism of action of RhoBTB1 in vascular smooth muscle. Inducible smooth muscle-specific restoration of RhoBTB1 fully corrected the hypertension and arterial stiffness by improving vasodilator function. Notably, the cardiovascular protection occurred despite preservation of increased agonist-mediated contraction and RhoA/Rho kinase activity, suggesting RhoBTB1 selectively controls vasodilation. RhoBTB1 augmented the cGMP response to nitric oxide by restraining the activity of phosphodiesterase 5 (PDE5) by acting as a substrate adaptor delivering PDE5 to the Cullin-3 E3 Ring ubiquitin ligase complex for ubiquitination inhibiting PDE5. Angiotensin-II infusion also caused RhoBTB1-deficiency and hypertension which was prevented by smooth muscle specific RhoBTB1 restoration. We conclude that RhoBTB1 protected from hypertension, vascular smooth muscle dysfunction, and arterial stiffness in at least two models of hypertension.

Abstract 121: Endothelial Cullin3 Mutation Causes Vascular Dysfunction, Arterial Stiffening, and Hypertension

Mutations in CULLIN3 gene (causing in-frame deletion of exon 9) cause human hypertension (HT), which is likely to be driven by a combination of renal tubular and vascular mechanisms. We have recently shown that smooth muscle expression of Cul3Δ9 mutant causes vascular dysfunction and HT via augmented RhoA/Rho-kinase signaling, strongly supporting a vascular role of Cul3 in BP regulation. To test the importance of endothelial Cul3 in vivo , we bred the conditionally activatable Cul3Δ9 mice with tamoxifen-inducible Tie2-CRE ERT2 mice. The resultant mice (E-Cul3Δ9) developed nocturnal hypertension (Night time peak systolic BP, E-Cul3Δ9: 138±3 vs Control: 121±4 mmHg, p<0.01) and arterial stiffening (pulse wave velocity, 3.7±0.3 vs 2.7±0.1 m/s, p<0.01). No difference was seen in daytime BP. Nitric oxide synthase (NOS) inhibitor L-NAME induced smaller increases in nocturnal peak SBP and DBP in E-Cul3Δ9 mice (15±1 vs 27±3 mmHg, p<0.01), suggesting their NOS activity is low. Of note, E-Cul3Δ9 mice exhibited impaired endothelial-dependent relaxation in carotid artery (Max ACh relaxation: 69% vs 84%, p<0.05) and cerebral resistance basilar artery (41% vs 77%, p<0.01). No difference in smooth muscle function was observed. To determine the molecular mechanisms, we isolated primary aortic endothelial cells from mice carrying the inducible Cul3Δ9 construct and induced Cul3Δ9 expression in vitro using adenovirus carrying Cre recombinase gene. Expression of Cul3Δ9 resulted in marked decreases in wild type Cul3 protein, phosphorylated eNOS, and nitric oxide production. Because protein phosphatase 2A (PP2A) is a known Cul3 substrate which dephosphorylates eNOS, we determined whether impaired eNOS activity was attributable to PP2A. Cul3Δ9-induced impairment of eNOS activity was rescued by a selective PP2A inhibitor Okadaic Acid (4 nM), but not by a Protein Phosphatase 1 inhibitor Tautomycetin (4 nM). These data define a novel regulatory pathway involving Cullin3/PP2A/phospho-eNOS in the endothelium. Selective endothelial expression of Cul3Δ9 partially phenocopies the hypertension observed in Cul3Δ9 patients, suggesting that mutations in Cullin-3 cause human hypertension in part through a vascular mechanism characterized by endothelial dysfunction.

Abstract 133: Endothelial-Specific Interference With PPARγ Increases the Susceptibility to Angiotensin II-Induced Endothelial Dysfunction in Adult Offspring Born from AVP-Infused Pregnancies

Mutations in the ligand-activated transcription factor PPARγ result in hypertension, and synthetic agonists of PPARγ reduce blood pressure. Previously we found that mice expressing dominant-negative (DN) PPARγ driven by an endothelium-specific promoter (E-DN) exhibit vascular dysfunction. Preeclampsia (PE) is a hypertensive disorder of pregnancy which carries cardiovascular risk to offspring. PE is also associated with vascular dysfunction. We hypothesized a role for endothelial PPARγ in the pathogenesis of PE and its sequelae. C57BL/6J dams were bred with E-DN sires, and symptoms of PE were induced by infusion of vasopressin (AVP, 24 ng/hr sc) throughout gestation. Phenotypes of PE were first assessed in pregnant dams and then in adult offspring. Compared to saline infusion (SAL), AVP elevated maternal blood pressure (SBP: 116±3 vs 107±3, p<0.05) at gestational day (GD) 14-15 and urine protein (70±6 vs 27±4 mg/mL, p<0.05) at GD17. Offspring were phenotyped in adulthood. Data were stratified to sex, genotype, and exposure to AVP or SAL. At 20 weeks of age, SBP and vasorelaxation responses to acetylcholine were similar in offspring exposed to PE compared to mice born from SAL pregnancies. Adult offspring were next exposed to a sub-pressor dose of Angiotensin II (ANG; 120ng/kg/hr) for 14 days. Adult male ANG-treated E-DN born to PE pregnancies, but not NT mice exhibited significant impairment in ACh-induced relaxation in carotid artery (% relaxation: 62±10 vs 86±11, p<0.05). Adult female ANG-treated E-DN exposed to PE also exhibited a trend for impaired endothelial function compared to NT controls (% relaxation: 63±9 vs 72±10). Endothelial dysfunction in male ANG-treated E-DN born to PE pregnancies was attenuated by tempol (relaxation improved from 56±9% vs 81±12%, p<0.05), indicative of oxidative stress, and by a Rho-kinase inhibitor (relaxation improved from 73±11% vs 89±12%, p<0.05). This data suggests that interference with endothelial PPARγ in pups born from PE pregnancies increases the risk for endothelial dysfunction upon exposure to a cardiovascular stressor in adulthood. Thus, conditions which impair PPARγ activity, such as obesity and diabetes, may predispose adult offspring born from PE pregnancy to cardiovascular disease.

Abstract 036: Interference With PPARγ in the Endothelium Produces Endothelial Dysfunction in the Cerebral Circulation in Response to Activation of the Endogenous Renin-Angiotensin System

Low salt diet (LSD) is beneficial in salt-sensitive hypertension but may provoke cardiovascular risk in patients with heart failure, diabetes, or other cardiovascular abnormalities because of renin-angiotensin system (RAS) activation. PPARγ is a transcription factor which promotes an anti-oxidant pathway in the endothelium. We studied transgenic mice expressing a dominant-negative mutation in PPARγ selectively in the endothelium (E-DN) to test the hypothesis that endothelial PPARγ plays a protective role in response to LSD-mediated RAS activation. Plasma renin and angiotensin were significantly and equally increased in all mice fed LSD for 6-weeks (Renin - NT: 39±7 vs 20±1 ng/ml; E-DN: 34±1 vs 16±4 ng/ml; Ang - NT: 257±54 vs 47±6 pg/ml; E-DN: 294±69 vs 63±14 pg/ml p<0.05, n=5). Vasorelaxation to acetylcholine was not affected in basilar artery from E-DN at baseline, but was significantly and selectively impaired in E-DN after LSD (33±5 vs 69±2%, p<0.05, n=6). Unlike basilar artery, LSD was not sufficient to induce vascular dysfunction in carotid artery (carotid artery: 86±4 vs 92±3%, n=5). Endothelial dysfunction in the basilar artery from E-DN mice fed LSD was attenuated by scavengers of superoxide (improved from 29±5% to 55±7%, n=6), inhibitors of NADPH oxidase (improved from 23±3% to 54±7%, p<0.05, n=6), or blockade of the angiotensin-II AT1 receptor (improved from 31±5% to 64±9%, p<0.05, n=5). Gene expression levels of Nox2 was elevated (2.1±0.3 vs 0.4±0.1, p<0.05, n=7) while those of antioxidant enzymes catalase and SOD3 were blunted in cerebral vessels of E-DN mice on a LSD (catalase: 0.5±0.1 vs 2.5±0.2; SOD3: 0.2±0.1 vs 1.1±0.1, p<0.05, n=7). Simultaneous AT1 and AT2 receptor blockade revealed the restoration of endothelial function after AT1 receptor blockade was not a consequence of AT2 receptor activation (59±10 vs 48±2, p<0.05, n=4). We conclude that interference with PPARγ in the endothelium produces endothelial dysfunction in the cerebral circulation in response to LSD-mediated activation of the endogenous RAS, 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 PPARγ activity and RAS activation.

Abstract 094: Smooth Muscle PPARγ Mutation Causes Impaired Renal Blood Flow and Salt-Sensitive Hypertension

Mutations in PPARγ cause hypertension (HT) while PPARγ activation lowers blood pressure (BP) in humans. To determine if vascular smooth muscle (VSM) PPARγ regulates salt sensitivity, we studied transgenic mice selectively expressing a HT-causing PPARγ mutant in VSM (S-P467L) and non-transgenic littermates (NT) fed a 4% high salt (HS) diet for 4 weeks. Salt equally suppressed plasma renin in both strains, but S-P467L mice exhibited increased systolic BP (S-P467L 136±3 mmHg vs NT 124±2 mmHg, p<0.01) and pulse wave velocity (3.1±0.1 vs 2.7±0.1 m/s, p<0.01) in response to HS. The salt-induced HT was not associated with changes in diastolic BP, sympathetic nerve activity, heart rate, or cardiac output. Thus, the pressor effect of HS was likely due to higher peripheral vascular resistance. HS-fed S-P467L mice developed impaired acetylcholine (ACh)- and sodium nitroprusside (SNP)-induced vasorelaxation in carotid (Max ACh relaxation: 31±4.9% vs 90±1.8%, p<0.01; Max SNP relaxation: 38±2.8% vs 89±2.6%, p<0.01) and basilar artery (Max ACh relaxation: -3.2±9.3% vs 57±5.9%, p<0.01). The impaired vasodilation rapidly developed after 3-day HS diet, preceding salt-induced BP elevation. Pre-incubation with a cyclooxygenase inhibitor indomethacin normalized ACh/SNP relaxation responses, and preliminary mass spectrometry indicated HS increased prostaglandin E2 in S-P467L aortas. HS-fed S-P467L mice had smaller renal artery luminal diameter (322±21 vs 389±22 μm, p<0.05) and blunted renal blood flow (36±3.6 vs. 50±6.4 μL/min/g, p<0.05). During the 4 th week of HS diet, S-P467L mice produced 31% less nitrate/nitrite in 24 hour urine compared to NT controls (2.2±0.3 vs 3.2±0.4 μmol, p<0.05), suggesting blunted renal bioavailability of nitric oxide, a potent inhibitor of Na-K-2Cl cotransporter (NKCC2). This was associated with a declined capacity of HS-fed S-P467L mice to excrete an acute volume/Na + load, which was rescued by an NKCC2 inhibitor furosemide, but not by the Na-Cl-cotransporter inhibitor hydrochlorothiazide. Our data support the novel concept that smooth muscle PPARγ regulates systemic vascular resistance, renal perfusion and tubular sodium transport, and loss of these protective actions of PPARγ predisposes to salt sensitivity and hypertension.

Abstract 110: Vascular Smooth Muscle RhoBTB1 Protects From Hypertension and Arterial Stiffness by Cullin-3 Dependent Ubiquitination of Phosphodiesterase 5

We previously reported that vascular smooth muscle cell (VSMC) selective expression of hypertension (HT)-causing mutations in either PPARγ or the E3 Ring Ubiquitin Ligase Cullin-3 causes nitric oxide resistance and HT. Here we sought to assess the physiological role of RhoBTB1, a VSMC PPARγ target gene and Cullin-3 substrate adaptor. S-P467L mice which selectively express dominant negative PPARγ-P467L in VSMC exhibit RhoBTB1-deficiency. We bred S-P467L mice with mice inducibly expressing RhoBTB1 in response to Cre-recombinase. Inducible VSMC-specific restoration of RhoBTB1 in S-P467L mice fully corrected the HT (SBP, 141±6 vs 124±3 mmHg, p<0.01, n=8-10), arterial stiffness (Aortic Pulse Wave Velocity, 3.8±0.2 vs 2.5±0.1 mm/ms, p<0.01, n=11-13), and vasodilator function (Aorta, 46±5 vs 80±2% ACh-induced relaxation, p<0.01, n=6-9). Notably, the cardiovascular protection occurred despite preservation of increased agonist-mediated contraction and RhoA/Rho kinase activity, suggesting RhoBTB1 selectively controls vasodilation. Sodium nitroprusside-induced production of cGMP in aorta was severely impaired in S-P467L but restored by RhoBTB1. Consistent with this, phosphodiesterase 5 (PDE5) activity in aorta was augmented 2.5±0.3 fold in S-P467L but was returned to normal by RhoBTB1. PDE5 and RhoBTB1 reciprocally co-immunoprecipitated in HEK293 cells. Ubiquitination of PDE5 by Cullin-3 in HEK293 cells was RhoBTB1-dependent. Consistent with a role for Cullin-3 in mediating turnover of PDE5, PDE5 activity was augmented in MLN4924-treated aorta, a Cullin inhibitor, and abrogated by PDE5 inhibitor. The beneficial cardiovascular effect of RhoBTB1 in S-P467L mice was phenocopied by PDE5 inhibition. Angiotensin-II infusion also causes RhoBTB1-deficiency and HT which was reversed by smooth muscle specific RhoBTB1 restoration. We conclude that RhoBTB1 augments the cGMP response to nitric oxide by restraining the activity of PDE5 by acting as a substrate adaptor delivering PDE5 to the Cullin-3 E3 Ring ubiquitin ligase complex for ubiquitination and proteasomal degradation. RhoBTB1 provides protection from HT, vascular smooth muscle dysfunction, and arterial stiffness in at least two models of HT.

Abstract 099: Smooth Muscle PPARγ Mutation Causes Salt-sensitive Hypertension

Abnormal increase in renal salt retention is traditionally believed to be an early pathophysiological event in the causation of salt-sensitive hypertension, whereas increase in systemic vascular resistance (SVR) is a secondary response caused by autoregulation. However, recent studies show that salt-resistant subjects vasodilate and reduce SVR during salt loading, while salt-sensitive humans fail to vasodilate and exhibit salt-induced blood pressure (BP) elevation. Therefore, we tested the hypothesis that primary vascular dysfunction predisposes to salt sensitive hypertension. We used mice with smooth muscle-specific expression of a human hypertension-causing mutation in PPARγ P467L (S-P467L). S-P467L transgenic mice and non-transgenic controls (NT) were fed regular diet (0.4% salt) or high salt diet (4% salt) for 4 weeks. S-P467L mice, but not NT controls, exhibited severe impairment in acetylcholine- and sodium nitroprusside-induced vasorelaxation (31±4.9% S-P467L salt vs. 70±9.5% regular diet, maximal relaxation at 30 μM acetylcholine). This was associated with salt-induced systolic BP elevation in S-P467L mice (142±5 mmHg salt vs 127±2 mmHg regular diet), but not in NT mice (120±2.7 mmHg salt vs 115±4.0 mmHg). These changes were not due to differences in food intake, weight gain or renal sympathetic nerve activity between the two strains. In the 3 rd week of high salt diet, S-P467L mice and NT controls both had increased water intake by 3-fold compared to those on regular diet; however, S-P467L mice excreted 32% less urine and produced 36% less NO in the kidney as indicated by 24-hour urinary nitrate/nitrite. To assess renal function, mice were subjected to an acute saline challenge (10% body weight, i.p. injection). S-P467L mice exhibited a marked decline in their capacity to excrete this volume/sodium load, indicative of renal dysfunction. Of note, the impaired vasorelaxation in S-P467L occurred as early as day 3 of high salt diet, while renal dysfunction did not develop until day 10, suggesting that vascular dysfunction may serve as an initiation mechanism that reinforces salt-induced hemodynamic changes. These data supports the concept that vascular dysfunction may predispose to renal abnormalities including increased salt sensitivity.

Abstract P264: Endothelial-specific Interference With PPARγ Activity in Offspring Born From AVP-induced Preeclamptic Pregnancies Has Cardio-renal and Metabolic Consequences

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated transcription factor known to regulate metabolic and vascular function. Mutations in PPARγ result in hypertension, and synthetic agonists of PPARγ reduce blood pressure. Previously we found that mice expressing dominant-negative (DN) PPARγ driven by an endothelium-specific promoter (E-DN) exhibit vascular dysfunction. Preeclampsia (PE) is a hypertensive disorder of pregnancy which carries cardiovascular and metabolic risk to offspring. PE is associated with vascular dysfunction, and we therefore hypothesized a role for endothelial PPARγ in the pathogenesis of PE and its sequelae. C57BL/6J dams were bred with E-DN sires, and symptoms of PE were induced by the infusion of vasopressin (AVP, 24 ng/hr sc) throughout gestation. We assessed phenotypes of PE first in pregnant dams, and then in offspring as adults. Compared to saline infusion (SAL), AVP elevated maternal blood pressure (SBP: 116±3 vs 107±3, p<0.05) at gestational day (GD) 14-15 and urine protein (70±6 vs 27±4 mg/mL, p<0.05) at GD17. Offspring from these pregnancies were phenotyped in adulthood to assess cardiovascular and metabolic function. Data were stratified to sex, genotype, and maternal exposure to AVP vs SAL. Systolic blood pressure in adult male and female offspring born to AVP-infused pregnancies was similar to mice born to SAL pregnancies. At 20 weeks of age, vasorelaxation responses to acetylcholine were not different in offspring exposed to PE compared to mice born from SAL pregnancies. However, urinary protein levels were significantly elevated in both male (58±13 vs 32±5 mg/ml, p<0.05) and female (38±3 vs 25±2 mg/ml, p<0.05) adult E-DN born to PE pregnancies compared to E-DN controls born from SAL pregnancies. Male E-DN offspring exposed to PE showed significantly increased gain in body weight over time compared to male NT exposed to PE (ΔBW: 20±8 vs 14±2 g). These data highlight the impact of in utero exposure to elevated AVP upon cardiovascular function in the mother, and the adverse renal and metabolic consequences of PE upon offspring. Moreover, our data suggests that interference with endothelial PPARγ in pups born from PE pregnancies increases the risk for renal and metabolic dysfunction.

Abstract 140: Endogenous Renin-angiotensin System Activation Causes Accelerated Cerebral Vascular Dysfunction in Mice Expressing Dominant-negative Mutations in PPARγ in Endothelium

Abnormal activation of the renin-angiotensin system (RAS) has been implicated in cardiovascular (CV) disease. Whereas low salt diet (LSD) may be beneficial in salt-sensitive hypertension, it has been proposed to induce CV risk due to RAS activation. Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated transcription factor which regulates the actions of angiotensin II (ANG) in the vasculature and promotes anti-oxidant pathways. We hypothesize that endothelial PPARγ plays a protective role in the vasculature in response to RAS activation. Transgenic mice specifically expressing dominant-negative (DN) mutations in PPARγ in the endothelium (E-DN) were fed a LSD and endothelial function was measured. Plasma renin and ANG were significantly increased in both non-transgenic (NT) and E-DN mice fed a LSD for 6 weeks compared with normal chow (Renin - NT: 39±7 vs 20±1 ng/ml; E-DN: 34±1 vs 16±4 ng/ml; AngII - NT: 257±54 vs 47±6 pg/ml; E-DN: 294±69 vs 63±14 pg/ml p<0.05, n=5). At baseline, vasorelaxation to acetylcholine (ACh) was not affected in E-DN compared to NT (basilar artery: 66±12 vs 64±4%; carotid artery: 93±4 vs 91±4%, n=5). Six weeks of LSD significantly impaired ACh-mediated relaxation in basilar artery of E-DN but not in NT (42±8 vs 74±5%, p<0.05, n=5). Unlike basilar artery, 6 weeks of LSD was not sufficient to induce vascular dysfunction in carotid artery of E-DN (carotid artery: 86±4 vs 92±3%, n=5). The endothelial dysfunction observed in the basilar artery of E-DN was attenuated upon in vitro incubation with tempol (improved from 29±5% to 55±7%, n=6). Further, administration of the AT1 receptor blocker, Losartan (0.6g/L drinking water) for the last 2 weeks of LSD blunted the endothelial dysfunction observed in the basilar artery of E-DN (improved from 24±2% to 64±9%, n=5). We conclude that interference with PPARγ in the endothelium produces endothelial dysfunction in the cerebral circulation in response to LSD-mediated activation of the endogenous RAS and this dysfunction is mediated, at least in part, through AT1 receptor activation and ROS signaling pathways. Moreover, our data suggest that the basilar artery and perhaps cerebral circulation is particularly sensitive to inhibition of PPARγ activity and activation of the RAS.

Abstract 124: RhoBTB1, a Novel PPARγ Target Gene, Rescues Hypertension and Vascular Dysfunction Caused by PPARγ Dysfunction

We reported that mice (S-DN) expressing dominant-negative peroxisome proliferator-activated receptor gamma (PPARγ) in smooth muscle cells (SMC) are hypertensive and exhibit impaired vascular relaxation due to increased RhoA/Rho kinase (ROCK) activity, and display reduced expression of a novel PPARγ target gene, RhoBTB1. We hypothesize that RhoBTB1 plays a protective role in vascular function and that the function of RhoBTB1 is disrupted in S-DN mice. To test this, we generated double transgenic mice (termed S-RhoBTB1) with tamoxifen-inducible, Cre-dependent expression of RhoBTB1 in SMC. S-RhoBTB1 mice were crossed with S-DN to produce mice (S-DN/S-RhoBTB1) in which tamoxifen-treatment (75 mg/kg, ip, 5 days) restored RhoBTB1 expression in aorta to normal. Thoracic aorta and basilar artery from S-DN showed severely impaired vasodilation to acetylcholine (ACh) and sodium nitroprusside, which was reversed by restoration of RhoBTB1 in SMC (Aorta, 46±5 vs 80±2% ACh-induced relaxation, p<0.01, n=6-9). Replacement of RhoBTB1 also reversed the hypertensive phenotype and aortic stiffness observed in S-DN mice within 1 week of treatment (Radiotelemetry SBP, 141±6 vs 124±3 mmHg, p<0.01, n=8-10; Aortic Pulse Wave Velocity, 3.8±0.2 vs 2.5±0.1 mm/ms, p<0.01, n=11-13). Increased phosphorylation of myosin phosphatase targeting protein was preserved in both S-DN and S-DN/S-RhoBTB1 aorta, suggesting that restoration of RhoBTB1 did not affect increased RhoA/ROCK activity (p<0.01, n=6). A phosphodiesterase (PDE) 5 inhibitor, Zaprinast improved vasodilation in S-DN (p<0.01, n=8). Consistent with this, a cGMP analog that is resistant to PDE hydrolysis, 8-pCPT-cGMP, induced equivalent relaxation in S-DN and non-transgenic mice (n=4), while S-DN exhibited impaired relaxation induced by PDE-sensitive 8-Bromo-cGMP (p<0.01, n=7). PDE activity was increased in S-DN aorta and was reduced to normal levels in S-DN/S-RhoBTB1 (p<0.01, n=6). We conclude: a) loss of RhoBTB1 function explains the vascular dysfunction and hypertension observed in response to interference with PPARγ in smooth muscle, b) DN PPARγ in SMC causes vascular dysfunction via promoting PDE activity, and c) restoration of RhoBTB1 in SMC facilitates vasodilatation by normalizing PDE activity.

Abstract 062: Vascular Dysfunction and Hypertension are Prevented by a Novel PPARγ Target Gene, RhoBTB1

RhoBTB1 is a novel peroxisome proliferator-activated receptor gamma (PPARγ) target gene expressed in smooth muscle cells (SMC) which may mediate some of the vascular protective and antihypertensive benefits of PPARγ. Here, we tested the hypothesis that RhoBTB1 can prevent angiotensin II (ANG)-induced hypertension. RhoBTB1 expression in aorta from C57BL/6 mice was decreased by 54±9% (n=16) in response to ANG infusion (490 ng/min/kg, 2 weeks). To test if RhoBTB1 expression is protective, we generated double transgenic mice with tamoxifen-inducible, Cre-dependent overexpression of RhoBTB1 specifically in SMC (S-RhoBTB1). S-RhoBTB1 and non-transgenic (NT) mice were treated with tamoxifen (Tx; 75 mg/kg, ip, 5 days) or vehicle (corn oil) and then ANG was infused. Although RhoBTB1 expression was decreased in ANG-infused control mice (p<0.01, n=8-10), RhoBTB1 expression in Tx-treated S-RhoBTB1 mice infused with ANG was restored to a level similar to NT treated with saline (n=11). Overexpression of RhoBTB1 did not alter baseline blood pressure (BP) in the absence of ANG (n=7-8). However, the increase in BP induced by ANG was significantly attenuated by RhoBTB1 restoration in S-RhoBTB1 mice with Tx compared to ANG-infused control mice (either NT with Tx, NT with corn oil, or S-RhoBTB1 with corn oil) in which RhoBTB1 was not restored (Systolic BP, 159±5 in control mice vs 132±6 mmHg in S-RhoBTB1 mice with Tx, p<0.01, n=7-8). We also observed increased heart weight in ANG-infused control mice, which was prevented in S-RhoBTB1 mice treated with Tx (p<0.05, n=8). Thoracic aorta and basilar artery from ANG-infused control mice exhibited impaired acetylcholine-induced endothelial-dependent relaxation (Aorta, 48±2%, p<0.01, n=6-8), which was prevented by restoration of RhoBTB1 in SMC (Aorta, 76±5%, p<0.01, n=6-8). Thoracic aorta from ANG-infused control mice also displayed decreased sodium nitroprusside-induced endothelial-independent relaxation with a right-shifted dose-response (76±9%, p<0.01, n=8), which was also prevented in tamoxifen-treated S-RhoBTB1 mice (95±10%, p<0.01, n=8). We conclude that the novel PPARγ target gene, RhoBTB1, functions in SMC to specifically facilitate vasodilation and mediates a protective anti-hypertensive effect.

Abstract P189: Endothelial Cullin3 Mutation Causes Vascular Dysfunction, Arterial Stiffening, and Hypertension

Mutations in CULLIN3 gene (causing in-frame deletion of exon 9) cause hypertension in humans. The hypertension phenotype is unlikely to be driven by renal tubular mechanisms, as kidney-specific deletion of Cullin3 (Cul3) in mice results in hypotension, not hypertension. We have recently shown that smooth muscle expression of Cul3Δ9 causes vascular dysfunction and elevation of blood pressure (BP) via augmented RhoA/Rho-kinase signaling, strongly supporting a vascular role of Cul3 in BP regulation. To test the importance of endothelial Cul3 in vivo , we bred the conditionally activatable Cul3α9 mice with Tek-CRE ERT2 mice specifically expressing tamoxifen-inducible Cre-recombinase in the endothelium. The resultant mice (E-Cul3α9) exhibited impaired endothelial-dependent relaxation in the basilar artery (maximal relaxation in response to 30 μM acetylcholine, 45% vs 85% in control mice) and carotid artery. No difference in smooth muscle function was observed. Moreover, E-Cul3α9 mice exhibited nocturnal hypertension as determined by radiotelemetry (night time peak BP, 141±3 mmHg vs 122±3 mmHg). However no difference was seen in daytime pressure. E-Cul3α9 mice also exhibited arterial stiffening as indicated by elevated pulse wave velocity (3.7±0.3 m/s vs 2.7±0.1 m/s). To determine the molecular mechanism of endothelial dysfunction, primary aortic endothelial cells were isolated from mice carrying the inducible Cul3α9 construct and Cul3α9 expression was robustly induced by adenovirus carrying Cre recombinase gene in vitro . Cul3α9 acted in a dominant negative manner by interfering with expression and function of wild type Cul3, leading to impaired turnover of a Cul3 substrate protein phosphatase 2A, marked reduction in phosphorylated eNOS, and decreased nitric oxide production. Treatment with a selective PP2A inhibitor Okadaic Acid (1 nM) rescued Cul3α9-induced impairment of eNOS activity. These data define a novel pathway involving Cullin-3/PP2A/phospho-eNOS in the endothelium. Selective endothelial expression of Cul3α9 partially phenocopies the hypertension observed in Cul3α9 patients, suggesting that mutations in Cullin-3 cause human hypertension in part through a vascular mechanism characterized by endothelial dysfunction.

Hypertension-Causing Mutation in Peroxisome Proliferator-Activated Receptor γ Impairs Nuclear Export of Nuclear Factor-κB p65 in Vascular Smooth Muscle

Selective expression of dominant negative (DN) peroxisome proliferator-activated receptor γ (PPARγ) in vascular smooth muscle cells (SMC) results in hypertension, atherosclerosis, and increased nuclear factor-κB (NF-κB) target gene expression. Mesenteric SMC were cultured from mice designed to conditionally express wild-type (WT) or DN-PPARγ in response to Cre recombinase to determine how SMC PPARγ regulates expression of NF-κB target inflammatory genes. SMC-specific overexpression of WT-PPARγ or agonist-induced activation of endogenous PPARγ blunted tumor necrosis factor α (TNF-α)-induced NF-κB target gene expression and activity of an NF-κB-responsive promoter. TNF-α-induced gene expression responses were enhanced by DN-PPARγ in SMC. Although expression of NF-κB p65 was unchanged, nuclear export of p65 was accelerated by WT-PPARγ and prevented by DN-PPARγ in SMC. Leptomycin B, a nuclear export inhibitor, blocked p65 nuclear export and inhibited the anti-inflammatory action of PPARγ. Consistent with a role in facilitating p65 nuclear export, WT-PPARγ coimmunoprecipitated with p65, and WT-PPARγ was also exported from the nucleus after TNF-α treatment. Conversely, DN-PPARγ does not bind to p65 and was retained in the nucleus after TNF-α treatment. Transgenic mice expressing WT-PPARγ or DN-PPARγ specifically in SMC (S-WT or S-DN) were bred with mice expressing luciferase controlled by an NF-κB-responsive promoter to assess effects on NF-κB activity in whole tissue. TNF-α-induced NF-κB activity was decreased in aorta and carotid artery from S-WT but was increased in vessels from S-DN mice. We conclude that SMC PPARγ blunts expression of proinflammatory genes by inhibition of NF-κB activity through a mechanism promoting nuclear export of p65, which is abolished by DN mutation in PPARγ.

Nervous System Expression of PPARγ and Mutant PPARγ Has Profound Effects on Metabolic Regulation and Brain Development

Peroxisome proliferator activated receptor (PPARγ) is a nuclear receptor transcription factor that regulates adipogenesis and energy homeostasis. Recent studies suggest PPARγ may mediate some of its metabolic effects through actions in the brain. We used a Cre-recombinase-dependent (using Nestin^Cre) conditionally activatable transgene expressing either wild-type (WT) or dominant-negative (P467L) PPARγ to examine mechanisms by which PPARγ in the nervous system controls energy balance. Inducible expression of PPARγ was evident throughout the brain. Expression of 2 PPARγ target genes, aP2 and CD36, was induced by WT but not P467L PPARγ in the brain. Surprisingly, Nes^Cre/PPARγ-WT mice exhibited severe microcephaly and brain malformation, suggesting that PPARγ can modulate brain development. On the contrary, Nes^Cre/PPARγ-P467L mice exhibited blunted weight gain to high-fat diet, which correlated with a decrease in lean mass and tissue masses, accompanied by elevated plasma GH, and depressed plasma IGF-1, indicative of GH resistance. There was no expression of the transgene in the pancreas but both fasting plasma glucose, and fed and fasted plasma insulin levels were markedly decreased. Nes^Cre/PPARγ-P467L mice fed either control diet or high-fat diet displayed impaired glucose tolerance yet exhibited increased sensitivity to exogenous insulin and increased insulin receptor signaling in white adipose tissue, liver, and skeletal muscle. These observations support the concept that alterations in PPARγ-driven mechanisms in the nervous system play a role in the regulation of growth and glucose metabolic homeostasis.

Abstract P205: Endothelium-specific Interference with PPARG Causes Cerebral Vascular Dysfunction in Response to Endogenous Renin-angiotensin System Activation

Abnormal activation of the endogenous renin-angiotensin system (RAS) has been implicated in various cardiovascular (CV) disorders including hypertension, atherosclerosis and stroke. Whereas a low salt diet may be beneficial in salt-sensitive hypertension, it has been proposed to also cause CV risk due to activation of the RAS. The molecular mechanism by which RAS activation mediates vascular dysfunction remains undefined. Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-activated transcription factor which activates anti-oxidant and anti-inflammatory processes and can regulate the actions of angiotensin II (AngII) in the vasculature. We examined endothelial function in transgenic mice specifically expressing dominant-negative (DN) mutations in PPARγ in the endothelium (E-V290M) fed a low salt diet to test the hypothesis that endothelial PPARγ plays a protective role in the vasculature in response to endogenous RAS activation. Circulating levels of renin were significantly increased in both non-transgenic (NT) and E-V290M mice fed a low-salt diet for 6 weeks compared to standard chow (NT: 39.3±7.4 vs 19.8±1.3 ng/ml; E-V290M: 34.3±0.8 vs 16.0±3.8 ng/ml, p<0.05, n=5). Under baseline conditions, responses to endothelium-dependent agonist acetylcholine were not affected in E-V290M mice compared to NT (basilar artery: 66.1±11.8 vs 63.5±3.7%; carotid artery: 93.3±3.6 vs 91.1±4.2%, n=5). Six weeks of low-salt diet significantly impaired acetylcholine-mediated dilation in the basilar artery of E-V290M mice but not in NT (41.7±7.7 vs 74.2±5.0%, p<0.05, n=5). Unlike basilar artery, 6 weeks of low salt diet was not sufficient to induce vascular dysfunction in carotid artery or aorta of E-V290M mice (carotid artery: 85.6±4.4 vs 91.9±2.5%, n=5; aorta: 80.8±5.4 vs 87.0±5.6%, n=3). The responses to endothelium-independent vasodilator sodium nitroprusside (SNP) were not different in E-V290M mice compared to NT controls. We conclude that endothelial-specific interference with PPARγ causes endothelial dysfunction in response to endogenous RAS activation induced by a low-salt diet. Moreover, the cerebral circulation is particularly susceptible to low salt diet-induced dysfunction in conjunction with PPARγ impairment.

Abstract P158: Cullin3 Regulated Endothelial Function by Modulating eNOS Activity

Pseudohypoaldosteronism type II (PHAII) patients expressing dominant negative cullin3 mutations exhibit increased renal NaCl reabsorption and develop hyperkalaemia, metabolic acidosis and hypertension. It is unclear whether loss of cullin3 function in extra-renal tissues contributes to the hypertensive phenotype. In the vasculature, endothelial Nrf2 stability is tightly regulated by cullin3-based E3 ubiquitin ligase via the redox-sensitive adaptor kelch-like ECH-associated protein 1. In the present study, we found that 24-hour treatment with a pan cullin inhibitor MLN4924 (1 μM) caused a 3-fold increase in Nrf2 protein in mouse lung endothelial cells (MLECs), while tert-butyl hydroperoxide (tBHP, 240 μM) had no effect on Nrf2 level. However, both MLN4924 and tBHP triggered time-dependent accumulation of Nrf2 in the nuclei, which peaked at 40 minutes following treatment. As a result, both treatments induced marked upregulation of antioxidant genes including NAD(P)H quinone oxidoreductase 1, heme oxygenase 1, glutamate cysteine ligase (rate-limiting enzyme in glutathione synthesis), and catalase both in MLECs and primary mouse aortic endothelial cells (MAECs). Of note, MLN4924 upregulated Nox4 expression (1.0 ± 0.15 vs 1.7 ± 0.2) and tBHP upregulated Nox1 (1.0 ± 0.2 vs 4.8 ± 1.1), while MLN4924 and tBHP both markedly increased intracellular superoxide as determined by dihydroethidium staining. In addition, intracellular nitric oxide was decreased by half in MLN4924-treated MLECs. This redox imbalance was likely due to impaired eNOS expression and activation as MLN4924 caused a 25% reduction in total eNOS and a 75% reduction in phosphorylated eNOS, while tBHP lead to a 50% reduction in phosphorylated eNOS with no effect on total eNOS. This suggests that decreased eNOS activation contributed to the oxidative stress induced by these agents. These data imply that suppression of cullin3 in arterial endothelial cells may dampen endothelium-dependent vascular relaxation and contribute to the blood pressure elevation observed in PHAII patients with global loss of cullin3 function. Although cullin3 also negatively regulates Nrf2-mediated antioxidant responses in vascular endothelial cells, this likely occurs as a compensatory mechanism.

Abstract 053: RhoBTB1 is a Novel Gene Protecting Against Hypertension

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand activated transcription factor regulating metabolic and vascular function. We previously reported that mice (S-DN) expressing dominant-negative PPARγ in smooth muscle cells (SMC) are hypertensive, exhibit impaired vascular relaxation and enhanced contraction, and display reduced expression of a novel PPARγ target gene, RhoBTB1. We hypothesized that RhoBTB1 may play a protective role in vascular function that is disrupted in S-DN mice and in other models of hypertension. We generated double transgenic mice (termed R+) with tamoxifen-inducible, Cre-dependent expression of RhoBTB1 in SMC. R+ mice were crossed with S-DN to produce mice (S-DN/R+) in which tamoxifen-treatment (75 mg/kg, ip, 5 days) restored RhoBTB1 expression in aorta to normal. Thoracic aorta and basilar artery from S-DN showed impaired acetylcholine (ACh)-induced endothelial-dependent relaxation, which was reversed by replacement of RhoBTB1 in SMC (thoracic aorta, 43.3±4.4 vs 74.2±1.1%, p<0.01, basilar artery, 19.9±6.7 vs 48.1±12.3%, p<0.05, n=6). Aorta from S-DN mice also displayed severely decreased sodium nitroprusside (SNP)-induced endothelial-independent relaxation with a right-shifted dose-response, which was also reversed in tamoxifen-treated S-DN/R+ mice (p<0.01, n=6). Importantly, replacement of RhoBTB1 also reversed the hypertensive phenotype observed in S-DN mice (Radiotelemetry SBP, 135.9±3.9 vs 123.7±3.0 mmHg, p<0.05, n=4). To examine if overexpression of RhoBTB1 in SMC has a protective effect on other hypertensive models, Ang-II (490 ng/min/kg) was infused in tamoxifen treated R+ mice for 2 wks. RhoBTB1 expression prevented Ang-II-induced impairment of ACh relaxation in basilar artery (17.0±8.6 in control mice vs 40.7±5.3 % in R+ mice, p<0.05, n=4) and decreased SBP (166.0±7.2 in control mice vs 133.3±5.1 mmHg in R+ mice, p<0.05, n=4). We conclude that a) loss of RhoBTB1 function explains the vascular dysfunction and hypertension observed in response to interference with PPARγ in smooth muscle, and b) RhoBTB1 in SMC has an anti-hypertensive effect and facilitates vasodilatation.

Effect of selective expression of dominant-negative PPARγ in pro-opiomelanocortin neurons on the control of energy balance

Peroxisome proliferator-activated receptor-γ (PPARγ), a master regulator of adipogenesis, was recently shown to affect energy homeostasis through its actions in the brain. Deletion of PPARγ in mouse brain, and specifically in the pro-opiomelanocortin (POMC) neurons, results in resistance to diet-induced obesity. To study the mechanisms by which PPARγ in POMC neurons controls energy balance, we constructed a Cre-recombinase-dependent conditionally activatable transgene expressing either wild-type (WT) or dominant-negative (P467L) PPARγ and the tdTomato reporter. Inducible expression of both forms of PPARγ was validated in cells in culture, in liver of mice infected with an adenovirus expressing Cre-recombinase (AdCre), and in the brain of mice expressing Cre-recombinase either in all neurons (NES(Cre)/PPARγ-P467L) or selectively in POMC neurons (POMC(Cre)/PPARγ-P467L). Whereas POMC(Cre)/PPARγ-P467L mice exhibited a normal pattern of weight gain when fed 60% high-fat diet, they exhibited increased weight gain and fat mass accumulation in response to a 10% fat isocaloric-matched control diet. POMC(Cre)/PPARγ-P467L mice were leptin sensitive on control diet but became leptin resistant when fed 60% high-fat diet. There was no difference in body weight between POMC(Cre)/PPARγ-WT mice and controls in response to 60% high-fat diet. However, POMC(Cre)/PPARγ-WT, but not POMC(Cre)/PPARγ-P467L, mice increased body weight in response to rosiglitazone, a PPARγ agonist. These observations support the concept that alterations in PPARγ-driven mechanisms in POMC neurons can play a role in the regulation of metabolic homeostasis under certain dietary conditions.

PPARγ Regulation in Hypertension and Metabolic Syndrome

Dysregulation of peroxisome proliferator-activated receptor gamma (PPARγ) activity leads to significant alterations in cardiovascular and metabolic regulation. This is most keenly observed by the metabolic syndrome-like phenotypes exhibited by patients carrying mutations in PPARγ. We will summarize recent findings regarding mechanisms of PPARγ regulation in the cardiovascular and nervous systems focusing largely on PPARγ in the smooth muscle, endothelium, and brain. Canonically, PPARγ exerts its effects by regulating the expression of target genes in these cells, and we will discuss mechanisms by which PPARγ targets in the vasculature regulate cardiovascular function. We will also discuss emerging evidence that PPARγ in the brain is a mediator of appetite and obesity. Finally, we will briefly review how novel PPARγ activators control posttranslational modifications of PPARγ and their prospects to offer new therapeutic options for treatment of metabolic diseases without the adverse side effects of thiazolidinediones which strongly activate transcriptional activity of PPARγ.

Endothelial PPAR-γ provides vascular protection from IL-1β-induced oxidative stress

Loss of peroxisome proliferator-activated receptor (PPAR)-γ function in the vascular endothelium enhances atherosclerosis and NF-κB target gene expression in high-fat diet-fed apolipoprotein E-deficient mice. The mechanisms by which endothelial PPAR-γ regulates inflammatory responses and protects against atherosclerosis remain unclear. To assess functional interactions between PPAR-γ and inflammation, we used a model of IL-1β-induced aortic dysfunction in transgenic mice with endothelium-specific overexpression of either wild-type (E-WT) or dominant negative PPAR-γ (E-V290M). IL-1β dose dependently decreased IκB-α, increased phospho-p65, and increased luciferase activity in the aorta of NF-κB-LUC transgenic mice. IL-1β also dose dependently reduced endothelial-dependent relaxation by ACh. The loss of ACh responsiveness was partially improved by pretreatment of the vessels with the PPAR-γ agonist rosiglitazone or in E-WT. Conversely, IL-1β-induced endothelial dysfunction was worsened in the aorta from E-V290M mice. Although IL-1β increased the expression of NF-κB target genes, NF-κB p65 inhibitor did not alleviate endothelial dysfunction induced by IL-1β. Tempol, a SOD mimetic, partially restored ACh responsiveness in the IL-1β-treated aorta. Notably, tempol only modestly improved protection in the E-WT aorta but had an increased protective effect in the E-V290M aorta compared with the aorta from nontransgenic mice, suggesting that PPAR-γ-mediated protection involves antioxidant effects. IL-1β increased ROS and decreased the phospho-endothelial nitric oxide synthase (Ser(1177))-to-endothelial nitric oxide synthase ratio in the nontransgenic aorta. These effects were completely abolished in the aorta with endothelial overexpression of WT PPAR-γ but were worsened in the aorta with E-V290M even in the absence of IL-1β. We conclude that PPAR-γ protects against IL-1β-mediated endothelial dysfunction through a reduction of oxidative stress responses but not by blunting IL-1β-mediated NF-κB activity.

Interference with PPARγ in endothelium accelerates angiotensin II-induced endothelial dysfunction

The ligand activated nuclear receptor peroxisome proliferator-activated receptor γ (PPARγ) in the endothelium regulates vascular function and blood pressure (BP). We previously reported that transgenic mice (E-V290M) with selectively targeted endothelial-specific expression of dominant negative PPARγ exhibited endothelial dysfunction when treated with a high-fat diet, and exhibited an augmented pressor response to angiotensin II (ANG II). We hypothesize that interference with endothelial PPARγ would exacerbate ANG II-induced endothelial dysfunction. Endothelial function was examined in E-V290M mice infused with a subpressor dose of ANG II (120 ng·kg(-1)·min(-1)) or saline for 2 wk. ANG II infusion significantly impaired the responses to the endothelium-dependent agonist acetylcholine both in basilar and carotid arteries from E-V290M but not NT mice. This impairment was not due to increased BP, which was not significantly different in ANG II-infused E-V290M compared with NT mice. Superoxide levels, and expression of the pro-oxidant Nox2 gene was elevated, whereas expression of the anti-oxidant genes Catalase and SOD3 decreased in carotid arteries from ANG II-infused E-V290M mice. Increased p65 and decreased Iκ-Bα suggesting increased NF-κB activity was also observed in aorta from ANG II-infused E-V290M mice. The responses to acetylcholine were significantly improved both in basilar and carotid arteries after treatment with Tempol (1 mmol/l), a scavenger of superoxide. These findings provide evidence that interference with endothelial PPARγ accelerates ANG II-mediated endothelial dysfunction both in cerebral and conduit arteries through an oxidative stress-dependent mechanism, suggesting a role for endothelial PPARγ in protecting against ANG II-induced endothelial dysfunction.

Abstract 001: Mutation in the PPARγ Ligand Binding Domain Impairs the Anti-inflammatory Action of PPARγ

Peroxisome proliferator-activated receptor gamma (PPARγ) has been proposed to antagonize the activities of nuclear factor kappa B (NFκB) to regulate inflammation. Transgenic mice expressing dominant negative (DN) PPARγ specifically in vascular smooth muscle cells (SMC) exhibited exacerbated atherosclerosis but the mechanism remains unknown. We hypothesized that DN PPARγ promotes NFκB-induced inflammation in SMC. To test this, we cultured mesenteric SMCs from transgenic mice that would conditionally express wild-type (WT) or DN PPARγ (P467L) in response to adenovirus expressing Cre-recombinase (AdCRE). PPARγ expression remained silent in control SMC infected with AdGFP. TNF-α (0.05 ng/ml, 6 hr) induced NFκB target gene (MCP-1, iNOS and MMP9) expression to a greater extent in P467L-Cre compared to P467L-GFP. For example, MMP9 expression was induced 6.3±0.2-fold in P467L-Cre vs 3.2±0.5-fold in P467L-GFP (p<0.01). The NFκB subunit, p65, mRNA level was not altered in these cells. There was no induction of the PPARγ target aP2 in P467L-Cre, but it was induced 6.5±1.7-fold in WT-SMC infected with AdCRE (WT-Cre). The ability of TNF-α to induce NFκB target gene expression was blunted or abrogated in WT-Cre cells, and their expression was significantly reduced in TNF-α-treated WT-Cre compared to WT-GFP (MMP9: 0.7±1.2 vs 6.0±0.3, p<0.01). To examine mechanisms in vivo, we crossbred transgenic mice expressing WT PPARγ specifically in SMC (S-WT) with mice expressing luciferase under control of a NFκB-responsive promoter. TNF-α (500 ng/ml, 24 hr)-induced NFκB activity was decreased in aorta and carotid artery from S-WT mice compared to control mice (aorta: 4.7±1.1 v s 6.7±0.7, p<0.05, carotid artery: 4.0±0.6 vs 8.7±1.2, p<0.01). Finally, to assess the mechanism preventing anti-inflammatory activity by DN PPARγ, we assessed its interaction with p65 protein when co-expressed in HEK293T cells. WT PPARγ co-precipitated with p65, but the interaction between p65 and P467L PPARγ was severely impaired (n=6). Other mutants (R165T, V290M) could bind to p65, suggesting that loss of the ability is specific to P467L PPARγ. We conclude that SMC-PPARγ has anti-inflammatory effects mediated through inhibition of NFκB activity, which is abolished by P467L mutation.

Abstract P128: RhoBTB1, a Novel PPARγ Target Gene Regulates Vascular Function

Peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand activated transcription factor regulating metabolic and vascular function. We previously reported that mice (S-DN) expressing a dominant-negative PPARγ mutation in smooth muscle cells (SMC) are hypertensive, exhibit impaired vascular relaxation and enhanced contraction, and display reduced expression of a novel PPARγ target gene, RhoBTB1. We hypothesized that RhoBTB1 may play a role in the PPARγ-mediated regulation of vascular function that is disrupted in S-DN mice. To test this, we generated transgenic mice (R+) with tamoxifen-inducible, Cre-dependent expression of RhoBTB1 in SMC. These mice were crossed with S-DN to produce mice (S-DN/R+) in which tamoxifen-treatment (75 mg/kg, ip, for 5 days) increased RhoBTB1 RNA expression in aorta from the reduced level seen in S-DN mice, and restored it to the level of non-transgenic mice. Thoracic aorta from S-DN showed impaired acetylcholine (ACh)-induced endothelial-dependent relaxation, which was reversed by replacement of RhoBTB1 in SMC (43.3±4.4 vs 74.2±1.1 %, p<0.01, n=6). A similar improvement was observed in basilar artery (19.9±6.7 vs 48.1±12.3 %, p<0.05, n=6). Aorta from S-DN mice also displayed severely decreased NO donor (sodium nitroprusside, SNP)-induced endothelial-independent relaxation with a right-shifted SNP dose-response, which was also reversed in aorta from tamoxifen-treated S-DN/R+ mice (p<0.01, n=6). To confirm that these effects were specifically due to replacement of RhoBTB1, we assessed vascular function in tamoxifen-treated S-DN mice. Notably, tamoxifen itself did not affect relaxation in response to ACh or SNP, or contraction in response to KCl, endothelin-1 (ET-1) or Prostaglandin F2α in aorta or basilar artery from S-DN (n=4). Interestingly, contraction induced by ET-1, but not KCl, was enhanced in S-DN aorta, and was not improved by restoring RhoBTB1 expression (n=6). This suggests that RhoBTB1 may function specifically by regulating vasodilation pathways. We conclude that RhoBTB1 plays an important role in facilitating vasodilatation in aorta and basilar artery, and loss of RhoBTB1 function explains the vascular dysfunction observed in response to interference with PPARγ in smooth muscle.

Methylglyoxal accumulation in arterial walls causes vascular contractile dysfunction in spontaneously hypertensive rats

Methylglyoxal (MGO) is a metabolite of glucose and perhaps mediates diabetes-related macrovascular complications including hypertension. In the present study, we examined if MGO accumulation affects vascular reactivity of isolated mesenteric artery from spontaneously hypertensive rats (SHR). Five-week-old SHR were treated with an MGO scavenger, aminoguanidine (AG), for 5 weeks. AG partially normalized increased blood pressure in SHR. In mesenteric artery from SHR treated with AG, increased accumulation of MGO-derived advanced glycation end-products was reversed. In mesenteric artery from SHR, AG normalized impaired acetylcholine (ACh)-induced relaxation and increased angiotensin (Ang) II-induced contraction. Reactive oxygen species (ROS) production increased in SHR mesenteric artery, and acute treatment with a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) inhibitor augmented ACh-induced relaxation. Protein expression of NOX1 and Ang II type 2 receptor (AT2R) increased in SHR mesenteric artery, which was normalized by AG. Acute treatment with an AT2R blocker but not a NOX inhibitor normalized the increased Ang II-induced contraction in SHR mesenteric artery. The present results demonstrate that MGO accumulation in mesenteric artery may mediate development of hypertension in SHR at least in part via increased ROS-mediated impairment of endothelium-dependent relaxation and AT2R-mediated increased Ang II contraction.

Exploring mechanisms of diabetes-related macrovascular complications: role of methylglyoxal, a metabolite of glucose on regulation of vascular contractility

Methylglyoxal (MGO) is a metabolite of glucose. MGO binds to and modifies arginine, lysine, and cysteine residues in proteins, which leads to formation of a variety of advanced glycation end-products (AGEs) such as argpyrimidine and N(ε)-(carboxyethyl)lysine. The concentration of MGO significantly increases in plasma from diabetic patients. Increased plasma MGO level seems to be associated with diabetic microvascular complications. In addition, MGO accumulates in large vascular tissues from spontaneous hypertensive rats, which is associated with increased blood pressure. Although it is logical to hypothesize that MGO could directly affect vascular reactivity, available reports are very limited. Our group has examined effects of MGO on vascular reactivity (contraction and relaxation) and explored underlying mechanisms. In this review article, we summarized our recent findings on 1) short-term effects of MGO, 2) long-term effects of MGO, and 3) effects of MGO accumulation in arterial walls on vascular reactivity. These findings may provide further mechanistic insights into the pathogenesis of diabetes-related macrovascular complications including hypertension.

Methylglyoxal augments angiotensin II-induced contraction in rat isolated carotid artery

Methylglyoxal (MGO), a metabolite of glucose, accumulates in vascular tissues of a hypertensive animal. In the present study, we examined the effect of MGO on angiotensin (Ang) II-induced contraction of rat carotid artery. Treatment of carotid artery with MGO (420 µM, 30 min) significantly augmented Ang II (0.1 to 30 nM)-induced concentration-dependent contraction. The effect was abolished by the removal of endothelium. BQ-123 (1, 5 µM), an endothelin A-receptor blocker, had no effect on the MGO-induced enhancement of Ang II-induced contraction. AL8810 (1 µM), a prostaglandin F(2α)-receptor blocker, or SQ29548 (1 µM), a thromboxane A(2)-receptor blocker, was also ineffective. However, tempol (10 µM), a superoxide scavenger, and catalase (5000 U/mL), which metabolizes hydrogen peroxide to water, significantly prevented the effect of MGO. Combined MGO and Ang II treatment increased reactive oxygen species (ROS) production. Apocynin (10 µM) or gp91ds-tat (3 µM), an inhibitor of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, significantly prevented the effect of MGO. Gp91ds-tat or an Ang II type 1-receptor (AT1R) blocker, losartan (10 µM), prevented the MGO-mediated increased ROS production. The present study revealed that MGO augments Ang II-induced contraction by increasing AT1R-mediated NADPH oxidase-derived superoxide and hydrogen peroxide production in endothelium of rat carotid artery.