New perspectives in hypertension research. Potentials of vascular biology

Antihypertensive, antioxidant, and renal protective impact of integrated GJD with captopril in spontaneously hypertensive rats

Hypertension is the most prevalent chronic disease World-wide, and the leading preventable risk factor for cardiovascular disease (CVD). Few patients accomplish the objective of decreasing blood pressure and avoiding hypertensive target organ damage after treatments with antihypertensive agents which opens the door for other treatments, such as herbal-and antihypertensive combination therapy. Captopril (CAP), as a-pril which inhibits angiotensin converting enzyme has long been used in the management of hypertension and CVD. Gedan Jiangya Decoction (GJD) is known for antihypertensive effects in prior studies. The research is aimed to determine whether GJD in combination with captopril has antihypertensive, kidney protective, antioxidant, and vasoactive effects in spontaneously hypertensive rats (SHR). Regular measurements of systolic and diastolic blood pressure (SBP and DBP), and body weight were monitored weekly. H&E staining was utilized to examine histopathology. The combined effects were studied using ELISA, immunohistochemistry, and qRT-PCR. Significant reductions in SBP, DBP, aortic wall thickness, and improvement in renal tissue were observed following GJD + CAP treatment, with increased serum levels of NO, SOD, GSH-Px, and CAT and decreases in Ang II, ET-1, and MDA. Similarly, GJD + CAP treatment of SHR's significantly decreased ET-1 and AGTR1 mRNA and protein expression while increasing eNOS mRNA and protein expression in thoracic aorta and kidney tissue. In conclusion, the present investigation found that GJD + CAP treatment decreases SHR blood pressure, improves aorta remodeling and renal protection, and that this effect could be attributable, in part, due to antioxidant and vascular tone improvement.

GJD Modulates Cardiac/Vascular Inflammation and Decreases Blood Pressure in Hypertensive Rats

Gedan Jiangya decoction (GJD) (aqueous ethanol extract), a traditional Chinese medicine formula which contain six botanical drugs (Uncaria rhynchophylla (Miq.) Miq., Salvia miltiorrhiza Bunge, Pueraria lobata (Willd.) Ohwi, Eucommia ulmoides Oliv., Prunella vulgaris L., and Achyranthes bidentata Blume) was designed to treat hypertension; however, the underlying mechanism of action is unclear. This study aimed to determine the mechanisms of action of GJD in the treatment of hypertension in spontaneously hypertensive rats (SHR). Male SHRs were randomly divided into five groups: GJD doses were low (1.36 g/kg/d), medium (2.72 g/kg/d), and high (5.44 g/kg/d), captopril (13.5 mg/kg/d), and SHR groups, with Wistar-Kyoto rats (WKY) serving as the control. Every rat was gavaged once a day. The ALC-NIBP, a noninvasive blood pressure device, measured systolic (SBP) and diastolic (DBP) blood pressures. Six weeks following treatment, all rats were anesthetized. The blood samples were obtained from the abdominal aorta and then serum isolated to assess endothelin-1 and angiotensin II, interleukin-1beta, interleukin-6, and TNF-alpha. The left ventricular and thoracic aortas were taken for HE staining, immunohistochemistry, RT-qPCR, and western blot examination. Following GJD therapy, SBP and DBP were significantly lowered, as were serum levels of endothelin-1 and angiotensin II. The thickness of the left ventricular and thoracic aorta walls reduced, as did type I collagen, type III collagen, and alpha-SMA expression in the left ventricular and aortic tissues. The GJD treatment significantly reduced serum levels of the inflammatory markers interleukin-1beta, interleukin-6, and TNF-alpha. Furthermore, interleukin-1 beta, interleukin-6, TNF-alpha, TAK1, and NF-κB/p65 levels were significantly reduced in left ventricular and aortic tissues, whereas IkB-alpha levels were significantly elevated. GJD has a dose-dependent effect on all parameters. In conclusion, GJD has been shown to lower blood pressure, improve cardiovascular remodeling, and reduce inflammation via regulating NF-κB in SHRs.

Impact of Lifestyles (Diet and Exercise) on Vascular Health: Oxidative Stress and Endothelial Function

Healthy lifestyle and diet are associated with significant reduction in risk of obesity, type 2 diabetes, and cardiovascular diseases. Oxidative stress and the imbalance between prooxidants and antioxidants are linked to cardiovascular and metabolic diseases. Changes in antioxidant capacity of the body may lead to oxidative stress and vascular dysfunction. Diet is an important source of antioxidants, while exercise offers many health benefits as well. Recent findings have evidenced that diet and physical factors are correlated to oxidative stress. Diet and physical factors have debatable roles in modulating oxidative stress and effects on the endothelium. Since endothelium and oxidative stress play critical roles in cardiovascular and metabolic diseases, dietary and physical factors could have significant implications on prevention of the diseases. This review is aimed at summarizing the current knowledge on the impact of diet manipulation and physical factors on endothelium and oxidative stress, focusing on cardiovascular and metabolic diseases. We discuss the friend-and-foe role of dietary modification (including different diet styles, calorie restriction, and nutrient supplementation) on endothelium and oxidative stress, as well as the potential benefits and concerns of physical activity and exercise on endothelium and oxidative stress. A fine balance between oxidative stress and antioxidants is important for normal functions in the cells and interfering with this balance may lead to unfavorable effects. Further studies are needed to identify the best diet composition and exercise intensity.

Semen Brassicae reduces thoracic aortic remodeling, inflammation, and oxidative damage in spontaneously hypertensive rats

BACKGROUND

This study aimed to evaluate the role of Semen Brassicae, a common Traditional Chinese Medicine, in the treatment of hypertension.

METHODS

Spontaneously hypertensive rats (SHRs) were divided into five groups and were gavaged with either distilled water, water-decocted solution from Semen Brassicae (0.5, 1 or 2 g/kg), or nifedipine (2.7 mg/kg). Normal rats gavaged with distilled water were used as a control. Systolic (SBP) and diastolic blood pressure (DBP) were measured using a non-invasive method. After 8 weeks of administration, all animals were anesthetized. Abdominal aortic serum was collected to measure serum factors; the thoracic aorta was collected for hematoxylin and eosin staining and western blot analysis.

RESULTS

Both SBP and DBP were significantly decreased after Semen Brassicae treatment. Endothelin-1 and angiotensin II levels in abdominal aortic serum, as well as the levels of inflammatory factors interleukin (IL)-1β, IL-6, and tumor necrosis factor-alpha, were significantly decreased after Semen Brassicae treatment. The wall thickness of the thoracic aorta was significantly reduced after Semen Brassicae treatment. Nitric oxide level and the activity of superoxide dismutase and glutathione peroxidase were significantly increased, and malondialdehyde level was significantly decreased in the abdominal aortic serum after Semen Brassicae treatment. Semen Brassicae treatment increased the levels of peroxisome proliferator-activated receptor gamma and IκB-α and decreased the levels of intercellular adhesion molecule 1, monocyte chemoattractant protein-1, von Willebrand factor, p-IκB-α and p-p65 NF-κB.

CONCLUSIONS

In conclusion, water-decocted solution from Semen Brassicae can decrease blood pressure, improve vascular remodeling, and attenuate oxidative stress and inflammation in SHRs.

Vascular Cell Glycocalyx-Mediated Vascular Remodeling Induced by Hemodynamic Environmental Alteration

Vascular remodeling induced by hemodynamic stimuli contributes to the pathophysiology of cardiovascular diseases. The importance of vascular cells (endothelial cells and smooth muscle cells) glycocalyx in the mechanotransduction of flow-induced shear stress at the cellular and molecular levels has been demonstrated over the past decade. However, its potential mechanotransduction role in vascular remodeling has triggered little attention. In the present study, a home-made apparatus was used to expose the rat abdominal aorta to sterile, flow or no flow, normal-pressure or high-pressure conditions for 4 days. The histomophometric, cellular, and molecular analysis of vessels were performed. The results showed that after exposing the vessels in the flow and high-pressure condition, the apoptotic rate, the cell number, and the RNA level of contractile marker gene smooth muscle 22 of smooth muscle cells were significantly increased, whereas the expression of nitric oxide synthase, α-smooth muscle actin, smoothelin, and calponion showed no significant differences compared with the flow and normal-pressure groups. Moreover, the histomophometric analysis of vascular walls suggested a remodeling induced by flow and high-pressure loading consistent with the classic hypertensive aortic phenotype, which is characterized by a thicker and more rigid vascular wall as well as increased aortic diameter. However, those phenomena were totally abolished after compromising the integrity of glycocalyx by the treatment of vessels with hyaluronidase, which provided evidence of the important mechanotransduction role of the vascular cells glycocalyx in vascular remodeling induced by hemodynamic stimuli.

Vascular Adaptation to Exercise in Humans: Role of Hemodynamic Stimuli

On the 400th anniversary of Harvey's Lumleian lectures, this review focuses on "hemodynamic" forces associated with the movement of blood through arteries in humans and the functional and structural adaptations that result from repeated episodic exposure to such stimuli. The late 20th century discovery that endothelial cells modify arterial tone via paracrine transduction provoked studies exploring the direct mechanical effects of blood flow and pressure on vascular function and adaptation in vivo. In this review, we address the impact of distinct hemodynamic signals that occur in response to exercise, the interrelationships between these signals, the nature of the adaptive responses that manifest under different physiological conditions, and the implications for human health. Exercise modifies blood flow, luminal shear stress, arterial pressure, and tangential wall stress, all of which can transduce changes in arterial function, diameter, and wall thickness. There are important clinical implications of the adaptation that occurs as a consequence of repeated hemodynamic stimulation associated with exercise training in humans, including impacts on atherosclerotic risk in conduit arteries, the control of blood pressure in resistance vessels, oxygen delivery and diffusion, and microvascular health. Exercise training studies have demonstrated that direct hemodynamic impacts on the health of the artery wall contribute to the well-established decrease in cardiovascular risk attributed to physical activity.

Role of Endogenous Sulfur Dioxide in Regulating Vascular Structural Remodeling in Hypertension

Sulfur dioxide (SO₂), an emerging gasotransmitter, was discovered to be endogenously generated in the cardiovascular system. Recently, the physiological effects of endogenous SO₂ were confirmed. Vascular structural remodeling (VSR), an important pathological change in many cardiovascular diseases, plays a crucial role in the pathogenesis of the diseases. Here, the authors reviewed the research progress of endogenous SO₂ in regulating VSR by searching the relevant data from PubMed and Medline. In spontaneously hypertensive rats (SHRs) and pulmonary hypertensive rats, SO₂/aspartate aminotransferase (AAT) pathway was significantly altered. SO₂ inhibited vascular smooth muscle cell (VSMC) proliferation, promoted apoptosis, inhibited the synthesis of extracellular collagen but promoted its degradation, and enhanced antioxidative capacity, thereby playing a significant role in attenuating VSR. However, the detailed mechanisms needed to be further explored. Further studies in this field would be important for the better understanding of the pathogenesis of systemic hypertension and pulmonary hypertension. Also, clinical trials are needed to demonstrate if SO₂ would be a potential therapeutic target in cardiovascular diseases.

Beta3 adrenergic receptor is involved in vascular injury in deoxycorticosterone acetate-salt hypertensive mice

Beta3 adrenergic receptor (ADRB3) mediates vessel relaxation in the endothelium while it modulates lipolysis in the adipose tissue. However, the function and regulation mechanism of ADRB3 in the perivascular adipose tissue (PVAT), especially in hypertension, is still unclear. We show that ADRB3 protein is upregulated in the PVAT of deoxycorticosterone acetate-salt (DOCA-salt) hypertensive mice, with the characteristics of PVAT browning and increased uncoupling protein 1 (UCP1) expression. Inhibition of ADRB3 with selective antagonist SR59230A caused serious vascular injury in vivo, even though UCP1 expression was downregulated. ADRB3 protein was regulated by let-7b, which was decreased in the PVAT of the DOCA-salt group. These data reveal that ADRB3 in PVAT contributes to vascular function in the progression of hypertension.

Involvement of vascular peroxidase 1 in angiotensin II-induced vascular smooth muscle cell proliferation

AIMS

Vascular peroxidase 1 (VPO1) is a newly identified haem-containing peroxidase that catalyses the oxidation of a variety of substrates by hydrogen peroxide (H(2)O(2)). Considering the well-defined effects of H(2)O(2) on the vascular remodelling during hypertension, and that VPO1 can utilize H(2)O(2) generated from co-expressed NADPH oxidases to catalyse peroxidative reactions, the aims of this study were to determine the potential role of VPO1 in vascular remodelling during hypertension.

METHODS AND RESULTS

The vascular morphology and the expression of VPO1 in arterial tissues of spontaneously hypertensive rats and Wistar-Kyoto rats were assessed. The VPO1 expression was significantly increased concomitantly with definite vascular remodelling assessed by evaluating the media thickness, lumen diameter, media thickness-to-lumen diameter ratio and mean nuclear area in artery media in spontaneously hypertensive rats. In addition, in cultured rat aortic smooth muscle cells we found that the angiotensin II-mediated cell proliferation was inhibited by knockdown of VPO1 using small hairpin RNA. Moreover, the NADPH oxidase inhibitor, apocynin, and the hydrogen peroxide scavenger, catalase, but not the ERK1/2 inhibitor, PD98059, attenuated angiotensin II-mediated up-regulation of VPO1 and generation of hypochlorous acid.

CONCLUSION

VPO1 is a novel regulator of vascular smooth muscle cell proliferation via NADPH oxidase-H(2)O(2)-VPO1-hypochlorous acid-ERK1/2 pathways, which may contribute to vascular remodelling in hypertension.

Molecular cloning of OSP94: A significant biomarker protein of hypertensive human heart and a member of HSP110 family

Heat shock proteins (HSPs) are upregulated in response to stress and play a protective function in refolding of cellular proteins. In hypertension, the heart is a vital organ that requires examination and investigation, and primary induction of HSPs is predominantly effected. Hypertension results from osmotic imbalance during renin-angiotensin cycle inefficiency. Osmotic stress protein 94 (OSP94) is a stress protein induced upon osmotic imbalance. It is therefore necessary to analyze its precise role in the hypertensive heart. We have first reported the cloning and expression of human heart OSP94 followed by an analysis of gene sequence and protein homology. Directional cloning of OSP94 by PCR amplification yielded a 2.5 kb amplicon and was cloned into pET-15b. Site-directed mutagenesis was essentially followed. mRNA expression levels were evaluated in correlation with HSPs. Gene analysis indicated a 2520 bp sequence with an 838-amino acid protein complement. Protein homology revealed highly conserved sequence similarity among mammalian sequences. Structural predictions of OSP94 protein were also investigated. OSP94 is therefore recognized as a significant stress protein for investigations in hypertensive heart tissues and is a highly conserved protein in the HSP110 subfamily.

Importance of hemodynamic forces as signals for exercise-induced changes in endothelial cell phenotype

Current evidence indicates that the ability of physical activity to sustain a normal phenotype of arterial endothelial cells (ECs) plays a central role in the beneficial effects of exercise (Ex) on atherosclerotic disease. Here we evaluate the strength of evidence that shear stress (SS) and/or circumferential wall stress (stretch) are the primary signals, produced by bouts of Ex, that signal altered gene expression in arterial ECs, thereby resulting in a less atherogenic EC phenotype. Current literature indicates that SS is a signal for expression of antiatherogenic genes in cultured ECs, in ECs of isolated arteries, and in ECs of arteries in intact animals. Furthermore, SS levels in the arteries of humans during Ex are in the range that produces beneficial changes. In contrast, complex flow profiles within recirculation zones and/or oscillatory flow patterns can cause proatherogenic gene expression in ECs. In vivo evidence indicates that Ex decreases oscillatory flow/SS in some portions of the arterial tree but may increase oscillatory flow in other areas of the arterial tree. Circumferential wall stress can increase expression of some beneficial EC genes as well, but circumferential wall stress also increases production of reactive oxygen species and increases the expression of adhesion factors and other proatherogenic genes. Interactions of arterial pressure and fluid SS play an important role in arterial vascular health and likely contribute to how Ex bouts signal changes in EC gene expression. It is also clear that other local and circulating factors interact with these hemodynamic signals during Ex to produce the healthy arterial EC phenotype. We conclude that available evidence suggests that exercise signals formation of beneficial endothelial cell phenotype at least in part through changes in SS and wall stretch in the arteries.

Improvement of vascular remodeling in spontaneous hypertensive rats with traditional Chinese medicine

Qin-Dan-Jiang-Ya-Tang (QDJYT) is a traditional Chinese herbal medicine for the treatment of hypertension. The effect of QDJYT on blood pressure (BP) and vascular remodeling in hypertension was investigated in the model of spontaneous hypertensive rats (SHR). Sixteen SHRs were divided into two groups: the SHR group and the SHR+ QDJYT group. Eight Wistar-Kyoto (WKY) rats were in the normal control group. QDJYT (750 mg/kg) was orally administered daily for 12 weeks to the SHR+QDJYT group. After 12 weeks, thoracic aortas were segregated. The media thickness (MT) and the lumen diameter (LD) of the aortic wall, the ratios of MT to LD, the expression of basic fibroblast growth factor (bFGF) mRNA, and the level of its proteinic production were examined by histology, real-time PCR, and Western blot analysis, respectively. It was observed in our study that MT, MT/LD, the expression of bFGF mRNA, and the level of its proteinic production in aortic walls were higher in SHRs than in WKY rats. However, in the SHRs treated with QDJYT, we found MT, MT/LD, the expression of bFGF mRNA and the level of its proteinic production were lower than SHRs. These results suggest that QDJYT can improve the vascular remodeling in SHRs, and the mechanisms may be related to the suppressive effect of QDJYT on bFGF mRNA and its proteic productions in the aortic walls of SHRs.

Effect of traditional Chinese medicine Qin-Dan-Jiang-Ya-Tang on remodeled vascular phenotype and osteopontin in spontaneous hypertensive rats

Qin-Dan-Jiang-Ya-Tang (QDJYT) is a traditional Chinese herbal medicine for the treatment of hypertension. The effect of QDJYT on blood pressure and on vascular remodeling in hypertension was investigated in the model of spontaneous hypertensive rats (SHR). Sixteen SHRs were divided into two groups, the SHR group and the SHR+QDJYT group. Eight WKY rats were a normal control group. QDJYT (750 mg/kg) was orally administered daily for 12 weeks in SHR+QDJYT group. After 12 weeks, thoracic aortas were segregated. Media thickness (MT), lumen diameter (LD), the ratio of MT to LD, the volume fraction of collagen (VFC) in media, the ultrastructure of vascular smooth muscle cells (VSMCs) and the expression of osteopontin (OPN) mRNA were examined by histological staining, transmission electron microscope (TEM), and real-time PCR, respectively. It was observed in our study that MT, MT/LD, VFC and the expression of OPN mRNA were higher in the SHRs than in the WKY rats, volume and numeral density of mitochondria in vascular smooth muscle cells (VSMCs) in media increased obviously. However, in the SHRs treated with QDJYT, we found MT, MT/LD, VFC and the expression of OPN gene were lower than in the SHRs, and the phenotype of VSMCs were close to normal. These results suggest that QDJYT could reverse the vascular remodeling in SHR, and the mechanisms may be related to the suppressive effect of QDJYT on the expression of OPN mRNA in arterial wall.

Research progress of vasculopathy in portal hypertension

Portal hypertension, one of the vascular diseases, not only has lesions in liver, but also changes in vascular structures and functions of extrahepatic portal system, systemic system and pulmonary circulation. The pathological changes of vasculopathy in portal hypertension include remodeling of arterialized visceral veins, intimal injury of visceral veins and destruction of contractile structure in visceral arterial wall. The mechanisms of vasculopathy in portal hypertension may be attributed to the changes of hemodynamics in portal system, immune response, gene modulation, vasoactive substances, and intrahepatic blood flow resistance. Portal hypertension can cause visceral hyperdynamic circulation, and the development and progression of visceral vasculopathy, while visceral vasculopathy can promote the development and progression of portal hypertension and visceral hyperdynamic circulation in turn. The aforementioned three factors interact in the pathogenesis of hepatic cirrhosis-induced portal hypertension and are involved in hemorrhage due to varicose vein rupture.

Regulation of Discoidin Domain Receptor 2 by Cyclic Mechanical Stretch in Cultured Rat Vascular Smooth Muscle Cells

Discoidin domain receptor 2 (DDR2) plays potential roles in the regulation of collagen turnover mediated by smooth muscle cells in atherosclerosis. How mechanical stretch affects the regulation of DDR2 in smooth muscle cells is not fully understood. We sought to investigate the cellular and molecular mechanisms of regulation of DDR2 by cyclic stretch in smooth muscle cells. Rat vascular smooth muscle cells grown on a flexible membrane base were stretched by vacuum to 20% of maximum elongation, at 60 cycles/min. Cyclic stretch significantly increased DDR2 protein and mRNA expression after stretch. Cyclic stretch also significantly increased DNA-protein binding activity of Myc-Max. Addition of SB203580, transforming growth factor-beta1 (TGF-beta1) monoclonal antibody, p38 small interfering RNA (siRNA), and c-myc siRNA 30 minutes before stretch inhibited the induction of DDR2 protein and abolished the DNA-protein binding activity induced by cyclic stretch. Cyclic stretch increased, whereas SB203580 abolished the phosphorylated p38 protein. Conditioned medium from stretched smooth muscle cells and exogenous administration of angiotensin II and TGF-beta1 recombinant proteins to the nonstretched cells increased DDR2 protein expression similar to that seen after stretch. In conclusion, cyclic mechanical stretch enhances DDR2 expression in cultured rat smooth muscle cells. The stretch-induced DDR2 is mediated by angiotensin II and TGF-beta1, at least in part, through p38 mitogen-activated protein kinase and Myc pathway.

Circulating soluble vascular cell adhesion molecule 1: Relationships with residual renal function, cardiac hypertrophy, and outcome of peritoneal dialysis patients

BACKGROUND

Vascular cell adhesion molecule 1 (VCAM-1) is involved in leukocyte-endothelial cell interaction and has a pivotal role in inflammation. Whether it contributes to excessive mortality in dialysis patients remains uncertain. In this study, we examined circulating soluble VCAM-1 (sVCAM-1) in relation to different clinical and biochemical parameters, as well as mortality and cardiovascular events, in peritoneal dialysis (PD) patients.

METHODS

Values for serum sVCAM-1, together with C-reactive protein (CRP), homocysteine, albumin, lipid profile, blood hemoglobin, and indices of dialysis adequacy, were determined at study baseline, and echocardiography was performed in 160 long-term PD patients. Patients were followed up for a mean of 35 +/- 16 (SD) months.

RESULTS

Serum sVCAM-1 levels were elevated in our continuous ambulatory PD (CAPD) patients and showed a negative correlation with residual glomerular filtration rate (GFR; P < 0.001) and low-density lipoprotein (LDL) cholesterol level (P = 0.004), but a positive correlation with left ventricular mass index (P = 0.025). Using Kaplan-Meier analysis, overall survival rates at 2 years were 96.2%, 75.2%, and 50.6% for patients in the lower, middle, and upper tertiles of sVCAM-1 levels, respectively (P < 0.0001). Fatal and nonfatal cardiovascular event-free survival rates were 58.2%, 56.9%, and 19.4% for patients in the lower, middle, and upper tertiles, respectively (P < 0.0001). Using Cox regression analysis with adjustment for confounding covariates, every 100-ng/mL increase in sVCAM-1 level was associated with 8% (95% confidence interval, 1.03 to 1.13) and 5% (95% confidence interval, 1.00 to 1.10) increases in risk for death and fatal and nonfatal cardiovascular events, respectively. Its significance for all-cause mortality remained with additional adjusting for LDL cholesterol level, but was lost when adjusting for residual GFR. Its association with cardiovascular events became insignificant when adjusting for LDL cholesterol level or residual GFR. Furthermore, patients with both sVCAM-1 and CRP levels elevated at the 50th percentile or greater were associated with the greatest death and fatal and nonfatal cardiovascular event rates compared with those with either CRP or sVCAM-1 level elevated at the 50th percentile or greater.

CONCLUSION

Circulating sVCAM-1 levels show an important link with residual renal function, LDL cholesterol level, and cardiac hypertrophy in CAPD patients. Furthermore, residual renal function, which correlates inversely with circulating sVCAM-1 level, shows an important association with all-cause mortality and cardiovascular events and displaces sVCAM-1 level from the models for all-cause mortality and future cardiovascular events in CAPD patients. Additional study is needed to explore possible mechanistic links between inflammation, soluble adhesion molecules, residual renal function, and cardiac hypertrophy in CAPD patients.

Fibroblast growth factor-2 represses platelet-derived growth factor receptor-alpha (PDGFR-alpha) transcription via ERK1/2-dependent Sp1 phosphorylation and an atypical cis-acting element in the proximal PDGFR-alpha promoter

Platelet-derived growth factor (PDGF) is a potent mitogen and chemoattractant for vascular smooth muscle cells (SMCs) whose biological activity is mediated via its high affinity interaction with specific cell surface receptors. The molecular mechanisms governing the expression of PDGF receptor-alpha (PDGFR-alpha) are poorly understood. Here we demonstrate that PDGFR-alpha protein and transcriptional regulation in SMCs is under the positive regulatory influence of the zinc finger nuclear protein, Sp1. Electrophoretic mobility shift, competition, and supershift analysis revealed the existence of an atypical G-rich Sp1-binding element located in the PDGFR-alpha promoter -61 to -52 bp upstream of the transcriptional start site. Mutation of this sequence ablated endogenous Sp1 binding and activation of the PDGFR-alpha promoter. PDGFR-alpha transcription, mRNA, and protein expression were repressed in SMCs exposed to fibroblast growth factor-2 (FGF-2). This inhibition was rescued by the blockade of extracellular signal-regulated kinase-1/2 (ERK1/2). FGF-2 repression of PDGFR-alpha transcription was abrogated upon mutation of this Sp1-response element. FGF-2 stimulated Sp1 phosphorylation in an ERK1/2- but not p38-dependent manner, the growth factor enhancing Sp1 interaction with the PDGFR-alpha promoter. Mutation of residues Thr(453) and Thr(739) in Sp1 (amino acids phosphorylated by ERK) blocked FGF-2 repression of PDGFR-alpha transcription. These findings, taken together, demonstrate that FGF-2 stimulates ERK1/2-dependent Sp1 phosphorylation, thereby repressing PDGFR-alpha transcription via the -61/-52 element in the PDGFR-alpha promoter. Phosphorylation triggered by FGF-2 switches Sp1 from an activator to a repressor of PDGFR-alpha transcription, a finding previously unreported in any Sp1-dependent gene.

Mechanical stretch-induced apoptosis in smooth muscle cells is mediated by beta1-integrin signaling pathways

Recently we demonstrated that mechanical stress induces apoptosis of vascular smooth muscle cells in vitro and in vein grafts (Mayr et al. FASEB J. 2000;15:261-270). The current study was designed to investigate molecular mechanisms of mechanical stretch-induced apoptosis. Smooth muscle cells cultivated on silicone elastomer plates precoated with collagen I, elastin, laminin, or Pronectin were subjected to cyclic mechanical stretch. Interestingly, in response to mechanical stress, the number of apoptotic cells increased significantly in cells growing on collagen I-coated plates but not on other matrixes. We therefore thought that receptors mediating binding to collagen I, such as integrin beta1 containing receptors, might be involved in signaling pathways leading to stretch-induced apoptosis. On collagen plates, mechanical stress rapidly activated p38 MAPK that phosphorylated p53 in smooth muscle cells. Lack of functional Rac completely abrogated p38 MAPK-p53 activation as well as apoptosis. Furthermore, mechanical stress resulted in increases of both integrin beta1 protein expression and activity as identified by Western blotting and Shc immunoprecipitation assays. Treatment with a beta1-integrin-blocking antibody or integrin signaling inhibitor cytochalasin B but not growth factor receptor inhibitor suramin abrogated both stretch-induced phosphorylation of p38 MAPK and p53 expression. Akin to the inhibition of p38 MAPK-p53 signaling, pretreatment with a beta1-integrin-blocking antibody or cytochalasin B but not suramin inhibited stretch-induced apoptosis on collagen plates. These results suggest that mechanical stress-induced apoptosis in vascular smooth muscle cells is mediated by beta1-integrin-rac-p38-p53 signaling pathways.

Is angiotensin I-converting enzyme a "master" disease gene?

Clustering of diseases has been appreciated by health insurers and epidemiologists for some time. Co-morbidity suggests shared pathways of disease. It is by now well agreed that common diseases have a strong genetic component. Here we present evidence that the angiotensin I-converting enzyme (ACE) deletion/deletion (D/D) genotype is associated with a large number of common adult diseases, including cardiovascular disease, cancer, and psychiatric disease. Since the ACE D/D genotype has been shown to be associated with increased levels of tissue ACE expression at the protein level, these data suggest that overactivity of ACE may be involved in the pathogenesis of common diseases, as well as the utility of effective ACE inhibition in their treatment and, perhaps, prevention.

Targeted overexpression of CCAAT/enhancer-binding protein-delta evokes enhanced gene transcription of platelet-derived growth factor alpha-receptor in vascular smooth muscle cells

Platelet-derived growth factor (PDGF) is thought to play a significant role in various models of vascular remodeling, particularly in the early process of vascular diseases. Its action is mediated by its specific receptor, the PDGF receptor. The PDGF alpha-receptor (PDGFalphaR) plays an important role in the growth and proliferation of vascular smooth muscle cells (VSMCs), and its gene expression is thought to be regulated by several potential transcriptional nuclear factors. However, the detailed mechanisms of tissue-specific transactivation of the PDGFalphaR gene in VSMCs remain to be clarified. We have previously demonstrated that the rat PDGFalphaR gene contains an enhancer core sequence for CCAAT/enhancer-binding proteins (C/EBPs) in its promoter region, and we have also suggested that C/EBP-delta is the principal factor involved in the induction of tissue-specific transcriptional activity of the PDGFalphaR gene in VSMCs. To explore the definitive roles of C/EBP-delta protein on PDGFalphaR gene transcription in VSMCs, we developed C/EBP-delta transgenic rats by using a chimeric fusion gene of the mouse smooth muscle alpha-actin promoter and an entire coding region of rat C/EBP-delta cDNA. This report describes the first successful targeted overexpression of C/EBP-delta capable of inducing PDGFalphaR gene transcription and modifying cell proliferative activity to PDGFs. Targeted overexpression of C/EBP-delta evokes high levels of PDGFalphaR gene expression, susceptibility to VSMC growth, and proliferation of VSMCs to PDGFs. The results obtained reveal evidence of a new role and new functional significance of C/EBP-delta on VSMC growth via the PDGFalphaR during the process of vascular remodeling and atherosclerosis.

Alpha(1)-adrenoceptors (alpha(1)-AR) and vascular smooth muscle cell growth

BACKGROUND

Smooth muscle cells in vascular tissue, like tissue within the urogenital sinus, undergo growth and proliferation.

METHODS

This review attempts to compare and contrast the mechanisms and controlling factors involved in prostatic and vascular tissue. There is a particular focus on the role of catecholamines and alpha-adrenoceptors (alpha-ARs), and on the effects of alpha(1)-AR antagonists (blockers) on cellular dynamics. RESULTS AND CONCLUSIONS The situation in vascular tissue appears analagous to that in prostatic tissue. Certain AR-antagonists, in addition to altering smooth muscle contraction, may have other actions on cellular dynamics.

Cyclic strain modulates resistance to oxidant stress by increasing G6PDH expression in smooth muscle cells

Vascular smooth muscle cells (VSMC) may be subjected to mechanical forces, such as cyclic strain, that promote the formation of reactive oxygen species (ROS). We hypothesized that VSMC modulate this adverse milieu by increasing the expression of glucose-6-phosphate dehydrogenase (G6PDH) to maintain or restore intracellular glutathione (GSH) levels. Cyclic strain increased superoxide formation, which resulted in diminished GSH because of an increase in oxidized glutathione formation; there was also an increase in glutathione peroxidase and glutathione reductase activities. G6PDH activity and protein expression were enhanced concomitant with decreases in GSH levels and remained elevated until intracellular GSH levels were restored. To confirm the role of G6PDH in repleting GSH stores, we inhibited G6PDH activity with DHEA or inhibited enzyme expression with an antisense oligodeoxynucleotide. Diminished G6PDH activity or expression was associated with persistently depleted GSH levels and inhibition of the cyclic strain-mediated increase in glutathione reductase activity. These observations demonstrate that cyclic strain promotes oxidant stress in VSMC, which, in turn, induces G6PDH expression. When G6PDH is inhibited, GSH levels are not restored because of impaired glutathione reductase activity. These data suggest that G6PDH is a critical determinant of the response to oxidant stress in VSMC.

Coronary microvascular endothelial cells cosecrete angiotensin II and endothelin-1 via a regulated pathway

Although endothelial cells produce angiotensin II (ANG II) and endothelin-1 (ET-1), it is not clear whether a single cell produces both peptides, with cosecretion in response to stimulation, or whether different subpopulations of endothelial cells secrete one or the other peptide, with secretion in response to different stimuli. Exposure of cultured coronary microvascular endothelial cells to cycloheximide for 60 min had no effect on ANG II or ET-1 secretion. This result suggested the existence of a preformed intracellular pool of ANG II and ET-1, which is a precondition for regulated secretion. Exposure of endothelial cells to isoproterenol, high extracellular potassium, or cadmium, all of which stimulate peptide secretion via different signaling pathways, significantly (P > 0.001) increased the secretion of both ANG II and ET-1 in a cell size-dependent manner. Sodium nitroprusside and S-nitroso-N-acetyl penicillamine significantly (P > 0.001) decreased ANG II and ET-1 secretion, whereas N(omega)-nitro-L-arginine-methyl ester enhanced it. The similar regulation of ANG II and ET-1 secretion and the presence of both peptides around individual endothelial cells indicate that the autocrine/paracrine regulation of cardiovascular function by endothelial cells is accomplished via cosecretion of ANG II and ET-1.

Phenotypic alterations in senescent large-vessel and microvascular endothelial cells

Endothelial cell senescence likely plays a key role in age-associated vascular diseases. A close relationship between in vitro and in vivo senescence of endothelial cells has been established. Therefore, elucidating the structural and functional changes occurring during long-term cultures of endothelial cells would contribute to clarifying the pathogenesis of vascular disorders in the elderly. We investigated the effects of replicative senescence on the architecture of bovine aortic vs microvascular endothelial cells. A marked increase in cell area was observed in both cell types, whereas dramatic morphological alterations were detected in microvascular endothelial cells only. The latter also showed age-associated reorganization of the actin cytoskeleton. Finally, both aortic and microvascular endothelial cells lost their migratory response to basic fibroblast growth factor with age. Our results highlight dramatic structural and functional alterations in senescent endothelial cells. Such rearrangements might account for in vivo endothelial cell alterations involved in age-associated vascular dysfunction.

Ras/Rac-Dependent activation of p38 mitogen-activated protein kinases in smooth muscle cells stimulated by cyclic strain stress

p38, a subfamily of the mitogen-activated protein kinases (MAPKs), is a crucial signal transducer between a variety of extracellular stimuli and gene expression in mammalian cells. This kinase is activated in cultured cells stimulated by heat shock, osmotic stress, and proinflammatory cytokines, but a similar activation of p38 MAPKs in vascular smooth muscle cells (SMCs) stimulated by mechanical stress has yet to be studied. We studied signal pathways leading to time- and strength-dependent p38 activation in rat SMCs in response to cyclic strain stress. p38 phosphorylation in stressed SMCs showed maximal activation at 10 minutes. This activation was significantly inhibited by pretreatment of the SMCs with pertussis toxin, a G-protein antagonist, and enhanced by treatment with suramin, a growth factor receptor antagonist, but opposite effects in the activation of extracellular signal-regulated kinases stimulated by mechanical forces were found. p38 activation was markedly reduced in stressed SMCs after protein kinase C depletion. Interestingly, SMC lines stably expressing dominant-negative ras (ras N17) or rac1 (rac1 N17) almost abolished p38 phosphorylation induced by cyclic strain stress. When p38 activation was inhibited by the specific inhibitor SB 202190, SMC migration, determined in a Boyden chamber in response to stimulation with platelet-derived growth factor-BB, and SMC proliferation, stimulated by cyclic strain stress, were abrogated. Thus, we provide the first evidence that cyclic strain stress rapidly activates p38 MAPKs via activation of protein kinase C ras/rac signal pathways, suggesting that p38 MAPKs are important signal transducers mediating the mechanical stress-induced cell responses essential for SMC migration and proliferation.

Gene therapy of hypertensive vascular injury

Hypertension and vascular injury usually require prolonged treatment, and compliance is a key to efficacy for pharmacologically-based antihypertensive therapy. Gene therapy has the potential to be long lasting, with few side effects. Recent studies have provided promising results, in which hypertension can be treated by either augmentation of vasodilation or inhibition of vasoconstriction through gene transfer in experimental models. Gene transfer is also becoming useful for the study of mechanisms of physiologic and pathophysiologic conditions, including hypertension. In this mini-review, we summarize some recent studies in this area of research, and suggest some areas where progress is needed to advance the research toward gene therapy.

Cyclic strain stress-induced mitogen-activated protein kinase (MAPK) phosphatase 1 expression in vascular smooth muscle cells is regulated by Ras/Rac-MAPK pathways

Recently, we demonstrated that mechanical stress results in rapid phosphorylation or activation of platelet-derived growth factor receptors in vascular smooth muscle cells (VSMCs) followed by activation of mitogen-activated protein kinases (MAPKs) and AP-1 transcription factors (Hu, Y., Bock, G., Wick, G., and Xu, Q. (1998) FASEB J. 12, 1135-1142). Herein, we provide evidence that VSMC responses to mechanical stress also include induction of MAPK phosphatase-1 (MKP-1), which may serve as a negative regulator of MAPK signaling pathways. When rat VSMCs cultivated on a flexible membrane were subjected to cyclic strain stress (60 cycles/min, 5-30% elongation), induction of MKP-1 proteins and mRNA was observed in time- and strength-dependent manners. Concomitantly, mechanical forces evoked rapid and transient activation of all three members of MAPKs, i.e. extracellular signal-regulated kinases (ERKs), c-Jun NH(2)-terminal protein kinases (JNKs), or stress-activated protein kinases (SAPKs), and p38 MAPKs. Suramin, a growth factor receptor antagonist, completely abolished ERK activation, significantly blocked MKP-1 expression, but not JNK/SAPK and p38 MAPK activation, in response to mechanical stress. Interestingly, VSMC lines stably expressing dominant negative Ras (Ras N17) or Rac (Rac N17) exhibited a marked decrease in MKP-1 expression; the inhibition of ERK kinases (MEK1/2) by PD 98059 or of p38 MAPKs by SB 202190 resulted in a down-regulation of MKP-1 induction. Furthermore, overexpressing MKP-1 in VSMCs led to the dephosphorylation and inactivation of ERKs, JNKs/SAPKs, and p38 MAPKs and inhibition of DNA synthesis. Taken together, our findings demonstrate that mechanical stress induces MKP-1 expression regulated by two signal pathways, including growth factor receptor-Ras-ERK and Rac-JNK/SAPK or p38 MAPK, and that MKP-1 inhibits VSMC proliferation via MAPK inactivation. These results suggest that MKP-1 plays a crucial role in mechanical stress-stimulated signaling leading to VSMC growth and differentiation.

Inhibition of neointima hyperplasia of mouse vein grafts by locally applied suramin

BACKGROUND

Saphenous vein grafts are widely used for aortocoronary bypass surgery as treatment for severe atherosclerosis and often are complicated by subsequent occlusion of the graft vessel.

METHODS AND RESULTS

We described a mouse model of venous bypass graft arteriosclerosis that can be effectively retarded by locally applied suramin, a growth factor receptor antagonist. Mouse isogeneic vessels of the vena cava veins pretreated with suramin were grafted end to end into the carotid arteries and enveloped with a mixture of suramin (1 mmol/L) and pluronic-127 gel. In the untreated group, vessel wall thickening was observed as early as 1 week after surgery and progressed to 4-fold and 10-fold the original thickness in grafted veins at 4 and 8 weeks, respectively. Pluronic-127 gel alone did not influence neointima formation. Suramin treatment reduced the neointima hyperplasia 50% to 70% compared with untreated controls. Immunohistochemical studies demonstrated that a significant proliferation of vascular smooth muscle cells (SMCs) constituted neointimal lesions between 4 and 8 weeks. The majority of SMCs expressed platelet-derived growth factor (PDGF) receptors-alpha and -beta, which were significantly reduced by suramin treatment. In vitro studies indicated that suramin completely blocked PDGF receptor activation or phosphorylation stimulated by PDGF-AB, inhibited activation of mitogen-activated protein kinase (ERK) kinases (MEK1/2) and ERK1/2, and abrogated transcription factor AP-1 DNA-binding activity.

CONCLUSIONS

Suramin inhibited SMC migration and proliferation in vivo and in vitro by blocking PDGF-initiated PDGF receptor and MAPK-AP-1 signaling. These findings indicate that locally applied suramin is effective in a mouse model of venous bypass graft arteriosclerosis.

Regulation of platelet-activating factor (PAF) activity in human diseases by phospholipase A2 inhibitors, PAF acetylhydrolases, PAF receptor antagonists and free radical scavengers

The aim of this review is to present recent findings indicating the likely involvement of platelet-activating factor (PAF) in human diseases, and possible ways of alleviating its harmful effects. PAF is a potent proinflammatory mediator and promotes adhesive interactions between leukocytes and endothelial cells, leading to transendothelial migration of leukocytes, by a process of juxtacrine intercellular signalling. This process leads to activation of leukocytes and the release of reactive oxygen radicals, lipid mediators, cytokines and enzymes. These reaction products subsequently contribute to the pathological features of various inflammatory diseases. The reactive oxygen radicals cause low density lipoprotein (LDL) oxidation which mediates the development of atherosclerosis. Oxidized LDL may damage cellular and subcellular membranes, leading to tissue injury and cell death. Among the therapeutic approaches considered are agents that inhibit/degrade proinflammatory mediators and thereby have anti-inflammatory and/or anti-atherogenic potential. These include inhibitors of phospholipase A2 activity, PAF-acetylhydrolases, PAF antagonists and free radical scavengers/antioxidants, the latter protecting against oxidized LDL-induced cytotoxicity.

A high level of CCAAT-enhancer binding protein-delta expression is a major determinant for markedly elevated differential gene expression of the platelet-derived growth factor-alpha receptor in vascular smooth muscle cells of genetically hypertensive rats

-Platelet-derived growth factor-alpha receptor (PDGF-alphaR) expression is markedly elevated in cultured vascular smooth muscle cells (VSMCs) from spontaneously hypertensive rats (SHR) when compared with normotensive rat strains, Sprague-Dawley, Wistar, and Wistar-Kyoto rats (WKY). This "almost-all-or-none" type of differential expression strongly suggests that PDGF-alphaR or its transcription-regulating mechanisms or factors are significantly related to genetic hypertension. To evaluate the role of PDGF-alphaR in vascular remodeling and hypertension, we have investigated the underlying molecular mechanism. We have recently shown that the regulatory domain responsible for this difference is localized to the PDGF-alphaR promoter region between -246 and -139, which contains an enhancer core sequence specific for CCAAT-enhancer binding proteins (C/EBPs). We defined the roles of this element for hypertensive strain-specific PDGF-alphaR gene transcription. DNA-protein binding studies by competition in electromobility shift and supershift assays revealed that 2 members, C/EBP-beta and C/EBP-delta, are mainly responsible for DNA-protein complex formation; the former acts as a transcriptional repressor and the latter as an activator of the PDGF-alphaR gene, respectively. Western or Northern blot analyses supported evidence for high expression of C/EBP-delta seen only in SHR-derived VSMCs. Furthermore, forced expression of C/EBP-delta transactivated the transcriptional efficiency of the PDGF-alphaR gene even in WKY-derived VSMCs, whereas that of C/EBP-beta had an opposite effect in SHR-derived VSMCs. These findings indicate that differential expression of members of the C/EBP family, mainly C/EBP-delta and possibly C/EBP-beta, are responsible for the strain-specific gene transcription of PDGF-alphaR in VSMCs.

Novel cis element for tissue-specific transcription of rat platelet-derived growth factor beta-receptor gene

Platelet-derived growth factor (PDGF) and its receptors are widely expressed in several tissues in the stage of cellular growth and development. In adulthood, PDGF beta-receptor (PDGFbetaR) is mainly detected in pathological conditions such as atherosclerotic lesions and injured vascular wall. The purpose of the present study was to elucidate the underlying mechanism of PDGFbetaR gene expression under pathological conditions in vascular smooth muscle cells (VSMC) and to identify the important cis elements responsible for tissue-specific gene transcription. Gel mobility shift assay and supershift assay indicated that the CCAAT motif located at -67 (C67) was mainly interacted with NF-YC, and this element drove the basal promoter activity of the gene as a putative promoter. On the other hand, another important sequence essential for the basal transcription was found at a 30-bp region (R30) spanning -150 to -121. To test whether R30 actually regulates the tissue-specific transcription of PDGFbetaR gene, electromobility shift pattern was compared between VSMC and hepatoma cell line (HTC). We obtained the result that DNA-protein complex seen only in nuclear extracts from HTC suppressed the promoter activity in HTC in a tissue-specific manner. Furthermore, cis element decoy transfection experiments for C67 and R30 also revealed that both elements were functionally important in mRNA expression of PDGFbetaR in VSMC. From these results, we concluded that the basal activity of PDGFbetaR gene expression was transactivated by the interaction or coordination of both C67 and R30, and the latter one mainly controlled the tissue-specific gene expression in VSMC.

Tissue angiotensin II as a modulator of erectile function. I. Angiotensin peptide content, secretion and effects in the corpus cavernosum

PURPOSE

Although Angiotensin II (Ang II) is a major modulator of regional blood flow in the extracavernosal segments of the vascular bed, its role in erectile function is unknown. The corpus cavernosum penis is a modified vascular tissue that contains endothelial and smooth muscle cells. In other segments of the vascular bed, these cell types produce Ang II. Therefore, we explored the presence and function of an Ang II producing paracrine system in the corpus cavernosum.

METHODS

The angiotensin content of the human corpus cavernosum was measured by radioimmunoassay. The distribution pattern of Ang II containing cells within the corpus cavernosum was assessed by an immunohistochemical technique, and the rate of its secretion was determined by superfusion. The effects of Ang II and its antagonist, losartan, on intracavernosal pressure were determined under in vivo conditions, in anesthetized dogs.

RESULTS

Human corpus cavernosum contained 1178 +/- 223 (SEM) fmol Ang II, 528 +/- 171 fmol Ang I, 475 +/- 67 fmol des-asp-Ang I, and 1897 +/- 371 fmol des-asp-Ang II/gm. tissue (n = 4). Ang II was found mainly in endothelial cells lining blood vessels and smooth muscle bundles within the corpus cavernosum. Superfused cavernosal tissue secreted immuno-reactive Ang II (Ang II(ir)) at a rate of 57 +/- 36.5 fmol Ang II(ir)/gm. tissue/minute (n = 10). The amount of Ang II released per gram of tissue in an hour was 3-fold greater than the Ang II content/gm. tissue, suggesting a local production of Ang II. Papaverine and prostaglandin E1 suppressed Ang II secretion significantly (p <0.001, p = 0.013). The responsiveness to inhibition was a function of the initial rate of Ang II secretion. Tissue samples with a high rate of secretion were less responsive to the inhibitors than tissue that secreted small amounts of Ang II (n = 6). In anesthetized dogs, intra-cavernosal injection of Ang II terminated spontaneous erections, while losartan increased the intracavernosal pressure in a dose dependent manner up to the mean arterial pressure (n = 4).

CONCLUSIONS

The corpus cavernosum produces and secretes physiologically relevant amounts of Ang II. The rate of Ang II secretion can be modulated by pharmacologic agents that regulate cytosolic calcium levels and are used clinically to treat erectile dysfunction. Intracavernosal injection of Ang II causes contraction of cavernosal smooth muscle and terminates spontaneous erection in anesthetized dog, while administration of an Ang II receptor antagonist results in smooth muscle relaxation and thus erection.

Mouse model of venous bypass graft arteriosclerosis

Saphenous vein grafts are widely used for treatment of severe atherosclerosis via aortocoronary bypass surgery, a procedure often complicated by later occlusion of the graft vessel. Because the molecular mechanisms of this process remain largely unknown, quantitative models of venous bypass graft arteriosclerosis in transgenic mice could be useful to study this process at the genetic level. We describe herein a new model of vein grafts in the mouse that allows us to take advantage of transgenic, knockout, or mutant animals. Autologous or isogeneic vessels of the external jugular or vena cava veins were end-to-end grafted into carotid arteries of C57BL/6J mice. Vessel wall thickening was observed as early as 1 week after surgery and progressed to 4-, 10-, 15-, and 18-fold original thickness in grafted veins at age 2, 4, 8, and 16 weeks, respectively. The lumen of grafted veins was significantly narrowed because of neointima hyperplasia. Histological and immunohistochemical analyses revealed three lesion processes: marked loss of smooth muscle cells in vein segments 1 and 2 weeks after grafting, massive infiltration of mononuclear cells (CD11b/18+) in the vessel wall between 2 and 4 weeks, and a significant proliferation of vascular smooth muscle cells (alpha-actin+) to constitute neointimal lesions between 4 and 16 weeks. Similar vein graft lesions were obtained when external jugular veins or vena cava were isografted into carotid arteries of C57BL/6J mice. Moreover, no significant intima hyperplasia in vein-to-vein isografts was found, although there was leukocyte infiltration in the vessel wall. Thus, this model, which reproduces many of the features of human vein graft arteriosclerosis, should prove useful for our understanding of the mechanism of vein graft disease and to evaluate the effects of drugs and gene therapy on vascular diseases.

Assessing the coronary circulation in hypertension

Systemic arterial hypertension is one of the major risk factors for coronary artery disease, coronary microangiopathy, and left ventricular hypertrophy, all of which can potentially lead to cardiac failure and sudden cardiac death. Coronary flow reserve is defined as the maximal increase in coronary flow above its resting, autoregulated level for a given perfusion pressure. In arterial hypertension functional and structural alterations are observed at the level of epicardial vessels as well as in resistive vessels requiring sophisticated approaches to assess coronary flow reserve and thus myocardial perfusion. Electrocardiographic tests and echocardiography can be regarded as monitoring and screening methods. Myocardial scintography is useful to semiquantitatively estimate hypertension-associated perfusion abnormalities, whereas positron emission tomography provides the only quantitative approach of a non-invasive technique for myocardial blood flow measurement. Invasive methods for the assessment of coronary blood flow need cardiac catheterization procedures, such as techniques requiring catheterization of the coronary sinus, angiographic methods, and guidewire based methods. Thermodilution and venous oxymetry in the coronary sinus systematically underestimate coronary flow reserve and are thus considered as only semiquantitative approaches. In contrast, the gas chromatographic argon method allows a quantitative measurement of coronary blood flow at baseline and during maximum vasodilation; thus it is possible to distinguish between an altered autoregulated and maximal flow as the major cause of a reduced coronary flow reserve and to evaluate long-term therapeutic interventions in hypertensive hearts. Videodensitometric and angiographic methods should be restricted only to patients with coronary microangiopathy or with coronary single-vessel disease. Guidewire-based Doppler techniques are suitable to semiquantitatively assess coronary flow reserve with a considerable spatial and time resolution. Myocardial biopsies may gain insight into hypertension-associated structural alterations in small arterioles. Long-term treatment of hypertensive heart disease aims to normalize blood pressure, to reduce left ventricular hypertrophy and to achieve cardioreparation including reversal of the abnormal structure and function of coronary circulation. Based on the different methods for assessment of coronary circulation the therapeutic value of different classes of antihypertensive therapeutics will be evaluated in this overview.

Decline of shear stress-induced activation of extracellular signal-regulated kinases, but not stress-activated protein kinases, in in vitro propagated endothelial cells

We investigated the involvement of mitogen-activated protein kinase (MAPK) signal transduction pathways in human endothelial cells in response to shear stress and alterations of these kinases in in vitro-propagated endothelial cells (ECs). Potent activation (10-fold) of extracellular signal-regulated kinase (ERK2), a member of the MAPK family, occurred within 10 min of shear stress (5 dynes/cm2), whereupon rapid inactivation ensued. Shear stress also induced activation of stress-activated protein kinase (SAPK) or c-Jun NH2-terminal protein kinase (JNK) in ECs. Suramin pretreatment completely inhibited shear stress stimulation of ERK2, but not SAPK/JNK, highlighting a role for growth factor receptors in ERK activation. Translocation of ERK2 from the cytoplasm to the nucleus was observed in shear-stressed endothelial cells. In addition, we compared activities of MAPKs in shear-stressed cells derived from passages 4 and 10 (older). The magnitude of ERK2 activation was significantly lower in aged ECs compared to those of passage 4, while SAPK/JNK was not altered in the in vitro aged ECs. A similar level of ERK2 activation was found in both young and older cells stimulated with phorbol-12-myristate-13-acetate (PMA), indicating an age-related alteration of the plasma membrane. Taken together, these findings suggest that MAP kinase activation may be crucial for the expression of many genes in ECs stimulated by shear stress, and that an alteration in MAPK activities could contribute to the age-related decline in proliferative capacity.

Activation of PDGF receptor alpha in vascular smooth muscle cells by mechanical stress

Hypertension increases mechanical force on the arterial wall by as much as 30%, resulting in marked alterations in signal transductions and gene expression in vascular smooth muscle cells (VSMCs) that contribute to matrix protein synthesis, cell proliferation, and differentiation. How the mechanical stimuli are converted into a biological signal in cells has yet to be studied. We investigated the role of both cyclic strain and shear stresses in initiating the cellular signaling on cultured VSMCs and found that mechanical forces evoked activation of mitogen-activated protein kinases, followed by enhanced DNA binding activity of transcription factor AP-1. Physical forces rapidly induced phosphorylation of platelet-derived growth factor receptor (PDGFR) alpha, an activated state. When GRB2, an adapter protein, was immunoprecipitated from treated VSMCs followed by Western blot analysis with anti-phosphotyrosine, -PDGFR alpha, and -GRB2 antibodies, respectively, phosphotyrosine positive staining was observed on PDGFR alpha bands of the same blot in stretch-stressed VSMCs, supporting the mechanical stress-induced activation of PDGFR alpha. Conditioned medium from stretch-stressed VSMCs did not result in PDGFR alpha phosphorylation, and antibodies binding to all forms of PDGFs did not block stress-induced PDGFR alpha activation. Thus, mechanical stresses may directly perturb the cell surface or alter receptor conformation, thereby initiating signaling pathways normally used by growth factors.

Stimulatory effect of lipoprotein (a) on proliferation of human mesangial cells: role of lipoprotein (a) in renal disease

As lipoprotein (a) [Lp(a)] abnormalities would accelerate glomerular injury, we studied the effect of Lp (a) on proliferation of cultured human mesangial cells (MC). Transfection of human apo (a) gene into human hepatoma cells, HepG2 cells, producing human apo B, resulted in the formation of Lp (a), while no Lp (a) was detected in control cells. In contrast, free apo (a) was detected in the medium of apo (a)-transfected MC. Incubation of cultured medium of HepG2 cells transfected with apo (a) gene with MC resulted in a significant increase in cell number compared to control (P<0.01). In contrast, little effect of transfection of apo (a) gene directly into MC on growth of MC was observed. Of importance, addition of LDL into the medium of MC transfected with apo (a) vector resulted in a significant increase in number of MC compared to control, whereas LDL did not show any effects on MC growth. As active TGF-beta was not detected in the medium of MC, and addition of neutralizing anti-TGF-beta antibody did not alter growth of MC, Lp (a) stimulated growth of MC via the independent mechanisms from the inhibition of TGF-beta activation.

Conditioned medium from HepG2 cells transfected with human apolipoprotein(a) gene stimulates growth of human vascular smooth muscle cells: effects of overexpression of human apolipoprotein(a) gene

Lipoprotein(a) [Lp(a)] is well known to stimulate growth of vascular smooth muscle cells (VSMCs), resulting in atherosclerosis. Its mechanism is postulated to be decreased in active transforming growth factor (TGF)-beta. However, the exact mechanisms and cellular processing from apolipoprotein(a) [apo(a)] to Lp(a) have not yet been clarified because no cultured cells producing apo(a) are available. Therefore, it is necessary to establish apo(a)-producing cells to study the role of apo(a). We evaluated the effects of overexpression of human apo(a) gene on human aortic VSMC growth. First, we tested whether transfection of apo(a) gene into human hepatoma cells, HepG2 cells, producing human apoB resulted in the formation of Lp(a). Transfection of apo(a) gene into HepG2 cells resulted in detectable levels of Lp(a) in the medium, as assessed by ELISA and Western blot, whereas no Lp(a) was detected in the medium of HepG2 cells transfected with control vector and untransfected HepG2 cells. Expression of apo(a) mRNA was also confirmed by reverse transcription-polymerase chain reaction. In contrast, Western blotting showed a single band detected by specific anti-apo(a) antibody, but not anti-apoB antibody, in the medium of apo(a)-transfected VSMCs. These results demonstrate that Lp(a) can be formed from apo(a) on HepG2 cells, whereas transfection of apo(a) gene into VSMCs resulted in the production of apo(a) alone but not Lp(a). Next, we examined the biological effects of overexpression of apo(a) gene on growth of VSMCs and endothelial cells. Incubation of cultured medium of HepG2 cells transfected with apo(a) gene with human VSMCs or endothelial cells resulted in a significant increase in cell number compared with the conditioned medium of HepG2 cells transfected with control vector. In contrast, transfection of apo(a) gene directly into VSMCs caused no significant effect on VSMC growth. Therefore, we measured TGF-beta concentration in the conditioned medium of VSMCs. However, using ELISA, only latent but not active TGF-beta was detected in the medium of VSMCs. Moreover, addition of neutralizing anti-TGF-beta antibody did not alter VSMC growth. These results suggest that Lp(a) could stimulate growth of VSMCs via the independent mechanisms from the inhibition of TGF-beta activation. Overall, these data demonstrate that overexpression of apo(a) gene in cells producing apoB results in formation of Lp(a), resulting in a mitogenic action on human endothelial cells and VSMCs. These results provide new information to understand the mechanisms of the mitogenic action of Lp(a) and suggest the role of Lp(a) in the pathogenesis of atherosclerosis.

Molecular structure and function of rat platelet-derived growth factor beta-receptor gene promoter

OBJECTIVE

To understand the regulatory mechanism of platelet-derived growth factor beta-receptor gene expression.

METHODS

A 1.7 kb genomic fragment was obtained from a rat genomic library. After we had determined an entire sequence of this fragment, transcription start sites were determined both by primer extension analysis and by riboprobe mapping. We performed a functional promoter assay by using a dual-luciferase reporter system. Progressive 5'-deletions of the fragment and site-directed mutagenesis for the CCAAT motif located at -67 or -94 were used for the assay, and their promoter activities in vascular smooth muscle cells were assessed. Gel-mobility shift analysis was also performed for the CCAAT motif at -67. Effects of the upstream sequence spanning -310 through -120 on heterologous gene promoters were also investigated.

RESULTS

Multiple transcription start sites were observed in the 5'-flanking region, and the 1.7 kb sequence was actually active as a functional promoter in vascular smooth muscle cells. Two important sequences responsible for the basal transcriptional activity were identified by the functional promoter assay. One was the CCAAT motif at -67 which acts as a promoter itself, and the other was the upstream region spanning -310 through -210 which positively regulates the basal promoter activity.

CONCLUSION

The basal promoter activity of the rat platelet-derived growth factor beta-receptor gene is mainly regulated by the interaction or coordination of two sequences, the CCAAT motif and the upstream control element.

Immunohistochemical analysis of growth factor expression and localization in gastric coronary vein of cirrhotic patients

This study was designed to investigate the expression and localization of PDGF, bFGF, EGF, and TGF alpha in gastric coronary vein of cirrhotic (n = 30) and non-cirrhotic patients (n = 10) using immunohistochemical technique. The strongly positive immunostaining rate were 93%, 89%, 70% and 68% respectively in cirrhotic patients. The immunostaining was negative in non-cirrhotic patients. The damage to endothelium, hypertrophy and hyperplasia of vascular smooth muscle cells and vascular remodeling were seen in gastric coronary vein of cirrhotic patients. These results suggested that gastric coronary vein could produce growth factor during cirrhosis, the growth factor can act on the vascular function and/or structure via autocrine-paracrine mechanism.

Mechanical strain tightly controls fibroblast growth factor-2 release from cultured human vascular smooth muscle cells

Although fibroblast growth factor-2 (FGF-2) participates in the response to vascular injury, the role of cellular deformation in FGF-2 release is incompletely understood. To test the hypothesis that mechanical strain tightly controls FGF-2 release, a novel device was used to impose homogeneous and uniform biaxial strain to human vascular smooth muscle cells. Release of FGF-2 increased with the number of cycles of strain (14%, 1 Hz); 1, 9, and 90 cycles of strain, respectively, released 0.55 +/- 0.06%, 2.9 +/- 0.3%, and 5.5 +/- 1.3% of the total cellular FGF-2 (versus 0.00 +/- 0.40% for control, P < .05), but release was not further increased for strain of 90 to 90,000 cycles. Mechanical release of FGF-2 depended on both the frequency and amplitude of deformation. For example, strain (90 cycles, 1 Hz) at 4% amplitude released only 0.1 +/- 0.1% of the total FGF-2, but strain at 14% and 33% amplitudes, respectively, released 5.7 +/- 0.5% and 19.0 +/- 3.0% of the FGF-2 cellular pool (P < .05), suggesting a strain amplitude threshold for FGF-2 release. Injury to a subpopulation of cells increased with the frequency and amplitude of strain, but cells were not injured by strains below 10% amplitude. Strain following pretreatment with heparin released 12.6 +/- 1.6% of the total FGF-2 (versus 15.8 +/- 0.9% for strain alone, P < .05), indicating that most FGF-2 was liberated from the nuclear or cytoplasmic pools and not from low-affinity extracellular receptors. Conversely, strain in the presence of heparin released 25.2 +/- 3.5% of the total FGF-2 (versus 15.6 +/- 2.6% for strain alone, P < .05). Thus, cellular strain closely modulates the release of intracellular FGF-2 from human vascular smooth muscle cells, but FGF-2 release is negligible in response to the smaller strains that occur in the normal artery. In addition, larger mechanical strains lead to transfer of intracellular FGF-2 to the extracellular low-affinity receptors, where FGF-2 may be displaced by heparin. These observations provide insight into the mechanisms by which deforming vascular injury, such as that produced by arterial interventions, may elicit a proliferative response.

Induction of growth hormone receptor and insulin-like growth factor-I mRNA in aorta and caval vein during hemodynamic challenge

Induction of two-kidney, one clip hypertension (renal hypertension) is characterized by a slow increase in left ventricular tension and aortic wall stress, as opposed to aortocaval fistula or shunt volume overload, which induces a marked and rapid onset of wall stress in the caval vein and right ventricle. In the present study, we applied hemodynamic challenge to study the growth response involving gene expression of insulin-like growth factor-I (IGF-I) and growth hormone receptor (GH-R) mRNA in aorta and caval vein. Volume overload and pressure overload were induced in Wistar rats by means of shunt and renal hypertension, respectively. Systolic pressure was measured before excision of the great vessels, which was performed between 2 and 12 days postoperatively. Aortic and caval vein IGF-I and GH-R mRNA expressions were measured by means of a solution hybridization assay, and the caval vein was analyzed for IGF-I protein by immunohistochemistry. In the volume-distended but not pressurized caval vein in shunt rats, verified by telemetry recordings, there was an eightfold increase in IGF-I and 3.5-fold increase in GH-R mRNA at day 4 versus control. The IGF-I protein appeared to be localized in smooth muscle cells. In the aorta of the renal hypertension group, changes were of a slower onset. At day 7, there was a fourfold increase in IGF-I and five-fold increase of GH-R mRNA expressions versus sham-operated rats. Both the shunt caval vein and renal hypertension aorta showed evidence of a structural adaptation of the growth response. The present study suggests that acute elevation in vascular wall stress is an important triggering factor for overexpression of IGF-I and GH-R mRNA in great vessels. The growth hormone/insulin-like growth factor axis may be an important link in mediating structurally adaptive growth responses in the blood vessel wall.

Evidence for a multifactorial process involved in the impaired flow response to nitric oxide in hypertensive patients with endothelial dysfunction

The assessment of endothelial function in hypertensive patients receiving acetylcholine has revealed conflicting results. Whether an impaired flow response to acetylcholine is explained solely by a diminished endothelial synthesis of nitric oxide (NO) remains unclear as yet. In the present study, we tested the hypothesis that mechanisms other than reduced NO synthesis contribute to the hypertension-associated impairment of endothelium-dependent vasodilation. Therefore, the dilatory response to endogenous and exogenous NO was measured in resistance arteries and cutaneous microvessels in the forearm circulation of 12 normotensive individuals and 17 hypertensive patients. In addition, the overall dilatory capacity was assessed by peak flow during reactive hyperemia after 3 minutes of ischemia. Forearm blood flow was quantified by venous occlusion plethysmography at rest, during application of the NO donor sodium nitroprusside, and during stimulation of endogenous NO synthesis by acetylcholine and bradykinin. Blood flow velocity in the cutaneous microvasculature was measured with laser-Doppler flowmetry in parallel. Resting forearm flow was comparable in both groups (3.1 +/- 0.2 and 3.4 +/- 0.2 mL.min-1.100mL-1 tissue), whereas blood pressure and thus peripheral vascular resistance was significantly elevated in hypertensive compared with normotensive subjects. Hyperemic peak flow was significantly blunted in hypertensive patients. Sodium nitroprusside, acetylcholine, and bradykinin increased flow in a dose-dependent manner to a comparable extent in the control group (13.3 +/- 0.8, 13.6 +/- 1.3, and 14.6 +/- 0.7 mL.min-1.100mL-1 tissue, respectively). In contrast, in hypertensive patients maximum increase in resting flow was significantly reduced (sodium nitroprusside, -36%; acetylcholine, -44%; and bradykinin, -56%). The flow response after stimulation of endogenous NO synthesis by bradykinin was significantly more blunted compared with that of exogenous NO after application of sodium nitroprusside. In the cutaneous microvasculature, bradykinin-induced increases in blood flow velocity were selectively impaired in hypertensive patients, whereas flow response to acetylcholine was preserved. Thus, we conclude that in arterial hypertension endothelium-dependent, NO-mediated dilation of resistance arteries and cutaneous microvessels of the forearm vasculature is heterogeneously impaired, depending on the type of endothelial receptor stimulated. Furthermore, the present data suggest that in hypertensive patients the impairment of NO-dependent dilation of resistance arteries is caused by at least three different mechanisms: (1) a reduced endothelial synthesis of NO due to either a disturbed signal-transduction pathway and/or a reduced activity of NO synthase, (2) an accelerated NO degradation within the vessel wall, and (3) alterations in the vessel architecture resulting in an overall reduced dilatory capacity of resistance arteries.

Portal hypertensive vascular lesions

The aim of present study is to assess the pathological changes of gastric coronary vein in cirrhotic patients (n = 30) by immunohistochemical and morphological observation. The damage to endothelium, hypertrophy and hyperplasia of smooth muscle and increament of ECM were found in gastric coronary vein of cirrhotic patients. The vessel wall hardened and thickened with decrease of elasticity. The results showed that the portal hypertension could accompany with portal hypertensive vascular lesions.