(Hypertension. 2004;44:264.)
© 2004 American Heart Association, Inc.
Scientific Contributions |
From the Department of Cardiovascular Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Correspondence to Kensuke Egashira, MD, PhD, Department of Cardiovascular Medicine, Graduate School of Medical Science, Kyushu University, 3-1-1, Maidashi, Higashi-ku, Fukuoka 812-8582, Japan. E-mail egashira{at}cardiol.med.kyushu-u.ac.jp
| Abstract |
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colocalized with VEGF-positive cell types. Blockade of VEGF by the soluble VEGF receptor 1 (sFlt-1) gene transfer attenuated the Ang IIinduced inflammation and remodeling. The sFlt-1 gene transfer also inhibited the increased expression of VEGF and inflammatory factors such as monocyte chemoattractant protein-1. In contrast, sFlt-1 gene transfer did not affect Ang IIinduced arterial hypertension and cardiac hypertrophy. VEGF is an essential mediator in Ang IIinduced vascular inflammation and structural changes through its proinflammatory actions.
Key Words: growth substances arteriosclerosis remodeling angiotensin II endothelial growth factors
| Introduction |
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VEGF is one of the most potent angiogenic factors known to date and is thought to function as an endogenous regulator of endothelial integrity.1518 Previous animals studies have reported that local delivery of VEGF after endothelial injury promotes endothelial regeneration, accelerates the recovery of endothelium-dependent relaxation, and reduces neointimal formation.18 However, there is still a considerable debate over the vasculoprotective versus pro-inflammatory/arteriosclerotic effects of VEGF.18 There is emerging evidence that VEGF induces migration and activation of monocytes through induction of adhesion molecules or chemokines such as monocyte chemoattractant protein-1 (MCP-1),19,20 and that VEGF enhances neointimal formation by stimulating intraplaque angiogenesis2123 or by increasing inflammation.24 Therefore, vasculoprotective versus proinflammatory/arteriosclerotic actions of VEGF remains to be inconclusive.
Accordingly, we aimed to determine the decisive role of VEGF in Ang IIinduced vascular remodeling (medial thickening and hypertrophy) in vivo. To determine the role of VEGF in vivo, we used a soluble form of the VEGF receptor-1 (sFlt-1) that blocks VEGF activity by directly sequestering VEGF and by functioning as a dominant-negative inhibitor against VEGF.25,26 We and other investigators have demonstrated that intramuscular transfection of sFlt-1 gene effectively blocks VEGF, and thus quenches activity of VEGF in vivo.27,28 We report here that sFlt-1 gene transfer attenuated Ang IIinduced vascular inflammation and remodeling in mice. The present study seems to be the first in vivo evidence for an essential role of VEGF in the pathogenesis of Ang II infusion-induced vascular inflammation and remodeling.
| Methods |
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Experimental Animals
The study protocol was reviewed and approved by the Committee of the Ethics of Animal Experiments, Kyushu University Graduate School of Medical Sciences. A part of this study was performed at the Kyushu University Station for Collaborative Research and the Morphology Core, Kyushu University School of Medicine Sciences.
Treatments
Male C57BL/6J wild-type mice were purchased from Jackson Laboratory (Bar Harbor, Me) and fed with commercial standard chow. Mice at 8 to 10 weeks old were randomly divided into 5 groups: (1) the untreated control group; (2) ones receiving Ang II infusion; (3) Ang II infusion plus sFlt-1 gene plasmid transfer; (4) Ang II infusion plus empty plasmid cDNA3 transfer; or (5) Ang II infusion and Ang II AT1 receptor blocker (olmesartan at 3.5 mg/kg per day, a gift from Sankyo Pharmaceutical Co, Tokyo, Japan) mixed in chow. For Ang II infusion, the osmotic mini-pump (Alzet) containing Ang II saline solution (discharging 1.9 mg/kg of Ang II per day) was implanted in the peritoneal cavity under anesthesia with ketamine (80 mg/kg IP) and xylazine (10 mg/kg IP). Treatment with olmesartan started 3 days before Ang II administration was begun. For gene transfer, either empty plasmid or sFlt-1 plasmid (150 µg/100 µL phosphate-buffered saline per mouse) was injected into both sides of femoral muscles using a 27-gauge needle 1 day before commitment of Ang II infusion, as we previously described.27,29,30
In all experiments, mice were euthanized at the indicated time points of treatments for analysis. Venous blood was collected immediately before the mice were euthanized. The aorta and hearts were isolated and either fixed in 10% buffered formalin or snap-frozen. Systolic blood pressure was measured by the tail-cuff method.
Immunohistochemistry, Histopathology, and Morphometry
Immunohistochemistry and histopathology were performed as described previously.6,29 Some of formalin-fixed and paraffin-embedded cross-sections of abdominal aorta were routinely stained with hematoxylin-eosin or Masson-trichrome. The other sections were subjected to immunostaining assay using antibodies against mouse VEGF and its receptors, Flt-1 and Flk-1 (Santa Cruz Biotech), macrophages (Mac-3; Serotec Inc, Raleigh, NC), proliferating cell nuclear antigen (DAKO, Denmark),
-smooth muscle cell actin (
-SMA; Boehringer Mannheim, Germany), hypoxia-inducible factor-1
(HIF-1
), CD31 (Santa Cruz Biotech), and von Willebrand factor (Sigma Chemical).
Fluorescein FITC-conjugated or rhodamine-conjugated secondary antibodies (Santa Cruz Biotech) were used for double-staining for localization of cell types expressing VEGF and its 2 receptors, or for coexpression of VEGF and HIF-1
. The degree of arteriosclerosis (the medial thickness and perivascular fibrosis) and left ventricle (LV) hypertrophy (LV-to-body weight ratios) on day 28 were measured as described previously.4,5,7
TaqMan Real-Time Reverse TranscriptasePolymerase Chain Reaction
Transcripts of 1 µg total RNA from thoracic and abdominal aorta were reverse-transcribed and the resultant cDNA was amplified by TaqMan real-time reverse transcriptasepolymerase chain reaction as previously described30 for the following genes: VEGF, Flt-1, Flk-1, HIF-1
, B-type natriuretic peptide, MCP-1, CCR2 (MCP-1 receptor), inteleukin-1 (IL-1), IL-6, transforming growth factor ß-1 (TGF-ß1), intercellular adhesion molecule-1, and vascular cell adhesion molecule-1. The sequences of sense primers, antisense primers, and the relevant probes were recorded (online Table I available at http://www.hypertensionaha.org). The probe and primers of GAPDH were obtained from Applied Biosystems.
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Plasma VEGF and sFlt-1 Measurements
The commercially available enzyme-linked immunosorbent assay kits (Biosource International, Camarillo, Calif) were used to measure mouse plasma VEGF and soluble Flt-1 according to the manufacturers instructions.
Statistical Analysis
Data are expressed as the mean±SE. Statistical analysis of differences was compared by analysis of variance. Post hoc analyses were performed using Bonferroni correction for multiple comparison tests. P<0.05 was considered to be statistically significant.
| Results |
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is a transcriptional factor for the control of VEGF expression,31 immunostaining and mRNA levels of HIF-1
were then examined. HIF-1
expression showed similar temporal and special changes as those of VEGF (Figure 1A and 1B). Keeping with rapid upregulation of VEGF in vascular tissues, serial measurements of plasma VEGF showed rapid and persistent increase in the Ang II group (Figure 1C).
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To localize VEGF and related signaling, immunofluorescent double staining was performed (Figure 2). On days 3 and 7, Mac-3positive monocytes recruited to the adventitia and outer layer of the media expressed VEGF and Flt-1 (Figure 2A), but did not express Flk-1 (data not shown). HIF-1
was colocalized in the cell types expressing VEGF (Figure 2B). On day 28, most
-SMApositive smooth muscle cells in the media expressed VEGF, and some
-SMApositive cells in the media expressed Flt-1 and Flk-1 (Figure 2C). Some
-SMApositive myofibroblastic cells in the adventitia expressed VEGF, Flt-1, and Flk-1 (Figure 2C).
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No apparent angiogenesis, as detected by von Willebrand factor or CD31 staining, was detected in the aortic wall of the control, Ang II, or Ang II+sFlt-1 groups (data not shown). Furthermore, the endothelial layer of the aorta was preserved in the 3 groups.
Effects of sFlt-1 on Vascular Inflammation and Remodeling
Mac-3positive monocytes and proliferating cell nuclear antigen-positive proliferating cells were used as the markers of inflammatory and proliferative changes. Infiltration of monocytes and appearance of proliferating cells was markedly increased in the aorta of mice receiving Ang II, particularly in the adventitia on days 3 and 7, which declined spontaneously on day 28. These Ang IIinduced inflammatory and proliferative changes in the aorta on day 7 were markedly attenuated in Ang II+sFlt-1 group, but not in the Ang II+empty plasmid group (Figure 3).
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Compared with control mice, vascular remodeling (medial wall thickening and perivascular fibrosis) developed in the aorta and coronary arteries from mice received Ang II for 28 days, which was attenuated by sFlt-1 gene transfer but not by empty plasmid transfer (Figure 4A and 4B).
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To gain mechanistic insight, mRNA levels of a variety of inflammatory cytokines, chemokines, and chemokine receptors were examined by real-time polymerase chain reaction on day 7 (Figure 5). The sFlt-1 transfection did not affect the increased gene expression of RANTES, MIP-1
, or MIP-2, but prevented or attenuated the increased gene expressions of VEGF, Flt-1 Flk-1, MCP-1, CCR2, IL-1ß, IL-6, TGF-ß1, vascular cell adhesion molecule-1, intercellular adhesion molecule-1, and HIF-1
(Figure 5). The sFlt-1 transfection also blunted Ang IIinduced increases in plasma VEGF (Figure 1C). Immunohistochemical study revealed that immunoreactive MCP-1, TGF-ß1, VEGF, Flt-1, and Flk-1 were increased in Ang II group on day 7 (Figure 6). In contrast, such increased immunostaining was attenuated in aortic sections from the Ang II+sFlt-1 group.
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Plasma sFlt-1 Concentration
To assess transfection efficacy, plasma sFlt-1 concentration was measured. In control mice, plasma sFlt-1 levels increased on days 3, 7, and 14 (Table 1), indicating that sFlt-1 was released to circulation from the transfected muscle. Similar increase in plasma sFlt-1 levels was noted in mice infused with Ang II.
Systolic Blood Pressure and LV Hypertrophy
Systolic blood pressure was significantly increased in mice receiving Ang II compared with control. There were no significant differences in systolic blood pressure between Ang II and Ang II+sFlt-1 groups (Table 2). To assess the degrees of LV hypertrophy, relative LV weight and B-type natriuretic peptide mRNA levels were determined on day 28 (Table 2). There were no significant differences in Ang IIinduced LV hypertrophy or in the increase in B-type natriuretic peptide mRNA levels between Ang II and Ang II+sFlt-1 groups.
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Effects of AT1 Receptor Blocker on Vascular Inflammation and Remodeling
Treatment with AT1 receptor blocker prevented or markedly attenuated Ang IIinduced arterial hypertension, LV hypertrophy (Table 2), and increased immunostaining and gene expression of VEGF, aortic wall inflammation, and arteriosclerotic changes (data not shown). These data suggest that the Ang IIinduced increases in VEGF expression and activity were mediated by Ang II AT1 receptor stimulation.
| Discussion |
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We examined time-related changes in cell types expressing VEGF and its receptors during Ang II infusion. VEGF was predominately expressed in the lesional monocytes and proliferative myofibroblast, mainly in the adventitial layer at early stages and in smooth muscle cells in the media. This local VEGF expression was associated with rapid and persistent increase in plasma VEGF level. In addition, Flt-1 was increased in lesional monocytes and medial smooth muscle cells at early stages and in medial smooth muscle cells at later stages. No increase in Flk-1 expression was detected in monocytes or myofibroblasts, whereas increased Flk-1 expression was noted in medial smooth muscle cells only at later stages. Our present data show that Ang II-mediated expressions of VEGF and its receptors have a biological effect in inducing vascular inflammation (monocyte infiltration) and proliferation, as well as in causing vascular structural changes. Interestingly, sFlt-1 gene transfer reduced increased local and systemic expression of VEGF, suggesting that sFlt-1 transfection might inhibit VEGF activity at least by trapping VEGF. Because sFlt-1 functions as a nonselective inhibitor of Flt-1 and Flk-1, further studies are needed to elucidate relative role of Flt-1 and Flk-1 in the pathogenesis of Ang IIinduced vascular pathobiology.
There are several reports demonstrating that VEGF is a proinflammatory factor.20,32 In the present study, we extended those observations by showing that sFlt-1 gene transfer attenuated Ang IIinduced increase in inflammatory factors in vivo. Regarding the mechanism of VEGF-mediated vascular inflammation, Yamada et al33 showed that MCP-1 is essential in VEGF-induced angiogenesis and inflammation. Bush et al34 showed that Ang IIinduced vascular inflammation and arteriosclerosis was blunted in mice deficient of MCP-1 receptor. MCP-1 has been shown to be the key chemokine in mediating vascular monocyte-mediated inflammation leading to vascular disease.35,36 Taken together, it is likely that sFlt-1 gene transfer blocked Ang IIinduced vascular structural changes mainly by suppressing inflammation (monocyte recruitment and activation) and subsequent production of growth factors. For example, VEGF-mediated overexpression of TGF-ß1 might contribute to Ang IIinduced vascular fibrosis. Another interpretation alternative to this conclusion is that increased VEGF and its receptors acted directly on smooth muscle cells, resulting in structural changes such as medial thickening. Several studies have reported that VEGF has direct actions on proliferation/migration of smooth muscle cells,37,38 which may not be mediated by inflammation (monocyte recruitment). It is possible therefore that some of the mechanism by which sFlt-1 gene transfer inhibited vascular structural changes might not be caused by inflammation.
Regarding the mechanism of Ang IIinduced expression of VEGF, we examined HIF-1
expression because HIF-1
plays a major role in the control of VEGF expression. Richard et al31 reported that Ang II induces VEGF production through HIF-1
in vascular smooth muscle cells in vitro. In the present study, we showed that Ang II infusion increased local HIF-1
expression in vascular wall cells that colocalized in VEGF-expressing cells types, suggesting that increased transcription of HIF-1
is involved in Ang IIinduced expression of VEGF.
It is noteworthy that sFlt-1 gene transfer did not affect Ang IIinduced arterial hypertension or indices of left ventricular hypertrophy. Arterial blood pressure was, however, measured by the tail-cuff method, a method that cannot provide reliable measure of the pressure changes associated with Ang II infusion. It is reported that arterial hypertension contributes to Ang IIinduced vascular remodeling.39 Furthermore, the dose of Ang II used in the present study was high, which is above the range of physiological condition. Nevertheless, our present observation suggests that VEGF may not be involved in the mechanism of Ang IIinduced hypertension or cardiac hypertrophy.
Perspectives
VEGF is likely to be an essential mediator in Ang IIinduced vascular inflammation and remodeling but is not involved in Ang IIinduced cardiac hypertrophy. Our present data support the notion that VEGF acts as a proinflammatory and proarteriosclerotic factor in Ang IIinduced hypertension.
| Acknowledgments |
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Received April 15, 2004; first decision May 4, 2004; accepted May 20, 2004.
| References |
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