Marco R. Schroeter

17β-Estradiol inhibition of NADPH oxidase expression in human endothelial cells

We investigated the hypothesis that the antiatherosclerotic effect of 17β‐estradiol (E2) is due to a shift in the nitric oxide (NO)/superoxide (O2-) balance in the vessel wall, thereby increasing the bio‐availability of NO. In human umbilical vein cultured endothelial cells, E2 (1–100 nmol/l), but not 17α‐estradiol, caused a time‐ and concentration‐dependent decrease in expression of the NADPH oxidase subunit gp91phox (up to 60% inhibition at both the mRNA and protein level). This effect was prevented by coincuba‐tion with the estrogen receptor antagonists tamoxifen and ICI 182,780 (1 μmol/1 each). Within the same concentration range, E2 also up‐regulated endothelial nitric oxide synthase expression (~two fold). Moreover, preincubation of the cells with E2 or a gp91phox antisense oligonucleotide significantly decreased their capacity to generate O2- on phorbol ester stimulation (i.e., assembly of the active NADPH oxidase complex). Blockade of NO synthase activity, on the other hand, had no effect on phorbol ester‐stimulated O2- formation. In addition, E2 (100 nmol/l) inhibited the increase in adhesion molecule and chemokine expression in cells exposed to cyclic strain. Cyclic strain enhanced endothelial O2- formation, thereby offsetting the inhibitory effect of NO on the expression of these gene products. E2 thus seems to act as an antioxidant at the genomic level which by improving the NO/O2- balance normalizes expression of proatherosclerotic gene products in endothelial cells.—Wagner, A. H., Schroeter, M. R., Hecker, M. 17β‐Estradiol inhibition of NADPH oxidase expression in human endothelial cells. FASEB J. 15, 2121–2130 (2001)

Leptin Enhances the Potency of Circulating Angiogenic Cells Via Src Kinase and Integrin αvβ5. Implications for Angiogenesis in Human Obesity

Objective—To investigate the capacity of the adipokine leptin to promote angiogenesis by modulating the function of circulating angiogenic cells (CACs). Methods and Results—In vitro, leptin specifically promoted CAC adhesion to tubular endothelial structures and migration along outgrowing sprouts of endothelial cells. In vivo, stimulation of CACs with leptin increased their capacity to promote new vessel formation in the chorioallantoic membrane of chicken embryos and to improve neovascularization of ischemic murine hind limbs. These effects required the phosphorylation of &agr;v&bgr;5 integrins, which depended on the interaction of leptin with its receptor ObR, and on Janus kinase (JAK) 2– and phospholipase C (PLC) &ggr;-mediated activation of Src kinase. Protein tyrosine phosphatase 1B, a negative regulator of leptin signaling, was overexpressed in CACs from obese, hyperleptinemic individuals, and this was associated with insensitivity of CACs to the angiogenic effects of leptin. Weight loss (by [mean±SD] 30±15 kg) normalized protein tyrosine phosphatase 1B expression in CACs and restored their responsiveness to leptin. A similar dose-dependent response was found after incubation of CACs from obese subjects with a protein tyrosine phosphatase 1B inhibitor ex vivo. Conclusion—Our results point to the ObR–Src kinase–&agr;v&bgr;5 cross talk as a distinct novel component of the network of specific interactions between integrins and cytokine receptors in angiogenesis.

Leptin promotes the mobilization of vascular progenitor cells and neovascularization by NOX2-mediated activation of MMP9

AIMS Bone marrow (BM) progenitors participate in new vessel formation and endothelial repair. The leptin receptor (ObR) is expressed on hematopoietic cells; however, the effects of leptin on BM progenitor cells and their angiogenic potential are unknown. METHODS AND RESULTS In the present study, we show that the short-term administration of leptin (over five consecutive days) into wild-type mice increased the number of circulating, BM-derived sca-1(+), flk-1(+) vascular progenitors, 95 ± 1.7% of which also expressed ObR. Ex vivo stimulation of BM cells with leptin enhanced the expression of NADPH oxidase isoform 2 (NOX2), and the leptin-induced increase in reactive oxygen species production, matrix metalloproteinase-9 (MMP9) expression and circulating soluble KitL levels was absent in mice lacking NOX2. Furthermore, intraperitoneal injections of leptin improved perfusion and increased the number of BM-derived, CD31-positive endothelial cells in ischaemic hindlimbs after femoral artery ligation. The effects of leptin on the mobilization of sca-1(+), flk-1(+) cells and neovascularization were abolished in mice transplanted with BM from ObR-deficient and in NOX2(-/-) mice. CONCLUSION Our findings suggest that the angiogenic effects of leptin involve sca-1(+), flk-1(+) vascular progenitor cells mobilized from the BM in response to ObR-mediated activation of NOX2, increased MMP9 expression, and sKitL release.

Leptin-Dependent and Leptin-Independent Paracrine Effects of Perivascular Adipose Tissue on Neointima Formation

Objective—Clinical and experimental evidence suggests that periadventitial adipose tissue may modulate vascular lesion formation. The aim of this study was to determine the role of perivascular leptin expression on neointima formation and to differentiate it from local inflammation and systemically elevated leptin levels. Approach and Results—Increased neointima formation after carotid artery injury was observed in hyperleptinemic, diet–induced obese wild-type mice, but not in leptin-deficient ob/ob mice. High-fat diet was associated with increased leptin expression in visceral adipose tissue (VAT) as well as in perivascular adipose tissue. Perivascular leptin overexpression achieved by adenoviral vectors enhanced intimal cell proliferation and neointima formation in wild-type mice, but not in leptin receptor–deficient mice. Perivascular transplantation of VAT from high-fat diet–induced obese wild-type mice around the carotid artery of immunodeficient mice also promoted neointima formation, without affecting body weight or systemic leptin levels, and this effect was absent, if VAT from ob/ob mice was used. On the contrary, perivascular transplantation of VAT from ob/ob mice fed high-fat diet, characterized by marked immune cell accumulation, promoted neointimal hyperplasia also in the absence of leptin. In vitro, recombinant leptin and VAT-conditioned medium increased human arterial smooth muscle cell proliferation in a (partly) leptin-dependent manner. Conclusions—Our findings suggest that locally elevated leptin levels may promote neointima formation, independent of obesity and systemic hyperleptinemia, but also underline the importance of perivascular inflammation in mediating the increased cardiovascular risk in obesity.

Overexpression of Integrin β5 Enhances the Paracrine Properties of Circulating Angiogenic Cells via Src Kinase–Mediated Activation of STAT3

Objective—To determine the intracellular mechanisms mediating the angiogenic effects of integrin &agr;v&bgr;5 overexpression in circulating angiogenic cells (CACs). Methods and Results—Integrin &agr;v&bgr;5 is expressed on angiogenic endothelial cells, and integrin &agr;v&bgr;5 activation was shown to improve the reparative functions of endothelial progenitors within the cardiovascular system. CACs were transiently transfected with the full-length cDNA of human integrin &bgr;5 (CAC-ITGB5) or control-vector (CAC-vector). Integrin &bgr;5 overexpression was confirmed using flow cytometry, Western blot, and PCR analysis; it enhanced the angiogenic capacities of CACs in vitro (spheroid and Matrigel angiogenesis assay) and stimulated new vessel formation in vivo (murine hind limb ischemia model). Overexpression of ITGB5 resulted in integrin &agr;v&bgr;5 phosphorylation and activation of Src kinase and signal transducer and activator of transcription (STAT) 3. Furthermore, elevated mRNA and protein expression of the CXC chemokine CXCL8 and the CC chemokine CCL2 was detected in CAC-ITGB5, and conditioned medium from CAC-ITGB5 enhanced the sprouting of coincubated human endothelial cells in a STAT3-, CXCL8-, and CCL2-dependent manner. Conclusion—Src kinase–mediated activation of STAT3 and subsequent angiogenic gene expression mediate the effects of integrin &agr;v&bgr;5 and may be exploited to enhance the paracrine activities of CACs.

Rosuvastatin reduces atherosclerotic lesions and promotes progenitor cell mobilisation and recruitment in apolipoprotein E knockout mice

Statins enhance incorporation of bone marrow-derived cells into experimental neointimal lesions. However, the contribution of progenitor cells to progression of spontaneous atherosclerotic plaques, and the possible modulatory role of statins in this process, remain poorly understood. We compared the effects of rosuvastatin (1 and 10mg/kg BW) and pravastatin (10mg/kg) on progenitor cell mobilisation, recruitment into atherosclerotic plaques, and lesion growth. Statins were administered over 8 weeks to apolipoprotein E knockout mice on atherogenic diet. In addition, mice were lethally irradiated, followed by transplantation of bone marrow from LacZ transgenic mice. Rosuvastatin reduced lesion area and intima-to-media ratio at the brachiocephalic artery compared to vehicle, while both parameters were not significantly altered by pravastatin. Rosuvastatin also augmented endothelialisation (P<0.05) and reduced the smooth muscle cells (SMC) content (P=0.042) of lesions. Numbers of c-kit, sca-1 and flk-1, sca-1 double-positive progenitor cells were significantly increased in rosuvastatin compared to control-treated mice, both in the bone marrow and the peripheral blood. Similarly, the number of spleen-derived acLDL, lectin double-positive progenitor cells (P=0.001) and colony-forming units (P=0.0104) was significantly increased in mice treated with rosuvastatin compared to vehicle alone. In the bone marrow, increased Akt and p42/44 MAP kinase phosphorylation and upregulated SDF1alpha mRNA expression were observed. Importantly, rosuvastatin treatment also increased the plasma levels of c-kit ligand (P=0.003), and the number of c-kit-positive cells within atherosclerotic lesions (P=0.041). Our findings suggest that rosuvastatin reduces the size of atherosclerotic plaques, and this effect appears to involve progenitor cell mobilisation and recruitment into vascular lesions.

Expression of the leptin receptor in different types of vascular lesions

Clinical and experimental evidence suggests that the adipokine leptin may be important for the development of cardiovascular complications associated with obesity, possibly through interaction with its receptor on vascular cells. In the present study, we systematically analysed expression of the leptin receptor in normal and diseased vascular specimens using immunohistochemistry, immunofluorescence and quantitative real time-PCR. In particular, human atherosclerotic plaques as well as experimental vascular lesions induced in hypercholesterolemic mice and minipigs, respectively, were examined. Our results demonstrate the presence of the leptin receptor in normal vessel wall segments as well as neointimal or atherosclerotic lesions. In the latter, ObR expressing cells were predominantly localised on the luminal border and within the subintima, and coexpression of von Willebrand factor, VEGF receptor-2 or VE cadherin identified them as endothelial cells. Moreover, CD14-positive monocytes/macrophages were strongly positive for the leptin receptor. In contrast, only few ObR-expressing smooth muscle cells could be detected in human atherosclerotic plaques. The findings of the present study thus support a possible action of leptin on the cardiovascular system by demonstrating expression of the leptin receptor in different types of vascular lesions.

Plasminogen Activator Inhibitor-1 From Bone Marrow–Derived Cells Suppresses Neointimal Formation After Vascular Injury in Mice

Objective—To investigate the ability of bone marrow (BM)–derived cells to modulate neointimal growth after injury by expressing plasminogen activator inhibitor-1 (PAI-1). Methods and Results—We performed BM transplantation (BMT) in lethally irradiated wild-type (WT) and PAI-1−/− mice. Three weeks after carotid injury with ferric chloride, analysis of Y-chromosome DNA expression in the vessel wall of female hosts revealed that 20.8±6.0% of the cells in the neointima and 37.6±5.7% of those in the media were of BM origin. Lack of PAI-1 in either the host or the donor cells did not affect recruitment of BM-derived cells into sites of vascular injury. The neointima consisted predominantly of smooth muscle cells, and a proportion of these cells expressed PAI-1. Overall, lack of PAI-1 was associated with enhanced neointimal formation. However, importantly, BMTWT→PAI-1−/− mice exhibited reduced neointimal area (P=0.05) and luminal stenosis (P=0.04) compared with BMTPAI-1−/−→PAI-1−/− mice. Although PAI-1–expressing cells were shown to be present in BMTWT→PAI-1−/− lesions, these mice did not exhibit detectable levels of the inhibitor in the circulation, suggesting that local production of PAI-1 by cells in the neointima and media was sufficient to reduce luminal stenosis. Conclusions—PAI-1 from BM-derived cells appears capable of suppressing neointimal growth after vascular injury.

Cigarette Smoke Exposure Promotes Arterial Thrombosis and Vessel Remodeling after Vascular Injury in Apolipoprotein E-Deficient Mice

Background: Cigarette smoking is a major risk factor for the development of cardiovascular disease. However, in terms of the vessel wall, the underlying pathomechanisms of cigarette smoking are incompletely understood, partly due to a lack of adequate in vivo models. Methods: Apolipoprotein E-deficient mice were exposed to filtered air (sham) or to cigarette mainstream smoke at a total particulate matter (TPM) concentration of 600 µg/l for 1, 2, 3, or 4 h, for 5 days/week. After exposure for 10 ± 1 weeks, arterial thrombosis and neointima formation at the carotid artery were induced using 10% ferric chloride. Results: Mice exposed to mainstream smoke exhibited shortened time to thrombotic occlusion (p < 0.01) and lower vascular patency rates (p < 0.001). Morphometric and immunohistochemical analysis of neointimal lesions demonstrated that mainstream smoke exposure increased the amount of α-actin-positive smooth muscle cells (p < 0.05) and dose-dependently increased the intima-to-media ratio (p < 0.05). Additional analysis of smooth muscle cellsin vitro suggested that 10 µg TPM/ml increased cell proliferation without affecting viability or apoptosis, whereas higher concentrations (100 and 500 µg TPM/ml) appeared to be cytotoxic. Conclusions: Taken together, these findings suggest that cigarette smoking promotes arterial thrombosis and modulates the size and composition of neointimal lesions after arterial injury in apolipoprotein E-deficient mice.

Leptin receptor is elevated in carotid plaques from neurologically symptomatic patients and positively correlated with augmented macrophage density.

BACKGROUND Carotid artery lesions from symptomatic patients are characterized by inflammation and neovascularization. The adipokine leptin promotes angiogenesis and activates inflammatory cells, and the leptin receptor (ob gene-encoded receptor), ObR, is expressed in advanced atherosclerotic lesions. The present study quantitatively analyzed ObR messenger RNA (mRNA) expression and immunoreactivity in carotid artery plaques from symptomatic and asymptomatic persons. Plaque angiogenesis, gene expression of vascular endothelial growth factor (VEGF), and macrophage density were also analyzed. METHODS Carotid endarterectomy specimens were collected from 26 patients undergoing surgery for hemispheric cerebrovascular symptoms (n = 13) or progressive asymptomatic internal carotid stenosis (n = 13). A representative sample, including part of the most active site, was collected from each lesion and evaluated by real-time polymerase chain reaction analysis for ObR(long) and ObR(common) isoforms, VEGF(165), and macrophage adhesion molecule-1 (Mac-1) mRNA, and by immunohistochemistry for ObR, von Willebrand factor (vWF), and CD68 antigen expression. RESULTS All plaques exhibited advanced atherosclerosis (American Heart Association class IV through VI). Transcript levels were preferentially elevated in symptomatic plaques for ObR(long) (P = .0006) and ObR(common) (P = .033), with a simultaneous upregulation of VEGF(165) (P = .001) and Mac-1 mRNA expression (P = .003). Immunohistochemical analysis confirmed a significant increase of ObR antigen levels (P = .011) and CD68-positive inflammatory cells (P = .049) in symptomatic plaques, whereas neovascularization, evident in all plaques, was similar in both groups (P = .7). CONCLUSION The ObR(long) and ObR(common) genes are upregulated and their protein preferentially synthesized in clinically symptomatic carotid plaques. Moreover, ObR expression is positively correlated with augmentation of gene transcripts related to macrophage density and neovascularization. These data suggest that ObR(long) and ObR(common) may be linked with histologic features of carotid plaque instability, which are associated with cerebral ischemic symptoms.