Objective-Circulating progenitors and stem cells have been reported to contribute to angiogenesis and arterial repair after injury. In the present study, we investigated whether the arterial wall could host permanently residing progenitor cells under physiological context. Methods and Results-Using the Hoechst-based flow cytometry method, we identified and isolated progenitor cells termed side population (SP) cells at a prevalence of 6.0Ϯ0.8% in the tunica media of adult mice aortas. Arterial SP cells expressed the ATP-binding cassette transporter subfamily G member 2, frequently present on SP cell surface, and displayed a Sca-1 ϩ c-kit -/low Lin Ϫ CD34 Ϫ/low profile. They did not form myeloid or lymphoid hematopoietic colonies after plating in methylcellulose-based medium. Importantly, cultured SP cells were able to acquire the phenotype of endothelial cells (CD31, VE-cadherin, and von Willebrand factor expression) or of smooth muscle cells (␣-smooth muscle actin, calponin, and smooth muscle myosin heavy chain expression), in presence of either vascular endothelial growth factor or transforming growth factor (TGF)-␤1/PDGF-BB, respectively. Moreover, they generated vascular-like branching structures, composed of both VE-cadherin ϩ cells and ␣-smooth muscle actin ϩ cells on Matrigel. Conclusions-In this study, we provide the first evidence to our knowledge that in the adult mice, the normal arterial wall harbors SP cells with vascular progenitor properties.

Objective-To clarify the impact of breast cancer resistance protein 1 (BCRP1)/ATP-binding cassette transporter subfamily G member 2 (ABCG2) expression on cardiac repair after myocardial infarction (MI). Methods and Results-The ATP-binding cassette transporter BCRP1/ABCG2 is expressed in various organs, including the heart, and may regulate several tissue defense mechanisms. BCRP1/ABCG2 was mainly expressed in endothelial cells of microvessels in the heart. MI was induced in 8-to 12-week-old wild-type (WT) and Bcrp1/Abcg2 knockout (KO) mice by ligating the left anterior descending artery. At 28 days after MI, the survival rate was significantly lower in KO mice than in WT mice because of cardiac rupture. Echocardiographic, hemodynamic, and histological assessments showed that ventricular remodeling was more deteriorated in KO than in WT mice. Capillary, myofibroblast, and macrophage densities in the peri-infarction area at 5 days after MI were significantly reduced in

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Objective-ATP-binding cassette transporter subfamily G member 2 (ABCG2), expressed in microvascular endothelial cells in the heart, has been suggested to regulate several tissue defense mechanisms. This study was performed to elucidate its role in pressure overload-induced cardiac hypertrophy. Methods and Results-Pressure overload was induced in 8-to 12-week-old wild-type and Abcg2 Ϫ/Ϫ mice by transverse aortic constriction (TAC). Abcg2 Ϫ/Ϫ mice showed exaggerated cardiac hypertrophy and ventricular remodeling after TAC compared with wild-type mice. In the early phase after TAC, functional impairment in angiogenesis and antioxidant response in myocardium was found in Abcg2 Ϫ/Ϫ mice. In vitro experiments demonstrated that ABCG2 regulates transport of glutathione, an important endogenous antioxidant, from microvascular endothelial cells. Besides, glutathione transported from microvascular endothelial cells in ABCG2-dependent manner ameliorated oxidative stress-induced cardiomyocyte hypertrophy. In vivo, glutathione levels in plasma and the heart were increased in wild-type mice but not in Abcg2 Ϫ/Ϫ mice after TAC. Treatment with the superoxide dismutase mimetic ameliorated cardiac hypertrophy in Abcg2 Ϫ/Ϫ mice after TAC to the same extent as that in wild-type mice, although cardiac dysfunction with impaired angiogenesis was observed in Abcg2 Ϫ/Ϫ mice. Conclusion-ABCG2 protects against pressure overload-induced cardiac hypertrophy and heart failure by promoting angiogenesis and antioxidant response.

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Objective— Lymphocyte activation is thought to play a major role in the pathogenesis of atherosclerotic complications such as plaque thrombosis. Circulating CD31 + T cells have been shown to regulate human T cell activation. Aim of this study was to evaluate whether the proportion of circulating immunoregulatory CD31 + T cells is correlated to the occurrence of plaque thrombosis in aged apolipoprotein (apo) E knockout (KO) mice. Methods and Results— CD31 + T cell depletion of spleen T cells enhanced proliferation ( P <0.05) and interferon-γ production ( P <0.01) while reducing interleukin (IL)-4 ( P <0.001) and IL-10 ( P =0.001) secretion in response to minimally modified low-density lipoprotein. CD31 + T cells were counted in 65 apoE KO mice (46-week-old) by flow cytometry. Organizing thrombi could be documented in 28 of 195 (14%) lesions and in at least one of the aorta root lesions in 23 of 65 mice (35%). CD31 + T cell count was significantly reduced in mice showing plaque thrombosis (72.3±1.5% versus 84.1±1.2%; P <0.0001), but such reduction did not follow induced plaque rupture or experimentally controlled thrombosis. Conclusions— Reduced CD31 + T cells in circulating blood is a hallmark of atherosclerotic plaque thrombosis. Our data suggest that CD31 + T cells may play an important regulatory role in the development of plaque thrombosis.

Administration of monoclonal antibodies directed against the leukocyte function-associated antigen 1 (LFA-1)-intercellular adhesion molecule 1 (ICAM-1) pathway showed that these costimulatory molecules play a key role in allograft rejection. Here, adenoviral gene transfer of an immunoadhesin, sICAM-1/Ig, was used to prolong islet allograft survival in a mouse model, and was compared with anti-LFA-1 antibody administration. A replication-deficient recombinant adenoviral vector encoding a chimeric protein, in which the extracellular domain of ICAM-1 is covalently linked to the C(H)2-C(H)3 domains of an IgG1, was used for gene transfer. C3H murine islets were transplanted under the kidney capsule of streptozotocin-induced diabetic BALB/c mice. Experimental groups underwent adenovirus vector administration either in vivo (intravenous injection) or ex vivo (gene transfer to the graft), and control groups received either an empty vector (Ad.null) or an anti-LFA-1 monoclonal antibody. Graft survival was significantly prolonged by in vivo sICAM-1/Ig gene transfer as compared with both Ad.null and anti-LFA-1 groups, but not by ex vivo gene transfer. Histological examination of the grafts showed the presence of a mononuclear infiltrate within functioning grafts, suggesting that the homing of alloreactive T cells was not altered. In vitro T cell proliferation experiments indicated that sICAM-1/Ig exerted agonist effects on both CD4(+) and CD8(+) T cells.

A growing body of evidence outlines the key roles of circulating endothelial progenitor cells (EPCs) in vascular repair and angiogenesis. Several mechanisms have been proposed to explain the beneficial effects of EPCs. It was reported that EPCs participate in the reendothelialization process after arterial injury. 1 However, under pathological conditions such as diabetes mellitus, hypertension, dyslipidemia, and aging, the functional capacities of EPCs appear to be impaired. 2 Thus, it is of clinical importance to elucidate the molecular signaling that ameliorates EPC function.In See accompanying article on page 464To gain insights into the role of the PGI 2 -IP axis in the regulation of EPC function, the authors performed bone marrow transplantation (BMT) from the IPϪ/Ϫ or IPϩ/ϩ donor mice into the IPϩ/ϩ or IPϪ/Ϫ recipients prior to wire-mediated endovascular injury. Previous studies had shown that neointima (NI) formation induced by arterial injury was enhanced in mice holding a ubiquitous deficiency in IP expression. 6 Data from the present work strongly suggest that such a phenotype could principally result from delayed reendothelialization due to impaired function of EPCs. Although the number of circulating EPCs increased in the IP-deficient mice, EPCs from IPϪ/Ϫ mice displayed poor adhesion to the denudated endothelium and impaired migration capacities in vivo (Figure). These adhesion defects induced by the disruption of IP were further confirmed by in vitro studies, which revealed that IPϪ/Ϫ EPCs had decreased expression of ␤1, ␤3, and ␣5 integrin subunits with poor binding capacity to fibronectin, which is supposed to be an important component of extracellular matrices during vascular healing. Moreover, IPϪ/Ϫ EPCs seemed to display diminished proliferation capacities in vitro, which could also account for the delayed reendothelialization observed in vivo.The investigators further demonstrated that selective disruption of IP in bone marrow resulted in enhanced NI formation. The NI in the BMT (IPϪ/Ϫ 3 IPϩ/ϩ) mice was comparable to that in the BMT (IPϪ/Ϫ 3 IPϪ/Ϫ) mice. Interestingly, the NI in the BMT (IPϩ/ϩ 3 IPϪ/Ϫ) mice was significantly more than that in the BMT (IPϩ/ϩ 3 IPϩ/ϩ) mice, suggesting that IP expression in tissues other than bone marrow could also participate in regulation of NI formation. In that respect, the authors propose that the PGI 2 -IP system in the vascular cells would be potentially involved in the pathogenesis of NI formation. In fact, the expression of IP in the arterial wall was previously shown to play a key role in vascular remodeling. 6 -8 In addition, adipose tissues may represent another tissue, whose deficiency in IP expression could affect arterial remodeling. PGI 2 was reported to promote adipocyte differentiation through its extracellular binding to IP on preadipose cells. 9 Recent studies 10,11 suggested that perivascular and visceral adipose tissues have positive and negative effects on vascular homeostasis and repair. It is plausible that adipose tissues, particularl...