Kimie Tanaka

Diverse Contribution of Bone Marrow Cells to Neointimal Hyperplasia After Mechanical Vascular Injuries

Abstract— We and others have suggested that bone marrow-derived progenitor cells may contribute to the pathogenesis of vascular diseases. On the other hand, it was reported that bone marrow cells do not participate substantially in vascular remodeling in other experimental systems. In this study, three distinct types of mechanical vascular injuries were induced in the same mouse whose bone marrow had been reconstituted with that of GFP or LacZ mice. All injuries are known to cause smooth muscle cell (SMC) hyperplasia. At 4 weeks after wire-mediated endovascular injury, a significant number of the neointimal and medial cells derived from bone marrow. In contrast, marker-positive cells were seldom detected in the lesion induced by perivascular cuff replacement. There were only a few bone marrow-derived cells in the neointima after ligation of the common carotid artery. These results indicate that the origin of intimal cells is diverse and that contribution of bone marrow-derived cells to neointimal hyperplasia depends on the type of model.

Potent Inhibitory Effect of Sirolimus on Circulating Vascular Progenitor Cells

Background—Neointimal hyperplasia is the major cause of in-stent restenosis (ISR). The sirolimus-eluting stent (SES) has emerged as a promising therapy to prevent ISR; however, the exact mechanism by which locally delivered sirolimus, an immunosuppressive agent, prevents ISR remains unknown. Recent evidence suggests that circulating progenitor cells may contribute to neointimal formation. Methods and Results—Mononuclear cells (MNCs) were isolated from peripheral blood of healthy human volunteers. Smooth muscle (SM)–like cells outgrew from the culture of MNCs (1×106) in the presence of platelet-derived growth factor-BB and basic fibroblast growth factor, whereas endothelial cell–like cells were obtained in the presence of vascular endothelial growth factor. Sirolimus potently inhibited SM-like cell outgrowth. The number of SM-like cells was significantly reduced at a concentration as low as 0.1 ng/mL (15.9±5.8% of control, P<0.001). Sirolimus also exerted an inhibitory effect on endothelial cell–like cells that originated from MNCs. Wire-mediated vascular injury was induced in femoral arteries of bone marrow chimeric mice. Either vehicle or sirolimus was administered locally to the perivascular area of the injured arteries. Sirolimus significantly reduced neointima hyperplasia at 4 weeks (intima/media ratio 2.0±0.3 versus 1.0±0.2, P<0.05) with a decreased number of bone marrow–derived SM-like cells and hematopoietic cells in the lesion. Reendothelialization was retarded in the arteries treated with sirolimus. Conclusions—The potent inhibitory effects of sirolimus on circulating smooth muscle progenitor cells may mediate the clinical efficacy of SES, at least in part. Sirolimus potentially may affect reendothelialization after stent implantation.

Circulating progenitor cells contribute to neointimal formation in nonirradiated chimeric mice

Recent evidence suggests that bone marrow‐derived cells may contribute to repair and lesion formation following vascular injury. In most studies, bone marrow‐derived cells were tracked by transplanting exogenous cells into bone marrow that had been compromised by irradiation. It remains to be determined whether endogenous circulating progenitors actually contribute to arterial remodeling under physiological conditions. Here, we established a parabiotic model in which two mice were conjoined subcutaneously without any vascular anastomosis. When wild‐type mice were joined with transgenic mice that expressed green fluorescent protein (GFP) in all tissues, GFP‐positive cells were detected not only in the peripheral blood but also in the bone marrow of the wild‐type mice. The femoral arteries of the wild‐type mice were mechanically injured by insertion of a large wire. At 4 wk, there was neointima hyperplasia that mainly consisted of α‐smooth muscle actin‐positive cells. GFP‐positive cells were readily detected in the neointima (14.8±4.5%) and media (31.1±8.8%) of the injured artery. Some GFP‐positive cells expressed α‐smooth muscle actin or an endothelial cell marker. These results indicate that circulating progenitors contribute to re‐endothelialization and neointimal formation after mechanical vascular injury even in nonirradiated mice. — Tanaka, K., Sata, M., Natori, T., Kim‐Kaneyama, J., Nose, K., Shibanuma, M., Hirata, Y., and Nagai, R. Circulating progenitor cells contribute to neointimal formation in nonirradiated chimeric mice. FASEB J. 22, 428–436 (2008)

Augmented angiogenesis in adventitia promotes growth of atherosclerotic plaque in apolipoprotein E-deficient mice

OBJECTIVE Accumulating evidence suggests that exaggerated formation of vasa vasorum (VV) plays an important role in the pathogenesis of atherosclerosis. However, it remains unclear whether augmented angiogenesis in the adventitia could promote hyperlipidemia-induced atherosclerotic lesion formation. METHODS AND RESULTS First, we analyzed the time course of VV development in apolipoprotein E-deficient (ApoE-/-) mice. VV proliferation was observed only after atherosclerotic lesion formation. Next, we investigated whether forced perivascular angiogenesis could promote plaque progression. Basic fibroblast growth factor (bFGF) (100 μg/body) incorporated in acid gelatin hydrogel microspheres (AGHM) (bFGF+AGHM group, n=10), AGHM alone (AGHM group, n=7), or PBS (control group, n=8) was administered into the periaortic area of the retroperitoneal space in 10- to 11-week-old male ApoE-/- mice. At 13 weeks after the operation, lesions were significantly larger in the bFGF+AGHM group than in others (bFGF+AGHM: 3.4 ± 0.7 × 10(4)μm(2); AGHM: 0.1 ± 0.1 × 10(4)μm(2); control: 0 μm(2); p<0.0001), which was associated with increased neovascularization in the adventitia. The number of adventitial capillaries correlated with plaque size (r=0.69, p<0.0001). In the bFGF+AGHM group, an increase in the number of VV and accumulation of Mac3-positive macrophages were observed prior to atherosclerotic lesion formation. CONCLUSIONS Our findings demonstrated that local administration of bFGF in the adventitia induced development of VV and accelerated plaque progression in ApoE-/- mice, supporting the notion that VV formation plays a crucial role in the pathogenesis of atherosclerosis.

The role of circulating precursors in vascular repair and lesion formation

The accumulation of smooth muscle cells (SMCs) plays a principal role in atherogenesis, post‐angioplasty restenosis and transplantation‐associated vasculopathy. Therefore, much effort has been expended in targeting the migration and proliferation of medial smooth muscle cells to prevent occlusive vascular remodeling. Recent evidence suggests that bone marrow‐derived circulating precursors can also give rise to endothelial cells and smooth muscle cells that contribute to vascular repair, remodeling, and lesion formation under physiological and pathological conditions. This article overviews recent findings on circulating vascular progenitor cells and describes potential therapeutic strategies that target these cells to treat occlusive vascular diseases.

Obesity-induced DNA released from adipocytes stimulates chronic adipose tissue inflammation and insulin resistance.

DNA released from obesity-induced degenerated adipocytes stimulates inflammation in adipose tissue and insulin resistance. Obesity stimulates chronic inflammation in adipose tissue, which is associated with insulin resistance, although the underlying mechanism remains largely unknown. Here we showed that obesity-related adipocyte degeneration causes release of cell-free DNA (cfDNA), which promotes macrophage accumulation in adipose tissue via Toll-like receptor 9 (TLR9), originally known as a sensor of exogenous DNA fragments. Fat-fed obese wild-type mice showed increased release of cfDNA, as determined by the concentrations of single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) in plasma. cfDNA released from degenerated adipocytes promoted monocyte chemoattractant protein-1 (MCP-1) expression in wild-type macrophages, but not in TLR9-deficient (Tlr9−/−) macrophages. Fat-fed Tlr9−/− mice demonstrated reduced macrophage accumulation and inflammation in adipose tissue and better insulin sensitivity compared with wild-type mice, whereas bone marrow reconstitution with wild-type bone marrow restored the attenuation of insulin resistance observed in fat-fed Tlr9−/− mice. Administration of a TLR9 inhibitory oligonucleotide to fat-fed wild-type mice reduced the accumulation of macrophages in adipose tissue and improved insulin resistance. Furthermore, in humans, plasma ssDNA level was significantly higher in patients with computed tomography–determined visceral obesity and was associated with homeostasis model assessment of insulin resistance (HOMA-IR), which is the index of insulin resistance. Our study may provide a novel mechanism for the development of sterile inflammation in adipose tissue and a potential therapeutic target for insulin resistance.

Comparison of Various Bone Marrow Fractions in the Ability to Participate in Vascular Remodeling After Mechanical Injury

In contrast to conventional assumption, recent reports propose the possibility that hematopoietic stem cells (HSCs) may have broader potential to differentiate into various cell types. Here, we tested the pluripotency of HSCs by comparing vascular lesions induced by mechanical injury after bone marrow reconstitution with total bone marrow (TBM) cells, c‐Kit+ Sca‐1+ Lin− (KSL) cells, or a single HSC cell (Tip‐SP CD34−KSL cell, CD34− c‐Kit+ Sca‐1+ Lin− cell with the strongest dye‐efflux activity) harboring green fluorescent protein (GFP). The lesions contained a significant number of GFP‐positive cells in the TBM and KSL groups, whereas GFP‐positive cells were rarely detected in the HSC group. These results suggest that transdifferentiation of a highly purified HSC seems to be a rare event, if it occurs at all, whereas bone marrow cells including the KSL fraction can give rise to vascular cells that substantially contribute to repair or lesion formation after mechanical injury.

Rivaroxaban, a novel oral anticoagulant, attenuates atherosclerotic plaque progression and destabilization in ApoE-deficient mice

OBJECTIVE Activated factor X (FXa) plays a key role in the coagulation cascade, whereas accumulating evidence suggests that it also contributes to the pathophysiology of chronic inflammation on the vasculature. In this study, we assessed the hypothesis that rivaroxaban (Riv), a direct FXa inhibitor, inhibits atherogenesis by reducing macrophage activation. METHODS AND RESULTS Expression levels of PAR-1 and PAR-2, receptors for FXa, increased in the aorta of apolipoprotein E-deficient (ApoE(-/-)) mice compared with wild-type mice (P < 0.01, P < 0.05, respectively). Administration of Riv (5 mg/kg/day) for 20 weeks to 8-week-old ApoE(-/-) mice reduced atherosclerotic lesion progression in the aortic arch as determined by en-face Sudan IV staining compared with the non-treated group (P < 0.05) without alteration of plasma lipid levels and blood pressure. Histological analyses demonstrated that Riv significantly decreased lipid deposition, collagen loss, macrophage accumulation and matrix metallopeptidase-9 (MMP-9) expression in atherosclerotic plaques in the aortic root. Quantitative RT-PCR analyses using abdominal aorta revealed that Riv significantly reduced mRNA expression of inflammatory molecules, such as MMP-9, tumor necrosis factor-α (TNF-α). In vitro experiments using mouse peritoneal macrophages or murine macrophage cell line RAW264.7 demonstrated that FXa increased mRNA expression of inflammatory molecules (e.g., interleukin (IL)-1β and TNF-α), which was blocked in the presence of Riv. CONCLUSIONS Riv attenuates atherosclerotic plaque progression and destabilization in ApoE(-/-) mice, at least in part by inhibiting pro-inflammatory activation of macrophages. These results indicate that Riv may be particularly beneficial for the management of atherosclerotic diseases, in addition to its antithrombotic activity.

Toll‐Like Receptor‐2 Mediates Adaptive Cardiac Hypertrophy in Response to Pressure Overload Through Interleukin‐1β Upregulation via Nuclear Factor κB Activation

Background Inflammation is induced in the heart during the development of cardiac hypertrophy. The initiating mechanisms and the role of inflammation in cardiac hypertrophy, however, remain unclear. Toll‐like receptor‐2 (TLR2) recognizes endogenous molecules that induce noninfectious inflammation. Here, we examined the role of TLR2‐mediated inflammation in cardiac hypertrophy. Methods and Results At 2 weeks after transverse aortic constriction, Tlr2−/− mice showed reduced cardiac hypertrophy and fibrosis with greater left ventricular dilatation and impaired systolic function compared with wild‐type mice, which indicated impaired cardiac adaptation in Tlr2−/− mice. Bone marrow transplantation experiment revealed that TLR2 expressed in the heart, but not in bone marrow–derived cells, is important for cardiac adaptive response to pressure overload. In vitro experiments demonstrated that TLR2 signaling can induce cardiomyocyte hypertrophy and fibroblast and vascular endothelial cell proliferation through nuclear factor–κB activation and interleukin‐1β upregulation. Systemic administration of a nuclear factor–κB inhibitor or anti–interleukin‐1β antibodies to wild‐type mice resulted in impaired adaptive cardiac hypertrophy after transverse aortic constriction. We also found that heat shock protein 70, which was increased in murine plasma after transverse aortic constriction, can activate TLR2 signaling in vitro and in vivo. Systemic administration of anti–heat shock protein 70 antibodies to wild‐type mice impaired adaptive cardiac hypertrophy after transverse aortic constriction. Conclusions Our results demonstrate that TLR2‐mediated inflammation induced by extracellularly released heat shock protein 70 is essential for adaptive cardiac hypertrophy in response to pressure overload. Thus, modulation of TLR2 signaling in the heart may provide a novel strategy for treating heart failure due to inadequate adaptation to hemodynamic stress.

Src kinase-mediates androgen receptor-dependent non-genomic activation of signaling cascade leading to endothelial nitric oxide synthase

Our previous study has demonstrated that testosterone rapidly activates endothelial nitric oxide synthase (eNOS), enhancing nitric oxide (NO) release from endothelial cells (ECs) via the phosphatidylinositol 3-kinase/Akt (PI3-kinase/Akt) pathway. The upstream regulators of this pathway are unknown. In this study, we further investigated the non-genomic action of testosterone in human aortic ECs. Acute (30 min) activation of eNOS caused by testosterone was unaffected by pretreatment with a transcriptional inhibitor, actinomycin D. Non-permeable testosterone-BSA rapidly induced Akt and eNOS phosphorylation. In contrast, luciferase reporter assay showed that the transcriptional activity of the androgen-responsive element (ARE) was increased by testosterone, but not by testosterone-BSA at 2h after stimulation. Immunostaining displayed co-localization of androgen receptor (AR) with caveolin-1. Fractional analysis showed that AR was expressed in caveolae-enriched membrane fractions. Immunoprecipitation assays revealed the association of AR with caveolin-1 and c-Src, suggesting complex formation among them. Testosterone rapidly increased the phosphorylation of c-Src on Tyr416, which was inhibited by an AR antagonist and by siRNA for AR. PP2, a specific-inhibitor of Src kinase, abolished the testosterone-induced phosphorylation of Akt and eNOS. Our data indicate that testosterone induces rapid assembly of a membrane signaling complex among AR, caveolin-1 and c-Src, which then facilitates activation of the c-Src/ PI3-kinase/Akt cascade, resulting in activation of eNOS.