摘要:

Abstract—Extracellular matrix (ECM) remodeling after myocardial infarction (MI) is an important determinant of cardiac function. Tumor necrosis factor-&agr; (TNF-&agr;) and angiotensin (Ang) II levels increase after MI and both factors affect fibroblast functions. The type 1 (AT1) receptor that mediates most Ang II effects is upregulated after MI in cardiac fibroblasts, and there is evidence that this is caused by TNF-&agr;. We sought to determine if TNF-&agr;–induced AT1receptor upregulation alters fibroblast responsiveness to Ang II and if this effect differs from direct TNF-&agr; effects on fibroblast functions. In cultured neonatal rat cardiac fibroblasts, TNF-&agr; reduced cellular [3H]-proline incorporation, increased matrix metalloproteinase-2 (MMP-2) activity and protein, and increased TIMP-1 protein levels. In cardiac fibroblasts with TNF-&agr;–induced AT1receptor upregulation, Ang II–stimulated [3H]proline incorporation and TIMP-1 protein production was approximately 2-fold greater than in nonpretreated fibroblasts. Angiotensin II reduced MMP-2 activity and protein level only in TNF-&agr;–pretreated fibroblasts. Angiotensin II effects were inhibited by selective AT1(but not AT2) receptor blockers. Thus, TNF-&agr;–induced AT1receptor upregulation enhances Ang II–mediated functions that favor fibrosis. These effects are mostly directionally opposite of direct TNF-&agr; effects on cardiac fibroblasts. Recognition of multifaceted TNF-&agr; effects provides new insights into post-MI ECM remodeling.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—Cardiac fibroblasts (CFs) produce extracellular matrix proteins and participate in the remodeling of the heart. It is unknown if brain natriuretic peptide (BNP) is synthesized by CFs and if BNP participates in the regulation of extracellular matrix turnover. In this study, we examined the production of BNP in adult canine CFs and the role of BNP and its signaling system on collagen synthesis and on the activation of matrix metalloproteinases (MMPs). BNP mRNA was detected in CFs, and a specific radioimmunoassay demonstrated that BNP1-32was secreted into the media at a rate of 11.2±1.0 pg/105cells per 48 hours (mean±SEM). The amount of BNP secretion was significantly (P<0.01) augmented by 10−7mol/L tumor necrosis factor-&agr; in a time-dependent manner. BNP significantly (P<0.01) inhibited de novo collagen synthesis as assessed by [3H]proline incorporation, whereas zymographic MMP-2 (gelatinase) abundance was significantly (P<0.05) stimulated by BNP between 10−7and 10−6mol/L. In addition, protein expression of MMP-1, -2, and -3 and membranous type-1 MMP was significantly increased by 10−6mol/L BNP. The cGMP analogue 8-bromo-cGMP (10−4mol/L) mimicked the BNP effect, whereas inhibition of protein kinase G by KT5823 (10−6mol/L) significantly (P<0.05) attenuated BNP-induced zymographic MMP-2 abundance. In summary, this study reports that BNP is present in cultured CFs and that BNP decreases collagen synthesis and increases MMPs via cGMP–protein kinase G signaling. These in vitro findings support a role for BNP as a regulator of myocardial structure via control of cardiac fibroblast function.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—Acute vascular or humoral rejection, a vexing outcome of organ transplantation, has been attributed by some to activation and by others to apoptosis of endothelial cells in the graft. We asked which of these processes causes acute vascular rejection by tracing the processes during the development of acute vascular rejection in porcine cardiac xenografts performed in baboons. Apoptosis, assayed by terminal deoxynucleotidyl transferase–mediated dUTP nick end-labeling (TUNEL), expression of activated caspase-3, and proapoptotic genes Bax and Bcl-xL, was not detected until acute vascular rejection was well advanced, and even then, apoptosis was largely confined to myocytes. Activation of the endothelium, as evidenced by expansion of rough endoplasmic reticulum and increased ribosomal antigen and phospho-p70 S6 kinase, occurred early in the course of acute vascular rejection and progressed through the disease process. These findings suggest that acute vascular rejection is caused by an active metabolic process and not by apoptosis in the endothelium.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—Angiotensin II (Ang II) may be a key molecule in the development of atherosclerosis. Because the incidence of coronary atherosclerosis in premenopausal women is lower than that observed in men or postmenopausal women, we have investigated the effect of estrogens on Ang II–induced leukocyte recruitment in vivo using intravital microscopy in the rat mesenteric microcirculation. Superfusion for 60 minutes with Ang II induced a significant increase in leukocyte rolling flux, adhesion, and emigration. Administration of 17-&bgr;-estradiol (17-&bgr;-E) after 30 minutes of Ang II superfusion produced a reduction of these leukocyte responses by 55.1%, 72.7%, and 70.9%, respectively, an additional 30 minutes later. The effect observed with 17-&bgr;-E was receptor-mediated and specific. 17-&bgr;-E superfusion did not modify either L-NAME or indomethacin-induced leukocyte responses. Inhibitory responses caused by 17-&bgr;-E were not altered by either 7-nitroindazole or actinomycin D cosuperfusion. Stimulation of endothelial cells with 17-&bgr;-E caused a rapid and dose-dependent release of prostacyclin. Finally, tamoxifen or ICI 182,780 administration provoked a significant increase in leukocyte–endothelial cell interactions 90 minutes later, which were significantly attenuated by systemic preadministration with an Ang II AT1receptor antagonist. Tamoxifen-induced leukocyte responses were also reduced by systemic pretreatment with an anti–P-selectin mAb and an anti–CD18 mAb. Hence, the antiatherogenic effects of estrogens may be mediated by inhibition of Ang II–induced leukocyte recruitment through endothelial NO and prostacyclin release. Furthermore, scarcity of estrogens resulted in decreased levels of vasodilators and the exposure of the endothelium to the deleterious action of Ang II, which may explain the higher incidence of coronary atherosclerosis in men and postmenopausal women.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—A novel approach with chimeric SM22&agr;/telokin promoters was used to identify gene regulatory modules that are required for regulating the expression of genes in distinct smooth muscle tissues. Conventional deletion or mutation analysis of promoters does not readily distinguish regulatory elements that are required for basal gene expression from those required for expression in specific smooth muscle tissues. In the present study, the mouse telokin gene was isolated, and a 370-bp (−190 to 180) minimal promoter was identified that directs visceral smooth muscle–specific expression in vivo in transgenic mice. The visceral smooth muscle–specific expression of the telokin promoter transgene is in marked contrast to the reported arterial smooth muscle–specific expression of a 536-bp minimal SM22&agr; (−475 to 61) promoter transgene. To begin to identify regulatory elements that are responsible for the distinct tissue-specific expression of these promoters, a chimeric promoter in which a 172-bp SM22&agr; gene fragment (−288 to −116) was fused to the minimal telokin promoter was generated and characterized. The −288 to −116 SM22&agr; gene fragment significantly increased telokin promoter activity in vascular smooth muscle cells in vitro and in vivo. Conversely, a fragment of the telokin promoter (−94 to −49) increased the activity of the SM22&agr; promoter in visceral smooth muscle cells of the bladder. Together, these data demonstrate that both vascular- and visceral smooth muscle–specific regulatory modules direct gene expression in subsets of smooth muscle tissues.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—Vascular endothelial growth factor (VEGF) induces angiogenesis by stimulating endothelial cell proliferation and migration, primarily through the receptor tyrosine kinase VEGF receptor2 (Flk1/KDR). Reactive oxygen species (ROS) derived from NAD(P)H oxidase are critically important in many aspects of vascular cell regulation, and both the small GTPase Rac1 and gp91phoxare critical components of the endothelial NAD(P)H oxidase complex. A role of NAD(P)H oxidase in VEGF-induced angiogenesis, however, has not been defined. In the present study, electron spin resonance spectroscopy is utilized to demonstrate that VEGF stimulates O2·−production, which is inhibited by the NAD(P)H oxidase inhibitor, diphenylene iodonium, as well as by overexpression of dominant-negative Rac1 (N17Rac1) and transfection of gp91phoxantisense oligonucleotides in human umbilical vein endothelial cells (ECs). Antioxidants, includingN-acetylcysteine (NAC), various NAD(P)H oxidase inhibitors, and N17Rac1 significantly attenuate not only VEGF-induced KDR tyrosine phosphorylation but also proliferation and migration of ECs. Importantly, these effects of VEGF are dramatically inhibited in cells transfected with gp91phoxantisense oligonucleotides. By contrast, ROS are not involved in mediating these effects of sphingosine 1-phosphate (S1P) on ECs. Sponge implant assays demonstrate that VEGF-, but not S1P-, induced angiogenesis is significantly reduced in wild-type mice treated with NAC and in gp91phox−/−mice, suggesting that ROS derived from gp91phox-containing NAD(P)H oxidase play an important role in angiogenesis in vivo. These studies indicate that VEGF-induced endothelial cell signaling and angiogenesis is tightly controlled by the reduction/oxidation environment at the level of VEGF receptor and provide novel insights into the NAD(P)H oxidase as a potential therapeutic target for angiogenesis-dependent diseases.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—Previous studies of arterial smooth muscle have shown that inositol 1,4,5-trisphosphate (IP3) and cyclic ADP-ribose mobilize Ca2+from the sarcoplasmic reticulum. In contrast, little is known about Ca2+mobilization by nicotinic acid adenine dinucleotide phosphate, a pyridine nucleotide derived from &bgr;-NADP+. We show here that intracellular dialysis of nicotinic acid adenine dinucleotide phosphate (NAADP) induces spatially restricted “bursts” of Ca2+release that initiate a global Ca2+wave and contraction in pulmonary artery smooth muscle cells. Depletion of sarcoplasmic reticulum Ca2+stores with thapsigargin and inhibition of ryanodine receptors with ryanodine, respectively, block the global Ca2+waves by NAADP. Under these conditions, however, localized Ca2+bursts are still observed. In contrast, xestospongin C, an IP3receptor antagonist, had no effect on Ca2+signals by NAADP. We propose that NAADP mobilizes Ca2+via a 2-pool mechanism, and that initial Ca2+bursts are amplified by subsequent sarcoplasmic reticulum Ca2+release via ryanodine receptors but not via IP3receptors.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—It is well known that the sodium current (INa) and the degree of gap-junctional electrical coupling are the key determinants of action potential (AP) conduction in cardiac tissue. Immunohistochemical studies have shown that sodium channels (NaChs) are preferentially located in intercalated disks (IDs). Using dual immunocytochemical staining, we confirmed the colocalization of NaChs with connexin43 in cultures of neonatal rat ventricular myocytes. In mathematical simulations of conduction using the Luo-Rudy dynamic model of the ventricular AP, we assessed the hypothesis that conduction could be modulated by the preferential localization of NaChs in IDs. Localization ofINaat the ID caused a large negative potential in the intercellular cleft, which influenced conduction in two opposing ways, depending on the degree of electrical coupling: (1) for normal and moderately reduced coupling, the negative cleft potential led to a large overshoot of the transmembrane potential resulting in a decreased driving force forINaitself (self-attenuation), which slowed conduction; (2) for greatly reduced coupling (<10%), the negative cleft potential induced byINain the prejunctional membrane led to suprathreshold depolarization of the postjunctional membrane, which facilitated and accelerated conduction. When cleft potential effects were not incorporated, conduction was not significantly affected by the ID localization ofINa. By enhancing conduction through the establishment of cleft potentials, the localization of NaChs in IDs might protect the myocardium from conduction block, very slow conduction, and microreentry under conditions of greatly reduced coupling. Conversely, by supporting moderately slow conduction, this mechanism could also promote arrhythmias.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—Dystrophin has a key role in striated muscle mechanotransduction. In mice lacking the gene encoding for dystrophin (mdx mice), the absence of dystrophin and several other proteins of the dystrophin-glycoprotein complex induces a defect in flow (shear stress)–mediated NO-dependent dilation (FMD). Because the endothelium is essential for the adaptation of arteries to chronic changes in blood flow, the long-term consequences of this vascular deficiency might affect flow-induced vascular remodeling. Thus, we submitted mouse mesenteric resistance arteries to chronic changes in flow by alternatively ligating arteries. Arteries were thus submitted to high flow (HF), low flow (LF), or normal flow. After 2 weeks, arteries were studied in vitro in an arteriograph. Increases in diameter (from 174±10 to 210±15 &mgr;m, pressure 75 mm Hg) found in HF arteries were not significant in mdx mice. Arterial diameters in LF arteries decreased similarly in control and mdx mice. FMD increased in HF arteries and decreased in LF arteries. FMD was not increased in HF arteries in mdx mice. NO-dependent FMD and NO synthase expression increased in the HF arteries of control mice but not in those of mdx mice. Dilatory and contractile tone, depending on the smooth muscle, was unaffected in HF arteries but decreased in LF arteries of both strains. We conclude that resistance arteries of mdx mice do not adapt properly to chronic changes in flow, inasmuch as the increases in diameter, endothelial NO synthase expression, and FMD did not occur in mdx mice submitted to HF for 2 weeks. This study suggests that blood flow regulation might be disturbed in dystrophin-related myopathies, possibly increasing organ damage.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Abstract—The effects of dynamic exercise on restenosis after vascular injury are still unknown. The consequences of balloon dilation–induced injury on neointimal hyperplasia, vascular negative remodeling, and reendothelialization were assessed in sedentary and trained rats. Ex vivo eNOS vascular expression and activity were investigated in carotid arteries isolated from sedentary and exercised rats. The in vivo effects of eNOS inhibition by L-NMMA on vessel wall after balloon dilation were evaluated in sedentary and exercised rats. We also investigated the effects of exercise on neointimal formation in a rat stent model of vascular injury. Compared with sedentary group, the arteries isolated from trained rats showed higher levels of eNOS protein expression and activity 7 days after balloon dilation. A significant reduction of both neointimal hyperplasia and negative remodeling was observed 14 days after balloon injury in trained compared with sedentary rats. Moreover, we demonstrated that exercise training produced accelerated reendothelialization of the balloon injured arterial segments compared with sedentary. L-NMMA administration eliminated the benefits of physical training on vessel wall after balloon dilation. Finally, a decrease of neointimal hyperplasia as well as of platelet aggregation was observed after stent deployment in trained rats compared with sedentary. In conclusion, physical exercise could favorably affect restenosis after balloon angioplasty and stenting. Increase in eNOS expression and activity might contribute to the potential beneficial effects of exercise on the vessel wall after vascular injury.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID