Toshimitsu Suhara

Homocysteine Enhances Endothelial Apoptosis via Upregulation of Fas-Mediated Pathways

Hyperhomocysteinemia is an independent risk factor for the development of atherosclerosis. However, the underlying mechanism of endothelial cell injury in hyperhomocysteinemia has not been elucidated. In this study, we examined the effect of homocysteine (Hcy) on Fas-mediated apoptosis in endothelial cells. Hcy-induced upregulation of Fas in endothelial cells (ECs) in a dose-dependent manner. At the same time, Hcy increased intracellular peroxide in ECs. Hcy-induced Fas expression was inhibited by the treatment with catalase. Hcy increased NF-κinding activity, and adenovirus-mediated transfection of a I κ-B mutant (Iκ-B mt) gene inhibited Hcy-induced Fas expression. ECs were sensitive to Fas-mediated apoptosis when exposed to Hcy. Under these condition, Iκ-B mt protected ECs from Fas-mediated apoptosis. In addition, Hcy inhibited expression of the caspase-8 inhibitor FLICE-inhibitory protein (FLIP). Adenovirus-mediated transfection of constitutively active Akt gene abolished the Hcy-mediated downregulation of FLIP. These data suggest that upregulation of Fas expression and downregulation of FLIP is a mechanism through which Hcy induces EC apoptosis.

Nifedipine Indirectly Upregulates Superoxide Dismutase Expression in Endothelial Cells via Vascular Smooth Muscle Cell–Dependent Pathways

Background—Calcium antagonists normalize endothelial dysfunction in many cardiovascular diseases. There is no known receptor, however, for calcium antagonists in endothelial cells (ECs). We hypothesized that vascular smooth muscle cells (VSMCs) are involved in the mechanism underlying the normalization of endothelial dysfunction by calcium antagonists. Methods and Results—Coculture studies with ECs and VSMCs were performed to determine whether VSMCs mediate modulation of endothelial superoxide dismutase (SOD) activity and expression induced by the calcium antagonist nifedipine. Nifedipine induced upregulation of SOD activity in rat aortic segments but had no effect on SOD expression or activity in ECs or VSMCs cultured individually. When ECs were cocultured with VSMCs, however, nifedipine upregulated SOD expression and activity in ECs. Nifedipine stimulated vascular endothelial growth factor (VEGF) production from VSMCs, and this stimulation of VEGF production was abolished by HOE-140, an antagonist of the bradykinin B2 receptor. A neutralizing antibody against VEGF inhibited the upregulation of endothelial SOD by nifedipine. In addition, recombinant VEGF induced an increase in the levels of SOD expression in ECs, and supernatant derived from nifedipine-treated VSMCs enhanced NO production from ECs. This increase in NO production by the supernatant was inhibited by preincubation of ECs with SOD antisense oligodeoxyribonucleotides. Conclusions—The calcium antagonist nifedipine indirectly upregulates endothelial SOD expression by stimulating VEGF production from adjacent VSMCs. This finding may provide further insight into the mechanism underlying the beneficial effects of calcium antagonists in cardiovascular diseases.

Possible participation of Fas-mediated apoptosis in the mechanism of atherosclerosis

Apoptosis is a programmed cell death that plays a major role during development, homeostasis, and in many diseases. Recent evidence has demonstrated the death of vascular smooth muscle cells (VSMCs) within advanced human atheroma. In the rat balloon-injury model, apoptotic cells were specifically identified in the neointima. The presence of apoptotic cells was demonstrated by in situ terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL). To clarify the mechanisms that trigger apoptosis in atherosclerotic lesions, we examined whether cytokines released from macrophages can modulate Fas, a death signal, in cultured human VSMCs. Simultaneous treatment with interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) but not with each cytokine alone induced upregulation of Fas in VSMCs. However, coincubation with NG-monomethyl-L-arginine, an inhibitor of nitric oxide (NO) synthesis, inhibited the upregulation of Fas induced by IL-1 and TNF-alpha. Incubation with sodium nitroprusside, a NO donor, also induced upregulation of Fas in VSMCs. Furthermore, fluorescent nuclear staining with Hoechst 33258 revealed that monoclonal antibody to human Fas significantly enhanced NO-induced apoptotis in VSMCs. These findings suggest that macrophage-derived cytokines can induce upregulation of Fas through a NO-dependent mechanism in VSMCs. Thus, Fas-mediated apoptosis may regulate apoptotic death of VSMCs during atherogenesis.

Increased Plasma Levels of the Soluble Form of Fas Ligand in Patients With Acute Myocardial Infarction and Unstable Angina Pectoris

OBJECTIVES To examine whether the Fas/Fas ligand system is involved in the pathogenesis of acute myocardial infarction (AMI), we measured the levels of the soluble form of the Fas ligand (sFasL) in the plasma of patients with AMI and stable or unstable angina pectoris (AP). BACKGROUND The Fas ligand (FasL) is rapidly cleaved off by a metalloproteinase from the cell membrane to become a soluble form as a cytokine. Fas is expressed in most cells, including cardiomyocytes, whereas FasL is mainly expressed in inflammatory cells such as macrophages, which are greatly accumulated in unstable plaque. METHODS Thirty patients with AMI, 10 patients with unstable AP, 10 patients with stable AP and 30 control subjects were enrolled in the present study. RESULTS Plasma sFasL levels were significantly elevated on hospital admission in patients with AMI and unstable AP, compared with control subjects. Time-course studies revealed that plasma sFasL levels rapidly decreased within 3 h and then increased again after percutaneous transluminal coronary angioplasty in patients with AMI, but not in patients with stable AP. Importantly, the sFasL levels were higher in the coronary sinus than in the circulation. In addition, in vitro studies showed that the expression of FasL messenger ribonucleic acid was upregulated in mononuclear cells isolated from patients with AMI and that hypoxia stimulated the release of sFasL from isolated mononuclear cells. CONCLUSIONS This demonstration of elevated levels of sFasL in patients with AMI and unstable AP suggests that activation of the Fas/FasL system may play a pathogenic role in AMI and acute coronary syndromes.

Eicosapentaenoic Acid Protects Endothelial Cells Against Anoikis Through Restoration of cFLIP

Abstract—Dietary supplementation with eicosapentaenoic acid (EPA) improves the prognosis of chronic inflammatory diseases, including atherosclerosis. The mechanism underlying these beneficial effects, however, remains to be elucidated. Here we show that EPA protects endothelial cells from anoikis through upregulation of the cellular FLICE (Fas-associating protein with death domain-like interleukin-1–converting enzyme)-inhibitory protein (cFLIP), an endogenous inhibitor of caspase-8. EPA-induced upregulation of cFLIP expression was partially suppressed by the phosphatidylinositol-3-kinase inhibitor wortmannin. Conversely, treatment with insulinlike growth factor-1 (IGF-1), an activator of phosphatidylinositol-3-kinase/Akt signaling, or infection with an adenoviral construct expressing the constitutively active Akt gene induced upregulation of cFLIP expression. In addition, pretreatment of endothelial cells with either EPA or IGF-1 protected them from anoikis, suggesting that EPA-induced protection against anoikis is partially mediated through activation of Akt. On the other hand, when endothelial cells were already detached, treatment of these cells with EPA but not with IGF-1 protected them against anoikis. Importantly, EPA restored cFLIP expression without activating Akt signaling in detached endothelial cells, whereas IGF-1 had no effect. Additionally, exogenously restored expression of cFLIP by the tetracycline-regulated adenovirus system protected endothelial cells against anoikis. Furthermore, EPA was protective against the loss of endothelium in an organ culture of rat aortas. These findings suggest that EPA protects against endothelial cell anoikis through restoration of cFLIP expression, which might contribute to the mechanism underlying the beneficial effects of EPA in patients with hypertension.

Hypoxia Stimulates Release of the Soluble Form of Fas Ligand That Inhibits Endothelial Cell Apoptosis

Fas ligand (FasL), an apoptosis-inducing cytokine, is constitutively expressed on endothelial cells (EC). Here, we report that the soluble form of FasL (sFasL) is released from EC and inhibits hypoxia-induced EC apoptosis. For hypoxia experiments, human EC were exposed to low oxygen tension in airtight chambers flushed with preanalyzed gas mixtures (1% oxygen, 5% CO2, 94% N2) at 37° C. Exposure of cultured EC to hypoxia transiently increased FasL mRNA and protein levels. The maximum increase was observed at 3 and 6 hours after exposure to hypoxia, respectively. Although sFasL protein was not detected in the supernatant from EC without hypoxia, sFasL protein level in the supernatant was transiently increased from 6 hours and disappeared again at 24 hours after the exposure to hypoxia. Interestingly, the supernatant from hypoxia-exposed EC inhibited EC apoptosis induced by hypoxia, which was abolished by a neutralizing antibody against FasL. In addition, incubation with KB8301, an inhibitor of metalloproteinase, suppressed the release of sFasL from EC and enhanced hypoxia-induced apoptosis in EC. Furthermore, exogenously added recombinant sFasL inhibited hypoxia-induced apoptosis. These findings indicate that sFasL released from EC may inhibit hypoxia-induced EC apoptosis. Therefore, the shedding of FasL could be a new therapeutic target in regulating hypoxia-induced EC injury.

Fas Signaling Induces Akt Activation and Upregulation of Endothelial Nitric Oxide Synthase Expression

Abstract—A growing body of evidence has shown that Fas, a death receptor, mediates apoptosis-unrelated biological effects. Here, we report that Fas engagement with Fas ligand induced activation of Akt and upregulation of endothelial nitric oxide synthase expression without induction of apoptosis. In the presence of the phosphatidylinositol 3-kinase inhibitor wortmannin, Fas ligand, however, induced apoptosis instead of upregulation of endothelial nitric oxide synthase expression. In vivo, systolic blood pressure was slightly higher in mutant mice with decreased cell surface Fas expression (lpr mice) compared with wild-type mice. In addition, chronic inhibition of nitric oxide synthesis by NG-nitro-l-arginine induced a progressive increase in the levels of blood pressure in wild-type mice, whereas no further increase in the levels of blood pressure was observed in lpr mice. Furthermore, acetylcholine caused a lesser endothelium-dependent relaxation of the strips from lpr mice compared with wild-type mice, although the vasoconstrictor potency of phenylephrine was not different between the two groups. These findings indicate that Fas signaling may have a role in the regulation of endothelial function and blood pressure through modulating endothelial nitric oxide synthase expression in the Akt signal-dependent manner.

Pranidipine Enhances the Action of Nitric Oxide Released From Endothelial Cells

Nitric oxide (NO) synthesis in vascular endothelium of patients with hypertension is altered. Calcium antagonists have been shown to improve endothelial function in hypertensive patients. Here we report that pranidipine, one of the latest long-acting calcium antagonists in the dihydropyridine group, enhances the actions of NO released from endothelial cells (ECs). Pranidipine significantly enhanced cGMP accumulation in vascular smooth muscle cells cocultured with ECs, whereas amlodipine and nifedipine had no significant effects. In addition, pranidipine also suppressed basal and thrombin-stimulated endothelin-1 production from ECs. Pranidipine also enhanced cGMP accumulation in rat aortic segments with endothelium but not in endothelium-denuded vessels. In contrast, pranidipine had no effect in the presence of N(G)-monomethyl-L-arginine, an inhibitor of NO synthesis. Pranidipine did not affect the basal expression of endothelial NO synthase in ECs. However, pranidipine upregulated the activity of superoxide dismutase in ECs. These findings suggest that pranidipine enhances NO action through inhibition of superoxide-induced NO decomposition in the vessel wall. Thus, pranidipine may be useful in the treatment of impaired endothelial function in patients with hypertension.

Nifedipine Inhibits Vascular Smooth Muscle Cell Dedifferentiation via Downregulation of Akt Signaling

Calcium is an essential signaling molecule that controls vascular smooth muscle cell (VSMC) contraction, proliferation, and differentiation. Here, we show that the calcium antagonist nifedipine inhibits VSMC dedifferentiation in vitro and in vivo. Differentiated VSMCs cultured on laminin-coated dishes were transferred to laminin-free dishes to induce dedifferentiation. Induction of dedifferentiation resulted in the upregulation of nonmuscle myosin heavy chain expression, a marker of dedifferentiation, and the downregulation of smooth muscle myosin heavy chain expression, a marker of differentiation. Nifedipine significantly inhibited both the induction of these phenotypic changes and upregulation of Akt signaling in these cells. Administration of nifedipine at a low concentration that did not affect blood pressure could inhibit the increase in nonmuscle myosin heavy chain expression and decrease in smooth muscle myosin heavy chain expression in a rat balloon-injury model. Furthermore, nifedipine suppressed neointimal hyperplasia and upregulation of Akt signaling. However, phospho-Akt expression was not suppressed in the regenerating arterial endothelium of the nifedipine-treated rats. The inhibitory effect of the downregulation of Akt signaling by dominant-negative Akt on the induction of VSMC dedifferentiation in the intima was identical to that of nifedipine. In contrast, upregulation of Akt signaling by transfection of the cells with a constitutively active Akt reversed the nifedipine-induced inhibition of VSMC dedifferentiation. In conclusion, nifedipine inhibits VSMC dedifferentiation by suppressing Akt signaling, thereby preventing neointimal thickening.

Interleukin-2 modulates the responsiveness to angiotensin II in cultured vascular smooth muscle cells.

Preincubation with interleukin-2 (IL-2), a T cell-derived cytokine, enhanced the increase in intracellular Ca2+ ([Ca2+]i) induced by angiotensin II (AII) in vascular smooth muscle cells (VSMC). IL-2 itself did not affect the basal [Ca2+]i level or the maximal response of [Ca2+]i increase induced by AII. Furthermore, IL-2-induced enhancement was not observed in the absence of extracellular Ca2+, suggesting that IL-2 enhances Ca2+ influx induced by AII. IL-2 also enhanced the stimulation of DNA synthesis induced by AII, although IL-2 alone did not stimulate DNA synthesis. Genistein, an inhibitor of protein tyrosine kinases, significantly inhibited IL-2-induced enhancement of both Ca2+ influx and DNA synthesis induced by AII. A neutralizing antibody against heparin-binding epidermal growth factor-like growth factor (HB-EGF) partially inhibited IL-2-induced enhancement of DNA synthesis induced by AII. These findings suggest that autocrine HB-EGF is partially involved in the mechanism of IL-2-induced enhancement of DNA synthesis. On the other hand IL-2 stimulated both glycosaminoglycan (GAG) and prostacyclin syntheses and enhanced the stimulation of both GAG and prostacyclin syntheses induced by AII. Therefore, IL-2 may play important roles in the pathogenesis of atherosclerosis and vascular disease by modulating the responsiveness to AII in VSMC.