Sensitivity to Fas-mediated apoptosis is determined below receptor level in human vascular smooth muscle cells

Smad2 inhibition of MET transcription potentiates human vascular smooth muscle cell apoptosis

Background:

Vascular smooth muscle cell (SMC) apoptosis is involved in major cardiovascular diseases. Smad2 is a transcription factor implicated in aortic aneurysm. The molecular mediators of Smad2-driven SMC apoptosis are not well defined. Here we have identified a Smad2-directed mechanism involving MET and FAS, both encoding cell membrane signaling receptors.

Methods and results:

Guided by microarray analysis in human primary aortic SMCs, loss/gain-of-function (siRNA/overexpression) indicated that Smad2 negatively and positively regulated, respectively, the gene expression of Met which was identified herein as anti-apoptotic and that of Fas, a known pro-apoptotic factor. While co-immunoprecipitation suggested a physical association of Smad2 with p53, chromatin immunoprecipitation followed by quantitative PCR revealed their co-occupancy in the same region of the MET promoter. Activating p53 with nutlin3a further potentiated the suppression of MET promoter-dependent luciferase activity and the exacerbation of SMC apoptosis that were caused by Smad2 overexpression. These results indicated that Smad2 in SMCs repressed the transcription of MET by cooperating with p53, and that Smad2 also activated FAS, a target gene of its transcription factor activity.

Conclusions:

Our study suggests a pro-apoptotic mechanism in human SMCs, whereby Smad2 negatively and positively regulates MET and FAS, genes encoding anti-apoptotic and pro-apoptotic factors, respectively.

Sapheno-Femoral Junction Pathology: Molecular Mechanism of Saphenous Vein Incompetence

A molecular mechanism responsible for varicose vein occurrence was investigated. The role of potential cell cycle regulator p21 and programmed cell death in the pathology leading to the proximal long saphenous vein (LSV) incompetence was investigated. Proximal LSV specimens were obtained from 40 patients with primary varicose veins who had undergone crossectomy. The expression of the p21, p53, and fas encoding genes was investigated by the means of real-time RT-QPCR. Immunostaining for gene product presence, proliferating cell nuclear antigen (PCNA), and apoptotic cells (TUNEL assay) was carried out. The results were compared to the control healthy vein specimens and correlated with pathologic examination findings (of the valve and vein structure). A significant increase in p21, p53, and fas mRNA expression were reported in the proximal incompetent veins. The expression of p21 correlated with expression of p53 (r = 0.658; p<0.05) and negative correlation between media apoptotic index and p21 mRNA expression was found (r = -0.493; p<0.05). Decrease in the muscular component within the media and disturbances of the local structure in the incompetent LSVs were reported. Fas overexpression did not correlate with p53 expression level and did not correlate with apoptotic cell number in the respective vein layers. PCNA-positive cells were present more frequently in the media of the control veins, especially in young subjects. Apoptosis downregulation, cell cycle inhibition and smooth muscle cell hypertrophy are important factors influencing vein wall disturbances related to sapheno-femoral junction incompetence.

MicroRNA-1 regulates the proliferation of vascular smooth muscle cells by targeting insulin-like growth factor 1

The aim of this study was to investigate the role of microRNAs (miRNAs or miRs) in vascular smooth muscle cell (VSMC) proliferation and to elucidate the underlying molecular mechanisms. In a previous study, using microarray analysis, differentially expressed miRNAs were identified in primary VSMCs isolated from the medial layer of the thoracic aorta obtained from spontaneously hypertensive rats (SHRs) and Wistar Kyoto (WKY) rats. Among others, miR-1 was identified to be downregulated in VSMCs from SHRs. Thus, in the present study, we focused on miR-1, the downregulation of which was confirmed by RT-qPCR and western blot analysis in VSMCs isolated from SHRs. We identified insulin-like growth factor 1 (IGF1) as a potential target gene of miR-1, and we subsequently validated IGF1 as a target gene of miR-1 by luciferase assay. The results revealed that the exogenous overexpression of miR-1 significantly suppressed the expression of IGF1. Additionally, we demonstrated that the downregulation of IGF1 by the introduction of miR-1 attenuated the proliferation of the VSMCs, suggesting that IGF1 is a target gene of miR-1 and that the effects of miR-1 are mediated through IGF1. In conclusion, the findings of our study demonstrate that miR-1 is significantly downregulated in VSMCs and that it is an important regulator of cell proliferation. Therefore, IGF1 may be involved in the regulation of VSMC proliferation by targeting miR-1.

Immune-mediated vascular injury and dysfunction in transplant arteriosclerosis

Solid organ transplantation is the only treatment for end-stage organ failure but this life-saving procedure is limited by immune-mediated rejection of most grafts. Blood vessels within transplanted organs are targeted by the immune system and the resultant vascular damage is a main contributor to acute and chronic graft failure. The vasculature is a unique tissue with specific immunological properties. This review discusses the interactions of the immune system with blood vessels in transplanted organs and how these interactions lead to the development of transplant arteriosclerosis, a leading cause of heart transplant failure.

The apoptotic effect of hesperetin on human cervical cancer cells is mediated through cell cycle arrest, death receptor, and mitochondrial pathways

Hesperetin, a flavonoid from citrus fruits, has several bioactivities such as anti-inflammatory, antihypertensive, antiatherogenic effects. However, studies elucidating the role and the mechanism(s) of action of hesperetin in cervical cancer are sparse. In this study, we investigated the mechanism of the antiproliferative and apoptotic actions exerted by hesperetin on human cervical cancer SiHa cells. The viability of SiHa cells was evaluated using the MTT assay, apoptosis by acridine orange/ethidium bromide, propidium iodide, TUNEL assay, and Annexin V-Cy3, cell cycle distribution and mitochondrial transmembrane potential using flow cytometry, and apoptotic marker genes using quantitative real-time PCR. The treatment of SiHa cells with hesperetin (IC50, 650 μm) showed a marked concentration- and time-dependent inhibition of proliferation and induced the G2/M phase in a dose-dependent manner after 24 h. There was an attenuation of mitochondrial membrane potential with increased expression of caspase-3, caspase-8, caspase-9, p53, Bax, and Fas death receptor and its adaptor protein Fas-associated death domain-containing protein (FADD), indicating the participation of both death receptor- and mitochondria-related mechanisms. Furthermore, hesperetin-induced apoptosis was confirmed by TUNEL and Annexin V-Cy3. This study shows that hesperetin exhibits a potential anticancer activity against human cervical cancer cell lines in vitro through the reduction in cell viability and the induction of apoptosis. Altogether, these data sustain our contention that hesperetin has anticancer properties and merits further investigation as a potential therapeutic agent.

TRAIL promotes caspase-dependent pro-inflammatory responses via PKCδ activation by vascular smooth muscle cells

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is best known for its selective cytotoxicity against transformed tumor cells. Most non-transformed primary cells and several cancer cell lines are not only resistant to death receptor-induced apoptosis, but also subject to inflammatory responses in a nuclear factor-κB (NF-κB)-dependent manner. Although the involvement of TRAIL in a variety of vascular disorders has been proposed, the exact molecular mechanisms are unclear. Here, we aimed to delineate the role of TRAIL in inflammatory vascular response. We also sought possible molecular mechanisms to identify potential targets for the prevention and treatment of post-angioplastic restenosis and atherosclerosis. Treatment with TRAIL increased the expression of intercellular adhesion molecule-1 by primary human vascular smooth muscle cells via protein kinase C (PKC)δ and NF-κB activation. Following detailed analysis using various PKCδ mutants, we determined that PKCδ activation was mediated by caspase-dependent proteolysis. The protective role of PKCδ was further confirmed in post-traumatic vascular remodeling in vivo. We propose that the TRAIL/TRAIL receptor system has a critical role in the pathogenesis of inflammatory vascular disorders by transducing pro-inflammatory signals via caspase-mediated PKCδ cleavage and subsequent NF-κB activation.

Apolipoprotein L6, induced in atherosclerotic lesions, promotes apoptosis and blocks Beclin 1-dependent autophagy in atherosclerotic cells

Inflammatory cytokine-regulated apoptosis and autophagy play pivotal roles in plaque rupture and thrombosis of atherosclerotic lesions. However, the molecular interplay between apoptosis and autophagy in vascular cells has not been investigated. Our prior study showed that human apolipoprotein L6 (ApoL6), a pro-apoptotic BH3-only member of the Bcl-2 family, was one of the downstream targets of interferon-γ (INFγ), which sensitizes atherosclerotic lesion-derived cells (LDCs) to Fas-induced apoptosis. To investigate whether ApoL6 plays a causal role in atherosclerotic apoptosis and autophagy, in this study, we demonstrate that IFNγ treatment itself strongly induces ApoL6, and ApoL6 is highly expressed and partially co-localized with activated caspase 3 in activated smooth muscle cells in atherosclerotic lesions. In addition, overexpression of ApoL6 promotes reactive oxygen species (ROS) generation, caspase activation, and subsequent apoptosis, which can be blocked by pan caspase inhibitor and ROS scavenger. Knockdown of ApoL6 expression by siApoL6 suppresses INFγ- and Fas-mediated apoptosis. Further, ApoL6 binds Bcl-X(L), one of the most abundant anti-death proteins in LDCs. Interestingly, forced ApoL6 expression in LDCs induces degradation of Beclin 1, accumulation of p62, and subsequent attenuation of LC3-II formation and translocation and thus autophagy, whereas siApoL6 treatment reverts the phenotype. Taken together, our results suggest that ApoL6 regulates both apoptosis and autophagy in SMCs. IFNγ-initiated, ApoL6-induced apoptosis in vascular cells may be an important factor causing plaque instability and a potential therapeutic target for treating atherosclerosis and cardiovascular disease.

High soluble Fas and soluble Fas Ligand serum levels before stent implantation are protective against restenosis

Percutaneous coronary intervention (PCI) represents the most important treatment of coronary artery stenosis today. But instent restenosis (ISR) is a limitation for the outcome. Fas and Fas Ligand have been implicated in apoptosis and vessel wall inflammation. Their role in ISR is not known so far. In this prospective study we studied 137 patients with stable coronary artery disease who underwent elective PCI. Blood samples were taken directly before and 24 hours after PCI. Soluble (s)Fas and sFas Ligand serum levels were measured by ELISA. Restenosis was evaluated six to eight months later either by coronary angiography or by exercise testing. During the follow-up period, 18 patients (13%) developed ISR. At baseline, patients with ISR had significantly lower median sFas, as well as sFas Ligand levels compared to patients without ISR (sFAS: ISR 492 pg/ml, no ISR 967 pg/ml, p=0.014; sFAS Ligand: ISR: 26 pg/ml, no ISR: 42 pg/ml, p=0.001). After PCI median sFas levels significantly decreased in patients with ISR compared to patients without ISR [ISR: -152 pg/ml (IQR -36 to -227), no ISR: -38 pg/ml (IQR -173 to +150 pg/ml), p=0.03]. sFas Ligand levels after PCI significantly increased in ISR patients compared to patients without ISR [ISR: 14 pg/ml (IQR -3 to +26 pg/ml), no ISR -6 pg/ml (IQR -22 to +21 pg/ml), p=0.014]. In conclusion, sFas and sFas Ligand seem to be associated with the development of ISR. Determination of serum levels before and after PCI might help identifying patients at higher risk of ISR.

Proteinase inhibitor 9 is reduced in human atherosclerotic lesion development

BACKGROUND

Granzyme B, a proapoptotic serine protease, is abundant in advanced, unstable atherosclerotic plaques, and it is suggested to contribute to plaque instability by inducing vascular smooth muscle cells apoptosis and by degrading plaque extracellular matrix. Proteinase inhibitor 9, the only known endogenous inhibitor of granzyme B in humans, confers protection against granzyme-B-induced apoptosis. However, the role of proteinase inhibitor 9 in atherosclerotic lesion development has yet to be determined. We hypothesized that atherosclerotic lesions have lower proteinase inhibitor 9 expression levels that will increase their susceptibility to granzyme-B-induced apoptosis.

METHODS

Serial sections of human coronary arteries exhibiting different stages of lesion development were assessed by immunohistochemistry for proteinase inhibitor 9, α-smooth muscle cells actin, granzyme B, CD8, and active caspase-3. Frozen samples were analyzed by Western blot to evaluate total proteinase inhibitor 9 levels.

RESULTS

Vascular smooth muscle cells express less proteinase inhibitor 9 as disease severity increases, and a significant difference in proteinase inhibitor 9 expression is observed between medial and intimal smooth muscle cells. High granzyme B levels colocalize with CD8+ cells and foam cells in the shoulder region and necrotic core area of advanced lesions. In advanced lesions, increased expression of activated caspase-3 in intimal SMC was associated with reduced proteinase inhibitor 9 expression in the presence of granzyme B.

CONCLUSION

Reduced proteinase inhibitor 9 expression in human vascular smooth muscle cells is associated with atherosclerotic disease progression and is inversely related to the extent of apoptosis within the intima. Reduced proteinase inhibitor 9 expression may contribute to increased smooth muscle cell susceptibility to granzyme-B-induced apoptosis within the plaque.

Cardiovascular inflammation and lesion cell apoptosis: a novel connection via the interferon-inducible immunoproteasome

OBJECTIVE

Increasing evidence suggests that chronic inflammation contributes to atherogenesis, and that acute inflammatory events cause plaque rupture, thrombosis, and myocardial infarction. The present studies examined how inflammatory factors, such as interferon-gamma (IFNgamma), cause increased sensitivity to apoptosis in vascular lesion cells.

METHODS AND RESULTS

Cells from the fibrous cap of human atherosclerotic lesions were sensitized by interferon-gamma (IFNgamma) to Fas-induced apoptosis, in a Bcl-X(L) reversible manner. Microarray profiling identified 72 INFgamma-induced transcripts with potential relevance to apoptosis. Half could be excluded because they were induced by IRF-1 overexpression, which did not sensitize to apoptosis. IFNgamma treatment strongly reduced Mcl-1, phospho-Bcl-2 (ser70), and phospho-Bcl-X(L) (ser62) protein levels. Candidate transcripts were modulated by siRNA, overexpression, or inhibitors to assess the effect on IFNgamma-induced Fas sensitivity. Surprisingly, siRNA knockdown of PSMB8 (LMP7), an "immunoproteasome" component, reversed IFNgamma-induced sensitivity to Fas ligation and prevented Fas/IFNgamma-induced degradation of Mcl-1, but did not protect p-Bcl-2 or p-Bcl-X(L). Proteasome inhibition markedly increased Mcl-1, p-Bcl-2, and p-Bcl-X(L) levels after IFNgamma treatment.

CONCLUSIONS

Although critical for antigen presentation, the immunoproteasome appears to be a key link between inflammatory factors and the control of vascular cell apoptosis and may thus be an important factor in plaque rupture and myocardial infarction.

Akt regulates the survival of vascular smooth muscle cells via inhibition of FoxO3a and GSK3

Apoptosis of vascular smooth muscle cells (VSMCs) may lead to atherosclerotic plaque instability and rupture, resulting in myocardial infarction, stroke, and sudden death. However, the molecular mechanisms mediating survival of VSMCs in atherosclerotic plaques remain unknown. Although plaque VSMCs exhibit increased susceptibility to apoptosis and reduced expression of the IGF1 receptor (IGF1R) when compared with normal VSMCs, a causative effect has not been established. Here we show that increased expression of the IGF1R can rescue plaque VSMCs from oxidative stress-induced apoptosis, demonstrating that IGF-1 signaling is a critical regulator of VSMC survival. Akt mediates the majority of the IGF1R survival signaling, and ectopic activation of Akt was sufficient to protect VSMCs in vitro. Both IGF1R and phospho-Akt expression were reduced in human plaque (intimal) VSMCs when compared with medial VSMCs, suggesting that Akt mediates survival signaling in atherosclerosis. Importantly, downstream targets of Akt were identified that mediate its protective effect as inhibition of FoxO3a or GSK3 by Akt-dependent phosphorylation protected VSMCs in vitro. We conclude that Akt and its downstream targets FoxO3a and GSK3 regulate a survival pathway in VSMCs and that their deregulation due to a reduction of IGF1R signaling may promote apoptosis in atherosclerosis.

Resistance to fas-induced apoptosis in cells from human atherosclerotic lesions: elevated Bcl-XL inhibits apoptosis and caspase activation

The inappropriate survival of cells in the neointima contributes to atherosclerotic plaque progression, while apoptosis in the fibrous cap of lesions contributes to myocardial infarction and stroke. Prior genomic-scale transcript profiling of human carotid artery plaque cells with known sensitivity or resistance to fas-induced apoptosis identified candidate genes involved in lesion cell apoptosis. Retroviral overexpression indicated that several candidate factors were not causative, but that Bcl-X(L) conferred complete resistance to apoptosis induced by fas ligation. Resistant cells failed to efficiently activate caspase 8, an effect which was also observed in Bcl-X(L)-transfected cells. Small-molecule Bcl-2/X(L) inhibitors and siRNA knockdown of Bcl-X(L) markedly sensitized resistant cells to apoptosis, and partially restored caspase 8 activation. Caspase 3, 6 and 9 inhibitors reduced caspase 8 activation and blocked apoptosis. Complete knockdown of caspase 9 did not reduce apoptosis, while knockdown of Bid suppressed apoptosis, suggesting that mitochondrial pathways independent of caspase 9, such as Smac/Diablo or AIF, provide a necessary mitochondrial input to efficient caspase activation. Bcl-X(L) appears to modulate lesion cell apoptosis by suppressing mitochondrial amplification of caspase activation loops. The results may have direct implications for controlling plaque instability/progression, and identify a new class of small molecules to inhibit restenosis.

Role of asymmetric dimethylarginine in homocysteine-induced apoptosis of vascular smooth muscle cells

Homocysteine (Hcy) could induce apoptosis of vascular smooth muscle cells (VSMC). Asymmetric dimethylarginine (ADMA) has been thought as a novel risk factor for cardiovascular diseases. We hypothesized that ADMA mediates homocysteine-induced apoptosis of VSMC. In this experiment the level of ADMA in the medium measured by high-performance liquid chromatography (HPLC) was elevated when the apoptosis of T/G HA-VSMC was induced by Hcy which was detected by Hoechst33342 staining or flow cytometry (FCM) with Annecin V+Propidium Iodide (PI). Exogenous ADMA induced the apoptosis of VSMC. At the same time, ADMA elevated the level of intracellular reactive oxidative species (ROS) determined by fluorescent ROS detection kit. The activation of JNK and p38MAPK contributed to ADMA-induced apoptosis of VSMC. The present results suggest that endogenous ADMA is involved in apoptosis of VSMC induced by Hcy, and the effects of ADMA is related to elevation of intracellular ROS and activation of JNK/p38MAPK signaling pathways.

DNA damage, p53, apoptosis and vascular disease

Atherosclerosis is the commonest cause of death in the Western world. The atherosclerotic plaque shows evidence of DNA damage, activation of damage repair pathways, p53 expression and apoptosis, involving a variety of different cell types. This review summarises the evidence for DNA damage in atherosclerosis, the likely stimuli inducing damage, and the increasing role of p53 in mediating apoptosis and its consequences in atherosclerosis.

Up-regulation of CD95 (Apo-1/Fas) is associated with spermatocyte apoptosis during the first round of spermatogenesis in the rat

Apoptosis plays a major role in controlling both the rate of sperm production and chromosomal abnormalities in adult male testes. However, little is known on the mechanisms controlling induction and execution of apoptosis under physiological conditions. In this work we have uncovered a major role for the cell death receptor Fas in both the extrinsic and intrinsic pathways in normal germ cell apoptosis. We show here that Fas levels increased significantly in a group of germ cell in 25 d old rats, which were identified as spermatocytes and only a few spermatogonia. In addition, we show that isolated spermatocytes expressing high levels of Fas display activation of caspase-8, -9, -3, -6 and -2, as well as increased levels of intracellular calcium and decreased pH, which coincides with stabilization of p53, and transcriptional activation of PUMA and Fas. Therefore, our data strongly suggests that transcriptional up regulation of Fas could predispose a group of spermatocytes to Fas ligand triggering apoptosis by the extrinsic and intrinsic pathway.

Endothelial Apoptosis Does Not Determine Symptom Status in Carotid Artery Disease

BACKGROUND

We examined the hypothesis that endothelial denudation in advanced carotid plaques (CPs) occurs by increased apoptosis of endothelial cells (ECs) using scanning electron microscopy (SEM) as well as markers of cellular proliferation and apoptosis in advanced symptomatic CPs (SCPs) and asymptomatic CPs (ACPs).

METHODS

93 consecutive patients underwent carotid endarterectomy. Five additional specimens were studied by SEM. We performed TUNEL assays, and immunostaining against Fas receptor (FasR), Fas ligand (FasL), activated caspase 3 (ACA3) and Ki-67.

RESULTS

SEM revealed morphological changes consistent with EC detachment. Surprisingly, ACA3 positivity was more pronounced on the endothelium of ACPs (4.6 +/- 0.7% of total EC count) than on SCPs (3.3 +/- 0.7%, p = 0.049), and was found to correlate positively with nuclear Ki-67 expression (r(s) = 0.275, p = 0.040). FasL expression was significantly increased on the endothelium of SCPs compared with ACPs (66.4 +/- 4.4 vs. 53.9 +/- 4.5%, p = 0.047).

CONCLUSIONS

Absence of increased positivity of apoptotic markers dismisses apoptosis as a dominant mechanism underlying endothelial detachment of SCPs. Rather, increased ACA3 with co-expression of Ki-67 in ACPs might suggest that renewal of endothelium by active cell turnover may contribute to clinically silent evolution of plaques with preserved EC integrity. These observations may assist in designing novel therapies to prevent endothelial decay and symptom generation in advanced carotid artery disease.

A20, a modulator of smooth muscle cell proliferation and apoptosis, prevents and induces regression of neointimal hyperplasia

A20 is a NF-kappaB-dependent gene that has dual anti-inflammatory and antiapoptotic functions in endothelial cells (EC). The function of A20 in smooth muscle cells (SMC) is unknown. We demonstrate that A20 is induced in SMC in response to inflammatory stimuli and serves an anti-inflammatory function via blockade of NF-kappaB and NF-kappaB-dependent proteins ICAM-1 and MCP-1. A20 inhibits SMC proliferation via increased expression of cyclin-dependent kinase inhibitors p21waf1 and p27kip1. Surprisingly, A20 sensitizes SMC to cytokine- and Fas-mediated apoptosis through a novel NO-dependent mechanism. In vivo, adenoviral delivery of A20 to medial rat carotid artery SMC after balloon angioplasty prevents neointimal hyperplasia by blocking SMC proliferation and accelerating re-endothelialization, without causing apoptosis. However, expression of A20 in established neointimal lesions leads to their regression through increased apoptosis. This is the first demonstration that A20 exerts two levels of control of vascular remodeling and healing. A20 prevents neointimal hyperplasia through combined anti-inflammatory and antiproliferative functions in medial SMC. If SMC evade this first barrier and neointima is formed, A20 has a therapeutic potential by uniquely sensitizing neointimal SMC to apoptosis. A20-based therapies hold promise for the prevention and treatment of neointimal disease.

Interferon-gamma induces Fas trafficking and sensitization to apoptosis in vascular smooth muscle cells via a PI3K- and Akt-dependent mechanism

Vascular smooth muscle cell (VSMC) apoptosis occurs in advanced atherosclerotic plaques where it may contribute to plaque instability. VSMCs express the death receptor Fas but are relatively resistant to Fas-induced apoptosis due in part to the intracellular sequestration of Fas. Although inflammatory cytokines such as interferon (IFN)-gamma present in plaques can prime VSMCs to FasL-induced death, the mechanism of this effect is unclear. We examined Fas expression and FasL-induced apoptosis in human VSMCs in response to IFN-gamma. IFN-gamma induced Fas trafficking to the cell surface within 24 hours, an effect that required Jak2/Stat1 activity. IFN-gamma also stimulated Akt activity, and both Fas trafficking and Stat1 activation were inhibited by blocking PI3K, Akt, or Jak-2. IFN-gamma increased Fas-induced apoptosis in vitro by 46 +/- 8% (mean +/- SEM, P = 0.04), an event that could be abrogated by inhibition of PI3K, Akt, or Jak-2. IFN-gamma also increased Fas-induced apoptosis in vivo 7.5- to 15-fold (P < 0.05) in human arteries transplanted into immunodeficient mice, accompanied by increased Fas and phospho-Ser727-Stat1. We conclude that IFN-gamma primes VSMCs to Fas-induced apoptosis, in part by relocation of Fas to the cell surface, a process that involves PI3K, Akt, and Jak-2/Stat1. IFN-gamma present in plaques may co-operate with FasL to induce VSMC apoptosis in atherosclerosis.

Plasminogen activation: a mediator of vascular smooth muscle cell apoptosis in atherosclerotic plaques

BACKGROUND

Apoptosis of vascular cells is considered to be a major determinant of atherosclerotic plaque vulnerability and potential rupture. Plasmin can be generated in atherosclerotic plaques and recent in vitro data suggest that plasminogen activation may trigger vascular smooth muscle cell (VSMC) apoptosis.

AIM

To determine whether plasminogen activation may induce aortic VSMC apoptosis ex vivo and in vivo.

METHODS AND RESULTS

Mice with single or combined deficiencies of apolipoprotein E (ApoE) and plasminogen activator inhibitor-1 (PAI-1) were used. Ex vivo incubation with plasminogen of isolated aortic tunica media from PAI-1-deficient mice induced plasminogen activation and VSMC apoptosis, which was inhibited by alpha2-antiplasmin. In vivo, levels of plasmin, active caspase 3 and VSMC apoptotic index were significantly higher in atherosclerotic aortas from mice with combined ApoE and PAI-1 deficiencies than in those from littermates with single ApoE deficiency. A parallel decrease in VSMC density was observed.

CONCLUSIONS

These data strongly suggest that plasminogen activation may contribute to VSMC apoptosis in atherosclerotic plaques.

Hydrogen peroxide predisposes neonatal rat ventricular myocytes to Fas-mediated apoptosis

Neonatal rat ventricular myocytes (NRVM) grown in normoxic environment are not susceptible to Fas-induced apoptosis. In the present work, we tested the hypothesis that free radical injury represented by transient exposure to H2O2 sensitizes NRVM to Fas-mediated apoptosis. NRVM were treated with H2O2 (0.5 mM) for 2-4 h and thereafter exposed for 7 h to recombinant Fas ligand (rFasL, 10 ng/ml) plus an enhancing antibody (1 microg/ml). Apoptotic cardiomyocytes were counted and apoptosis-related proteins were measured by Western blot. H2O2 alone induced apoptosis (9.4+/-1.0%) that was preceded by activation of caspases-8 and -3, and PARP degradation. Incubation of NRVM with H2O2, followed by exposure to rFasL, increased the apoptotic index to 13.8+/-2.0%, but did not change caspase-8 or PARP activation. To investigate the mechanism underlying the sensitizing affect of H2O2 towards Fas-induced apoptosis, we studied the effects of H2O2 on the expression of key apoptosis signaling proteins. Incubation with H2O2 for 2-4 h decreased Fas expression and the expression of the Fas-related antiapoptotic proteins FLIP(L) and ARC, and increased the expression of the antiapoptotic proteins bcl-2 and xIAP. FADD expression was unchanged. Next, we tested the effect of H2O2 on the apoptosis-inducing, Fas-dependent Daxx-ASK-1-JUN kinase pathway. H2O2 dramatically increased ASK-1 expression and JUN kinase activation, but did not effect Daxx expression. Based on these findings we concluded that H2O2 sensitizes NRVM to Fas-mediated apoptosis by activating the Daxx-ASK-1-JUN kinase pathway, and by shifting the balance between proapoptotic and antiapoptotic proteins towards the former.

Modulation of smooth muscle cell proliferation and migration: role of smooth muscle cell heterogeneity

Proliferation and migration of smooth muscle cells (SMCs) from the media towards the intima are key events in atherosclerosis and restenosis. During these processes, SMC undergo phenotypic modulations leading to SMC dedifferentiation. The identification and characterization of factors controlling these phenotypic changes are crucial in order to prevent the formation of intimal thickening. One of the questions which presently remains open, is to know whether any SMCs of the media are capable of accumulating into the intima or whether only a predisposed medial SMC subpopulation is involved in this process. The latter hypothesis implies that arterial SMCs are phenotypically heterogenous. In this chapter, we will describe the distinct SMC phenotypes identified in arteries of various species, including humans. Their role in the formation of intimal thickening will be discussed.

Redistribution of CD95, DR4 and DR5 in rafts accounts for the synergistic toxicity of resveratrol and death receptor ligands in colon carcinoma cells

The natural phytoalexin resveratrol (3, 5, 4'-trihydroxystilbene) exhibits both chemopreventive and antitumor activities through a variety of mechanisms. We have shown previously that resveratrol-induced apoptosis of a human colon cancer cell line involved the redistribution of CD95 (Fas/Apo-1) into lipid rafts. Here, we show that, in colon cancer cells that resist to resveratrol-induced apoptosis, the polyphenol also induces a redistribution of death receptors into lipid rafts. This effect sensitizes these tumor cells to death receptor-mediated apoptosis. In resveratrol-treated cells, tumor necrosis factor (TNF), anti-CD95 antibodies and TNF-related apoptosis-inducing ligand (TRAIL) activate a caspase-dependent death pathway that escapes Bcl-2-mediated inhibition. Resveratrol does not enhance the number of death receptors at the surface of tumor cells but induces their redistribution into lipid rafts and facilitates the caspase cascade activation in response to death receptor stimulation. The cholesterol sequestering agent nystatin prevents resveratrol-induced death receptor redistribution and cell sensitization to death receptor stimulation. Thus, whatever its ability to induce apoptosis in a tumor cell, resveratrol induces redistribution of death receptors into lipid rafts. This redistribution sensitizes the cells to death receptor stimulation. Such a sensitizing effect may be of therapeutic interest if TRAIL agonists are introduced in clinics.

Mitogenic actions of neuropeptide Y in vascular smooth muscle cells: synergetic interactions with the beta-adrenergic system

Neuropeptide Y (NPY), a sympathetic cotransmitter and vasoconstrictor, also stimulates vascular smooth muscle cell (VSMC) growth, but which of its Y1-Y5 receptors are involved remains unclear. In quiescent rat VSMCs, NPY receptor mRNAs were undetectable (reverse transcription-polymerase chain reaction), but Y1, Y2, and Y5 expression were upregulated or induced following NPY treatment. Concomitantly, NPY increased up to twofold [3H]thymidine incorporation and cell number bimodally, with a high-affinity peak at pM and low affinity peak at nM concentrations. The Y1 or Y5 (not Y2) antagonist alone did not change the high-affinity peak but decreased the low affinity peak by 50% and fully blocked NPY's response when combined. In VSMCs lacking NPY receptors and responsiveness, transient Y1 cDNA transfection restored their mitogenic response (blocked by the Y1 antagonist). In VSMCs with low or no NPY responsiveness, pre-exposure to beta-adrenergic receptor agonist (isoproterenol), forskolin, or dibutyryl cAMP augmented NPY's mitogenic effect, while upregulating Y1, Y2, and Y5 receptor expression (isoproterenol only). Thus, NPY is a potent vascular mitogen acting via Y1 and Y5 receptors. However, since their expression is low in nonproliferating cells, amplification of NPY's mitogenic responses requires upregulation of at least the Y1 receptor by NPY itself or beta-adrenergic, cAMP-dependent activation.

Oxidized low density lipoprotein potentiation of Fas-induced apoptosis through lectin-like oxidized-low density lipoprotein receptor-1 in human umbilical vascular endothelial cells

Under normal conditions, vascular endothelial cells are resistant to Fas-mediated apoptosis, although they express detectable Fas on their cell surface. Because oxidized Low density lipoprotein (Ox-LDL) is thought to promote atherogenesis, the potential role that Ox-LDL may play in Fas-mediated apoptosis was investigated in human umbilical vascular endothelial cells (HUVECs), focusing particularly on the involvement of the lectin-like Ox-LDL receptor-1 (LOX-1). HUVECs were treated with agonistic anti-Fas antibody (CH11) and Ox-LDL and then the degree of apoptosis was determined by cell death ELISA. Ox-LDL concentration-dependently sensitized Fas-mediated apoptosis. Flow cytometry demonstrated that Ox-LDL dose-dependently up-regulated cell surface Fas expression. On the other hand, treating HUVECs with Ox-LDL did not lead to any significant change in the expression of death mediators, including Fas, Fas ligand (FasL), FADD, and FLICE as assessed by multiplex polymerase chain reaction amplification. More importantly, these effects of Ox-LDL on Fas-mediated apoptosis were significantly blocked by a neutralizing LOX-1 monoclonal antibody, which can block LOX-1-mediated cellular uptake of Ox-LDL. Ox-LDL may be an important factor involved in the regulation of Fas-induced apoptosis via Ox-LDL/LOX-1 interaction in vascular endothelial cells. The results may provide insights into the pathogenesis of accelerated atherosclerosis in patients with hyperlipidemia.

Notch3 signaling in vascular smooth muscle cells induces c-FLIP expression via ERK/MAPK activation. Resistance to Fas ligand-induced apoptosis

Mutations in the Notch3 receptor result in the cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephelopathy (CADASIL) syndrome, a heritable arteriopathy predisposing to early onset stroke. Based upon clinical evidence that CADASIL arteriopathy results in degeneration and loss of vascular smooth muscle cells (VSMC) from the arterial wall, we postulated that Notch3 signaling is a critical determinant of VSMC survival. We initially established that both transient and constitutive Notch3 signaling promoted VSMC survival in response to the proapoptotic Fas ligand (FasL). Resistance to FasL-induced apoptosis was associated with the induction of c-FLIP, a primary inhibitor of the FasL signaling pathway. We determined that Notch3's regulation of c-FLIP was independent of the activity of the classical DNA-binding protein, RBP-Jk, but dependent upon cross-talk activation of the ERK/MAPK pathway. We extended our observations to the in vivo context by determining a coordinate regulation of Notch3 and c-FLIP within the arterial wall in response to injury. Furthermore, we defined that expression levels of Notch3 and c-FLIP are coordinately up-regulated within the neointima of remodeled arteries. Taken together, these findings provide initial evidence that Notch3 signaling may be a critical determinant of VSMC survival and vascular structure by modulating the expression of downstream mediators of apoptosis via signaling cross-talk with the ERK/MAPK pathway.

Hypoxia predisposes neonatal rat ventricular myocytes to apoptosis induced by activation of the Fas (CD95/Apo-1) receptor: Fas activation and apoptosis in hypoxic myocytes

OBJECTIVE

Since apoptosis is an important contributor to heart diseases in which ischemia and hypoxia are key elements, we tested the hypothesis that hypoxia predisposes neonatal rat ventricular myocytes (NRVM) to Fas-mediated apoptosis, by shifting the balance between antiapoptotic and proapoptotic proteins towards the latter.

METHODS

Normoxic or hypoxic (22 h, 1% O(2)) cultured NRVM were exposed to recombinant Fas L (rFasL) for 7 h, and apoptosis measured thereafter.

RESULTS

Whereas in normoxic NRVM, rFasL did not cause apoptosis measured by the TUNEL assay (4.8+/-0.5% in control versus 4.5+/-0.9% in rFasL), in hypoxic cultures rFasL increased the background apoptosis level by 100%. That Fas was functional in normoxic NRVM, despite its inability to mediate apoptosis, was evidenced by the finding that Fas activation increased the diastolic [Ca(2+)](i) levels measured by Fura 2 fluorescence, and caused arrhythmias. In support of our working hypothesis, hypoxia increased Fas expression by 200% (measured by quantitative Western blot), and the expression of the proapoptotic proteins ARTS and FADD by 323 and 250%, respectively, and decreased the expression of the antiapoptotic proteins ARC and FLIP by 90 and 60%, respectively.

CONCLUSION

By upregulating Fas expression and key proapoptotic proteins, and by downregulating antiapoptotic proteins, hypoxia predisposes ventricular myocytes to Fas-induced apoptosis.

Activation of the Fas/Fas ligand pathway in hypertensive renal disease in Dahl/Rapp rats

BACKGROUND

Hypertensive nephrosclerosis is the second most common cause of end-stage renal failure in the United States. The mechanism by which hypertension produces renal failure is incompletely understood. Recent evidence demonstrated that an unscheduled and inappropriate increase in apoptosis occurred in the Dahl/Rapp rat, an inbred strain of rat that uniformly develops hypertension and hypertensive nephrosclerosis; early correction of the hypertension prevents the renal injury. The present study examined the role of the Fas/FasL pathway in this process.

METHODS

Young male Dahl/Rapp salt-sensitive (S) and Sprague-Dawley rats were fed diets that contained 0.3% or 8.0% NaCl diets. Kidneys were examined at days 7 and 21 of the study.

RESULTS

An increase in Fas and FasL expression was observed in glomerular and tubular compartments of kidneys of hypertensive S rats, whereas dietary salt did not change expression of either of these molecules in normotensive Sprague-Dawley rats. Associated with this increase was cleavage of Bid and activation of caspase-8, the initiator caspase in this apoptotic pathway, by day 21 of the study.

CONCLUSIONS

Augmented expression of apoptotic signaling by the Fas/FasL pathway occurred during development of end-stage renal failure in this model of hypertensive nephrosclerosis.

Propionyl-L-carnitine reduces intimal hyperplasia after injury in normocholesterolemic rabbit carotid artery by modulating proliferation and caspase 3-dependent apoptosis of vascular smooth muscle cells

Previously we documented that propionyl-L-carnitine (PLC) reduces the growth of atherosclerotic lesions in cholesterol-fed aged rabbits in association with a decrease of plaque smooth muscle cell (SMC) proliferation and plasma triglycerides. To clarify whether PLC might influence SMC growth through mechanisms other than triglyceride lowering, we investigated the effect of a daily treatment per os with PLC on carotid intimal hyperplasia after ballooning in normocholesterolemic rabbits. PLC did not induce variations of plasma triglyceride and cholesterol. One week later, the number of proliferating SMCs was reduced in PLC as compared with controls. After 3 weeks, morphometric analysis demonstrated a reduced neointimal relative volume and percentage of stenosis but not vessel area in PLC as compared with controls. This associated with an intimal reduced SMC number and an increased apoptotic rate as detected by nick-end labelling (TUNEL) and ligation-mediated polymerase chain reaction (PCR). Western blotting also demonstrated an increase of caspase-3 cleavage in PLC carotids. Antiproliferative and pro-apoptotic effects of PLC were confirmed in vitro on actively proliferating and serum deprived SMCs, respectively. Molecules with an additional cell-specific, pro-apoptotic action may represent a new therapeutic tool in reducing intimal SMC hyperplasia following angioplasty or stenting procedures.

Apoptosis in atherosclerosis: focus on oxidized lipids and inflammation

An increasing body of evidence from both animal models and human specimens suggests that apoptosis or programmed cell death is a major event in the pathophysiology of atherosclerosis. Although the significance of apoptosis in atherosclerosis remains unclear, it has been proposed that apoptotic cell death contributes to plaque instability, rupture and thrombus formation. Biochemical and genetic analyses of apoptosis provide an increasingly detailed picture of the intracellular signaling pathways involved. Nevertheless, it remains to be determined whether apoptosis can become a clinically important approach to modulate plaque progression. In this review, we have outlined some of the most recent results concerning apoptosis in atherosclerosis with a special focus on oxidized lipids, inflammation and therapeutic regulation of the apoptotic cell death process.

Endothelial cell apoptosis: biochemical characteristics and potential implications for atherosclerosis

The high turnover of endothelial cells (EC) in atherosclerosis suggests that an increase in the frequency of both cell proliferation and cell death is important in the pathogenesis of this common disorder. Further, increased apoptosis of EC, smooth muscle cells (SMC) and immune cells has been observed in atheromatous plaques. Many pro-atherogenic factors, including oxidized low-density lipoproteins, angiotensin II and oxidative stress, can induce EC apoptosis. Such damage to the endothelium may be an initiating event in atherogenesis since EC apoptosis may compromise vasoregulation, increase SMC proliferation, SMC migration and blood coagulation. In addition, EC overlying vascular lesions have been shown to increase their expression of pro-apoptotic proteins, such as Fas and Bax, while decreasing levels of anti-apoptotic factors. Therefore, understanding EC apoptotic pathways that are altered in atherosclerosis may enable a greater understanding of disease pathogenesis and foster the development of new therapies. The present discussion outlines the biochemical characteristics of EC apoptosis and the role that altered regulation of apoptosis plays in vasculopathy.

Smooth muscle cell apoptosis in arteriosclerosis

Arteriosclerosis, a paradigmatic age-related disease, encompasses (spontaneous) atherosclerosis, restenosis after percutaneous transluminal coronary angioplasty, autologous arterial or vein graft arteriosclerosis and transplant arteriosclerosis. In all types of arteriosclerosis, vascular smooth muscle cell (SMC) accumulation in the intima is a key event, but abundant evidence also indicates the importance of SMC apoptosis in the development of arteriosclerosis. Because SMC proliferation and apoptosis coincide in arteriosclerotic lesions, the balance between these two processes could be a determinant during vessel remodeling and disease development. Various stimuli, including oxidized lipoproteins, altered hemodynamic stress and free radicals, can induce SMC apoptosis in vitro. As risk factors for arteriosclerosis, these stimuli may also lead to vascular cell apoptosis in vivo. The presence of apoptotic cells in atherosclerotic and restenotic lesions could have potential clinical implications for atherogenesis and contributes to the instability of the lesion. Based on the progress in this field, this review focuses on the mechanism and impact of SMC apoptosis in the pathogenesis of arteriosclerosis and highlights the role of biomechanical stress in SMC apoptosis.

Proteasome inhibitors sensitize human vascular smooth muscle cells to Fas (CD95)-mediated death

It was investigated whether proteasome activity was implicated in susceptibility of human vascular smooth muscle cells (VSMCs) to Fas-mediated death. Human fetal aorta smooth muscle cells were treated with agonistic anti-Fas antibody (CH11) and proteasome inhibitors (MG115 or MG132) and then cell death was determined by morphology, viability, and DNA fragmentation. The present study reports that: (a) crosslinking of Fas receptor with anti-Fas antibody in the presence of proteasome inhibitor-induced death and DNA degradation in human VSMCs that were blocked by caspases inhibitor z-DEVD.fmk; (b) cotreatment with anti-Fas antibody and proteasome inhibitor activated caspase-3; (c) proteasome inhibitors did not influence expression of procaspase-8, procaspase-3, c-FLIP, and Bcl-2; and (d) proteasome inhibitors up-regulated Fas and FADD. The data indicate that proteasome activity is important in survival of VSMCs and provide the first evidence that proteasome is involved in Fas signal transduction. The present study proposes novel mechanism(s) by which VSMCs become susceptible to FasL.

Apoptosis in atherosclerosis. Does it contribute to plaque instability?

Several reports have demonstrated apoptosis in the advanced human atheroma. Most clinical events however, are precipitated by plaque rupture, to a lesser extent erosion, and the development of occlusive thrombi. Whether the extent of apoptosis can influence lesion stability is not precisely known, however, there is emerging data supporting this role. Obvious difficulties arise when studying apoptosis in atherosclerotic plaques because of the complex nature of the disease and lack of an experimental model of plaque instability. This article applies a systematic approach to discuss the issue of apoptosis in context of early disease to complex symptomatic lesions that may become fatal.

25-Hydroxycholesterol activates a cytochrome c release-mediated caspase cascade

We have previously shown that 25-hydroxycholesterol (25-OHC) treated CHO-K1 cells could be used as a model to investigate the signaling pathway of apoptosis induced by oxidized LDL in vascular cells. In the present study, we examine the execution phase of the apoptotic pathway in CHO-K1 cell death induced by 25-OHC. Oxysterol-induced apoptosis in CHO-K1 was accompanied by caspase activation and was preceded by mitochondrial cytochrome c release. The addition of a competitive caspase-3 inhibitor, Ac-DEVD-CHO, prevented 25-OHC-induced apoptotic cell death. Furthermore, immunoblot analysis showed that 25-OHC treatment induced the degradation of poly(ADP-ribose) polymerase (PARP)-a substrate for caspase 3 and a key enzyme involved in genome surveillance and DNA repair. Thus, we could demonstrate in CHO-K1 cells that 25-OHC activates the apoptotic machinery through induction of the release of cytochrome c from mitochodria into the cytosol and activation of a typical caspase cascade.