Modulation of endothelial cell apoptosis: mechanisms and pathophysiological roles

Mechanism Exploration of Dietary Supplement Astaxanthin on Improving Atherosclerosis through an Integrated Strategy Encompassing Artificial Intelligence Virtual Screening and Experimental Validation

Atherosclerosis (AS) is a major and common pathological basis of ischemic intestinal infarction, myocardial infarction, stroke, renal failure, and other highly lethal and disabling diseases. Current pharmacological interventions (e.g., statins) often cause adverse effects, limiting their long-term use. Natural compounds, with their multitarget efficacy and superior safety profiles, have emerged as promising alternatives for AS treatment. As a potent antioxidant carotenoid, astaxanthin exhibits unique therapeutic potential by simultaneously targeting inflammation, oxidative stress, and lipid metabolism, which are key drivers of AS pathogenesis. This study will systematically decipher astaxanthin's therapeutic mechanisms through an integrative strategy encompassing artificial intelligence virtual screening and experimental validation. Notably, five proteins, including CTSD, DPP4, FABP5, ITGAL, and MMP9, were identified as core targets for astaxanthin intervention in AS via network pharmacology and machine learning. Meanwhile, the results from molecular dynamic simulations confirmed that these core targets can stable binding with astaxanthin. Furthermore, in vitro experiments further validated astaxanthin can inhibit foam cell formation, restore redox balance, and suppress inflammation. Moreover, a close correlation has been found between them. These findings position astaxanthin as a multitarget natural agent to combat AS, addressing both efficacy advantage and safety concerns of current therapies.

Vitamin D decreases cell death and inflammation in human umbilical vein endothelial cells and placental explants from pregnant women with preeclampsia cultured with TNF-α

This study evaluated the impact of vitamin D on Human Umbilical Vein Endothelial Cells (HUVEC) and inflammation in placental explants from women with preeclampsia (PE). HUVEC and explants from 10 late-onset PE (LOPE), 10 early-onset (EOPE), and 10 normotensive (NT) pregnant women were cultured with/without tumor necrosis factor (TNF-α) and VD. Interleukin-1β (IL-1β), 18 (IL-18), TNF-α, and TNF-related apoptosis-inducing ligand (TRAIL) were detected by ELISA. High mobility group box 1 (HMGB1) was determined by qPCR/Western blotting, and cell death by flow cytometry. Statistical significance was accepted at p < .05. Compared to the NT group, the endogenous levels of IL-1β, TNF-α, and IL-18 were higher in the PE group. The stimulus with TNF-α increased cytokines in NT, TNF-α in EOPE/LOPE, IL-18 in LOPE, and all cytokines in HUVEC. TNF-α+VD treatment decreased cytokines in explant and HUVEC supernatants. TRAIL was higher in EOPE versus NT, while TNF-α increased this receptor in NT versus control. In HUVEC, TNF-α increased TRAIL versus control, and TNF-α+VD decreased levels compared to only TNF-α stimulus. Protein expression of HMGB1 was higher in explant cultures treated with TNF-α and decreased after TNF-α+VD treatment in all groups, and gene/protein expression in HUVEC. Gene expression was elevated in EOPE versus NT and LOPE, and TNF-α increased HMGB1 in NT versus control, while TNF-α+VD decreased mRNA levels in EOPE. TNF-α stimulus increased late apoptosis in HUVEC, while VD increased viability. These in vitro observations suggest that VD administration to women with preeclampsia may be beneficial in reducing placental inflammation and cell death.

Hydroxysafflor Yellow A Attenuates Hydrogen Peroxide-Induced Oxidative Damage on Human Umbilical Vein Endothelial Cells

Oxidative stress of endothelial cells is thought to be a principal cause that induces many cardiovascular diseases. Hydroxysafflor yellow A (HSYA) is a major active component in traditional Chinese medicine safflower and has been used to cure ischemic cardiovascular diseases in China for many years. This study aims to investigate whether HSYA has a repairing effect on oxidative damage of human umbilical vein endothelial cells (HUVECs) induced by H2O2 and to provide a theoretical basis for the clinical treatment of cardiovascular diseases related to traditional Chinese medicine. Based on the establishment of an H2O2-induced HUVEC oxidative injury model, the cell viability and proliferation rate were measured by the MTT assay and EdU staining. The intracellular GSH/GSSG ratio and SOD activity were determined by kits. The ROS level was detected by flow cytometry. And the BAX, Bcl-2, PTEN, and AKT expressions were evaluated with western blotting methods. The results showed that HSYA treatment significantly attenuated the H2O2-induced HUVEC cell damage, increased the intracellular GSH/GSSG ratio and unit SOD activity also, and decreased the intracellular ROS levels. Furthermore, HSYA increased the expressions of AKT and Bcl-2 proteins and inhibited the expressions of BAX and PTEN proteins. These suggest that HSYA exerts repair effects on H2O2-induced oxidative damage in HUVECs, and the mechanisms may be related to the influence of BAX/Bcl-2 expression and AKT/PTEN signal pathway expression.

E3 Ubiquitin ligase NEDD4 family‑regulatory network in cardiovascular disease

Protein ubiquitination represents a critical modification occurring after translation. E3 ligase catalyzes the covalent binding of ubiquitin to the protein substrate, which could be degraded. Ubiquitination as an important protein post-translational modification is closely related to cardiovascular disease. The NEDD4 family, belonging to HECT class of E3 ubiquitin ligases can recognize different substrate proteins, including PTEN, ENaC, Nav1.5, SMAD2, PARP1, Septin4, ALK1, SERCA2a, TGFβR3 and so on, via the WW domain to catalyze ubiquitination, thus participating in multiple cardiovascular-related disease such as hypertension, arrhythmia, myocardial infarction, heart failure, cardiotoxicity, cardiac hypertrophy, myocardial fibrosis, cardiac remodeling, atherosclerosis, pulmonary hypertension and heart valve disease. However, there is currently no review comprehensively clarifying the important role of NEDD4 family proteins in the cardiovascular system. Therefore, the present review summarized recent studies about NEDD4 family members in cardiovascular disease, providing novel insights into the prevention and treatment of cardiovascular disease. In addition, assessing transgenic animals and performing gene silencing would further identify the ubiquitination targets of NEDD4. NEDD4 quantification in clinical samples would also constitute an important method for determining NEDD4 significance in cardiovascular disease.

Role of WW domain E3 ubiquitin protein ligase 2 in modulating ubiquitination and Degradation of Septin4 in oxidative stress endothelial injury

Oxidative stress-associated endothelial injury is the initial event and major cause of multiple cardiovascular diseases such as atherosclerosis and hypertensive angiopathy. A protein homeostasis imbalance is a critical cause of endothelial injury, and homologous to E6AP C-terminus (HECT)-type E3 ubiquitin ligases are the core factors controlling protein homeostasis. Although HECT-type E3 ubiquitin ligases are involved in the regulation of cardiac development and diseases, their roles in endothelial injury remain largely unknown. This study aimed to identify which HECT-type E3 ubiquitin ligase is involved in endothelial injury and clarify the mechanisms at molecular, cellular, and organism levels. We revealed a novel role of the HECT-type E3 ubiquitin ligase WWP2 in regulating endothelial injury and vascular remodeling after endothelial injury. Endothelial/myeloid-specific WWP2 knockout in mice significantly aggravated angiotensin II/oxidative stress-induced endothelial injury and vascular remodeling after endothelial injury. The same results were obtained from in vitro experiments. Mechanistically, the endothelial injury factor Septin4 was identified as a novel physiological substrate of WWP2. In addition, WWP2 interacted with the GTPase domain of Septin4, ubiquitinating Septin4-K174 to degrade Septin4 through the ubiquitin-proteasome system, which inhibited the Septin4-PARP1 endothelial damage complex. These results identified the first endothelial injury-associated physiological pathway regulated by HECT-type E3 ubiquitin ligases in vivo as well as a unique proteolytic mechanism through which WWP2 controls endothelial injury and vascular remodeling after endothelial injury. These findings might provide a novel treatment strategy for oxidative stress-associated atherosclerosis and hypertensive vascular diseases.

Subendothelial matrix components influence endothelial cell apoptosis in vitro

The programmed form of cell death (apoptosis) is essential for normal development of multicellular organisms. Dysregulation of apoptosis has been linked with embryonal death and is involved in the pathophysiology of various diseases. Specifically, endothelial apoptosis plays pivotal roles in atherosclerosis whereas prevention of endothelial apoptosis is a prerequisite for neovascularization in tumors and metastasis. Endothelial biology is intertwined with the composition of subendothelial basement membrane proteins. Apoptosis was induced by addition of tumor necrosis factor-α to cycloheximide-sensitized endothelial cells. Cells were either grown on polystyrene culture plates or on plates precoated with healthy basement membrane proteins (collagen IV, fibronectin, or laminin) or collagen I. Our results reveal that proteins of healthy basement membrane alleviate cytokine-induced apoptosis whereas precoating with collagen type I had no significant effect on apoptosis by addition of tumor necrosis factor-α to cycloheximide-sensitized endothelial cells compared with cells cultured on uncoated plates. Yet, treatment with transforming growth factor-β1 significantly reduced the rate of apoptosis endothelial cells grown on collagen I. Detailed analysis reveals differences in intracellular signaling pathways for each of the basement membrane proteins studied. We provide additional insights into the importance of basement membrane proteins and the respective cytokine milieu on endothelial biology. Exploring outside-in signaling by basement membrane proteins may constitute an interesting target to restore vascular function and prevent complications in the atherosclerotic cascade.

Effects of miR-503-5p on apoptosis of human pulmonary microvascular endothelial cells in simulated microgravity

Recent studies have shown that microRNA (miRNAs) can play important roles in the regulation of endothelial cell (EC) function. However, the expression profile of miRNAs and their effects on the apoptosis of ECs under microgravity conditions remains unclear. In this study, the apoptosis of human pulmonary microvascular endothelial cells (HPMECs) under simulated microgravity was identified by Annexin V and propidium iodide double staining and transmission electron microscopy. miRNA microarray assay was used to screen the differentially expressed miRNAs in HPMECs under simulated microgravity, and eight differentially expressed miRNAs were identified. Specifically, miR-503-5p, which was found to be most significantly upregulated in both microarray and quantitative reverse-transcription polymerase chain reaction assays, was selected for further functional investigation. Overexpression of miR-503-5p induced apoptosis of HPMECs under normal gravity and aggravated the negative effects of simulated microgravity on HPMECs. Furthermore, silencing of miR-503-5p expression effectively attenuated the negative effects of simulated microgravity on HPMECs. Further experiments showed that the mRNA and protein expression of anti-apoptotic factor B-cell lymphoma-2 (Bcl-2), which has been confirmed as a direct target of miR-503-5p, was inhibited by the upregulation of miR-503-5p and increased by the downregulation of miR-503-5p. Taken together, our findings demonstrate, for the first time, that miR-503-5p can induce apoptosis of HPMECs under simulated microgravity through, at least in part, inhibiting the expression of Bcl-2.

Astragalus polysaccharide ameliorates H2O2-induced human umbilical vein endothelial cell injury

Endothelial dysfunction caused by reactive oxygen species (ROS) has been implicated in numerous cardiovascular diseases. Astragalus polysaccharide (APS), an important bioactive component extracted from the Chinese herb Astragalus membranaceus, has been widely used for the treatment of cardiovascular disease. The present study aimed to investigate the effects of APS on hydrogen peroxide (H₂O₂)-induced human umbilical vein endothelial cell (HUVEC) injury. Following treatment with 400 µM H₂O₂ for 24 h, cell viability was decreased and apoptosis was increased. However, pretreatment with APS for 1 h significantly attenuated H₂O₂-induced injury in HUVECs. In addition, APS decreased intracellular ROS levels, increased the protein expression of endothelial nitric oxide synthase and copper-zinc superoxide dismutase, elevated intracellular cyclic guanosine monophosphate (an activity marker for nitric oxide) levels and restored the mitochondrial membrane potential, compared with cells treated with H₂O₂ only. In conclusion, the results of the present study suggested that APS may protect HUVECs from injury induced by H₂O₂ via increasing the cell antioxidant capacity and nitric oxide (NO) bioavailability, which may contribute to the improvement of the imbalance between ROS and NO levels.

Protective effects of casein-derived peptide VLPVPQK against hydrogen peroxide–induced dysfunction and cellular oxidative damage in rat osteoblastic cells

Oxidative stress inhibits osteoblast differentiation and function that lead to the development of osteoporosis. Casein-derived peptide VLPVPQK (PEP), a potent antioxidant, was isolated from β-casein of buffalo milk. We used an in vitro oxidative stress model induced by hydrogen peroxide (H2O2) in rat osteoblastic cells to investigate the protective effects of PEP against H2O2-induced dysfunction and oxidative damage. Cells were pretreated with PEP (50–200 ng/mL) for 2, 7 or 21 days followed by 0.3 mM H2O2 treatment for 24 h and then markers of osteogenic development, oxidative damage and apoptosis were examined. PEP significantly increased the viability and differentiation markers of osteoblast cells such as alkaline phosphatase and calcium mineralization. Moreover, PEP suppressed the production of reactive oxygen species (ROS), lipid peroxidation and ameliorated H2O2-induced reduction in glutathione, superoxide dismutase and catalase activities. In addition, PEP partially inhibited caspase-9 and-3 activities and reduced propidium iodide–positive cells. Altogether, our results demonstrated that PEP could protect rat osteoblast against H2O2-induced dysfunction and oxidative damage by reduction of ROS production, lipid peroxidation and increased antioxidant enzyme activities. Thus, our data suggest that PEP might be a valuable protective agent against oxidative stress–related diseases such as osteoporosis.

Protective Effect of 2,4',5'-Trihydroxyl-5,2'-dibromo diphenylmethanone, a New Halophenol, against Hydrogen Peroxide-Induced EA.hy926 Cells Injury

Vascular endothelial cells produce reactive oxygen species (ROS) during the process of energy metabolism in aerobic respiration. A growing body of evidence indicates that excessive ROS is implicated in the pathogenesis of cardiovascular diseases including atherosclerosis. The newly synthesized halophenol, 2,4',5'-trihydroxyl-5,2'-dibromo diphenylmethanone (TDD), exhibits antioxidative and cytoprotective activities in vitro. In this study, the protective effect of TDD against hydrogen peroxide (H2O2)-induced oxidative injury of EA.hy926 cells was investigated. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-dephenyltetrazolium bromide (MTT) assay, while the effect of TDD on the transcription profile of EA.hy926 cells subjected to H2O2-induced oxidative injury was evaluated by microarray analysis. Several signaling pathways, including apoptosis, were significantly associated with TDD. Flow cytometric analysis was used to evaluate anti-apoptotic effect of TDD. Subsequently, RT-PCR and Western blot were used to detect the expressions of the apoptosis-associated protein, Bcl-2 and Bax. Meanwhile the expression of cleaved caspase-3, an executioner of apoptosis, was also detected by Western blot. The results showed that pretreatment of EA.hy926 cells with TDD prevented the decrease of cell viability induced by H2O2, and attenuated H2O2-induced elevation of Bax and cleaved caspase-3 while increased Bcl-2 expressions. In summary, TDD inhibited H2O2-induced oxidative injury of EA.hy926 cells through negative regulation of apoptosis. These findings suggest that TDD is a potential candidate for therapeutic intervention in oxidative stress-associated cardiovascular diseases.

Saponin monomer 13 of dwarf lilyturf tuber (DT-13) protects serum withdrawal-induced apoptosis through PI3K/Akt in HUVEC

Dwarf lilyturf tuber is widely used in clinics to prevent cardiovascular diseases. DT-13, the saponin monomer 13 of dwarf lilyturf tuber, shows protective activities in anti-thrombosis, anti-inflammation, and cardioprotective. However, little is known about the cellular function of DT-13 in cardiovascular system. Vascular endothelial cells (EC) are important to maintain the integrity of the vasculature throughout entire body. Dysregulation of EC may lead to pathophysiological processes of numerous cardiovascular diseases. We thus tested the function of DT-13 in EC. In the present study, we are the first to report that DT-13 has anti-apoptosis activity on human umbilical vein endothelial cells (HUVEC), potentially through down regulation of cleaved caspase-3 and cleaved PARP expression. DT-13 also increased mitochondrial membrane potential. To explore the potential mechanism, we investigated the effect of DT-13 on Akt and MAPK pathways and found that DT-13 was involved in Akt signaling confirmed by using PI3K/Akt inhibitor LY294002. Thus, DT-13 could improve survival of EC and therefore be a potential clinical use in the treatment of cardiovascular diseases.

Beneficial effects of polyphenols on cardiovascular disease

In recent years, numerous studies have demonstrated the health benefits of polyphenols, and special attention has been paid to their beneficial effects against cardiovascular disease, the leading cause of death in the world today. Polyphenols present vasodilator effects and are able to improve lipid profiles and attenuate the oxidation of low density lipoproteins. In addition, they present clear anti-inflammatory effects and can modulate apoptotic processes in the vascular endothelium. It has been suggested that most of these effects are a consequence of the antioxidant properties of polyphenols, but this idea is not completely accepted, and many other mechanisms have been proposed recently to explain the health effects of these compounds. In fact, different signaling pathways have been linked to polyphenols. This review brings together some recent studies which establish the beneficial properties of polyphenols for cardiovascular disease and analyzes the mechanisms involved in these properties.

Effects of Low-Dose versus High-Dose γ-Tocotrienol on the Bone Cells Exposed to the Hydrogen Peroxide-Induced Oxidative Stress and Apoptosis

Oxidative stress and apoptosis can disrupt the bone formation activity of osteoblasts which can lead to osteoporosis. This study was conducted to investigate the effects of γ-tocotrienol on lipid peroxidation, antioxidant enzymes activities, and apoptosis of osteoblast exposed to hydrogen peroxide (H₂O₂). Osteoblasts were treated with 1, 10, and 100 μM of γ-tocotrienol for 24 hours before being exposed to 490 μM (IC₅₀) H₂O₂ for 2 hours. Results showed that γ-tocotrienol prevented the malondialdehyde (MDA) elevation induced by H₂O₂ in a dose-dependent manner. As for the antioxidant enzymes assays, all doses of γ-tocotrienol were able to prevent the reduction in SOD and CAT activities, but only the dose of 1 μM of GTT was able to prevent the reduction in GPx. As for the apoptosis assays, γ-tocotrienol was able to reduce apoptosis at the dose of 1 and 10 μM. However, the dose of 100 μM of γ-tocotrienol induced an even higher apoptosis than H₂O₂. In conclusion, low doses of γ-tocotrienol offered protection for osteoblasts against H₂O₂ toxicity, but itself caused toxicity at the high doses.

The biocompatibility of a polyelectrolyte vitreous body substitute on a high resistance in vitro model of the blood-retinal barrier

The vitreous body can be regarded as a fascinating simple but important tissue, since it represents the main compartment of the eye and plays a crucial role for proper vision. Several diseases require its removal with following substitution using a liquid artificial vitreous body replacement. We explore the biocompatibility of a poly(AMPS-Na+)-graft-poly(NIPAAm) polyelectrolyte following the innovative concept of thermo-responsive behaviour, exhibiting enhanced shear viscosity at physiological temperatures. As a powerful model for the blood-retinal barrier, we use the well-established in vitro cell culture model based on highly differentiated porcine brain capillary endothelial cells. Via the quantification of the transendothelial electrical resistance and immunocytochemical staining of tight junction proteins, we are able to show that a barrier integrity affecting impact of the polyelectrolyte was only transient and nearly reversible. Furthermore, the polyelectrolyte hydrogel is characterized by the absence of any acute cell morphology, cell vitality or proliferation affecting impacts. It does not trigger acute apoptotic processes, as can be substantiated via caspase-3 activity and DNA fragmentation assays. In view of the results of this study, it is shown that the polyelectrolyte does not affect the vitality parameters of our porcine brain capillary endothelial cells. It can be suggested that the tested thermo-responsive polyelectrolyte does not affect the sensitive retinal barrier integrity. Thus from the cellular tolerance it might serve as a potential liquid artificial vitreous body replacement to overcome the most prominent difficulties of common vitreal endotamponades.

Curculigoside attenuates human umbilical vein endothelial cell injury induced by H2O2

AIM OF THE STUDY

Vessel endothelium injury caused by reactive oxygen species (ROS) including H(2)O(2) plays a critical role in the pathogenesis of cardiovascular disorders. Therefore, agents or antioxidants that can inhibit production of ROS has highly clinical values in cardiovascular therapy. Curculigoside is the major bioactive compounds present in Curculigo orchioides, and possess potent antioxidant properties against oxidative stress insults through undefined mechanism(s). The present study was designed to test the hypothesis that curculigoside can inhibit H(2)O(2)-induced injury in human umbilical vein endothelial cells.

MATERIALS AND METHODS

Human umbilical vein endothelial cells (HUVECs) were treated with curculigoside in the presence/absence of hydrogen peroxide (H(2)O(2)). The protective effects of curculigoside OP-D against H(2)O(2) were evaluated.

RESULTS

HUVECs incubated with 400 μM H(2)O(2) had significantly decreased the viability of endothelial cells, which was accompanied with apparent cells apoptosis, the activation of caspase-3 and the upregulation of p53 mRNA expression. In addition, H(2)O(2) treatment induced a marked increase of MDA, LDH content and in intracellular ROS, decreased the content of nitric oxide (NO) and GSH-Px activities in endothelial cells. However, pretreatment with 0.5.5,10 μM curculigoside resulted in a significant recovery from H(2)O(2)-induced cell apoptosis. Also, it decreased other H(2)O(2)-induced damages in a concentration-dependent manner. Furthermore, pretreatment with curculigoside decreased the activity of caspase-3 and p53 mRNA expression, which was known to play a key role in H(2)O(2)-induced cell apoptosis.

CONCLUSION

The present study shows that curculigoside can protect endothelial cells against oxidative injury induced by H(2)O(2), suggesting that this compound may constitute a promising intervention against cardiovascular disorders.

Protective effects of diosgenin in the hyperlipidemic rat model and in human vascular endothelial cells against hydrogen peroxide-induced apoptosis

Hyperlipidemia is a major cause of atherosclerosis and atherosclerosis-associated conditions in cardiovascular diseases. Oxidative stress, as a main risk factor causes vascular endothelial cell apoptosis, which is implicated in the pathogenesis of cardiovascular disorders. Diosgenin, an aglycone of steroidal saponins, has been reported to exert anti-proliferative and proapoptotic actions on cancer cells widely. In this study, we propose that diosgenin can protect the hyperlipidemic rats and prevent endothelial apoptosis under oxidative stress. We investigated the hypolipidemic and antioxidative effects of diosgenin on rats fed with high cholesterol and high fat diet for 6 weeks. Serum total cholesterol (TC), triglyceride (TG), low-density lipoprotein cholesterol (LDL-C), glutathione peroxidase (GSH-PX), nitric oxide synthase (NOS), hepatic malondialdehyde (MDA), lipoprotein lipase (LPL), hepaticlipase (HL) and superoxide dismutase (SOD) activities were evaluated. Then we explored the effects and mechanism of diosgenin against hydrogen peroxide-induced apoptosis of human vein endothelium cells (HUVECs). Intracellular reactive oxygen species (ROS), glutathione (GSH), nitric oxide (NO), DNA fragment formation and mitochondrial membrane potentials (DeltaPsim) were determined. Diosgenin treatment increased LPL, HL, SOD, GSH-PX and NOS activities, thus attenuated oxygen free radicals, decreased MDA, TC, TG and LDL-C levels in hyperlipidemic rats. Diosgenin pretreatment significantly attenuated H(2)O(2)-induced apoptosis in HUVECs, intracellular ROS, GSH depletion, DNA fragment formation, and restored NO, DeltaPsim. These results suggested that diosgenin is a very useful compound to control hyperlipidemia by both improving the lipid profile and modulating oxidative stress and prevent H(2)O(2)-induced apoptosis of HUVECs, in partly through regulating mitochondrial dysfunction pathway.

Rutin inhibits hydrogen peroxide-induced apoptosis through regulating reactive oxygen species mediated mitochondrial dysfunction pathway in human umbilical vein endothelial cells

Apoptosis of human vein endothelium cell caused by reactive oxygen species is implicated in the pathogenesis of cardiovascular diseases. Rutin, an active flavonoid compound, is well known to possess potent antioxidant properties against oxidative stress insults through undefined mechanism(s). In this study, we first investigated the possible protective effects of rutin against apoptosis of human umbilical vein endothelial cells (HUVECs) induced by hydrogen peroxide (H(2)O(2)) and the associated signaling pathways. Decreased viability and increased apoptosis were observed in the HUVECs incubated with 200microM H(2)O(2) for 12h. By examining the effect of rutin on H(2)O(2)-induced apoptosis in HUVECs, we found that rutin pretreatment significantly attenuated H(2)O(2)-induced apoptosis in HUVECs. We next examined the signaling involved in rutin-mediated anti-apoptotic effects. It was found that rutin pretreatment attenuated excessive reactive oxygen species in HUVECs exposed to H(2)O(2). Rutin also prevented the increased DNA fragment formation and glutathione (GSH) depletion and inhibited the collapse of mitochondrial membrane potentials (DeltaPsim) that occurred in HUVECs exposed to H(2)O(2), which protected HUVECs against oxidative damage and the further mitochondrial membrane integrity impairment, leading to apoptosis. In conclusion, the results suggested that rutin (50microM) blocked apoptosis in HUVECs through decreasing reactive oxygen species, increasing GSH, restoring DeltaPsim and thus protecting DNA damage. Our research indicated that rutin protected the intracellular GSH antioxidant system and prevented H(2)O(2)-induced apoptosis of HUVECs through regulating reactive oxygen species mediated mitochondrial dysfunction pathway.

Effects of equol on oxidized low-density lipoprotein-induced apoptosis in endothelial cells

AIM

Equol is the main active product of daidzein metabolism, produced via specific microflora in the gut. This study aimed to clarify the effects of equol on oxidized low-density lipoprotein (OX-LDL)-stimulated apoptosis in human umbilical vein endothelial cells (HUVECs).

METHODS

HUVECs were cultured in the presence of OX-LDL, and cell apoptosis was monitored by evaluating of DNA fragmentation and the production of cytoplasmic histone-associated DNA fragments. We simultaneously evaluated the level of cellular superoxide and nitric oxide (NO) and the effects of the anti-oxidant activity of equol on apoptosis.

RESULTS

We found that equol inhibited the induction of apoptosis in response to exposure of HUVECs to OX-LDL. Treatment of cells with equol led to a significant reduction in superoxide production by NAD(P)H oxidase and also to a significant increase in NO production. We further observed an effect of equol on the suppression of OX-LDL uptake.

CONCLUSIONS

These results suggested that equol might contribute to a reduced level of OX-LDL-stimulated apoptosis linked to the reduced generation of intracellular reactive oxygen species (ROS).

Forkhead factor, FOXO3a, induces apoptosis of endothelial cells through activation of matrix metalloproteinases

BACKGROUND

The forkhead factor, FOXO3a, is known to induce apoptosis in endothelial cells (ECs). However, its effects on extracellular matrices (ECM), which are important in EC survival, remained unknown. Here, we evaluated the role of FOXO3a on EC-ECM interaction.

METHODS AND RESULTS

Constitutively active FOXO3a was transduced to human umbilical vein endothelial cells by adenoviral vector (Ad-TM-FOXO3a). Ad-TM-FOXO3a transfection led to dehiscence of ECs from fibronectin-coated plates, resulting in anoikis, which was significantly reversed by matrix metalloproteinase (MMP) inhibitor, GM6001. FOXO3a increased the expression of MMP-3 (stromelysin-1) but decreased the expression of tissue inhibitors of metalloproteinases-1 (TIMP-1), which was associated with increased MMP enzymatic activity in zymography. Pathophysiologic conditions such as serum starvation or heat shock also induced activation of endogenous FOXO3a, leading to activation of MMP-3 and apoptosis, which was reversed by GM6001. Delivery of Ad-TM-FOXO3a to the intraluminal surface in vivo led to EC denudation, disrupted vascular integrity, and impaired endothelium-dependent vasorelaxation.

CONCLUSIONS

Activation of MMPs and possible ECM disruption represent novel mechanisms of FOXO3a-mediated apoptosis in ECs.

Cartilage oligometric matrix protein-angiopoietin-1 promotes revascularization through increased survivin expression in dermal endothelial cells of skin grafts in mice

The present study examined the effects of cartilage oligometric matrix protein angiopoietin-1 (COMP-Ang1) on the revascularization of mice skin grafts. Full-thickness skin grafts were autotransferred into BALB/c mice. The donor grafts were soaked in COMP-Ang1 protein (50 mug/ml, n = 10) or in bovine serum albumin (BSA) (50 mug/ml, n = 10) dissolved in 1 ml of sterile, phosphate-buffered saline for 5 minutes before transfer. Revascularization of the grafts was monitored using an intravital microscope on postoperative days 3, 4, and 5. Morphological and immunohistochemical analyses were performed to evaluate platelet-endothelial cell adhesion molecule-1 and survivin expression and apoptotic signal in the transplanted grafts. Grafts soaked in COMP-Ang1 (COMP-Ang1 group) showed significantly increased revascularization compared with grafts soaked in BSA (BSA group) on intravital microscopy and platelet-endothelial cell adhesion molecule-1 staining. The COMP-Ang1 group showed a significant increase of survivin expression in the endothelial cells and a reduction of apoptotic signal in comparison to the BSA group. Therefore, we believe that COMP-Ang1 provides the therapeutic benefit of enhancing the survival of vascular endothelial cells during transplantation of skin graft.

Protective effects of icariin on human umbilical vein endothelial cell injury induced by H2O2 in vitro

Icariin is a flavonoid isolated from Epimedium and is considered to be the major pharmacological active component of Epimedii Herba. In the present investigation, we studied and confirmed the protective activity of icariin on H2O2-induced injury in human umbilical vein endothelial cell line: ECV-304. Eighteen-hour treatment with 750 micromol l(-1) H2O2 significantly decreased the viability of ECV-304 cells, which was accompanied with apparent apoptotic features, including distinct cell morphological alteration and the increase of caspase-3 expression. In addition, it is observed that H2O2 increased the amounts of malondialdenhyde (MDA) and the dehydrogenase (LDH), and decreased the content of nitric oxide (NO) in ECV-304 cells. However, pretreatment with 0.1-50 micromol l(-1) icariin resulted in a significant recovery from H2O2-induced cell apoptosis. Also, it decreased other H2O2-induced damage in a concentration-dependent manner. Furthermore, pretreatment with icariin decreased the expression of caspase-3, which was known to be involved as a key role executor in H2O2-induced cell apoptosis. The endothelial cells apoptosis were detected by acridine orange/ethidium bromide (AO/EB) dual staining as well as flow cytometry, and the expression of pro-apoptotic factor caspase-3 were detected by immunocytochemical method. Taken together, these data suggest that protective effects of icariin against oxidative injuries of ECV-304 cells may be achieved via decreasing of caspase expression.

Protective effects of silybin on human umbilical vein endothelial cell injury induced by H2O2 in vitro

Oxidative injury induces cellular and nuclear damages that lead to cell injury. Agents or antioxidants that can inhibit production of reactive oxygen species can prevent injury. We tested the hypothesis that silybin can inhibit H2O2-induced injury in human umbilical vein endothelial cells. Eighteen hours of treatment with 750 micromol l(-1) H2O2 significantly stimulated expression of caspase-3 and cell apoptosis. In addition, it is observed that H2O2 increased the amounts of malondialdenhyde (MDA), the dehydrogenase (LDH) leakage, and decreased the activity of GSH-Px and NO contents in ECV-304 cells. In the H2O2 apoptosis model, the addition of 6.25-25 mg/L of silybin, which has in vitro radical scavenging activity, partially restored cell viability with a reduction in H2O2-induced apoptotic DNA damage, and decreased the expression of caspase-3. Moreover, it decreased other H2O2-induced damage in a concentration-dependent manner. The endothelial cell apoptosis was detected by AO/EB dual staining as well as flow cytometry, and the activity of pro-apoptotic factor caspase-3 was detected by immunocytochemical method. Our results suggest that the antioxidant, silybin, protects ECV-304 cells against H2O2-induced injury probably through its antioxidant activity, increasing the NO content, the activity GSH-Px and inhibiting signaling pathways mediated by caspase-3.

Expression of vascular endothelial growth factor, apoptosis inhibitors (survivin and p16) and CCL27 in alopecia areata before and after diphencyprone treatment: an immunohistochemical study

BACKGROUND

Alopecia areata (AA) is a relatively common inflammatory form of nonscarring hair loss of unknown pathogenesis, but possibly of autoimmune origin. Topical immunotherapy, using a potent contact allergen such as diphencyprone (DPC), is currently considered the most effective mode of treatment. However, the way in which DPC operates on hair follicles in AA still remains to be elucidated. Vascular endothelial growth factor (VEGF), essential for angiogenesis and vascular permeability, may be responsible for maintaining proper vasculature around hair follicles, and several studies provide evidence that apoptosis is a central element in the regulation of hair follicle and vascular regression. The cutaneous lymphocyte-associated antigen (CLA) and the skin-associated chemokine CCL27 highlight an important role for epithelial cells in controlling homeostatic lymphocyte trafficking.

OBJECTIVES

To determine the expression pattern of VEGF, factor (F)VIII, survivin, p16, CD4, CD8, CLA and CCL27 in alopecic skin before and after treatment with DPC. Methods Immunohistochemical staining methods were applied to skin biopsy specimens obtained from alopecic areas of 14 patients before and after DPC treatment and from five healthy subjects. Sections were incubated with monoclonal antibodies against VEGF, FVIII, survivin, p16, CCL27, CLA, CD4 and CD8, and their immunohistochemical expression was evaluated by light microscopy.

RESULTS

The intensity of VEGF staining in alopecic human hair follicles was significantly lower than in healthy scalp tissue. FVIII immunostaining showed a significantly reduced development of the microvasculature in AA in comparison with healthy scalp tissue. After DPC therapy, cells of alopecic hair follicles showed a significant increase of VEGF immunopositivity, and the number of capillary vessels expressing FVIII was markedly increased in comparison with untreated scalp tissue. The increase in microvessels was associated with strong survivin expression in endothelial cells after treatment. All alopecic specimens showed expression of p16 in the hair follicle outer root sheath (ORS), with a significant increase after therapy. After treatment we observed a significantly decreased number of CD4+ cells and an increase of CD8+ cells (CD4/CD8 ratio 0.85) in alopecic skin compared with untreated scalp tissue (CD4/CD8 ratio 3.45). Most of the T lymphocytes found in inflammatory skin lesions expressed CLA antigen and after therapy we observed a significantly higher CLA positivity in hair follicles (50% or more) in comparison with untreated alopecic scalp tissue. Alopecic patients showed a CCL27 immunopositivity significantly lower than in normal scalp tissue. After DPC therapy the labelling intensity for CCL27 showed a significant increase both in the ORS and in the inner root sheath; similarly, in the basal interfollicular keratinocytes we observed a moderate increase in CCL27 expression.

CONCLUSIONS

Topical immunotherapy exerts an important role in angiogenesis, upregulating VEGF in human hair follicle keratinocytes and upregulating survivin to preserve endothelial cell viability. Moreover, it considerably alters the peribulbar CD4/CD8 ratio, restoring a condition close to normal scalp skin. Our study could contribute to explaining some aspects of AA pathogenesis that are still unknown and aid understanding of how DPC could act in this complex disease.

Endothelial cells preparing to die by apoptosis initiate a program of transcriptome and glycome regulation

The protein-based changes that underlie the cell biology of apoptosis have been extensively studied. In contrast, mRNA- and polysaccharide-based changes have received relatively little attention. We have combined transcriptome and glycome analyses to show that apoptotic endothelial cell cultures undergo programmed changes to RNA transcript abundance and cell surface polysaccharide profiles. Although a few of the transcriptome changes were protective, most appeared to prepare cells for apoptosis by decreasing the reception and transduction of pro-survival signals, increasing pro-death signals, increasing abundance of apoptotic machinery, inhibiting cellular proliferation, recruiting phagocytes to regions of cell death, and promoting phagocytosis. Additional transcriptomal changes appeared to alter the synthesis and modification of cell surface glycosaminoglycans. The resultant reduced abundance of sulphated cell surface glycosaminoglycans may further promote cell death by inhibiting the presentation of extracellular matrix-tethered survival factors to their receptors on dying cells. We propose that the transcriptome and glycome regulation presented here synergize with previously described protein-based changes to guide the apoptotic program.

Interactions Between p38 Mitogen-Activated Protein Kinase and Caspase-3 in Cerebral Endothelial Cell Death After Hypoxia-Reoxygenation

Background and Purpose— The emerging concept of the neurovascular unit in stroke reemphasizes the need to focus on endothelial responses in brain. In this study we examined the role of mitogen-activated protein (MAP) kinase signaling in the regulation of hypoxic cell death in cerebral endothelial cells.

Methods— Human cerebral microvascular endothelial cells were exposed to 4 to 12 hours of hypoxia followed by 12 to 24 hours of reoxygenation. Cytotoxicity was measured by quantifying lactate dehydrogenase release. DNA laddering and caspase-3 activity were assessed to document a role for caspase-dependent cell death. zVAD-fmk and zDEVD-fmk were used to inhibit caspases. Activation of extracellular signal–regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK) was assessed with Western blotting and kinase activity assays. U0126, SB203580, and SP600125 were used to interrupt the ERK, p38, and JNK pathways, respectively.

Results— Endothelial cell death occurred primarily during reoxygenation. DNA laddering and caspase activation were observed, and cytotoxicity was ameliorated by caspase inhibitors (20 μmol/L of zVAD-fmk or zDEVD-fmk). Among the 3 major MAP kinases, only p38 was transiently activated during reoxygenation, and inhibition with 10 μmol/L of SB203580 significantly reduced cytotoxicity. No effects were observed with other MAP kinase inhibitors. Cytoprotection with SB203580 was not accompanied by caspase downregulation. In contrast, cytoprotection with zVAD-fmk was associated with a decrease in p38 activation. Furthermore, cleavage of MEKK1 (an upstream kinase of p38) was significantly reduced by zVAD-fmk.

Conclusions— Cerebral endothelial cell death after hypoxia-reoxygenation is mediated by interactions between caspases and p38 MAP kinase. Surprisingly, p38 pathways lie downstream of caspase mechanisms in this model system.

Apoptosis of endothelial cells may be mediated by genes of peroxisome proliferator-activated receptor gamma 1 (PPARgamma 1) and PPARalpha genes

Apoptosis in human umbilical vein endothelial cells (HUVECs) was prevented by transfection with the gene for the human full-length peroxisome proliferator-activated receptor alpha (PPARalpha), or acyl-coenzyme A synthetase (AcylCS) into HUVECs. In contrast, ligands/activators of PPARgamma 1 induced apoptosis by a cytochrome c-dependent mechanism in HUVECs transfected with human full-length PPARgamma 1, but not in hepatocytes. Co-transfection of PPARgamma 1 and PPARalpha protected the HUVEC apoptosis. The results suggest that the apoptosis of endothelial cells may be mediated by genes of PPARgamma1 and PPARalpha.

Transcriptional repressor activating transcription factor 3 protects human umbilical vein endothelial cells from tumor necrosis factor-alpha-induced apoptosis through down-regulation of p53 transcription

Activating transcription factor 3 (ATF3) is a transcriptional repressor that is rapidly induced in cells exposed to a wide range of stress stimuli. To clarify the role of ATF3 in determining cell fate, we overexpressed it in human umbilical vein endothelial cells (HUVECs) by adenovirus-mediated gene transfer. ATF3 protected these cells from tumor necrosis factor (TNF)-alpha-induced apoptosis, as measured by flow cytometric analysis, trypan blue exclusion assay, and cleavage of procaspase 3 and poly(ADP-ribose) polymerase. Northern blot and nuclear run on assay showed that the transcription of tumor suppressor gene p53 was down-regulated in the ATF3-overexpressing cells. In the transient expression assay, ATF3 suppressed the p53 gene promoter activity through its specific binding to an atypical AP-1 element, PF-1 site, in the p53 gene promoter. Furthermore, the cell-protecting effect of ATF3 was remarkably reduced in p53-deficient cells. These results demonstrate that overexpression of ATF3 suppresses TNF-alpha-induced cell death of HUVECs, at least in part, through down-regulating the transcription of p53 gene. ATF3 may function as a cell survival factor of endothelial cells during vascular inflammation and atherogenesis.

Interferon-gamma augments CD95(APO-1/Fas) and pro-caspase-8 expression and sensitizes human vascular endothelial cells to CD95-mediated apoptosis

We have examined the effects of interferon (IFN)-gamma on expression and function of CD95 (APO-1/Fas) and associated proteins in cultured human umbilical vein and dermal microvascular endothelial cells (HUVEC and HDMEC, respectively). Unstimulated cells express only low levels of CD95; IFN-gamma produces a time- and concentration-dependent increase of CD95 in both cell types at the mRNA and cell surface protein levels. IFN-gamma also produces an increase in expression of pro-caspase-8 (FLICE/MACH) but does not significantly change expression of either Fas-associated death domain (FADD) protein or cellular FLICE inhibitory protein (cFLIP), other proteins associated with the CD95 death-inducing signaling complex (DISC). Neither resting nor IFN-gamma-treated EC express detectable CD95L mRNA or protein. Untreated HUVEC and HDMEC show minimal apoptosis when transduced to express CD95L. Treatment of CD95L-transduced cells with IFN-gamma causes apoptosis within 24 to 36 hours that can be blocked by antagonistic anti-CD95 antibody or by the caspase-inhibitory peptide zVAD-FMK. The extent of apoptosis is increased by co-treatment with either the protein synthesis inhibitor cycloheximide or the phosphatidylinositol 3-kinase inhibitor LY294002. Untransduced HUVEC treated with IFN-gamma also undergo CD95-initiated apoptosis when mixed with CD95L-transduced HUVEC or when incubated with pharmacologically activated cytolytic T lymphocytes. Overexpression of CD95 in HUVEC confers sensitivity to CD95L in the absence of IFN-gamma-treatment. We conclude that IFN-gamma induces sensitivity of endothelium to CD95L-mediated apoptosis, and that this response may result from increased expression of CD95 and/or pro-caspase-8.

p53 protein and p21 mRNA levels and caspase-3 activity are altered by zinc status in aortic endothelial cells

The influence of zinc status on the levels of p53, as well as downstream targets of p53 in cell repair and survival, was examined in human aortic endothelial cells (HAECs). A serum-reduced low-zinc medium (ZD) was used to deplete zinc over one passage. Other treatments included zinc-normal control (ZN), zinc-adequate (ZA), and zinc-supplemented (ZS) treatment with 3.0, 16.0, and 32.0 microM zinc, respectively. Cellular zinc levels in the ZD cells were 64% of ZN controls; levels in the ZA cells were not different, but levels in ZS cells were significantly higher (40%) than in ZN cells. No difference in p53 mRNA abundance was detected among all treatments; however, p53 nuclear protein levels were >100% higher in the ZD and ZS cells and almost 200% higher in the ZA cells than in ZN controls. In addition, p21 mRNA abundance, a downstream target of p53 protein, was increased in the ZS cells compared with both the ZN control and ZD cells. In the ZS cells, bax and mcl-1 were also approximately 50% higher compared with ZN controls, whereas bcl-2 mRNA was increased compared with ZA cells. Moreover, caspase-3 activity of ZD cells was not different from that of ZN controls but was reduced to 83 and 69% of ZN controls in ZA and ZS cells, respectively. Thus p53 protein and p53 downstream target genes appeared to be modulated by intracellular zinc status in HAECs.

Doxorubicin induces apoptosis and CD95 gene expression in human primary endothelial cells through a p53-dependent mechanism

Regulation of the homeostasis of vascular endothelium is critical for the processes of vascular remodeling and angiogenesis under physiological and pathological conditions. Here we show that doxorubicin (Dox), a drug used in antitumor therapy, triggered a marked accumulation of p53 and induced CD95 gene expression and apoptosis in proliferating human umbilical vein endothelial cells (HUVECs). Transfection and site-directed mutagenesis experiments using the CD95 promoter fused to an intronic enhancer indicated the requirement for a p53 site for Dox-induced promoter activation. Furthermore, the p53 inhibitor pifithrin-alpha (PFT-alpha) blocked both promoter inducibility and protein up-regulation of CD95 in response to Dox. Up-regulated CD95 in Dox-treated cells was functional in eliciting apoptosis upon incubation of the cells with an agonistic CD95 antibody. However, Dox-mediated apoptosis was independent of CD95/CD95L interaction. The analysis of apoptosis in the presence of PFT-alpha and benzyloxycarbonyl-Val-Ala-dl-Asp-fluoromethylketone revealed that both p53 and caspase activation are required for Dox-mediated apoptosis of HUVECs. Finally, Dox triggered Bcl-2 down-regulation, cytochrome c release from mitochondria, and the activation of caspases 9 and 3, suggesting the involvement of a mitochondrially operated pathway of apoptosis. These results highlight the role of p53 in the response of primary endothelial cells to genotoxic drugs and may reveal a novel mechanism underlying the antitumoral properties of Dox, related to its ability to induce apoptosis in proliferating endothelial cells.

Testosterone (T) enhances apoptosis-related damage in human vascular endothelial cells

Androgens may contribute to higher cardiovascular risk in men via deleterious effects on vascular endothelial cells (EC). We examined the effects of androgens on male human umbilical vein EC (EA.hy926) in culture. [(3)H]Thymidine incorporation assays showed that after 24-h serum deprivation, testosterone (T) (but not dehydroepiandrosterone nor 17beta-E2) induced significant dose-dependent decreases in DNA synthesis (10-16% at 1-100 nmol/liter); the AR antagonist flutamide (100 nmol/liter) abolished this effect of T. After 48-h serum deprivation, typical apoptotic DNA patterns were detected in agarose gels, and the number of floating cells indicative of severe damage was significantly greater after T treatment for 48 and 72 h (13.7 +/- 0.5% and 30.2 +/- 2.5%, respectively) than the control values (9.7 +/- 1.05% and 23.7 +/- 3.0%). Analysis of attached cells by annexin V-fluorescein isothiocyanate/propidium iodide staining showed that after 48-h serum deprivation, T significantly increased the number of cells in the early (16.0 +/- 1.1%) and late (8.3 +/- 0.3%) stages of apoptosis compared with control (6.8 +/- 1.0% and 4.0 +/- 0.2%, respectively); such increases in apoptosis-related damage were also observed, to a lesser degree, in serum-enriched culture. Western blotting showed that B cell leukemia/lymphoma-2 protein (Bcl-2) expression decreased significantly in serum-deprived EC treated with T. Thus, T reduces DNA synthesis and enhances apoptosis after serum deprivation in EC, possibly related to reduced Bcl-2 expression.

Suppression of vascular endothelial growth factor-mediated endothelial cell protection by survivin targeting

The protective genes that mediate endothelial cell (EC) survival during angiogenesis have not been completely characterized. Here, we show that an antisense oligonucleotide to the apoptosis inhibitor survivin suppressed de novo expression of survivin in ECs by vascular endothelial cell growth factor (VEGF). In contrast, the survivin antisense oligonucleotide did not affect anti-apoptotic bcl-2 levels in endothelium. When assessed in cell death assays, antisense targeting of survivin abolished the anti-apoptotic function of VEGF against tumor necrosis factor-alpha- or ceramide-induced cell death, enhanced caspase-3 activity, promoted the generation of a approximately 17-kd active caspase-3 subunit, and increased cleavage of the caspase substrate, polyADP ribose polymerase. In contrast, the survivin antisense oligonucleotide had no effect on EC viability in the absence of VEGF. Antisense oligonucleotides to platelet-endothelial cell adhesion molecule-1 (PECAM-1, CD31), lymphocyte function-associated molecule-3 (LFA-3, CD58), or intercellular adhesion molecule-1 (ICAM-1, CD54) did not reduce the anti-apoptotic function of VEGF in endothelium. When tested on other angiogenic activities mediated by VEGF, survivin antisense treatment induced rapid regression of three-dimensional vascular capillary networks, but did not affect EC migration/chemotaxis. These data suggest that the anti-apoptotic properties of VEGF during angiogenesis are primarily mediated by the induced expression of survivin in ECS: Manipulation of this pathway may increase EC viability in compensatory angiogenesis or facilitate EC apoptosis and promote vascular regression during tumor angiogenesis.

Matrix attachment regulates Fas-induced apoptosis in endothelial cells: a role for c-flip and implications for anoikis

Survival of endothelial cells is critical for cellular processes such as angiogenesis. Cell attachment to extracellular matrix inhibits apoptosis in endothelial cells both in vitro and in vivo, but the molecular mechanisms underlying matrix-induced survival signals or detachment-induced apoptotic signals are unknown. We demonstrate here that matrix attachment is an efficient regulator of Fas-mediated apoptosis in endothelial cells. Thus, matrix attachment protects cells from Fas-induced apoptosis, whereas matrix detachment results in susceptibility to Fas-mediated cell death. Matrix attachment modulates Fas-mediated apoptosis at two different levels: by regulating the expression level of Fas, and by regulating the expression level of c-Flip, an endogenous antagonist of caspase-8. The extracellular signal-regulated kinase (Erk) cascade functions as a survival pathway in adherent cells by regulating c-Flip expression. We further show that detachment-induced cell death, or anoikis, itself results from activation of the Fas pathway by its ligand, Fas-L. Fas-L/Fas interaction, Fas-FADD complex formation, and caspase-8 activation precede the bulk of anoikis in endothelial cells, and inhibition of any of these events blocks anoikis. These studies identify matrix attachment as a survival factor against death receptor-mediated apoptosis and provide a molecular mechanism for anoikis and previously observed Fas resistance in endothelial cells.

Endothelial apoptosis is induced by serum of patients after cardiopulmonary bypass

OBJECTIVE

Increased serum levels of a multitude of mediators like interleukins, tumor necrosis factor, elastase, adhesion molecules, and endotoxin have been described following cardiopulmonary bypass (CPB). The biological consequences of this complex response are unclear.

METHODS

Serum samples of nine patients scheduled for elective coronary artery bypass grafting were obtained preoperatively and 1, 6, and 12 h after weaning from CPB. Additional serum samples were obtained perioperatively from four patients undergoing major lung resection and from four healthy volunteers. The apoptosis-inducing activity of serum samples on endothelial cells was examined using a tissue culture assay system. Endothelial cells were derived from human umbilical cords and incubated for 48 h with serum samples in various dilutions during their second passage. The culture plates were fixed with methanol/acetone and stained with the DNA dye diamidinophenylindole. Apoptotic and normal cells were identified and counted using phase contrast and fluorescence microscopy.

RESULTS

The proportion of apoptotic endothelial cells was 5.6-fold higher in culture plates incubated with diluted (30%) serum samples obtained at 6 h after weaning from CPB when compared to plates incubated with preoperative samples (P=0.0077). A smaller effect occurred already at 1 h in some patients, whereas at 12 h after weaning from CPB no increased endothelial apoptosis was observed. No proapoptotic activity was found in preoperative as well as in control samples from patients undergoing lung resection or from healthy volunteers.

CONCLUSIONS

Serum of patients after CPB exerts a strong apoptosis inducing activity on human endothelial cells. Apoptotic death of endothelial cells following CPB may be responsible for postoperative vascular and bypass dysfunction including phenomena like increased capillary permeability.

Chemical hypoxia-ischemia induces apoptosis in cerebromicrovascular endothelial cells

Cerebral endothelial cell (CEC) death from ischemia may exacerbate brain injury by altering microvascular integrity, but little is known concerning the pattern of CEC death and disruption of tight junction between two CECs to ischemia. To address these questions, CECs were isolated from bovine, cultured, and placed in glucose-free medium containing sodium cyanide. Trypan blue staining shown that sodium cyanide resulted in a dose-dependent insult of CECs (10-80 mM). CEC injury increased progressively with the duration of 20 mM cyanide exposure, becoming significant (71%) after 12 h. The mode of cell death induced by cyanide is clearly apoptosis in CECs, as shown by Hoechst 33,342 staining and transmission electron microscope, i.e. cyanide induced condensation and margination of chromatin, nuclear fragmentation and shrinkage of cell body and condensed apoptotic bodies in CECs. Most importantly, we found that the tight junction between two CECs was disrupted 12 h after chemical-ischemia, i.e. when CECs underwent apoptosis, the tight junctional complexes became thinner and rough; the cleft of tight junction between two CECs became blurred and more wider, and membranes of tight junction were course and irregular; and the adherens junctions were damaged. These results indicate that chemical hypoxia-ischemia induces apoptotic cell death in CECs and alters the microvascular integrity by disrupting tight junction complexes, and suggest that CEC apoptotic death and disruption of tight junction may exacerbate ischemic insults to brain. Thus, prevention of CEC apoptotic death may contribute to improvements of ischemic insults.

Reverse signaling through transmembrane TNF confers resistance to lipopolysaccharide in human monocytes and macrophages

We have previously reported that the CD14+ monocytic subpopulation of human PBMC induces programmed cell death (apoptosis) in cocultured endothelial cells (EC) when stimulated by bacterial endotoxin (LPS). Apoptosis is mediated by two routes, first via transmembrane TNF-alpha (mTNF) expressed on PBMC and, in addition, by TNF-independent soluble factors that trigger apoptosis in EC. Neutralizing anti-TNF mAb completely blocked coculture-mediated apoptosis, despite the fact that there should have been additional soluble cell death factors. This led to the hypothesis that a reverse signal is transmitted from the TNF receptor on EC to monocytes (MO) via mTNF that prevents the production of soluble apoptotic factors. Here we have tested this hypothesis. The results support the idea of a bidirectional cross-talk between MO and EC. Peripheral blood MO, MO-derived macrophages (MPhi), or the monocytic cell line Mono Mac 6 were preincubated with human microvascular EC that constitutively express TNF receptor type I (TNF-R1) and subsequently stimulated with LPS. Cell-free supernatants of these preparations no longer induced EC apoptosis. The preincubation of MO/MPhi with TNF-reactive agents, such as mAb and soluble receptors, also blocked the production of death factors, providing further evidence for reverse signaling via mTNF. Finally, we show that reverse signaling through mTNF mediated LPS resistance in MO/MPhi as indicated by the down-regulation of LPS-induced soluble TNF and IL-6 as well as IL-1 and IL-10.

[Apoptosis in cardiovascular diseases]

Apoptosis consists of a distinct form of cell death that displays characteristic alterations in cell morphology and cell fate which are different than death due to oncosis or necrosis. In terms of tissue kinetics, apoptosis may be considered a mechanism that counterbalances the effect of cell proliferation by mitotic division. In fact, deregulated apoptosis has been implicated in the development a wide variety of human diseases. Excessive apoptotic cell death may cause organ atrophy and organ failure. On the other hand, insufficient elimination of redundant cells may lead to organ and tissue structural remodeling. In recent years, apoptosis has become a highly fashionable and competitive area of research. Fortunately, it has not escaped the attention of the cardiovascular community. Sightings of apoptosis have been reported from every corner of cardiovascular medicine ranging from conduction system defects to congestive heart failure, and from atherosclerosis to aneurysms. There is no question that these sightings will eventually be converted into mechanistic etiopathogenic and physiopathological insights and will form the basis for designing new diagnostic modalities and novel therapies.

Control of apoptosis during angiogenesis by survivin expression in endothelial cells

Mechanisms controlling endothelial cell survival during angiogenesis were investigated. Stimulation of quiescent endothelial cells with mitogens, including vascular endothelial growth factor and basic fibroblast growth factor, induced up to approximately 16-fold up-regulation of the cell cycle-regulated apoptosis inhibitor survivin. Mitogen stimulation rapidly increased survivin RNA expression in endothelial cells, which peaked after 6 to 10 hours in culture and decreased by 24 hours. Inflammatory cytokines, tumor necrosis factor alpha, and interleukin-1 did not induce survivin expression in endothelial cells. Formation of three-dimensional vascular tubes in vitro was associated with strong induction of survivin in endothelial cells, as compared with two-dimensional cultures. By immunohistochemistry, survivin was minimally expressed in endothelium of nonproliferating capillaries of normal skin, whereas it became massively up-regulated in newly formed blood vessels of granulation tissue in vivo. Recombinant expression of green fluorescent protein survivin in endothelial cells reduced caspase-3 activity and counteracted apoptosis induced by tumor necrosis factor alpha/cycloheximide. These findings identify survivin as a novel growth factor-inducible protective gene expressed by endothelial cells during angiogenesis. Therapeutic manipulation of survivin expression and function in endothelium may influence compensatory or pathological (tumor) angiogenesis.

Inflammation and stroke: putative role for cytokines, adhesion molecules and iNOS in brain response to ischemia

Ischemic stroke is a leading cause of death and disability in developed countries. Yet, in spite of substantial research and development efforts, no specific therapy for stroke is available. Several mechanism for neuroprotection have been explored including ion channels, excitatory amino acids and oxygen radicals yet none has culminated in an effective therapeutic effect. The review article on "inflammation and stroke" summarizes key data in support for the possibility that inflammatory cells and mediators are important contributing and confounding factors in ischemic brain injury. In particular, the role of cytokines, endothelial cells and leukocyte adhesion molecules, nitric oxide and cyclooxygenase (COX-2) products are discussed. Furthermore, the potential role for certain cytokines in modulation of brain vulnerability to ischemia is also reviewed. The data suggest that novel therapeutic strategies may evolve from detailed research on some specific inflammatory factors that act in spatial and temporal relationships with traditionally recognized neurotoxic factors. The dual nature of some mediators in reformatting of brain cells for resistance or sensitivity to injury demonstrate the delicate balance needed in interventions based on anti-inflammatory strategies.

c-Jun triggers apoptosis in human vascular endothelial cells

In endothelial cells (ECs), the transcription factor c-Jun is induced by a variety of stimuli that perturb EC function. To extend our understanding of the role of c-Jun in EC physiology, we have directed overexpression of c-Jun in human umbilical vein ECs by using a tetracycline-regulated adenoviral expression system. In this study, we report a novel observation using this system. Specific expression of c-Jun is a sufficient trigger for ECs to undergo apoptosis, as demonstrated by a set of combined assays including an ELISA specific for histone-associated DNA fragmentation, DNA laddering, and TdT-mediated dUTP nick end labeling (TUNEL). Tetracycline can effectively shut off c-Jun overexpression and prevent EC apoptosis. Cleavage of poly(ADP-ribose) polymerase was also detected in ECs overexpressing c-Jun. Moreover, inhibitors of cysteine proteases blocked the apoptosis, suggesting a caspase-associated mechanism involved in proapoptotic effects of c-Jun. To gain further insight into the role of c-Jun as a pathophysiological regulator of EC death, TAM67, a dominant-negative mutant of c-Jun, was overexpressed in human umbilical vein ECs to abrogate endogenous c-Jun/activator protein-1 activation. H(2)O(2)-triggered apoptosis was largely attenuated in ECs overexpressing TAM67. Together, these results suggest that c-Jun, as a proapoptotic molecule, may play a role in mediating the cell death program in vascular endothelium.

Endothelial Cells Undergoing Apoptosis Become Proadhesive for Nonactivated Platelets

Under normal conditions, platelets do not adhere to endothelium. However, when platelets or endothelial cells are stimulated by thrombin or cytokines, respectively, platelets bind avidly to endothelium. Because there is accumulating evidence that endothelial cells may become apoptotic under certain proinflammatory or prothrombotic conditions, we investigated whether endothelial cells undergoing apoptosis may become proadhesive for nonactivated platelets. Human umbilical vein endothelial cells (HUVEC) were induced to undergo apoptosis by staurosporine, a nonspecific protein kinase inhibitor, or by culture in suspension with serum-deprivation. After treatment of HUVEC or platelets with different receptor antagonists, nonactivated, washed human platelets were allowed to adhere to HUVEC for 20 minutes. To exclude matrix involvement, platelet binding was measured in suspension by using flow cytometry. Independent of the method of apoptosis induction, there was a marked increase in platelet binding to apoptotic HUVEC. Although HUVEC exhibited maximal adhesiveness for platelets after 2 to 4 hours, complete DNA fragmentation of HUVEC occurred only several hours later. Adhesion assays after blockade of different platelet receptors showed only involvement of β1-integrins. Platelet binding to apoptotic HUVEC was inhibited by more than 70% when platelets were treated with blocking anti-β1 antibodies. Treatment of apoptotic HUVEC with blocking antibodies to different potential platelet receptors, including known ligands for β1-integrins, did not affect platelet binding. As assessed by determination of β-thromboglobulin and platelet factor 4 in the supernatants, platelets bound to apoptotic HUVEC became slightly activated. However, significant expression of platelet P-selectin (CD62P) was not found. These data provide further evidence that endothelial cells undergoing apoptosis may contribute to thrombotic events.

Endothelial Cells Undergoing Apoptosis Become Proadhesive for Nonactivated Platelets

Under normal conditions, platelets do not adhere to endothelium. However, when platelets or endothelial cells are stimulated by thrombin or cytokines, respectively, platelets bind avidly to endothelium. Because there is accumulating evidence that endothelial cells may become apoptotic under certain proinflammatory or prothrombotic conditions, we investigated whether endothelial cells undergoing apoptosis may become proadhesive for nonactivated platelets. Human umbilical vein endothelial cells (HUVEC) were induced to undergo apoptosis by staurosporine, a nonspecific protein kinase inhibitor, or by culture in suspension with serum-deprivation. After treatment of HUVEC or platelets with different receptor antagonists, nonactivated, washed human platelets were allowed to adhere to HUVEC for 20 minutes. To exclude matrix involvement, platelet binding was measured in suspension by using flow cytometry. Independent of the method of apoptosis induction, there was a marked increase in platelet binding to apoptotic HUVEC. Although HUVEC exhibited maximal adhesiveness for platelets after 2 to 4 hours, complete DNA fragmentation of HUVEC occurred only several hours later. Adhesion assays after blockade of different platelet receptors showed only involvement of β1-integrins. Platelet binding to apoptotic HUVEC was inhibited by more than 70% when platelets were treated with blocking anti-β1 antibodies. Treatment of apoptotic HUVEC with blocking antibodies to different potential platelet receptors, including known ligands for β1-integrins, did not affect platelet binding. As assessed by determination of β-thromboglobulin and platelet factor 4 in the supernatants, platelets bound to apoptotic HUVEC became slightly activated. However, significant expression of platelet P-selectin (CD62P) was not found. These data provide further evidence that endothelial cells undergoing apoptosis may contribute to thrombotic events.

The nuclear factor-kappa B/inhibitor of kappa B autoregulatory system and atherosclerosis

Nuclear factor-kappa B is a ubiquitous transcription factor that can be activated by diverse proatherogenic stimuli such as inflammatory cytokines, lipopolysaccharide, oxidant stress and physical forces. Recently, there have been major advances in understanding signal transduction from the tumor necrosis factor receptor, a model activator of the nuclear factor-kappa B system. One set of signals from the receptor initiates a phosphorylation cascade resulting in the activation of a kinase complex which phosphorylates an inhibitor of nuclear factor-kappa B, or inhibitor of kappa B. Degradation of the inhibitor occurs in parallel with activation and nuclear accumulation of the transcription factor. Subsequent changes in gene expression induce the production of multiple cytokines and adhesion molecules, which are important in early atherosclerotic lesion formation, and generation of survival signals, which could be important in lesion progression. A second set of signals from the tumor necrosis factor receptor leads to cell death. Understanding these competing pathways in vascular cells may help to clarify the role of this transcription factor in the proliferative lesions of atherogenesis.

Localization of mRNA for the apoptosis-linked gene ALG-2 in young and aged rat brain

ALG-2 is a recently described pro-apoptosis gene that codes for a Ca2+-binding protein involved in T-cell receptor-, Fas- and glucocorticoid-induced cell death. We have used in situ hybridization histochemistry to examine the regional distribution of ALG-2 mRNA in the brain of 3- and 24-month old rats. There was widespread, predominantly neuronal distribution of ALG-2 mRNA throughout the brain. Areas expressing high levels included the granule and pyramidal cell layers of the hippocampus, choroid plexus, area postrema, and a number of hindbrain nuclei. ALG-2 mRNA levels in aged rats were not significantly different to young animals. The pattern of expression of ALG-2 mRNA in adult brain is similar to other apoptosis-related genes and suggests it may be involved in neuronal survival.