Role of AIF in human coronary artery endothelial cell apoptosis

Exploring the role of parthanatos in CNS injury: Molecular insights and therapeutic approaches

BACKGROUND

Central nervous system (CNS) injury causes severe organ damage due to both damage resulting from the injury and subsequent cell death. However, there are currently no effective treatments for countering the irreversible loss of cell function. Parthanatos is a poly (ADP-ribose) polymerase 1 (PARP-1)-dependent form of programmed cell death that is partly responsible for neural cell death. Consequently, the mechanism by which parthanatos promotes CNS injury has attracted significant scientific interest.

AIM OF REVIEW

Our review aims to summarize the potential role of parthanatos in CNS injury and its molecular and pathophysiological mechanisms. Understanding the role of parthanatos and related molecules in CNS injury is crucial for developing effective treatment strategies and identifying important directions for future in-depth research.

KEY SCIENTIFIC CONCEPTS OF REVIEW

Parthanatos (from Thanatos, the personification of death according to Greek mythology) is a type of programmed cell death that is initiated by the overactivation of PARP-1. This process triggers a cascade of reactions, including the accumulation of poly(ADP-ribose) (PAR), the nuclear translocation of apoptosis-inducing factor (AIF) after its release from mitochondria, and subsequent massive DNA fragmentation caused by migration inhibitory factor (MIF) forming a complex with AIF. Secondary molecular mechanisms, such as excitotoxicity and oxidative stress-induced overactivation of PARP-1, significantly exacerbate neuronal damage following initial mechanical injury to the CNS. Furthermore, parthanatos is not only associated with neuronal damage but also interacts with various other types of cell death. This review focuses on the latest research concerning the parthanatos cell death pathway, particularly considering its regulatory mechanisms and functions in CNS damage. We highlight the associations between parthanatos and different cell types involved in CNS damage and discuss potential therapeutic agents targeting the parthanatos pathway.

ROS-triggered endothelial cell death mechanisms: Focus on pyroptosis, parthanatos, and ferroptosis

The endothelium is a single layer of epithelium covering the surface of the vascular system, and it represents a physical barrier between the blood and vessel wall that plays an important role in maintaining intravascular homeostasis. However, endothelial dysfunction or endothelial cell death can cause vascular barrier disruption, vasoconstriction and diastolic dysfunction, vascular smooth muscle cell proliferation and migration, inflammatory responses, and thrombosis, which are closely associated with the progression of several diseases, such as atherosclerosis, hypertension, coronary atherosclerotic heart disease, ischemic stroke, acute lung injury, acute kidney injury, diabetic retinopathy, and Alzheimer's disease. Oxidative stress caused by the overproduction of reactive oxygen species (ROS) is an important mechanism underlying endothelial cell death. Growing evidence suggests that ROS can trigger endothelial cell death in various ways, including pyroptosis, parthanatos, and ferroptosis. Therefore, this review will systematically illustrate the source of ROS in endothelial cells (ECs); reveal the molecular mechanism by which ROS trigger pyroptosis, parthanatos, and ferroptosis in ECs; and provide new ideas for the research and treatment of endothelial dysfunction-related diseases.

Mixed plasticizers aggravated apoptosis by NOD2-RIP2-NF-κB pathway in grass carp hepatocytes

The wide application of plastics led to the wide exposure of plasticizers to the environment. As a new environmental pollutant, plasticizers' toxicity researches were far from enough in fish. To further explore these mechanisms, we used two common plasticizers (Diethylhexyl phthalate (DEHP) and dibutyl phthalate (DBP) expose to grass carp hepatocytes (L8824). The results showed that the mRNA levels of NOD2-RIP2-NF-κB signal pathway and its downstream inflammatory genes were significantly increased compared to those in control group. Then, the levels of mRNAs and proteins of apoptosis markers were changed, and hepatocytes apoptosis was induced. After DBP and DEHP exposure together, there were higher levels of inflammatory factors and the proportion of apoptotic cells. After NOD2 inhibitor treatment, the phenomena mentioned above were obviously alleviated. We conclude that DBP and DEHP exposure at least partially activated the NOD2-RIP2-NF-κB signal pathway in grass carp hepatocytes, and caused inflammation and apoptosis. In terms of hepatotoxicity, there was synergistic relationship between DBP and DEHP. In addition, we put forward new views on the use of plasticizers: select low toxicity plasticizers, then reduce the types of plasticizers used and reduce the high toxicity level of mixed plasticizers.

Human cytomegalovirus-encoded miR-US25-1 aggravates the oxidised low density lipoprotein-induced apoptosis of endothelial cells

Human cytomegalovirus (HCMV) infection is linked to the development and severity of the cardiovascular disease atherosclerosis; however, there is little known about the promotion of atherosclerosis. miR-US25-1 is one of HCMV-encoded miRNAs and targets cellular genes that are essential for virus growth to control the life cycle of the virus and host cells. The prominent regulation on cell cycle genes of the miR-US25-1 attracts us to explore its role in the atherosclerosis promotion. It was indicated that miR-US25-1 level was upregulated in subjects or in endothelial cells with HCMV infection; and the miR-US25-1 downregulated the expression of BRCC 3 by targeting the 5′ UTR of BRCC 3. And a miR-US25-1 mimics transfection could reduce the EAhy926 cell viability but did not induce apoptosis in EAhy926 cells. And what is more, miR-US25-1 mimicis transfection deteriorated the ox-LDL-induced apoptosis and aggravated the upregulation of apoptosis-associated molecules by oxidised low density lipoprotein (ox-LDL) in EAhy926 cells. And we have also confirmed the deregulation of BRCC 3 expression by miR-US25-1 by targeting the 5′ UTR of it. Given the vital role of BRCC 3 in DNA damage repairing, we speculated that the targeting inhibition of BRCC 3 by miR-US25-1 may contribute to the aggravation of ox-LDL-promoted apoptosis of endothelial EAhy926 cells.

Vasohibin-1 is identified as a master-regulator of endothelial cell apoptosis using gene network analysis

BACKGROUND

Apoptosis is a critical process in endothelial cell (EC) biology and pathology, which has been extensively studied at protein level. Numerous gene expression studies of EC apoptosis have also been performed, however few attempts have been made to use gene expression data to identify the molecular relationships and master regulators that underlie EC apoptosis. Therefore, we sought to understand these relationships by generating a Bayesian gene regulatory network (GRN) model.

RESULTS

ECs were induced to undergo apoptosis using serum withdrawal and followed over a time course in triplicate, using microarrays. When generating the GRN, this EC time course data was supplemented by a library of microarray data from EC treated with siRNAs targeting over 350 signalling molecules.The GRN model proposed Vasohibin-1 (VASH1) as one of the candidate master-regulators of EC apoptosis with numerous downstream mRNAs. To evaluate the role played by VASH1 in EC, we used siRNA to reduce the expression of VASH1. Of 10 mRNAs downstream of VASH1 in the GRN that were examined, 7 were significantly up- or down-regulated in the direction predicted by the GRN.Further supporting an important biological role of VASH1 in EC, targeted reduction of VASH1 mRNA abundance conferred resistance to serum withdrawal-induced EC death.

CONCLUSION

We have utilised Bayesian GRN modelling to identify a novel candidate master regulator of EC apoptosis. This study demonstrates how GRN technology can complement traditional methods to hypothesise the regulatory relationships that underlie important biological processes.

CopA3 peptide from Copris tripartitus induces apoptosis in human leukemia cells via a caspase-independent pathway

Our previous study demonstrated that CopA3, a disulfide dimer of the coprisin peptide analogue (LLCIALRKK), has antibacterial activity. In this study, we assessed whether CopA3 caused cellular toxicity in various mammalian cell lines. CopA3 selectively caused a marked decrease in cell viability in Jurkat T, U937, and AML-2 cells (human leukemia cells), but was not cytotoxic to Caki or Hela cells. Fragmentation of DNA, a marker of apoptosis, was also confirmed in the leukemia cell lines, but not in the other cells. CopA3-induced apoptosis in leukemia cells was mediated by apoptosis inducing factor (AIF), indicating induction of a caspase-independent signaling pathway.

Different mechanisms preserve translation of programmed cell death 8 and JunB in virus-infected endothelial cells

OBJECTIVE

Translation initiation of eukaryotic mRNAs typically occurs by cap-dependent ribosome scanning mechanism. However, certain mRNAs are translated by ribosome assembly at internal ribosome entry sites (IRESs). Whether IRES-mediated translation occurs in stressed primary human endothelial cells (ECs) is unknown.

METHODS AND RESULTS

We performed microarray analysis of polyribosomal mRNA from ECs to identify IRES-containing mRNAs. Cap-dependent translation was disabled by poliovirus (PV) infection and confirmed by loss of polysome peaks, detection of eukaryotic initiation factor (eIF) 4G cleavage, and decreased protein synthesis. We found that 87.4% of mRNAs were dissociated from polysomes in virus-infected ECs. Twelve percent of mRNAs remained associated with polysomes, and 0.6% were enriched ≥2-fold in polysome fractions from infected ECs. Quantitative reverse transcription-polymerase chain reaction confirmed the microarray findings for 31 selected mRNAs. We found that enriched polysome associations of programmed cell death 8 (PDCD8) and JunB mRNA resulted in increased protein expression in PV-infected ECs. The presence of IRESs in the 5' untranslated region of PDCD8 mRNA, but not of JunB mRNA, was confirmed by dicistronic analysis.

CONCLUSIONS

We show that microarray profiling of polyribosomal mRNA transcripts from PV-infected ECs successfully identifies mRNAs whose translation is preserved in the face of stress-induced, near complete cessation of cap-dependent initiation. Nevertheless, internal ribosome entry is not the only mechanism responsible for this privileged translation.

Cryptotanshinone has diverse effects on cell cycle events in melanoma cell lines with different metastatic capacity

PURPOSE

Cryptotanshinone is a major active component of Salvia miltiorrhiza, which is often used as Chinese herbal medicine in cancer therapy. Here, we systematically assessed the anti-tumor effect of Cryptotanshinone on two melanoma cell lines with low/high-metastatic capacity (B16/B16BL6).

METHODS

MTT and LDH assays were used to evaluate cell growth and cytotoxicity. We assessed the effect of Cryptotanshinone on cell apoptosis or proliferation by Annexin V, TUNEL or BrdU assay. Cell cycle distribution was detected by flow cytometry. The integrity of cell cycle checkpoints was determined by mutational analyses of B-RAF and N-RAS, and the expression of cell cycle-associated proteins by western blotting.

RESULTS

Treatment with Cryptotanshinone had no obvious effect on cell apoptosis but significantly inhibited cell proliferation. Cryptotanshinone slightly increased the expression of p53, Chk1, and Chk2 in both B16 and B16BL6. Interestingly, Cryptotanshinone induced G1 arrest with a concomitant increase in p21 expression in B16BL6 cells. However, in B16 cells, Cryptotanshinone induced the G2/M arrest through its induction of Cdc25c. Regulation of Cyclin A1, Cyclin B1 and Cdk1/cdc2 expression might contribute to the different cell cycle patterns in B16 and B16BL6 after Cryptotanshinone treatment.

CONCLUSIONS

Cryptotanshinone could have diverse effects on cell cycle events in melanoma cell lines with different metastatic capacity. This property might offer an opportunity to study underlying mechanisms for the different antitumor effects of administered Cryptotanshinone in B16 and B16BL6 cells.

Oxidized low-density lipoprotein (oxLDL) induces cell death in neuroblastoma and survival autophagy in schwannoma cells

Oxidized low-density lipoprotein (oxLDL) induces apoptosis or autophagy in dependence on the cell type. We here investigated the effect of oxLDL on the B104 neuroblastoma and RN22 schwannoma cells being popular in neuroscience research. Cells were cultivated with and without oxLDL. To generate oxLDL, we added 50 μg/ml nLDL and 50 μM CuSO(4) into the culture medium. After a 24-h-long treatment, oxLDL was detectable in media from both cell culture types and its concentration was approximately 16 μg/ml. In the oxLDL-treated B104 neuroblastoma cell cultures 75% cells died after the 24-h exposure. The intact cells showed impaired mitochondria at the ultrastructural level. Western blot analysis revealed the increased expression of AIF 57 kDa (AIF(57)) protein, as a sign of caspase-independent cell death. In RN22 schwannoma cell cultures, oxLDL did not have any effect on cleaved caspase-3 and AIF(57) protein levels indicating absence of cell death. Treated RN22 schwannoma cells underwent survival autophagy by forming conspicuous autophagosomes and by processing LC3-I into LC3-II protein. Collectively, oxLDL induces AIF-dependent cell death in B104 neuroblastoma cells whereas in RN22 schwannoma cells enhanced signs of survival autophagy are noted.

High glucose and oxidative/nitrosative stress conditions induce apoptosis in retinal endothelial cells by a caspase-independent pathway

Diabetic retinopathy (DR) is a leading cause of vision loss among working-age adults. Retinal endothelial cell apoptosis is an early event in DR, and oxidative stress is known to play an important role in this pathology. Recently, we found that high glucose induces apoptosis in retinal neural cells by a caspase-independent mechanism. Here, we investigated the mechanisms underlying retinal endothelial cell apoptosis induced by high glucose and oxidative/nitrosative stress conditions. Endothelial cells (TR-iBRB2 rat retinal endothelial cell line) were exposed to high glucose (long-term exposure, 7 days), or to NOC-18 (nitric oxide donor; 250microM) or H(2)O(2) (100microM) for 24h. Cell viability was assessed by the MTT assay and cell proliferation by [methyl-(3)H]-thymidine incorporation into DNA. Apoptotic cells were detected with Hoechst or Annexin V staining. Active caspases were detected by an apoptosis detection kit. Active caspase-3 and apoptosis-inducing factor (AIF) protein levels were assessed by Western blot or immunohistochemistry. High glucose, NOC-18 and H(2)O(2) increased apoptosis in retinal endothelial cells. High glucose and mannitol decreased cell proliferation, but mannitol did not induce apoptosis. Caspase activation did not increase in high glucose- or NOC-18-treated cells, but it increased in cells exposed to H(2)O(2). However, the protein levels of AIF decreased in mitochondrial fractions and increased in nuclear fractions, in all conditions. These results are the first demonstrating that retinal endothelial cell apoptosis induced by high glucose is independent of caspase activation, and is correlated with AIF translocation to the nucleus. NOC-18 and H(2)O(2) also activate a caspase-independent apoptotic pathway, although H(2)O(2) can also induce caspase-mediated apoptosis.

Understanding endothelial cell apoptosis: what can the transcriptome, glycome and proteome reveal?

Endothelial cell (EC) apoptosis may play an important role in blood vessel development, homeostasis and remodelling. In support of this concept, EC apoptosis has been detected within remodelling vessels in vivo, and inactivation of EC apoptosis regulators has caused dramatic vascular phenotypes. EC apoptosis has also been associated with cardiovascular pathologies. Therefore, understanding the regulation of EC apoptosis, with the goal of intervening in this process, has become a current research focus. The protein-based signalling and cleavage cascades that regulate EC apoptosis are well known. However, the possibility that programmed transcriptome and glycome changes contribute to EC apoptosis has only recently been explored. Traditional bioinformatic techniques have allowed simultaneous study of thousands of molecular signals during the process of EC apoptosis. However, to progress further, we now need to understand the complex cause and effect relationships among these signals. In this article, we will first review current knowledge about the function and regulation of EC apoptosis including the roles of the proteome transcriptome and glycome. Then, we assess the potential for further bioinformatic analysis to advance our understanding of EC apoptosis, including the limitations of current technologies and the potential of emerging technologies such as gene regulatory networks.

Nuclear translocation of apoptosis inducing factor is associated with cisplatin induced apoptosis in LNCaP prostate cancer cells

Prostate cancer (PC) is considered resistant to cisplatin chemotherapy. In order to identify novel causes of resistance to cisplatin, we explored the role of Apoptosis Inducing Factor (AIF) that mediates caspase independent apoptosis in cisplatin induced cell death in PC. Similar to treatment with pancaspase inhibitor Z-VAD-fmk, cisplatin induced apoptosis in LNCaP cells was inhibited by AIF inhibitor N-acetyl-L-cysteine (NAC), treatment of LNCaP cells with NAC prevented AIF translocation to the nucleus and over-expression of recombinant AIF gene increased apoptosis. Our results suggest that AIF is associated with cisplatin induced apoptosis in PC.

No upregulation of lectin-like oxidized low-density lipoprotein receptor-1 in serum-deprived EA.hy926 endothelial cells under oxLDL exposure, but increase in autophagy

The oxidized low-density lipoprotein (oxLDL)-dependent activation of the lectin-like oxLDL receptor-1 (LOX-1) triggers apoptosis in vascular cells and appears to be involved in atherosclerosis. Autophagy might be an alternate to apoptosis in endothelial cells. The EA.hy926 endothelial cell line has been reported to undergo necrosis under oxLDL stimulation. For this reason, we studied the expression of LOX-1 and its oxLDL-dependent function in EA.hy926 cells under serum starvation. Untreated and oxLDL-treated cells expressed the LOX-1 protein at similar levels 6h after starvation. After 24h without oxLDL and with native LDL (nLDL), statistically significant higher levels were found in LOX-1 than in the oxLDL-treated probes. The oxLDL cultures with low LOX-1 expression displayed stronger features of autophagy than those with nLDL as there were remodelling of actin filaments, disrupture of adherens junctions (immunofluorescence staining), and autophagosomes with the characteristic double membrane at the ultrastructural level. For the advanced oxLDL exposure times (18 and 24 h), autophagic vacuoles/autophagolysosomes were morphologically identified accompanied by a decrease in lysosomes. The autophagosome marker protein MAP LC3-II (Western blotting) was significantly augmented 6 and 18 h after oxLDL treatment compared with cultures treated with nLDL and medium alone. Signs of apoptosis were undetectable in cultures under oxLDL exposure, yet present under staurosporin (apoptosis inducer), i.e. presence of apoptotic bodies and cleaved caspase 3. We conclude that serum starvation upregulates LOX-1 in EA.hy926 cells, whereas the additional oxLDL treatment downregulates the receptor and intensifies autophagy probably by increase in oxidative stress.

Diphenyleneiodonium suppresses apoptosis in cerulein-stimulated pancreatic acinar cells

NADPH oxidase has been considered a major source of reactive oxygen species in phagocytic and non-phagocytic cells. Apoptosis linked to oxidative stress has been implicated in pancreatitis. Recently, we demonstrated that NADPH oxidase subunits Nox1, p27phox, p47phox, and p67phox are constitutively expressed in pancreatic acinar cells, which are activated by cerulein, a cholecystokinin analogue. Cerulein induces an acute and edematous form of pancreatitis. We investigated whether inhibition of NADPH oxidase by diphenyleneiodonium suppresses the production of reactive oxygen species and apoptosis by determining viable cell numbers, DNA fragmentation, TUNEL staining, caspase-3 activity, and the expression of apoptosis-inducing factor in pancreatic acinar AR42J cells stimulated with cerulein. Inhibition on NADPH oxidase by diphenyleneiodonium was assessed by the alterations in NADPH oxidase activity and translocation of the cytosolic subunits p67phox and p47phox to the membrane. Intracellular Ca2+ level was monitored to investigate the relationship between NADPH oxidase and Ca2+ in cells stimulated with cerulein. As a result, cerulein induced the activation of NADPH, increased production of reactive oxygen species, and apoptotic indices determined by the expression of apoptosis-inducing factor, caspase-3 activation, TUNEL staining, DNA fragmentation, and cell viability. Treatment with DPI inhibited cerulein-induced activation of NADPH oxidase, the production of reactive oxygen species, and apoptosis, but not the increase of intracellular Ca2+ levels in pancreatic acinar cells. These results demonstrate that the cerulein-induced increase in intracellular Ca2+ level may be an upstream event of NADPH oxidase activation. Diphenyleneiodonium, an NADPH oxidase inhibitor, inhibits the expression of apoptosis-inducing factor and caspase-3 activation, and thus apoptosis in pancreatic acinar cells.

Bcl-2 protein family: implications in vascular apoptosis and atherosclerosis

Apoptosis has been recognized as a central component in the pathogenesis of atherosclerosis, in addition to the other human pathologies such as cancer and diabetes. The pathophysiology of atherosclerosis is complex, involving both apoptosis and proliferation at different phases of its progression. Oxidative modification of lipids and inflammation differentially regulate the apoptotic and proliferative responses of vascular cells during progression of the atherosclerotic lesion. Bcl-2 proteins act as the major regulators of extrinsic and intrinsic apoptosis signalling pathways and more recently it has become evident that they mediate the apoptotic response of vascular cells in response to oxidation and inflammation either in a provocative or an inhibitory mode of action. Here we address Bcl-2 proteins as major therapeutic targets for the treatment of atherosclerosis and underscore the need for the novel preventive and therapeutic interventions against atherosclerosis, which should be designed in the light of molecular mechanisms regulating apoptosis of vascular cells in atherosclerotic lesions.

Chlamydia (Chlamydophila) pneumoniae-induced cell death in human coronary artery endothelial cells is caspase-independent and accompanied by subcellular translocations of Bax and apoptosis-inducing factor

Atherosclerosis and coronary heart disease are causing high morbidity and mortality worldwide. Different risk factors have been demonstrated, but the exact mechanisms behind these diseases are still not fully understood. Recent studies have suggested Chlamydia pneumoniae to be involved in the pathogenesis, and increased apoptotic indexes in atherosclerotic plaques have been documented. In this study, we show that C. pneumoniae induces apoptosis and necrosis in populations of human coronary artery endothelial cells. Apoptosis was determined by TUNEL and flow cytometry after staining of cells with annexin V and propidium iodide, and defined as TUNEL-reactive or annexin V-positive, propidium iodide-negative cells. The apoptosis was induced within 2 h postinfection and increased with inoculation dose. The general caspase inhibitor z-VAD-fmk did not affect apoptotic frequencies. By immunochemistry and immunoblot, we demonstrated activation and subcellular translocation of the proapoptotic protein Bax, and translocation of apoptosis-inducing factor from the cytosol to the nucleus. These results indicate that C. pneumoniae-induced apoptosis in human coronary artery endothelial cells is caspase-independent and regulated by Bax and apoptosis-inducing factor.

Genistein blocks homocysteine-induced alterations in the proteome of human endothelial cells

Dietary isoflavones from soy are suggested to protect endothelial cells from damaging effects of endothelial stressors and thereby to prevent atherosclerosis. In search of the molecular targets of isoflavone action, we analyzed the effects of the major soy isoflavone, genistein, on changes in protein expression levels induced by the endothelial stressor homocysteine (Hcy) in EA.hy 926 endothelial cells. Proteins from cells exposed for 24 h to 25 microM Hcy alone or in combination with 2.5 microM genistein were separated by two-dimensional gel electrophoresis and those with altered spot intensities were identified by peptide mass fingerprinting. Genistein reversed Hcy-induced changes of proteins involved in metabolism, detoxification, and gene regulation; and some of those effects can be linked functionally to the antiatherosclerotic properties of the soy isoflavone. Alterations of steady-state levels of cytoskeletal proteins by genistein suggested an effect on apoptosis. As a matter of fact genistein caused inhibition of Hcy-mediated apoptotic cell death as indicated by inhibition of DNA fragmentation and chromatin condensation. In conclusion, proteome analysis allows the rapid identification of cellular target proteins of genistein action in endothelial cells exposed to the endothelial stressor Hcy and therefore enables the identification of molecular pathways of its antiatherosclerotic action.

Wood smoke extract induces oxidative stress-mediated caspase-independent apoptosis in human lung endothelial cells: role of AIF and EndoG

Although a link between toxic smoke and oxidant lung vascular injury has been indicated, the cellular mechanisms of smoke-induced injury to lung endothelial cells are unknown. We investigated oxidative stress and apoptosis induced by wood smoke extract (SE) in human pulmonary artery endothelial cells (HPAECs) and delineated their relationship. We found that SE increased intracellular reactive oxygen species (ROS), depleted intracellular glutathione, and upregulated Cu/Zn superoxide dismutase and heme oxygenase-1 (2 antioxidant enzymes), but it failed to alter the expression of catalase and glutathione peroxidase. In addition, SE promoted apoptosis as indicated by the external exposure of membrane phosphatidylserine, the loss of mitochondrial membrane potential, an increase in the level of Bax (a proapoptotic protein), and enhanced DNA fragmentation. This apoptosis was associated with mitochondrial-to-nuclear translocation of apoptosis-inducing factor (AIF) and endonuclease G (EndoG) (2 apoptogenic proteins) but was independent of caspase cascade activation. Whereas N-acetylcysteine (an antioxidant) effectively reversed the SE-induced increase in ROS and depletion of glutathione, it also suppressed SE-induced nuclear translocation of either AIF or EndoG and prevented the enhanced DNA fragmentation that would have resulted from this. We conclude that 1) although SE upregulates Cu/Zn superoxide dismutase and heme oxygenase-1, it nevertheless increases intracellular oxidative stress in HPAECs, and 2) SE promotes oxidative stress-mediated caspase-independent HPAEC apoptosis that involves mitochondrial-to-nuclear translocation of AIF and EndoG. Thus modulations of the expression of antioxidant enzymes and the caspase-independent apoptotic pathway are possible target choices for potential therapeutic regimes to treat smoke-induced lung injury.

Two Distinct Calcium-Dependent Mitochondrial Pathways Are Involved in Oxidized LDL-Induced Apoptosis

Objective— Oxidized low-density lipoprotein (oxLDL)-induced apoptosis of vascular endothelial cells may contribute to plaque erosion and rupture. We aimed to clarify the relationship between the oxLDL-induced calcium signal and induction of apoptotic pathways.

Methods and Results— Apoptosis was evaluated by biochemical methods, including studies of enzyme activities, protein processing, release of proapoptotic factors, chromatin cleavage, and especially by morphological methods that evaluate apoptosis/necrosis by SYTO-13/propidium iodide fluorescent labeling. The oxLDL-induced sustained calcium rise activated 2 distinct calcium-dependent mitochondrial apoptotic pathways in human microvascular endothelial cells. OxLDLs induced calpain activation and subsequent Bid cleavage and cytochrome C release, which were blocked by calpeptin. Cyclosporin-A inhibited cytochrome C release, possibly by inhibiting the opening of the mitochondrial permeability transition pore (mPTP). Calcineurin, another cyclosporin-sensitive step, was not implicated, because oxLDLs inhibited calcineurin and FK-506 treatment was ineffective. Cytochrome C release in turn induced caspase-3 activation. In addition, oxLDLs triggered release and nuclear translocation of mitochondrial apoptosis-inducing factor through a mechanism dependent on calcium but independent of calpains, mPTP, and caspases.

Conclusions— OxLDL-induced apoptosis involves 2 distinct calcium-dependent pathways, the first mediated by calpain/mPTP/cytochrome C/caspase-3 and the second mediated by apoptosis-inducing factor, which is cyclosporin-insensitive and caspase-independent.