Oxidized LDL-Mediated Macrophage Survival Involves Elongation Factor-2 Kinase

Evaluating the effects of zinc oxide nanoparticles on a sentinel aquatic invertebrate species: Transcriptomic analysis and potential implications for ecosystem health

The widespread use of zinc oxide nanoparticles (ZnO NPs) in various products raises significant ecological concerns due to their potential toxic effects in aquatic environments. This study employed the Asian green mussel (Perna viridis) as a model to explore the molecular and ecological risks of ZnO NP exposure using transcriptomics. Mussels exposed to ZnO NPs (5, 10, and 15 mg/L) for 28 days showed significant gene expression changes in gill tissues, affecting immune response, calcium homeostasis, and cellular stress. Disrupted pathways such as FOXO, Wnt, and TGFβ reveal complex toxicity mechanisms. These findings provide crucial insights into the environmental impact of nanoparticle pollution, emphasizing the need for stringent regulations. Furthermore, the shared molecular pathways suggest that similar mechanisms may occur in humans, highlighting potential health risks associated with nanoparticle exposure.

Control of CD4+ T cells to restrain inflammatory diseases via eukaryotic elongation factor 2 kinase

CD4+ T cells, particularly IL-17-secreting helper CD4+ T cells, play a central role in the inflammatory processes underlying autoimmune disorders. Eukaryotic Elongation Factor 2 Kinase (eEF2K) is pivotal in CD8+ T cells and has important implications in vascular dysfunction and inflammation-related diseases such as hypertension. However, its specific immunological role in CD4+ T cell activities and related inflammatory diseases remains elusive. Our investigation has uncovered that the deficiency of eEF2K disrupts the survival and proliferation of CD4+ T cells, impairs their ability to secrete cytokines. Notably, this dysregulation leads to heightened production of pro-inflammatory cytokine IL-17, fosters a pro-inflammatory microenvironment in the absence of eEF2K in CD4+ T cells. Furthermore, the absence of eEF2K in CD4+ T cells is linked to increased metabolic activity and mitochondrial bioenergetics. We have shown that eEF2K regulates mitochondrial function and CD4+ T cell activity through the upregulation of the transcription factor, signal transducer and activator of transcription 3 (STAT3). Crucially, the deficiency of eEF2K exacerbates the severity of inflammation-related diseases, including rheumatoid arthritis, multiple sclerosis, and ulcerative colitis. Strikingly, the use of C188-9, a small molecule targeting STAT3, mitigates colitis in a murine immunodeficiency model receiving eEF2K knockout (KO) CD4+ T cells. These findings emphasize the pivotal role of eEF2K in controlling the function and metabolism of CD4+ T cells and its indispensable involvement in inflammation-related diseases. Manipulating eEF2K represents a promising avenue for novel therapeutic approaches in the treatment of inflammation-related disorders.

Machine learning and bioinformatics analysis to identify autophagy-related biomarkers in peripheral blood for rheumatoid arthritis

Background: Although rheumatoid arthritis (RA) is a common autoimmune disease, the precise pathogenesis of the disease remains unclear. Recent research has unraveled the role of autophagy in the development of RA. This research aims to explore autophagy-related diagnostic biomarkers in the peripheral blood of RA patients. Methods: The gene expression profiles of GSE17755 were retrieved from the gene expression ontology (GEO) database. Differentially expressed autophagy-related genes (DE-ARGs) were identified for the subsequent research by inserting autophagy-related genes and differentially expressed genes (DEGs). Three machine learning algorithms, including random forest, support vector machine recursive feature elimination (SVM-RFE), and least absolute shrinkage and selection operator (LASSO), were employed to identify diagnostic biomarkers. A nomogram model was constructed to assess the diagnostic value of the biomarkers. The CIBERSORT algorithm was performed to investigate the correlation of the diagnostic biomarkers with immune cells and immune factors. Finally, the diagnostic efficacy and differential expression trend of diagnostic biomarkers were validated in multiple cohorts containing different tissues and diseases. Results: In this study, 25 DE-ARGs were identified between RA and healthy individuals. In addition to "macroautophagy" and "autophagy-animal," DE-ARGs were also associated with several types of programmed cell death and immune-related pathways according to GO and KEGG analysis. Three diagnostic biomarkers, EEF2, HSP90AB1 and TNFSF10, were identified by the random forest, SVM-RFE, and LASSO. The nomogram model demonstrated excellent diagnostic value in GSE17755 (AUC = 0.995, 95% CI: 0.988-0.999). Furthermore, immune infiltration analysis showed a remarkable association between EEF2, HSP90AB1, and TNFSF10 expression with various immune cells and immune factors. The three diagnostic biomarkers also exhibited good diagnostic efficacy and demonstrated the same trend of differential expression in multiple validation cohorts. Conclusion: This study identified autophagy-related diagnostic biomarkers based on three machine learning algorithms, providing promising targets for the diagnosis and treatment of RA.

Eukaryotic elongation factor 2 kinase regulates foam cell formation via translation of CD36

Eukaryotic elongation factor 2 kinase (eEF2K) is an atypical protein kinase that controls protein synthesis in cells under stress. Although well studied in cancer, less is known about its roles in chronic inflammatory diseases. Here, we examined its regulation of macrophage cholesterol handling in the context of atherosclerosis. eEF2K mRNA expression and protein activity were upregulated in murine bone marrow-derived macrophages (BMDMs) exposed to oxidized low-density lipoprotein cholesterol (oxLDL). When incubated with oxLDL, BMDMs from eEF2K knockout (Eef2k^-/- ) mice formed fewer Oil Red O⁺ foam cells than Eef2k^+/+ BMDMs (12.5% ± 2.3% vs. 32.3% ± 2.0%, p < .01). Treatment with a selective eEF2K inhibitor, JAN-384, also decreased foam cell formation for C57BL/6J BMDMs and human monocyte-derived macrophages. Disabling eEF2K selectively decreased protein expression of the CD36 cholesterol uptake receptor, mediated by a reduction in the proportion of translationally active Cd36 mRNA. Eef2k^-/- mice bred onto the Ldlr^-/- background developed aortic sinus atherosclerotic plaques that were 30% smaller than Eef2k^+/+ -Ldlr^-/- mice after 16 weeks of high cholesterol diet (p < .05). Although accompanied by a reduction in plaque CD36⁺ staining (p < .05) and lower CD36 expression in circulating monocytes (p < .01), this was not associated with reduced lipid content in plaques as measured by oil red O staining. Finally, EEF2K and CD36 mRNA levels were higher in blood mononuclear cells from patients with coronary artery disease and recent myocardial infarction compared to healthy controls without coronary artery disease. These results reveal a new role for eEF2K in translationally regulating CD36 expression and foam cell formation in macrophages. Further studies are required to explore therapeutic targeting of eEF2K in atherosclerosis.

Therapeutic Potential of Thymoquinone in Triple-Negative Breast Cancer Prevention and Progression through the Modulation of the Tumor Microenvironment

To date, the tumor microenvironment (TME) has gained considerable attention in various areas of cancer research due to its role in driving a loss of immune surveillance and enabling rapid advanced tumor development and progression. The TME plays an integral role in driving advanced aggressive breast cancers, including triple-negative breast cancer (TNBC), a pivotal mediator for tumor cells to communicate with the surrounding cells via lymphatic and circulatory systems. Furthermore, the TME plays a significant role in all steps and stages of carcinogenesis by promoting and stimulating uncontrolled cell proliferation and protecting tumor cells from the immune system. Various cellular components of the TME work together to drive cancer processes, some of which include tumor-associated adipocytes, fibroblasts, macrophages, and neutrophils which sustain perpetual amplification and release of pro-inflammatory molecules such as cytokines. Thymoquinone (TQ), a natural chemical component from black cumin seed, is widely used traditionally and now in clinical trials for the treatment/prevention of multiple types of cancer, showing a potential to mitigate components of TME at various stages by various pathways. In this review, we focus on the role of TME in TNBC cancer progression and the effect of TQ on the TME, emphasizing their anticipated role in the prevention and treatment of TNBC. It was concluded from this review that the multiple components of the TME serve as a critical part of TNBC tumor promotion and stimulation of uncontrolled cell proliferation. Meanwhile, TQ could be a crucial compound in the prevention and progression of TNBC therapy through the modulation of the TME.

Two-faced Janus: The dual role of macrophages in atherosclerotic calcification

Calcification is an independent predictor of atherosclerosis-related cardiovascular events. Microcalcification is linked to inflamed, unstable lesions, in comparison to the fibrotic stable plaque phenotype generally associated with advanced calcification. This paradox relates to recognition that calcification presents in a wide spectrum of manifestations that differentially impact plaque’s fate. Macrophages, the main inflammatory cells in atherosclerotic plaque, have a multifaceted role in disease progression. They crucially control the mineralization process, from microcalcification to the osteoid metaplasia of bone-like tissue. It is a bilateral interaction that weighs heavily on the overall plaque fate but remains rather unexplored. This review highlights current knowledge about macrophage phenotypic changes in relation to and interaction with the calcifying environment. On the one hand, macrophage-led inflammation kickstarts microcalcification through a multitude of interlinked mechanisms, which in turn stimulates phenotypic changes in vascular cell types to drive microcalcification. Macrophages may also modulate the expression/activity of calcification inhibitors and inducers, or eliminate hydroxyapatite nucleation points. Contrarily, direct exposure of macrophages to an early calcifying milieu impacts macrophage phenotype, with repercussions for plaque progression and/or stability. Macrophages surrounding macrocalcification deposits show a more reparative phenotype, modulating extracellular matrix, and expressing osteoclast genes. This phenotypic shift favours gradual displacement of the pro-inflammatory hubs; the lipid necrotic core, by macrocalcification. Parallels to bone metabolism may explain many of these changes to macrophage phenotype, with advanced calcification able to show homeostatic osteoid metaplasia. As the targeted treatment of vascular calcification developing in atherosclerosis is thus far severely lacking, it is crucial to better understand its mechanisms of development.

Potential role of perivascular adipose tissue in modulating atherosclerosis

Perivascular adipose tissue (PVAT) directly juxtaposes the vascular adventitia and contains a distinct mixture of mature adipocytes, preadipocytes, stem cells, and inflammatory cells that communicate via adipocytokines and other signaling mediators with the nearby vessel wall to regulate vascular function. Cross-talk between perivascular adipocytes and the cells in the blood vessel wall is vital for normal vascular function and becomes perturbed in diseases such as atherosclerosis. Perivascular adipocytes surrounding coronary arteries may be primed to promote inflammation and angiogenesis, and PVAT phenotypic changes occurring in the setting of obesity, hyperlipidemia etc., are fundamentally important in determining a pathogenic versus protective role of PVAT in vascular disease. Recent discoveries have advanced our understanding of the role of perivascular adipocytes in modulating vascular function. However, their impact on cardiovascular disease (CVD), particularly in humans, is yet to be fully elucidated. This review will highlight the complex mechanisms whereby PVAT regulates atherosclerosis, with an emphasis on clinical implications of PVAT and emerging strategies for evaluation and treatment of CVD based on PVAT biology.

Eukaryotic elongation factor-2 kinase (eEF2K) signaling in tumor and microenvironment as a novel molecular target

Eukaryotic elongation factor-2 kinase (eEF2K), an atypical member of alpha-kinase family, is highly overexpressed in breast, pancreatic, brain, and lung cancers, and associated with poor survival in patients. eEF2K promotes cell proliferation, survival, and aggressive tumor characteristics, leading to tumor growth and progression. While initial studies indicated that eEF2K acts as a negative regulator of protein synthesis by suppressing peptide elongation phase, later studies demonstrated that it has multiple functions and promotes cell cycle, angiogenesis, migration, and invasion as well as induction of epithelial-mesenchymal transition through induction of integrin β1, SRC/FAK, PI3K/AKT, cyclin D1, VEGF, ZEB1, Snail, and MMP-2. Under stress conditions such as hypoxia and metabolic distress, eEF2K is activated by several signaling pathways and slows down protein synthesis and helping cells to save energy and survive. In vivo therapeutic targeting of eEF2K by genetic methods inhibits tumor growth in various tumor models, validating it as a potential molecular target. Recent studies suggest that eEF2K plays a role in tumor microenvironment cells by monocyte chemoattractant protein-1 (MCP-1) and accumulation of tumor-associated macrophages. Due to its clinical significance and the pivotal role in tumorigenesis and progression, eEF2K is considered as an important therapeutic target in solid tumors. However, currently, there is no specific and potent inhibitor for translation into clinical studies. Here, we aim to systematically review current knowledge regarding eEF2K in tumor biology, microenvironment, and development of eEF2K targeted inhibitors and therapeutics.

Eukaryotic elongation factor 2 kinase inhibitor, A484954 potentiates β-adrenergic receptor agonist-induced acute decrease in diastolic blood pressure in rats

Eukaryotic elongation factor 2 (eEF2) kinase (eEF2K) acts to inhibit protein translation through phosphorylating a specific substrate, eEF2. We previously found that the increased eEF2K expression in mesenteric artery mediates hypertension development in spontaneously hypertensive rats. More recently, we have revealed that a selective eEF2K inhibitor, A484954 induced vasorelaxation via opening inward rectifier K⁺ channel and activating β₂-adrenergic receptor in smooth muscle of rat isolated mesenteric artery, which contributes to prevent noradrenaline-induced acute increase in blood pressure (BP). In this study, we further explored acute effects of A484954 on BP in rats, especially focusing the action on β-adrenergic receptor. We also examined whether A484954 affects contraction and heart rate (HR) of isolated heart. BP and HR were measured by a carotid cannulation method in rats. Isometric contraction and HR in rat isolated atria were also measured pharmacologically. A484954 potentiated adrenaline-induced decrease in diastolic BP (DBP) but not increase in systolic BP (SBP). A484954 potentiated isoproterenol-induced decrease in DBP but not SBP. Contrastingly, A484954 prevented a non-β-adrenergic receptor agonist, angiotensin II-induced increase in both SBP and DBP. In isolated left atria, A484954 caused contraction, which was prevented by a β-adrenergic receptor antagonist, propranolol. In isolated right atria, A484954 increased HR. In conclusion, we for the first time demonstrated that A484954 potentiates β-adrenergic receptor agonist-induced decrease in DBP possibly through vasorelaxation mediated via activating β₂-adrenergic receptor. It was also demonstrated that A484954 causes contraction of rat isolated heart via activating β₁-adrenergic receptor.

Mechanisms underlying the relaxation by A484954, a eukaryotic elongation factor 2 kinase inhibitor, in rat isolated mesenteric artery

Eukaryotic elongation factor 2 kinase (eEF2K) is a calmodulin-related protein kinase which regulates protein translation. A484954 is an inhibitor of eEF2K. In the present study, we investigated the acute effects of A484954 on contractility of isolated blood vessels. Isometric contraction of rat isolated aorta and main branch of superior mesenteric artery (MA) was measured. Expression of an inward rectifier K⁺ (K_ir) channel subtype mRNA and protein was examined. A484954 caused relaxation in endothelium-intact [E (+)] and -denuded [E (-)] aorta or MA precontracted with noradrenaline (NA). The relaxation was higher in MA than aorta. The relaxation was partially inhibited by a nitric oxide (NO) synthase inhibitor, N^G-nitro-l-arginine methyl ester (300 μM) in E (+) MA. The relaxation was significantly smaller in MA precontracted with high K⁺ than NA. The A484954-induced relaxation was significantly inhibited by a K_ir channel blocker, BaCl₂ (1 mM) compared with vehicle control in E (-) MA. Expression of K_ir2.2 mRNA and protein was significantly higher in MA than aorta. We for the first time revealed that A484954 induces relaxation through opening smooth muscle K_ir (K_ir2.2) channel and through endothelium-derived NO in MA.

Recent Advances in Fluorescent Angioscopy for Molecular Imaging of Human Atherosclerotic Coronary Plaque

PURPOSE OF REVIEW

In vivo imaging of the native substances, including lipoproteins, that comprise human atherosclerotic plaques is currently beyond the scope of any available imaging techniques. Color and near-infrared fluorescent angioscopy (CFA and NIRFA, respectively) systems have been recently developed for molecular imaging of lipoproteins within the human coronary arterial wall ex vivo and/or in vivo. The author reviews recent findings on lipoprotein deposition in human coronary plaques obtained by these imaging techniques.

RECENT FINDINGS

Using specific biomarkers, native pro-atherogenic substances such as oxidized low-density lipoprotein (ox-LDL), LDL, triglycerides (TG), apolipoprotein B-100 (ApoB-100), and lysophosphatidylcholine (LPC), and the anti-atherogenic substance such as high-density lipoprotein (HDL) were visualized by CFA, and LDL and cholesterol by NIRFA, in coronary plaques obtained from autopsy subjects. The relationship between incidence and plaque morphology differed for each substance. The incidence of ox-LDL and LDL on color fluorescence microscopy correlated well with that observed using immunohistochemical techniques. During coronary catheterization in patients, ox-LDL, LDL, and HDL in coronary plaques were visualized by CFA or NIRFA.

CONCLUSIONS

Using CFA or NIRFA, the distribution of the major native pro-atherogenic and anti-atherogenic lipoproteins and their components within human coronary plaques can be evaluated ex vivo and/or in vivo. Fluorescent angioscopy could help our understanding of the molecular mechanisms of coronary atherosclerosis and in the evaluation of the effects of therapy targeting the substances comprising atherosclerotic coronary plaques.

Complete deletion of Cd39 is atheroprotective in apolipoprotein E-deficient mice

Cd39 scavenges extracellular ATP and ADP, ultimately generating adenosine, a nucleoside, which has anti-inflammatory effects in the vasculature. We have evaluated the role of Cd39 in the development of atherosclerosis in hyperlipidemic mice. ApoE KO (Cd39^+/+/ApoE^−/−) and Cd39/ApoE double KO (DKO) (Cd39^−/−/ApoE^−/−) mice were maintained on chow or Western diet for up to 20 weeks before evaluation of atherosclerotic lesions. We found that DKO mice exhibited significantly fewer atherosclerotic lesions than ApoE KO mice, irrespective of diet. Analyses of plaque composition revealed diminished foam cells in the fatty streaks and smaller necrotic cores in advanced lesions of DKO mice, when compared with those in ApoE KO mice. This atheroprotective phenotype was associated with impaired platelet reactivity to ADP in vitro and prolonged platelet survival, suggesting decreased platelet activation in vivo. Further studies with either genetic deletion or pharmacological inhibition of Cd39 in macrophages revealed increased cholesterol efflux mediated via ABCA1 to ApoA1. This phenomenon was associated with elevated plasma HDL levels in DKO mice. Our findings indicate that complete deletion of Cd39 paradoxically attenuates development of atherosclerosis in hyperlipidemic mice. We propose that this phenotype occurs, at least in part, from diminished platelet activation, increased plasma HDL levels, and enhanced cholesterol efflux and indicates the complexity of purinergic signaling in atherosclerosis.

Aβ and Inflammatory Stimulus Activate Diverse Signaling Pathways in Monocytic Cells: Implications in Retaining Phagocytosis in Aβ-Laden Environment

Background: Accumulation of amyloid β (Aβ) is one of the main hallmarks of Alzheimer’s disease (AD). The enhancement of Aβ clearance may provide therapeutic means to restrict AD pathology. The cellular responses to different forms of Aβ in monocytic cells are poorly known. We aimed to study whether different forms of Aβ induce inflammatory responses in monocytic phagocytes and how Aβ may affect monocytic cell survival and function to retain phagocytosis in Aβ-laden environment.

Methods: Monocytic cells were differentiated from bone marrow hematopoietic stem cells (HSC) in the presence of macrophage-colony stimulating factor. Monocytic cells were stimulated with synthetic Aβ42 and intracellular calcium responses were recorded with calcium imaging. The formation of reactive oxygen species (ROS), secretion of cytokines and cell viability were also assessed. Finally, monocytic cells were introduced to native Aβ deposits ex vivo and the cellular responses in terms of cell viability, pro-inflammatory activation and phagocytosis were determined. The ability of monocytic cells to phagocytose Aβ plaques was determined after intrahippocampal transplantation in vivo.

Results: Freshly solubilized Aβ induced calcium oscillations, which persisted after removal of the stimulus. After few hours of aggregation, Aβ was not able to induce oscillations in monocytic cells. Instead, lipopolysaccharide (LPS) induced calcium responses divergent from Aβ-induced response. Furthermore, while LPS induced massive production of pro-inflammatory cytokines, neither synthetic Aβ species nor native Aβ deposits were able to induce pro-inflammatory activation of monocytic cells, contrary to primary microglia. Finally, monocytic cells retained their viability in the presence of Aβ and exhibited phagocytic activity towards native fibrillar Aβ deposits and congophilic Aβ plaques.

Conclusion: Monocytic cells carry diverse cellular responses to Aβ and inflammatory stimulus LPS. Even though Aβ species cause specific responses in calcium signaling, they completely lack the ability to induce pro-inflammatory phenotype of monocytic cells. Monocytes retain their viability and function in Aβ-laden brain.

ORP4L Facilitates Macrophage Survival via G-Protein-Coupled Signaling: ORP4L-/- Mice Display a Reduction of Atherosclerosis

RATIONALE

Macrophage survival within the arterial wall is a central factor contributing to atherogenesis. Oxysterols, major components of oxidized low-density lipoprotein, exert cytotoxic effects on macrophages.

OBJECTIVE

To determine whether oxysterol-binding protein-related protein 4 L (ORP4L), an oxysterol-binding protein, affects macrophage survival and the pathogenesis of atherosclerosis.

METHODS AND RESULTS

By hiring cell biological approaches and ORP4L^-/- mice, we show that ORP4L coexpresses with and forms a complex with Gα_q/11 and phospholipase C (PLC)-β3 in macrophages. ORP4L facilitates G-protein-coupled ligand-induced PLCβ3 activation, IP₃ production, and Ca²⁺ release from the endoplasmic reticulum. Through this mechanism, ORP4L sustains antiapoptotic Bcl-XL expression through Ca²⁺-mediated c-AMP responsive element binding protein transcriptional regulation and thus protects macrophages from apoptosis. Excessive stimulation with the oxysterol 25-hydroxycholesterol disassembles the ORP4L/Gα_q/11/PLCβ3 complexes, resulting in reduced PLCβ3 activity, IP₃ production, and Ca²⁺ release, as well as decreased Bcl-XL expression and increased apoptosis. Overexpression of ORP4L counteracts these oxysterol-induced defects. Mice lacking ORP4L exhibit increased apoptosis of macrophages in atherosclerotic lesions and a reduced lesion size.

CONCLUSIONS

ORP4L is crucial for macrophage survival. It counteracts the cytotoxicity of oxysterols/oxidized low-density lipoprotein to protect macrophage from apoptosis, thus playing an important role in the development of atherosclerosis.

Oxidized Low-density Lipoprotein (ox-LDL) Cholesterol Induces the Expression of miRNA-223 and L-type Calcium Channel Protein in Atrial Fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia causing high morbidity and mortality. While changing of the cellular calcium homeostasis plays a critical role in AF, the L-type calcium channel α1c protein has suggested as an important regulator of reentrant spiral dynamics and is a major component of AF-related electrical remodeling. Our computational modeling predicted that miRNA-223 may regulate the CACNA1C gene which encodes the cardiac L-type calcium channel α1c subunit. We found that oxidized low-density lipoprotein (ox-LDL) cholesterol significantly up-regulates both the expression of miRNA-223 and L-type calcium channel protein. In contrast, knockdown of miRNA-223 reduced L-type calcium channel protein expression, while genetic knockdown of endogenous miRNA-223 dampened AF vulnerability. Transfection of miRNA-223 by adenovirus-mediated expression enhanced L-type calcium currents and promoted AF in mice while co-injection of a CACNA1C-specific miR-mimic counteracted the effect. Taken together, ox-LDL, as a known factor in AF-associated remodeling, positively regulates miRNA-223 transcription and L-type calcium channel protein expression. Our results implicate a new molecular mechanism for AF in which miRNA-223 can be used as an biomarker of AF rheumatic heart disease.

Human pericoronary adipose tissue as storage and possible supply site for oxidized low-density lipoprotein and high-density lipoprotein in coronary artery

BACKGROUND

Thickening of the pericoronary adipose tissue (PCAT) is a proven risk factor for coronary artery disease, but it is poorly understood whether PCAT stores pro-atherogenic substances with oxidized low-density lipoprotein (oxLDL) and low-density lipoprotein (LDL), and an anti-atherogenic substance with high-density lipoprotein (HDL) and supply them to the coronary intima.

METHODS

Using immunohistochemical techniques, the localization of oxLDL, LDL and HDL in PCAT and its adjacent coronary segments was examined in 30 epicardial coronary arteries excised from 11 human autopsy cases.

RESULTS

PCAT stored oxLDL and HDL in all, but LDL rarely, in 77 specimens examined, irrespective of the presence or absence of coronary plaques and underlying disease. The percentage (%) incidence of oxLDL, HDL and LDL deposits in intima was, respectively, 28, 10, 35 in 29 normal segments, 80 (p<0.05 vs. normal segments), 12, 75 in 19 white plaques (growth stage), 57, 36, 90 in 15 yellow plaques without necrotic core (NC; mature stage), and 40, 21, 100 (p<0.05 vs. normal segments) in 14 yellow plaques with NC (end-stage of maturation) as classified by angioscopy and histology. In coronary intima, oxLDL deposited in either a dotted or diffuse pattern whereas HDL and LDL showed diffuse patterns. Dotted oxLDL deposits were contained in CD68(+)-macrophages traversing the border of PCAT and adventitia, external and internal elastic laminae. Diffuse oxLDL and HDL deposits colocalized with intimal vasa vasorum.

CONCLUSIONS

The results suggested that, as a hitherto unrecognized supplying route, the human PCAT stores oxLDL and HDL and oxLDL is supplied to coronary intima either by CD68(+)-macrophages or vasa vasorum and HDL by vasa vasorum, and that deposition of oxLDL and HDL in the intima increased with plaque growth but the former decreased while the latter increased further with plaque maturation. Molecular therapy targeting PCAT before plaque maturation could be effective in preventing atherosclerosis.

Oxysterols and mechanisms of survival signaling

Oxysterols, a family of oxidation products of cholesterol, are increasingly drawing attention of scientists to their multifaceted biochemical properties, several of them of clear relevance to human pathophysiology. Taken up by cells through both vesicular and non-vesicular ways or often generated intracellularly, oxysterols contribute to modulate not only the inflammatory and immunological response but also cell viability, metabolism and function by modulating several signaling pathways. Moreover, they have been recognized as elective ligands for the most important nuclear receptors. The outcome of such a complex network of intracellular reactions promoted by these cholesterol oxidation products appears to be largely dependent not only on the type of cells, the dynamic conditions of the cellular and tissue environment but also on the concentration of the oxysterols. Here focus has been given to the cascade of molecular events exerted by relatively low concentrations of certain oxysterols that elicit survival and functional signals in the cells, with the aim to contribute to further expand the knowledge about the biological and physiological potential of the biochemical reactions triggered and modulated by oxysterols.

Pericoronary Adipose Tissue as Storage and Supply Site for Oxidized Low-Density Lipoprotein in Human Coronary Plaques

OBJECTIVES

It is generally believed that low-density lipoprotein enters the vascular wall from its lumen and oxidized (oxLDL), after which it plays an important role in atherosclerosis. Because voluminous epicardial adipose tissue is a risk factor for coronary events, there is a possibility that the pericoronary adipose tissue (PCAT), which is a part of epicardial adipose tissue, acts as a risk factor by supplying oxLDL to the coronary arterial wall. The present study was performed whether PCAT stores and supplies oxLDL to the coronary wall.

METHODS

Localization of oxLDL in PCAT and its relation to plaque morphology were examined by immunohistochemical techniques in 27 epicardial coronary arteries excised from 9 human autopsy cases.

RESULTS

OxLDL deposited in all PCAT of the studied cases. The percent (%) incidence of oxLDL in the intima of 25 normal segment, 19 white plaques, 15 yellow plaques without necrotic core (NC) and 10 yellow plaques with NC, was 32, 84, 93 (p<0.05 vs normal segments and yellow plaques with NC), and 30, respectively. OxLDL deposited either in dotted or diffuse pattern. Double immunohistochemical staining revealed that the dotted oxLDL was that contained in CD68(+)-macrophages. The oxLDL-containing macrophages were observed in the interstitial space but not inside of the vasa vasorum, and they traversed PCAT, adventitia, external and internal elastic laminae, suggesting their migration towards the intima. Diffuse oxLDL deposits were observed in 17 preparations, the majority of which were co-localized with the vasa vasorum in outer or in both inner and outer halves of intima, and rarely in the inner half alone.

CONCLUSIONS

The results suggested that PCAT is a supply source of oxLDL to coronary intima and acts as a risk factor for coronary events, that oxLDL increasingly deposits in the intima with plaque growth and decreases after plaque maturation, and therefore molecular therapies targeting the PCAT before plaque growth could be effective in preventing human coronary atherosclerosis.

Molecular Imaging of Native Low-Density Lipoprotein by Near-Infrared Fluorescent Angioscopy in Human Coronary Plaques

Low-density lipoprotein (LDL) is an important risk factor for coronary artery disease, but its localization within the human coronary arterial wall is poorly understood. Imaging of LDL in 30 coronary arteries excised from 15 subjects who underwent autopsy was performed using near-infrared fluorescent angioscopy system and using indocyanine green dye as a biomarker of LDL. The percentage incidence of LDL in 28 normal segments, 24 white plaques (early stage of plaque growth), and 21 yellow plaques (mature stage of plaque) classified by conventional angioscopy, was 14.2, 79.1 (p <0.01 vs normal segments and p <0.05 vs yellow plaques), and 28.5, respectively. Coronary near-infrared fluorescent angioscopy showed similar results in 7 patients in vivo. Our results suggested that LDL begins to deposit in the human coronary arterial wall in the early stage of atherosclerosis, increasingly deposits with plaque growth and decreases in the mature stage; and therefore, molecular therapy targeting LDL should be started before plaque maturation.

Eukaryotic elongation factor 2 kinase as a drug target in cancer, and in cardiovascular and neurodegenerative diseases

Eukaryotic elongation factor 2 kinase (eEF2K) is an unusual protein kinase that regulates the elongation stage of protein synthesis by phosphorylating and inhibiting its only known substrate, eEF2. Elongation is a highly energy-consuming process, and eEF2K activity is tightly regulated by several signaling pathways. Regulating translation elongation can modulate the cellular energy demand and may also control the expression of specific proteins. Growing evidence links eEF2K to a range of human diseases, including cardiovascular conditions (atherosclerosis, via macrophage survival) and pulmonary arterial hypertension, as well as solid tumors, where eEF2K appears to play contrasting roles depending on tumor type and stage. eEF2K is also involved in neurological disorders and may be a valuable target in treating depression and certain neurodegenerative diseases. Because eEF2K is not required for mammalian development or cell viability, inhibiting its function may not elicit serious side effects, while the fact that it is an atypical kinase and quite distinct from the vast majority of other mammalian kinases suggests the possibility to develop it into compounds that inhibit eEF2K without affecting other important protein kinases. Further research is needed to explore these possibilities and there is an urgent need to identify and characterize potent and specific small-molecule inhibitors of eEF2K. In this article we review the recent evidence concerning the role of eEF2K in human diseases as well as the progress in developing small-molecule inhibitors of this enzyme.

Apigenin Attenuates Atherogenesis through Inducing Macrophage Apoptosis via Inhibition of AKT Ser473 Phosphorylation and Downregulation of Plasminogen Activator Inhibitor-2

Macrophage survival is believed to be a contributing factor in the development of early atherosclerotic lesions. Dysregulated apoptosis of macrophages is involved in the inflammatory process of atherogenesis. Apigenin is a flavonoid that possesses various clinically relevant properties such as anti-inflammatory, antiplatelet, and antitumor activities. Here we showed that apigenin attenuated atherogenesis in apoE (-/-) mice in an in vivo test. In vitro experiments suggested that apigenin induced apoptosis of oxidized low density lipoprotein- (OxLDL-) loaded murine peritoneal macrophages (MPMs). Proteomic analysis showed that apigenin reduced the expression of plasminogen activator inhibitor 2 (PAI-2). PAI-2 has antiapoptotic effects in OxLDL-loaded MPMs. Enhancing PAI-2 expression significantly reduced the proapoptosis effects of apigenin. Molecular docking assay with AutoDock software predicted that residue Ser473 of Akt1 is a potential binding site for apigenin. Lentiviral-mediated overexpression of Akt1 wild type weakened the proapoptosis effect of apigenin in OxLDL-loaded MPMs. Collectively, apigenin executes its anti-atherogenic effects through inducing OxLDL-loaded MPMs apoptosis. The proapoptotic effects of apigenin were at least partly attributed to downregulation of PAI-2 through suppressing phosphorylation of AKT at Ser473.

The role of the FPR2/ALX receptor in atherosclerosis development and plaque stability

AIMS

The formyl peptide receptor (FPR) subtype FPR2/ALX transduces pro-inflammatory responses and participates in the resolution of inflammation depending on activation. The aim of the present study was to unravel the role of FPR2/ALX signalling in atherosclerosis.

METHODS AND RESULTS

Expression of FPR2/ALX was analysed in 127 human carotid atherosclerotic lesions and revealed that this receptor was expressed on macrophages, smooth muscle cells (SMCs), and endothelial cells. Furthermore, FPR2/ALX mRNA levels were significantly up-regulated in atherosclerotic lesions compared with healthy vessels. In multiple regression, age, creatinine, and clinical signs of increased cerebral ischaemia were independent predictors of FPR2/ALX expression. To provide mechanistic insights into these observations, we generated Ldlr(-/-)xFpr2(-/-) mice, which exhibited delayed atherosclerosis development and less macrophage infiltration compared with Ldlr(-/-)xFpr2(+/+) mice. These findings were reproduced by transplantation of Fpr2(-/-) bone marrow into Ldlr(-/-) mice and further extended by in vitro experiments, demonstrating a lower inflammatory state in Fpr2(-/-) macrophages. FPR2/ALX expression correlated with chemo- and cytokines in human atherosclerotic lesions and leucocytes. Finally, atherosclerotic lesions in Ldlr(-/-)xFpr2(-/-) mice exhibited decreased collagen content, and Fpr2(-/-) SMCs exhibited a profile of increased collagenase and decreased collagen production pathways.

CONCLUSION

FPR2/ALX is proatherogenic due to effects on bone marrow-derived cells, but promoted a more stable plaque phenotype through effects on SMCs. Taken together, these results suggest a dual role of FPR2/ALX signalling in atherosclerosis by way of promoting disease progression and but increasing plaque stability.

Impairing eukaryotic elongation factor 2 kinase activity decreases atherosclerotic plaque formation

We tested whether loss of eukaryotic elongation factor 2 kinase (eEF2K) activity in macrophages suppresses development of atherosclerosis by transplanting bone marrow from mice with mutant eEF2K into ldlr^−/− mice. Sixteen weeks after high-fat diet feeding, mutant eEF2K hematopoietic chimeras had a dramatically reduced level of atherosclerotic plaque formation. M1-skewed macrophages from eEF2K knock-in mice have less tumour necrosis factor-α release and a lesser ability to induce expression of endothelial cell markers, providing a potential explanation for the role of eEF2K. Because eEF2K activity in cells of the hematopoietic compartment contributes to atherosclerosis development, drugs inhibiting eEF2K might have a beneficial effect in treatment of atherosclerosis.

Afferent regulation of chicken auditory brainstem neurons: rapid changes in phosphorylation of elongation factor 2

The relationships between protein synthesis and neuronal survival are poorly understood. In chicken nucleus magnocellularis (NM), significant alterations in overall protein synthesis precede neuronal death induced by deprivation of excitatory afferent activity. Previously we demonstrated an initial reduction in the overall rate of protein synthesis in all deprived NM neurons, followed by quick recovery (starting at 6 hours) in some, but not all, neurons. Neurons with recovered protein synthesis ultimately survive, whereas others become "ghost" cells (no detectable Nissl substance) at 12-24 hours and die within 48 hours. To explore the mechanisms underlying this differential influence of afferent input on protein synthesis and cell survival, the current study investigates the involvement of eukaryotic translation elongation factor 2 (eEF2), the phosphorylation of which reduces overall protein synthesis. Using immunocytochemistry for either total or phosphorylated eEF2 (p-eEF2), we found significant reductions in the level of phosphorylated, but not total, eEF2 in NM neurons as early as 0.5-1 hour following cochlea removal. Unexpectedly, neurons with low levels of p-eEF2 show reduced protein synthesis at 6 hours, indicated by a marker for active ribosomes. At 12 hours, all "ghost" cells exhibited little or no p-eEF2 staining, although not every neuron with a comparable low level of p-eEF2 was a "ghost" cell. These observations demonstrate that a reduced level of p-eEF2 is not responsible for immediate responses (including reduced overall protein synthesis) of a neuron to compromised afferent input but may impair the neuron's ability to initiate recovery signaling for survival and make the neuron more vulnerable to death.

Localization of oxidized low-density lipoprotein and its relation to plaque morphology in human coronary artery

OBJECTIVES

Oxidized low-density lipoprotein (oxLDL) plays a key role in the formation of atherosclerotic plaques. However, its localization in human coronary arterial wall is not well understood. The present study was performed to visualize deposition sites and patterns of native oxLDL and their relation to plaque morphology in human coronary artery.

METHODS

Evans blue dye (EB) elicits a violet fluorescence by excitation at 345-nm and emission at 420-nm, and a reddish-brown fluorescence by excitation at 470-nm and emission at 515-nm characteristic of oxLDL only. Therefore, native oxLDL in excised human coronary artery were investigated by color fluorescent microscopy (CFM) using EB as a biomarker.

RESULTS

(1) By luminal surface scan with CFM, the % incidence of oxLDL in 38 normal segments, 41 white plaques and 32 yellow plaques that were classified by conventional angioscopy, was respectively 26, 44 and 94, indicating significantly (p<0.05) higher incidence in the latter than the former two groups. Distribution pattern was classified as patchy, diffuse and web-like. Web-like pattern was observed only in yellow plaques with necrotic core. (2) By transected surface scan, oxLDL deposited within superficial layer in normal segments and diffusely within both superficial and deep layers in white and yellow plaques. In yellow plaques with necrotic core, oxLDL deposited not only in the marginal zone of the necrotic core but also in the fibrous cap.

CONCLUSION

Taken into consideration of the well-known process of coronary plaque growth, the results suggest that oxLDL begins to deposit in human coronary artery wall before plaque formation and increasingly deposits with plaque growth, exhibiting different deposition sites and patterns depending on morphological changes.

Molecular imaging of low-density lipoprotein in human coronary plaques by color fluorescent angioscopy and microscopy

Objectives

Low-density lipoprotein (LDL) is an important risk factor for coronary artery disease. However, its localization in human coronary plaques is not well understood. The present study was performed to visualize LDL in human coronary artery wall.

Methods

(1) The fluorescence characteristic of LDL was investigated by color fluorescent microscopy (CFM) with excitation at 470-nm and emission at 515-nm using Nile blue dye (NB) as a biomarker. (2) Native LDL in 40 normal segments, 42 white plaques and 35 yellow plaques (20 with necrotic core) of human coronary arteries was investigated by color fluorescent angioscopy (CFA) and CFM.

Results

(1) NB elicited a brown, golden and red fluorescence characteristic of LDL, apolipoprotein B-100, and lysophosphatidylcholine/triglyceride, respectively. (2) The % incidence of LDL in normal segments, white, and yellow plaques was 25, 38 and 14 by CFA and 42, 42 and 14 by CFM scan of their luminal surface, respectively, indicating lower incidence (p<0.05) of LDL in yellow plaques than white plaques, and no significant differences in detection sensitivity between CFA and CFM. By CFM transected surface scan, LDL deposited more frequently and more diffusely in white plaques and yellow plaques without necrotic core (NC) than normal segments and yellow plaques with NC. LDL was localized to fibrous cap in yellow plaques with NC. Co-deposition of LDL with other lipid components was observed frequently in white plaques and yellow plaques without NC.

Conclusions

(1) Taken into consideration of the well-known process of coronary plaque growth, the results of the present study suggest that LDL begins to deposit before plaque formation; increasingly deposits with plaque growth, often co-depositing with other lipid components; and disappears after necrotic core formation. (2) CFA is feasible for visualization of LDL in human coronary artery wall.

Involvement of calmodulin and calmodulin kinase II in tumor necrosis factor alpha-induced survival of bone marrow derived macrophages

We previously showed that survival signaling in TNFα-treated, human THP1-derived macrophages (TDMs) has an obligatory requirement for constitutive Ca(2+) influx through a mechanism involving calmodulin/calmodulin kinase II (CAM/CAMKII). We also demonstrated that such requirement also applies to the protective actions of TNFα in murine bone marrow-derived macrophages (BMDMs) and that TRPC3 channels mediate constitutive Ca(2+) influx. Using a pharmacological approach we here examined if in BMDMs, similarly to TDMs, TNFα-induced survival signaling also involves CAM/CAMKII. In BMDMs, TNFα induced rapid activation of the survival pathways NFκB, AKT and p38MAPK. All these routes were activated in a PI3K-dependent fashion. Activation of AKT and NFκB, but not that of p38MAPK, was abrogated by the CAM inhibitor W7, while KN-62, a CAMKII inhibitor, prevented activation of AKT and p38MAPK but not that of NFκB. Inhibition of CAM or CAMKII completely prevented the protective actions of TNFα. Our observations indicate that in BMDMs CAM and CAMKII have differential contributions to the components of TNFα-dependent survival signaling and underscore a complex interplay among canonical survival routes. These findings set a signaling framework to understand how constitutive Ca(2+) influx couples to macrophage survival in BMDMs.

Fluorescent adducts formed by reaction of oxidized unsaturated fatty acids with amines increase macrophage viability

Macrophages are prominent components of human atherosclerotic lesions and they are believed to accelerate the progression and/or complications of both early and advanced atherosclerotic lesions. We and others have shown that oxidized low-density lipoprotein (oxLDL) induces growth and inhibits apoptosis in murine bone marrow-derived macrophages. In this study, we sought to characterize the oxidative modification of LDL that is responsible for this prosurvival effect. We found that both the modified lipid and the modified protein components of oxLDL can increase the viability of macrophages. The key modification appeared to involve derivatization of amino groups in apoB or in phosphatidylethanolamine by lipid peroxidation products. These reactive oxidation products were primarily unfragmented hydroperoxide- or endoperoxide-containing oxidation products of linoleic acid or arachidonic acid. LC-MS/MS studies showed that some of the arachidonic acid-derived lysine adducts were isolevuglandins that contain lactam and hydroxylactam rings. MS/MS analysis of linoleic acid autoxidation adducts was consistent with 5- or 6-membered nitrogen-containing heterocycles derived from unfragmented oxidation products. The amine modification by oxidation products generated a fluorescence pattern with an excitation maximum at 350nm and emission maximum at 430nm. This is very similar to the fluorescence spectrum of copper-oxidized LDL.

OxLDL-mediated survival of macrophages does not require LDL internalization or signalling by major pattern recognition receptors

Macrophages play a key role in the pathogenesis of atherosclerosis, in part by destabilizing plaques. We and others have shown that low concentrations of oxidized LDL (oxLDL) inhibit macrophage apoptosis. As oxLDL is present in lesions, this may be a mechanism by which macrophage populations in the intima are expanded. We have previously shown that oxLDL activates prosurvival signalling pathways such as the phosphoinositide 3-kinase (PI3K) pathway in bone marrow derived macrophages (BMDMs). However, little is known about more upstream signalling events especially at the receptor level. The endocytic pattern recognition receptors (PRRs), scavenger receptor A (SR-A) and CD36, are the main receptors on macrophages for uptake of oxLDL and are therefore important in foam cell formation. The signalling PRRs such as toll-like receptor (TLR) 2 and 4 also bind some types of oxLDL. This study was done to determine if any of the known PRRs are required for the anti-apoptotic effects of oxLDL in BMDMs. To do this, we tested the effect of oxLDL on viability of BMDMs lacking both SR-A and CD36 or lacking TLR2, TLR4, CD14, FcγRIIb, or RAGE. Our results indicate that none of these receptors are essential for activating the oxLDL prosurvival pathway. Furthermore, we show that the anti-apoptotic effect is not dependent on the uptake of oxLDL.

Heat-shock proteins in cardiovascular disease

Heat-shock proteins (HSPs) belong to a group of highly conserved families of proteins expressed by all cells and organisms and their expression may be constitutive or inducible. They are generally considered as protective molecules against different types of stress and have numerous intracellular functions. Secretion or release of HSPs has also been described, and potential roles for extracellular HSPs reported. HSP expression is modulated by different stimuli involved in all steps of atherogenesis including oxidative stress, proteolytic aggression, or inflammation. Also, antibodies to HSPs may be used to monitor the response to different types of stress able to induce changes in HSP levels. In the present review, we will focus on the potential implication of HSPs in atherogenesis and discuss the limitations to the use of HSPs and anti-HSPs as biomarkers of atherothrombosis. HSPs could also be considered as potential therapeutic targets to reinforce vascular defenses and delay or avoid clinical complications associated with atherothrombosis.

Visualization of lipid components in human coronary plaques using color fluorescence angioscopy

BACKGROUND

If oxidized low-density lipoprotein (oxLDL), LDL, lysophosphatidylcholine (LPC) and apolipoprotein B (apoB) can be visualized simultaneously, their roles in the initiation, progression and destabilization of atherosclerotic plaques can be objectively evaluated.

METHODS AND RESULTS

(1) The fluorescence characteristic of each atherogenic substance was investigated by microscopy using a band-pass filter (470 nm) and a band-absorption filter (520 nm) with homidium bromide (Ho) and trypan blue (TB) as indicators. (2) 50 excised human coronary plaques were classified by their autofluorescence into green, greenish-yellow and yellow, and the localization of oxLDL, LDL, LPC and apoB were investigated by color fluorescence angioscopy (CFA). The plaque colors were white, yellow and glistening yellow by conventional angioscopy. (1) OxLDL and LDL exhibited golden fluorescence, whereas LPC and apoB exhibited red fluorescence. (2) By CFA, 16 of 19 greenish-yellow and 1 of 8 yellow plaques exhibited red and golden fluorescence in a mosaic pattern, indicating co-deposition of oxLDL/LDL and LPC/apoB; 3 greenish-yellow and 7 yellow plaques exhibited red fluorescence, indicating solitary deposition of apoB; 23 green plaques infrequently exhibited these fluorescence colors.

CONCLUSIONS

OxLDL/LDL and LPC/apoB were successfully visualized as co-deposited in greenish-yellow autofluorescence plaques, but only LPC/apoB in yellow autofluorescence plaques. 

Differential expression of genes in the calcium-signaling pathway underlies lesion development in the LDb mouse model of atherosclerosis

OBJECTIVE

Atherosclerosis is influenced by the interaction of environmental and genetic susceptibility risk factors. We used global microarray expression profiling to investigate differentially regulated genes in aorta during development of atherosclerosis in a susceptible genetically modified mouse model in response to the interaction between risk factors including hyperlipidemic genotype, shear stress, diet, and age.

METHODS AND RESULTS

In this study we investigated transcriptional changes in lesion-prone and lesion-resistant regions of aortas in genetically modified mice lacking both genes of the LDL receptor and the apolipoprotein B mRNA editing enzyme (LDb; Ldlr(-/-)Apobec1(-/-)). Risk factors including hyperlipidemic genotype (LDb vs. C57BL/6 wildtype), shear stress (lesion-prone vs. lesion resistant aortic regions), diet (chow vs. Western high-fat), and age (2- vs. 8-months) were studied. We hybridized aortic RNA samples with microarray chips containing probes for 45,000 mouse genes and expressed sequence tags (ESTs). Overall, the differentially expressed genes were components of 20 metabolic and physiological pathways. Notably, calcium signaling is the major pathway identified with differential regulation of 30 genes within this pathway. We also found differential expression of calcium-signaling genes in cultured primary endothelial cells from lesion-prone and lesion-resistant arterial regions (LDb mice vs. C57BL/6 controls), providing further support for involvement of calcium signaling in the pathogenesis of atherosclerosis. Moreover, we demonstrated protein expression of genes in the calcium-signaling pathway using Western blot analysis and immunofluorescence.

CONCLUSIONS

Our results suggest that calcium signaling may play an important role in regulation of genes expressed in aorta during development of atherosclerosis. Calcium signaling may act via mechanistic responses to genetic, mechanical, and environmental insults that trigger an imbalance of intracellular calcium homeostasis, resulting in altered biological processes leading to lesion development.

Sphingosine kinase regulates oxidized low density lipoprotein-mediated calcium oscillations and macrophage survival

We recently reported that oxidized LDL (oxLDL) induces an oscillatory increase in intracellular calcium ([Ca(2+)](i)) levels in macrophages. Furthermore, we have shown that these [Ca(2+)](i) oscillations mediate oxLDL's ability to inhibit macrophage apoptosis in response to growth factor deprivation. However, the signal transduction pathways by which oxLDL induces [Ca(2+)](i) oscillations have not been elucidated. In this study, we show that these oscillations are mediated in part by intracellular mechanisms, as depleting extracellular Ca(2+) did not completely abolish the effect. Inhibiting sarco-endoplasmic reticulum ATPase (SERCA) completely blocked [Ca(2+)](i) oscillations, suggesting a role for Ca(2+) reuptake by the ER. The addition of oxLDL resulted in an almost immediate activation of sphingosine kinase (SK), which can increase sphingosine-1-phosphate (S1P) levels by phosphorylating sphingosine. Moreover, S1P was shown to be as effective as oxLDL in blocking macrophage apoptosis and producing [Ca(2+)](i) oscillations. This suggests that the mechanism in which oxLDL generates [Ca(2+)](i) oscillations may be 1) activation of SK, 2) SK-mediated increase in S1P levels, 3) S1P-mediated Ca(2+) release from intracellular stores, and 4) SERCA-mediated Ca(2+) reuptake back into the ER.