Asymmetric dimethylarginine confers the communication between endothelial and smooth muscle cells and leads to VSMC migration through p38 and ERK1/2 signaling cascade

Communication between endothelial and smooth muscle cells (SMCs) contributes to atherosclerosis induced by atherogenic factors, such as oxide LDL. Asymmetric dimethylarginine (ADMA), a newly found cardiovascular risk factor, accumulates in the culture medium of oxide LDL (oxLDL)-treated endothelial cells and positively correlates with atherosclerosis. This study demonstrates that ADMA mediates the communication between endothelial cells and SMCs induced by oxLDL leading to SMC migration. In addition, the present study suggests exogenous ADMA directly induces SMC migration via p38 and ERK1/2 MAPK signaling transduction way. Investigations to identify the factors regulating VSMC migration may provide novel insights into atherosclerosis and its complications.     

The chemokine and scavenger receptor CXCL16/SR-PSOX is expressed in human vascular smooth muscle cells and is induced by interferon gamma

Atherosclerosis is an inflammatory disease that is characterised by the involvement of chemokines that are important for the recruitment of leukocytes and scavenger receptors that mediate foam cell formation. Several cytokines are involved in the regulation of chemokines and scavenger receptors in atherosclerosis. CXCL16 is a chemokine and scavenger receptor and found in macrophages in human atherosclerotic lesions. Using double-labelled immunohistochemistry, we identified that smooth muscle cells in human lesions express CXCL16. We then analysed the effects of IFN-gamma, TNF-alpha, IL-12, IL-15, IL-18, and LPS on CXCL16 expression in cultured aortic smooth muscle cells. IFN-gamma was the most potent CXCL16 inducer and increased mRNA, soluble form, membrane form, and total cellular levels of CXCL16. The IFN-gamma induction of CXCL16 was also associated with increased uptake of oxLDL into these cells. Taken together, smooth muscle cells express CXCL16 in atherosclerotic lesions, which may play a role in the attraction of T cells to atherosclerotic lesions and contribute to the cellular internalisation of modified LDL.     

LOX‐1: Its cytotopographical variance and disease stress

Lectin‐like oxidized low‐density lipoprotein receptor‐1 (LOX‐1) is a canonical receptor for oxidized LDL (oxLDL) among the known modified LDL particles. Topographical variance on LOX‐1 expression in different cell types and its influence on the atherogenic potential of the particular cell type is the main focus of this review. Characteristic features of LOX‐1 on the atherogenic potential of aortic endothelial cells, macrophages, platelets, and vascular smooth muscle cells have been discussed. Nonspecificity of ligands, besides oxLDL, is also the highlight of this review to show the chameleon characteristics in the functional activity of the receptor protein. Induction of LOX‐1 has been reported in diseases like atherosclerosis, diabetes, and hypertension, as well as in the inflammatory response of immune reactions. The expression of LOX‐1 is upregulated by the vicious cycle of stimulatory response from proatherogenic molecules.     

Modified LDLs induce proliferation-mediated death of human vascular endothelial cells through MAPK pathway

The ability of modified low-density lipoptoteins (LDLs) to induce both proliferation and death of endothelial cells is considered to be a mechanism of early atherosclerosis development. We previously showed that carbamylated LDL (cLDL) induces human coronary artery endothelial cell (HCAEC) death in vitro. This effect is similar to the atherogenic action of oxidized LDL (oxLDL) that induces the proliferation and death of endothelial cells. The present study was designed to analyze a potential proliferative effect of cLDL and whether proliferation caused by modified LDLs is related to cell death. Cultured HCAECs were exposed to different concentrations of modified LDL or native LDL for varying periods of time. Cell proliferation measured by bromodeoxyuridine incorporation and S-phase analysis was dose-dependently increased in the presence of cLDL (6.25-200 microg/ml). The proliferation induced by cLDL or oxLDL was associated with cell death and increased phosphorylation of extracellular signal-regulated kinase (ERK) and c-Jun NH(2)-terminal kinase (JNK). Inhibition of cLDL- or oxLDL-induced proliferation by aphidicolin (1 microg/ml) was protective against both short-term cell death measured by lactate dehydrogenase release into the medium and long-term cell viability visualized by cell multiplication. Inhibition of ERK phosphorylation led to a significant decrease of DNA synthesis and cell rescue from injury by modified LDLs, while inhibition of JNK phosphorylation had an only partial rescue effect without involvement in cell proliferation. These data are the first evidence that endothelial cell death induced by cLDL or oxLDL is mediated by cell proliferation through the mitogen-activated protein kinase pathway.     

Oxidized low density lipoprotein inhibits macrophage apoptosis through activation of the PI 3-kinase/PKB pathway

Oxidized LDL (oxLDL) is known to induce endothelial adhesion molecule and monocyte chemoattractant protein 1 expression and this is thought to be involved in monocyte recruitment into atherosclerotic lesions. oxLDL has also been found to induce macrophage proliferation. The purpose of the present study was to determine whether oxLDL might also have the ability to increase macrophage populations by inhibiting apoptosis. We found that oxLDL caused a dose-dependent inhibition of the apoptosis that occurs in cultured bone marrow-derived macrophages after macrophage colony-stimulating factor (M-CSF) withdrawal without inducing proliferation. Incubation of macrophages with either native LDL or acetylated LDL had no effect on apoptosis. The prosurvival effect of oxLDL was not inhibited by neutralizing antibodies to granulocyte-macrophage colony-stimulating factor, was maintained in mice homozygous for a mutation in the M-CSF gene, and was not due to other secreted cytokines or growth factors. oxLDL caused activation of the mitogen-activated protein kinases ERK1/2 (extracellular signal-regulated kinases 1 and 2) as well as protein kinase B (PKB), a target of phosphatidylinositol 3-kinase (PI 3-kinase). Furthermore, there was phosphorylation of two important prosurvival PKB targets, I-kappaBalpha(Ser-32) and Bad(Ser-136). The MEK inhibitors PD 98059 and U0126 blocked ERK1/2 activation but did not diminish survival. Conversely, the PI 3-kinase inhibitors LY 294002 and wortmannin blocked PKB activation, and the ability of oxidized LDL to promote macrophage survival.Taken together, these results indicate that oxLDL can directly activate a PI 3-kinase/PKB-dependent pathway that permits macrophage survival in the absence of growth factors.     

Source and role of intestinally derived lysophosphatidic acid in dyslipidemia and atherosclerosis

We previously reported that i) a Western diet increased levels of unsaturated lysophosphatidic acid (LPA) in small intestine and plasma of LDL receptor null (LDLR^−/−) mice, and ii) supplementing standard mouse chow with unsaturated (but not saturated) LPA produced dyslipidemia and inflammation. Here we report that supplementing chow with unsaturated (but not saturated) LPA resulted in aortic atherosclerosis, which was ameliorated by adding transgenic 6F tomatoes. Supplementing chow with lysophosphatidylcholine (LysoPC) 18:1 (but not LysoPC 18:0) resulted in dyslipidemia similar to that seen on adding LPA 18:1 to chow. PF8380 (a specific inhibitor of autotaxin) significantly ameliorated the LysoPC 18:1-induced dyslipidemia. Supplementing chow with LysoPC 18:1 dramatically increased the levels of unsaturated LPA species in small intestine, liver, and plasma, and the increase was significantly ameliorated by PF8380 indicating that the conversion of LysoPC 18:1 to LPA 18:1 was autotaxin dependent. Adding LysoPC 18:0 to chow increased levels of LPA 18:0 in small intestine, liver, and plasma but was not altered by PF8380 indicating that conversion of LysoPC 18:0 to LPA 18:0 was autotaxin independent. We conclude that i) intestinally derived unsaturated (but not saturated) LPA can cause atherosclerosis in LDLR^−/− mice, and ii) autotaxin mediates the conversion of unsaturated (but not saturated) LysoPC to LPA.     

Salusin-β accelerates inflammatory responses in vascular endothelial cells via NF-κB signaling in LDL receptor-deficient mice in vivo and HUVECs in vitro

The bioactive peptide salusin-β is highly expressed in human atheromas; additionally, infusion of antiserum against salusin-β suppresses the development of atherosclerosis in atherogenic mice. This study examined the roles of salusin-β in vascular inflammation during atherogenesis. Infusion of antiserum against salusin-β attenuated the induction of VCAM-1, monocyte chemoattractant protein (MCP)-1, and IL-1β and as well as nuclear translocation of NF-κB in aortic endothelial cells (ECs) of LDL receptor-deficient mice, which led to the prevention of monocyte adhesion to aortic ECs. In vitro experiments indicated that salusin-β directly enhances the expression levels of proinflammatory molecules, including VCAM-1, MCP-1, IL-1β, and NADPH oxidase 2, as well as THP-1 monocyte adhesion to cultured human umbilical vein ECs (HUVECs). Both salusin-β-induced VCAM-1 induction and monocyte/HUVEC adhesion were suppressed by pharmacological inhibitors of NF-κB, e.g., Bay 11-7682 and curcumin. Furthermore, the VCAM-1 induction was significantly prevented by the phosphatidylinositol 3-kinase (PI3K) inhibitor LY-294002, whereas it was accelerated by the ERK inhibitor, U-0126. Treatment of HUVECs with salusin-β, but not with salusin-α, accelerated oxidative stress and nuclear translocation of NF-κB as well as phosphorylation and degradation of IκB-α, an endogenous inhibitor of NF-κB. Thus, salusin-β enhanced monocyte adhesion to vascular ECs through NF-κB-mediated inflammatory responses in ECs, which can be modified by PI3K or ERK signals. These findings are suggestive of a novel role of salusin-β in atherogenesis.     

Oxidized Low-Density Lipoprotein Contributes to Atherogenesis via Co-activation of Macrophages and Mast Cells

Oxidized low-density lipoprotein (OxLDL) is a risk factor for atherosclerosis, due to its role in endothelial dysfunction and foam cell formation. Tissue-resident cells such as macrophages and mast cells release inflammatory mediators upon activation that in turn cause endothelial activation and monocyte adhesion. Two of these mediators are tumor necrosis factor (TNF)-α, produced by macrophages, and histamine, produced by mast cells. Static and microfluidic flow experiments were conducted to determine the number of adherent monocytes on vascular endothelium activated by supernatants of oxLDL-treated macrophages and mast cells or directly by oxLDL. The expression of adhesion molecules on activated endothelial cells and the concentration of TNF-α and histamine in the supernatants were measured by flow cytometry and enzyme-linked immunosorbent assay, respectively. A low dose of oxLDL (8 μg/ml), below the threshold for the clinical presentation of coronary artery disease, was sufficient to activate both macrophages and mast cells and synergistically increase monocyte-endothelium adhesion via released TNF-α and histamine. The direct exposure of endothelial cells to a much higher dose of oxLDL (80 μg/ml) had less effect on monocyte adhesion than the indirect activation via oxLDL-treated macrophages and mast cells. The results of this work indicate that the co-activation of macrophages and mast cells by oxLDL is an important mechanism for the endothelial dysfunction and atherogenesis. The observed synergistic effect suggests that both macrophages and mast cells play a significant role in early stages of atherosclerosis. Allergic patients with a lipid-rich diet may be at high risk for cardiovascular events due to high concentration of low-density lipoprotein and histamine in arterial vessel walls.     

Electronegative low-density lipoprotein

PURPOSE OF REVIEW: The occurrence in blood of an electronegatively charged LDL was described in 1988. During the 1990s reports studying electronegative LDL (LDL(-)) were scant and its atherogenic role controversial. Nevertheless, recent reports have provided new evidence on a putative atherogenic role of LDL(-). This review focuses on and discusses these new findings. RECENT FINDINGS: In recent years, LDL(-) has been found to be involved in several atherogenic features through its action on cultured endothelial cells. LDL(-) induces the production of chemokines, such as IL-8 and monocyte chemotactic protein 1, and increases tumor necrosis factor-alpha-induced production of vascular cell adhesion molecule 1, with these molecules being involved in early phases of leukocyte recruitment. LDL(-) from familial hypercholesterolemic patients also decreases DNA synthesis and intracellular fibroblast growth factor 2 production, which may contribute to impaired angiogenesis and increased apoptosis. In addition, the preferential association of platelet-activating factor acetylhydrolase with LDL(-) has been reported, suggesting a proinflammatory role of this enzyme in LDL(-). SUMMARY: Recent findings suggest that LDL(-) could contribute to atherogenesis via several mechanisms, including proinflammatory, proapoptotic and anti-angiogenesis properties. Further studies are required to define the role of LDL(-) in atherogenesis more precisely and to clarify mechanisms involved in endothelial cell activation.     

Lipoprotein-X reduces LDL atherogenicity in primary biliary cirrhosis by preventing LDL oxidation

Hypercholesterolemic human LDL contains oxidized subfractions that have atherogenic properties. Paradoxically, atherosclerosis incidence is low in patients with primary biliary cirrhosis (PBC), a disease characterized by marked increases in plasma LDL, including the LDL subfraction lipoprotein-X (Lp-X). To investigate the mechanisms underlying this paradox, we first examined the propensity to oxidation of unfractionated LDL isolated from PBC patients. After prolonged incubation with copper, PBC-LDL failed to increase the oxidation index or electrophoretic mobility noted in control LDL. An admixture of PBC-LDL or Lp-X with control LDL prevented oxidation of the latter in a dose-dependent manner. PBC-LDL was also noncompetitive against copper-oxidized LDL (oxLDL) for binding with a murine monoclonal anti-oxLDL antibody in a competitive ELISA. OxLDL exerts its proapoptotic and antiangiogenic effects in part by inhibiting fibroblast growth factor 2 (FGF2) expression. Preincubation of oxLDL with PBC-LDL, but not control LDL, attenuated the inhibitory effects of oxLDL on FGF2 expression in cultured bovine aortic endothelial cells (ECs). The antioxidant and prosurvival properties of PBC-LDL diminished after the patients underwent orthotopic liver transplantation. These results suggest that Lp-X reduces LDL atherogenicity by preventing LDL oxidation to protect EC integrity in the presence of hypercholesterolemia. They also suggest that altering LDL composition may be as important as reducing LDL concentration in preventing or treating atherosclerosis.     

Lysophospholipids increase IL-8 and MCP-1 expressions in human umbilical cord vein endothelial cells through an IL-1-dependent mechanism

Lysophosphatidic acid (LPA) and sphingosine 1-phosphate (S1P) are both low-molecular-weight lysophospholipid (LPL) ligands which are recognized by the Edg family of G protein-coupled receptors (GPCRs). In endothelial cells, these two ligands activate Edg receptors resulting in cell proliferation and cell migration. Interleukin-8 (IL-8) is a C-X-C chemokine and acts as a chemoattractant of neutrophils, whereas monocyte chemoattractant protein-1 (MCP-1) is a C-C chemokine and functions mainly as a chemoattractant of monocytes/macrophages. Both factors are secreted from endothelial cells and have been implicated in the processes leading to atherosclerosis. We examined the effects of LPLs on the expression of IL-8 and MCP-1, key regulators of leukocyte recruitment in human umbilical cord vein endothelial cells (HUVECs). Work illustrated in this article showed that LPA and S1P enhanced IL-8 and MCP-1 mRNA expressions, and protein secretions in dose- and time-dependent fashions. Maximal mRNA expression appeared at 16 hr post-ligand treatment. Using prior treatments with chemical inhibitors, LPLs enhanced IL-8 and MCP-1 expressions through a Gi-, Rho-, and NFkappaB-dependent mechanism. In a chemotaxis assay system, LPL treatments of endothelial cells enhanced monocyte recruitment through upregulating IL-8 and MCP-1 protein secretions. Pre-incubation with AF12198, an IL-1 receptor antagonist or IL-1 functional blocking antibody both suppressed the enhanced effects elicited by LPLs of IL-8 and MCP-1 mRNA expressions in HUVECs. These results suggest that LPLs released by activated platelets might enhance the IL-8- and MCP-1-dependent chemoattraction of monocytes toward the endothelium through an IL-1-dependent mechanism, which may play an important role in facilitating wound-healing and inflammation processes.     

Modification of LDL with human secretory phospholipase A(2) or sphingomyelinase promotes its arachidonic acid-releasing propensity

Oxidation and lipolytic remodeling of LDL are believed to stimulate LDL entrapment in the arterial wall, expanding the inflammatory response and promoting atherosclerosis. However, the cellular responses and molecular mechanisms underlying the atherogenic effects of lipolytically modified LDL are incompletely understood. Human THP-1 monocytes were prelabeled with [(3)H]arachidonic acid (AA) before incubation with LDL or LDL lipolytically modified by secretory PLA(2) (sPLA(2)) or bacterial sphingomyelinase (SMase). LDL elicited rapid and dose-dependent extracellular release of AA in monocytes. Interestingly, LDL modified by sPLA(2) or SMase displayed a marked increase in AA mobilization relative to native LDL, and this increase correlated with enhanced activity of cytosolic PLA(2) (cPLA(2)) assayed in vitro as well as increased monocyte tumor necrosis factor-alpha secretion. The AA liberation was attenuated by inhibitors toward cPLA(2) and sPLA(2), indicating that both PLA(2) enzymes participate in LDL-induced AA release. In conclusion, these results demonstrate that LDL lipolytically modified by sPLA(2) or SMase potentiates cellular AA release and cPLA(2) activation in human monocytes. From our results, we suggest novel atherogenic properties for LDL modified by sPLA(2) and SMase in AA release and signaling, which could contribute to the inflammatory gene expression observed in atherosclerosis.     

Pathophysiological significance of cylindromatosis in the vascular endothelium and macrophages for the initiation of age-related atherogenesis

Cardiovascular disease is one of the leading causes of death in the elderly, and novel therapeutic targets against atherogenesis are urgent. The initiation of atherosclerotic changes of monocyte adhesion on the vascular endothelium and subsequent foam cell formation are noteworthy pathophysiologies when searching for strategies to prevent the progression of age-related atherosclerosis. We report the significance of the deubiquitinating enzyme cylindromatosis (CYLD) in vascular remodeling by interference with inflammatory responses regulated by NF-κB signaling. The purpose of this study was to elucidate the pathological functions of CYLD in the early phase of atherogenesis associated with aging.Treatment with inflammatory cytokines induced endogenous CYLD in aortic endothelial cells (HAECs) and THP-1?cells. siRNA-mediated CYLD silencing led to enhanced monocyte adhesion along with increased adhesion molecules in HAECs treated with TNFα. In siRNA-mediated CYLD silenced RAW 264.7 macrophages treated with oxidized LDL (oxLDL), augmented lipid accumulation was observed, along with increased expression of the class A macrophage scavenger receptor (SR-A), lectin-like oxidized LDL receptor-1 (LOX-1), CD36, fatty acid binding protein 4 (FABP4), the cholesterol ester synthase acyl-CoA cholesterol acyltransferase (ACAT1), MCP-1, and IL-1β and decreased expression of scavenger receptor class B type I (SR-BI). Intriguingly, CYLD gene expression was significantly reduced in bone marrow-derived macrophages of aged mice compared that of young mice, as well as in senescent HAECs compared with young cells.These findings suggest that age-related attenuation of CYLD expression in endothelial cells (ECs) and macrophages triggers the initiation of age-related atherogenesis by exacerbating monocyte adhesion on the endothelium and foam cell formation. CYLD in the vasculature may be a novel therapeutic target, especially in the early preventive intervention against the initiation of age-related atherogenesis.     

OxLDL induces endothelial dysfunction and death via TRAF3IP2: Inhibition by HDL3 and AMPK activators

Oxidized low-density lipoprotein (oxLDL) induces endothelial cell death through the activation of NF-κB and AP-1 pathways. TRAF3IP2 is a redox-sensitive cytoplasmic adapter protein and an upstream regulator of IKK/NF-κB and JNK/AP-1. Here we show that oxLDL-induced death in human primary coronary artery endothelial cells (ECs) was markedly attenuated by the knockdown of TRAF3IP2 or the lectin-like oxLDL receptor 1 (LOX-1). Further, oxLDL induced Nox2/superoxide-dependent TRAF3IP2 expression, IKK/p65 and JNK/c-Jun activation, and LOX-1 upregulation, suggesting a reinforcing mechanism. Similarly, the lysolipids present in oxLDL (16:0-LPC and 18:0-LPC) and minimally modified LDL also upregulated TRAF3IP2 expression. Notably, whereas native HDL3 reversed oxLDL-induced TRAF3IP2 expression and cell death, 15-lipoxygenase-modified HDL3 potentiated its proapoptotic effects. The activators of the AMPK/Akt pathway, adiponectin, AICAR, and metformin, attenuated superoxide generation, TRAF3IP2 expression, and oxLDL/TRAF3IP2-mediated EC death. Further, both HDL3 and adiponectin reversed oxLDL/TRAF3IP2-dependent monocyte adhesion to endothelial cells in vitro. Importantly, TRAF3IP2 gene deletion and the AMPK activators reversed oxLDL-induced impaired vasorelaxation ex vivo. These results indicate that oxLDL-induced endothelial cell death and dysfunction are mediated via TRAF3IP2 and that native HDL3 and the AMPK activators inhibit this response. Targeting TRAF3IP2 could potentially inhibit progression of atherosclerotic vascular diseases.     

OxLDL诱导人血管内皮细胞及平滑肌细胞DNA加合物生成

目的探讨oxLDL参与动脉粥样硬化发生的可能机制。方法培养人血管内皮细胞及平滑肌细胞,以50μg/L oxLDL刺激24、48h后,收获细胞用于后续实验:①免疫组化染色检测DNA加合物εdA水平;②免疫组化方法检测细胞内4-HNE修饰蛋白;③western blot法检测细胞内4-HNE修饰蛋白水平。结果oxLDL刺激EC及SMC中DNA加合物εdA水平及4-HNE修饰蛋白水平均较未刺激细胞组明显升高。结果 oxLDL诱导的氧化应激、脂质过氧化反应及其继发的DNA损伤可能为oxLDL参与动脉粥样硬化发生的重要机制。     

Angiogenesis: how a tumor adapts to hypoxia

Early atherosclerotic lesions are characterized by increased monocyte adhesion to the overlying endothelium. Oxidized LDL (oxLDL) stimulates the adhesion of human monocytes to endothelial cells, in part, by increasing expression of ICAM-1. However, the cellular role of oxLDL in endothelial adhesiveness is not well understood. The peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the nuclear receptor superfamily, is expressed in vascular endothelial cells. Whether it can be activated by a synthetic ligand, troglitazone, as well as by natural ligands, oxLDL and its lipid components (i.e., 9- and 13-HODE), has not yet been explored. This study was undertaken to determine whether PPARgamma is expressed in ECV304 human vascular endothelial cells and if so to define the biological effects of its activation by these agonists. Our results demonstrate that PPARgamma mRNA is expressed in ECV304 cells, and transfected cells with a PPARE luciferase construct respond to these agonists. In addition, ligand-dependent PPARgamma activation increased ICAM-1 protein expression and enhanced adherence of monocytes to ECV304 cells by two- to threefold. These findings suggest that the PPARgamma signaling pathway might contribute to the atherogenicity of oxLDL in vascular endothelial cells.     

Athero- and thrombogenic actions of lysophosphatidic acid and sphingosine-1-phosphate

Lysophosphatidic acid (LPA) and sphingosine-1-phosphate (S1P) are potent bioactive phospholipids with specific and multiple effects on blood cells and cells of the vessel wall. Released by activated platelets, LPA and S1P mediate physiological wound healing processes such as vascular repair. Evidence is accumulating that these lipid mediators can, however, under certain conditions become athero- and thrombogenic molecules that might aggravate cardiovascular disease. For example, LPA present in minimally modified LDL and within the intima of atherosclerotic lesions may play a role in the early phase of atherosclerosis by inducing barrier dysfunction and increased monocyte adhesion of the endothelium, as well as in the late phase by triggering platelet activation and intra-arterial thrombus formation upon rupture of the atherosclerotic plaque. Moreover, LPA and S1P, by stimulating the proliferation of fibroblasts and by enhancing the survival of inflammatory cells are likely to play a central role in the excessive fibroproliferative and inflammatory response to vascular injury that characterizes the progression of atherosclerosis. Furthermore, LPA can cause the phenotypic dedifferentiation of medial vascular smooth muscle cells, and S1P is able to stimulate the migration and proliferation of intimal vascular smooth muscle cells; both processes ultimately lead to the formation of the neointima. Most importantly, as LPA and S1P bind to and activate multiple G-protein receptors, it emerges that the beneficial or harmful action of LPA and S1P are critically dependent on the expression profile of their receptor subtypes and their coupling to different signal transduction pathways in the target cells. By targeting specific subtypes of LPA and S1P receptors in selective cells of the vascular wall and blood, new strategies for the prevention and therapy of cardiovascular diseases can be envisioned.     

Modulation of LPA Receptor Expression in the Human Brain Following Neurotrauma

Lysophosphatidic acid (LPA) is involved in physiological and pathological states, including in neural development and inflammation. We assessed the expression pattern of the LPA receptors 1-3 and of LPA-producing enzyme autotaxin in post-mortem human brain tissue, both in normal individuals and in individuals who died following traumatic brain injury. We found that LPA receptors and autotaxin are weakly expressed in the normal control adult brain. Quantitative PCR for the LPA receptors and autotaxin mRNA showed an increase of LPAR₂ and a decrease of autotaxin mRNA expression in the cortex following brain injury. Immunohistochemical analysis showed that LPAR₁ colocalized with astrocytes and that LPAR₂ is present on the ependymal cells lining the lateral ventricle in the brain samples from individuals who died following severe head injury. This work shows for the first time that key components of the LPA pathway are modulated following TBI in humans.     

Role of lipoprotein-associated lysophospholipids in migratory activity of coronary artery smooth muscle cells

The migration of vascular smooth muscle cells (SMCs) is a hallmark of the pathogenesis of atherosclerosis and restenosis after angioplasty. Plasma low-density lipoprotein (LDL), but not high-density lipoprotein (HDL), induced the migration of human coronary artery SMCs (CASMCs). Among bioactive lipids postulated to be present in LDL, lysophosphatidic acid (LPA) appreciably mimicked the LDL action. In fact, the LDL-induced migration was markedly inhibited by pertussis toxin, an LPA receptor antagonist Ki-16425, and a small interfering RNA (siRNA) targeted for LPA(1) receptors. Moreover, LDL contains a higher amount of LPA than HDL does. HDL markedly inhibited LPA- and platelet-derived growth factor (PDGF)-induced migration, and sphingosine 1-phosphate (S1P), the content of which is about fourfold higher in HDL than in LDL, mimicked the HDL action. The inhibitory actions of HDL and S1P were suppressed by S1P(2) receptor-specific siRNA. On the other hand, the degradation of the LPA component of LDL by monoglyceride lipase or the antagonism of LPA receptors by Ki-16425 allowed LDL to inhibit the PDGF-induced migration. The inhibitory effect of LDL was again suppressed by S1P(2) receptor-specific siRNA. In conclusion, LPA/LPA(1) receptors and S1P/S1P(2) receptors mediate the stimulatory and inhibitory migration response to LDL and HDL, respectively. The balance of not only the content of LPA and S1P in lipoproteins but also the signaling activity between LPA(1) and S1P(2) receptors in the cells may be critical in determining whether the lipoprotein is a positive or negative regulator of CASMC migration.