Oxidized LDL-Induced Smooth Muscle Cell Proliferation Involves the EGF Receptor/PI-3 Kinase/Akt and the Sphingolipid Signaling Pathways

Abstract

Objective-Oxidized low-density lipoprotein (oxLDL)-induced smooth muscle cell (SMC) proliferation requires the coactivation of various signaling pathways, namely sphingomyelin/ceramide/sphingosine-1-phosphate, epithelial growth factor receptor (EGFR), and phosphoinositide 3-kinase (PI-3K) pathways. This study aimed to clarify the respective role and the hypothetical cross-talk between sphingomyelin/ceramide/sphingosine-1-phosphate, EGFR, and PI-3K/Akt pathways in the balance between mitogenic and cytotoxic effects elicited by oxLDL. Methods and Results-Coimmunoprecipitation experiments and the use of inhibitors and dominant-negative mutantshowed that oxLDL-induced PI-3K activation is dependent on EGFR. PI-3K activation is independent of the sphingomyelin/ceramide/sphingosine-1-phosphate pathway, because PI-3K inhibition by LY294002 or dominantnegative ⌬p85 mutant does not abrogate sphingomyelin hydrolysis, and, conversely, the use of permeant C2-ceramide and of N,N-dimethyl-sphingosine, a sphingosine kinase inhibitor, does not alter PI-3K activity. Activation of Akt/PKB by oxLDL requires PI-3K, as shown by the inhibition by LY204002 and in ⌬p85 SMC. The inhibition of Akt/PKB by PI-3K inhibitor LY204002 or by overexpression of kinase-dead Akt shifted the mitogenic effect of oxLDL toward apoptosis, thus suggesting that the PI-3K/Akt pathway acts as a survival pathway. Conclusions-SMC proliferation elicited by moderate concentrations of oxLDL involves the sphingomyelin/ceramide/ sphingosine-1-phosphate pathway, which leads to extracellular regulated kinase 1/2 activation and DNA synthesis, and the EGFR/PI-3K/Akt pathway, which prevents the apoptotic effect of oxLDL. Key Words: proliferation Ⅲ survival Ⅲ oxidized low-density lipoprotein Ⅲ phosphoinositide 3-kinase Ⅲ epithelial growth factor receptor Ⅲ ceramide S mooth muscle cell (SMC) proliferation plays a critical role in the formation of the fibrous cap and plaque stability, whereas toxic events are potentially involved in necrotic core formation, endothelial cell injury, and plaque rupture. 1,2 Oxidized low-density lipoproteins (oxLDLs) exert various biological effects potentially involved in atherosclerosis development, such as chemotaxis, cell proliferation, or cytotoxicity. [3][4][5][6][7] OxLDL-induced SMC proliferation involves the activation of the sphingomyelin-ceramide pathway that results in the generation of the mitogenic mediator sphingosine-1-phosphate. 3,8 On the other hand, oxLDLs elicit activation of tyrosine kinase receptors such as epithelial growth factor receptor (EGFR), 9 which could play a role in cell proliferation. Recent studies provided evidence that phosphatidylinositol 3-kinase (PI-3K) is implicated in macrophage proliferation induced by oxLDL. 5 PI-3K is activated by growth factors and peptide hormones 10 -12 and regulates multiple cellular processes required for cell survival and proliferation. 13 A cross-talk between the sphingomyelinceramide and PI-3K pathways has been reported, but the data are relatively conflicting, because the ...

Differential effects of chlorinated and oxidized phospholipids in vascular tissue: implications for neointima formation

“…PAPC also induces monocyte adhesion and inflammation in atherosclerotic mice in vivo [26]. Several studies, including some conducted in vivo, have demonstrated that oxidized phospholipids can influence many of the processes involved in vascular remodelling such as VSMC proliferation, migration and ECM production [27][28][29][30].…”

Modified Forms of LDL in Plasma

“…Related to the inflammatory activity of oxLDL is its ability to promote the expression of growth factors and colony stimulating factors. This proliferative activity is mediated by oxidation-derived lipids, and in smooth muscle cells it induces the change of the normal contractile phenotype to a proliferative phenotype (Auge, 2002). The proliferative phenotype of smooth muscle cells is characterized by the high production of collagen that will contribute decisively to the thickening of the arterial wall (Negishi, 2004).…”

Signalisation apototique induite par les LDL oxydées Implication dans l’athérosclérose

“…Les LDL oxydées induisent également une diminution d'expression des enzymes antioxydantes telles que la Cu/Zn superoxide dismutase et la glutathion peroxydase [51-53], ce qui contribue à maintenir un niveau de ROS intracellulaire élevé. Les ROS participent largement à la signalisation induite par les LDL oxydées, en particulier dans la prolifération (activation de récepteurs à tyrosine kinase et de facteurs de transcription tels que NF-jB) [15][16][17]54]. Le rôle des ROS dans la toxicité des LDL est basé sur l'observation que les antioxydants ou la surexpression d'enzymes antioxydantes protègent de la mort induite par les LDL [52][53][54][55][56].…”

“…D'autre part, les LDL oxydées induisent une séquence de signalisation complexe, qui participe à la dysfonction endothé-liale, la migration et la prolifération des cellules musculaires lisses, l'attraction dans la paroi des cellules mononuclées, et l'apoptose ou la nécrose des cellules vasculaires, potentiellement impliquées dans la stabilité/instabilité de la plaque [12,13]. À faible concentration, les LDL oxydées induisent la prolifération des CML, via diverses voies de signalisation [13], telles que la voie sphingomyéline/céramide/ sphingosine-1-phosphate (Spm/Cer/S1P), impliquée dans la synthèse d'ADN, et la voie EGFR/PI3K/Akt, impliquée dans la survie [14,15], ainsi que la génération de radicaux oxygé-nés intracellulaires (ROS) qui participent à l'activation du récepteur au PDGF et à l'activation de NFjB par les LDL oxydées [16, 17]. À forte concentration, les LDL oxydées sont cytotoxiques pour les cellules vasculaires et induisent de la nécrose ou de l'apoptose, en fonction de leur concentration, du type cellulaire et l'expression de Bcl2 [18].…”