Abstract 872: Novel Proatherogenic Effect of Highly Oxidized Low Density Lipoprotein: Inhibition of Aortic Smooth Muscle Cell Migration Via a Redox-Sensitive Mechanism
Increased smooth muscle cell (SMC) migration in response to mechanical or biochemical stimuli contributes to the development of intimal growth which is a hallmark of developing atherosclerotic plaque; however advanced atherosclerotic plaques are characterized by reduced SMC migratory capacity and relative SMC depletion which play an important role in plaque destabilization. To determine mechanisms we studied the effect of the pro-atherogenic molecule highly oxidized LDL (>20 nmol malondialdehyde per milligram protein) or native LDL (control) on SMC migration using a wound healing assay. OxLDL (60 ug/ml, 16h) reduced SMC migration by 75±10% compared to control and this effect was completely blocked by anti-CD36 scavenger receptor antibody (20 ug/ml FA6–152). Antioxidants (Trolox or Tiron, 1 mM) suppressed OxLDL-induced superoxide production (by 18±2% and 21±3%, respectively (dihydroethidium assay)) and peroxide generation (by 88±4% and 92±4%, respectively (CDC assay)) and completely blunted OxLDL-induced reduction in SMC migration, indicating involvement of reactive oxygen species (ROS). Because lipoxygenase (LOX) inhibitors (AA-861, 5 uM or NDGA, 10 uM) and NADPH oxidase blockers (Apocynin, 50 uM or AEBSF, 1 mM) also decreased OxLDL-induced ROS we studied the role of LOX and NADPH oxidase in OxLDL effects on SMC migration using SMC cultured from the aorta of 5-LOX-, 12/15-LOX-, p47phox (NADPH oxidase subunit)-deficient and wild type (WT, control) mice. 12/15-LOX or p47phox deficiency markedly reduced OxLDL-induced peroxides (62±7% and 82±7% reduction compared to control, respectively), however 5-LOX deficiency had no effect. OxLDL inhibited migration of WT and 5-LOX-null SMC (56±9% and 35±7% reduction, respectively) but not of 12/15-LOX or p47phox-deficient SMC. In summary, highly oxidized LDL markedly reduces SMC migration via a CD36 receptor-dependent mechanism that is mediated by NADPH oxidase- and 12/15-lipoxygenase-dependent ROS generation. Our data have major implication for understanding mechanisms of SMC depletion in advanced atherosclerotic plaques leading to plaque rupture and acute coronary events.