Abstract 5330: CD36 Participates in a Signaling Pathway That Regulates Reactive Oxygen Species Formation
Previous studies showed that CD36 promotes reactive oxygen species (ROS) formation in mouse models of cerebral and cardiac ischemia. Using CD36−/− and wild type (WT) mice and cultured murine aortic vascular smooth muscle cells (VSMC), we examined the mechanisms by which CD36 regulates ROS formation and their potential functional significance. Two-Dimensional Difference Gel Electrophoresis and Mass Spectrometry analysis revealed significantly increased expression of Peroxiredoxin 2 (Prdx 2), an antioxidant enzyme known to detoxify ROS, in carotid arteries from CD36−/− mice. Immunohistochemistry confirmed the increase and revealed that expression was mainly in smooth muscle. Western blots showed increased Prdx2 expression in isolated VSMC from CD36−/− mice compared to WT, as well as increased levels of Nrf2, a transcription factor known to regulate anti-oxidant systems. Chromatin immunoprecipitation assays revealed that Nrf2 bound to the antioxidant responsive elements in the Prdx2 promoter and transfection of Nrf2 cDNA into HEK293 cells induced Prdx2 expression. In CD36−/− VSMC exposure to oxidant stress (H2O2) induced higher Prdx2 expression than in WT cells. Pharmacologic inhibition of Src kinases increased nuclear accumulation of Nrf2 in VSMC, suggesting that CD36 signaling through src kinases contributes to Nrf2 nuclear export or degradation. We previously showed that CD36−/− mice had prolonged thrombosis times after carotid artery injury induced by FeCl3. We therefore monitored ROS production in the vessel wall after injury using hydroethidine, a fluorescent superoxide probe. FeCl3 dose dependently induced accumulation of ROS; however, the degree was significantly lower in CD36−/− than in WT mice. Direct injection of Edavarone, a free radical scavenger, significantly prolonged time to thrombosis in all mice but the effect was much less in CD36−/− animals than in WT. We also found fewer endothelial cell-derived microparticles in plasma of CD36−/− mice after FeCl3 treatment, suggesting less endothelial injury. We conclude that CD36 mediated down-regulation of antioxidant systems in vascular cells may contribute to its pro-thrombotic and atherogenic effects.