Abstract 442: D-4F, an Apolipoprotein A-I Mimetic Peptide, Protects Macrophages From Oxidized Low-Density Lipoprotein--Induced Apoptosis by Inhibiting the Endoplasmic Reticulum Stress-C/EBP Homologous Protein Pathway

Abstract

Objective: D-4F, an apolipoprotein A-I (apoA-I) mimetic peptide, exerts a variety of atheroprotective functions similar to apoA-I, the major protein component of high density lipoprotein (HDL), including acting as an antioxidant, mediating cholesterol efflux from foam cells and direct anti-inflammatory effects. Our previous studies have demonstrated that endoplasmic reticulum (ER) stress promotes macrophage-derived foam cell formation by upregulating CD36 expression and mediates oxidized low-density lipoprotein (ox-LDL)-induced macrophage apoptosis. The goal of this study was to investigate the protective effect of D-4F on ox-LDL-induced macrophage cytotoxicity and specifically the ER stress-C/EBP homologous protein (CHOP) pathway-mediated apoptosis. Methods and Results: Treatment with D-4F (12.5, 25 and 50 mg/L) attenuated ox-LDL (100 mg/L)-induced cholesterol accumulation in RAW264.7 macrophages and foam cell formation in a dose-dependent manner. Similar to tunicamycin (TM), a classical ER stress inducer, ox-LDL reduced cell viability and induced apoptosis in RAW264.7 macrophages. The cytotoxic effects of ox-LDL (100 mg/L) and TM (5 mg/L) were remarkably inhibited by D-4F treatment. Interestingly, we found that D-4F also significantly suppressed the ox-LDL- and TM-induced CD36 upregulation and activation of ER stress signaling events, including the phosphorylation of inositol-requiring enzyme 1 (IRE1) and nuclear translocation of activating transcription factor 6 (ATF6). In addition, exposure of RAW264.7 macrophages to ox-LDL or TM resulted in a significant increase in the expression of CHOP, a proapoptotic transcription factor regulated by IRE1 and ATF6 under conditions of ER stress. D-4F blocked these effects in a dose-dependent manner. Moreover, administration of apoE –/– mice with D-4F (1 mg/kg per day) suppressed apoptosis and the upregulation of CD36, phospho-IRE1, GRP78 and CHOP in macrophage-dense atherosclerotic lesions. Conclusion: These data indicate that D-4F can protect macrophages from ox-LDL-induced apoptosis and that the mechanism at least partially involves its ability to inhibit the ER stress-CHOP signaling pathway.