Inhibition of Macrophage CD36 Expression and Cellular Oxidized Low Density Lipoprotein (oxLDL) Accumulation by Tamoxifen: APEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR (PPAR)γ-DEPENDENTMECHANISM

Meixiu Jiang,Miao Yu,Xiaoxiao Yang,Yajun Duan,Xiaoju Li,Yuanli Chen,Jihong Han,Shengzhong Duan,Shuang Zhang,Wenwen Zhang,Yan Li

doi:10.1074/jbc.m116.740092

Abstract

Macrophage CD36 binds and internalizes oxidized low density lipoprotein (oxLDL) to facilitate foam cell formation. CD36 expression is activated by peroxisome proliferator-activated receptor γ (PPARγ). Tamoxifen, an anti-breast cancer medicine, has demonstrated pleiotropic functions including cardioprotection with unfully elucidated mechanisms. In this study, we determined that treatment of ApoE-deficient mice with tamoxifen reduced atherosclerosis, which was associated with decreased CD36 and PPARγ expression in lesion areas. At the cellular level, we observed that tamoxifen inhibited CD36 protein expression in human THP-1 monocytes, THP-1/PMA macrophages, and human blood monocyte-derived macrophages. Associated with decreased CD36 protein expression, tamoxifen reduced cellular oxLDL accumulation in a CD36-dependent manner. At the transcriptional level, tamoxifen decreased CD36 mRNA expression, promoter activity, and the binding of the PPARγ response element in CD36 promoter to PPARγ protein. Tamoxifen blocked ligand-induced PPARγ nuclear translocation and CD36 expression, but it increased PPARγ phosphorylation, which was due to that tamoxifen-activated ERK1/2. Furthermore, deficiency of PPARγ expression in macrophages abolished the inhibitory effect of tamoxifen on CD36 expression or cellular oxLDL accumulation both in vitro and in vivo Taken together, our study demonstrates that tamoxifen inhibits CD36 expression and cellular oxLDL accumulation by inactivating the PPARγ signaling pathway, and the inhibition of macrophage CD36 expression can be attributed to the anti-atherogenic properties of tamoxifen.

Highlights

Inhibition of Atherosclerosis by Tamoxifen Is Associated with Decreased CD36, FABP4, and PPAR␥ Expression in Lesion Areas—The inhibitory effects of tamoxifen on atherosclerosis have been reported with different animal models (4 – 6)
In contrast to our previous report that demonstrates that tamoxifen reduces total and LDL-cholesterol levels in C57BL/6 wild type mice fed normal chow [28], in the current study, we determined that tamoxifen had little effect on serum lipid profiles of mice fed HFD (Fig. 1B), which suggests that the effect of tamoxifen on the lipid profile might be in an animal model-dependent manner, and the inhibition of lesions in ApoEϪ/Ϫ mice by tamoxifen should be completed by mechanisms other than amelioration of lipid profiles
When we determined expression of CD36 and FABP4 in lesion areas by immunofluorescent staining the cross-sections of aortic root, we found that both of them were substantially reduced by tamoxifen (Fig. 1C, top and middle panels, and D, left and middle panels)

Summary

Introduction

The presence of anti-CD36 antibody attenuated tamoxifen and 4hydroxytamoxifen-reduced oxLDL accumulation in macrophages (Fig. 2G, bottom panel) confirming that the reduction of cellular oxLDL accumulation/foam cell formation by tamoxifen or 4-hydroxytamoxifen mainly depends on inhibition of CD36 expression. We determined that tamoxifen inhibited CD36 expression and cellular oxLDL accumulation in control cells but not Ppar␥ deficient cells (Fig. 6, C and D), the deficiency of PPAR␥ expression substantially reduced basal levels of CD36 expression and cellular lipid content, which implies it might be difficult to observe the further reduction of both by tamoxifen treatment, which is due to the sensitivity of detections.

Results

Conclusion