Abstract 565: Nuclear Receptor NR4A1 Represses SDF1a expression in macrophages and Reduces Atherosclerosis.

Abstract

Rationale NR4A1 is a nuclear receptor, also known as Nur77 and is expressed in human atherosclerotic lesions in macrophages, endothelial cells, T cells and smooth muscle cells. NR4A1-knockout (NR4A1 -/- ) mice lack Ly6C - monocytes, but have normal LyC6 + numbers. Macrophages play a critical role in atherosclerosis and we have demonstrated that NR4A1 has an anti-inflammatory function in THP-1 macrophages. The aim of the current study is to assess the function of this receptor in myeloid cells in atherosclerosis. Objective This study aims to delineate the function of Nuclear Receptor NR4A1 in macrophages in atherosclerosis. Methods and results Bone marrow-derived macrophages (BMM) from wild-type and NR4A1 -/- mice were cultured and classically activated with LPS or alternatively activated with IL4. NR4A1 -/- BMM exhibit changed expression of M2-specific markers and a pro-inflammatory polarization in response to LPS with enhanced expression of IL12, IFNγ, and SDF1α. Nitric oxide synthesis is also strongly induced in (non)-stimulated NR4A1 -/- BMM. SDF1α is a potent chemotactic factor for B cells and monocytes. The chemoattractive activity of NR4A1 -/- BMM is abolished by SDF1α inhibiting antibodies as well as by overexpression of NR4A1 in the NR4A1-deficient cells. Luciferase experiments show that NR4A1 binds directly to several response elements present in the mouse and human SDF1α promoter. A ChIP assay confirms these results. The effect of bone marrow-specific NR4A1-deficiency on atherosclerosis was studied in low density lipoprotein receptor-deficient (Ldlr -/- ) mice. Ldlr -/- mice with a NR4A1 -/- bone marrow develop 2.1-fold larger lesions than wild type bone marrow transplanted mice; containing more macrophages, T cells, smooth muscle cells and larger necrotic cores. SDF1α expression is also higher in these lesions, which may explain the observed aggravation of lesion formation, since SDF1α is not only a chemoattractant for monocytes but also enhances smooth muscle cell proliferation. Conclusion In macrophages the nuclear receptor NR4A1 has an anti-inflammatory function, represses SDF1α expression and, most importantly, bone-marrow transplantation studies in Ldlr -/- mice revealed that NR4A1 inhibits atherosclerosis.