Leukocyte Bim deficiency does not impact atherogenesis in ldlr\u2212/\u2212 mice, despite a pronounced induction of autoimmune inflammation

Lieve Temmerman,Kim L L Habets,Thomas G Cotter,Niek Van Bree,Tom G H Keulers,Erik A L Biessen,Theo J C Van Berkel,Ilze Bot,Bart J M Van Vlijmen,Johan Van Der Vlag,Martine Bot,Marijke M Westra

doi:10.1038/s41598-017-02771-4

Abstract

Proapoptotic Bcl-2 family member Bim is particularly relevant for deletion of autoreactive and activated T and B cells, implicating Bim in autoimmunity. As atherosclerosis is a chronic inflammatory process with features of autoimmune disease, we investigated the impact of hematopoietic Bim deficiency on plaque formation and parameters of plaque stability. Bim−/− or wild type bone marrow transplanted ldlr−/− mice were fed a Western type diet (WTD) for 5 or 10 weeks, after which they were immunophenotyped and atherosclerotic lesions were analyzed. Bim−/− transplanted mice displayed splenomegaly and overt lymphocytosis. CD4+ and CD8+ T cells were more activated (increased CD69 and CD71 expression, increased interferon gamma production). B cells were elevated by 147%, with a shift towards the pro-atherogenic IgG-producing B2 cell phenotype, resulting in a doubling of anti-oxLDL IgG1 antibody titers in serum of bim−/− mice. Bim−/− mice displayed massive intraplaque accumulation of Ig complexes and of lesional T cells, although this did not translate in changes in plaque size or stability features (apoptotic cell and macrophage content). The surprising lack in plaque phenotype despite the profound pro-atherogenic immune effects may be attributable to the sharp reduction of serum cholesterol levels in WTD fed bim−/− mice.

Highlights

Atherosclerosis is a chronic inflammatory disease of the large vessels characterized by lipid accumulation in the intimal wall[1]
Bim is essential for apoptosis of various leukocyte subsets, including T and B cells, dendritic cells, macrophages and granulocytes[14, 15, 21]
We show that hematopoietic Bim deficiency impacts on inflammatory status, an effect that is counteracted by an unexpected lowering of plasma cholesterol levels and a dampening of the Western type diet (WTD)-induced monocytosis

Summary

Introduction

Atherosclerosis is a chronic inflammatory disease of the large vessels characterized by lipid accumulation in the intimal wall[1]. The Bcl-2 family of pro- and anti-apoptotic proteins regulates apoptosis induced by cellular stressors such as DNA damage, UV radiation and oxidative stres[8]. Proteins of this family share one to four Bcl-2 homology (BH) domains[8]. In the present study we have investigated the role of Bim regulated leukocyte apoptosis in atherosclerosis-prone ldlr−/− mice. Our study shows that hematopoietic Bim deficiency in ldlr−/− mice results in increased atherosclerotic lesion T cell content and massive immunoglobulin deposition as well as increased circulating T and B cells and high levels of anti-oxidized LDL autoantibodies. We demonstrate that loss of leukocyte Bim interferes with lipid metabolism

Methods

Results

Conclusion