Abstract 617: Inhibition of Bone Marrow Derived CD40 Limits Atherosclerosis by Reducing Leukocyte Adhesion, Involving the CD40-TRAF6 Axis
Systemic inhibition of CD40L decreases atherosclerosis and induces plaque stability. However, when CD40L is absent in bone marrow-derived cells in LDLR±/±mice, plaque extent and phenotype were not affected. Here we investigated the role of bone marrow derived CD40, the receptor for CD40L, in atherosclerosis. LDLR−/− mice (n=45) were lethally irradiated and CD40−/− or wild type (WT) bone marrow was transplanted. Mice were fed a 1.25% cholesterol diet for 26 wks and the aortic arch including its main branch points was analyzed. Transplantation of CD40−/− bone marrow resulted in a 37.0% decrease in plaque area (wt 9.10E105±6.91E104μm2 n=22 vs CD40−/− 5.73E105±6.43μm2 n=23; p<0.05). This was due to a decreased number of plaques (wt 6.5±0.2 vs CD40−/− 4.8±0.2; p<0.05), and to an impaired plaque progression (# advanced plaques: wt 4.1±0.3 vs CD40−/− 2.7±0.4; p<0.05). Advanced plaques exhibited a different phenotype. Although the number of lipid cores did not differ between both groups, lipid cores of the LDLR−/− mice that received CD40−/− bone marrow were significantly smaller (wt 33.1±2.1% vs CD40−/− 16.0±1.9%; p<0.05). Moreover, initial and advanced plaques contained less CD45+ cells (initial: wt 9.8±0.9% vs CD40−/− 2.6±0.6%; p<0.05; advanced: wt 6.1±0.4% vs CD40−/− 1.3±0.1%; p<0.05), and advanced plaques showed a 22.4% (p<0.05) decrease in macrophage (Mac3) content. In a laminar flow assay using murine CD40−/− or WT monocytes (CD11b+ cells) onto TNF-α stimulated endothelial cells (SVECs), deficiency of leukocyte CD40 decreased CD11b+ cell adhesion to the endothelium with 66.6% (p<0.05). To reveal which downstream CD40 adaptor molecule is crucial in this process, we cultured bone marrow derived macrophages obtained from mice that had a deficient CD40-TRAF2/3/5, CD40-TRAF6 or CD40-TRAF2/3/5/6 signaling and stimulated them with 10ng/ml LPS. Analysis of inflammatory markers such as MCP-1, IL6 and MIP-1α showed a 2–5 fold decrease in mRNA expression in absence of CD40-TRAF6 and CD40-TRAF2/ 3/5/6 interactions. Thus these data show that bone marrow-derived CD40 decreases atherosclerosis and induces plaque stability, which is the result of a decreased adhesion of leukocytes to the endothelium. This process is mediated by CD40-TRAF6 interactions.