MRas- knock-out mouse: B-cell phenotype and reduced macrophage infiltration in atherosclerotic plaques at the aortic root

Background: Recently, we identified by genome-wide association study the MRas gene locus on human chromosome 3q22 to be associated with coronary artery disease (CAD) (rs9818870; p=7.44x10-13). M-Ras is a member of the Ras superfamily of small GTPases, which act as molecular switches in diverse cellular functions and thereby regulate a variety of biological processes. M-Ras has been implicated in the regulation of TNFα-stimulated LFA-1 activation and integrin-mediated leukocyte adhesion downstream of various inflammatory cytokines. Aim: To further study the pathomechanism underlying the association between MRas and CAD in a knockout mouse model. Methods: We crossbred the MRas-KO mice onto the ApoE-KO background and fed these mice with western diet. In parallel, we performed adhesion and migration assays with macrophages, monocytes, B- and T-cells to study the influence of MRas on adhesion and migration as a potential pathomechanism of atherosclerosis. Results: The MRas/ApoE-KO mouse showed no difference in plaque size at the aortic root in comparison to the ApoE-KO mouse after 10 weeks of high fat diet, but there were significant less macrophages in the plaque (n=19/10/15; ∼10%; p=0.002). In addition, the ratio between macrophage and collagen in the plaque at the aortic root was significant higher in the MRas/ApoE-KO than in the ApoE-KO under high fat diet (n=19/9/15; p=0.002). Furthermore, we observed a 15% reduction of CD19+ B-cells in lymphnodes in MRas-KO mice (p<0.05), but not in bone marrow, spleen and blood. Moreover, we noticed a 20% reduction of leukocyte adhesion in in vitro assays with an endothelial cell line (p<0.05). Again, especially B-cell adhesion was reduced in MRas-KO mice in comparison to WT mice. In vitro migration assays show also a reduced migration of B-cells towards the chemokine CxCl12 (p<0.01). Conclusion: Our data suggests that MRas-KO has no effect on plaque formation at the aortic root but on the plaque stability by less macrophage infiltration. This could be linked to the reduction of adhesion and migration by B-cells.