Gerdes, Norbert

The CD40-CD40L co-stimulatory dyad has been identified as critical player in atherosclerosis. Our previous work has shown that CD40 and CD40L have cell divergent effects on atherosclerosis. Deficiency of the CD40-CD40L dendritic cell-T cell axis decreased atherosclerosis via reducing T helper 1 responses, whereas deficiency of macrophages CD40 reduced atherosclerosis by enhancing efferocytosis and reducing necrotic core content. CD40 is highly expressed on B cells and interacts with CD40L on T cells to induce antibody production and T follicular helper cell responses. We therefore hypothesize that deletion of CD40 will reduce atherosclerosis. We aim to unravel the role of B cell CD40 in atherosclerosis. CD40 expression on B cell subsets was determined on peripheral blood mononuclear cells of patients and correlated with severity of coronary artery disease (CAD). Atherosclerosis was analyzed in CD19 Cre CD40 flfl ApoE -/- mice that were fed an atherogenic diet for 14 weeks. Patients with CAD showed a decrease in CD40 on their putative B1 cells, which was associated with increased plaque burden and decreased plaque fibrosis as detected by coronary intravascular ultrasound. Depletion of CD40 on B cells in ApoE -/- mice resulted in a decreased germinal center formation and inadequate IgM production as expected. However, in line with our patient data, absence of B cell-CD40 increased atherosclerosis. This was caused by a reduction in B1 cells and consequently a reduction in atheroprotective anti-oxidation specific epitope (OSE) IgMs. Transfer of CD40-competent B1b cells in B cell-CD40-deficient mice restored anti-OSE IgM levels and prevented the increase in atherosclerosis. CD40-deficient B1b cells have an altered mTOR signaling pathway, impaired mitochondrial function, excessive uptake of lipids, increased cellular stress and accelerated cell death. Data indicate that CD40-deficiency promotes phosphorylation of RAPTOR and protein kinase B (AKT). We have identified a novel function of CD40 on B1b cells. B1b cell-CD40 exerts an anti-atherogenic role by regulating B1b cell metabolic homeostasis via mTOR pathway. Further mechanistic insights into how CD40 mounts adequate atheroprotective anti-OSE IgM production are currently being investigated.

Abstract Aims CD40 and its ligand, CD40L, play a critical role in driving atherosclerotic plaque development. Disrupted CD40-signalling reduces experimental atherosclerosis and induces a favourable stable plaque phenotype. We recently showed that small molecule-based inhibition of CD40-tumour necrosis factor receptor associated factor-6 interactions attenuates atherosclerosis in hyperlipidaemic mice via macrophage-driven mechanisms. The present study aims to detail the function of myeloid CD40 in atherosclerosis using myeloid-specific CD40-deficient mice. Method and Results Cd40flox/flox and LysM-cre Cd40flox/flox mice on an Apoe−/− background were generated (CD40wt and CD40mac−/−, respectively). Atherosclerotic lesion size, as well as plaque macrophage content, was reduced in CD40mac−/− compared to CD40wt mice, and their plaques displayed a reduction in necrotic core size. Transcriptomics analysis of the CD40mac−/− atherosclerotic aorta revealed downregulated pathways of immune pathways and inflammatory responses. Loss of CD40 in macrophages changed the representation of aortic macrophage subsets. Mass cytometry analysis revealed a higher content of a subset of alternative or resident-like CD206+CD209b− macrophages in the atherosclerotic aorta of CD40mac−/− compared to CD40wt mice. RNA-sequencing of bone marrow-derived macrophages of CD40mac−/− mice demonstrated upregulation of genes associated with alternatively activated macrophages (including Folr2, Thbs1, Sdc1, and Tns1). Conclusions We here show that absence of CD40 signalling in myeloid cells reduces atherosclerosis and limits systemic inflammation by preventing a shift in macrophage polarization towards pro-inflammatory states. Our study confirms the merit of macrophage-targeted inhibition of CD40 as a valuable therapeutic strategy to combat atherosclerosis.