FOR 809: Chemokines and Adhesion Molecules in Cardiovascular Pathogenesis
Final Report Abstract
Members of FOR809 have made seminal contributions to the field over the past decade and two funding periods. For instance, the intriguing structural relationship with chemokines initiated the major discovery of CXCR2 and CXCR4 as the first 3mmune3ng (chemokine) receptors for macrophage migration inhibitory factor (MIF) in a collaboration of Drs. Bernhagen (TP1) and Weber (TP4). This explained the pleiotropic chemokine-like functions of MIF as a novel non-canonical and dual ligand for CXCR2 and CXCR4 in leukocyte recruitment during atherogenesis and inflammation. As a therapeutically relevant structural element in MIF mediating its atherogenic CXCR2 function, a pseudo-ELR motif resembling that in CXCL8 but discontinuous was identified. A new dimension to the functional plasticity and fine-tuning of chemokine activities was opened by the paradigm of heteromeric chemokine interactions. Sophisticated biophysical and molecular dynamics methods established a structural model of the prototypic chemokine heteromer CXCL4-CCL5. The rational design and synthesis of a stable cyclic peptide, selectively disrupting heteromers without side-effects on the immune system, represents a novel approach to reduce atherosclerosis and provided first evidence that heteromer formation of platelet chemokines is functionally relevant in vivo, allowing for therapeutic targeting. The chemokine interactome derived from prototypic heteromers (TP2 von Hundelshausen/Koenen) represents a new regulatory principle for their combinatorial diversity, which is applicable to other chemokine complexes or pathologies. Further work by Dr. Zernecke (TP3) demonstrated a functional role of the mature DC-derived chemokine CCL17 in suppressing the atheroprotective maintenance of regulatory T cells. Whereas CCL17+ DCs accumulate in lesions to aggravate atherosclerosis, the genetic deletion or antibody blockade of CCL17 resulted in a Treg-mediated reduction of atherosclerosis, underscoring a role of CCL17-bearing DCs as central effectors in Treg homeostasis and identifying CCL17 as a target possibly interacting with other chemokines. It has been revealed that atherosclerosis can also be counteracted by the athero-protective chemokine ligand-receptor axis CXCL12/CXCR4. Genetic deficiency or interference with CXCR4 clearly exacerbated atherosclerosis, due to a disturbed homeostasis of neutrophils, unveiling their unexpected contribution to early atherogenesis. On the other hand, a new mechanism, by which endothelial apoptotic microparticles induce atheroprotective CXCL12, was identified. Released during endothelial damage in early atherosclerosis, these microparticles can confer microRNA-126 to unleash an autocrine feedback, which enhances local CXCL12 expression and recruitment of angiogenic progenitor cells to promote endothelial regeneration and atheroprotection. Additional work in TP4 identified miR-126-5p-mediated mechanisms that control endothelial cell proliferation, determine flow-dependent susceptibility to atherosclerosis and can be therapeutically exploited using nanoparticle-mediated delivery of mimics. Junctional adhesion molecule-A (JAM-A) was identified as a ligand of the integrin LFA-1 during transendothelial leukocyte migration. In interplay with 3mmune3ng3 JAM-A interactions, this mechanism serves as a molecular zipper for extravasation of immune cells that can be targeted in vascular inflammation. In TP6, the specific role of endothelial JAM-A in guiding monocytes to predilection sites of atherosclerosis and promoting lesion formation has recently been revealed. The characterization of co-stimulatory pathways underlying atherogenesis has uncovered new therapeutic strategies (TP11). Specific disruption of the CD40-TRAF6 interaction site without disturbing other CD40 signaling cascades limits atherosclerosis of an unstable phenotype by skewing the immune response toward a protective profile and may circumvent thrombo-embolic complications associated with CD40L-specific antibody administration in man. Lysophosphatidyl LPA derived from minimally modified LDL has been implicated in atherogenesis, given increased LPA levels in plaques or serum in hyperlipidemia and its involvement in vascular cell activation and interactions. Notably, Dr. Schober et al. (TP8) found that unsaturated LPA promotes macrophage accumulation and lesion progression in atherosclerosis-prone mice, whereas combined LPAR1/3 receptor blockade reduced foam cell content and atherogenesis. The effects were attributable to binding of unsaturated LPA to endothelial LPAR1/3, inducing a secretion and surface presentation of CXCL1 to mediate arterial monocyte adhesion. Neutrophils and their mediators have been detected in human or mouse atherosclerotic lesions by Dr. Söhnlein. Neutrophils use the CCL5 receptors CCR1 and CCR5 for entering atherosclerotic plaques, compared to a restricted use of CCR2 and CXCR2 for peripheral venous recruitment. Likewise, classical monocytes use CCR1/5 for recruitment to the lesion but CXCL1/CXCR2 and CCR2 for mobilization into the circulation. Notably, hyperlipidemia also triggers neutrophilia by stimulating granulopoiesis and bone marrow egress, involving elevated CXCL1 plasma levels, and circulating neutrophil numbers closely correlate with plaque size. Activated neutrophils release nuclear content termed NETs as a scaffold containing antimicrobial proteins such as LL-37 and may participate in chronic atherogenesis (TP9).
