Platelet CD40 Exacerbates Atherosclerosis by Transcellular Activation of Endothelial Cells and Leukocytes.

OBJECTIVE: Beyond their eminent role in hemostasis and thrombosis, platelets are recognized as mediators of inflammation. Platelet cluster of differentiation 40 (CD40) ligand (CD40L and CD154) plays a key role in mediating platelet-induced inflammation in atherosclerosis. CD40, the receptor for CD40L, is present on platelets; however, the role of CD40 on this cell type is until now undefined. APPROACH AND RESULTS: We found that in both mice and humans, platelet CD40 mediates the formation of platelet-leukocyte aggregates and the release of chemokine (C-X-C motif) ligand 4. Leukocytes were also less prone to adhere to CD40-deficient thrombi. However, platelet CD40 was not involved in platelet aggregation. Activated platelets isolated from Cd40(-/-)Apoe(-/-) mice adhered less to the endothelium upon injection into Apoe(-/-) mice when compared with CD40-sufficient platelets. Furthermore, lack of CD40 on injected platelets led to reduced leukocyte recruitment to the carotid artery as assayed by intravital microscopy. This was accompanied by a decrease in endothelial vascular cell adhesion molecule-1, platelet endothelial cell adhesion molecule, VE-cadherin, and P-selectin expression. To investigate the effect of platelet CD40 in atherosclerosis, Apoe(-/-) mice received thrombin-activated Apoe(-/-) or Cd40(-/-)Apoe(-/-) platelets every 5 days for 12 weeks, starting at the age of 17 weeks, when atherosclerotic plaques had already formed. When compared with mice that received Apoe(-/-) platelets, those receiving Cd40(-/-)Apoe(-/-) platelets exhibited a >2-fold reduction in atherosclerosis. Plaques of mice receiving CD40-deficient platelets were less advanced, contained less macrophages, neutrophils, and collagen, and displayed smaller lipid cores. CONCLUSIONS: Platelet CD40 plays a crucial role in inflammation by stimulating leukocyte activation and recruitment and activation of endothelial cells, thereby promoting atherosclerosis.

Controlled intramyocardial release of engineered chemokines by biodegradable hydrogels as a treatment approach of myocardial infarction.

Myocardial infarction (MI) induces a complex inflammatory immune response, followed by the remodelling of the heart muscle and scar formation. The rapid regeneration of the blood vessel network system by the attraction of hematopoietic stem cells is beneficial for heart function. Despite the important role of chemokines in these processes, their use in clinical practice has so far been limited by their limited availability over a long time-span in vivo. Here, a method is presented to increase physiological availability of chemokines at the site of injury over a defined time-span and simultaneously control their release using biodegradable hydrogels. Two different biodegradable hydrogels were implemented, a fast degradable hydrogel (FDH) for delivering Met-CCL5 over 24 hrs and a slow degradable hydrogel (SDH) for a gradual release of protease-resistant CXCL12 (S4V) over 4 weeks. We demonstrate that the time-controlled release using Met-CCL5-FDH and CXCL12 (S4V)-SDH suppressed initial neutrophil infiltration, promoted neovascularization and reduced apoptosis in the infarcted myocardium. Thus, we were able to significantly preserve the cardiac function after MI. This study demonstrates that time-controlled, biopolymer-mediated delivery of chemokines represents a novel and feasible strategy to support the endogenous reparatory mechanisms after MI and may compliment cell-based therapies.

Contribution of platelet CX(3)CR1 to platelet-monocyte complex formation and vascular recruitment during hyperlipidemia.

OBJECTIVE: The chemokine receptor CX(3)CR1 is an inflammatory mediator in vascular diseases. On platelets, its ligation with fractalkine (CX(3)CL1) induces platelet activation followed by leukocyte recruitment to activated endothelium. Here, we evaluated the expression and role of platelet-CX(3)CR1 during hyperlipidemia and vascular injury. METHODS AND RESULTS: The existence of CX(3)CR1 on platelets at mRNA and protein level was analyzed by RT-PCR, quantitative (q)PCR, FACS analysis, and Western blot. Elevated CX(3)CR1 expression was detected on human platelets after activation and, along with increased binding of CX(3)CL1, platelet CX(3)CR1 was also involved in the formation of platelet-monocyte complexes. Interestingly, the expression of CX(3)CR1 was elevated on platelets from hyperlipidemic mice. Accordingly, CX(3)CL1-binding and the number of circulating platelet-monocyte complexes were increased. In addition, CX(3)CR1 supported monocyte arrest on inflamed smooth muscle cells in vitro, whereas CX(3)CR1-deficient platelets showed decreased adhesion to the denuded vessel wall in vivo. CONCLUSIONS: Platelets in hyperlipidemic mice display increased CX(3)CR1-expression and assemble with circulating monocytes. The formation of platelet-monocyte complexes and the detection of platelet-bound CX(3)CL1 on inflamed smooth muscle cells suggest a significant involvement of the CX(3)CL1-CX(3)CR1 axis in platelet accumulation and monocyte recruitment at sites of arterial injury in atherosclerosis.

Blocking CCL5-CXCL4 heteromerization preserves heart function after myocardial infarction by attenuating leukocyte recruitment and NETosis.

Myocardial infarction (MI) is a major cause of death in Western countries and finding new strategies for its prevention and treatment is thus of high priority. In a previous study, we have demonstrated a pathophysiologic relevance for the heterophilic interaction of CCL5 and CXCL4 in the progression of atherosclerosis. A specifically designed compound (MKEY) to block this CCL5-CXCR4 interaction is investigated as a potential therapeutic in a model of myocardial ischemia/reperfusion (I/R) damage. 8 week-old male C57BL/6 mice were intravenously treated with MKEY or scrambled control (sMKEY) from 1 day before, until up to 7 days after I/R. By using echocardiography and intraventricular pressure measurements, MKEY treatment resulted in a significant decrease in infarction size and preserved heart function as compared to sMKEY-treated animals. Moreover, MKEY treatment significantly reduced the inflammatory reaction following I/R, as revealed by specific staining for neutrophils and monocyte/macrophages. Interestingly, MKEY treatment led to a significant reduction of citrullinated histone 3 in the infarcted tissue, showing that MKEY can prevent neutrophil extracellular trap formation in vivo. Disrupting chemokine heterodimers during myocardial I/R might have clinical benefits, preserving the therapeutic benefit of blocking specific chemokines, and in addition, reducing the inflammatory side effects maintaining normal immune defence.

Exchange of extracellular domains of CCR1 and CCR5 reveals confined functions in CCL5-mediated cell recruitment.

The chemokine CCL5 recruits monocytes into inflamed tissues by triggering primarily CCR1-mediated arrest on endothelial cells, whereas subsequent spreading is dominated by CCR5. The CCL5-induced arrest can be enhanced by heteromer formation with CXCL4. To identify mechanisms for receptor-specific functions, we employed CCL5 mutants and transfectants expressing receptor chimeras carrying transposed extracellular regions. Mutation of the basic 50s cluster of CCL5, a coordinative site for CCL5 surface presentation, reduced CCR5- but not CCR1-mediated arrest and transmigration. Impaired arrest was restored by exchanging the CCR5-N-terminus for that of CCR1, which supported arrest even without the 50s cluster, whereas mutation of the basic 40s cluster essential for proteoglycan binding of CCL5 could not be rescued. The enhancement of CCL5-induced arrest by CXCL4 was mediated by CCR1 requiring its third extracellular loop. The domain exchanges did not affect formation and co-localisation of receptor dimers, indicating a sensing role of the third extracellular loop for hetero-oligomers in an arrest microenvironment. Our data identify confined targetable regions of CCR1 specialised to facilitate CCL5-induced arrest and enhanced responsiveness to the CXCL4-CCL5 heteromer.

Distinct functions of chemokine receptor axes in the atherogenic mobilization and recruitment of classical monocytes.

We used a novel approach of cytostatically induced leucocyte depletion and subsequent reconstitution with leucocytes deprived of classical (inflammatory/Gr1(hi) ) or non-classical (resident/Gr1(lo) ) monocytes to dissect their differential role in atheroprogression under high-fat diet (HFD). Apolipoprotein E-deficient (Apoe(-/-) ) mice lacking classical but not non-classical monocytes displayed reduced lesion size and macrophage and apoptotic cell content. Conversely, HFD induced a selective expansion of classical monocytes in blood and bone marrow. Increased CXCL1 levels accompanied by higher expression of its receptor CXCR2 on classical monocytes and inhibition of monocytosis by CXCL1-neutralization indicated a preferential role for the CXCL1/CXCR2 axis in mobilizing classical monocytes during hypercholesterolemia. Studies correlating circulating and lesional classical monocytes in gene-deficient Apoe(-/-) mice, adoptive transfer of gene-deficient cells and pharmacological modulation during intravital microscopy of the carotid artery revealed a crucial function of CCR1 and CCR5 but not CCR2 or CX3 CR1 in classical monocyte recruitment to atherosclerotic vessels. Collectively, these data establish the impact of classical monocytes on atheroprogression, identify a sequential role of CXCL1 in their mobilization and CCR1/CCR5 in their recruitment.

Platelets: key players in vascular inflammation.

Platelets play a crucial role in the physiology of the primary hemostasis and in the pathophysiological activity of arterial thrombosis, provide rapid protection against bleeding, and catalyze the formation of stable blood clots via the coagulation cascade. Over the past years, it has become clear that platelets are important, not only in hemostasis and thrombosis but also in inflammation and in distinct aspects of atherosclerosis. Nowadays, platelets are known to have a large variety of functions. Platelets are able to interact with a large variety of cell types, such as leukocytes, endothelial cells, and SMCs, and these interactions have been implicated in the pathophysiology of vascular inflammation. In addition, platelets carry a highly inflammatory payload and are able to transport, synthesize, and deposit cytokines, chemokines, and lipid mediators, thereby initiating and propagating atherosclerotic disease. In this review, the current state of the art of the proinflammatory functions in the context of atherosclerotic cardiovascular disease will be outlined.