Contribution of Platelet CX ₃ CR1 to Platelet–Monocyte Complex Formation and Vascular Recruitment During Hyperlipidemia

Abstract

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. Conclusion-Platelets

Hyperreactivity of Junctional Adhesion Molecule A-Deficient Platelets Accelerates Atherosclerosis in Hyperlipidemic Mice

“…The endothelial cells were assembled in a flow chamber, and platelets were perfused for 20 minutes, followed by leukocytes for 5 minutes and additional washing of nonadherent cells (all at 0.15 N/m 2 ). 29 Cell adhesion was expressed as percentage surface coverage of platelets or leukocytes over multiple microscopic fields using ImageJ software (National Institutes of Health).…”

“…Activated platelets have been described to form complexes with leukocytes, 11,29 which might be relevant during acute coronary events. 35,36 To investigate whether JAM-A deficiency leads to increased interactions with leukocytes, activated platelets isolated from trJAM-A -/-apoe -/-mice were incubated with leukocytes.…”

Differential expression of the fractalkine chemokine receptor (CX3CR1) in human monocytes during differentiation

“…Accordingly, the importance of the CX 3 CR1-CX 3 CL1 axis in pathogenesis has been highlighted in several studies. It is involved in atherosclerosis, 26,[41][42]45,46 vascular and renal inflammation 37,48,53 and cancer, 50 it stimulates actin reorganization in microglia 49,54 and it promotes leukocyte-renal endothelial cell interactions during hemolytic uremic syndrome, thereby contributing to the renal microvascular dysfunction and thrombotic microangiopathy. 55,56 To improve our understanding of the biological role of the interaction between fractalkine and CX 3 CR1 in monocytic populations, we analyzed CX 3 CR1 surface protein expression as well as mRNA expression in freshly Mo, MAC and DC populations.…”

“…CX 3 CR1 is expressed on a number of leukocytes, including monocytes, T-cell subsets and NK cells, 24,25 and CX 3 CR1 expression has been recently described in platelets. 26 However, a comprehensive knowledge about CX 3 CR1 expression during monocyte differentiation and the intracellular signals and pathways that underlie this process have not been explored.…”

Neutrophils Usher Monocytes Into Sites of Inflammation

“…4,5 It is therefore not surprising that other cells (or, in the case of platelets, cell fragments) can act as chaperones for monocytes. Neutrophils are excellent chaperone candidates because they are among the first to respond and because they contain large quantities of preformed granular proteins.…”