CCN1/CYR61-mediated meticulous patrolling by Ly6C ^low monocytes fuels vascular inflammation

Abstract

Inflammation is characterized by the recruitment of leukocytes from the bloodstream. The rapid arrival of neutrophils is followed by a wave of inflammatory lymphocyte antigen 6 complex (Ly6C)-positive monocytes. In contrast Ly6C low monocytes survey the endothelium in the steady state, but their role in inflammation is still unclear. Here, using confocal intravital microscopy, we show that upon Toll-like receptor 7/8 (TLR7/8)-mediated inflammation of mesenteric veins, platelet activation drives the rapid mobilization of Ly6C low monocytes to the luminal side of the endothelium. After repeatedly interacting with platelets, Ly6C low monocytes commit to a meticulous patrolling of the endothelial wall and orchestrate the subsequent arrival and extravasation of neutrophils through the production of proinflammatory cytokines and chemokines. At a molecular level, we show that cysteine-rich protein 61 (CYR61)/CYR61 connective tissue growth factor nephroblastoma overexpressed 1 (CCN1) protein is released by activated platelets and enables the recruitment of Ly6C low monocytes upon vascular inflammation. In addition endothelium-bound CCN1 sustains the adequate patrolling of Ly6C low monocytes both in the steady state and under inflammatory conditions. Blocking CCN1 or platelets with specific antibodies impaired the early arrival of Ly6C low monocytes and abolished the recruitment of neutrophils. These results refine the leukocyte recruitment cascade model by introducing endothelium-bound CCN1 as an inflammation mediator and by demonstrating a role for platelets and patrolling Ly6C low monocytes in acute vascular inflammation.

Toll‐like receptors elicit different recruitment kinetics of monocytes and neutrophils in mouse acute inflammation

“…Agonists for TLR2 and TLR9 induced a strong early recruitment of crawling monocytes within 30 min of stimulation, and an early but weaker response with TLR5 ( Fig. 1A and B), as previously observed for TLR7/8 [6]. Conversely, agonists for TLR3 and TLR4 induced only a late arrival of patrolling monocytes, about 2.5 h after the initiation of inflammation ( Fig.…”

“…Our results show three kind of kinetics in mesenteric veins: (i) previously reported early recruitment of Ly6C low monocytes followed by late neutrophil arrival (TLR7/8) , (ii) early monocyte and neutrophil recruitment (TLR2, TLR5 and TLR9) and (c) early neutrophils followed by late and weak monocyte recruitment (TLR3 and TLR4).…”

“…Together our data show that CCN1 release and induction of meticulous patrolling does not result from direct TLR activation in platelets but from another thrombin‐activating system, as shown during TLR7/8‐mediated vascular inflammation .…”

“…C and D) in contrast to their late arrival in response to TLR7/8 (Fig. , ). Our data for TLR4 agree with previously published lack of Ly6C low monocyte recruitment in kidney capillaries .…”

Evaluation of Serum Cysteine-Rich Protein 61 levels in Patients with Coronary Artery Disease

“…On the other hand, Cyr61 is recognized as a mediator of inflammation [33,35]. Cyr61 enables monocytes recruitment upon vascular inflammation, and endothelial-bound Cyr61 sustains monocyte patrolling under inflammation condition, while blocking Cyr61, impairs early arrival of monocyte and abolishes neutrophil recruitment [34]. Other studies showed that Cyr61 promotes monocyte chemotaxis and macrophage migration, support macrophage adhesion and activates proinflammatory genetic program by activating NFκB-mediated transcription, and upregulating expression of cytokines and chemokines in macrophages [35,36], indicating an important role of Cyr61 in inflammatory responses and its essential role in atherosclerostic pathogenesis.…”