CLEC-2 Prevents Accumulation and Retention of Inflammatory Macrophages During Murine Peritonitis

Abstract

Platelets play a key role in the development, progression and resolution of the inflammatory response during sterile inflammation and infection, although the mechanism is not well understood. Here we show that platelet CLEC-2 reduces tissue inflammation by regulating inflammatory macrophage activation and trafficking from the inflamed tissues. The immune regulatory function of CLEC-2 depends on the expression of its ligand, podoplanin, upregulated on inflammatory macrophages and is independent of platelet activation and secretion. Mechanistically, platelet CLEC-2 and also recombinant CLEC-2-Fc accelerates actin rearrangement and macrophage migration by increasing the expression of podoplanin and CD44, and their interaction with the ERM proteins. During ongoing inflammation, induced by lipopolysaccharide, treatment with rCLEC-2-Fc induces the rapid emigration of peritoneal inflammatory macrophages to mesenteric lymph nodes, thus reducing the accumulation of inflammatory macrophages in the inflamed peritoneum. This is associated with a significant decrease in pro-inflammatory cytokine, TNF-α and an increase in levels of immunosuppressive, IL-10 in the peritoneum. Increased podoplanin expression and actin remodelling favour macrophage migration towards CCL21, a soluble ligand for podoplanin and chemoattractant secreted by lymph node lymphatic endothelial cells. Macrophage efflux to draining lymph nodes induces T cell priming. In conclusion, we show that platelet CLEC-2 reduces the inflammatory phenotype of macrophages and their accumulation, leading to diminished tissue inflammation. These immunomodulatory functions of CLEC-2 are a novel strategy to reduce tissue inflammation and could be therapeutically exploited through rCLEC-2-Fc, to limit the progression to chronic inflammation.

Platelet‐inspired nanomedicine in hemostasis thrombosis and thromboinflammation

“…98,99 Beside its prothrombotic role, CLEC-2-podoplanin interaction has also been implicated in acute respiratory distress syndrome (ARDS), sepsis and peritoinitis in mice. [100][101][102] Such findings suggest the therapeutic potential of targeting CLEC-2 and GPVI interactions to regulate thrombosis and thromboinflammation. Emerging research during the current COVID-19 pandemic has revealed that COVID-19 patients have hyperactive and procoagulant platelets, as well as platelet-leukocyte aggregates characteristic of thr omboinflammation.…”

“…Recently, platelet ITAM receptors C‐type lectin‐like receptor 2 (CLEC‐2) and GPVI have emerged as novel targets in thromboinflammatory diseases, due to the finding that CLEC‐2 interaction with its ligand podoplanin promotes venous thrombosis 98,99 . Beside its prothrombotic role, CLEC‐2‐podoplanin interaction has also been implicated in acute respiratory distress syndrome (ARDS), sepsis and peritoinitis in mice 100–102 . Such findings suggest the therapeutic potential of targeting CLEC‐2 and GPVI interactions to regulate thrombosis and thromboinflammation.…”

The Role of Podoplanin in the Immune System and Inflammation

“… 36 Moreover, Bourne et al reported that crosslinking podoplanin using recombinant CLEC-2-Fc limited the inflammatory environment by reducing inflammatory macrophage accumulation in the inflamed tissue during murine peritonitis. 37 Platelet CLEC-2 induces a loss of phosphorylation of the serine residues in the intracellular podoplanin tail, which is associated with a rapid translocation of podoplanin from intracellular stores to the surface of inflammatory macrophages. 38 Additionally, the interaction between podoplanin and CLEC-2 induced the reorganisation of the actin cytoskeleton and increased podoplanin interaction with ERM proteins and CD44, promoting macrophage migration.…”

“… 38 Additionally, the interaction between podoplanin and CLEC-2 induced the reorganisation of the actin cytoskeleton and increased podoplanin interaction with ERM proteins and CD44, promoting macrophage migration. 37 Cheok et al also proposed that during Helicobacter pylori infection, podoplanin drives motility of active macrophages via regulating Filamin C, a member of actin-crosslinking protein family that stabilizes and links actin web to the cell membrane. 39 , 40 They demonstrated that podoplanin may promote Filamin C transactivation through interacting with the ERM complex and activating Rho GTPase signaling pathway, but further investigation is required to confirm this notion.…”

Platelet CLEC2-Podoplanin Axis as a Promising Target for Oral Cancer Treatment

“…It has been reported that the CLEC2-PDPN axis can regulate cell contractility and migration through activation of ERM proteins in non-cancerous settings ( 153 – 155 ). In this regard, it is plausible that the PDPN-ERM axis could be recruited by tumors bound to platelets via CLEC2-PDPN interaction, conferring cancer cells metastatic potentials ( Figure 1 ).…”