Mural cell-derived chemokines provide a protective niche to safeguard vascular macrophages and limit chronic inflammation.

Maladaptive, non-resolving inflammation contributes to chronic inflammatory diseases such as atherosclerosis. Because macrophages remove necrotic cells, defective macrophage programs can promote chronic inflammation with persistent tissue injury. Here, we investigated the mechanisms sustaining vascular macrophages. Intravital imaging revealed a spatiotemporal macrophage niche across vascular beds alongside mural cells (MCs)-pericytes and smooth muscle cells. Single-cell transcriptomics, co-culture, and genetic deletion experiments revealed MC-derived expression of the chemokines CCL2 and MIF, which actively preserved macrophage survival and their homeostatic functions. In atherosclerosis, this positioned macrophages in viable plaque areas, away from the necrotic core, and maintained a homeostatic macrophage phenotype. Disruption of this MC-macrophage unit via MC-specific deletion of these chemokines triggered detrimental macrophage relocalizing, exacerbated plaque necrosis, inflammation, and atheroprogression. In line, CCL2 inhibition at advanced stages of atherosclerosis showed detrimental effects. This work presents a MC-driven safeguard toward maintaining the homeostatic vascular macrophage niche.

Distinct Pathogenesis of Pancreatic Cancer Microvesicle-Associated Venous Thrombosis Identifies New Antithrombotic Targets In Vivo.

OBJECTIVE: Cancer patients are at high risk of developing deep venous thrombosis (DVT) and venous thromboembolism, a leading cause of mortality in this population. However, it is largely unclear how malignant tumors drive the prothrombotic cascade culminating in DVT. APPROACH AND RESULTS: Here, we addressed the pathophysiology of malignant DVT compared with nonmalignant DVT and focused on the role of tumor microvesicles as potential targets to prevent cancer-associated DVT. We show that microvesicles released by pancreatic adenocarcinoma cells (pancreatic tumor-derived microvesicles [pcMV]) boost thrombus formation in a model of flow restriction of the mouse vena cava. This depends on the synergistic activation of coagulation by pcMV and host tissue factor. Unlike nonmalignant DVT, which is initiated and propagated by innate immune cells, thrombosis triggered by pcMV was largely independent of myeloid leukocytes or platelets. Instead, we identified externalization of the phospholipid phosphatidylethanolamine as a major mechanism controlling the prothrombotic activity of pcMV. Disrupting phosphatidylethanolamine-dependent activation of factor X suppressed pcMV-induced DVT without causing changes in hemostasis. CONCLUSIONS: Together, we show here that the pathophysiology of pcMV-associated experimental DVT differs markedly from innate immune cell-promoted nonmalignant DVT and is therefore amenable to distinct antithrombotic strategies. Targeting phosphatidylethanolamine on tumor microvesicles could be a new strategy for prevention of cancer-associated DVT without causing bleeding complications.

Disulfide HMGB1 derived from platelets coordinates venous thrombosis in mice.

Deep venous thrombosis (DVT) is one of the most common cardiovascular diseases, but its pathophysiology remains incompletely understood. Although sterile inflammation has recently been shown to boost coagulation during DVT, the underlying molecular mechanisms are not fully resolved, which could potentially identify new anti-inflammatory approaches to prophylaxis and therapy of DVT. Using a mouse model of venous thrombosis induced by flow reduction in the vena cava inferior, we identified blood-derived high-mobility group box 1 protein (HMGB1), a prototypical mediator of sterile inflammation, to be a master regulator of the prothrombotic cascade involving platelets and myeloid leukocytes fostering occlusive DVT formation. Transfer of platelets into Hmgb1-/- chimeras showed that this cell type is the major source of HMGB1, exposing reduced HMGB1 on their surface upon activation thereby enhancing the recruitment of monocytes. Activated leukocytes in turn support oxidation of HMGB1 unleashing its prothrombotic activity and promoting platelet aggregation. This potentiates the amount of HMGB1 and further nurtures the accumulation and activation of monocytes through receptor for advanced glycation end products (RAGE) and Toll-like receptor 2, leading to local delivery of monocyte-derived tissue factor and cytokines. Moreover, disulfide HMGB1 facilitates formation of prothrombotic neutrophil extracellular traps (NETs) mediated by RAGE, exposing additional HMGB1 on their extracellular DNA strands. Eventually, a vicious circle of coagulation and inflammation is set in motion leading to obstructive DVT formation. Therefore, platelet-derived disulfide HMGB1 is a central mediator of the sterile inflammatory process in venous thrombosis and could be an attractive target for an anti-inflammatory approach for DVT prophylaxis.