{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,7,30]],"date-time":"2025-07-30T15:55:58Z","timestamp":1753890958640,"version":"3.41.2"},"reference-count":33,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2025,4,17]],"date-time":"2025-04-17T00:00:00Z","timestamp":1744848000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Immunol."],"abstract":"<jats:sec><jats:title>Background<\/jats:title><jats:p>Our group recently reported that chymase, a serine protease synthetized and released by mast cells, plays a pivotal role in thrombi stabilization in murine deep vein thrombosis (DVT) models, by interfering with the fibrinolytic properties of endogenous plasmin within thrombi. However, the impact of mast cell-derived chymase on endogenous plasmin activity in human blood clots has yet to be explored.<\/jats:p><\/jats:sec><jats:sec><jats:title>Methods<\/jats:title><jats:p>The antifibrinolytic properties of human recombinant chymase (rCMA-1) were investigated using an <jats:italic>in vitro<\/jats:italic> thrombolysis assay based on halo-shaped human blood clots. In addition, a fluorogenic assay was used to detect chymase activity in human thromboembolic biopsies. In both assays, the activity of human chymase was validated using a specific chymase inhibitor, fulacimstat (BAY 1142524).<\/jats:p><\/jats:sec><jats:sec><jats:title>Results<\/jats:title><jats:p>Although rapidly neutralized in plasma, rCMA-1 remains active within the local microenvironment of a blood clot, inducing resistance to endogenous plasmin-mediated fibrinolysis in the presence of recombinant tissue plasminogen activator (tPA). This leads to a concentration-dependent decrease in clot lysis by rCMA-1. The plasmin-inactivating properties of rCMA-1 were inhibited by fulacimstat, resulting in an accelerated clot dissolution. The pro-fibrinolytic effects of fulacimstat in human blood clots were reversed by a plasminogen\/plasmin inhibitor, BAY 1214237. Finally, fulacimstat-sensitive chymase activity was identified in thrombi collected from thrombectomy patients, supporting the potential role of the mast cell-derived serine protease in human blood clot stabilization under pathological conditions.<\/jats:p><\/jats:sec><jats:sec><jats:title>Conclusion<\/jats:title><jats:p>These <jats:italic>in vitro<\/jats:italic> experiments with human whole blood suggest that mast cell-derived chymase impairs blood clot resolution by interfering with the fibrinolytic activity of endogenous intra-clot plasmin. Our findings provide evidence that recombinant mast cell chymase interferes with endogenous plasmin activity in human whole blood clots <jats:italic>in vitro<\/jats:italic> and support the potential of chymase inhibitors, such as fulacimstat, as fibrinolytic agents for thrombotic and thromboembolic disorders.<\/jats:p><\/jats:sec>","DOI":"10.3389\/fimmu.2025.1511990","type":"journal-article","created":{"date-parts":[[2025,4,17]],"date-time":"2025-04-17T04:11:12Z","timestamp":1744863072000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Recombinant chymase inhibits fibrinolysis induced by endogenous plasmin in clotted human 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