Clots Are Potent Triggers of Inflammatory Cell Gene Expression: Indications for Timely Fibrinolysis

Objective: Blood vessel wall damage often results in the formation of a fibrin clot that traps inflammatory cells, including monocytes. The effect of clot formation and subsequent lysis on the expression of monocyte-derived genes involved in the development and progression of ischemic stroke and other vascular diseases, however, is unknown. Determine if clot formation and lysis regulates the expression of human monocyte-derived genes that modulate vascular diseases.Approach and Results: We performed Next Generation RNA sequencing on monocytes extracted from whole blood clots. Thousands of mRNAs were differentially expressed by monocytes from clotted versus unclotted whole blood, including upregulation of interleukin 8 (IL-8) and monocyte chemoattractant protein-1 (MCP-1). Clotted plasma also increased expression of IL-8 and MCP-1, which far exceeded responses observed in LPS-stimulated monocytes. Upregulation of IL-8 and MCP-1 occurred in a thrombin-independent, but fibrin-dependent manner. Fibrinolysis initiated shortly after plasma clot formation (i.e., 1-2 hours) reduced the synthesis of IL-8 and MCP-1, while delayed fibrinolysis was far less effective. Consistent with these in vitro models, monocytes embedded in unresolved thrombi from patients undergoing thrombectomy stained positively for IL-8 and MCP-1.Conclusions: These findings demonstrate that clots are potent inducers of monocyte gene expression, and that timely fibrinolysis attenuates inflammatory responses, specifically with IL-8 and MCP-1. Dampening of inflammatory gene expression by timely clot lysis may contribute to the clinically-proven efficacy of fibrinolytic drug treatment within hours of stroke onset.