Platelets-driven monocyte activation promotes hypoxic thromboinflammation through the HIF-1α-NLRP3-EGR-1 axis.

Abstract

Hypoxia exacerbates thromboembolism and sterile inflammation through NLRP3 inflammasome, which is directly activated by HIF-1α that plays a pivotal role in potentiating deep vein thrombosis (DVT). One of the clinical manifestations of thromboinflammation is DVT, characterized by formation and propagation of clot in the lower extremity of the body. The underlying inflammatory milieu promotes immune cell recruitment and platelet hyperactivation, further promoting a prothrombotic state. However, the intricate relationship between hypoxia, thromboembolism, and sterile inflammation is not fully understood. To address this knowledge gap, we integrated in vitro cell lines, ex vivo human primary blood mononuclear cells (hPBMCs), in vivo animal models, and human patient-based studies to uncover the role of cellular interactions in driving hypoxia-induced thrombosis. We identified the early mechanistic insights and subsequently tested the translational potential in human samples who developed DVT at high altitudes (altitude >11,000 feet). Our investigation revealed that hypoxia increased monocyte adhesion to endothelial surface, mediated through CD11a/CD18 (β2 integrin) and F11R (Junctional adhesion molecule-1; JAM-1). We identified the significance of the HIF-1α- NLRP3-Egr1-TF/FVII axis in inflammation-induced coagulation under sterile conditions operating through NLRP3 elevating Egr-1, which subsequently augments tissue factor. This axis increases platelet hyperactivation and platelets' association amplifying thromboinflammation. Human patients who developed high altitude thrombosis revealed enhanced HIF-1α, NLRP3, Egr1, and TF/FVII levels, confirming clinical relevance. Finally, abrogating these molecules either with pharmacological inhibitors or siRNAs have demonstrated a potential to reverse these pathophysiological processes. These finding identify the HIF-1α-NLRP3-Egr1-TF/FVII axis as a potential therapeutic target for mitigating hypoxia induced thromboinflammation.