Aberrant protein citrullination is associated with many pathologies; however, the specific effects of this modification remain unknown. We have previously demonstrated that serine protease inhibitors (SERPINs) are highly citrullinated in rheumatoid arthritis (RA) patients. These citrullinated SERPINs include antithrombin, antiplasmin, and t-PAI, which regulate the coagulation and fibrinolysis cascades. Notably, citrullination eliminates their inhibitory activity. Here, we demonstrate that citrullination of antithrombin and t-PAI impairs their binding to their cognate proteases. By contrast, citrullination converts antiplasmin into a substrate. We recapitulate the effects of SERPIN citrullination using in vitro plasma clotting and fibrinolysis assays. Moreover, we show that citrullinated antithrombin and antiplasmin are increased and decreased in a deep vein thrombosis (DVT) model, accounting for how SERPIN citrullination shifts the equilibrium toward thrombus formation. These data provide a direct link between increased citrullination and the risk of thrombosis in autoimmunity and indicate that aberrant SERPIN citrullination promotes pathological thrombus formation.

异常的蛋白质瓜氨酸化与许多病症有关；但是，这种修改的具体效果仍然未知。我们之前已经证明丝氨酸蛋白酶抑制剂 (SERPIN) 在类风湿性关节炎 (RA) 患者中高度瓜氨酸化。这些瓜氨酸化 SERPIN 包括抗凝血酶、抗纤溶酶和 t-PAI，它们调节凝血和纤维蛋白溶解级联反应。值得注意的是，瓜氨酸化消除了它们的抑制活性。在这里，我们证明抗凝血酶和 t-PAI 的瓜氨酸化会损害它们与其同源蛋白酶的结合。相反，瓜氨酸化将抗纤溶酶转化为底物。我们使用体外概括了 SERPIN 瓜氨酸化的作用血浆凝固和纤维蛋白溶解测定。此外，我们表明瓜氨酸化抗凝血酶和抗纤溶酶在深静脉血栓形成 (DVT) 模型中增加和减少，解释了 SERPIN 瓜氨酸化如何将平衡转向血栓形成。这些数据提供了瓜氨酸化增加与自身免疫性血栓形成风险之间的直接联系，并表明异常的 SERPIN 瓜氨酸化促进了病理性血栓形成。