Origin of Serpin-Mediated Regulation of Coagulation and Blood Pressure

Vertebrates evolved an endothelium-lined hemostatic system and a pump-driven pressurized circulation with a finely-balanced coagulation cascade and elaborate blood pressure control over the past 500 million years. Genome analyses have identified principal components of the ancestral coagulation system, however, how this complex trait was originally regulated is largely unknown. Likewise, little is known about the roots of blood pressure control in vertebrates. Here we studied three members of the serpin superfamily that interfere with procoagulant activity and blood pressure of lampreys, a group of basal vertebrates. Angiotensinogen from these jawless fish was found to fulfill a dual role by operating as a highly selective thrombin inhibitor that is activated by heparin-related glycosaminoglycans, and concurrently by serving as source of effector peptides that activate type 1 angiotensin receptors. Lampreys, uniquely among vertebrates, thus use angiotensinogen for interference with both coagulation and osmo- and pressure regulation. Heparin cofactor II from lampreys, in contrast to its paralogue angiotensinogen, is preferentially activated by dermatan sulfate, suggesting that these two serpins affect different facets of thrombin’s multiple roles. Lampreys also express a lineage-specific serpin with anti-factor Xa activity, which demonstrates that another important procoagulant enzyme is under inhibitory control. Comparative genomics suggests that orthologues of these three serpins were key components of the ancestral hemostatic system. It appears that, early in vertebrate evolution, coagulation and osmo- and pressure regulation crosstalked through antiproteolytically active angiotensinogen, a feature that was lost during vertebrate radiation, though in gnathostomes interplay between these traits is effective.在过去5亿年的演化历程中，脊椎动物逐渐形成了由内皮衬里的止血系统（endothelium-lined hemostatic system）与泵驱动的加压循环系统，并演化出精细平衡的凝血级联反应（coagulation cascade）与精密的血压调控机制。基因组分析已确定了祖先凝血系统的主要组成成分，但目前对于这一复杂性状的原始调控机制仍知之甚少。同样，关于脊椎动物血压调控的起源，我们的认知也极为有限。本研究针对丝氨酸蛋白酶抑制剂（serpin）超家族的三个成员展开分析，这些成员可调控七鳃鳗（lampreys）——一类基底脊椎动物——的促凝血活性与血压水平。研究发现，这类无颌鱼类的血管紧张素原（angiotensinogen）兼具双重功能：一方面可作为高选择性凝血酶（thrombin）抑制剂，经肝素类糖胺聚糖（heparin-related glycosaminoglycans）激活；另一方面可作为效应肽的前体，激活1型血管紧张素受体（type 1 angiotensin receptors）。因此，七鳃鳗是脊椎动物中独有的类群，可通过血管紧张素原同时调控凝血过程与渗透压及血压稳态。与旁系同源蛋白血管紧张素原不同，七鳃鳗的肝素辅因子II（heparin cofactor II）优先被硫酸皮肤素（dermatan sulfate）激活，这表明这两种丝氨酸蛋白酶抑制剂可分别作用于凝血酶多种功能的不同层面。七鳃鳗还表达一种谱系特异性的丝氨酸蛋白酶抑制剂，具备抗Xa因子活性（anti-factor Xa activity），这证明另一种关键促凝血酶也处于抑制性调控之下。比较基因组学分析表明，这三种丝氨酸蛋白酶抑制剂的直系同源基因（orthologues）是祖先止血系统的关键组成部分。由此可见，在脊椎动物演化早期，凝血过程与渗透压及血压调控可通过具有蛋白水解抑制活性的血管紧张素原实现交叉对话，但这一特征在脊椎动物辐射演化过程中逐渐丢失——不过在有颌脊椎动物（gnathostomes）中，这两类性状的相互调控依然有效。