# Endothelial Cell‐Specific Molecule‐1 (ESM1): An Endogenous Anticoagulant and Protective Factor in Venous Thrombosis

## TL;DR

ESM1 is a natural anticoagulant that prevents blood clots in veins by activating HCII, offering a new therapeutic target for treating venous thrombosis.

## Contribution

ESM1 is newly identified as an endogenous anticoagulant that activates HCII through its glycosaminoglycans.

## Key findings

- ESM1 deficiency causes vascular occlusion in zebrafish and mice, while overexpression reduces venous thrombosis.
- ESM1's anticoagulant effect relies on its glycosaminoglycans activating heparin cofactor II (HCII).
- Human ESM1 protein rescues coagulation defects in Esm1 knockout mice.

## Abstract

Deficiencies in endogenous anticoagulation pathways can lead to vascular occlusion and thrombosis. Endothelial cell‐specific molecule‐1 (ESM1), a proteoglycan secreted by endothelial cells, is elevated in patients with venous thromboembolism (VTE), yet its role in coagulation regulation remains undefined. Serum ESM1 concentrations are significantly higher in individuals with VTE (498.54 pg/mL) than in healthy controls (198.68 pg/mL), and the combination of ESM1 and D‐dimer increases diagnostic discrimination. The anticoagulant potential of ESM1 is assessed using time‐to‐occlusion (TTO) assays in zebrafish and mouse models, complemented by in vitro analyses of endogenous thrombin inhibitor activation. The anticoagulant effect of recombinant human ESM1 was further examined in mouse model. Loss of esm1 in zebrafish results in vascular occlusion in the cardinal vein, whereas esm1 overexpression dose‐dependently reduces venous thrombosis and prolongs TTO. Similarly, Esm1 knockout in mice leads to an alteration of coagulation function, which is rescued by human ESM1 protein. Mechanistically, ESM1's anticoagulant function is found to rely on its covalently linked glycosaminoglycans (GAGs), which activate the thrombin inhibitor heparin cofactor II (HCII). This study uncovers a novel function of ESM1 in anticoagulation through HCII activation, highlighting its potential as a therapeutic target for preventing venous thrombus formation.

This study identifies ESM1 as an endogenous anticoagulant that modulates venous thrombosis. It shows that ESM1 deficiency triggers vascular occlusion in zebrafish and mice, whereas its restoration or overexpression prolongs clot‐formation time. Mechanistic analyses reveal that ESM1 activates HCII through its dermatan‐sulfate chain, uncovering a previously unrecognized pathway for thrombin inhibition and a potential therapeutic target.