OTULIN coordinates with LUBAC to edit linear polyubiquitin chains in embryonic development, autoimmunity, and inflammatory diseases. However, the mechanism by which angiogenesis, especially that of endothelial cells (ECs), is regulated by linear ubiquitination remains unclear. Here, we reveal that constitutive or EC-specific deletion of Otulin resulted in arteriovenous malformations and embryonic lethality. LUBAC conjugates linear ubiquitin chains onto Activin receptor-like kinase 1 (ALK1), which is responsible for angiogenesis defects, inhibiting ALK1 enzyme activity and Smad1/5 activation. Conversely, OTULIN deubiquitinates ALK1 to promote Smad1/5 activation. Consistently, embryonic survival of Otulin-deficient mice was prolonged by BMP9 pretreatment or EC-specific ALK1^Q200D (constitutively active) knockin. Moreover, mutant ALK1 from type 2 hereditary hemorrhagic telangiectasia (HHT2) patients exhibited excessive linear ubiquitination and increased HOIP binding. As such, a HOIP inhibitor restricted the excessive angiogenesis of ECs derived from ALK1^G309S-expressing HHT2 patients. These results show that OTULIN and LUBAC govern ALK1 activity to balance EC angiogenesis.

OTULIN 与 LUBAC 配合编辑胚胎发育、自身免疫和炎症性疾病中的线性多聚泛素链。然而，血管生成，尤其是内皮细胞（EC）血管生成受线性泛素化调节的机制仍不清楚。在这里，我们揭示了Otulin的组成型或 EC 特异性缺失会导致动静脉畸形和胚胎致死。 LUBAC 将线性泛素链缀合到激活素受体样激酶 1 (ALK1) 上，后者负责血管生成缺陷、抑制 ALK1 酶活性和 Smad1/5 激活。相反，OTULIN 使 ALK1 去泛素化，促进 Smad1/5 激活。一致地，BMP9 预处理或 EC 特异性ALK1 ^Q200D （组成型活性）敲入可延长Otulin缺陷小鼠的胚胎存活时间。此外，来自 2 型遗传性出血性毛细血管扩张症 (HHT2) 患者的突变ALK1表现出过度的线性泛素化和 HOIP 结合增加。因此，HOIP抑制剂限制源自表达ALK1 ^G309S的HHT2患者的EC的过度血管生成。这些结果表明 OTULIN 和 LUBAC 控制 ALK1 活性以平衡 EC 血管生成。