BACKGROUND Arteriovenous malformations (AVMs) are characteristic of hereditary hemorrhagic telangiectasia. Loss-of-function mutations in the activin receptor-like kinase 1 (Alk1) are linked to hemorrhagic telangiectasia type 2. METHODS Endothelial-specific deletion of Alk1, endothelial lineage tracing, transcriptomics of single-cell analysis, and electron microscopy were performed to examine the vascular phenotype and characteristics of ALK1-deficient endothelial cells (ECs) after EC-specific Alk1 deletion. Ischemia assays were used to examine the cell capacity for vascular malformation. Connectivity Map with transcriptomic analysis was applied to identify chemical compounds. Specific methods for arteriovenous malformations, such as micro-computed tomography, with other molecular and cell biological tools were also performed. RESULTS We performed endothelial-specific deletion of Alk1 in mice and found severe arteriovenous malformations and vascular leakage. The transcriptomics of single-cell analysis revealed a new distinctive cell cluster formed after Alk1 deletion where the cells coexpressed arterial and lymphatic endothelial markers. The analysis projected that these cells potentially originated from arterial ECs after Alk1 deletion. This new population was referred to as arterial-lymphatic-like ECs according to its cellular markers, and its appearance was validated in the pulmonary small arteries after Alk1 deletion. Transplantation of these cells caused vascular malformations. Endothelial lineage tracing confirmed that these new arterial-lymphatic-like ECs were derived from ALK1 depleted ECs, potentially arterial ECs. We discovered that SOX17 (SRY-box transcription factor 17) induction was responsible for the derivation of these arterial-lymphatic-like ECs. We showed that direct binding of MDM2 (mouse double minute 2) was required for Sox17 to execute this activity. Inhibition of MDM2 reduced the arteriovenous malformations in the mouse model. CONCLUSIONS Together, our studies revealed the mechanistic underpinnings of ALK1 signaling in regulating the endothelial phenotype and provided possibilities for new therapeutic strategies in hemorrhagic telangiectasia type 2.

中文翻译：

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动脉淋巴样内皮细胞出现在遗传性出血性毛细血管扩张症 2 中，并导致血管渗漏和动静脉畸形。


背景 动静脉畸形 （AVM） 是遗传性出血性毛细血管扩张症的特征。激活素受体样激酶 1 （Alk1） 的功能丧失突变与 2 型出血性毛细血管扩张症有关。方法 进行 Alk1 内皮特异性缺失、内皮谱系示踪、单细胞分析转录组学和电子显微镜检查，以检查 EC 特异性 Alk1 缺失后 ALK1 缺陷内皮细胞 （ECs） 的血管表型和特征。缺血测定用于检查血管畸形的细胞容量。应用带有转录组学分析的连通图来识别化合物。还使用了其他分子和细胞生物工具治疗动静脉畸形的特定方法，例如显微计算机断层扫描。结果 我们在小鼠中进行了 Alk1 的内皮特异性缺失，发现严重的动静脉畸形和血管渗漏。单细胞分析的转录组学揭示了 Alk1 缺失后形成的一个新的独特细胞簇，其中细胞共表达动脉和淋巴内皮标志物。分析预测这些细胞可能起源于 Alk1 缺失后的动脉 EC。根据其细胞标志物，这个新群体被称为动脉淋巴样 EC，其外观在 Alk1 缺失后在肺小动脉中得到验证。这些细胞的移植导致血管畸形。内皮谱系追踪证实，这些新的动脉淋巴样 ECs 来源于 ALK1 耗尽的 EC，可能是动脉 EC。我们发现 SOX17 （SRY-box 转录因子 17） 诱导负责这些动脉淋巴样 ECs 的衍生。 我们发现 Sox17 需要直接结合 MDM2 （小鼠双分钟 2） 才能执行此活动。抑制 MDM2 可减少小鼠模型中的动静脉畸形。结论 我们的研究共同揭示了 ALK1 信号转导在调节内皮表型中的机制基础，并为 2 型出血性毛细血管扩张症的新治疗策略提供了可能性。