Controlled Induction of ALK1 in ACVRL1-null hiPSC-derived Endothelial Cells Provides Insight into Organ-Restricted AVMs in HHT

van Kampen, S. J.; Blanch-Asensio, A.; Gallant, J. L.; van der Vaart, B.; Freund, C. M. A. H.; Davis, R. P.; Mummery, C. L.; Orlova, V. V.

doi:10.1101/2025.08.22.671484

bioRxiv · 10.1101/2025.08.22.671484

Controlled Induction of ALK1 in ACVRL1-null hiPSC-derived Endothelial Cells Provides Insight into Organ-Restricted AVMs in HHT

van Kampen, S. J.·Blanch-Asensio, A.·Gallant, J. L.·van der Vaart, B.·Freund, C. M. A. H.·Davis, R. P.·Mummery, C. L.·Orlova, V. V.

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Abstract

Genetic alterations in activin receptor-like kinase 1 (ACVRL1, ALK1) are linked to hereditary hemorrhagic telangiectasia (HHT), a condition characterized by hemorrhages, arteriovenous malformations (AVMs) and endothelial cell (EC) dysfunction. Haploinsufficiency is considered the central disease-driving mechanism, but it remains unclear why vascular lesions are tissue-restricted. To investigate whether ACVRL1 gene dosage in human ECs plays a role in organ-specific susceptibility, we developed a tunable human in vitro model by deleting ACVRL1 in human induced pluripotent stem cells (hiPSCs), and then reintroduced wild-type ACVRL1 under control of a doxycycline-inducible promoter. This enabled temporal, dose-dependent induction of ALK1 expression in ECs, allowing definition of threshold levels required to restore endothelial function and support vascular homeostasis. ALK1-deficient hiPSC-ECs displayed disrupted SMAD1/5 signaling, hyperproliferation, altered tip/stalk cell specification, and dysregulated transcriptional programs. Even low-level reinduction of ALK1 was sufficient to restore endothelial function, indicating threshold-dependence for ALK1 in vascular homeostasis. These data indicated that one mechanism underlying tissue-restricted prevalence of AVMs in vascular beds with low basal ACVRL1 expression, such as the liver, is a minimal requirement for ALK1 in sustaining EC functionality. This tunable human platform offers a powerful tool for dissecting HHT pathobiology and a platform for identifying strategies to restore ALK1 signaling therapeutically in affected tissues.

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van Kampen, S. J., Blanch-Asensio, A., Gallant, J. L., van der Vaart, B., Freund, C. M. A. H., Davis, R. P., Mummery, C. L., Orlova, V. V.. 2025-08-27. Controlled Induction of ALK1 in ACVRL1-null hiPSC-derived Endothelial Cells Provides Insight into Organ-Restricted AVMs in HHT. https://doi.org/10.1101/2025.08.22.671484

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