Cell signaling in blood and lymphatic vessel malformation : insights into the mechanisms of human genetic diseases

Dysregulation of mechanisms controlling the development of the blood and the lymphatic vascular systems may cause structural abnormalities known as vascular malformations. These vascular malformations can be very limiting to the patients, not only because of symptomatology but also because of the social impact these anomalies have in their lives. Therefore, it is important to develop new therapies that can improve the quality of life of these patients.

An example of vascular malformation affecting the blood vasculature is the arteriovenous malformation (AVM), which is a direct shunt between arteries and veins. AVMs are a hallmark of Hereditary Hemorrhagic Telangiectasia (HHT), an autosomal dominant disease where patients suffer from frequent bleedings and cardiac problems. HHT is caused by mutations in different members of the BMP9/10 signaling cascade, that regulates homeostatic angiogenesis.

An abnormal vascular development can also cause lymphatic vessel overgrowth, like in Lymphangioleiomyomatosis (LAM), where patients can suffer from respiratory failure. LAM is caused by mutations in TSC1/2, an endogenous inhibitor of the mTORC1 pathway, that controls metabolism, cellular growth and proliferation.

Despite knowing some of the mutations causing vascular abnormalities, it remains unclear how these abnormalities arise. Increasing the knowledge about how vascular anomalies emerge is key to developing effective therapeutic approaches.

This thesis contributes to understanding the molecular mechanisms underlying AVM development. In Paper I, by using different mouse models of HHT and targeting the expression of different components of mTORC1 in endothelial cells (EC), we studied the contribution of EC mTORC1 to the development of AVMs and we concluded that, despite AVMs presented increased mTORC1 activity, EC mTORC1 is not driving either initiation or expansion of these malformations. In Paper III, by using a mosaic mouse model of HHT targeting endoglin (ENG) expression in ECs and single cell RNA sequencing, we studied the transcriptional changes associated with AVM development and we concluded that ENG modulation has a differential impact in the transcriptomes of arterial cells, tip cells and capillary ECs. The capillary ECs were the most affected by ENG modulation, which suggests they drive AVM development.

In Paper IV, we refined a clearing protocol for the eye and, through Light-Sheet Fluorescence Microscopy, obtained a 3D picture of the complete eye vasculature. In Paper II, we studied the development of abnormalities in lymphatic vessels. By targeting the expression of Tsc1 in ECs and lymphatic ECs (LECs), we studied the role of EC mTORC1 in the development of the dermal lymphatic vasculature and concluded that increased EC or LEC mTORC1 activity can cause overgrowth of the dermal lymphatic vasculature and abnormal collecting vessel development.

Taken together, the results presented in this thesis contribute to a better understanding of the molecular mechanisms underlying vascular malformations.

List of scientific papers

I. Antonio Queiro-Palou, Yi Jin and Lars Jakobsson. Genetic and pharmacological targeting of mTORC1 in mouse models of arteriovenous malformation expose non-cell autonomous signalling in HHT. Angiogenesis, 2025, 28, 6. https://doi.org/10.1007/s10456-024-09961-5

II. Antonio Queiro-Palou, Anna Kawaguchi, Taija Mäkinen and Lars Jakobsson. mTORC1-driven lymphatic vessel hyperplasia relies on active lymphangiogenesis. [Manuscript]

III. Maria Garcia-Collado, Antonio Queiro-Palou, Jaromir Mikes, Liqun He, Yi Jin, Christer Betsholtz, Lars Muhl, and Lars Jakobsson. Dissecting mechanisms of HHT-related arteriovenous malformation through single-cell transcriptomics. [Manuscript]

IV. Luc Thomas Krimpenfort, Maria Garcia-Collado, Tom van Leeuwen, Filippo Locri, Anna-Liisa Luik, Antonio Queiro-Palou, Shigeaki Kanatani, Helder André, Per Uhlen and Lars Jakobsson. Anatomy of the complete mouse eye vasculature explored by light- sheet fluorescence microscopy exposes subvascular-specific remodeling in development and pathology. Experimental Eye Research, 2023, 237. https://doi.org/10.1016/j.exer.2023.109674