Figure 8. Model of brain cavernoma development based on the scRNA-seq analysis of Pdcd10-ko brain endothelial cells complemented with the findings obtained by immunofluorescence microscopy and spatial transcriptomics (Visium).

Brain ECs (gray) are a heterogeneous population distributed in different clusters on the basis of their gene expression in both Pdcd10-wt (A) and Pdcd10-ko (B). Besides arterial, arterial capillary, venous, venous-capillary also tip cell and mitotic endothelial clusters could be detected at the developmental stage examined, P8 (orange and light blue , respectively). Besides, tip-like cells could be recognized morphologically (yellow). They are significantly increased in Pdcd10-ko, but their transcriptomic features remain to be studied. Resident endothelial cell progenitor cells (pink) were detected in all clusters, although in different proportions, which indicates that they are heterogeneous and share several transcriptional features with the ECs of the vessels where they reside. In (A) dashed square on the left is enlarged for the image on the right. (B) Although Pdcd10 deletion takes place comparably in arterial and venous ECs, only venous ECs can respond to Pdcd10 deletion. Pdcd10-ko venous cells follow defective differentiation and angiogenic programs, with abnormal tip cell traits and increased mitosis, giving rise to cavernous branching and mulberry lesions. Moreover, the venous compartment responds to Pdcd10 deletion with increased numbers and expression levels of venous resident endothelial cell progenitors. Arterial ECs are instead resilient to Pdcd10 deletion. It appears that the resistance of these cells is maintained by a relatively large set of putative defensive genes, some of which modulated by Pdcd10 deletion. In parallel, endothelial progenitor cells within arterial cluster C8 neither increased in number nor were transcriptionally modified by Pdcd10 deletion.