miR126-mediated alteration of vascular integrity in Rett syndrome.

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in methyl-CpG binding protein 2 (MeCP2). MeCP2 is a non-cell type-specific DNA binding protein, and its mutation influences not only neural cells but also non-neural cells in the brain, including vasculature-associated endothelial cells. Vascular integrity is crucial for maintaining brain homeostasis, and its alteration may be linked to the pathology of neurodegenerative diseases, but a non-neurogenic effect, such as the relationship between vascular alteration and RTT pathogenesis, has not been shown. Here, we developed a microvascular network model using RTT patient-derived induced pluripotent stem (iPS) cells that carry the MeCP2[R306C] or MeCP2[R168X] mutation to investigate early developmental vascular impact. To expedite endothelial cell differentiation, doxycycline-inducible ETV2 expression vectors were inserted into the AAVS1 locus of RTT patient-derived iPS cells and their isogenic controls by CRISPR/Cas9. With these endothelial cells, we established a disease microvascular network and observed higher permeability in RTT microvascular networks than in isogenic controls, indicating that the barrier function is altered by MeCP2 mutation. Furthermore, by microRNA profiling and RNAseq, we found that hyperpermeability is associated with up-regulation of miR126-3p in RTT patient-derived endothelial cells and can be rescued by restoring miR126-3p levels. Overall, our findings point to miR126-3p-mediated vascular impairment in RTT patients and suggest potential therapeutic approaches for restoring function.