Modeling Rett syndrome with iPSCs-derived neurons

Rett syndrome is a severe neurodevelopmental disorder. The condition affects approximately one in every 10.000 females and is only rarely seen in males. Causative mutations in the transcriptional regulator MeCP2 have been identified in more than 95% of classic Rett patients; mutations in CDKL5 are responsible for the early onset seizures Rett variant and mutations in FOXG1 gene lead to the congenital Rett variant. To shed light on molecular mechanisms underlying Rett syndrome onset and progression in disease-relevant cells, we took advantage of the breakthrough genetic reprogramming technology and we investigated changes in iPSC-derived neurons from patients with different MECP2 and FOXG1 mutations and in the brain of Foxg1+/- mice. In total brains from Foxg1+/ − mutants we noticed a statistically significant overexpression of a group of neuropeptides expressed in the basal ganglia, cortex, hippocampus and hypothalamus: Oxytocin (Oxt), Arginine vasopressin (Avp) and Neuronatin (Nnat).Moreover, in iPSC-derived neuronal precursors and neurons mutated in FOXG1 and in Foxg1+/− mouse embryonic brain (E11.5) compared to wild type controls we found an increase in the expression of GluD1 and inhibitory synaptic markers, such as GAD67 and GABA AR-α1 and a decreased expression of excitatory synaptic markers, such as VGLUT1, GluA1, GluN1 and PSD-95, suggesting an excitation/inhibition imbalance in the developing brain of the congenital RTT variant. Furthermore, we investigated transcriptome changes in neurons differentiated from MECP2 mutated iPSC-derived neurons and we noticed a prominent GABAergic circuit disruption and a perturbation of cytoskeleton dynamics. In particular, in MECP2-mutated neurons we identified a significant decrease of acetylated α-tubulin which can be reverted by treatment with a selective inhibitor of HDAC6, the main α-tubulin deacetylase. Taken togheter, these findings contribute to shed light on Rett pathogenic mechanisms and provide hints for the definition of new therapeutic strategies for Rett syndrome.