Increasing MeCP2 protein in Pitt-Hopkins syndrome model (Tcf4+/-) mice does not affect abnormal myelination but induces the generation of astrocytes.

Pitt-Hopkins syndrome (PTHS) is a rare neurodevelopmental disorder that results from loss-of-function (LOF) mutations in the Transcription Factor 4 (TCF4) gene. PTHS closely resembles Rett syndrome (RTT), another neurodevelopmental disorder caused by mutations in the gene encoding Methyl CpG Binding Protein 2 (MECP2). We have recently shown that increasing MeCP2 levels, either genetically or via a viral vector approach, normalizes reciprocal behavioral phenotypes observed in Tcf4+/- and MECP2-overexpressing animals; in the current manuscript, we show that behavioral rescue also extends to a contextual fear learning task. Tcf4 heterozygous and knock-in mouse lines exhibit consistent myelination abnormalities, with an arrest of oligodendrocytes (OLs) at an immature stage. To address the hypothesis that correction of myelination defects is the potential mechanism underlying the behavioral rescue induced by MeCP2 increases in Tcf4+/- animals, we performed RNA-sequencing and protein expression studies. These experiments revealed that increasing MeCP2 does not dramatically affect the transcriptional profile induced by heterozygosity at Tcf4, as well as vice-versa, and subsequent molecular experiments suggest that OL gene expression and molecular phenotypes in Tcf4+/- animals are unchanged in the presence of an MECP2 transgene. However, we also find increased levels of Olig2 and Gfap co-expressing cells in Tcf4+/- mice in the presence of the MECP2 transgene, as well as the presence of cells with astrocytic morphology in the brains of these animals, suggesting a potential interplay of MeCP2 and TCF4 in astrocyte development.