Interregulation between fragile X mental retardation protein and methyl CpG binding protein 2 in the mouse posterior cerebral cortex

Abstract

Several X-linked neurodevelopmental disorders including Rett Syndrome, induced by mutations in the MECP2 gene, and Fragile X Syndrome (FXS), caused by mutations in the FMR1 gene, share autism-related features. The mRNA coding for Methyl CpG binding protein 2 (MeCP2) has previously been identified as a substrate for the mRNA-binding protein Fragile X Mental Retardation Protein (FMRP), which is silenced in FXS. Here, we report a homeostatic relationship between these two key regulators of gene expression in mouse models of FXS (Fmr1 KO) and Rett syndrome (MeCP2 KO). We found that the level of MeCP2 protein in the cerebral cortex was elevated in Fmr1 KO mice, whereas MeCP2 KO mice displayed reduced levels of FMRP, implicating interplay between the activities of MeCP2 and FMRP. Indeed, knockdown of MeCP2 with short hairpin RNAs led to a reduction of FMRP in mouse Neuro2A and in human HEK-293 cells, suggesting a reciprocal coupling in the expression level of these two regulatory proteins. Intra-cerebroventricular injection of an adeno-associated viral vector coding for FMRP (AAV-FMRP) led to a concomitant reduction in MeCP2 expression in vivo, and partially corrected locomotor hyperactivity. Additionally, the level of MeCP2 in the posterior cortex correlated with the severity of the hyperactive phenotype in Fmr1 KO mice. These results demonstrate that MeCP2 and FMRP operate within a previously undefined homeostatic relationship. Our findings also suggest that MeCP2 overexpression in Fmr1 KO mouse posterior cerebral cortex may contribute to the fragile X locomotor hyperactivity phenotype.

Gene therapy using an ortholog of human fragile X mental retardation protein partially rescues behavioral abnormalities and EEG activity

“…The rationale was based on a general pattern of co-expression of FMRP and the transcription regulator MeCP2 in neurons and on the recently documented inter-regulation between the two proteins. 16 Using western blotting, we observed that at PND 30 in the frontal cortex of AAV-X3 injected rats, the expression level of the X3 transgene was higher than the combined expression of all of the endogenously expressed isoforms of FMRP in the WT. However, X3 expression declined by PND 70 (Figures 2D and 2E).…”

Rett Syndrome and Fragile X Syndrome: Different Etiology With Common Molecular Dysfunctions

“…Recently, it was reported that MeCP2 expression is elevated in Fmr1 KO mice cerebral cortex, while FMRP levels are reduced in mice mutants for Mecp2 (Arsenault et al, 2020). This reciprocal relationship was confirmed using MeCP2 knockdown mouse N2A, and human HEK-293 cells lines (Arsenault et al, 2020). MeCP2 association with FMR1 gene has been shown in silico (Bach et al, 2020).…”

“…These commonalities can be explained by the interplay between MeCP2 and FMRP, and by the common targets between both molecules. Recently, it was reported that MeCP2 expression is elevated in Fmr1 KO mice cerebral cortex, while FMRP levels are reduced in mice mutants for Mecp2 (Arsenault et al, 2020). This reciprocal relationship was confirmed using MeCP2 knockdown mouse N2A, and human HEK-293 cells lines (Arsenault et al, 2020).…”

Target-agnostic discovery of Rett Syndrome therapeutics by coupling computational network analysis and CRISPR-enabled in vivo disease modeling

“…Interestingly, analysis of gene co-expression networks identified substantial reorganization from control animals ( 1 ) following MeCP2 knock down ( 1 ), characterized by a loss of strong connectivity among genes involved in the regulation of MeCP2 (FMR1 and TRKB receptor NTRK2 19, 20 ), neuronal development (BDNF 21, 22 ),, and circadian rhythm (PER1, PER2 23 ) all of which are altered in Rett patients 21, 24 . Notably, after MeCP2 knock down, BDNF strengthened as a network hub and exhibited greater co-expression connectivity amongst gene nodes ( 1 ).…”