MECP2 truncating mutations cause histone H4 hyperacetylation in Rett syndrome

Area of Science:

• Neuroscience
• Genetics
• Epigenetics

Background:

• Rett syndrome (RTT) is a neurodevelopmental disorder affecting females, characterized by developmental regression, loss of speech, and seizures.
• RTT is primarily caused by mutations in the MECP2 gene, located on the X chromosome.
• MeCP2 protein regulates gene expression through DNA binding and recruitment of transcriptional silencing complexes, leading to chromatin condensation.

Purpose of the Study:

• To investigate the impact of common truncating MECP2 mutations (R168X and 803delG) on MeCP2 protein expression and global histone acetylation.
• To determine the specific histone acetylation changes associated with the absence of functional MeCP2 protein in RTT.

Main Methods:

• Analysis of mutant MeCP2 expression in clonal cell cultures from RTT patients (female R168X and male 803delG).
• Western blot analysis using antibodies against acetylated histones H3 and H4.
• Investigation of specific acetylated lysine residues on histone H4 using targeted antibodies.

Main Results:

• Truncating MECP2 mutations (R168X, 803delG) produced stable RNA but no intact MeCP2 protein.
• Histone H4, but not H3, showed hyperacetylation in cells with mutant MECP2 alleles.
• The observed H4 hyperacetylation was specifically linked to increased acetylation at lysine 16 (H4K16).

Conclusions:

• Expression of endogenous truncating MECP2 alleles, without functional MeCP2 protein, is associated with H4K16 hyperacetylation.
• This epigenetic alteration may lead to overexpression of MeCP2 target genes, contributing to RTT pathogenesis.
• H4K16 acetylation represents a potential therapeutic target for Rett syndrome.