Epigenetic changes as a common trigger of muscle weakness in congenital myopathies

Area of Science:

• Molecular Biology
• Genetics
• Neurology

Background:

• Congenital myopathies are diverse genetic disorders causing severe muscle weakness.
• Mutations in the ryanodine receptor gene (RYR1) are the most common cause.
• Reduced ryanodine receptor 1 protein is a hallmark of recessive RYR1 mutations.

Purpose of the Study:

• To investigate the mechanisms behind reduced ryanodine receptor 1 protein in congenital myopathies.
• To explore the role of epigenetic factors in RYR1-related muscle disorders.

Main Methods:

• Analysis of muscle biopsies from patients with recessive RYR1 mutations.
• Expression analysis of muscle-specific microRNAs (miRNAs) and class II histone deacetylases (HDACs).
• DNA methylation analysis.
• Experiments using transgenic mouse muscle fibers and siRNA knockdown.

Main Results:

• Patients with recessive RYR1 mutations showed decreased muscle-specific miRNA expression, increased DNA methylation, and increased class II HDAC expression.
• Over-expression of HDAC-4/HDAC-5 in mouse muscle fibers led to decreased RYR1 and miRNA expression.
• Knockdown of RYR1 in mouse muscle fibers resulted in upregulation of HDAC-4/HDAC-5.
• Similar epigenetic changes were observed in patients with nemaline myopathy.

Conclusions:

• Epigenetic alterations, including changes in miRNAs and class II HDACs, contribute to reduced ryanodine receptor 1 protein in congenital myopathies.
• A common pathophysiological pathway involving epigenetic changes is implicated in certain congenital neuromuscular disorders.
• These findings offer potential therapeutic targets for RYR1-related myopathies and potentially other congenital neuromuscular disorders.