Actin mutations in hypertrophic and dilated cardiomyopathy cause inefficient protein folding and perturbed filament formation

Area of Science:

• Molecular Biology
• Cardiovascular Genetics
• Protein Biochemistry

Background:

• Hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) are common inherited heart conditions linked to sudden cardiac death.
• Mutations in alpha-cardiac actin are implicated in both HCM and DCM, but the precise molecular mechanisms remain unclear.

Purpose of the Study:

• To investigate the role of protein folding pathways in the pathogenesis of HCM and DCM caused by alpha-cardiac actin variants.
• To correlate actin variant folding properties with their cellular incorporation into filaments.

Main Methods:

• Utilized a cell-free coupled translation assay to assess actin variant folding and interaction with chaperonins (TRiC/CCT).
• Evaluated the propensity of actin variants to acquire native conformation and form detergent-insoluble aggregates.
• Overexpressed variant actin proteins in mammalian cell lines to examine their incorporation into actin filaments.

Main Results:

• Actin variants exhibited varying degrees of association with TRiC/CCT and distinct folding efficiencies; some variants were stalled and failed to fold properly.
• A subset of variant polypeptides showed signs of misfolding, including ubiquitination and detergent insolubility.
• Overexpressed variant actins displayed impaired incorporation into cellular actin filaments, correlating with observed misfolding in vitro.

Conclusions:

• The protein-folding pathway and subsequent fiber assembly defects of alpha-cardiac actin variants are likely contributors to the molecular mechanisms underlying HCM and DCM.
• Understanding these folding abnormalities provides a basis for future therapeutic strategies targeting hereditary cardiomyopathies.