The hypertrophic cardiomyopathy-associated A331P actin variant enhances basal contractile activity and elicits...

Area of Science:

• Cardiovascular Biology
• Muscle Physiology
• Molecular Genetics

Background:

• Hypertrophic cardiomyopathy (HCM) is a genetic heart disease.
• The A331P mutation in cardiac actin has been linked to HCM, but its precise mechanism remains unclear.
• Actin-tropomyosin interactions are crucial for regulating muscle contraction.

Purpose of the Study:

• To elucidate the mechanistic basis of hypertrophic cardiomyopathy caused by the A331P cardiac actin mutation.
• To investigate the effects of the A331P mutation on actin-tropomyosin interactions and muscle contractility.

Main Methods:

• Utilized a multidisciplinary approach including transgenic Drosophila models and in vitro biochemical assays.
• Reconstituted A331P thin filaments using recombinant human cardiac actin.
• Performed cryo-electron microscopy (Cryo-EM) and in silico molecular dynamics simulations.

Main Results:

• Transgenic Drosophila expressing A331P actin showed skeletal muscle hypercontraction and elevated myocardial activity.
• In vitro studies revealed increased myosin-based sliding speeds of A331P thin filaments at low calcium concentrations.
• Cryo-EM showed no structural changes in F-actin, but in silico analysis indicated reduced mobility and altered tropomyosin interactions.

Conclusions:

• The A331P mutation in cardiac actin disrupts normal actin-tropomyosin interactions, leading to increased resting muscle activity.
• These altered interactions may contribute to the pathogenesis of hypertrophic cardiomyopathy.
• The findings provide a mechanistic link between the A331P mutation and disease development.