MYBPC3 D389V Variant Induces Hypercontractility in Cardiac Organoids.

Area of Science:

• Cardiovascular Biology
• Genetics
• Stem Cell Biology

Background:

• MYBPC3 mutations are a leading cause of hypertrophic cardiomyopathy (HCM).
• The MYBPC3 D389V variant, prevalent in South Asians, is linked to hyperdynamic heart function.
• The precise molecular mechanisms of D389V-associated HCM remain unclear.

Purpose of the Study:

• Investigate the molecular mechanisms of HCM pathogenesis linked to the MYBPC3 D389V variant.
• Utilize human-induced pluripotent stem cell (hiPSC)-derived cardiac organoids (hCOs) to model the variant's effects.
• Define the cellular and functional changes caused by the MYBPC3 D389V variant.

Main Methods:

• Generated hiPSC-derived cardiomyocytes and cardiac organoids from carriers and non-carriers of the MYBPC3 D389V variant.
• Performed confocal and electron microscopy, functional assays (contraction, calcium cycling), and biochemical analyses (protein phosphorylation, oxidative stress).
• Utilized recombinant proteins for in vitro binding and motility assays and treated organoids with myosin inhibitor mavacamten.

Main Results:

• MYBPC3 D389V cardiac organoids exhibited hypercontractility, faster calcium cycling, and increased contraction velocity.
• Increased cMyBP-C phosphorylation, higher oxidative stress, and lower mitochondrial membrane potential were observed in D389V organoids.
• Reduced binding affinity between D389V cMyBP-C and myosin S2 was identified as a potential cause of hypercontraction, which was reversed by mavacamten.

Conclusions:

• Human cardiac organoids are a feasible model for studying HCM mechanisms, demonstrating the MYBPC3 D389V hypercontractile phenotype.
• Faster sarcomere kinetics due to reduced protein binding affinity underlie the hypercontractility, leading to secondary mitochondrial defects.
• Mavacamten effectively rescued the hypercontractile phenotype, suggesting potential therapeutic benefits for MYBPC3 D389V carriers.