HRAS-Mutant Cardiomyocyte Model of Multifocal Atrial Tachycardia

Area of Science:

• Cardiovascular Biology
• Genetics
• Stem Cell Biology

Background:

• Costello syndrome (CS) is caused by germline HRAS gain-of-function variants.
• Multifocal atrial tachycardia (MAT), a treatment-resistant tachyarrhythmia, affects 50% of CS patients in early childhood.
• The pathogenesis of MAT in CS remains unknown.

Purpose of the Study:

• To investigate how overactive HRAS signaling triggers arrhythmogenesis in atrial-like cardiomyocytes (ACMs).
• To establish a human-induced pluripotent stem cell (hiPSC) model for studying MAT in CS.

Main Methods:

• Generated hiPSC-ACMs from CS patients with HRAS Gly12 mutations.
• Assessed electrophysiological properties (action potentials, calcium transients, funny currents) using automated patch clamping.
• Analyzed transcriptomic data for differential gene expression and gene ontology.
• Evaluated protein expression via immunoblotting.

Main Results:

• HRAS variant ACMs exhibited higher beating rates and increased pacemaker-like cell populations with elevated funny current densities.
• Specific inhibitors (ivabradine, flecainide, verapamil) modulated beating rates and irregularity.
• Mutant ACMs showed upregulated gene expression related to heart rate, calcium homeostasis, and nodal programming.
• MAPK activity was suppressed in mutant ACMs.

Conclusions:

• Gain-of-function HRAS mutations in hiPSC-derived ACMs induce transcriptional changes promoting enhanced automaticity and arrhythmias.
• This hiPSC model elucidates the mechanistic basis of multifocal atrial tachycardia in Costello syndrome.