Abstract P3129: Strain-induced Cardiac Arrhythmias Caused By A Noonan Syndrome Mutation In Raf1 Can Be Suppressed By Modulation Of The Ras-mapk Pathway In Vitro

The gain of function mutation RAF1 S257L/+ , accounting for more than 50% of Noonan syndrome (NS) cases, results in a hyperactive RAS-MAPK pathway. Individuals suffer from myocardial dysfunction including electrophysiological abnormalities. Resulting arrhythmias may be potentially life-threatening, if sinus rhythm is not restored expeditiously. Intensive research has provided insights into structural anomalies. However, electrophysiological abnormalities contributing to arrhythmia initiation and maintenance in affected NS patients have not yet been investigated in-depth.To delineate the role of RAF1 S257L/+ in cardiac rhythm disturbance in vitro , we used cardiomyocytes differentiated from NS patient-derived (RAF1 S257L/+ ) and isogenic gene-corrected (RAF1 corr/+ ) iPS cells to generate 3D bioartificial cardiac tissues (BCTs). In a custom-made bioreactor system, we applied mechanical preload to BCTs to resemble an in vivo physiological stress condition. Here, in RAF1 S257L/+ BCTs, we observed a high susceptibility to arrhythmias compared to RAF1 corr/+ myocardium. This abnormality came alongside with a severely stiffened myocardium, and an impaired myocardial relaxation, pointing towards a diastolic disfunction. Electrophysiological analysis revealed a potentially arrhythmogenic shortening in action potential duration in RAF1 S257L/+ BCTs. Furthermore, the presence of spontaneous ectopic foci resulted in unstable excitation patterns. Long-term modulation of the hyperactive RAS-MAPK pathway by treatment with a MEK inhibitor, significantly reduced these arrhythmogenic parameters accompanied with a normalization of RAF1 S257L/+ BCT compliance, eventually stabilizing beating rhythm significantly.For the first time, our study provides an in-depth characterization of the RAF1 S257L/+ -associated arrhythmogenic phenotype in vitro . Shortened action potential durations, instable pace maker regions and a stiffened myocardium may contribute to the initiation and maintenance of severe cardiac rhythm anomalies. Moreover, we successfully rescued this distinct phenotype by pharmacological intervention. Our findings may have implications for future preventive treatment strategies for NS patients.