Analysis of iPSC-CM Contractility following Mavacamten treatment using MYOCYTER
Authors: Anfinson Melissa , Zhang Emily , Atkinson Grant , Li Irene , Mitchell Yukiko , Perera Thevindu , Kodgi Suraksha , Zhang Ethan , Wang David , Kumar Rohith , Kumar Shilpa , Jia Mellynda , Mir Eiman , Ikem Oge , Balaji Nithila , Holland Hayden , Tomita-Mitchell Aoy 
Published: May 2023

Hypoplastic Left Heart Syndrome (HLHS) is a rare and complex congenital heart defect characterized by hypoplasia of the left ventricle, proximal aorta, as well as stenosis or atresia of the mitral and/or aortic valves. There is strong evidence for a genetic contribution to HLHS, including our lab’s previous discovery of 19 rare, predicted-damaging MYH6 variants that were significantly enriched in HLHS patients. The MYH6 gene encodes for the α-myosin heavy chain (α-MHC), a key contractile protein in cardiac sarcomere. Variants affecting cardiac MHC isoforms are thought to impact the strength, speed, and patterns of myocardial contractions. Reduced myocardial contractility due to MYH6 variants may impair cardiac blood flow and cause underdevelopment of the left heart. Mavacamten is a novel pharmacological agent that has shown promise in phase III clinical trials for treatment of hypertrophic obstructive cardiomyopathy. Mavacamten selectively acts on cardiac MHC to reduce cardiac muscle contractility. Given this specificity, Mavacamten may offer a promising way to treat diastolic dysfunction in (i.e. hypercontractility) in patients with HLHS, including those with MYH6 variants. We tested the in vitro efficacy of Mavacamten in patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) exhibiting hypercontractility and investigated video-based analysis as a high-throughput method for evaluating iPSC-CM contractility, which would allow for repeated assessment of cells at different timepoints following drug treatment. Many packages for video-based contractility assessment lack precision and can be subject to disturbances such as cellular fragments, movement of cell media, and small differences in media color. They are also complex and require advanced programming knowledge. MYOCYTER is an open-source macro for ImageJ that improves upon previous plugins available by allowing for users to optimize parameters for contractility evaluation, while minimizing background noise. The aim of our study was to determine if MYOCYTER can be reliably used to detect small changes in iPSC-CM contractility following treatment with Mavacamten, and if the workflow is user-friendly enough such that reproducible analysis can be done by a high school science team.Our analysis revealed that MYOCYTER can detect baseline hypercontractility of iPSC-CMs carrying MYH6 variants compared to wild-type iPSC-CMs (p = 0.033). These differences in amplitude were eliminated following five, ten, and fifteen minutes of treatment with 500nM Mavacamten in a single experiment. Our results suggest that this method can be used to further evaluate the effect of myosin modulators, such as Mavacamten, in patient-specific iPSC-CMs. Children's Research Institute This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.