The novel MYH6-E1584K tail domain variant associated with hypoplastic left heart syndrome leads to hypercontractility in vitro

Abstract

Hypoplastic left heart syndrome (HLHS) is a complex form of congenital heart disease (CHD) characterized by hypoplasia of the left ventricle and proximal aorta, as well as stenosis or atresia of the mitral and aortic valves. Our lab previously identified that rare, predicted-damaging variants in the gene encoding for α-myosin heavy chain ( MYH6, α-MHC), a key contractile protein in the heart, are enriched in HLHS. It has been shown that pathological variants in the MHC head domain directly alter force generation, but mechanisms by which tail domain variants cause contractile defects are less clear.In double-blind analyses, patient-specific induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) carrying the MYH6 E1584K tail domain variant (VAR) showed significant structural and functional deficits compared to wild-type (WT). Consistent with our previously reported findings in atrial tissue from a patient carrying MYH6 E1584K, VAR iPSC-CMs exhibited sarcomere disarray (p<0.001) and altered sarcomeric gene expression (p<0.05). VAR iPSC-CMs display a hypercontractile phenotype compared to WT, with increased amplitude (2.16μm VAR, 1.32μm WT; p<0.05) and duration (233 msec VAR, 173 msec WT; p<0.05) of contraction and elongated relaxation times (270 msec VAR, 190 msec WT; p<0.01). Hypercontractility was also observed in bulk culture, where VAR iPSC-CMs demonstrated increased amplitude (1413.4 a.u. VAR, 993.6 a.u. WT, p<0.05) and velocity of contraction (1493.7 a.u./msec VAR, 982.2 a.u./msec WT, p<0.05). Notably, this is different than our previous reports of iPSC-CMs carrying the head domain variant MYH6 R443P, which exhibited decreased contraction velocity.Our data demonstrate the mechanism of MYH6 pathogenicity is distinct between variants, emphasizing the importance of mechanistic studies to inform clinical decision-making. Furthermore, this work will direct future investigations into the genetic etiology and physiology of CHD and provide a framework upon which personalized treatment strategies can be developed. Future studies will examine the effect of myosin modulators omecamtiv mecarbil (OM) and mavacamten on MYH6 variant iPSC-CMs. Advancing a Healthier Wisconsin Endowment 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.