Hypertrophic cardiomyopathy (HCM) is a severe inherited cardiac disorder. Its hallmarks are hypertrophy of the left ventricular wall and septum, diastolic dysfunction and and increased risk of arrhythmias and sudden cardiac death. One of the most frequently affected genes is
MYBPC3 encoding the cardiac myosin-binding protein C (cMyBP-C). These mutations are predominantly heterozygous and a resulting haploinsufficiency could be shown in many cases. Moreover, in patient heart tissue sections with the heterozygous
MYBPC3 c.927-2A>G mutation a variable sarcomeric content of cMyBP-C from cell to cell together with burst-like transcription of
MYBPC3 and functional heterogeneity in calcium sensitivity and force generation among individual cardiomyocytes were observed.
Our hypothesis is that cell-to-cell variability in cMyBP-C levels disturbs contractile function and thereby contributes to HCM progression. We developed a human induced pluripotent stem cell-derived cardiomyocyte (hiPSC-CM) model carrying the known pathogenic heterozygous truncating mutation MYBPC3 c.927-2A>G as well as the fluorescent protein NeonGreen tagged onto titin at the Z-disc. In long-term 2D-culture we studied the effects on contractile function by fluorescence microscopy-based real-time sarcomere visualization and single-cell contractility analysis within multicellular clusters. In this model, preliminary analyses comparing cMyBP-C positive and negative cardiomyocytes within mutant clusters revealed altered contraction-relaxation dynamics. These findings are consistent with previous studies of single cardiomyocytes from HCM patient myocardium, suggesting that cMyBP-C haploinsufficiency can potentially develop into contractile imbalance at the single-cell level.
Moreover, using a heart-forming organoid (HFO) model, we investigated potential developmental defects of cMyBP-C deficiency.
Thus, our MYBPC3 c.927-2A>G hiPSC models enable direct correlation of sarcomeric cMyBP-C expression with contractile behaviour at the single-cell level within 2D hiPSC-CM clusters, as well as investigation of the impact of cMyBP-C deficiency on heart development in a simplified organoid model. Together, these complementary systems provide valuable platforms to study how cMyBP-C haploinsufficiency contributes to HCM pathomechanisms and to explore potential therapeutic targets.
