Abstract 281: Studying Structural And Contractility Defects Of Cardiomyocytes In An In Vitro Model Of Human Hypertrophic Cardiomyopathy
Hypertrophic Cardiomyopathy (HCM) is a cardiac disease, morphologically characterized by cardiac hypertrophy, fibrosis and impaired heart function. HCM is primarily associated with mutations in sarcomeric proteins. Mutations in sarcomeric Myosin Binding Protein C (MYBPC3) account for approximately 25% of all HCM patients. The majority of mutations in MYBPC3 are nonsense mutations, predicted to produce truncated proteins. However, instead of truncated proteins, lower levels of full-length protein of MYPBC3 are frequently found in heart samples of patients with mutations in MYBPC3, strongly suggesting that haploinsufficiency is responsible for the cardiac disease phenotype. It has been previously shown that upon ablation of MYBPC3 the myosin cross-bridges are localized closer to the actin filament, suggesting that MYBPC3 functions as a structural restraint, holding a fraction of the myosin heads at a specific distance from the actin filament. We hypothesize that the shortening of the distance between the myosin cross-bridges and the actin filaments is responsible for the increase of stretch activation kinetics leading to an increase in calcium sensitivity and contractile dysfunction. In order to develop a human in vitro model for HCM we mimicked MYBPC3 haploinsufficiency by generating stable lines in human pluripotent stem cells-derived cardiomyocytes (hPSC-CM) in which MYPBC3 protein levels were reduced by 40 to 90% using short-hairpin RNA sequences. To analyze structural and Ca2+ kinetic changes induced by the MYBPC3 knockdown we are using stochastic optical reconstruction microscopy (STORM), a superresolution fluorescence imaging method, to measure the distances between sarcomeric proteins in combination with Ca2+ imaging using a ratiometric method. At a mechanical level we are able to measure total cell force of contraction by measuring the deflection of pillars on a micropillar array generated by control and MYBPC3 knockdown hPS-CM during contraction. In conclusion, we successfully developed a human in vitro model for cardiac MYBPC3 haploinsufficiency in combination with state of the art biophysical and imaging techniques, which will allow us to comprehend the molecular mechanisms responsible for the development of HCM.
- © 2013 by American Heart Association, Inc.