Myofibrillar Structural Variability Underlies Contractile Function in Stem Cell-Derived Cardiomyocytes
SummaryDisease modeling and pharmaceutical testing using cardiomyocytes derived from induced pluripotent stem cell (iPSC-CMs) requires accurate assessment of contractile function. Micropatterning iPSC-CMs on elastic substrates controls cell shape and alignment to enable contractile studies, but the determinants of intrinsic variability in this system have been incompletely characterized. The primary objective of this study was to determine the impact of myofibrillar structure on contractile function in iPSC-CMs. After labeling micropatterned iPSC-CMs with a cell permeant F-actin dye, we imaged both myofibrillar structure and contractile function. Using automated myofibrillar image analysis, we demonstrate that myofibrillar abundance is widely variable among individual iPSC-CMs and strongly correlates with contractile function. This variability is not reduced by subcloning from single iPSCs to reduce genetic heterogeneity, persists with two different iPSC-CM purification methods, and similarly is present for embryonic stem cell-derived cardiomyocytes. This analysis provides compelling evidence that myofibrillar structure should be quantified and controlled for in studies investigating contractile function in iPSC-CMs.