A Method to Investigate the Mechanical Properties of Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes at the Single-Cell Level

Background: Human pluripotent stem cell–derived cardiomyocytes (hPSC-CMs) provided exciting tools for cardiovascular research. Current platforms assessing the mechanical properties of single hPSC-CM have inherent limitations that require numerous assumptions, and most importantly do not allow studying single cell mechanics at different loading conditions.

Objective: We aimed to establish a novel methodology to overcome the aforementioned limitations by directly measuring hPSC-CMs forces at different stretch levels. We then aimed to evaluate the potential of this approach for different pathophysiological studies and drug testing.

Methods and Results: Single hPSC-CMs were attached to two optical-fibers; one serves as a length-controller, allowing to stretch the cell, and the other is connected to a highly-sensitive optical-force transducer that measures the forces with nano-Newton resolution. HPSC-CM were paced and stretched in a step-wise manner, hPSC-CMs demonstrated a positive length-tension relationship (Frank-Starling law) with increasing active and passive tension. Next, we examined the effect of isoproterenol on hPSC-CM’s mechanics at 3 stretch levels, isoproterenol application increased the active forces amplitude, contraction and relaxation velocities at all steps. Finally, we evaluated the effect of the anti-neoplastic agent doxorubicin on the contractility of these cells. Morphologically, doxorubicin-treated hPSC-CMs displayed disrupted sarcomeres with reduced myofibrillar content. Mechanically, doxorubicin-treated hPSC-CMs exhibited reduced active tensions and altered kinetics at all stretch levels. When investigating the force-frequency relationship, doxorubicin-treated group demonstrated exaggerated negative force-frequency with apparent mechanical alternans compared to healthy hPSC-CMs.

Conclusion: A novel method that allows direct active and passive force measurements from single hPSC-CMs at different loading conditions was established for the first time and validated. Our results highlight the potential implications of this novel approach for pharmacological and disease modeling studies; as we were able to identify drug-induced changes in the contractile properties of the cells after isoproterenol stimulation and as a result of doxorubicin cardiotoxicity.