Conventional rigid 2D substrates cause complex contractile signals in monolayers of human induced pluripotent stem cell-derived cardiomyocytes

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CM) in monolayers interact mechanically via cell-cell and cell-substrate adhesion. Spatiotemporal features of contraction were analysed in hiPSC-CM monolayers (1) attached to glass or plastic (Young's modulus (E) >1 GPa), (2) detached (substrate-free) and (3) attached to a flexible collagen hydrogel (E = 22 kPa). The effects of isoprenaline on contraction were compared between rigid and flexible substrates. To clarify the underlying mechanisms, further gene expression and computational studies were performed. HiPSC-CM monolayers exhibited multiphasic contractile profiles on rigid surfaces in contrast to hydrogels, substrate-free cultures or single cells where only simple twitch-like time-courses were observed. Isoprenaline did not change the contraction profile on either surface, but its lusitropic and chronotropic effects were greater in hydrogel compared with glass. There was no significant difference between stiff and flexible substrates in regard to expression of the stress-activated genes NPPA and NPPB. A computational model of cell clusters demonstrated similar complex contractile interactions on stiff substrates as a consequence of cell-to-cell functional heterogeneity. Rigid biomaterial surfaces give rise to unphysiological, multiphasic contractions in hi PSC-CM monolayers. Flexible substrates are necessary for normal twitch-like contractility kinetics and interpretation of inotropic interventions.

Automated summary

Human induced pluripotent stem cell-derived cardiomyocytes in monolayers exhibit multiphasic contractile profiles on rigid surfaces but normal twitch-like kinetics on flexible substrates. Isoprenaline has greater lusitropic and chronotropic effects on flexible substrates compared to glass, while there is no significant difference in stress-activated gene expression between stiff and flexible substrates. Computational models show complex contractile interactions on stiff substrates due to cell-to-cell functional heterogeneity.