Development of a laser injury model using human cardiac spheroids

Myocardial infarction is a leading cause of death and leads to irreversible loss of cardiomyocytes and the deposition of a fibrotic scar. Here, we developed a human cardiac microtissue model that enables controlled induction of focal laser injury to model cardiac injury-induced cellular responses. This system is based on self-assembly of troponin-I1-EGFP-positive human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) and cardiac fibroblasts (iPSC-CFs) into contracting spheroids. Targeted UV-laser ablation induced a localized injury affecting nearly 30% of the spheroid area and led to both necrosis and cardiomyocyte apoptosis at the injury site. The procedure transiently reduced contractility, which recovered after 1 week of culture. Laser injury did not stimulate cell proliferation, but evoked a limited fibrotic response, evidenced by proteomics and immunostaining of cryosections and cleared spheroid preparations. Our findings establish cardiac spheroids as a human in vitro model to study the effects of cardiac injury on a cardiomyocyte and fibroblast co-culture system, with the potential to study cell interactions and screen for compounds promoting reparative or regenerative processes.