The need for a better understanding of the pathophysiological mechanisms underlying cardiovascular diseases of genetic origin has led to the progressive use of cardiomyocytes derived from human induced pluripotent stem cells as a model. Despite the structural and functional immaturity of the cardiomyocytes inherent in this model, numerous studies have shown that the use of different cardiac cell types in three-dimensional co-culture allows cardiomyocytes to mature more rapidly. While the addition of other cell types is known to improve the functionality of the cardiac micro-tissue, little is known about the contribution of the spatial organisation of the cells to this improvement.

In line with the study presented at the 2024 edition of the “Printemps de la Cardiologie”, this study focuses on assessing the impact of endothelial cell spatial organization on the function of cardiac micro-tissue and the maturation of the cardiomyocytes that constitute it.

A 3D co-culture model, known as a ‘spheroid’, is created using cardiomyocytes derived from induced pluripotent stem cells through the self-aggregation of various cardiac cell types. Spheroids with the same composition (70% cardiomyocytes+15% cardiac fibroblasts+15% endothelial cells) but different organisations (endothelial cells homogeneously distributed or concentrated at the centre of the spheroid) are compared. In addition to the assessment of contractility and calcium dynamics already carried out the previous year, an electron microscopy analysis of the ultrastructural organisation and an assessment of cell death by immunohistochemical labelling were carried out to evaluate the cellular integrity of the spheroids. Finally, RNA-Seq analysis is used for an overall analysis of gene expression in each group, which could potentially explain the origin of the differences observed.

As shown last year, the amplitude of contraction and calcium kinetics differed between spheroids pre-formed with a core of endothelial cells and those with homogeneous distribution of cells. Analyses using electron microscopy, RNA-seq and immunohistochemistry show that the functional differences are also reflected at cell level, particularly in terms of cell organisation and viability.

The development of this model highlights the importance of the role played by cell organisation in improving the maturation of human cardiomyocytes made possible by 3D co-culture of cardiac cells.