Direct Contact Between Human Cardiac Fibroblasts and Human Induced Pluripotent Stem Cell-Derived Cardiomyocytes Counteracts Changes in Calcium Cycling Induced by Soluble Mediators

Cardiac fibroblasts influence cardiomyocyte structure and function through direct physical interaction and/or by the secretion of soluble factors. A role for cardiac fibroblasts in cardiomyopathies has been proposed but clear mechanisms are still lacking. This in vitro study set out to characterise the influence of cardiac fibroblasts from patients with dilated cardiomyopathy on cardiomyocyte Ca2+ cycling, a fundamental mechanism of cardiac function universally altered in cardiac disease. Human induced pluripotent stem cell-derived cardiomyocytes (iPS-CMs) were cultured with human DCM ventricular fibroblasts at a ratio of 2:1 (120,000 fibroblasts to 60,000 iPS-CMs) for 24 hours in three groups: iPS-CMs with fibroblast conditioned medium, co-cultured in transwells to allow bi-directional paracrine communication but prevent physical contact, and iPS-CMs in direct contact with fibroblasts. iPS-CMs alone were used as a baseline. iPS-CMs were field-stimulated at 1Hz and calcium transients were recorded optically. TGF-β, a cytokine previously shown to be important in fibroblast-myocyte interaction, was measured in culture supernate using an ELISA assay. Versus iPS-CMs alone, Ca2+ transient amplitude was reduced in the conditioned medium group but increased in co-culture (p