Mechanical history shapes phenotypic plasticity and fibroblast-autonomous 3D remodeling in iPSC-derived cardiac fibroblasts

Human induced pluripotent stem cell-derived cardiac fibroblasts (iPSC-cFBs) offer a renewable, genetically defined stromal cell source for studying cardiac fibrosis and cardiomyocyte-fibroblast crosstalk during development and disease. Because cardiac fibroblasts are proliferative, expansion of iPSC-cFBs in culture is attractive for applications requiring large cell numbers, including drug screening and tissue engineering. However, phenotypic drift during expansion, particularly premature fibroblast-to-myofibroblast transition (FMT), remains a concern. Here, we investigated how differentiation protocol, mechanical culture history, and serial expansion shape iPSC-cFB phenotype, transforming growth factor beta 1 (TGF-beta1) responsiveness, and fibroblast-autonomous remodeling in three-dimensional (3D) tissues. Initial studies of iPSC-cFBs expanded on conventional tissue-culture polystyrene (TCP) revealed passage-associated increases in projected cell area and alpha-smooth muscle actin (alpha-SMA) expression, two markers associated with FMT. These findings prompted us to examine how the stiffness of poly(dimethylsiloxane) (PDMS) substrates (15 kPa or 2 MPa) used during iPSC-cFB derivation and expansion influences basal phenotype and response to TGF-beta1. Across two independent differentiation protocols, mechanical culture history shaped passage-dependent basal phenotypes and responses to TGF-beta1. Notably, its effects on collective TGF-beta1 responses in three-dimensional cultures differed from those observed after replating cells onto two-dimensional substrates. Together, these findings demonstrate that mechanical culture history modulates iPSC-cFB responsiveness and tissue-remodeling behavior without irreversibly determining fibroblast state. Subsequent passage and microenvironmental conditions can attenuate or re-express these history-dependent phenotypes. This work supports the use of iPSC-cFBs in basic biological discovery and future tissue engineering applications.