Cardiac fibroblast-mediated ECM remodeling regulates maturation in an in vitro 3D engineered cardiac tissue.

Cardiac fibroblasts play an important role in heart homeostasis, regeneration, and disease by producing extracellular matrix (ECM) proteins and remodeling enzymes. Under normal conditions, fibroblasts exist in a quiescent state and maintain homeostasis, such as tissue structure and ECM turnover. However, if they become activated upon stimuli, such as injury, aging, or mechanical stress, which can lead to disease through excessive cell proliferation and ECM production. In addition to their role in disease progression, it remains unclear how cardiac fibroblasts contribute to cardiac maturation during development and whether the mechanism driving cytokine and ECM production during development aligns with those observed in pathological conditions. In this study, we investigated the functional and structural maturation of engineered cardiac tissue by modulating fibroblast activity within a three-dimensional (3D) in vitro model. In this model, human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and human primary cardiac fibroblasts (FBs) were co-cultured in a fibrin gel and their morphology, beating characteristics, beating force, and mRNA expression profiles were analyzed. The results demonstrate that functional and structural maturation were enhanced by fibroblast-driven tissue contraction and collagen deposition, while inhibition of ECM remodeling impaired both processes. However, excessive collagen accumulation reduced functional maturation by limiting contractile efficiency. Our data suggest that ECM remodeling by cardiac fibroblasts is essential for cardiac tissue maintenance and maturation. Additionally, the regulation of collagen deposition by fibroblast activity will be a key focus of future research, as it may critically influence both cardiac development and the progression of heart disease.