Figure 1. The ECM facilitates communication among fibroblasts, cardiomyocytes and macrophages in the heart.

Fibroblasts are activated by cues such as mechanical tension and inflammatory cytokines and chemokines that are typical of injury. Activated fibroblasts (myofibroblasts) modify the ECM, which in turn regulates behaviors of myocardial cells such as myocytes and macrophages. The ECM affects these cell populations through changes in mechanical tension, as well as availability of growth factors and other matricellular proteins. It remains unclear exactly how macrophages and cardiomyocytes might exert influences on the ECM, although growth factor signaling is likely key. It is also unknown the degree to which myofibroblasts convert back to a quiescent/homeostatic phenotype. Abbreviations: GF, growth factors; ECM, extracellular matrix.