Figure 1 |. Current categories of resident cardiac fibroblasts.

At least three gene-expression profiles can be used to describe fibroblasts in the adult heart^{10−12,87,88}. Mature, resident fibroblasts are interspersed in the myomesial space throughout the heart and are proposed to maintain the extracellular matrix (ECM). They have a low level of proliferation and do not express smooth muscle α-actin (α-SMA) or periostin. After injury, a population of fibroblasts, often associated with inflammatory cell accumulation and cardiomyocyte death, rapidly proliferate and become activated to express many of the gene products shown. Later in the response, a smaller population of these activated fibroblasts further differentiate into presumed myofibroblasts, which express α-SMA and other genetic signatures shown. In the past, these myofibroblasts were reported to have increased ECM deposition and contractile capacities⁸⁹, although in vivo contractile activity has been predominantly documented in skin myofibroblasts⁹⁰. Myofibroblasts have also been shown to regress their activated gene-expression profile and morphology back to the more ‘quiescent’ and resident fibroblast state¹¹. Ddr2, discoidin domain-containing receptor 2; NA, not available; Pdgfr-α, platelet-derived growth factor receptor-α; Tcf21; transcription factor 21.