Fig. 2.

Types and transformations of fibroblasts. This review emphasizes four major types of fibroblasts: quiescent fibroblasts, normal activated fibroblasts (NAFs), cancer associated fibroblasts (CAFs) and senescent fibroblasts. When quiescent fibroblasts are exposed to some stimuli, fibroblasts can become activated reversibly or irreversibly. The reversible one usually appears in the process of wound healing in order to facilitate repair and regeneration. The irreversible one, which is triggered by some perpetual and unabated injurious stimuli, is characterized by epigenetic regulation. Both normal fibroblasts and CAFs can be converted into senescent fibroblasts because of anti-tumor therapies, genetic mutations, natural aging and so forth