fibroblast

Fibroblasts are mesenchymal-derived spindle-shaped cells found throughout connective tissue. Their primary function is to produce and maintain the extracellular matrix (ECM), synthesizing type I and III collagen, elastin, fibronectin, and proteoglycans. During wound healing, fibroblasts migrate into the wound site during the proliferative phase (days 3-5), stimulated by growth factors such as PDGF, TGF-beta, and FGF released by platelets and macrophages. They lay down granulation tissue and later differentiate into myofibroblasts (expressing alpha-smooth muscle actin) under TGF-beta influence, which contract the wound edges. In the remodeling phase, fibroblasts continue to remodel collagen (type III converted to type I) via matrix metalloproteinases (MMPs), increasing tensile strength of the scar over weeks to months. Clinically, dysregulated fibroblast activity underlies fibrotic diseases such as pulmonary fibrosis, liver cirrhosis, systemic sclerosis (scleroderma), and keloid/hypertrophic scar formation. Fibroblasts also have roles in tumor stroma (cancer-associated fibroblasts) promoting tumor growth and immune evasion. In genetic disorders like osteogenesis imperfecta and Ehlers-Danlos syndrome, fibroblast dysfunction in collagen synthesis leads to connective tissue fragility. Fibroblasts are distinguished histologically from fibrocytes (quiescent, less active) and are key targets in antifibrotic drug development (e.g., pirfenidone for idiopathic pulmonary fibrosis).