Myofibroblasts. I. Paracrine cells important in health and disease

Myofibroblasts are a unique group of smooth-muscle-like fibroblasts that ha ve a similar appearance and function regardless of their tissue of residenc e. Through the secretion of inflammatory and antiinflammatory cytokines, ch emokines, growth factors, both lipid and gaseous inflammatory mediators, as well as extracellular matrix proteins and proteases, they play an importan t role in organogenesis and oncogenesis, inflammation, repair, and fibrosis in most organs and tissues. Platelet-derived growth factor (PDGF) and stem cell factor are two secreted proteins responsible for differentiating myof ibroblasts from embryological stem cells. These and other growth factors ca use proliferation of myofibroblasts, and myofibroblast secretion of extrace llular matrix (ECM) molecules and various cytokines and growth factors caus es mobility, proliferation, and differentiation of epithelial or parenchyma l cells. Repeated cycles of injury and repair lead to organ or tissue fibro sis through secretion of ECM by the myofibroblasts. Transforming growth fac tor-p and the PDGF family of growth factors are the key factors in the fibr otic response. Because of their ubiquitous presence in all tissues, myofibr oblasts play important roles in various organ diseases and perhaps in multi system diseases as well.