Mechanisms of fibrogenesis.

Fibrogenesis is a mechanism of wound healing and repair. However, prolonged injury causes deregulation of normal processes and results in extensive deposition of extracellular matrix (ECM) proteins and fibrosis. The current review will discuss similarities and differences of fibrogenesis in different organs and systems and focus on the origin of collagen producing cells. Although the relative contribution will vary in different tissues and different injuries, there are three general sources of fibrogenic cells: endogenous fibroblasts or fibroblast-like cells, epithelial to mesenchymal transition, and recruitment of fibrocytes from the bone marrow.