Figure 1

Possible origins of myofibroblast-like cells in liver and kidney. It is recognized that the fibrogenic cells in both liver and kidney are heterogeneous in their origin and behavior. In general, matrix-producing cells in chronic wound repair are derived from resident fibroblasts, respectively portal fibroblasts in the liver and interstitial fibroblasts in the kidney. Besides fibroblasts, the major contributors to the excessive ECM deposition are specialized pericytes, such as hepatic stellate cells and mesangial cells. In vitro and in vivo evidence is available for the possibility of epithelial-to-mesenchymal transition (EMT) and endothelial-to-mesenchymal transition (EndoMT). Finally, several studies have suggested that bone marrow-derived stem cells or fibrocytes could transdifferentiate within adult tissues to form mature matrix-producing cells; however, the amount of ECM produced by these cells appears to be negligible.