Transient Overexpression of TGF-β1 Induces Epithelial Mesenchymal Transition in the Rodent Peritoneum

Epithelial mesenchymal transition (EMT), a process involved in many growth and repair functions, has been identified in the peritoneal tissues of patients who undergo peritoneal dialysis. The sequence of changes in gene regulation and cellular events associated with EMT after TGF-beta1-induced peritoneal fibrosis is reported. Sprague-Dawley rats received an intraperitoneal injection of an adenovirus vector that transfers active TGF-beta1 (AdTGF-beta1) or control adenovirus, AdDL. Animals were killed 0 to 21 days after infection. Peritoneal effluent and tissue were analyzed for markers of EMT. In the animals that were treated with AdTGF-beta1, an increase in expression of genes associated with EMT and fibrosis, such as type I collagen A2, alpha-smooth muscle actin, and the zinc finger regulatory protein Snail, was identified. Transition of mesothelial cells 4 to 7 d after infection, with appearance of epithelial cells in the submesothelial zone 7 to 14 d after exposure to AdTGF-beta1, was demonstrated. This phase was associated with disruption of the basement membrane and increased expression of matrix metalloproteinase 2. By 14 to 21 d after infection, there was evidence of restoration of normal submesothelial architecture. These findings suggest that EMT occurs in vivo after TGF-beta1 overexpression in the peritoneum. Cellular changes and gene regulation associated with EMT are evident throughout the fibrogenic process and are not limited to early time points. This further supports the central role of TGF-beta1 in peritoneal fibrosis and provides an important model to study the sequence of events involved in TGF-beta1-induced EMT.