Vascular endothelial growth factor expression in peritoneal mesothelial cells undergoing transdifferentiation

Objective: To analyze gene expression of localized peritoneal tissue structures in a rodent model of peritoneal fibrosis. Methods: Female Sprague Dawley rats were treated with an intraperitoneal injection of an adenovirus expressing active transforming growth factor-beta or control adenovirus. Four and 7 days after infection, animals were sacrificed and frozen sections of parietal peritoneum were subjected to immunofluorescence-aided laser capture microdissection in order to isolate vascular, mesothelial, and submesothelial structures. RNA was extracted from microdissected tissue and gene expression was analyzed by quantitative reverse-transcript polymerase chain reaction. We analyzed genes involved in angiogenesis, epithelial-to-mesenchymal transdifferentiation, and fibrosis. Vascular endothelial growth factor and alpha-smooth muscle actin expression was analyzed with immunohistochemistry of formalin-fixed tissue. Results: Transforming growth factor-beta(1) induced expression of Snail and alpha-smooth muscle actin genes in the peritoneal mesothelium. This same cell population also demonstrated increased gene expression of vascular endothelial growth factor. The distribution of this growth factor was confirmed by immunohistochemistry. The fibrogenic growth factor, connective tissue growth factor, was also strongly induced in the peritoneal mesothelium. Conclusions: Using immunofluorescence-aided laser capture microdissection, we were able to study gene expression in subcompartments of the peritoneal tissue. We demonstrated that mesothelial cells exhibiting mesenchymal transdifferentiation are associated with increased expression of genes associated with fibrosis and angiogenesis.