OBJECTIVES: The aim of this study was to evaluate the role of angiotensin II (AT-II) and its main mediator, transforming growth factor beta 1 (TGF-��1), in the development of feline renal fibrosis.
METHODS: Expression of marker genes indicating epithelial-to-mesenchymal transition (EMT), profibrotic mediators and matricellular proteins was measured in feline kidney epithelial cells (Crandell Rees feline kidney [CRFK] cells) after incubation with AT-II and/or TGF-��1.
RESULTS: Cells incubated with TGF-��1 or the combination of TGF-��1 with AT-II showed clear EMT with more stretched fibroblastic cells, whereas the cells incubated without TGF-��1 and AT-II (control) showed more epithelial cells. Gene expression of collagen type I (), tenascin-C (), trombospondin-1 (), connective tissue growth factor () and alpha-smooth muscle actin () increased significantly after incubation of the CRFK cells with TGF-��1 or TGF-��1 in combination with AT-II for 12 h. As incubation of the CRFK cells with only AT-II did not show any significant rise in gene expression of the above-mentioned genes, this was further investigated. In contrast to healthy feline kidney tissue, CRFK cells showed almost no expression of the AT-II type 1 (AT) receptor.
CONCLUSIONS AND RELEVANCE: TGF-��1 significantly induced expression of the EMT marker gene ��-SMA, profibrotic mediator , and fibrogenic proteins , and in CRFK cells. The effect of TGF-��1 on myofibroblast formation was also observed by the stretched appearance of the CRFK cells. As CRFK cells expressed almost no AT receptors, this cell line proved not suitable for testing the efficacy of drugs that interact with the AT receptor. As AT-II stimulates the effects of TGF-��1 in mammals, the results of this study suggest an indirect profibrotic effect of AT-II besides the demonstrated profibrotic effect of TGF-��1 and thus the development of feline renal fibrosis. Modulation of EMT or proliferation of myofibroblasts could serve as a diagnostic tool and a novel therapeutic target to inhibit renal fibrogenesis, and could possibly serve in the therapy of feline renal fibrosis.
