Localisation and phenotypical characterisation of collagen-producing cells in TGF-β1-induced renal interstitial fibrosis

Transforming growth factor beta1 (TGF-beta1) contributes to the accumulation of extracellular matrix (ECM) in the tubulointerstitial space in chronic renal diseases. Identification of target cells and the contribution of epithelial-mesenchymal transformation (EMT) in TGF-beta1-induced fibrosis in vivo are currently under investigation. We have developed a transgenic model of slowly developing TGF-beta1-driven tubulointerstitial fibrosis (TIF). By using this model our aim was to localise the ECM-producing cells, to investigate the temporal and spatial distribution of the cellular markers a-smooth muscle cell actin (alphaSM-actin), Fsp1 and Hsp47 and to explore the possible involvement of EMT in TGF-beta1-induced TIF in vivo. We utilised a combination of in situ hybridisation, immunohistochemistry and western blotting techniques and found that alphaSM-actin-positive interstitial cells are the main source of collagen types I and III and fibronectin, whereas collagen type IV(alpha1/alpha2) originates mainly from the tubular epithelial cells. Furthermore, macrophages are not important combatants during the early course of TGF-beta1-induced TIF. Finally, EMT is not necessary for the initiation of TGF-beta1-induced TIF. We conclude, that intervention directed against the recruitment of activated interstitial cells may avoid the development of end-stage renal disease.