TRANSFORMING GROWTH-FACTOR-BETA MEDIATES THE ANGIOTENSIN-II-INDUCED STIMULATION OF COLLAGEN TYPE-IV SYNTHESIS IN CULTURED MURINE PROXIMAL TUBULAR CELLS

Background. Angiotensin II (Ang II) stimulates synthesis of type IV co llagen in a cultured murine proximal tubular cell line (MCT cells). In addition, Ang II also induces the expression of TGF-beta(1) in these cells. Since TGF-beta has well-known stimulatory effects on the transc ription of various collagens, we tested whether the Ang-II-mediated st imulation of type IV collagen is due to induction of endogenous TGF-be ta(1) synthesis in MCT cells. Results. A neutralizing monoclonal anti- TGF-beta(1-3) antibody abolished the Ang II-stimulated release of type IV collagen in culture supernatants. The anti-TGF-beta(1-3) antibody also partly blocked Ang-II-mediated incorporation of (3)[H]proline int o de novo synthesized collagens. Moreover, 5 mu M TGF-beta(1) antisens e oligonucleotides, but not the same concentration of sense oligonucle otides, completely blocked Ang-II-stimulated (3)[H]proline incorporati on. MCT cells incubated with TGF-beta(1) antisense phosphorothioate-mo dified oligonucleotides failed to synthesize TGF-beta(1) protein after Ang II treatment as measured by a sandwich ELISA in culture supernata nts. SDS-polyacrylamide electrophoresis of (3)[H] proline-labelled col lagens and comparison with standard collagens also demonstrated that t he neutralizing anti-TGF-beta(1-3) antibody abolished the Ang-II-media ted stimulation in type IV collagen. Semiquantitative cDNA amplificati on for collagen type alpha 1(IV) transcripts revealed that the anti-TG F-beta(1-3) antibody abrogates the increase in mRNA after Ang II treat ment. Transient transfection studies in MCT cells using murine collage n alpha 1(IV) enhancer/promoter promoter constructs also demonstrated the suppressive effect of the neutralizing antibody on Ang-II-stimulat ed gene transcription. Conclusions. Our data collectively suggest that the Ang-II-mediated increase in type IV collagen in MCT cells is medi ated by endogenous synthesis and autocrine action of TGF-beta(1). Thes e findings may be important in changes of the tubulointerstitial archi tecture during the progression of renal disease.