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 collagen in a cultured murine proximal tubular cell line (MCT cells). In addition, Ang II also induces the expression of TGF-beta1 in these cells. Since TGF-beta has well-known stimulatory effects on the transcription of various collagens, we tested whether the Ang-II-mediated stimulation of type IV collagen is due to induction of endogenous TGF-beta1 synthesis in MCT cells. RESULTS A neutralizing monoclonal anti-TGF-beta1-3 antibody abolished the Ang II-stimulated release of type IV collagen in culture supernatants. The anti-TGF-beta1-3 antibody also partly blocked Ang-II-mediated incorporation of 3[H]proline into de novo synthesized collagens. Moreover, 5 microM TGF-beta1 antisense oligonucleotides, but not the same concentration of sense oligonucleotides, completely blocked Ang-II-stimulated 3[H]proline incorporation. MCT cells incubated with TGF-beta1 antisense phosphorothioate-modified oligonucleotides failed to synthesize TGF-beta1 protein after Ang II treatment as measured by a sandwich ELISA in culture supernatants. SDS-polyacrylamide electrophoresis of 3[H]proline-labelled collagens and comparison with standard collagens also demonstrated that the neutralizing anti-TGF-1-3 antibody abolished the Ang-II-mediated stimulation in type IV collagen. Semiquantitative cDNA amplification for collagen type alpha1 (IV) transcripts revealed that the anti-TGF-beta1-3 antibody abrogates the increase in mRNA after Ang II treatment. Transient transfection studies in MCT cells using murine collagen alpha1 (IV) enhancer/promoter constructs also demonstrated the suppressive effect of the neutralizing antibody on Ang-II-stimulated gene transcription. CONCLUSIONS Our data collectively suggest that the Ang-II-mediated increase in type IV collagen in MCT cells is mediated by endogenous synthesis and autocrine action of TGF-beta1. These findings may be important in changes of the tubulointerstitial architecture during the progression of renal disease.