Angiotensin II Induces α3(IV) Collagen Expression in Cultured Murine Proximal Tubular Cells

Abstract

Angiotensin II (ANG II) induces cellular hypertrophy of cultured proximal tubular cells from various species. This hypertrophic response is associated with an increase in synthesis of basement membrane–associated collagen type IV. Previous investigations by our group have shown that ANG II stimulates mRNA and protein expression of the “classic”α1 and α2(IV) chains in cultured murine proximal tubular cells (murine cortical tubules [MCT cells]). Since it is clearer today that kidney basement membranes also contain heterotrimers of novel type IV collagens, the aim of the present study was to evaluate whether ANG II may influence the expression of α3 and α5(IV) collagen chains in MCT cells. A single dose of 10⁻⁸–10⁻⁶ M ANG II stimulated mRNA expression of α3(IV), but not of α5(IV), in MCT cells cultured in serum‐free media. This response was mediated through AT₁‐receptors because losartan, but not an AT₂‐receptor antagonist, abolished the ANG II–induced expression of α3(IV) transcripts. Transient transfection of MCT cells with transforming growth factor–β₁ (TGF‐β₁) antisense phosphorothioate‐modified oligonucleotides partly abolished the ANG II–induced α3(IV) mRNA expression. Furthermore, Western blots of cellular lysates incubated with polyclonal antibodies generated against the recombinant collagen chains revealed that ANG II stimulated α3(IV) but not α5(IV) protein expression. This stimulation was partly prevented by co‐incubation with a neutralizing anti‐TGF‐β_1‐3 antibody. In summary, our data indicate that ANG II stimulates expression of the α3(IV) collagen chain in cultured MCT cells, due in part to TGF‐β₁ activation.