Estradiol suppresses type I collagen synthesis in mesangial cells via activation of activator protein-1

Background. Estradiol suppresses the synthesis of type I collagen by murine mesangial cells. However, neither the α₁(I) nor the α₂(I) collagen gene contains an estrogen-response element. Because estradiol modulates the transcription of several genes that lack an estrogen-response element but contain a regulatory activator protein-1 (AP-1) binding motif, we hypothesized that AP-1 may mediate estradiol-induced suppression of type I collagen synthesis. Methods. We measured type I collagen synthesis in murine mesangial cells exposed to estradiol, phorbol 12-myristate 13-acetate (an activator of AP-1), or curcumin (an inhibitor of AP-1). We also assessed the effects of estradiol on the steady-state level of c-fos and c-jun mRNA and on the binding of mesangial cell nuclear extracts to an AP-1 consensus binding site oligonucleotide. Results. Estradiol (10^-10 M to 10^-7 M) suppressed type I collagen synthesis by murine mesangial cells in a dose-dependent manner (10^-7 M, 43.7 ± 8.2% of control values, P < 0.001). Phorbol 12- myristate 13-acetate (10 μM, four-hr exposure) also decreased type I collagen in the media. In contrast, curcumin (1 μM) increased type I collagen. Estradiol increased the steady-state level of c-fos mRNA twofold at 30 minutes, with a return to basal levels at one hour. This was associated with a greater than threefold increase in the binding of nuclear extracts from estradiol-treated mesangial cells to an AP-1 consensus binding site oligonucleotide. Estradiol-enhanced binding of nuclear extracts to the AP-1 oligonucleotide was reversed by cycloheximide. Conclusions. These data suggest that estradiol suppresses collagen I synthesis by murine mesangial cells via enhanced AP-1 activity.