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

Calcium channel blockers inhibit proliferation and matrix production in rat mesangial cells: possible mechanism of suppression of AP-1 and CREB activities

BACKGROUND

Calcium channel blockers (CCBs) are reported to attenuate the loss of renal function in various glomerulonephritides.

METHODS

To determine the mechanism of action of these drugs, we investigated the effects of CCBs on cell proliferation and extracellular matrix (ECM) production in cultured rat mesangial cells.

RESULTS

While stimulation with 5% fetal calf serum (FCS) increased [(3)H]thymidine and [(3)H]proline incorporation into quiescent mesangial cells, incubation with nifedipine and cilnidipine inhibited the increase in a dose-dependent manner. Northern blot analysis demonstrated that 5% FCS increased the expression of transforming growth factor beta (TGF-beta) and fibronectin (FN) mRNA and that CCBs significantly reduced this induction, indicating that CCBs may reduce ECM production through inhibiting TGF-beta and FN. Since activator protein 1 (AP-1) regulates cell proliferation and TGF-beta expression, we evaluated the AP-1 activity by gel mobility shift analysis. Nuclear extracts of FCS-treated cells showed a strong binding to AP-1-specific oligonucleotides which was suppressed by CCBs, suggesting that these agents may inhibit cell proliferation by suppressing AP-1. CCBs also inhibited the binding activity of cyclic adenosine monophosphate responsive element binding protein which regulates FN gene expression. However, neither CCBs nor FCS affected the NFkappaB activity.

CONCLUSION

These results suggest that CCBs may, in part, inhibit the progression of glomerulonephritis through non-hemodynamic actions that include the suppression of mesangial cell proliferation and the production of ECM.

Effect of gender on the progression of nondiabetic renal disease: a meta-analysis

There is previously published evidence that male gender is associated with a more rapid rate of progression of nondiabetic chronic renal disease. However, some investigators have concluded that no such association exists. To help resolve this issue, a meta-analysis was performed using 68 studies that met defined criteria and contained a total of 11,345 patients to evaluate the effect of gender on the progression of nondiabetic chronic renal disease. The results indicate that men with chronic renal disease of various etiologies show a more rapid decline in renal function with time than do women.

Estradiol suppresses mesangial cell type I collagen synthesis via activation of the MAP kinase cascade

We have previously shown that estradiol suppresses the synthesis of type I collagen by murine mesangial cells grown in the presence of serum via activation of the transcription factor activator protein-1 (AP-1). We hypothesized that estradiol upregulates AP-1 via activation of the mitogen-activated protein (MAP) kinase cascade, a signal transduction pathway that regulates AP-1 activity. Estradiol (10(-10) to 10(-7) M) upregulated the MAP kinase pathway in murine mesangial cells grown in the presence of serum in a dose-dependent manner. Activation was evident by 1 min, peaked at 10 min, and was completely dissipated by 2 h. In contrast, estradiol had no significant effect on total (phosphorylated + unphosphorylated) p44 extracellular signal-related protein kinase (ERK) or p42 ERK. Nuclear extracts isolated from mesangial cells treated with estradiol showed increased binding to a consensus sequence AP-1 binding oligonucleotide in gel shift assays. In contrast, nuclear extracts from cells exposed to PD-98059, a highly selective inhibitor of MAP kinase-ERK kinase 1 (MEK1) and MEK2, showed reduced binding. In addition, PD-98059 antagonizes the enhanced binding induced by estradiol. Estradiol (10(-9) M) suppressed mesangial cell type I collagen synthesis (37.8 +/- 2.4%, expressed as a percentage of control values, P < 0.001 vs. control). In contrast, PD-98059 increased type I collagen synthesis (344.6 +/- 98.8, P < 0.01) and reversed the suppression of type I collagen synthesis induced by estradiol. The effects of estradiol, PD-98059, and PD-98059 plus estradiol on type I collagen protein synthesis were closely paralleled by their effects on steady-state levels of mRNA for the alpha(1) chain of type I collagen. These data suggest that estradiol suppresses type I collagen synthesis via upregulation of the MAP kinase cascade, leading to stimulation of AP-1 activity.

Glomerulosclerosis in aging humans is not influenced by gender

Aging male rats develop progressive glomerulosclerosis, proteinuria, and loss of renal function, whereas females are remarkably resistant to the development of these abnormalities. Although sex hormones appear to contribute to gender-related differences in the development of glomerulosclerosis in aging rats, it is not clear that sexual dimorphism characterizes glomerular obsolescence in aging humans. To study this question further, the glomerular histology of males and females ranging in age from infancy to 90 years was compared in 250 autopsy specimens. We found no differences between the sexes in the development of glomerulosclerosis in aging humans. These data disprove the hypothesis that testosterone is an important factor contributing to progressive glomerulosclerosis in aging men. Conversely, any renoprotective effects of estrogen would be limited by the onset of menopause because significant glomerulosclerosis did not develop until after the age of 50 years.