Differential effects of continuous and intermittent 17β-estradiol replacement and tamoxifen therapy on the prevention of glomerulosclerosis: Modulation of the mesangial cell phenotype in vivo

Female ROP Os/+ mice are partially protected by endogenous estrogens against progressive glomerulosclerosis (GS) during their reproductive period; however, ovariectomy accelerates GS progression. We examined the effects of continuous and intermittent 17β-estradiol (E₂) replacement and tamoxifen therapy on the development of GS in ovariectomized (Ovx) ROP Os/+ mice. Continuous E₂ replacement (CE₂) throughout 9 months prevented microalbuminuria and excess extracellular matrix accumulation in Ovx ROP Os/+, not only compared to placebo-treated Ovx mice but also in comparison to intact female ROP Os/+. Tamoxifen had a similar effect, but of lesser magnitude. Intermittent 3-month on-off-on E₂ did not reduce the kidney changes. Mesangial cells (MCs) from CE₂ mice maintained their estrogen responsiveness. E₂ in vitro prevented transforming growth factor-β1 stimulation of a Smad-responsive reporter construct and increased MMP-2 expression and activity in MCs isolated from CE₂ mice. MCs from mice on either placebo or intermittent E₂ treatment did not respond to added E₂, consistent with a stable alteration of their estrogen responsiveness. Tamoxifen protection against GS was less pronounced in ROP Os/+ mice. Thus, prolonged estrogen deficiency promotes GS and renders MCs insensitive to subsequent estrogen treatment. This underscores the importance of continuous estrogen exposure for maintaining glomerular function and structure in females susceptible to progressive GS.