Estrogen Receptor Alpha Expression in Podocytes Mediates Protection against Apoptosis In-Vitro and In-Vivo

Abstract

Context/ObjectiveEpidemiological studies have demonstrated that women have a significantly better prognosis in chronic renal diseases compared to men. This suggests critical influences of gender hormones on glomerular structure and function. We examined potential direct protective effects of estradiol on podocytes.MethodsExpression of estrogen receptor alpha (ERα) was examined in podocytes in vitro and in vivo. Receptor localization was shown using Western blot of separated nuclear and cytoplasmatic protein fractions. Podocytes were treated with Puromycin aminonucleoside (PAN, apoptosis induction), estradiol, or both in combination. Apoptotic cells were detected with Hoechst nuclear staining and Annexin-FITC flow cytometry. To visualize mitochondrial membrane potential depolarization as an indicator for apoptosis, cells were stained with tetramethyl rhodamine methylester (TMRM). Estradiol-induced phosphorylation of ERK1/2 and p38 MAPK was examined by Western blot. Glomeruli of ERα knock-out mice and wild-type controls were analysed by histomorphometry and immunohistochemistry.ResultsERα was consistently expressed in human and murine podocytes. Estradiol stimulated ERα protein expression, reduced PAN-induced apoptosis in vitro by 26.5±24.6% or 56.6±5.9% (flow cytometry or Hoechst-staining, respectively; both p<0.05), and restored PAN-induced mitochondrial membrane potential depolarization. Estradiol enhanced ERK1/2 phosphorylation. In ERα knockout mice, podocyte number was reduced compared to controls (female/male: 80/86 vs. 132/135 podocytes per glomerulus, p<0.05). Podocyte volume was enhanced in ERα knockout mice (female/male: 429/371 µm3 vs. 264/223 µm3 in controls, p<0.05). Tgfβ1 and collagen type IV expression were increased in knockout mice, indicating glomerular damage.ConclusionsPodocytes express ERα, whose activation leads to a significant protection against experimentally induced apoptosis. Possible underlying mechanisms include stabilization of mitochondrial membrane potential and activation of MAPK signalling. Characteristic morphological changes indicating glomerulopathy in ERα knock-out mice support the in vivo relevance of the ERα for podocyte viability and function. Thus, our findings provide a novel model for the protective influence of female gender on chronic glomerular diseases.

Podocytes, Signaling Pathways, and Vascular Factors in Diabetic Kidney Disease

“…Estrogen effects are mediated by two distinct estrogen receptor subtypes, ERá and ERâ and both receptors are present in podocytes 54 . Estradiol has been shown to stimulate ERá protein expression as well as to reduce podocyte apopotosis after puromycin aminonucleoside exposure 55 . There is less compelling evidence that ER signaling is protective in diabetic models or humans.…”

The Renal Effects of Prenatal Testosterone in Rats

“…16 Podocytes also express estrogen receptor a, which can be activated by estradiol, the metabolite of Tst after conversion by aromatase. 17 Genetic models with targeted mutations of the particular steroid receptors in podocytes are needed to determine the mechanism in detail.…”

Yi Qi Qing Re Gao Attenuates Podocyte Injury and Inhibits Vascular Endothelial Growth Factor Overexpression in Puromycin Aminonucleoside Rat Model

“…Podocyte apoptosis is an early and important manifestation in PAN nephrosis, with apparent cell membrane inversion and mitochondrial membrane potential depolarization [27]. Estrogen receptor α and nestin are demonstrated to protect podocyte from apoptosis [27, 28].…”