Classical Estrogen Receptors and ERα Splice Variants in the Mouse

Estrogens exert a variety of effects in both reproductive and non-reproductive tissues. With the discovery of ER alpha splice variants, prior assumptions concerning tissue-specific estrogen signaling need to be re-evaluated. Accordingly, we sought to determine the expression of the classical estrogen receptors and ER alpha splice variants across reproductive and nonreproductive tissues of male and female mice. Western blotting revealed that the full-length ER alpha 66 was mainly present in female reproductive tissues but was also found in non-reproductive tissues at lower levels. ER alpha 46 was most highly expressed in the heart of both sexes. ER alpha 36 was highly expressed in the kidneys and liver of female mice but not in the kidneys of males. ER beta was most abundant in non-reproductive tissues and in the ovaries. Because the kidney has been reported to be the most estrogenic non-reproductive organ, we sought to elucidate ER renal expression and localization. Immunofluorescence studies revealed ER alpha 66 in the vasculature and the glomerulus. It was also found in the brush border of the proximal tubule and in the cortical collecting duct of female mice. ER alpha 36 was evident in mesangial cells and tubular epithelial cells of both sexes, as well as podocytes of females but not males. ER beta was found primarily in the podocytes in female mice but was also present in the mesangial cells in both sexes. Within the renal cortex, ER alpha 46 and ER alpha 36 were mainly located in the membrane fraction although they were also present in the cytosolic fraction. Given the variability of expression patterns demonstrated herein, identification of the specific estrogen receptors expressed in a tissue is necessary for interpreting estrogenic effects. As this study revealed expression of the ER alpha splice variants at multiple sites within the kidney, further studies are warranted in order to elucidate the contribution of these receptors to renal estrogen responsiveness.