Otabek Imamov

Role of estrogen receptor β in uterine stroma and epithelium: Insights from estrogen receptor β−/− mice

In this study, we compared the uterine tissue of estrogen receptor (ER)β−/− mice and their WT littermates for differences in morphology, proliferation [the percentage of labeled cells 2 h after BrdUrd injection and EGF receptor (EGFR) expression], and differentiation (expression of progesterone receptor, E-cadherin, and cytokeratins). In ovariectomized mice, progesterone receptor expression in the uterine epithelium was similar in WT and ERβ−/− mice, but E-cadherin and cytokeratin 18 expression was lower in ERβ−/− mice. The percentage of cells in S phase was 1.5% in WT mice and 8% in ERβ−/− mice. Sixteen hours after injection of 17β-estradiol (E2), the number of BrdUrd-labeled cells increased 20-fold in WT mice and 80-fold in ERβ−/− mice. Although ERα was abundant in intact mice, after ovariectomy, ERα could not be detected in the luminal epithelium of either WT or ERβ−/− mice. In both untreated and E2-treated mice, ERα and ERβ were colocalized in the nuclei of many stromal and glandular epithelial cells. However, upon E2 + progesterone treatment, ERα and ERβ were not coexpressed in any cells. In WT mice, EGFR was located on the membranes and in the cytoplasm of luminal epithelium, but not in the stroma. In ERβ−/− mice, there was a marked expression of EGFR in the nuclei of epithelial and stromal cells. Upon E2 treatment, EGFR on cell membranes was down-regulated in WT but not in ERβ−/− mice. These findings reveal an important role for ERβ in response to E2 and in the organization, growth, and differentiation of the uterine epithelium.

Estrogen Receptor-Beta Regulates Epithelial Cell Differentiation in the Mouse Ventral Prostate

The epithelium of the ventral prostate expresses high levels of ERβ (but no ERα). ERα is expressed in the stroma. Thus, in addition to the indirect effects of estrogen on the epithelium which are reported to be mediated by ERα, there is a direct estrogenic influence on prostatic epithelium mediated by ERβ. We have reported that loss of ERβ results in epithelial hypercellularity in the ventral prostate. In ERβ–/– mouse prostates, there is overexpression of the androgen receptor and of the antiapoptotic factor Bcl-2 in the prostate. Bcl-2 is an estrogen-regulated gene. It is normally expressed only in the basal cells in the prostate. This apparent expansion of the ‘stem cell-like population’ in the ERβ–/– mouse prostate has been further examined. We found a higher expression of cytokeratin 5 in ERβ–/– mouse prostates so that the ratio of cytokeratin 5 to that of 19 is much higher in ERβ–/– than in wild-type littermates. In addition, labeling of DNA with BrdU showed a 3.5-fold higher proliferation rate in ERβ–/– mouse prostate. Despite these clear differences, the piling up of epithelial cells never progressed to high-grade PIN-like lesions. Hyperplastic foci in ERβ–/– mice show accumulation of cells without signs of atypia, resembling low-grade PIN in humans. The reason for this appeared to be a high rate of cellular detachment and subsequent fall off into the lumen in ERβ–/– mice. The fall off phenomenon is possibly related to the finding that the expression of the cell adhesion molecule E-cadherin was very reduced. We conclude that in ERβ–/– mouse prostates, the epithelial cell population contains more epithelial cells in the intermediate stage of differentiation, possessing both the ability to proliferate as the basal cells and the ability to secrete as the highly differentiated luminal epithelium.

Estrogen receptor β-deficient female mice develop a bladder phenotype resembling human interstitial cystitis

Interstitial cystitis/painful bladder syndrome is a disease seen mostly in women, and symptoms tend to be worse premenopausally or during ovulation. The four cardinal symptoms of interstitial cystitis/painful bladder syndrome are bladder pain, urgency, frequency, and nocturia. Estrogen has been implicated in the etiology of this disease, but the role of the two estrogen receptors (ER), ERα and ERβ, has not been investigated. We found that, in the bladders of WT mice, ERβ is expressed in the basal cell layer of the urothelium. Bladders of male ERβ−/− mice were intact and morphologically indistinguishable from those of their WT littermates. However, in female ERβ−/− mice, there was ulceration and atrophy of bladder urothelium concomitant with infiltration of γδ T cells concentrated in the areas of atrophy and shedding of urothelium. The data support the idea that activated γδ T cells are causing the damage to the urothelium. The hyperactivity of T cells may be because of an imbalance between ERα and ERβ signaling in female ERβ−/− mice. Our data suggest that reduced ERβ signaling might have a role in the pathogenesis of interstitial cystitis, and ERβ could be a candidate for a target of medical therapy.