Effects of metformin on mammalian target of rapamycin in a mouse model of endometrial hyperplasia

Abstract

Objective The effects of metformin on S6K1, which is a crucial effector of mTOR signaling, and on endometrium were studied in a mouse model of endometrial hyperplasia induced by unopposed estradiol or tamoxifen. Study design Forty-eight oophorectomized Balb/c mice were randomly assigned to receive saline, tamoxifen citrate (4 mg/kg), 17-beta estradiol hemihydrate (4 mg/kg), metformin (50 mg/kg), tamoxifen citrate (4 mg/kg) with metformin (50 mg/kg), or estradiol (4 mg/kg) with metformin (50 mg/kg) for 3 days. Histological markers of uterotrophy, including luminal epithelial cell height and density of endometrial glands were quantified for each slide. Immunohistochemical expression of PCNA and S6K1 was evaluated. H-score was used for S6K1 expression. Statistical analysis was performed using Student's t-test for comparison of two continous variables and one-way ANOVA for comparison of multiple variables. Results Mice treated either with tamoxifen or estradiol had significantly increased density of endometrial glands and epithelial heights compared to vehicle-only or metformin-only group ( p < 0.001). Addition of metformin to tamoxifen or estradiol treated mice significantly decreased the density of endometrial glands and epithelial cell heights ( p < 0.05). Addition of metformin to tamoxifen significantly decreased the H-score of S6K1 ( p < 0.05) and the immunohistochemical expression of PCNA ( p < 0.05) in uterine lining epithelium, glandular and stromal cells. Addition of metformin to estradiol significantly decreased the H-score of S6K1 ( p < 0.05) and the immunohistochemical expression of PCNA ( p < 0.05) in uterine lining epithelium, glandular and stromal cells. Conclusion Metformin seems to have possible antiproliferative effects on the endometrium of estradiol or tamoxifen treated mice via inhibiting the mTOR mediated S6K1 activation.