The Role of Autophagy in Human Endometrium1

Abstract

Autophagy appears to play an important role in the normal development and maintenance of homeostasis in a variety of tissues, including the female reproductive tract. However, the role of autophagy and the association between autophagy and apoptosis in cyclic remodeling of the human endometrium have not been described. Therefore, we investigated the involvement of autophagy during the human endometrial cycle and its association with apoptosis. Endometrial samples were obtained from 15 premenopausal, nonpregnant women who underwent hysterectomies for benign gynecological reasons. The autophagy-associated protein, microtubule-associated protein 1 light chain 3 alpha (MAP1LC3A), was immunolocalized, and its expression level was measured by Western blot analysis. Apoptosis was evaluated by measuring the expression level of cleaved caspase 3 protein. MAP1LC3A protein was primarily expressed within the endometrial glandular cells and increased during the secretory phase. The expression level of the membrane-bound form of MAP1LC3A (MAP1LC3A-II) also increased as the menstrual cycle progressed, reaching a maximum level during the late secretory phase. This pattern coincided with the expression of cleaved caspase 3. Furthermore, expression of MAP1LC3A-II and cleaved caspase 3 increased in the in vitro-cultured endometrial cancer cells when estrogen and/or progesterone were withdrawn from the culture media to mimic physiological hormonal changes. These findings suggest that endometrial cell autophagy is directly involved in the cyclic remodeling of the human endometrium and is correlated with apoptosis. In addition, we inhibited autophagic processes using 3-methyladenine (3-MA) or bafilomycin A1 (Baf A1) to evaluate the role of autophagy in apoptosis induction in endometrial cancer cells. While the inhibition of autophagosome formation using 3-MA did not decrease apoptosis or cell death, the inhibition of autophagosome degradation by fusion with lysosomes using Baf A1 increased apoptosis and cell death, suggesting that the accumulation of autophagosomes induces apoptosis. Furthermore, Baf A1-induced apoptotic cell death was decreased by the apoptosis inhibitor N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (Z-VAD-FMK). In conclusion, these results indicate that autophagy is involved in the endometrial cell cycle affecting apoptosis and is most prominent during the late secretory phase.