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Extracellularly Signal-Regulated Kinase Activity in the Human Endometrium: Possible Roles in the Pathogenesis of Endometriosis

Department of Obstetrics, Gynecology, and Reproductive Sciences (W.M., H.C., U.A.K., A.A.), Yale University School of Medicine, New Haven, Connecticut 06520; and Departments of Obstetrics and Gynecology (C.S.A.) and Pathology (A.H., A.E.), Ankara University School of Medicine, Ankara, Turkey

Address all correspondence and requests for reprints to: Aydin Arici, M.D., Department of Obstetrics, Gynecology, and Reproductive Sciences, Yale University School of Medicine, 333 Cedar Street, New Haven, Connecticut 06520-8063. E-mail: aydin.arici{at}yale.edu.

Context: Endometriosis is an estrogen-dependent disease characterized by the presence of endometrial tissue outside of the uterine cavity, causing pelvic pain and infertility in 10% of reproductive-aged women. It is unclear why ectopic endometrium remains viable in only a subset of women. ERK1/2 plays key intracellular roles in activating cellular survival and differentiation processes.

Objective: We sought to determine ERK1/2 activity in patients with endometriosis and its possible roles in regulating endometrial cell survival.

Design: ERK1/2 phosphorylation and expression throughout the menstrual cycle were evaluated in vivo in normal and endometriotic human endometrium, and in vitro techniques assessed the steroidal regulation of ERK1/2 and its effect on endometrial cell survival.

Results: Total ERK1/2 remained constant in normal and endometriotic endometrium throughout the menstrual cycle. Phospho-ERK1/2 was high in the late proliferative and secretory phases in normal endometrium (P < 0.05). In endometriotic glandular cells, there was no cyclical variation in phospho-ERK1/2. In endometriotic stromal cells, there was also a reduction in phospho-ERK1/2 variation, with higher levels in the early-mid secretory phase (P < 0.05). In cultured endometrial stromal cells (ESCs), estrogen plus progesterone increased ERK1/2 phosphorylation within 15 min (P < 0.05). Although estrogen alone did not induce ERK1/2 phosphorylation in normal ESCs, there was a significant response to estrogen in ESCs isolated from eutopic endometriotic endometrium (P < 0.05). ERK1/2 inhibition in ESCs reduced proliferation and increased apoptosis (P < 0.05).

Conclusion: Abnormally high levels of ERK1/2 activity may be involved in endometriosis, possibly by stimulating endometrial cell survival.