Abstract
PurposeClaudins as the major components of tight junctions are important in maintaining cell–cell integrity and thus function as a barrier. Dysregulation of the claudins is often associated with loss of the epithelial phenotype, a process called epithelial–mesenchymal transition (EMT), which most often results in gain of migrative and invasive properties. However, the role of claudins in the endometrium or endometriosis has only rarely been examined.MethodsIn this study, we investigated localization of claudin-2 and claudin-3 in the eutopic and ectopic endometrium with immunohistochemistry. A detailed quantification with HSCORE was performed for claudin-2 and claudin-3 in endometrium without endometriosis and in cases with endometriosis compared to the three endometriotic entities: peritoneal, ovarian, and deep-infiltrating endometriosis.ResultsWe found a preferential localization of both claudins in the glandular and the luminal epithelial cells in the endometrium with and without endometriosis. Quantification of localization of both claudins showed no differences in eutopic endometrium of control cases compared to cases with endometriosis. Furthermore, both claudins are localized highly similar in the ectopic compared to the eutopic endometrium, which is in clear contrast to previously published data for claudin-3.ConclusionFrom our results, we conclude that localization of claudin-2 and claudin-3 is highly stable in eutopic and ectopic endometrium without any loss of the epithelial phenotype and thus do not contribute to the pathogenesis of endometriosis.
Highlights
Endometriosis is characterized by the presence of endometrial glands and stroma outside the normal localization, irrespective of location, the histological appearance of endometriotic glands always resembles uterine endometrial glands [1]
Positivity for claudin-2 was further identified in the majority of endometriotic epithelial cells and lesions irrespective of the three endometriotic entities: ovarian (Fig. 2a), peritoneal (Fig. 2b) or deep-infiltrating endometriosis (Fig. 2c)
As the HSCORE showed no significant differences between eutopic endometrium with and without endometriosis (Table 2), we merged both datasets and found no significant differences between the eutopic and ectopic endometrium (Table 3)
Summary
Endometriosis is characterized by the presence of endometrial glands and stroma outside the normal localization, irrespective of location, the histological appearance of endometriotic glands always resembles uterine endometrial glands [1]. Despite the high rate of retrograde menstruation ranging from 76 to 90% [4, 5], only approximately 0.8–2.0% of women in their reproductive age acquire endometriosis as shown in large population-based studies of low-risk patients [6,7,8,9,10]. This discrepancy suggests secondary factors like immune dysfunction for the establishment of endometriotic lesions [11]. The composition of claudins determines the properties of epithelial barriers such as sealing claudins
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