Introduction: Unscheduled breakthrough-bleeding (‘spotting’) is a common problem in progestin only contraceptive (POC) users. A major feature of POC-endometria is the presence of ‘fragile’ luminal epithelium (LE), susceptible to shedding/bleeding. We propose that disturbances in Wnt signalling, mediated by signals from the decidualized stroma in POC-endometria, cause LE alterations underlying fragility and bleeding events.
Materials & methods: Wnt5a and 7a, β-catenin, E-cadherin and DKK1 were examined by immunohistochemistry in POC- and normal endometrium. Primary human endometrial stromal cells (HESC) were treated with estrogen (10-8M) and progesterone (MPA, 10-7M), both prolactin (PRL) and DKK1 were assessed by ELISA in decidualized (DEC, day 12) versus non-DEC (day 2) media. β-catenin, phospho(P)-β-catenin, APC and Wnt7a localization was examined by immunocytochemistry in recombinant human (rh)-DKK1 treated endometrial epithelial cells (EEC) and P-β-catenin abundance was determined by western immunoblot (WB). The impact of DEC- versus non-DEC media and rhDKK1 on real-time EEC proliferation and migration was determined using the xCelligence system.
Results: Wnt-5a, Wnt7a, β-catenin and E-cadherin localized to luminal/glandular epithelial cells in cycling endometrium. DKK1 localized to luminal epithelium in proliferative-phase, and stroma in secretory-phase endometria. In the POC-endometrium, Wnt7a, β-catenin and E-cadherin had disappeared/displayed abnormal localization while DKK-1 strongly localized to DEC-stroma. DEC-HESC secreted elevated levels of PRL and DKK1 versus non-DEC. Treatment of endometrial epithelial cells (EEC) with DEC-media or rhDKK1 reduced EEC proliferation and increased migration. rhDKK1 treatment of EEC resulted in a down-regulation of Wnt7a, and β-catenin at cell-cell junctions, and up-regulation of P-β-catenin and APC, while WB demonstrated an elevation in P-β-catenin upon rhDKK1 treatment.
Conclusions: Wnt signalling molecules are altered in the POC-endometrium and rhDKK1 treated EEC. Alterations in Wnt signalling pathways impact cell function. This data suggests that stromal signals (DKK1) impact on signalling and function in the epithelium, contributing to epithelial fragility in POC-endometria.