Introduction: The placenta is a multifaceted organ of pregnancy, serving as the interface between the maternal and fetal circulation. Its outermost layer is composed of the syncytiotrophoblast – a multi-nucleated epithelial cell comprising the placenta’s surface. Apical-basal polarization is a fundamental property of epithelial cells, enabling efficient transport functions. The syncytiotrophoblast exhibits high apical-basal polarity at term, and dysregulation of polarity is associated with placental pathology; however, the mechanisms governing apical-basal polarity within the syncytiotrophoblast are unknown.
The Par complex is an evolutionarily-conserved protein complex containing atypical protein kinase C (aPKC) – an integral kinase known to govern polarity in epithelial cells. Restriction of aPKC to the apical membrane is essential for its function. However, the expression and localization of aPKC in the placenta has never been examined. We hypothesize that aPKC will be localized at the apical membrane of the syncytiotrophoblast in early gestation and regulate apical-basal polarity.
Methods: Five-to-ten week and term placentas were analyzed via immunofluorescent staining with antibodies against aPKC-ζ, aPKC- ι, E-cadherin, epidermal growth factor receptor (EGFR), and phalloidin. Images were captured with confocal microscopy, and the overlap correlation coefficient of voxel intensity (ranging from 0.00-1.00) of proteins with apically-localized phalloidin was quantified.
Results: Apical localization of aPKC-ζ slightly increased from five (0.34±0.13) to eight weeks gestation (0.70); however, aPKC- ι exhibited consistently low apical localization (0.46±0.08). aPKC-ζ was apically-localized at term (0.79). Additionally, apical polarization of EGFR was observed at all gestational ages.
Conclusion: aPKC does not exhibit consistent apical localization within the syncytiotrophoblast, despite polarization of other proteins in early gestation. This suggest that aPKC may not regulate polarity until the end of the first trimester. Future characterization of the mechanisms governing apical-basal polarity within the syncytiotrophoblast may provide insight into placental development and pathogenesis, leading to the identification of novel therapeutic targets.
Jasmine Nguyen– Undergradute Student, Obstetrics and Gynaecology, and Physiology, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
Saba Saadat– Undergradute Student, Obstetrics and Gynaecology, and Physiology, University of Alberta, Edmonton, Alberta, Canada T6G 2S2
Meghan Riddell– Principal Investigator, University of Alberta, Department of Obstetrics & Gynecology