Trophoblast Differentiation: Interest in the Controversial HTR-8/SVneo Cell Line as Model of Extravillous Trophoblast Differentiation and Specification

Abstract

Background: The human placenta is a transient organ that provides the interface between the fetus and the mother. Trophoblasts, the functional cell type of the placenta, differentiate along two pathways; the villous or the extra-villous pathway. A successful pregnancy outcome largely depends on the ability of progenitor cytotrophoblasts (CTBs) to exit the cell cycle, change from epithelial to mesenchymal phenotype through EMT process and differentiate into various subtypes of extra-villous CTBs (evCTBs), including the interstitial CTBs. Due to limiting access to human first trimester placentas and the scarcity of models in the field, HTR-8/SVneo cell line has been widely used in elucidating extra-villous trophoblast biology and functions. Recently, our group used various experimental approaches to prove that the HTR-8/SVneo cell line undergoes EMT under normal culture conditions.

Objective: Our aim is to investigate the ability of HTR-8/SVneo cells to fully recapitulate the phenotypic heterogeneity of evCTB differentiation pathway observed in vivo.

Methods: The morphology of cells from various passages was assessed using phase-contrast microscopy. Moreover, the expression of classical EMT markers was interrogated using quantitative real-time PCR and immunofluorescence (IF) analysis. Furthermore, spheres formation assay was conducted on different cell passages, after which spheres were transferred onto 5% matrigel in 2D culture. A morphological assessment of the cells propagating from the spheres was conducted, in addition to evaluating the expression of the epithelial and mesenchymal markers using immunofluorescence.

Results: Morphological assessment using IF analysis revealed that an epithelial large polygonal-like morphology prevailed in culture alongside the appearance of large multinucleated cells. These observations were further corroborated by the shift in the mesenchymal gene expression profile in sorted cells that have undergone EMT towards a mainly epithelial gene expression pattern in cells at late passages. Furthermore, our IF analysis showed that cells propagating from spheres generated from cells at late passages had an epithelial large polygonal-like phenotype.

Conclusion/Future Perspectives: In summary, our data provide solid evidence that the the HTR-8/SVneo cell line serves as a reliable model for evCTB differentiation. Further investigation is required to unravel the molecular mechanisms underpinning this differentiation process.