The involvement of apoptotic regulators during in vitro decidualization
Objectives: The uterus responds to an implanting blastocyst by undergoing extensive tissue modification leading to decidualization. This modification includes differentiation and apoptosis of epithelial as well as stromal cell compartments. It is generally accepted that the decidual cell regression pattern is similar to the pattern of initial differentiation, suggesting that decidual cell death is the end point of timed differentiation. However, the molecular mechanisms controlling these events are not understood clearly. Therefore, we aimed to investigate the involvement of apoptotic factors using an in vitro cell culture system. Design: In order to assess the role of apoptotic factors during decidualization, we used a decidual cell line (GG-AD) that had been transformed with a temperature-sensitive SV-40 mutant. At the non-permissive temperature (39°C), these cells showed the characteristics of differentiated decidual cells. They dedifferentiated into stromal cells when the temperature was shifted back to 33°C. Methods: We performed Northern blot analysis for bax, bcl-XL and bcl-2 at both temperatures. The onset of apoptosis was examined by Annexin V staining. The expression of p53 protein was also determined by Western blot. Results: We found an increase in the expression of bax when GG-AD cells were grown at 39°C. We also showed apoptosis with Annexin V staining at 39°C. The p53 protein expression was also similar to that of the animal models, suggesting that the programmed cell death of the decidual cells occurred in a p53-independent manner. Conclusions: These data indicate that a parallelism exists between the increased expression of pro-apoptotic genes and decidual cell death, similar to animal models. Therefore, an in vitro model of GG-AD cells can be used to assess directly the relationship between apoptotic regulators and decidualization and could be used to study the mechanism of decidual cell regression.