Downregulation of p53 drives autophagy during human trophoblast differentiation

A functional placental barrier is crucial for the supply of the embryo or foetus throughout pregnancy. It is formed by the syncytiotrophoblast, which develops via fusion of cytotrophoblast cells. How this “differentiation-by-fusion” is regulated is only partially understood. Here we analysed transcriptome changes during in vitro cytotrophoblast fusion. Pathway analyses yielded the tumor suppressor p53 as upstream negative regulator and indicated an upregulation of autophagy-related genes. We further showed that, during differentiation, p53 is downregulated on the mRNA and protein levels, while the autophagy marker LC3B-II (lipidated LC3B) is increased. In first-trimester placentae, we find reciprocal expression patterns of p53 and LC3B, with p53 expression primarily in cytotrophoblasts and predominant LC3B expression in the apical side of the syncytiotrophoblast layer. Furthermore, in the syncytiotrophoblast, we could show increased autophagic flux, which is alleviated by ectopically overexpression of p53. This was also shown in placental explants treated with a pharmacological p53 activator. On the contrary, in a fusion-deficient trophoblast cell line we could not see an interdependency of p53 and LC3B lipidation. In summary our data suggests, that the downregulation of p53 during syncytialization is a prerequisite for the activation of autophagy in the placental barrier. Trophoblast cell line BeWo was used as in vitro model to study global transcriptome changes in villous trophoblast differentiation. For this purpose BeWo cells were cultured for 48h in presence of forskolin, a compound well described to induce syncytiotrophoblast formation. Control cells were treated with solvent for 48 hours (DMSO). Each group comprised three replicates.