The human placenta provides the vital interface between mother and fetus and is composed primarily of trophoblast cells derived from the outer layer of the blastocyst. Among these, villous cytotrophoblasts (VCTs) accompany placental development throughout pregnancy: some fuse to form the syncytiotrophoblast, the site of gas and nutrient exchange, while others, having become extravillous cytotrophoblasts (EVCTs), invade the maternal uterus and anchor the chorionic villi. Defective EVCT invasion or impaired VCT differentiation and fusion contributes to several gestational disorders, such as miscarriage, preterm birth, and preeclampsia, whose mechanisms remain poorly understood. The nuclear receptor PPARγ (peroxisome proliferator-activated receptor γ) plays a well-established role in placentation: its absence in mice leads to abnormalities in trophoblast differentiation and vasculogenesis, and its activation curbs the invasion of first-trimester EVCTs while inducing the differentiation of term VCTs. These contrasting effects according to cell subtype prompted a comparative genome-wide analysis.
To map these effects, the authors purified EVCTs and VCTs from human chorionic villi, cultured them in vitro, and then treated them with rosiglitazone, a PPARγ agonist. The transcriptomes of the two cell types were quantified by DNA microarrays. Differentially expressed genes were then filtered and subjected to Gene Ontology (GO) annotation and signaling pathway analysis using ClueGO. Protein–protein interactions involving PPARγ were predicted with STRING, binding sites on target promoters with iRegulon, and GO terms were compared between the two populations using clusterProfiler, with all results visualized in Cytoscape.
The analysis identified 139 differentially expressed genes in treated EVCTs and 197 in treated VCTs. Downstream annotations reveal the similarities and divergences between the two subtypes regarding the biological processes, molecular functions, cellular components, and KEGG pathways affected by the treatment. Several proteins appearing to interact directly with PPARγ had already been experimentally validated, including ANGPTL4, ABCG2, APOB, FABP4, HMOX1, and SERPINE1. Only one gene, ATXN1, emerged in both cell types, but with opposite responses—upregulated in EVCTs and repressed in VCTs—suggesting a possible involvement in the distinct responses of the two populations to PPARγ activation.
The authors emphasize that the use of DNA microarrays inherently limits detection to the probe set employed, and that an RNAseq approach would help fill potential gaps. Nevertheless, this work offers an overview of the biological processes modulated by PPARγ in trophoblasts and facilitates the subsequent search for genes or pathways that could constitute therapeutic targets in the human placenta.