Project description:Abstract Background During equine implantation, two trophoblast subpopulations are distinguished: the invasive (chorionic girdle) and non-invasive (allantochorion). The invasive chorionic girdle is believed to interact with the maternal immune system and contribute to embryo attachment to the endometrium. However, the mechanism regulating attachment and immune tolerance to these two distinct trophoblast subpopulations remain incompletely understood. The present study aimed to investigate the regulation of gene expression and the biological processes involved in trophoblast attachment, development and maintenance of immune tolerance by comparing the transcriptomes and methylomes of the allantochorion and chorionic girdle trophoblast before and after implantation, that is, between days 33 and 42 of gestation. Results Irrespective of gestational day, allantochorion (N=4) was enriched in TGFB and its receptors TGFBR1 and TGFBR2. Across implantation, expression of regulatory macrophage markers, as IL33, IL4|1, PLG-RKT, or CD163, also increased in that membrane in addition to TFEB and SERPINE1. Invasive chorionic girdle (CG33, N=4) had higher, than the non-invasive allantochorion (ALC33, N=4), expression of NLRC5, a transcriptional regulator of MHC I, and expression of that factor further decreased in allantochorion from gestational day 33 to 42. Furthermore, B2M, which encodes the MHC I light chain, was hypermethylated in the allantochorion. Some genes were differentially methylated and expressed between the two trophoblasts (CAVIN1, LHB, INSR) or beginning and end of implantation (IFNGR1, CD177). Analysis of GOterms and canonical pathways showed that both differentially expressed and methylated genes were involved in critical for implantation processes and pathways as these including cell movement and adhesion, TGFB signaling, fibrosis, wound healing, or leukocyte extravasation. Conclusions Allantochorion may contribute to the formation of the attachment with the endometrium and maintenance of maternal tolerance. Expression of IL33, IL4|1 or CD163 suggests involvement of regulatory macrophages in the implantation. TFEB might be involved in the support of allantochorion steroidogenic functions and maturation. Spatial-temporal differential methylation of genes expressed by the chorionic girdle and allantochorion may contribute to the control of trophoblast invasion and its attachment to endometrium. Finally, methylation of B2M and differential expression of NLRC5, are involved in the control of MHC I expression on equine trophoblasts during implantation. Background: During equine implantation, two distinct trophoblast subpopulations are identified: the invasive chorionic girdle (CG) and the non-invasive allantochorion. The invasive CG is believed to modulate the maternal immune response and facilitates embryo attachment to the endometrium, while the allantochorion contributes to placental development without breaching the endometrium. However, the mechanisms underlying differential adhesion and immune modulation by these two lineages remains poorly understood. This study aimed to investigate the regulation of biological processes underlying trophoblast attachment, development and maintenance of immune tolerance by comparing the transcriptomes and methylomes of CG and allantochorion trophoblasts before and after implantation, that is, between gestational days 33 and 42. Results: Irrespective of gestational day, allantochorion (n=4) was enriched in TGFB and its receptors TGFBR1 and TGFBR2. Across the implantation window, expression of regulatory macrophage markers such as IL33, IL4|1, PLG-RKT, and CD163 increased in the allantochorion, along with upregulation of TFEB and SERPINE1. The invasive GC (CG33, n=4) showed higher expression of NLRC5, a transcriptional regulator of MHC I, compared to the non-invasive allantochorion (ALC33, n=4). Notably, NLRC5 expression declined in the allantochorion from day 33 to 42. Furthermore, B2M, which encodes the MHC I light chain, was hypermethylated in the allantochorion. Several genes, including CAVIN1, LHB, and INSR, were both differentially expressed and methylated between the two trophoblast types, while others, such as IFNGR1, CD177, showed differential regulation across the implantation window. Gene Ontology and pathway analyses revealed that differentially expressed and methylated genes were enriched in biological processes and pathways critical for implantation, including cell migration and adhesion, TGFB signaling, fibrosis, wound healing, and leukocyte extravasation.Conclusions: The allantochorion plays an active role in establishing the attachment to the endometrium and sustaining maternal immune tolerance during implantation. The upregulation of IL33, IL4|1, and CD163 suggests the that the allantochorion may promote the recruitment or polarization of macrophages toward a regulatory phenotype, thereby modulating the local immune environment. TFEB may contribute to the steroidogenic activity and functional maturation of the allantochorion. Spatial and temporal differences in gene methylation between CG and allantochorion suggest involvement of epigenetic regulation in trophoblast invasion and attachment to the endometrium. Finally, combined B2M hypermethylation and differential expression of NLRC5 point to epigenetic and transcriptional control of MHC I expression in the equine trophoblasts during implantation.
2025-08-05 | GSE303997 | GEO