Lewis x-Carrying O-glycans are Candidate Modulators for Conceptus Attachment in Pigs

Successful attachment of conceptus to the uterine luminal epithelium (LE) is crucial for establishing a functional placenta in pigs. However, the underlying mechanisms are yet to be elucidated. The uterine LE-conceptus interface is enriched in various glycoconjugates essential to implantation. Using MALDI-MS profiling, we identified for the first time the O-glycan repertoire in pig endometrium during the conceptus attachment stage. The expression pattern of blood group A, O(H), Lewis x, y, a, b (Le(x), Le(y), Le(a), and Le(b)), the sialylated and sulfated Le(x) antigens in the uterine LE-conceptus interface was assessed using immunofluorescence assays. Notably, the Le(x)-carrying O-glycans exhibited a temporal-spatial expression pattern. They were absent in the endometrium on estrous cycle days but strongly and spatially presented in the conceptus and uterine LE to which the conceptus apposes during the early conceptus attachment stage. In addition, Le(x)-carrying O-glycans were co-localized with secreted phosphoprotein 1 (SPP1), a well-characterized factor that plays a role in promoting conceptus attachment through interacting with integrin αVβ3 and integrin αVβ6. Meanwhile, the immunoprecipitation assays revealed an interaction between the Le(x)-carrying O-glycans and SPP1, integrin αV, and integrin β6. Furthermore, we provided evidence that the β1,4-galactosyltransferase 1 (B4GALT1) gene is a potential regulator for Le(x) antigen expression in the uterine LE-conceptus interface during the early conceptus attachment stage. In conclusion, our findings show that Le(x)-carrying O-glycans, presumably dependent on B4GALT1 gene expression, might modulate conceptus attachment by interacting with the SPP1-integrin receptor complex in pigs.