C/EBP-beta contributes to pig endometrial LE receptivity by targeting cell remodeling genes during implantation

In brief: Transforming the endometrial luminal epithelium (LE) into a receptive state is a requisite event for successful embryo implantation. This study suggests the role of a transcription factor in regulating endometrial LE receptivity. The endometrial luminal epithelium (LE) undergoes extensive remodeling during implantation to establish receptivity of the uterus in response to the conceptus signals, such as interleukin 1 beta (IL1B). But the mechanisms remain to be fully understood. This study investigated the role of CCAAT/enhancer-binding protein beta (C/EBP-beta) in regulating pig endometrial LE receptivity. Our results showed that C/EBP-beta was expressed and activated only in the endometrial LE in an implantation-dependent manner. In addition, C/EBP-beta was highly activated at the pre-attachment stage compared to the attachment stage, and its activation was correlated with the expression of IL1B-dependent extracellular signal-regulated kinases1/2-p90 ribosomal S6 kinase signaling axis. Subsequent chromatin immunoprecipitation (ChIP)-sequencing analysis revealed that the binding of C/EBP-beta within the promoter was positively associated with the transcription of genes related to cell remodeling. One such gene is matrix metalloproteinase 8 (MMP8), which is responsible for extracellular matrix degradation. The expression of MMP8 was abundant at the pre-attachment stage but dramatically declined at the attachment stage in the endometrial LE. Consistent with C/EBP-beta, the expression and activation of MMP8 were limited to the endometrial LE in an implantation-dependent manner. Using ChIP-qPCR and electrophoresis mobility shift assay approaches, we demonstrated that C/EBP-beta regulated the expression of the MMP8 gene during implantation. Furthermore, we detected that MMP8 and one of its substrates, type II collagen, showed a mutually exclusive expression pattern in pig endometrial LE during implantation. Our findings indicate that C/EBP-beta plays a role in pig endometrial LE receptivity by regulating cell remodeling-related genes, such as MMP8, in response to conceptus signals during implantation.