FBXO18/Circrna211/Mir-431/CSF1 Axis Regulates the Establishment of Endometrial Receptivity Though Activating MAPK and CSF1R/PI3K/AKT/Mtor Pathways in Dairy Goats

Abstract Background: Endometrial epithelial cells proliferation and secretion of various cytokines have a strong impact on the formation of receptive endometrium, which is known as a physiological status that allows an activated embryo to attach to the endometrium for a limited time. Circular RNAs and miRNAs can be involved in the dynamic physiological changes of endometrium by regulating relevant functional target genes in the uterus. Our work presented here with the ultimate purpose of revealing the latent molecular mechanism of FBXO18/circRNA211/miR-431/CSF1 axis in the establishment of endometrial receptivity of dairy goats.Results: In vitro, we found a regulatory network of FBXO18/circRNA211/miR-431/CSF1 in goat endometrial epithelial cells that circRNA211 severed as a sponge for miR-431, resulting in weakening the inhibition of miR-431 on target genes CSF1 and FBXO18. FBXO18/circRNA211/miR-431/CSF1 axis promoted the proliferation through regulating the key proteins of Ras, Raf, MEK, ERK in MAPK pathway via CCK-8, EdU, flow cytometry and Western blot assays. Furthermore, FBXO18/circRNA211/miR-431/CSF1 axis activated the phosphorylation of key proteins PI3K, AKT and mTOR in PI3K-mTOR pathway by CSF1R, thereby promoting the establishment of endometrial receptivity. In vivo models, mice injected with miR-431 agomir showed that the endometrial thickness and the number of pinopodes were significantly decreased by HE staining and scanning electron microscope. Immunohistochemistry results showed that VEGF and OPN proteins were down-regulated and MUC1 protein was up-regulated under the treatment of miR-431 agomir. Further study demonstrated that miR-431 inhibited embryo implantation by impeding the establishment of endometrial receptivity.Conclusion: Ultimately, our study revealed a regulatory mechanism of FBXO18/circRNA211/miR-431/CSF1 axis in goat endometrial epithelial cells. This circRNA/miRNA/mRNA regulatory network presented here in vitro and in vivo models may provide a novel insight into the potentially regulating endometrium biological functions and promoting the formation of endometrium receptivity.