The sialyltransferase ST3Gal3 facilitates the receptivity of the uterine endometrium in vitro and in vivo

: The receptive uterine endometrium specifically expresses certain glycosyltransferases, and the corresponding oligosaccharides play important roles in accepting the embryo. The sialyltransferase β-galactoside-α2,3-sialyltransferase III (ST3Gal3) is the key enzyme responsible for sialyl Lewis X (sLeX) oligosaccharide biosynthesis, but the expression and function of ST3Gal3 in the receptive endometrium is still elusive. Here, we found that human endometrial tissues at secretory phase expressed a 4-fold higher ST3Gal3 level relative to the tissues at proliferative phase. Meanwhile, downregulation of ST3Gal3 or sLeX epitope blockage significantly impaired the receptive ability of human endometrial RL95-2 cells to trophoblastic cells in vitro and inhibited implantation in pregnant mice. This study suggests that ST3Gal3 facilitates endometrial receptivity through increasing sLeX oligosaccharide, which gives a better understanding of the glycobiology of implantation.