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 beta-galactoside-alpha 2,3-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.