Fatty Acid-Binding Protein 4 in Endometrial Epithelium Is Involved in Embryonic Implantation

Aims: To clarify the role of fatty acid-binding protein 4 (FABP4) of endometrial epithelial cell in the establishment and maintenance of pregnancy and the involvement in the pathogenesis of pregnancy loss. Methods: The expression of FABP4 and uterine receptive factor (LIF, Integrin-β3 and Claudin 4) was determined by Western blotting or quantitative PCR. FABP4 siRNA was used to silence FABP4 while FABP4 inhibitor was used to inhibit the function of FABP4 in endometrial epithelial cell. ICR mice were raised to evaluate the effect of FABP4 silence or inhibition on embryo implantation in vivo after FABP4 siRNA mixture or inhibitor was injected into uterus, and an embryonic adhesion system using trophoblast spheroids mimicking embryos was set up to assess the effect of FABP4 silence or inhibition on embryonic adhesion onto endometrial cell in vitro. Results: The expression of FABP4 mRNA was significantly decreased in the deciduas of women with pregnancy loss compared with that of women with normal pregnancy. FABP4 siRNA significantly reduced the number of embryos implanted and FABP4 expression in ICR mice. FABP4 inhibition also significantly decreased the number of embryos implanted. Either silence or inhibition of FABP4 in endometrial epithelial cell abolished the expression of uterine receptive factors induced by the combination of estrogen and progesterone-induced, and reduced the number of trophoblast spheroids adhered onto endometrial cell. Conclusions: FABP4 regulates embryo implantation via altering uterine receptivity and decreased expression of FABP4 in endometrium may be linked with pregnancy loss, indicating FABP4 has biological role in the establishment and maintenance of pregnancy and subsequently is involved in pathogenesis of pregnancy loss.