Early pregnancy loss (EPL), a common and severe complication in pregnancy, has a long-term personal and social impact. It was previously reported that follistatin-like 3(FSTL3), an activin A binding protein, contributes to the invasion and migration of trophoblast. Simultaneously, activin A induces the release of FSTL3 and the elevated activin A is found to be associated with pregnancy loss in women. This study aimed to identify the roles of FSTL3 in the establishment and maintenance of pregnancy, and to determine whether FSTL3 is involved in the pathophysiology of EPL.

Endometrial Ishikawa cells and JAR cells were cultured and FSTL3 siRNA was used to silence FSTL3. The trophoblast spheroids mimicking embryos were used in an embryonic adhesion system. The system aimed to investigate the role of FSTL3 silence on embryonic adhesion onto endometrial cell in vitro. The ICR mice model in vivo was used to investigate whether the FSTL3 works in embryonic implantation. The western blotting was used to determine the expression of FSTL3 and activin A.

In the in vitro study, silence of FSTL3 in JAR cells significantly reduced the number of trophoblast spheroids adhered onto Ishikawa cells compared with the scramble siRNA. For the in vivo study, the number of embryos implanted in the uterine horn injected with FATL3 siRNA mixture was significantly less than that in control group. In the case control study, both the expression of FSTL3 and activin A in EPL women were significantly higher than that in controls.

FSTL3 plays a biological role in the establishment and maintenance of normal pregnancy. Moreover, FSTL3 may be involved in the early pregnancy loss via neutralizing the elevated activin A.