circFAM120A participates in repeated implantation failure by regulating decidualization via the miR-29/ABHD5 axis

Repeated implantation failure (RIF) is a major problem that limits the pregnancy rate associated with assisted reproductive technology. However, the pathogenesis of RIF is still unknown. Recently, the expression levels of circular RNAs (circRNAs) were profiled in the endometrial tissues of patients with RIF. However, the exact role of circRNAs in RIF remains unclear. In our study, we found that circFAM120A levels were significantly down-regulated in the endometrium at the window of implantation in RIF patients compared with non-RIF controls. The suppression of circFAM120A expression inhibited decidualization in human endometrial stromal cells (hESCs). Furthermore, RNA-seq analysis after circFAM120A knockdown revealed ABHD5 as a potential downstream target gene of circFAM120A. As expected, down-regulating ABHD5 in hESCs also inhibited decidualization. Using the starBase and TargetScan databases, we predicted that miR-29 may interact with ABHD5, based on nucleotide sequence matching. Luciferase reporter assay showed that miR-29 bound to the 3' UTR of ABHD5 at the predicted complementary sites. Moreover, miR-29 mimics efficiently reduced ABHD5 expression levels and suppressed the decidualization process, whereas a miR-29 inhibitor partly rescued ABHD5 mRNA expression level and decidualization reduced by the knockdown of circFAM120A. Therefore, circFAM120A modulated decidualization in RIF through the miR-29/ABHD5 axis.