A novel identified circ-ANKHD1 targets the miR-27a-3p/SFRP1 signaling pathway and modulates the apoptosis of granulosa cells

The specific expression profile and function of circular RNAs (circRNAs) in mammalian ovarian follicles, especially during the atresia process, are unclear. In this study, we verified and explored the expression and function of circ-ANKHD1 in granulosa cells. Our results showed that abundance of circ-ANKHD1 was significantly lower in the granulosa cells than that of ANKHD1. The expression of ANKHD1 was highest in the granulosa cells from follicles with a diameter of 5-6 mm and lowest in that with a diameter of 3-4 mm. Furthermore, the expression level of circ-ANKHD1 in the ovarian tissue of 1-day-old piglets was significantly higher than that of 17-month-old multiparous sows. The luciferase reporter assay showed the potential interaction between circ-ANKHD1 and miR-27a-3p/miR-142-5p. Furthermore, circ-ANKHD1 overexpression up-regulated SFRP1 expression, while miR-27a-3p overexpression suppressed SFRP1 expression in granulosa cells. Circ-ANKHD1 overexpression significantly decreased the cell apoptotic rates of the granulosa cells and repressed the cell population at G0/G1 and S phases but increased cell population at G2/M phase. Finally, circ-ANKHD1 overexpression increased the mRNA expression levels of Bcl-2 and cyclin D1 in the granulosa cells, while there are no effects on the mRNA expression levels of caspase-3, p53, Bax, and proliferating cell nuclear antigen. In conclusion, our study for the first time identified a novel circRNA, circ-ANKHD1 that may be associated with the biological functions of granulosa cells. Circ-ANKHD1 may promote the granulosa cell proliferation, but attenuate apoptosis, and these effects may be associated with modulation of miR-27a-3p/SFRP1.