Temporal Changes in Cyclin D-CDK4/CDK6 and Cyclin E-CDK2 Pathways: Implications for the Mechanism of Deficient Decidualization in an Immune-Based Mouse Model of Unexplained Recurrent Spontaneous Abortion

Abstract Deficient endometrial decidualization has been associated with unexplained recurrent spontaneous abortion (URSA). However, the underlying mechanism is poorly understood. Here, we aimed to investigate the temporal cytokine changes and the involvement of the cyclin D-cyclin-dependent kinase (CDK)4/CDK6 and cyclin E-CDK2 pathways in the regulation of the G1 phase of the cell cycle during decidualization in a murine model of URSA. Serum and decidual tissues of URSA group and normal pregnant (NP) group mice were collected from gestation day 4 (GD4) to GD8. The embryo resorption and abortion rates were observed on GD8 and the decidual tissue status was assessed using hematoxylin and eosin staining. Cytokine levels in decidual tissues were analyzed using western blotting and reverse transcription polymerase chain reaction. We found that the embryo resorption rate was significantly increased in the URSA group compared to that in the NP group on GD8. The expression of the decidualization marker prolactin in the serum and decidual lysate of the URSA group was significantly decreased on GD6-8 compared to that of the NP group. Cyclin D, CDK4, CDK6, cyclin E, CDK2 and pRb levels in the URSA group mice were significantly lower compared to those in the NP group mice on GD6-8. Our results suggest that the hyperactivated cyclin D-CDK4/CDK6 and cyclin E CDK2 pathways inhibit the decidualization process on GD4, leading to deficient decidualization on GD8. Moreover, they clarify the role of cytokines in the cyclin D-CDK4/6 and cyclin E-CDK2 pathways during decidualization and provide new insight into URSA pathogenesis.