Alteration of the PI3K/Akt signaling pathway by swainsonine affects 17β-Estradiol secretion in ovary cells

Background: The ingestion of locoweed that contains the toxic indolizidine alkaloid swainsonine (SW) disrupts ovarian function, accompanied by delayed estrus, increased estrous cycle length, delayed conception, and abortion.

Goals: The direct effects of SW on ovary cell steroidogenesis remain unclear.

Materials and methods: In this study, Chinese hamster ovary (CHO) cells were used to investigate the effects of SW on estradiol (E2) secretion and cell viability and the mechanisms involved in these processes.

Results: CHO cells were treated with SW. 17 β-Estradiol mRNA expression was decreased in the SW group compared to that in the control group. Various concentrations of E2 and SW were added to cultured cells for 12 h and 36 h. Compared to the control group cells, CYP19A1 expression was decreased in the SW and SW + E2 treatment groups at 12 h and 36 h (P < 0.05). This showed that SW mainly inhibits the last step of estrogen synthesis. When CHO cells were treated with SW, the p-Akt protein levels were significantly decreased compared to that in the control group cells at 12 h and 36 h (P < 0.05). However, the p-Akt expression in the SW + E2 group was not significantly different compared to that in the control group cells (P > 0.05). When CHO cells were treated with SW and SW + E2, the PI3K protein levels were significantly down-regulated compared to that in the control group cells at 12 h and 36 h.

Conclusion: Taken together, these studies demonstrate that SW is an inhibitor of PI3K/Akt signaling pathway. However, SW blocked PI3K activation in estrogen induction without blocking p-Akt activation in CHO cells. Therefore, SW + E2 blocked upstream but did not affect the downstream of the PI3K/Akt signaling pathway.