17β-estradiol inhibits interleukin-1β-induced rat nucleus pulposus cell apoptosis through the PI3K/Akt/mTOR signal pathway

The apoptosis of nucleus pulposus cells (NPCs) is the main cellular process of intervertebral disc degeneration (IVDD). Our previous studies showed that 17β-estradiol (E2) protects rat NPCs from interleukin-1β (IL-1β)-induced apoptosis via the PI3K/Akt signaling pathway. This study was aimed to investigate whether downstream proteins of PI3K/Akt pathway were involved in inhibition of E2 on NPCs' apoptosis. Primary culture of rat NPCs was isolated by trypsin digestion. Being pretreated with E2 and different inhibitors of downstream proteins of PI3K/Akt pathway, the NPCs were treated with IL-1β. Cellular apoptosis was detected by Annexin V/PI staining. Cell viability was detected by CCK-8. Cell adhesion was evaluated by cell-collagen binding assay. Phosphorylation levels of mammalian target of Rapamycin (mTOR), glycogen synthase kinase-3β (GSK-3β) and nuclear factor κB (NF-κB) were detected by Western blot. The results showed that E2 significantly inhibited the IL-1β-induced apoptosis of NPCs, reversed the decrease of cell viability and adhesion induced by IL-1β, and inhibited the down-regulation of mTOR phosphorylation level induced by IL-1β. Rapamycin could block these protective effects of E2. These results suggest that E2 may inhibit IL-1β-induced NPCs' apoptosis through the PI3K/Akt/mTOR signaling pathway.