Downregulation of Aquaporin 3 Promotes Hyperosmolarity-Induced Apoptosis of Nucleus Pulposus Cells Through PI3K/Akt/mTOR Pathway Suppression

Background Hyperosmolarity, a key pathological feature of intervertebral disc degeneration (IVDD), significantly contributes to nucleus pulposus cell (NPC) apoptosis. Aquaporin 3 (AQP3), an osmolyte channel, is markedly downregulated in degenerative discs. However, its role in hyperosmotic stress-induced NPC apoptosis remains unclear. Methods Rat NPCs were exposed to hyperosmotic conditions in vitro. Lentiviral vectors were employed to overexpress AQP3, while a selective inhibitor was used to block its function. Western blotting, flow cytometry, and mitochondrial membrane potential assays were performed to assess PI3K/Akt/mTOR signaling, apoptosis, and oxidative stress. An in vivo rat IVDD model was established, and disc integrity was evaluated histologically. Results Hyperosmolarity suppressed AQP3 expression, inhibited PI3K/Akt/mTOR signaling, induced mitochondrial dysfunction, and increased ROS production, thereby promoting NPC apoptosis. AQP3 overexpression restored PI3K/Akt/mTOR activation, attenuated oxidative stress, and reduced apoptosis. In rat models, AQP3 overexpression alleviated IVDD progression and preserved disc structure, whereas AQP3 inhibition exacerbated extracellular matrix degradation and tissue destruction. Conclusions AQP3 deficiency contributes to hyperosmolarity-induced NPC apoptosis through suppression of PI3K/Akt/mTOR signaling, forming a pathological cycle that accelerates IVDD progression. These findings suggest that AQP3 may serve as a promising therapeutic target for delaying IVDD.