Aquaporin 9 drives macrophage M1 polarization and intervertebral disc degeneration by stabilizing p65 to activate NF-κB signaling

Introduction Intervertebral disc degeneration (IVDD) is a primary cause of low back pain, but its molecular mechanisms remain poorly understood, limiting therapeutic development. This study investigates the role of aquaporin 9 (AQP9) in IVDD and its regulation of macrophage M1 polarization through the NF-κB pathway. Methods AQP9 expression was examined in degenerated nucleus pulposus (NP) tissues from both rodent models and human clinical samples. The functional role of AQP9 was assessed using AAV-mediated AQP9 overexpression and pharmacological inhibition of AQP9. The involvement of the NF-κB pathway was evaluated using an NF-κB specific inhibitor, with M1/M2 macrophage polarization analyzed in vivo and in vitro . Results AQP9 expression was significantly upregulated in degenerated NP tissues from both rodent models and human clinical samples. Functionally, AAV-mediated AQP9 overexpression exacerbated IVDD and extracellular matrix (ECM) degradation, while pharmacological inhibition of AQP9 exerted protective effects. Mechanistically, AQP9 directly bound to p65, inhibiting its ubiquitin-proteasome degradation and thereby prolonging p65 protein half-life and enhancing its stability. This sustained p65 activation continuously stimulated the NF-κB pathway, driving macrophage polarization toward a pro-inflammatory M1 phenotype, as evidenced by increased M1 markers and an elevated M1/M2 ratio in vivo and in vitro . The pro-inflammatory and catabolic effects of AQP9 were completely abrogated by an NF-κB specific inhibitor, confirming pathway dependence. Discussion Our findings elucidate a non-canonical function of AQP9 as a p65 stabilizer, establishing a novel “AQP9-p65-macrophage plasticity” axis that drives IVDD. This work positions AQP9 as a promising diagnostic biomarker and therapeutic target for IVDD, and suggests its potential relevance in other inflammatory degenerative diseases.