Aquaporin-1 Expression in Herniated Human Lumbar Intervertebral Discs

STUDY DESIGN: Case series. OBJECTIVE: Intervertebral disc (IVD) degeneration is the cause of spondylosis. The pathogenesis is poorly understood, but disc dehydration often plays a role. In this study, we aim to identify and quantify aquaporin-1 (AQP1) in ex vivo human degenerated IVDs obtained intraoperatively and to investigate the relationship between AQP1 levels and magnetic resonance imaging (MRI) T2 intensity of the disc. METHODS: Ex vivo samples of nucleus pulposus (NP) tissue from lumbar IVDs were obtained from 18 consecutive patients who underwent surgery for disc herniation at L4/5 and L5/S1 level. Immunohistochemistry was performed to determine the presence of AQP1 expression, and this was quantified by Western blot analysis. AQP1 expression was compared to preoperative IVD signal intensity on T2-weighted MRI. RESULTS: NP tissue was obtained from 18 patients (9 for L4/5 level and 9 for L5/S1 level). AQP1 expression was detected in all samples by Western blot and immunohistochemistry. AQP1 expression had a linear correlation with the preoperative IVD signal intensity on T2-weighted MRI at L4/5 level (R (2) = 0.90) and at L5/S1 level (R (2) = 0.92). AQP1 expression was 52.2 ± 59.0 at L5/S1 level and 15.9 ± 20.6 at L4/5 (P = .10). CONCLUSIONS: Our results show that AQP1 can be detected in IVD obtained from live human subjects. Increased AQP1 expression is associated with greater disc hydration as measured by signal intensity on T2-weighted MRI. AQP1 may have a role in the dehydration associated with disc degeneration.