Expression of Nemo-like kinase after spinal cord injury in rats

Wnt can induce signal transduction via the canonical pathway, which was involved in many processes in the nervous system. Nemo-like kinase (NLK) acts as a negative regulator of beta-catenin/T-cell factor/lymphoid enhancer factor (LEF) and functions downstream of transforming growth factor beta-activated kinase-1 in the Wnt signaling pathway. In this study, we performed a spinal cord injury (SCI) test in adult Sprague-Dawley rats and investigated the dynamic changes and role of NLK expression in the spinal cord. Western blot analysis revealed that NLK expression was low in normal spinal cord. It then increased markedly, peaked at 3 days, and declined to basal levels from 5 days after injury. Immunohistochemistry confirmed that NLK immunoactivity was expressed at low levels in gray and white matter under normal conditions and increased prominently in gray matter after the SCI test. Double immunofluorescent staining for NLK, caspase-3, beta-catenin, and NeuN (neuronal nuclei) revealed that NLK and beta-catenin were markedly increased and colocalized in apoptotic neurons. Coimmunoprecipitation data demonstrated that overexpression of NLK protein reduced beta-catenin binding to LEF-1. Our results suggested that NLK was associated with neuronal apoptosis through attenuating the Wnt/beta-catenin signaling pathway after SCIs.