Abstract Nogo-66 plays a central role in the myelin- mediated inhibition of neurite outgrowth. Tau is a micro- tubule-associated protein involved in microtubule assembly and stabilization. It remains unverified whether tau inter- acts directly with growth factor receptors, or engages in cross-talk with regeneration inhibitors like Nogo-66. Here, we report that plasmid overexpression of tau significantly elevated the protein levels of total tau, phosphorylated tau, and microtubule-affinity regulating kinase （MARK）. Nogo- 66 transiently elevated the total tau protein level and per- sistently reduced the level of p-s262 tau （tau phosphory- lated at serine 262）, whereas it had little influence on the level of p-T205 tau （tau phosphorylated at threonine 205）. Nogo-66 significantly decreased the protein level of MARK. Hymenialdisine, an inhibitor of MARK, signifi- cantly reduced the level of p-S262 tau. Overexpression of tau rescued the Nogo-66-induced inhibition of neurite outgrowth in neuroblastoma cortical neurons. However, 2a （N2a） cells and primary concomitant inhibition ofMARK abolished the rescue of neurite outgrowth by tan in N2a cells. We conclude that dephosphorylation of tau at S262 is able to regulate Nogo-66 signaling, and that overexpression of tau can rescue the Nogo-66-induced inhibition of neurite outgrowth in vitro.
Evidence suggested that glycogen synthase kinase-3β（GSK-3β） is involved in Nogo-66 inhibiting axonal regeneration in vitro, but its effect in vivo was poorly understood. We showed that stereotactic injection of sh RNA GSK-3β-adeno associated virus（GSK-3β-AAV） diminished syringomyelia and promoted axonal regeneration after spinal cord injury（SCI）, using stereotactic injection of sh RNA GSK-3β-AAV（tested with Western blotting and RT-PCR） into the sensorimotor cortex of rats with SCI and by the detection of biotin dextran amine（BDA）-labeled axonal regeneration. We also determined the right position to inject into the sensorimotor cortex. Our findings consolidate the hypothesis that downregulation of GSK-3β promotes axonal regeneration after SCI.
