Nogo-66 plays a central role in the myelinmediated inhibition of neurite outgrowth.Tau is a microtubule-associated protein involved in microtubule assembly and stabilization.It remains unverified whether tau interacts 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 persistently reduced the level of p-S262 tau(tau phosphorylated 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,significantly reduced the level of p-S262 tau.Overexpression of tau rescued the Nogo-66-induced inhibition of neurite outgrowth in neuroblastoma 2a(N2a) cells and primary cortical neurons.However,concomitant inhibition of MARK abolished the rescue of neurite outgrowth by tau in N2 a 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.
