Functional recovery of injured peripheral neurons often remains incomplete, but the clinical outcome can be improved by increasing the axonal growth rate. Adult transgenic GSK3αS/A/βS/A knock-in mice with sustained GSK3 activity show markedly accelerated sciatic nerve regeneration. Here, we unraveled the molecular mechanism underlying this phenomenon, which led to a novel pharmacological approach for the promotion of functional recovery after nerve injury. In vitro and in vivo analysis of GSK3 single knock-in mice revealed the unexpected contribution of GSK3α in addition to GSK3β, as both GSK3S/A knock-ins improved axon regeneration. Moreover, growth stimulation depended on overall GSK3 activity, correlating with increased phosphorylation of microtubule-associated protein 1B and reduced microtubule detyrosination in axonal tips. Pharmacological inhibition of detyrosination by parthenolide or cnicin mimicked this axon growth promotion in wild-type animals, although it had no effect in GSK3αS/A/βS/A mice. These results support the conclusion that sustained GSK3 activity primarily targets microtubules in growing axons, maintaining them in a more dynamic state to facilitate growth. Accordingly, further manipulation of microtubule stability using either paclitaxel or nocodazole compromised the effects of parthenolide. Strikingly, either local or systemic application of parthenolide in wild-type mice dose-dependently accelerated in vivo axon regeneration and functional recovery similar to GSK3αS/A/βS/A mice. Thus, reducing microtubule detyrosination in axonal tips may be a novel, clinically suitable strategy to treat nerve damage.
SIGNIFICANCE STATEMENT Peripheral nerve regeneration often remains incomplete, due to an insufficient growth rate of injured axons. Transgenic mice with sustained GSK3 activity showed markedly accelerated nerve regeneration upon injury. Here, we identified the molecular mechanism underlying this phenomenon and provide a novel therapeutic principle for promoting nerve repair. Analysis of transgenic mice revealed a dependence on overall GSK3 activity and reduction of microtubule detyrosination in axonal tips. Pharmacological inhibition of detyrosination by parthenolide fully mimicked this axon growth promotion in wild-type mice. Strikingly, local or systemic treatment with parthenolide in vivo markedly accelerated axon regeneration and functional recovery. Thus, pharmacological inhibition of microtubule detyrosination may be a novel, clinically suitable strategy for nerve repair with potential relevance for human patients.