Time-restricted release of multiple neurotrophic factors promotes axonal regeneration and functional recovery after peripheral nerve injury

Delivery of multiple neurotrophic factors (NTFs), especially with time-restricted release kinetics, holds great potential for nerve repair. In this study, we utilized the tetracycline-regulatable Tet-On 3G system to control the expression of c-Jun, which is a common regulator of multiple NTFs in Schwann cells (SCs). In vitro, Tet-On/c-Jun–modified SCs showed a tightly controllable secretion of multiple NTFs, including glial cell line–derived NTF, nerve growth factor, brain-derived NTF, and artemin, by the addition or removal of doxycycline (Dox). When Tet-On/c-Jun–transduced SCs were grafted in vivo, the expression of NTFs could also be regulated by oral administration or removal of Dox. Fluoro-Gold retrograde tracing results indicated that a biphasic NTF expression scheme (Dox+3/−9, NTFs were up-regulated for 3 wk and declined to physiologic levels for another 9 wk) achieved more axonal regeneration than continuous up-regulation of NTFs (Dox+12) or no NTF induction (Dox−12). More importantly, the Dox+3/−...