Peripheral glial Schwann cells switch to a repair state after nerve injury, proliferate to supply lost cell population, migrate to form regeneration tracks, and contribute to the generation of a permissive microenvironment for nerve regeneration. Exploring essential regulators of the repair responses of Schwann cells may benefit the clinical treatment for peripheral nerve injury. In the present study, we find that FOSL1, a AP-1 member that encodes transcription factor FOS Like 1, is highly expressed at the injured sites following peripheral nerve crush. Interfering FOSL1 decreases the proliferation rate and migration ability of Schwann cells, leading to impaired nerve regeneration. Mechanism investigations demonstrate that FOSL1 regulates Schwann cell proliferation and migration by directly binding to the promoter of EPH Receptor B2 (EPHB2) and promoting EPHB2 transcription. Collectively, our findings reveal the essential roles of FOSL1 in regulating the activation of Schwann cells and indicate that FOSL1 can be targeted as a novel therapeutic approach to orchestrate the regeneration and functional recovery of injured peripheral nerves.

Peripheral nerves have limited regeneration ability following nerve injury. Applying growth factors with neurotrophic roles is beneficial for accelerating peripheral nerve regeneration. Here we show that after rat sciatic nerve injury, growth factor amphiregulin (AREG) is upregulated in Schwann cells of sciatic nerves. Elevated AREG stimulates the proliferation and migration of Schwann cells by activating ERK1/2 cascade. Schwann cell-secreted AREG further facilitates the outgrowth of neurites and the elongation of injured axons. Administration of AREG to injured sciatic nerves stimulates the proliferation of Schwann cells to replace lost cell population, encourages the migration of Schwann cells to form cell cords, and facilitates the regrowth of axons. Overall, our results identify AREG as an important neurotrophic factor and thus provide a promising therapeutic avenue towards peripheral nerve injury.

The object of this study was to explore the effect of rapamycin regulating the proliferation of Schwann cells through activating the extracellular signal-regulated kinase (ERK) signaling pathway on rats with spinal cord injury (SCI). The rat Schwann cells were cultured and divided into solvent (DMSO) group, rapamycin (Rapa) group (1.5 nM, 3.0 nM, 6.0 nM, 12.0 nM, 24.0 nM and 48.0 nM), and Rapa + ERK inhibitor (PD98059) group (40 mM). The proliferation of Schwann cells was detected by MTS. Western blot was used to evaluate the expression of ERK and p-ERK protein. Moreover, the spinal cord compression injury rat model was established, and the rats were divided into normal control group, SCI group and Schwann cell transplantation group. The animal experiment ended 7 weeks after Schwann cells had been injected every day into the injured rats. In the second animal experiment, the rats were divided into DMSO group, Rapa group and Rapa + PD98059 group. The motor recovery of rats was evaluated using the Basso-Beattie-Bresnahan (BBB) score every week, and the proliferation of Schwann cells at the site of SCI was detected using immunohistochemistry. It was verified that lowdose rapamycin (1.5 nM) could significantly promote the proliferation of Schwann cells cultured in vitro (P<0.001), most significantly at 48 h. Rapamycin could activate the ERK signaling pathway. The results of the first animal experiment showed that the BBB score in Schwann cell transplantation group rose with time compared with that in SCI group (P<0.05). The BBB score was obviously increased in Rapa group compared with that in DMSO group and Rapa + PD98059 group (P<0.05). According to the results of Ki67 immunohistochemistry, the proliferation ability of Schwann cells at the site of SCI was remarkably stronger than that in the other two groups. Rapamycin regulates the proliferation of Schwann cells through the ERK signaling pathway. The proliferation of Schwann cells can effectively repair the damaged nerve cells and neurological function in SCI rats.