NG2 glia promote injured spinal cord repair through neuronal transdifferentiation and keratins expression in juvenile mice.

Background context: Spinal cord injury (SCI) causes severe nerve damage, and there are still considerable challenges in treatment due to its complex pathological mechanisms. Juvenile mice are characterized by robust regenerative and reparative abilities. Specifically, neonatal mice can attain scar-free healing subsequent to SCI. Nevertheless, mature neurons, astrocytes, ependymal cells and microglia possess restricted neuronal regenerative potential. Therefore, the cellular origin of cells that facilitate neuronal regeneration following SCI in neonatal mice or juvenile mice remains elusive.

Purpose: NG2 glia could proliferate, migrate, and differentiate into mature oligodendrocytes. NG2 glia are also considered multipotent neural progenitor cells capable of differentiating into neurons. We previously found that NG2 glia upregulated the expression of neuronal markers following SCI. Thus, our study aimed to determine that whether NG2 glia are responsible for neuroregeneration in juvenile mice following SCI.

Study design: Primary NG2 glia were obtained from the cerebral cortices of postnatal day 1-2 (P1-2) Sprague Dawley rats, OLN-93 cells (rat NG2 glia) and MO3.13 cells (human NG2 glia) were used to detect the transdifferentiation of NG2 glia via immunofluorescence. Juvenile C57BL/6J mice aged 1 to 2 weeks and 8-week-old C57BL/6J female mice were subjected to spinal cord crush injury.

Methods: By integrating cell culture, immunofluorescence staining, transcriptome RNA sequencing, and molecular experiments, we investigated the role and underlying mechanism of NG2 glia in neuroregeneration and repair subsequent to SCI.

Results: We discovered that NG2 glia are capable of forming oligospheres and transdifferentiating into neuron-like cells both in vitro and in vivo. We observed that juvenile mice aged 1 to 2 weeks can spontaneously repair their injured spinal cords and significantly contribute to neuroregeneration and repair following SCI. NG2 glia migrated from the white matter of spinal cord to the injury area. Their numbers increased significantly on the first day after SCI, reached a peak on day 3, and gradually declined after the repair process. Additionally, we revealed that keratinization-related signals were significantly activated in juvenile mice after SCI. During the self - repair process, the expression of keratins in NG2 glia at the injury site was significantly upregulated.

Conclusions: In conclusion, NG2 glia play a crucial role in neuroregeneration and repair after SCI through transdifferentiating into neuron-like cells and expressing keratins.

Clinical significance: Keratin biomaterials have been shown to support locomotor functional recovery and may modify the acute inflammatory response after SCI. Thus, targeting NG2 glia may be a vital strategy for promoting spinal cord healing following SCI.