Bioengineering strategy to promote CNS nerve growth and regeneration via chronic glutamate signaling

Being part of the mature mammalian central nervous system, impairments of the retina and optic nerves caused by trauma or diseases often cannot be restored. Progressive degeneration of retinal ganglion cells (RGCs) in glaucoma and other optic neuropathies gradually leads to permanent vision loss, which currently has no cure. The purpose of this study is to develop a biocompatible scaffold to support RGC survival and guide axon growth, facilitating optic nerve repair and regeneration. We here report that electrical stimulation (ES) significantly promoted neurite outgrowth and elongation from primary RGCs, mediated through glutamate receptor signaling. To mimic prolonged glutamate stimulation and facilitate sustained nerve growth, we fabricated biocompatible poly-γ-benzyl-L-glutamate (PBG) scaffolds for controlled glutamate release. These PBG scaffolds supported RGC survival and robust long-distance nerve growth in both retinal explants and isolated RGC cultures. In contrast, control polycaprolactone (PCL) scaffolds with similar physical structures showed little benefits on RGC survival or nerve growth. Moreover, PBG scaffolds promoted the differentiation and neurite outgrowth from embryonic stem cell-derived RGC progenitors. The aligned PBG scaffold drove directed nerve elongation along the fiber alignment. Transplantation of PBG-coated biocompatible conduits induced robust optic nerve regeneration in adult mice following nerve transection. Together, the findings present the exciting possibility of driving optic nerve regeneration and RGC progenitor cell differentiation by imitating ES or glutamate signaling. PBG presents a permissive biomaterial in supporting robust and directed axon growth with promising clinical applications in the future. STATEMENT OF SIGNIFICANCE: We here reported compelling findings that demonstrate the potent regenerative effects of a bioengineered scaffold incorporating poly-γ-benzyl-L-glutamate (PBG) on the optic nerve. Retinal ganglion cell (RGC) axons, which form the optic nerve, are incapable of regenerating in adulthood, posing a significant hurdle in restoring vision for patients with optic nerve diseases or injuries. Built upon the finding that electrical stimulation promotes RGC axonal growth through glutamate signaling, we developed PBG scaffolds to provide sustained glutamate stimulation and showed their exceptional effects on driving directed axonal elongation in cultured RGCs and neural progenitors, as well as supporting robust optic nerve regeneration after transection in vivo. The findings hold great promise for reversing vision loss in patients with optic nerve conditions.