Identifying Unique Therapeutic Targets To Rescue Retinal Ganglion Cells From Degeneration After Optic Nerve Crush

Central nervous system (CNS) trauma and neurodegenerative disorders trigger a cascade of cellular and molecular events resulting in neuronal apoptosis and regenerative failure. The pathogenic mechanisms and gene expression changes associated with these detrimental events can be effectively studied using a rodent optic nerve crush (ONC) model. The purpose of this study was to use a mouse ONC model to: (a) evaluate changes in retina and ON gene expression, (b) identify neurodegenerative pathogenic pathways, (c) discover potential new therapeutic targets, and (d) evaluate the neuroprotective and axogenic properties of one selected therapeutic target on axotomized RGCs in vitro and the optic nerve crush (ONC) mouse model in vivo. Meta-analysis of altered gene expression (≥1.5 changes and ≤1.5 changes, p [less than] 0.05 demonstrated 29 up- and 20 downregulated retinal gene clusters and 82 up- and 42 down-regulated optic nerve clusters. Regulated gene clusters included regenerative change, synaptic plasticity, axonogenesis, neuron projection, and neuron differentiation related genes. Expression of selected genes (Vsnl1, Syt1, Synpr and Nrn1) from retinal and ON neuronal clusters was qualitatively and quantitatively examined for their relation to axonal neurodegeneration by immunohistochemistry and qRT-PCR. Axotomized RGCs treated with recombinant hNrn1 (selected target) significantly increased survival of RGCs by 29% (n=8, p [less than] 0.01) and neurite outgrowth of cultured neurons by 261% compared to controls in cultured neurons (n=5-7, p [less than] 0.05). RGC transduction with AAV2-CAG-hNRN1 prior to ONC promoted RGC survival (42%, n=5-8, p [less than] 0.05) and significantly preserved ERG RGC function by 41% until 28 dpc (n=6, p [less than] 0.05) compared to the control AAV2-CAG-GFP transduction group. These ONC induced neuronal loss and regenerative failure associated clusters can be extrapolated to changes occurring in other forms of CNS trauma or in clinical neurodegenerative pathological settings. In conclusion, this study identified potential therapeutic targets to address two key mechanisms of CNS trauma and neurodegeneration: neuronal loss and regenerative failure and presented Nrn1 as a potential therapeutic target for CNS neurodegenerative diseases.