Neuritin 1 Drives Therapeutic Preservation of Retinal Ganglion Cells in an Ex Vivo Human Glaucoma Model

Purpose: Glaucoma is a leading cause of irreversible blindness. Glaucomatous intraocular pressure (IOP) triggers deleterious effects, including gliosis, optic nerve (ON) axonal retraction, neurotrophic factor deprivation, inflammation, and other pathological events, leading to retinal ganglion cell (RGC) loss. Trophic factor impairment enhances RGC apoptosis susceptibility. Neuritin 1 (NRN1), a neurotrophic protein downstream of various neurotrophins, exhibited RGC protection and regeneration in axotomy models. We evaluated human recombinant NRN1's impact on human RGCs cultured in pressurized conditions within the ex vivo translaminar autonomous system to simulate glaucoma pathogenesis. Methods: Human glaucomatous and non-glaucomatous donor eyes were obtained from eye banks according to the Declaration of Helsinki. Initially, we evaluated NRN1and RGC marker expression in glaucoma and non-glaucomatous retina to determine the NRN1 level and its association with RGC loss. Further, we evaluated NRN1's therapeutic potential by treating pressurized human eyes at normal and high IOP for seven days. Retina, ON, and conditioned medium were analyzed for RGC survival (THY1, RBPMS), gliosis (GFAP), apoptosis (CASP3, CASP7), and extracellular matrix deposition (COLIV, FN) by qRT-PCR and western blotting. Paraphenylenediamine staining assessed ON axonal degeneration, whereas ex vivo electroretinogram assessed retinal activity. Results: Glaucomatous retinas exhibited significant reductions in both NRN1 (*p = 0.007, n = 5) and RGC marker expression (*p = 0.04, n = 5). NRN1 treatment reduced gliosis, extracellular matrix deposition, ON degeneration, and increased retinal activity in pressure-perfused eyes. Conclusions: Our study confirms that NRN1 enhances human RGC survival and improves retinal function in degenerative conditions, substantiating it as a promising candidate for rescuing human RGCs from degeneration.