Human Retinal Ganglion Cells Respond to Evolutionarily Conserved Chemotropic Cues for Intra Retinal Guidance and Regeneration

Abstract

Retinal ganglion cells (RGCs) connect the retina with the higher centers in the brain for visual perception. Their degeneration leads to irreversible vision loss in glaucoma patients. Since human RGCs (hRGCs) are born during fetal development and connections with the central targets are established before birth, the mechanism underlying their axon growth and guidance remains poorly understood. Here, using RGCs directly generated from human embryonic stem cells, we demonstrate that hRGCs express a battery of guidance receptors. These receptors allow hRGCs to read the spatially arrayed chemotropic cues in the developing rat retina for the centripetal orientation of axons toward the optic disc, suggesting that the mechanism of intra-retinal guidance is conserved in hRGCs. The centripetal orientation of hRGCs axons is not only in response to chemo-repulsion but also involves chemo-attraction, mediated by Netrin-1/DCC interactions. The spatially arrayed chemotropic cues differentially influence hRGCs physiological responses, suggesting that neural activity of hRGCs may facilitate axon growth during inter-retinal guidance. Additionally, we demonstrate that Netrin-1/DCC interactions, besides promoting axon growth, facilitate hRGCs axon regeneration by recruiting the mTOR signaling pathway. The diverse influence of Netrin-1/DCC interactions ranging from axon growth to regeneration may involve recruitment of multiple intracellular signaling pathways as revealed by transcriptome analysis of hRGCs. From the perspective of ex-vivo stem cell approach to glaucomatous degeneration, our findings posit that ex-vivo generated human RGCs are capable of reading the intra-retinal cues for guidance toward the optic disc, the first step toward connecting with the central target to restore vision.