Full-length optic nerve regeneration in the absence of genetic manipulations

Summary The inability of mature retinal ganglion cells (RGCs) to regenerate axons after optic nerve injury can be partially reversed by manipulating cell-autonomous and/or -non-autonomous factors, among which are neuroimmune interactions. We report here that preconditioning resulting from a mild lens injury (conditioning LI, cLI) prior to optic nerve damage induces far greater axon regeneration than LI or the pro-inflammatory agent zymosan after nerve injury or preconditioning with Zymosan. Unlike other instances of immune-supported regeneration, cLI is unaltered by depleting mature neutrophils, T cells or blocking receptors for identified inflammation-associated growth factors (Oncomodulin, SDF1, CCL5), and is only partially diminished by suppressing peripheral monocyte recruitment. Repeated LI leads to full-length optic nerve regeneration, and pharmacological removal of local resident macrophages with the colony stimulating factor 1 receptor (CSF-1R) inhibitor PLX5622 enables some axons to re-innervate the brain in just 6 weeks. Thus, cell non-autonomous interventions not involving genetic manipulations can induce high levels of optic nerve regeneration, paving the way to uncover potent, translatable therapeutic targets for CNS repair.