Unilateral optic nerve axotomy in pigmented mice causes RGCs loss in the contralateral uninjured retina that is prevented by microglial inhibition

Abstract

AbstractPurposeUnilateral optic nerve crush (ONC) causes in adult mice microglial activation and phagocytosis in contralateral un‐injured retinas [1]. Minocycline is a tetracycline antibiotic that penetrates the central nervous system and inhibits microglial activation. The purpose is to evaluate if an unilateral axotomy (ONC) causes RGC loss in the contralateral retina, and to study if this death is modulated by microglial inhibition with minocycline.MethodsThe left optic nerve of adult male C57Bl/6 mice was crushed at 2 mm from the optic disk. Animals were treated daily by an intraperitoneal injection of minocycline. Both retinas were analyzed 3, 9 or 90 days after the lesion. Controls were retinas from intact animals, and ONC matched groups treated with vehicle. mRNA levels of Casp3, Pou4f1, Rbpms, Sncg were assessed by qPCR. For anatomical analyses retinas were dissected and immunolabelled for Brn3a and Iba1. The total number of RGCs was automatically quantified and their topography assessed by neighbour maps.ResultsIn the injured retinas, the loss of RGCs is first significant at day 3, and proceeds up to 90 days when only 1.5% of the original population survives. In the contralateral retinas, there is a significant loss of 15% of the RGCs at day 9 post‐lesion that does not proceed further, at least up to 90 days. Casp3 mRNA is up‐regulated at 3 and 9 days post‐ONC in the injured retinas, and at 3 days in their contralateral ones. The expression of RGC markers decreases over time in the injured retinas, while in their contralateral ones is transiently down‐regulated at 3 days. Minocycline treatment does not rescue RGCs in the injured retinas, but prevents RGC death in their contralateral ones.ConclusionsIn adult pigmented mice, ONC induces RGC loss in the contralateral uninjured retina that may be prevented with systemic minocycline treatment.Reference Galindo‐Romero et al., 2013.