Abstract
Purpose :
Optic neuropathies are characterized by damage to axons of the optic nerve resulting in visual impairments. We previously showed that activation of the Wingless-type (Wnt) signaling pathway using Wnt3a ligand promoted retinal ganglion cell (RGC) survival and axonal regeneration after optic nerve crush (ONC) in mice. Interestingly, Wnt3a-injected retinas showed significantly more microglia/macrophages, suggesting a role for inflammation in Wnt3a-induced axonal regeneration. In this study, we investigated how inflammation contributes to Wnt3a-mediated axonal regeneration and RGC neuroprotection.
Methods :
Mice were injected with Wnt3a (20 ng) or saline intravitreally then immediately underwent ONC injury. Mice received IP injections of the anti-inflammatory agent minocycline (45 mg/kg) or water on the day of ONC, then three times a week for 2.5 weeks. Immunohistochemistry on retinal sections and flatmounts was used to detect RBPMS for quantification of RGCs. Axonal regeneration was measured using cholera toxin B injection, quantifying the number of axons at 100 um intervals past the crush site.
Results :
Intravitreal injections of Wnt3a resulted in significant axonal regrowth past the lesion site and increased RGC survival compared with saline controls (n=4-6, p<0.05). Wnt3a-injected mice treated with minocycline had equivalent axonal growth as Wnt3a-injected mice without minocycline (n=6-9, two-way ANOVA). In contrast, in the absence of Wnt3a (saline control), minocycline induced significantly more axons growing past the lesion site compared with saline injected mice without minocycline (p=0.026, n=5-9, two-way ANOVA). Furthermore, minocycline eliminated the neuroprotective effect of Wnt3a (n=5, ANOVA).
Conclusions :
These data demonstrate that inflammation is a double-edge sword after ONC, which inhibits basal regeneration but promotes RGC survival. Wnt3a was able to overcome the inhibitory effect of inflammation on axon growth but not RGC survival. Therefore, these results increase our understanding of the role of inflammation in optic nerve regeneration.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.