Abstract
Purpose :
Optic neuropathies are a major cause of irreversible blindness worldwide. While risk factors are known, the molecular progression that ultimately leads to neuronal apoptosis and blindness has yet to be fully elucidated. Recent studies show ephrin signaling as one of the most dysregulated signaling pathways in the pathophysiology of optic neuropathies. In this study, we hypothesize that neuropathic progression is initiated in part by the anachronic reactivation of repulsive ephrin forward signaling within the neural retina.
Methods :
We used two optic neuropathic models, DBA/2J (D2J) mice which develop hereditary glaucomatous defects and the optic nerve crush (ONC) model in C57BL/6 (C57) mice. Semi-quantitative immunoblotting was used to assay the activation of several Eph receptors (Ephs) temporally in the D2J mice (2mo – 23mo) and ONC mice (24-, and 48-hr post-injury). Immunofluorescent (IF) staining was used to confirm the localization of activated Ephs within the retina.
Results :
Our results show an age-dependent increase in the activation of several Ephs in the retina of D2J mice, with the majority of Ephs present in a hyperphosphorylated state at age 23mo. Interestingly, results show that EphA1, A3, A6, A7, B1, B2, and B6, are significantly phosphorylated as early as 2mo of age (p=<0.05). Additionally, several Ephs are activated within 24hrs of ONC with a significantly greater phosphorylation occurring after 48hrs.
IF images determined the localization of Ephs to the RGC layer. IF analysis further showed that D2J retinas exhibit an age-dependent activation of the EphB1 and B2 receptors throughout the inner retina. IF imaging of the ONC mice shows that EphA2, A3, A4, B1, and B2 become phosphorylated after injury (24hr) and that their spatial distribution is predominately in the inner retina.
Conclusions :
These results indicate that Ephs activation and repulsive forward signaling may play a role in the neuropathic progression of both hereditary and traumatic optic neuropathy. These results demonstrate that Ephs can be observed as early as 2mo of age in hereditary optic neuropathy and 24hr in traumatic optic neuropathy. Together these studies underscore the need to explore this repulsive pathway in early optic neuropathies and it provides a glimpse of the number of receptors that are present in the retina of mice, and which are engaged in neuropathic states.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.