Ecel1 expression is promoted by damage to axonal flow and protects retinal ganglion cells after optic nerve crush in mice

Abstract

Purpose : Previously, we showed that endothelin converting enzyme-like 1 (Ecel1) was one of the most highly induced genes in the retina of mice after optic nerve crush. The present study investigated whether Ecel1 had a neuroprotective effect in the RGCs of mice after optic nerve crush.

Methods : This study used 8-12-week-old male C57BL/6J mice. The optic nerve was exposed and crushed approximately 2 mm posterior to the eyeball with forceps for 5 seconds under deep anesthesia. On days 2, 4, and 7 after optic nerve crush, retinas were collected and Ecel1 expression was investigated with qRT-PCR, western blotting and immunohistochemistry. In separate groups, NMDA (30 nmol) was injected into the vitreous cavity to induce excitotoxic RGC damage, and the optic nerve was exposed to vinblastine (3 mM) to induce damage to axonal flow. Furthermore, Ecel1 protein was knocked down in a separate group of mice with the AAV2-Crisp/Cas9 system. Four weeks after AAV2-Crisp/Cas9 injection, the RGCs were retrogradely labeled with 2% Fluorogold.

Results : The transcriptional level of Ecel1 was significantly higher in the nerve crush group than a sham operation group (p<0.001). The protein expression of Ecel1 in the retina had a similar pattern as the transcriptional level: a very high increase 4 and 7 days after optic nerve crush. Similar to optic nerve crush, vinblastine treatment also strongly promoted the mRNA expression of Ecel1. On the other hand, NMDA damage did not induce Ecel1 expression. The AAV2-Crisp/Cas9-induced Ecel1-knockdown mice showed successfully reduced Ecel1 expression 4 days after optic nerve crush, and the number of surviving RGCs was significantly reduced 7 days after optic nerve crush (AAV2-Crisp/Cas9-Ecel1-331: 829 ± 138 cells/mm², AAV2-Crisp/Cas9-Ecel1-385: 894 ± 171 cells/mm²), in comparison with control retinas injected with AAV2-Crisp/Cas9-CFP136 (1123 ± 178 cells/mm²).

Conclusions : Here, we showed that Ecel1 had a neuroprotective effect in the RGCs of mice after optic nerve crush, and that damage to axonal flow induced Ecel1 expression. These findings might provide insight into novel therapeutic targets for the attenuation of RGC damage, either after optic nerve injury, such as in trauma, or in glaucoma.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.