Examination of retrotransposon expression in optic neuropathies

Abstract

Purpose : Retrotransposons are repetitive DNA sequences constituting more than half of the human or mouse genome that can translocate from one location to another. Retrotransposons were considered as “junk DNA;” however, recent studies suggest that they are involved in many cellular activities, including in neurodegeneration. Optic neuropathies are a group of neurodegenerative diseases caused by damage to retinal ganglion cell (RGC) axons in the optic nerve. Our preliminary data showed that retrotransposons were induced by optic nerve injury in RGCs; here we determine whether retrotransposons play a role in optic neuropathy.

Methods : We performed optic nerve crush (ONC) on the left eyes of 6-8 week old adult mice on day 0, and then isolated RGCs from these animals or from healthy control eyes on day one or day five after ONC. Total RNA was extracted from RGCs and converted to cDNA for qPCR using primers amplifying different classes of retrotransposons, including LINE, SINE, and ERVs.
To inhibit retrotransposon expression in RGCs, we use antiviral drugs stavudine or lamivudine to inhibit their reverse transcription. We performed ONC and intravitreal injection of either drug on day 0 followed by daily intraperitoneal injection of the drug for two weeks. Two days before sacrifice, mice received an intravitreal injection of CTB-555 to anterogradely label RGC axons. Mice were transcardially perfused under deep anesthesia with 4% PFA on day 14. Retinas and optic nerves were further dissected, processed, and examined by fluorescent confocal microscopy.

Results : We found that retrotransposon expression levels were elevated in RGCs after optic nerve injury, especially the LINE family, which increased two- to four-fold after ONC. Inhibition of reverse transcription by antiviral drugs did not promote RGC axon regeneration after optic nerve injury in mice.

Conclusions : Our findings suggest that retrotransposon expression is induced by optic nerve injury in RGCs. Inhibition of retrotransposon reverse transcription by antiviral drugs didn’t promote RGC axon regeneration, but may promote neuroprotection. Our future studies will focus on this question, as well as manipulation of retrotransposon expression itself by shRNA knockdown in RGCs.

This is a 2021 ARVO Annual Meeting abstract.