Abstract
Purpose :
A number of neurodegenerative disorders appear to involve dysregulated protein degradation via proteosomal and/or autophagic pathways. Therapeutic intervention may therefore require regulation of these pathways. We recently showed that proteasome inhibition in rat retina causes inner retinal degeneration including loss of retinal ganglion cells (RGC) (Kageyama et al., 2019). Here, we tested whether cellular autophagy could counteract the detrimental effects of proteosomal inhibition using an in vivo mouse model of retinal degeneration.
Methods :
Beclin1 Heterozygous (Bcn1+/-) mice were used as the animal model with autophagic dysfunction. Mice (n=4-8/grp) were intravitreally-injected (ivt) with either/or a proteasome inhibitor (MG262,40pmol/eye), an endoplasmic reticulum (ER)-stress inducer (tunicamycin,2.5ug/eye), neurotoxic amount of N-methyl-D-aspartate (NMDA,20nmol/eye), a potent vasoconstrictor (endothelin1;ET1,100pmol/eye), an inflammation inducer (lypopolysaccaride; LPS,2ug/eye). RNA was isolated 4 days post injection, or 1 day following ET1 injection. Wildtype (WT) and Bcn1+/- eyes were immunostained for LC3 to detect autophagic activity. Expression of neurofilament (Nfl) and rhodopsin (Rho) gene was measured to quantify RGC and photoreceptor cell loss, respectively. Two-way ANOVA followed by Sidak’s post-hoc test was used to determine statistical significance.
Results :
As in our recent study in rats, we obtained consistent results in mice where ivt of MG262 induced 69±5% (p<0.0001) loss of RGC and 29±3% (p<0.0001) loss of photoreceptors, and where ivt of tunicamycin induced a 79±4% (p<0.0001) loss of photoreceptors without significantly effecting RGC. However, there was no statistically significant difference in RGC and photoreceptor cell loss between WT and Bcn1+/- mice, when both were subjected to ivt MG262 or tunicamycin. Furthermore, RGC in WT and Bcn1+/- mice retinas were equally sensitive to the deleterious effects of ivt delivered NMDA, ET1, and LPS.
Conclusions :
This study suggests that autophagy does not play a key compensatory retinal protective role in the presence of impaired proteasomal activity or under ER stress. Additionally, autophagy may not be an effective intrinsic retinal protective mechanism against excitotoxic and/or neuroinflammatory insults. Further studies are needed to delineate the precise role that autophagy may play in rescuing retinal neurons under other pathological conditions.
This is a 2020 ARVO Annual Meeting abstract.