Abstract
Purpose :
Photoreceptor (PR) death is the cause of vision loss in many forms of retinal degeneration. Our lab has shown that ML-265, an activator of PKM2, can delay PR cell death in acute retinal detachment. Reprogramming of PR metabolism may also serve as a novel modality to improve PR survival under chronic retinal stress. The sodium iodate (NaIO3) model of RPE death is widely used to study cell death in AMD. We now aim to determine if ML-265 can similarly enhance PR survival under chronic retinal stress in an in-vivo rat model of NaIO3 induced atrophic retinal degeneration.
Methods :
NaIO3 (35mg/kg) was injected into the femoral vein of adult brown-norway rats. OCT was used to assess retinal thickness weekly for 4 weeks. Whole eyes were enucleated for paraffin sectioning or flat-mounting of RPE or neural retinal. Flat-mounted RPE was stained with GLUT1 and ACTB. The extent of RPE death was examined by determining the ratio of damaged/undamaged RPE. Whole eye sections were stained using GLUT1/RPE65/ARR3/DAPI or processed for H&E histology. Total cell counts of the ONL and surviving cones were counted. For ML-265 experiments, animals were pre-treated 24 hours prior to NaIO3 injection via intravitreal injection of 2uL of 7.5mM ML-265. A repeat injection was performed immediately following NaIO3 injection, and again 2 weeks later.
Results :
RPE flat-mounts demonstrate significant loss of RPE with an average damage ratio of 0.634 + 0.02 (N=5 eyes). OCT showed rapid and significant thinning of total retinal thickness (TRT) by 1 week (207um + 4.6 vs 194.7 +6.3um, p< 6E-06, N=10-23 eyes) post NaIO3 injection with progressive thinning by 4 weeks (189.1 + 4.4um, p<5E-08, N=10-23 eyes) post-injection. This is due to loss of ONL and outer segment equivalent length (OSEL) thickness. The inner layers of the retina were unchanged. H&E revealed total absence of IS/OS in regions lacking RPE. Interestingly, PRs appeared completely normal in the periphery where there was no RPE loss. However, PRs close to the transition zone progressively lose IS/OS the closer the PRs are to the area lacking RPE.
Conclusions :
We have successfully implemented the model of NaIO3 induced RPE injury in our lab and shown disruption to the outer retina in the regions lacking healthy RPE cells. Our follow-up studies include determining the effect of ML-265 on PR survival in the transition zone between healthy RPE and absent RPE.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.