Abstract
Purpose :
Leber congenital amaurosis type 9 (LCA9) is a blinding retinal degenerative disease characterized by early childhood onset associated with a mutation in the gene coding for nicotinamide mononucleotide adenylyltransferase 1 (NMNAT1). We demonstrated in mice that a germline NMNAT1 null mutation caused photoreceptor degeneration that was prevented by concurrently knocking out the inducible NAD+ cleavage enzyme, sterile alpha and TIR motif containing 1 (SARM1). We aim to assess the viability of knocking down SARM1 in other retinal degeneration and NMNAT1 mutation models to explore the relevance of SARM1 as a therapeutic candidate to prevent retinal degeneration.
Methods :
SARM1 knockout mice were crossed with NMNAT1 floxed CAG-CreERT2, NMNAT1 E247K, rd10, and RhoP23H mice respectively to create SARM1 double knockout mice with different retinal degeneration models. A SARM1 dominant negative expressing AAV7m8 (SARM1DN) was injected intravitreally as a tractable modality of SARM1 knockdown in the aforementioned models. Mice were characterized for retinal phenotypes using funduscopy/optical coherence tomography (OCT), in vivo electroretinography (ERG), and histology.
Results :
ERG (n=7) showed no appreciable scotopic a and b, and photopic b waveforms 33 days post-tamoxifen injection in NMNAT1 KO while NMNAT1/SARM1 KO showed no significant changes compared to wild-types. Hematoxylin and eosin (H&E) staining of retina sections and OCT imaging of NMNAT1 KO mice showed outer nuclear cell loss unseen in imaging of NMNAT1/SARM1 double knockout retinas. NMNAT1 KO mice injected with SARM1DN showed transient preservation of ERG waveforms 1 week after injection that is undetectable 18 days after injection. RhoP23H mice 10 weeks after SARM1DN injection showed no ERG (n=3) significant differences in scotopic waves, but showed significant differences in 15, 20, and 25 dB intensities of photopic measurments by Bonferroni multiple comparisons test. ERG (n=3) of rd10/SARM1 KO showed no appreciable waveforms.
Conclusions :
SARM1 inhibition directly plays a role in NMNAT1 null related retinal degeneration. SARM1DN can be a promising tool to test for relevance of SARM1 in models of retinal degeneration. SARM1 may play a role in cone preservation in RhoP23H degeneration. Further investigation is warranted to test the relevance of SARM1 in other models of degeneration.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.