Abstract
Purpose :
GOT1 is a cytosolic aspartate transaminase that reversibly catalyzes the transfer of an amino group between glutamate and aspartate and is an important aspect of the malate-aspartate shuttle, which transfers reducing equivalents from the cytosol to the mitochondria matrix. Previous work has demonstrated that the activity of this enzyme is highest in photoreceptor inner segments. Furthermore, ex vivo studies have demonstrated that the retina relies on aspartate transaminase for amino acid metabolism. Importantly, aspartate transaminase has been suggested to be an early biomarker of retinal degeneration in retinitis pigmentosa and a possible target for neuroprotection. The purpose of this study is to develop a comprehensive in vivo understanding of the contribution of GOT1 to photoreceptor metabolism, function, and survival.
Methods :
Mice carrying a floxed Got1 allele were crossed to mice harboring a Cre recombinase under the control of the rhodopsin promoter to create animals with conditional deletion of Got1 from rod photoreceptors, specifically. The survival of photoreceptors was examined using OCT and histology. Whole eyes were fixed and sectioned for H&E staining and immunohistochemistry. Western blot analysis was performed to assess the abundance of GOT1 protein in the retina of wild-type and conditional knockout animals. Neural retina was harvested for RNA or metabolite extraction and subsequent qRT-PCR or metabolomics analysis, respectively.
Results :
Knockdown of GOT1 (Got1 cKO) was confirmed by western blot analysis. OCT analysis showed a shortening of outer segments by 4 months of age and thinning of the outer nuclear layer (ONL) by 50% at 6 months of age. H&E-stained retina showed a significant loss of photoreceptors at 6 months of age compared to control animals. Metabolomics analyses are ongoing.
Conclusions :
This study demonstrates that loss of GOT1 in rod photoreceptors leads to outer segment shortening followed by degeneration. GOT1 is critical for PR survival. Understanding the metabolic perturbations that result in photoreceptor degeneration in this transgenic mouse model may provide a foundation for novel neuroprotective strategies.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.