Ryals, R. | bioRxiv Science

bioRxiv2026

Redox imbalance dictates dependence on GOT1 versus GOT2 for rod photoreceptor health during aging and stress

Photoreceptor (PR) loss causes vision loss in many blinding diseases, and effective therapies to prevent this cell loss are lacking. Aspartate aminotransferases (GOTs), located in the cytosol (GOT1) and mitochondria (GOT2), are key components of the malate-aspartate shuttle, which transfers reducing equivalents from cytosol to mitochondria. Previous work has implicated the GOTs as potential modulators of blinding retinal disease. To determine the roles of GOT1 and GOT2 in rod PRs, we generated rod PR-specific Got1 or Got2 conditional knockout mice (Got1 or Got2 cKO). We previously showed that Got1 cKO causes PR degeneration and is accompanied by NADH accumulation and a decreased retinal NAD+/NADH ratio. Here, we show that NADH oxidation via metabolic or genetic means prolongs PR survival in Got1 cKO animals, implicating NADH accumulation, or reductive stress, as a key driver of PR degeneration. In contrast, Got2 cKO causes minimal PR degeneration and alterations in retinal NADH and the NAD+/NADH ratio that oppose reductive stress. Interestingly, GOT2, but not GOT1, is decreased in multiple models of PR degeneration, including retinal detachment (RD) where the NAD+/NADH ratio favors a reductive state. Notably, loss of Got2 in PRs demonstrates a neuroprotective effect after experimental RD suggesting decreased GOT2 expression may be part of a stress response to promote PR survival. Overall, this study illustrates the differential dependence on the GOTs for PR health, provides evidence that an overly reductive environment is detrimental to PR survival, and identifies GOT2 as a novel therapeutic target with potentially broad application in blinding diseases.

neuroscience↗

bioRxiv2023

Spontaneous allelic variant in Ush1g resulting in an expanded phenotype

Strategies to reveal the discovery of the relationships between novel phenotypic behaviors and specific genetic alterations can be achieved via either target-specific, directed mutagenesis or phenotypic selection following random chemical mutagenesis. As an alternative approach, one can exploit deficiencies in DNA repair pathways that are responsible for the maintenance of genetic integrity in response to spontaneously-induced damage. In the genetic background of mice deficient in the DNA glycosylase NEIL1, elevated numbers of spontaneous mutations arise from translesion DNA synthesis past unrepaired, oxidatively-induced base damage. Several litters of Neil1 knockout mice included animals that were distinguished by their backwards-walking behavior in open-field environments, while maintaining frantic forward movements in their home cage environment. Other phenotypic manifestations included swim test failures, head tilting, and circling. Mapping of the mutation that conferred these behaviors revealed the introduction of a stop codon at amino acid 4 of the Ush1g gene; the allele was Ush1gbw, reflecting the backwards-walking phenotype. Ush1gbw/bw null mice displayed auditory and vestibular defects that are commonly seen with mutations affecting inner-ear hair-cell function, including a complete lack of auditory brainstem responses and vestibular-evoked potentials. As in other Usher syndrome type I mutant mouse lines, hair-cell phenotypes included disorganized and split hair bundles, as well as altered distribution of proteins for stereocilia that localize to the tips of row 1 or row 2. Disruption to the bundle and kinocilium displacement suggested that USH1G is essential for forming the hair cells kinocilial links. Due to the vestibular dysfunction, however, visual behavior as measured with optokinetic tracking could not be assessed in Ush1gbw/bw mice. Consistent with other Usher type 1 models, however, Ush1gbw/bw mice had no substantial retinal degeneration compared to Ush1gbw/+ controls out to six months. In contrast to previously-described Ush1g alleles, this new allele provides the first knockout model for this gene.

neuroscience↗