Loss of Oxidation Resistance 1, OXR1, Is Associated with an Autosomal-Recessive Neurological Disease with Cerebellar Atrophy and Lysosomal Dysfunction

Abstract

We report an early-onset autosomal-recessive neurological disease with cerebellar atrophy and lysosomal dysfunction. We identified biallelic loss-of-function (LoF) variants in Oxidative Resistance 1 (OXR1) in five individuals from three families; these individuals presented with a history of severe global developmental delay, current intellectual disability, language delay, cerebellar atrophy, and seizures. While OXR1 is known to play a role in oxidative stress resistance, its molecular functions are not well established. OXR1 contains three conserved domains: LysM, GRAM, and TLDc. The gene encodes at least six transcripts, including some that only consist of the C-terminal TLDc domain. We utilized Drosophila to assess the phenotypes associated with loss of mustard (mtd), the fly homolog of OXR1. Strong LoF mutants exhibit late pupal lethality or pupal eclosion defects. Interestingly, although mtd encodes 26 transcripts, severe LoF and null mutations can be rescued by a single short human OXR1 cDNA that only contains the TLDc domain. Similar rescue is observed with the TLDc domain of NCOA7, another human homolog of mtd. Loss of mtd in neurons leads to massive cell loss, early death, and an accumulation of aberrant lysosomal structures, similar to what we observe in fibroblasts of affected individuals. Our data indicate that mtd and OXR1 are required for proper lysosomal function; this is consistent with observations that NCOA7 is required for lysosomal acidification.

Zebrafish Oxr1a Knockout Reveals Its Role in Regulating Antioxidant Defenses and Aging

“…The OXR1 gene has been documented to be associated with longevity, and the oxidative stress produced by OXR1 mutation accelerates animal aging [ 16 , 24 , 37 ]. Therefore, we gave priority to the investigation of the impact of oxr1a mutation on zebrafish lifespan.…”

“…According to previous reports [ 24 , 37 ], it is speculated that the aging and premature ovarian failure in oxr1a −/− mutants may be induced by oxr1a mutation impairing antioxidant defenses, thereby increasing oxidative damage events. Thus, we examined the sensitivity of oxr1a −/− mutants toward oxidative stress.…”

“…In this work, we successfully created a homozygous oxr1a -knockout line in zebrafish via CRISPR/Cas9 gene editing technology. This mutation was a deletion of 8 bp in exon 8 of the oxr1a gene, which leads to a frameshift mutation and generated a truncated protein that loses the GRAM and TLDc domain; the latter is well-known to be the core domain for antioxidant defenses of OXR1 [ 16 , 37 ]. Our data demonstrate that zebrafish with oxr1a deficiency displayed a shortened lifespan, reduced fertility and decreased resistance to oxidative stress.…”

“…Oxidative stress has been implicated in the aging process [ 42 ]. It is well documented that mutations in the OXR1 gene results in increased sensitivity to oxidative stress, and the lifespan of various animal models lacking OXR1 , including Caenorhabditis elegans [ 24 ], Drosophila melanogaster [ 37 ] and mice [ 16 ], is significantly reduced, revealing an important role for OXR1 in regulating the aging process. In our present study, similar to previous reports, oxr1a −/− mutant zebrafish displayed a shorter lifespan than WT zebrafish.…”

ROS Generation in Microglia: Understanding Oxidative Stress and Inflammation in Neurodegenerative Disease

“…The TLDc domain is a highly conserved c-terminal domain motif shared by a small family of proteins that protect against oxidative stress in the CNS, such as oxidation resistance 1 (OXR1) and nuclear receptor coactivator 7 (NCOA7) [ 182 ]. The mechanism by which TLDc proteins confer stress resistance is unclear, however, specific disruption of the OXR1 TLDc domain in mice is sufficient to cause neurodegeneration and loss-of-function polymorphisms in human TLDc proteins result in a neurodegenerative phenotype [ 182 , 183 ]. Loss of OXR1 results in pronounced microgliosis whilst neuronal OXR1 overexpression delays inflammation, indicating OXR1 regulation of microglial activation in a non-cell-autonomous fashion [ 184 ].…”