Asparaginyl-tRNA synthetase (NARS1) variants implicated in dominant neurological phenotypes display dominant-negative properties

Aminoacyl-tRNA synthetases (ARSs) are essential, ubiquitously expressed enzymes that ligate amino acids to cognate tRNAs in the cytoplasm and mitochondria. To date, seven dimeric ARS enzymes have been implicated in dominant inherited neuropathy, suggesting that tRNA charging-exacerbated by a dominant-negative effect-is a component of the peripheral nervous system (PNS) phenotype. Interestingly, heterozygosity for missense and protein-truncating variants in the gene encoding dimeric, cytoplasmic asparaginyl-tRNA synthetase (NARS1) have been associated with distinct clinical phenotypes where patients present with either an isolated PNS neuropathy or with a complex phenotype that includes both PNS and central nervous system (CNS) features. Thus, NARS1 variants are associated with a spectrum of dominant neurological diseases. Here, we test pathogenic NARS1 variants for dominant-negative properties to determine if this mechanism is a common feature of ARS-related dominant neurological disease. Furthermore, we assess if variable dominant-negative effects explain the observed clinical heterogeneity. We performed yeast complementation assays to test NARS1 variants in isolation, which revealed loss-of-function effects. To test for dominant-negative properties, we co-expressed mutant human NARS1 with wild-type human NARS1. These studies revealed that NARS1 variants interact with the wild-type subunit and that the majority of variants repress the ability of the wild-type allele to support cellular growth, consistent with a dominant-negative effect. Furthermore, our data suggest that NARS1 variants associated with CNS and PNS phenotypes have a more severe dominant-negative effect compared with those associated with an isolated PNS phenotype.