Therapeutic rescue of pathogenic asparaginyl-tRNA synthetase alleles

Pathogenic alleles in the cytoplasmic asparaginyl-tRNA synthetase (NARS1) are associated with infant- and juvenile-onset disease, with no current disease-specific treatments. We developed a tractable human cell system to study disease-causing NARS1 alleles that can be adapted to investigate NARS1 and other aminoacyl-tRNA synthetase (ARS) alleles. We found that two dominant NARS1 nonsense alleles, R534X and R522X, cause a cytotoxic phenotype and elicit the integrated stress response (ISR). Proteomic and phenotypic changes were rescued by asparagine supplementation in the human cell model. Asparagine supplementation completely restored cell proliferation defects in patient-derived fibroblasts and prevented activation of the ISR. We also tested therapeutic cognate transfer RNA (tRNA) supplementation, which reduced the cytotoxicity of pathogenic NARS1 alleles but did not ameliorate activation of the ISR. A general control nonderepressible 2 (GCN2) inhibitor suppressed ISR activation and reduced cytotoxicity but did not restore changes to the proteome caused by the NARS1 nonsense alleles. The data reveal molecular and cellular defects caused by premature termination codons in NARS1 alleles. Our data also indicate asparagine supplementation as a feasible therapeutic approach to address the underlying cause of NARS1 disease, a rare disease for which currently no treatment is available.