Inhibition of the integrated stress response rescues a histidyl-tRNA synthetase variant associated with Charcot-Marie-Tooth disease.

Cytoplasmic histidyl-tRNA synthetase (HARS1) is an essential protein in translation, ligating histidine to its cognate tRNA(His). HARS1 is one of several aminoacyl-transfer RNA (tRNA) synthetases associated with Charcot-Marie-Tooth disease, an axonal peripheral neuropathy. Advances in genetic testing identify many variants of uncertain significance. We characterize a novel heterozygous allele in HARS1, c.1200G > T (p.Leu400Phe) with a familial inheritance pattern of peripheral neuropathy. Using a humanized yeast model and biochemical assays, we determined that HARS-L400F causes HARS aggregation, reduced thermal stability, and a temperature-dependent reduction of aminoacylation activity. In humanized yeast, L400F leads to a pronounced growth defect, especially at elevated temperatures. Contrary to previously described pathogenic HARS alleles, cognate amino acid or tRNA substrate supplementation does not ameliorate the growth defect. We show that, in a humanized yeast model, HARS L400F leads to the activation of the integrated stress response (ISR) and upregulated chaperone expression. The yeast growth phenotype can be rescued by inhibition of the ISR using a specific inhibitor of general control non-depressible 2 (GCN2) kinase, opening a novel therapeutic avenue for pathogenic HARS1 alleles that do not respond to substrate supplementation.