A cell model of YARS2-associated childhood-onset mitochondrial disease

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PROJECT SUMMARY We hypothesize that pathogenic variants in the family of the nuclear ARS2 genes, encoding mitochondrial aminoacyl-tRNA synthetases (mt-aaRSs), cause disease primarily by disrupting nutrient sensing and cell signaling. Each mt-aaRS is responsible for charging its cognate mitochondrial tRNA (mt-tRNA) with its specific amino acid, as required for the dedicated mitochondrial protein synthesis machinery. Loss-of-function variants of each ARS2 have been linked to human diseases, showing central nervous system involvement, myopathy, sensorineural hearing loss, ovarian dysgenesis, and pulmonary hypertension. However, the correlation is poor between the enzymatic activity of individual variants and manifestation of the disease phenotypes. This suggests that disease is mediated not necessarily via loss of tRNA charging, but by other functions of mt-aaRSs. Given that the cytosolic counterpart ARS1 genes are often implicated in non-canonical functions, beyond aminoacylation, we will test the hypothesis that ARS2s mediate nutrient-sensing and cell-signaling processes that are disrupted by pathogenic variants resulting in disease development. To test this hypothesis, as a pilot model, we will generate a human subject-derived induced pluripotent stem cell (iPSC) line with pathogenic variants in the YARS2 gene, encoding mt-TyrRS. Pathogenic variants of YARS2 result in the MLASA (myopathy, lactic acidosis and sideroblastic anemia) syndrome. Previous studies of pathogenic YARS2 variants have shown no appreciable effect on tRNA aminoacylation. Here we focus on a pair of novel compound heterozygous mutations that we identified in a human subject with neonatal fatal disease, the most severe clinical case observed to date. This provides a unique model where the largest changes in nutrient sensing and cell signaling are expected to occur. In Aim 1, we will create an iPSC line from an established fibroblast line of the human subject. We will use CRISPR/Cas to generate an isogenic control line that corrects the genetic mutations. In Aim 2, we will differentiate the patient and control iPSC lines to disease-relevant cell types. We will focus on myocytes, as skeletal myopathy is the most notable feature of clinical cases of YARS2 variants. We will also focus on peripheral neurons, which are affected in most clinical cases of other ARS2 variants. We will identify changes of gene expression in nutrient sensing or cell signaling of the subject line. Combined, this work will produce an isogenic pair of subject and control iPSC lines that will be shared with the research community. This pair of iPSC lines will serve as the foundation for understanding the implications of nutrient sensing and cell signaling in YARS2 variants, which will provide a template that is generalizable to other ARS2-associated disease.