Selective degradation of tRNASer(AGY) is the primary driver for mitochondrial seryl-tRNA synthetase-related disease

Abstract

Mitochondrial translation is of high significance for cellular energy homeostasis. Aminoacyl-tRNA synthetases (aaRSs) are crucial translational components. Mitochondrial aaRS variants cause various human diseases. However, the pathogenesis of the vast majority of these diseases remains unknown. Here, we identified two novel SARS2 (encoding mitochondrial seryl-tRNA synthetase) variants that cause a multisystem disorder. c.654–14T > A mutation induced mRNA mis-splicing, generating a peptide insertion in the active site; c.1519dupC swapped a critical tRNA-binding motif in the C-terminus due to stop codon readthrough. Both mutants exhibited severely diminished tRNA binding and aminoacylation capacities. A marked reduction in mitochondrial tRNASer(AGY) was observed due to RNA degradation in patient-derived induced pluripotent stem cells (iPSCs), causing impaired translation and comprehensive mitochondrial function deficiencies. These impairments were efficiently rescued by wild-type SARS2 overexpression. Either mutation caused early embryonic fatality in mice. Heterozygous mice displayed reduced muscle tissue-specific levels of tRNASers. Our findings elucidated the biochemical and cellular consequences of impaired translation mediated by SARS2, suggesting that reduced abundance of tRNASer(AGY) is a key determinant for development of SARS2-related diseases.

Disease models of mitochondrial aminoacyl‐tRNA synthetase defects

“…For example, a homozygous splicing variant in SARS2 that we identified in a patient who had early‐onset spastic paresis, led to a 95% reduction in the amount of SARS2 protein but had no apparent effect on mitochondrial protein synthesis in cultured skin fibroblasts 17 . SARS2 charges two different mitochondrial seryl‐tRNAs, and SARS2 mutations have been shown to selectively affect the stability of tRNA Ser AGY , which is an unusually small mitochondrial tRNA lacking the entire D domain 16,17,22 . The degree of tRNA instability varies between mutation and cell type.…”

“…Even if the mutation site was conserved in mice, obtaining a useful disease model can be challenging. It was recently reported that compound heterozygous SARS2 variants identified in a patient with a multisystem phenotype were both embryonic lethal as homozygotes in mice, as well as in compound heterozygosity, 22 suggesting species‐specific differences to tolerance of mitoARS defects.…”

“…17 SARS2 charges two different mitochondrial seryl-tRNAs, and SARS2 mutations have been shown to selectively affect the stability of tRNA Ser AGY , which is an unusually small mitochondrial tRNA lacking the entire D domain. 16,17,22 The degree of tRNA instability varies between mutation and cell type. Another example of how the mutation type may cause tissue-specific effects is the most common mutation in DARS2, which is an intronic variant affecting the splicing of DARS2.…”

Recessive aminoacyl-tRNA synthetase disorders: lessons learned from in vivo disease models

“…Homozygous expression of a Fars2 mutation (p.Asp142Tyr), which severely compromises mt-PheRS aminoacylation activity and causes hereditary spastic paraplegia in humans, is embryonically lethal in mice during early gestation, at a similar timepoint to Fars2 knockout mice ( Yang et al, 2016 ; Chen et al, 2022 ). Similarly, homozygous or compound heterozygous expression of human disease-causing Sars2 variants was embryonically lethal in mice ( Yu et al, 2022 ). The specific factors underlying the variation in phenotype severity between mouse and human carriers of isogenic ARS mutations are not known, however, these species differences should be considered when evaluating novel ARS disease models.…”

The Role of Nuclear-Encoded Mitochondrial tRNA Charging Enzymes in Human Inherited Disease

“…Another gene associated with an interesting spectrum of clinical phenotypes is mitochondrial seryl-tRNA synthetase ( SARS2 ). Patients with SARS2 variants present with (i) a progressive spastic paresis [ 53 ]; (ii) a syndrome characterized by hyperuricemia, pulmonary hypertension, renal failure in infancy, and alkalosis (HUPRA) that is typically lethal within the first few years of life [ 52 ]; or (iii) a syndrome that includes both neurological and HUPRA phenotypes [ 77 , 78 , 79 ]. Interestingly, HUPRA syndrome is exclusively associated with SARS2 , providing another example of unique mt-ARS phenotype.…”