Progressive Early-Onset Leukodystrophy Related to Biallelic Variants in the KARS Gene: The First Case Described in Latin America

KARS Mutations Impair Brain Myelination by Inducing Oligodendrocyte Deficiency: One Potential Mechanism and Improvement by Melatonin

It is very crucial to investigate key molecules that are involved in myelination to gain an understanding of brain development and injury. We have reported for the first time that pathogenic variants p.R477H and p.P505S in KARS, which encodes lysyl-tRNA synthetase (LysRS), cause leukoencephalopathy with progressive cognitive impairment in humans. The role and action mechanisms of KARS in brain myelination during development are unknown. Here, we first generated Kars knock-in mouse models through the CRISPR-Cas9 system. Kars knock-in mice displayed significant cognitive deficits. These mice also showed significantly reduced myelin density and content, as well as significantly decreased myelin thickness during development. In addition, Kars mutations significantly induced oligodendrocyte differentiation arrest and reduction in the brain white matter of mice. Mechanically, oligodendrocytes' significantly imbalanced expression of differentiation regulators and increased capase-3-mediated apoptosis were observed in the brain white matter of Kars knock-in mice. Furthermore, Kars mutations significantly reduced the aminoacylation and steady-state level of mitochondrial tRNALys and decreased the protein expression of subunits of oxidative phosphorylation complexes in the brain white matter. Kars knock-in mice showed decreased activity of complex IV and significantly reduced ATP production and increased reactive oxygen species in the brain white matter. Significantly increased percentages of abnormal mitochondria and mitochondrion area were observed in the oligodendrocytes of Kars knock-in mouse brain. Finally, melatonin (a mitochondrion protectant) significantly attenuated mitochondrion and oligodendrocyte deficiency in the brain white matter of KarsR504H/P532S mice. The mice treated with melatonin also showed significantly restored myelination and cognitive function. Our study first establishes Kars knock-in mammal models of leukoencephalopathy and cognitive impairment and indicates important roles of KARS in the regulation of mitochondria, oligodendrocyte differentiation and survival, and myelination during brain development and application prospects of melatonin in KARS (or even aaRS)-related diseases.

Expansion of the phenotypic spectrum of KARS1-related disorders to include arthrogryposis multiplex congenita and summary of experiences with lysine supplementation

There are currently multiple disorders of aminoacyl-tRNA synthetases described, including KARS1-related disorder resulting from dysfunctional lysyl-tRNA synthetases. In this report, we describe four novel KARS1 variants in three affected individuals, two of whom displayed arthrogryposis-like phenotypes, suggestive of phenotypic expansion. We also highlight subjective clinical improvement in one subject following lysine supplementation in conjunction with a protein-fortified diet, suggesting its potential as a novel treatment modality for KARS1-related disorders. This report offers additional insight into the etiology and management of KARS1-related disorders and expands our ability to provide guidance to affected individuals and their families.

Aminoacyl-tRNA synthetase - a molecular multitasker

Aminoacyl-tRNA synthetases (AaRSs) are valuable "housekeeping" enzymes that ensure the accurate transmission of genetic information in living cells, where they aminoacylated tRNA molecules with their cognate amino acid and provide substrates for protein biosynthesis. In addition to their translational or canonical function, they contribute to nontranslational/moonlighting functions, which are mediated by the presence of other domains on the proteins. This was supported by several reports which claim that AaRS has a significant role in gene transcription, apoptosis, translation, and RNA splicing regulation. Noncanonical/ nontranslational functions of AaRSs also include their roles in regulating angiogenesis, inflammation, cancer, and other major physio-pathological processes. Multiple AaRSs are also associated with a broad range of physiological and pathological processes; a few even serve as cytokines. Therefore, the multifunctional nature of AaRSs suggests their potential as viable therapeutic targets as well. Here, our discussion will encompass a range of noncanonical functions attributed to Aminoacyl-tRNA Synthetases (AaRSs), highlighting their links with a diverse array of human diseases.

Biallelic variants in KARS1 are associated with neurodevelopmental disorders and hearing loss recapitulated by the knockout zebrafish

PURPOSE

Pathogenic variants in Lysyl-tRNA synthetase 1 (KARS1) have increasingly been recognized as a cause of early-onset complex neurological phenotypes. To advance the timely diagnosis of KARS1-related disorders, we sought to delineate its phenotype and generate a disease model to understand its function in vivo.

METHODS

Through international collaboration, we identified 22 affected individuals from 16 unrelated families harboring biallelic likely pathogenic or pathogenic in KARS1 variants. Sequencing approaches ranged from disease-specific panels to genome sequencing. We generated loss-of-function alleles in zebrafish.

RESULTS

We identify ten new and four known biallelic missense variants in KARS1 presenting with a moderate-to-severe developmental delay, progressive neurological and neurosensory abnormalities, and variable white matter involvement. We describe novel KARS1-associated signs such as autism, hyperactive behavior, pontine hypoplasia, and cerebellar atrophy with prevalent vermian involvement. Loss of kars1 leads to upregulation of p53, tissue-specific apoptosis, and downregulation of neurodevelopmental related genes, recapitulating key tissue-specific disease phenotypes of patients. Inhibition of p53 rescued several defects of kars1^-/- knockouts.

CONCLUSION

Our work delineates the clinical spectrum associated with KARS1 defects and provides a novel animal model for KARS1-related human diseases revealing p53 signaling components as potential therapeutic targets.