Activation of the integrated stress response contributes to developmental delay and seizures caused by mitochondrial prolyl-tRNA synthetase (PARS2) deficiency

Mutations in mitochondrial aminoacyl-tRNA synthetases (mtARSs) causes mitochondrial defects and serious, progressive and usually lethal diseases with exceptional heterogeneous and tissue-specific clinical manifestations. However, the pathogenic mechanisms for specific mtARS related diseases are largely unknown and currently there is no highly effective treatment or cure for these diseases. In the present study, we generate Drosophila models with human mitochondrial prolyl-tRNA synthetase (PARS2) deficiency by knocking out or knocking down dPARS2, the Drosophila ortholog of human PARS2, and further characterize the disease-associated defects and explore the molecular basis of these phenotypes. Inactivation of dPARS2 in Drosophila causes developmental delay and seizure, two main clinical features in human PARS2 deficiency-associated patients. Biochemical analysis demonstrates that loss of dPARS2 activity results in reduced mitochondrial tRNA^Pro aminoacylation, decreased levels of OXPHOS complex proteins, defective assembly and altered enzyme activities of OXPHOS complexes. Interestingly, we discover that dPARS2 deficiency activates the integrated stress response (ISR), which reduces global protein translation and increases activity of ATF4 in our neuronal dPARS2 knockdown model. Importantly, blockade of ISR activation by genetic suppression of GCN2 kinase prevents developmental delay and seizure phenotypes in dPARS2-deficient flies. Furthermore, the genetic suppression of ATF4, the ISR key effector, also reverses these developmental and behavioral abnormalities associated with dPARS2 deficiency. Furthermore, a disease-associated PARS2 V95I variant causes mitochondrial dysfunction and ISR activation in human cells, verifying the findings in the Drosophila models. Together, these results not only provide evidence for PARS2 deficiency associated mitochondrial dysfunction, but also reveal a novel pathogenic mechanism involved in ISR activation in the PARS2 deficiency related disease, indicating a novel disease treatment approach by targeting ISR.