Mitochondrial tRNA processing defects reprogram mitochondrial and cellular homeostasis

Mitochondrial tRNA processing defects have been associated with some clinical presentations including deafness. Especially, a deafness-linked m.7516delA mutation impaired the 5' end processing of RNA precursors and mitochondrial translation. In this study, we investigated the mechanism by m.7516delA mutation-induced deficiencies mitigate organellar and cellular integrity. The m.7516delA mutation downregulated the expression of nucleus-encoding subunits and upregulated assembly factors of complex IV and altered the assembly and activities of oxidative phosphorylation (OXPHOS) complexes. The impairment of OXPHOS alleviated mitochondrial quality control processes, including the imbalanced mitochondrial dynamics via increasing fission with abnormal mitochondrial morphology. The m.7516delA mutation upregulated both ubiquitin-dependent and independent mitophagy pathways, evidenced by increasing levels of Parkin, BNIP3, NIX, and MFN2-ubiquitination and altering interaction between MFN2 and MUL1 or Parkin, to facilitate the degradation of severely damaged mitochondria. Strikingly, the m.7516delA mutation activated the integrated stress response (ISR) pathway, evidenced by upregulation of GCN2, P-GCN2, p-eIF2α, CHOP, ATF4, and elevated the nuclear location of ATF5 to minimize the damages in defective mitochondria. Both activation of the ISR and PINK1/Parkin mitophagy pathways ameliorate the cell homeostasis via elevating the autophagy process and upregulating apoptotic pathways. Our findings provide new insights into underlying aberrant RNA processing-induced dysfunctions, reprogrammed organelles, and cellular integrity.