Abstract Fri140: Regulation of Mitochondrial tRNAs as a Potential Strategy for Restoring Mitochondrial Function in Proteotoxic Stress

Mitochondrial dysfunction is closely associated with the progression of heart failure. Mice harboring a mutated mitochondrial DNA polymerase gamma (POLG ,D257A) suffer catastrophic metabolic dysfunction and were previously reported to display gene/protein expression patterns consistent with non-canonical mitochondrial unfolded protein response (UPR mt ). These mice also displayed changes in mitochondrial encoded tRNAs in a pattern that suggested reduced expression of tRNAs whose partner amino acid had high amyloidogenic potential. We sought to determine if mitochondrial health could be improved by manipulating mitochondrial tRNAs that handle amyloidogenic amino acids when in the presence of mitochondrial proteotoxic stress. For feasibility, we opted to target the nuclear-encoded mitochondrial tRNA synthetases, which charge the tRNA with its partner amino acid. H9C2 cells were treated with gain and loss of function reagents for YARS2 (mitochondrial tyrosyl-tRNA synthetase charging mitochondrial tRNA-tyr (MT-TY), high amyloidogenic potential) and TARS2 (mitochondrial threonyl-tRNA synthetase charging mitochondrial tRNA-thr, low amyloidogenic potential), then subjected to mitochondrial proteotoxic stress via the mitochondrial HSP90 inhibitor gamitrinib-triphenylphosphonium (GTPP). Though still ongoing, we have demonstrated that YARS2 expression mirrors that of MT-TY in proteotoxic stress conditions (GTPP, H2O2, FCCP). With 24 hours of YARS2-Knockdown (KD) via siRNA, there were no significant changes of UPR mt at the protein level, but mtROS increased, and cell viability was reduced. Seahorse experiments indicated that, both GTPP treatment and YARS2 KD led to lower ATP production and maximal respiration. In conclusion, the knockdown of YARS2 (and presumably MT-TY) is not beneficial in mitochondrial proteotoxicity conditions. This interpretation may be confounded by recently reported noncanonical role of YARS2 in binding and stabilizing the mitochondrial ETC supercomplex (I, III, IV).