PGC-1ɑ Mediated-EXOG, a Specific Repair Enzyme for Mitochondrial DNA, Plays an Essential Role in the Rotenone-Induced Neurotoxicity of PC12 Cells

Abstract

Mitochondria harbor small circular genomes (mtDNA) that encode 13 oxidative phosphorylation (OXPHOS) proteins, and types of damage to mtDNA may contribute to neuronal damage. Recent studies suggested that regulation of mtDNA repair proteins may be a potential strategy for treating neuronal damage. The mtDNA repair system contains its own repair enzymes and is independent from the nuclear DNA repair system. Endo/exonuclease G-like(EXOG) is a mitochondria-specific 5-exo/endonuclease required for repairing endogenous single-strand breaks (SSBs) in mtDNA. However, whether EXOG plays a key role in neuronal damage induced by rotenone remains unknown. Thus, in this study, we aimed to investigate the effect of EXOG on mtDNA repair and mitochondrial functional maintenance in rotenone-induced neurotoxicity. Our results indicated that rotenone influenced the expression and location of EXOG in PC12 cells. Meanwhile, after rotenone exposure, the expression was reduced for proteins responsible for mtDNA repair, including DNA polymerase γ (POLG), high-temperature requirement protease A2 (HtrA2), and the heat-shock factor 1-single-stranded DNA-binding protein 1 (HSF1-SSBP1) complex. Further analysis demonstrated that EXOG knockdown led to reduced mtDNA copy number and mtDNA transcript level and increased mtDNA deletion, which further aggravated the mtDNA damage and mitochondrial dysfunction under rotenone stress. In turn, EXOG overexpression protected PC12 cells from mtDNA damage and mitochondrial dysfunction induced by rotenone. As a result, EXOG knockdown reduced cell viability and tyrosine hydroxylase expression, while EXOG overexpression alleviated rotenone's effect on cell viability and tyrosine hydroxylase expression in PC12 cells. Further, we observed that EXOG influenced mtDNA repair by regulating protein expression of the HSF1-SSBP1 complex and POLG. Furthermore, our study showed that PGC-1α upregulation with ZLN005 led to increased protein levels of EXOG, POLG, HSF1, and SSBP1, all of which contribute to mtDNA homeostasis. Therefore, PGC-1α may be involved in mtDNA repair through interacting with multiple mtDNA repair proteins, especially with the help of EXOG. In summary, EXOG regulation by PGC-1α plays an essential role in rotenone-induced neurotoxicity in PC12 cells. EXOG represents a protective effect strategy in PC12 cells exposed to rotenone.

Keywords: EXOG; Mitochondrial DNA; Mitochondrial homeostasis; PGC-1α; Rotenone.