Control of RNA oxidation as a novel mechanism for preventing mitochondrial dysfunction

Mitochondria generate energy through oxidative phosphorylation in eukaryotic cell and produce large amount of reactive oxygen species ROS as byproducts during this process. In particular in mitochondria, oxidative modifications of biomolecules by ROS can cause their inactivation. The situation is exacerbated during oxidative stress when excessive amounts of ROS are produced. Oxidative damage of macromolecules causes mitochondrial dysfunction and eventually leads to numerous diseases such as cardiovascular and neural disorders. Although the deleterious effects of oxidized DNA, proteins and lipids have been extensively characterized, little is known about the potential causative effects of oxidized RNA. Here, we assessed RNA oxidation levels in the mitochondria and cytosol of cultured human cells, which was analyzed by using 8-hydroxyguanosine 8-oxo-G on the RNA as a marker for oxidative stress. Interestingly, our result revealed that 8-oxo-G levels of mitochondrial mt-RNA was relatively higher than that of cytosolic RNA suggesting that RNA is one of the contributing factors leading to mitochondrial dysfunction. To further evaluate the consequence of RNA oxidation, we will examine mitochondrial functionality, permeability, and cell viability to determine a correlation with the levels of 8-oxo-G in mt-RNA. We previously showed that human polynucleotide phosphorylase hPNPase, which mainly localizes to mitochondria and binds oxidized RNA with high affinity, reduces RNA oxidation and protects HeLa cell during oxidative stress. We intend to elucidate the potential role of hPNPase and its associated RNA helicase, hSUV3, in reducing mt-RNA oxidation which is of relevance to diseases associated with mitochondrial dysfunction.