The Molecular Mechanism Of Mitochondrial Damage In Heart And Brain Of Rats Exposed To SO₂

Sulfur dioxide is a common environmental pollutant. It was widespreadly concerned to the relationship between SO2 exposure and disease. Epidemiological studies show that SO2 inhalation increases the risk and mortality of cardiovascular and cerebrovascular disease. Therefore, it was particularly important to research the toxicological mechanisms of SO2.In the present study, heart-derived H9C2 cells were treated with different concentrations of sulfur dioxide derivatives (10 μM,30 μM,100 μM of NaHSO3) for 24 h. Then the mitochondria, DNA, RNA and protein of H9C2 cells were extracted to detecting relevant indicators. Mitochondrial membrane potential (MMP) was assessed using the lipophilic cationic probe JC-1. Cytochrome C oxidase activity was measured by oxidating reduced cytochrome C. The amount of ATP was measured by the luciferinluciferase method. Analyses of mitochondrial replication and transcription were performed by real time PCR. The protein levels were detected using Western blotting. Nextly, male Wistar rats were housed in exposure chambers and treated with 3.5,7 and 14 mg/m3 SO2 for 4 h/d for 30 days, while control rats were exposed to filtered air in the same condition. After SO2 exposure, brain and heart from Wistar rats were removed and relevant indicators were detected according to the above described in vitro.Our results showed that mitochondrial dysfunction is caused in heart of rat by SO2 inhalation. Mitochondrial membrane potential (MMP), cytochrome C oxidase activity and the content of ATP was significantly reduced in rat heart after SO2 and its derivatives exposure. Moreover, SO2 or its derivatives exposure decrease the mRNA levels of subunits of cytochrome C oxidase and ATPase, such as CO1, CO2, CO3, ATP6&8, which was encoded by mtDNA, while the mRNA levels of CO4, which encoded by nDNA, was not changed after SO2 or NaHSO3 exposure. SO2 exposure also reduced transcriptional and translational levels of three regulatory genes (PGC-la, NRF1 and TFAM) in H9C2 cell and rat heart. These results suggest that SO2 can cause mitochondrial dysfuction by decreasing transcriptional and translational levels of three regulatory genes, leading to heart failure, arrhythmias and other cardiovascular diseases. Differenting from heart, SO2 stimulated mitochondrial biogenesis in rat brain, mainly in the exaltation of mitochondrial membrane potential, cytochrome C oxidase activity and ATP content. SO2 exposure also increased mRNA expression levels of subunits of critical components of oxidative phosphorylation pathway. In addition, SO2 exposure increased transcriptional and translational levels of NRF1 and TFAM, whereas PGC-la was not changed. It is suggested that NRF1 and TFAM might be the key factors involved in the regulation of mitochondrial oxidative phosphorylation in rat brain after SO2 exposure.Based on the above results, it was found that SO2 inhalation stimulated mitochondrial biogenesis in rat brain, but interfered with mitochondria energy metabolism in rat heart. It might be due to the tissue specific of SO2 on mitochondrial biosynthesis.