Introduction. Asbestos is a well-established human carcinogen. The studies presented in this thesis mainly investigated the contribution of mitochondria-originated oxidative stress to asbestos-induced genotoxicity in human small airway epithelial (SAE) cells. Furthermore, we determined the role of mitochondrial DNA (mtDNA) alterations in promoting mitochondrial dysfunction and mitochondria respiration chain-derived oxidants in response to asbestos exposure. Additionally, this thesis investigated whether mitochondria-derived oxidants regulate redox-responsive signaling in asbestos-exposed SAE cells.
Background. Asbestos is a well known carcinogen that causes lung cancers and mesothelioma, as well as non-malignant asbestosis in human. Currently, asbestos is still used in many countries. World-wide, about 125 million people are still exposed to asbestos and each year more than 90,000 of them develop lung cancer, mesothelioma or asbestosis due to occupational exposure. In countries where asbestos use has been completely banned, asbestos related mortality rate resulting from exposure in 1960s is still increasing due to the long latency of asbestos-induced diseases. Moreover, many existing asbestos-containing products that were made before 1970s are currently still in use in banned countries.
Despite the fact that cellular and molecular mechanisms of asbestos-induced malignancy have been extensively studied over the past three decades, the precise mechanisms of cancer induction are still not fully understood. Evidence from existing studies suggests that the prolonged induction of reactive intermediate species (ROS and RNS) by asbestos plays a pivotal role in asbestos-associated carcinogenesis. Asbestos-induced oxidative stress promotes nuclear DNA oxidative damage and mutations, and mediates various cellular signaling cascades involved in regulating cell death and apoptosis, inflammation, cell growth and proliferation, contributing to asbestos-induced malignant transformation. However, the precise origins of asbestos-induced ROS and RNS as well as the mechanisms of how they are generated remain unclear.
Methods. In these studies, we utilized a mitochondrial respiration function deficient cell (designated as ρ0 cell) model to investigate the role of mitochondria-derived reactive intermediate species in mediating asbestos-induced mutagenicity. First, we compared the asbestos-induced nuclear DNA oxidative damage and mutation levels in mitochondrial dysfunctional ρ0 SAE cells versus the parental SAE cells. Then the asbestos-initiated overall intracellular ROS and RNS production was determined in both ρ0 and parental SAE cells. Next we determined asbestos-induced multiple mtDNA alterations as well as mitochondrial respiration function in SAE cells. Finally, asbestos-initiated changes in the expression of redox-responsive inflammation related and immune genes in ρ 0 and parental SAE cells were assayed using low density array.
Results. Data from the current studies demonstrated that asbestos induced dose-dependent increases of nuclear DNA oxidative damage and micronuclei (MN) formation in SAE cells, whereas in mitochondrial dysfunctional ρ 0 SAE cells, the effects of asbestos were much less significant at all dosages examined. Consistently, asbestos-induced a significant increase in intracellular oxidants production in SAE cells while such an effect is not seen in ρ0 SAE cells. The findings in this thesis also indicate that asbestos induced a decrease of mtDNA copy number and an increase of a mtDNA 5-kb common deletion in a dose-dependent manner. As a result, the mitochondrial oxygen consumption rate and cytochrome c oxidase (COX) activity also decreased gradually with the increase of asbestos dose. Finally, our study showed that asbestos induced a time-dependent increase in the expression of genes involved in regulating MAPK (mitogen-activated protein kinase), NFκB (nuclear transcription factor kappa-B), and pro-inflammation related signaling cascades in SAE cells but not ρ0 SAE cells.
Conclusions. Overall, the results in this thesis indicate an important role of mitochondrial-derived reactive intermediate species in directly mediating asbestos-induced nuclear oxidative damage and lesions, as well as redox-responsive signaling in SAE cells. The production of mitochondrial-originated oxidants is mediated through asbestos-induced mtDNA mutations and mitochondrial respiration dysfunction. These data, collectively, suggest that mitochondria are a primary extra-nucleus target of asbestos, and, thus, might be a potential therapeutic target in the treatment of asbestos-induced human diseases.
|School Location:||United States -- New York|
|Source:||DAI-B 70/12, Dissertation Abstracts International|
|Keywords:||Asbestos, Mitochondria, Reactive intermediate species|
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