Combination of low level environmental toxicants with chemotherapeutics disturbs oligodendrocyte progenitor cell function through activation of the redox/Fyn/c-Cbl pathway

Thesis (Ph. D.)--University of Rochester. School of Medicine and Dentistry. Dept. of Biomedical Genetics, 2008.In this study, we focused on studying the combined toxicity of environmental toxicants and chemotherapeutic agents on oligodendrocyte-type-2 astrocyte precursor cells, also referred as oligodendrocyte progenitor cells (O-2A/OPCs). There are tens of thousands of environmental toxicants and these diverse toxicants often cause their toxic effects by unknown mechanisms. Recent studies have shown that chemically diverse toxicants converge on activation of Fyn and c-Cbl to disrupt precursor cell function as a consequence of the generation of reactive oxygen species (ROS). Many environmental toxicants, such as mercury, lead, and paraquat, have been well characterized as strong oxidants. Other insults, such as chemotherapeutic drugs, inflammatory cytokines, etc., also cause damage by the generation of ROS. We conducted our research on O-2A/OPCs, which have been extensively studied and well characterized. O-2A/OPCs have the ability to self-renew and differentiate, and this balance appears to be regulated by the intracellular redox state. In this study, we found that O-2A/OPCs pretreated with environmental toxicants were more vulnerable to secondary insults, including chemotherapeutic agents, glutamate and oxygen–glucose deprivation by disturbing cell proliferation and differentiation. Oligodendrocytes pretreated with environmental toxicants were also more vulnerable to tumor necrosis factor alpha (TNF-α). Cancer cell lines pretreated with same environmental toxicants were not as vulnerable as glial progenitor cells of CNS to secondary insults, demonstrating the importance of conducting such analysis on primary cells. We also found that MeHg and BCNU synergistically induced generation of ROS and decrease of glutathione levels, and synergistically activated the Fyn/c-Cbl pathway, which caused enhanced degradation of platelet-derived growth factor receptor alpha (PDGFRα). Blockage of the Fyn/c-Cbl pathway, using either pharmacological agents or biological means (i.e., the dominant negative form of c-Cbl or siRNAs for both Fyn and c-Cbl), protected cells from combined toxicity reactions. Our findings appear to be the first to reveal that O-2A/OPCs are sensitive to combined toxicity of environmental toxicants and chemotherapeutic agents at environmentally or physiologically relevant concentrations and that this combinatorial toxicity requires activation of redox/Fyn/c-Cbl pathway