PCB-induced priming of microglial activity across sexes and development

PROJECT SUMMARY / ABSTRACT Polychlorinated biphenyls (PCBs) remain ubiquitous environmental contaminants and exposure to them is associated with increased risk of neurodevelopmental and mood disorders. These disorders tend to occur more frequently in infant male and adolescent female individuals, and are associated with altered function of microglia, the resident immune cells of the brain. While significant gains have been made in understanding effects of PCBs on neurons, direct effects of PCBs and most other environmental toxicants on microglia are unknown. The overall objective of this proposal is to identify direct effects and putative mechanisms of PCB action on microglial function and possible neuronal consequences. The central hypothesis is that PCBs will prime microglia to produce exaggerated responses to a secondary challenge in age- and sex-specific ways. The application proposes to use microglia acutely isolated from male and female neonatal and adolescent whole brains and treated to individual PCB congeners, an environmentally representative mixture, or vehicle in vitro prior to a control or immune challenge. Aim 1 is to evaluate the effects of PCB exposure on microglial cytokine signaling and regulation. IL1b and TNFa expression and release will be assayed with qPCR and ELISA. Expression and localization of pro-inflammatory TLR4 receptor and NFkB transcription factor required for cytokine expression will also be determined with immunocytochemistry. Aim 2 is to interrogate effects and putative mechanisms of PCBs on microglial oxidative stress. Production of ROS/RNS and peroxynitrite- associated cell damage in mixed cell cultures, and expression of PCB-sensitive receptors that modulate calcium and ROS/RNS production in microglia, will be determined. Aim 3 is to identify effects and putative mechanisms of PCBs on microglial phagocytosis. Microglial phagocytosis of fluorescently labeled latex beads and expression of phagocytosis-related genes will be determined by flow cytometry and qPCR. Microglia morphology associated with phagocytosis will be determine in mixed cell cultures by immunohistochemistry. The proposed work is innovative in that it is the first to directly study sex differences in microglial responses to environmental toxicants and use acute isolation techniques to better maintain in vivo phenotypes. These studies are expected to contribute to a conceptual framework for identifying mechanistic targets of PCB action in microglia. This knowledge could provide a strong foundation for the pursuit of microglia-directed therapeutic strategies aimed at treating or preventing toxicant-induced neurodevelopmental disorders. This information could also inform population-targeted exposure mitigation strategies. As an AREA-R15 application, these studies will engage students in independent and meritorious research, strengthening the institutional research environment at an institution serving a large number of students underrepresented in science.