Superfund Research Program
Mechanisms and Biomarkers of Metal Olfactory Injury in Salmon
Final Progress Reports
Year: 2016 2014
The goal of this project is to understand how exposures to Superfund chemicals interfere with olfactory function in Pacific salmon and, based upon this information, generate mechanism–based biomarkers to evaluate salmon health and effectiveness of Superfund site remediation.
Dr. Gallagher and his research team tested the hypothesis that exposure to cadmium (Cd) at levels relevant to Superfund sites may cause prolonged olfactory deficits. In vivo exposures to waterborne Cd (0.3, 3, 30 and 300 ppb) inhibited odorant detection in salmon. This loss of olfaction persisted after a 2-week recovery, and was accompanied by loss of gene expression of olfactory odorant receptors, indicating that these molecular biomarkers can reflect outcomes of Cd exposures in salmon migrating through aquatic Superfund sites. A high throughput qPCR platform comprising 30 diverse salmonid olfactory receptors representing the major receptor classes was developed for use in helping assess salmon olfactory function in northwest Superfund sites. The team also analyzed the results of an experiment in which salmon were acutely exposed to 9 exposure scenarios involving mixtures of the pesticides chlorpyrifos and malathion. Their results showed non-acetylcholinesterase mechanisms of olfactory injury, including mitochondrial injury in olfactory cells, whereas microarray analysis identified molecular pathways underlying unanticipated neurotoxic effects of exposure to the mixtures. The research team submitted for publication a study that analyzed the molecular mechanisms of saltwater acclimation in migrating salmon and the potential interactions with Superfund pollutants. Analysis revealed similarities between the molecular machinery of osmoregulation and sensory signal transduction, the latter being a target of neurotoxicants. This was validated in a study showing that hypersaline acclimation increased the acute toxicity of chlorpyrifos via non-acetylcholinesterase mechanisms. They also made substantial progress in developing and utilizing transgenic zebrafish to better understand the sensitivity of different fish olfactory sensory neuron (OSN) populations to metals. They imaged double-transgenic zebrafish larvae co-expressing two fluorescent markers, which differentially label the ciliated (OMP:RFP) and microvillous OSNs (TRPC2:Venus) via confocal microscopy. Preliminary studies on characterizing OSN death in these two sensory neuron populations following acute cadmium exposure are underway. Using the same two OSN promoters for ciliated and microvillous OSNs (OMP and TRPC2, respectively), they are also developing two additional transgenic zebrafish lines to express the genetically-encoded calcium indicator GCaMP6s in these OSNs for analyzing calcium changes as a mechanism of OSN injury during metal exposures. These transgenic tools can also be applied to studying olfactory signal transduction in fish, and for use in studies of smell disorders.