Superfund Research Program
Estrogen Receptor-Arylhydrocarbon Receptor Interactions in the CNS
Project Leader: Gloria V. Callard
Grant Number: P42ES007381
Funding Period: 2000-2012
These investigators use zebrafish as a model to identify environmental chemicals that mimic or block hormone-regulated processes of CNS (central nervous system) development. These chemicals are called endocrine disrupting chemicals (EDC). By virtue of their hormone-like activity, many different chemicals, even at low doses or transient exposures, can have lifelong effects on the anatomy and functioning of the animal.
Project investigators are testing chemicals for potential endocrine disrupting activity in the CNS by measuring neural gene markers of estrogen effect. During the course of these studies, they identified additional gene markers that have utility for detecting the effects of dioxin-like chemicals on the developing gonad. Currently, they are extending these studies by optimizing and validating the zebrafish embryo gene expression system for use as a high throughput microassay (or test) for rapid screening and classification of multiple classes and mixtures of EDC. Development of an assay of this type has significance for categorizing the endocrine disrupting potential of some of the >87,000 chemicals in commercial use. Also, the investigators are using the zebrafish embryo assay to detect unknown EDC in environmental samples (e.g., pond water and sediment from Superfund sites). The advantage of the test is that low doses of EDC can be detected without a priori knowledge of their chemical nature, concentration, or mechanism of action.
Preliminary results show that the assay can detect EDC in complex contaminant mixtures, can discriminate between polluted and unpolluted sites, and is consistent with results from indigenous species from the same environments. The zebrafish assay has potential significance for development as a bioassay for isolating and characterizing biologically active chemical contaminants. Such data would help in interpreting epidemiological studies from the same sites.
Additional data are designed to characterize consequences of embryonic exposure to estrogen-like chemicals. Although the ultimate goal is to identify anatomic and functional perturbations of the developing CNS after chemical exposure of embryos, due to the complexity of the CNS, the researchers are now using highly sensitive molecular markers to help pinpoint affected brain regions and neural processes. The same approach is being extended to investigate the potential of embryonic chemical exposure to alter chemical responsiveness and repair mechanisms in the adult and aging CNS.
Project investigators are also characterizing mechanisms by which chemicals act on the CNS to alter neurodevelopment. In addition to generally recognized effects on transcriptional mechanisms of neural gene expression, these studies have revealed that estrogen- and dioxin-like chemicals, as well as contaminated environmental samples, can alter splicing of the gene products. Alternate splicing can lead to biologically active vs. inert proteins. Even if gene expression is normal or elevated, the gene product could be inert. These results identify a novel mechanism of neural toxicity and a new level of complexity to our understanding of EDC actions. If proven to have general relevance for other EDC and gene target, such a mechanism could assist in selecting end-points for chemical testing.