University of Florida (Denslow)

Summary

Transient and permanent reproductive dysfunction in fish has been linked to chemicals that disrupt the endocrine system, but the mechanisms involved are unclear. Many endocrine-disrupting chemicals (EDCs) interact with sex hormone receptors by acting as agonists to induce gene expression at inappropriate times or act as antagonists to prevent the normal functioning of the receptors. Other EDCs may act indirectly by altering the processes involved in regulating sex steroid synthesis and metabolism. Poor reproduction and altered plasma hormone levels have been observed in largemouth bass living in ecosystems polluted with organochlorine pesticides (OCPs), including the Superfund site at Lake Apopka and its surrounding muck farms, suggesting that OCP exposure has adversely affected their reproduction. In past research, the project's researchers have identified three estrogen receptors (a, pi, and (32) in largemouth bass, which exhibit tissue specific expression and respond differently to 17-p-estradiol at the message and activity level. These differences are important to control normal reproductive function. Project researchers have evidence that EDCs can alter their normal expression and activity patterns, possibly disrupting reproduction. In addition, the researchers have preliminary evidence that expression of enzymes involved in the synthesis and metabolism of EDCs is affected by the OCPs. The proposed studies are testing the central hypothesis that exposure of largemouth bass to concentrations of OCPs found in the Lake Apopka region disrupts endocrine system function by sex hormone receptor mediated and sex hormone receptor independent mechanisms. In this study the researchers have designed a set of interrelated experiments from the organismal level where pleiotropic effects of OCPs can be measured to the cellular level where specific molecular mechanisms of action can be assessed. They are exposing largemouth bass to methoxychlor (and its metabolites), p,p' DDE, dieldrin and toxaphene. The researcher's objectives include:

1. Develop biomarkers of exposure to organochlorinated pesticides in vivo, via the use of microarrays and novel proteomics methodologies,
2. Determine the effect of in vivo OCP exposure on LME steroid synthesis and metabolism, and
3. Evaluate the effects of OCPs on the molecular mechanisms of action of the three estrogen receptors.

Project researchers are using exposures to compounds with known modes of action as controls to determine mode of action specific gene expression patterns against which they compare the patterns of gene expression changes induced by the OCPs. They are checking these pattern changes against reproductive endpoints including the ability of eggs to mature (germinal vesicle breakdown) and sperm function (sperm motility). Fish are useful as sentinels of environmental quality and are perfect models to monitor adverse effects in reproduction caused by contaminants in Superfund sites. By extrapolation fish can report on the potential of OCPs to harm human health.