Superfund Research Program
Molecular Mechanisms of Endocrine Disruption in Largemouth Bass
Project Leader: Nancy D. Denslow
Grant Number: R01ES015449
Funding Period: 2006-2009
This research project investigated the impact of organochlorine pesticides (OCPs) on multiple molecular and physiological endpoints along the reproductive axis of male and female largemouth bass (LMB). Studies were conducted in both laboratory and environmental settings. Specific goals of the project were to:
- Develop biomarkers of exposure to OCPs
- Determine the effect of OCP exposure on LMB steroid synthesis and metabolism Evaluate the effects of OCPs on the molecular mechanisms of action of the three estrogen receptors (ERs) alpha, beta-a and beta-b.
The over-arching hypothesis for this project was that OCPs affect signaling pathways that are critically involved in the reproductive process in LMB (i.e. gonadal growth and development, follicular growth and maturation, steroidogenesis).
The research team successfully developed LMB as an excellent in vivo model for testing the effects of OCP exposure. LMB are top predators in the food chain and serve as an economically important game fish; their habitats span diverse aquatic environments throughout the United States, including polluted superfund sites such as Lake Apopka and the north shore muck farms used for agricultural purposes during previous years. LMB serve as an excellent model for experimentation because their reproductive cycle is predominantly synchronous and gradually progresses for several months prior to spawning.
Based on data collected from the research team throughout the project, the team concluded that:
- LMB exposed to the muck farm sediments in a mesocosm for 4 months bioaccumulate OCP pesticides
- Exposure to environmentally relevant levels of OCPs by dietary administration can be achieved in the laboratory
- Exposure to specific OCPs, as well as selected mixtures thereof, have profound effects on gene regulation in tissues of the reproductive axis
- Changes in gene expression suggest that OCPs are affecting several biochemical pathways that are related to reproduction. These pathways may be associated with depressed sex steroid and vitellogenin production in LMB.
The researchers also developed ex vivo culture systems using minced ovaries and testis, in order to test the gonad-specific effects of OCPs in the presence and absence of gonadotropin (hCG). This suggests that reproduction, specifically gonadal steroidogenesis, can be directly targeted by these OCPs.
This research has made significant inroads in elucidating the impacts of OCP exposure on LMB. Fish exposed in the laboratory show the same dysregulation of hormone homeostasis as found in fish collected from the Lake Apopka/muck farms. They have shown that exposure of fish to the muck farms results in bioaccumulation of contaminants in the tissues and that these levels are sufficient to affect gene transcription of regulatory proteins involved in growth, reproduction and susceptibility to disease. The research team has developed and validated a unique new tool for toxicogenomic application to LMB. Their 15,000 gene microarrays will be made available to anyone wishing to characterize health impacts on LMB exposed to superfund chemicals. The LMB model can now be used for a variety of monitoring experiments to determine the health and reproductive impacts of exposure to pesticides, which appear to function as endocrine disruptors.