Duke University

Center for Environmental Gemonics

Elwood Linney, Ph.D.
elwood.linney@duke.edu

Project Description

Despite the tremendous inter-individual variability in the response to environmental toxins, we simply do not understand why certain people develop disease when challenged with environmental agents and others remain healthy. Yet, there is emerging consensus that many of the complex (and prevalent) diseases that humans develop occur as a result of multiple biologically unique gene-gene and gene-environment interactions. The recent advances in human and molecular genetics has provided an unparalleled opportunity to understand how genes and genetic changes interact with environmental stimuli to either preserve health or cause disease. The theme of our Center is to use gene expression profiling to understand the effect of environmental stresses on human health. This will be accomplished by establishing an interdisciplinary Center that supports the use of complementary biologic systems (humans, mice, zebrafish, and worms) to investigate the role of genetic susceptibility in the pathogenic response to specific types of environmental stress (bacteria, malnutrition, and metals). This approach will enable us to develop and investigate environmental models of human disease that represent biologically unique gene-environment-pathophysiological phenotypes. Microarray analyses will be used to comprehensively evaluate the biological response to environmental stress and to identify pathogenic mechanisms that are relevant to innate immunity, neural tube defects, and transition metal toxicity. The end result is a broad based yet highly integrated program that has the potential to make a number of novel, related observations. The overall hypothesis unifying this research program is that gene expression profiling will identify genes and pathogenic processes that are critical to human environmental health and disease. In aggregate, the coupled scientific findings from the proposed program will substantially enhance our understanding of environmental toxicology and genomics.

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Project 1: The Genetics of Innate Immunity

Principal Investigator: Vance Fowler, M.D.
Fowle003@mc.duke.edu

The goal of this project is to identify polymorphisms in genes that regulate the innate immune response to endotoxin or lipopolysaccharide (LPS) in humans. The environmental, clinical, and biologic significance of this project is supported by the following observations. First, endotoxin is ubiquitous in the environment and is associated with the development and progression of asthma and other forms of airway disease. In the domestic setting, the concentration of endotoxin is associated with the clinical severity of asthma, and among exposed workers endotoxin is the most significant component of the bioaerosol that is associated with the development and progression of airway disease. Endotoxin may also play a role in the pathophysiology of air pollution, and experimentally we have found that inhaled LPS can cause all of the signs of asthma - reversible airflow obstruction and airway inflammation, and persistent airway hyperreactivity and airway remodeling. Second, the ability of the host to respond to LPS is highly variable. In mice, differences in responsiveness to LPS are well established; C3H/HeJ, C57BL/10ScCR, and TLR4 -/- inbred strains are hyporesponsive to LPS. We have recently found that normal healthy, non-asthmatic subjects demonstrate a reproducible airway response to an incremental LPS inhalation challenge test; some subjects develop airflow obstruction when challenged with low concentrations of LPS and others are virtually unaffected by high concentrations of inhaled LPS. Third, innate immunity provides a first line of host defense against microbial pathogens that is conserved over a wide variety of species from flies to mammals. In fact, TLR4, a recently described transmembrane receptor for LPS, was first discovered in drosophila and subsequently found in mammals. Emerging evidence suggests that innate immunity also plays an important role in shaping antigen specific immunity. Finally, we have found that mutations in TLR4 are associated with hyporesponsiveness to inhaled LPS in both inbred strains of mice and in humans, and also predispose humans to gramnegative sepsis. However, our data also demonstrate that mutations in TLR4 account for only a portion of the endotoxin phenotype in either mice or humans, and our findings indicate that other genes are involved in regulating the response to LPS. The overall hypothesis of this investigation is that polymorphisms of genes identified by gene expression profiling in phenotypically distinct strains of mice following airway or systemic challenge with LPS regulate the pathophysiologic response to LPS in humans.

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Project 2: The Genetics of Neural Tube Development

Principal Investigator: Elwood Linney
elwood.linney@duke.edu

The development of the vertebrate neural tube is an integration of many events synchronized to produce a functional product. The complexity is evident from the relatively high frequency of neural tube defects (NTDs) in both human and vertebrate animal populations. Both genetic and environmental factors have been implicated in the pathogenesis of NTDs; the observation that there are distinct differences in neural tube defect prevalence in different human populations coupled with the established reduction in risk associated with maternal supplement with exogenous folate prior to and during early pregnancy confirm the importance of environmental influences. However, studying the events occurring during neural tube development is currently impossible with humans and limited at best with rodent model systems. To dissect and understand these processes, one would like to identify a signature set of genes whose expression are affected during the development of a neural tube abnormality. A gene set is only a partial picture and ideally it would be valuable to develop a correlation between the actual morphology of a developing, abnormal neural tube for comparison with that of normal events. In this proposal, we set forth plans to use the visibility of the zebrafish embryo, one's ability to easily capture its embryonic development microscopically, the use of a new "morphant" technique for knocking down the expression of selected genes, plus the visible segmentation of the developing nervous system through transgenic fluorescent reporter zebrafish embryos to attempt to uncover the events and genes involving in neural tube formation. This work will identify candidate genes that will be tested in a series of human neural tube defect families.

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