Dissertation Defenses

Doctoral Dissertation Announcement

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Candidate: Trisha M. Basford

Degree of: Doctor of Philosophy

Department: Chemistry

Title: The Global Hepatic Transcriptional Response of Male Fisher Rats to Dietary Aroclor 1254 Exposure

Committee:
Dr. Jay C. Means, Chair
Dr. Susan Stapleton
Dr. Elke Schoffers
Dr. Lisa Baker

Date: Wednesday, May 23, 2007 9:00 a.m. – 11:00 a.m.
2734 Wood Hall

Abstract:
Dietary intake is a primary route for biomagnification of environmentally persistent polychlorinated biphenyls (PCBs) within humans and animals. Aroclor 1254, a mixture of PCBs, is associated with a variety of toxic responses including alterations in blood and lipid biochemistry and tumor promotion. Measurement of the transcriptional responses to low-level dietary exposure to A1254 has not been reported to date, and is important given the persistence of PCBs, and range of effects associated with exposure. The aims of this study are to characterize changes in rat hepatic global gene expression due to sub-acute and sub-chronic dietary exposure to A1254, and to compare transcriptional profiles at sub-acute and sub-chronic exposure times to characterize the shift in gene expression profile due to duration of exposure. Fisher rats were fed control diet or diet containing 5.6 ppm or 18 ppm A1254, for 7 or 84 days. Affymetrix microarrays (RGU34A) were prepared from liver mRNA for each treatment group (n=3) and time point, and comparisons were made between controls and treated rats at each time. Class comparison and gene ontology (GO) analysis of microarray data showed that most significant changes in expression were in animals consuming high doses of A1254. Upregulation of genes involved in sulfur redox, and PCB metabolism and detoxification were seen in treated animals after 1 week, accounting for more than 50% of the significantly changed GO categories at that time. After 12 weeks exposure, changes were also observed in transcription of genes involved in fatty acid (FA) transport and metabolism, small GTPase-mediated signaling, and transcription--approximately 40% of significantly changed GO categories. Quantitative RT-PCR Taqman assays were used to verify changes in expression of some genes measured by microarray. Genes chosen to represent changes in important GO categories include Cd36 and Me1 for FA-related changes, Cyp2b15 for Phase I metabolism, and Rab11a for GTP-related. Ca3 and Hmgcs2 were chosen to verify decreases in expression, and Ceacam10 as a unique, AhR-responsive gene. Quantitative PCR confirmed gene expression changes measured by microarray.