The response of Drosophila melanogaster to methamphetamine and oxidative stress

Lijie Sun, Purdue University

Abstract

Drosophila melanogaster has long been used as a model organism to study development, population genetics, and diseases. It also has great potential to give us important insights into how organisms tolerate xenobiotic stresses. In the following thesis I investigated the molecular responses of three compounds known to cause stress: methamphetamine, hydrogen peroxide, and DDT. The former two are known to cause oxidative stress, and the third one is a second-generation pesticide. In Drosophila DDT resistance is associated with increased cytochrome P450 expression; overtransciption of P450s are also associated with oxidative stress. Although work has been done of specific genes and proteins that are responsive to methamphetamine, at the current moment little is known about the overall "omic" response of organisms to this illicit substance. We performed metabolome, proteome, and transcriptome profiling with Drosophila treated with methamphetamine. The proteomic profiling revealed responses associated with known physiological problems that occur with methamphetamine use in mammals. The metabolite trehalose was decreased significantly after methamphetamine exposure, suggesting an oxidative stress response to this drug. Many of the differentially transcribed genes, which included detoxification enzymes, had the potential transcriptional factor-binding motif YY1 associated with their upstream regulatory regions. YY1 is known to be responsive to amphetamines in mammals. I also studied the responses of Drosophila to the oxidative stressors (i) hydrogen peroxide and (ii) DDT. Metabolic DDT resistance in Drosophila melanogaster is associated with increased constitutive cytochrome P450 expression. Increased P450 activity has also been associated with increased oxidative stress. In contrast, over-transcription of glutathione S transferases (GST) has been associated with resistance to oxidative stress. We investigated the transcriptional expression of GSTs and P450s in DDT resistant (Wisconsin) and susceptible (Canton-S) Drosophila strains in response to exposure to DDT and the oxidative stressor H2O2. Wisconsin, which constitutively over-transcribed P450s also under-transcribed 27% of its GSTs, and was more susceptible to H2O2 than Canton-S. DDT exposure induced GST expression only in the Wisconsin strain. These results are consistent with the hypothesis that pesticide resistant and susceptible insects have differences in their transcriptional responses to xenobiotic challenges. Interestingly, one gene, CYP12D1, a mitochondrial P450, was differentially transcribed due to exposure by all three of the xenobiotics (methaphetamines, hydrogen peroxide, and DDT) that I studied. Additionally, in Sun et al. (2006) we observed that CYP12D1 transcriptional expression was induced by phenobarbital. These results suggest that CYP12D1 may be part of a generalizable response to xenobiotics.

Degree

Ph.D.

Advisors

Pittendrigh, Purdue University.

Subject Area

Entomology

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