The long-term goal of this project is to understand the role that SYP1A1 (cytochrome P1-450) plays in toxicity caused by environmental pollutants. Cyp1a1 is a member of the dioxin-inducible [ah] battery, the genes of which are up-regulated by the ah receptor (AHR). The CYP1A1 enzyme oxgenates halogenated and polycyclic aromatic hydrocarbons, e.g. polychlorniated biphenyls (PCBs) and benzo[a]pyrene(BaP). AHR ligands include dioxin (which is metabolised extremely slowly) and PCBs and BaP (which are metabolised more rapidly). The [Ah] battery plays a major role in toxicity of the skin, bone marrow, liver, eye, ovary, and immune system--as well as carcinogenesis. In the mouse the dosage and route of BaP administration are important determinants in target organ toxicity. Genetic differences in BaP toxicity depends upon the high-affinity C57BL/6-type (Ahr(b) allele) or the low-affinity DBA/2-type(Ahr(d) allele) of Ah receptor. Expression of mouse CYP1A1 mRNA is constitutively low absent, but is highly inducible in virtually every tissue and cell type in the body--following exposure to polycyclic aromatic chemicals. Toxicity can occur by either metabolism-dependent or receptor-dependent (metabolism- independent) mechanism. This laboratory has recently collaborated in making the Ahr(-/-) knockout mouse line. To investigate the mechanisms of CYP1A1 metabolism-mediated, vs. AHR-mediated toxicity caused by environmental chemicals, we therefore propose to: [1] develop a conventional, as well as an inducible, Cypla(-/-) knockout transgenic mouse line; [2] develop a (global, rather than tissue-specific) Cyp1a1(u/u) (ultra-expression) transgenic mouse line, and then generate, by breeding, the combined mouse lines Cyp1a1(-/-)Ahr(-/-), Cyp1a1 (-/-)Ahrd/d), Cyp1a1(-/-)Ahr(b/b), Cyp1a1(u/u)Ahr(-/-), Cyp1a1(u/u)Ahr(d/d), and Cyp1a1(u/u)Ahr(b/b). [3] study bone marrow toxicity and skin inflammation, following treatment of these mouse lines with oral BaP and with topical 7,12-dimethylbenzo[a]anthracene(DMBA), respectively, to determine which forms of environmental toxicity are dependent on CYP1A1 metabolism, and which forms of toxicity are dependent on the Ah receptor. These studies will greatly enhance our understanding of CYP1A1 metabolism-dependent, compared with AHR-dependent, toxicity caused by environmental pollutants. Because of conservation between human and mouse, and human polymorphisms in the CYP1A1 and AHR genes are known to exist, studies in these intact mice should help elucidate the mechanisms surrounding genetic differences in susceptibility to toxicity caused by substrates of CYP1A1, as well as ligands of the AHR.
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