Biomedical Sciences ETDs

Njotu Agbor

Publication Date

12-1-2012

Abstract

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor involved in the metabolism of environmental pollutants including halogenated aromatic hydrocarbons, for example, 2,3,7,8-tetrachlorodibenzo-ρ-dioxin (TCDD). The AHR and its downstream target gene cytochrome P4501A1 (CYP1A1) are also involved in cardiovascular development. AHR knockout (KO) mice are hypotensive, with cardiac hypertrophy. Additionally, CYP1A1 is involved in the production of potent vasodilator metabolites from omega-3 polyunsaturated fatty acids (n-3 PUFAs) metabolism. Thus, we hypothesize that the AHR and its downstream target gene, CYP1A1, both contribute to normal vascular reactivity of blood vessels and to blood pressure (BP) regulation. We generated mice with conditional deletion of the AHR from the endothelium (ECahr-/-), to elucidate the degree to which loss of AHR contributes to vasoreactivity and BP regulation in vivo. BP and heart rate (HR) was assessed prior to and following angiotensin (Ang) II injection, or chronic treatment with an angiotensin converting enzyme inhibitor, captopril. Vasoreactivity was assessed in aorta in presence of perivascular adipose tissue. Immunoblot was used to assess Ang 1 receptor A (AT1R) protein expression in the aorta. We used CYP1A1 KO mice to determine the degree to which global deletion of CYP1A1 contributes to vasoreactivity in the aorta and mesenteric arterioles, and to BP regulation. BP and HR was measured ± nitric oxide synthase (NOS) inhibitor, LNNA. Vasoreactivity to eicosapentaenoic acids (EPA) and docosahexaenoic acids (DHA) were conducted in aorta and mesenteric arterioles. CYP1A1 WT and KO mice were provided n-3 or n-6 PUFA-enriched diets for 2 months, and BP and HR measured ± LNNA. Endothelial NOS (eNOS) and phospho-eNOS protein were measured in the aorta of all diet treated mice. Our data showed that ECahr-/- mice are hypotensive, associated with reduced responses to Ang II, and reduced aortic AT1R expression. Moreover, CYP1A1 KO mice exhibited elevated BP compared to WT mice, with attenuated vasodilation to EPA and DHA. Further, supplementation with an n-3 PUFA-enriched diet normalizes BP in CYP1A1 KO mice to WT levels. In contrast, an n-6 PUFA-enriched diet increased BP in WT mice to levels seen in CYP1A1 KO mice on standard chow. Phospho-eNOS protein expression was reduced in aorta of CYP1A1 KO mice fed an n-3 PUFA-enriched diet, compared to WT mice. Taken together, these data suggest that endothelial AHR and global CYP1A1 have a physiologically important role in the regulation of vascular function and BP, and involve different mechanisms. The clinical implications are that n-3 PUFA-enriched diets could be recommended in the treatment of hypertension in humans. Additionally, AHR antagonists and stable analogues of CYP1A1 n-3 PUFA metabolites could be used in the treatment of long term resistant hypertension.

Keywords

"Aryl hydrocarbon receptor, Cytochrome P4501A1, omega-3 polyunsaturated fatty acids, vasorelaxation, blood pressure"

Document Type

Dissertation

Language

English

Degree Name

Biomedical Sciences

Level of Degree

Doctoral

Department Name

Biomedical Sciences Graduate Program

First Committee Member (Chair)

KANAGY, NANCY

Second Committee Member

BOSC, LAURA

Third Committee Member

CAMPEN, MATTHEW

Fourth Committee Member

WALKER, MARY

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