In utero exposure to di-(2-ethylhexyl) phthalate reveals the presence of an adrenal-testis axis regulating androgen formation
Description
Thesis (Ph.D.)--Georgetown University, 2011.; Includes bibliographical references.; Text (Electronic thesis) in PDF format. Phthalates are endocrine disruptors with short- and long- term antiadrogenic properties. In the adult, in utero exposure to di-(2-ethylhexyl) phthalate (DEHP) results in decreased testosterone levels despite normal serum levels of LH, proteins and enzymes involved in cholesterol transport, and biosynthesis suggesting that the effects of DEHP are independent of the classic steroidogenic pathway. The purpose of this body of work is to identify the mechanism mediating this antiandrogenic effect of DEHP. The mineralocorticoid receptor (NR3C2; MR) mediates testosterone production and we show that in utero exposure to DEHP decreases MR-expression in Leydig cells. The reduced MR expression was accompanied by a decrease in circulating levels of aldosterone biosynthesized in the adrenal gland and was similar in magnitude to the decrease seen in testosterone. In search of the mechanism underlying the reduced aldosterone formation, we observed that DEHP decreases the expression of angiotensin II (ATII) receptors despite normal serum levels of the main aldosterone stimulants, ATII and potassium. The ATII receptor decrease did not have an impact on the proteins and enzymes involved in aldosterone biosynthesis. Paradoxically, the pathways for extracellular cholesterol and de novo cholesterol synthesis were up regulated and were accompanied with accumulation of lipid droplets in the zona glomerulosa.; Global gene expression of PND60 adrenals showed an up regulation of genes involved in the potassium response and resulted in the identification of the potassium channels Kcnk5 and Kcnn2 as novel targets of DEHP exposure. The deregulation of potassium sensing pathway was confirmed in vitro using NCI-H295R human adrenal cortical tumor cells exposed to the bioactive DEHP metabolite mono-2-ethylhexyl phthalate (MEHP).; The data obtained suggest that a deregulation in potassium channel gene expression can lead to a chronic activation of the adrenal zona glomerulosa, leading to reduction of ATII receptor expression and inhibition of aldosterone production. Reduction of circulating aldosterone levels together with a decrease of MR levels in Leydig cells could account for the antiandrogenic effects of DEHP in testis.; Taken together these results demonstrate that in utero exposure to DEHP induces long lasting effects on the endocrine system in the rat and unveiled the presence of adrenal-testis interactions driving androgen formation.
Permanent Link
http://hdl.handle.net/10822/552848Date Published
2011Type
Publisher
Georgetown University
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