Location: Reproduction ResearchTitle: Porcine Hypothalamic Aromatase Cytochrome P450: Isoform Characterization, Sex-Dependent Activity, Regional Expression, and Regulation by Enzyme Inhibition in Neonatal Boars) Author
Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2009
Publication Date: 8/1/2009
Publication URL: http://handle.nal.usda.gov/10113/42274
Citation: Corbin, C.J., Berger, T., Ford, J.J., Roselli, C.E., Sienkiewicz, W., Trainor, B.C., Roser, J.F., Vidal, J.D., Harada, N., Conley, A.J. 2009. Porcine Hypothalamic Aromatase Cytochrome P450: Isoform Characterization, Sex-Dependent Activity, Regional Expression, and Regulation by Enzyme Inhibition in Neonatal Boars. Biology of Reproduction. 81(2):388-395. Interpretive Summary: Aromatase, the enzyme that converts androgens to estrogens, differs in pigs from other investigated mammalian species in that pigs have 3 functional genes for this protein whereas other species have only 1 functional gene. Each of the 3 porcine genes determines tissue specific expression with one unique for the gonads, another for placenta and the third for the early conceptus. Local production of estrogen within the hypothalamus plays a central role in sexual differentiation and in activation of reproductive behavior in rodents. The objective of the current series of studies was to determine if this enzyme is present within the hypothalamus of pigs and, if so, which of the 3 genes is expressed there. Hypothalami and pituitary glands were collected from sexually mature pigs and evaluated for aromatase activity. Aromatase expression was 4-fold higher in male than female hypothalami, and, based on analyses confirmed by cloning and sequencing of transcripts, porcine hypothalami express the gonadal form of aromatase. Additionally, microsomal protein isolated from hypothalmi was sensitive to the gonadal-selective inhibitor, etomidate, and synthesized 1-hydroxy-testosterone, a steroid uniquely produced by gonadal aromatase. No detectable activity was found in microsomal protein from female pituitary glands. These findings have value to other investigators who seek solutions to problems related to porcine reproductive behavior and to the regulation of reproductive hormones that are produced in the anterior pituitary gland.
Technical Abstract: Domestic pigs have three CYP19 genes encoding functional paralogues of the enzyme aromatase cytochrome P450 (P450arom) that are expressed in the gonads, placenta and pre-implantation blastocyst. All catalyze estrogen synthesis, but the “gonadal” type enzyme is unique in also synthesizing a nonaromatizable, biopotent testosterone metabolite, 1OH-testosterone (1OH-T). P450arom is expressed in the vertebrate brain, is higher in males than females, but has not been investigated in pigs. Therefore, these studies defined which of the porcine CYP19 genes was expressed, and at what level, in adult male and female hypothalamus. Regional expression was examined in mature boars, and regulation of P450arom expression in neonatal boars was investigated by inhibition P450arom with letrozole which is known to re-program testicular expression. Pig hypothalami expressed the “gonadal” form of P450arom (redesignated the “gonadal/hypothalamic” porcine CYP19 gene and paralogue) based on functional analysis confirmed by cloning and sequencing transcripts. Hypothalamic tissue synthesized 1OH-T and was sensitive to the selective P450arom inhibitor, etomidate. Levels were 4-fold higher in male than female hypothalami, with expression in the medial pre-optic area and lateral borders of the ventro-medial hypothalamus of boars. In vivo, letrozole-treated neonates had increased aromatase activity in hypothalami but decreased activity in testes. Therefore, though the same CYP19 gene is expressed in both tissues, expression is regulated differently in the hypothalamus than testis. These, the first such studies in pig brain, demonstrate unusual aspects of P450arom expression and regulation in the hypothalamus, offering promise of gaining better insight into roles of P450arom in reproductive function.