Aromatase is localized in the endoplasmic reticulum where it is regulated by tissue-specific promoters that are in turn controlled by hormones, cytokines, and other factors. It catalyzes the last steps of estrogen biosynthesis from androgens (specifically, it transforms androstenedione to estrone and testosterone to estradiol). These steps include three successive hydroxylations of the 19-methyl group of androgens, followed by simultaneous elimination of the methyl group as formate and aromatization of the A-ring.
General reaction for the conversion of testosterone to estradiol catalyzed by aromatase. Steroids are composed of four fused rings (labeled A-D). Aromatase converts the ring labeled "A" into an aromatic state.
The gene expresses two transcript variants.[2] In humans, the gene CYP19, located on chromosome 15q21.1, encodes the aromatase enzyme.[3] The gene has nine coding exons and a number of alternative non-coding first exons that regulate tissue specific expression.[4]
Aromatase is generally highly present during the differentiation of ovaries.[6][7] It is also susceptible to environmental influences, particularly temperature. In species with temperature-dependent sex determination, aromatase is expressed in higher quantities at temperatures that yield female offspring.[6] Despite the fact that data suggest temperature controls aromatase quantities, other studies have shown that aromatase can overpower the effects of temperature: if exposed to more aromatase at a male-producing temperature, the organism will develop female and conversely, if exposed to less aromatase at female-producing temperatures, the organism will develop male (see sex reversal).[6] In organisms that develop through genetic sex determination, temperature does not affect aromatase expression and function, suggesting that aromatase is the target molecule for temperature during TSD[6] (for challenges to this argument, see temperature-dependent sex determination). It varies from species to species whether it is the aromatase protein that has different activity at different temperatures or whether the amount of transcription undergone by the aromatase gene is what is temperature-sensitive, but in either case, differential development is observed at different temperatures.[8]
Role in neuroprotection
Aromatase in the brain is usually only expressed in neurons. However, following penetrative brain injury of both mice and zebra finches, it has been shown to be expressed in astrocytes.[9] Furthermore, it has also been shown to decrease apoptosis following brain injury in zebra finches.[10] This is thought to be due to the neuroprotective actions of estrogens, including estradiol. Research has found that two pro-inflammatory cytokines, interleukin-1β (IL-1β) and interleukin-6 (IL-6), are responsible for the induction of aromatase expression in astrocytes following penetrative brain injury in the zebra finch.[11]
A number of investigators have reported on a rather rare syndrome of excess aromatase activity. In boys, it can lead to gynecomastia, and in girls to precocious puberty and gigantomastia. In both sexes, early epiphyseal closure leads to short stature. This condition is due to mutations in the CYP19A1 gene which encodes aromatase.[12] It is inherited in an autosomal dominant fashion.[13] It has been suggested that the pharaoh Akhenaten and other members of his family may have suffered from this disorder,[14] but more recent genetic tests suggest otherwise.[15] It is one of the causes of familial precocious puberty—a condition first described in 1937.[16]
This syndrome is due to a mutation of gene CYP19 and inherited in an autosomal recessive pattern. It occurs due to inability to synthesize estrogens from androgens. Accumulations of androgens during pregnancy may lead to masculinization and virilization of a female at birth (males are not affected). Females will have primary amenorrhea. Individuals of both sexes will be tall, as lack of estrogen does not bring the epiphyseal lines to closure. Mothers affected may present with virilization during pregnancy as androgen hormones cross the placenta.
Inhibition of aromatase
The inhibition of aromatase can cause hypoestrogenism (low estrogen levels). The following natural products have been found to have inhibiting effects on aromatase.
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↑ 6.06.16.26.3Duffy TA, Picha ME, Won ET, Borski RJ, McElroy AE, Conover DO (August 2010). "Ontogenesis of gonadal aromatase gene expression in atlantic silverside (Menidia menidia) populations with genetic and temperature-dependent sex determination". Journal of Experimental Zoology. Part A, Ecological Genetics and Physiology. 313 (7): 421–31. doi:10.1002/jez.612. PMID20623799.
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↑Fukami M, Shozu M, Soneda S, Kato F, Inagaki A, Takagi H, Hanaki K, Kanzaki S, Ohyama K, Sano T, Nishigaki T, Yokoya S, Binder G, Horikawa R, Ogata T (June 2011). "Aromatase excess syndrome: identification of cryptic duplications and deletions leading to gain of function of CYP19A1 and assessment of phenotypic determinants". The Journal of Clinical Endocrinology and Metabolism. 96 (6): E1035–43. doi:10.1210/jc.2011-0145. PMID21470988.
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