Aromatase--a Brief Overview

Annual Review of Physiology. 2002  |  Pubmed ID: 11826265

There is growing awareness that androgens and estrogens have general metabolic roles that are not directly involved in reproductive processes. These include actions on vascular function, lipid and carbohydrate metabolism, as well as bone mineralization and epiphyseal closure in both sexes. In postmenopausal women, as in men, estrogen is no longer solely an endocrine factor but instead is produced in a number of extragonadal sites and acts locally at these sites in a paracrine and intracrine fashion. These sites include breast, bone, vasculature, and brain. Within these sites, aromatase action can generate high levels of estradiol locally without significantly affecting circulating levels. Circulating C19 steroid precursors are essential substrates for extragonadal estrogen synthesis. The levels of these androgenic precursors decline markedly with advancing age in women, possible from the mid-to-late reproductive years. This may be a fundamental reason why women are at increased risk for bone mineral loss and fracture, and possibly decline of cognitive function, compared with men. Aromatase expression in these various sites is under the control of tissue-specific promotors regulated by different cohorts of transcription factors. Thus in principle, it should be possible to develop selective aromatase modulators (SAMs) that block aromatase expression, for example, in breast, but allow unimpaired estrogen synthesis in other tissues such as bone.

Orexin-A Augments Voltage-gated Ca2+ Currents and Synergistically Increases Growth Hormone (GH) Secretion with GH-releasing Hormone in Primary Cultured Ovine Somatotropes

Endocrinology. Dec, 2002  |  Pubmed ID: 12446588

Orexins are recently discovered neuropeptides that play an important role in the regulation of hormone secretion, and their receptors have been recently demonstrated in the pituitary. The effects of orexin-A on voltage-gated Ca2+ currents and GH release in primary cultured ovine somatotropes were examined. The expression of orexin-1 receptor was demonstrated by RT-PCR in ovine somatotropes, from which Ca2+ currents were also isolated as L, T, and N currents. Application of orexin-A (100 nM) significantly and reversibly increased only the L current, and coadministration of orexin-A and GHRH (10 nM) showed an additive effect on this current, but no effect of orexin-A was observed on either T or N current. Furthermore, the orexin-A-induced increase in the L current was completely abolished by the inhibition of protein kinase C (PKC) activity using calphostin C (100 nM), phorbal 12,13-dibutyrate pretreatment (0.5 micro M) for 16 h or specific PKC inhibitory peptide PKC(19-36) (1 mM). However, the increase in L current by orexin-A was sustained when cells were preincubated with a specific protein kinase A blocker H89 (1 micro M) or a specific intracellular Ca2+ store depleting reagent thapsigargin (1 micro M). Finally, orexin-A alone did not significantly increase GH release, but coadministration of orexin-A and GHRH showed a synergistic effect on GH secretion in vitro. Our results therefore suggest that orexin-A may play an important role in regulating GHRH-stimulated GH secretion through the enhancement of the L-type Ca2+ current and the PKC-mediated signaling pathway in ovine somatotropes.

Cellular and Molecular Characterization of the Adipose Phenotype of the Aromatase-deficient Mouse

Endocrinology. Apr, 2003  |  Pubmed ID: 12639931

Estrogen deficiency in the aromatase knockout (ArKO) mouse leads to the development of obesity by as early as 3 months of age, which is characterized by a marked increase in the weights of gonadal and infrarenal fat pads. Humans with natural mutations of the aromatase gene also develop a metabolic syndrome. In the present study cellular and molecular parameters were investigated in gonadal adipose tissue from 10-wk-old wild-type (WT) and ArKO female mice treated with 17beta-estradiol or placebo to identify the basis for the increase in intraabdominal obesity. Stereological examination revealed that adipocytes isolated from ArKO mice were significantly larger and more abundant than adipocytes isolated from WT mice. Upon treatment with estrogen, the volume of these adipocytes was greatly reduced, whereas the reduction in the number of adipocytes was much less pronounced. Transcriptional analysis using real-time PCR revealed concomitant changes with adipocyte volume in the levels of transcripts encoding leptin and lipoprotein lipase, whereas peroxisome proliferator-activated receptor gamma levels followed a pattern closer to that of adipocyte number. Little change was observed in levels of transcripts for factors involved in de novo fatty acid synthesis, beta-oxidation, and lipolysis, suggesting that changes in the uptake of lipids from the circulation are the main mechanisms by which estrogen regulates lipid metabolism in these mice.

The Aromatase Knockout Mouse Presents with a Sexually Dimorphic Disruption to Cholesterol Homeostasis

Endocrinology. Sep, 2003  |  Pubmed ID: 12933663

The aromatase knockout (ArKO) mouse cannot synthesize endogenous estrogens due to disruption of the Cyp19 gene. We have shown previously, that ArKO mice present with age-progressive obesity and hepatic steatosis, and by 1 yr of age both male and female ArKO mice develop hypercholesterolemia. In this present study 10- to 12-wk-old ArKO mice were challenged for 90 d with high cholesterol diets. Our results show a sexually dimorphic response to estrogen deficiency in terms of cholesterol homeostasis in the liver. ArKO females presented with elevated serum cholesterol; conversely, ArKO males had elevated hepatic cholesterol levels. In response to dietary cholesterol, 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase transcript levels were significantly reduced in females, whereas males showed more modest changes. Neither low density lipoprotein nor sterol regulatory element-binding protein expression levels were significantly altered by diet or genotype. The expression of Cyp7a, which encodes cholesterol 7 alpha-hydroxylase, was significantly reduced in ArKO females compared with wild-type females and was increased by cholesterol feeding. Cyp7a expression was significantly elevated in the wild-type males on the high cholesterol diet, although no difference was seen between genotypes on the control diet. The ATP-binding cassette G5 and ATP-binding cassette G8 transporters do not appear to be regulated by estrogen. The expression of acyl-coenzyme A:cholesterol acyltransferase 2 showed a sexually dimorphic response, where estrogen appeared to have a stimulatory effect in females, but not males. This study reveals a sexually dimorphic difference in mouse hepatic cholesterol homeostasis and roles for estrogen in the regulation of cholesterol uptake, biosynthesis, and catabolism in the female, but not in the male.

Estrogen Deficiency Leads to Apoptosis in Dopaminergic Neurons in the Medial Preoptic Area and Arcuate Nucleus of Male Mice

Molecular and Cellular Neurosciences. Dec, 2004  |  Pubmed ID: 15555924

The aromatase knockout (ArKO) mouse is unable to synthesize estrogens. Immunohistochemical studies on active caspase-3 and tyrosine hydroxylase (TH) revealed apoptosis of dopaminergic neurons in the medial preoptic area (MPO) and arcuate nucleus (Arc) of the hypothalamus of 1-year-old (1yo) male ArKO mice while no active caspase-3 was detected in wild type (WT). Furthermore, the number of TH-positive cells in the MPO and caudal Arc was significantly decreased in 1yo ArKO compared to WT. RNase protection assays support the presence of apoptosis in 1yo ArKO hypothalamus, revealing an up-regulation of pro-apoptotic genes: FASL, FADD, and caspase-8. Concomitantly, the ratio of bcl-2-related anti-apoptotic genes to pro-apoptotic genes in the hypothalamus of 1yo ArKO mice was significantly down-regulated. Previously, we have reported that no such changes were observed in the hypothalamus of female ArKO mice. Thus, we have provided direct evidence that estrogen is required to maintain the survival and functional integrity of dopaminergic neurons in the MPO and Arc of male, but not female mice.

Adipose Aromatase Gene Expression is Greater in Older Women and is Unaffected by Postmenopausal Estrogen Therapy

Menopause (New York, N.Y.). Mar, 2005  |  Pubmed ID: 15772569

Although natural menopause is associated with loss of ovarian estrogen production, this life phase is followed by a significant increase in estrogen-related cancers, namely breast and endometrial cancer. These tissues, as well as adipose, skeletal, and vascular tissues and the brain are important sites of postmenopausal estrogen production. Circulating C19 steroid precursors are essential substrates for extragonadal estrogen synthesis; however, the levels of these androgenic precursors decline markedly with advancing age. This implies an increase in capacity for extragonadal tissues to produce estrogen with age.

Differential Expression of Factors Involved in Fat Metabolism with Age and the Menopause Transition

Maturitas. Jul, 2005  |  Pubmed ID: 15978974

Changes in the hormonal milieu at the menopause are associated with an increase in total adiposity and a more android pattern of fat distribution, with the latter associated with an increased risk of the metabolic syndrome. The aim of this study was to explore potential mechanisms that might contribute to the changes in body composition associated with the menopause transition.

Estrogen, a Fundamental Player in Energy Homeostasis

The Journal of Steroid Biochemistry and Molecular Biology. May, 2005  |  Pubmed ID: 16054355

Hippocampal NMDA Receptor Subunit Expression and Watermaze Learning in Estrogen Deficient Female Mice

Brain Research. Molecular Brain Research. Oct, 2005  |  Pubmed ID: 16083992

The aromatase knockout (ArKO) mouse is estrogen deficient. Using reverse-transcription and real-time PCR, we showed that transcript levels of the N-methyl-d-aspartate (NMDA) receptor subunit NR2B are significantly higher in the hippocampus of female ArKO mice compared to wild-type (WT) littermates. Expression levels of NR1, NR2A, but not NR2C, also tended to be higher in ArKO mice. In the Morris watermaze test for spatial memory, both genotypes displayed equal significant improvement in the latency in locating the invisible platform over the 5-day training period. These findings show that selective loss of estrogen synthesis is associated with changes in NMDA receptor subunit expression in the hippocampus but little change in spatial learning ability.

Of Mice and Men: the Evolving Phenotype of Aromatase Deficiency

Trends in Endocrinology and Metabolism: TEM. Mar, 2006  |  Pubmed ID: 16480891

We are rapidly becoming aware of the importance of estrogen in maintaining virtually all facets of male health. In order for estrogens to be synthesized endogenously, the enzyme responsible for their synthesis from androgens, aromatase, must be functional. The seven known men in whom aromatase is nonfunctional all have a mutation in either exon V or IX of the CYP19 gene, which encodes aromatase. Collectively, these men are reported to have undetectable estrogen; normal to high levels of testosterone and gonadotropins; tall stature with delayed skeletal maturation and epiphyseal closure; osteoporosis; impaired lipid and insulin metabolism; and impaired reproductive function. The aromatase knockout mouse presents with a phenotype that is similar in many aspects and provides a valuable tool with which to examine and manipulate the actions of estrogen. By studying the naturally occurring aromatase-deficient humans, together with studies of the aromatase-knockout mouse, we are expanding our understanding of the essential role of estrogen in male physiology.

Estrogen Deficient Male Mice Develop Compulsive Behavior

Biological Psychiatry. Feb, 2007  |  Pubmed ID: 16566897

Aromatase converts androgen to estrogen. Thus, the aromatase knockout (ArKO) mouse is estrogen deficient. We investigated the compulsive behaviors of these animals and the protein levels of catechol-O-methyltransferase (COMT) in frontal cortex, hypothalamus and liver.

Recognizing Rare Disorders: Aromatase Deficiency

Nature Clinical Practice. Endocrinology & Metabolism. May, 2007  |  Pubmed ID: 17452968

Aromatase deficiency is rare in humans. Affected individuals cannot synthesize endogenous estrogens. Aromatase is the enzyme that catalyzes conversion of androgens into estrogens, and if aromatase is nonfunctional because of an inactivating mutation, estrogen synthesis cannot occur. If the fetus lacks aromatase activity, dehydroepiandrosterone sulfate produced by the fetal adrenal glands cannot be converted to estrogen by the placenta, so is converted to testosterone peripherally and results in virilization of both fetus and mother. Virilization manifests as pseudohermaphroditism in female infants, with hirsutism and acne in the mother; the maternal indicators resolve following delivery. To date, only seven males and seven females with aromatase deficiency have been reported. Affected females are typically diagnosed at birth because of the pseudohermaphroditism. Cystic ovaries and delayed bone maturation can occur during childhood and adolescence in these girls, who present at puberty with primary amenorrhea, failure of breast development, virilization, and hypergonadotrophic hypogonadism. Affected males, on the other hand, do not present with obvious defects at birth, so are diagnosed much later in life, presenting with clinical symptoms, which include tall stature, delayed skeletal maturation, delayed epiphyseal closure, bone pain, eunuchoid body proportions and excess adiposity. Estrogen replacement therapy reverses the symptoms in male and female patients.

Fas/FasL-mediated Apoptosis in the Arcuate Nucleus and Medial Preoptic Area of Male ArKO Mice is Ameliorated by Selective Estrogen Receptor Alpha and Estrogen Receptor Beta Agonist Treatment, Respectively

Molecular and Cellular Neurosciences. Oct, 2007  |  Pubmed ID: 17716913

The aromatase (ArKO) knockout mouse is estrogen deficient. Our previous analysis revealed apoptosis of dopaminergic neurons in the arcuate nucleus (Arc) and medial preoptic area (MPO) of 1-year-old male ArKO mice. We sought to determine which estrogen receptor (ER) is involved in the anti-apoptotic action of estrogen. Male ArKO (9.5-month-old) mice were treated with 16alpha-LE(2) (ERalpha-specific agonist) or 8beta-VE(2) (ERbeta-specific agonist). Daily injections (6 weeks) with 16alpha-LE(2) prevented dopaminergic cell death in the Arc of male ArKO mice, with no significant effect of 8beta-VE(2) treatment. In contrast, 8beta-VE(2) prevented dopaminergic cell death in the MPO, while 16alpha-LE(2) had no significant effect. Concomitant decreases in Fas and FasL protein levels were found upon 16alpha-LE(2) and 8beta-VE(2) treatment in the Arc and MPO, respectively. Our results indicate that anti-apoptotic effects of estrogen are ER mediated, and the specific ER subtype involved in regulating apoptosis depends on the particular brain nucleus in question.

The Estrogenic Component of Tibolone Reduces Adiposity in Female Aromatase Knockout Mice

Menopause (New York, N.Y.). May-Jun, 2009  |  Pubmed ID: 19182696

To explore the effects of tibolone on adiposity in the absence of aromatase and determine which of the hormonal properties of tibolone are exerting these effects.

Estrogen Deficiency Results in Apoptosis in the Frontal Cortex of Adult Female Aromatase Knockout Mice

Molecular and Cellular Neurosciences. May, 2009  |  Pubmed ID: 19185610

The aromatase knockout (ArKO) mouse is completely estrogen deficient. We previously detected apoptosis in the hypothalamus of 1 year-old male ArKO mice. This study shows that 12 week-old female ArKO mice display spontaneous apoptosis of pyramidal neurons in the frontal cortex while wild-type (WT) littermates show no signs of apoptosis. Concomitantly, bcl-2 related anti-apoptotic genes are down-regulated whereas the pro-apoptotic gene TRADD is up-regulated in the female ArKO frontal cortex. This phenotype can be rescued by 3-week replacement of 17beta-estradiol. Furthermore, the apoptosis phenotype is exacerbated in 12-15 month-old female ArKO mice, which have 30% less neurons in the frontal cortex and lower brain weights than WT counterparts. These data show that estrogens are essential for the survival of female cortical neurons even in the absence of pathological conditions or external assaults. Our observations also demonstrate the sexually dimorphic susceptibility of neurons to estrogen deficiency.

Postnatal Development of an Estradiol-kisspeptin Positive Feedback Mechanism Implicated in Puberty Onset

Endocrinology. Jul, 2009  |  Pubmed ID: 19299459

The regulation of GnRH neurons by kisspeptin is critical for normal puberty onset in mammals. In the rodent the kisspeptin neurons innervating GnRH neurons are thought to reside in the rostral periventricular area of the third ventricle (RP3V). Using kisspeptin immunocytochemistry we show that kisspeptin peptide expression in the RP3V of female mice begins around postnatal d 15 (P15) and rapidly increases to achieve adult-like levels by P30, the time of puberty onset. Ovariectomy of female pups at P15 resulted in a 70-90% reduction (P < 0.01) in kisspeptin peptide expression within the RP3V of P30 or P60 mice. Replacement of 17-beta-estradiol (E2) in P15-ovariectomized mice from P15-30 or P22-30 resulted in a complete restoration of kisspeptin peptide expression in the RP3V (P < 0.01). Kisspeptin-immunoreactive fibers throughout the hypothalamus, including the arcuate nucleus, followed the same pattern of estrogen-dependent expression. To test the absolute necessity of estrogen for kisspeptin expression in the RP3V, aromatase knockout mice were examined. Kisspeptin-immunoreactive cells were detected in the arcuate nucleus, but there was a complete absence of kisspeptin peptide in RP3V neurons of aromatase knockout adult females. These results demonstrate that E2 is essential for the prepubertal development of kisspeptin peptide within RP3V neurons and suggest that an E2-kisspeptin positive feedback mechanism exists before puberty. This implies that RP3V kisspeptin neurons are E2-dependent amplifiers of GnRH neuron activity in the prepubertal period.

Estrogens, Brain, and Behavior: Lessons from Knockout Mouse Models

Seminars in Reproductive Medicine. May, 2009  |  Pubmed ID: 19401953

The use of animal models to effectively replicate problems such as hormone deficiencies, neurologic diseases, and brain injury and stroke has certainly made a vast contribution to understanding the neuroprotective effects of estrogen in the brain. Studies using gonadectomy procedures followed by 17beta-estradiol replacement have effectively demonstrated the positive effects that estrogen provides in cognitive performance and memory performance tasks. A major problem with such studies is that local brain aromatase (the estrogen-synthesizing enzyme) may still convert locally produced androgens to estrogens. Hence, such "estrogen-deficient" models may not be completely void of estrogen. The generation of the aromatase knockout (ArKO) and estrogen receptor knockout (ERKO) mouse models has enabled researchers to characterize the effects of complete estrogen deficiency within the brain and hence behavior. This review aims to compare and contrast the results of these various mouse models.

Alternative 5'-untranslated First Exons of the Mouse Cyp19A1 (aromatase) Gene

The Journal of Steroid Biochemistry and Molecular Biology. Jul, 2009  |  Pubmed ID: 19500729

The human aromatase gene (CYP19A1) has eleven tissue-specific untranslated first exons, while only three have been described in the mouse Cyp19A1 namely brain-, ovary- and testis-specific exons 1. The present study aims to elucidate the complete structure of the mouse Cyp19A1 gene. We detected aromatase transcripts in mouse bone, aorta, hypothalamus, adipose, gonads and placenta, but not nulliparous mammary fat pad. BestFit algorithm analysis against the human CYP19A1 has identified ten putative first exons upstream of mouse Cyp19A1. Based on these putative sequences, we were able to design specific primers for RT-PCR and detected for the first time, the presence of exons I.4 and I.3 in murine fat and gonads, respectively. These are novel 5'UTRs of mouse Cyp19A1. Using RT-PCR and 5' RACE, we confirmed the expression of exon 1f in the hypothalamus and proximal exon P2 in the ovary. The testis-specific exon 1 begins 217bp further upstream than previously reported. Putative exons 2a, I.5, I.7, I.6 and I.2 were not detected in mouse tissues. Therefore, we showed that mouse Cyp19A1 contains more tissue-specific first exons than previously thought and displays a similar genomic organization to human CYP19A1.

Behavioural Phenotype of APPC100.V717F Transgenic Mice Over-expressing a Mutant Abeta-bearing Fragment is Associated with Reduced NMDA Receptor Density

Behavioural Brain Research. May, 2010  |  Pubmed ID: 20085783

The aim of this study was to characterize APPC100.V717F transgenic (TgC100.V717F) mice which over-express a mutant C100 fragment of the amyloid precursor protein. The mice were compared to TgC100 wild type mice (TgC100.WT) and non-transgenic controls at 4-9 and 16-22 months of age. TgC100.V717F mice showed behavioural hyperactivity, particularly at a younger age, as shown by increased numbers of elevated plus maze arm entries and Y-maze arm entries, enhanced baseline locomotor activity in the open field, and enhanced amphetamine-induced hyperlocomotion. This hyperactivity was less pronounced in TgC100.WT which only displayed significant differences to non-transgenic controls at a younger age for the number of Y-maze arm entries and baseline locomotor activity in the open field. In addition, TgC100.V717F mice, but not TgC100.WT, demonstrated cognitive deficits, as shown by reduced spontaneous alternation in the Y-maze and markedly reduced retention in a passive avoidance test. At an older age, TgC100.V717F mice showed enhanced startle and increased immobility time in the forced swim test. In the TgC100.V717F mice, but not TgC100.WT, the behavioural changes were paralleled by a significant reduction in the expression of hippocampal NMDA receptor subunits types 1 and 2A. Concomitantly, we detected axonal disruption and apoptosis in the hippocampus of TgC100.V717F mice. In conclusion, these data demonstrate that the mutant C100 fragment is an effector of biochemical and both cognitive and non-cognitive behaviours. These transgenic mice may be a model for the psychotic features associated with early Alzheimer's disease.

The Multiple Roles of Estrogens and the Enzyme Aromatase

Progress in Brain Research. 2010  |  Pubmed ID: 20478440

Aromatase is the enzyme that catalyzes the last step of estrogen biosynthesis. It is expressed in many tissues such as the gonads, brain and adipose tissue. The regulation of the level and activity of aromatase determines the levels of estrogens that have endocrine, paracrine and autocrine effects on tissues. Estrogens play many roles in the body, regulating reproduction, metabolism and behavior. In the brain, cell survival and the activity of neurons are affected by estrogens and hence aromatase.

Differential Effect of Amphetamine on C-fos Expression in Female Aromatase Knockout (ArKO) Mice Compared to Wildtype Controls

Psychoneuroendocrinology. Jun, 2011  |  Pubmed ID: 21093158

Estrogen may be involved in psychosis by an interaction with central dopaminergic activity. Aromatase knockout mice are unable to produce estrogen and have been shown to display altered behavioural responses and effects of the dopamine releaser, amphetamine. This study investigates the effect of gonadal status on amphetamine-induced c-fos expression in the brains of female aromatase knockout and wildtype mice. Six groups of mice were treated intraperitoneally with saline or 5mg/kg amphetamine. Fos immunoreactivity was assessed in the cingulate cortex, caudate putamen and nucleus accumbens. Aromatase knockout mice showed markedly reduced amphetamine-induced Fos immunoreactivity compared to wildtype mice. However, the amphetamine response was restored in aromatase-knockout mice after ovariectomy, which reduced this effect in wildtype controls. Estrogen supplementation reversed the effect of ovariectomy in wildtype mice but had no additional significant effect in aromatase-knockout mice. These results indicate that mechanisms involved in amphetamine-induced c-fos expression are altered in aromatase knockout mice and that the primary hormone involved in this effect is not estrogen, but may be another factor released from the ovaries, such as an androgen. These results provide new insight into the effect of gonadal hormones on amphetamine induced c-fos expression in this mouse model of estrogen deficiency. These results could be important for our understanding of the role of sex steroid hormones in psychosis.

Aromatase and Its Inhibition in Behaviour, Obsessive Compulsive Disorder and Parkinsonism

Steroids. Jul, 2011  |  Pubmed ID: 21477611

Oestrogens regulate normal behaviour and have been implicated in modulating pathological behaviour such as obsessive compulsive disorder and neurological disorder such as Parkinsonism. Therefore, by regulating the expression of the oestrogen-synthesising enzyme, aromatase, we may identify what behaviour is regulated by oestrogen. Inhibition of aromatase either genetically or pharmacologically has been reported to induce sexual behaviour impairment, compulsive behaviour and susceptibility to neurodegeneration.

Acoustic Microstreaming Increases the Efficiency of Reverse Transcription Reactions Comprising Single-cell Quantities of RNA

BioTechniques. Feb, 2011  |  Pubmed ID: 21486252

Correlating gene expression with behavior at the single-cell level is difficult, largely because the small amount of available mRNA (<1 pg) degrades before it can be reverse transcribed into a more stable cDNA copy. This study tested the capacity for a novel acoustic microstreaming method ("micromixing"), which stirs fluid at microliter scales, to improve cDNA yields from reverse transcription (RT) reactions comprising single-cell quantities of RNA. Micromixing significantly decreased the number of qPCR cycles to detect cDNA representing mRNA for hypoxanthine phosphoribosyl-transferase (Hprt) and nuclear receptor-related 1 (Nurr1) by ~9 and ~15 cycles, respectively. The improvement was equivalent to performing RT with 10- to 100-fold more cDNA in the absence of micromixing. Micromixing enabled reliable detection of the otherwise undetectable, low-abundance transcript, Nurr1. It was most effective when RNA concentrations were low (0.1-1 pg/µL, a "single-cell equivalent") but had lesser effects at higher RNA concentrations (~1 ng/µL). This was supported by imaging experiments showing that micromixing improved mixing of a low concentration (20 pg/µL) of fluorescence-labeled RNA but not a higher concentration (1 ng/µL). We conclude that micromixing significantly increases RT yields obtainable from single-cell quantities of RNA.

A Doxycycline-inducible, Tissue-specific Aromatase-expressing Transgenic Mouse

Transgenic Research. May, 2011  |  Pubmed ID: 21614586

Aromatase converts androgens to estrogens and it is expressed in gonads and non-reproductive tissues (e.g. brain and adipose tissues). As circulating levels of estrogens in males are low, we hypothesize that local estrogen production is important for the regulation of physiological functions (e.g. metabolism) and pathological development (e.g. breast and prostate cancers) by acting in a paracrine and/or intracrine manner. We generated a tissue-specific doxycycline-inducible, aromatase transgenic mouse to test this hypothesis. The transgene construct (pTetOAROM) consists of a full-length human aromatase cDNA (hAROM) and a luciferase gene under the control of a bi-directional tetracycline-responsive promoter (pTetO), which is regulated by transactivators (rtTA or tTA) and doxycycline. Our in vitro studies using MBA-MB-231tet cells stably expressing rtTA, showed that doxycycline treatment induced transgene expression of hAROM transcripts by 17-fold (P = 0.01), aromatase activity by 26-fold, (P = 0.0008) and luciferase activity by 9.6-fold (P = 0.0006). Pronuclear microinjection of the transgene generated four pTetOAROM founder mice. A male founder was bred with a female mammary gland-specific rtTA mouse (MMTVrtTA) to produce MMTVrtTA-pTetOAROM double-transgenic mice. Upon doxycycline treatment via drinking water, human aromatase expression was detected by RT-PCR, specifically in mammary glands, salivary glands and seminal vesicles of double-stransgenic mice. Luciferase expression and activity was detected in these tissues by in vivo bioluminescence imaging, in vitro luciferase assay and RT-PCR. In summary, we generated a transgenic mouse model that expresses the human aromatase transgene in a temporal- and spatial-specific manner, which will be a useful model to study the physiological importance of local estrogen production.

A Selective Estrogen Receptor α Agonist Ameliorates Hepatic Steatosis in the Male Aromatase Knockout Mouse

The Journal of Endocrinology. Sep, 2011  |  Pubmed ID: 21705395

Male aromatase knockout mice (ArKO; an estrogen-deficient model) present with male-specific hepatic steatosis that is reversible upon 17β-estradiol replacement. This study aims to elucidate which estrogen receptor (ER) subtype, ERα or ERβ, is involved in the regulation of triglyceride (TG) homeostasis in the liver. Nine-month-old male ArKO mice were treated with vehicle, ERα- or ERβ-specific agonists via s.c. injection, daily for 6 weeks. Male ArKO mice treated with ERα agonist had normal liver histology and TG contents compared with vehicle-treated ArKO; omental (gonadal) and infra-renal (visceral) fat pad weights were normalized to those of vehicle-treated wild-type (WT). In contrast, ERβ agonist treatment did not result in the similar reversal of these ArKO phenotypes. In vehicle-treated ArKO mice, hepatic transcript expression of fatty acid synthase (Fasn) and stearoyl-coenzyme A desaturase 1 (key enzymes in de novo FA synthesis) were significantly elevated compared with vehicle-treated WT, but only Fasn expression was lowered to WT level after ERα agonist treatment. There were no significant changes in the transcript levels of carnitine palmitoyl transferase 1 (required for transfer of FA residues into the mitochondria for β-oxidation) and sterol regulatory element-binding factor 1c (the upstream regulator of de novo FA synthesis). We also confirmed by RT-PCR that only ERα is expressed in the mouse liver. There were no changes in hepatic androgen receptor transcript level across all treatment groups. Our data suggest that estrogens act via ERα to regulate TG homeostasis in the ArKO liver. Since the liver, adipose tissue and arcuate nucleus express mainly ERα, estrogens could regulate hepatic functions via peripheral and central pathways.

Relaxin and Castration in Male Mice Protect From, but Testosterone Exacerbates, Age-related Cardiac and Renal Fibrosis, Whereas Estrogens Are an Independent Determinant of Organ Size

Endocrinology. Jan, 2012  |  Pubmed ID: 22028442

This study determined the effects of castration and hormone replacement therapy on the age-related cardiac and renal pathology of male relaxin gene-knockout (RlnKO) and age-matched wild-type (RlnWT) mice and that of aged male aromatase knockout (ArKO) mice, which lack estrogens and have 5-10 times the androgen levels of male wild-type mice. One-month-old RlnWT and RlnKO mice were bilaterally gonadectomized or sham operated and maintained until 12 months. Subgroups of castrated animals received testosterone or 17β-estradiol treatment from 9 to 12 months. Male ArKO mice and aromatase wild-type mice were aged to 12 months. Collected heart and kidney tissues were assessed for changes in organ size and fibrosis. Castration reduced body, heart, left ventricle, and kidney weights in both RlnKO and RlnWT mice, and the cardiac/renal fibrosis that was seen in sham RlnKO animals (all P < 0.05 vs. respective sham). Testosterone normalized organ weights and organ weight to body weight ratio of castrated animals and increased cardiac/renal collagen concentration to levels measured in or beyond that of sham RlnKO mice (all P < 0.05 vs. respective castrated mice). Furthermore, expression of TGF-β1, mothers against decapentaplegic homolog 2 (Smad2), and myofibroblast differentiation paralleled the above changes (all P < 0.05 vs. respective castrated mice), whereas matrix metalloproteinase-13 was decreased in testosterone-treated RlnKO mice. Conversely, 17β-estradiol only restored changes in organ size. Consistent with these findings, intact ArKO mice demonstrated increased cardiac/renal fibrosis in the absence of changes in organ size. These findings suggest that relaxin and castration protect, whereas androgens exacerbate, cardiac and renal fibrosis during ageing, whereas estrogens, in synergy with relaxin, regulates age-related changes in organ size.