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Endocrinology Vol. 147, No. 12 5907-5913
Copyright © 2006 by The Endocrine Society

Regulation of Adenosine 5',Monophosphate-Activated Protein Kinase and Lipogenesis by Androgens Contributes to Visceral Obesity in an Estrogen-Deficient State

Kerry J. McInnes, Anne Corbould, Evan R. Simpson and Margaret E. Jones

Prince Henry’s Institute of Medical Research (K.J.M., A.C., E.R.S., M.E.J.), Clayton, Victoria 3168, Australia; and Departments of Anatomy and Cell Biology (K.J.M., M.E.J.) and Biochemistry (E.R.S.), Monash University, Clayton, Victoria 3800, Australia

Address all correspondence and requests for reprints to: Kerry McInnes, Prince Henry’s Institute of Medical Research, P.O. Box 5152, Clayton, Victoria 3168, Australia. E-mail: kerry.mcinnes{at}princehenrys.org.


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Menopause is associated with an accumulation of visceral fat. An emerging concept suggests that relatively elevated levels of circulating androgens, compared with estrogens in postmenopausal women, underlie this shift in body fat distribution. In this study we administered dihydrotestosterone (DHT) to ovariectomized mice to examine the effect of relative androgen excess on adipose tissue distribution and function in estrogen-deficient mice. Compared with controls, DHT-treated mice exhibited increased body weight and visceral fat mass associated with triglyceride accumulation. Phosphorylation of AMP-activated protein kinase (AMPK) and acetyl CoA carboxylase was significantly decreased by DHT in visceral fat. In 3T3-L1 cells, DHT decreased phosphorylation of AMPK in a dose-dependent manner. In addition, DHT increased the expression of lipogenic genes (fatty acid synthase, sterol regulatory element binding protein-2, and lipoprotein lipase) in visceral fat. These data provide the first in vivo evidence that an increased androgen to estrogen ratio can promote visceral fat accumulation by inhibiting AMPK activation and stimulating lipogenesis.


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
THE ONSET OF menopause in women is often associated with increased central (visceral) body fat (1). The accumulation of fat in this area has emerged as a cardiovascular risk factor independent of overall obesity (2). Although the association between central adiposity and the metabolic syndrome is well known, the underlying pathophysiology is not clear. Many studies have investigated the role of estrogen in the development of central obesity during menopause; however, less attention has been paid to the role of androgens. Estrogen levels decline rapidly around menopause, whereas simultaneously there is a more gradual decline of androgen levels (3). This creates a period of relative androgen excess (4). Clinical observations have suggested a role for androgens in adipose tissue metabolism, and several in vivo and in vitro studies have shown that androgens play an important role in altering fat accumulation and distribution (5). Functional androgen receptors (ARs) are present in adipose tissue, both in stromal cells and adipocytes. Furthermore, there are regional differences in AR complement, with more ARs present in visceral than sc preadipocytes (6). This suggests that androgens may influence adipose tissue distribution and that androgen action may be amplified in the more detrimental visceral bed. However, the molecular mechanisms underlying the metabolic actions of androgens are poorly understood.

Given the possible opposite effects of estrogens and androgens on fat metabolism, we hypothesized that relative androgen excess may better predict the increased risk of developing the metabolic syndrome than decreased estrogen levels alone. To address this issue, we compared adipose distribution and function in ovariectomized (ovx) mice (estrogen deficient) with ovx mice treated with the nonaromatizable androgen, dihydrotestosterone (DHT; estrogen deficient with androgen excess).


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Mice
The ethics committee of our institution approved all animal procedures. One-year-old female C57/Bl6 mice were subjected to either dorsal ovariectomy or sham operation under general anesthesia. At the same time, ovx mice were implanted sc at the site of incision with dihydrotestosterone pellets, which released a dose of 8 µg/d (0.5 mg in 60 d) or placebo pellets (Innovative Research of America, Sarasota, FL). Mice were housed in groups under specific pathogen-free conditions on a 12 h light, 12-h dark cycle and were fed a soy-free mouse chow with water ad libitum as previously described (7).

Tissue collection
After 6 wk mice were humanely killed by cervical dislocation. Blood was collected after decapitation and allowed to clot. Serum was separated and stored at –20 C. Visceral, renal, and brown adipose tissue was removed and the wet mass measured. The tissue was then snap frozen in liquid nitrogen and stored at –80 C.

Serum testosterone
Serum testosterone was measured as previously described (8).

Ambulatory activity
To measure ambulatory activity, mice were individually housed in cages equipped with four infrared sensor devices to record their movements over 4 continuous days/nights. Recordings of number of times the mice passed through the sensors were taken every 12 h. Total recordings over the 4 d and 4 nights were then added and analyzed statistically.

Food intake measurement
For food intake measurement, mice were individually housed with food and water ad libitum. Food consumption was measured every day during a 4-d period.

Adipocyte number
Adipocyte number in fresh visceral adipose tissue was determined as described previously (9).

Adipose tissue triglyceride content
Visceral adipose triglyceride content was determined by ethanolic KOH saponification followed by spectrophotometric assay for glycerol using free glycerol reagent (Sigma-Aldrich, St. Louis, MO).

Western blot analysis
Visceral fat was homogenized in ice-cold buffer (5 mM HEPES, 137 mM NaCl, 1 mM MgCl2, 1 mM CaCl2, 10 mM NaF, 2 mM EDTA, 10 mM Na pyrophosphate, 2 mM NaVO4, 1% Nonidet P-40, 10% glycerol) containing protease inhibitors (Complete Mini; Roche, Mannheim, Germany), incubated on ice for 45 min, and centrifuged for 15 min at 14,000 x g before assay of supernatants for protein content by the bicinchoninic acid method (Pierce Biotechnology, Rockford, IL). Fifty micrograms of protein were diluted in sample buffer containing dithiothreitol, boiled, run on 8% polyacrylamide gels, and transferred to nitrocellulose for Western blotting. Phosphorylation of AMP-activated protein kinase (AMPK) and acetyl CoA carboxylase (ACC) in visceral fat was assayed by Western blotting with antibodies to phosphopeptides based on the amino acid sequence surrounding Thr172 of the {alpha}-subunit of human AMPK (Cell Signaling, Beverly, MA) and Ser79 of rat ACC (Cell Signaling), respectively. The level of phosphorylation was normalized to the level of total AMPK and ACC protein using antibodies against the catalytic {alpha}1- and {alpha}2-subunits of AMPK (Cell Signaling) and ACC (Cell Signaling), respectively. Proteins were visualized with an Alexa Fluor 680 goat antirabbit secondary antibody (Molecular Probes, Inc., Eugene, OR), and band intensities were quantified using the Odyssey infrared imaging system (Licor Biosciences, Lincoln, NE).

Tissue culture
3T3-L1 fibroblasts were seeded at 3 x 105/ml in six-well plates and maintained at no higher than 70% confluence in DMEM (Trace Scientific Ltd., Melbourne, Australia) supplemented with 10% (vol/vol) fetal-calf serum (Trace Scientific), 100 IU/ml penicillin, 100 µg/ml streptomycin, and 200 mM L-glutamine (Life Technologies, Inc., Auckland, New Zealand). For differentiation, cells were grown 2 d postconfluence in DMEM/fetal calf serum (FCS) and then for 2 d in DMEM/FCS containing 10 nM insulin (Novo Nordisk, Copenhagen, Denmark), 1 µM dexamethasone (Sigma-Aldrich), and 0.5 mM 3-isobutyl-1-methylxanthine (Sigma-Aldrich). The media were then changed to DMEM/FCS supplemented only with 10 nM insulin for 2 d and then to DMEM/FCS alone for 3–5 d. Media were replaced 24 h before treatment with DHT (Sigma-Aldrich) with phenol-red free and serum-free DMEM. Phosphorylation of AMPK was assessed in cells treated for 24 h with DHT alone (1–1000 nM in ethanol at < 0.1%) or in the presence of estrogen (1–1000 nM in ethanol at < 0.1%) or 5-aminoimidazole-4-carboxamide-1-ß-D-ribofuranoside (AICAR) (1 µM). Cells were lysed in lysis buffer and subjected to Western blot analysis as described above. All experiments were carried out in triplicate.

Gene analysis
Total RNA was isolated from frozen visceral adipose tissue using the phenol/chloroform extraction method (TRIzol; Invitrogen Life Technologies, Auckland, New Zealand) and quantified spectrophotometrically. One microgram RNA was reverse transcribed. cDNA was diluted 10-fold and amplified by real-time PCR in the Lightcycler (Roche) using Fast Start Master SYBR Green 1 (Roche) and specific primer pairs (sequences available upon request). All samples were normalized to 18S transcript levels.

Statistical analysis
All data are expressed as mean ± SE. Data were analyzed by independent t tests of group means. Statistical significance was defined as P < 0.05.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
DHT increases body weight and fat mass in ovx female mice
To directly assess the effect of androgen excess on body weight and fat mass in estrogen-deficient female mice, 1-yr-old ovx mice (n = 6) were treated with DHT for 6 wk. DHT treatment resulted in a significant increase in serum DHT, compared with sham-ovx and ovx controls (0.18 ± 0.04 vs. 0.06 ± 0.01 and 0.08 ± 0.03 ng/ml, respectively, P < 0.05). DHT treatment also resulted in a significant increase in serum testosterone, compared with sham-ovx and ovx controls (0.43 ± 0.04 vs. 0.26 ± 0.02 and 0.22 ± 0.06 ng/ml, respectively, P < 0.05). This was most likely due to the cross-reactivity of DHT with respect to testosterone in the immunoassay used. There were no significant differences in body weights in the three groups before treatment (Fig. 1AGo). However, after 6 wk of DHT treatment ovx mice (ovx + DHT) gained significantly more body weight than sham-ovx and ovx mice (7 ± 0.1 vs. 0.7 ± 0.35 and 1.6 ± 0.7 g, respectively) (Fig. 1AGo). The higher body weight gain observed in DHT-treated mice was not due to differential energy intake or expenditure because no significant differences in food intake or ambulatory activity between DHT-treated mice and controls were observed (Fig. 1Go, B and C).


Figure 1
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  		FIG. 1. Weight gain, food intake, and ambulatory activity with DHT treatment. Ovx mice were randomized to either placebo (ovx-control) or DHT pellets (ovx +DHT). A sham-ovx group was included to control for the effect of ovariectomy (sham-ovx; n = 6 each group). A, After 6 wk, DHT-treated mice gained more weight than control mice (initial weight, {square}; final weight, {blacksquare}). *, P = 0.0005 vs. ovx + DHT initial weight; #, P < 0.01 vs. control group final weights. B, Food intake was measured over a 4-d period in which mice were given food and water ad libitum. C, Ambulatory activity over 24 h. Results are shown as mean ± SE.

 
Because changes in body weight are usually associated with alterations in adipose tissue mass, we next examined the weight of the visceral and gonadal white adipose tissue depots. Ovariectomy alone did not produce any differences in adipose tissue mass in either depot. With DHT treatment the metabolically disadvantageous visceral fat depot weights were significantly increased both in absolute terms and relative to body weight, compared with sham-ovx and ovx mice (62.7 ± 6 vs. 25 ± 6 and 34.9 ± 6 mg, respectively) (Fig. 2AGo). The renal fat depot weights were increased in DHT-treated mice, compared with controls; however, this did not reach significance (Fig. 2BGo). We did not observe any change in the weight of other organs including liver and brown adipose tissue (data not shown). These results indicate that the higher body weight was due to an increase in adipose tissue mass.


Figure 2
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  		FIG. 2. Effects of DHT on fat distribution and triglyceride (TG) homeostasis in ovx mice. A, DHT significantly increased visceral fat mass relative to body mass in ovx mice. *, P < 0.05 vs. sham-ovx and ovx mice. B, DHT increased renal fat mass relative to body mass in ovx mice. C, DHT increased triglyceride accumulation in visceral adipose tissue. *, P < 0.05 vs. sham-ovx mice.

 
An increase in adipose tissue mass may arise from an increase in the number of adipose cells, an increase in triglyceride storage in the preexisting adipocytes, or a combination of both processes. No changes in cell number were found in the visceral fat depots of the experimental groups (data not shown). In contrast, a significantly higher triglyceride accumulation was observed in visceral fat depots of DHT-treated mice, compared with controls (Fig. 2CGo).

DHT regulates adipose gene expression to promote triglyceride accumulation
To determine whether the increase in adipose tissue triglyceride levels was accompanied by an enhancement of lipogenesis, expression levels of several genes involved in lipogenesis were assessed by real-time PCR in visceral adipose tissue of ovx + DHT mice, compared with ovx alone. Fatty-acid synthase (FAS), a key lipogenic enzyme that catalyzes all steps of the biosynthesis of long-chain fatty acids from malonyl-CoA, was significantly up-regulated by DHT treatment (Fig. 3Go). FAS activity has been shown to depend on the transcriptional activity of the sterol regulatory element binding proteins (SREBPs) (10). SREBP1c mRNA expression was unchanged in visceral fat from DHT-treated mice (data not shown) whereas SREBP2 mRNA expression was significantly increased in visceral fat with DHT administration (Fig. 3Go). DHT treatment also significantly increased the transcript levels of lipoprotein lipase (LPL), an enzyme that promotes adipocyte uptake of circulating lipids for triglyceride formation (11) (Fig. 3Go) and PPAR{gamma}, a master gene that controls adipocyte differentiation and triglyceride synthesis (12) (Fig. 3Go). The mRNA level of the lipolytic factor, hormone-sensitive lipase was unchanged with DHT treatment (data not shown). Together these data suggest that DHT promotes visceral obesity in estrogen-deficient mice by increasing lipogenesis, both de novo and by uptake of the products of lipoprotein lipase activity.


Figure 3
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  		FIG. 3. DHT increases adipose tissue gene expression to promote triglyceride accumulation. Real-time PCR of visceral adipose tissue was done. DHT increases FAS, SREBP2, LPL, and peroxisomal proliferator-activated receptor (PPAR)-{gamma} mRNA expression in ovx mice (ovx, {square}; and ovx + DHT, {blacksquare}). *, P < 0.05; **, P < 0.01 vs. ovx mice.

 
DHT decreases phosphorylation of AMPK and ACC in visceral fat of ovx mice
Given the role of AMPK in lipid metabolism, we assessed the impact of excess androgens in estrogen-deficient mice on the activation of AMPK in visceral fat. Ovariectomy alone did not change the phosphorylation level of AMPK or ACC. However, DHT treatment of ovx mice significantly decreased phosphorylation of AMPK by 13%, compared with control (Fig. 4AGo). This decrease in phosphorylated AMPK was accompanied by a significant decrease (44%) in phosphorylated ACC. (Fig. 4BGo). The total levels of AMPK and ACC protein were unchanged with DHT treatment. Thus, the stimulatory effect of DHT on body weight and fat mass may be caused by a decrease in fatty acid oxidation.


Figure 4
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  		FIG. 4. DHT treatment decreases phosphorylation (p) of AMPK and ACC in visceral fat. A, Western blots of phosphorylated (thr172) AMPK (upper blot) and total AMPK (lower blot). *, P < 0.05 vs. sham-ovx. B, Western blots of phosphorylated ACC (ser79) (upper blot) and total ACC (lower blot). *, P < 0.05 vs. sham-ovx. Each lane represents one animal. DHT-treated mice have lower AMPK and ACC activity in gonadal fat determined by decreased phosphorylation levels.

 
DHT directly inhibits phosphorylation of AMPK and ACC in vitro
To assess whether DHT could directly inhibit AMPK, we investigated the ability of DHT to inhibit AMPK in 3T3-L1 adipocytes. Twenty-four-hour treatment with DHT inhibited basal phosphorylation of AMPK in these cells in a dose-dependent manner (Fig. 5AGo). We next investigated whether DHT can inhibit stimulated AMPK activity. AMPK can be activated pharmacologically by the AMP analog AICAR independent of changes in the AMP to ATP ratio. DHT significantly diminished AICAR phosphorylation of AMPK (Fig. 5BGo). Addition of estrogen (17ß-estradiol) to the media at the same time as DHT reversed the negative effect of DHT on AMPK activity and returned phosphorylated levels of AMPK to that of basal (Fig. 6Go).


Figure 5
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  		FIG. 5. DHT inhibits AMPK in 3T3-L1 cells. A, DHT (24 h treatment) inhibits phosphorylation (p) of AMPK in differentiated 3T3-L1 cells in a dose-dependent manner. Western blots of phosphorylated (thr172) AMPK (upper blot) and total AMPK (lower blot) are shown. *, P < 0.05 vs. vehicle (v); **, P < 0.01 vs. vehicle. B, DHT treatment decreases AICAR phosphorylation of AMPK. Western blots of phosphorylated (thr172) AMPK (upper blot) and total AMPK (lower blot) are shown. Data are mean ± SE of three experiments, each performed in triplicate. #, P < 0.05 vs. basal; *, P < 0.05 vs. AICAR. Data are mean ± SE of three experiments, each performed in triplicate.

 

Figure 6
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  		FIG. 6. Estrogen (E2) reverses the effect of DHT on AMPK in 3T3-L1 cells. 17ß-estradiol (24 h treatment) reverses the negative effect of DHT on AMPK phosphorylation. Western blots of phosphorylated (thr172) AMPK (upper blot) and total AMPK (lower blot) are shown. *, P < 0.05 vs. 100 nM DHT. Data are mean ± SE of three experiments, each performed in triplicate.

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
The emergence of visceral obesity with the menopause has been associated with estrogen deficiency (1); however, the effects of treatment with estrogens remain controversial. Several large studies have shown that hormone replacement therapy with estrogen increases body weight (13), whereas other studies found no effect or a small decrease (14). An emerging concept suggests that the relative increase in androgen to estrogen ratio is likely to be an important factor for the shift in fat distribution in postmenopausal women (3, 15). The increased visceral fat mass exhibited by ovx + DHT mice in this study is indeed consistent with such a hypothesis. This androgen-associated increase in adipose tissue mass in ovx mice is consistent with the obese phenotype of a previously published ovx rat model supplemented with testosterone (16) and the aromatase knockout mouse (7), which is estrogen deficient but has elevated testosterone levels (17, 18).

There is an increasing body of evidence that alterations in triglyceride metabolism may predispose to obesity. The increases in adipose triglyceride levels observed in this study could be related to increases in the uptake of free fatty acids and sn-2 monoglyceride from plasma, an enhanced rate of de novo FAS, and/or a dysregulation of intracellular lipid partitioning in which fatty acid oxidation is impaired (19, 20). To date, only interactions between androgens and catecholamine-induced lipolysis have been investigated in humans (21) in whom the lipolytic effect of catecholamines was decreased in sc adipocytes from polycystic ovary syndrome patients (22). In this study, we show for the first time that DHT can have adverse effects on fatty acid metabolism by inhibiting the activation of AMPK in adipose tissue. AMPK activation in adipose tissue has been shown to inhibit lipogenesis and stimulate fatty acid ß-oxidation by phosphorylation and inhibition of ACC. Therefore, the increase in adiposity observed in our study seems to be due, in part, to an enhanced lipogenesis and impaired ß-oxidation as a consequence of decreased phosphorylation of AMPK by DHT and a consequent reduction in AMPK activity.

Our results are consistent with that of the AMPK{alpha}2 knockout mouse, which exhibit higher body weights with a specific increase in adipose tissue mass. Similarly, the increase in adipose tissue mass observed in these mice was due to an enhanced triglyceride accumulation in the preexisting adipocytes (23). Twenty-four-hour DHT treatment of differentiated 3T3-L1 cells, a well-characterized adipocyte model, also resulted in inhibition of basal and stimulated AMPK activity. It is possible that this inhibition of AMPK by DHT occurs through genomic activation of the AR because we did not find any difference in AMPK phosphorylation with more rapid incubation times (data not shown). Consistent with previous reports (24) estrogen status in our mice did not alter AMPK activity in visceral adipose tissue. However, in 3T3-L1 cells, incubation with 17ß-estradiol reversed the negative effects of DHT on AMPK activation. The mechanism whereby estrogen can overcome the effect of DHT on AMPK remains unclear. One possible mechanism is that the effect of DHT on AMPK is via its metabolite 5{alpha}-androstan-3ß,17ß-diol (3ß-diol). DHT is metabolized to 3ß-diol by the enzyme 3ß-hydroxysteroid dehydrogenase types IV and V. 3ß-Diol has estrogenic properties and can bind to estrogen receptor-ß (25) with a relatively high affinity, albeit less than 17ß-estradiol (26). Therefore, incubation with 17ß-estradiol may displace 3ß-diol from the receptor and prevent the inhibition of AMPK. 3ß-hydroxysteroid dehydrogenase activity has been detected in adipose tissue of primates (27, 28); however, the relative importance of this pathway in human adipose tissue is unknown and is the object of ongoing investigations in this laboratory.

In the visceral fat, we observed a larger decrease in ACC phosphorylation, compared with the decrease in AMPK phosphorylation. A similar difference has previously been observed in skeletal muscle cells incubated with resistin (29). This result could imply that DHT can inhibit another kinase capable of phosphorylating ACC. However, this is unlikely because in this study we examined the critical phosphorylation site (Ser-79) for inactivation of ACC exclusively by AMPK. The only other protein kinase capable of phosphorylating ACC is protein kinase A (PKA) (30). This effect of PKA has been identified only in vitro and is entirely mediated by the phosphorylation of Ser-1200 (31). In addition, we have shown that incubation of differentiated 3T3-L1 cells with a specific PKA inhibitor had no effect on phosphorylation of ACC (McInnes, K. J., and E. R. Simpson, unpublished results).

In addition to inhibiting AMPK activation, DHT appears to promote lipogenesis by increasing the expression of FAS and LPL, which promote adipocyte triglyceride synthesis. Previous studies in male rodents have shown that androgens can increase the expression of FAS in normal androgen target tissues, e.g. the ventral prostate and lacrimal glands (32), and in retroperitoneal adipose tissue (33), but this effect has not previously been shown in female rodents. Our observation that LPL expression is increased with DHT treatment is consistent with that of Anderson et al. (34), who reported that incubation of isolated sc adipocytes from female patients with DHT increased LPL protein expression. It is likely that the regulation of LPL expression by androgens is mediated via the AR because incubation with the AR antagonist, flutamide, inhibited LPL expression (34). In the previously mentioned aromatase knockout mouse, an increase in adiposity was also accompanied by an increase in expression of LPL in the fat depots (9). This was accounted for by the lack of estrogen in this model because estrogen has been shown to suppress transcription of LPL via an estrogen response element on the LPL promoter (35). However, from this study it is possible that the increased androgen to estrogen ratio contributes to the elevated LPL expression in adipose tissue in the aromatase knockout mouse and not just estrogen deficiency.

It is believed that FAS activity is controlled primarily at the transcriptional level by the sterol-regulated family of transcription factors. Transgenic mice overexpressing SREBP1 develop fatty livers and FAS gene expression is highly stimulated (36), and forced expression of SREBP1 in fibroblasts induces FAS gene expression (37). In our study, DHT treatment did not stimulate SREBP1 expression; however, SREBP2 expression was significantly increased. This is consistent with previous reports that overexpression of SREBP2 in transgenic mice results in an increase in FAS gene expression (38). Boizard et al. (10) also demonstrated that in adipocytes from obese Zucker rats, SREBP2 is highly expressed and is able to displace SREBP1 from the sterol regulatory element site, providing a link between SREBP2 activation and loss of negative control on FAS gene transcription. The increase in FAS expression with DHT is therefore possibly due to the observed increase in the expression of the transcription factor SREBP2. This is consistent with previous reports that coordinated stimulation of lipogenic gene expression by androgens involves activation of the SREBP pathway in prostate cancer cell lines (39). AMPK has been shown to suppress FAS by inhibiting the generation of SREBP1c (40); however, the effect of AMPK on SREBP2 has not yet been investigated.

In conclusion, our study demonstrates that an increase in the androgen to estrogen ratio and not estrogen deficiency alone leads to the development of visceral obesity in female mice. The current data represent the first evidence that excess androgens can inhibit AMPK activity in adipose tissue and promote visceral obesity as a result of increased lipogenesis. We anticipate that therapeutic inhibition of adipose androgenic activity in postmenopausal women will reduce lipogenesis and counteract the accumulation of visceral fat and its related metabolic abnormalities.


   Footnotes
 
Disclosure statement: The authors have nothing to disclose.

First Published Online September 21, 2006

Abbreviations: ACC, Acetyl CoA carboxylase; AICAR, 5-aminoimidazole-4-carboxamide-1-ß-D-ribofuranoside; AMPK, AMP-activated protein kinase; AR, androgen receptor; DHT, dihydrotestosterone; 3ß-diol, 5{alpha}-androstan-3ß,17ß-diol; FAS, fatty-acid synthase; FCS, fetal calf serum; LPL, lipoprotein lipase; ovx, ovariectomized; PKA, protein kinase A; SREBP, sterol regulatory element binding protein.

Received July 3, 2006.

Accepted for publication September 11, 2006.


   References
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

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