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. 2010 Apr 28;151(7):3125–3132. doi: 10.1210/en.2010-0018

Myocyte Androgen Receptors Increase Metabolic Rate and Improve Body Composition by Reducing Fat Mass

Shannon M Fernando 1, Pengcheng Rao 1, Lee Niel 1, Diptendu Chatterjee 1, Marijana Stagljar 1, D Ashley Monks 1
PMCID: PMC2903941  PMID: 20427479

Abstract

Testosterone and other androgens are thought to increase lean body mass and reduce fat body mass in men by activating the androgen receptor. However, the clinical potential of androgens for improving body composition is hampered by our limited understanding of the tissues and cells that promote such changes. Here we show that selective overexpression of androgen receptor in muscle cells (myocytes) of transgenic male rats both increases lean mass percentage and reduces fat mass. Similar changes in body composition are observed in human skeletal actin promoter driving expression of androgen receptor (HSA-AR) transgenic mice and result from acute testosterone treatment of transgenic female HSA-AR rats. These shifts in body composition in HSA-AR transgenic male rats are associated with hypertrophy of type IIb myofibers and decreased size of adipocytes. Metabolic analyses of transgenic males show higher activity of mitochondrial enzymes in skeletal muscle and increased O2 consumption by the rats. These results indicate that androgen signaling in myocytes not only increases muscle mass but also reduces fat body mass, likely via increases in oxidative metabolism.

Expression of androgen receptor in muscle is sufficient to decrease fat body mass and increase oxidative metabolism.

Androgens, such as testosterone (T), promote skeletal muscle mass and reduce fat mass in men (1,2,3,4). Increasing lean mass and reducing fat mass are generally associated with reduced incidence of disease and improved health (5). However, despite these beneficial effects on body composition, therapeutic applications of androgens are limited by concerns about their potential for unwanted side effects, including masculinizing secondary sexual characteristics in women, increased risk of coronary heart disease, and prostate cancer in men (6). Therefore, an improved understanding of how androgens affect body composition is necessary to identify new targets for drug discovery.

Androgen receptor (AR) has long been suspected to mediate androgenic effects on body composition, and recent genetic analyses of AR have largely supported this notion but have also yielded some surprising findings (7). These studies find that genetic ablation of AR (ARKO), either ubiquitously or selectively in myocytes, results in muscular atrophy in males (8,9), whereas selective overexpression of AR in myocytes increases lean body mass percentage (LBM%) of males (10). Less straightforward are results relating to regulation of adipose by androgens. Notably, adipocyte-specific ARKO mice do not exhibit late-onset obesity typical of ARKO mice (11,12,13), suggesting that AR in white adipose tissue (WAT) is unnecessary for this kind of androgenic reduction of adiposity. However, myocyte-specific ARKO mice also show a reduction in fat mass (9), contrary to expectation. Thus, the available evidence suggests myocyte AR promotes lean body mass (LBM), but the site of androgen action in reducing fat remains unclear.

To shed further light on this issue, we examined body composition of transgenic (Tg) rats that overexpress AR in myocytes (10). These human skeletal actin promoter-driving expression of AR (HSA-AR) Tg rats were also crossed with rats carrying the testicular feminization mutation (Tfm), a loss of function AR mutation (14). Resulting HSA-AR/Tfm animals express functional AR in myocytes only and nonfunctional Tfm mutant AR in other tissues (10). This allows for investigation of effects of the transgene that rely solely on the myocyte population.

Materials and Methods

Animals

All but the final experiment were performed using HSA-AR Tg and/or Tfm Sprague Dawley rats. LBM% data at 6 wk of age have been previously published for a subset of the animals used in the current experiments (10).

The final experiment was performed using HSA-AR mice on a C57BL/6J background. All animals were bred locally at the University of Toronto at Mississauga. All procedures involving animals in this study were approved by the Office of Research Ethics at the University of Toronto and adhered to federal and National Institutes of Health guidelines. Generation of HSA-AR and HSA-AR/Tfm rats and mice (including genotyping) was performed as described previously (10,15).

Body composition analysis

Whole-body composition was determined using dual-energy x-ray absorptiometry (DXA) scanning (QDR 4500; Hologic, Waltham, MA). We examined effects of the HSA-AR transgene on body composition of wild-type (WT) males (n = 11), WT females (n = 8), HSA-AR males (n = 11), HSA-AR females (n = 9), Tfm males (n = 7), Tfm females (n = 7), HSA-AR/Tfm males (n = 9), and HSA-AR/Tfm females (n = 7). Animals were scanned biweekly, starting at 4 wk of age until 10 wk of age. Measurements of LBM, fat body mass (FBM), LBM%, FBM percentage (FBM%), and total mass were obtained for each scan. Scans were analyzed using rat whole-body software (Hologic QDR Software, version 12.3).

Indirect calorimetry

Measures of O2 consumption were recorded at 12 wk of age. Animals were placed inside a 700-ml (8.5-cm diameter, 13.0-cm length) cylindrical gas-exchange chamber (model G114; Qubit Systems, Kingston, Ontario, Canada). Room air was pumped through the chamber at a flow rate of 400 ml/min, and outflow oxygen concentration was measured by a flow-through oxygen analyzer (model S102; Qubit Systems). Concentration of outflow oxygen was analyzed and displayed by gas-exchange software (Logger Pro version 3; Vernier Software, Beaverton, OR). Animals were kept in the chamber until outflow oxygen concentration levels were stable, which was defined by no deviation in concentration of more than 0.02% over a period of 30 min. The difference between final outflow oxygen concentration and inflow concentration (i.e. concentration of oxygen in room air) was used to determine oxygen uptake (in microliters per minute). Animals were matched for time of day at which the measures were recorded. Indirect calorimetry was measured for WT (n = 10), HSA-AR (n = 12), Tfm (n = 7), and HSA-AR/Tfm (n = 10) males.

Dissections

At 16 wk of age, these animals were overdosed with sodium pentobarbital and dissected for enzyme activity assays, histology, and/or measurement of transgene expression as described below. Dissections were performed on WT (n = 10), HSA-AR (n = 12), Tfm (n = 7), and HSA-AR/Tfm (n = 10) males. Individual extensor digitorum longus (EDL) muscles and perigonadal fat pads were dissected.

Adipose histology

Excised fad pads were placed in 10% phosphate-buffered formalin and embedded in paraffin. Blocks were sliced at a thickness of 6 μm, and slides were stained with hematoxylin/eosin. Sections were analyzed systematically with respect to cell size and number. Images were acquired using an Olympus bright-field microscope (model BX51; Olympus, Tokyo, Japan), a ×4 objective, and a color video camera (Cool Snap Pro Color; Roper Scientific, Duluth, GA) with Image Pro Plus software (Media Cybernetics Inc., Silver Spring, MD). Photomicrographs were imported into ImageJ software (National Institutes of Health, Bethesda, MD), which was used to trace cell size. Analysis was performed on WT (n = 6), HSA-AR (n = 6), Tfm (n = 6), and HSA-AR/Tfm (n = 4) males.

Enzyme activity assays

EDL muscles were stored at −80 C for mitochondrial enzyme activity assays. Biochemical assays of mitochondrial enzyme activity in these muscles were performed as described by Kirby et al. (16).

Measurement of transgene expression

HSA is a fragment of the promoter region of a muscle-specific gene (ACTA1) cloned from human genomic DNA (17). This promoter is specific for skeletal muscle myocytes in mice (15), but a truncated version of HSA was used to generate HSA-AR rats as described previously (10). We therefore wanted to assess the specificity of this transgene.

Transgene expression in various tissues was examined after 16 wk of age for WT and heterozygous HSA-AR Tg rats (n = 3 per group). EDL muscle, heart (cardiac) muscle, kidney, urinary bladder (smooth muscle), and WAT were analyzed. Tissues were fresh dissected, frozen in liquid nitrogen, and kept at −80 C until RNA isolation. RT-PCR was performed as previously described (10).

Skeletal muscle histology

EDL muscles were dissected, frozen in optimal cutting temperature embedding medium (Tissue-Tek; distributed by Somagen Diagnostics, Edmonton, Alberta, Canada), and stored at −80 C until being processed for fiber typing. Fiber typing was accomplished using adjacent transverse cryostat sections of EDL stained for succinate dehydrogenase, and with a fast myosin heavy-chain antibody (My32; Sigma-Aldrich, Oakville, Ontario, Canada).

For myosin staining, sections were fixed with 4% paraformaldehyde and washed with PBS. Sections were then blocked in 10% normal horse serum (Vector Laboratories Inc., Burlingame, CA) in PBS before incubation with My32 primary antibody (diluted 1:1000 in 4% normal horse serum-PBS) for 45 h at 4 C. Sections were then washed and incubated for 1 h with rat-adsorbed horse antimouse secondary antibody (Vector) diluted 1:100 in 10% normal horse serum-PBS. Sections were then washed in PBS before incubation with ABC solution and Chromagen reaction with nickel-enhanced diaminobenzidine. Slides were then dehydrated in graded ethanols, cleared in xylenes, and coverslipped using Permount.

For succinate dehydrogenase reactions, sections were incubated in 0.5% nitroblue tetrazolium solution for 1 h at 37 C and then rinsed in distilled water. Slides were then dehydrated in graded ethanols, cleared in xylenes, and coverslipped using Permount.

Photomicrographs were then overlayed to identify fibers as slow, fast glycolytic, or fast oxidative. Three sampling areas in the belly of the muscle were used to estimate total number of fibers; proportion slow, fast glycolytic, and fast oxidative fibers; and the average size of each of these. Analysis was performed on WT (n = 5) and HSA-AR (n = 7) male EDL muscles.

T treatment of females

Exogenous T was provided to WT (n = 8) and HSA-AR (n = 9) females, aged 24–30 wk. Females had baseline body composition measured using DXA. The following day, SILASTIC brand capsules (Dow Corning Corp., Midland, MI) filled with 20 mm of T (Steraloids, Newport, RI) were constructed and sc implanted surgically as previously described (18,19,20,21). Animals were then scanned weekly for 4 wk using DXA. After this period, animals underwent another surgery during which the T capsules were removed, and empty (vehicle) capsules were inserted in their place. Animals were again DXA scanned weekly for the following 4 wk.

Statistical analysis

Body composition, adipocyte size, O2 consumption, basal metabolic rate (BMR), and electron-transport chain (ETC) data from intact males were examined using ANOVA with HSA-AR genotype and Tfm genotype as between-subject factors. Pair-wise comparisons were performed using Tukey-Kramer correction for family-wise error rate, and these comparisons were only made within weeks.

Muscle fiber morphology measurements were examined using independent-sample t tests.

Female T treatment data were examined using a repeated-measures ANOVA with HSA-AR genotype as a between-subject factor and body mass, LBM%, FBM%, and raw LBM or raw FBM as the within-subject factor. Analyses were run separately for the first 5 wk (baseline and 4 wk of T treatment) and for wk 4–8 (final week of T treatment and 4 wk after cessation of T treatment). Pairwise comparisons were performed using unprotected paired t tests in cases in which an interaction between the within-subject and between-subject factors were observed. Otherwise, a Dunnett correction for family-wise error was applied. Pairwise comparisons were made with each week being compared with baseline (wk 1–4) or wk 4 (wk 5–8). These two epochs were used to evaluate effects of T treatment and T withdrawal respectively. Unless otherwise noted, α was set at P ≤ 0.05.

Results of statistical analyses can be found in the Supplemental Data published on The Endocrine Society’s Journals Online web site at http://endo.endojournals.org.

Results

Transgene specificity

Specificity of transgene expression was confirmed by RT-PCR using transgene-specific primers. We detected HSA-AR mRNA expression in skeletal muscle, urinary bladder (smooth muscle), and heart (cardiac muscle) of Tg animals but not WAT or kidney (Fig. 1).

Figure 1.

Figure 1

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HSA-AR transgene expression is muscle specific in Tg rats. RT-PCR using transgene-specific primers was performed. HSA-AR mRNA expression is detectable in SM (skeletal muscle), urinary bladder (smooth muscle), and heart (cardiac muscle) of Tg but not WT rats. No transgene expression was detected in adipose or kidney of Tg animals. Glyceraldehyde 3′ phosphate dehydrogenase (GAPDH) mRNA expression was used as a positive control.

Body composition of HSA-AR Tg males

Using DXA analysis of body composition, we measured body mass, LBM%, FBM%, LBM uncorrected for body mass, and FBM uncorrected for body mass (Fig. 2).

Figure 2.

Figure 2

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Body composition of males measured at 4, 6, 8, and 10 wk of age using DXA. Representative DXA scan images of 10-wk-old WT (A), HSA-AR Tg (B), Tfm (C), and Tg/Tfm males (D). Note the decreased abdominal girth in the Tg and Tfm rats. Overexpression of AR in muscle of Tg males results in increased LBM as a percentage of total body mass (F). Differences between Tg and WT brothers in fat (I) but not LBM (H) persist when uncorrected for total body mass. Tfm males were found to have reduced body mass (E), increased LBM% (F), decreased fat mass percentage (G) as well as both decreased LBM (H) and FBM (I). No statistical interaction was observed between Tfm and HSA-AR genotype on any measure. #, Significant main effect of Tfm genotype; *, significant main effect of HSA-AR. LBM% data at 6 wk of age have been previously published for a subset of the animals used in the current experiments (10).

Body mass was significantly reduced in Tfm rats relative to WT brothers, whereas HSA-AR had no effect. These main effects were apparent starting at 8 wk of age.

HSA-AR males were found to have increased LBM% and reduced FBM% relative to WT brothers. These main effects were apparent starting at 6 wk of age.

HSA-AR rats also had reduced FBM uncorrected for total body mass starting at 6 wk of age, but uncorrected LBM did not differ between Tg rats and WT brothers.

Unexpectedly, the loss of AR function Tfm mutation resulted in increased LBM% and reduced FBM% relative to WT brothers, likely related to reduced body mass of Tfm rats. Similar main effects of Tfm on uncorrected FBM starting at 6 wk and uncorrected LBM starting at 8 wk were also observed.

No statistically significant interaction between HSA-AR and Tfm factors was obtained for any of these measures.

Effects of T treatment of HSA-AR Tg females

We next evaluated androgen dependence of the effect of HSA-AR on body composition by treating both WT and Tg females with T for 4 wk and performing DXA before, during, and after this treatment (Fig. 3). Whereas this dosing regimen was insufficient to alter body composition in WT females, it did increase LBM% and reduce FBM% in Tg females during the course of treatment, and these effects were reversed within 2 wk after cessation of T treatment. These results suggest that effects of HSA-AR on body composition likely result from acute androgenic actions.

Figure 3.

Figure 3

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Body composition is altered by T treatment of HSA-AR females. WT and Tg females were treated with T for 4 wk, at which point T was removed. Body composition was measured weekly using DXA. A, DXA scan images of a Tg female and WT sister before, during, and after T treatment. Note decreased abdominal girth in the Tg female during T treatment. B, T treatment of Tg females transiently resulted in increased LBM and decreased FBM, either when corrected or uncorrected for overall body mass. No such effects were seen in WT females. *, Significant difference within the Tg female group, compared with baseline values (wk 0 for wk 1–4 or wk 4 for wk 5–8).

Skeletal muscle and adipose histology

Dissection of tissues and histological analyses of HSA-AR Tg males confirmed the effects of HSA-AR on LBM and FBM. Although there was no effect of HSA-AR on the total number of myofibers in the EDL (Fig. 4A) or on fiber-type proportion in the EDL, (Fig. 4B), selective hypertrophy was seen in type IIb (fast twitch, glycolytic) myofibers in the EDL of HSA-AR males (Fig. 4C).

Figure 4.

Figure 4

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Hypertrophy of type IIb fibers in HSA-AR Tg males. No difference was observed in EDL muscle fiber number (A) and fiber typing of this muscle indicated no significant shift in fiber type (B), but a selective increase in the size of type IIb muscle fibers is seen (C). Minor ellipse was used as a measure of size because it is more resistant to variation in orientation than cross-sectional area. *, Significantly greater in Tg males.

ANOVA performed on dissected perigonadal WAT pad mass and adipocyte size indicated a main effect of HSA-AR but not Tfm and no interaction between these factors. Pads were lighter and adipocytes smaller in HSA-AR males than WT males (Fig. 5).

Figure 5.

Figure 5

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HSA-AR expression reduces adipose tissue mass and adipocyte size. A, Dissected perigonadal fat pads are heavier in WT males than HSA-AR Tg males. No main effect of Tfm genotype on perigonadal fat pad mass was observed. No interaction was observed between HSA-AR and Tfm. B, Adipocyte size is reduced in HSA-AR Tg males. A main effect of HSA-AR but not Tfm genotype on adipocyte size was observed. No interaction was observed between HSA-AR and Tfm. C, Frequency distributions for adipocyte size indicate that WT males have an increased proportion of larger adipocytes than HSA-AR males. *, Significant main effect of HSA-AR genotype.

Oxidative metabolism of HSA-AR Tg rats

We hypothesized that the decreased fat mass of Tg males might be caused, at least in part, by an increase in oxidative metabolism (all results shown in Table 1). ANOVA of indirect calorimetry measures among males indicated a main effect of HSA-AR genotype on O2 consumption but no main effect of Tfm or interaction. A main effect of Tfm but not HSA-AR was observed in ANOVA of calculated BMR, although an interaction between HSA-AR and Tfm was observed. Pairwise comparisons indicated a significant difference between HSA-AR/WT and HSA-AR/Tfm but not between any other relevant group comparisons, although the difference between WT/Tfm and HSA-AR/Tfm approached significance (P = 0.054). The discrepancy between O2 and BMR results likely reflects body mass differences between WT and Tfm males.

Table 1.

Metabolic rate and muscular ETC activity of male rats

WT HSA-AR Tfm HSA-AR/Tfm
O2 uptake (μl/min) 848.4 ± 20.0 957.3 ± 46.0a 839.4 ± 34.0 971.2 ± 29.0a
BMR (J/g−1 · min−1) 0.0092 ± 0.0003 0.0110 ± 0.0007 0.0103 ± 0.0005b 0.0121 ± 0.0005b
Complex I activity 67.7 ± 3.6 109.8 ± 5.2a 36.1 ± 1.4b 61.4 ± 3.6a,b
Complex II activity 142.0 ± 3.7 167.9 ± 2.6a 110.0 ± 4.1b 143.4 ± 2.5a,b
Complex III activity 568.9 ± 16.1 700.9 ± 11.2a 346.8 ± 12.2b 550.7 ± 13.5a,b
Complex IV activity 449.9 ± 14.0 638.1 ± 23.9a 341.9 ± 16.4b 471.0 ± 14.9a,b
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Resting metabolic rate was estimated at 12 wk of age by measuring rate of O2 consumption and calculating BMR, based on body mass. Resting O2 consumption was increased in HSA-AR but not Tfm males. BMR was increased in Tfm males but not HSA-AR males, although a statistical interaction between these two genotypes was observed using ANOVA. ETC enzyme activity of dissected EDL muscle was measured in nanomoles per minute per milligram of protein and subsequently normalized to citrate synthase to control for total mitochondrial content. HSA-AR had increased enzyme activity, and Tfm rats had reduced enzyme activity of all complexes. 

a

Significant main effect of HSA-AR genotype. 

b

Significant main effect of Tfm genotype. A statistically significant interaction was observed between these factors for BMR and complex I and complex III activity. 

Analysis of mitochondrial ETC enzyme activity in dissected EDL skeletal muscle of males shows a main effect of both HSA-AR and Tfm on enzyme activity of complexes I-IV. An interaction between HSA-AR and Tfm genotype was observed for complexes I and III. Pairwise comparisons indicated that all relevant group comparisons were statistically significant. Taken together, these results indicate increased oxidative capacity in muscle due to transgene expression and suggest a possible mechanism for the reduced adiposity seen in HSA-AR animals.

Body composition of HSA-AR Tg mice

Finally, we examined body composition of HSA-AR Tg mice (15). This comparison allowed us to assess the generalizability of our findings in rats and also allowed us to rule out several trivial explanations, such as transgene effects being due to ectopic expression in cardiac and smooth myocytes or an insertional mutation. We examined adult male Tg mice from the L78 line in relation to their WT brothers and found similar results to those seen in HSA-AR Tg rats (Fig. 6). Male Tg mice have reduced body mass, greater LBM%, and lower FBM%, similar to male Tg rats. Furthermore, raw FBM measurements were less in Tg than WT brothers. As expected, raw LBM measurements were reduced in Tg males, reflecting mild muscular atrophy in the males of this line (15).

Figure 6.

Figure 6

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Body composition of HSA-AR mice. Male mice with a HSA-AR transgene (L78 Tg; see Ref. 15) were DXA scanned at 24 wk of age. A, Representative DXA scan images. Note decreased abdominal girth in HSA-AR Tg. B, Tg mice have reduced body mass, increased lean mass percentage, and reduced fat mass percentage relative to WT brothers (n = 6 Tg, n = 5 WT) similar to effects of HSA-AR in rats. Tg males have significantly reduced LBM when uncorrected for total body size. Nonetheless, fat mass is reduced in Tg males. These data demonstrate that overexpression of AR in myocytes affects body composition similarly in mice and rats. *, Significant difference between L78 Tg and WT.

Discussion

The present results demonstrate that increased AR signaling in myocytes is sufficient to promote increases in LBM%, decreases in FBM%, and an increase in muscle and systemic oxidative metabolism. These results are somewhat surprising because androgens are thought to affect adipose tissue by acting on AR in adipocytes themselves, primarily by inhibiting differentiation of preadipocytes (22,23). Although our findings do not address any action of AR within adipocytes/preadipocytes, such mechanisms cannot account for the differences that we see in HSA-AR Tg animals as HSA-AR mRNA expression was not found in WAT of Tg rats (Fig. 1) or Tg mice (15). Furthermore, HSA-AR/Tfm males also have reduced FBM (Fig. 2), independent of functional AR in any nonmuscle tissue (including WAT). These results demonstrate that increased AR signaling in myocytes is sufficient to promote increased LBM and decreased FBM.

Less straightforward is whether our results address the necessity of myocyte AR for T’s effects on body composition. Although our studies were not explicitly designed to test this notion, our findings might help explain the lack of effect of adipocyte-specific ARKO on adipose mass (13). The obesity of ARKO mice is associated with reduced basal metabolism (12) and low T (24,25). The current results indicate that reduced basal metabolism of Tfm rats can be rescued by myocyte-specific AR (Table 1). However, we also found that Tfm males, which have a loss of AR function and high T (26), nonetheless have unexpectedly increased LBM% and reduced FBM% relative to WT brothers. These effects of globally reduced AR signaling appear paradoxically similar to those of the HSA-AR transgene, which increases AR signaling in myocytes. On the face of it, reduced FBM in Tfm males seems to speak against the necessity of AR in myocytes for T’s effects on body composition. However, we did not evaluate body composition at the later ages at which obesity is apparent in ARKO mice, so it remains possible that older Tfm male rats would go on to exhibit obesity.

It seems likely that the beneficial shift in body composition seen in Tfm males is not due to a deficiency in myocyte AR because replacing myocyte AR with the HSA-AR transgene shifts them further in the same direction, rather than normalizing their body composition.

Tfm males have reduced AR signaling in all tissues but intact estrogenic signaling. Although adipose and brain are thought to primarily mediate adipolytic effects of estrogens (27,28,29), estrogenic actions within muscle have not been ruled out. We must therefore consider the possibility of estrogenic actions of T when explaining reduced adiposity of Tfm male rats.

Similarly, because we did not ovariectomize our rats in the T treatment study, it might be argued that T treatment had only secondary effects by suppressing ovarian hormone. This explanation seems improbable for at least two reasons: 1) ovariectomy results in increased fat mass in females (30), whereas in our study T treatment results in the opposite effect and 2) T treatment affected only HSA-AR females, indicating that AR mediates the observed effects. Nonetheless, it remains possible that the transgene AR ultimately increases estrogenic signaling within muscle. Speaking against this final possibility, estrogens are ineffective in reducing body mass of HSA-AR female mice, whereas either T or dihydrotestosterone is effective (31), indicating that estrogenic mechanisms do not easily account for the phenotype of these mice.

One might also think that variations in endogenous T between HSA-AR and WT males could explain the observed differences between these groups. Although it seems unlikely that myocyte-specific AR would influence circulating T, we cannot rule out this possibility because we did not measure T in our samples. Nonetheless, it seems unlikely that differences in circulating T alone could explain our results because equal doses of T reproduced body composition changes similar to Tg males in HSA-AR females but not WT sisters.

Taken as a whole, our results suggest a model in which increased AR signaling in myocytes is sufficient to decrease adiposity by virtue of increased muscular and systemic oxidative metabolism. Similar findings have recently been reported in the context of muscle-specific Akt1 activation that, in Tg mice, results in resistance to obesity associated with hypertrophy of type IIb muscle fibers and increased oxidative metabolism (32). In fact, there is a relative paucity of mitochondria and reduced ETC activity in thigh muscle biopsies taken from individuals with simple obesity (33,34). Furthermore, higher skeletal muscle oxidative metabolism appears protective against obesity in healthy young men (35). Identifying the cellular and molecular mechanism(s) whereby myocyte AR might stimulate increased mitochondrial respiration, and the application of this knowledge, provides an important avenue for future research.

Supplementary Material

[Supplemental Data]
en.2010-0018_index.html (715B, html)

Acknowledgments

HSA-AR rats were generously provided by Ligand Pharmaceuticals (San Diego, CA).

Footnotes

This work was supported by National Institute of Neurological Disorders and Stroke Grant R01-NS51257 and Natural Sciences and Engineering Research Council of Canada Grant RGPIN 312458-06 (to D.A.M.). Additional support was obtained from a postdoctoral fellowship from NSERC (to L.N.) and an Ontario Graduate Scholarship (to S.M.F.).

Disclosure Summary: The authors have nothing to declare.

First Published Online April 28, 2010

Abbreviations: AR, Androgen receptor; ARKO, genetic ablation of AR; BMR, basal metabolic rate; DXA, dual-energy x-ray absorptiometry; EDL, extensor digitorum longus; ETC, electron-transport chain; FBM, fat body mass; FBM%, FBM percentage; HSA-AR, human skeletal actin promoter-driving expression of AR; LBM, lean body mass; LBM%, lean body mass percentage; T, testosterone; Tfm, testicular feminization mutation; Tg, transgenic; WAT, white adipose tissue; WT, wild type.

References

  1. Bhasin S, Storer TW, Berman N, Callegari C, Clevenger B, Phillips J, Bunnell TJ, Tricker R, Shirazi A, Casaburi R 1996 The effects of supraphysiologic doses of testosterone on muscle size and strength in normal men. N Engl J Med 335:1–7 [DOI] [PubMed] [Google Scholar]
  2. Emmelot-Vonk MH, Verhaar HJ, Nakhai Pour HR, Aleman A, Lock TM, Bosch JL, Grobbee DE, van der Schouw YT 2008 Effect of testosterone supplementation on functional mobility, cognition, and other parameters in older men: a randomized controlled trial. JAMA 299:39–52 [DOI] [PubMed] [Google Scholar]
  3. Snyder PJ, Peachey H, Berlin JA, Hannoush P, Haddad G, Dlewati A, Santanna J, Loh L, Lenrow DA, Holmes JH, Kapoor SC, Atkinson LE, Strom BL 2000 Effects of testosterone replacement in hypogonadal men. J Clin Endocrinol Metab 85:2670–2677 [DOI] [PubMed] [Google Scholar]
  4. Forbes GB, Porta CR, Herr BE, Griggs RC 1992 Sequence of changes in body composition induced by testosterone and reversal of changes after drug is stopped. JAMA 267:397–399 [PubMed] [Google Scholar]
  5. Friedman JM 2009 Obesity: causes and control of excess body fat. Nature 459:340–342 [DOI] [PubMed] [Google Scholar]
  6. Miner MM, Seftel AD 2007 Testosterone and ageing: what have we learned since the Institute of Medicine report and what lies ahead? Int J Clin Pract 61:622–632 [DOI] [PubMed] [Google Scholar]
  7. MacLean HE, Handelsman DJ 2009 Unraveling androgen action in muscle: genetic tools probing cellular mechanisms. Endocrinology 150:3437–3439 [DOI] [PubMed] [Google Scholar]
  8. MacLean HE, Chiu WS, Notini AJ, Axell AM, Davey RA, McManus JF, Ma C, Plant DR, Lynch GS, Zajac JD 2008 Impaired skeletal muscle development and function in male, but not female, genomic androgen receptor knockout mice. FASEB J 22:2676–2689 [DOI] [PubMed] [Google Scholar]
  9. Ophoff J, Van Proeyen K, Callewaert F, De Gendt K, De Bock K, Vanden Bosch A, Verhoeven G, Hespel P, Vanderschueren D 2009 Androgen signaling in myocytes contributes to the maintenance of muscle mass and fiber type regulation but not to muscle strength or fatigue. Endocrinology 150:3558–3566 [DOI] [PubMed] [Google Scholar]
  10. Niel L, Shah AH, Lewis GA, Mo K, Chatterjee D, Fernando SM, Hong MH, Chang WY, Vollmayr P, Rosen J, Miner JN, Monks DA 2009 Sexual differentiation of the spinal nucleus of the bulbocavernosus is not mediated solely by androgen receptors in muscle fibers. Endocrinology 150:3207–3213 [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Lin HY, Xu Q, Yeh S, Wang RS, Sparks JD, Chang C 2005 Insulin and leptin resistance with hyperleptinemia in mice lacking androgen receptor. Diabetes 54:1717–1725 [DOI] [PubMed] [Google Scholar]
  12. Fan W, Yanase T, Nomura M, Okabe T, Goto K, Sato T, Kawano H, Kato S, Nawata H 2005 Androgen receptor null male mice develop late-onset obesity caused by decreased energy expenditure and lipolytic activity but show normal insulin sensitivity with high adiponectin secretion. Diabetes 54:1000–1008 [DOI] [PubMed] [Google Scholar]
  13. Yu IC, Lin HY, Liu NC, Wang RS, Sparks JD, Yeh S, Chang C 2008 Hyperleptinemia without obesity in male mice lacking androgen receptor in adipose tissue. Endocrinology 149:2361–2368 [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Yarbrough WG, Quarmby VE, Simental JA, Joseph DR, Sar M, Lubahn DB, Olsen KL, French FS, Wilson EM 1990 A single base mutation in the androgen receptor gene causes androgen insensitivity in the testicular feminized rat. J Biol Chem 265:8893–8900 [PubMed] [Google Scholar]
  15. Monks DA, Johansen JA, Mo K, Rao P, Eagleson B, Yu Z, Lieberman AP, Breedlove SM, Jordan CL 2007 Overexpression of wild-type androgen receptor in muscle recapitulates polyglutamine disease. Proc Natl Acad Sci USA 104:18259–18264 [DOI] [PMC free article] [PubMed] [Google Scholar]
  16. Kirby DM, Thorburn DR, Turnbull DM, Taylor RW 2007 Biochemical assays of respiratory chain complex activity. Methods Cell Biol 80:93–119 [DOI] [PubMed] [Google Scholar]
  17. Brennan KJ, Hardeman EC 1993 Quantitative analysis of the human α-skeletal actin gene in transgenic mice. J Biol Chem 268:719–725 [PubMed] [Google Scholar]
  18. Monks DA, Getsios S, MacCalman CD, Watson NV 2001 N-cadherin is regulated by gonadal steroids in adult sexually dimorphic spinal motoneurons. J Neurobiol 47:255–264 [DOI] [PubMed] [Google Scholar]
  19. Monks DA, Getsios S, MacCalman CD, Watson NV 2001 N-cadherin is regulated by gonadal steroids in the adult hippocampus. Proc Natl Acad Sci USA 98:1312–1316 [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Monks DA, Vanston CM, Watson NV 1999 Direct androgenic regulation of calcitonin gene-related peptide expression in motoneurons of rats with mosaic androgen insensitivity. J Neurosci 19:5597–5601 [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Monks DA, Watson NV 2001 N-cadherin expression in motoneurons is directly regulated by androgens: a genetic mosaic analysis in rats. Brain Res 895:73–79 [DOI] [PubMed] [Google Scholar]
  22. Singh R, Artaza JN, Taylor WE, Gonzalez-Cadavid NF, Bhasin S 2003 Androgens stimulate myogenic differentiation and inhibit adipogenesis in C3H 10T1/2 pluripotent cells through an androgen receptor-mediated pathway. Endocrinology 144:5081–5088 [DOI] [PubMed] [Google Scholar]
  23. Singh R, Artaza JN, Taylor WE, Braga M, Yuan X, Gonzalez- Cadavid NF, Bhasin S 2006 Testosterone inhibits adipogenic differentiation in 3T3-L1 cells: nuclear translocation of androgen receptor complex with β-catenin and T-cell factor 4 may bypass canonical Wnt signaling to down-regulate adipogenic transcription factors. Endocrinology 147:141–154 [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Jones RD, Pugh PJ, Hall J, Channer KS, Jones TH 2003 Altered circulating hormone levels, endothelial function and vascular reactivity in the testicular feminised mouse. Eur J Endocrinol 148:111–120 [DOI] [PubMed] [Google Scholar]
  25. Murphy L, O'Shaughnessy PJ 1991 Testicular steroidogenesis in the testicular feminized (Tfm) mouse: loss of 17 α-hydroxylase activity. J Endocrinol 131:443–449 [DOI] [PubMed] [Google Scholar]
  26. Naess O, Haug E, Attramadal A, Aakvaag A, Hansson V, French F 1976 Androgen receptors in the anterior pituitary and central nervous system of the androgen “insensitive” (Tfm) rat: correlation between receptor binding and effects of androgens on gonadotropin secretion. Endocrinology 99:1295–1303 [DOI] [PubMed] [Google Scholar]
  27. Cooke PS, Heine PA, Taylor JA, Lubahn DB 2001 The role of estrogen and estrogen receptor-α in male adipose tissue. Mol Cell Endocrinol 178:147–154 [DOI] [PubMed] [Google Scholar]
  28. Gao Q, Mezei G, Nie Y, Rao Y, Choi CS, Bechmann I, Leranth C, Toran-Allerand D, Priest CA, Roberts JL, Gao XB, Mobbs C, Shulman GI, Diano S, Horvath TL 2007 Anorectic estrogen mimics leptin’s effect on the rewiring of melanocortin cells and Stat3 signaling in obese animals. Nat Med 13:89–94 [DOI] [PubMed] [Google Scholar]
  29. Jones ME, McInnes KJ, Boon WC, Simpson ER 2007 Estrogen and adiposity—utilizing models of aromatase deficiency to explore the relationship. J Steroid Biochem Mol Biol 106:3–7 [DOI] [PubMed] [Google Scholar]
  30. Wade GN, Gray JM, Bartness TJ 1985 Gonadal influences on adiposity. Int J Obes 9(Suppl 1):83–92 [PubMed] [Google Scholar]
  31. Monks DA, Rao P, Mo K, Johansen JA, Lewis G, Kemp MQ 2008 Androgen receptor and Kennedy disease/spinal bulbar muscular atrophy. Horm Behav 53:729–740 [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Izumiya Y, Hopkins T, Morris C, Sato K, Zeng L, Viereck J, Hamilton JA, Ouchi N, LeBrasseur NK, Walsh K 2008 Fast/Glycolytic muscle fiber growth reduces fat mass and improves metabolic parameters in obese mice. Cell Metab 7:159–172 [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Ritov VB, Menshikova EV, Azuma K, Wood RJ, Toledo FG, Goodpaster BH, Ruderman NB, Kelley DE 3 November 2009 Deficiency of electron transport chain in human skeletal muscle mitochondria in type 2 diabetes mellitus and obesity. Am J Physiol Endocrinol Metab DOI: 10.1152/ajpendo.00317.2009 [DOI] [PMC free article] [PubMed] [Google Scholar]
  34. Ritov VB, Menshikova EV, He J, Ferrell RE, Goodpaster BH, Kelley DE 2005 Deficiency of subsarcolemmal mitochondria in obesity and type 2 diabetes. Diabetes 54:8–14 [DOI] [PubMed] [Google Scholar]
  35. Sun G, Ukkola O, Rankinen T, Joanisse DR, Bouchard C 2002 Skeletal muscle characteristics predict body fat gain in response to overfeeding in never-obese young men. Metabolism 51:451–456 [DOI] [PubMed] [Google Scholar]

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