Effects of testosterone treatment on markers of skeletal muscle ribosome biogenesis

Mechanisms of mechanical overload-induced skeletal muscle hypertrophy: current understanding and future directions

Mechanisms underlying mechanical overload-induced skeletal muscle hypertrophy have been extensively researched since the landmark report by Morpurgo (1897) of "work-induced hypertrophy" in dogs that were treadmill trained. Much of the preclinical rodent and human resistance training research to date supports that involved mechanisms include enhanced mammalian/mechanistic target of rapamycin complex 1 (mTORC1) signaling, an expansion in translational capacity through ribosome biogenesis, increased satellite cell abundance and myonuclear accretion, and postexercise elevations in muscle protein synthesis rates. However, several lines of past and emerging evidence suggest that additional mechanisms that feed into or are independent of these processes are also involved. This review first provides a historical account of how mechanistic research into skeletal muscle hypertrophy has progressed. A comprehensive list of mechanisms associated with skeletal muscle hypertrophy is then outlined, and areas of disagreement involving these mechanisms are presented. Finally, future research directions involving many of the discussed mechanisms are proposed.

Pharmacological hypogonadism impairs molecular transducers of exercise-induced muscle growth in humans

BACKGROUND

The relative role of skeletal muscle mechano-transduction in comparison with systemic hormones, such as testosterone (T), in regulating hypertrophic responses to exercise is contentious. We investigated the mechanistic effects of chemical endogenous T depletion adjuvant to 6 weeks of resistance exercise training (RET) on muscle mass, function, myogenic regulatory factors, and muscle anabolic signalling in younger men.

METHODS

Non-hypogonadal men (n = 16; 18-30 years) were randomized in a double-blinded fashion to receive placebo (P, saline n = 8) or the GnRH analogue, Goserelin [Zoladex (Z), 3.6 mg, n = 8], injections, before 6 weeks of supervised whole-body RET. Participants underwent dual-energy X-ray absorptiometry (DXA), ultrasound of m. vastus lateralis (VL), and VL biopsies for assessment of cumulative muscle protein synthesis (MPS), myogenic gene expression, and anabolic signalling pathway responses.

RESULTS

Zoladex suppressed endogenous T to within the hypogonadal range and was well tolerated; suppression was associated with blunted fat free mass [Z: 55.4 ± 2.8 to 55.8 ± 3.1 kg, P = 0.61 vs. P: 55.9 ± 1.7 to 57.4 ± 1.7 kg, P = 0.006, effect size (ES) = 0.31], composite strength (Z: 40 ± 2.3% vs. P: 49.8 ± 3.3%, P = 0.03, ES = 1.4), and muscle thickness (Z: 2.7 ± 0.4 to 2.69 ± 0.36 cm, P > 0.99 vs. P: 2.74 ± 0.32 to 2.91 ± 0.32 cm, P < 0.0001, ES = 0.48) gains. Hypogonadism attenuated molecular transducers of muscle growth related to T metabolism (e.g. androgen receptor: Z: 1.2 fold, P > 0.99 vs. P: 1.9 fold, P < 0.0001, ES = 0.85), anabolism/myogenesis (e.g. IGF-1Ea: Z: 1.9 fold, P = 0.5 vs. P: 3.3 fold, P = 0.0005, ES = 0.72; IGF-1Ec: Z: 2 fold, P > 0.99 vs. P: 4.7 fold, P = 0.0005, ES = 0.68; myogenin: Z: 1.3 fold, P > 0.99 vs. P: 2.7 fold, P = 0.002, ES = 0.72), RNA/DNA (Z: 0.47 ± 0.03 to 0.53 ± 0.03, P = 0.31 vs. P: 0.50 ± 0.01 to 0.64 ± 0.04, P = 0.003, ES = 0.72), and RNA/ASP (Z: 5.8 ± 0.4 to 6.8 ± 0.5, P > 0.99 vs. P: 6.5 ± 0.2 to 8.9 ± 1.1, P = 0.008, ES = 0.63) ratios, as well as acute RET-induced phosphorylation of growth signalling proteins (e.g. AKT^ser473 : Z: 2.74 ± 0.6, P = 0.2 vs. P: 5.5 ± 1.1 fold change, P < 0.001, ES = 0.54 and mTORC1^ser2448 : Z: 1.9 ± 0.8, P > 0.99 vs. P: 3.6 ± 1 fold change, P = 0.002, ES = 0.53). Both MPS (Z: 1.45 ± 0.11 to 1.50 ± 0.06%·day^-1 , P = 0.99 vs. P: 1.5 ± 0.12 to 2.0 ± 0.15%·day^-1 , P = 0.01, ES = 0.97) and (extrapolated) muscle protein breakdown (Z: 93.16 ± 7.8 vs. P: 129.1 ± 13.8 g·day^-1 , P = 0.04, ES = 0.92) were reduced with hypogonadism result in lower net protein turnover (3.9 ± 1.1 vs. 1.2 ± 1.1 g·day^-1 , P = 0.04, ES = 0.95).

CONCLUSIONS

We conclude that endogenous T sufficiency has a central role in the up-regulation of molecular transducers of RET-induced muscle hypertrophy in humans that cannot be overcome by muscle mechano-transduction alone.

Spermidine is not an independent factor regulating limb muscle mass in mice following androgen deprivation

Maintaining a critical amount of skeletal muscle mass is linked to reduced morbidity and mortality. In males, testicular androgens regulate muscle mass with a loss of androgens being critical as it is associated with muscle atrophy. Atrophy of the limb muscles is particularly important, but the pathways by which androgens regulate limb muscle mass remain equivocal. We used microarray analysis to identify changes to genes involved with polyamine metabolism in the tibialis anterior (TA) muscle of castrated mice. Of the polyamines, the concentration of spermidine (SPD) was significantly reduced in the TA of castrated mice. To assess whether SPD was an independent factor by which androgens regulate limb muscle mass, we treated castrated mice with SPD for 8 weeks and compared them with sham operated mice. Though this treatment paradigm effectively restored SPD concentrations in the TA muscles of castrated mice, mass of the limb muscles (i.e., TA, gastrocnemius, plantaris, and soleus) were not increased to the levels observed in sham animals. Consistent with those findings, muscle force production was also not increased by SPD treatment. Overall, these data demonstrate for the first time that SPD is not an independent factor by which androgens regulate limb skeletal muscle mass. Novelty: Polyamines regulate growth in various cells/tissues. Spermidine concentrations are reduced in the limb skeletal muscle following androgen depletion. Restoring spermidine concentrations in the limb skeletal muscle does not increase limb muscle mass or force production.

Hormonal and Metabolic Changes of Aging and the Influence of Lifestyle Modifications

Increased life expectancy combined with the aging baby boomer generation has resulted in an unprecedented global expansion of the elderly population. The growing population of older adults and increased rate of age-related chronic illness has caused a substantial socioeconomic burden. The gradual and progressive age-related decline in hormone production and action has a detrimental impact on human health by increasing risk for chronic disease and reducing life span. This article reviews the age-related decline in hormone production, as well as age-related biochemical and body composition changes that reduce the bioavailability and actions of some hormones. The impact of hormonal changes on various chronic conditions including frailty, diabetes, cardiovascular disease, and dementia are also discussed. Hormone replacement therapy has been attempted in many clinical trials to reverse and/or prevent the hormonal decline in aging to combat the progression of age-related diseases. Unfortunately, hormone replacement therapy is not a panacea, as it often results in various adverse events that outweigh its potential health benefits. Therefore, except in some specific individual cases, hormone replacement is not recommended. Rather, positive lifestyle modifications such as regular aerobic and resistance exercise programs and/or healthy calorically restricted diet can favorably affect endocrine and metabolic functions and act as countermeasures to various age-related diseases. We provide a critical review of the available data and offer recommendations that hopefully will form the groundwork for physicians/scientists to develop and optimize new endocrine-targeted therapies and lifestyle modifications that can better address age-related decline in heath.

The Expression of Hormone Receptors as a Gateway toward Understanding Endocrine Actions in Female Pelvic Floor Muscles

OBJECTIVE

To provide an overview of the hormone actions and receptors expressed in the female pelvic floor muscles, relevant for understanding the pelvic floor disorders.

METHODS

We performed a literature review focused on the expression of hormone receptors mainly in the pelvic floor muscles of women and female rats and rabbits.

RESULTS

The impairment of the pelvic floor muscles can lead to the onset of pelvic floor dysfunctions, including stress urinary incontinence in women. Hormone milieu is associated with the structure and function alterations of pelvic floor muscles, a notion supported by the fact that these muscles express different hormone receptors. Nuclear receptors, such as steroid receptors, are up till now the most investigated. The present review accounts for the limited studies conducted to elucidate the expression of hormone receptors in pelvic floor muscles in females.

CONCLUSION

Hormone receptor expression is the cornerstone in some hormone-based therapies, which require further detailed studies on the distribution of receptors in particular pelvic floor muscles, as well as their association with muscle effectors, involved in the alterations relevant for understanding pelvic floor disorders.

An animal model study on the gene expression profile of meniscal degeneration

Meniscal degeneration is a very common condition in elderly individuals, but the underlying mechanisms of its occurrence are not completely clear. This study examines the molecular mechanisms of meniscal degeneration. The anterior cruciate ligament (ACL) and lateral collateral ligament (LCL) of the right rear limbs of seven Wuzhishan mini-pigs were resected (meniscal degeneration group), and the left rear legs were sham-operated (control group). After 6 months, samples were taken for gene chip analysis, including differentially expressed gene (DEG) analysis, gene ontology (GO) analysis, clustering analysis, and pathway analysis. The selected 12 DEGs were validated by real time reverse transcription-polymerase chain reaction (RT-PCR). The two groups showed specific and highly clustered DEGs. A total of 893 DEGs were found, in which 537 are upregulated, and 356 are downregulated. The GO analysis showed that the significantly affected biological processes include nitric oxide metabolic process, male sex differentiation, and mesenchymal morphogenesis, the significantly affected cellular components include the endoplasmic reticulum membrane, and the significantly affected molecular functions include transition metal ion binding and iron ion binding. The pathway analysis showed that the significantly affected pathways include type II diabetes mellitus, inflammatory mediator regulation of TRP channels, and AMPK signaling pathway. The results of RT-PCR indicate that the microarray data accurately reflects the gene expression patterns. These findings indicate that several molecular mechanisms are involved in the development of meniscal degeneration, thus improving our understanding of meniscal degeneration and provide molecular therapeutic targets in the future.

Growth Hormone(s), Testosterone, Insulin-Like Growth Factors, and Cortisol: Roles and Integration for Cellular Development and Growth With Exercise

Hormones are largely responsible for the integrated communication of several physiological systems responsible for modulating cellular growth and development. Although the specific hormonal influence must be considered within the context of the entire endocrine system and its relationship with other physiological systems, three key hormones are considered the "anabolic giants" in cellular growth and repair: testosterone, the growth hormone superfamily, and the insulin-like growth factor (IGF) superfamily. In addition to these anabolic hormones, glucocorticoids, mainly cortisol must also be considered because of their profound opposing influence on human skeletal muscle anabolism in many instances. This review presents emerging research on: (1) Testosterone signaling pathways, responses, and adaptations to resistance training; (2) Growth hormone: presents new complexity with exercise stress; (3) Current perspectives on IGF-I and physiological adaptations and complexity these hormones as related to training; and (4) Glucocorticoid roles in integrated communication for anabolic/catabolic signaling. Specifically, the review describes (1) Testosterone as the primary anabolic hormone, with an anabolic influence largely dictated primarily by genomic and possible non-genomic signaling, satellite cell activation, interaction with other anabolic signaling pathways, upregulation or downregulation of the androgen receptor, and potential roles in co-activators and transcriptional activity; (2) Differential influences of growth hormones depending on the "type" of the hormone being assayed and the magnitude of the physiological stress; (3) The exquisite regulation of IGF-1 by a family of binding proteins (IGFBPs 1-6), which can either stimulate or inhibit biological action depending on binding; and (4) Circadian patterning and newly discovered variants of glucocorticoid isoforms largely dictating glucocorticoid sensitivity and catabolic, muscle sparing, or pathological influence. The downstream integrated anabolic and catabolic mechanisms of these hormones not only affect the ability of skeletal muscle to generate force; they also have implications for pharmaceutical treatments, aging, and prevalent chronic conditions such as metabolic syndrome, insulin resistance, and hypertension. Thus, advances in our understanding of hormones that impact anabolic: catabolic processes have relevance for athletes and the general population, alike.

Disruptions to the limb muscle core molecular clock coincide with changes in mitochondrial quality control following androgen depletion

Androgen depletion in humans leads to significant atrophy of the limb muscles. However, the pathways by which androgens regulate limb muscle mass are unclear. Our laboratory previously showed that mitochondrial degradation was related to the induction of autophagy and the degree of muscle atrophy following androgen depletion, implying that decreased mitochondrial quality contributes to muscle atrophy. To increase our understanding of androgen-sensitive pathways regulating decreased mitochondrial quality, total RNA from the tibialis anterior of sham and castrated mice was subjected to microarray analysis. Using this unbiased approach, we identified significant changes in the expression of genes that compose the core molecular clock. To assess the extent to which androgen depletion altered the limb muscle clock, the tibialis anterior muscles from sham and castrated mice were harvested every 4 h throughout a diurnal cycle. The circadian expression patterns of various core clock genes and known clock-controlled genes were disrupted by castration, with most genes exhibiting an overall reduction in phase amplitude. Given that the core clock regulates mitochondrial quality, disruption of the clock coincided with changes in the expression of genes involved with mitochondrial quality control, suggesting a novel mechanism by which androgens may regulate mitochondrial quality. These events coincided with an overall increase in mitochondrial degradation in the muscle of castrated mice and an increase in markers of global autophagy-mediated protein breakdown. In all, these data are consistent with a novel conceptual model linking androgen depletion-induced limb muscle atrophy to reduced mitochondrial quality control via disruption of the molecular clock.

Androgens induce growth of the limb skeletal muscles in a rapamycin-insensitive manner

Signaling through the mechanistic target of rapamycin complex 1 (mTORC1) has been well defined as an androgen-sensitive transducer mediating skeletal muscle growth in vitro; however, this has yet to be tested in vivo. As such, male mice were subjected to either sham or castration surgery and allowed to recover for 7 wk to induce atrophy of skeletal muscle. Then, castrated mice were implanted with either a control pellet or a pellet that administered rapamycin (~2.5 mg·kg^-1·day^-1). Seven days postimplant, a subset of castrated mice with control pellets and all castrated mice with rapamycin pellets were given once weekly injections of nandrolone decanoate (ND) to induce muscle growth over a six-week period. Effective blockade of mTORC1 by rapamycin was noted in the skeletal muscle by the inability of insulin to induce phosphorylation of ribosomal S6 kinase 1 70 kDa (Thr389) and uncoordinated-like kinase 1 (Ser⁷⁵⁷). While castration reduced tibialis anterior (TA) mass, muscle fiber cross-sectional area, and total protein content, ND administration restored these measures to sham levels in a rapamycin-insensitive manner. Similar findings were also observed in the plantaris and soleus, suggesting this rapamycin-insensitive effect was not specific to the TA or fiber type. Androgen-mediated growth was not due to changes in translational capacity. Despite these findings in the limb skeletal muscle, rapamycin completely prevented the ND-mediated growth of the heart. In all, these data indicate that mTORC1 has a limited role in the androgen-mediated growth of the limb skeletal muscle; however, mTORC1 was necessary for androgen-mediated growth of heart muscle.

REDD1 induction regulates the skeletal muscle gene expression signature following acute aerobic exercise

The metabolic stress placed on skeletal muscle by aerobic exercise promotes acute and long-term health benefits in part through changes in gene expression. However, the transducers that mediate altered gene expression signatures have not been completely elucidated. Regulated in development and DNA damage 1 (REDD1) is a stress-induced protein whose expression is transiently increased in skeletal muscle following acute aerobic exercise. However, the role of this induction remains unclear. Because REDD1 altered gene expression in other model systems, we sought to determine whether REDD1 induction following acute exercise altered the gene expression signature in muscle. To do this, wild-type and REDD1-null mice were randomized to remain sedentary or undergo a bout of acute treadmill exercise. Exercised mice recovered for 1, 3, or 6 h before euthanization. Acute exercise induced a transient increase in REDD1 protein expression within the plantaris only at 1 h postexercise, and the induction occurred in both cytosolic and nuclear fractions. At this time point, global changes in gene expression were surveyed using microarray. REDD1 induction was required for the exercise-induced change in expression of 24 genes. Validation by RT-PCR confirmed that the exercise-mediated changes in genes related to exercise capacity, muscle protein metabolism, neuromuscular junction remodeling, and Metformin action were negated in REDD1-null mice. Finally, the exercise-mediated induction of REDD1 was partially dependent upon glucocorticoid receptor activation. In all, these data show that REDD1 induction regulates the exercise-mediated change in a distinct set of genes within skeletal muscle.

Endurance training lowers ribosome density despite increasing ribosome biogenesis markers in rodent skeletal muscle

Objective

The purpose of this study was to examine if: (a) high sugar/high fat Western diet (WD)-feeding affects skeletal muscle ribosome biogenesis markers in hyperphagic, diabetic-prone Otsuka Long-Evans Tokushima Fatty (OLETF) rats, and (b) 12 weeks of treadmill training rescued potential detriments that WD feeding exerted on these markers.

Methods

Eight week-old male OLETF rats were fed a low-fat control diet (O-CON, n = 10) or high/sucrose/cholesterol Western diet (WD). At weeks 20–32 of age, WD-fed rats were divided into WD sedentary (O-WD/SED, n = 16), or WD treadmill trained (5 days/week, 60 min/day) (O-WD/EX, n = 10) conditions.

Results

Interestingly, total RNA (i.e., ribosome density) was 2.3-fold greater in O-WD/SED versus O-WD/EX rats (p = 0.003) despite levels of upstream binding factor protein, RNA polymerase I protein and pre-45S rRNA being greater in O-WD/EX rats. Ribophagy (USP10 and G3BP1) and TRAMP-exosome rRNA degradation pathway (EXOSC10 and SKIV2L2) proteins were assayed to determine if these pathways were involved with lower ribosome density in O-WD/EX rats. While USP10 was higher in O-CON versus O-WD/SED and O-WD/EX rats (p < 0.001 and p < 0.001, respectively), G3BP1, EXOSC10 and SKIV2L2 did not differ between groups. Nop56 and Ncl mRNAs, ribosome assembly markers, were highest in O-WD/EX rats. However, Fbl mRNA and 28S rRNA, downstream ribosome processing markers, were lowest in O-WD/EX rats. Collectively these data suggest that, in WD-fed rats, endurance training increases select skeletal muscle ribosome biogenesis markers. However, endurance training may reduce muscle ribosome density by interfering with rRNA processing and/or export through mechanisms independent of ribophagy or rRNA degradation.

Aging in Rats Differentially Affects Markers of Transcriptional and Translational Capacity in Soleus and Plantaris Muscle

Alterations in transcriptional and translational mechanisms occur during skeletal muscle aging and such changes may contribute to age-related atrophy. Herein, we examined markers related to global transcriptional output (i.e., myonuclear number, total mRNA and RNA pol II levels), translational efficiency [i.e., eukaryotic initiation and elongation factor levels and muscle protein synthesis (MPS) levels] and translational capacity (ribosome density) in the slow-twitch soleus and fast-twitch plantaris muscles of male Fischer 344 rats aged 3, 6, 12, 18, and 24 months (n = 9-10 per group). We also examined alterations in markers of proteolysis and oxidative stress in these muscles (i.e., 20S proteasome activity, poly-ubiquinated protein levels and 4-HNE levels). Notable plantaris muscle observations included: (a) fiber cross sectional area (CSA) was 59% (p < 0.05) and 48% (p < 0.05) greater in 12 month vs. 3 month and 24 month rats, respectively, suggesting a peak lifetime value near 12 months and age-related atrophy by 24 months, (b) MPS levels were greatest in 18 month rats (p < 0.05) despite the onset of atrophy, (c) while regulators of ribosome biogenesis [c-Myc and upstream binding factor (UBF) protein levels] generally increased with age, ribosome density linearly decreased from 3 months of age and RNA polymerase (Pol) I protein levels were lowest in 24 month rats, and d) 20S proteasome activity was robustly up-regulated in 6 and 24 month rats (p < 0.05). Notable soleus muscle observations included: (a) fiber CSA was greatest in 6 month rats and was maintained in older age groups, and (b) 20S proteasome activity was modestly but significantly greater in 24 month vs. 3/12/18 month rats (p < 0.05), and (c) total mRNA levels (suggestive of transcriptional output) trended downward in older rats despite non-significant between-group differences in myonuclear number and/or RNA Pol II protein levels. Collectively, these findings suggest that plantaris, not soleus, atrophy occurs following 12 months of age in male Fisher rats and this may be due to translational deficits (i.e., changes in MPS and ribosome density) and/or increases in proteolysis rather than increased oxidative stress and/or alterations in global transcriptional mechanisms.

The role of androgens in the regulation of muscle oxidative capacity following aerobic exercise training

Reduced production or bioavailability of androgens, termed hypogonadism, occurs in a variety of pathological conditions. While androgens target numerous tissues throughout the body, hypogonadism specifically reduces the ability of skeletal muscle to produce adenosine triphosphate aerobically, i.e., muscle oxidative capacity. This has important implications for overall health as muscle oxidative capacity impacts a number of metabolic processes. Although androgen replacement therapy is effective at restoring muscle oxidative capacity in hypogonadal individuals, this is not a viable therapeutic option for all who are experiencing hypogonadism. While aerobic exercise may be a viable alternative to increase muscle oxidative capacity, it is unknown whether androgen depletion affects this adaptation. To determine this, sham and castrated mice were randomized to remain sedentary or undergo 8 weeks of aerobic treadmill exercise training. All mice were fasted overnight prior to sacrifice. Though exercise increased markers of muscle oxidative capacity independent of castration (cytochrome c oxidase subunit IV and cytochrome c), these measures were lower in castrated mice. This reduction was not due to a difference in peroxisome proliferator activated receptor gamma coactivator 1 alpha protein content, as expression was increased to a similar absolute value in sham and castrated animals following exercise training. However, markers of BCL2/Adenovirus E1B 19 kDa Interacting Protein 3 (BNIP3)-mediated mitophagy were increased by castration independent of exercise. Together, these data show that exercise training can increase markers of muscle oxidative capacity following androgen depletion. However, these values are reduced by androgen depletion likely due in part to elevated BNIP3-mediated mitophagy.

Androgen-mediated regulation of skeletal muscle protein balance

Androgens significantly alter muscle mass in part by shifting protein balance in favor of net protein accretion. During various atrophic conditions, the clinical impact of decreased production or bioavailability of androgens (termed hypogonadism) is important as a loss of muscle mass is intimately linked with survival outcome. While androgen replacement therapy increases muscle mass in part by restoring protein balance, this is not a comprehensive treatment option due to potential side effects. Therefore, an understanding of the mechanisms by which androgens alter protein balance is needed for the development of androgen-independent therapies. While the data in humans suggest androgens alter protein balance (both synthesis and breakdown) in the fasted metabolic state, a predominant molecular mechanism(s) behind this observation is still lacking. This failure is likely due in part to inconsistent experimental design between studies including failure to control nutrient/feeding status, the method of altering androgens, and the model systems utilized.

Testosterone inhibits expression of lipogenic genes in visceral fat by an estrogen-dependent mechanism

The influence of the aromatase enzyme on the chronic fat-sparing effects of testosterone requires further elucidation. Our purpose was to determine whether chronic anastrozole (AN, an aromatase inhibitor) treatment alters testosterone-mediated lipolytic/lipogenic gene expression in visceral fat. Ten-month-old Fischer 344 rats (n = 6/group) were subjected to sham surgery (SHAM), orchiectomy (ORX), ORX + treatment with testosterone enanthate (TEST, 7.0 mg/wk), or ORX + TEST + AN (0.5 mg/day), with drug treatment beginning 14 days postsurgery. At day 42, ORX animals exhibited nearly undetectable serum testosterone and 29% higher retroperitoneal fat mass than SHAM animals (P < 0.001). TEST produced a ∼380-415% higher serum testosterone than SHAM (P < 0.001) and completely prevented ORX-induced visceral fat gain (P < 0.001). Retroperitoneal fat was 21% and 16% lower in ORX + TEST than SHAM (P < 0.001) and ORX + TEST + AN (P = 0.007) animals, while serum estradiol (E₂) was 62% (P = 0.024) and 87% (P = 0.010) higher, respectively. ORX stimulated lipogenic-related gene expression in visceral fat, demonstrated by ∼84-154% higher sterol regulatory element-binding protein-1 (SREBP-1, P = 0.023), fatty acid synthase (P = 0.01), and LPL (P < 0.001) mRNA than SHAM animals, effects that were completely prevented in ORX + TEST animals (P < 0.01 vs. ORX for all). Fatty acid synthase (P = 0.061, trend) and LPL (P = 0.043) mRNA levels were lower in ORX + TEST + AN than ORX animals and not different from SHAM animals but remained higher than in ORX + TEST animals (P < 0.05). In contrast, the ORX-induced elevation in SREBP-1 mRNA was not prevented by TEST + AN, with SREBP-1 expression remaining ∼117-171% higher than in SHAM and ORX + TEST animals (P < 0.01). Across groups, visceral fat mass and lipogenic-related gene expression were negatively associated with serum testosterone, but not E₂ Aromatase inhibition constrains testosterone-induced visceral fat loss and the downregulation of key lipogenic genes at the mRNA level, indicating that E₂ influences the visceral fat-sparing effects of testosterone.