Voluntary running, skeletal muscle gene expression, and signaling inversely regulated by orchidectomy and testosterone replacement

Musculoskeletal and body composition response to high-dose testosterone with finasteride after chronic incomplete spinal cord injury-a randomized, double-blind, and placebo-controlled pilot study

Background

High-dose testosterone replacement therapy (TRT), paired with finasteride (type II 5α-reductase inhibitor), improves body composition, muscle strength, and bone mineral density (BMD) in older men, without inducing prostate enlargement-a side effect associated with TRT. Men with spinal cord injury (SCI) exhibit neuromuscular impairment, muscle atrophy, bone loss, and increased central adiposity, along with low testosterone. However, sparse evidence supports TRT efficacy after SCI.

Methods

This parallel-group, double-blind, placebo-controlled, and randomized clinical trial (RCT) is a pilot study that enrolled men (N = 12) with low to low-normal testosterone and gait impairments after chronic motor-incomplete SCI. Participants received high-dose intramuscular TRT (testosterone-enanthate, 125 mg/week) with finasteride (5 mg/day) vs. vehicle+placebo for 12 months. Change relative to baseline was determined for body composition, musculoskeletal outcomes, and prostate size, with effect sizes calculated between groups using Hedges' g. Adverse events and feasibility were assessed.

Results

TRT + finasteride consistently increased testosterone (g = 1.16-3.08) and estradiol (g = 0.43-3.48), while concomitantly reducing dihydrotestosterone (g = 0.31-2.27). Very large effect sizes at both 6 and 12 months suggest TRT + finasteride increased whole-body fat-free (lean) mass (+3-4% vs. baseline, g = 2.12-2.14) and knee extensor (KE) whole-muscle cross-sectional area (+8-11% vs. baseline, g = 2.06-2.53) more than vehicle+placebo. Moderate-to-large effect sizes suggest TRT + finasteride increased KE maximal voluntary isometric torque (+15-40% vs. baseline, g = 0.47-1.01) and femoral neck and distal femur BMD from 6 months onward (g = 0.51-1.13), compared with vehicle+placebo, and reduced fat mass 9-14% within the whole-body, trunk, and android (visceral) regions at 12 months (g = 0.77-1.27). TRT + finasteride also produced small effect sizes favoring lesser prostate growth than vehicle+placebo (g = 0.31-0.43). The participant retention, drug compliance, and incidence and severity of adverse events were similar among the groups.

Conclusion

These data provide proof-of-concept and rationale for larger RCTs aimed at discerning the impact of TRT + finasteride on body composition, musculoskeletal health, and physical function in men with SCI, along with effect sizes and variance of responses to assist in planning subsequent trials.

Clinical trial registration

ClinicalTrials.gov, identifier NCT02248701.

Sex and timing of gonadectomy relative to puberty interact to influence weight, body composition, and feeding behaviors in mice

Gonadal sex steroids are important regulators of energy balance in adult rodents, and gonadectomy (GDX) has opposing effects on weight gain in sexually mature males and females. Puberty is associated with the emergence of sex differences in weight, body composition, and feeding behaviors, yet the role of gonadal hormones at puberty remains unclear. To address this, we performed GDX or sham surgery in male and female C57Bl/6 mice at postnatal day (P)25 (prepubertal) or P60 (postpubertal) timepoints and measured weight and body composition for 35 days, after which ad libitum and operant food intake was measured using Feeding Experimentation Device 3 (FED3s) in the home cage. Consistent with previous studies, postpubertal GDX caused weight gain in females and weight loss in males and increased adiposity in both sexes. However, prepubertal GDX decreased weight gain and altered body composition across the adolescent transition (P25 to P60) in males but had no effect in females. Despite the varied effects on weight, GDX decreased food intake and motivation for food as assessed in operant tasks regardless of sex or timing of surgery relative to puberty. Our findings indicate that GDX interacts with both sex and age at surgery to influence weight, body composition, and feeding behavior.

Androgen and androgen receptor control of mitochondrial function

The effects of androgens have been extensively studied in a variety of organs and cell types with increasing focus on the sexually dimorphic role androgens play not only with respect to cellular functions but also in metabolism. Although the classical mechanism of androgen action is via ligand-dependent binding with the nuclear transcription factor, androgen receptor (AR), cytosolic AR can also activate second messenger signaling pathways. Given that cytosolic AR can signal in this manner, there has been increased interest in the mechanisms by which androgens may control cellular organelle function. This review highlights the effects that androgens have on mitochondrial structure and function with emphasis on biogenesis, fusion/fission, mitophagy, bioenergetics (oxidative phosphorylation), and reactive oxygen species production. There are a number of publications on the effects of androgens in these general areas of mitochondrial function. However, the precise mechanisms by which androgens cause these effects are not known. Additionally, given that the nucleus and mitochondria work in tandem to control mitochondrial function and the mitochondria has its own DNA, future research efforts should focus on the direct, mechanistic effects of androgens on mitochondrial function.

Cholesteryl Ester Transfer Protein Impairs Triglyceride Clearance via Androgen Receptor in Male Mice

Elevated postprandial triacylglycerols (TAG) are an important risk factor for cardiovascular disease. Men have higher plasma TAG and impaired TAG clearance compared to women, which may contribute to sex differences in risk of cardiovascular disease. Understanding mechanisms of sex differences in TAG metabolism may yield novel therapeutic targets to prevent cardiovascular disease. Cholesteryl ester transfer protein (CETP) is a lipid shuttling protein known for its effects on high-density lipoprotein (HDL) cholesterol levels. Although mice lack CETP, we previously demonstrated that transgenic CETP expression in female mice alters TAG metabolism. The impact of CETP on TAG metabolism in males, however, is not well understood. Here, we demonstrate that CETP expression increases plasma TAG in males, especially in very-low density lipoprotein (VLDL), by impairing postprandial plasma TAG clearance compared to wild-type (WT) males. Gonadal hormones were required for CETP to impair TAG clearance, suggesting a role for sex hormones for this effect. Testosterone replacement in the setting of gonadectomy was sufficient to restore the effect of CETP on TAG. Lastly, liver androgen receptor (AR) was required for CETP to increase plasma TAG. Thus, expression of CETP in males raises plasma TAG by impairing TAG clearance via testosterone signaling to AR. Further understanding of how CETP and androgen signaling impair TAG clearance may lead to novel approaches to reduce TAG and mitigate risk of cardiovascular disease.

Effect of Periodized Resistance Training on Skeletal Muscle During Androgen Deprivation Therapy for Prostate Cancer: A Pilot Randomized Trial

PURPOSE

Prostate cancer survivors (PCS) receive androgen deprivation therapy (ADT) as treatment for recurrent cancer, yet ADT is associated with loss of skeletal muscle and physical function. Resistance training can counter both muscle and physical function loss; however, an understanding of the molecular responses of skeletal muscle to resistance training during ADT is still undefined. This sub-analysis of the original randomized, controlled pilot trial investigated effects of 12 weeks of periodized resistance training on mRNA expression of the anabolic genes IGF-1, myogenin, PGC-1α4 and the catabolic genes myostatin and MuRF-1 in skeletal muscle of PCS on ADT. Secondary aims investigated if changes in lean mass and physical function correlated with changes in mRNA expression.

METHODS

PCS on ADT (n = 17) were randomized to 12 weeks of supervised resistance training (EXE, n = 9) or home-based stretching (STRETCH, n = 8) 3 days per week. Outcomes were assessed at baseline and post-intervention. Muscle biopsies were analyzed by RT-PCR for mRNA expression. Body composition was assessed through dual-energy X-ray absorptiometry, and physical function through muscular strength, timed up and go, stair climb, and 400 m walk.

RESULTS

MuRF-1 mRNA expression was significantly greater in EXE compared to STRETCH post-intervention (P = .005). Change in MuRF-1 mRNA expression significantly correlated with improvements in strength and physical function (P < .05), while change in IGF-1 expression correlated with change in lean mass (P = .015).

CONCLUSION

Twelve weeks of resistance training increased mRNA expression of MuRF-1 in skeletal muscle of PCS on ADT. Elevations in resting mRNA expression of IGF-1, myogenin and PGC-1α4, and reduction in mRNA expression of myostatin that are typically expected following resistance training were not observed.

Vascular dysfunction as a potential culprit of sarcopenia

Aging-related changes to biological structures such as cardiovascular and musculoskeletal systems contribute to the development of comorbid conditions including cardiovascular disease and frailty, and ultimately lead to premature death. Although, frail older adults often demonstrate both cardiovascular and musculoskeletal comorbidities, the etiology of sarcopenia, and especially the contribution of cardiovascular aging is unclear. Aging-related vascular calcification is prevalent in older adults and is a known risk factor for cardiovascular disease and death. The effect vascular calcification has on function during aging is not well understood. Emerging findings suggest vascular calcification can impact skeletal muscle perfusion, negatively affecting nutrient and oxygen delivery to skeletal muscle, ultimately accelerating muscle loss and functional decline. The present review summarizes existing evidence on the biological mechanisms linking vascular calcification with sarcopenia during aging.

Effect of long-term testosterone therapy on molecular regulators of skeletal muscle mass and fibre-type distribution in aging men with subnormal testosterone

BACKGROUND

Long-term testosterone replacement therapy (TRT) increases muscle mass in elderly men with subnormal testosterone levels. However, the molecular mechanisms underlying this effect of TRT on protein balance in human skeletal muscle in vivo remain to be established.

METHODS

Here, we examined skeletal muscle biopsies obtained before and 24-h after the last dose of treatment with either testosterone gel (n = 12) or placebo (n = 13) for 6 months in aging men with subnormal bioavailable testosterone levels. The placebo-controlled, testosterone-induced changes (β-coefficients) in mRNA levels, protein expression and phosphorylation were examined by quantitative real-time PCR and western blotting.

RESULTS

Long-term TRT increased muscle mass by β = 1.6 kg (p = 0.01) but had no significant effect on mRNA levels of genes involved in myostatin/activin/SMAD or IGF1/FOXO3 signalling, muscle-specific E3-ubiquitin ligases, upstream transcription factors (MEF2C, PPARGC1A-4) or myogenic factors. However, TRT caused a sustained decrease in protein expression of SMAD2 (β = -36%, p = 0.004) and SMAD3 (β = -32%, p = 0.001), which was accompanied by reduced protein expression of the muscle-specific E3-ubiquitin ligases, MuRF1 (β = -26%, p = 0.004) and Atrogin-1/MAFbx (β = -20%, p = 0.04), but with no changes in FOXO3 signalling. Importantly, TRT did not affect muscle fibre type distribution between slow-oxidative (type 1), fast-oxidative (type 2a) and fast-glycolytic (type 2×) muscle fibres.

CONCLUSIONS

Our results indicate that long-term TRT of elderly men with subnormal testosterone levels increases muscle mass, at least in part, by decreasing protein breakdown through the ubiquitin proteasome pathway mediated by a sustained suppression of SMAD-signalling and muscle-specific E3-ubiquitin ligases.

Long-Term Effects of Fatherhood on Morphology, Energetics, and Exercise Performance in California Mice (Peromyscus californicus)

In male mammals that provide care for their offspring, fatherhood can lead to changes in behavioral, morphological, and physiological traits, some of which might constitute trade-offs. However, relatively little is known about these changes, especially across multiple reproductive bouts, which are expected to magnify differences between fathers and nonreproductive males. We evaluated consequences of fatherhood in the monogamous, biparental California mouse (Peromsycus californicus) across seven consecutive reproductive bouts. We compared breeding adult males (housed with sham-ovariectomized females) with two control groups: nonbreeding males (housed with ovariectomized females treated with estrogen and progesterone to induce estrous behavior) and virgin males (housed with untreated ovariectomized females). At five time points (before pairing, early postpartum of the first litter, late postpartum of the second litter, early postpartum of the sixth litter, and late postpartum of the seventh litter or comparable time points for nonbreeding and virgin males), we measured males' body composition, hematocrit, predatory aggression, resting metabolic rate, maximal oxygen consumption (V˙O2 max⁡), grip strength, and sprint speed. We also weighed organs at the final time point. We predicted that fathers would have lower relative body fat and lower performance abilities compared with control groups and that these effects would become more pronounced with increasing parity. Contrary to predictions, breeding and control males differed in surprisingly few measures, and the number and magnitude of differences did not increase with parity. Thus, our expectations regarding trade-offs were not met. As reported in studies of single reproductive events, these results suggest that fatherhood has few costs in this species when housed under standard laboratory conditions, even across multiple reproductive bouts.

Interplay between hormones and exercise on hippocampal plasticity across the lifespan

The hippocampus is a brain structure known to play a central role in cognitive function (namely learning and memory) as well as mood regulation and affective behaviors due in part to its ability to undergo structural and functional changes in response to intrinsic and extrinsic stimuli. While structural changes are achieved through modulation of hippocampal neurogenesis as well as alterations in dendritic morphology and spine remodeling, functional (i.e., synaptic) changes can be noted through the strengthening (i.e., long-term potentiation) or weakening (i.e., long-term depression) of the synapses. While age, hormone homeostasis, and levels of physical activity are some of the factors known to module these forms of hippocampal plasticity, the exact mechanisms through which these factors interact with each other at a given moment in time are not completely understood. It is well known that hormonal levels vary throughout the lifespan of an individual and it is also known that physical exercise can impact hormonal homeostasis. Thus, it is reasonable to speculate that hormone modulation might be one of the various mechanisms through which physical exercise differently impacts hippocampal plasticity throughout distinct periods of an individual's life. The present review summarizes the potential relationship between physical exercise and different types of hormones (namely sex, metabolic, and stress hormones) and how this relationship may mediate the effects of physical activity during three distinct life periods, adolescence, adulthood, and senescence. Overall, the vast majority of studies support a beneficial role of exercise in maintaining hippocampal hormonal levels and consequently, hippocampal plasticity, cognition, and mood regulation.

Testosterone suppression does not exacerbate disuse atrophy and impairs muscle recovery that is not rescued by high protein

Androgen deprivation therapy (ADT) decreases muscle mass, force, and physical activity levels, but it is unclear whether disuse atrophy and testosterone suppression are additive. Additionally, conflicting reports exist on load-mediated hypertrophy during ADT and if protein supplementation offsets these deficits. This study sought to determine the role of testosterone suppression and a high-protein diet on 1) immobilization-induced atrophy and 2) muscle regrowth during reloading. Eight-week-old male Fischer 344 rats underwent sham surgery (Sham), castration surgery (ORX), or ORX and a high-casein diet supplemented with branched-chain amino acids (BCAA) (ORX+CAS/AA) followed by 10 days of unilateral immobilization (IMM) and 0, 6, or 14 days of reloading. With IMM, body mass gains were ~8% greater than ORX and ORX+CAS/AA that increased to 15% during reloading (both P < 0.01). IMM reduced muscle mass by 11-34% (all P < 0.01) and extensor digitorum longus and soleus (SOL) force by 21% and 49% (both P < 0.01), respectively, with no group differences. During reloading, castration reduced gastrocnemius mass (~12%) at 6 days and SOL mass (~20%) and SOL force recovery (~46%) at 14 days relative to Sham (all P < 0.05). Specific force reduced castration deficits, indicating that muscle atrophy was a key contributor. IMM decreased SOL cross-sectional area by 30.3% (P < 0.001), with a trend for reduced regrowth in ORX and ORX+CAS/AA following reloading (P = 0.083). Castration did not exacerbate disuse atrophy but may impair recovery of muscle function, with no benefit from a CAS/AA diet during reloading. Examining functional outcomes in addition to muscle mass during dietary interventions provides novel insights into muscle regrowth during ADT.NEW & NOTEWORTHY Low testosterone levels during skeletal muscle disuse did not worsen declines in muscle mass and function, although hypogonadism may attenuate recovery during subsequent reloading. Diets high in casein did not improve outcomes during immobilization or reloading. Practical strategies are needed that do not compromise caloric intake yet provide effective protein doses to augment these adverse effects.

Effect of voluntary exercise on intracellular signalling pathways of angiogenesis in the sciatic nerve of type 1 diabetic castrated male rats

Objectives

Impaired angiogenesis in sciatic nerve is a major complication of diabetic neuropathy. Protein kinase B (AKT) and extracellular signal regulated kinase (ERK) signaling pathways play critical roles during capillary-like network formation in the angiogenesis process.

Methods

Twenty-four adult male Wistar rats (weight: 250–300 g) were used in the research. The rats were randomly divided into four groups (n = 6): (1) diabetic (Dia), (2) diabetic + castration (Dia-Cas), (3) diabetic + exercise (Dia-E), and (4) diabetic + castration + exercise (Dia-Cas-E). Type 1 diabetes (T1D) was induced with streptozotocin (50 mg/kg). After 6 weeks, sciatic nerve was separated and used for histological evaluation and determination of phosphorylated AKT (P-AKT) and phosphorylated ERK (P-ERK) levels by ELISA method.

Results

Glucose levels decreased in the Dia-E group compared to the Dia-Cas group (p < 0.01). In addition, our finding shows that exercise in the Dia-Cas group diminished blood glucose levels compared to the Dia-Cas group but this effect of exercise was not significant. Voluntary exercise in the diabetic castrated group decreased P-AKT protein and increased P-ERK 1/2 protein levels in the sciatic tissue compared to the diabetes group significantly (p < 0.05). Histopathological findings showed that Dia-Cas group with 6-week exercise training significantly raised the number of microvascular density in the sciatic tissue of diabetic rats compared to the diabetic group (p < 0.05).

Conclusions

Voluntary exercise in diabetic rats increases angiogenesis in the sciatic nerve. The possible mechanism is the increase of P-ERK 1/2 but not P-AKT levels in the sciatic nerve of T1D rats.

Alteration of Testosterone Levels Changes Brain Wave Activity Patterns and Induces Aggressive Behavior in Rats

Testosterone is responsible for several changes in the brain, including behavioral and emotional responses, memory, and cognition. Given this, we investigated changes in the brain wave profile caused by supplementation with exogenous testosterone in both castrated and non-castrated rats. We also investigated the serum testosterone levels, renal and hepatic function, and the lipid and behavioral profiles. We found changes in the spectral wave power in both groups (castrated and non-castrated animals) supplemented with exogenous testosterone, consistent with an aggressive/hostile profile. These changes were observed in the electrocorticographic evaluation associated with increased power in low-frequency (delta and theta) and high-frequency (beta and gamma) activity in the supplemented animals. The castrated animals presented a significant decrease of wave power in the alpha frequency. This correlated with a decrease of the performance of the animals in the elevated plus-maze evaluation, given that the alpha wave is linked to the execution and visualization of motor processes. In the behavioral evaluation, the castrated animals presented a reduced permanence time in the elevated-plus maze, although this was prevented by the supplementation of testosterone. Testosterone supplementation induced aggressive behavior in non-castrated animals, but not in castrated ones. Supplemented animals had significantly elevated serum testosterone levels, while their urea levels were significantly lower, but without clinical significance. Our data indicate that testosterone supplementation in non-castrated rats, but not in castrated ones, causes electrocorticographic changes that could be associated with more aggressive and hostile behavior, in addition to indicating a potential for personality disorder. However, further studies are required to elucidate the cellular and molecular changes caused by acute testosterone supplementation.

Sex Differences in Autophagy Contribute to Female Vulnerability in Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia, with over 5. 4 million cases in the US alone (Alzheimer's Association, 2016). Clinically, AD is defined by the presence of plaques composed of Aβ and neurofibrillary pathology composed of the microtubule associated protein tau. Another key feature is the dysregulation of autophagy at key steps in the pathway. In AD, disrupted autophagy contributes to disease progression through the failure to clear pathological protein aggregates, insulin resistance, and its role in the synthesis of Aβ. Like many psychiatric and neurodegenerative diseases, the risk of developing AD, and disease course are dependent on the sex of the patient. One potential mechanism through which these differences occur, is the effects of sex hormones on autophagy. In women, the loss of hormones with menopause presents both a risk factor for developing AD, and an obvious example of where sex differences in AD can stem from. However, because AD pathology can begin decades before menopause, this does not provide the full answer. We propose that sex-based differences in autophagy regulation during the lifespan contribute to the increased risk of AD, and greater severity of pathology seen in women.

Effects of varying doses of estrogen and caudal pressure on wheel running in orchidectomized male mice

Physical inactivity is a leading cause of hypokinetic diseases - obesity, heart disease, diabetes, and certain types of cancers. Increased city walkability, better access to fitness facilities, and remediation of socioeconomic barriers prove successful for limited populations within the confines of stringently controlled environments; however, these strategies fail to reverse the ever-increasing physical inactivity epidemic on a global scale indicating the existence of other unidentified factors. These purported biological factors remain critical targets to understand the regulation of this complex phenotype. An estrogenic mechanism that incompletely or slowly adjusts physical activity levels following reintroduction of estrogenic compounds to surgically gonadectomized mice has been postulated to exist. Currently, this mechanism remains scrutinized due to concerns that elevated estrogen levels induce urinary bladder distension. The distension of the urinary bladder may mechanically disrupt physical activity, masking any physiological effects estrogen has on physical activity. The purpose of this study was to evaluate the effects of estrogen on physical activity levels while employing dose-related strategies to alleviate distension in mice. Wheel running data were collected under normal physiological conditions, following removal of endogenous sex steroids via orchidectomy, and during estrogen replacement at various doses (0%, 10%, 50% or 100% estrogen-containing implants) to induce varying degrees of urinary bladder distension. Wheel running distance (P = 0.005) and duration (P = 0.006) decreased after orchidectomy, but slowly increased following estrogen replacement. During the study, wheel running did not return to the levels observed in physiologically intact mice. Significant distension was not observed between estrogen treatment groups indicating that a slow-responding estrogen effect exists in male mice that prevents wheel running from returning to normal levels immediately following steroid reintroduction. The limited increase in wheel running during estrogen treatment following orchidectomy is not an artifact of induced urinary bladder distension.

Prolonged Effects of Elevated 17β-Estradiol on Physical Activity after Orchidectomy

The biological mechanisms regulating physical activity patterns appear to be linked to the sex hormones. Elucidation of these regulatory mechanisms may enhance individual physical activity patterns producing positive gains in health.

PURPOSE

The purpose of this study was to evaluate the prolonged effects of estrogen on wheel running distance, duration, and speed in orchidectomized mice.

METHODS

The physical activity patterns of 9-wk-old C57BL/6j male mice (n = 28) were observed. Wheel running distance, duration, and speed were assessed under physiological conditions for 7 d. Next, physical activity patterns were evaluated after bilateral orchidectomy (n = 14) or sham orchidectomy (n = 14) for an additional 7 d. Orchidectomized mice were provided estrogen containing capsules for three additional weeks; control mice were provided estrogen-free capsules. Wheel running distance, duration, and speed were analyzed by three two-way (treatment group-phase of study) analysis of variance tests.

RESULTS

Wheel running speed was unaffected by sex hormone status. Distance (mean ± SD = 6.74 ± 2.13 km at baseline) decreased significantly after orchidectomy (2.27 ± 1.55 km) and remained low after initial estrogen treatment (3.04 ± 1.05 km). Prolonged estrogen exposure sustained a significant elevation of daily distance (4.47 ± 1.87 km). Prolonged estrogen exposure recovered and significantly sustained wheel running duration (baseline, 248 ± 60 min; postorchidectomy, 102 ± 53 min; prolonged exposure, 170 ± 63 min).

CONCLUSIONS

Wheel running behavior was reduced significantly after orchidectomy and remained low after initial treatment with estrogens, but recovered to near control levels after 2 wk of exposure to estrogens. The estrogenic mechanism regulating wheel running behavior in male mice appears to induce an extensive but slow acting biological mechanism. Understanding the biological drive behind this mechanism may aid in developing useful therapeutic strategies to combat health issues related to physical inactivity.

Axonal transport in a peripheral diabetic neuropathy model: sex-dimorphic features

Background

Disruption of axonal transport plays a pivotal role in diabetic neuropathy. A sex-dimorphism exists in the incidence and symptomatology of diabetic neuropathy; however, no studies so far have addressed sex differences in axonal motor proteins expression in early diabetes as well as the possible involvement of neuroactive steroids. Interestingly, recent data point to a role for mitochondria in the sexual dimorphism of neurodegenerative diseases. Mitochondria have a fundamental role in axonal transport by producing the motors’ energy source, ATP. Moreover, neuroactive steroids can also regulate mitochondrial function.

Methods

Here, we investigated the impact of short-term diabetes in the peripheral nervous system of male and female rats on key motor proteins important for axonal transport, mitochondrial function, and neuroactive steroids levels.

Results

We show that short-term diabetes alters mRNA levels and axoplasm protein contents of kinesin family member KIF1A, KIF5B, KIF5A and Myosin Va in male but not in female rats. Similarly, the expression of peroxisome proliferator-activated receptor γ co-activator-1α, a subunit of the respiratory chain complex IV, ATP levels and the key regulators of mitochondrial dynamics were affected in males but not in females. Concomitant analysis of neuroactive steroid levels in sciatic nerve showed an alteration of testosterone, dihydrotestosterone, and allopregnanolone in diabetic males, whereas no changes were observed in female rats.

Conclusions

These findings suggest that sex-specific decrease in neuroactive steroid levels in male diabetic animals may cause an alteration in their mitochondrial function that in turn might impact in axonal transport, contributing to the sex difference observed in diabetic neuropathy.

Testosterone boosts physical activity in male mice via dopaminergic pathways

Low testosterone (T) in men, especially its free fraction, has been associated with loss of energy. In accordance, orchidectomy (ORX) in rodents results in decreased physical activity. Still, the mechanisms through which T stimulates activity remain mostly obscure. Here, we studied voluntary wheel running behavior in three different mouse models of androgen deficiency: ORX, androgen receptor (AR) knock-out (ARKO) and sex hormone binding globulin (SHBG)-transgenic mice, a novel mouse model of “low free T”. Our results clearly show a fast and dramatic action of T stimulating wheel running, which is not explained by its action on muscle, as evidenced by neuromuscular studies and in a muscle-specific conditional ARKO mouse model. The action of T occurs via its free fraction, as shown by the results in SHBG-transgenic mice, and it implies both androgenic and estrogenic pathways. Both gene expression and functional studies indicate that T modulates the in vivo sensitivity to dopamine (DA) agonists. Furthermore, the restoration of wheel running by T is inhibited by treatment with DA antagonists. These findings reveal that the free fraction of T, both via AR and indirectly through aromatization into estrogens, stimulates physical activity behavior in male mice by acting on central DA pathways.

Amelioration of sexual behavior and motor activity deficits in a castrated rodent model with a selective androgen receptor modulator SARM-2f

Sarcopenia and cachexia present characteristic features of a decrease in skeletal muscle mass and strength, anorexia, and lack of motivation. Treatments for these diseases have not yet been established, although selective androgen receptor modulators (SARMs) are considered as therapeutic targets. We previously reported that a novel SARM compound, SARM-2f, exhibits anabolic effect on muscles, with less stimulatory effect on prostate weight compared with testosterone, in rat Hershberger assays and cancer cachexia models. In this study, we studied the mechanism of action for SARM-2f selectivity and also assessed whether the muscle increase by this compound might lead to improvement of muscle function and physical activity. First, we examined the tissue distribution of SARM-2f. Tissue concentration was 1.2-, 1.6-, and 1.9-fold as high as the plasma concentration in the levator ani muscle, brain, and prostate, respectively. This result showed that the tissue-selective pharmacological effect did not depend on SARM-2f concentration in the tissues. The ability of SARM-2f to influence androgen receptor (AR)-mediated transcriptional activation was examined by reporter assays using human normal prostate epithelial cells (PrEC) and skeletal muscle cells (SKMC). SARM-2f exerted higher activity against AR in SKMC than in PrEC. Mammalian two hybrid assays showed different co-factor recruitment patterns between SARM-2f and dihydrotestosterone. Next, we studied the effect of SARM-2f on motivation and physical functions such as sexual behavior and motor activities in castrated rat or mouse models. SARM-2f restored the sexual behavior that was lost by castration in male rats. SARM-2f also increased voluntary running distance and locomotor activities. These results suggest that tissue-specific AR regulation by SARM-2f, but not tissue distribution, might account for its tissue specific androgenic effect, and that the muscle mass increase by SARM-2f leads to improvement of physical function. Together, these findings suggest that SARM-2f might represent an effective treatment for sarcopenia and cachexia.

Androgen interacts with exercise through the mTOR pathway to induce skeletal muscle hypertrophy

This study was designed to investigate the effects of exogenous androgen and resistance exercise on skeletal muscle hypertrophy and the role of the mammalian target of rapamycin (mTOR) signalling during the process. A total of 24 male Sprague-Dawley rats were randomly assigned to sham operation and dihydrotestosterone (DHT) implantation groups with subgroups subjected to sedentary conditions or resistance exercise (SHAM+SED, SHAM+EX, DHT+SED, and DHT+EX). The experimental procedure lasted for 10 days. The mRNA expression of androgen receptor (AR) and insulin-like growth factor I (IGF-I), the expression of myosin heavy chain (MHC), as well as the phosphorylation statuses of AR, mTOR, p70 ribosomal S6 kinase (p70S6K), and eukaryotic translation initiation factor 4E-binding protein 1 (4EBP1) were determined in the white gastrocnemius muscle. The cross sectional area and wet mass of the muscle were also measured. The cross sectional area and MHC expression were significantly higher in SHAM+EX, DHT+SED, and DHT+EX than in SHAM+SED. There was no significant difference among groups in muscle mass. The mRNA expression of AR and IGF-I and the phosphorylation of mTOR, p70S6K, and 4EBP1 were significantly increased in DHT+SED and SHAM+EX and were significantly enhanced in DHT+EX compared with either DHT or exercise alone. These data show that DHT causes hypertrophy in skeletal muscle and that exercise has a synergistic effect on DHT-induced hypertrophy. Exercise enhances androgen-induced rapid anabolic action, which involves activation of the mTOR pathway.

Actin alpha cardiac muscle 1 gene expression is upregulated in the skeletal muscle of men undergoing androgen deprivation therapy for prostate cancer

Androgen deprivation therapy (ADT) decreases muscle mass and function but no human studies have investigated the underlying genetic or cellular effects. We tested the hypothesis that ADT will lead to changes in skeletal muscle gene expression, which may explain the adverse muscle phenotype seen clinically. We conducted a prospective cohort study of 9 men with localised prostate cancer who underwent a vastus lateralis biopsy before and after 4 weeks of ADT. Next-generation RNA sequencing was performed and genes differentially expressed following ADT underwent gene ontology mining using Ingenuity Pathway Analysis. Differential expression of genes of interest was confirmed by quantitative PCR (Q-PCR) on gastrocnemius muscle of orchidectomised mice and sham controls (n=11/group). We found that in men, circulating total testosterone decreased from 16.5±4.3nmol/L at baseline to 0.4±0.15nmol/L post-ADT (p<0.001). RNA sequencing identified 19 differentially expressed genes post-ADT (all p<0.05 after adjusting for multiple testing). Gene ontology mining identified 8 genes to be of particular interest due to known roles in androgen-mediated signalling; ABCG1, ACTC1, ANKRD1, DMPK, THY1, DCLK1, CST3 were upregulated and SLC38A3 was downregulated post-ADT. Q-PCR in mouse gastrocnemius muscle confirmed that only one gene, Actc1 was concordantly upregulated (p<0.01) in orchidectomised mice compared with controls. In conclusion, given that ACTC1 upregulation is associated with improved muscle function in certain myopathies, we hypothesise that upregulation of ACTC1 may represent a compensatory response to ADT-induced muscle loss. Further studies will be required to evaluate the role and function of ACTC1.

Urolithin B, a newly identified regulator of skeletal muscle mass

BACKGROUND

The control of muscle size is an essential feature of health. Indeed, skeletal muscle atrophy leads to reduced strength, poor quality of life, and metabolic disturbances. Consequently, strategies aiming to attenuate muscle wasting and to promote muscle growth during various (pathological) physiological states like sarcopenia, immobilization, malnutrition, or cachexia are needed to address this extensive health issue. In this study, we tested the effects of urolithin B, an ellagitannin-derived metabolite, on skeletal muscle growth.

METHODS

C2C12 myotubes were treated with 15 μM of urolithin B for 24 h. For in vivo experiments, mice were implanted with mini-osmotic pumps delivering continuously 10 μg/day of urolithin B during 28 days. Muscle atrophy was studied in mice with a sciatic nerve denervation receiving urolithin B by the same way.

RESULTS

Our experiments reveal that urolithin B enhances the growth and differentiation of C2C12 myotubes by increasing protein synthesis and repressing the ubiquitin-proteasome pathway. Genetic and pharmacological arguments support an implication of the androgen receptor. Signalling analyses suggest a crosstalk between the androgen receptor and the mTORC1 pathway, possibly via AMPK. In vivo experiments confirm that urolithin B induces muscle hypertrophy in mice and reduces muscle atrophy after the sciatic nerve section.

CONCLUSIONS

This study highlights the potential usefulness of urolithin B for the treatment of muscle mass loss associated with various (pathological) physiological states.

Gonad-related factors promote muscle performance gain during postnatal development in male and female mice

To better define the role of male and female gonad-related factors (MGRF, presumably testosterone, and FGRF, presumably estradiol, respectively) on mouse hindlimb skeletal muscle contractile performance/function gain during postnatal development, we analyzed the effect of castration initiated before puberty in male and female mice. We found that muscle absolute and specific (normalized to muscle weight) maximal forces were decreased in 6-mo-old male and female castrated mice compared with age- and sex-matched intact mice, without alteration in neuromuscular transmission. Moreover, castration decreased absolute and specific maximal powers, another important aspect of muscle performance, in 6-mo-old males, but not in females. Absolute maximal force was similarly reduced by castration in 3-mo-old muscle fiber androgen receptor (AR)-deficient and wild-type male mice, indicating that the effect of MGRF was muscle fiber AR independent. Castration reduced the muscle weight gain in 3-mo mice of both sexes and in 6-mo females but not in males. We also found that bone morphogenetic protein signaling through Smad1/5/9 was not altered by castration in atrophic muscle of 3-mo-old mice of both sexes. Moreover, castration decreased the sexual dimorphism regarding muscle performance. Together, these results demonstrated that in the long term, MGRF and FGRF promote muscle performance gain in mice during postnatal development, independently of muscle growth in males, largely via improving muscle contractile quality (force and power normalized), and that MGFR and FGRF also contribute to sexual dimorphism. However, the mechanisms underlying MGFR and FGRF actions remain to be determined.

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.

TGFβ Superfamily Members Mediate Androgen Deprivation Therapy-Induced Obese Frailty in Male Mice

First line treatment for recurrent and metastatic prostate cancer is androgen deprivation therapy (ADT). Use of ADT has been increasing in frequency and duration, such that side effects increasingly impact patient quality of life. One of the most significant side effects of ADT is sarcopenia, which leads to a loss of skeletal muscle mass and function, resulting in a clinical disability syndrome known as obese frailty. Using aged mice, we developed a mouse model of ADT-induced sarcopenia that closely resembles the phenotype seen in patients, including loss of skeletal muscle strength, reduced lean muscle mass, and increased adipose tissue. Sarcopenia onset occurred about 6 weeks after castration and was blocked by a soluble receptor (ActRIIB-Fc) that binds multiple TGFβ superfamily members, including myostatin, growth differentiation factor 11, activin A, activin B, and activin AB. Analysis of ligand expression in both gastrocnemius and triceps brachii muscles demonstrates that each of these proteins is induced in response to ADT, in 1 of 3 temporal patterns. Specifically, activin A and activin AB levels increase and decline before onset of strength loss at 6 weeks after castration, and myostatin levels increase coincident with the onset of strength loss and then decline. In contrast, activin B and growth differentiation factor 11 levels increase after the onset of strength loss, 8-10 weeks after castration. The observed patterns of ligand induction may represent differential contributions to the development and/or maintenance of sarcopenia. We hypothesize that some or all of these ligands are targets for therapy to ameliorate ADT-induced sarcopenia in prostate cancer patients.

The role of sex steroid hormones in the pathophysiology and treatment of sarcopenia

Sex steroids influence the maintenance and growth of muscles. Decline in androgens, estrogens and progesterone by aging leads to the loss of muscular function and mass, sarcopenia. These steroid hormones can interact with different signaling pathways through their receptors. To date, sex steroid hormone receptors and their exact roles are not completely defined in skeletal and smooth muscles. Although numerous studies focused on the effects of sex steroid hormones on different types of cells, still many unexplained molecular mechanisms in both skeletal and smooth muscle cells remain to be investigated. In this paper, many different molecular mechanisms that are activated or inhibited by sex steroids and those that influence the growth, proliferation, and differentiation of skeletal and smooth muscle cells are reviewed. Also, the similarities of cellular and molecular pathways of androgens, estrogens and progesterone in both skeletal and smooth muscle cells are highlighted. The reviewed signaling pathways and participating molecules can be targeted in the future development of novel therapeutics.

Temporal associations between individual changes in hormones, training motivation and physical performance in elite and non-elite trained men

To advance our understanding of the hormonal contribution to athletic performance, we examined the temporal associations between individual changes in testosterone (T) and/or cortisol (C) concentrations, training motivation and physical performance in elite and non-elite trained men. Two male cohorts classified as elites (n = 12) and non-elites (n = 12) completed five testing sessions over a six-week period. The athletes were tested for salivary T, C, T/C ratio, self-perceived training motivation, countermovement jump (CMJ) height and isometric mid-thigh pull peak force (IMTP PF), after which an actual training workout was performed. The elite men reported higher motivation to train and they produced greater CMJ height overall, whereas the non-elites had higher pooled T levels (p < 0.05). No significant group differences in C concentrations, T/C ratio or IMTP PF were found. The individual changes in T levels were positively associated with training motivation in the elite men only (p = 0.033), but the hormonal and motivation measures did not predict CMJ height or IMTP PF in either group. The monitoring of elite and non-elite men across a short training block revealed differences in T levels, motivation and lower-body power, which may reflect training and competitive factors in each group. Despite having lower T levels, the elite athletes showed better linkage between pre-training T fluctuations and subsequent motivation to train. The nature of the performance tests (i.e. single repetition trials) could partly explain the lack of an association with the hormonal and motivational measures.

Review article: sarcopenia in cirrhosis--aetiology, implications and potential therapeutic interventions

BACKGROUND

Sarcopenia (loss of muscle mass) is common in cirrhosis and is associated with poor outcomes. Current teaching recommends the use of protein supplementation and exercise, however, this fails to address many other factors which contribute to muscle loss in this setting.

AIMS

To summarise existing knowledge regarding the aetiology of sarcopenia in cirrhosis, diagnostic modalities and the clinical significance of this condition. In addition to discuss recent research findings that may allow the development of more effective treatments.

METHODS

We conducted a Medline and PubMed search using the search terms 'sarcopenia', 'muscle', 'body composition', 'cirrhosis', 'liver' and 'malnutrition' from inception to October 2015.

RESULTS

Cirrhotic patients with sarcopenia have reduced survival, experience increased rates of infection and have worse outcomes following liver transplantation. The aetiology of this condition is more complex than simple protein and calorie malnutrition. Cirrhosis also results in depleted glycogen stores and metabolic alterations that cause excessive protein catabolism, increased activation of the ubiquitin-proteasome pathway and inappropriate muscle autophagy. Satellite cell differentiation and proliferation is also reduced due to a combination of elevated myostatin levels, reduced IGF-1 and hypogonadism. Although there is some evidence supporting the use of late evening snacks, branched chain amino acid supplementation and high protein/high calorie diets, well designed clinical trials addressing the effects of treatment on body composition in cirrhosis are lacking.

CONCLUSION

Sarcopenia in cirrhosis has a complex pathogenesis and simple dietary interventions are insufficient. Improved understanding of the multiple mechanisms involved should allow the development of more effective therapies, which target the specific underlying metabolic derangements.

Regulation of mTORC1 by growth factors, energy status, amino acids and mechanical stimuli at a glance

The mechanistic/mammalian target of rapamycin complex 1 (mTORC1) plays a pivotal role in the regulation of skeletal muscle protein synthesis. Activation of the complex leads to phosphorylation of two important sets of substrates, namely eIF4E binding proteins and ribosomal S6 kinases. Phosphorylation of these substrates then leads to an increase in protein synthesis, mainly by enhancing translation initiation. mTORC1 activity is regulated by several inputs, such as growth factors, energy status, amino acids and mechanical stimuli. Research in this field is rapidly evolving and unraveling how these inputs regulate the complex. Therefore this review attempts to provide a brief and up-to-date narrative on the regulation of this marvelous protein complex. Additionally, some sports supplements which have been shown to regulate mTORC1 activity are discussed.

Consequences of Fatherhood in the Biparental California Mouse (Peromyscus californicus): Locomotor Performance, Metabolic Rate, and Organ Masses

Although effects of motherhood on mothers have been well documented in mammals, the effects of fatherhood on fathers are not well known. We evaluated effects of being a father on key metabolic and performance measures in the California mouse, Peromyscus californicus. California mice are genetically monogamous in the wild, and fathers show similar parental behavior to mothers, with the exception of lactation. To investigate the impact of fatherhood on fathers, focal males were paired with an intact female (breeding males), a tubally ligated female (nonbreeding males), or another male (virgins). Starting 3-5 d after the birth of each breeding pair's first litter, males were tested for locomotor performance (maximum sprint speed, treadmill endurance), basal metabolic rate (BMR), and maximum oxygen consumption ([Formula: see text]). At the end of the 11-d test period, mice were euthanized, hematocrit was determined, and organs were weighed. Speed, endurance, and [Formula: see text] were significantly repeatable between two replicate measurement days but did not differ among groups, nor did BMR. Breeding males had significantly larger hind limb muscles than did nonbreeding males, whereas virgin males had heavier subcutaneous fat pads than did nonbreeding and breeding males. Several correlations were observed at the level of individual variation (residuals from ANCOVA models), including positive correlations for endurance with [Formula: see text], [Formula: see text] with testes mass, and some of the digestion-related organs with each other. These results indicate that fatherhood may not have pronounced performance, metabolic, or morphological effects on fathers, at least under standard laboratory conditions and across a single breeding cycle.

Androgen Deficiency Exacerbates High-Fat Diet-Induced Metabolic Alterations in Male Mice

Androgen deficiency is associated with obesity, metabolic syndrome, and type 2 diabetes mellitus in men, but the mechanisms behind these associations remain unclear. In this study, we investigated the combined effects of androgen deficiency and high-fat diet (HFD) on body composition and glucose homeostasis in C57BL/6J male mice. Two models of androgen deficiency were used: orchidectomy (ORX) and androgen receptor knockout mice. Both models displayed higher adiposity and serum leptin levels upon HFD, whereas no differences were seen on a regular diet. Fat accumulation in HFD ORX animals was accompanied by increased sedentary behavior and occurred in spite of reduced food intake. HFD ORX mice showed white adipocyte hypertrophy, correlated with decreased mitochondrial content but not function as well as increased lipogenesis and decreased lipolysis suggested by the up-regulation of fatty acid synthase and the down-regulation of hormone-sensitive lipase. Both ORX and androgen receptor knockout exacerbated HFD-induced glucose intolerance by impairing insulin action in liver and skeletal muscle, as evidenced by the increased triglyceride and decreased glycogen content in these tissues. In addition, serum IL-1β levels were elevated, and pancreatic insulin secretion was impaired after ORX. Testosterone but not dihydrotestosterone supplementation restored the castration effects on body composition and glucose homeostasis. We conclude that sex steroid deficiency in combination with HFD exacerbates adiposity, insulin resistance, and β-cell failure in 2 preclinical male mouse models. Our findings stress the importance of a healthy diet in a clinical context of androgen deficiency and may have implications for the prevention of metabolic alterations in hypogonadal men.

Targeting muscle signaling pathways to minimize adverse effects of androgen deprivation

Androgen deprivation therapy (ADT) is a highly effective treatment used in ∼30% of men with prostate cancer. Adverse effects of ADT on muscle are significant with consistent losses in muscle mass. However, effects of ADT on muscle strength and physical function, of most relevance to the patient, are less well understood. This is in part due to the fact that muscle effects of ADT at the cellular, genetic and protein level, critical to the understanding of the pathophysiology of sarcopenia, have come into focus only recently. This review highlights the complexity of androgen-dependent signaling in muscle with an emphasis on recent findings in the regulation of muscle growth and muscle atrophy pathways. Furthermore, the effects of ADT and testosterone on skeletal muscle histology, gene expression and protein transcription are discussed. A better mechanistic understanding of the regulation of muscle mass and function by androgens should not only pave the way for developing targeted promyogenic interventions for men with prostate cancer receiving ADT but also may have wider implications for age-associated sarcopenia in the general population.

Voluntary Exercise Improves Estrous Cyclicity in Prenatally Androgenized Female Mice Despite Programming Decreased Voluntary Exercise: Implications for Polycystic Ovary Syndrome (PCOS)

Prenatal androgen (PNA) exposure in mice produces a phenotype resembling lean polycystic ovary syndrome. We studied effects of voluntary exercise on metabolic and reproductive parameters in PNA vs vehicle (VEH)-treated mice. Mice (8 wk of age) were housed individually and estrous cycles monitored. At 10 weeks of age, mice were divided into groups (PNA, PNA-run, VEH, VEH-run, n = 8-9/group); those in the running groups received wheels allowing voluntary running. Unexpectedly, PNA mice ran less distance than VEH mice; ovariectomy eliminated this difference. In ovary-intact mice, there was no difference in glucose tolerance, lower limb muscle fiber types, weight, or body composition among groups after 16 weeks of running, although some mitochondrial proteins were mildly up-regulated by exercise in PNA mice. Before running, estrous cycles in PNA mice were disrupted with most days in diestrus. There was no change in cycles during weeks 1-6 of running (10-15 wk of age). In contrast, from weeks 11 to 16 of running, cycles in PNA mice improved with more days in proestrus and estrus and fewer in diestrus. PNA programs reduced voluntary exercise, perhaps mediated in part by ovarian secretions. Exercise without weight loss improved estrous cycles, which if translated could be important for fertility in and counseling of lean women with polycystic ovary syndrome.

The emerging role of skeletal muscle oxidative metabolism as a biological target and cellular regulator of cancer-induced muscle wasting

While skeletal muscle mass is an established primary outcome related to understanding cancer cachexia mechanisms, considerable gaps exist in our understanding of muscle biochemical and functional properties that have recognized roles in systemic health. Skeletal muscle quality is a classification beyond mass, and is aligned with muscle's metabolic capacity and substrate utilization flexibility. This supplies an additional role for the mitochondria in cancer-induced muscle wasting. While the historical assessment of mitochondria content and function during cancer-induced muscle loss was closely aligned with energy flux and wasting susceptibility, this understanding has expanded to link mitochondria dysfunction to cellular processes regulating myofiber wasting. The primary objective of this article is to highlight muscle mitochondria and oxidative metabolism as a biological target of cancer cachexia and also as a cellular regulator of cancer-induced muscle wasting. Initially, we examine the role of muscle metabolic phenotype and mitochondria content in cancer-induced wasting susceptibility. We then assess the evidence for cancer-induced regulation of skeletal muscle mitochondrial biogenesis, dynamics, mitophagy, and oxidative stress. In addition, we discuss environments associated with cancer cachexia that can impact the regulation of skeletal muscle oxidative metabolism. The article also examines the role of cytokine-mediated regulation of mitochondria function, followed by the potential role of cancer-induced hypogonadism. Lastly, a role for decreased muscle use in cancer-induced mitochondrial dysfunction is reviewed.

Enobosarm (GTx-024) Modulates Adult Skeletal Muscle Mass Independently of the Androgen Receptor in the Satellite Cell Lineage

Androgens increase skeletal muscle mass, but their clinical use is hampered by a lack of tissue selectivity and subsequent side effects. Selective androgen receptor modulators elicit muscle-anabolic effects while only sparingly affecting reproductive tissues. The selective androgen receptor modulator, GTx-024 (enobosarm), is being investigated for cancer cachexia, sarcopenia, and muscle wasting diseases. Here we investigate the role of muscle androgen receptor (AR) in the anabolic effect of GTx-024. In mice lacking AR in the satellite cell lineage (satARKO), the weight of the androgen-sensitive levator ani muscle was lower but was decreased further upon orchidectomy. GTx-024 was as effective as DHT in restoring levator ani weights to sham levels. Expression of the muscle-specific, androgen-responsive genes S-adenosylmethionine decarboxylase and myostatin was decreased by orchidectomy and restored by GTx-024 and DHT in control mice, whereas the expression was low and unaffected by androgen status in satARKO. In contrast, insulin-like growth factor 1Ea expression was not different between satARKO and control muscle, decreased upon castration, and was restored by DHT and GTx-024 in both genotypes. These data indicate that GTx-024 does not selectively modulate AR in the satellite cell lineage and that cells outside this lineage remain androgen responsive in satARKO muscle. Indeed, residual AR-positive cells were present in satARKO muscle, coexpressing the fibroblast-lineage marker vimentin. AR positive, muscle-resident fibroblasts could therefore be involved in the indirect effects of androgens on muscle. In conclusion, both DHT and GTx-024 target AR pathways in the satellite cell lineage, but cells outside this lineage also contribute to the anabolic effects of androgens.

Effects of sex steroids on bones and muscles: Similarities, parallels, and putative interactions in health and disease

Estrogens and androgens influence the growth and maintenance of bones and muscles and are responsible for their sexual dimorphism. A decline in their circulating levels leads to loss of mass and functional integrity in both tissues. In the article, we highlight the similarities of the molecular and cellular mechanisms of action of sex steroids in the two tissues; the commonality of a critical role of mechanical forces on tissue mass and function; emerging evidence for an interplay between mechanical forces and hormonal and growth factor signals in both bones and muscles; as well as the current state of evidence for or against a cross-talk between muscles and bone. In addition, we review evidence for the parallels in the development of osteoporosis and sarcopenia with advancing age and the potential common mechanisms responsible for the age-dependent involution of these two tissues. Lastly, we discuss the striking difference in the availability of several drug therapies for the prevention and treatment of osteoporosis, as compared to none for sarcopenia. This article is part of a Special Issue entitled "Muscle Bone Interactions".

Effects of tail suspension on serum testosterone and molecular targets regulating muscle mass

INTRODUCTION

The contribution of reduced testosterone levels to tail suspension (TS)-induced muscle atrophy remains equivocal. The molecular mechanism by which testosterone regulates muscle mass during TS has not been investigated.

METHODS

Effects of TS on serum testosterone levels, muscle mass, and expression of muscle atrophy- and hypertrophy-inducing targets were measured in soleus (SOL) and extensor digitorum longus (EDL) muscles after testosterone administration during 1, 5, and 14 days of TS in male mice.

RESULTS

TS produced an increase followed by a transient drop in testosterone levels. Muscle atrophy was associated with downregulation of Igf1 and upregulation of Mstn, Redd1, Atrogin-1, and MuRF1 mRNA with clear differences in Igf1, Mstn, and MAFbx/Atrogin-1 gene expression between SOL and EDL. Testosterone supplementation did not affect muscle mass or protein expression levels during TS. Conclusions The known anabolic effects of testosterone are not sufficient to ameliorate loss of muscle mass during TS.

Testosterone and obesity

Testosterone is a key hormone in the pathology of metabolic diseases such as obesity. Low testosterone levels are associated with increased fat mass (particularly central adiposity) and reduced lean mass in males. These morphological features are linked to metabolic dysfunction, and testosterone deficiency is associated with energy imbalance, impaired glucose control, reduced insulin sensitivity and dyslipidaemia. A bidirectional relationship between testosterone and obesity underpins this association indicated by the hypogonadal-obesity cycle and evidence weight loss can lead to increased testosterone levels. Androgenic effects on enzymatic pathways of fatty acid metabolism, glucose control and energy utilization are apparent and often tissue specific with differential effects noted in different regional fat depots, muscle and liver to potentially explain the mechanisms of testosterone action. Testosterone replacement therapy demonstrates beneficial effects on measures of obesity that are partially explained by both direct metabolic actions on adipose and muscle and also potentially by increasing motivation, vigour and energy allowing obese individuals to engage in more active lifestyles. The degree of these beneficial effects may be dependent on the treatment modality with longer term administration often achieving greater improvements. Testosterone replacement may therefore potentially be an effective adjunctive treatment for weight management in obese men with concomitant hypogonadism.

Effects of loaded voluntary wheel exercise on performance and muscle hypertrophy in young and old male C57Bl/6J mice

This study compared the capacity of young and old male C57Bl/6J mice to exercise with increasing resistance over 10 weeks, and its impact on muscle mass. Young mice (aged 15-25 weeks) were subjected to low (LR) and high (HR) resistance exercise, whereas only LR was used for old mice (107-117 weeks). Weekly patterns of voluntary wheel activity, food consumption and body weights were measured. Running patterns changed over time and with age, with two peaks of activity detected for young, but only one for old mice: speed and distance run was also less for old mice. The mass for six limb muscles was measured at the end of the experiment. The most pronounced increase in mass in response to exercise was for the soleus in young and old mice, and also quadriceps and gastrocnemius in young mice. Soleus and quadriceps muscles were analyzed histologically for myofiber number and size. A striking feature was the many small myofibers in response to exercise in young (but not old) soleus, whereas these were not present after exercise in young or old quadriceps. Overall, there was a striking difference in response to exercise between muscles and this was influenced by age.

Acute effect of androgens on maximal force-generating capacity and electrically evoked calcium transient in mouse skeletal muscles

As androgens might have rapid androgen-receptor (AR) independent action on muscle cells, we analysed the in vivo acute effect of androgens on maximal force generation capacity and electrically evoked calcium transient responsible for the excitation-contraction coupling in skeletal muscle from wild-type male mice and muscle fibre androgen receptor (AR) deficient (AR(skm-/y)) male mice. We tested the hypothesis that acute in vivo androgen treatment improves contractility and modifies calcium transient in mouse hindlimb muscles. In addition, we determined whether the reduced maximal force generation capacity of AR(skm-/y) mice is caused by an alteration in calcium transient. We found that acute dehydrotestosterone (DHT) and testosterone treatment of mice does not change in situ maximal force, power or fatigue resistance of tibialis anterior muscles. In agreement with this observation, maximal force and twitch kinetics also remained unchanged when both whole extensor digitorum longus (EDL) muscle or fibre bundles were incubated in vitro with DHT. Electrically evoked calcium transient, i.e. calcium amplitude, time to peak and decay, was also not modified by DHT treatment of EDL muscle fibre bundles. Finally, we found no difference in calcium transient between AR(skm-/y) and wild-type mice despite the reduced maximal force in EDL fibre bundles of AR(skm-/y) mice. In conclusion, acute androgen treatment has no ergogenic effect on muscle contractility and does not affect calcium transient in response to stimulation. In addition, the reduced maximal force of AR(skm-/y) mice is not related to calcium transient dysfunction.

Developmental treatment with ethinyl estradiol, but not bisphenol A, causes alterations in sexually dimorphic behaviors in male and female Sprague Dawley rats

The developing central nervous system may be particularly sensitive to bisphenol A (BPA)-induced alterations. Here, pregnant Sprague Dawley rats (n = 11-12/group) were gavaged daily with vehicle, 2.5 or 25.0 μg/kg BPA, or 5.0 or 10.0 μg/kg ethinyl estradiol (EE2) on gestational days 6-21. The BPA doses were selected to be below the no-observed-adverse-effect level (NOAEL) of 5 mg/kg/day. On postnatal days 1-21, all offspring/litter were orally treated with the same dose. A naïve control group was not gavaged. Body weight, pubertal age, estrous cyclicity, and adult serum hormone levels were measured. Adolescent play, running wheel activity, flavored solution intake, female sex behavior, and manually elicited lordosis were assessed. No significant differences existed between the vehicle and naïve control groups. Vehicle controls exhibited significant sexual dimorphism for most behaviors, indicating these evaluations were sensitive to sex differences. However, only EE2 treatment caused significant effects. Relative to female controls, EE2-treated females were heavier, exhibited delayed vaginal opening, aberrant estrous cyclicity, increased play behavior, decreased running wheel activity, and increased aggression toward the stimulus male during sexual behavior assessments. Relative to male controls, EE2-treated males were older at testes descent and preputial separation and had lower testosterone levels. These results suggest EE2-induced masculinization/defeminization of females and are consistent with increased volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) at weaning in female siblings of these subjects (He, Z., Paule, M. G. and Ferguson, S. A. (2012) Low oral doses of bisphenol A increase volume of the sexually dimorphic nucleus of the preoptic area in male, but not female, rats at postnatal day 21. Neurotoxicol. Teratol. 34, 331-337). Although EE2 treatment caused pubertal delays and decreased testosterone levels in males, their behaviors were within the range of control males. Conversely, BPA treatment did not alter any measured endpoint. Similar to our previous reports (Ferguson, S. A., Law, C. D. Jr and Abshire, J. S. (2011) Developmental treatment with bisphenol A or ethinyl estradiol causes few alterations on early preweaning measures. Toxicol. Sci. 124, 149-160; Ferguson, S. A., Law, C. D. and Abshire, J. S. (2012) Developmental treatment with bisphenol A causes few alterations on measures of postweaning activity and learning. Neurotoxicol. Teratol. 34, 598-606), the BPA doses and design used here produced few alterations.

Effect of testosterone on markers of mitochondrial oxidative phosphorylation and lipid metabolism in muscle of aging men with subnormal bioavailable testosterone

OBJECTIVE

Recent studies have indicated that serum testosterone in aging men is associated with insulin sensitivity and expression of genes involved in oxidative phosphorylation (OxPhos), and that testosterone treatment increases lipid oxidation. Herein, we investigated the effect of testosterone therapy on regulators of mitochondrial biogenesis and markers of OxPhos and lipid metabolism in the skeletal muscle of aging men with subnormal bioavailable testosterone levels.

METHODS

Skeletal muscle biopsies were obtained before and after treatment with either testosterone gel (n=12) or placebo (n=13) for 6 months. Insulin sensitivity and substrate oxidation were assessed by euglycemic-hyperinsulinemic clamp and indirect calorimetry. Muscle mRNA levels and protein abundance and phosphorylation of enzymes involved in mitochondrial biogenesis, OxPhos, and lipid metabolism were examined by quantitative real-time PCR and western blotting.

RESULTS

Despite an increase in lipid oxidation (P<0.05), testosterone therapy had no effect on insulin sensitivity or mRNA levels of genes involved in mitochondrial biogenesis (PPARGC1A, PRKAA2, and PRKAG3), OxPhos (NDUFS1, ETFA, SDHA, UQCRC1, and COX5B), or lipid metabolism (ACADVL, CD36, CPT1B, HADH, and PDK4). Consistently, protein abundance of OxPhos subunits encoded by both nuclear (SDHA and UQCRC1) and mitochondrial DNA (ND6) and protein abundance and phosphorylation of AMP-activated protein kinase and p38 MAPK were unaffected by testosterone therapy.

CONCLUSION

The beneficial effect of testosterone treatment on lipid oxidation is not explained by increased abundance or phosphorylation-dependent activity of enzymes known to regulate mitochondrial biogenesis or markers of OxPhos and lipid metabolism in the skeletal muscle of aging men with subnormal bioavailable testosterone levels.

A satellite cell-specific knockout of the androgen receptor reveals myostatin as a direct androgen target in skeletal muscle

Androgens have well-established anabolic actions on skeletal muscle, although the direct effects of the androgen receptor (AR) in muscle remain unclear. We generated satellite cell-specific AR-knockout (satARKO) mice in which the AR is selectively ablated in satellite cells, the muscle precursor cells. Total-limb maximal grip strength is decreased by 7% in satARKO mice, with soleus muscles containing ∼10% more type I fibers and 10% less type IIa fibers than the corresponding control littermates. The weight of the perineal levator ani muscle is markedly reduced (-52%). Thus, muscle AR is involved in fiber-type distribution and force production of the limb muscles, while it is a major determinant of the perineal muscle mass. Surprisingly, myostatin (Mstn), a strong inhibitor of skeletal muscle growth, is one of the most androgen-responsive genes (6-fold reduction in satARKO) through direct transcription activation by the AR. Consequently, muscle hypertrophy in response to androgens is augmented in Mstn-knockout mice. Our finding that androgens induce Mstn signaling to restrain their own anabolic actions has implications for the treatment of muscle wasting disorders.-Dubois, V., Laurent, M. R., Sinnesael, M., Cielen, N., Helsen, C., Clinckemalie, L., Spans, L., Gayan-Ramirez, G., Deldicque, L., Hespel, P., Carmeliet, G., Vanderschueren, D., and Claessens, F. A satellite cell-specific knockout of the androgen receptor reveals myostatin as a direct androgen target in skeletal muscle.

Mitochondrial and sex steroid hormone crosstalk during aging

Decline in circulating sex steroid hormones accompanies several age-associated pathologies which may influence human healthspan. Mitochondria play important roles in biosynthesis of sex steroid hormones, and these hormones can also regulate mitochondrial function. Understanding the cross talk between mitochondria and sex steroid hormones may provide insights into the pathologies associated with aging. The aim of this review is to summarize the current knowledge regarding the interplay between mitochondria and sex steroid hormones during the aging process. The review describes the effect of mitochondria on sex steroid hormone production in the gonads, and then enumerates the contribution of sex steroid hormones on mitochondrial function in hormone responsive cells. Decline in sex steroid hormones and accumulation of mitochondrial damage may create a positive feedback loop that contributes to the progressive degeneration in tissue function during aging. The review further speculates whether regulation between mitochondrial function and sex steroid hormone action can potentially influence healthspan.

Androgenic and estrogenic regulation of Atrogin-1, MuRF1 and myostatin expression in different muscle types of male mice

PURPOSE

The molecular factors targeted by androgens and estrogens on muscle mass are not fully understood. The current study aimed to explore gene and protein expression of Atrogin-1, MuRF1, and myostatin in an androgen deprivation-induced muscle atrophy model.

METHODS

We examined the effects of Orx either with or without testosterone (T) or estradiol (E2) administration on Atrogin-1 gene expression, and MuRF1 and myostatin gene and protein expression. Measurements were made in soleus (SOL), extensor digitorum longus (EDL) and levator ani/bulbocavernosus (LA/BC) of male C57BL/6 mice.

RESULTS

Thirty days of Orx resulted in a reduction in weight gain and muscle mass. These effects were prevented by T. In LA/BC, Atrogin-1 and MuRF1 mRNA was increased throughout 30 days of Orx, which was fully reversed by T and partially by E2 administration. In EDL and SOL, a less pronounced upregulation of both genes was only detectable at the early stages of Orx. Myostatin mRNA levels were downregulated in LA/BC and upregulated in EDL following Orx. T, but not E2, reversed these effects. No changes in protein levels of MuRF1 and myostatin were found in EDL at any time point following Orx.

CONCLUSIONS

The atrophy in SOL and EDL in response to androgen deprivation, and its restoration by T, is accompanied by only minimal changes in atrogenes and myostatin gene expression. The marked differences in muscle atrophy and atrogene and myostatin mRNA between LA/BC and the locomotor muscles suggest that the murine LA/BC is not an optimal model to study Orx-induced muscle atrophy.

Characterization of the male ApcMin/+ mouse as a hypogonadism model related to cancer cachexia

Cancer cachexia, the unintentional loss of lean body mass, is associated with decreased quality of life and poor patient survival. Hypogonadism, involving a reduction in circulating testosterone, is associated with the cachectic condition. At this time there is a very limited understanding of the role of hypogonadism in cancer cachexia progression. This gap in our knowledge is related to a lack of functional hypogonadal models associated with cancer cachexia. The Apc^Min/+ mouse is an established colorectal cancer model that develops an IL-6 dependent cachexia which is physiologically related to human disease due to the gradual progression of tumor development and cachexia. The purpose of this study was to assess the utility of the Apc^Min/+ mouse for the examination of hypogonadism during cancer cachexia and to investigate if IL-6 has a role in this process. We report that Apc^Min/+ mice that are weight stable have comparable testosterone levels and gonad size compared to wild type mice. Cachectic Apc^Min/+ mice exhibit a reduction in circulating testosterone and gonad size, which has a significant association with the degree of muscle mass and functional strength loss. Circulating testosterone levels were also significantly associated with the suppression of myofibrillar protein synthesis. Skeletal muscle and testes androgen receptor expression were decreased with severe cachexia. Although testes STAT3 phosphorylation increased with severe cachexia, systemic IL-6 over-expression for 2 weeks was not sufficient to reduce either testes weight or circulating testosterone. Inhibition of systemic IL-6 signaling by an IL-6 receptor antibody to Apc^Min/+ mice that had already initiated weight loss was sufficient to attenuate a reduction in testes size and circulating testosterone. In summary, the Apc^Min/+ mouse becomes hypogonadal with the progression of cachexia severity and elevated circulating IL-6 levels may have a role in the development of hypogonadism during cancer cachexia.

The effects of testosterone deprivation and supplementation on proteasomal and autophagy activity in the skeletal muscle of the male mouse: differential effects on high-androgen responder and low-androgen responder muscle groups

Men with prostate cancer who receive androgen deprivation therapy show profound skeletal muscle loss. We hypothesized that the androgen deficiency activates not only the ubiquitin-proteasome systems but also the autophagy and affects key aspects of the molecular cross talk between protein synthesis and degradation. Here, 2-month-old male mice were castrated and treated with either testosterone (T) propionate or vehicle for 7 days (short term) or 43 days (long term), and with and without hydroxyflutamide. Castrated mice showed rapid and profound atrophy of the levator ani muscle (high androgen responder) at short term and lesser atrophy of the triceps muscle (low androgen responder) at long term. Levator ani and triceps muscles of castrated mice showed increased level of autophagy markers and lysosome enzymatic activity; only the levator ani showed increased proteasomal enzymatic activity. The levator ani muscle of the castrated mice showed increased level and activation of forkhead box protein O3A, the inhibition of mechanistic target of rapamicyn, and the activation of tuberous sclerosis complex protein 2 and 5'-AMP-activated protein kinase. Similar results were obtained in the triceps muscle of castrated mice. T rescued the loss of muscle mass after orchiectomy and inhibited lysosome and proteasome pathways dose dependently and in a seemingly IGF-I-dependent manner. Hydroxyflutamide attenuated the effect of T in the levator ani muscle of castrated mice. In conclusion, androgen deprivation in adult mice induces muscle atrophy associated with proteasomal and lysosomal activity. T optimizes muscle protein balance by modulating the equilibrium between mechanistic target of rapamicyn and 5'-AMP-activated protein kinase pathways.

Signaling pathways controlling skeletal muscle mass

The molecular mechanisms underlying skeletal muscle maintenance involve interplay between multiple signaling pathways. Under normal physiological conditions, a network of interconnected signals serves to control and coordinate hypertrophic and atrophic messages, culminating in a delicate balance between muscle protein synthesis and proteolysis. Loss of skeletal muscle mass, termed "atrophy", is a diagnostic feature of cachexia seen in settings of cancer, heart disease, chronic obstructive pulmonary disease, kidney disease, and burns. Cachexia increases the likelihood of death from these already serious diseases. Recent studies have further defined the pathways leading to gain and loss of skeletal muscle as well as the signaling events that induce differentiation and post-injury regeneration, which are also essential for the maintenance of skeletal muscle mass. In this review, we summarize and discuss the relevant recent literature demonstrating these previously undiscovered mediators governing anabolism and catabolism of skeletal muscle.

Testosterone and insulin resistance in the metabolic syndrome and T2DM in men

Obesity, type 2 diabetes mellitus and the metabolic syndrome are major risk factors for cardiovascular disease. Studies have demonstrated an association between low levels of testosterone and the above insulin-resistant states, with a prevalence of hypogonadism of up to 50% in men with type 2 diabetes mellitus. Low levels of testosterone are also associated with an increased risk of all-cause and cardiovascular mortality. Hypogonadism and obesity share a bidirectional relationship as a result of the complex interplay between adipocytokines, proinflammatory cytokines and hypothalamic hormones that control the pituitary-testicular axis. Interventional studies have shown beneficial effects of testosterone on components of the metabolic syndrome, type 2 diabetes mellitus and other cardiovascular risk factors, including insulin resistance and high levels of cholesterol. Biochemical evidence indicates that testosterone is involved in promoting glucose utilization by stimulating glucose uptake, glycolysis and mitochondrial oxidative phosphorylation. Testosterone is also involved in lipid homeostasis in major insulin-responsive target tissues, such as liver, adipose tissue and skeletal muscle.

Carboxyl terminus of Hsp70-interacting protein (CHIP) is required to modulate cardiac hypertrophy and attenuate autophagy during exercise

The carboxyl terminus of Hsp70-interacting protein (CHIP) is a ubiquitin ligase/cochaperone critical for the maintenance of cardiac function. Mice lacking CHIP (CHIP-/-) suffer decreased survival, enhanced myocardial injury and increased arrhythmias compared with wild-type controls following challenge with cardiac ischaemia reperfusion injury. Recent evidence implicates a role for CHIP in chaperone-assisted selective autophagy, a process that is associated with exercise-induced cardioprotection. To determine whether CHIP is involved in cardiac autophagy, we challenged CHIP-/- mice with voluntary exercise. CHIP-/- mice respond to exercise with an enhanced autophagic response that is associated with an exaggerated cardiac hypertrophy phenotype. No impairment of function was identified in the CHIP-/- mice by serial echocardiography over the 5 weeks of running, indicating that the cardiac hypertrophy was physiologic not pathologic in nature. It was further determined that CHIP plays a role in inhibiting Akt signalling and autophagy determined by autophagic flux in cardiomyocytes and in the intact heart. Taken together, cardiac CHIP appears to play a role in regulating autophagy during the development of cardiac hypertrophy, possibly by its role in supporting Akt signalling, induced by voluntary running in vivo.

Testosterone regulation of Akt/mTORC1/FoxO3a signaling in skeletal muscle

Low endogenous testosterone production, known as hypogonadism is commonly associated with conditions inducing muscle wasting. Akt signaling can control skeletal muscle mass through mTOR regulation of protein synthesis and FoxO regulation of protein degradation, and this pathway has been previously identified as a target of androgen signaling. However, the testosterone sensitivity of Akt/mTOR signaling requires further understanding in order to grasp the significance of varied testosterone levels seen with wasting disease on muscle protein turnover regulation. Therefore, the purpose of this study is to determine the effect of androgen availability on muscle Akt/mTORC1/FoxO3a regulation in skeletal muscle and cultured C(2)C(12) myotubes. C57BL/6 mice were either castrated for 42 days or castrated and treated with the nandrolone decanoate (ND) (6 mg/kg bw/wk). Testosterone loss (TL) significantly decreased volitional grip strength, body weight, and gastrocnemius (GAS) muscle mass, and ND reversed these changes. Related to muscle mass regulation, TL decreased muscle IGF-1 mRNA, the rate of myofibrillar protein synthesis, Akt phosphorylation, and the phosphorylation of Akt targets, GSK3β, PRAS40 and FoxO3a. TL induced expression of FoxO transcriptional targets, MuRF1, atrogin1 and REDD1. Muscle AMPK and raptor phosphorylation, mTOR inhibitors, were not altered by low testosterone. ND restored IGF-1 expression and Akt/mTORC1 signaling while repressing expression of FoxO transcriptional targets. Testosterone (T) sensitivity of Akt/mTORC1 signaling was examined in C(2)C(12) myotubes, and mTOR phosphorylation was induced independent of Akt activation at low T concentrations, while a higher T concentration was required to activate Akt signaling. Interestingly, low concentration T was sufficient to amplify myotube mTOR and Akt signaling after 24 h of T withdrawal, demonstrating the potential in cultured myotubes for a T initiated positive feedback mechanism to amplify Akt/mTOR signaling. In summary, androgen withdrawal decreases muscle myofibrillar protein synthesis through Akt/mTORC1 signaling, which is independent of AMPK activation, and readily reversible by anabolic steroid administration. Acute Akt activation in C(2)C(12) myotubes is sensitive to a high concentration of testosterone, and low concentrations of testosterone can activate mTOR signaling independent of Akt.