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.

Genetic variations in the androgen receptor are associated with steroid concentrations and anthropometrics but not with muscle mass in healthy young men.

OBJECTIVE: The relationship between serum testosterone (T) levels, muscle mass and muscle force in eugonadal men is incompletely understood. As polymorphisms in the androgen receptor (AR) gene cause differences in androgen sensitivity, no straightforward correlation can be observed between the interindividual variation in T levels and different phenotypes. Therefore, we aim to investigate the relationship between genetic variations in the AR, circulating androgens and muscle mass and function in young healthy male siblings. DESIGN: 677 men (25-45 years) were recruited in a cross-sectional, population-based sibling pair study. METHODS: Relations between genetic variation in the AR gene (CAGn, GGNn, SNPs), sex steroid levels (by LC-MS/MS), body composition (by DXA), muscle cross-sectional area (CSA) (by pQCT), muscle force (isokinetic peak torque, grip strength) and anthropometrics were studied using linear mixed-effect modelling. RESULTS: Muscle mass and force were highly heritable and related to age, physical activity, body composition and anthropometrics. Total T (TT) and free T (FT) levels were positively related to muscle CSA, whereas estradiol (E2) and free E2 (FE2) concentrations were negatively associated with muscle force. Subjects with longer CAG repeat length had higher circulating TT, FT, and higher E2 and FE2 concentrations. Weak associations with TT and FT were found for the rs5965433 and rs5919392 SNP in the AR, whereas no association between GGN repeat polymorphism and T concentrations were found. Arm span and 2D:4D finger length ratio were inversely associated, whereas muscle mass and force were not associated with the number of CAG repeats. CONCLUSIONS: Age, physical activity, body composition, sex steroid levels and anthropometrics are determinants of muscle mass and function in young men. Although the number of CAG repeats of the AR are related to sex steroid levels and anthropometrics, we have no evidence that these variations in the AR gene also affect muscle mass or function.

The need for transparency and good practices in the qPCR literature.

Two surveys of over 1,700 publications whose authors use quantitative real-time PCR (qPCR) reveal a lack of transparent and comprehensive reporting of essential technical information. Reporting standards are significantly improved in publications that cite the Minimum Information for Publication of Quantitative Real-Time PCR Experiments (MIQE) guidelines, although such publications are still vastly outnumbered by those that do not.

Gene expression of carnosine-related enzymes and transporters in skeletal muscle.

Chronic oral beta-alanine supplementation can elevate muscle carnosine (beta-alanyl-L-histidine) content and improve high-intensity exercise performance. However, the regulation of muscle carnosine levels is poorly understood. The uptake of the rate-limiting precursor beta-alanine and the enzyme catalyzing the dipeptide synthesis are thought to be key steps. The aims of this study were to investigate the expression of possible carnosine-related enzymes and transporters in both human and mouse skeletal muscle in response to carnosine-altering stimuli. Human gastrocnemius lateralis and mouse tibialis anterior muscle samples were subjected to HPLC and qPCR analysis. Mice were subjected to chronic oral supplementation of beta-alanine and carnosine or to orchidectomy (7 and 30 days, with or without testosterone replacement), stimuli known to, respectively, increase and decrease muscle carnosine and anserine. The following carnosine-related enzymes and transporters were expressed in human and/or mouse muscles: carnosine synthase (CARNS), carnosinase-2 (CNDP2), the carnosine/histidine transporters PHT1 and PHT2, the beta-alanine transporters TauT and PAT1, beta-alanine transaminase (ABAT) and histidine decarboxylase (HDC). Six of these genes showed altered expression in the investigated interventions. Orchidectomy led to decreased muscle carnosine content, which was paralleled with decreased TauT expression, whereas CARNS expression was surprisingly increased. Beta-alanine supplementation increased both muscle carnosine content and TauT, CARNS and ABAT expression, suggesting that muscles increase beta-alanine utilization through both dipeptide synthesis (CARNS) and deamination (ABAT) and further oxidation, in conditions of excess availability. Collectively, these data show that muscle carnosine homeostasis is regulated by nutritional and hormonal stimuli in a complex interplay between related transporters and enzymes.

Sex hormone-binding globulin at the crossroad of body composition, somatotropic axis and insulin/glucose homeostasis in young healthy men.

OBJECTIVES: Sex hormone-binding globulin (SHBG) modulates the bioavailability of sex steroids at tissue level. Genetic, hormonal and lifestyle-related factors determine the SHBG levels, and low SHBG levels are a known risk factor for the development of the metabolic syndrome, diabetes and cardiovascular diseases. We investigated to what extent different determinants contribute to the variation in SHBG levels in healthy young men. DESIGN AND PATIENTS: Healthy male siblings (n = 677) aged 25-45 year were recruited in a cross-sectional, population-based study. MEASUREMENTS: Lean and fat mass were measured using dual-energy X-ray absorptiometry (DXA), and immunoassays were used to determine the serum hormonal levels. Additional information about smoking and physical activity was obtained using questionnaires. Carriers of two SHBG polymorphisms, the Asp327Asn polymorphism and the (TAAAA)(n) repeat polymorphism, were identified. RESULTS: Weight, BMI, whole body fat mass and truncal fat mass were negatively associated with SHBG levels. Body composition characteristics did not differ between SHBG genotype groups, indicating that body composition controls SHBG levels rather than the other way around. The associations may be mediated by adipokines because leptin and adiponectin were, respectively, inversely and positively associated with SHBG levels. Insulin and glucose were negatively associated with SHBG levels, as well as IGF-1 and IGF-BP3, while no associations were found with free thyroid hormone status. CONCLUSIONS: In conclusion, we found that fat mass, insulin and IGF-1 levels are important negative determinants of SHBG levels in young healthy men. The association with fat mass could be mediated by the effects of adiponectin and/or leptin on SHBG synthesis.

Combined gene and protein expression of hormone-sensitive lipase and adipose triglyceride lipase, mitochondrial content, and adipocyte size in subcutaneous and visceral adipose tissue of morbidly obese men.

AIMS: Lipotoxicity in obesity might be a failure of adipocytes to respond sufficiently adequate to persistent energy surplus. To evaluate the role of lipolytic enzymes or mitochondria in lipotoxicity, we studied expression levels of genes and proteins involved in lipolysis and mitochondrial DNA (mtDNA) content. METHODS: As differences in lipid metabolism between men and women are extremely complex, we recruited only men (lean and morbidly obese) and collected subcutaneous and visceral adipose tissue during abdominal surgery for real-time PCR gene expression, protein expression, and microscopic study. RESULTS: Although mRNA levels of hormone-sensitive lipase (HSL) and adipose triglyceride lipase (ATGL) were increased in visceral adipose tissue of morbidly obese men, this was not paralleled by alterations in protein expression and phosphorylation of HSL and ATGL. mtDNA content of visceral adipose tissue was increased in morbidly obese men as compared to lean controls (p < 0.013). Positive correlations were observed between visceral adipocyte size and serum triacylglycerol (r = 0.6, p < 0.007) as well as between visceral adipocyte size and CRP (r = 0.6, p < 0.009) in analyses performed separately in obese men. CONCLUSION: Lipotoxicity of morbidly obese men might be related to the quantitative impact of the visceral fat depot rather than to important dysregulation of involved lipolytic enzymes or adipocyte mitochondria.

Effects of sprint training combined with vegetarian or mixed diet on muscle carnosine content and buffering capacity.

Carnosine is an abundant dipeptide in human skeletal muscle with proton buffering capacity. There is controversy as to whether training can increase muscle carnosine and thereby provide a mechanism for increased buffering capacity. This study investigated the effects of 5 weeks sprint training combined with a vegetarian or mixed diet on muscle carnosine, carnosine synthase mRNA expression and muscle buffering capacity. Twenty omnivorous subjects participated in a 5 week sprint training intervention (2-3 times per week). They were randomized into a vegetarian and mixed diet group. Measurements (before and after the intervention period) included carnosine content in soleus, gastrocnemius lateralis and tibialis anterior by proton magnetic resonance spectroscopy ((1)H-MRS), true-cut biopsy of the gastrocnemius lateralis to determine in vitro non-bicarbonate muscle buffering capacity, carnosine content (HPLC method) and carnosine synthase (CARNS) mRNA expression and 6 × 6 s repeated sprint ability (RSA) test. There was a significant diet × training interaction in soleus carnosine content, which was non-significantly increased (+11%) with mixed diet and non-significantly decreased (-9%) with vegetarian diet. Carnosine content in other muscles and gastrocnemius buffer capacity were not influenced by training. CARNS mRNA expression was independent of training, but decreased significantly in the vegetarian group. The performance during the RSA test improved by training, without difference between groups. We found a positive correlation (r = 0.517; p = 0.002) between an invasive and non-invasive method for muscle carnosine quantification. In conclusion, this study shows that 5 weeks sprint training has no effect on the muscle carnosine content and carnosine synthase mRNA.

Birth weight in relation to sex steroid status and body composition in young healthy male siblings.

CONTEXT: Sex steroid concentrations have a strong genetic determination, but environmental factors and body composition play an important role. From studies in children with intrauterine growth restriction, low birth weight has been associated with altered gonadotropin concentrations. OBJECTIVE: We aim to investigate sex steroid concentrations in healthy young brothers in relation to birth weight (normal gestational age), body composition, and parental steroid concentrations. DESIGN AND SETTING: We conducted a cross-sectional, population-based sibling pair study with inclusion of parental data. PARTICIPANTS: A total of 677 men (25-45 yr old) were included in this study, with 296 independent pairs of brothers and 122 fathers. MAIN OUTCOMES: We measured testosterone, estradiol, leptin, adiponectin, IGF-I (immunoassays), and free steroid hormones (calculated) in relation to birth weight and changes in body composition (dual-energy x-ray absorptiometry). RESULTS: Birth weight was associated with serum testosterone (P = 0.0004) and SHBG (P = 0.0001), independent from weight, age, or fat mass, whereas no association with (free) estradiol, LH, or FSH was found. Paternal testosterone (P = 0.02), estradiol (P = 0.04), and SHBG (P = 0.0004) were associated with the respective sex steroid concentrations in the brothers. Weight increase (population rank) during life, was associated with lower testosterone (-15%; P < 0.001), independent from current weight and with higher free estradiol concentrations (+8%; P = 0.002), whereas weight decrease was associated with higher testosterone (+13%; P < 0.001). CONCLUSION: Birth weight and paternal steroid concentrations are associated with testosterone concentrations, independent from adult weight. These findings support the concept of in utero programming across the range of birth weight.