The relationship of testosterone and AR CAG repeat genotype with knee extensor muscle function of young and older men

Relationships of sex hormones with muscle mass and muscle strength in male adolescents at different stages of puberty

This study analysed the associations of sex steroids with fat-free mass (FFM) and handgrip strength in 641 Chinese boys. Serum total testosterone (TT) and oestradiol were measured by chemiluminescence immunoassay. Free testosterone (FT) and oestradiol were calculated. FFM and handgrip strength were measured by bioelectrical impedance analysis and a hand dynamometer, respectively. Generalised additive models and multiple linear regression were used to explore the relationships. A subgroup analysis was conducted in early-mid pubertal and late-post pubertal groups. Age, height, weight, physical activity, intake of dietary protein and/or stage of puberty were adjusted. TT and FT were positively related to FFM and handgrip strength, with a curvilinear relationship being detected for handgrip strength (p<0.050). This curvilinear relationship was only observed in the late-post pubertal group, suggesting a potential threshold effect (FT>11.99ng/dL, β = 1.275, p = 0.039). In the early-mid pubertal group, TT and/or FT were linearly or near-linearly related to FFM or handgrip strength (β = 0.003-0.271, p<0.050). The association between FT and FFM was stronger than that in the late-post pubertal group. This study found that serum T had different associations with muscle parameters in Chinese early-mid pubertal and late-post pubertal boys. In the late-post pubertal boys, serum T was curvilinearly related to muscle strength with a threshold effect and its link with muscle mass was weaker.

Androgen receptor gene microsatellite polymorphism is associated with muscle mass and strength in bodybuilders and power athlete status

BACKGROUND

The androgen receptor (AR) gene contains a polymorphic trinucleotide (CAG) microsatellite repeat sequence (short or long alleles) that has been associated with fat-free mass in untrained men, which needs to be replicated in athletic cohorts.

AIM

The purpose of this study was to explore the AR (CAG)_n polymorphism in trained individuals.

SUBJECTS AND METHODS

A total of 61 professional bodybuilders (40 males, 21 females), 73 elite male sprinters and weightlifters and 186 male controls were enrolled in this study. The influence of the AR (CAG)_n polymorphism on muscle mass and strength was assessed in bodybuilders, while the frequencies of AR (CAG)_n alleles were compared between power athletes and non-athletes.

RESULTS

The polymorphism was associated with anthropometric and strength measurements in bodybuilders of both genders. Those with ≥21 CAG repeats (i.e. carriers of long alleles) exhibited greater (p < 0.05) body mass index, absolute muscle mass, arm/thigh circumference and upper/lower limb strength compared to those with <21 CAG repeats. Furthermore, carriers of ≥21 CAG repeats were more frequent among power athletes compared to controls (p = 0.0076).

CONCLUSIONS

Long alleles of the AR (CAG)_n polymorphism were associated with greater muscle mass and strength in bodybuilders, and power athlete status.

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

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

Evolving the neuroendocrine physiology of human and primate cooperation and collective action

While many hormones play vital roles in facilitating or reinforcing cooperative behaviour, the neurohormones underlying competitive and cooperative behaviours are largely conserved across all mammals. This raises the question of how endocrine mechanisms have been shaped by selection to produce different levels of cooperation in different species. Multiple components of endocrine physiology--from baseline hormone concentrations, to binding proteins, to the receptor sensitivity and specificity--can evolve independently and be impacted by current socio-ecological conditions or individual status, thus potentially generating a wide range of variation within and between species. Here, we highlight several neurohormones and variation in hormone receptor genes associated with cooperation, focusing on the role of oxytocin and testosterone in contexts ranging from parenting and pair-bonding to reciprocity and territorial defence. While the studies reviewed herein describe the current state of the literature with regard to hormonal modulators of cooperation and collective action, there is still a paucity of research on hormonal mechanisms that help facilitate large-scale collective action. We end by discussing several potential areas for future research.

Six weeks of conditioning exercise increases total, but not free testosterone in lifelong sedentary aging men

INTRODUCTION

Advancing age is associated with a gradual decline in circulating androgens, and the putative role of exercise training on systemic androgens remains to be adequately defined.

METHODS

The present investigation examined the impact of 6 weeks of supervised exercise training on resting levels of systemic hormones in a cohort of lifelong sedentary men [SED (n = 28), 62.5 ± 5.3 years], compared with a positive control group of age-matched lifelong exercisers [LE (n = 20), 60.4 ± 4.7 years, >30 years training history]. Blood hormones were sampled pre- and post-intervention from an antecubital forearm vein and analysed using electrochemiluminescent immunoassay. Cardiorespiratory fitness ([Formula: see text]) was determined via indirect calorimetry during an incremental cycle test to volitional exhaustion.

RESULTS

Analysis of variance (ANOVA) revealed a lack of significant change in any parameter amongst LE, whilst SED experienced a significant exercise-induced improvement in cardiorespiratory fitness and total testosterone (all p < 0.05). Concurrent increases in sex hormone-binding globulin (SHBG; p < 0.05) resulted in a lack of change to either bioavailable or calculated free testosterone (p > 0.05) amongst SED.

CONCLUSIONS

Although resting levels of systemic total testosterone increased in response to 6 weeks of exercise training, increases in SHBG negated any potential relationship between calculated-free or bioavailable testosterone. These findings indicate that increases in bioavailable testosterone fraction are not required for cardiorespiratory fitness improvements in aging men.

Exercise training and DNA methylation in humans

The response to exercise training (trainability) has been shown to have a strong heritable component. There is growing evidence suggesting that traits such as trainability do not only depend on the genetic code, but also on epigenetic signals. Epigenetic signals play an important role in the modulation of gene expression, through mechanisms such as DNA methylation and histone modifications. There is an emerging evidence to show that physical activity influences DNA methylation in humans. The present review aims to summarize current knowledge on the link between DNA methylation and physical activity in humans. We have critically reviewed the literature and only papers focused on physical activity and its influence on DNA methylation status were included; a total of 25 papers were selected. We concluded that both acute and chronic exercises significantly impact DNA methylation, in a highly tissue- and gene-specific manner. This review also provides insights into the molecular mechanisms of exercise-induced DNA methylation changes, and recommendations for future research.

Androgen effects on skeletal muscle: implications for the development and management of frailty

Androgens have potent anabolic effects on skeletal muscle and decline with age in parallel to losses in muscle mass and strength. This loss of muscle mass and function, known as sarcopenia, is the central event in development of frailty, the vulnerable health status that presages adverse outcomes and rapid functional decline in older adults. The potential role of falling androgen levels in the development of frailty and their utility as function promoting therapies in older men has therefore attracted considerable attention. This review summarizes current concepts and definitions in muscle ageing, sarcopenia and frailty, and evaluates recent developments in the study of androgens and frailty. Current evidence from observational and interventional studies strongly supports an effect of androgens on muscle mass in ageing men, but effects on muscle strength and particularly physical function have been less clear. Androgen treatment has been generally well–tolerated in studies of older men, but concerns remain over higher dose treatments and use in populations with high cardiovascular risk. The first trials of selective androgen receptor modulators (SARMs) suggest similar effects on muscle mass and function to traditional androgen therapies in older adults. Important future directions include the use of these agents in combination with exercise training to promote functional ability across different populations of older adults, as well as more focus on the relationships between concurrent changes in hormone levels, body composition and physical function in observational studies.

Correlation study between the polymorphism of repetitive sequence in gene CAG of androgen receptor and the occurrence and progression of prostate cancer

OBJECTIVE

To explore the relation between the polymorphism of repetitive sequence in gene CAG of androgen receptor (AR) and the susceptibility and clinical stages as well as pathological grading of prostate cancer among Han population.

METHOD

Sixty-eight cases with prostate cancer hospitalized in Urinary Surgery Department from Feb. 2010 to Feb. 2012 and 60 healthy cases were chosen as research subjects. Methods of PCR and direct sequencing were adopted to detect DNA sequence of AR gene and the length of repetitive sequence in CAG.

RESULTS

The lengths of repetitive sequence in CAG of patients with prostate cancer and healthy people were (22.3±4.6) and (23.0±4.9), respectively showing no statistical significance. Comparing length (repetitive sequence of CAG)>22, those with that < 22 suffer a remarkably higher risk of prostate cancer (P<0.05). The number of repetitive sequence in CAG of patients at clinical stage C-D was less than that of patients at stage B, and the number of repetitive sequence in CAG of patients with poorly differentiated prostate cancer was also less than that of patients with moderately and highly differentiated prostate cancer. But there was no statistical significance int the difference (P>0.05); the proportion of patients with length <22 at clinical stage C-D was much larger than that of patients at clinical stage B (P<0.05), and as the aggravation of pathological grading, the proportion of patients with the length <22 was also remarkably increased and there was significant difference between patients with highly differentiated prostate cancer and those with poorly differentiated prostate cancer (P<0.05).

CONCLUSIONS

There is correlation between the occurrence and development of prostate cancer in Han population and the polymorphism of repetitive sequence in gene CAG of androgen receptor. The less the number of repetitive sequence in CAG is, the higher the risk of prostate cancer will be and the more severe the clinical stage and pathological grading will be.

Advances in exercise, fitness, and performance genomics in 2012

A small number of excellent articles on exercise genomics issues were published in 2012. A new PYGM knock-in mouse model will provide opportunities to investigate the exercise intolerance and very low activity level of people with McArdle disease. New reports on variants in ACTN3 and ACE have increased the level of uncertainty regarding their true role in skeletal muscle metabolism and strength traits. The evidence continues to accumulate on the positive effects of regular physical activity on body mass index or adiposity in individuals at risk of obesity as assessed by their FTO genotype or by the number of risk alleles they carry at multiple obesity-susceptibility loci. The serum levels of triglycerides and the risk of hypertriglyceridemia were shown to be influenced by the interactions between a single nucleotide polymorphism (SNP) in the NOS3 gene and physical activity level. Allelic variation at nine SNPs was shown to account for the heritable component of the changes in submaximal exercise heart rate induced by the HERITAGE Family Study exercise program. SNPs at the RBPMS, YWHAQ, and CREB1 loci were found to be particularly strong predictors of the changes in submaximal exercise heart rate. The 2012 review ends with comments on the importance of relying more on experimental data, the urgency of identifying panels of genomic predictors of the response to regular exercise and particularly of adverse responses, and the exciting opportunities offered by recent advances in our understanding of the global architecture of the human genome as reported by the Encyclopedia of DNA Elements project.

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.

Strength Training in the Elderly People

Proces starzenia się człowieka charakteryzuje się licznymi zmianami, które dotyczą struktur na poziomie molekularnym, komórkowym, narządowym oraz całego organizmu. Jednym ze skutków zmniejszającej się aktywności fizycznej oraz postępujących procesów starzenia się organizmu człowieka jest systematyczne obniżanie się siły mięśniowej, któremu towarzyszy pogorszenie sprawności w podstawowych czynnościach codziennych. Ćwiczenia fizyczne, w tym ćwiczenia ukierunkowane na zwiększenie siły mięśniowej, wykonywane przez osoby starsze spowalniają proces starzenia się i zapobiegają występowaniu wielu chorób. Jakkolwiek nawet stała i regularna aktywność fizyczna nie może zapobiec spadkowi siły wraz z wiekiem, to zmiany adaptacyjne w centralnym układzie nerwowym i mięśniowym wywołane stosowaniem ćwiczeń siłowych w dużym stopniu mogą rekompensować ten proces.

Ćwiczenia ukierunkowane na zwiększenie siły i masy mięśniowej, nazywane ćwiczeniami siłowymi, są na świecie powszechnie znane i stosowane przez ludzi w podeszłym wieku. W Polsce model usprawniania fizycznego osób starszych bazuje prawie wyłącznie na ćwiczeniach wytrzymałościowych i rozciągających, a stosowanie klasycznych ćwiczeń siłowych często wywołuje obawy.

Celem pracy jest uzasadnienie potrzeby stosowania ćwiczeń ukierunkowanych na zwiększenie siły mięśniowej w usprawnianiu osób starszych i przedstawienie efektów ich zastosowania.

Genes, physical fitness and ageing

Persons aged 80 years and older are the fastest growing segment of the population. As more individuals live longer, we should try to understand the mechanisms involved in healthy ageing and preserving functional independence in later life. In elderly people, functional independence is directly dependent on physical fitness, and ageing is inevitably associated with the declining functions of systems and organs (heart, lungs, blood vessels, skeletal muscles) that determine physical fitness. Thus, age-related diminished physical fitness contributes to the development of sarcopenia, frailty or disability, all of which severely deteriorate independent living and thus quality of life. Ageing is a complex process involving many variables that interact with one another, including - besides lifestyle factors or chronic diseases - genetics. Thus, several studies have examined the contribution of genetic endowment to a decline in physical fitness and subsequent loss of independence in later life. In this review, we compile information, including data from heritability, candidate-gene association, linkage and genome-wide association studies, on genetic factors that could influence physical fitness in the elderly.