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

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

High-Load Resistance Exercise Augments Androgen Receptor-DNA Binding and Wnt/β-Catenin Signaling without Increases in Serum/Muscle Androgens or Androgen Receptor Content

The purpose of this study was (1) to determine the effect of single bouts of volume- and intensity-equated low- (LL) and high-load (HL) full-body resistance exercise (RE) on AR-DNA binding, serum/muscle testosterone and dihydrotestosterone, muscle androgen receptor (AR), and AR-DNA binding; and, (2) to determine the effect of RE on sarcoplasmic and nucleoplasmic β-catenin concentrations in order to determine their impact on mediating AR-DNA binding in the absence/presence of serum/muscle androgen and AR protein. In a cross-over design, 10 resistance-trained males completed volume- and intensity-equated LL and HL full-body RE. Blood and muscle samples were collected at pre-, 3 h-, and 24 h post-exercise. Separate 2 × 3 factorial analyses of variance (ANOVAs) with repeated measures and pairwise comparisons with a Bonferroni adjustment were used to analyze the main effects. No significant differences were observed in muscle AR, testosterone, dihydrotestosterone, or serum total testosterone in either condition (p > 0.05). Serum-free testosterone was significantly decreased 3 h post-exercise and remained significantly less than baseline 24 h post-exercise in both conditions (p < 0.05). In response to HL, AR-DNA binding significantly increased at 3 h post-exercise (p < 0.05), whereas no significant differences were observed at any time in response to LL (p > 0.05). Moreover, sarcoplasmic β-catenin was significantly greater in HL (p < 0.05) without significant changes in nucleoplasmic β-catenin (p > 0.05). In conclusion, increases in AR-DNA binding in response to HL RE indicate AR signaling may be load-dependent. Furthermore, despite the lack of increase in serum and muscle androgens or AR content following HL RE, elevations in AR-DNA binding with elevated sarcoplasmic β-catenin suggests β-catenin may be facilitating this response.

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.

Recovery responses of testosterone, growth hormone, and IGF-1 after resistance exercise

The complexity and redundancy of the endocrine pathways during recovery related to anabolic function in the body belie an oversimplistic approach to its study. The purpose of this review is to examine the role of resistance exercise (RE) on the recovery responses of three major anabolic hormones, testosterone, growth hormone(s), and insulin-like growth factor 1. Each hormone has a complexity related to differential pathways of action as well as interactions with binding proteins and receptor interactions. Testosterone is the primary anabolic hormone, and its concentration changes during the recovery period depending on the upregulation or downregulation of the androgen receptor. Multiple tissues beyond skeletal muscle are targeted under hormonal control and play critical roles in metabolism and physiological function. Growth hormone (GH) demonstrates differential increases in recovery with RE based on the type of GH being assayed and workout being used. IGF-1 shows variable increases in recovery with RE and is intimately linked to a host of binding proteins that are essential to its integrative actions and mediating targeting effects. The RE stress is related to recruitment of muscle tissue with the glandular release of hormones as signals to target tissues to support homeostatic mechanisms for metabolism and tissue repair during the recovery process. Anabolic hormones play a crucial role in the body’s response to metabolism, repair, and adaptive capabilities especially in response to anabolic-type RE. Changes of these hormones following RE during recovery in the circulatory biocompartment of blood are reflective of the many mechanisms of action that are in play in the repair and recovery process.

Upper-body resistance exercise augments vastus lateralis androgen receptor-DNA binding and canonical Wnt/β-catenin signaling compared to lower-body resistance exercise in resistance-trained men without an acute increase in serum testosterone

The purpose of the study was to determine the effect of single bouts of lower-body (LB) and upper- and lower-body (ULB) resistance exercise on serum testosterone concentrations and the effects on muscle testosterone, dihydrotestosterone (DHT), androgen receptor (AR) protein content, and AR-DNA binding. A secondary purpose was to determine the effects on serum wingless-type MMTV integration site (Wnt4) levels and skeletal muscle β-catenin content. In a randomized cross-over design, exercise bouts consisted of a LB and ULB protocol, and each bout was separated by 1 week. Blood and muscle samples were obtained before exercise and 3 and 24h post-exercise; blood samples were also obtained at 0.5, 1, and 2 h post-exercise. Statistical analyses were performed by separate two-way factorial analyses of variance (ANOVA) with repeated measures. No significant differences from baseline were observed in serum total and free testosterone and skeletal muscle testosterone and DHT with either protocol (p>0.05). AR protein was significantly increased at 3 h post-exercise and decreased at 24 h post-exercise for ULB, whereas AR-DNA binding was significantly increased at 3 and 24h post-exercise (p<0.05). In response to ULB, serum Wnt4 was significantly increased at 0.5, 1, and 2 h post-exercise (p<0.05) and β-catenin was significantly increased at 3 and 24 h post-exercise (p<0.05). It was concluded that, despite a lack of increase in serum testosterone and muscle androgen concentrations from either mode of resistance exercise, ULB resistance exercise increased Wnt4/β-catenin signaling and AR-DNA binding.

Genome-wide analysis of DNA methylation before-and after exercise in the thoroughbred horse with MeDIP-Seq

Athletic performance is an important criteria used for the selection of superior horses. However, little is known about exercise-related epigenetic processes in the horse. DNA methylation is a key mechanism for regulating gene expression in response to environmental changes. We carried out comparative genomic analysis of genome-wide DNA methylation profiles in the blood samples of two different thoroughbred horses before and after exercise by methylated-DNA immunoprecipitation sequencing (MeDIP-Seq). Differentially methylated regions (DMRs) in the pre-and post-exercise blood samples of superior and inferior horses were identified. Exercise altered the methylation patterns. After 30 min of exercise, 596 genes were hypomethylated and 715 genes were hypermethylated in the superior horse, whereas in the inferior horse, 868 genes were hypomethylated and 794 genes were hypermethylated. These genes were analyzed based on gene ontology (GO) annotations and the exercise-related pathway patterns in the two horses were compared. After exercise, gene regions related to cell division and adhesion were hypermethylated in the superior horse, whereas regions related to cell signaling and transport were hypermethylated in the inferior horse. Analysis of the distribution of methylated CpG islands confirmed the hypomethylation in the gene-body methylation regions after exercise. The methylation patterns of transposable elements also changed after exercise. Long interspersed nuclear elements (LINEs) showed abundance of DMRs. Collectively, our results serve as a basis to study exercise-based reprogramming of epigenetic traits.

Acute and chronic effects of resistance exercise on the testosterone and cortisol responses in obese males: a systematic review

The biosynthesis and metabolism of testosterone and cortisol are altered by the high levels of adipose tissue and the constant state of low-grade inflammation of obesity. Resistance exercise (REx) has become one of the main lifestyle interventions prescribed to obese individuals due to its ability to positively influence body composition and some biomarkers, such as cholesterol and insulin resistance. Yet, little research has been done in obese examining the effects of REx on the testosterone and blood cortisol responses, two integral hormones in both exercise and obesity. The obese testosterone response to REx and whether or not it is blunted compared to lean individuals remains elusive. Conflicting findings concerning the blood cortisol response have also been reported, likely due to variance in REx protocol and the level of obesity in the participants in studies. Comparatively, both of these hormones have been extremely well studied in untrained lean males, which could be used as a basis for future research in obese males. However, without this endocrinological information, it is unknown if the current acute REx prescriptions are appropriate for eliciting a favorable acute endocrinological response, and ultimately, a positive chronic adaptation in obese males.

Aging and sequential resistance exercise bout effects on housekeeping gene messenger RNA expression in human skeletal muscle

The purpose of this study was to investigate how age and 1 week of conventional resistance exercise affects commonly used housekeeping gene (HKG) messenger RNAs (mRNAs) in skeletal muscle. Ten college-aged (18-25 years) and 10 older (60-76 years) men completed 3 lower-body resistance exercise bouts on Monday, Wednesday, and Friday, and muscle samples were obtained before bout 1 (T1), 48 hours after the first (T2) and second bouts (T3), and 24 hours after the third bout (T4). Raw Ct values indicated that β-actin and cyclophilin were more highly expressed in older vs. younger males (p < 0.01) at T1. When normalizing each HKG mRNA to the other 4 HKG mRNAs, CYC increased at T3 and glyceraldehyde-3-phosphate dehydrogenase decreased at T2 (p < 0.05) in younger men. This is one of the few studies to suggest that explicit HKG mRNAs should be used depending upon age group and resistance exercise intervention.

Postexercise myogenic gene expression: are human findings lost during translation?

Muscle progenitor cell (MPC) activity is exercise responsive. Post resistance-exercise alterations in myogenic messenger RNAs (mRNAs) found by us and others may initiate these events. However, these mRNA data in the absence of microscopic MPC activity data have limited this interpretation. Alternatively, with our acute exercise data as our basis, we propose that these genes may control other hypertrophic processes in postmitotic fibers.

Acute loading and aging effects on myostatin pathway biomarkers in human skeletal muscle after three sequential bouts of resistance exercise

To determine the influence of age and resistance exercise on myostatin pathway-related genes, younger (n = 10; 28 ± 5 years) and older (n = 10; 68 ± 6 years) men underwent four testing conditions (T1-T4). A baseline (T1) muscle sample was obtained, whereas the second and third biopsies were obtained 48 hours following the first and second training sessions (T2, T3), and a final biopsy was taken 24 hours following T3. The training sessions consisted of 3 sets of 10 repetitions (80% of one repetition maximum) on leg press, hack squat, and leg extension exercises. Follistatin (FST) messenger RNA was greater in older compared with younger men at T1 and T2 (p < .05). Follistatin-like 3 (FSTL3) messenger RNA was greater in older compared with younger men at T1 and T4 (p < .05). In older men, there was a significant decrease in myostatin (MSTN) messenger RNA at T4 (p < .05). Older men contained less active (Ser-425 phosphorylated) SMAD3 (p-SMAD3) protein than younger men at T3 and T4 (p < .05).Although it is well known that younger individuals possess a greater hypertrophic potential to resistance exercise, it appears that older individuals may paradoxically possess a more favorable resistance exercise response regarding myostatin pathway-related genes and a protein marker of pathway activity. Future research is warranted to examine the physiological significance of this age-dependent mechanism.

Myogenic mRNA markers in young and old human skeletal muscle prior to and following sequential exercise bouts

This study examined how multiple bouts of conventional resistance training affected the mRNA expression of transcripts and a protein associated with satellite cell activity in human skeletal muscle. Ten younger men (means ± SE; age, 21.0 ± 0.5 years; body mass, 82.3 ± 4.2 kg; height, 178.4 ± 2.2 cm; percent body fat, 15.4% ± 2.9%) and 10 older men (age, 66.4 ± 1.6 years; body mass, 94.2 ± 3.7 kg; height, 180.9 ± 2.2 cm; percent body fat, 27.4% ± 1.8%) completed 3 lower-body workouts (Monday, Wednesday, Friday; 9 sets of 10 repetitions at 80% 1 repetition maximum). Vastus lateralis muscle biopsies were collected prior to intervention (T1), 48 h following workout 1 (T2), 48 h following workout 2 (T3), and 24 h following workout 3 (T4). Real-time reverse transcription-polymerase chain reaction was performed to assess genes of interest, and muscle proliferating cell nuclear antigen (PCNA) was assessed using Western blotting. The CYCLIN D1 gene was expressed more highly in the older vs. younger men (p < 0.05), whereas the expression of all other genes and muscle PCNA were similar between age groups. MYOD mRNA expression increased at T2 (p < 0.05) and MHCEMB gene expression modestly increased (p < 0.05) at T4 relative to baseline expression values in the younger men. Baseline elevations in CYCLIN D1 mRNA expression in older persons may indicate that a compensatory expression of this transcript is occurring in an attempt to retain the muscle's proliferative potential. Increases in MYOD and MHCEMB indicate that 1 week of conventional resistance exercise may i crease myogenic activity, including satellite cell proliferation and differentiation, respectively, in younger men.

Effects of age on serum hormone concentrations and intramuscular proteolytic signaling before and after a single bout of resistance training

This study examined mRNA expression patterns for atrogin-1 and muscle ring finger-1 (MuRF-1) before and 24 hours after a resistance training bout. Furthermore, basal, 5-minute and 24-hour postexercise serum concentrations of cortisol and insulin like growth factor-1 (IGF-1) and the relationships between these hormones and the genetic expression patterns of atrogin-1 and MuRF-1 were examined. Younger and older men completed a resistance exercise bout consisting of 3 × 10 repetitions at 80% of their predetermined 1 repetition maximum for Smith squat, leg press and leg extension. Muscle biopsies from the vastus lateralis were obtained before and 24 hours after exercise. Basal and postexercise gene expression differences between age groups were analyzed using the Mann-Whitney U test, whereas separate 2 × 3 repeated measures analyses of variance were performed to analyze changes in hormone concentrations. Spearman's correlations were performed to examine relationships between gene expression patterns and hormone concentrations. Serum cortisol was significantly greater in younger men before and 24 hours after exercise (p < 0.05), whereas serum IGF-1 was significantly greater in younger men at all time points (p < 0.001). Exercise significantly increased cortisol 5 minutes after exercise in both groups (p < 0.05), whereas older men experienced significant elevations in IGF-1 24 hours postexercise (p < 0.05). At baseline, MuRF-1 gene expression was significantly greater in older men (p = 0.03), whereas no age-related differences were found for atrogin-1 (p = 0.24). Fold change in atrogin-1 and MuRF-1 24 hours postexercise revealed no significant differences between younger and older men. Differential baseline expression of MuRF-1 may suggest a regulatory attempt by the aging transcriptome to accommodate changes necessary for homeostatic maintenance. An enhanced understanding of molecular and genetic level adaptations can aid researchers in developing optimal therapeutic and exercise interventions to mitigate decrements in force, power, and loss of muscle mass seen in aging and many clinical populations.

Heavy resistance exercise training and skeletal muscle androgen receptor expression in younger and older men

Effects of heavy resistance exercise on serum testosterone and skeletal muscle androgen receptor (AR) concentrations were examined before and after a 21-week resistance training period. Seven healthy untrained young adult men (YT) and ten controls (YC) as well as ten older men (OT) and eight controls (OC) volunteered as subjects. Heavy resistance exercise bouts (5 × 10 RM leg presses) were performed before and after the training period. Muscle biopsies were obtained before and 1h and 48 h after the resistance exercise bouts from m.vastus lateralis (VL) to determine cross-sectional area of muscle fibers (fCSA) and AR mRNA expression and protein concentrations. No changes were observed in YC and OC while resistance training led to significant increases in maximal strength of leg extensors (1 RM), fCSA and lean body mass in YT and OT. Acute increases occurred in serum testosterone concentrations due to resistance exercises but basal testosterone remained unaltered. Mean AR mRNA expression and protein concentration remained unchanged after heavy resistance exercise bouts compared to pre-values. The individual pre- to post-training changes in resting (pre-exercise) AR protein concentration correlated with the changes in fCSA and lean body mass in the combined group of YT and OT. Similarly, it correlated with the changes in 1 RM in YT. Although mean AR expression did not changed due to the resistance exercise training, the present findings suggest that the individual changes of AR protein concentration in skeletal muscle following resistance training may have an impact on training-induced muscular adaptations in both younger and older men.