Frequent sequence variation in the human myostatin (GDF8) gene as a marker for analysis of muscle-related phenotypes

Genetic variants in myostatin and its receptors promote elite athlete status

BACKGROUND

While product of the myostatin gene (MSTN) is an important factor influencing muscle growth, which is well confirmed in nonhuman species, it has not been clearly confirmed whether MSTN expression influences interindividual differences in skeletal muscle mass, affects posttraining changes, or plays a role in the age-related loss of muscle mass and function in humans. Although the inconclusive results are usually explained by ethnic differences and the low frequency of some alleles, it is possible that the role of receptors (ACVR2A and ACVR2B) that affect the biological activity of myostatin is crucial. Therefore, we investigated the sequences of the MSTN, ACVR2A, and ACVR2B genes and determined the interaction between allelic variants and athletic performance and competition level in the Caucasian population. One hundred-two athletes were recruited for the sequencing study, and whole-genome sequencing (WGS) was performed. Second, 330 athletes and 365 controls were included, and real-time PCR was performed.

RESULTS

The sequence analysis revealed two polymorphisms relatively common in the athlete cohort, and the alternate allele showed overrepresentation in athletes: MSTN rs11333758 and ACVR2A rs3764955. Regarding the polymorphic site MSTN rs11333758, there was a significant overrepresentation of the -/- genotype in all high-elite and mixed-sport high-elite athletes. Carriers of the ACVR2A rs3764955 CC and GG genotypes were more likely to be elite and high-elite athletes. In addition, carriers of the CC genotype were more likely to be in the mixed-sport subelite group. The gene‒gene interaction analysis revealed that mixed-sport high elite athletes showed significant underrepresentation of the ACVR2A rs3764955 GC - MSTN rs11333758 AA genotype combination. In the same group, we observed a significant overrepresentation of the ACVR2A rs3764955 GC - MSTN rs11333758 -/- and the ACVR2A rs3764955 CC - MSTN rs11333758 -/- genotype combinations.

CONCLUSIONS

We showed that the specific genotypes of the MSTN rs11333758 and ACVR2A rs3764955, either individually or in gene‒gene combination, are significantly associated with athletes' competition level in the Polish population, especially in the mixed-sports athlete group. Thus, although further research is required, these polymorphisms, alone or in combination with other polymorphisms, are among the numerous candidates that could explain individual variations in muscle phenotypes.

Associations Between Circulating Levels of Myostatin and Plasma β-Amyloid 42/40 in a Biracial Cohort of Older Adults

BACKGROUND

Myostatin, a cytokine produced by skeletal muscle, may influence Alzheimer's disease (AD) pathogenesis, but sparse evidence exists in humans. We assessed the association between circulating levels of myostatin at Year 1 and plasma levels of β-amyloid 42/40 at Year 2, a marker of AD pathology, in a biracial cohort of older adults.

METHODS

We studied 403 community-dwelling older adults enrolled in the Health, Aging and Body Composition Study from Memphis, Tennessee, and Pittsburgh, PA. Mean age was 73.8 ± 3 years; 54% were female; and 52% were Black. Serum myostatin levels were measured at Year 1, plasma β-amyloid 42/40 levels in Year 2 (higher ratio indicating lower amyloid load). Multivariable linear regression analyses tested the association of serum myostatin with plasma levels of β-amyloid 42/40 adjusted for computed-tomography-derived thigh muscle cross-sectional area, demographics, APOe4 allele, and risk factors for dementia. We tested for 2-way.interactions between myostatin and race or sex; results were stratified by race and sex.

RESULTS

In multivariable models, myostatin was positively associated with plasma levels of β-amyloid 42/40 (standardized regression coefficient: 0.145, p = .004). Results were significant for white men and women (0.279, p = .009, and 0.221, p = .035, respectively) but not for Black men or women; interactions by race and gender were not statistically significant.

CONCLUSIONS

Higher serum myostatin was associated with lower amyloid burden, independently of APOe4 alleles, muscle area and other established risk factors for dementia. The role of myostatin in AD pathogenesis and the influence of race should be further investigated.

Association of Myostatin Gene Polymorphisms with Strength and Muscle Mass in Athletes: A Systematic Review and Meta-Analysis of the MSTN rs1805086 Mutation

Polymorphism (rs1805086), c.458A>G, p.Lys(K)153Arg(R), (K153R) of the myostatin gene (MSTN) has been associated with a skeletal muscle phenotype (hypertrophic response in muscles due to strength training). However, there are not enough reliable data to demonstrate whether MSTN rs1805086 K and R allelic variants are valid genetic factors that can affect the strength phenotype of athletes' skeletal muscles. The aim is to conduct a systematic review and meta-analysis of the association of MSTN rs1805086 polymorphism with the strength phenotype of athletes. This study analyzed 71 research articles on MSTN and performed a meta-analysis of MSTN K153R rs1805086 polymorphism in strength-oriented athletes and a control (non-athletes) group. It was found that athletes in the strength-oriented athlete group had a higher frequency of the R minor variant than that in the control group (OR = 2.02, P = 0.05). Thus, the obtained results convincingly demonstrate that there is an association between the studied polymorphism and strength phenotype of athletes; therefore, further studies on this association are scientifically warranted.

Genetic polymorphisms of muscular fitness in young healthy men

The effects of genetic polymorphisms on muscle structure and function remain elusive. The present study tested for possible associations of 16 polymorphisms (across ten candidate genes) with fittness and skeletal muscle phenotypes in 17- to 37-year-old healthy Caucasian male endurance (n = 86), power/strength (n = 75) and team athletes (n = 60), and non-athletes (n = 218). Skeletal muscle function was measured with eight performance tests covering multiple aspects of muscular fitness. Along with body mass and height, the upper arm and limb girths, and maximal oxygen uptake were measured. Genotyping was conducted on DNA extracted from blood. Of the 16 polymorphisms studied, nine (spanning seven candidate genes and four gene families/signalling pathways) were independently associated with at least one skeletal muscle fitness measure (size or function, or both) measure and explained up to 4.1% of its variation. Five of the studied polymorphisms (activin- and adreno-receptors, as well as myosine light chain kinase 1) in a group of one to three combined with body height, age and/or group explained up to 20.4% of the variation of muscle function. ACVR1B (rs2854464) contributed 2.0–3.6% to explain up to 14.6% of limb proximal girths. The G allele (genotypes AG and GG) of the ACVR1B (rs2854464) polymorphism was significantly overrepresented among team (60.4%) and power (62.0%) athletes compared to controls (52.3%) and endurance athletes (39.2%), and G allele was also most consistently/frequently associated with muscle size and power. Overall, the investigated polymorphisms determined up to 4.1% of the variability of muscular fitness in healthy young humans.

Effect of quercetin on muscle growth and antioxidant status of the dark sleeper Odontobutis potamophila

Quercetin is a flavanol beneficial in reducing fat, promoting muscle growth, and Anti-oxidation. To study its effects in freshwater fish, the full-length cDNA of the follistatin (FST) and myostatin (MSTN) genes of the dark sleeper Odontobutis potamophila were cloned for the first time. Juvenile individual O. potamophila was exposed to quercetin at one of four concentrations (0, 2.5, 5, and 10 mg/L) for 21 days. The expression level of MSTN which inhibits muscle growth in the quercetin solution was lower than in the unexposed control group. The genes that promote muscle growth are in TGF-β superfamily like FST, TGF-β1 (transforming growth factor-beta 1), and Myogenic regulatory factors (MRFs) like Myf5 (myogenic factor 5), MyoD (myogenic differentiation), MyoG (myogenin), were higher than in the control group. Apolipoprotein and growth hormone receptor transcription levels in the quercetin-treated fish were significantly lower than in the control group. The concentrations of triglyceride, low-density lipoprotein cholesterol, and high-density lipoprotein cholesterol in the muscle tissue decreased, and the lipid-lowering function of quercetin was also demonstrated at the biochemical level. In this study, we analyzed the mRNA levels of AKT, Keap1 (kelch-like ECH-associated protein 1), Nrf2 (NF-E2-related factor 2) oxidation-related genes in the Nrf2/ARE antioxidant pathway, and Malondialdehyde (MDA), catalase (CAT) activity and glutathione (GSH) content in the hepatopancreas of O. potamophila after quercetin treatment, the mRNA expression of AKT, Nrf2 and CAT activity and GSH content are higher than in the control group. Quercetin enhances antioxidant properties and positively affects muscle growth. The results showed that quercetin has no significant effects on the growth performance of O. potamophila, but is effective in increasing muscle growth rate and lowering muscle fat content.

Genetics and sports performance: the present and future in the identification of talent for sports based on DNA testing

The impact of genetics on physiology and sports performance is one of the most debated research aspects in sports sciences. Nearly 200 genetic polymorphisms have been found to influence sports performance traits, and over 20 polymorphisms may condition the status of the elite athlete. However, with the current evidence, it is certainly too early a stage to determine how to use genotyping as a tool for predicting exercise/sports performance or improving current methods of training. Research on this topic presents methodological limitations such as the lack of measurement of valid exercise performance phenotypes that make the study results difficult to interpret. Additionally, many studies present an insufficient cohort of athletes, or their classification as elite is dubious, which may introduce expectancy effects. Finally, the assessment of a progressively higher number of polymorphisms in the studies and the introduction of new analysis tools, such as the total genotype score (TGS) and genome-wide association studies (GWAS), have produced a considerable advance in the power of the analyses and a change from the study of single variants to determine pathways and systems associated with performance. The purpose of the present study was to comprehensively review evidence on the impact of genetics on endurance- and power-based exercise performance to clearly determine the potential utility of genotyping for detecting sports talent, enhancing training, or preventing exercise-related injuries, and to present an overview of recent research that has attempted to correct the methodological issues found in previous investigations.

High ovarian GDF-8 levels contribute to elevated estradiol production in ovarian hyperstimulation syndrome by stimulating aromatase expression

Rationale: Growth differentiation factor-8 (GDF-8), also known as myostatin, belongs to the transforming growth factor-beta (TGF-β) superfamily. GDF-8 is expressed in the ovary and regulates various ovarian functions. Ovarian hyperstimulation syndrome (OHSS) is one of the most serious disorders during in vitro fertilization treatment. Aromatase, encoded by the CYP19A1 gene, is the enzyme that catalyzes the final step in estradiol (E2) biosynthesis. It has been demonstrated that high serum E2 levels are associated with the development of OHSS. However, the effects of GDF-8 on aromatase expression and its roles in the pathogenesis of OHSS remain unclear. Methods: The effect of GDF-8 on aromatase expression and the underlying mechanisms were explored by a series of in vitro experiments in primary human granulosa-lutein (hGL) and KGN cells. Rat OHSS model and human follicular fluid samples were used to examine the roles of the GDF-8 system in the pathogenesis of OHSS. Results: We demonstrate that GDF-8 stimulates aromatase expression and E2 production in hGL and KGN cells. In addition, TGF-β type I receptor ALK5-mediated SMAD2/3 signaling is required for GDF-8-induced aromatase expression and E2 production. Using a rat OHSS model, we show that the aromatase and GDF-8 levels are upregulated in the ovaries of OHSS rats. Blocking the function of ALK5 by the administration of its inhibitor, SB431542, alleviates OHSS symptoms and the upregulation of aromatase. Clinical results reveal that the protein levels of GDF-8 are upregulated in the follicular fluid of OHSS patients. Moreover, the expression of GDF-8 is increased in hGL cells of OHSS patients. Conclusions: This study helps to elucidate the mechanisms mediating the expression of aromatase in human granulosa cells, which may lead to the development of alternative therapeutic approaches for OHSS.

Association study of performance-related polymorphisms in Brazilian combat-sport athletes highlights variants in the GABPB1 gene

Combat sports are an intermittent sport, with mixed anaerobic and aerobic energy production. Here, we investigated whether the polymorphisms that have been previously suggested as genetic markers for endurance or power phenotypes were associated with combat-sport athletic status. A total of 23 previously reported performance-related polymorphisms were examined in a cohort of 1,129 Brazilian individuals (164 combat-sport athletes and 965 controls), using a case-control association study. We found that the GA-binding protein transcription factor subunit beta 1 (GABPβ1) gene (also known as nuclear respiratory factor 2; NRF2) was associated with athletic status, with the minor G (rs7181866) and T (rs8031031) alleles overrepresented in athletes (P ≤ 0.003), especially among world-class athletes (P ≤ 0.0002). These findings indicate that single-nucleotide polymorphisms (SNPs) within the GABPβ1 gene increase the likelihood of an individual being a combat-sport athlete, possibly because of a better mitochondrial response to intermittent exercises.

Myostatin A55T Genotype is Associated with Strength Recovery Following Exercise-Induced Muscle Damage

Myostatin A55T genotype is one of the candidates showing inter-individual variation in skeletal muscle phenotypes. The aim of this study was to investigate the effect of the myostatin A55T genotype on markers of muscle damage after eccentric exercise. Forty-eight young, healthy male college students (age = 24.8 ± 2.2 years, height = 176.7 ± 5.3 cm, weight = 73.7 ± 8.3 kg) were enrolled in this study, and muscle damage was induced through 50 reps of maximal eccentric muscle contraction. As markers of muscle damage, maximal isometric strength (MIS), muscle soreness, creatine kinase (CK), and aspartate transaminase (AST) were measured. Myostatin A55T genotypes were classified into homozygous myostatin A55T allele (AA, n = 34, 72%), heterozygous myostatin A55T allele (AT, n = 13, 26%), and homozygous mutant carriers (TT, n = 1, 2%). After eccentric exercise, the subjects with heterozygous for AT showed markedly quicker MIS recovery compared to the AA group (p = 0.042). However, there were no significant variations in muscle soreness (p = 0.379), CK (p = 0.955), and AST (p = 0.706) among the groups. These results suggest that AT in myostatin A55T genotype may be associated with quicker strength recovery following exercise-induced muscle damage.

Beyond the Big Five: Investigating Myostatin Structure, Polymorphism and Expression in Camelus dromedarius

Myostatin, a negative regulator of skeletal muscle mass in animals, has been shown to play a role in determining muscular hypertrophy in several livestock species, and a high degree of polymorphism has been previously reported for this gene in humans and cattle. In this study, we provide a characterization of the myostatin gene in the dromedary (Camelus dromedarius) at the genomic, transcript and protein level. The gene was found to share high structural and sequence similarity with other mammals, notably Old World camelids. 3D modeling highlighted several non-conservative SNP variants compared to the bovine, as well as putative functional variants involved in the stability of the myostatin dimer. NGS data for nine dromedaries from various countries revealed 66 novel SNPs, all of them falling either upstream or downstream the coding region. The analysis also confirmed the presence of three previously described SNPs in intron 1, predicted here to alter both splicing and transcription factor binding sites (TFBS), thus possibly impacting myostatin processing and/or regulation. Several putative TFBS were identified in the myostatin upstream region, some of them belonging to the myogenic regulatory factor family. Patterns of SNP distribution across countries, as suggested by Bayesian clustering of the nine dromedaries using the 69 SNPs, pointed to weak geographic differentiation, in line with known recurrent gene flow at ancient trading centers along caravan routes. Myostatin expression was investigated in a set of 8 skeletal muscles, both at transcript and protein level, via Digital Droplet PCR and Western Blotting, respectively. No significant differences were observed at the transcript level, while, at the protein level, the only significant differences concerned the promyostatin dimer (75 kDa), in four pair-wise comparisons, all involving the tensor fasciae latae muscle. Beside the mentioned band at 75 kDa, additional bands were observed at around 40 and 25 kDa, corresponding to the promyostatin monomer and the active C-terminal myostatin dimer, respectively. Their weaker intensity suggests that the unprocessed myostatin dimers could act as important reservoirs of slowly available myostatin forms. Under this assumption, the sequential cleavage steps may contribute additional layers of control within an already complex regulatory framework.

Myostatin gene promoter: structure, conservation and importance as a target for muscle modulation

Myostatin (MSTN) is one of the key factors regulating myogenesis. Because of its role as a negative regulator of muscle mass deposition, much interest has been given to its protein and, in recent years, several studies have analysed MSTN gene regulation. This review discusses the MSTN gene promoter, focusing on its structure in several animal species, both vertebrate and invertebrate. We report the important binding sites considering their degree of phylogenetic conservation and roles they play in the promoter activity. Finally, we discuss recent studies focusing on MSTN gene regulation via promoter manipulation and the potential applications they have both in medicine and agriculture.

Equine skeletal muscle adaptations to exercise and training: evidence of differential regulation of autophagosomal and mitochondrial components

BACKGROUND

A single bout of exercise induces changes in gene expression in skeletal muscle. Regular exercise results in an adaptive response involving changes in muscle architecture and biochemistry, and is an effective way to manage and prevent common human diseases such as obesity, cardiovascular disorders and type II diabetes. However, the biomolecular mechanisms underlying such responses still need to be fully elucidated. Here we performed a transcriptome-wide analysis of skeletal muscle tissue in a large cohort of untrained Thoroughbred horses (n = 51) before and after a bout of high-intensity exercise and again after an extended period of training. We hypothesized that regular high-intensity exercise training primes the transcriptome for the demands of high-intensity exercise.

RESULTS

An extensive set of genes was observed to be significantly differentially regulated in response to a single bout of high-intensity exercise in the untrained cohort (3241 genes) and following multiple bouts of high-intensity exercise training over a six-month period (3405 genes). Approximately one-third of these genes (1025) and several biological processes related to energy metabolism were common to both the exercise and training responses. We then developed a novel network-based computational analysis pipeline to test the hypothesis that these transcriptional changes also influence the contextual molecular interactome and its dynamics in response to exercise and training. The contextual network analysis identified several important hub genes, including the autophagosomal-related gene GABARAPL1, and dynamic functional modules, including those enriched for mitochondrial respiratory chain complexes I and V, that were differentially regulated and had their putative interactions 're-wired' in the exercise and/or training responses.

CONCLUSION

Here we have generated for the first time, a comprehensive set of genes that are differentially expressed in Thoroughbred skeletal muscle in response to both exercise and training. These data indicate that consecutive bouts of high-intensity exercise result in a priming of the skeletal muscle transcriptome for the demands of the next exercise bout. Furthermore, this may also lead to an extensive 're-wiring' of the molecular interactome in both exercise and training and include key genes and functional modules related to autophagy and the mitochondrion.

The combined frequency of IGF and myostatin polymorphism among track & field athletes and swimmers

OBJECTIVE

The IGF C-1245T (rs35767) and the myostatin (MSTN) Lys(K)-153Arg(R) genetic polymorphism may influence skeletal muscle phenotypes and athletic performance. Carrying the minor IGF T allele and the myostatin rare R allele was associated with higher circulating IGF-I levels, greater muscle mass and improved performance. The aim of the present study was to assess the combined frequency of the IGF 1245T (rs35767) and MSTN 153Arg(R) polymorphism among Israeli track and field athletes (n=111) and swimmers (n=80).

DESIGN

Track & field athletes were divided to long distance runners (major event 5000m-marathon, n=63) and power athletes (major event 100-200m sprints and long jump, n=48). Swimmers were divided into long-distance swimmers (major event: 400-1500m, n=38), and short-distance swimmers (major event: 50-100m, n=42).

RESULTS

Carrying both mutations was significantly higher (p<0.05) among long distance runners (LDR, 17%) compared to short distance runners (SDR, 10%), long distance swimmers (LDS, 8%), short distance swimmers (SDS, 2%) and controls (n=111, 7%). Carrying both mutations was significantly higher (p<0.05) among LDS compared to SDS (8% versus 2%, p<0.05). Among LDR and LDS carriers of both mutations, 40% and 25% were of elite level, respectively. Despite the fact that carrying both mutations among SDR and SDS was not greater than controls, all SDR and SDS carriers were elite athletes.

CONCLUSION

Our finding suggests that carrying both IGF 1245T and MSTN 153Arg(R) polymorphisms may contribute for long distance running success but not necessarily to elite performance. In contrast, although the frequency was not higher than the general population, all carriers of both mutations among short distance runners and swimmers were of elite competitive caliber. Whether evaluation of the IGF 1245T and MSTN 153R polymorphism can be used for sports selection in young athletes needs to be further studied.

Muscle-Related Polymorphisms (MSTN rs1805086 and ACTN3 rs1815739) Are Not Associated with Exceptional Longevity in Japanese Centenarians

Myostatin (MSTN) and α-actinin-3 (ACTN3) genes are potentially associated with preservation of muscle mass and oxidative capacity, respectively. To explore the possible role of these genes in exceptional longevity (EL), the allele/genotype frequency distribution of two polymorphisms in MSTN (rs1805086, K153R) and ACTN3 (rs1815739, R577X) was studied in Japanese centenarians of both sexes (n = 742) and healthy controls (n = 814). The rs1805086 R-allele (theoretically associated with muscle mass preservation at the expense of oxidative capacity) was virtually absent in the two groups, where genotype distributions were virtually identical. Likewise, no differences in allele (p = 0.838 (women); p = 0.193 (men); p = 0.587 (both sexes)) or genotype distribution were found between groups for ACTN3 rs1815739 (p = 0.975 (women), p = 0.136 (men), p = 0.752 (both sexes)). Of note, however, the frequency of the rs1805086 R-allele observed here is the lowest been reported to date whereas that of the ‘highly oxidative/efficient’ rs1815739 XX genotype in Japanese male centenarians (33.3%) or supercentenarians of both sexes (≥110 years) are the highest (32.6%), for a non-American population. No definite conclusions can be inferred in relation to EL owing to its lack of association with both rs1815739 and rs1805086. However, it cannot be excluded that these gene variants could eventually be related to a “healthy” metabolic phenotype in the Japanese population. Further research might determine if such metabolic profile is among the factors that can potentially predispose these individuals to live longer than Caucasians and what genetic variants might be actually involved.

Biochemistry and Biology of GDF11 and Myostatin: Similarities, Differences, and Questions for Future Investigation

Growth differentiation factor 11 (GDF11) and myostatin (or GDF8) are closely related members of the transforming growth factor β superfamily and are often perceived to serve similar or overlapping roles. Yet, despite commonalities in protein sequence, receptor utilization and signaling, accumulating evidence suggests that these 2 ligands can have distinct functions in many situations. GDF11 is essential for mammalian development and has been suggested to regulate aging of multiple tissues, whereas myostatin is a well-described negative regulator of postnatal skeletal and cardiac muscle mass and modulates metabolic processes. In this review, we discuss the biochemical regulation of GDF11 and myostatin and their functions in the heart, skeletal muscle, and brain. We also highlight recent clinical findings with respect to a potential role for GDF11 and/or myostatin in humans with heart disease. Finally, we address key outstanding questions related to GDF11 and myostatin dynamics and signaling during development, growth, and aging.

The potential role of myostatin and neurotransmission genes in elite sport performances

Elite athletes are those who represent their sport at such major competition as the Olympic Games or World contests. The most outstanding athletes appear to emerge as a result of endogenous biologic characteristics interacting with exogenous influences of the environment, often described as a 'Nature and Nurture' struggle. In this work, we assessed the contribution given by 4 genes involved in muscles development (MSTN) and behavioural insights (5HTT, DAT and MAOA) to athletic performances. As for neurotransmission, 5HTT, DAT and MAOA genes have been considered as directly involved in the management of aggressiveness and anxiety. Genotypes and allelic frequencies of 5HTTLPR, MAOA-u VNTR, DAT VNTR and MSTN K153R were determined in 50 elite athletes and compared with 100 control athletes. In this work we found a significant correlation between the dopamine transporter genotype 9/9 and allele 9 and elite sport performances. On the contrary, no association was found between muscle development regulation or serotonin pathway and elite performances. Our data, for the first time, suggest a strong role of dopamine neurotransmitter in determining sport success, highlighting the role of emotional control and psycological management to reach high-level performances.

Biology of frailty: Modulation of ageing genes and its importance to prevent age-associated loss of function

Frailty is associated with loss of functional reserve as well as with the prediction of adverse events in the old population. The traditional criteria of frailty are based on five physical determinations described in the Cardiovascular Health Study. We propose that biological and genetic markers of frailty should be used to increase the predictive capacity of the established clinical indeces. In recent times, research for biological markers of frailty has gained impetus. Finding a biological markers with diagnostic and prognostic capacity would be a major milestone to identify frailty risk, and also pre-frailty status. In the first section of the manuscript, we review the available biomarkers that help to monitor and prevent the evolution and the efficacy of interventions to delay the onset of frailty and to prevent its progression to incapacity. We also discuss the contribution of genetics to frailty. There are scientific bases that support that genetics influences frailty, although environmental factors probably will have the highest contribution. We review the known SNPs of the genes associated with frailty and classify them, taking into account the pathway in which they are involved. We also highlight the importance of longevity genes and their possible relation with frailty, citing centenarians who reach a very old age as an example of successful ageing. Finally, the reversibility of frailty is discussed. It can potentially be treated with nutritional or pharmacological interventions. However, physical exercise seems to be the most effective strategy to treat and prevent frailty. The last section of the manuscript is devoted to explaining the recommendations on the appropriate design of an exercise protocol to maximize its beneficial effects in a population of frail individuals.

Frequency of the MSTN Lys(K)-153Arg(R) polymorphism among track & field athletes and swimmers

The myostatin (MSTN) Lys(K)-153Arg(R) polymorphism may influence skeletal muscle phenotypes. Carrying the rare R allele was associated with greater muscle mass.

PURPOSE

The aim of the present study was to assess the frequency of the MSTN Lys(K)-153Arg(R) polymorphism among Israeli track and field athletes (n=185) and swimmers (n=80).

METHODS

Track and field athletes were divided into long distance runners (major event 5000 m-marathon, n=113) and power athletes (major event 100200 m sprints and long jump, n=72). Swimmers were divided into long-distance swimmers (major event: 800-1500 m, n=38), and short-distance swimmers (major event: 50-100 m, n=42). The control group included 118 non-athletes healthy participants.

RESULTS

Twenty-seven track and field athletes (14.6%) and 7 swimmers (8.8%) were carriers of the rare MSTN R allele, and only two carried the 153RR genotype (0.8%). MSTN 153R allele frequency was significantly higher in top-compared to national-level among long-distance runners (26% versus 8%, p<0.05), short distance runners (16% versus 9%, p<0.05), and all runners combined (20% versus 8%, p<0.05), but not in top- compared to national-level swimmers. The frequency of arginine carriers was significantly greater among long compared to short-distance swimmers (16% versus 2%, p<0.03).

CONCLUSION

In contrast to elite endurance and power track and field athletes, the MSTN 153RR genotype was not found in short distance-swimmers, and among the long distance-swimmers it was not associated with top level swimming performance. Whether evaluation of the MSTN K153R polymorphism can be used for sports selection in young athletes needs to be further studied.

Myostatin Gene Polymorphism in an Elderly Sarcopenic Turkish Population

INTRODUCTION

One of the genetic contributors to sarcopenia predisposition is Myostatin (MSTN), which in humans encodes myostatin, a 376 amino acid growth factor protein that negatively regulates muscle growth. The aim of this study was to investigate MSTN polymorphisms in an elderly sarcopenic population in Turkey and determine how they relate to sarcopenia.

MATERIALS AND METHODS

The study included nursing home residents who were aged ≥65 years. Sarcopenia screening was performed using "The European Working Group on Sarcopenia in Older People" guidelines. Blood sample was taken from each participant and DNA was obtained from the peripheral blood. MSTN polymorphisms were genotyped by polymerase chain reaction and restriction fragment length polymorphism methods.

RESULTS

A total of 152 elderly patients were included in the study. The rate of sarcopenia was determined to be 41.4%. The DNA nucleotide sequence of all three MSTN exons was determined for each study participant. Among the 152 patients, only 6 (3.9%) showed an MSTN K153R heterozygous mutation. Among these, three participants were sarcopenic and three were nonsarcopenic. No statistically significant difference in the polymorphism frequency between the sarcopenic and control groups was observed (p=0.664).

CONCLUSIONS

MSTN genotyping revealed that only 3.9% (6/152) of participants had the MSTN K153R heterozygous mutation. Despite the detection of this mutation in the study group, no relationship was found between this mutation and sarcopenia.

Systems biology analysis merging phenotype, metabolomic and genomic data identifies Non-SMC Condensin I Complex, Subunit G (NCAPG) and cellular maintenance processes as major contributors to genetic variability in bovine feed efficiency

Feed efficiency is a paramount factor for livestock economy. Previous studies had indicated a substantial heritability of several feed efficiency traits. In our study, we investigated the genetic background of residual feed intake, a commonly used parameter of feed efficiency, in a cattle resource population generated from crossing dairy and beef cattle. Starting from a whole genome association analysis, we subsequently performed combined phenotype-metabolome-genome analysis taking a systems biology approach by inferring gene networks based on partial correlation and information theory approaches. Our data about biological processes enriched with genes from the feed efficiency network suggest that genetic variation in feed efficiency is driven by genetic modulation of basic processes relevant to general cellular functions. When looking at the predicted upstream regulators from the feed efficiency network, the Tumor Protein P53 (TP53) and Transforming Growth Factor beta 1 (TGFB1) genes stood out regarding significance of overlap and number of target molecules in the data set. These results further support the hypothesis that TP53 is a major upstream regulator for genetic variation of feed efficiency. Furthermore, our data revealed a significant effect of both, the Non-SMC Condensin I Complex, Subunit G (NCAPG) I442M (rs109570900) and the Growth /differentiation factor 8 (GDF8) Q204X (rs110344317) loci, on residual feed intake and feed conversion. For both loci, the growth promoting allele at the onset of puberty was associated with a negative, but favorable effect on residual feed intake. The elevated energy demand for increased growth triggered by the NCAPG 442M allele is obviously not fully compensated for by an increased efficiency in converting feed into body tissue. As a consequence, the individuals carrying the NCAPG 442M allele had an additional demand for energy uptake that is reflected by the association of the allele with increased daily energy intake as observed in our study.

K153R polymorphism in myostatin gene increases the rate of promyostatin activation by furin

Recent studies demonstrated an association between the K153R polymorphism in the myostatin gene with extreme longevity, lower muscle strength and obesity but the molecular basis of these associations has not been clarified. Here, we show that the K153R mutation significantly increases the rate of proteolysis of promyostatin by furin, but has no effect on the activity of the latent complex or the cleavage of the latent complex by bone morphogenetic protein 1 (BMP-1). The increased rate of activation of K153R mutant promyostatin may explain why this polymorphism is associated with obesity, lower muscle strength and extension of lifespan.

From gene engineering to gene modulation and manipulation: can we prevent or detect gene doping in sports?

During the last 2 decades, progress in deciphering the human gene map as well as the discovery of specific defective genes encoding particular proteins in some serious human diseases have resulted in attempts to treat sick patients with gene therapy. There has been considerable focus on human recombinant proteins which were gene-engineered and produced in vitro (insulin, growth hormone, insulin-like growth factor-1, erythropoietin). Unfortunately, these substances and methods also became improper tools for unscrupulous athletes. Biomedical research has focused on the possible direct insertion of gene material into the body, in order to replace some defective genes in vivo and/or to promote long-lasting endogenous synthesis of deficient proteins. Theoretically, diabetes, anaemia, muscular dystrophies, immune deficiency, cardiovascular diseases and numerous other illnesses could benefit from such innovative biomedical research, though much work remains to be done. Considering recent findings linking specific genotypes and physical performance, it is tempting to submit the young athletic population to genetic screening or, alternatively, to artificial gene expression modulation. Much research is already being conducted in order to achieve a safe transfer of genetic material to humans. This is of critical importance since uncontrolled production of the specifically coded protein, with serious secondary adverse effects (polycythaemia, acute cardiovascular problems, cancer, etc.), could occur. Other unpredictable reactions (immunogenicity of vectors or DNA-vector complex, autoimmune anaemia, production of wild genetic material) also remain possible at the individual level. Some new substances (myostatin blockers or anti-myostatin antibodies), although not gene material, might represent a useful and well-tolerated treatment to prevent progression of muscular dystrophies. Similarly, other molecules, in the roles of gene or metabolic activators [5-aminoimidazole-4-carboxamide 1-β-D-ribofuranoside (AICAR), GW1516], might concomitantly improve endurance exercise capacity in ischaemic conditions but also in normal conditions. Undoubtedly, some athletes will attempt to take advantage of these new molecules to increase strength or endurance. Antidoping laboratories are improving detection methods. These are based both on direct identification of new substances or their metabolites and on indirect evaluation of changes in gene, protein or metabolite patterns (genomics, proteomics or metabolomics).

The effect of leader peptide mutations on the biological function of bovine myostatin gene

The growth of muscle fibers can be negatively regulated by bovine myostatin. The first two exons of myostatin gene code for the N-propeptide and its third exon codes for the C-polypeptide. Myostatin is secreted as a latent configuration formed by dimerization of two matured C peptides non-covalently linked with the N terminal pro-peptide. Pro-peptide has two distinct functions in guiding protein folding and regulating biological activity of myostatin. When the structure of the leader peptide is altered via mutations resulting in more tight binding with the mature peptide, myostatin function is inhibited, resulting in the changes of P21 and CDK2 expression levels which are related to the regulation of cell cycle. In the present study, the coding region of bMSTN (bovine myostatin) gene was amplified and mutated (A224C and G938A) through fusion PCR, and the mutated bMSTN gene (bMSTN-mut) was inserted in frame into the pEF1a-IRES-DsRed-Express2 vector and transfected into bovine fibroblast cells. The expression levels of bMSTN-mut, P21 and CDK2 (cyclin dependent kinase 2) were examined with qPCR and Western-blotting. Changes in cell cycle after transfection were also analyzed with flow cytometry. The results indicated that leader peptide mutation resulted in down-regulation of P21 expression levels and up-regulation of CDK2 expression levels. The flow cytometry results showed that the proportion of cells in the G0/G1-phase was lower and that of cells in the S-phase was higher in bMSTN-mut transfected group than that in the control group. The proliferation rate of bMSTN-mut transfected cells was also significantly higher than that of the control cells. In conclusion, the studies have shown that the pEF1a-IRES-DsRed-Express2-bMSTN-mut recombinant plasmid could effectively promote the proliferation of bovine fibroblast cells. The site-directed mutagenesis of bMSTN gene leader peptide and in vitro expression in bovine fibroblast cells could be helpful to further the studies of bMSTN in regulating bovine muscle cell growth and development.

Association of the K153R polymorphism in the myostatin gene and extreme longevity

The myostatin (MSTN) gene is a candidate to influence extreme longevity owing to its role in modulating muscle mass and sarcopenia and especially in inhibiting the main nutrient-sensing pathway involved in longevity, i.e. mammalian target of rapamycin. We compared allele/genotype distributions of the exonic MSTN variants K153R (rs1805086), E164K (rs35781413), I225T and P198A, in Spanish centenarians (cases, n = 156; 132 women, age range 100-111 years) and younger adults (controls, n = 384; 167 women, age <50 years). No subject of either group carried a mutant allele of the E164K, I225T or P198A variation. The frequency of the variant R allele was significantly higher in centenarians (7.1%) than in controls (2.7%) (P = 0.001). The odds ratio of being a centenarian if the subject had the R allele was 3.48 (95% confidence interval 1.67-7.28, P = 0.001), compared to the control group, after adjusting for sex. The results were replicated in an Italian cohort (centenarians, n = 79 (40 women), age range 100-104 years; younger controls, n = 316 (155 women), age <50 years), where a higher frequency of the R allele in centenarians (7.6%) compared to controls (3.0%) (P = 0.004) was independently confirmed. Although more research is needed, the variant allele of the MSTN K153R polymorphism could be among the genetic contributors associated with exceptional longevity.

A systems biology approach using metabolomic data reveals genes and pathways interacting to modulate divergent growth in cattle

BACKGROUND

Systems biology enables the identification of gene networks that modulate complex traits. Comprehensive metabolomic analyses provide innovative phenotypes that are intermediate between the initiator of genetic variability, the genome, and raw phenotypes that are influenced by a large number of environmental effects. The present study combines two concepts, systems biology and metabolic analyses, in an approach without prior functional hypothesis in order to dissect genes and molecular pathways that modulate differential growth at the onset of puberty in male cattle. Furthermore, this integrative strategy was applied to specifically explore distinctive gene interactions of non-SMC condensin I complex, subunit G (NCAPG) and myostatin (GDF8), known modulators of pre- and postnatal growth that are only partially understood for their molecular pathways affecting differential body weight.

RESULTS

Our study successfully established gene networks and interacting partners affecting growth at the onset of puberty in cattle. We demonstrated the biological relevance of the created networks by comparison to randomly created networks. Our data showed that GnRH (Gonadotropin-releasing hormone) signaling is associated with divergent growth at the onset of puberty and revealed two highly connected hubs, BTC and DGKH, within the network. Both genes are known to directly interact with the GnRH signaling pathway. Furthermore, a gene interaction network for NCAPG containing 14 densely connected genes revealed novel information concerning the functional role of NCAPG in divergent growth.

CONCLUSIONS

Merging both concepts, systems biology and metabolomic analyses, successfully yielded new insights into gene networks and interacting partners affecting growth at the onset of puberty in cattle. Genetic modulation in GnRH signaling was identified as key modifier of differential cattle growth at the onset of puberty. In addition, the benefit of our innovative concept without prior functional hypothesis was demonstrated by data suggesting that NCAPG might contribute to vascular smooth muscle contraction by indirect effects on the NO pathway via modulation of arginine metabolism. Our study shows for the first time in cattle that integration of genetic, physiological and metabolomics data in a systems biology approach will enable (or contribute to) an improved understanding of metabolic and gene networks and genotype-phenotype relationships.

Sarcopenic obesity: how do we treat it?

PURPOSE OF REVIEW

The increasing prevalence of sarcopenic obesity in older adults has heightened interest in identifying the most effective treatment. This review highlights recent progress in the management, with an emphasis on lifestyle interventions and pharmacologic therapy aimed at reversing sarcopenic obesity.

RECENT FINDINGS

Whereas weight loss and exercise independently reverse sarcopenic obesity, they act synergistically in combination to improve body composition and physical function, beyond which is observed with either intervention alone. Optimizing protein intake appears to have beneficial effects on net muscle protein accretion in older adults. Myostatin inhibition is associated with favorable changes in body composition in animal studies, although experience in humans is relatively limited. Testosterone and growth hormone offer improvements in body composition, but the benefits must be weighed against potential risks of therapy. GHRH-analog therapy shows promise, but further studies are needed in older adults.

SUMMARY

At present, lifestyle interventions incorporating both diet-induced weight loss and regular exercise appear to be the optimal treatment for sarcopenic obesity. Maintenance of adequate protein intake is also advisable. Ongoing studies will determine whether pharmacologic therapy such as myostatin inhibitors or GHRH analogs have a role in the treatment of sarcopenic obesity.

Genes and the ageing muscle: a review on genetic association studies

Western populations are living longer. Ageing decline in muscle mass and strength (i.e. sarcopenia) is becoming a growing public health problem, as it contributes to the decreased capacity for independent living. It is thus important to determine those genetic factors that interact with ageing and thus modulate functional capacity and skeletal muscle phenotypes in older people. It would be also clinically relevant to identify 'unfavourable' genotypes associated with accelerated sarcopenia. In this review, we summarized published information on the potential associations between some genetic polymorphisms and muscle phenotypes in older people. A special emphasis was placed on those candidate polymorphisms that have been more extensively studied, i.e. angiotensin-converting enzyme (ACE) gene I/D, α-actinin-3 (ACTN3) R577X, and myostatin (MSTN) K153R, among others. Although previous heritability studies have indicated that there is an important genetic contribution to individual variability in muscle phenotypes among old people, published data on specific gene variants are controversial. The ACTN3 R577X polymorphism could influence muscle function in old women, yet there is controversy with regards to which allele (R or X) might play a 'favourable' role. Though more research is needed, up-to-date MSTN genotype is possibly the strongest candidate to explain variance among muscle phenotypes in the elderly. Future studies should take into account the association between muscle phenotypes in this population and complex gene-gene and gene-environment interactions.

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.

Association of the Myostatin gene with obesity, abdominal obesity and low lean body mass and in non-diabetic Asian Indians in north India

BACKGROUND

To determine the association of the A55T and K153R polymorphisms of the Myostatin gene with obesity, abdominal obesity and lean body mass (LBM) in Asian Indians in north India.

MATERIALS AND METHODS

A total of 335 subjects (238 men and 97 women) were assessed for anthropometry, % body fat (BF), LBM and biochemical parameters. Associations of Myostatin gene polymorphisms were evaluated with anthropometric, body composition and biochemical parameters. In A55T polymorphism, BMI (p=0.04), suprailiac skinfold (p=0.05), total skinfold (p=0.008), %BF (p=0.002) and total fat mass (p=0.003) were highest and % LBM (p=0.03) and total LBM (Kg) were lowest (p=0.04) in subjects with Thr/Thr genotype as compared to other genotypes. Association analysis of K153R polymorphism showed that subjects with R/R genotype had significantly higher BMI (p=0.05), waist circumference (p=0.04), %BF (p=0.04) and total fat mass (p=0.03), and lower %LBM (p=0.02) and total LBM [(Kg), (p=0.04)] as compared to other genotypes. Using a multivariate logistic regression model after adjusting for age and sex, subjects with Thr/Thr genotype of A55T showed high risk for high %BF (OR, 3.92, 95% Cl: 2.61-12.41), truncal subcutaneous adiposity (OR, 2.9, 95% Cl: 1.57-6.60)] and low LBM (OR, 0.64, 95% CI: 0.33-0.89) whereas R/R genotype of K153R showed high risk of obesity (BMI; OR, 3.2, 95% CI: 1.2-12.9; %BF, OR, 3.6, 95% CI: 1.04-12.4), abdominal obesity (OR, 2.12, 95% CI: 2.71-14.23) and low LBM (OR, 0.61, 95% CI: 0.29-0.79).

CONCLUSIONS/SIGNIFICANCE

We report that variants of Myostatin gene predispose to obesity, abdominal obesity and low lean body mass in Asian Indians in north India.

Human genetic variation: new challenges and opportunities for doping control

Sport celebrates differences in competitors that lead to the often razor-thin margins between victory and defeat. The source of this variation is the interaction between the environment in which the athletes develop and compete and their genetic make-up. However, a darker side of sports may also be genetically influenced: some anti-doping tests are affected by the athlete's genotype. Genetic variation is an issue that anti-doping authorities must address as more is learned about the interaction between genotype and the responses to prohibited practices. To differentiate between naturally occurring deviations in indirect blood and urine markers from those potentially caused by doping, the "biological-passport" program uses intra-individual variability rather than population values to establish an athlete's expected physiological range. The next step in "personalized" doping control may be the inclusion of genetic data, both for the purposes of documenting an athlete's responses to doping agents and doping-control assays as well facilitating athlete and sample identification. Such applications could benefit "clean" athletes but will come at the expense of risks to privacy. This article reviews the instances where genetics has intersected with doping control, and briefly discusses the potential role, and ethical implications, of genotyping in the struggle to eliminate illicit ergogenic practices.

Genetic aspects of skeletal muscle strength and mass with relevance to sarcopenia

Skeletal muscle is a highly heritable quantitative trait, with heritability estimates ranging 30-85% for muscle strength and 50-80% for lean mass. That strong genetic contribution indicates the possibility of using genetic information to individualize treatments for sarcopenia or even aid in prevention strategies through the use of genetic screening prior to the functional limitations. Though these possibilities provide the rationale for genetic studies of skeletal muscle traits, few genes have been identified that appear to contribute to variation in either skeletal muscle strength or mass phenotypes, and sarcopenia per se is remarkably understudied as a trait in this regard. This review examines the heritability of skeletal muscle traits, findings of linkage and genome-wide association analyses and impact of specific genes and gene-sequence variants on these traits as relevant to sarcopenia. Despite considerable work in the area, the genetic underpinnings of skeletal muscle traits remain largely unknown and the genetic aspects of sarcopenia are even less clear. Large-scale longitudinal clinical studies relying on advanced genome-wide association and other techniques are needed to provide further insights into the genes and gene variants that contribute to skeletal muscle strength and mass, and ultimately to susceptibility to sarcopenia.

Genetic risk for malignant hyperthermia in non-anesthesia-induced myopathies

Malignant hyperthermia (MH) is a pharmacogenetic, autosomal dominantly inherited disorder of skeletal muscle triggered by volatile anesthetics and infrequently by extreme exertion and heat exposure. MH has variable penetrance with an incidence ranging from 1 in 5000 to 1 in 50,000-100,000 anesthesias. Mutations in the ryanodine receptor gene, RYR1, are found in 50-70% of cases. We hypothesized that a portion of patients with drug-induced muscle diseases, unrelated to anesthesia, such as severe statin myopathy, have underlying genetic liability that may include RYR1 gene mutations. DNA samples were collected from 885 patients in 4 groups: severe statin myopathy (n=197), mild statin myopathy (n=163), statin-tolerant controls (n=133), and non-drug-induced myopathies of unknown etiology characterized by exercise-induced muscle pain and weakness (n=392). Samples were screened for 105 mutations and variants in 26 genes associated with 7 categories of muscle disease including 34 mutations and variants in the RYR1 gene. Disease-causing mutations or variants in RYR1 were present in 3 severe statin myopathy cases, 1 mild statin myopathy case, 8 patients with non-drug-induced myopathy, and none in controls. These results suggest that disease-causing mutations and certain variants in the RYR1 gene may contribute to underlying genetic risk for non-anesthesia-induced myopathies and should be included in genetic susceptibility screening in patients with severe statin myopathy and in patients with non-statin-induced myopathies of unknown etiology.

Molecular genetic studies of gene identification for sarcopenia

Sarcopenia, which is characterized by a progressive decrease of skeletal muscle mass and function with aging, is closely related to several common diseases (such as cardiovascular and airway diseases) and functional impairment/disability. Strong genetic determination has been reported for muscle mass and muscle strength, two most commonly recognized and studied risk phenotypes for sarcopenia, with heritability ranging from 30 to 85% for muscle strength and 45-90% for muscle mass. Sarcopenia has been the subject of increasing genetic research over the past decade. This review is designed to comprehensively summarize the most important and representative molecular genetic studies designed to identify genetic factors associated with sarcopenia. We have methodically reviewed whole-genome linkage studies in humans, quantitative trait loci mapping in animal models, candidate gene association studies, newly reported genome-wide association studies, DNA microarrays and microRNA studies of sarcopenia or related skeletal muscle phenotypes. The major results of each study are tabulated for easy comparison and reference. The findings of representative studies are discussed with respect to their influence on our present understanding of the genetics of sarcopenia. This is a comprehensive review of molecular genetic studies of gene identification for sarcopenia, and an overarching theme for this review is that the currently accumulating results are tentative and occasionally inconsistent and should be interpreted with caution pending further investigation. Consequently, this overview should enhance recognition of the need to validate/replicate the genetic variants underlying sarcopenia in large human cohorts and animal. We believe that further progress in understanding the genetic etiology of sarcopenia will provide valuable insights into important fundamental biological mechanisms underlying muscle physiology that will ultimately lead to improved ability to recognize individuals at risk for developing sarcopenia and our ability to treat this debilitating condition.

The K153R polymorphism in the myostatin gene and muscle power phenotypes in young, non-athletic men

The Lys(K)153Arg(R) polymorphism in exon 2 (rs1805086, 2379 A>G replacement) of the myostatin (MSTN) gene is a candidate to influence skeletal muscle phenotypes. We examined the association between the MSTN K153R polymorphism and 'explosive' leg power, assessed during sprint (30 m) and stationary jumping tests [squat (SJ) and counter-movement jumps (CMJ)] in non-athletic young adults (University students) [n = 281 (214 men); age: 21-32 years]. We also genotyped the MSTN exonic variants E164K (rs35781413), I225T, and P198A, yet no subject carried any of these variant MSTN alleles. As for the K153R polymorphism, we found only one woman with the KR genotype; thus, we presented the results only for men. The results of a one-way ANCOVA (with age, weight and height entered as covariates) showed that men with the KR genotype (n = 15) had a worse performance in vertical jumps compared with those with the KK genotype [SJ: vertical displacement of center of gravity (CG) of 35.17 ± 1.42 vs. 39.06 ± 0.39 cm, respectively, P = 0.009; CMJ: vertical displacement of CG of 36.44 ± 1.50 vs. 40.63 ± 0.41 cm, respectively, P = 0.008]. The results persisted after adjusting for multiple comparisons according to Bonferroni. Performance in 30 m sprint tests did however not differ by K153R genotypes. In summary, the MSTN K153R polymorphism is associated with the ability to produce 'peak' power during muscle contractions, as assessed with vertical jump tests, in young non-athletic men. Although more research is still needed, this genetic variation is among the numerous candidates to explain, alone or in combination with other polymorphisms, individual variations in muscle phenotypes.

The Role of Genetic Variation in Muscle Strength

Skeletal muscle is an important link to an individual’s health and quality of life. The primary clinical interest in skeletal muscle is muscle strength. Muscle strength is a complex trait, influenced by biological, morphological, psychological, and environmental factors. Muscle strength is highly variable among individuals and has a strong genetic component. Though several genetic variants have been associated with muscle strength, genes comprising this genetic component are generally unknown. Research examining associations between genetic variants and muscle strength suffers from scientific challenges such as lack of replication, population stratification, and complexity of defining muscle phenotypes. Additionally, non-scientific challenges such as privacy and protection of genetic information and the questionable value of direct-to-consumer genetic marketing exist. How these challenges will influence research examining genetics and muscle strength is uncertain. Findings from this research may lead to improved treatment for muscle-related disease as well as improved health and quality of life. This may be realized through the development of genetic profiles that clinicians can implement into personalized treatment plans. This review will summarize the current literature regarding genetic variation and muscle strength. The authors’ focus will be on the muscle strength response to resistance training. Additionally, the authors discuss challenges and implications of this research.

The K153R variant in the myostatin gene and sarcopenia at the end of the human lifespan

We studied the A55T, E164K, I225T, K153R and P198A variants in the myostatin (GDF8) gene, muscle strength and mass, and physical function during daily living in 41 nonagenarians [33 women, age range, 90, 97]. No participant carried a mutant allele of the aforementioned variants, except three participants (all women), who carried the R allele of the K153R polymorphism, with one of them (woman aged 96 years) being homozygous. Overall, in KR women muscle phenotype values (1RM leg press and estimated muscle mass) were low-to-normal compared to the whole group (approximately 25th-50th percentile), and their functional capacity (Barthel and Tinetti tests) was normal. In the woman bearing the RR genotype, values of muscle mass and functional capacity were below the 25th percentile. She is the first RR Caucasian whose phenotype has been characterised specifically. In summary, heterozygosity for the GDF8 K153R polymorphism does not seem to exert a negative influence on the muscle phenotypes of women who are at the end of the human lifespan, yet homozygosity might do so. More research on larger cohorts of nonagenarians is needed to corroborate the present findings.

Can we identify a power-oriented polygenic profile?

Using the model originally developed by Williams and Folland (J Physiol 586: 113-121, 2008), we determined 1) a "total genotype score" (TGS, from the accumulated combination of the 6 polymorphisms, with a maximum value of "100" for the theoretically optimal polygenic score) in a group of elite power athletes, endurance athletes, and nonathletic controls, and 2) the probability for the occurrence of Spanish individuals with the "perfect" power-oriented profile (i.e., TGS = 100). We analyzed six polymorphism that are candidates to explain individual variations in elite power athletic status or power phenotypes (ACE I/D, ACTN3 R577X, AGT Met235Thr, GDF-8 K153R, IL6 -174 G/C, and NOS3 -786T>C) in 53 elite track and field power athletes (jumpers, sprinters), 100 nonathletic controls, and 100 elite endurance athletes (distance runners and road cyclists) (all Spanish Caucasian males). The mean TGS was significantly higher in power athletes (70.8 +/- 17.3) compared with endurance athletes (60.4 +/- 15.9; P < 0.001) and controls (63.3 +/- 13.2; P = 0.012), whereas it did not differ between the latter two groups (P = 0.366). A total of five power athletes (9.4%, all sprinters) had a theoretically "optimal" TGS of 100 vs. 0 subjects in the other two groups. The probability of a Spanish individual possessing a theoretically optimal polygenic profile for up to the six candidate polymorphisms we studied was very small, i.e., approximately 0.2% (or 1 in 500 Spanish individuals). We have identified a polygenic profile that allows us, at least partly, to distinguish elite power athletes from both endurance athletes and nonathletic population.

Myostatin and follistatin polymorphisms interact with muscle phenotypes and ethnicity

PURPOSE

We examined associations among myostatin (MSTN) 2379 A > G and 163 G > A and follistatin (FST) -5003 A > T and -833 G > T single nucleotide polymorphisms (SNP) on the muscle size and the strength response to resistance training (RT).

METHODS

Subjects (n = 645, age = 24.1 +/- 0.2 yr, body mass index [BMI] = 24.2 +/- 0.2 kg x m(-2)) self-disclosed themselves as Caucasian (78.9%), African American (3.6%), Asian (8.4%), Hispanic (5.0%), or Other (4.2%). They were genotyped for MSTN 2379 A > G (n = 645), MSTN 163 G > A (n = 639), FST -5003 A > T (n = 580), and FST -833 G > T (n = 603). We assessed dynamic (one repetition maximum [1RM]) and isometric (maximum voluntary contraction [MVC]) muscle strength and size (cross-sectional area [CSA]) of the elbow flexors before and after 12 wk of unilateral upper-arm RT. Repeated-measures ANCOVA tested associations among genetic variants and muscle phenotypes with age and BMI as covariates.

RESULTS

Baseline MVC was greater among African Americans who were carriers of the MSTN G(2379) allele (AG/GG, n = 15) than the A2379A homozygotes (n = 8; 64.2 +/- 6.8 vs 49.8 +/- 8.7 kg). African Americans who were carriers of the FST T(-5003) allele (n = 12) had greater baseline 1RM (11.9 +/- 0.7 vs 8.8 +/- 0.5 kg) and CSA (24.4 +/- 1.3 vs 19.1 +/- 1.2 cm(2)) than African Americans with the A-5003A genotype (n = 14; P < 0.05). No MSTN or FST genotype and muscle phenotype associations were found among the other ethnic groups (P >or= 0.05).

CONCLUSION

MSTN 2379 A > G and FST -5003 A > T were associated with baseline muscle strength and size among African Americans only. These ethnic-specific associations are hypothesis generating and should be confirmed in a larger sample of African Americans.

Is there an optimum endurance polygenic profile?

We analysed seven genetic polymorphisms that are candidates to explain individual variations in human endurance phenotypic traits, at least in Caucasian people (ACE Ins/Del, ACTN3 Arg577Ter, AMPD1 Gln12Ter, CKMM 1170 bp/985 + 185 bp, HFE His63Asp, GDF-8 Lys153Arg and PPARGC1A Gly482Ser) in 46 world-class endurance athletes and 123 controls (all Spanish Caucasians). Using the model developed by Williams & Folland we determined (1) the 'total genotype score' (TGS, from the accumulated combination of the seven polymorphisms, with a maximum value of '100' for the theoretically optimal polygenic score) in the non-athlete (control) group, in the athlete group and in the total Spanish population, and (2) the probability for the occurrence of Spanish individuals with the 'perfect' polygenic endurance profile (i.e. TGS = 100). The probability of a Spanish individual possessing a theoretically optimal polygenic profile for up to the seven candidate genetic polymorphisms we studied was very small, i.e. approximately 0.07% (or 1 in 1351 Spanish individuals). The mean TGS was higher in athletes (70.22 +/- 15.58) than in controls (62.43 +/- 11.45) and also higher than predicted for the total Spanish population (60.80 +/- 12.1), suggesting an overall more 'favourable' polygenic profile in the athlete group. However, only three of the best Spanish endurance athletes (who are also amongst the best in the world) had the best possible score for up to six genes and none of them had the optimal profile. Other polymorphisms yet undiscovered as well as several factors independent of genetic endowment may explain why some individuals reach the upper end of the endurance performance continuum.

Association between myostatin gene polymorphisms and peak BMD variation in Chinese nuclear families

We identified 17 polymorphisms in myostatin by sequencing, and three informative single nucleotide polymorphisms (SNPs) were selected for further observation for their association with peak BMD of women in 401 Chinese nuclear families. Our results suggest that genetic polymorphisms in myostatin likely play a role in attainment of peak BMD in Chinese women.

INTRODUCTION

Myostatin is a TGF-beta family member that is a negative regulator of skeletal muscle growth.

MATERIALS AND METHODS

We identified SNPs in myostatin by direct sequencing. Furthermore, using a quantitative transmission disequilibrium test (QTDT). we tested and further test whether SNPs were associated with peak bone mineral density (BMD) variation at the spines and hips of 401 Chinese nuclear families. We identified 17 polymorphisms in myostatin by sequencing. Next, we selected three informative SNPs for further observation of an association with peak BMD of premenopausal women in 401 Chinese nuclear families.

RESULTS

Using QTDT for the within-family association, we found significant association between rs2293284 and total hip, femoral neck, and trochanter BMD (all p < 0.05), while rs7570532 was associated with total hip and trochanter BMD (p = 0.034 and p = 0.035, respectively). The within-family association was significant between BMI and +2278G > A (p = 0.022). Subsequent permutations were in agreement with these significant within-family association results. Moreover, analyses of the haplotypes confer further evidence for association of rs2293284 and rs7570532 with hip peak BMD variation.

CONCLUSIONS

These results suggest, for the first time, the genetic polymorphisms in myostatin likely play a role in attainment of peak BMD in Chinese women.

The ACTN3 R577X nonsense allele is under-represented in elite-level strength athletes

Previous reports have shown a lower proportion of the ACTN3 X/X genotype (R577X nonsense polymorphism) in sprint-related athletes compared to the general population, possibly attributed to impairment of muscle function related to alpha-actinin-3 deficiency. In the present study, we examined the frequency of the X/X genotype in both Black and White elite-level bodybuilders and strength athletes in comparison to the general population. A reference population of 668 Whites (363 men and 305 women) and 208 Blacks (98 men and 110 women) was genotyped for the ACTN3 R577X polymorphism. Strength athletes (52 white and 23 black; 4 women) consisting predominantly of world class and locally competitive bodybuilders, and elite powerlifters were recruited and similarly genotyped. Significantly lower X/X genotype frequencies were observed in the athletes (6.7%) vs controls (16.3%; P=0.005). The X/X genotype was significantly lower in White athletes (9.7%) vs controls (19.9%; P=0.018). No black athletes (0%) were observed with the X/X genotype, though this finding only approached statistical significance vs controls (4.8%; P=0.10). The results indicate that the ACTN3 R577X nonsense allele (X) is under-represented in elite strength athletes, consistent with previous reports indicating that alpha-actinin-3 deficiency appears to impair muscle performance.