Association of the ACTN3 R577X polymorphism with glucose tolerance and gene expression of sarcomeric proteins in human skeletal muscle

Exploring protein relative relations in skeletal muscle proteomic analysis for insights into insulin resistance and type 2 diabetes

The escalating prevalence of insulin resistance (IR) and type 2 diabetes mellitus (T2D) underscores the urgent need for improved early detection techniques and effective treatment strategies. In this context, our study presents a proteomic analysis of post-exercise skeletal muscle biopsies from individuals across a spectrum of glucose metabolism states: normal, prediabetes, and T2D. This enabled the identification of significant protein relationships indicative of each specific glycemic condition. Our investigation primarily leveraged the machine learning approach, employing the white-box algorithm relative evolutionary hierarchical analysis (REHA), to explore the impact of regulated, mixed mode exercise on skeletal muscle proteome in subjects with diverse glycemic status. This method aimed to advance the diagnosis of IR and T2D and elucidate the molecular pathways involved in its development and the response to exercise. Additionally, we used proteomics-specific statistical analysis to provide a comparative perspective, highlighting the nuanced differences identified by REHA. Validation of the REHA model with a comparable external dataset further demonstrated its efficacy in distinguishing between diverse proteomic profiles. Key metrics such as accuracy and the area under the ROC curve confirmed REHA's capability to uncover novel molecular pathways and significant protein interactions, offering fresh insights into the effects of exercise on IR and T2D pathophysiology of skeletal muscle. The visualizations not only underscored significant proteins and their interactions but also showcased decision trees that effectively differentiate between various glycemic states, thereby enhancing our understanding of the biomolecular landscape of T2D.

The ACTN3 R577X polymorphism is associated with metabolic alterations in a sex-dependent manner in subjects from western Mexico

BACKGROUND

The ACTN3 gene is primarily expressed in fast skeletal muscle fibres. A common nonsense polymorphism in this gene is ACTN3 R577X (rs1815739), which causes an absolute deficiency of α-actinin-3 protein and alterations in muscle metabolism. Considering metabolic alterations are influenced by nutrition and genetic factors, as well as lifestyle factors, we hypothesise a possible association of the ACTN3 R577X polymorphism with metabolic alterations.

METHODS

In this cross-sectional study, 397 adults met the inclusion criteria. Body composition was measured by electrical bioimpedance. Dietary data were analysed using Nutritionist Pro™ software. Biochemical variables were determined by dry chemistry. Genomic DNA was extracted from peripheral leukocytes and genotyping of the ACTN3 R577X polymorphism was determined by allelic discrimination using TaqMan probes. The statistical analyses were performed using SPSS statistical software. p < 0.05 was considered statistically significant.

RESULTS

The ACTN3 577XX genotype was associated with high glucose, triglyceride and very low density lipoprotein-cholesterol levels and a higher frequency of hypertriglyceridaemia and insulin resistance in women. In males, the genetic variant showed a trend towards significance for insulin resistance.

CONCLUSIONS

The ACTN3 R577X polymorphism was associated with metabolic alterations in women and a tendency was observed in men variant carriers. Thus, this common genetic variant could be implicated in the development of chronic metabolic diseases.

Combination of ACTN3 R577X and ACE I/D polymorphisms as a tool for prediction of obesity risk in children

The genetic influence in obesity prevalence is well described, but the role of genetic markers related to athletic strength/ endurance performance remains controversial. We investigated associations between obesity and the genetic polymorphisms alpha-actinin-3 (ACTN3) R577X and angiotensin-converting enzyme (ACE) I/D in schoolchildren aged 4-13 years from Southern Brazil. We collected sociodemographic data from parents through a questionnaire and conducted an anthropometric assessment. DNA was extracted from buccal cells and genotyping was performed by PCR. We found that 1.9% of the individuals were classified as low weight-for-age, 57.6% as normal weight and 40.5% as overweight/ obesity. Regarding allelic distribution, we found that 52.5% of individuals were DD, 30.8% ID, and 16.7% II for ACE; and 38.8% of individuals were RR, 40.2% RX and 21.0% XX for ACTN3. When both polymorphisms were combined, we observed a clear association between the composed genetic profile of these alleles and severe obesity in schoolchildren. Our data suggest that the combined analysis of ACTN3 R577X and ACE I/D polymorphisms may serve as a predictor for the risk of severe obesity in children. These data can contribute to a better understanding of the relationship between these polymorphisms and the body weight development of school-age children.

Goalkeepers Live Longer than Field Players: A Retrospective Cohort Analysis Based on World-Class Football Players

The purpose of this article is to study whether the position occupied by footballers on the pitch influences their life duration. It is known that various types of sporting activity (endurance, resistance, or mixed) may influence lifespan in different ways. However, there is a paucity of data regarding the role of different positions played in team sports such as football. Our research was based on elite international football players born before 1923 who took part in the first three football World Cups (n = 443) or played in the 1946/1947 season in the leading clubs of the main European leagues (n = 280). Goalkeepers were characterized by a 5–8-year longer life duration compared to their colleagues playing in other positions (World Cup: 82.0 ± 7.0 vs. 74.0 ± 8.0, p = 0.0047; European leagues: 83.0 ± 7.5 vs. 78.0 ± 8.0, p = 0.0023), with an absence of differences between defenders, midfielders, and forwards. Moreover, in both of the analyzed subgroups, the rate of survival until the 85th birthday was significantly higher among goalkeepers than among field players (p = 0.0102 and p = 0.0048, for both studied groups, respectively).

ACTN3 R577X Genotype and Exercise Phenotypes in Recreational Marathon Runners

Background: Homozygosity for the X-allele in the ACTN3 R577X (rs1815739) polymorphism results in the complete absence of α-actinin-3 in sarcomeres of fast-type muscle fibers. In elite athletes, the ACTN3 XX genotype has been related to inferior performance in speed and power-oriented sports; however, its influence on exercise phenotypes in recreational athletes has received less attention. We sought to determine the influence of ACTN3 genotypes on common exercise phenotypes in recreational marathon runners. Methods: A total of 136 marathoners (116 men and 20 women) were subjected to laboratory testing that included measurements of body composition, isometric muscle force, muscle flexibility, ankle dorsiflexion, and the energy cost of running. ACTN3 genotyping was performed using TaqMan probes. Results: 37 runners (27.2%) had the RR genotype, 67 (49.3%) were RX and 32 (23.5%) were XX. There was a difference in body fat percentage between RR and XX genotype groups (15.7 ± 5.8 vs. 18.8 ± 5.5%; effect size, ES, = 0.5 ± 0.4, p = 0.024), whereas the distance obtained in the sit-and-reach-test was likely lower in the RX than in the XX group (15.3 ± 7.8 vs. 18.4 ± 9.9 cm; ES = 0.4 ± 0.4, p = 0.046). Maximal dorsiflexion during the weight-bearing lunge test was different in the RR and XX groups (54.8 ± 5.8 vs. 57.7 ± 5.1 degree; ES = 0.5 ± 0.5, p = 0.044). Maximal isometric force was higher in the RR than in the XX group (16.7 ± 4.7 vs. 14.7 ± 4.0 N/kg; ES = −0.5 ± 0.3, p = 0.038). There was no difference in the energy cost of running between genotypes (~4.8 J/kg/min for all three groups, ES ~0.2 ± 0.4). Conclusions: The ACTN3 genotype might influence several exercise phenotypes in recreational marathoners. Deficiency in α-actinin-3 might be accompanied by higher body fatness, lower muscle strength and higher muscle flexibility and range of motion. Although there is not yet a scientific rationale for the use of commercial genetic tests to predict sports performance, recreational marathon runners who have performed such types of testing and have the ACTN3 XX genotype might perhaps benefit from personalized strength training to improve their performance more than their counterparts with other ACTN3 genotypes.

The Effect of ACTN3 Gene Doping on Skeletal Muscle Performance

Loss of expression of ACTN3, due to homozygosity of the common null polymorphism (p.Arg577X), is underrepresented in elite sprint/power athletes and has been associated with reduced muscle mass and strength in humans and mice. To investigate ACTN3 gene dosage in performance and whether expression could enhance muscle force, we performed meta-analysis and expression studies. Our general meta-analysis using a Bayesian random effects model in elite sprint/power athlete cohorts demonstrated a consistent homozygous-group effect across studies (per allele OR = 1.4, 95% CI 1.3-1.6) but substantial heterogeneity in heterozygotes. In mouse muscle, rAAV-mediated gene transfer overexpressed and rescued α-actinin-3 expression. Contrary to expectation, in vivo "doping" of ACTN3 at low to moderate doses demonstrated an absence of any change in function. At high doses, ACTN3 is toxic and detrimental to force generation, to demonstrate gene doping with supposedly performance-enhancing isoforms of sarcomeric proteins can be detrimental for muscle function. Restoration of α-actinin-3 did not enhance muscle mass but highlighted the primary role of α-actinin-3 in modulating muscle metabolism with altered fatiguability. This is the first study to express a Z-disk protein in healthy skeletal muscle and measure the in vivo effect. The sensitive balance of the sarcomeric proteins and muscle function has relevant implications in areas of gene doping in performance and therapy for neuromuscular disease.

ACTN3 genotype and physical function and frailty in an elderly Chinese population: the Rugao Longevity and Ageing Study

Objective

To examine the associations of the actinin alpha 3 gene (ACTN3) R577X polymorphism with physical performance and frailty in an older Chinese population.

Methods

Data from 1,463 individuals (57.8% female) aged 70-87 years from the Rugao Longevity and Ageing Study were used. The associations between R577X and timed 5-m walk, grip strength, timed Up and Go test, and frailty index (FI) based on deficits of 23 laboratory tests (FI-Lab) were examined. Analysis of variance and linear regression models were used to evaluate the genetic effects of ACTN3 R577X on physical performance and FI-Lab.

Results

The XX and RX genotypes of the ACTN3 R557X polymorphism accounted for 17.1 and 46.9%, respectively. Multivariate regression analysis revealed that in men aged 70-79 years, the ACTN3 577X allele was significantly associated with physical performance (5-m walk time, regression coefficient (β) = 0.258, P = 0.006; grip strength, β = -1.062, P = 0.012; Up and Go test time β = 0.368, P = 0.019). In women aged 70-79 years, a significant association between the ACTN3 577X allele and the FI-Lab score was observed, with a regression coefficient of β = 0.019 (P = 0.003). These findings suggest an age- and gender-specific X-additive model of R577X for 5-m walk time, grip strength, Up and Go Test time, and FI-Lab score.

Conclusion

The ACTN3 577X allele is associated with an age- and sex-specific decrease in physical performance and an increase in frailty in an older population.

ACTN3, Morbidity, and Healthy Aging

As human longevity increases, recent research has focused on the maintenance of optimal health during old age. One such area of focus is that of muscle function in the elderly, with a loss of muscle mass increasing the risk of negative outcomes such as sarcopenia and a decrease in bone mineral density. In this mini-review, we focus on the impact of a single nucleotide polymorphism in ACTN3, shown to impact muscle phenotype in elite athletes, on loss of muscle function, maintenance of bone mineral density, and metabolic disorder risk in an elderly population. From the surveyed research, this polymorphism has a clear and demonstrable impact on muscle phenotype and bone mineral density in this population, and acts as a potential modulator for metabolic disorders. As such, knowledge of an individual's ACTN3 genotype may better inform the management of risk factors in the elderly, as well as driving innovations in exercise program design. Subsequently, such insights may contribute to the prolonged maintenance of health and function long into old age.

Transcriptomic analysis of chicken Myozenin 3 regulation reveals its potential role in cell proliferation

Embryonic muscle development and fibre type differentiation has always been a topic of great importance due to its impact on both human health and farm animal financial values. Myozenin3 (Myoz3) is an important candidate gene that may regulate these processes. In the current study, we knocked down and overexpressed Myoz3 in chicken embryonic fibroblasts (CEFs) and chicken myoblasts, then utilized RNA-seq technology to screen genes, pathways and biological processes associated with Myoz3. Multiple differentially expressed genes were identified, including MYH10, MYLK2, NFAM1, MYL4, MYL9, PDZLIM1; those can in turn regulate each other and influence the development of muscle fibres. Gene ontology (GO) terms including some involved in positive regulation of cell proliferation were enriched. We further validated our results by testing the activity of cells by cell counting kit-8(CCK-8) and confirmed that under the condition of Myoz3 overexpression, the proliferation rate of CEFs and myoblasts was significantly upregulated, in addition, expression level of fast muscle specific gene was also significantly upregulated in myoblasts. Pathway enrichment analysis revealed that the PPAR (Peroxisome Proliferator-Activated Receptor) pathway was enriched, suggesting the possibility that Myoz3 regulates muscle fibre development and differentiation through the PPAR pathway. Our results provide valuable evidence regarding the regulatory functions of Myoz3 in embryonic cells by screening multiple candidate genes, biological processes and pathways associated with Myoz3.

Molecular Cloning, Expression Profiling, and Marker Validation of the Chicken Myoz3 Gene

Myozenin3 (Myoz3) has been reported to bind multiple Z-disc proteins and hence play a key role in signal transduction and muscle fiber type differentiation. The purpose of current study is to better understand the basic characteristics of Myoz3. Firstly, we cloned the ORF (open reading frame) of the Myoz3 gene. AA (amino acid) sequence analysis revealed that the Myoz3 gene encodes a 26 kDa protein which have 97% identities with that of turkey. Expression profiling showed that Myoz3 mRNA is mainly expressed in leg muscle and breast muscle. Furthermore, we investigated Myoz3 gene polymorphisms in two broiler breeds, the Yellow Bantam (YB) and the Avian. Five SNPs (single nucleotide polymorphisms) were identified in the YB breed and 3 were identified in the Avian breed. Genotypes and haplotype were constructed and their associations with carcass traits were analyzed. In the YB breed, c.516 C>T had a strong effect on both shank bone length and the [Formula: see text] value of breast muscle, and the H1H3 diplotype had the highest FC compared to other diplotypes. The markers identified in this study may serve as useful targets for the marker-assisted selection (MAS) of growth and meat quality traits in chickens.

Exploring the relationship between α-actinin-3 deficiency and obesity in mice and humans

Obesity is a worldwide health crisis, and the identification of genetic modifiers of weight gain is crucial in understanding this complex disorder. A common null polymorphism in the fast fiber-specific gene ACTN3 (R577X) is known to influence skeletal muscle function and metabolism. α-Actinin-3 deficiency occurs in an estimated 1.5 billion people worldwide, and results in reduced muscle strength and a shift towards a more efficient oxidative metabolism. The X-allele has undergone strong positive selection during recent human evolution, and in this study, we sought to determine whether ACTN3 genotype influences weight gain and obesity in mice and humans. An Actn3 KO mouse has been generated on two genetic backgrounds (129X1/SvJ and C57BL/6J) and fed a high-fat diet (HFD, 45% calories from fat). Anthropomorphic features (including body weight) were examined and show that Actn3 KO 129X1/SvJ mice gained less weight compared to WT. In addition, six independent human cohorts were genotyped for ACTN3 R577X (Rs1815739) and body mass index (BMI), waist-to-hip ratio-adjusted BMI (WHRadjBMI) and obesity-related traits were assessed. In humans, ACTN3 genotype alone does not contribute to alterations in BMI or obesity.

Optimum polygenic profile to resist exertional rhabdomyolysis during a marathon

Purpose

Exertional rhabdomyolysis can occur in individuals performing various types of exercise but it is unclear why some individuals develop this condition while others do not. Previous investigations have determined the role of several single nucleotide polymorphisms (SNPs) to explain inter-individual variability of serum creatine kinase (CK) concentrations after exertional muscle damage. However, there has been no research about the interrelationship among these SNPs. The purpose of this investigation was to analyze seven SNPs that are candidates for explaining individual variations of CK response after a marathon competition (ACE = 287bp Ins/Del, ACTN3 = p.R577X, CKMM = NcoI, IGF2 = C13790G, IL6 = 174G>C, MLCK = C37885A, TNFα = 308G>A).

Methods

Using Williams and Folland’s model, we determined the total genotype score from the accumulated combination of these seven SNPs for marathoners with a low CK response (n = 36; serum CK <400 U·L^-1) vs. marathoners with a high CK response (n = 31; serum CK ≥400 U·L^-1).

Results

At the end of the race, low CK responders had lower serum CK (290±65 vs. 733±405 U·L^-1; P<0.01) and myoglobin concentrations (443±328 vs. 1009±971 ng·mL^-1, P<0.01) than high CK responders. Although the groups were similar in age, anthropometric characteristics, running experience and training habits, total genotype score was higher in low CK responders than in high CK responders (5.2±1.4 vs. 4.4±1.7 point, P = 0.02).

Conclusion

Marathoners with a lower CK response after the race had a more favorable polygenic profile than runners with high serum CK concentrations. This might suggest a significant role of genetic polymorphisms in the levels of exertional muscle damage and rhabdomyolysis. Yet other SNPs, in addition to exercise training, might also play a role in the values of CK after damaging exercise.

eMERGE Phenome-Wide Association Study (PheWAS) identifies clinical associations and pleiotropy for stop-gain variants

BACKGROUND

We explored premature stop-gain variants to test the hypothesis that variants, which are likely to have a consequence on protein structure and function, will reveal important insights with respect to the phenotypes associated with them. We performed a phenome-wide association study (PheWAS) exploring the association between a selected list of functional stop-gain genetic variants (variation resulting in truncated proteins or in nonsense-mediated decay) and an extensive group of diagnoses to identify novel associations and uncover potential pleiotropy.

RESULTS

In this study, we selected 25 stop-gain variants: 5 stop-gain variants with previously reported phenotypic associations, and a set of 20 putative stop-gain variants identified using dbSNP. For the PheWAS, we used data from the electronic MEdical Records and GEnomics (eMERGE) Network across 9 sites with a total of 41,057 unrelated patients. We divided all these samples into two datasets by equal proportion of eMERGE site, sex, race, and genotyping platform. We calculated single effect associations between these 25 stop-gain variants and ICD-9 defined case-control diagnoses. We also performed stratified analyses for samples of European and African ancestry. Associations were adjusted for sex, site, genotyping platform and the first three principal components to account for global ancestry. We identified previously known associations, such as variants in LPL associated with hyperglyceridemia indicating that our approach was robust. We also found a total of three significant associations with p < 0.01 in both datasets, with the most significant replicating result being LPL SNP rs328 and ICD-9 code 272.1 "Disorder of Lipoid metabolism" (pdiscovery = 2.59x10-6, preplicating = 2.7x10-4). The other two significant replicated associations identified by this study are: variant rs1137617 in KCNH2 gene associated with ICD-9 code category 244 "Acquired Hypothyroidism" (pdiscovery = 5.31x103, preplicating = 1.15x10-3) and variant rs12060879 in DPT gene associated with ICD-9 code category 996 "Complications peculiar to certain specified procedures" (pdiscovery = 8.65x103, preplicating = 4.16x10-3).

CONCLUSION

In conclusion, this PheWAS revealed novel associations of stop-gained variants with interesting phenotypes (ICD-9 codes) along with pleiotropic effects.

Analysis of the ACTN3 heterozygous genotype suggests that α-actinin-3 controls sarcomeric composition and muscle function in a dose-dependent fashion

A common null polymorphism (R577X) in ACTN3 causes α-actinin-3 deficiency in ∼ 18% of the global population. There is no associated disease phenotype, but α-actinin-3 deficiency is detrimental to sprint and power performance in both elite athletes and the general population. However, despite considerable investigation to date, the functional consequences of heterozygosity for ACTN3 are unclear. A subset of studies have shown an intermediate phenotype in 577RX individuals, suggesting dose-dependency of α-actinin-3, while others have shown no difference between 577RR and RX genotypes. Here, we investigate the effects of α-actinin-3 expression level by comparing the muscle phenotypes of Actn3(+/-) (HET) mice to Actn3(+/+) [wild-type (WT)] and Actn3(-/-) [knockout (KO)] littermates. We show reduction in α-actinin-3 mRNA and protein in HET muscle compared with WT, which is associated with dose-dependent up-regulation of α-actinin-2, z-band alternatively spliced PDZ-motif and myotilin at the Z-line, and an incremental shift towards oxidative metabolism. While there is no difference in force generation, HET mice have an intermediate endurance capacity compared with WT and KO. The R577X polymorphism is associated with changes in ACTN3 expression consistent with an additive model in the human genotype-tissue expression cohort, but does not influence any other muscle transcripts, including ACTN2. Overall, ACTN3 influences sarcomeric composition in a dose-dependent fashion in mouse skeletal muscle, which translates directly to function. Variance in fibre type between biopsies likely masks this phenomenon in human skeletal muscle, but we suggest that an additive model is the most appropriate for use in testing ACTN3 genotype associations.

The ACTN3 R577X polymorphism affects the lipid profile and the prognosis of nutritional intervention in HIV-positive patients

The hypothesis of the present study is that the polymorphisms in the APOC3, CEPT, ACE, and ACTN3 genes can affect the outcome of nutritional intervention and the plasma lipid profile of HIV+ patients. To test the hypothesis, genetic material was collected from buccal cells, and serum was collected for biochemical analysis. Sixty-five patients were analyzed. The incorporation of protease inhibitor (PI) was more frequent in women (77% vs 33% in men). Nutritional intervention improved anthropometric parameters independent of the genotype. Patients with the RR genotype for the ACTN3 R577X polymorphism had lower glycemia (RR = 95.4 ± 6.5 mg/dL, RX = 102.6 ± 10.6 mg/dL, XX = 110.1 ± 16.3 mg/dL; P = .03) and a greater reduction in low-density lipoproteins (LDL) after intervention (LDL: RR = -23.7 ± 15.8 mg/dL, RX = 1.32 ± 5.13 mg/dL, XX = 30.21 ± 24.4 mg/dL; P = .01). Patients using PI had a negative response to dietary intervention regarding the levels of high-density lipoprotein (-2.4 ± 1.70 with PI, 2.56 ± 1.60 mg/dL without PI; P = .02), very low density lipoprotein (0.84 ± 2.73 with IP, -5.46 ± 3.37 mg/dL without PI; P = .03), and triglycerides (1.79 ± 13.22 with PI, -34.00 ± 17.67 mg/dL without PI; P = .052). This response was also independent of the genotype (P > 0.05) and suggested the need for oral lipid-lowering drugs in all HIV+ patients using PI. Our results indicate that the ACTN3 R577X polymorphism is a good predictor of both the lipid profile and the prognosis of nutritional intervention in reducing LDL in HIV+ patients.

Rodent models for resolving extremes of exercise and health

The extremes of exercise capacity and health are considered a complex interplay between genes and the environment. In general, the study of animal models has proven critical for deep mechanistic exploration that provides guidance for focused and hypothesis-driven discovery in humans. Hypotheses underlying molecular mechanisms of disease and gene/tissue function can be tested in rodents to generate sufficient evidence to resolve and progress our understanding of human biology. Here we provide examples of three alternative uses of rodent models that have been applied successfully to advance knowledge that bridges our understanding of the connection between exercise capacity and health status. First we review the strong association between exercise capacity and all-cause morbidity and mortality in humans through artificial selection on low and high exercise performance in the rat and the consequent generation of the "energy transfer hypothesis." Second we review specific transgenic and knockout mouse models that replicate the human disease condition and performance. This includes human glycogen storage diseases (McArdle and Pompe) and α-actinin-3 deficiency. Together these rodent models provide an overview of the advancements of molecular knowledge required for clinical translation. Continued study of these models in conjunction with human association studies will be critical to resolving the complex gene-environment interplay linking exercise capacity, health, and disease.