ACTN3 genotype influences skeletal muscle mass regulation and response to dexamethasone

Polymorphisms of PPARα and ACTN3 Among Adolescent Egyptian Athletes: A Case-Control Study

BACKGROUND

Athletic performance is a complex phenotype affected by individual traits, environmental conditions, training, and genetics. The peroxisome proliferator-activated receptor-alpha (PPARα) and alpha-actinin-3 (ACTN3) are two genes with the potential to influence human performance. The objective of the present study was to assess the genotype frequencies of ACTN3 (R/X) and PPARα (G/C) and to conduct a comparison of these frequencies among Egyptian adolescent athletes.

METHODS

This case-control study involved 228 individuals (118 elite-level athletes and 110 sedentary controls).

RESULTS

This study identified a statistically significant increase in the frequencies of the ACTN3 'R' allele (77.5% compared to 55.9%; p < 0.001) and the PPARα 'C' allele (86.4% compared to 14.1%; p < 0.001) among athletes relative to the control groups. A similar pattern was noted for adolescent athletes in comparison to the control group in terms of both the R/R genotype (61.9% compared to 27.3%; p < 0.001) and the C/C genotype (80.5% compared to 2.7%; p < 0.001). In conclusion, these results imply that polymorphisms in ACTN3 and PPARα could be significant predictors for assessing the performance of adolescent Egyptian athletes.

Poncirus trifoliata Extract and Its Active Coumarins Alleviate Dexamethasone-Induced Skeletal Muscle Atrophy by Regulating Protein Synthesis, Mitochondrial Biogenesis, and Gut Microbiota

Sarcopenia, an age-related decline in skeletal muscle mass and function, contributes to frailty and increased morbidity in the elderly. This necessitates the development of effective interventions to combat muscle atrophy. This study investigated the therapeutic potential of Poncirus trifoliata ethanol extract (PT) and its coumarin derivatives against dexamethasone (DEX)-induced muscle atrophy. We employed in vitro and in vivo models of DEX-induced muscle atrophy. C2C12 myotubes were used for mechanistic studies. C57BL/6J mice received DEX injections and oral PT supplementation (50 mg/kg/day) to evaluate effects on muscle mass, function, gene expression, and gut microbiota composition. In vitro, PT enhanced protein synthesis, mitochondrial biogenesis, and myogenic differentiation in DEX-exposed myotubes, with auraptene, ponciol, and triphasiol identified as key bioactive coumarins. In vivo, PT significantly attenuated DEX-induced muscle atrophy, increasing tibialis anterior muscle mass by 36% (p < 0.01), grip strength by 31% (p < 0.001), and maximal running speed by 18% (p < 0.05). Mechanistically, PT upregulated genes associated with muscle function and mitochondrial health. Furthermore, PT modulated gut microbiota composition, notably increasing Phocaeicola vulgatus abundance 2.2-fold, which correlated with improved muscle performance (R = 0.58, p < 0.01). These findings suggest that PT and its coumarin derivatives, particularly auraptene, ponciol, and triphasiol, hold promise as therapeutic agents for combating muscle atrophy. The observed benefits may be mediated through enhanced protein synthesis, improved mitochondrial function, and modulation of the gut-muscle axis.

EGR1 mRNA expression levels and polymorphisms are associated with slaughter performance in chickens

With the implementation of the policy of "centralized slaughtering and chilled to market" and the development of the livestock processing industry, numerous researchers have begun to focus on the selection and breeding of broilers bred for slaughter. The selection of breeds with excellent slaughtering performance and high meat production performance has become one of the most important selective breeding goals. In our previous study, we conducted transcriptome sequencing on chicken breast tissues with high and low breast muscle rates and found higher early growth response protein 1 (EGR1) expression in breast tissues with a low breast muscle ratio, thus hypothesizing that the EGR1 gene is involved in the growth and development process of chicken muscle tissues. Therefore, we analyzed the gene functions and polymorphisms of EGR1 to investigate its association with slaughter traits. We used various experimental methods, including RT-qPCR, Cell Counting Kit 8, 5-ethynyl-2'-deoxyuridine, western blot, flow cytometry, and immunofluorescence, to validate EGR1's role in chicken primary myoblasts. The results of our functional validation experiments indicate that EGR1 is highly expressed in breast tissues with a low breast muscle content and plays a key role in regulating of muscle growth and development by promoting proliferation and inhibiting the differentiation of chicken primary myoblasts. In addition, we explored the relationship between the EGR1 gene polymorphisms and slaughter traits using mixed linear models for the first time. In a population of Jiangfeng M3 lineage partridge chickens, we identified 4 EGR1 single-nucleotide polymorphisms, 2 of which were significantly associated with slaughter traits, including live weight, slaughter weight, semi-eviscerated weight, eviscerated weight, leg weight, wing weight, and breast muscle rate. In summary, ectopic expression of EGR1 promotes the proliferation and differentiation of chicken primary myoblasts. In addition, polymorphisms in EGR1 were associated with slaughter performance, providing a potential basis for further utilization of EGR1 as a breeding marker.

The recent development, application, and future prospects of muscle atrophy animal models

Muscle atrophy, characterized by the loss of muscle mass and function, is a hallmark of sarcopenia and cachexia, frequently associated with aging, malignant tumors, chronic heart failure, and malnutrition. Moreover, it poses significant challenges to human health, leading to increased frailty, reduced quality of life, and heightened mortality risks. Despite extensive research on sarcopenia and cachexia, consensus in their assessment remains elusive, with inconsistent conclusions regarding their molecular mechanisms. Muscle atrophy models are crucial tools for advancing research in this field. Currently, animal models of muscle atrophy used for clinical and basic scientific studies are induced through various methods, including aging, genetic editing, nutritional modification, exercise, chronic wasting diseases, and drug administration. Muscle atrophy models also include in vitro and small organism models. Despite their value, each of these models has certain limitations. This review focuses on the limitations and diverse applications of muscle atrophy models to understand sarcopenia and cachexia, and encourage their rational use in future research, therefore deepening the understanding of underlying pathophysiological mechanisms, and ultimately advancing the exploration of therapeutic strategies for sarcopenia and cachexia.

Overexpression of enhanced yellow fluorescent protein fused with Channelrhodopsin-2 causes contractile dysfunction in skeletal muscle

Skeletal muscle activation using optogenetics has emerged as a promising technique for inducing noninvasive muscle contraction and assessing muscle function both in vivo and in vitro. Transgenic mice overexpressing the optogenetic fusion protein, Channelrhodopsin 2-EYFP (ChR2-EYFP) in skeletal muscle are widely used; however, overexpression of fluorescent proteins can negatively impact the functionality of activable tissues. In this study, we characterized the contractile properties of ChR2-EYFP skeletal muscle and introduced the ChR2-only mouse model that expresses light-responsive ChR2 without the fluorescent EYFP in their skeletal muscles. We found a significant reduction in the contractile ability of ChR2-EYFP muscles compared with ChR2-only and WT mice, observed under both electrical and optogenetic stimulation paradigms. Bulk RNAseq identified the downregulation of genes associated with transmembrane transport and metabolism in ChR2-EYFP muscle, while the ChR2-only muscle did not demonstrate any notable deviations from WT muscle. The RNAseq results were further corroborated by a reduced protein-level expression of ion channel-related HCN2 in ChR2-EYFP muscles and gluconeogenesis-modulating FBP2 in both ChR2-EYFP and ChR2-only muscles. Overall, this study reveals an intrinsic skeletal dysfunction in the widely used ChR2-EYFP mice model and underscores the importance of considering alternative optogenetic models, such as the ChR2-only, for future research in skeletal muscle optogenetics.

Mesenchymal stem cells alleviate dexamethasone-induced muscle atrophy in mice and the involvement of ERK1/2 signalling pathway

BACKGROUND

High dosage of dexamethasone (Dex) is an effective treatment for multiple diseases; however, it is often associated with severe side effects including muscle atrophy, resulting in higher risk of falls and poorer life quality of patients. Cell therapy with mesenchymal stem cells (MSCs) holds promise for regenerative medicine. In this study, we aimed to investigate the therapeutic efficacy of systemic administration of adipose-derived mesenchymal stem cells (ADSCs) in mitigating the loss of muscle mass and strength in mouse model of DEX-induced muscle atrophy.

METHODS

3-month-old female C57BL/6 mice were treated with Dex (20 mg/kg body weight, i.p.) for 10 days to induce muscle atrophy, then subjected to intravenous injection of a single dose of ADSCs ([Formula: see text] cells/kg body weight) or vehicle control. The mice were killed 7 days after ADSCs treatment. Body compositions were measured by animal DXA, gastrocnemius muscle was isolated for ex vivo muscle functional test, histological assessment and Western blot, while tibialis anterior muscles were isolated for RNA-sequencing and qPCR. For in vitro study, C2C12 myoblast cells were cultured under myogenic differentiation medium for 5 days following 100 [Formula: see text]M Dex treatment with or without ADSC-conditioned medium for another 4 days. Samples were collected for qPCR analysis and Western blot analysis. Myotube morphology was measured by myosin heavy chain immunofluorescence staining.

RESULTS

ADSC treatment significantly increased body lean mass (10-20%), muscle wet weight (15-30%) and cross-sectional area (CSA) (~ 33%) in DEX-induced muscle atrophy mice model and down-regulated muscle atrophy-associated genes expression (45-65%). Hindlimb grip strength (~ 37%) and forelimb ex vivo muscle contraction property were significantly improved (~ 57%) in the treatment group. Significant increase in type I fibres (~ 77%) was found after ADSC injection. RNA-sequencing results suggested that ERK1/2 signalling pathway might be playing important role underlying the beneficial effect of ADSC treatment, which was confirmed by ERK1/2 inhibitor both in vitro and in vivo.

CONCLUSIONS

ADSCs restore the pathogenesis of Dex-induced muscle atrophy with an increased number of type I fibres, stronger muscle strength, faster recovery rate and more anti-fatigue ability via ERK1/2 signalling pathway. The inhibition of muscle atrophy-associated genes by ADSCs offered this treatment as an intervention option for muscle-associated diseases. Taken together, our findings suggested that adipose-derived mesenchymal stem cell therapy could be a new treatment option for patient with Dex-induced muscle atrophy.

Is dexamethasone-induced muscle atrophy an alternative model for naturally aged sarcopenia model?

Background

Primary sarcopenia is usually known as age-related skeletal muscle loss; however, other factors like endocrine, lifestyle and inflammation can also cause muscle loss, known as secondary sarcopenia. Although many studies have used different sarcopenia animal models for exploring the underlying mechanism and therapeutic approaches for sarcopenia, limited study has provided evidence of the relevance of these animal models. This study aims to investigate the similarity and difference in muscle qualities between primary and secondary sarcopenia mice models, using naturally aged mice and dexamethasone-induced mice.

Methods

21-month-old mice were used as naturally aged primary sarcopenia mice and 3-month-old mice received daily intraperitoneal injection of dexamethasone (20 mg/ kg body weight) for 10 days were used as secondary sarcopenia model. This study provided measurements for muscle mass and functions, including Dual-energy X-ray absorptiometry (DXA) scanning, handgrip strength test and treadmill running to exhaustion test. Besides, muscle contraction, muscle fibre type measurements and gene expression were also performed to provide additional information on muscle qualities.

Results

The results suggest two sarcopenia animal models shared a comparable decrease in forelimb lean mass, muscle fibre size, grip strength and muscle contraction ability. Besides, the upregulation of protein degradation genes was also observed in two sarcopenia animal models. However, only primary sarcopenia mice were identified with an early stage of mtDNA deletion.

Conclusion

Collectively, this study evaluated that the dexamethasone-induced mouse model could be served as an alternative model for primary sarcopenia, according to the comparable muscle mass and functional changes. However, whether dexamethasone-induced mice can be used as an animal model when studying the molecular mechanisms of sarcopenia needs to be carefully evaluated.

The translational potential of this article

The purpose of sarcopenia research is to investigate appropriate treatments for reversing the loss of skeletal muscle mass and functions. Using animal models for the preclinical study could predict the safety and efficacy of the treatments. This study compared the typical age-related sarcopenia mice model and dexamethasone-induced secondary sarcopenia mice to provide evidence of the pathological and functional changes in the mice models.

Associations of the Alpha-Actinin Three Genotype with Bone and Muscle Mass Loss among Middle-Aged and Older Adults

Bone and muscle mass loss are known to occur simultaneously. The alpha-actinin three (ACTN3) genotype has been shown to potentially affect bone and muscle mass. In this study, we investigated the association between the ACTN3 genotype and bone and muscle mass loss in community-dwelling adults aged ≥ 60 years. This study was a cross-sectional analysis of data from 295 participants who participated in a community health checkup. The ACTN3 genotypes were classified as RR, RX, or XX types. Bone mass loss was defined as a calcaneal speed of sound T-score of <−1.32 and <−1.37, and muscle mass loss was defined as an appendicular skeletal muscle index of <7.0 kg/m2 and <5.7 kg/m2 in men and women, respectively. The percentages of XX, RX, and RR in the combined bone and muscle mass loss group were 33.8%, 30.8%, and 16.7%, respectively, with a significantly higher trend for XX. Multinomial logistic regression analysis showed that XX had an odds ratio of 3.00 (95% confidence interval 1.05−8.54) of being in the combined bone and muscle mass loss group compared to the RR group (covariates: age, sex, grip strength, and medications). The ACTN3 genotype of XX is associated with a higher rate of comorbid bone and muscle mass loss. Therefore, ACTN3 genotyping should be considered for preventing combined bone and muscle mass loss.

Response to Wyckelsma et al.: Loss of α-actinin-3 during human evolution provides superior cold resilience and muscle heat generation

The common loss-of-function mutation R577X in the structural muscle protein ACTN3 emerged as a potential target of positive selection from early studies and has been the focus of insightful physiological work suggesting a significant impact on muscle metabolism. Adaptation to cold climates has been proposed as a key adaptive mechanism explaining its global allele frequency patterns. Here, we re-examine this hypothesis analyzing modern (n = 3,626) and ancient (n = 1,651) genomic data by using allele-frequency as well as haplotype homozygosity-based methods. The presented results are more consistent with genetic drift rather than selection in cold climates as the main driver of the ACTN3 R577X frequency distribution in human populations across the world. This Matters Arising paper is in response to Wyckelsma et al. (2021),1 published in The American Journal of Human Genetics. See also the response by Wyckelsma et al. (2022),2 published in this issue.

Population Genetic Polymorphism of Skeletal Muscle Strength Related Genes in Five Ethnic Minorities in North China

Musculoskeletal performance is a complex trait influenced by environmental and genetic factors, and it has different manifestations in different populations. Heilongjiang province, located in northern China, is a multi-ethnic region with human cultures dating back to the Paleolithic Age. The Daur, Hezhen, Ewenki, Mongolian and Manchu ethnic groups in Heilongjiang province may have strong physical fitness to a certain extent. Based on the genetic characteristics of significant correlation between some important genes and skeletal muscle function, this study selected 23 SNPs of skeletal muscle strength-related genes and analyzed the distribution of these loci and genetic diversity in the five ethnic groups. Use Haploview (version 4.1) software to calculate the chi-square and the Hardy-Weinberg equilibrium to assess the difference between the two ethnic groups. Use R (version 4.0.2) software to perform principal component analysis of different ethnic groups. Use MEGA (version 7.0) software to construct the phylogenetic tree of different ethnic groups. Use POPGENE (version 1.32) software to calculate the heterozygosity and the F_ST values of 23 SNPs. Use Arlequin (version 3.5.2.2) software to analyze molecular variance (AMOVA) among 31 populations. The results showed that there was haplotype diversity of VDR, angiotensin-converting enzyme, ACTN3, EPO and IGF1 genes in the five ethnic groups, and there were genetic differences in the distribution of these genes in the five ethnic groups. Among them, the average gene heterozygosity (AVE_HET) of the 23 SNPs in the five populations was 0.398. The F_ST values of the 23 SNPs among the five ethnic groups varied from 0.0011 to 0.0137. According to the principal component analysis, the genetic distance of Daur, Mongolian and Ewenki is relatively close. According to the phylogenetic tree, the five ethnic groups are clustered together with the Asian population. These data will enrich existing genetic information of ethnic minorities.