Expression of genes in the skeletal muscle of individuals with cachexia/sarcopenia: A systematic review

Oral Administration of Nacre Extract from Pearl Oyster Shells Has Anti-Aging Effects on Skin and Muscle, and Extends the Lifespan in SAMP8 Mice

Pearl oysters have been extensively utilized in pearl production; however, most pearl oyster shells are discarded as industrial waste. In a previous study, we demonstrated that the intraperitoneal administration of pearl oyster shell-derived nacre extract (NE) prevented d-galactose-induced brain and skin aging. In this study, we examined the anti-aging effects of orally administered NE in senescence-accelerated mice (SAMP8). Feeding SAMP8 mice NE prevented the development of aging-related characteristics, such as coarse and dull hair, which are commonly observed in aged mice. Additionally, the NE mitigated muscle aging in SAMP8 mice, such as a decline in grip strength. Histological analysis of skeletal muscle revealed that the NE suppressed the expression of aging markers, cyclin-dependent kinase inhibitor 2A (p16) and cyclin-dependent kinase inhibitor 1 (p21), and increased the expression of sirtuin1 and peroxisome proliferator-activated receptor gamma coactivator 1 (PGC1)- α, which are involved in muscle synthesis. These findings suggest that the oral administration of NE suppresses skeletal muscle aging. Moreover, NE administration suppressed skin aging, including a decline in water content. Interestingly, oral administration of NE significantly extended the lifespan of SAMP8 mice, suggesting that its effectiveness as an anti-aging agent of various tissues including skeletal muscle, skin, and adipose tissue.

Sex-specific alteration in human muscle transcriptome with age

Sarcopenia is a medical condition that progressively develops with age and results in reduced skeletal muscle mass, alteration in muscle composition, and decreased muscle strength. Several clinical studies suggested that sarcopenia disproportionally affects males and females with age. Despite this knowledge, the molecular mechanism governing the pathophysiology is not well understood in a sex-specific manner. In this study, we utilized human gastrocnemius muscles from males and females to identify differentially regulated genes with age. We found 269 genes with at least a twofold expression difference in the aged muscle transcriptome. Among the female muscle samples, there were 239 differentially regulated genes, and the novel protein-coding genes include KIF20A, PIMREG, MTRNR2L6, TRPV6, EFNA2, RNF24, and SFN. In aged male skeletal muscle, there were 166 differentially regulated genes, and the novel-protein coding genes are CENPK, CDKN2A, BHLHA15, and EPHA. Gene Ontology (GO) enrichment revealed glucose catabolism, NAD metabolic processes, and muscle fiber transition pathways that are involved in aged female skeletal muscle, whereas replicative senescence, cytochrome C release, and muscle composition pathways are disrupted in aged male skeletal muscle. Targeting these novels, differentially regulated genes, and signaling pathways could serve as sex-specific therapeutic targets to combat the age-related onset of sarcopenia and promote healthy aging.

Main Pathogenic Mechanisms and Recent Advances in COPD Peripheral Skeletal Muscle Wasting

Chronic obstructive pulmonary disease (COPD) is a worldwide prevalent respiratory disease mainly caused by tobacco smoke exposure. COPD is now considered as a systemic disease with several comorbidities. Among them, skeletal muscle dysfunction affects around 20% of COPD patients and is associated with higher morbidity and mortality. Although the histological alterations are well characterized, including myofiber atrophy, a decreased proportion of slow-twitch myofibers, and a decreased capillarization and oxidative phosphorylation capacity, the molecular basis for muscle atrophy is complex and remains partly unknown. Major difficulties lie in patient heterogeneity, accessing patients' samples, and complex multifactorial process including extrinsic mechanisms, such as tobacco smoke or disuse, and intrinsic mechanisms, such as oxidative stress, hypoxia, or systemic inflammation. Muscle wasting is also a highly dynamic process whose investigation is hampered by the differential protein regulation according to the stage of atrophy. In this review, we report and discuss recent data regarding the molecular alterations in COPD leading to impaired muscle mass, including inflammation, hypoxia and hypercapnia, mitochondrial dysfunction, diverse metabolic changes such as oxidative and nitrosative stress and genetic and epigenetic modifications, all leading to an impaired anabolic/catabolic balance in the myocyte. We recapitulate data concerning skeletal muscle dysfunction obtained in the different rodent models of COPD. Finally, we propose several pathways that should be investigated in COPD skeletal muscle dysfunction in the future.

Minimal adaptation of the molecular regulators of mitochondrial dynamics in response to unilateral limb immobilisation and retraining in middle-aged men

PURPOSE

Mitochondrial dynamics are regulated by the differing molecular pathways variously governing biogenesis, fission, fusion, and mitophagy. Adaptations in mitochondrial morphology are central in driving the improvements in mitochondrial bioenergetics following exercise training. However, there is a limited understanding of mitochondrial dynamics in response to inactivity.

METHODS

Skeletal muscle biopsies were obtained from middle-aged males (n = 24, 49.4 ± 3.2 years) who underwent sequential 14-day interventions of unilateral leg immobilisation, ambulatory recovery, and resistance training. We quantified vastus lateralis gene and protein expression of key proteins involved in mitochondrial biogenesis, fusion, fission, and turnover in at baseline and following each intervention.

RESULTS

PGC1α mRNA decreased 40% following the immobilisation period, and was accompanied by a 56% reduction in MTFP1 mRNA, a factor involved in mitochondrial fission. Subtle mRNA decreases were also observed in TFAM (17%), DRP1 (15%), with contrasting increases in BNIP3L and PRKN following immobilisation. These changes in gene expression were not accompanied by changes in respective protein expression. Instead, we observed subtle decreases in NRF1 and MFN1 protein expression. Ambulatory recovery restored mRNA and protein expression to pre-intervention levels of all altered components, except for BNIP3L. Resistance training restored BNIP3L mRNA to pre-intervention levels, and further increased mRNA expression of OPA-1, MFN2, MTFP1, and PINK1 past baseline levels.

CONCLUSION

In healthy middle-aged males, 2 weeks of immobilisation did not induce dramatic differences in markers of mitochondria fission and autophagy. Restoration of ambulatory physical activity following the immobilisation period restored altered gene expression patterns to pre-intervention levels, with little evidence of further adaptation to resistance exercise training.

Differential effects of calorie restriction and rapamycin on age-related molecular and functional changes in skeletal muscle

Aging is a multifactorial process associated with progressive degradation of physiological integrity and function. One of the greatest factors contributing to the deleterious effects of aging is the decline of functional ability due to loss of muscle mass, strength, and function, a condition termed sarcopenia. Calorie restriction (CR) has consistently been shown to extend lifespan and delay the onset and progression of various age-related diseases, including sarcopenia. Additional anti-aging interventions that are receiving scientific attention are CR mimetics. Of these pharmacological compounds, rapamycin has shown similar CR-related longevity benefits without the need for diet restrictions. To investigate the potential role of rapamycin as an anti-sarcopenic alternative to CR, we conducted a study in male and female C57BL/6 J mice to assess the effects of rapamycin on age-related gene expression changes in skeletal muscle associated with loss of muscle mass, strength, and function, relative to control. We hypothesize that the effects of rapamycin will closely align with CR with respect to physical function and molecular indices associated with muscle quality. Our results indicate CR and rapamycin provide partial protection against age-related decline in muscle, while engaging uniquely different molecular pathways in skeletal muscle. Our preclinical findings of the therapeutic potential of rapamycin or a CR regimen on geroprotective benefits in muscle should be extended to translational studies towards the development of effective strategies for the prevention and management of sarcopenia.

Aberrant mitochondrial homeostasis at the crossroad of musculoskeletal ageing and non-small cell lung cancer

Cancer cachexia is accompanied by muscle atrophy, sharing multiple common catabolic pathways with sarcopenia, including mitochondrial dysfunction. This study investigated gene expression from skeletal muscle tissues of older healthy adults, who are at risk of age-related sarcopenia, to identify potential gene biomarkers whose dysregulated expression and protein interference were involved in non-small cell lung cancer (NSCLC). Screening of the literature resulted in 14 microarray datasets (GSE25941, GSE28392, GSE28422, GSE47881, GSE47969, GSE59880 in musculoskeletal ageing; GSE118370, GSE33532, GSE19804, GSE18842, GSE27262, GSE19188, GSE31210, GSE40791 in NSCLC). Differentially expressed genes (DEGs) were used to construct protein-protein interaction networks and retrieve clustering gene modules. Overlapping module DEGs were ranked based on 11 topological algorithms and were correlated with prognosis, tissue expression, and tumour purity in NSCLC. The analysis revealed that the dysregulated expression of the mammalian mitochondrial ribosomal proteins, Mitochondrial Ribosomal Protein S26 (MRPS26), Mitochondrial Ribosomal Protein S17 (MRPS17), Mitochondrial Ribosomal Protein L18 (MRPL18) and Mitochondrial Ribosomal Protein L51 (MRPL51) were linked to reduced survival and tumour purity in NSCLC while tissue expression of the same genes followed an opposite direction in healthy older adults. These results support a potential link between the mitochondrial ribosomal microenvironment in ageing muscle and NSCLC. Further studies comparing changes in sarcopenia and NSCLC associated cachexia are warranted.

Association between polygenetic risk scores related to sarcopenia risk and their interactions with regular exercise in a large cohort of Korean adults

BACKGROUND & AIMS

Sarcopenia elevates metabolic disorders in the elderly, and genetic and environmental factors influence the risk of sarcopenia. The purpose of the study was to examine the hypothesis that polygenetic variants for sarcopenic risk had interactions with metabolic disorders and lifestyles associated with sarcopenia risk in adults >50 years in a large urban hospital cohort.

METHODS

Sarcopenia was defined as an appendicular skeletal muscle mass/body weight (SMI) < 29.0% for men and <22.8% for women estimated from participants aged 18-39 years in the KNHANES 2009-2010. Genetic variants were selected using a genome-wide association study for sarcopenia (sarcopenia, n = 1368; control, n = 15,472). The best model showing the gene-gene interactions was selected using a generalized multifactor dimensionality reduction. The polygenic risk scores (PRS) were generated by summing the selected SNP risk alleles in the best model.

RESULTS

SMI was much higher in the control subjects than the sarcopenia subjects in both genders, and the fat mass index was opposite the SMI. The five-single nucleotide polymorphisms (SNPs) model included FADS2_rs97384, MYO10_rs31574 KCNQ5_rs6453647, DOCK5_rs11135857, and LRP1B_ rs74659977. Sarcopenia risk was positively associated with the PRS of the five-SNP model (ORs = 1.977, 95% CI = 1.634-2.393). The PRS interacted with age (P < 0.0001), metabolic syndrome (P = 0.01), grip strength (P = 0.007), and serum total cholesterol concentrations (P = 0.005) for the sarcopenia risk. There were no interactions of PRS with the lifestyle components except for exercise.

CONCLUSION

The genetic impact may be offset in the elderly, having metabolic syndrome, high serum total cholesterol concentrations, and high grip strength, but only exercise in the lifestyle factors can overcome the genetic effect. Middle-aged and elderly participants with a genetic risk for sarcopenia may require regular exercise to maintain high grip strength and prevent metabolic syndrome.

Skeletal muscle wasting after a severe burn is a consequence of cachexia and sarcopenia

Muscle wasting is common and persistent in severely burned patients, worsened by immobilization during treatment. In this review, we posit two major phenotypes of muscle wasting after severe burn, cachexia and sarcopenia, each with distinguishing characteristics to result in muscle atrophy; these characteristics are also likely present in other critically ill populations. An online search was conducted from the PubMed database and other available online resources and we manually extracted published articles in a systematic mini review. We describe the current definitions and characteristics of cachexia and sarcopenia and relate these to muscle wasting after severe burn. We then discuss these putative mechanisms of muscle atrophy in this condition. Severe burn and immobilization have distinctive patterns in mediating muscle wasting and muscle atrophy. In considering these two pathological phenotypes (cachexia and sarcopenia), we propose two independent principal causes and mechanisms of muscle mass loss after burns: (1) inflammation-induced cachexia, leading to proteolysis and protein degradation, and (2) sarcopenia/immobility that signals inhibition of expected increases in protein synthesis in response to protein loss. Because both are present following severe burn, these should be considered independently in devising treatments. Discussing cachexia and sarcopenia as independent mechanisms of severe burn-initiated muscle wasting is explored. Recognition of these associated mechanisms will likely improve outcomes.

The biphasic and age-dependent impact of klotho on hallmarks of aging and skeletal muscle function

Aging is accompanied by disrupted information flow, resulting from accumulation of molecular mistakes. These mistakes ultimately give rise to debilitating disorders including skeletal muscle wasting, or sarcopenia. To derive a global metric of growing 'disorderliness' of aging muscle, we employed a statistical physics approach to estimate the state parameter, entropy, as a function of genes associated with hallmarks of aging. Escalating network entropy reached an inflection point at old age, while structural and functional alterations progressed into oldest-old age. To probe the potential for restoration of molecular 'order' and reversal of the sarcopenic phenotype, we systemically overexpressed the longevity protein, Klotho, via AAV. Klotho overexpression modulated genes representing all hallmarks of aging in old and oldest-old mice, but pathway enrichment revealed directions of changes were, for many genes, age-dependent. Functional improvements were also age-dependent. Klotho improved strength in old mice, but failed to induce benefits beyond the entropic tipping point.

Is inflammatory signaling involved in disease-related muscle wasting? Evidence from osteoarthritis, chronic obstructive pulmonary disease and type II diabetes

Muscle loss is an important feature that occurs in multiple pathologies including osteoarthritis (OA), chronic obstructive pulmonary disease (COPD) and type II diabetes (T2D). Despite differences in pathogenesis and disease-related complications, there are reasons to believe that some fundamental underlying mechanisms are inherent to the muscle wasting process, irrespective of the pathology. Recent evidence shows that inflammation, either local or systemic, contributes to the modulation of muscle mass and/or muscle strength, via an altered molecular profile in muscle tissue. However, it remains ambiguous to which extent and via which mechanisms inflammatory signaling affects muscle mass in disease. Therefore, the objective of the present review is to discuss the role of inflammation on skeletal muscle anabolism, catabolism and functionality in three pathologies that are characterized by an eventual loss in muscle mass (and muscle strength), i.e. OA, COPD and T2D. In OA and COPD, most rodent models confirmed that systemic (COPD) or muscle (OA) inflammation directly induces muscle loss or muscle dysfunctionality. However, in a patient population, the association between inflammation and muscular maladaptations are more ambiguous. For example, in T2D patients, systemic inflammation is associated with muscle loss whereas in OA patients this link has not consistently been established. T2D rodent models revealed that increased levels of advanced glycation end-products (AGEs) and a decreased mTORC1 activation play a key role in muscle atrophy, but it remains to be elucidated whether AGEs and mTORC1 are interconnected and contribute to muscle loss in T2D patients. Generally, if any, associations between inflammation and muscle are mainly based on observational and cross-sectional data. There is definitely a need for longitudinal evidence through well-powered randomized control trials that take into account confounders such as age, disease-phenotypes, comorbidities, physical (in) activity etc. This will allow to improve our understanding of the complex interaction between inflammatory signaling and muscle mass loss and hence contribute to the development of therapeutic strategies to combat muscle wasting in these diseases.

MicroRNAs as potential therapeutic targets for muscle wasting during cancer cachexia

PURPOSE OF REVIEW

Muscle wasting in cancer cachexia remains an unmet clinical need due to lack of effective therapies associated with the complexity of the disease. Here, we discuss microRNAs, robust regulators of the expression of multiple genes, only recently characterized in cancer cachexia in humans and their therapeutic potential for muscle wasting.

RECENT FINDINGS

Changes in microRNAs in muscle of cancer patients have been demonstrated for the first time and these are associated with dysregulated signalling networks during muscle wasting. These data, together with studies in animal models, indicate that microRNAs are attractive therapeutic candidates for maintaining muscle mass, both during and following cancer treatment ultimately improving patient outcomes.

SUMMARY

Cancer cachexia is a complex metabolic condition associated with muscle wasting. Maintenance of muscle mass in cancer patients can improve their response to therapy and prognosis. microRNAs, which can act as oncogenes or tumour suppressors, are also dysregulated in muscle of cachexia patients. Studies in animal models of muscle wasting have demonstrated that microRNAs regulate muscle mass and strength. With more microRNA-based therapeutics in clinical trials and first RNA drugs approved, microRNAs present an attractive novel therapeutic avenue for maintaining muscle homeostasis in cachexia patients to improve their prognosis.

Zebrafish models of sarcopenia

Sarcopenia – the accelerated age-related loss of muscle mass and function – is an under-diagnosed condition, and is central to deteriorating mobility, disability and frailty in older age. There is a lack of treatment options for older adults at risk of sarcopenia. Although sarcopenia's pathogenesis is multifactorial, its major phenotypes – muscle mass and muscle strength – are highly heritable. Several genome-wide association studies of muscle-related traits were published recently, providing dozens of candidate genes, many with unknown function. Therefore, animal models are required not only to identify causal mechanisms, but also to clarify the underlying biology and translate this knowledge into new interventions. Over the past several decades, small teleost fishes had emerged as powerful systems for modeling the genetics of human diseases. Owing to their amenability to rapid genetic intervention and the large number of conserved genetic and physiological features, small teleosts – such as zebrafish, medaka and killifish – have become indispensable for skeletal muscle genomic studies. The goal of this Review is to summarize evidence supporting the utility of small fish models for accelerating our understanding of human skeletal muscle in health and disease. We do this by providing a basic foundation of the (zebra)fish skeletal muscle morphology and physiology, and evidence of muscle-related gene homology. We also outline challenges in interpreting zebrafish mutant phenotypes and in translating them to human disease. Finally, we conclude with recommendations on future directions to leverage the large body of tools developed in small fish for the needs of genomic exploration in sarcopenia.

Summary: Zebrafish and other small fish have become powerful disease models. Here, we summarize the evidence for the utility of small teleost models for genetic research in sarcopenia – the age-related loss of muscle mass and function.