Sarcopenia--The search for emerging biomarkers

A Pound of Flesh: What Cachexia Is and What It Is Not

Body weight loss, mostly due to the wasting of skeletal muscle and adipose tissue, is the hallmark of the so-called cachexia syndrome. Cachexia is associated with several acute and chronic disease states such as cancer, chronic obstructive pulmonary disease (COPD), heart and kidney failure, and acquired and autoimmune diseases and also pharmacological treatments such as chemotherapy. The clinical relevance of cachexia and its impact on patients’ quality of life has been neglected for decades. Only recently did the international community agree upon a definition of the term cachexia, and we are still awaiting the standardization of markers and tests for the diagnosis and staging of cancer-related cachexia. In this review, we discuss cachexia, considering the evolving use of the term for diagnostic purposes and the implications it has for clinical biomarkers, to provide a comprehensive overview of its biology and clinical management. Advances and tools developed so far for the in vitro testing of cachexia and drug screening will be described. We will also evaluate the nomenclature of different forms of muscle wasting and degeneration and discuss features that distinguish cachexia from other forms of muscle wasting in the context of different conditions.

Sarcopenia during COVID-19 lockdown restrictions: long-term health effects of short-term muscle loss

The COVID-19 pandemic is an extraordinary global emergency that has led to the implementation of unprecedented measures in order to stem the spread of the infection. Internationally, governments are enforcing measures such as travel bans, quarantine, isolation, and social distancing leading to an extended period of time at home. This has resulted in reductions in physical activity and changes in dietary intakes that have the potential to accelerate sarcopenia, a deterioration of muscle mass and function (more likely in older populations), as well as increases in body fat. These changes in body composition are associated with a number of chronic, lifestyle diseases including cardiovascular disease (CVD), diabetes, osteoporosis, frailty, cognitive decline, and depression. Furthermore, CVD, diabetes, and elevated body fat are associated with greater risk of COVID-19 infection and more severe symptomology, underscoring the importance of avoiding the development of such morbidities. Here we review mechanisms of sarcopenia and their relation to the current data on the effects of COVID-19 confinement on physical activity, dietary habits, sleep, and stress as well as extended bed rest due to COVID-19 hospitalization. The potential of these factors to lead to an increased likelihood of muscle loss and chronic disease will be discussed. By offering a number of home-based strategies including resistance exercise, higher protein intakes and supplementation, we can potentially guide public health authorities to avoid a lifestyle disease and rehabilitation crisis post-COVID-19. Such strategies may also serve as useful preventative measures for reducing the likelihood of sarcopenia in general and in the event of future periods of isolation.

Concentrations of Circulating Irisin and Myostatin in Race and Endurace Purebred Arabian Horses-Preliminary Study

Simple Summary

Irisin and myostatin are regulatory proteins produced by muscle cells. The aim of the study was to evaluate the effect of exercise on plasma irisin and myostatin concentrations in horses in different types of training (speed versus endurance). To find out, we tested 20 Arabian horses, submitted to the two different equestrian disciplines, and consequently different training regimes. The first group of horses realized a short-term, high-speed bout of exercise whereas the second group of horses were submitted to long-lasting, endurance effort. The obtained results showed that the single bout of exercise induced an increase in plasma myostatin concentration. Plasma irisin level decreased during the race season in racehorses. This means that irisin and myostatin may play a regulatory role in the maintenance of the energy balance processes.

Abstract

Skeletal muscle is considered to be the largest endocrine organ determining the maintenance of energy homeostasis. Adaptive changes in skeletal muscles in response to physical exercise influence the production as well as secretion of myokines, which are bioactive factors that play a crucial role in energy expenditure processes. The aim of the study was to investigate the impact of two different types of exercise on the circulating level of two of these, myostatin and irisin, in trained horses. Twenty purebred Arabian horses were involved in the study: 10 three-year-old horses trained on the racetrack and 10 endurance horses aged 7.4 ± 1.9 years. The horses from both groups were regularly trained throughout the entire season, during which they also participated in Polish National competitions. To assess the influence of the training sessions on plasma myostatin and irisin concentrations, blood samples taken at rest and 30 min after the end of exercise were analyzed. In the studied horses, the single bout of exercise did not influence plasma irisin but induced an increase in plasma myostatin concentration. In racehorses, plasma irisin concentration decreased with the length of the training season. Plasma myostatin was higher in endurance horses than in three-year-old racehorses. Lack of exercise-induced fluctuation in circulating irisin in studied horses suggests that myostatin released in response to exercise provides a negative feedback signal to irisin release.

Motoneuron deafferentation and gliosis occur in association with neuromuscular regressive changes during ageing in mice

BACKGROUND

The cellular mechanisms underlying the age-associated loss of muscle mass and function (sarcopenia) are poorly understood, hampering the development of effective treatment strategies. Here, we performed a detailed characterization of age-related pathophysiological changes in the mouse neuromuscular system.

METHODS

Young, adult, middle-aged, and old (1, 4, 14, and 24-30 months old, respectively) C57BL/6J mice were used. Motor behavioural and electrophysiological tests and histological and immunocytochemical procedures were carried out to simultaneously analyse structural, molecular, and functional age-related changes in distinct cellular components of the neuromuscular system.

RESULTS

Ageing was not accompanied by a significant loss of spinal motoneurons (MNs), although a proportion (~15%) of them in old mice exhibited an abnormally dark appearance. Dark MNs were also observed in adult (~9%) and young (~4%) animals, suggesting that during ageing, some MNs undergo early deleterious changes, which may not lead to MN death. Old MNs were depleted of cholinergic and glutamatergic inputs (~40% and ~45%, respectively, P < 0.01), suggestive of age-associated alterations in MN excitability. Prominent microgliosis and astrogliosis [~93% (P < 0.001) and ~100% (P < 0.0001) increase vs. adults, respectively] were found in old spinal cords, with increased density of pro-inflammatory M1 microglia and A1 astroglia (25-fold and 4-fold increase, respectively, P < 0.0001). Ageing resulted in significant reductions in the nerve conduction velocity and the compound muscle action potential amplitude (~30%, P < 0.05, vs. adults) in old distal plantar muscles. Compared with adult muscles, old muscles exhibited significantly higher numbers of both denervated and polyinnervated neuromuscular junctions, changes in fibre type composition, higher proportion of fibres showing central nuclei and lipofuscin aggregates, depletion of satellite cells, and augmented expression of different molecules related to development, plasticity, and maintenance of neuromuscular junctions, including calcitonin gene-related peptide, growth associated protein 43, agrin, fibroblast growth factor binding protein 1, and transforming growth factor-β1. Overall, these alterations occurred at varying degrees in all the muscles analysed, with no correlation between the age-related changes observed and myofiber type composition or muscle topography.

CONCLUSIONS

Our data provide a global view of age-associated neuromuscular changes in a mouse model of ageing and help to advance understanding of contributing pathways leading to development of sarcopenia.

Intensive Care Unit-Acquired Weakness: A Review of Recent Progress With a Look Toward the Future

Intensive care unit-acquired weakness (ICU-AW), a common neuromuscular complication associated with patients in the ICU, is a type of skeletal muscle dysfunction that commonly occurs following sepsis, mobility restriction, hyperglycemia, and the use of glucocorticoids or neuromuscular blocking agents. ICU-AW can lead to delayed withdrawal of mechanical ventilation and extended hospitalization. Patients often have poor prognosis, limited mobility, and severely affected quality of life. Currently, its pathogenesis is uncertain, with unavailability of specific drugs or targeted therapies. ICU-AW has gained attention in recent years. This manuscript reviews the current research status of the epidemiology, pathogenesis, diagnosis, and treatment methods for ICU-AW and speculates the novel perspectives for future research.

Association between serum irisin concentrations and sarcopenia in patients with liver cirrhosis: a cross-sectional study

Sarcopenia is an independent predictor of mortality in patients with liver cirrhosis. However, evidence has emerged that skeletal muscles mediate their protective effect against sarcopenia by secreting myokines. Therefore, we investigated whether irisin was associated with sarcopenia in patients with liver cirrhosis. This was an observational cross-sectional study of data collected from 187 cirrhotic patients. Sarcopenia was defined by computed tomography (CT) scans using specific cutoffs of the 3rd lumbar vertebra skeletal muscle index (L₃ SMI). Morning irisin levels were obtained in all patients. Of the 187 patients, sarcopenia was noted in 73 (39%). Irisin concentrations were lower in sarcopenic patients (32.40 pg/ml [interquartile range (IQR): 18.70, 121.26], p < 0.001) than in nonsarcopenic patients. There was a weak correlation between L₃ SMI and irisin levels (r = 0.516, p < 0.001). Multivariable regression analysis including L₃ SMI, body mass index (BMI), very-low-density lipoprotein (VLDL)-cholesterol, aspartate aminotransferase (AST), adiponectin, and irisin levels showed that L₃ SMI (odds ratio [OR] = 0.915, p = 0.023), adiponectin levels (OR = 1.074, p = 0.014), irisin levels (OR = 0.993, p < 0.001) and BMI (OR = 0.456, p = 0.004) were independently associated with sarcopenia. Irisin levels are associated with sarcopenia in patients with liver cirrhosis. This paper addresses a gap in the literature and facilitates the future transition into clinical treatment.

Assessment of muscle mass in critically ill patients: role of the sarcopenia index and images studies

PURPOSE OF REVIEW

Sarcopenia is a progressive generalized decline in skeletal muscle mass, strength, and function. This condition is highly prevalent in critically ill patients and is associated with poor outcomes in the ICU. In this review, we describe the use, evidence, and limitations of the most common validated imaging studies used to assess muscle mass in ICU, and we provide an overview of the benefits of using the sarcopenia index [(serum creatinine/serum cystatin C) × 100]) in the ICU.

RECENT FINDINGS

Currently, the determination of muscle mass using anthropometric measurements and serum biomarkers is unreliable. Several new techniques, including a dual-energy X-ray absorptiometry, computed tomography scan, ultrasonography, and bioimpedance analysis, have been studied and validated for the diagnosis and prognosis of sarcopenia in the ICU. However, these techniques are often not accessible for the majority of critically ill patients. The sarcopenia index constitutes an accurate method to diagnose sarcopenia, predict ICU outcomes, and nutritional status in critically ill patients.

SUMMARY

Diagnosis of sarcopenia has substantial implications in ICU patients. Choosing the correct test to identify patients who may need preventive or therapeutic support for this condition will favorably impact ICU outcomes.

Sarcopenic obesity: Myokines as potential diagnostic biomarkers and therapeutic targets?

Sarcopenic obesity (SO) is a condition characterized by the occurrence of both sarcopenia and obesity and imposes a heavy burden on the health of the elderly. Controversies and challenges regarding the definition, diagnosis and treatment of SO still remain because of its complex pathogenesis and limitations. Over the past few decades, numerous studies have revealed that myokines secreted from skeletal muscle play significant roles in the regulation of muscle mass and function as well as metabolic homeostasis. Abnormalities in myokines may trigger and promote the pathogenesis underlying age-related and metabolic diseases, including obesity, sarcopenia, type 2 diabetes (T2D), and SO. This review mainly focuses on the role of myokines as potential biomarkers for the early diagnosis and therapeutic targets in SO.

The association of the serum levels of myostatin, follistatin, and interleukin-6 with sarcopenia, and their impacts on survival in patients with hepatocellular carcinoma

Background/Aims

The role of serum myokine levels in sarcopenia and the outcome of hepatocellular carcinoma (HCC) patients are not clear. This study investigated the serum levels of myostatin, follistatin, and interleukin-6 (IL-6) in HCC patients and their association with sarcopenia and survival.

Methods

Using prospectively collected pretreatment samples from 238 HCC patients in a hospital from 2012 to 2015, the serum levels of 3 myokines were determined and compared to 50 samples from age and sex-matched healthy controls. Sarcopenia was evaluated using the psoas muscle index (PMI) measured at the third lumbar level in the computed tomography, and clinical data were collected until 2017.

Results

The median levels of the 3 myokines for the male and female HCC patients were as follow: myostatin (3,979.3 and 2,976.3 pg/mL), follistatin (2,118.5 and 2,174.6 pg/mL), and IL-6 (2.5 and 2.7 pg/mL), respectively. Those in the HCC patients were all significantly higher than in the healthy controls. In the HCC patient, the median PMI was 4.43 (males) and 2.17 cm²/m² (females) with a sarcopenic prevalence of 56.4%. The serum levels of myostatin, IL-6 and follistatin in the HCC patients showed a positive, negative, and no correlation with PMI, respectively. The serum follistatin level was an independent factor for poor survival in HCC patients.

Conclusions

The serum levels of myostatin, follistatin, and IL-6 and their correlation with sarcopenia and survival were presented in HCC patients for the first time. The role of the serum follistatin level as a poor prognostic biomarker warrants further study.

The effect of Korean Red Ginseng on sarcopenia biomarkers in type 2 diabetes patients

BACKGROUND

The elderly population is growing rapidly worldwide and sarcopenia, which is considered as a new geriatric syndrome has become an important issue. In particular, diabetes is known to be an important risk factor for sarcopenia. In this study, we investigated the effects of Korean Red Ginseng (KRG) on biomarkers of sarcopenia in middle and old age diabetes patients.

PATIENTS AND METHODS

This study was a randomized, double-blind, placebo-controlled trial. Participants were randomly allocated to either the placebo or KRG group and took corresponding tablets for 24 weeks. The primary outcomes were changes in sarcopenia biomarkers at week 24. Secondary outcomes were changes in inflammatory and antioxidant markers and lean body mass at week 24.

RESULTS

Fifty-nine patients completed the study. Follistatin and sex hormone binding globulin (SHBG) were significantly improved in KRG group. In the subgroup analysis, female postmenopausal patients over the age of 55 showed a significant improvement in serum SHBG, follistatin, and growth differentiation factor 15 (GDF-15) and an attenuated reduction in Troponin T (TNT) after the administration of KRG.

CONCLUSION

Twenty-four week administration of KRG in diabetes patients resulted in a significant improvement in follistatin and SHBG levels, especially in old postmenopausal women. A further, larger population study with a longer follow-up period is warranted to verify and understand the effects of KRG on sarcopenia.

Replication of FTO Gene associated with lean mass in a Meta-Analysis of Genome-Wide Association Studies

Sarcopenia is characterized by low skeletal muscle, a complex trait with high heritability. With the dramatically increasing prevalence of obesity, obesity and sarcopenia occur simultaneously, a condition known as sarcopenic obesity. Fat mass and obesity-associated (FTO) gene is a candidate gene of obesity. To identify associations between lean mass and FTO gene, we performed a genome-wide association study (GWAS) of lean mass index (LMI) in 2207 unrelated Caucasian subjects and replicated major findings in two replication samples including 6,004 unrelated Caucasian and 38,292 unrelated Caucasian. We found 29 single nucleotide polymorphisms (SNPs) in FTO significantly associated with sarcopenia (combined p-values ranging from 5.92 × 10⁻¹² to 1.69 × 10⁻⁹). Potential biological functions of SNPs were analyzed by HaploReg v4.1, RegulomeDB, GTEx, IMPC and STRING. Our results provide suggestive evidence that FTO gene is associated with lean mass.

Viewpoint on the role of tissue maintenance in ageing: focus on biomarkers of bone, cartilage, muscle, and brain tissue maintenance

Specific hallmarks are thought to underlie the ageing process and age-related functional decline. In this viewpoint, we put forward the hypothesis that disturbances in the process of tissue maintenance are an important common denominator that may lie in between specific hallmarks of ageing (i.e. damage and responses to damage) and their ultimate (patho)physiological consequences (i.e. functional decline and age-related disease). As a first step towards verifying or falsifying this hypothesis, it will be important to measure biomarkers of tissue maintenance in future studies in different study populations. The main aim of the current paper is to discuss potential biomarkers of tissue maintenance that could be used in such future studies. Among the many tissues that could have been chosen to explore our hypothesis, to keep the paper manageable, we chose to focus on a selected number of tissues, namely bone, cartilage, muscle, and the brain, which are important for mobility and cognition and affected in several common age-related diseases, including osteoporosis, osteoarthritis, sarcopenia, and neurodegenerative diseases. Furthermore, we discuss the advantages and limitations of potential biomarkers for use in (pre)clinical studies. The proposed biomarkers should be validated in future research, for example by measuring these in humans with different rates of ageing.

Inflammaging as a common ground for the development and maintenance of sarcopenia, obesity, cardiomyopathy and dysbiosis

Sarcopenia, obesity and their coexistence, obese sarcopenia (OBSP) as well as atherosclerosis-related cardio-vascular diseases (ACVDs), including chronic heart failure (CHF), are among the greatest public health concerns in the ageing population. A clear age-dependent increased prevalence of sarcopenia and OBSP has been registered in CHF patients, suggesting mechanistic relationships. Development of OBSP could be mediated by a crosstalk between the visceral and subcutaneous adipose tissue (AT) and the skeletal muscle under conditions of low-grade local and systemic inflammation, inflammaging. The present review summarizes the emerging data supporting the idea that inflammaging may serve as a mutual mechanism governing the development of sarcopenia, OBSP and ACVDs. In support of this hypothesis, various immune cells release pro-inflammatory mediators in the skeletal muscle and myocardium. Subsequently, the endothelial structure is disrupted, and cellular processes, such as mitochondrial activity, mitophagy, and autophagy are impaired. Inflamed myocytes lose their contractile properties, which is characteristic of sarcopenia and CHF. Inflammation may increase the risk of ACVD events in a hyperlipidemia-independent manner. Significant reduction of ACVD event rates, without the lowering of plasma lipids, following a specific targeting of key pro-inflammatory cytokines confirms a key role of inflammation in ACVD pathogenesis. Gut dysbiosis, an imbalanced gut microbial community, is known to be deeply involved in the pathogenesis of age-associated sarcopenia and ACVDs by inducing and supporting inflammaging. Dysbiosis induces the production of trimethylamine-N-oxide (TMAO), which is implicated in atherosclerosis, thrombosis, metabolic syndrome, hypertension and poor CHF prognosis. In OBSP, AT dysfunction and inflammation induce, in concert with dysbiosis, lipotoxicity and other pathophysiological processes, thus exacerbating sarcopenia and CHF. Administration of specialized, inflammation pro-resolving mediators has been shown to ameliorate the inflammatory manifestations. Considering all these findings, we hypothesize that sarcopenia, OBSP, CHF and dysbiosis are inflammaging-oriented disorders, whereby inflammaging is common and most probably the causative mechanism driving their pathogenesis.

Aging: therapeutics for a healthy future

Increased healthcare and pharmaceutical understanding has led to the eradication of many childhood, infectious and preventable diseases; however, we are now experiencing the impact of aging disorders as the lifespan increases. These disorders have already become a major burden on society and threaten to become a defining challenge of our generation. Indications such as Alzheimer's disease gain headlines and have focused the thinking of many towards dementia and cognitive decline in aging. Indications related to neurological function and related behaviors are thus an extremely important starting point in the consideration of therapeutics.However, the reality is that pathological aging covers a spectrum of significant neurological and peripheral indications. Development of therapeutics to treat aging and age-related disorders is therefore a huge need, but represents a largely unexplored path. Fundamental scientific questions need to be considered as we embark towards a goal of improving health in old age, including how we 1) define aging as a therapeutic target, 2) model aging preclinically and 3) effectively translate from preclinical models to man. Furthermore, the challenges associated with identifying novel therapeutics in a financial, regulatory and clinical sense need to be contemplated carefully to ensure we address the unmet need in our increasingly elderly population. The complexity of the challenge requires different perspectives, cross-functional partnerships and diverse concepts. We seek to raise issues to guide the field, considering the current state of thinking to aid in identifying roadblocks and important challenges early. The need for therapeutics that address aging and age-related disorders is acute, but the promise of effective treatments provides huge opportunities that, as a community, we all seek to enable effectively as soon as possible.

CCN1 induces adipogenic differentiation of fibro/adipogenic progenitors in a chronic kidney disease model

Previous studies have shown that sarcopenic obesity is highly prevalent in patients with chronic kidney disease (CKD). Here, the association between CKD and sarcopenic obesity were investigated. The 5/6 nephrectomy was performed to establish CKD in mice. Fluorescence-activated cell sorting (FACS), quantitative real-time PCR, ELISA kits assay, immunohistochemistry, and cell proliferation assay were carried out to investigate the condition of muscle loss and fatty infiltration were in CKD mice and the origin of adipocytes. Muscle atrophy occurred and adipogenic gene expression, Perilipin and FABP4 were markedly increased in the hind limb muscle of CKD mice. Results indicated that fibro/adipogenic progenitors (FAPs) are the precursor of adipocytes in the muscle of CKD mice. Meanwhile, the content of extracellular matrix protein CCN1 was notably increased in serum of CKD patients with sarcopenic obesity which was also found in muscle and serum of CKD mice. CCN1 induced the differentiation of FAPs into adipocytes. These results suggest that CKD mice are susceptible to sarcopenic obesity. CCN1 may be a novel activator of the differentiation of FAPs in CKD muscle.

Pharmacological Interventions for Treatment of Sarcopenia: Current Status of Drug Development for Sarcopenia

Sarcopenia, the loss of skeletal muscle mass and function with age, was first recognized as a disease in the International Classification of Diseases, Tenth Revision, Clinical Modification (ICD-10-CM) (M62.84) and has recently attracted attention as aged populations increase. However, the diagnostic criteria for sarcopenia remain controversial and there are as yet no US Food and Drug Administration-approved medications for sarcopenia. Given that both intrinsic and extrinsic factors contribute to sarcopenia onset and development, understanding the mechanism of sarcopenia is important for the development of therapeutic strategies. In this review, we described a variety of drugs for sarcopenia under investigation, including myostatin/ActR2 signaling inhibitors, exercise mimetics, anabolic hormones, and natural compounds. However, the combination of non-drug therapies with exercise and nutritional supplements are also needed as more easily accessible intervention strategies against sarcopenia rather than pharmacological treatments alone. Many approaches to develop therapeutic methods to overcome sarcopenia may lead to healthy aging.

A Sensitive and Selective Immunoassay for the Quantitation of Serum Latent Myostatin after In Vivo Administration of SRK-015, a Selective Inhibitor of Myostatin Activation

Myostatin, a member of the transforming growth factor β (TGFβ) superfamily, is a key regulator of skeletal muscle mass and a therapeutic target for muscle wasting diseases. We developed a human monoclonal antibody, SRK-015, that selectively binds to and inhibits proteolytic processing of myostatin precursors, thereby preventing growth factor release from the latent complex. As a consequence of antibody binding, latent myostatin accumulates in the circulation of animals treated with SRK-015 or closely related antibodies, suggesting that quantitation of latent myostatin in serum may serve as a biomarker for target engagement. To accurately measure SRK-015 target engagement, we developed a sensitive plate-based electrochemiluminescent immunoassay to quantitate latent myostatin in serum samples. The assay selectively recognizes latent myostatin without cross-reactivity to promyostatin, mature myostatin, or closely related members of the TGFβ superfamily. To enable use of the assay in samples from animals dosed with SRK-015, we incorporated a low-pH step that dissociates SRK-015 from latent myostatin, improving drug tolerance of the assay. The assay meets inter- and intra-assay accuracy and precision acceptance criteria, and it has a lower limit of quantitation (LLOQ) of 10 ng/mL. We then tested serum samples from a pharmacology study in cynomolgus monkeys treated with SRK-015. Serum latent myostatin increases after treatment with SRK-015, reaches a dose-dependent plateau approximately 20 days after dosing, and trends back toward baseline after cessation of antibody dosing. Taken together, these data suggest that this assay can be used to accurately measure levels of the primary circulating form of myostatin in population-based or pharmacodynamic studies.

Circulating Irisin and Myostatin as Markers of Muscle Strength and Physical Condition in Elderly Subjects

Background and objective

Aging is a physiological process known to produce changes in body composition, affecting the musculature and leading to decreased muscle strength. Muscle in response to exercise acts as an endocrine organ, producing and releasing myokines such as irisin and myostatin that modulate muscular growth. Here, we aimed to evaluate the effects of low intensity resistance exercise, with or without protein supplementation, on body composition, anthropometric parameters and circulating irisin and myostatin in elderly subjects.

Methods

This is a prospective and controlled clinical trial in which subjects were randomized into 3 groups: (1) control group (n = 20), (2) low intensity resistance exercise group (RE) (n = 14), and (3) low intensity resistance exercise and nutritional support group (RENS) (n = 9). Participants, aged 60-75 years, were studied at baseline and 16 weeks thereafter. Body composition was evaluated through bioelectric impedance. Serum irisin and myostatin was measured using ELISA.

Results

At follow-up, RENS resulted in a significant increase in fat free mass (47.4 ± 7.4 vs. 46.5 ± 7.4, p = 0.046), the calf muscle circumference (36.4 ± 1.3 vs. 32.3 ± 4.3, p = 0.025), and circulating irisin (3 ± 1.1 vs. 2.6 ± 1.3, p = 0.030) compared to baseline. RE resulted in a significant increase in grip strength (17.2 ± 4.6 vs. 15.3 ± 4.6, p = 0.011) and irisin (3.1 ± 0.8 vs. 2.4 ± 0.3, p = 0.011) and decreased walking speed at different distance (p < 0.02). Opposite findings in these parameters were observed in control intervention. In line with these findings, the percent change of calf muscle circumference (p = 0.003) and fat free mass (p < 0.0001) were significantly increased in RENS compared to control, whereas fat mass (p = 0.033) was decreased. Interestingly, in this group, strength was positively correlated with fat free mass (r = 0.782, p = 0.008), and circulating irisin was significantly decreased in those participants with strength loss at the end of the study (p = 0.002). No significant correlation between circulating irisin and myostatin in any group was observed.

Conclusion

Circulating irisin, but not myostatin, constitutes a marker for improved muscular performance in elderly subjects.

The effects of resveratrol feeding and exercise training on the skeletal muscle function and transcriptome of aged rats

This study investigated the effects of resveratrol feeding and exercise training on the skeletal muscle function and transcriptome of aged rats. Male SD rats (25 months old) were divided into the control group (Old), the daily exercise training group (Trained), and the resveratrol feeding group (Resveratrol). After 6 weeks of intervention, the body mass, grip strength, and gastrocnemius muscle mass were determined, and the muscle samples were analyzed by transcriptome sequencing. The differentially expressed genes were analyzed followed by GO enrichment analysis and KEGG analysis. The Old group showed positive increases in body mass, while both the Trained and Resveratrol groups showed negative growth. No significant differences in the gastrocnemius muscle index and absolute grip strength were found among the three groups. However, the relative grip strength was higher in the Trained group than in the Old group. Only 21 differentially expressed genes were identified in the Trained group vs. the Old group, and 12 differentially expressed genes were identified in the Resveratrol group vs. the Old group. The most enriched GO terms in the Trained group vs. the Old group were mainly associated with RNA metabolic processes and transmembrane transporters, and the significantly upregulated KEGG pathways included mucin-type O-glycan biosynthesis, drug metabolism, and pyrimidine metabolism. The most enriched GO terms in the Resveratrol group vs. the Old group were primarily associated with neurotransmitter transport and synaptic vesicle, and the upregulated KEGG pathways included synaptic vesicle cycle, nicotine addiction, retinol metabolism, insulin secretion, retrograde endocannabinoid signaling, and glutamatergic synapse. Neither exercise training nor resveratrol feeding has a notable effect on skeletal muscle function and related gene expression in aged rats. However, both exercise training and resveratrol feeding have strong effects on weight loss, which is beneficial for reducing the exercise loads of the elderly.

Circulating Biomarkers of Testosterone's Anabolic Effects on Fat-Free Mass

BACKGROUND

Biomarkers that predict response to anabolic therapies could expedite the development of function promoting anabolic drugs. This study aimed to identify serum biomarkers that are responsive to testosterone administration and associated with increases in fat-free mass (FFM).

METHODS

Serum samples were obtained from the 5α-Reductase Trial, a randomized trial that compared the effects of graded doses of testosterone enanthate for 20-weeks in healthy men randomized to placebo or dutasteride (dual SRD5A inhibitor). Testosterone's effects on FFM or strength measures did not differ between placebo vs dutasteride groups. Accordingly, 54 subjects treated with testosterone plus placebo were included in the Discovery Cohort, and 48 randomized to dutasteride were included in the Validation Cohort. 1162 biomarkers were evaluated using pre-specified criteria.

RESULTS

In the Discovery Cohort, testosterone administration increased PRO-C3 and PRO-C6 levels in a dose- and concentration-dependent manner; increases in these biomarkers from baseline to week-12 were associated with changes in FFM from baseline to week-20 (PRO-C3: r2=0.437, p<0.001; PRO-C6: r2=0.434, p<0.001). Changes in PRO-C3 and PRO-C6 levels were significantly associated with changes in chest press strength (PRO-C3: r2=0.394, p<0.001; PRO-C6: r2=0.530, p<0.001). In the SOMAscan, changes in insulin-like growth factor binding protein-6 (IGFBP6) and Glypican 3 (GPC3) were associated with changes in total and free testosterone levels and FFM. These findings were replicated in the Validation Cohort.

CONCLUSION

PRO-C3, PRO-C6, IGFBP6 and GPC3 fulfilled the pre-specified criteria for biomarkers of testosterone-induced muscle anabolism: changes in these biomarkers were associated with changes in total and free testosterone concentrations and with testosterone-induced gains in FFM.

Serum biomarkers for predicting overall survival and early mortality in older patients with metastatic solid tumors

OBJECTIVES

We aimed to explore serum biomarkers for predicting survival of older patients with metastatic solid tumors who received first line palliative chemotherapy.

MATERIALS AND METHODS

Serum samples were prospectively collected before first-line chemotherapy at 11 academic centers in Korea. All patients were participants in a prospective cohort study of older patients with metastatic solid tumors. Serum levels of C-reactive protein (CRP), CXCL10, SIRT1, VEGF-A, activin A, C-terminal telopeptide of type I collagen (CTx), total 25-hydroxyvitamin D were measured by ELISA and interleukin-6 (IL-6), myostatin, irisin, FGF-19, FGF-21, FGF-23 by Luminex multiplex assay. Overall survival (OS) was determined.

RESULTS

Serum samples from 138 patients (median age: 75 years, range: 70-92 years) were collected from February 2014 to December 2016. During a median follow up time of 13.8 months, 73 (52.9%) patients died. Among 13 serum markers, CRP (log-rank, P = 0.009), activin A (P = 0.007), and myostatin (P = 0.047) were significantly correlated with OS in univariate analyses. Activin A (hazard ratio [HR] 2.22, 95% confidence interval [CI] 1.32-3.72; P = 0.003) and myostatin (HR 3.02, 95% CI 1.39-6.57; P = 0.005) were significantly associated with OS after adjustment for other clinical factors. In predicting early (6-month) mortality, two inflammatory markers, IL-6 and CRP, were included in the decision-tree model.

CONCLUSION

In older patients with cancer, high serum concentrations of activin A and myostatin were predictive of poor OS. IL-6 and CRP might be useful to select older patients at risk of early mortality. These markers could be incorporated into predictive tools for clinical decision-making and warrant further investigation.

Tocotrienol-Rich Fraction (TRF) Treatment Promotes Proliferation Capacity of Stress-Induced Premature Senescence Myoblasts and Modulates the Renewal of Satellite Cells: Microarray Analysis

Human skeletal muscle is a vital organ involved in movement and force generation. It suffers from deterioration in mass, strength, and regenerative capacity in sarcopenia. Skeletal muscle satellite cells are involved in the regeneration process in response to muscle loss. Tocotrienol, an isomer of vitamin E, was reported to have a protective effect on cellular aging. This research is aimed at determining the modulation of tocotrienol-rich fraction (TRF) on the gene expressions of stress-induced premature senescence (SIPS) human skeletal muscle myoblasts (CHQ5B). CHQ5B cells were divided into three groups, i.e., untreated young control, SIPS control (treated with 1 mM hydrogen peroxide), and TRF-posttreated groups (24 hours of 50 μg/mL TRF treatment after SIPS induction). The differential gene expressions were assessed using microarray, GSEA, and KEGG pathway analysis. Results showed that TRF treatment significantly regulated the gene expressions, i.e., p53 (RRM2B, SESN1), ErbB (EREG, SHC1, and SHC3), and FoxO (MSTN, SMAD3) signalling pathways in the SIPS myoblasts compared to the SIPS control group (p < 0.05). TRF treatment modulated the proliferation capacity of SIPS myoblasts through regulation of ErbB (upregulation of expression of EREG, SHC1, and SHC3) and FoxO (downregulation of expression of MSTN and SMAD3) and maintaining the renewal of satellite cells through p53 signalling (upregulation of RRM2B and SESN1), MRF, cell cycle, and Wnt signalling pathways.

Towards frailty biomarkers: Candidates from genes and pathways regulated in aging and age-related diseases

OBJECTIVE

Use of the frailty index to measure an accumulation of deficits has been proven a valuable method for identifying elderly people at risk for increased vulnerability, disease, injury, and mortality. However, complementary molecular frailty biomarkers or ideally biomarker panels have not yet been identified. We conducted a systematic search to identify biomarker candidates for a frailty biomarker panel.

METHODS

Gene expression databases were searched (http://genomics.senescence.info/genes including GenAge, AnAge, LongevityMap, CellAge, DrugAge, Digital Aging Atlas) to identify genes regulated in aging, longevity, and age-related diseases with a focus on secreted factors or molecules detectable in body fluids as potential frailty biomarkers. Factors broadly expressed, related to several "hallmark of aging" pathways as well as used or predicted as biomarkers in other disease settings, particularly age-related pathologies, were identified. This set of biomarkers was further expanded according to the expertise and experience of the authors. In the next step, biomarkers were assigned to six "hallmark of aging" pathways, namely (1) inflammation, (2) mitochondria and apoptosis, (3) calcium homeostasis, (4) fibrosis, (5) NMJ (neuromuscular junction) and neurons, (6) cytoskeleton and hormones, or (7) other principles and an extensive literature search was performed for each candidate to explore their potential and priority as frailty biomarkers.

RESULTS

A total of 44 markers were evaluated in the seven categories listed above, and 19 were awarded a high priority score, 22 identified as medium priority and three were low priority. In each category high and medium priority markers were identified.

CONCLUSION

Biomarker panels for frailty would be of high value and better than single markers. Based on our search we would propose a core panel of frailty biomarkers consisting of (1) CXCL10 (C-X-C motif chemokine ligand 10), IL-6 (interleukin 6), CX3CL1 (C-X3-C motif chemokine ligand 1), (2) GDF15 (growth differentiation factor 15), FNDC5 (fibronectin type III domain containing 5), vimentin (VIM), (3) regucalcin (RGN/SMP30), calreticulin, (4) PLAU (plasminogen activator, urokinase), AGT (angiotensinogen), (5) BDNF (brain derived neurotrophic factor), progranulin (PGRN), (6) α-klotho (KL), FGF23 (fibroblast growth factor 23), FGF21, leptin (LEP), (7) miRNA (micro Ribonucleic acid) panel (to be further defined), AHCY (adenosylhomocysteinase) and KRT18 (keratin 18). An expanded panel would also include (1) pentraxin (PTX3), sVCAM/ICAM (soluble vascular cell adhesion molecule 1/Intercellular adhesion molecule 1), defensin α, (2) APP (amyloid beta precursor protein), LDH (lactate dehydrogenase), (3) S100B (S100 calcium binding protein B), (4) TGFβ (transforming growth factor beta), PAI-1 (plasminogen activator inhibitor 1), TGM2 (transglutaminase 2), (5) sRAGE (soluble receptor for advanced glycosylation end products), HMGB1 (high mobility group box 1), C3/C1Q (complement factor 3/1Q), ST2 (Interleukin 1 receptor like 1), agrin (AGRN), (6) IGF-1 (insulin-like growth factor 1), resistin (RETN), adiponectin (ADIPOQ), ghrelin (GHRL), growth hormone (GH), (7) microparticle panel (to be further defined), GpnmB (glycoprotein nonmetastatic melanoma protein B) and lactoferrin (LTF). We believe that these predicted panels need to be experimentally explored in animal models and frail cohorts in order to ascertain their diagnostic, prognostic and therapeutic potential.

Myostatin and other musculoskeletal markers in lung transplant recipients

Recipients of lung transplantation (LuTx) may experience impaired muscle function and bone metabolism even after rehabilitation. We investigated the potential use of musculoskeletal markers in identifying the impairment of muscle function and bone function in these patients. Biochemical parameters, bodily functions, and lung function of 37 LuTx recipients were evaluated at the time of their discharge from the hospital stay and about 6 months later. The biomarkers were also assessed in 30 healthy age and gender distribution-matched controls. Compared to controls, the negative muscle regulator myostatin was elevated in LuTx recipients at baseline and follow-up, whereas its opponent follistatin only showed a group-specific difference at follow-up. LuTx recipients had reduced serum levels of sclerostin and increased levels of dickkopf 1 and periostin. Lung function and physical function were improved during follow-up. The change in lung function was correlated with the change in chair-rising time and the 6-min walking test. At follow-up, all musculoskeletal markers of LuTx recipients differed from those of controls, thus reflecting their still reduced lung function and bodily functions. Among the tested biomarkers, myostatin, sclerostin, dickkopf 1, and periostin were useful to detect impaired musculoskeletal function in LuTx recipients. Myostatin may serve as a target of treatment in the future.

Hyperphosphatemia Promotes Senescence of Myoblasts by Impairing Autophagy Through Ilk Overexpression, A Possible Mechanism Involved in Sarcopenia

In mammalians, advancing age is associated with sarcopenia, the progressive and involuntary loss of muscle mass and strength. Hyperphosphatemia is an aging-related condition involved in several pathologies. The aim of this work was to assess whether hyperphosphatemia plays a role in the age-related loss of mass muscle and strength by inducing cellular senescence in murine myoblasts and to explore the intracellular mechanism involved in this effect. Cultured mouse C2C12 cells were treated with 10 mM beta-glycerophosphate (BGP] at different periods of time to induce hyperphosphatemia. BGP promoted cellular senescence after 24 h of treatment, assessed by the increased expression of p53, acetylated-p53 and p21 and senescence associated β-galactosidase activity. In parallel, BGP increased ILK expression and activity, followed by mTOR activation and autophagy reduction. Knocking-down ILK expression increased autophagy and protected cells from senescence induced by hyperphosphatemia. BGP also reduced the proliferative capacity of cultured myoblasts. Old mice (24-months-old] presented higher serum phosphate concentration, lower forelimb strength, higher expression of p53 and ILK and less autophagy in vastus muscle than young mice (5-months-old]. In conclusion, we propose that hyperphosphatemia induces senescence in cultured myoblasts through ILK overexpression, reducing their proliferative capacity, which could be a mechanism involved in the development of sarcopenia, since old mice showed loss of muscular strength correlated with high serum phosphate concentration and increased levels of ILK and p53.

Developing a toolkit for the assessment and monitoring of musculoskeletal ageing

The complexities and heterogeneity of the ageing process have slowed the development of consensus on appropriate biomarkers of healthy ageing. The Medical Research Council–Arthritis Research UK Centre for Integrated research into Musculoskeletal Ageing (CIMA) is a collaboration between researchers and clinicians at the Universities of Liverpool, Sheffield and Newcastle. One of CIMA’s objectives is to ‘Identify and share optimal techniques and approaches to monitor age-related changes in all musculoskeletal tissues, and to provide an integrated assessment of musculoskeletal function’—in other words to develop a toolkit for assessing musculoskeletal ageing. This toolkit is envisaged as an instrument that can be used to characterise and quantify musculoskeletal function during ‘normal’ ageing, lend itself to use in large-scale, internationally important cohorts, and provide a set of biomarker outcome measures for epidemiological and intervention studies designed to enhance healthy musculoskeletal ageing. Such potential biomarkers include: biochemical measurements in biofluids or tissue samples, in vivo measurements of body composition, imaging of structural and physical properties, and functional tests. This review assesses candidate biomarkers of musculoskeletal ageing under these four headings, details their biological bases, strengths and limitations, and makes practical recommendations for their use. In addition, we identify gaps in the evidence base and priorities for further research on biomarkers of musculoskeletal ageing.

Low grip strength predicts incident diabetes among mid-life women: the Michigan Study of Women's Health Across the Nation

Background

skeletal muscle is the primary site of glucose uptake, yet the impact of age-related changes in muscle strength on diabetes risk is unknown.

Methods

four hundred and twenty-four participants (60% Black, 40% White) from the Michigan site of the Study of Women's Health Across the Nation contributed annual grip strength measures and were followed from 1996 to 2012 to identify incident cases of diabetes. Diabetes was defined as self-reported physician-diagnosed diabetes, use of anti-diabetic medications or measured fasting glucose ≥126 mg/dl or haemoglobin A1c > 6.5%.

Results

the 16-year diabetes incidence was 37%. The average baseline weight-normalised grip strength (NGS, kg per kg body weight) was 0.41 ± 0.12 and a mean of 0.29 ± 0.14 kg of absolute grip strength was lost per year. Each 0.1 higher NGS was associated with a 19% lower hazard of incident diabetes (P = 0.006) after adjustment for age, race/ethnicity, economic strain, smoking, menopause status, hormone use, physical activity and waist-hip ratio. In race/ethnic-stratified models, each 0.10 increase in NGS was associated with a 54% lower hazard of incident diabetes (P < 0.0001) among White women but the association among Black women was not statistically significant. In models without adjustment for waist-hip ratio or restricted to women <48 years of age at baseline, there was a statistically significant association between baseline NGS and incident diabetes among Black women. The rate of change in grip strength was not associated with diabetes incidence.

Conclusion

the mid-life is an important risk period for diabetes onset. Improving muscle strength. during mid-life may contribute to preventing diabetes among women.

Skeletal muscle-gut axis: emerging mechanisms of sarcopenia for intestinal and extra intestinal diseases

In recent years, there has been an increasing interest on muscle wasting, considering the reduction of quality of life and the increase of morbidity and mortality associated. Sarcopenia and cachexia represent two conditions of reduction of muscle mass, sharing several elements involved in their pathogenesis, such as systemic inflammation, impaired muscle protein synthesis, increased muscle apoptosis, mitochondrial dysfunction in skeletal muscle tissue and insulin resistance. These features often characterize cancer, inactivity or denervation, but also inflammatory diseases, such as chronic obstructive pulmonary disease, renal failure, cardiac failure, rheumatoid arthritis, inflammatory bowel disease and aging in general. The gastrointestinal tract and gut microbiota are thought to be deeply associated with muscle function and metabolism, although the exact mechanisms that link gut with skeletal muscle are still not well known. This review summarized the potential pathways linking gut with muscle, in particular in conditions as sarcopenia and cachexia. The main emerging pathways implicated in the skeletal muscle-gut axis are: the myostatin/activin signaling pathway, the IGF1/PI3K/AKT/mTOR signaling pathway, which results suppressed, the NF-kB signaling pathway and the FOXO signaling pathway. Further researches in this field are necessary to better explain the linkage between gut microbiota and muscle wasting and the possible emerging therapies associated.

Current Status of Sarcopenia in Korea: A Focus on Korean Geripausal Women

Sarcopenia is defined as an age-associated decline in muscle mass and function caused by several etiologies and mechanisms. Muscle mass and function do not decrease concurrently, and a loss of muscle function may be more highly associated with adverse health outcomes. Despite the clinical significance of sarcopenia, no universally operational definition of sarcopenia or standardized intervention programs are currently available. Sarcopenia, osteoporosis, and obesity share several pathophysiological mechanisms, and a combination of these entities may lead to an increased risk of musculoskeletal, cardio-metabolic, and psychological morbidities especially in geripause populations. Treatment for sarcopenia is mainly nonpharmacological, however, various drugs are currently being developed. It is conceivable that sarcopenia is the next immediate clinical target in musculoskeletal science.

Prediction of sarcopenia using a combination of multiple serum biomarkers

Sarcopenia is a gradual loss of skeletal muscle mass and function with aging. Given that sarcopenia has been recognized as a disease entity, effective molecular biomarkers for early diagnosis are required. We recruited 46 normal subjects and 50 patients with moderate sarcopenia aged 60 years and older. Sarcopenia was clinically identified on the basis of the appendicular skeletal muscle index by applying cutoff values derived from the Asian Working Group for Sarcopenia. The serum levels of 21 potential biomarkers were analyzed and statistically examined. Interleukin 6, secreted protein acidic and rich in cysteine, macrophage migration inhibitory factor, and insulin-like growth factor 1 levels differed significantly between the normal and sarcopenia groups. However, in each case, the area under the receiver operating characteristics curve (AUC) was <0.7. Subsequent combination of the measurements of these biomarkers into a single risk score based on logistic regression coefficients enhanced the accuracy of diagnosis, yielding an AUC value of 0.763. The best cutoff value of 1.529 had 70.0% sensitivity and 78.3% specificity (95% CI = 2.80–21.69, p < 0.0001). Combined use of the selected biomarkers provides higher diagnostic accuracy than individual biomarkers, and may be effectively utilized for early diagnosis and prognosis of sarcopenia.

Improving the comprehension of sarcopenic state determinants: An multivariate approach involving hormonal, nutritional, lifestyle and genetic variables

It is known that sarcopenia is a multifaceted phenomenon, which involves genetic, nutritional, hormonal and living habits aspects. Then, an integrated analysis, as a multivariate approach, could improve the comprehension about the determinants of sarcopenic state in old adults. The present study aimed to investigate the interaction among serum vitamin D, daily caloric and protein intake, lifestyle habits, ACE I/D gene polymorphism and sarcopenic state in community-dwelling old adults. One hundred one community-dwelling old adults were clinically stratified as sarcopenic or non-sarcopenic. Serum vitamin D, daily caloric and protein intake, lifestyle habits (smoking, physical activity level and sedentary behavior) and ACE I/D gene polymorphism were recorded. A multivariate logistic regression technique was applied to investigate the interaction among the selected independent variables and the sarcopenic state. The independent variables age, smoking, serum Vitamin D and ACE I/D polymorphism achieved the statistical criteria to be inserted in the multivariate analysis. After a stepwise procedure from the multivariate logistic regression, the variables age, serum Vitamin D and ACE I/D polymorphism remained, together, in the final model. Sarcopenic state was significantly associated to older age, II-genotype and low serum Vitamin D in old adults from 60 years old.

Dkk3 dependent transcriptional regulation controls age related skeletal muscle atrophy

Age-related muscle atrophy (sarcopenia) is the leading cause for disability in aged population, but the underlying molecular mechanisms are poorly understood. Here we identify a novel role for the secreted glycoprotein Dickkopf 3 (Dkk3) in sarcopenia. Forced expression of Dkk3 in muscles in young mice leads to muscle atrophy. Conversely, reducing its expression in old muscles restores both muscle size and function. Dkk3 induces nuclear import of β-catenin and enhances its interaction with FoxO3, which in turn activates the transcription of E3 ubiquitin ligase Fbxo32 and Trim63, driving muscle atrophy. These findings suggest that Dkk3 may be used as diagnostic marker and as therapeutic target for age-related muscle atrophy, and reveal a distinct transcriptional control of Fbxo32 and Trim63.

The Vicious Cycle of Myostatin Signaling in Sarcopenic Obesity: Myostatin Role in Skeletal Muscle Growth, Insulin Signaling and Implications for Clinical Trials

The age-related loss of skeletal muscle (sarcopenia) is a major health concern as it is associated with physical disability, metabolic impairments, and increased mortality. The coexistence of sarcopenia with obesity, termed 'sarcopenic obesity', contributes to skeletal muscle insulin resistance and the development of type 2 diabetes, a disease prevalent with advancing age. Despite this knowledge, the mechanisms contributing to sarcopenic obesity remain poorly understood, preventing the development of targeted therapeutics. This article will discuss the clinical and physiological consequences of sarcopenic obesity and propose myostatin as a potential candidate contributing to this condition. A special emphasis will be placed on examining the role of myostatin signaling in impairing both skeletal muscle growth and insulin signaling. In addition, the role of myostatin in regulating muscle-to fat cross talk, further exacerbating metabolic dysfunction in the elderly, will be highlighted. Lastly, we discuss how this knowledge has implications for the design of myostatin-inhibitor clinical trials.

The Effects of Physical Training are Varied and Occur in an Exercise Type-Dependent Manner in Elderly Men

Regular exercise can decrease the deleterious effects of aging and limit the development and progression of chronic disease in elderly people, depending on the type, intensity, frequency, and duration of exercise. This study aimed to investigate the potential protective effects of different physical training programs on oxidative stress parameters and inflammatory and neurotrophic mediators in the serum of elderly men. Healthy male volunteers [60 to 80 years; n=55] were divided into four groups: control [Ctr, n=14], aerobic training on dry land [ATdl, n=12]; and combined training on dry land [CTdl, n=12] or in water [CTw, n=17]. The training protocols were performed over 8 weeks, three times per week. Each 1 h session included 5 min warming-up exercise, 50 min specific training [aerobic, strength, or combined], and 5 min stretching. Blood samples were drawn 72 h before [baseline] the beginning of the 8 weeks’ protocol and 48 h after the last training session, processed, and the serum was aliquoted and stored at -70 °C until biochemical assessment of oxidative damage, antioxidant system and neurotrophic, growth and inflammatory factors. Elevated BDNF or IGF-1 levels were observed in the ATdl or CTdl groups, respectively. Overall oxidative stress parameters were improved including reduced lipid oxidative damage and increased thioredoxin reductase and glutathione peroxidase activities and total glutathione. Significant decreases in the inflammatory mediators IL-6 and IL-8 were observed; IL-6 was more susceptible to the effects of type of physical training. Thus, the effects of training in elderly men vary in an exercise type-dependent manner.

Emerging biomarkers and screening for cognitive frailty

Physical frailty and cognitive frailty are two important targets of secondary intervention in aging research to narrow the gap between life and health span. The objective of the present narrative review was to examine clinical and epidemiological studies investigating the recently proposed construct of cognitive frailty and its subtypes, with a focus on operational definitions, clinical criteria, and emerging biomarkers potentially useful for the screening of this novel entity. Both physical frailty and frailty indexes with a multidimensional nature were associated with late-life cognitive impairment/decline, incident dementia, Alzheimer's disease (AD), mild cognitive impairment, vascular dementia, non-AD dementias, and AD pathology proposing cognitive frailty as a clinical entity with cognitive impairment related to physical causes with a potential reversibility. The new clinical and research AD criteria established by the National Institute on Aging-Alzheimer's Association and the American Psychiatric Association could improve the differential diagnosis of cognitive impairment within the cognitive frailty construct. The emerging biomarkers of sarcopenia, physical frailty, and cognitive impairment will provide the basis to establish more reliable clinical and research criteria for cognitive frailty, using different operational definitions for frailty and cognitive impairment and useful clinical, biological, and imaging markers for this novel clinical construct.

Overweight in elderly people induces impaired autophagy in skeletal muscle

Sarcopenia is the gradual loss of skeletal muscle mass, strength and quality associated with aging. Changes in body composition, especially in skeletal muscle and fat mass are crucial steps in the development of chronic diseases. We studied the effect of overweight on skeletal muscle tissue in elderly people without reaching obesity to prevent this extreme situation. Overweight induces a progressive protein breakdown reflected as a progressive withdrawal of anabolism against the promoted catabolic state leading to muscle wasting. Protein turnover is regulated by a network of signaling pathways. Muscle damage derived from overweight displayed by oxidative and endoplasmic reticulum (ER) stress induces inflammation and insulin resistance and forces the muscle to increase requirements from autophagy mechanisms. Our findings showed that failure of autophagy in the elderly deprives it to deal with the cell damage caused by overweight. This insufficiently efficient autophagy leads to an accumulation of p62 and NBR1, which are robust markers of protein aggregations. This impaired autophagy affects myogenesis activity. Depletion of myogenic regulatory factors (MRFs) without links to variations in myostatin levels in overweight patients suggest a possible reduction of satellite cells in muscle tissue, which contributes to declined muscle quality. This discovery has important implications that improve the understanding of aged-related atrophy caused by overweight and demonstrates how impaired autophagy is one of the main responsible mechanisms that aggravate muscle wasting. Therefore, autophagy could be an interesting target for therapeutic interventions in humans against muscle impairment diseases.

Agrin-LRP4-MuSK signaling as a therapeutic target for myasthenia gravis and other neuromuscular disorders

INTRODUCTION

Signal transduction at the neuromuscular junction (NMJ) is compromised in a diverse array of diseases including myasthenia gravis, Lambert-Eaton myasthenic syndrome, Isaacs' syndrome, congenital myasthenic syndromes, Fukuyama-type congenital muscular dystrophy, amyotrophic lateral sclerosis, and sarcopenia. Except for sarcopenia, all are orphan diseases. In addition, the NMJ signal transduction is impaired by tetanus, botulinum, curare, α-bungarotoxin, conotoxins, organophosphate, sarin, VX, and soman to name a few. Areas covered: This review covers the agrin-LRP4-MuSK signaling pathway, which drives clustering of acetylcholine receptors (AChRs) and ensures efficient signal transduction at the NMJ. We also address diseases caused by autoantibodies against the NMJ molecules and by germline mutations in genes encoding the NMJ molecules. Expert opinion: Representative small compounds to treat the defective NMJ signal transduction are cholinesterase inhibitors, which exert their effects by increasing the amount of acetylcholine at the synaptic space. Another possible therapeutic strategy to enhance the NMJ signal transduction is to increase the number of AChRs, but no currently available drug has this functionality.

A Novel Egr-1-Agrin Pathway and Potential Implications for Regulation of Synaptic Physiology and Homeostasis at the Neuromuscular Junction

Synaptic transmission requires intricate coordination of the components involved in processing of incoming signals, formation and stabilization of synaptic machinery, neurotransmission and in all related signaling pathways. Changes to any of these components cause synaptic imbalance and disruption of neuronal circuitry. Extensive studies at the neuromuscular junction (NMJ) have greatly aided in the current understanding of synapses and served to elucidate the underlying physiology as well as associated adaptive and homeostatic processes. The heparan sulfate proteoglycan agrin is a vital component of the NMJ, mediating synaptic formation and maintenance in both brain and muscle, but very little is known about direct control of its expression. Here, we investigated the relationship between agrin and transcription factor early growth response-1 (Egr-1), as Egr-1 regulates the expression of many genes involved in synaptic homeostasis and plasticity. Using chromatin immunoprecipitation (ChIP), cell culture with cell lines derived from brain and muscle, and animal models, we show that Egr-1 binds to the AGRN gene locus and suppresses its expression. When compared with wild type (WT), mice deficient in Egr-1 (Egr-1−/−) display a marked increase in AGRN mRNA and agrin full-length and cleavage fragment protein levels, including the 22 kDa, C-terminal fragment in brain and muscle tissue homogenate. Because agrin is a crucial component of the NMJ, we explored possible physiological implications of the Egr-1-agrin relationship. In the diaphragm, Egr-1−/− mice display increased NMJ motor endplate density, individual area and area of innervation. In addition to increased density, soleus NMJs also display an increase in fragmented and faint endplates in Egr-1−/− vs. WT mice. Moreover, the soleus NMJ electrophysiology of Egr-1−/− mice revealed increased quantal content and motor testing showed decreased movement and limb muscle strength compared with WT. This study provides evidence for the potential involvement of a novel Egr-1-agrin pathway in synaptic homeostatic and compensatory mechanisms at the NMJ. Synaptic homeostasis is greatly affected by the process of aging. These and other data suggest that changes in Egr-1 expression may directly or indirectly promote age-related pathologies.

Handgrip strength is associated with, but poorly predicts, disability in older women with acute low back pain: A 12-month follow-up study

BACKGROUND

Older women with low back pain (LBP) constitute a special subpopulation at risk of severe and permanent disability. It is important to identify factors limiting functionality in this population in order to reduce costs and improve both prevention and intervention. Handgrip strength (HGS) is a biomarker of aging associated with several adverse health outcomes, but long-term associations with disability in older patients with LBP are not known.

OBJECTIVE

To examine whether HGS predicts disability in older women with acute low back pain (LBP).

METHODS

Longitudinal analyses were conducted with a sample of 135 older women from the international multicenter study Back Complaints in the Elders (BACE-Brazil). Women aged 60 years and over with a new episode of acute LBP were included. HGS was assessed with Jamar^® dynamometer, and disability was assessed using the Roland Morris questionnaire and gait speed test. Variables were assessed at baseline and at 12-month follow-up. Linear regression models explored associations between HGS and disability measures.

RESULTS

Significant association was found between HGS at baseline and gait speed at 12-month follow-up (r=-0.24; p=0.004). A multivariable-adjusted model showed that this association was independent of age, body mass index, and pain intensity (adjusted R²=0.13; p<0.001). A final prediction model showed an incremental difference of only 2.1% in gait speed after inclusion of HGS as an independent variable. No association was found between HGS and score on the Roland Morris questionnaire.

CONCLUSION

Caution is needed regarding the use of HGS as a predictive measure of disability in older women with acute LBP. Changes in gait speed were very small and unlikely to be of clinical relevance.

Non-human primates as a model for aging

There has been, and continues to be, a dramatic shift in the human population towards older ages necessitating biomedical research aimed at better understanding the basic biology of aging and age-related diseases and facilitating new and improved therapeutic options. As it is not practical to perform the breadth of this research in humans, animal models are necessary to recapitulate the complexity of the aging environment. The mouse model is most frequently chosen for these endeavors, however, they are frequently not the most appropriate model. Non-human primates, on the other hand, are more closely related to humans and recapitulate the human aging process and development of age-related diseases. Extensive aging research has been performed in the well-characterized rhesus macaque aging model. More recently, the common marmoset, a small non-human primate with a shorter lifespan, has been explored as a potential aging model. This model holds particular promise as an aging disease model in part due to the successful creation of transgenic marmosets. Limitations to the use of non-human primates in aging research exist but can be mitigated somewhat by the existence of available resources supported by the National Institutes of Health. This article is part of a Special Issue entitled: Animal models of aging - edited by "Houtkooper Riekelt".

Aging human body: changes in bone, muscle and body fat with consequent changes in nutrient intake

Aging affects almost all physiological processes, but changes in body composition and body phenotype are most observable. In this review, we focus on these changes, including loss of bone and muscle and increase in body fat or redistribution of the latter, possibly leading to osteosarcopenic obesity syndrome. We also address low-grade chronic inflammation, prevalent in aging adults and a cause of many disorders including those associated with body composition. Changes in dietary intake and nutritional requirements of older individuals, that all may lead to some disturbances on tissue and organ levels, are discussed as well. Finally, we discuss the hormonal changes in the aging body, considering each of the tissues, bone, muscle and fat as separate endocrine organs, but yet in the continuous interface and communication with each other. Although there are still many unanswered questions in this field, this review will enable the readers to better understand the aging human body and measures needing to be implemented toward reducing impaired health and disability in older individuals.

Sarcopenia

Sarcopenia refers to age-related muscle loss, defined using a combination of appendicular muscle mass, muscle strength, and physical performance measures. The pathogenesis depends on a balance between positive and negative regulators of muscle growth. Sarcopenia increases the risk for falls, fractures, dependency, use of hospital services, institutionalization, poor quality of life, and mortality. In clinical practice, brief screening tools, such as the 5-item SARC-F score, may be useful. Although pharmacologic treatments are actively being studied, the current mainstay consists of optimizing nutrition status, in particular protein and vitamin D status, and resistance exercises.