Molecular routes to sarcopenia and biomarker development: per aspera ad astra

Bidirectional Association between Sarcopenia and Depressive Symptoms among Chinese Middle- and Older-Aged Adults: Longitudinal Observational Study

BACKGROUND

The study aimed to examine the bidirectional relationship between sarcopenia and depressive symptoms in a national, community-based cohort study, despite the unclear temporal sequence demonstrated previously.

METHODS

Data were derived from four waves (2011 baseline and 2013, 2015, and 2018 follow-ups) of the China Health and Retirement Longitudinal Study (CHARLS). A total of 17,708 participants aged 45 years or older who had baseline data on both sarcopenia status and depressive symptoms in 2011 were included in the study. For the two cohort analyses, a total of 8092 adults without depressive symptoms and 11,292 participants without sarcopenia in 2011 were included. Sarcopenia status was defined according to the Asian Working Group for Sarcopenia 2019 (AWGS 2019) criteria. Depressive symptoms were defined as a score of 20 or higher on the 10-item Center for Epidemiologic Studies Depressive Scale (CES-D-10). Cox proportional hazard regression models were conducted to examine the risk of depressive symptoms and sarcopenia risk, while cross-lagged panel models were used to examine the temporal sequence between depressive symptoms and sarcopenia over time.

RESULTS

During a total of 48,305.1 person-years follow-up, 1262 cases of incident depressive symptoms were identified. Sarcopenia exhibited a dose-response relationship with a higher risk of depressive symptoms (HR = 1.7, 95%CI: 1.2-2.3 for sarcopenia, and HR = 1.5, 95%CI: 1.2-1.8 for possible sarcopenia, p trend < 0.001). In the second cohort analysis, 240 incident sarcopenia cases were identified over 39,621.1 person-years. Depressive symptoms (HR = 1.5, 95%CI: 1.2-2.0) are significantly associated with a higher risk of developing sarcopenia after multivariable adjustment (p < 0.001, Cross-lagged panel analyses demonstrated that depressive symptoms were associated with subsequent sarcopenia (β = 0.003, p < 0.001). Simultaneously, baseline sarcopenia was also associated with subsequent depressive symptoms (β = 0.428, p < 0.001).

CONCLUSION

This study identified a bidirectional relationship between depressive symptoms and sarcopenia. It seems more probable that baseline sarcopenia is associated with subsequent depressive symptoms in a stronger pattern than the reverse pathway. The interlinkage indicated that maintaining normal muscle mass and strength may serve as a crucial intervention strategy for alleviating mood disorders.

Development of multiple biomarker panels for prediction of sarcopenia in community-dwelling older adults

BACKGROUND

It is required to consider multiple biomarkers simultaneously to predict sarcopenia and to understand its complex pathological mechanisms. This study aimed to develop multiple biomarker panels for predicting sarcopenia in older adults and to further examine its association with the incidence of sarcopenia.

METHODS

A total of 1,021 older adults were selected from the Korean Frailty and Aging Cohort Study. Sarcopenia was defined by the Asian Working Group for Sarcopenia 2019 criteria. Among the 14 biomarker candidates at baseline, eight biomarkers that could optimally detect individuals with sarcopenia were selected to develop a multi-biomarker risk score (range from 0 to 10). The utility of developed multi-biomarker risk score in discriminating sarcopenia was investigated using receiver operating characteristic (ROC) analysis.

RESULTS

The multi-biomarker risk score had an area under the ROC curve (AUC) of 0.71 with an optimal cut-off of 1.76 score, which was significantly higher than all single biomarkers with AUC of <0.7 (all, p<0.01). During the two-year follow-up, the incidence of sarcopenia was 11.1%. Continuous multi-biomarker risk score was positively associated with incidence of sarcopenia after adjusting confounders (odds ratio [OR]=1.63; 95% confidence interval [CI]=1.23-2.17). Participants with a high risk score had higher odds of sarcopenia than those with a low risk score (OR=1.82; 95% CI=1.04-3.19).

CONCLUSIONS

Multi-biomarker risk score, which was a combination of eight biomarkers with different pathophysiologies, better discriminated the presence of sarcopenia than a single biomarker, and it could further predict the incidence of sarcopenia over two years in older adults.

Sarcopenia and Cognitive Decline in Older Adults: Targeting the Muscle-Brain Axis

Declines in physical performance and cognition are commonly observed in older adults. The geroscience paradigm posits that a set of processes and pathways shared among age-associated conditions may also serve as a molecular explanation for the complex pathophysiology of physical frailty, sarcopenia, and cognitive decline. Mitochondrial dysfunction, inflammation, metabolic alterations, declines in cellular stemness, and altered intracellular signaling have been observed in muscle aging. Neurological factors have also been included among the determinants of sarcopenia. Neuromuscular junctions (NMJs) are synapses bridging nervous and skeletal muscle systems with a relevant role in age-related musculoskeletal derangement. Patterns of circulating metabolic and neurotrophic factors have been associated with physical frailty and sarcopenia. These factors are mostly related to disarrangements in protein-to-energy conversion as well as reduced calorie and protein intake to sustain muscle mass. A link between sarcopenia and cognitive decline in older adults has also been described with a possible role for muscle-derived mediators (i.e., myokines) in mediating muscle-brain crosstalk. Herein, we discuss the main molecular mechanisms and factors involved in the muscle-brain axis and their possible implication in cognitive decline in older adults. An overview of current behavioral strategies that allegedly act on the muscle-brain axis is also provided.

Serum Retinol Binding Protein 4 as a Potential Biomarker for Sarcopenia in Older Adults

Sarcopenia is characterized by progressive loss of muscle mass and function due to aging. Retinol-binding protein 4 (RBP4) is an adipokine with pro-inflammatory effects. However, the change of RBP4 concentration and its role in sarcopenia remains unclear. The aim of this study was to evaluate the association of serum RBP4 level with sarcopenia in the older adults. A total of 816 community-dwelling older adults aged ≥60 years were enrolled. Serum RBP4 was measured by enzyme-linked immunosorbent assay. Appendicular skeletal muscle mass index (ASMI), grip strength, and gait speed were measured. We found that serum RBP4 levels were higher in patients with sarcopenia when compared with those without sarcopenias (44.3 [33.9-57.7] vs 38.0 [28.0-48.4] μg/mL). Receiver operating characteristic curve analysis indicated that the optimal cutoff value of serum RBP4 level that predicted sarcopenia was 38.79 μg/mL with a sensitivity of 67.8% and a specificity of 53.3%. Multivariate logistic regression analysis showed that the subjects with a higher level of RBP4 had a higher risk of sarcopenia (adjusted odds ratio [OR] = 2.036, 95% CI = 1.449-2.861). Serum RBP4 concentration was negatively correlated with grip strength (r = -.098), gait speed (r = -.186), and AMSI (r = -.096). Moreover, serum RBP4 levels were higher in patients with severe sarcopenia when compared with those with moderate sarcopenia (49.0 [37.3-61.2] vs 40.4 [31.3-51.2] μg/mL). Taken together, our results demonstrate that serum RBP4 level is correlated with the risk and severity of sarcopenia in the older adults, indicating that RBP4 might serve as a surrogate biomarker for the screening and evaluation of sarcopenia.

Fiber-Type Shifting in Sarcopenia of Old Age: Proteomic Profiling of the Contractile Apparatus of Skeletal Muscles

The progressive loss of skeletal muscle mass and concomitant reduction in contractile strength plays a central role in frailty syndrome. Age-related neuronal impairments are closely associated with sarcopenia in the elderly, which is characterized by severe muscular atrophy that can considerably lessen the overall quality of life at old age. Mass-spectrometry-based proteomic surveys of senescent human skeletal muscles, as well as animal models of sarcopenia, have decisively improved our understanding of the molecular and cellular consequences of muscular atrophy and associated fiber-type shifting during aging. This review outlines the mass spectrometric identification of proteome-wide changes in atrophying skeletal muscles, with a focus on contractile proteins as potential markers of changes in fiber-type distribution patterns. The observed trend of fast-to-slow transitions in individual human skeletal muscles during the aging process is most likely linked to a preferential susceptibility of fast-twitching muscle fibers to muscular atrophy. Studies with senescent animal models, including mostly aged rodent skeletal muscles, have confirmed fiber-type shifting. The proteomic analysis of fast versus slow isoforms of key contractile proteins, such as myosin heavy chains, myosin light chains, actins, troponins and tropomyosins, suggests them as suitable bioanalytical tools of fiber-type transitions during aging.

Mammalian Target of Rapamycin (mTOR) Signaling at the Crossroad of Muscle Fiber Fate in Sarcopenia

The mammalian target of rapamycin (mTOR) is a major regulator of skeletal myocyte viability. The signaling pathways triggered by mTOR vary according to the type of endogenous and exogenous factors (e.g., redox balance, nutrient availability, physical activity) as well as organismal age. Here, we provide an overview of mTOR signaling in skeletal muscle, with a special focus on the role played by mTOR in the development of sarcopenia. Intervention strategies targeting mTOR in sarcopenia (e.g., supplementation of plant extracts, hormones, inorganic ions, calorie restriction, and exercise) have also been discussed.

Nutritional and Nutrition-Related Biomarkers as Prognostic Factors of Sarcopenia, and Their Role in Disease Progression

Due to the multifactorial pathogenesis of sarcopenia, it is crucial to identify biomarkers that are risk factors for sarcopenia, and which therefore have a prognostic function. Aim: This narrative review aims to define a set of biomarkers associated with nutrition and sarcopenia. These biomarkers could contribute to individualized monitoring and enable preventive and therapeutic methods. Methods: Two electronic databases, PubMed and Google Scholar, were used. The search strategy was based on a controlled vocabulary (MeSH) and includes studies published up to February 2022. Discussion: Higher levels of serum uric acid are associated with higher handgrip strength and better muscle function in elderly people and, thus, may slow the progression of sarcopenia. Leptin, an adipokine secreted by adipose tissue, promotes the production of pro-inflammatory cytokines, which in turn lead to sarcopenia. This makes leptin a significant indirect biomarker for physical disability and sarcopenic obesity. Additionally, creatinine is a reliable biomarker for muscle mass status because of its easy accessibility and cost-effectiveness. Vitamin D status acts as a useful biomarker for predicting total mortality, hip fractures, early death, and the development of sarcopenia. Therefore, there is an increasing interest in dietary antioxidants and their effects on age-related losses of muscle mass and function. On the other hand, 3-Methylhistidine is a valuable biomarker for detecting increased muscle catabolism, as it is excreted through urine during muscle degradation. In addition, IGF-1, whose concentration in plasma is stimulated by food intake, is associated with the loss of skeletal muscle mass, which probably plays a crucial role in the progression of sarcopenia. Conclusions: Many nutritional biomarkers were found to be associated with sarcopenia, and can therefore be used as prognostic indexes and risk factors. Nutrition plays an important role in the prevention and management of sarcopenia, affecting muscle mass, strength, and function in elderly people.

Multisystem derangements in frailty and sarcopenia: a source for biomarker discovery

PURPOSE OF REVIEW

Multisystem derangements, encompassing metabolic, musculoskeletal and stress-response systems, occur during aging and are associated with the development of physical frailty and sarcopenia. These modular changes are relevant sources for the identification of biomarkers for the two conditions. Here, we provide an up-to-date overview on existing biomarkers of physical frailty and sarcopenia and discuss emerging approaches for biomarker discovery.

RECENT FINDINGS

Inflammatory, metabolic and hematologic markers are shared between physical frailty and sarcopenia. Gut microbial derivatives and damage-associated molecular patterns transferred via extracellular vesicles have been indicated as possible gut-muscle axis regulators and candidate markers of physical frailty and sarcopenia.

SUMMARY

Mediators of metabolic, musculoskeletal and stress-response system dysregulation are shared by physical frailty and sarcopenia and indicate the existence of common pathophysiological pathways. Multiplatform biomarker analyses have been proposed as an innovating approach for tracking the multifaceted and dynamic nature of physical frailty and sarcopenia. Upon validation, the identified biomarkers may support diagnostic makeup and tracking of the two conditions in both research and clinical settings.

Relationships Between Depressive Symptoms, Dietary Inflammatory Potential, and Sarcopenia: Mediation Analyses

Background

Sarcopenia is a major public health problem. Depressive symptoms and dietary inflammatory potential play important roles in the development of sarcopenia. We aimed to disentangle the relationships between depressive symptoms, dietary inflammatory potential, and sarcopenia.

Methods

A total of 6,082 participants from the National Health and Nutrition Examination Survey (NHANES) were included in the analyses. Sarcopenia was defined according to the Foundation for the National Institutes for Health (FNIH) criteria. The Depressive symptoms were assessed using the nine-item Patient Health Questionnaire (PHQ-9). Dietary Inflammatory Index (DII) was calculated based on 24-h dietary recall interview. Two sets of mediation models were constructed separately.

Results

Depressive symptoms and DII were associated with sarcopenia, with odds ratios [ORs] (95% CIs) 2.54 (1.27, 5.13) and 1.17 (1.00, 1.37), respectively. DII score mediated the association of depressive symptoms with low muscle mass, explaining a total of 10.53% of the association (indirect effect = 0.004). Depressive symptoms had a significant mediating effects on the association between DII with low muscle mass, explaining a total of 12.50% of the association (indirect effect = 0.001).

Conclusions

Our findings suggested that both depressive symptoms and dietary inflammatory potential had direct effects, and indirect effects on low muscle mass, handgrip strength, muscle mass, through each other. It provides important insights into integrated nutritional and psychological intervention strategies in preventing sarcopenia.

Serum Sestrin-1 Concentration Is Higher in Frail than Non-Frail Older People Living in Nursing Homes

Given the increasing prevalence of frailty and its implications for public health, the identification of biomarkers to detect frailty is essential. Sestrin-1 is a protein with a protective role in muscle function. This study aimed to determine whether the serum sestrin-1 concentration differed between frail and non-frail populations and to investigate its association with frailty-related variables in 225 older women and men living in nursing homes (Gipuzkoa, Spain). Serum sestrin-1 concentration was measured by ELISA. Frailty, dependence, anthropometry, physical function, and physical activity were determined by validated tests and tools. The associations between sestrin-1 concentration and the other variables were determined using generalized linear models. The differences between frail and non-frail individuals were analyzed by the Mann–Whitney U-test, and receiver operating characteristic (ROC) curves were constructed to calculate the capability of sestrin-1 to detect frailty. Unexpectedly, frail individuals—according to the Fried Frailty Phenotype or the Clinical Frailty Scale—had higher serum sestrin-1 concentrations than non-frail individuals. Furthermore, the higher serum sestrin-1 concentration was associated with the increased frailty scores and dependence as well as the poorer physical function and the less physical activity. Given the contradictory results regarding serum sestrin-1 and frailty, further investigation is required to propose it as a molecular biomarker of frailty.