Differential genomic responses in old vs. young humans despite similar levels of modest muscle damage after resistance loading

Functional role of myosin-binding protein H in thick filaments of developing vertebrate fast-twitch skeletal muscle

Myosin-binding protein H (MyBP-H) is a component of the vertebrate skeletal muscle sarcomere with sequence and domain homology to myosin-binding protein C (MyBP-C). Whereas skeletal muscle isoforms of MyBP-C (fMyBP-C, sMyBP-C) modulate muscle contractility via interactions with actin thin filaments and myosin motors within the muscle sarcomere "C-zone," MyBP-H has no known function. This is in part due to MyBP-H having limited expression in adult fast-twitch muscle and no known involvement in muscle disease. Quantitative proteomics reported here reveal that MyBP-H is highly expressed in prenatal rat fast-twitch muscles and larval zebrafish, suggesting a conserved role in muscle development and prompting studies to define its function. We take advantage of the genetic control of the zebrafish model and a combination of structural, functional, and biophysical techniques to interrogate the role of MyBP-H. Transgenic, FLAG-tagged MyBP-H or fMyBP-C both localize to the C-zones in larval myofibers, whereas genetic depletion of endogenous MyBP-H or fMyBP-C leads to increased accumulation of the other, suggesting competition for C-zone binding sites. Does MyBP-H modulate contractility in the C-zone? Globular domains critical to MyBP-C's modulatory functions are absent from MyBP-H, suggesting that MyBP-H may be functionally silent. However, our results suggest an active role. In vitro motility experiments indicate MyBP-H shares MyBP-C's capacity as a molecular "brake." These results provide new insights and raise questions about the role of the C-zone during muscle development.

Multiparametric identification of putative senescent cells in skeletal muscle via mass cytometry

Senescence is an irreversible arrest of the cell cycle that can be characterized by markers of senescence such as p16, p21, and KI-67. The characterization of different senescence-associated phenotypes requires selection of the most relevant senescence markers to define reliable cytometric methodologies. Mass cytometry (a.k.a. Cytometry by time of flight, CyTOF) can monitor up to 40 different cell markers at the single-cell level and has the potential to integrate multiple senescence and other phenotypic markers to identify senescent cells within a complex tissue such as skeletal muscle, with greater accuracy and scalability than traditional bulk measurements and flow cytometry-based measurements. This article introduces an analysis framework for detecting putative senescent cells based on clustering, outlier detection, and Boolean logic for outliers. Results show that the pipeline can identify putative senescent cells in skeletal muscle with well-established markers such as p21 and potential markers such as GAPDH. It was also found that heterogeneity of putative senescent cells in skeletal muscle can partly be explained by their cell type. Additionally, autophagy-related proteins ATG4A, LRRK2, and GLB1 were identified as important proteins in predicting the putative senescent population, providing insights into the association between autophagy and senescence. It was observed that sex did not affect the proportion of putative senescent cells among total cells. However, age did have an effect, with a higher proportion observed in fibro/adipogenic progenitors (FAPs), satellite cells, M1 and M2 macrophages from old mice. Moreover, putative senescent cells from muscle of old and young mice show different expression levels of senescence-related proteins, with putative senescent cells of old mice having higher levels of p21 and GAPDH, whereas putative senescent cells of young mice had higher levels of IL-6. Overall, the analysis framework prioritizes multiple senescence-associated proteins to characterize putative senescent cells sourced from tissue made of different cell types.

Functional role of myosin-binding protein H in thick filaments of developing vertebrate fast-twitch skeletal muscle

Myosin-binding protein H (MyBP-H) is a component of the vertebrate skeletal muscle sarcomere with sequence and domain homology to myosin-binding protein C (MyBP-C). Whereas skeletal muscle isoforms of MyBP-C (fMyBP-C, sMyBP-C) modulate muscle contractility via interactions with actin thin filaments and myosin motors within the muscle sarcomere "C-zone," MyBP-H has no known function. This is in part due to MyBP-H having limited expression in adult fast-twitch muscle and no known involvement in muscle disease. Quantitative proteomics reported here reveal MyBP-H is highly expressed in prenatal rat fast-twitch muscles and larval zebrafish, suggesting a conserved role in muscle development, and promoting studies to define its function. We take advantage of the genetic control of the zebrafish model and a combination of structural, functional, and biophysical techniques to interrogate the role of MyBP-H. Transgenic, FLAG-tagged MyBP-H or fMyBP-C both localize to the C-zones in larval myofibers, whereas genetic depletion of endogenous MyBP-H or fMyBP-C leads to increased accumulation of the other, suggesting competition for C-zone binding sites. Does MyBP-H modulate contractility from the C-zone? Globular domains critical to MyBP-C's modulatory functions are absent from MyBP-H, suggesting MyBP-H may be functionally silent. However, our results suggest an active role. Small angle x-ray diffraction of intact larval tails revealed MyBP-H contributes to the compression of the myofilament lattice accompanying stretch or contraction, while in vitro motility experiments indicate MyBP-H shares MyBP-C's capacity as a molecular "brake". These results provide new insights and raise questions about the role of the C-zone during muscle development.

A novel deep proteomic approach in human skeletal muscle unveils distinct molecular signatures affected by aging and resistance training

The skeletal muscle proteome alterations to aging and resistance training have been reported in prior studies. However, conventional proteomics in skeletal muscle typically yields wide protein abundance ranges that mask the detection of lowly expressed proteins. Thus, we adopted a novel deep proteomics approach whereby myofibril (MyoF) and non-MyoF fractions were separately subjected to protein corona nanoparticle complex formation prior to digestion and Liquid Chromatography Mass Spectrometry (LC-MS). Specifically, we investigated MyoF and non-MyoF proteomic profiles of the vastus lateralis muscle of younger (Y, 22±2 years old; n=5) and middle-aged participants (MA, 56±8 years old; n=6). Additionally, MA muscle was analyzed following eight weeks of resistance training (RT, 2d/week). Across all participants, the number of non-MyoF proteins detected averaged to be 5,645±266 (range: 4,888-5,987) and the number of MyoF proteins detected averaged to be 2,611±326 (range: 1,944-3,101). Differences in the non-MyoF (8.4%) and MyoF (2.5%) proteomes were evident between age cohorts, and most differentially expressed non-MyoF proteins (447/543) were more enriched in MA versus Y. Biological processes in the non-MyoF fraction were predicted to be operative in MA versus Y including increased cellular stress, mRNA splicing, translation elongation, and ubiquitin-mediated proteolysis. RT in MA participants only altered ~0.3% of MyoF and ~1.0% of non-MyoF proteomes. In summary, aging and RT predominantly affect non-contractile proteins in skeletal muscle. Additionally, marginal proteome adaptations with RT suggest more rigorous training may stimulate more robust effects or that RT, regardless of age, subtly alters basal state skeletal muscle protein abundances.

Understanding the variation in exercise responses to guide personalized physical activity prescriptions

Understanding the factors that contribute to exercise response variation is the first step in achieving the goal of developing personalized exercise prescriptions. This review discusses the key molecular and other mechanistic factors, both extrinsic and intrinsic, that influence exercise responses and health outcomes. Extrinsic characteristics include the timing and dose of exercise, circadian rhythms, sleep habits, dietary interactions, and medication use, whereas intrinsic factors such as sex, age, hormonal status, race/ethnicity, and genetics are also integral. The molecular transducers of exercise (i.e., genomic/epigenomic, proteomic/post-translational, transcriptomic, metabolic/metabolomic, and lipidomic elements) are considered with respect to variability in physiological and health outcomes. Finally, this review highlights the current challenges that impede our ability to develop effective personalized exercise prescriptions. The Molecular Transducers of Physical Activity Consortium (MoTrPAC) aims to fill significant gaps in the understanding of exercise response variability, yet further investigations are needed to address additional health outcomes across all populations.

Paraspinal muscles in individuals undergoing surgery for lumbar spine pathology lack a myogenic response to an acute bout of resistance exercise

Background

Lumbar spine pathology (LSP) is a common source of low back or leg pain, and paraspinal muscle in these patients demonstrates fatty and fibrotic infiltration, and cellular degeneration that do not reverse with exercise-based rehabilitation. However, it is unclear of this lack of response is due to insufficient exercise stimulus, or an inability to mount a growth response. The purpose of this study was to compare paraspinal muscle gene expression between individuals with LSP who do and do not undergo an acute bout of resistance exercise.

Methods

Paraspinal muscle biopsies were obtained from 64 individuals with LSP undergoing spinal surgery. Eight participants performed an acute bout of machine-based lumbar extension resistance exercise preoperatively. Gene expression for 42 genes associated with adipogenic/metabolic, atrophic, fibrogenic, inflammatory, and myogenic pathways was measured, and differential expression between exercised and non-exercised groups was evaluated for (a) the full cohort, and (b) an age, gender, acuity, and etiology matched sub-cohort. Principal components analyses were used to identify gene expression clustering across clinical phenotypes.

Results

The exercised cohort demonstrated upregulation of inflammatory gene IL1B, inhibition of extracellular matrix components (increased MMP3&9, decreased TIMP1&3, COL1A1) and metabolic/adipogenic genes (FABP4, PPARD, WNT10B), and downregulation of myogenic (MYOD, ANKRD2B) and atrophic (FOXO3) genes compared to the non-exercised cohort, with similar patterns in the matched sub-analysis. There were no clinical phenotypes significantly associated with gene expression profiles.

Conclusion

An acute bout of moderate-high intensity resistance exercise did not result in upregulation of myogenic genes in individuals with LSP. The response was characterized by mixed metabolic and fibrotic gene expression, upregulation of inflammation, and downregulation of myogenesis.

Data-driven detection of age-related arbitrary monotonic changes in single-cell gene expression distributions

Identification of genes whose expression increases or decreases with age is central to understanding the mechanisms behind aging. Recent scRNA-seq studies have shown that changes in single-cell expression profiles with aging are complex and diverse. In this study, we introduce a novel workflow to detect changes in the distribution of arbitrary monotonic age-related changes in single-cell expression profiles. Since single-cell gene expression profiles can be analyzed as probability distributions, our approach uses information theory to quantify the differences between distributions and employs distance matrices for association analysis. We tested this technique on simulated data and confirmed that potential parameter changes could be detected in a set of probability distributions. Application of the technique to a public scRNA-seq dataset demonstrated its potential utility as a straightforward screening method for identifying aging-related cellular features.

Fast and slow muscle fiber transcriptome dynamics with lifelong endurance exercise

We investigated fast and slow muscle fiber transcriptome exercise dynamics among three groups of men: lifelong exercisers (LLE, n = 8, 74 ± 1 yr), old healthy nonexercisers (OH, n = 9, 75 ± 1 yr), and young exercisers (YE, n = 8, 25 ± 1 yr). On average, LLE had exercised ∼4 day·wk-1 for ∼8 h·wk-1 over 53 ± 2 years. Muscle biopsies were obtained pre- and 4 h postresistance exercise (3 × 10 knee extensions at 70% 1-RM). Fast and slow fiber size and function were assessed preexercise with fast and slow RNA-seq profiles examined pre- and postexercise. LLE fast fiber size was similar to OH, which was ∼30% smaller than YE (P < 0.05) with contractile function variables among groups, resulting in lower power in LLE (P < 0.05). LLE slow fibers were ∼30% larger and more powerful compared with YE and OH (P < 0.05). At the transcriptome level, fast fibers were more responsive to resistance exercise compared with slow fibers among all three cohorts (P < 0.05). Exercise induced a comprehensive biological response in fast fibers (P < 0.05) including transcription, signaling, skeletal muscle cell differentiation, and metabolism with vast differences among the groups. Fast fibers from YE exhibited a growth and metabolic signature, with LLE being primarily metabolic, and OH showing a strong stress-related response. In slow fibers, only LLE exhibited a biological response to exercise (P < 0.05), which was related to ketone and lipid metabolism. The divergent exercise transcriptome signatures provide novel insight into the molecular regulation in fast and slow fibers with age and exercise and suggest that the ∼5% weekly exercise time commitment of the lifelong exercisers provided a powerful investment for fast and slow muscle fiber metabolic health at the molecular level.NEW & NOTEWORTHY This study provides the first insights into fast and slow muscle fiber transcriptome dynamics with lifelong endurance exercise. The fast fibers were more responsive to exercise with divergent transcriptome signatures among young exercisers (growth and metabolic), lifelong exercisers (metabolic), and old healthy nonexercisers (stress). Only lifelong exercisers had a biological response in slow fibers (metabolic). These data provide novel insights into fast and slow muscle fiber health at the molecular level with age and exercise.

Interleukin-6: Unravelling its role in sarcopenia pathogenesis and exploring therapeutic avenues

This review explores the intricate relationship between interleukin-6 (IL-6) and sarcopenia, a prevalent condition characterized by progressive skeletal muscle loss, particularly in aging populations. Emphasizing the rising prevalence and health challenges posed by sarcopenia, the paper delves into the multifunctional roles of IL-6 in immune response, inflammation and inflammaging associated with sarcopenia. Significantly elevated in sarcopenic individuals, IL-6 prompts an exploration of its molecular impact on muscle wasting. The review critically assesses IL-6 as a potential biomarker for sarcopenia diagnosis and prognosis while also examining therapeutic interventions targeting IL-6 signaling pathways, offering a foundation for future research and the development of targeted therapeutic strategies to alleviate the impact of this debilitating condition.

Muscle Inflammation Susceptibility: A Potential Phenotype for Guiding Precision Rehabilitation After Total Hip Arthroplasty in End-Stage Osteoarthritis

The progression of osteoarthritis of the hip to its end stage and ultimately to total hip arthroplasty (THA) is complex; the multifactorial pathophysiology involves myriad collaborating tissues in and around the diseased joint. We have named the heightened state of periarticular muscle inflammation at the time of surgery "muscle inflammation susceptibility" (MuIS) because it is distinct from systemic inflammation. In this review article, we discuss how MuIS and heightened atrophy-associated signaling in the periarticular skeletal muscles may contribute to reduced muscle mass, impaired muscle quality (ie, through fibrosis), and a muscle microenvironment that challenges regenerative capacity and thus functional recovery from THA. We also review directions for future research that should advance understanding of the key determinants of precision for optimized success of THA for each individual.

The Effect of Lower Limb Combined Neuromuscular Electrical Stimulation on Skeletal Muscle Signaling for Glucose Utilization, Myofiber Distribution, and Metabolic Function after Spinal Cord Injury

Maintaining healthy myofiber type and metabolic function early after spinal cord injury (SCI) may prevent chronic metabolic disorders. This study compares the effects of a 2-5 week combined (aerobic + resistance) neuromuscular electrical stimulation (Comb-NMES) regimen versus a sham control treatment on muscle protein signaling for glucose uptake, myofiber type distribution, and metabolic function. Twenty participants (31 ± 9 years of age) with an SCI (C4-L1, AIS level A-C) within 14 days of the SCI were randomly assigned to control (N = 8) or Comb-NMES (N = 12). Sessions were given three times per week. Fasting blood samples and vastus lateralis muscle biopsies were collected 24-48 h before or after the last session. Western blots were performed to quantify proteins, immunohistochemical analyses determined muscle myofiber distribution, and enzymatic assays were performed to measure serum glucose, insulin, and lipids. Our main findings include a decrease in fasting glucose (p < 0.05) and LDL-C (p < 0.05) levels, an upregulation of CamKII and Hexokinase (p < 0.05), and an increase in type I (+9%) and a decrease in type IIx (-36%) myofiber distribution in response to Comb-NMES. Our findings suggest that maintaining healthy myofiber type and metabolic function may be achieved via early utilization of Comb-NMES.

Human primary myoblasts derived from paraspinal muscle reflect donor age as an experimental model of sarcopenia

BACKGROUND

Low back pain is a general phenomenon of aging, and surgery is an unavoidable choice to relieve severe back pain. The discarded surgical site during surgery is of high value for muscle and muscle-related research. This study investigated the age-dependent properties of patients' paraspinal muscles at the cellular level.

METHODS

To define an association of paraspinal muscle degeneration with sarcopenia, we analyzed lumbar paraspinal muscle and myoblasts isolated from donors of various ages (25-77 years). Preoperative evaluations were performed by bioimpedance analysis using the InBody 720, magnetic resonance (MR) imaging of the lumbar spine, and lumbar extension strength using a lumbar extension dynamometer. In addition, the growth and differentiation capacity of myoblasts obtained from the donor was determined using proliferation assay and western blotting.

RESULTS

The cross-sectional area of the lumbar paraspinal muscle decreased with age and was also correlated with the appendicular skeletal muscle index (ASM/height2). Human primary myoblasts isolated from paraspinal muscle preserved their proliferative capacity in vitro, which tended to decrease with donor age. The age-dependent decline in myoblast proliferation was correlated with levels of cell cycle inhibitory proteins (p16INK4a, p21CIP1, and p27KIP1) associated with cellular senescence. Primary myoblasts isolated from younger donors differentiated into multinucleate myotubes earlier and at a higher rate than those from older donors in vitro. Age-dependent decline in myogenic potential of the isolated primary myoblasts was likely correlated with the inactivation of myogenic transcription factors such as MyoD, myogenin, and MEF2c.

CONCLUSIONS

Myoblasts isolated from human paraspinal muscle preserve myogenic potential that correlates with donor age, providing an in vitro model of sarcopenia.

In primary total hip arthroplasty, the direct anterior approach leads to higher levels of creatine kinase and lower levels of C-reactive protein compared to the posterolateral approach: a propensity score matching analysis of short-term follow-up data

BACKGROUND

This retrospective study compares the invasiveness of the direct anterior approach (DAA) and the posterolateral approach (PLA) in total hip arthroplasty (THA) by assessing three widely used inflammation-related serum markers in the first ten post-operative days.

METHODS

The database of our institution was mined for primary THAs conducted by the DAA or the PLA from February 2020 to June 2022. Demographics and creatine kinase (CK), C-reactive protein (CRP), and white blood cells were compared. Propensity Score Matching (PSM) analysis (1:1 ratio) was conducted based on multiple variables.

RESULTS

PSM analysis yielded 44 pairs of DAA and PLA patients. CK was significantly higher (p < 0.001) in the DAA than in the PLA group on postoperative day (POD) 2, 5 and 10. The POD2, POD5 and POD10 CK/preoperative CK ratio was 12.9, 5.0 and 0.8 in DAA and 8.8, 3.3 and 0.6 in PLA (p = 0.017, p = 0.012 and p = 0.025, respectively). The POD2, POD5 and POD10 CRP/preoperative CRP ratio was 95.1, 65.6 and 22.8 in PLA and 34.7, 23.3 and 8.9 in DAA (p < 0.001, p = 0.002 and p < 0.001, respectively).

CONCLUSION

PSM analysis of early postoperative CK and CRP values demonstrated that the DAA should be considered as a less stressful approach, not as a muscle-sparing or a minimally invasive THA approach.

A novel deep proteomic approach in human skeletal muscle unveils distinct molecular signatures affected by aging and resistance training

We examined the myofibrillar (MyoF) and non-myofibrillar (non-MyoF) proteomic profiles of the vastus lateralis (VL) muscle of younger (Y, 22±2 years old; n=5) and middle-aged participants (MA, 56±8 years old; n=6), and MA following eight weeks of knee extensor resistance training (RT, 2d/week). Shotgun/bottom-up proteomics in skeletal muscle typically yields wide protein abundance ranges that mask lowly expressed proteins. Thus, we adopted a novel approach whereby the MyoF and non-MyoF fractions were separately subjected to protein corona nanoparticle complex formation prior to digestion and Liquid Chromatography Mass Spectrometry (LC-MS) analysis. A total of 10,866 proteins (4,421 MyoF and 6,445 non-MyoF) were identified. Across all participants, the number of non-MyoF proteins detected averaged to be 5,645±266 (range: 4,888-5,987) and the number of MyoF proteins detected averaged to be 2,611±326 (range: 1,944-3,101). Differences in the non-MyoF (8.4%) and MyoF (2.5%) proteome were evident between age cohorts. Further, most of these age-related non-MyoF proteins (447/543) were more enriched in MA versus Y. Several biological processes in the non-MyoF fraction were predicted to be operative in MA versus Y including (but not limited to) increased cellular stress, mRNA splicing, translation elongation, and ubiquitin-mediated proteolysis. Non-MyoF proteins associated with splicing and proteostasis were further interrogated, and in agreement with bioinformatics, alternative protein variants, spliceosome-associated proteins (snRNPs), and proteolysis-related targets were more abundant in MA versus Y. RT in MA non-significantly increased VL muscle cross-sectional area (+6.5%, p=0.066) and significantly increased knee extensor strength (+8.7%, p=0.048). However, RT modestly altered the MyoF (~0.3%, 11 upregulated and two downregulated proteins) and non-MyoF proteomes (~1.0%, 56 upregulated and eight downregulated proteins, p<0.01). Further, RT did not affect predicted biological processes in either fraction. Although participant numbers were limited, these preliminary results using a novel deep proteomic approach in skeletal muscle suggest that aging and RT predominantly affects protein abundances in the non-contractile protein pool. However, the marginal proteome adaptations occurring with RT suggest either: a) this may be an aging-associated phenomenon, b) more rigorous RT may stimulate more robust effects, or c) RT, regardless of age, subtly affects skeletal muscle protein abundances in the basal state.

Recovery from Resistance Exercise in Older Adults: A Systematic Scoping Review

BACKGROUND

Resistance exercise is recommended for maintaining muscle mass and strength in older adults. However, little is known about exercise-induced muscle damage and recovery from resistance exercise in older adults. This may have implications for exercise prescription. This scoping review aimed to identify and provide a broad overview of the available literature, examine how this research has been conducted, and identify current knowledge gaps relating to exercise-induced muscle damage and recovery from resistance exercise in older adults.

METHODS

Studies were included if they included older adults aged 65 years and over, and reported any markers of exercise-induced muscle damage after performing a bout of resistance exercise. The following electronic databases were searched using a combination of MeSH terms and free text: MEDLINE, Scopus, Embase, SPORTDiscus and Web of Science. Additionally, reference lists of identified articles were screened for eligible studies. Data were extracted from eligible studies using a standardised form. Studies were collated and are reported by emergent theme or outcomes.

RESULTS

A total of 10,976 possible articles were identified and 27 original research articles were included. Findings are reported by theme; sex differences in recovery from resistance exercise, symptoms of exercise-induced muscle damage, and biological markers of muscle damage.

CONCLUSIONS

Despite the volume of available data, there is considerable variability in study protocols and inconsistency in findings reported. Across all measures of exercise-induced muscle damage, data in women are lacking when compared to males, and rectifying this discrepancy should be a focus of future studies. Current available data make it challenging to provide clear recommendations to those prescribing resistance exercise for older people.

Altered T cell infiltration and enrichment of leukocyte regulating pathways within aged skeletal muscle are associated impaired muscle function following influenza infection

Older adults have diminished immune responses that increase susceptibility to infectious diseases, such as influenza (flu). In older adults, flu infection can lead to hospitalization, catastrophic disability, and mortality. We previously demonstrated severe and prolonged muscle degradation and atrophy in aged mice during flu infection. Here, we utilized an unbiased transcriptomic analysis to elucidate mechanisms of flu-induced muscular declines in a mouse model. Our results showed age-related gene expression differences including downregulation of genes associated with muscle regeneration and organization and upregulation of genes associated with pro-inflammatory cytokines and migratory immune pathways in aged mice when compared to young. Pathway analysis revealed significant enrichment of leukocyte migration and T cell activation pathways in the aged muscle during infection. Intramuscular CD4 T cells increased in both young and aged mice during infection, while intramuscular CD8 T cells increased exclusively in aged muscle. CD4 T cells in young muscle were regulatory T cells (Treg), while those in aged were T follicular helper (Tfh) and Th2 cells. Correspondingly, IL-33, an important cytokine for Treg accumulation within tissue, increased only in young flu-infected muscle. Conversely, CXCL10 (IP-10) increased only in aged muscle suggesting a continued recruitment of CD8 T cells into the aged muscle during flu infection. Overall, our findings elucidate a link between flu-induced disability and dysregulated intracellular T cell recruitment into flu-injured muscle with aging. Furthermore, we uncovered potential pathways involved that can be targeted to develop preventative and therapeutic interventions to avert disability and maintain independence following infection.

Different Resistance Exercise Loading Paradigms Similarly Affect Skeletal Muscle Gene Expression Patterns of Myostatin-Related Targets and mTORC1 Signaling Markers

Although transcriptome profiling has been used in several resistance training studies, the associated analytical approaches seldom provide in-depth information on individual genes linked to skeletal muscle hypertrophy. Therefore, a secondary analysis was performed herein on a muscle transcriptomic dataset we previously published involving trained college-aged men (n = 11) performing two resistance exercise bouts in a randomized and crossover fashion. The lower-load bout (30 Fail) consisted of 8 sets of lower body exercises to volitional fatigue using 30% one-repetition maximum (1 RM) loads, whereas the higher-load bout (80 Fail) consisted of the same exercises using 80% 1 RM loads. Vastus lateralis muscle biopsies were collected prior to (PRE), 3 h, and 6 h after each exercise bout, and 58 genes associated with skeletal muscle hypertrophy were manually interrogated from our prior microarray data. Select targets were further interrogated for associated protein expression and phosphorylation induced-signaling events. Although none of the 58 gene targets demonstrated significant bout x time interactions, ~57% (32 genes) showed a significant main effect of time from PRE to 3 h (15↑ and 17↓, p < 0.01), and ~26% (17 genes) showed a significant main effect of time from PRE to 6 h (8↑ and 9↓, p < 0.01). Notably, genes associated with the myostatin (9 genes) and mammalian target of rapamycin complex 1 (mTORC1) (9 genes) signaling pathways were most represented. Compared to mTORC1 signaling mRNAs, more MSTN signaling-related mRNAs (7 of 9) were altered post-exercise, regardless of the bout, and RHEB was the only mTORC1-associated mRNA that was upregulated following exercise. Phosphorylated (phospho-) p70S6K (Thr389) (p = 0.001; PRE to 3 h) and follistatin protein levels (p = 0.021; PRE to 6 h) increased post-exercise, regardless of the bout, whereas phospho-AKT (Thr389), phospho-mTOR (Ser2448), and myostatin protein levels remained unaltered. These data continue to suggest that performing resistance exercise to volitional fatigue, regardless of load selection, elicits similar transient mRNA and signaling responses in skeletal muscle. Moreover, these data provide further evidence that the transcriptional regulation of myostatin signaling is an involved mechanism in response to resistance exercise.

Genoprotective activity of the Pleurotus eryngii mushrooms following their in vitro and in vivo fermentation by fecal microbiota

Pleurotus eryngii mushrooms are commercially cultivated and widely consumed due to their organoleptic properties, and the low caloric and high nutritional value. In addition, they contain various biologically active and health-promoting compounds; very recently, their genoprotective effect in Caco-2 cells after their fermentation by the human fecal microbiota was also documented. In the current study, the effect of P. eryngii pre- and post-fermentation supernatants in micronuclei formation was evaluated in human lymphocytes. In addition, the genoprotective properties of increasing concentrations of aqueous extracts from P. eryngii mushrooms (150, 300, 600 mg/kg) against the cyclophosphamide-induced DNA damage were studied in young and elderly female and male mice in bone marrow and whole blood cells. The ability of the highest dose (600 mg/kg) to regulate the main cellular signaling pathways was also evaluated in gut and liver tissues of female animals by quantifying the mRNA expression of NrF2, Nfkβ, DNMT1, and IL-22 genes. P. eryngii post-fermentation, but not pre-fermentation, supernatants were able to protect human lymphocytes from the mitomycin C-induced DNA damage in a dose-dependent manner. Similarly, genoprotection was also observed in bone marrow cells of mice treated by gavage with P. eryngii extract. The effect was observed in all the experimental groups of mice (young and elderly, male and female) and was more potent in young female mice. Overexpression of all genes examined was observed in both tissues, mainly among the elderly animals. In conclusion, P. eryngii mushrooms were shown to maintain genome integrity through protecting cells from genotoxic insults. These beneficial effects can be attributed to their antioxidant and immunomodulatory properties, as well as their ability to regulate the cell's epigenetic mechanisms and maintain cell homeostasis.

Sex-specific transcriptome differences in a middle-aged frailty cohort

BACKGROUND

Frailty is a clinical syndrome described as reduced physiological reserve and increased vulnerability. Typically examined in older adults, recent work shows frailty occurs in middle-aged individuals and is associated with increased mortality. Previous investigation of global transcriptome changes in a middle-aged cohort from the Healthy Aging in Neighborhoods of Diversity across the Life Span (HANDLS) study demonstrated inflammatory genes and pathways were significantly altered by frailty status and race. Transcriptome differences in frailty by sex remain unclear. We sought to discover novel genes and pathways associated with sex and frailty in a diverse middle-aged cohort using RNA-Sequencing.

METHODS

Differential gene expression and pathway analyses were performed in peripheral blood mononuclear cells for 1) frail females (FRAF, n = 4) vs non-frail females (NORF, n = 4), 2) frail males (FRAM, n = 4) vs non-frail males (NORM, n = 4), 3) FRAM vs FRAF, and 4) NORM vs NORF. We evaluated exclusive significant genes and pathways, as well as overlaps, between the comparison groups.

RESULTS

Over 80% of the significant genes exclusive to FRAF vs NORF, FRAM vs NORM, and FRAM vs FRAF, respectively, were novel and associated with various biological functions. Pathways exclusive to FRAF vs NORF were associated with reduced inflammation, while FRAM vs NORM exclusive pathways were related to aberrant musculoskeletal physiology. Pathways exclusive to FRAM vs FRAF were associated with reduced cell cycle regulation and activated catabolism and Coronavirus pathogenesis.

CONCLUSIONS

Our results indicate sex-specific transcriptional changes occur in middle-aged frailty, enhancing knowledge on frailty progression and potential therapeutic targets to prevent frailty.

State of Knowledge on Molecular Adaptations to Exercise in Humans: Historical Perspectives and Future Directions

For centuries, regular exercise has been acknowledged as a potent stimulus to promote, maintain, and restore healthy functioning of nearly every physiological system of the human body. With advancing understanding of the complexity of human physiology, continually evolving methodological possibilities, and an increasingly dire public health situation, the study of exercise as a preventative or therapeutic treatment has never been more interdisciplinary, or more impactful. During the early stages of the NIH Common Fund Molecular Transducers of Physical Activity Consortium (MoTrPAC) Initiative, the field is well-positioned to build substantially upon the existing understanding of the mechanisms underlying benefits associated with exercise. Thus, we present a comprehensive body of the knowledge detailing the current literature basis surrounding the molecular adaptations to exercise in humans to provide a view of the state of the field at this critical juncture, as well as a resource for scientists bringing external expertise to the field of exercise physiology. In reviewing current literature related to molecular and cellular processes underlying exercise-induced benefits and adaptations, we also draw attention to existing knowledge gaps warranting continued research effort. © 2021 American Physiological Society. Compr Physiol 12:3193-3279, 2022.

Skeletal muscle transcriptome response to a bout of endurance exercise in physically active and sedentary older adults

Age-related declines in cardiorespiratory fitness and physical function are mitigated by regular endurance exercise in older adults. This may be due, in part, to changes in the transcriptional program of skeletal muscle following repeated bouts of exercise. However, the impact of chronic exercise training on the transcriptional response to an acute bout of endurance exercise has not been clearly determined. Here, we characterized baseline differences in muscle transcriptome and exercise-induced response in older adults who were active/endurance trained or sedentary. RNA-sequencing was performed on vastus lateralis biopsy specimens obtained before, immediately after, and 3 h following a bout of endurance exercise (40 min of cycling at 60%-70% of heart rate reserve). Using a recently developed bioinformatics approach, we found that transcript signatures related to type I myofibers, mitochondria, and endothelial cells were higher in active/endurance-trained adults and were associated with key phenotypic features including V̇o_2peak, ATP_max, and muscle fiber proportion. Immune cell signatures were elevated in the sedentary group and linked to visceral and intermuscular adipose tissue mass. Following acute exercise, we observed distinct temporal transcriptional signatures that were largely similar among groups. Enrichment analysis revealed catabolic processes were uniquely enriched in the sedentary group at the 3-h postexercise timepoint. In summary, this study revealed key transcriptional signatures that distinguished active and sedentary adults, which were associated with difference in oxidative capacity and depot-specific adiposity. The acute response signatures were consistent with beneficial effects of endurance exercise to improve muscle health in older adults irrespective of exercise history and adiposity.NEW & NOTEWORTHY Muscle transcript signatures associated with oxidative capacity and immune cells underlie important phenotypic and clinical characteristics of older adults who are endurance trained or sedentary. Despite divergent phenotypes, the temporal transcriptional signatures in response to an acute bout of endurance exercise were largely similar among groups. These data provide new insight into the transcriptional programs of aging muscle and the beneficial effects of endurance exercise to promote healthy aging in older adults.

Influence of Polymorphism on the NFkB1 Gene (rs28362491) on the Susceptibility to Sarcopenia in the Elderly of the Brazilian Amazon

BACKGROUND

Sarcopenia is a disease characterized by progressive reduction in muscle mass and strength or function. Although it is known that sarcopenia may be associated with environmental factors, studies suggest the identification of genes related to skeletal muscle maintenance that explain the susceptibility to the disease.

OBJECTIVE

To analyze the influence of NFkB1 gene polymorphism on susceptibility to sarcopenia in the elderly.

METHODS

This is a case-control study, which included 219 elderly people, 74 elderly people with sarcopenia, and 145 without sarcopenia. Samples were analyzed for NFkB1 gene polymorphism (rs28362491), genotyped in PCR, and followed by fragment analysis. To avoid misinterpretation due to population substructure, we applied a previously developed set of 61 informative ancestral markers that were genotyped by multiplex PCR. We used logistic regression to identify differences in genotypic frequencies between elderly people with and without sarcopenia.

RESULTS

It was observed that the NFkB1 gene polymorphism presented frequencies of 24%, 50%, and 26% for the genotype DEL/DEL, DEL/INS, and INS/INS, respectively. Furthermore, elderly individuals with the INS/INS genotype had increased chances (p = 0.010; OR:2.943; 95%CI:1.301-6.654) for the development of sarcopenia.

CONCLUSION

The INDEL polymorphism of the NFkB1 gene (rs28362491) may influence the susceptibility to sarcopenia in the elderly in elderly people in the Amazon.

Understanding of sarcopenia: from definition to therapeutic strategies

Sarcopenia refers to the gradual loss of skeletal muscle mass and function along with aging and is a social burden due to growing healthcare cost associated with a super-aging society. Therefore, researchers have established guidelines and tests to diagnose sarcopenia. Several studies have been conducted actively to reveal the cause of sarcopenia and find an economic therapy to improve the quality of life in elderly individuals. Sarcopenia is caused by multiple factors such as reduced regenerative capacity, imbalance in protein turnover, alteration of fat and fibrotic composition in muscle, increased reactive oxygen species, dysfunction of mitochondria and increased inflammation. Based on these mechanisms, nonpharmacological and pharmacological strategies have been developed to prevent and treat sarcopenia. Although several studies are currently in progress, no treatment is available yet. This review presents the definition of sarcopenia and summarizes recent understanding on the detailed mechanisms, diagnostic criteria, and strategies for prevention and treatment.

Resistance Exercise, Aging, Disuse, and Muscle Protein Metabolism

Skeletal muscle is the organ of locomotion, its optimal function is critical for athletic performance, and is also important for health due to its contribution to resting metabolic rate and as a site for glucose uptake and storage. Numerous endogenous and exogenous factors influence muscle mass. Much of what is currently known regarding muscle protein turnover is owed to the development and use of stable isotope tracers. Skeletal muscle mass is determined by the meal- and contraction-induced alterations of muscle protein synthesis and muscle protein breakdown. Increased loading as resistance training is the most potent nonpharmacological strategy by which skeletal muscle mass can be increased. Conversely, aging (sarcopenia) and muscle disuse lead to the development of anabolic resistance and contribute to the loss of skeletal muscle mass. Nascent omics-based technologies have significantly improved our understanding surrounding the regulation of skeletal muscle mass at the gene, transcript, and protein levels. Despite significant advances surrounding the mechanistic intricacies that underpin changes in skeletal muscle mass, these processes are complex, and more work is certainly needed. In this article, we provide an overview of the importance of skeletal muscle, describe the influence that resistance training, aging, and disuse exert on muscle protein turnover and the molecular regulatory processes that contribute to changes in muscle protein abundance. © 2021 American Physiological Society. Compr Physiol 11:2249-2278, 2021.

Discovery and application of dietary compounds to optimize human health, a focus on skeletal muscle regeneration

Worldwide, the number of persons over the age of 65 years and those at risk of malnutrition (over and under) is growing, and the prevalence of diet-related chronic disease is at a record high. Pathologies that are linked to poor nutrition underlie the leading causes of death. Safe and effective strategies to improve human health outcomes are urgently required. Identification of nutrient needs for health outcomes has led to the development of food products, supplements, and dietary pattern recommendations. Application of these nutrient-based therapies have the potential to optimize clinical outcomes, such as tissue regeneration post-skeletal muscle trauma. However, despite progress in identifying nutrient needs there is often a delay in the utilization of products in clinical practice.

M. Simoes D. Exercise Training-Induced Extracellular Matrix Protein Adaptation in Locomotor Muscles: A Systematic Review

Exercise training promotes muscle adaptation and remodelling by balancing the processes of anabolism and catabolism; however, the mechanisms by which exercise delays accelerated muscle wasting are not fully understood. Intramuscular extracellular matrix (ECM) proteins are essential to tissue structure and function, as they create a responsive environment for the survival and repair of the muscle fibres. However, their role in muscle adaptation is underappreciated and underinvestigated. The PubMed, COCHRANE, Scopus and CIHNAL databases were systematically searched from inception until February 2021. The inclusion criteria were on ECM adaptation after exercise training in healthy adult population. Evidence from 21 studies on 402 participants demonstrates that exercise training induces muscle remodelling, and this is accompanied by ECM adaptation. All types of exercise interventions promoted a widespread increase in collagens, glycoproteins and proteoglycans ECM transcriptomes in younger and older participants. The ECM controlling mechanisms highlighted here were concerned with myogenic and angiogenic processes during muscle adaptation and remodelling. Further research identifying the mechanisms underlying the link between ECMs and muscle adaptation will support the discovery of novel therapeutic targets and the development of personalised exercise training medicine.

Skeletal muscle transcriptome in healthy aging

Age-associated changes in gene expression in skeletal muscle of healthy individuals reflect accumulation of damage and compensatory adaptations to preserve tissue integrity. To characterize these changes, RNA was extracted and sequenced from muscle biopsies collected from 53 healthy individuals (22-83 years old) of the GESTALT study of the National Institute on Aging-NIH. Expression levels of 57,205 protein-coding and non-coding RNAs were studied as a function of aging by linear and negative binomial regression models. From both models, 1134 RNAs changed significantly with age. The most differentially abundant mRNAs encoded proteins implicated in several age-related processes, including cellular senescence, insulin signaling, and myogenesis. Specific mRNA isoforms that changed significantly with age in skeletal muscle were enriched for proteins involved in oxidative phosphorylation and adipogenesis. Our study establishes a detailed framework of the global transcriptome and mRNA isoforms that govern muscle damage and homeostasis with age.

Muscular HSP70 content is higher in elderly compared to young, but is normalized after 12 weeks of strength training

Purpose

Aging is associated with increased myocellular stress and loss of muscle mass and function. Heat shock proteins (HSPs) are upregulated during periods of stress as part of the cells protective system. Exercise can affect both acute HSP regulation and when repeated regularly counteract unhealthy age-related changes in the muscle. Few studies have investigated effects of exercise on HSP content in elderly. The aim of the study was to compare muscular HSP levels in young and elderly and to investigate how training affects HSP content in muscles from aged males and females.

Methods

Thirty-eight elderly were randomized to 12 weeks of strength training (STG), functional strength training (FTG) or a control group (C). To compare elderly to young, 13 untrained young performed 11 weeks of strength training (Y). Muscle biopsies were collected before and after the intervention and analyzed for HSP27, αB-crystallin and HSP70.

Results

Baseline HSP70 were 35% higher in elderly than in young, whereas there were no differences between young and elderly in HSP27 or αB-crystallin. After the training intervention, HSP70 were reduced in STG (− 33 ± 32%; P = 0.001) and FTG (− 28 ± 30%; P = 0.012). The decrease in HSP70 was more pronounced in the oldest. In contrast, Y increased HSP27 (134 ± 1%; P < 0.001) and αB-crystallin (84 ± 94%; P = 0.008).

Conclusion

Twelve weeks of STG or FTG decreased the initial high levels of HSP70 in aged muscles. Thus, regular strength training can normalize some of the increases in cellular stress associated with normal aging, and lead to a healthier cellular environment in aged muscle cells.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00421-021-04633-4.

Improved recovery from skeletal muscle damage is largely unexplained by myofibrillar protein synthesis or inflammatory and regenerative gene expression pathways

The contribution of myofibrillar protein synthesis (MyoPS) to recovery from skeletal muscle damage in humans is unknown. Recreationally active men and women consumed a daily protein-polyphenol beverage targeted at increasing amino acid availability and reducing inflammation (PPB; n = 9), both known to affect MyoPS, or an isocaloric placebo (PLA; n = 9) during 168 h of recovery from 300 maximal unilateral eccentric contractions (EE). Muscle function was assessed daily. Muscle biopsies were collected for 24, 27, 36, 72, and 168 h for MyoPS measurements using ²H₂O and expression of 224 genes using RT-qPCR and pathway analysis. PPB improved recovery of muscle function, which was impaired for 5 days after EE in PLA (interaction P < 0.05). Acute postprandial MyoPS rates were unaffected by nutritional intervention (24-27 h). EE increased overnight (27-36 h) MyoPS versus the control leg (PLA: 33 ± 19%; PPB: 79 ± 25%; leg P < 0.01), and PPB tended to increase this further (interaction P = 0.06). Daily MyoPS rates were greater with PPB between 72 and 168 h after EE, albeit after function had recovered. Inflammatory and regenerative signaling pathways were dramatically upregulated and clustered after EE but were unaffected by nutritional intervention. These results suggest that accelerated recovery from EE is not explained by elevated MyoPS or suppression of inflammation.NEW & NOTEWORTHY The present study investigated the contribution of myofibrillar protein synthesis (MyoPS) and associated gene signaling to recovery from 300 muscle-damaging, eccentric contractions. Measured with ²H₂O, MyoPS rates were elevated during recovery and observed alongside expression of inflammatory and regenerative signaling pathways. A nutritional intervention accelerated recovery; however, MyoPS and gene signaling were unchanged compared with placebo. These data indicate that MyoPS and associated signaling do not explain accelerated recovery from muscle damage.

Rehabilitative Impact of Exercise Training on Human Skeletal Muscle Transcriptional Programs in Parkinson's Disease

Parkinson's disease (PD) is the most common motor neurodegenerative disease, and neuromuscular function deficits associated with PD contribute to disability. Targeting these symptoms, our laboratory has previously evaluated 16-week high-intensity resistance exercise as rehabilitative training (RT) in individuals with PD. We reported significant improvements in muscle mass, neuromuscular function (strength, power, and motor unit activation), indices of neuromuscular junction integrity, total and motor scores on the unified Parkinson's disease rating scale (UPDRS), and total and sub-scores on the 39-item PD Quality of Life Questionnaire (PDQ-39), supporting the use of RT to reverse symptoms. Our objective was to identify transcriptional networks that may contribute to RT-induced neuromuscular remodeling in PD. We generated transcriptome-wide skeletal muscle RNA-sequencing in 5 participants with PD [4M/1F, 67 ± 2 years, Hoehn and Yahr stages 2 (n = 3) and 3 (n = 2)] before and after 16-week high intensity RT to identify transcriptional networks that may in part underpin RT-induced neuromuscular remodeling in PD. Following RT, 304 genes were significantly upregulated, notably related to remodeling and nervous system/muscle development. Additionally, 402 genes, primarily negative regulators of muscle adaptation, were downregulated. We applied the recently developed Pathway-Level Information ExtractoR (PLIER) method to reveal coordinated gene programs (as latent variables, LVs) that differed in skeletal muscle among young (YA) and old (OA) healthy adults and PD (n = 12 per cohort) at baseline and in PD pre- vs. post-RT. Notably, one LV associated with angiogenesis, axon guidance, and muscle remodeling was significantly lower in PD than YA at baseline and was significantly increased by exercise. A different LV annotated to denervation, autophagy, and apoptosis was increased in both PD and OA relative to YA and was also reduced by 16-week RT in PD. Thus, this analysis identified two novel skeletal muscle transcriptional programs that are dysregulated by PD and aging, respectively. Notably, RT has a normalizing effect on both programs in individuals with PD. These results identify potential molecular transducers of the RT-induced improvements in neuromuscular remodeling and motor function that may aid in optimizing exercise rehabilitation strategies for individuals with PD.

The acute transcriptional response to resistance exercise: impact of age and contraction mode

Optimization of resistance exercise (RE) remains a hotbed of research for muscle building and maintenance. However, the interactions between the contractile components of RE (i.e. concentric (CON) and eccentric (ECC)) and age, are poorly defined. We used transcriptomics to compare age-related molecular responses to acute CON and ECC exercise. Eight young (21±1 y) and eight older (70±1 y) exercise-naïve male volunteers had vastus lateralis biopsies collected at baseline and 5 h post unilateral CON and contralateral ECC exercise. RNA was subjected to next-generation sequencing and differentially expressed (DE) genes tested for pathway enrichment using Gene Ontology (GO). The young transcriptional response to CON and ECC was highly similar and older adults displayed moderate contraction-specific profiles, with no GO enrichment. Age-specific responses to ECC revealed 104 DE genes unique to young, and 170 DE genes in older muscle, with no GO enrichment. Following CON, 15 DE genes were young muscle-specific, whereas older muscle uniquely expressed 147 up-regulated genes enriched for cell adhesion and blood vessel development, and 28 down-regulated genes involved in mitochondrial respiration, amino acid and lipid metabolism. Thus, older age is associated with contraction-specific regulation often without clear functional relevance, perhaps reflecting a degree of stochastic age-related dysregulation.

Recent advances in understanding resistance exercise training-induced skeletal muscle hypertrophy in humans

Skeletal muscle plays a pivotal role in the maintenance of physical and metabolic health and, critically, mobility. Accordingly, strategies focused on increasing the quality and quantity of skeletal muscle are relevant, and resistance exercise is foundational to the process of functional hypertrophy. Much of our current understanding of skeletal muscle hypertrophy can be attributed to the development and utilization of stable isotopically labeled tracers. We know that resistance exercise and sufficient protein intake act synergistically and provide the most effective stimuli to enhance skeletal muscle mass; however, the molecular intricacies that underpin the tremendous response variability to resistance exercise-induced hypertrophy are complex. The purpose of this review is to discuss recent studies with the aim of shedding light on key regulatory mechanisms that dictate hypertrophic gains in skeletal muscle mass. We also aim to provide a brief up-to-date summary of the recent advances in our understanding of skeletal muscle hypertrophy in response to resistance training in humans.

Network analysis of human muscle adaptation to aging and contraction

Resistance exercise (RE) remains a primary approach for minimising aging muscle decline. Understanding muscle adaptation to individual contractile components of RE (eccentric, concentric) might optimise RE-based intervention strategies. Herein, we employed a network-driven pipeline to identify putative molecular drivers of muscle aging and contraction mode responses. RNA-sequencing data was generated from young (21±1 y) and older (70±1 y) human skeletal muscle before and following acute unilateral concentric and contralateral eccentric contractions. Application of weighted gene co-expression network analysis identified 33 distinct gene clusters ('modules') with an expression profile regulated by aging, contraction and/or linked to muscle strength. These included two contraction 'responsive' modules (related to 'cell adhesion' and 'transcription factor' processes) that also correlated with the magnitude of post-exercise muscle strength decline. Module searches for 'hub' genes and enriched transcription factor binding sites established a refined set of candidate module-regulatory molecules (536 hub genes and 60 transcription factors) as possible contributors to muscle aging and/or contraction responses. Thus, network-driven analysis can identify new molecular candidates of functional relevance to muscle aging and contraction mode adaptations.

Protein and amino acids for skeletal muscle health in aging

Proteins and its building blocks, amino acids, have many physiological roles in the body. While some amino acids can be synthesized endogenously, exogenous protein and amino acids are necessary to maintain homeostasis. Because skeletal muscle contains a large portion of endogenous protein and plays important roles in movement, regulation, and metabolism, imbalanced protein and amino acid availability may result in clinical conditions including skeletal muscle atrophy, impaired muscle growth or regrowth, and functional decline. Aging is associated with changes in protein metabolism and multiple physiological and functional alterations in the skeletal muscle that are accentuated by decreased dietary protein intake and impaired anabolic responses to stimuli. Inactivity and chronically elevated inflammation of the skeletal muscle can initiate and/or augment pathological remodeling of the tissue (i.e., increase of fat and fibrotic tissues and atrophy of the muscle). Defining an adequate amount of dietary protein that is appropriate to maintain the availability of amino acids for biological needs is necessary but is still widely debated for older adults. This chapter will provide (i) an overview of dietary protein and amino acids and their role in skeletal muscle health; (ii) an overview of skeletal muscle structure and function and the deterioration of muscle that occurs with advancing age; (iii) a discussion of the relationship between protein/amino acid metabolism and skeletal muscle decline with aging; and (iv) a brief discussion of optimal protein intakes for older adults to maintain skeletal muscle health in aging.

The impact of age and frailty on skeletal muscle autophagy markers and specific strength: A cross-sectional comparison

Aging is associated with reduced specific strength, defined as strength normalized to the cross-sectional area of a given muscle or muscle group. Dysregulated autophagy, impairing removal of dysfunctional proteins and organelles, is suggested as one of the underlying mechanisms. The aim of this study was to investigate levels of autophagic markers in skeletal muscle in groups known to differ in specific strength. Sixty-two volunteers were assigned to the following study groups: young, old non-frail, old pre-frail, and old frail individuals. Leg lean mass was assessed with dual-energy X-ray absorptiometry and quadriceps femoris muscle strength by isometric maximal voluntary contraction. The abundance of autophagic proteins within skeletal muscle cytosolic and membrane sub-fractions were determined by western blotting. In addition, the level of heat shock proteins and proteins involved in the regulation of protein synthesis were measured. The abundance of LC3-I was higher in old frail compared to young individuals. If the three elderly groups were pooled, the level of LC3-II was higher in old compared to young subjects. Pre-frail and frail elderly also displayed higher levels of certain heat shock proteins. No between-group differences were observed for p62, LC3-II/LC3-I ratio, or any of the anabolic signaling molecules. A negative correlation was observed between cytosolic LC3-I and specific strength. Higher levels of LC3-I in the frail elderly might represent attenuated autophagosome formation. However, higher LC3-II levels indicate an increased abundance of autophagosomes. These findings may therefore imply that both the process of autophagosome formation and autophagosome-lysosome fusion are affected in frail elderly. Higher levels of heat shock proteins might represent an auto-protective mechanism against increased levels of misfolded proteins, possibly due to inefficient degradation. In conclusion, the reduction in specific strength with aging and frailty may partly be caused by alterations in muscle protein quality control.

Identification of Candidate Genes for Skeletal Muscle Injury Prevention in Two Different Types

The study aims to uncover mechanisms on repair process of two different types of skeletal muscle injuries, freezing injury (FI) and contraction-induced injury (CI). GSE5413 was utilized, including 11 eccentric CI, 11 FI, and 3 control samples at 4 time points (6 hours, 1 day, 3 days, and 7 days after injury). Differentially expressed genes (DEGs) separately were selected in FI and CI. Correlation analysis of samples at different time points was performed. Clustering analysis was conducted for DEGs in FI and CI, respectively. Moreover, enrichment analysis and protein/protein interaction network analysis were performed for the specific DEGs. There were 616 and 465 DEGs separately in FI and CI samples. For both FI and CI, samples between 6 hours and 1 day, and between 3 and 7 days, had a close distance. DEGs in FI and CI separately were enriched in leukocyte transendothelial migration (e.g., ICAM1 [intercellular adhesion molecule 1], ITGAM, MMP9) and protein processing in endoplasmic reticulum pathway (e.g., HSPH1, HSP90AA1). In addition, MMP9 (matrix metallopeptidase 9) and ITGAM, and MYC, HSPA1B, and HSPA1A were hub nodes in the networks in FI and CI, respectively. ICAM1, ITGAM, and MMP9 in FI, and MYC and HSP70 family members in CI were biomarkers for injury prevention.

Micro(RNA)-managing muscle wasting

Progressive skeletal muscle wasting is a natural consequence of aging and is common in chronic and acute diseases. Loss of skeletal muscle mass and function (strength) often leads to frailty, decreased independence, and increased risk of hospitalization. Despite progress made in our understanding of the mechanisms underlying muscle wasting, there is still no treatment available, with exercise training and dietary supplementation improving, but not restoring, muscle mass and/or function. There has been slow progress in developing novel therapies for muscle wasting, either during aging or disease, partially due to the complex nature of processes underlying muscle loss. The mechanisms of muscle wasting are multifactorial, with a combination of factors underlying age- and disease-related functional muscle decline. These factors include well-characterized changes in muscle such as changes in protein turnover and more recently described mechanisms such as autophagy or satellite cell senescence. Advances in transcriptomics and other high-throughput approaches have highlighted significant deregulation of skeletal muscle gene and protein levels during aging and disease. These changes are regulated at different levels, including posttranscriptional gene expression regulation by microRNAs. microRNAs, potent regulators of gene expression, modulate many processes in muscle, and microRNA-based interventions have been recently suggested as a promising new therapeutic strategy against alterations in muscle homeostasis. Here, we review recent developments in understanding the aging-associated mechanisms of muscle wasting and explore potential microRNA-based therapeutic avenues.

Study on relationship between elderly sarcopenia and inflammatory cytokine IL-6, anti-inflammatory cytokine IL-10

Background and objectives

The pathophysiological mechanism of sarcopenia in the elderly has not yet been fully understood. Here, we aim to explore the relationship between sarcopenia and the inflammatory cytokine interleukin-6 (IL-6), and the anti-inflammatory cytokine interleukin-10 (IL-10) in an elderly population.

Methods

Our study comprised 118 males and 46 females aged between 61 and 90 who had received a general medical examination in Tianjin First Central Hospital. Subjects were divided into a sarcopenia group and a non-sarcopenia group, defined according to the criteria of the Asian Working Group for Sarcopenia (AWGS). We compared body composition, handgrip strength (HS), gait speed (GS), biochemical indexes, levels of IL-6 and IL-10, living habits, and disease status between these groups.

Results

Non-sarcopenia subjects undertook more regular physical exercise than sarcopenia patients. Sarcopenia subjects had higher nutrition risk but lower body mass index (BMI), serum albumin (ALB), triglyceride (TG), and creatinine (Cr) levels compared to non-sarcopenia subjects. Sarcopenia subjects were older and had higher visceral fat tissue (VFA) than non-sarcopenia subjects (P < 0.05), along with higher IL-6 and IL-10 levels. Furthermore, IL-6/IL-10 ratios were higher in subjects with sarcopenia (P < 0.05). Age, BMI, levels of physical activity, nutritional risk, VFA, IL-6, IL-10, IL-6/IL-10 ratio were independently associated with the presence of sarcopenia in univariate regression analyses. Following adjustment for confounding factors, the presence of sarcopenia was positively correlated with IL-6, IL-10, IL-6/IL-10 ratio and inversely correlated with BMI. Age is associated with increased presence of sarcopenia.

Conclusions

The levels of inflammation cytokine IL-6, anti-inflammatory IL-10 and IL-6/IL-10 ratio were increased in elderly sarcopenia subjects. Sarcopenia was associated with increased levels of inflammatory cytokine IL-6, anti-inflammatory cytokine IL-10, and IL-6/IL-10 ratios.

Age-specific response of skeletal muscle extracellular matrix to acute resistance exercise: A pilot study

The extracellular matrix (ECM) plays an essential role in the development, growth and repair of skeletal muscles and serves to transmit contractile force. However, its regulation is poorly understood. This study investigates the age-specificity of the effects of acute resistance exercise on ECM gene expression. To this purpose, five young (YM, 23.8 ± 2.2 yrs.) and 5 elderly (EM, 66.8 ± 4.1 yrs.) men performed one session of unilateral leg press and leg extension exercises. Six hours post-exercise, biopsies were taken from the vastus lateralis muscles of both legs. A PCR array was used to profile the expression of 84 ECM-related genes, of which 6 were validated by qPCR. The PCR array found 9 and 4 ECM-associated genes to be selectively altered (>1.5-fold change) in YM or EM only. Four further genes were upregulated in YM but downregulated in EM. Of the 6 genes validated on individual samples MMP9 expression increased in YM (9.7-fold) and decreased (0.2-fold) in EM. MMP15 was downregulated in EM only (0.6-fold). A significant correlation between leg extension 1 RM and changes in COL7A1 expression (ρ = 0.71) suggests a potential influence of fitness levels. In conclusion, acute resistance exercise affects ECM gene expression at least partly in an age-specific manner. The altered expression of genes encoding matrix metalloproteinases (MMP3, MMP9, MMP15) highlights the role of remodelling processes in the response to an acute bout of resistance exercise. Larger studies are required to verify the age-associated differences in gene expression profiles and establish their functional implications.

Age-related changes in skeletal muscle: changes to life-style as a therapy

As we age, there is an age-related loss in skeletal muscle mass and strength, known as sarcopenia. Sarcopenia results in a decrease in mobility and independence, as well as an increase in the risk of other morbidities and mortality. Sarcopenia is therefore a major socio-economical problem. The mechanisms behind sarcopenia are unclear and it is likely that it is a multifactorial condition with changes in numerous important mechanisms all contributing to the structural and functional deterioration. Here, we review the major proposed changes which occur in skeletal muscle during ageing and highlight evidence for changes in physical activity and nutrition as therapeutic approaches to combat age-related skeletal muscle wasting.

Resistance training in young men induces muscle transcriptome-wide changes associated with muscle structure and metabolism refining the response to exercise-induced stress

BACKGROUND

Gene expression is an important process underpinning the acute and chronic adaptive response to resistance exercise (RE) training.

PURPOSE

To investigate the effect of training status on vastus lateralis muscle global transcriptome at rest and following acute RE.

METHODS

Muscle biopsies of nine young men (age: 26(2) years; body mass: 69(9) kg; height 172(6) cm) who undertook RE training for 10 weeks were collected pre and 24 h post-RE in the untrained (W1) and trained (W10) states and analysed using microarray. Tests of differential expression were conducted for rested and after RE contrasts in both training states. To control for false discovery rate (FDR), multiple testing correction was performed at a cut-off of FDR < 0.05.

RESULTS

Unaccustomed RE (at W1) upregulated muscle gene transcripts related to stress (e.g., heat shock proteins), damage and inflammation, structural remodelling, protein turnover and increased translational capacity. Trained muscles (at W10) showed changes in the transcriptome signature regarding the regulation of energy metabolism, favouring a more oxidative one, upregulated antioxidant- and immune-related genes/terms, and gene transcripts related to the cytoskeleton and extracellular matrix, muscle contraction, development and growth.

CONCLUSIONS

These results highlight that chronic repetition of RE changes muscle transcriptome response towards a more refined response to RE-induced stress.

A high-protein diet or combination exercise training to improve metabolic health in individuals with long-standing spinal cord injury: a pilot randomized study

We compared the effects of an 8-week iso-caloric high-protein (HP) diet versus a combined exercise regimen (Comb-Ex) in individuals with long-standing spinal cord injury (SCI). Effects on metabolic profiles, markers of inflammation, and signaling proteins associated with glucose transporter 4 (GLUT-4) translocation in muscles were evaluated. Eleven participants with SCI completed the study (HP diet: n = 5; Comb-Ex: n = 6; 46 ± 8 years; C5-T12 levels; American Spinal Injury Association Impairment Scale A or B). The Comb-Ex regimen included upper body resistance training (RT) and neuromuscular electrical stimulation-induced-RT for paralytic quadriceps muscles, interspersed with high-intensity (80-90% VO2 peak) arm cranking exercises 3 days/week. The HP diet included ~30% total energy as protein (carbohydrate to protein ratio <1.5, ~30% energy from fat). Oral glucose tolerance tests and muscle biopsies of the vastus lateralis (VL) and deltoid muscles were performed before and after the trial. Fasting plasma glucose levels decreased in the Comb-Ex (P < 0.05) group compared to the HP-diet group. A decrease in areas under the curve for insulin and TNF-α concentrations was observed for all participants regardless of group assignment (time effect, P < 0.05). Although both groups exhibited a quantitative increase in insulin sensitivity as measured by the Matsuda Index, the change was clinically meaningful only in the HP diet group (HP diet: pre, 4.6; post, 11.6 vs. Comb-Ex: pre, 3.3; post, 4.6). No changes were observed in proteins associated with GLUT-4 translocation in VL or deltoid muscles. Our results suggest that the HP-diet and Comb-Ex regimen may improve insulin sensitivity and decrease TNF-α concentrations in individuals with SCI.

Systemic IL-6 and Myoglobin Response to Three Different Resistance Exercise Intensities in Older Men

The purpose of this research was to identify if three different intensities of resistance exercise would acutely and differentially effect the systemic release of interleukin-6 (IL-6) and myoglobin in older men (≥65 years). A total of 11 older men performed isovolume resistance exercise on six different apparatuses at three different intensities (144 reps at 60%, 120 reps at 72%, and 108 reps at 80% of 1-repetition maximum), with the intensity order randomly allocated, to determine the systemic release of IL-6 and myoglobin in the blood. Blood samples were collected at six time points, including preexercise, immediately postexercise, and 3, 6, 24, and 48 hr postexercise. There were no differences between intensity levels; therefore, data for all conditions were pooled. IL-6 did not show any change from baseline values throughout all time points (p > .05), whereas myoglobin was elevated at 3, 6, and 24 hr postexercise and returned to baseline after 48 hr (p < .05).

Paralytic and nonparalytic muscle adaptations to exercise training versus high-protein diet in individuals with long-standing spinal cord injury

This study compares the effects of an 8-wk isocaloric high-protein (HP) diet versus a combination exercise (Comb-Ex) regimen on paralytic vastus lateralis (VL) and nonparalytic deltoid muscle in individuals with long-standing spinal cord injury (SCI). Fiber-type distribution, cross-sectional area (CSA), levels of translation initiation signaling proteins (Erk-1/2, Akt, p70S6K1, 4EBP1, RPS6, and FAK), and lean thigh mass were analyzed at baseline and after the 8-wk interventions. A total of 11 participants (C5-T12 levels, 21.8 ± 6.3 yr postinjury; 6 Comb-Ex and 5 HP diet) completed the study. Comb-Ex training occurred 3 days/wk and consisted of upper body resistance training (RT) in addition to neuromuscular electrical stimulation (NMES)-induced-RT for paralytic VL muscle. Strength training was combined with high-intensity arm-cranking exercises (1-min intervals at 85-90%, V̇o2peak) for improving cardiovascular endurance. For the HP diet intervention, protein and fat each comprised 30%, and carbohydrate comprised 40% of total energy. Clinical tests and muscle biopsies were performed 24 h before and after the last exercise or diet session. The Comb-Ex intervention increased Type IIa myofiber distribution and CSA in VL muscle and Type I and IIa myofiber CSA in deltoid muscle. In addition, Comb-Ex increased lean thigh mass, V̇o2peak, and upper body strength ( P < 0.05). These results suggest that exercise training is required to promote favorable changes in paralytic and nonparalytic muscles in individuals with long-standing SCI, and adequate dietary protein consumption alone may not be sufficient to ameliorate debilitating effects of paralysis. NEW & NOTEWORTHY This study is the first to directly compare the effects of an isocaloric high-protein diet and combination exercise training on clinical and molecular changes in paralytic and nonparalytic muscles of individuals with long-standing spinal cord injury. Our results demonstrated that muscle growth and fiber-type alterations can best be achieved when the paralyzed muscle is sufficiently loaded via neuromuscular electrical stimulation-induced resistance training.

Transcriptome response of human skeletal muscle to divergent exercise stimuli

Aerobic (AE) and resistance exercise (RE) elicit unique adaptations in skeletal muscle that have distinct implications for health and performance. The purpose of this study was to identify the unique transcriptome response of skeletal muscle to acute AE and RE. In a counterbalanced, crossover design, six healthy, recreationally active young men (27 ± 3 yr) completed acute AE (40 min of cycling, ∼70% maximal HR) and RE [8 sets, 10 reps, ∼65% 1-repetition maximum (1RM)], separated by ∼1 wk. Muscle biopsies (vastus lateralis) were obtained before and at 1 and 4 h postexercise. Whole transcriptome RNA sequencing (HiSeq2500; Illumina) was performed on cDNA synthesized from skeletal muscle RNA. Sequencing data were analyzed using HTSeq, and differential gene expression was identified using DESeq2 [adjusted P value (FDR) <0.05, >1.5-fold change from preexercise]. RE resulted in a greater number of differentially expressed genes at 1 (67 vs. 48) and 4 h (523 vs. 221) compared with AE. We identified 348 genes that were differentially expressed only following RE, whereas 48 genes were differentially expressed only following AE. Gene clustering indicated that AE targeted functions related to zinc interaction, angiogenesis, and ubiquitination, whereas RE targeted functions related to transcription regulation, cytokine activity, cell adhesion, kinase activity, and the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. ESRRG and TNFSRF12A were identified as potential targets related to the specific response of skeletal muscle to AE and RE, respectively. These data describe the early postexercise transcriptome response of skeletal muscle to acute AE and RE and further highlight that different forms of exercise stimulate unique molecular activity in skeletal muscle. NEW & NOTEWORTHY Whole transcriptome RNA sequencing was used to determine the early postexercise transcriptome response of skeletal muscle to acute aerobic (AE) and resistance exercise (RE) in untrained individuals. Although a number of shared genes were stimulated following both AE and RE, several genes were uniquely responsive to each exercise mode. These findings support the need for future research focused to better identify the role of exercise mode as it relates to targeting specific cellular skeletal muscle abnormalities.

Posterolateral vs Direct Anterior Approach in Total Hip Arthroplasty (POLADA Trial): A Randomized Controlled Trial to Assess Differences in Serum Markers

BACKGROUND

The direct anterior approach (DAA) for total hip arthroplasty has claimed to be a true tissue-sparing minimally invasive approach that has less tissue damage and a faster recovery when compared to the posterolateral approach (PLA). The aim of this randomized controlled trial is to measure the differences in serum markers and functional outcomes between the DAA and PLA for total hip arthroplasty.

METHODS

Forty-six patients were prospectively included and randomized for either the DAA (n = 23) or PLA (n = 23). All surgical procedures were performed by 3 well-trained orthopedic surgeons. The degree of tissue damage was assessed by measuring creatine kinase (CK) and C-reactive protein levels (CRP) preoperatively and 2 hours, 1 day, 2 weeks, and 6 weeks postoperatively. Generalized linear mixed models analyses were used to assess differences between serum markers over time; correction for possible confounding factors was performed. The Hip disability and Osteoarthritis Outcome Score and the Harris Hip Score were assessed preoperatively and 6 weeks postoperatively.

RESULTS

There were no differences in patient demographics. The DAA had a longer operative time (P = .001). CK and CRP levels increased postoperatively, but no significant differences between the groups were found on any of the time points. Functional outcomes were also similar in both approaches.

CONCLUSION

No difference in tissue damage measured with serum markers CK and CRP were found between the DAA and PLA for total hip arthroplasty.

Sustained NFκB inhibition improves insulin sensitivity but is detrimental to muscle health

Older adults universally suffer from sarcopenia and approximately 60-70% are diabetic or prediabetic. Nonetheless, the mechanisms underlying these aging-related metabolic disorders are unknown. NFκB has been implicated in the pathogenesis of several aging-related pathologies including sarcopenia and type 2 diabetes and has been proposed as a target against them. NFκB also is thought to mediate muscle wasting seen with disuse, denervation, and some systemic diseases (e.g., cancer, sepsis). We tested the hypothesis that lifelong inhibition of the classical NFκB pathway would protect against aging-related sarcopenia and insulin resistance. Aged mice with muscle-specific overexpression of a super-repressor IκBα mutant (MISR) were protected from insulin resistance. However, MISR mice were not protected from sarcopenia; to the contrary, these mice had decreases in muscle mass and strength compared to wild-type mice. In MISR mice, NFκB suppression also led to an increase in proteasome activity and alterations in several genes and pathways involved in muscle growth and atrophy (e.g., myostatin). We conclude that the mechanism behind aging-induced sarcopenia is NFκB independent and differs from muscle wasting due to pathologic conditions. Our findings also indicate that, while suppressing NFκB improves insulin sensitivity in aged mice, this transcription factor is important for normal muscle mass maintenance and its sustained inhibition is detrimental to muscle function.

Understanding Age-Related Changes in Skeletal Muscle Metabolism: Differences Between Females and Males

Skeletal muscle is the largest metabolic organ system in the human body. As such, metabolic dysfunction occurring in skeletal muscle impacts whole-body nutrient homeostasis. Macronutrient metabolism changes within the skeletal muscle with aging, and these changes are associated in part with age-related skeletal muscle remodeling. Moreover, age-related changes in skeletal muscle metabolism are affected differentially between males and females and are likely driven by changes in sex hormones. Intrinsic and extrinsic factors impact observed age-related changes and sex-related differences in skeletal muscle metabolism. Despite some support for sex-specific differences in skeletal muscle metabolism with aging, more research is necessary to identify underlying differences in mechanisms. Understanding sex-specific aging skeletal muscle will assist with the development of therapies to attenuate adverse metabolic and functional outcomes.

MicroRNA Dysregulation in Aging and Pathologies of the Skeletal Muscle

Skeletal muscle is one of the biggest organs of the body with important mechanistic and metabolic functions. Muscle homeostasis is controlled by environmental, genetic, and epigenetic factors. Indeed, MiRNAs, small noncoding RNAs robust regulators of gene expression, have and have been shown to regulate muscle homeostasis on several levels: through controlling myogenesis, muscle growth (hypertrophy) and atrophy, as well as interactions of muscle with other tissues. Given the large number of MiRNA target genes and the important role of MiRNAs in most physiological processes and various diseases, MiRNAs may have an enormous potential as therapeutic targets against numerous disorders, including pathologies of muscle. The purpose of this review is to present the current knowledge of the role of MiRNAs in skeletal muscle homeostasis and pathologies and the potential of MiRNAs as therapeutics for skeletal muscle wasting, with particular focus on the age- and disease-related loss of muscle mass and function.