Dkk3 dependent transcriptional regulation controls age related skeletal muscle atrophy

Human CD29+/CD56+ myogenic progenitors display tenogenic differentiation potential and facilitate tendon regeneration

Tendon injury occurs at high frequency and is difficult to repair. Identification of human stem cells being able to regenerate tendon will greatly facilitate the development of regenerative medicine for tendon injury. Genetic and functional analyses identify human CD29+/CD56+ myogenic progenitors with tenogenic differentiation potential in vitro and in vivo. Transplantation of human CD29+/CD56+ myogenic progenitors contributes to injured tendon repair and thus improves locomotor function. Interestingly, the tendon differentiation potential in mouse muscle stem cells is minimal and the higher TGFβ signaling level may be the key for the distinct feature of human CD29+/CD56+ myogenic progenitors. The discovery of bi-potential CD29+/CD56+ myogenic progenitors highlights their potential as a novel adult stem cell source for tendon regeneration.

A Novel Research Paradigm for Sarcopenia of Limb Muscles: Lessons From the Perpetually Working Diaphragm's Anti-Aging Mechanisms

BACKGROUND

Skeletal muscle function and mass continuously decrease during aging. Most studies target limb muscles owing to their direct impact on mobility and falls risk. The diaphragm (DIA), also a type of skeletal muscle with different phenotype, has received less attention. Comparative research of the DIA and limb muscles can reveal their distinct aging characteristics. Critically, the potential endogenous anti-aging mechanisms of DIA that may provide new insights into the mechanisms of sarcopenia in limb muscles remain scarce.

METHODS

Treadmill and grip tests assessed limb muscle function, while a lung function system evaluated respiratory function in both adult (6-month-old) and old (22-month-old) mice. Histological assessments evaluated muscle mass in both the DIA and tibialis anterior (TA). Transcriptome sequencing identified differentially expressed genes (DEGs) between the DIA and TA with aging. Adeno-associated virus (AAV)-encoding short hairpin (sh) RNA targeting gene was injected into adult mice's TA muscles to knockdown target gene level in TA, and AAV-gene was injected into old mice's TA to overexpress target gene level.

RESULTS

Old mice displayed significantly reduced running distance (p = 0.0026), maximal speed (p = 0.0019), time to exhaustion (p = 0.0033) and grip strength (p = 0.0055) compared with adult mice, alongside TA's weight loss, decreased myofibre cross-sectional area (CSA) and autophagy deficiency. However, lung function indicators (respiratory rate, tidal volume, minute ventilation volume, forced vital capacity and ratio of forced expiratory volume in 100 or 200 ms to forced vital capacity), as well as DIA weight and morphology remained stable in old mice. Transcriptional analysis revealed 61 DEGs, with significant upregulation or downregulation observed in TA, but without changes in DIA during aging. Smox (spermine oxidase) is one of the DEGs, responsible for catalysing the conversion of spermine to spermidine. It was reported that in muscle atrophy models such as limb immobilisation, fasting and denervation, Smox's levels are positively correlated with muscle mass and function. Additionally, an increase in Smox also promotes mitochondrial biogenesis. In our study, AAV-shSmox adult mice decreased running distance, speed and time, myofibre CSA alongside mitochondrial function, compared with controls. In contrast, old mice with Smox overexpression showed enhanced mitochondrial function.

CONCLUSIONS

In conclusion, this study reveals aging diversities of TA and DIA, explores the sarcopenia of limb muscles based on the anti-aging properties of DIA, which offers a novel perspective on limb sarcopenia. Our findings suggest Smox as a potential target for developing strategies to mitigate sarcopenia progression.

Advances and insights for DKK3 in non-cancerous diseases: a systematic review

This review delves into the role of Dickkopf-3 (DKK3), a secreted glycoprotein and member of the Dickkopf family, in non-malignant diseases. DKK3 is particularly known for its regulatory effects on the Wnt signaling pathway, a critical mediator in various biological processes including cell proliferation, differentiation, and migration. Our review highlights DKK3's influence in disorders of the cardiovascular, respiratory, renal, and muscular systems, where it contributes to disease progression by modulating these key biological processes. As an emerging biomarker, DKK3's levels have been found to correlate with various disease states, underscoring its potential diagnostic and therapeutic implications.

Pore-Forming Protein LIN-24 Enhances Starvation Resilience in Caenorhabditis elegans by Modulating Lipid Metabolism and Mitochondrial Dynamics

The ability to survive starvation is a critical evolutionary adaptation, yet the molecular mechanisms underlying this capability remain incompletely understood. Pore-forming proteins (PFPs) are typically associated with immune defense, where they disturb the membranes of target cells. However, the role of PFPs in non-immune functions, particularly in metabolic and structural adaptations to starvation, is less explored. Here, we investigate the aerolysin-like PFP LIN-24 in Caenorhabditis elegans and uncover its novel function in enhancing starvation resistance. We found that LIN-24 expression is upregulated during starvation, leading to increased expression of the lipase-encoding gene lipl-3. This upregulation accelerates the mobilization and degradation of lipid stores, thereby sustaining energy levels. Additionally, LIN-24 overexpression significantly preserves muscle integrity, as evidenced by the maintenance of muscle structure compared to wild-type worms. Furthermore, we demonstrate that LIN-24 induces the formation of donut-shaped mitochondria, a structural change likely aimed at reducing ATP production to conserve energy during prolonged nutrient deprivation. This mitochondrial remodeling depends on genes involved in mitochondrial dynamics, including mff-1, mff-2, drp-1, and clk-1. Collectively, these findings expand our understanding of PFPs, demonstrating their multifaceted role in stress resistance beyond immune defense. LIN-24's involvement in regulating metabolism, preserving muscle structure, and remodeling mitochondria highlights its crucial role in the adaptive response to starvation, offering novel insights into the evolution of stress resistance mechanisms and potential therapeutic targets for conditions related to muscle preservation and metabolic regulation.

DKK3 as a diagnostic marker and potential therapeutic target for sarcopenia in chronic obstructive pulmonary disease

Sarcopenia, characterized by the progressive loss of muscle mass and function, significantly affects patients with chronic obstructive pulmonary disease (COPD) and worsens their morbidity and mortality. The pathogenesis of muscle atrophy in patients with COPD involves complex mechanisms, including protein imbalance and mitochondrial dysfunction, which have been identified in the muscle tissues of patients with COPD. DKK3 (Dickkopf-3) is a secreted glycoprotein involved in the process of myogenesis. However, the role of DKK3 in the regulation of muscle mass is largely unknown. This study investigated the role of DKK3 in COPD-related sarcopenia. DKK3 was found to be overexpressed in cigarette smoking-induced muscle atrophy and in patients with COPD. Importantly, plasma DKK3 levels in COPD patients with sarcopenia were significantly higher than those without sarcopenia, and plasma DKK3 levels could effectively predict sarcopenia in patients with COPD based on two independent cohorts. Mechanistically, DKK3 is secreted by skeletal muscle cells that acts in autocrine and paracrine manners and interacts with the cell surface-activated receptor cytoskeleton-associated protein 4 (CKAP4) to induce mitochondrial dysfunction and myotube atrophy. The inhibition of DKK3 by genetic ablation prevented cigarette smoking-induced skeletal muscle dysfunction. These results suggest that DKK3 is a potential target for the diagnosis and treatment of sarcopenia in patients with COPD.

Therapeutic targeting of GDF11 in muscle atrophy: Insights and strategies

The exploration of novel therapeutic avenues for skeletal muscle atrophy is imperative due to its significant health impact. Recent studies have spotlighted growth differentiation factor 11 (GDF11), a TGFβ superfamily member, for its rejuvenating role in reversing age-related tissue dysfunction. This review synthesizes current findings on GDF11, elucidating its distinct biological functions and the ongoing debates regarding its efficacy in muscle homeostasis. By addressing discrepancies in current research outcomes and its ambiguous role due to its homological identity to myostatin, a negative regulator of muscle mass, this review aims to clarify the role of GDF11 in muscle homeostasis and its potential as a therapeutic target for muscle atrophy. Through a thorough examination of GDF11's mechanisms and effects, this review provides insights that could pave the way for innovative treatments for muscle atrophy, emphasizing the need and strategies to boost endogenous GDF11 levels for therapeutic potential.

Wnt/β-catenin signaling pathway as an important mediator in muscle and bone crosstalk: A systematic review

Background

The interaction between muscle and bone is shown to be clinically important but the underlying mechanisms are largely unknown. The canonical Wnt/β-catenin signaling pathway is reported to be involved in muscle-bone crosstalk, but its detailed function remains unclear. This systematic review aims to investigate and elucidate the role of the Wnt/β-catenin signaling pathways in muscle-bone crosstalk.

Methods

We conducted a literature search on the Web of Science, PubMed, EBSCO and Embase with keywords "Wnt*", "bone*" and "muscle*". A systematic review was completed according to the guideline of preferred reporting items of systematic reviews and meta-analyses (PRISMA). Data synthesis included species (human, animal or cell type used), treatments involved, outcome measures and key findings with respect to Wnts.

Results

Seventeen papers were published from 2007 to 2021 and were extracted from a total of 1529 search results in the databases of Web of Science (468 papers), PubMed (457 papers), EBSCO (371) and Embase (233). 12 Wnt family members were investigated in the papers, including Wnt1, Wnt2, Wnt2b, Wnt3a, Wnt4, Wnt5a, Wnt8a, Wnt8b, Wnt9a, Wnt10a, Wnt10b and Wnt16. Many studies showed that muscles were able to increase or decrease osteogenesis of bone, while bone increased myogenesis of muscle through Wnt/β-catenin signaling pathways. Wnt3a, Wnt4 and Wnt10b were shown to play important roles in the crosstalk between muscle and bone.

Conclusions

Wnt3a, Wnt4 and Wnt10b are found to play important mediatory roles in muscle-bone crosstalk. The role of Wnt4 was mostly found to regulate muscle from the bone side. Whilst the role of Wnt10b during muscle ageing was proposed, current evidence is insufficient to clarify the specific role of Wnt/β-catenin signaling in the interplay between sarcopenia and osteoporosis. More future studies are required to investigate the exact regulatory roles of Wnts in muscle-bone crosstalk in musculoskeletal disease models such as sarcopenia and osteoporosis.

Translational potential of this article

The systematic review provides an extensive overview to reveal the roles of Wnt/β-catenin signaling pathways in muscle-bone crosstalk. These results provide novel research directions to further understand the underlying mechanism of sarcopenia, osteoporosis, and their crosstalk, finally helping the future development of new therapeutic interventions.

Transcriptome profiling of fast/glycolytic and slow/oxidative muscle fibers in aging and obesity

Aging and obesity pose significant threats to public health and are major contributors to muscle atrophy. The trends in muscle fiber types under these conditions and the transcriptional differences between different muscle fiber types remain unclear. Here, we demonstrate distinct responses of fast/glycolytic fibers and slow/oxidative fibers to aging and obesity. We found that in muscles dominated by oxidative fibers, the proportion of oxidative fibers remains unchanged during aging and obesity. However, in muscles dominated by glycolytic fibers, despite the low content of oxidative fibers, a significant decrease in proportion of oxidative fibers was observed. Consistently, our study uncovered that during aging and obesity, fast/glycolytic fibers specifically increased the expression of genes associated with muscle atrophy and inflammation, including Dkk3, Ccl8, Cxcl10, Cxcl13, Fbxo32, Depp1, and Chac1, while slow/oxidative fibers exhibit elevated expression of antioxidant protein Nqo-1 and downregulation of Tfrc. Additionally, we noted substantial differences in the expression of calcium-related signaling pathways between fast/glycolytic fibers and slow/oxidative fibers in response to aging and obesity. Treatment with a calcium channel inhibitor thapsigargin significantly increased the abundance of oxidative fibers. Our study provides additional evidence to support the transcriptomic differences in muscle fiber types under pathophysiological conditions, thereby establishing a theoretical basis for modulating muscle fiber types in disease treatment.

Myokines: metabolic regulation in obesity and type 2 diabetes

Skeletal muscle plays a vital role in the regulation of systemic metabolism, partly through its secretion of endocrine factors which are collectively known as myokines. Altered myokine levels are associated with metabolic diseases, such as type 2 diabetes (T2D). The significance of interorgan crosstalk, particularly through myokines, has emerged as a fundamental aspect of nutrient and energy homeostasis. However, a comprehensive understanding of myokine biology in the setting of obesity and T2D remains a major challenge. In this review, we discuss the regulation and biological functions of key myokines that have been extensively studied during the past two decades, namely interleukin 6 (IL-6), irisin, myostatin (MSTN), growth differentiation factor 11 (GDF11), fibroblast growth factor 21 (FGF21), apelin, brain-derived neurotrophic factor (BDNF), meteorin-like (Metrnl), secreted protein acidic and rich in cysteine (SPARC), β-aminoisobutyric acid (BAIBA), Musclin, and Dickkopf 3 (Dkk3). Related to these, we detail the role of exercise in myokine expression and secretion together with their contributions to metabolic physiology and disease. Despite significant advancements in myokine research, many myokines remain challenging to measure accurately and investigate thoroughly. Hence, new research techniques and detection methods should be developed and rigorously tested. Therefore, developing a comprehensive perspective on myokine biology is crucial, as this will likely offer new insights into the pathophysiological mechanisms underlying obesity and T2D and may reveal novel targets for therapeutic interventions.

Divergent Regulatory Roles of Transcriptional Variants of the Chicken LDB3 Gene in Muscle Shaping

LIM domain binding 3 (LDB3) serves as a striated muscle-specific Z-band alternatively spliced protein that plays an important role in mammalian skeletal muscle development, but its regulatory role and molecular mechanism in avian muscle development are still unclear. In this study, we reanalyzed RNA sequencing data sets of 1415 samples from 21 chicken tissues published in the NCBI GEO database. First, three variants (LDB3-X, LDB3-XN1, and LDB3-XN2) generated by alternative splicing of the LDB3 gene were identified in chicken skeletal muscle, among which LDB3-XN1 and LDB3-XN2 are novel variants. LDB3-X and LDB3-XN1 are derived from exon skipping in chicken skeletal muscle at the E18-D7 stage and share three LIM domains, but LDB3-XN2 lacks a LIM domain. Our results preliminarily suggest that the formation of three variants of LDB3 is regulated by RBM20. The three splice isomers have divergent functions in skeletal muscle according to in vitro and in vivo assays. Finally, we identified the mechanism by which different variants play different roles through interactions with IGF2BP1 and MYHC, which promote the proliferation and differentiation of chicken myoblasts, in turn regulating chicken myogenesis. In conclusion, this study revealed the divergent roles of three LDB3 variants in chicken myogenesis and muscle remodeling and demonstrated their regulatory mechanism through protein-protein interactions.

Microbiota-derived 3-phenylpropionic acid promotes myotube hypertrophy by Foxo3/NAD+ signaling pathway

BACKGROUND

Gut microbiota and their metabolites play a regulatory role in skeletal muscle growth and development, which be known as gut-muscle axis. 3-phenylpropionic acid (3-PPA), a metabolite produced by colonic microorganisms from phenylalanine in the gut, presents in large quantities in the blood circulation. But few study revealed its function in skeletal muscle development.

RESULTS

Here, we demonstrated the beneficial effects of 3-PPA on muscle mass increase and myotubes hypertrophy both in vivo and vitro. Further, we discovered the 3-PPA effectively inhibited protein degradation and promoted protein acetylation in C2C12 and chick embryo primary skeletal muscle myotubes. Mechanistically, we supported that 3-PPA reduced NAD+ synthesis and subsequently suppressed tricarboxylic acid cycle and the mRNA expression of SIRT1/3, thus promoting the acetylation of total protein and Foxo3. Moreover, 3-PPA may inhibit Foxo3 activity by directly binding.

CONCLUSIONS

This study firstly revealed the effect of 3-PPA on skeletal muscle growth and development, and newly discovered the interaction between 3-PPA and Foxo3/NAD+ which mechanically promote myotubes hypertrophy. These results expand new understanding for the regulation of gut microbiota metabolites on skeletal muscle growth and development.

CREG1 deficiency impaired myoblast differentiation and skeletal muscle regeneration

BACKGROUND

CREG1 (cellular repressor of E1A-stimulated genes 1) is a protein involved in cellular differentiation and homeostasis regulation. However, its role in skeletal muscle satellite cells differentiation and muscle regeneration is poorly understood. This study aimed to investigate the role of CREG1 in myogenesis and muscle regeneration.

METHODS

RNA sequencing data (GSE8479) was analysed from the Gene Expression Omnibus database (GEO, https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi). We generated Creg1 knockdown and skeletal muscle satellite cells specific Creg1 overexpression mice mediated by adeno-associated virus serotype 9 (AAV9), skeletal muscle mature myofibre Creg1 knockout mice (myoblast/Creg1MKO), and control mice Creg1flox/flox (Creg1fl/fl) as in vivo models. The mice were injected into tibialis anterior (TA) muscle with 100 μL of 10 μM cardiotoxin to establish a muscle regeneration model. Creg1fl/fl and Creg1MKO mice were treated with AAV-sh-C-Cbl (2 × 1010 genomic copies/mouse) to silence C-Cbl in the TA muscle. 293T and C2C12 cells were transfected with plasmids using lipofectamine RNAi MAX in vitro. Mass spectrometry analyses and RNA sequencing transcriptomic assay were performed.

RESULTS

We analysed the transcriptional profiles of the skeletal muscle biopsies from healthy older (N = 25) and younger (N = 26) adult men and women in GSE8479 database, and the results showed that Creg1 was associated with human sarcopenia. We found that Creg1 knockdown mice regenerated less newly formed fibres in response to cardiotoxin injection (~30% reduction, P < 0.01); however, muscle satellite cells specific Creg1 overexpression mice regenerated more newly formed fibres (~20% increase, P < 0.05). AMPKa1 is known as a key mediator in the muscle regeneration process. Our results revealed that CREG1 deficiency inhibited AMPKa1 signalling through C-CBL E3-ubiquitin ligase-mediated AMPKa1 degradation (P < 0.01). C-CBL-mediated AMPKa1 ubiquitination was attributed to the K48-linked polyubiquitination of AMPKa1 at K396 and that the modification played an important role in the regulation of AMPKa1 protein stability. We also found that Creg1MKO mice regenerated less newly formed fibres compared with Creg1fl/fl mice (~30% reduction, P < 0.01). RNA-seq analysis showed that CREG1 deletion in impaired muscles led to the upregulation of inflammation and DKK3 expression. The TA muscles of Creg1MKO mice were injected with AAV-vector or AAV-shC-Cbl, silencing C-CBL (P < 0.01) in the skeletal muscles of Creg1MKO mice significantly improved muscle regeneration induced by CTX injury (P < 0.01).

CONCLUSIONS

Our findings suggest that CREG1 may be a potential therapeutic target for skeletal muscle regeneration.

Asynchronous Pattern of MAPKs' Activity during Aging of Different Tissues and of Distinct Types of Skeletal Muscle

The MAPK p38α was proposed to be a prominent promoter of skeletal muscle aging. The skeletal muscle tissue is composed of various muscle types, and it is not known if p38α is associated with aging in all of them. It is also not known if p38α is associated with aging of other tissues. JNK and ERK were also proposed to be associated with aging of several tissues. Nevertheless, the pattern of p38α, JNK, and ERK activity during aging was not documented. Here, we documented the levels of phosphorylated/active p38α, Erk1/2, and JNKs in several organs as well as the soleus, tibialis anterior, quadriceps, gastrocnemius, and EDL muscles of 1-, 3-, 6-, 13-, 18-, and 24-month-old mice. We report that in most tissues and skeletal muscles, the MAPKs' activity does not change in the course of aging. In most tissues and muscles, p38α is in fact active at younger ages. The quadriceps and the lungs are exceptions, where p38α is significantly active only in mice 13 months old or older. Curiously, levels of active JNK and ERKs are also elevated in aged lungs and quadriceps. RNA-seq analysis of the quadriceps during aging revealed downregulation of proteins related to the extra-cellular matrix (ECM) and ERK signaling. A panel of mRNAs encoding cell cycle inhibitors and senescence-associated proteins, considered to be aging markers, was not found to be elevated. It seems that the pattern of MAPKs' activation in aging, as well as expression of known 'aging' components, are tissue- and muscle type-specific, supporting a notion that the process of aging is tissue- and even cell-specific.

Functional force stimulation alters motor neuron discharge patterns

Introduction

Beneficial effects have been observed for mechanical vibration stimulation (MVS), which are mainly attributed to tonic vibration reflex (TVR). TVR is reported to elicit synchronized motor unit activation during locally applied vibration. Similar effects are also observed in a novel vibration system referred to as functional force stimulation (FFS). However, the manifestation of TVR in FFS is doubted due to the use of global electromyography (EMG) features in previous analysis. Our study aims to investigate the effects of FFS on motor unit discharge patterns of the human biceps brachii by analyzing the motor unit spike trains decoded from the high-density surface EMG.

Methods

Eighteen healthy subjects volunteered in FFS training with different amplitudes and frequencies. One hundred and twenty-eight channel surface EMG was recorded from the biceps brachii and then decoded after motion-artifact removal. The discharge timings were extracted and the coherence between different motor unit spike trains was calculated to quantify synchronized activation.

Results and discussion

Significant synchronization within the vibration cycle and/or its integer multiples is observed for all FFS trials, which increases with increased FFS amplitude. Our results reveal the basic physiological mechanism involved in FFS, providing a theoretical foundation for analyzing and introducing FFS into clinical rehabilitation programs.

Pharmacologic Inhibition of Myostatin With a Myostatin Antibody Improves the Skeletal Muscle and Bone Phenotype of Male Insulin-Deficient Diabetic Mice

Type 1 diabetes (T1D) is associated with low bone and muscle mass, increased fracture risk, and impaired skeletal muscle function. Myostatin, a myokine that is systemically elevated in humans with T1D, negatively regulates muscle mass and bone formation. We investigated whether pharmacologic myostatin inhibition in a mouse model of insulin-deficient, streptozotocin (STZ)-induced diabetes is protective for bone and skeletal muscle. DBA/2J male mice were injected with low-dose STZ (diabetic) or vehicle (non-diabetic). Subsequently, insulin or palmitate Linbits were implanted and myostatin (REGN647-MyoAb) or control (REGN1945-ConAb) antibody was administered for 8 weeks. Body composition and contractile muscle function were assessed in vivo. Systemic myostatin, P1NP, CTX-I, and glycated hemoglobin (HbA1c) were quantified, and gastrocnemii were weighed and analyzed for muscle fiber composition and gene expression of selected genes. Cortical and trabecular parameters were analyzed (micro-computed tomography evaluations of femur) and cortical bone strength was assessed (three-point bending test of femur diaphysis). In diabetic mice, the combination of insulin/MyoAb treatment resulted in significantly higher lean mass and gastrocnemius weight compared with MyoAb or insulin treatment alone. Similarly, higher raw torque was observed in skeletal muscle of insulin/MyoAb-treated diabetic mice compared with MyoAb or insulin treatment. Additionally, muscle fiber cross-sectional area (CSA) was lower with diabetes and the combination treatment with insulin/MyoAb significantly improved CSA in type II fibers. Insulin, MyoAb, or insulin/MyoAb treatment improved several parameters of trabecular architecture (eg, bone volume fraction [BV/TV], trabecular connectivity density [Conn.D]) and cortical structure (eg, cortical bone area [Ct. Ar.], minimum moment of inertia [Imin]) in diabetic mice. Lastly, cortical bone biomechanical properties (stiffness and yield force) were also improved with insulin or MyoAb treatment. In conclusion, pharmacologic myostatin inhibition is beneficial for muscle mass, muscle function, and bone properties in this mouse model of T1D and its effects are both independent and additive to the positive effects of insulin. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Advances in research on cell models for skeletal muscle atrophy

Skeletal muscle, the largest organ in the human body, plays a crucial role in supporting and defending the body and is essential for movement. It also participates in regulating the processes of protein synthesis and degradation. Inhibition of protein synthesis and activation of degradation metabolism can both lead to the development of skeletal muscle atrophy, a pathological condition characterized by a decrease in muscle mass and fiber size. Many physiological and pathological conditions can cause a decline in muscle mass, but the underlying mechanisms of its pathogenesis remain incompletely understood, and the selection of treatment strategies and efficacy evaluations vary. Moreover, the early symptoms of this condition are often not apparent, making it easily overlooked in clinical practice. Therefore, it is necessary to develop and use cell models to understand the etiology and influencing factors of skeletal muscle atrophy. In this review, we summarize the methods used to construct skeletal muscle cell models, including hormone, inflammation, cachexia, genetic engineering, drug, and physicochemical models. We also analyze, compare, and evaluate the various construction and assessment methods.

An efficient protocol for studying human pluripotent stem cell-derived myotube senescence

Sarcopenia, an age-related skeletal muscle condition characterized by a progressive decline in muscle mass and function, is linked to increased vulnerability, a higher likelihood of falls, and higher mortality rates in older individuals. A comprehensive understanding of the intricate mechanisms driving skeletal muscle aging is of great significance in both scientific and clinical fields. Consequently, myotube models that facilitate studying regulatory mechanisms underlying skeletal muscle aging are important tools required to advance intervention strategies against skeletal muscle aging and associated disorders. Here, we provide a detailed protocol to generate human pluripotent stem cells-derived myotubes and describe their applications in aging studies, as well as a troubleshooting for potential problems. Overall, this protocol serves as a valuable methodological reference for exploring the role and mechanism of genes involved in skeletal muscle aging.

Is the myonuclear domain ceiling hypothesis dead?

Muscle fibres are multinuclear cells, and the cytoplasmic territory where a single myonucleus controls transcriptional activity is called the myonuclear domain (MND). MND size shows flexibility during muscle hypertrophy. The MND ceiling hypothesis states that hypertrophy results in the expansion of MND size to an upper limit or MND ceiling, beyond which additional myonuclei via activation of satellite cells are required to support further growth. However, the debate about the MND ceiling hypothesis is far from settled, and various studies show conflicting results about the existence or otherwise of MND ceiling in hypertrophy. The aim of this review is to summarise the literature about the MND ceiling in various settings of hypertrophy and discuss the possible factors contributing to a discrepancy in the literature. We conclude by describing the physiological and clinical significance of the MND ceiling limit in the muscle adaptation process in various physiological and pathological conditions.

Biomarkers of aging

Aging biomarkers are a combination of biological parameters to (i) assess age-related changes, (ii) track the physiological aging process, and (iii) predict the transition into a pathological status. Although a broad spectrum of aging biomarkers has been developed, their potential uses and limitations remain poorly characterized. An immediate goal of biomarkers is to help us answer the following three fundamental questions in aging research: How old are we? Why do we get old? And how can we age slower? This review aims to address this need. Here, we summarize our current knowledge of biomarkers developed for cellular, organ, and organismal levels of aging, comprising six pillars: physiological characteristics, medical imaging, histological features, cellular alterations, molecular changes, and secretory factors. To fulfill all these requisites, we propose that aging biomarkers should qualify for being specific, systemic, and clinically relevant.

Insights into Pathogenesis, Nutritional and Drug Approach in Sarcopenia: A Systematic Review

Sarcopenia is a multifactorial condition related to the loss of muscle mass and strength due to aging, eating habits, physical inactivity, or even caused by another disease. Affected individuals have a higher risk of falls and may be associated with heart disease, respiratory diseases, cognitive impairment, and consequently an increased risk of hospitalization, in addition to causing an economic impact due to the high cost of care during the stay in hospitals. The standardization of appropriate treatment for patients with sarcopenia that could help reduce pathology-related morbidity is necessary. For these reasons, this study aimed to perform a systematic review of the role of nutrition and drugs that could ameliorate the health and quality of life of sarcopenic patients and PRISMA guidelines were followed. Lifestyle interventions have shown a profound impact on sarcopenia treatment but using supplements and different drugs can also impact skeletal muscle maintenance. Creatine, leucine, branched-chain amino acids, omega 3, and vitamin D can show benefits. Although with controversial results, medications such as Metformin, GLP-1, losartan, statin, growth hormone, and dipeptidyl peptidase 4 inhibitors have also been considered and can alter the sarcopenic's metabolic parameters, protect against cardiovascular diseases and outcomes, while protecting muscles.

The landscape of aging

Aging is characterized by a progressive deterioration of physiological integrity, leading to impaired functional ability and ultimately increased susceptibility to death. It is a major risk factor for chronic human diseases, including cardiovascular disease, diabetes, neurological degeneration, and cancer. Therefore, the growing emphasis on "healthy aging" raises a series of important questions in life and social sciences. In recent years, there has been unprecedented progress in aging research, particularly the discovery that the rate of aging is at least partly controlled by evolutionarily conserved genetic pathways and biological processes. In an attempt to bring full-fledged understanding to both the aging process and age-associated diseases, we review the descriptive, conceptual, and interventive aspects of the landscape of aging composed of a number of layers at the cellular, tissue, organ, organ system, and organismal levels.

Wnt Signaling and Aging of the Gastrointestinal Tract

Aging is considered a risk factor for various diseases including cancers. In this aging society, there is an urgent need to clarify the molecular mechanisms involved in aging. Wnt signaling has been shown to play a crucial role in the maintenance and differentiation of tissue stem cells, and intensive studies have elucidated its pivotal role in the aging of neural and muscle stem cells. However, until recently, such studies on the gastrointestinal tract have been limited. In this review, we discuss recent advances in the study of the role of Wnt signaling in the aging of the gastrointestinal tract and aging-related carcinogenesis.

Crystallographic mining of ASK1 regulators to unravel the intricate PPI interfaces for the discovery of small molecule

Protein seldom performs biological activities in isolation. Understanding the protein–protein interactions’ physical rewiring in response to pathological conditions or pathogen infection can help advance our comprehension of disease etiology, progression, and pathogenesis, which allow us to explore the alternate route to control the regulation of key target interactions, timely and effectively. Nonalcoholic steatohepatitis (NASH) is now a global public health problem exacerbated due to the lack of appropriate treatments. The most advanced anti-NASH lead compound (selonsertib) is withdrawn, though it is able to inhibit its target Apoptosis signal-regulating kinase 1 (ASK1) completely, indicating the necessity to explore alternate routes rather than complete inhibition. Understanding the interaction fingerprints of endogenous regulators at the molecular level that underpin disease formation and progression may spur the rationale of designing therapeutic strategies. Based on our analysis and thorough literature survey of the various key regulators and PTMs, the current review emphasizes PPI-based drug discovery’s relevance for NASH conditions. The lack of structural detail (interface sites) of ASK1 and its regulators makes it challenging to characterize the PPI interfaces. This review summarizes key regulators interaction fingerprinting of ASK1, which can be explored further to restore the homeostasis from its hyperactive states for therapeutics intervention against NASH.

A multistrain probiotic reduces sarcopenia by modulating Wnt signaling biomarkers in patients with chronic heart failure

BACKGROUND

The muscle decline due to aging, called sarcopenia and functional compromise, are common occurrences in patients with chronic heart failure (CHF). Intestinal dysbiosis and the alterations in Wnt signaling may partly account for these findings. We investigated the effects of a multistrain probiotic on Wnt signaling biomarkers and their associations with sarcopenia and functional capacity in CHF patients.

METHODS

The CHF patients were randomized into placebo (n = 48) and probiotic (n = 44) groups for 12 weeks. We measured circulating markers of intestinal permeability (zonulin) and Wnt signaling (dickkopf-1, Dkk-1; dickkopf-3, Dkk-3), and sterol regulatory element-binding protein-1 (SREBP1), handgrip strength (HGS), and short physical performance battery (SPPB) scores at baseline and after probiotics treatment.

RESULTS

Probiotics treatment improved HGS, gait speed, and plasma Dkk-1, and reduced plasma zonulin, Dkk-3, and SREBP1 in CHF patients (all p < 0.05). Among sarcopenia indexes, HGS showed robust correlations with the three Wnt biomarkers (all p < 0.05). Probiotic treatment also improved the SPPB scores in CHF patients, which were strongly correlated with Dkk-3, followed by Dkk-1, and SREBP1 (all p < 0.05). SREBP1 and Dkk-3 demonstrated significant potential in diagnosing sarcopenia in CHF patients. Probiotics also reduced the plasma markers of inflammation and oxidative stress in CHF patients.

CONCLUSION

The multistrain probiotic reduces sarcopenia and improves functional capacity in CHF patients by modulating Wnt signaling.

Msi2-mediated MiR7a-1 processing repression promotes myogenesis

BACKGROUND

Most of the microRNAs (MiRs) involved in myogenesis are transcriptional regulated. The role of MiR biogenesis in myogenesis has not been characterized yet. RNA-binding protein Musashi 2 (Msi2) is considered to be one of the major drivers for oncogenesis and stem cell proliferation. The functions of Msi2 in myogenesis have not been explored yet. We sought to investigate Msi2-regulated biogenesis of MiRs in myogenesis and muscle stem cell (MuSC) ageing.

METHODS

We detected the expression of Msi2 in MuSCs and differentiated myotubes by quantitative reverse transcription PCR (RT-qPCR) and western blot. Msi2-binding partner human antigen R (HuR) was identified by immunoprecipitation followed by mass spectrometry analysis. The cooperative binding of Msi2 and HuR on MiR7a-1 was analysed by RNA immunoprecipitation and electrophoresis mobility shift assays. The inhibition of the processing of pri-MiR7a-1 mediated by Msi2 and HuR was shown by Msi2 and HuR knockdown. Immunofluorescent staining, RT-qPCR and immunoblotting were used to characterize the function of MiR7a-1 in myogenesis. Msi2 and HuR up-regulate cryptochrome circadian regulator 2 (Cry2) via MiR7a-1 was confirmed by the luciferase assay and western blot. The post-transcriptional regulatory cascade was further confirmed by RNAi and overexpressing of Msi2 and HuR in MuSCs, and the in vivo function was characterized by histopathological and molecular biological methods in Msi2 knockout mice.

RESULTS

We identified a post-transcription regulatory cascade governed by a pair of RNA-binding proteins Msi2 and HuR. Msi2 is enriched in differentiated muscle cells and promotes MuSC differentiation despite its pro-proliferation functions in other cell types. Msi2 works synergistically with another RNA-binding protein HuR to repress the biogenesis of MiR7a-1 in an Msi2 dose-dependent manner to regulate the translation of the key component of the circadian core oscillator complex Cry2. Down-regulation of Cry2 (0.6-fold, vs. control, P < 0.05) mediated by MiR7a-1 represses MuSC differentiation. The disruption of this cascade leads to differentiation defects of MuSCs. In aged muscles, Msi2 (0.3-fold, vs. control, P < 0.01) expression declined, and the Cry2 protein level also decreases (0.5-fold, vs. control, P < 0.05), suggesting that the disruption of the Msi2-mediated post-transcriptional regulatory cascade could attribute to the declined ability of muscle regeneration in aged skeletal muscle.

CONCLUSIONS

Our findings have identified a new post-transcriptional cascade regulating myogenesis. The cascade is disrupted in skeletal muscle ageing, which leads to declined muscle regeneration ability.

Genome-Wide Epigenomic Analyses in Patients With Nociceptive and Neuropathic Chronic Pain Subtypes Reveals Alterations in Methylation of Genes Involved in the Neuro-Musculoskeletal System

Nociceptive pain involves the activation of nociceptors without damage to the nervous system, whereas neuropathic pain is related to an alteration in the central or peripheral nervous system. Chronic pain itself and the transition from acute to chronic pain may be epigenetically controlled. In this cross-sectional study, a genome-wide DNA methylation analysis was performed using the blood DNA reduced representation bisulfite sequencing (RRBS) technique. Three prospective cohorts including 20 healthy controls (CTL), 18 patients with chronic nociceptive pain (NOCI), and 19 patients with chronic neuropathic pain (NEURO) were compared at both the single CpG and differentially methylated region (DMR) levels. Genes with DMRs were seen in the NOCI and NEURO groups belonged to the neuro-musculoskeletal system and differed between NOCI and NEURO patients. Our results demonstrate that the epigenetic disturbances accompanying nociceptive pain are very different from those accompanying neuropathic pain. In the former, among others, the epigenetic disturbance observed would affect the function of the opioid analgesic system, whereas in the latter it would affect that of the GABAergic reward system. This study presents biological findings that help to characterize NOCI- and NEURO-affected pathways and opens the possibility of developing epigenetic diagnostic assays. PERSPECTIVE: Our results help to explain the various biological pathways modifications underlying the different clinical manifestations of nociceptive and neuropathic pains. Furthermore, the new targets identified in our study might help to discover more specific treatments for nociceptive or neuropathic pains.

The protein inputs of an ultra-predictive aging clock represent viable anti-aging drug targets

Machine learning models capable of predicting age given a set of inputs are referred to as aging clocks. We recently developed an aging clock that utilizes 491 plasma protein inputs, has an exceptional accuracy, and is capable of measuring biological age. Here, we demonstrate that this clock is extremely predictive (r = 0.95) when used to measure age in a novel plasma proteomic dataset derived from 370 human subjects aged 18-69 years. Over-representation analyses of the proteins that make up this clock in the Gene Ontology and Reactome databases predominantly implicated innate and adaptive immune system processes. Immunological drugs and various age-related diseases were enriched in the DrugBank and GLAD4U databases. By performing an extensive literature review, we find that at least 269 (54.8 %) of these inputs regulate lifespan and/or induce changes relevant to age-related disease when manipulated in an animal model. We also show that, in a large plasma proteomic dataset, the majority (57.2 %) of measurable clock proteins significantly change their expression level with human age. Different subsets of proteins were overlapped with distinct epigenetic, transcriptomic, and proteomic aging clocks. These findings indicate that the inputs of this age predictor likely represent a rich source of anti-aging drug targets.

Transcriptome Analysis of Differentially Expressed mRNA Related to Pigeon Muscle Development

The mechanisms behind the gene expression and regulation that modulate the development and growth of pigeon skeletal muscle remain largely unknown. In this study, we performed gene expression analysis on skeletal muscle samples at different developmental and growth stages using RNA sequencing (RNA-Seq). The differentially expressed genes (DEGs) were identified using edgeR software. Weighted gene co-expression network analysis (WGCNA) was used to identify the gene modules related to the growth and development of pigeon skeletal muscle based on DEGs. A total of 11,311 DEGs were identified. WGCNA aggregated 11,311 DEGs into 12 modules. Black and brown modules were significantly correlated with the 1st and 10th day of skeletal muscle growth, while turquoise and cyan modules were significantly correlated with the 8th and 13th days of skeletal muscle embryonic development. Four mRNA-mRNA regulatory networks corresponding to the four significant modules were constructed and visualised using Cytoscape software. Twenty candidate mRNAs were identified based on their connectivity degrees in the networks, including Abca8b, TCONS-00004461, VWF, OGDH, TGIF1, DKK3, Gfpt1 and RFC5, etc. A KEGG pathway enrichment analysis showed that many pathways were related to the growth and development of pigeon skeletal muscle, including PI3K/AKT/mTOR, AMPK, FAK, and thyroid hormone pathways. Five differentially expressed genes (LAST2, MYPN, DKK3, B4GALT6 and OGDH) in the network were selected, and their expression patterns were quantified by qRT-PCR. The results were consistent with our sequencing results. These findings could enhance our understanding of the gene expression and regulation in the development and growth of pigeon muscle.

miR-129-5p Promotes Osteogenic Differentiation of BMSCs and Bone Regeneration via Repressing Dkk3

Objective

Accumulating evidence indicates that microRNAs (miRNAs) play crucial roles in osteogenic differentiation. However, the associated mechanisms remain elusive. This paper is aimed at exploring the role of miR-129-5p in regulating bone marrow mesenchymal stem cell (BMSC) differentiation and bone regeneration in vivo and in vitro.

Methods

BMSCs were transduced by miR-129-5p mimic, miR-129-5p inhibitor, and negative control lentivirus. The ability of BMSC differentiation to osteoblast was tested by alkaline phosphatase (ALP) and alizarin red staining (ARS). The expression of osteogenic genes (Runx2, Bmp2, and OCN) was examined via quantitative RT-PCR and western blot. A mouse model of calvaria defect was investigated by Micro-CT, immunohistochemistry, and histological examination. The luciferase reporter gene assay was performed to confirm the binding between Dkk3 and miR-129-5p. For the transfection experiments, lipofectamine 3000 was used to transfect pcDNA-Dkk3 into BMSCs to overexpress Dkk3. Coimmunoprecipitation and immunofluorescent localization assay were included for exploring the role of Dkk3 and β-catenin.

Results

miR-129-5p was induced in BMSCs and MSC cell line C3H10T1/2 cells under osteogenic medium. Overexpression of miR-129-5p significantly promoted osteogenic differentiation of BMSCs in vitro. Moreover, BMSCs transduced with miR-129-5p mimic exhibited better bone regeneration compared with BMSCs transduced with control counterpart in vivo. Luciferase and western blot data showed that Dickkopf3 (Dkk3) is a target gene of miR-129-5p and the expression of Dkk3 was inhibited in BMSCs transduced with miR-129-5p mimic but enhanced in BMSCs transduced with miR-129-5p inhibitor. In addition, Dkk3 interacted with β-catenin directly.

Conclusions

miR-129-5p promotes osteogenic differentiation of BMSCs and bone regeneration, and miR-129-5p/Dkk3 axis may be new potential targets for the treatment of bone defect and bone loss.

Cellular and plasma proteomic determinants of COVID-19 and non-COVID-19 pulmonary diseases relative to healthy aging

We examine the cellular and soluble determinants of coronavirus disease 2019 (COVID-19) relative to aging by performing mass cytometry in parallel with clinical blood testing and plasma proteomic profiling of ~4,700 proteins from 71 individuals with pulmonary disease and 148 healthy donors (25-80 years old). Distinct cell populations were associated with age (GZMK⁺CD8⁺ T cells and CD25^low CD4⁺ T cells) and with COVID-19 (TBET^-EOMES^- CD4⁺ T cells, HLA-DR⁺CD38⁺ CD8⁺ T cells and CD27⁺CD38⁺ B cells). A unique population of TBET⁺EOMES⁺ CD4⁺ T cells was associated with individuals with COVID-19 who experienced moderate, rather than severe or lethal, disease. Disease severity correlated with blood creatinine and urea nitrogen levels. Proteomics revealed a major impact of age on the disease-associated plasma signatures and highlighted the divergent contribution of hepatocyte and muscle secretomes to COVID-19 plasma proteins. Aging plasma was enriched in matrisome proteins and heart/aorta smooth muscle cell-specific proteins. These findings reveal age-specific and disease-specific changes associated with COVID-19, and potential soluble mediators of the physiological impact of COVID-19.

Exercise Training-Increased FBXO32 and FOXO1 in a Gender-Dependent Manner in Mild Cognitively Impaired African Americans: GEMS-1 Study

The ubiquitin proteasome system (UPS) and FOXOs transcription factors play a pivotal role in cellular clearance and minimizing the accumulation of Aβ in neurodegeneration (ND). In African Americans (AAs) with mild cognitive impairment (MCI), the role of components of UPS and FOXOs; and whether they are amenable to exercise effects is unknown. We hypothesized that exercise can enhance cellular clearance systems during aging and ND by increasing expressions of FBXO32 and FOXO1. To test this hypothesis, we used TaqMan gene expression analysis in peripheral blood (PB) to investigate the component of UPS and FOXOs; and provide mechanistic insight at baseline, during exercise, and in both genders. At baseline, levels of FBXO32 were higher in women than in men. In our attempt to discern gender-specific exercise-related changes, we observed that levels of FBXO32 increased in men but not in women. Similarly, levels of FOXO1 increased in men only. These data suggest that a graded dose of FBXO32 and FOXO1 may be beneficial when PB cells carrying FBXO32 and FOXO1 summon into the brain in response to Alzheimer's disease (AD) perturbation (docking station PB cells). Our observation is consistent with emerging studies that exercise allows the trafficking of blood factors. Given the significance of FBXO32 and FOXO1 to ND and associated muscle integrity, our findings may explain, at least in part, the benefits of exercise on memory, associated gait, and balance perturbation acknowledged to herald the emergence of MCI.

Comprehensive Analysis of the Transcriptome-Wide m6A Methylome of Heart via MeRIP After Birth: Day 0 vs. Day 7

Aim: To systematically classify the profile of the RNA m6A modification landscape of neonatal heart regeneration.

Materials and Methods: Cardiomyocyte proliferation markers were detected via immunostaining. The expression of m6A modification regulators was detected using quantitative real-time PCR (qPCR) and Western blotting. Genome-wide profiling of methylation-modified transcripts was conducted with methylation-modified RNA immunoprecipitation sequencing (m6A-RIP-seq) and RNA sequencing (RNA-seq). The Gene Expression Omnibus database (GEO) dataset was used to verify the hub genes.

Results: METTL3 and the level of m6A modification in total RNA was lower in P7 rat hearts than in P0 ones. In all, 1,637 methylation peaks were differentially expressed using m6A-RIP-seq, with 84 upregulated and 1,553 downregulated. Furthermore, conjoint analyses of m6A-RIP-seq, RNA-seq, and GEO data generated eight potential hub genes with differentially expressed hypermethylated or hypomethylated m6A levels.

Conclusion: Our data provided novel information on m6A modification changes between Day 0 and Day 7 cardiomyocytes, which identified that increased METTL3 expression may enhance the proliferative capacity of neonatal cardiomyocytes, providing a theoretical basis for future clinical studies on the direct regulation of m6A in the proliferative capacity of cardiomyocytes.

Association of Monocyte Chemotactic Protein-1 and Dickkopf-1 with Body Composition and Physical Performance in Community-Dwelling Older Adults in Singapore

Objective

We aim to determine the association of monocyte chemotactic protein-1 (MCP-1) and dickkopft-1 (DKK-1) as potential biomarkers that may predict changes in body composition and physical performance in healthy older adults from Singapore.

Methods

Two-hundred community-dwelling older adults (mean age: 67.9 years; 68.5% females) were classified into elevated versus non-elevated groups based on quintile cut-offs of MCP-1 and DKK-1 levels (156.02 pg/mL and 606.31 pg/mL, respectively). Multiple linear regression was performed to examine the relationship between MCP-1 and DKK-1 with body composition and physical performance, adjusted for age, gender and ethnicity.

Results

MCP-1 was significantly associated with higher fat mass, fat mass index, percentage body fat, waist circumference and trunk-limb ratio for fat mass (all p<0.01), and repeated chair stand (p=0.004). DKK-1 was not associated with body composition and physical performance measures. Utilising the Asian Working Group for Sarcopenia (AWGS) 2019 criteria, there were 39 (19.5%) sarcopenia and 161 (80.5%) non-sarcopenia participants respectively, with MCP-1 levels significantly higher in sarcopenia compared with non-sarcopenia (p=0.046), but not for DKK-1 (p=0.525).

Conclusions

Elevated MCP-1 are associated with changes in fat composition, physical performance and sarcopenia, suggesting its usefulness in identifying at-risk group with sarcopenic obesity.

Vitamin D sufficiency enhances differentiation of patient-derived prostate epithelial organoids

Vitamin D is an essential steroid hormone that regulates systemic calcium homeostasis and cell fate decisions. The prostate gland is hormonally regulated, requiring steroids for proliferation and differentiation of secretory luminal cells. Vitamin D deficiency is associated with an increased risk of lethal prostate cancer, which exhibits a dedifferentiated pathology, linking vitamin D sufficiency to epithelial differentiation. To determine vitamin D regulation of prostatic epithelial differentiation, patient-derived benign prostate epithelial organoids were grown in vitamin D-deficient or -sufficient conditions. Organoids were assessed by phenotype and single-cell RNA sequencing. Mechanistic validation demonstrated that vitamin D sufficiency promoted organoid growth and accelerated differentiation by inhibiting canonical Wnt activity and suppressing Wnt family member DKK3. Wnt and DKK3 were also reduced by vitamin D in prostate tissue explants by spatial transcriptomics. Wnt dysregulation is a known contributor to aggressive prostate cancer, thus findings further link vitamin D deficiency to lethal disease.

Mechanisms of muscle atrophy and hypertrophy: implications in health and disease

Skeletal muscle is the protein reservoir of our body and an important regulator of glucose and lipid homeostasis. Consequently, the growth or the loss of muscle mass can influence general metabolism, locomotion, eating and respiration. Therefore, it is not surprising that excessive muscle loss is a bad prognostic index of a variety of diseases ranging from cancer, organ failure, infections and unhealthy ageing. Muscle function is influenced by different quality systems that regulate the function of contractile proteins and organelles. These systems are controlled by transcriptional dependent programs that adapt muscle cells to environmental and nutritional clues. Mechanical, oxidative, nutritional and energy stresses, as well as growth factors or cytokines modulate signaling pathways that, ultimately, converge on protein and organelle turnover. Novel insights that control and orchestrate such complex network are continuously emerging and will be summarized in this review. Understanding the mechanisms that control muscle mass will provide therapeutic targets for the treatment of muscle loss in inherited and non-hereditary diseases and for the improvement of the quality of life during ageing.

Loss of muscle mass is associated with ageing and with a number of diseases such as cancer. Here, the authors review the signaling pathways that modulate protein synthesis and degradation and gain or loss of muscle mass, and discuss therapeutic implications and future directions for the field.

Circulating Biomarkers of Accelerated Sarcopenia in Respiratory Diseases

Skeletal muscle dysfunction is a critical finding in many respiratory diseases. However, a definitive biomarker to assess muscle decline in respiratory diseases is not known. We analyzed the association of plasma levels of glycoprotein Dickkopf-3 (Dkk-3), c-terminal agrin fragment-22 (CAF22) and microRNAs miR-21, miR-134a, miR-133 and miR-206 with hand-grip strength (HGS) and appendicular skeletal mass index (ASMI) in male, 54-73-year-old patients with chronic obstructive pulmonary diseases (COPD), asthma or pulmonary TB (n = 83-101/group). Patients with respiratory diseases showed a reduction in HGS and gait speed, while a reduction in ASMI was only found in patients with pulmonary TB. Among the sarcopenia indexes, HGS showed the strongest correlation with plasma CAF22, miR-21 and miR-206 levels while ASMI showed the strongest correlation with Dkk-3 and miR-133 in respiratory diseases. We found a modest-to-significant increase in the plasma markers of inflammation, oxidative stress and muscle damage, which had varying degrees of correlations with Dkk-3, CAF22 and selected micro RNAs (miRs) in respiratory diseases. Taken together, our data show that plasma levels of Dkk-3, CAF22 and selected miRs can be useful tools to assess accelerated sarcopenia phenotype in the elderly with respiratory diseases.

Isoquercitrin Delays Denervated Soleus Muscle Atrophy by Inhibiting Oxidative Stress and Inflammation

Although denervated muscle atrophy is common, the underlying molecular mechanism remains unelucidated. We have previously found that oxidative stress and inflammatory response may be early events that trigger denervated muscle atrophy. Isoquercitrin is a biologically active flavonoid with antioxidative and anti-inflammatory properties. The present study investigated the effect of isoquercitrin on denervated soleus muscle atrophy and its possible molecular mechanisms. We found that isoquercitrin was effective in alleviating soleus muscle mass loss following denervation in a dose-dependent manner. Isoquercitrin demonstrated the optimal protective effect at 20 mg/kg/d, which was the dose used in subsequent experiments. To further explore the protective effect of isoquercitrin on denervated soleus muscle atrophy, we analyzed muscle proteolysis via the ubiquitin-proteasome pathway, mitophagy, and muscle fiber type conversion. Isoquercitrin significantly inhibited the denervation-induced overexpression of two muscle-specific ubiquitin ligases—muscle RING finger 1 (MuRF1) and muscle atrophy F-box (MAFbx), and reduced the degradation of myosin heavy chains (MyHCs) in the target muscle. Following isoquercitrin treatment, mitochondrial vacuolation and autophagy were inhibited, as evidenced by reduced level of autophagy-related proteins (ATG7, BNIP3, LC3B, and PINK1); slow-to-fast fiber type conversion in the target muscle was delayed via triggering expression of peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α); and the production of reactive oxygen species (ROS) in the target muscle was reduced, which might be associated with the upregulation of antioxidant factors (SOD1, SOD2, NRF2, NQO1, and HO1) and the downregulation of ROS production-related factors (Nox2, Nox4, and DUOX1). Furthermore, isoquercitrin treatment reduced the levels of inflammatory factors—interleukin (IL)-1β, IL-6, and tumor necrosis factor-α (TNF-α)—in the target muscle and inactivated the JAK/STAT3 signaling pathway. Overall, isoquercitrin may alleviate soleus muscle atrophy and mitophagy and reverse the slow-to-fast fiber type conversion following denervation via inhibition of oxidative stress and inflammatory response. Our study findings enrich the knowledge regarding the molecular regulatory mechanisms of denervated muscle atrophy and provide a scientific basis for isoquercitrin as a protective drug for the prevention and treatment of denervated muscle atrophy.

Signaling Pathways That Control Muscle Mass

The loss of skeletal muscle mass under a wide range of acute and chronic maladies is associated with poor prognosis, reduced quality of life, and increased mortality. Decades of research indicate the importance of skeletal muscle for whole body metabolism, glucose homeostasis, as well as overall health and wellbeing. This tissue’s remarkable ability to rapidly and effectively adapt to changing environmental cues is a double-edged sword. Physiological adaptations that are beneficial throughout life become maladaptive during atrophic conditions. The atrophic program can be activated by mechanical, oxidative, and energetic distress, and is influenced by the availability of nutrients, growth factors, and cytokines. Largely governed by a transcription-dependent mechanism, this program impinges on multiple protein networks including various organelles as well as biosynthetic and quality control systems. Although modulating muscle function to prevent and treat disease is an enticing concept that has intrigued research teams for decades, a lack of thorough understanding of the molecular mechanisms and signaling pathways that control muscle mass, in addition to poor transferability of findings from rodents to humans, has obstructed efforts to develop effective treatments. Here, we review the progress made in unraveling the molecular mechanisms responsible for the regulation of muscle mass, as this continues to be an intensive area of research.

Emerging molecular mediators and targets for age-related skeletal muscle atrophy

The age-associated decline in muscle mass has become synonymous with physical frailty among the elderly due to its major contribution in reduced muscle function. Alterations in protein and redox homeostasis along with chronic inflammation, denervation, and hormonal dysregulation are all hallmarks of muscle wasting and lead to clinical sarcopenia in older adults. Reduction in skeletal muscle mass has been observed and reported in the scientific literature for nearly 2 centuries; however, identification and careful examination of molecular mediators of age-related muscle atrophy have only been possible for roughly 3 decades. Here we review molecular targets of recent interest in age-related muscle atrophy and briefly discuss emerging small molecule therapeutic treatments for muscle wasting in sarcopenic susceptible populations.

Roles of Dkk2 in the Linkage from Muscle to Bone during Mechanical Unloading in Mice

Mechanical unloading simultaneously induces muscle and bone loss, but its mechanisms are not fully understood. The interactions between skeletal muscle and bone have been recently noted. Although canonical wingless-related integration site (Wnt)/β-catenin signaling is crucial for bone metabolism, its roles in the muscle and bone interactions have remained unknown. Here, we performed comprehensive DNA microarray analyses to clarify humoral factors linking muscle to bone in response to mechanical unloading and hypergravity with 3 g in mice. We identified Dickkopf (Dkk) 2, a Wnt/β-catenin signaling inhibitor, as a gene whose expression was increased by hindlimb unloading (HU) and reduced by hypergravity in the soleus muscle of mice. HU significantly elevated serum Dkk2 levels and Dkk2 mRNA levels in the soleus muscle of mice whereas hypergravity significantly decreased those Dkk2 levels. In the simple regression analyses, serum Dkk2 levels were negatively and positively related to trabecular bone mineral density and mRNA levels of receptor activator of nuclear factor-kappa B ligand (RANKL) in the tibia of mice, respectively. Moreover, shear stress significantly suppressed Dkk2 mRNA levels in C2C12 cells, and cyclooxygenase inhibitors significantly antagonized the effects of shear stress on Dkk2 expression. On the other hand, Dkk2 suppressed the mRNA levels of osteogenic genes, alkaline phosphatase activity and mineralization, and it increased RANKL mRNA levels in mouse osteoblasts. In conclusion, we showed that muscle and serum Dkk2 levels are positively and negatively regulated during mechanical unloading and hypergravity in mice, respectively. An increase in Dkk2 expression in the skeletal muscle might contribute to disuse- and microgravity-induced bone and muscle loss.

Effect of tobacco smoking on the epigenetic age of human respiratory organs

BACKGROUND

Smoking leads to the aging of organs. However, no studies have been conducted to quantify the effect of smoking on the aging of respiratory organs and the aging-reversing ability of smoking cessation.

RESULTS

We collected genome-wide methylation datasets of buccal cells, airway cells, esophagus tissue, and lung tissue from non-smokers, smokers, and ex-smokers. We used the "epigenetic clock" method to quantify the epigenetic age acceleration in the four organs. The statistical analyses showed the following: (1) Smoking increased the epigenetic age of airway cells by an average of 4.9 years and lung tissue by 4.3 years. (2) After smoking ceased, the epigenetic age acceleration in airway cells (but not in lung tissue) slowed to a level that non-smokers had. (3) The epigenetic age acceleration in airway cells and lung tissue showed no gender difference.

CONCLUSIONS

Smoking can accelerate the epigenetic age of human respiratory organs, but the effect varies among organs and can be reversed by smoking cessation. Our study provides a powerful incentive to reduce tobacco consumption autonomously.

High-resolution genome-wide expression analysis of single myofibers using SMART-Seq

Skeletal muscle is a heterogeneous tissue. Individual myofibers that make up muscle tissue exhibit variation in their metabolic and contractile properties. Although biochemical and histological assays are available to study myofiber heterogeneity, efficient methods to analyze the whole transcriptome of individual myofibers are lacking. Here, we report on a single-myofiber RNA-sequencing (smfRNA-Seq) approach to analyze the whole transcriptome of individual myofibers by combining single-fiber isolation with Switching Mechanism at 5' end of RNA Template (SMART) technology. Using smfRNA-Seq, we first determined the genes that are expressed in the whole muscle, including in nonmyogenic cells. We also analyzed the differences in the transcriptome of myofibers from young and old mice to validate the effectiveness of this new method. Our results suggest that aging leads to significant changes in the expression of metabolic genes, such as Nos1, and structural genes, such as Myl1, in myofibers. We conclude that smfRNA-Seq is a powerful tool to study developmental, disease-related, and age-related changes in the gene expression profile of skeletal muscle.

Inhibition of microRNA-92a increases blood vessels and satellite cells in skeletal muscle but does not improve duchenne muscular dystrophy-related phenotype in mdx mice

INTRODUCTION

The vasculature and blood flow in muscle are perturbed in Duchenne muscular dystrophy (DMD) and its mdx mouse model. MicroRNA-92a (miR-92a) is enriched in endothelial cells, especially during ischemic injury.

METHODS

Because antagonizing miR-92a was shown to result in increased proliferation and migration of endothelial cells and recovery from ischemia, we assessed the effects of Antagomir-92a in vitro in muscle stem cell culture and in vivo in mdx mice.

RESULTS

miR-92a was found to be highly expressed in muscle endothelial cells and satellite cells. Treatment with Antagomir-92a increased capillary density and tissue perfusion, which was accompanied by an increase in satellite cells. However, Antagomir-92a-treated mdx mice showed no histological improvement and had worse muscle function. Antagomir-92a suppressed myogenic differentiation in satellite cell culture.

DISCUSSION

AntagomiR-92a improves the vasculature but not the muscle in mdx mice, possibly due to its side effects on satellite cell differentiation. Muscle Nerve 59:594-594, 2019.