Effects of IGF-1 isoforms on muscle growth and sarcopenia

Anti-PEc: Development of a novel monoclonal antibody against prostate cancer

BACKGROUND

The Ec peptide (PEc) that defines the IGF-1Ec isoform, is associated with prostate cancer progression by inducing proliferation, metastases, and tumour repair. On these grounds, an anti-PEc monoclonal antibody (MAb) was developed. Our objective is to examine the effects of this antibody on prostate cancer and its possible side effects.

METHODS

The effects of the obtained MAb were examined in cancer and non-cancerous cell lines (unmodified and modified either to overexpress or silence PEc) and in tumours in SCID mice injected with unmodified prostate cancer cells. The investigation was obtained with respect to cellular proliferation, migration, invasion, toxicity to tumours, effects on the cell cycle, immune response activation, effects on mesenchymal stem cell mobilisation leading to tumour repair, tissue distribution, and toxicity to mice.

RESULTS

Anti-PEc MAb treatment led to a significant decrease in cellular proliferation, migration, and invasion compared to the untreated cell lines (p < 0.0005 in every case). Mechanistically, these effects were associated with the downregulation of pERK1/2 and vimentin and the upregulation of E-Cadherin. In vivo, anti-PEc MAb treatment was associated with a significant decrease in tumour size and metastases rate (p < 0.0005 in every case) by reversing the tumours mesenchymal phenotype. It also inhibited host stem cell mobilisation towards the tumour, leading to apoptosis. Anti-PEc MAb assessment in respect to distribution and toxicity, indicated its tumour specificity and lack of toxicity.

CONCLUSIONS

These data indicate that the therapeutic targeting of PEc with the anti-PEc MAb may have considerable clinical benefit for prostate cancer patients.

Post-natal muscle growth and protein turnover: a narrative review of current understanding

A model explaining the dietary-protein-driven post-natal skeletal muscle growth and protein turnover in the rat is updated, and the mechanisms involved are described, in this narrative review. Dietary protein controls both bone length and muscle growth, which are interrelated through mechanotransduction mechanisms with muscle growth induced both from stretching subsequent to bone length growth and from internal work against gravity. This induces satellite cell activation, myogenesis and remodelling of the extracellular matrix, establishing a growth capacity for myofibre length and cross-sectional area. Protein deposition within this capacity is enabled by adequate dietary protein and other key nutrients. After briefly reviewing the experimental animal origins of the growth model, key concepts and processes important for growth are reviewed. These include the growth in number and size of the myonuclear domain, satellite cell activity during post-natal development and the autocrine/paracrine action of IGF-1. Regulatory and signalling pathways reviewed include developmental mechanotransduction, signalling through the insulin/IGF-1-PI3K-Akt and the Ras-MAPK pathways in the myofibre and during mechanotransduction of satellite cells. Likely pathways activated by maximal-intensity muscle contractions are highlighted and the regulation of the capacity for protein synthesis in terms of ribosome assembly and the translational regulation of 5-TOPmRNA classes by mTORC1 and LARP1 are discussed. Evidence for and potential mechanisms by which volume limitation of muscle growth can occur which would limit protein deposition within the myofibre are reviewed. An understanding of how muscle growth is achieved allows better nutritional management of its growth in health and disease.

Ablation of specific insulin-like growth factor I forms reveals the importance of cleavage for regenerative capacity and glycosylation for skeletal muscle storage

Insulin-like growth factor-I (IGF-I) facilitates mitotic and anabolic actions in all tissues. In skeletal muscle, IGF-I can promote growth and resolution of damage by promoting satellite cell proliferation and differentiation, suppressing inflammation, and enhancing fiber formation. While the most well-characterized form of IGF-I is the mature protein, alternative splicing and post-translational modification complexity lead to several additional forms of IGF-I. Previous studies showed muscle efficiently stores glycosylated pro-IGF-I. However, non-glycosylated forms display more efficient IGF-I receptor activation in vitro, suggesting that the removal of the glycosylated C terminus is a necessary step to enable increased activity. We employed CRISPR-Cas9 gene editing to ablate IGF-I glycosylation sites (2ND) or its cleavage site (3RA) in mice to determine the necessity of glycosylation or cleavage for IGF-I function in postnatal growth and during muscle regeneration. 3RA mice had the highest circulating and muscle IGF-I content, whereas 2ND mice had the lowest levels compared to wild-type mice. After weaning, 4-week-old 2ND mice exhibited higher body and skeletal muscle mass than other strains. However, by 16 weeks of age, muscle and body size differences disappeared. Even though 3RA mice had more IGF-I stored in muscle in homeostatic conditions, regeneration was delayed after cardiotoxin-induced injury, with prolonged necrosis most evident at 5 days post injury (dpi). In contrast, 2ND displayed improved regeneration with reduced necrosis, and greater fiber size and muscle mass at 11 and 21 dpi. Overall, these results demonstrate that while IGF-I glycosylation may be important for storage, cleavage is needed to enable IGF-I to be used for efficient activity in postnatal growth and following acute injury.

The impact of ageing mechanisms on musculoskeletal system diseases in the elderly

Ageing is an inevitable process that affects various tissues and organs of the human body, leading to a series of physiological and pathological changes. Mechanisms such as telomere depletion, stem cell depletion, macrophage dysfunction, and cellular senescence gradually manifest in the body, significantly increasing the incidence of diseases in elderly individuals. These mechanisms interact with each other, profoundly impacting the quality of life of older adults. As the ageing population continues to grow, the burden on the public health system is expected to intensify. Globally, the prevalence of musculoskeletal system diseases in elderly individuals is increasing, resulting in reduced limb mobility and prolonged suffering. This review aims to elucidate the mechanisms of ageing and their interplay while exploring their impact on diseases such as osteoarthritis, osteoporosis, and sarcopenia. By delving into the mechanisms of ageing, further research can be conducted to prevent and mitigate its effects, with the ultimate goal of alleviating the suffering of elderly patients in the future.

Lactobacillus gasseri BNR17 Ameliorates Dexamethasone-Induced Muscle Loss in BALB/c Mice and C2C12 Myotubes

This study aimed to investigate the effects and mechanism of Lactobacillus gasseri BNR17, a probiotic strain isolated from human breast milk, on dexamethasone-induced muscle loss in mice and cultured myotubes. BALB/c mice were intraperitoneally injected with dexamethasone, and orally administered L. gasseri BNR17 for 21 days. L. gasseri BNR17 treatment ameliorated dexamethasone-induced decline in muscle function, as evidenced by an increase in forelimb grip strength, treadmill running time, and rotarod retention time in both female and male mice. In addition, L. gasseri BNR17 treatment significantly increased the mass of the gastrocnemius and quadriceps muscles. Dual-energy X-ray absorptiometry showed a significant increase in lean body mass and a decrease in fat mass in both whole body and hind limb after treatment with L. gasseri BNR17. It was found that L. gasseri BNR17 treatment downregulated serum myostatin level and the protein degradation pathway composed of muscle-specific ubiquitin E3 ligases, MuRF1 and MAFbx, and their transcription factor FoxO3. In contrast, L. gasseri BNR17 treatment upregulated serum insulin-like growth factor-1 level and Akt-mTOR-p70S6K signaling pathway involved in protein synthesis in muscle. As a result, L. gasseri BNR17 treatment significantly increased the levels of major muscular proteins such as myosin heavy chain and myoblast determination protein 1. Consistent with in vivo results, L. gasseri BNR17 culture supernatant significantly ameliorated dexamethasone-induced C2C12 myotube atrophy in vitro. In conclusion, L. gasseri BNR17 ameliorates muscle loss by downregulating the protein degradation pathway and upregulating the protein synthesis pathway.

Recent Advances in the Use of Stem Cells in Tissue Engineering and Adjunct Therapies for Tendon Reconstruction and Future Perspectives

Due to their function, tendons are exposed to acute injuries. This type of damage to the musculoskeletal system represents a challenge for clinicians when natural regeneration and treatment methods do not produce the expected results. Currently, treatment is long and associated with long-term complications. In this review, we discuss the use of stem cells in the treatment of tendons, including how to induce appropriate cell differentiation based on gene therapy, growth factors, tissue engineering, proteins involved in regenerative process, drugs and three-dimensional (3D) structures. A multidirectional approach as well as the incorporation of novel components of the therapy will improve the techniques used and benefit patients with tendon injuries in the future.

Improving sarcopenia in older adults: a systematic review and meta-analysis of randomized controlled trials of whey protein supplementation with or without resistance training

OBJECTIVES

The aim of the study was to comprehensively analyze the effects of whey protein (WP)-enriched supplement intake with or without resistance training (RT) in older patients, either from the community or hospital, who were diagnosed with sarcopenia according to the EWGSOP or AWGS criteria.

METHODS

This meta-analysis study was registered in PROSPERO (CRD42023407885). We searched the PubMed, Embase, Web of Science, and Cochrane Library databases for RCTs up to June 1, 2023. Standardized mean differences (SMD) with 95% confidence intervals (CI) were used to estimate the pooled results.

RESULTS

Ten RCT studies, including 1154 participants, were included and analyzed. The primary outcomes were the changes in muscle mass, strength, and physical performance. In WP group versus (vs.) Isocaloric placebo (PLA)/Routine consultation (RC) group, WP significantly increased the appendicular skeletal muscle mass index (SMD: 0.47, 95%CI: 0.23, 0.71), appendicular skeletal muscle mass (SMD: 0.28, 95%CI: 0.11, 0.45) and gait speed (SMD: 1.13, 95%CI: 0.82, 1.44) in older patients with sarcopenia. In WP with RT group vs. PLA/ RC group, there was significant increase in handgrip strength (SMD: 0.67, 95%CI: 0.29, 1.04). In addition, in the secondary outcomes, WP significantly reduced interleukin-6, significantly increased insulin-like growth factor-1 and albumin, promoted participants' intake of total energy and protein, enhanced activities of daily living scores in patients, and had no significant effect on BMI, weight, or fat mass.

CONCLUSION

This review confirms that WP can improve various aspects of older adult with sarcopenia, thereby enhancing their overall physical condition. More studies should be conducted to validate this result and further explore the effects of WP and RT in patients with sarcopenia.

Identification of lncRNA-based regulatory mechanisms of Takifugu rubripes growth traits in fast and slow-growing family lines

Family selection is an important method in fish aquaculture because growth is the most important economic trait. Fast-and slow-growing families of tiger puffer fish (Takifugu rubripes) have been established through family selection. The development of teleost fish is primarily controlled by the growth hormone (GH)-insulin-like growth factor 1 (IGF-1) axis that includes the hypothalamus-pituitary-liver. In this study, the molecular mechanisms underlying T. rubripes growth were analyzed by comparing transcriptomes from fast- and slow-growing families. The expressions of 214 lncRNAs were upregulated, and those of 226 were downregulated in the brain tissues of the fast-growing T. rubripes family compared to those of the slow-growing family. Differentially expressed lncRNAs centrally regulate mitogen-activated protein kinase (MAPK) and forkhead box O (FoxO) signaling pathways. Based on the results of lncRNA-gene network construction, we found that lncRNA3133.13, lncRNA23169.1, lncRNA23145.1, and lncRNA23141.3 regulated all four genes (igf1, mdm2, flt3, and cwf19l1). In addition, lncRNA7184.10 may be a negative regulator of rasgrp2 and a positive regulator of gadd45ga, foxo3b, and dusp5. These target genes are associated with the growth and development of organisms through the PI3K/AKT and MAPK/ERK pathways. Overall, transcriptomic analyses of fast- and slow-growing families of T. rubripes provided insights into the molecular mechanisms of teleost fish growth rates. Further, these analyses provide evidence for key genes related to growth regulation and the lncRNA expression regulatory network that will provide a framework for improving puffer fish germplasm resources.

Kinesin light chain 1 stabilizes insulin receptor substrate 1 to regulate the IGF-1-AKT signaling pathway during myoblast differentiation

The IGF signaling pathway plays critical role in regulating skeletal myogenesis. We have demonstrated that KIF5B, the heavy chain of kinesin-1 motor, promotes myoblast differentiation through regulating IGF-p38MAPK activation. However, the roles of the kinesin light chain (Klc) in IGF pathway and myoblast differentiation remain elusive. In this study, we found that Klc1 was upregulated during muscle regeneration and downregulated in senescence mouse muscles and dystrophic muscles from mdx (X-linked muscular dystrophic) mice. Gain- and loss-of-function experiments further displayed that Klc1 promotes AKT-mTOR activity and positively regulates myogenic differentiation. We further identified that the expression levels of IRS1, the critical node of IGF-1 signaling, are downregulated in Klc1-depleted myoblasts. Coimmunoprecipitation study revealed that IRS1 interacted with the 88-154 amino acid sequence of Klc1 via its PTB domain. Notably, the reduced Klc1 levels were found in senescence and osteoporosis skeletal muscle samples from both mice and human. Taken together, our findings suggested a crucial role of Klc1 in the regulation of IGF-AKT pathway during myogenesis through stabilizing IRS1, which might ultimately influence the development of muscle-related disorders.

IGF1R deficiency in vascular smooth muscle cells impairs myogenic autoregulation and cognition in mice

Introduction

Cerebrovascular pathologies contribute to cognitive decline during aging, leading to vascular cognitive impairment and dementia (VCID). Levels of circulating insulin-like growth factor 1 (IGF-1), a vasoprotective hormone, decrease during aging. Decreased circulating IGF-1 in animal models leads to the development of VCID-like symptoms, but the cellular mechanisms underlying IGF-1-deficiency associated pathologies in the aged cerebrovasculature remain poorly understood. Here, we test the hypothesis that vascular smooth muscle cells (VSMCs) play an integral part in mediating the vasoprotective effects of IGF-1.

Methods

We used a hypertension-based model of cerebrovascular dysfunction in mice with VSMC-specific IGF-1 receptor (Igf1r) deficiency and evaluated the development of cerebrovascular pathologies and cognitive dysfunction.

Results

VSMC-specific Igf1r deficiency led to impaired cerebral myogenic autoregulation, independent of blood pressure changes, which was also associated with impaired spatial learning and memory function as measured by radial arm water maze and impaired motor learning measured by rotarod. In contrast, VSMC-specific IGF-1 receptor knockdown did not lead to cerebral microvascular rarefaction.

Discussion

These studies suggest that VSMCs are key targets for IGF-1 in the context of cerebrovascular health, playing a role in vessel stability alongside other cells in the neurovascular unit, and that VSMC dysfunction in aging likely contributes to VCID.

D-galactose might mediate some of the skeletal muscle hypertrophy-promoting effects of milk-A nutrient to consider for sarcopenia?

Sarcopenia is a process of progressive aging-associated loss of skeletal muscle mass (SMM) recognized as a serious global health issue contributing to frailty and increased all-cause mortality. Exercise and nutritional interventions (particularly intake of dairy products and milk) demonstrate good efficacy, safety, and broad applicability. Here, we propose that at least some of the well-documented favorable effects of milk and milk-derived protein supplements on SMM might be mediated by D-galactose, a monosaccharide present in large quantities in milk in the form of disaccharide lactose (milk sugar). We suggest that ingestion of dairy products results in exposure to D-galactose in concentrations metabolized primarily via the Leloir pathway with the potential to (i) promote anabolic signaling via maintenance of growth factor (e.g., insulin-like growth factor 1 [IGF-1]) receptor mature glycosylation patterns; and (ii) provide extracellular (liver glycogen) and intracellular substrates for short (muscle glycolysis) and long-term (muscle glycogen, intramyocellular lipids) energy availability. Additionally, D-galactose might optimize the metabolic function of skeletal muscles by increasing mitochondrial content and stimulating glucose and fatty acid utilization. The proposed potential of D-galactose to promote the accretion of SMM is discussed in the context of its therapeutic potential in sarcopenia.

Endothelial deficiency of insulin-like growth factor-1 receptor leads to blood-brain barrier disruption and accelerated endothelial senescence in mice, mimicking aspects of the brain aging phenotype

INTRODUCTION

Age-related blood-brain barrier (BBB) disruption, cerebromicrovascular senescence, and microvascular rarefaction substantially contribute to the pathogenesis of vascular cognitive impairment (VCI) and Alzheimer's disease (AD). Previous studies established a causal link between age-related decline in circulating levels of insulin-like growth factor-1 (IGF-1), cerebromicrovascular dysfunction, and cognitive decline. The aim of our study was to determine the effect of IGF-1 signaling on senescence, BBB permeability, and vascular density in middle-age and old brains.

METHODS

Accelerated endothelial senescence was assessed in senescence reporter mice (VE-Cadherin-CreERT2 /Igf1rfl/fl × p16-3MR) using flow cytometry. To determine the functional consequences of impaired IGF-1 input to cerebromicrovascular endothelial cells, BBB integrity and capillary density were studied in mice with endothelium-specific knockout of IGF1R (VE-Cadherin-CreERT2 /Igf1rfl/fl ) using intravital two-photon microscopy.

RESULTS

In VE-Cadherin-CreERT2 /Igf1rfl/fl mice: (1) there was an increased presence of senescent endothelial cells; (2) cumulative permeability of the microvessels to fluorescent tracers of different molecular weights (0.3-40 kDa) is significantly increased, as compared to that of control mice, whereas decline in cortical capillary density does not reach statistical significance.

CONCLUSIONS

These findings support the notion that IGF-1 signaling plays a crucial role in preserving a youthful cerebromicrovascular endothelial phenotype and maintaining the integrity of the BBB.

Handelin alleviates cachexia- and aging-induced skeletal muscle atrophy by improving protein homeostasis and inhibiting inflammation

BACKGROUND

Handelin is a bioactive compound from Chrysanthemum indicum L. that improves motor function and muscle integrity during aging in Caenorhabditis elegans. This study aimed to further evaluate the protective effects and molecular mechanisms of handelin in a mouse muscle atrophy model induced by cachexia and aging.

METHODS

A tumour necrosis factor (TNF)-α-induced atrophy model was used to examine handelin activity in cultured C2C12 myotubes in vitro. Lipopolysaccharide (LPS)-treated 8-week-old model mice and 23-month-old (aged) mice were used to examine the therapeutic effects of handelin on cachexia- and aging-induced muscle atrophy, respectively, in vivo. Protein and mRNA expressions were analysed by Western blotting, ELISA and quantitative PCR, respectively. Skeletal muscle mass was measured by histological analysis.

RESULTS

Handelin treatment resulted in an upregulation of protein levels of early (MyoD and myogenin) and late (myosin heavy chain, MyHC) differentiation markers in C2C12 myotubes (P < 0.05), and enhanced mitochondrial respiratory (P < 0.05). In TNF-α-induced myotube atrophy model, handelin maintained MyHC protein levels, increased insulin-like growth factor (Igf1) mRNA expression and phosphorylated protein kinase B protein levels (P < 0.05). Handelin also reduced atrogin-1 expression, inhibited nuclear factor-κB activation and reduced mRNA levels of interleukin (Il)6, Il1b and chemokine ligand 1 (Cxcl1) (P < 0.05). In LPS-treated mice, handelin increased body weight (P < 0.05), the weight (P < 0.01) and cross-sectional area (CSA) of the soleus muscle (P < 0.0001) and improved motor function (P < 0.05). In aged mice, handelin slightly increased the weight of the tibialis anterior muscle (P = 0.06) and CSA of the tibialis anterior and gastrocnemius muscles (P < 0.0001). In the tibialis anterior muscle of aged mice, handelin upregulated mRNA levels of Igf1 (P < 0.01), anti-inflammatory cytokine Il10 (P < 0.01), mitochondrial biogenesis genes (P < 0.05) and antioxidant-related enzymes (P < 0.05) and strengthened Sod and Cat enzyme activity (P < 0.05). Handelin also reduced lipid peroxidation and protein carbonylation, downregulated mRNA levels of Fbxo32, Mstn, Cxcl1, Il1b and Tnf (P < 0.05), and decreased IL-1β levels in serum (P < 0.05). Knockdown of Hsp70 or using an Hsp70 inhibitor abolished the ameliorating effects of handelin on myotube atrophy.

CONCLUSIONS

Handelin ameliorated cachexia- and aging-induced skeletal muscle atrophy in vitro and in vivo, by maintaining homeostasis of protein synthesis and degradation, possibly by inhibiting inflammation. Handelin is a potentially promising drug candidate for the treatment of muscle wasting.

Muscle Fiber Characteristics and Transcriptome Analysis in Slow- and Fast-Growing Megalobrama amblycephala

Growth is an important trait in aquaculture that is influenced by various factors, among which genetic regulation plays a crucial role. Megalobrama amblycephala, one of the most important freshwater species in China, exhibits wide variations in body mass among individuals of the same age within the same pool. But the molecular mechanisms underlying wide variation in body mass remain unclear. Here, we performed muscle histological and transcriptome analysis of muscle tissues from Fast-Growing (FG) and Slow-Growing (SG) M. amblycephala at the age of 4 months old (4 mo) and 10 months old (10 mo) to elucidate its muscle development and growth mechanism. The muscle histological analysis showed smaller diameter and higher total number of muscle fibers in FG compared to SG at 4 mo, while larger diameter and total number of muscle fibers were detected in FG at 10 mo. The transcriptome analysis of muscle tissue detected 1171 differentially expressed genes (DEGs) between FG and SG at 4 mo, and 718 DEGs between FG and SG at 10 mo. Furthermore, 44 DEGs were consistently up-regulated in FG at both 4 mo and 10 mo. Up-regulated DEGs in FG at 4 mo were mainly enriched in the pathways related to cell proliferation, while down-regulated DEGs were significantly enriched in cell fusion and muscle contraction. Up-regulated DEGs in FG at 10 mo were mainly enriched in the pathways related to cell proliferation and protein synthesis. Therefore, these results provide novel insights into the molecular mechanism of M. amblycephala muscle growth at different stages, and will be of great guiding significance to promote the fast growth of M. amblycephala.

The super-healing MRL strain promotes muscle growth in muscular dystrophy through a regenerative extracellular matrix

The Murphy Roths Large (MRL) mouse strain has "super-healing" properties that enhance recovery from injury. In mice, the DBA/2J strain intensifies many aspects of muscular dystrophy, so we evaluated the ability of the MRL strain to suppress muscular dystrophy in the Sgcg-null mouse model of limb girdle muscular dystrophy. A comparative analysis of Sgcg-null mice in the DBA/2J versus MRL strains showed greater myofiber regeneration, with reduced structural degradation of muscle in the MRL strain. Transcriptomic profiling of dystrophic muscle indicated strain-dependent expression of extracellular matrix (ECM) and TGF-β signaling genes. To investigate the MRL ECM, cellular components were removed from dystrophic muscle sections to generate decellularized myoscaffolds. Decellularized myoscaffolds from dystrophic mice in the protective MRL strain had significantly less deposition of collagen and matrix-bound TGF-β1 and TGF-β3 throughout the matrix. Dystrophic myoscaffolds from the MRL background, but not the DBA/2J background, were enriched in myokines like IGF-1 and IL-6. C2C12 myoblasts seeded onto decellularized matrices from Sgcg-/- MRL and Sgcg-/- DBA/2J muscles showed the MRL background induced greater myoblast differentiation compared with dystrophic DBA/2J myoscaffolds. Thus, the MRL background imparts its effect through a highly regenerative ECM, which is active even in muscular dystrophy.

Pharmacological interventions targeting the microcirculation following traumatic spinal cord injury

Traumatic spinal cord injury is a devastating disorder characterized by sensory, motor, and autonomic dysfunction that severely compromises an individual's ability to perform activities of daily living. These adverse outcomes are closely related to the complex mechanism of spinal cord injury, the limited regenerative capacity of central neurons, and the inhibitory environment formed by traumatic injury. Disruption to the microcirculation is an important pathophysiological mechanism of spinal cord injury. A number of therapeutic agents have been shown to improve the injury environment, mitigate secondary damage, and/or promote regeneration and repair. Among them, the spinal cord microcirculation has become an important target for the treatment of spinal cord injury. Drug interventions targeting the microcirculation can improve the microenvironment and promote recovery following spinal cord injury. These drugs target the structure and function of the spinal cord microcirculation and are essential for maintaining the normal function of spinal neurons, axons, and glial cells. This review discusses the pathophysiological role of spinal cord microcirculation in spinal cord injury, including its structure and histopathological changes. Further, it summarizes the progress of drug therapies targeting the spinal cord microcirculation after spinal cord injury.

Identification of molecular mediators of renal sarcopenia risk: a mendelian randomization analysis

BACKGROUND

Observational studies have shown an association between reduced renal function and the risk of sarcopenia. However, the causal relationship and the underlying biological mechanisms remain uncertain. Using a Mendelian randomization (MR) framework, we investigated the causal role of 27 hypothetical risk mediators, including metabolites, hormones, inflammation, and stress traits, on the risk of sarcopenia.

METHODS

Instrumental variables (IVs) to proxy renal function were identified by selecting single nucleotide polymorphisms (SNPs) reliably associated with creatinine and cystatin C-based glomerular filtration rate (GFR) in CKDGen summary data. IVs for putative risk traits and sarcopenia traits were constructed from relevant genome-wide association studies (GWAS). MR estimated effects were obtained using an inverse-variance weighted effects model, and various sensitivity analyses were performed. The mediating role of hypothetical risk factors in the relationship between GFR and sarcopenia was assessed through multivariate MR.

RESULTS

Genetically predicted reduced GFRcrea was associated with higher odds of appendicular lean mass (ALM) (odds ratio (OR): 0.64, 95% confidence interval (CI) 0.37 to 0.68) and grip strength (OR: 0.67; 95% CI 0.58 to 0.78). Likewise, GFRcys highlighted a causal relationship with ALM (OR: 0.52; 95% CI 0.42 to 0.65) and grip strength (OR: 0.66; 95% CI 0.59 to 0.74). Both estimated GFR (eGFR) were negatively associated with IGF-1, IL-16, 25(OH)D, triglycerides (range of effect size per standard deviation: -0.81 to -0.30), and positively correlated with HDL cholesterol (0.62, 0.31). There was a positive correlation between IGF-1, fasting insulin and ALM as well as grip strength (OR range: 1.04-1.67) and a negative correlation between serum CRP and ALM (OR: 0.95) as well as grip strength (OR: 0.98). Additionally, genetically predicted IL-1β (OR: 0.95) and total cholesterol (OR: 0.96) were negatively associated with ALM. We found evidence that IGF-1 mediates the relationship between eGFR and risk for muscle mass and strength.

CONCLUSIONS

This MR study provides insight into the potential causal mechanisms between renal function and the risk of sarcopenia and proposes IGF-1 as a potential target for the prevention of renal sarcopenia.

Antisense Oligonucleotide-Mediated Downregulation of IGFBPs Enhances IGF-1 Signaling

Insulin-like growth factor-1 (IGF-1) has been considered as a therapeutic agent for muscle wasting conditions including Duchenne muscular dystrophy as it stimulates muscle regeneration, growth and function. Several preclinical and clinical studies have been conducted to show the therapeutic potential of IGF-1, however, delivery issues, short half-life and isoform complexity have impose challenges. Antisense oligonucleotides (AONs) are able to downregulate target proteins by interfering with their transcripts. Here, we investigated the feasibility of enhancing IGF-1 signaling by downregulation of IGF-binding proteins. We observed that out of frame exon skipping of Igfbp1 and Igfbp3 downregulated their protein expression, which increased Akt phosphorylation on the downstream IGF-1 signaling in vitro. 3'RNA sequencing analysis revealed the related transcriptome in C2C12 cells in response to IGFBP3 downregulation. The AONs did however not induce any exon skipping or protein knockdown in mdx mice after 6 weeks of systemic treatment. We conclude that IGFBP downregulation could be a good strategy to increase IGF-1 signaling but alternative tools are needed for efficient delivery and knockdown in vivo.

Associations between handgrip strength and skeletal muscle mass with all-cause mortality and cardiovascular mortality in people with type 2 diabetes: A prospective cohort study of the UK Biobank

AIMS

To explore the associations between handgrip strength (HGS) and skeletal muscle mass (SMM) with all-cause and cardiovascular disease (CVD) mortality risk in type 2 diabetes (T2DM) patients.

MATERIALS AND METHODS

Data were obtained from the UK Biobank. Baseline survey was conducted between 2006 and 2010, and followed up for a median of 12.52 years. HGS was measured using dynamometer, and SMM was measured using bioelectrical impedance method. Mortality was available via links to the National Health Service Information Centre. Sex-specific analyses were conducted.

RESULTS

A total of 13 392 T2DM participants were included, with a mean age of 60.39 years and 52.35% men. During the follow-up, there were 3006 (22.45%) deaths, including 746 (5.57%) CVD deaths. The risk for all-cause mortality and CVD mortality among both men and women increased progressively with decreasing HGS quartiles (p trend <.05). A 1 SD decrease in HGS was found to both increase the all-cause risk (HR: 1.31 [95% CI: 1.24-1.38]) and CVD mortality risk (HR: 1.35 [95% CI: 1.22-1.50]) for men, and all-cause risk (HR: 1.26 [95% CI: 1.11-1.42]) and CVD mortality risk (HR: 1.43 [95% CI: 1.09-1.89]) for women. There was no statistically significant trend association between SMM/height2 and mortality risk, and the restricted cubic regression splines indicated that SMM/height2 showed a U-shaped nonlinear relationship (pnonlinear  <.05).

CONCLUSIONS

Grip strength displayed a linear downward trend with mortality risk among T2DM patients, whereas muscle mass showed a U-shaped relationship. Low grip strength seemed to be a better predictor for mortality compared to low muscle mass.

A comprehensive review on the risks assessment and treatment options for Sarcopenia in people with diabetes

Objectives

This comprehensive review aims to examine the reciprocal interplay between Type 2 diabetes mellitus (T2DM) and sarcopenia, identify prevailing research gaps, and discuss therapeutic approaches and measures to enhance healthcare practices within hospital settings.

Methods

A thorough literature review was conducted to gather relevant studies and articles on the relationship between T2DM and sarcopenia. Various databases were searched, including Google Scholar, PubMed, Scopus, and Science Direct databases. The search terms included T2DM, sarcopenia, inflammation, insulin resistance, advanced glycation end products, oxidative stress, muscle dimensions, muscle strength, muscle performance, aging, nutrition, hormone levels, and physical activity. The collected articles were critically analysed to extract key findings and identify gaps in current research.

Results

The prevalence and incidence of metabolic and musculoskeletal disorders, notably T2DM and sarcopenia, have surged in recent years. T2DM is marked by inflammation, insulin resistance, accumulation of advanced glycation end products, and oxidative stress, while sarcopenia involves a progressive decline in skeletal muscle mass and function. The review underscores the age-related correlation between sarcopenia and adverse outcomes like fractures, falls, and mortality. Research gaps regarding optimal nutritional interventions for individuals with T2DM and sarcopenia are identified, emphasizing the necessity for further investigation in this area.

Conclusions

The reciprocal interplay between T2DM and sarcopenia holds significant importance. Further research is warranted to address knowledge gaps, particularly in utilizing precise measurement tools during clinical trials. Lifestyle modifications appear beneficial for individuals with T2DM and sarcopenia. Additionally, practical nutritional interventions require investigation to optimize healthcare practices in hospital settings.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40200-023-01262-w.

Pathophysiology of sarcopenia: Genetic factors and their interplay with environmental factors

Sarcopenia is a geriatric disorder characterized by a progressive decline in muscle mass and function. This disorder has been associated with a range of adverse health outcomes, including fractures, functional deterioration, and increased mortality. The pathophysiology of sarcopenia is highly complex and multifactorial, involving both genetic and environmental factors as key contributors. This review consolidates current knowledge on the genetic factors influencing the pathogenesis of sarcopenia, particularly focusing on the altered gene expression of structural and metabolic proteins, growth factors, hormones, and inflammatory cytokines. While the influence of environmental factors such as physical inactivity, chronic diseases, smoking, alcohol consumption, and sleep disturbances on sarcopenia is relatively well understood, there is a dearth of studies examining their mechanistic roles. Therefore, this review emphasizes the interplay between genetic and environmental factors, elucidating their cumulative role in exacerbating the progression of sarcopenia beyond their individual effects. The unique contribution of this review lies in synthesizing the latest evidence on the genetic factors and their interaction with environmental factors, aiming to inform the development of novel therapeutic or preventive interventions for sarcopenia.

Alternative Transcripts Diversify Genome Function for Phenome Relevance to Health and Diseases

Manipulation using alternative exon splicing (AES), alternative transcription start (ATS), and alternative polyadenylation (APA) sites are key to transcript diversity underlying health and disease. All three are pervasive in organisms, present in at least 50% of human protein-coding genes. In fact, ATS and APA site use has the highest impact on protein identity, with their ability to alter which first and last exons are utilized as well as impacting stability and translation efficiency. These RNA variants have been shown to be highly specific, both in tissue type and stage, with demonstrated importance to cell proliferation, differentiation and the transition from fetal to adult cells. While alternative exon splicing has a limited effect on protein identity, its ubiquity highlights the importance of these minor alterations, which can alter other features such as localization. The three processes are also highly interwoven, with overlapping, complementary, and competing factors, RNA polymerase II and its CTD (C-terminal domain) chief among them. Their role in development means dysregulation leads to a wide variety of disorders and cancers, with some forms of disease disproportionately affected by specific mechanisms (AES, ATS, or APA). Challenges associated with the genome-wide profiling of RNA variants and their potential solutions are also discussed in this review.

Cryopreservation Alters Tissue Structure and Improves Differentiation of Engineered Skeletal Muscle

Tissue-engineered skeletal muscle can play an important role in regenerative medicine, disease modeling, drug testing, as well as the actuation of biohybrid machines. As the applications of engineered muscle tissues expand, there exists a growing need to cryopreserve and store these tissues without impairing function. In a previous study, we developed a cryopreservation protocol in which engineered skeletal muscle tissues are frozen before myogenic differentiation. In that study, we found that this cryopreservation process led to a three-fold increase in the force generation of the differentiated muscle. Here, we perform further testing to determine the mechanisms by which cryopreservation enhances engineered skeletal muscle function. We found that cryopreservation alters the microstructure of the tissue by increasing pore size and decreasing elastic modulus of the extracellular matrix (ECM), which leads to increased expression of genes related to cell migration, cell-matrix adhesion, ECM secretion, and protease activity. Specifically, cryopreservation leads to the upregulation of many ECM proteins, including laminin, fibronectin, and several types of collagens, as well as integrins and matrix metalloproteinases. These changes to ECM structure and composition were associated with enhanced myogenic differentiation, as evidenced by the upregulation of late-stage myogenic markers and increased force generation. These results highlight the need to understand the effects of cryopreservation on the ECM of other tissues as we strive to advance tissue and organ cryopreservation protocols for regenerative medicine.

Lower muscle protein synthesis in humans with obesity concurrent with lower expression of muscle IGF1 splice variants

OBJECTIVE

This study tested the hypothesis that expression of insulin-like growth factor 1 (IGF-1) protein and mRNA splice variants is lower in skeletal muscle of humans with obesity who have a lower mixed-muscle protein fractional synthesis rate (MMP-FSR) when compared with individuals without obesity.

METHODS

The study included nine participants with obesity (OB, mean [SD],  BMI = 35 [3] kg/m2 , MMP-FSR = 0.06%/h [0.02%/h]) and nine participants without obesity (W-OB, BMI = 24 [3] kg/m2 , MMP-FSR = 0.08%/h [0.02%/h]; for both BMI and MMP-FSR p < 0.05). MMP-FSR and mitochondrial protein FSR were measured following an overnight fast.

RESULTS

Along with lower MMP-FSR, OB participants displayed lower mitochondrial protein FSR (p = 0.03) compared with W-OB participants. Expression of IGF-1 (p = 0.04) and IGF-1 receptor (p < 0.01) proteins was lower in muscle of OB participants. In addition, OB participants had lower (p < 0.05) mRNA expression of IGF1 variants Eb and Ec. This study demonstrates that lower protein synthesis in muscle of humans with obesity occurs concurrently with lower expression of muscle IGF-1 and IGF-1 receptor proteins, as well as lower mRNA expression of the IGF1 splice variants.

CONCLUSIONS

These findings indicate that lower protein synthesis observed in muscle of humans with obesity may result from diminished muscle IGF1 gene expression.

A Korean Nationwide Cross-Sectional Study Investigating Risk Factors, Prevalence, and Characteristics of Sarcopenia in Men in Early Old Age

The present study investigated the risk factors, prevalence, and characteristics of sarcopenia among men aged 50-64 years. A total of 2868 participants were enrolled in this study. Of these, 328 individuals were classified into a sarcopenia group; the remaining 2540 were assigned to a control group. This study examined several variables, including skeletal muscle mass index, age, height, weight, body mass index, waist circumference, systolic and diastolic blood pressure, fasting glucose, triglyceride and total cholesterol levels, alcohol consumption, and tobacco use. It employed a stratified, clustered, and multistage probability sampling design. Complex sampling was used for the data analysis. The prevalence of sarcopenia was 10.25% (95% CI: 8.98-11.69). All anthropometric measures, including height, weight, BMI, and waist circumference, were significantly different between the two groups (p < 0.05). In terms of blood pressure, only systolic blood pressure (SBP) was significant (p < 0.05), and fasting glucose and triglyceride levels were risk factors for sarcopenia (p < 0.05). Tobacco use differed significantly between the two groups (p < 0.05). This study reported the specific prevalence of sarcopenia and identified its risk factors among men in early old age.

Challenges in the care of individuals with severe primary insulin-like growth factor-I deficiency (SPIGFD): an international, multi-stakeholder perspective

BACKGROUND

Severe primary insulin-like growth factor-I (IGF-I) deficiency (SPIGFD) is a rare growth disorder characterized by short stature (standard deviation score [SDS] ≤ 3.0), low circulating concentrations of IGF-I (SDS ≤ 3.0), and normal or elevated concentrations of growth hormone (GH). Laron syndrome is the best characterized form of SPIGFD, caused by a defect in the GH receptor (GHR) gene. However, awareness of SPIGFD remains low, and individuals living with SPIGFD continue to face challenges associated with diagnosis, treatment and care.

OBJECTIVE

To gather perspectives on the key challenges for individuals and families living with SPIGFD through a multi-stakeholder approach. By highlighting critical gaps in the awareness, diagnosis, and management of SPIGFD, this report aims to provide recommendations to improve care for people affected by SPIGFD globally.

METHODS

An international group of clinical experts, researchers, and patient and caregiver representatives from the SPIGFD community participated in a virtual, half-day meeting to discuss key unmet needs and opportunities to improve the care of people living with SPIGFD.

RESULTS

As a rare disorder, limited awareness and understanding of SPIGFD amongst healthcare professionals (HCPs) poses significant challenges in the diagnosis and treatment of those affected. Patients often face difficulties associated with receiving a formal diagnosis, delayed treatment initiation and limited access to appropriate therapy. This has a considerable impact on the physical health and quality of life for patients, highlighting a need for more education and clearer guidance for HCPs. Support from patient advocacy groups is valuable in helping patients and their families to find appropriate care. However, there remains a need to better understand the burden that SPIGFD has on individuals beyond height, including the impact on physical, emotional, and social wellbeing.

CONCLUSIONS

To address the challenges faced by individuals and families affected by SPIGFD, greater awareness of SPIGFD is needed within the healthcare community, and a consensus on best practice in the care of individuals affected by this condition. Continued efforts are also needed at a global level to challenge existing perceptions around SPIGFD, and identify solutions that promote equitable access to appropriate care. Medical writing support was industry-sponsored.

Stromal vascular fraction in the treatment of myositis

Muscle regeneration is a physiological process that converts satellite cells into mature myotubes under the influence of an inflammatory environment progressively replaced by an anti-inflammatory environment, with precise crosstalk between immune and muscular cells. If the succession of these phases is disturbed, the immune system can sometimes become auto-reactive, leading to chronic muscular inflammatory diseases, such as myositis. The triggers of these autoimmune myopathies remain mostly unknown, but the main mechanisms of pathogenesis are partially understood. They involve chronic inflammation, which could be associated with an auto-reactive immune response, and gradually with a decrease in the regenerative capacities of the muscle, leading to its degeneration, fibrosis and vascular architecture deterioration. Immunosuppressive treatments can block the first part of the process, but sometimes muscle remains weakened, or even still deteriorates, due to the exhaustion of its capacities. For patients refractory to immunosuppressive therapies, mesenchymal stem cells have shown interesting effects but their use is limited by their availability. Stromal vascular fraction, which can easily be extracted from adipose tissue, has shown good tolerance and possible therapeutic benefits in several degenerative and autoimmune diseases. However, despite the increasing use of stromal vascular fraction, the therapeutically active components within this heterogeneous cellular product are ill-defined and the mechanisms by which this therapy might be active remain insufficiently understood. We review herein the current knowledge on the mechanisms of action of stromal vascular fraction and hypothesise on how it could potentially respond to some of the unmet treatment needs of refractory myositis.

Blocking insulin-like growth factor 1 receptor signaling pathway inhibits neuromuscular junction regeneration after botulinum toxin-A treatment

Botulinum toxin-A (BTX) administration into muscle is an established treatment for conditions with excessive muscle contraction. However, botulinum therapy has short-term effectiveness, and high-dose injection of BTX could induce neutralizing antibodies against BTX. Therefore, prolonging its effects could be beneficial in a clinical situation. Insulin-like growth factor-1 receptor (IGF1R) and its ligands, insulin-like growth factor (IGF) -I and II, regulate the physiological and pathological processes of the nervous system. It has been suggested that IGF1R is involved in the process after BTX administration, but the specific regeneration mechanism remains unclear. Therefore, this study aimed to determine how inhibition of IGF1R signaling pathway affects BTX-induced muscle paralysis. The results showed that anti-IGF1R antibody administration inhibited the recovery from BTX-induced neurogenic paralysis, and the synaptic components at the neuromuscular junction (NMJ), mainly post-synaptic components, were significantly affected by the antibody. In addition, the wet weight or frequency distribution of the cross-sectional area of the muscle fibers was regulated by IGF1R, and sequential antibody administration following BTX treatment increased the number of Pax7+-satellite cells in the gastrocnemius (GC) muscle, independent of NMJ recovery. Moreover, BTX treatment upregulated mammalian target of rapamycin (mTOR)/S6 kinase signaling pathway, HDAC4, Myog, Fbxo32/MAFbx/Atrogin-1 pathway, and transcription of synaptic components, but not autophagy. Finally, IGF1R inhibition affected only mTOR/S6 kinase translational signaling in the GC muscle. In conclusion, the IGF1R signaling pathway is critical for NMJ regeneration via specific translational signals. IGF1R inhibition could be highly beneficial in clinical practice by decreasing the number of injections and total dose of BTX due to the prolonged duration of the effect.

Mini Nutrition Assessment-Short Form score is associated with sarcopenia even among nourished people - A result of a feasibility study of a registry

Objectives

This study aims to identify a new barrier to the use of the Mini-Nutrition Assessment Short-Form (MNA-SF), which is a malnutrition assessment tool for the risk assessment of sarcopenia in a nourished population.

Methods

The MNA-SF was completed, and individuals with a score of > 11 were considered nourished in this cross-sectional feasibility study of a registry. Sarcopenia was assessed in 766 healthy, nourished adults (33.4% men, 64.9 ± 7.1 years) based on the European Working Group on Sarcopenia in Older People 2 (EWGSOP2).

Results

The MNA-SF scores for non-sarcopenia, pre-, confirmed, and severe sarcopenia were 13.59 ± 0.69, 13.73 ± 0.60, 12.64 ± 0.74, and 12.5 ± 0.71, respectively. The higher MNA-SF score association with pre-sarcopenia [odds ratio (OR): 1.41, 95% confidence interval (CI): 1.06-1.86, P = 0.02], confirmed sarcopenia (OR = 0.25, 95% CI: 0.13-0.49, P < 0.001), and severe sarcopenia (OR = 0.20, 95% CI: 0.09-0.46, P < 0.001) was as significant as in the MNA-SF categories. Individuals with a score = 13 (compared with 14), had a higher risk of confirmed sarcopenia (OR = 10.07, 95% CI: 1.92-52.71, P = 006) and severe sarcopenia (OR = 12.09, 95% CI: 1.24-117.50, P = 0.032). Individuals with a score of 12 had a higher risk of confirmed sarcopenia (OR = 30.94, 95% CI: 4.25-103.02, P < 0.001) and severe sarcopenia (OR = 35.90, 95% CI: 4.25-303.07, P = 0.001) compared with subjects with a score of 14. The models also showed that MNA-SF < 13 could predict sarcopenia.

Conclusion

There was a significant association between MNA-SF and confirmed and severe sarcopenia in nourished people. Sarcopenia assessment in people with MNA-SF < 13 can be beneficial. Developing a tool to identify the risk of malnutrition and sarcopenia at the same time based on MNA-SF can be considered.

Autophagy in sarcopenia: Possible mechanisms and novel therapies

With global population aging, age-related diseases, especially sarcopenia, have attracted much attention in recent years. Characterized by low muscle strength, low muscle quantity or quality and low physical performance, sarcopenia is one of the major factors associated with an increased risk of falls and disability. Much effort has been made to understand the cellular biological and physiological mechanisms underlying sarcopenia. Autophagy is an important cellular self-protection mechanism that relies on lysosomes to degrade misfolded proteins and damaged organelles. Research designed to obtain new insight into human diseases from the autophagic aspect has been carried out and has made new progress, which encourages relevant studies on the relationship between autophagy and sarcopenia. Autophagy plays a protective role in sarcopenia by modulating the regenerative capability of satellite cells, relieving oxidative stress and suppressing the inflammatory response. This review aims to reveal the specific interaction between sarcopenia and autophagy and explore possible therapies in hopes of encouraging more specific research in need and unlocking novel promising therapies to ameliorate sarcopenia.

Aerobic exercise enhances mitochondrial homeostasis to counteract D-galactose-induced sarcopenia in zebrafish

Sarcopenia is a common skeletal muscle degenerative disease characterized by decreased skeletal muscle mass and mitochondrial dysfunction that involves microRNAs (miR) as regulatory factors in various pathways. Exercise reduces age-related oxidative damage and chronic inflammation and increases autophagy, among others. Moreover, whether aerobic exercise can regulate mitochondrial homeostasis by modulating the miR-128/insulin-like growth factor-1 (IGF-1) signaling pathway and can improve sarcopenia requires further investigation. Interestingly, zebrafish have been used as a model for aging research for over a decade due to their many outstanding advantages. Therefore, we established a model of zebrafish sarcopenia using d-galactose immersion and observed substantial changes, including reduced skeletal muscle cross-sectional area, increased tissue fibrosis, decreased motility, increased skeletal muscle reactive oxygen species, and notable alterations in mitochondrial morphology and function. We found that miR-128 expression was considerably upregulated, where as Igf1 and peroxisome proliferator-activated receptor gamma coactivator 1-alpha were significantly downregulated; moreover, mitochondrial homeostasis was reduced. Four weeks of aerobic exercise delayed sarcopenia progression and prevented the disruption of mitochondrial function and homeostasis. The genes related to atrophy and miR-128 were downregulated, Igf1 expression was considerably upregulated, and the phosphorylation levels of Pi3k, Akt, and Foxo3a were upregulated. Furthermore, mitochondrial respiration and homeostasis were enhanced. In conclusion, aerobic exercise improved skeletal muscle quality and function via the miR-128/IGF-1 signaling pathway, consequently ameliorating mitochondrial homeostasis in aging skeletal muscle.

Sleep Duration and Sarcopenia: An Updated Systematic Review and Meta-Analysis

OBJECTIVES

In adults, short and long sleep duration has been associated with sarcopenia risk. Studies have shown that various factors, including biological and psychological factors, could be the underlying cause of the association between aberrant sleep duration and sarcopenia risk. In this study, we have qualitatively and quantitatively summarized previously published studies on sleep duration to assess the relationship between sleep duration and sarcopenia risk in adults. This would aid in enhancing our understanding of recent advancements in this field and the association between sleep duration and sarcopenia risk.

DESIGN

Systematic review and meta-analysis.

SETTING AND PARTICIPANTS

In this review, we included studies evaluating the association between the duration of sleep and sarcopenia in adults in observational studies.

METHODS

Five electronic databases (PubMed, EMBASE, Cochrane Library, China National Knowledge Infrastructure, and Web of Science) were searched to April 20, 2023, to identify studies related to sarcopenia and sleep duration. Next, we calculated the odds ratios (ORs) for sarcopenia prevalence based on the adjusted data from individual studies. Statistical analyses were performed using Stata 11.0.

RESULTS

Sarcopenia prevalence was high (18%) in adults with long sleep duration. Our results showed a significant association between short duration of sleep and high sarcopenia prevalence in older adults (OR 1.2, 95% CI 1.02-1.41, I2 = 56.6%). Furthermore, a significant association was observed between all participants with long-duration sleep and high sarcopenia prevalence (OR 1.53, 95% CI 1.34-1.75, I2 = 56.8%). We also observed significant heterogeneity in the adjusted ORs.

CONCLUSIONS AND IMPLICATIONS

There was a correlation between sarcopenia and short or long sleep duration, especially in older adults. In adults with a long duration of sleep, sarcopenia prevalence was relatively high.

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.

The super-healing MRL strain promotes muscle growth in muscular dystrophy through a regenerative extracellular matrix

Genetic background shifts the severity of muscular dystrophy. In mice, the DBA/2J strain confers a more severe muscular dystrophy phenotype, whereas the Murphy's Roth Large (MRL) strain has "super-healing" properties that reduce fibrosis. A comparative analysis of the Sgcg null model of Limb Girdle Muscular Dystrophy in the DBA/2J versus MRL strain showed the MRL background was associated with greater myofiber regeneration and reduced structural degradation of muscle. Transcriptomic profiling of dystrophic muscle in the DBA/2J and MRL strains indicated strain-dependent expression of the extracellular matrix (ECM) and TGF-β signaling genes. To investigate the MRL ECM, cellular components were removed from dystrophic muscle sections to generate decellularized "myoscaffolds". Decellularized myoscaffolds from dystrophic mice in the protective MRL strain had significantly less deposition of collagen and matrix-bound TGF-β1 and TGF-β3 throughout the matrix, and dystrophic myoscaffolds from the MRL background were enriched in myokines. C2C12 myoblasts were seeded onto decellularized matrices from Sgcg-/- MRL and Sgcg-/- DBA/2J matrices. Acellular myoscaffolds from the dystrophic MRL background induced myoblast differentiation and growth compared to dystrophic myoscaffolds from the DBA/2J matrices. These studies establish that the MRL background also generates its effect through a highly regenerative ECM, which is active even in muscular dystrophy.

Down-regulated Smyd1 participated in the inhibition of myoblast differentiation induced by cigarette smoke extract

The histone methyltransferase Smyd1 is essential for muscle development; however, its role in smoking-induced skeletal muscle atrophy and dysfunction has not been investigated thus far. In this study, Smyd1 was overexpressed or knocked down in C2C12 myoblasts by an adenovirus vector and cultured in differentiation medium containing 5% cigarette smoke extract (CSE) for 4 days. CSE exposure resulted in inhibition of C2C12 cell differentiation and downregulation of Smyd1 expression, whereas Smyd1 overexpression reduced the degree of inhibition of myotube differentiation caused by CSE exposure. CSE exposure activated P2RX7-mediated apoptosis and pyroptosis, caused increased intracellular reactive oxygen species (ROS) levels, and impaired mitochondrial biogenesis and increased protein degradation by downregulating PGC1α, whereas Smyd1 overexpression partially restored the altered protein levels caused by CSE exposure. Smyd1 knockdown alone produced a phenotype similar to CSE exposure, and Smyd1 knockdown during CSE exposure aggravated the degree of inhibition of myotube differentiation and the degree of activation of P2RX7. CSE exposure suppressed H3K4me2 expression, and chromatin immunoprecipitation confirmed the transcriptional regulation of P2rx7 by H3K4me2 modification. Our findings suggest that CSE exposure mediates C2C12 cell apoptosis and pyroptosis through the Smyd1-H3K4me2-P2RX7 axis, and inhibits PGC1α expression to impair mitochondrial biosynthesis and increase protein degradation by inhibiting Smyd1 expression, ultimately leading to abnormal C2C12 myoblasts differentiation and impaired myotube formation.

Mechanisms Underlying the Effects of the Green Tea Polyphenol EGCG in Sarcopenia Prevention and Management

Sarcopenia is prevalent among the older population and severely affects human health. Tea catechins may benefit for skeletal muscle performance and protect against secondary sarcopenia. However, the mechanisms underlying their antisarcopenic effect are still not fully understood. Despite initial successes in animal and early clinical trials regarding the safety and efficacy of (-)-epigallocatechin-3-gallate (EGCG), a major catechin of green tea, many challenges, problems, and unanswered questions remain. In this comprehensive review, we discuss the potential role and underlying mechanisms of EGCG in sarcopenia prevention and management. We thoroughly review the general biological activities and general effects of EGCG on skeletal muscle performance, EGCG's antisarcopenic mechanisms, and recent clinical evidence of the aforesaid effects and mechanisms. We also address safety issues and provide directions for future studies. The possible concerted actions of EGCG indicate the need for further studies on sarcopenia prevention and management in humans.

Mitochondrial transplantation as a possible therapeutic option for sarcopenia

With advancing age, the skeletal muscle phenotype is characterized by a progressive loss of mass, strength, and quality. This phenomenon, known as sarcopenia, has a negative impact on quality of life and increases the risk of morbidity and mortality in older adults. Accumulating evidence suggests that damaged and dysfunctional mitochondria play a critical role in the pathogenesis of sarcopenia. Lifestyle modifications, such as physical activity, exercise, and nutrition, as well as medical interventions with therapeutic agents, are effective in the management of sarcopenia and offer solutions to maintain and improve skeletal muscle health. Although a great deal of effort has been devoted to the identification of the best treatment option, these strategies are not sufficient to overcome sarcopenia. Recently, it has been reported that mitochondrial transplantation may be a possible therapeutic approach for the treatment of mitochondria-related pathological conditions such as ischemia, liver toxicity, kidney injury, cancer, and non-alcoholic fatty liver disease. Given the role of mitochondria in the function and metabolism of skeletal muscle, mitochondrial transplantation may be a possible option for the treatment of sarcopenia. In this review, we summarize the definition and characteristics of sarcopenia and molecular mechanisms associated with mitochondria that are known to contribute to sarcopenia. We also discuss mitochondrial transplantation as a possible option. Despite the progress made in the field of mitochondrial transplantation, further studies are needed to elucidate the role of mitochondrial transplantation in sarcopenia. KEY MESSAGES: Sarcopenia is the progressive loss of skeletal muscle mass, strength, and quality. Although the specific mechanisms that lead to sarcopenia are not fully understood, mitochondria have been identified as a key factor in the development of sarcopenia. Damaged and dysfunctional mitochondria initiate various cellular mediators and signaling pathways, which largely contribute to the age-related loss of skeletal muscle mass and strength. Mitochondrial transplantation has been reported to be a possible option for the treatment/prevention of several diseases. Mitochondrial transplantation may be a possible therapeutic option for improving skeletal muscle health and treating sarcopenia. Mitochondrial transplantation as a possible treatment option for sarcopenia.

Unlocking the Therapeutic Potential of Irisin: Harnessing Its Function in Degenerative Disorders and Tissue Regeneration

Physical activity is well-established as an important protective factor against degenerative conditions and a promoter of tissue growth and renewal. The discovery of Fibronectin domain-containing protein 5 (FNDC5) as the precursor of Irisin in 2012 sparked significant interest in its potential as a diagnostic biomarker and a therapeutic agent for various diseases. Clinical studies have examined the correlation between plasma Irisin levels and pathological conditions using a range of assays, but the lack of reliable measurements for endogenous Irisin has led to uncertainty about its prognostic/diagnostic potential as an exercise surrogate. Animal and tissue-engineering models have shown the protective effects of Irisin treatment in reversing functional impairment and potentially permanent damage, but dosage ambiguities remain unresolved. This review provides a comprehensive examination of the clinical and basic studies of Irisin in the context of degenerative conditions and explores its potential as a therapeutic approach in the physiological processes involved in tissue repair/regeneration.

The role of insulin-like growth factor-1 in bone remodeling: A review

Insulin-like growth factor (IGF)-1 is a polypeptide hormone with vital biological functions in bone cells. The abnormal expression of IGF-1 has a serious effect on bone growth, particularly bone remodeling. Evidence from animal models and human disease suggested that both IGF-1 deficiency and excess cause changes in bone remodeling equilibrium, resulting in profound alterations in bone mass and development. Here, we first introduced the functions and mechanisms of the members of IGFs in bone. Subsequently, the critical role of IGF-1 in the process of bone remodeling were emphasized from the aspects of bone resorption and bone formation respectively. This review explains the mechanism of IGF-1 in maintaining bone mass and bone homeostasis to a certain extent and provides a theoretical basis for further research.

Stem cell therapy combined with controlled release of growth factors for the treatment of sphincter dysfunction

Sphincter dysfunction often occurs at the end of tubule organs such as the urethra, anus, or gastroesophageal sphincters. It is the primary consequence of neuromuscular impairment caused by trauma, inflammation, and aging. Despite intensive efforts to recover sphincter function, pharmacological treatments have not achieved significant improvement. Cell- or growth factor-based therapy is a promising approach for neuromuscular regeneration and the recovery of sphincter function. However, a decrease in cell retention and viability, or the short half-life and rapid degradation of growth factors after implantation, remain obstacles to the translation of these therapies to the clinic. Natural biomaterials provide unique tools for controlled growth factor delivery, which leads to better outcomes for sphincter function recovery in vivo when stem cells and growth factors are co-administrated, in comparison to the delivery of single therapies. In this review, we discuss the role of stem cells combined with the controlled release of growth factors, the methods used for delivery, their potential therapeutic role in neuromuscular repair, and the outcomes of preclinical studies using combination therapy, with the hope of providing new therapeutic strategies to treat incontinence or sphincter dysfunction of the urethra, anus, or gastroesophageal tissues, respectively.

MyMD-1 Improves Health Span and Prolongs Life Span in Old Mice: A Noninferiority Study to Rapamycin

Aging and age-related diseases represent a compelling therapeutic goal for senolytics and drugs targeting inflammatory or metabolic pathways. We compared MyMD-1, a synthetic derivative of the alkaloid myosmine capable of suppressing TNF-α production, to rapamycin, the best characterized drug endowed with antiaging properties. In vivo, a longitudinal cohort of 54 C57BL/6 mice, 19-month-old at the start, was randomized to receive MyMD-1, high-dose (126 ppm) rapamycin, or low-dose (14 ppm) rapamycin plus metformin. Each treatment arm included 18 mice (10 females and 8 males) and was followed for 16 months or until death. Life span was significantly longer in MyMD-1 than rapamycin (p = .019 vs high-dose and .01 vs low-dose) in a Cox survival model that accounted for sex and serum levels of IL-6, TNF-α, and IL-17A. MyMD-1 also improved several health span characteristics, resulting in milder body weight loss, greater muscle strength, and slower progression to frailty. In vitro, MyMD-1 and rapamycin were compared using a panel of 12 human primary cell systems (BioMAP Diversity PLUS), where a total of 148 biomarkers were measured. MyMD-1 possessed antiproliferative, anti-inflammatory, and antifibrotic properties. Many were shared with rapamycin, but MyMD-1 was more active in the inhibition of proinflammatory and profibrotic biomarkers. Overall, MyMD-1 emerges as a new compound that, even when begun at an advanced age, induces beneficial effects on health and life span by modulating inflammation and tissue remodeling.

Impact of Sarcopenia on Non-Alcoholic Fatty Liver Disease

With the increasing incidence of non-alcoholic fatty liver disease (NAFLD) and the aging of the population, sarcopenia is attracting attention as one of the pathological conditions involved in the development and progression of NAFLD. In NAFLD, sarcopenia is closely associated with insulin resistance and results from the atrophy of skeletal muscle, an insulin target organ. In addition, inflammatory cytokines that promote skeletal muscle protein breakdown, low adiponectin levels leading to decreased insulin sensitivity, and hyperleptinemia are also involved in NAFLD pathogenesis. The presence of sarcopenia is a prognostic factor and increases the risk of mortality in patients with cirrhosis and post-treatment liver cancer. Sarcopenia, the presence of which mainly occurs due to decreased muscle mass, combined with increased visceral fat, can lead to sarcopenia-associated obesity, which increases the risk of NASH, liver fibrosis, and cardiovascular disease. In order to treat sarcopenia, it is necessary to properly evaluate sarcopenia status. Patients with high BMI, as in sarcopenic obesity, may improve with caloric restriction. However, inadequate oral intake may lead to further loss of muscle mass. Aerobic and resistance exercise should also be used appropriately.

Sarcopenia: Molecular regulatory network for loss of muscle mass and function

Skeletal muscle is the foundation of human function and plays a key role in producing exercise, bone protection, and energy metabolism. Sarcopenia is a systemic disease, which is characterized by degenerative changes in skeletal muscle mass, strength, and function. Therefore, sarcopenia often causes weakness, prolonged hospitalization, falls and other adverse consequences that reduce the quality of life, and even lead to death. In recent years, sarcopenia has become the focus of in-depth research. Researchers have suggested some molecular mechanisms for sarcopenia according to different muscle physiology. These mechanisms cover neuromuscular junction lesion, imbalance of protein synthesis and breakdown, satellite cells dysfunction, etc. We summarize the latest research progress on the molecular mechanism of sarcopenia in this review in order to provide new ideas for future researchers to find valuable therapeutic targets and develop relevant prevention strategies.

In Vitro and In Vivo Effects of IGF-1 Delivery Strategies on Tendon Healing: A Review

Tendon injuries suffer from a slow healing, often ending up in fibrovascular scar formation, leading to inferior mechanical properties and even re-rupture upon resumption of daily work or sports. Strategies including the application of growth factors have been under view for decades. Insulin-like growth factor-1 (IGF-1) is one of the used growth factors and has been applied to tenocyte in vitro cultures as well as in animal preclinical models and to human patients due to its anabolic and matrix stimulating effects. In this narrative review, we cover the current literature on IGF-1, its mechanism of action, in vitro cell cultures (tenocytes and mesenchymal stem cells), as well as in vivo experiments. We conclude from this overview that IGF-1 is a potent stimulus for improving tendon healing due to its inherent support of cell proliferation, DNA and matrix synthesis, particularly collagen I, which is the main component of tendon tissue. Nevertheless, more in vivo studies have to be performed in order to pave the way for an IGF-1 application in orthopedic clinics.

Male sex hormones, aging, and inflammation

Adequate levels of androgens (eugonadism), and specifically testosterone, are vital compounds for male quality of life, longevity, and positive health outcomes. Testosterone exerts its effects by binding to the androgen receptor, which is expressed in numerous tissues throughout the body. Significant research has been conducted on the impact of this steroid hormone on skeletal, muscle and adipose tissues and on the cardiovascular, immune, and nervous systems. Testosterone levels have also been studied in relation to the impact of diseases, aging, nutrition and the environment on its circulating levels. Conversely, the impact of testosterone on health has also been evaluated with respect to its cardiac and vascular protective effects, body composition, autoimmunity and all-cause mortality. The male aging process results in decreasing testosterone levels over time. The exact mechanisms and impact of these changes in testosterone levels with age on health- and life-span are still not completely clear. Further research is needed to determine the optimal testosterone and androgen levels to protect from chronic age-related conditions such as frailty and osteoporosis.

Melatonin improves muscle injury and differentiation by increasing Pax7 expression

A balance between muscle injury and regeneration is critical for sustaining muscle function during myogenesis. Melatonin is well recognized for its involvement in neuroprotective activities, immune system regulation and suppression of inflammatory responses. This study set out to provide evidence that melatonin improves muscle regeneration during skeletal muscle differentiation. We began with cloning a stable cell line expressing Pax7 knockdown C2C12 cells. We then investigated markers of muscle degradation and regeneration after treating growth medium and differentiated medium with melatonin. Bioinformatics analysis of RNA sequencing results revealed that melatonin regulates muscle differentiation and that Wnt cascades are involved in the mechanism of muscle differentiation. Screening of miRNA online databases revealed that miR-3475-3p is a specific binding site on Pax7 and acts as a negative regulator of Pax7, which is involved in melatonin-induced muscle differentiation. We then investigated the effects of melatonin treatment in the early stage of glycerol-induced skeletal muscle injury in mice. Rotarod performance, micro-computed tomography and immunohistochemistry findings showed that melatonin-induced increases in Pax7 expression rapidly rescue skeletal muscle differentiation and improve muscle fiber morphology in glycerol-induced muscle injury. Our data support the hypothesis that melatonin rapidly rescues skeletal muscle differentiation and the melatonin/Pax7 axis could therefore serve as an important therapeutic target to optimize muscle healing after injury.

Aging and aging-related diseases: from molecular mechanisms to interventions and treatments

Aging is a gradual and irreversible pathophysiological process. It presents with declines in tissue and cell functions and significant increases in the risks of various aging-related diseases, including neurodegenerative diseases, cardiovascular diseases, metabolic diseases, musculoskeletal diseases, and immune system diseases. Although the development of modern medicine has promoted human health and greatly extended life expectancy, with the aging of society, a variety of chronic diseases have gradually become the most important causes of disability and death in elderly individuals. Current research on aging focuses on elucidating how various endogenous and exogenous stresses (such as genomic instability, telomere dysfunction, epigenetic alterations, loss of proteostasis, compromise of autophagy, mitochondrial dysfunction, cellular senescence, stem cell exhaustion, altered intercellular communication, deregulated nutrient sensing) participate in the regulation of aging. Furthermore, thorough research on the pathogenesis of aging to identify interventions that promote health and longevity (such as caloric restriction, microbiota transplantation, and nutritional intervention) and clinical treatment methods for aging-related diseases (depletion of senescent cells, stem cell therapy, antioxidative and anti-inflammatory treatments, and hormone replacement therapy) could decrease the incidence and development of aging-related diseases and in turn promote healthy aging and longevity.

Effect of Mechanical Loading of Senescent Myoblasts on Their Myogenic Lineage Progression and Survival

BACKGROUND

During aging, muscle cell apoptosis increases and myogenesis gradually declines. The impaired myogenic and survival potential of the aged skeletal muscle can be ameliorated by its mechanical loading. However, the molecular responses of aged muscle cells to mechanical loading remain unclear. This study examined the effect of mechanical loading of aged, proliferating, and differentiated myoblasts on the gene expression and signaling responses associated with their myogenic lineage progression and survival.

METHODS

Control and aged C2C12 cells were cultured on elastic membranes and underwent passive stretching for 12 h at a low frequency (0.25 Hz) and different elongations, varying the strain on days 0 and 10 of myoblast differentiation. Activation of ERK1/2 and Akt, and the expression of focal adhesion kinase (FAK) and key myogenic regulatory factors (MRFs), MyoD and Myogenin, were determined by immunoblotting of the cell lysates derived from stretched and non-stretched myoblasts. Changes in the expression levels of the MRFs, muscle growth, atrophy, and pro-apoptotic factors in response to mechanical loading of the aged and control cells were quantified by real-time qRT-PCR.

RESULTS

Mechanical stretching applied on myoblasts resulted in the upregulation of FAK both in proliferating (day 0) and differentiated (day 10) cells, as well as in increased phosphorylation of ERK1/2 in both control and aged cells. Moreover, Akt activation and the expression of early differentiation factor MyoD increased significantly after stretching only in the control myoblasts, while the late differentiation factor Myogenin was upregulated in both the control and aged myoblasts. At the transcriptional level, mechanical loading of the proliferating myoblasts led to an increased expression of IGF-1 isoforms and MRFs, and to downregulation of muscle atrophy factors mainly in control cells, as well as in the upregulation of pro-apoptotic factors both in control and aged cells. In differentiated cells, mechanical loading resulted in an increased expression of the IGF-1Ea isoform and Myogenin, and in the downregulation of atrophy and pro-apoptotic factors in both the control and aged cells.

CONCLUSIONS

This study revealed a diminished beneficial effect of mechanical loading on the myogenic and survival ability of the senescent muscle cells compared with the controls, with a low strain (2%) loading being most effective in upregulating myogenic/anabolic factors and downregulating atrophy and pro-apoptotic genes mainly in the aged myotubes.

HMGB1 Promotes In Vitro and In Vivo Skeletal Muscle Atrophy through an IL-18-Dependent Mechanism

Skeletal muscle atrophy occurs due to muscle wasting or reductions in protein associated with aging, injury, and inflammatory processes. High-mobility group box-1 (HMGB1) protein is passively released from necrotic cells and actively secreted by inflammatory cells, and is implicated in the pathogenesis of various inflammatory and immune diseases. HMGB1 is upregulated in muscle inflammation, and circulating levels of the proinflammatory cytokine interleukin-18 (IL-18) are upregulated in patients with sarcopenia, a muscle-wasting disease. We examined whether an association exists between HMGB1 and IL-18 signaling in skeletal muscle atrophy. HMGB1-induced increases of IL-18 levels enhanced the expression of muscle atrophy markers and inhibited myogenic marker expression in C2C12 and G7 myoblast cell lines. HMGB1-induced increases of IL-18 production in C2C12 cells involved the RAGE/p85/Akt/mTOR/c-Jun signaling pathway. HMGB1 short hairpin RNA (shRNA) treatment rescued the expression of muscle-specific differentiation markers in murine C2C12 myotubes and in mice with glycerol-induced muscle atrophy. HMGB1 and IL-18 signaling was suppressed in the mice after HMGB1 shRNA treatment. These findings suggest that the HMGB1/IL-18 axis is worth targeting for the treatment of skeletal muscle atrophy.