RAGE in the pathophysiology of skeletal muscle

Myeloma extracellular vesicle-derived RAGE increases inflammatory responses and myotube atrophy in multiple myeloma through activation of the TLR4/NF-κB p65 pathway

Sarcopenia manifests as muscle atrophy and loss that is complicated with malignancy. This study explored the mechanism of extracellular vesicles (EVs) in multiple myeloma (MM) with sarcopenia. SP2/0 conditioned medium (CM) was collected to isolate SP2/0-EVs. C2C12 cells were incubated with SP2/0 CM or SP2/0-EVs. ROS, TNF-α, IL-6, MuRF1 and MyHC levels were detected by DCF-DA fluorescent probe, ELISA, and Western blot. GW4869 was used to inhibit EV secretion in SP2/0 to confirm its effect on muscle atrophy. Serum was collected from MM patients with or without sarcopenia to detect RAGE mRNA expression. SP2/0 cells were transfected with RAGE siRNA and C2C12 cells were treated with the isolated si-RAGE-EVs or/and TLR4 agonist. SP2/0 tumor-bearing mouse model was established. Healthy mice and SP2/0-tumor bearing mice were treated with SP2/0-EVs or si-RAGE-EVs. SP2/0 CM or SP2/0-EVs stimulated ROS, inflammatory responses, and myotube atrophy in C2C12 cells. GW4869 blocked EV secretion and the effects of SP2/0 CM. RAGE mRNA expression in serum EVs was increased in MM&Sarcopenia patients and RAGE knockdown in SP2/0-EVs partially nullified SP2/0-EVs' effects. SP2/0-EVs activated the TLR4/NF-κB p65 pathway by translocating RAGE. SP2/0-EVs-derived RAGE elevated ROS production, inflammation, and myotube atrophy in C2C12 cells and caused muscle loss in SP2/0 tumor-bearing mice by activating the TLR4/NF-κB p65 pathway. SP2/0-EVs partially recapitulated muscle loss in healthy mice. SP2/0-EVs-derived RAGE increased ROS production, inflammation, and myotube atrophy in MM through TLR4/NF-κB p65 pathway activation.

Efferocytosis by macrophages in physiological and pathological conditions: regulatory pathways and molecular mechanisms

Efferocytosis is defined as the highly effective phagocytic removal of apoptotic cells (ACs) by professional or non-professional phagocytes. Tissue-resident professional phagocytes ("efferocytes"), such as macrophages, have high phagocytic capacity and are crucial to resolve inflammation and aid in homeostasis. Recently, numerous exciting discoveries have revealed divergent (and even diametrically opposite) findings regarding metabolic immune reprogramming associated with efferocytosis by macrophages. In this review, we highlight the key metabolites involved in the three phases of efferocytosis and immune reprogramming of macrophages under physiological and pathological conditions. The next decade is expected to yield further breakthroughs in the regulatory pathways and molecular mechanisms connecting immunological outcomes to metabolic cues as well as avenues for "personalized" therapeutic intervention.

S100b treatment overcomes RAGE signaling deficits in myoblasts on advanced glycation end-product cross-linked collagen and promotes myogenic differentiation

Advanced glycation end-products (AGEs) stochastically accrue in skeletal muscle and on collagen over an individual's lifespan, stiffening the muscle and modifying the stem cell (MuSC) microenvironment while promoting proinflammatory, antiregenerative signaling via the receptor for advanced glycation end-products (RAGEs). In the present study, a novel in vitro model was developed of this phenomenon by cross linking a 3-D collagen scaffold with AGEs and investigating how myoblasts responded to such an environment. Briefly, collagen scaffolds were incubated with d-ribose (0, 25, 40, 100, or 250 mM) for 5 days at 37°C. C2C12 immortalized mouse myoblasts were grown on the scaffolds for 6 days in growth conditions for proliferation, and 12 days for differentiation and fusion. Human primary myoblasts were also used to confirm the C2C12 data. AGEs aberrantly extended the DNA production stage of C2C12s (but not in human primary myoblasts) which is known to delay differentiation in myogenesis, and this effect was prevented by RAGE inhibition. Furthermore, the differentiation and fusion of myoblasts were disrupted by AGEs, which were associated with reductions in integrins and suppression of RAGE. The addition of S100b (RAGE agonist) recovered the differentiation and fusion of myoblasts, and the addition of RAGE inhibitors (FPS-ZM1 and Azeliragon) inhibited the differentiation and fusion of myoblasts. Our results provide novel insights into the role of the AGE-RAGE axis in skeletal muscle aging, and future work is warranted on the potential application of S100b as a proregenerative factor in aged skeletal muscle.NEW & NOTEWORTHY Collagen cross-linked by advanced glycation end-products (AGEs) induced myoblast proliferation but prevented differentiation, myotube formation, and RAGE upregulation. RAGE inhibition occluded AGE-induced myoblast proliferation, while the delivery of S100b, a RAGE ligand, recovered fusion deficits.

Association Between Advanced Glycation End Products and Sarcopenia: The Mediating Role of Osteoporosis

CONTEXT

Advanced glycation end products (AGEs) are a group of molecules formed through nonenzymatic reactions. These compounds are associated with several age-related diseases, including sarcopenia and osteoporosis.

OBJECTIVE

This work aimed to investigate the relationships between AGEs, osteoporosis, and sarcopenia in community-dwelling older adults.

METHODS

This cross-sectional study included 1991 older adults aged 72.37 ± 5.90 years from China. AGE levels were measured by the AGE Reader device. Bone mineral density was assessed using dual-energy X-ray absorptiometry, and osteoporosis was diagnosed based on a T score of less than -2.5. Sarcopenia was defined as loss of muscle mass plus loss of muscle strength and/or reduced physical performance. Presarcopenia was defined as low muscle mass with normal muscle strength and normal physical performance.

RESULTS

The prevalence of sarcopenia was 18.5%, and that of osteoporosis was 40.5%. Compared to the lowest AGE quartile, the highest AGE quartile showed a significant association with sarcopenia (odds ratio [OR] 2.42; 95% CI, 1.60-3.66) (P for trend <.001), but not with presarcopenia. Per-SD increase in AGE was associated with higher odds of sarcopenia (OR 1.44; 95% CI, 1.26-1.66). Additionally, in the mediation analysis, when AGEs were treated as a continuous variable (the mediation effect is denoted by Za*Zb = 18.81; 95% CI, 8.07-32.32]-the 95% CI does not contain zero, representing a significant mediating effect) or a categorical variable (the mediating effect is expressed as Zmediation = 3.01 > 1.96, which represents a significant mediating effect), osteoporosis played a partial mediating role in the association between AGEs and sarcopenia.

CONCLUSION

Elevated AGEs are associated with sarcopenia but not with presarcopenia. This association was partially mediated by osteoporosis.

Advanced glycation end products inhibit proliferation and primary cilia formation of myoblasts through receptor for advanced glycation end products pathway

The loss of skeletal muscle mass leads to various adverse conditions and shortened lifespan. The inhibition of myoblast proliferation is one of the causes that trigger muscle atrophy. Advanced glycation end products (AGEs) contribute to muscle atrophy. Since primary cilia are crucial organelles for proliferation, AGEs may inhibit primary cilia formation of myoblasts, thereby leading to impaired proliferation. Therefore, we aimed to clarify whether AGEs impeded the proliferation and formation of primary cilia of C2C12 skeletal muscle cells. AGE treatment inhibited the proliferation and formation of primary cilia. However, the inhibitor of the receptor for advanced glycosylation end products (RAGEs) abolished the inhibition of the proliferation and the primary cilia formation of C2C12 cells by AGEs, suggesting that AGEs cause these inhibitions through the RAGE pathway. In summary, our findings suggested that AGEs suppress the proliferation and formation of primary cilia of myoblasts through the RAGE pathway.

Modulating the RAGE-Induced Inflammatory Response: Peptoids as RAGE Antagonists

While the primary pathology of Alzheimer's disease (AD) is defined by brain deposition of amyloid-β (Aβ) plaques and tau neurofibrillary tangles, chronic inflammation has emerged as an important factor in AD etiology. Upregulated cell surface expression of the receptor for advanced glycation end-products (RAGE), a key receptor of innate immune response, is reported in AD. In parallel, RAGE ligands, including Aβ aggregates, HMGB1, and S100B, are elevated in AD brain. Activation of RAGE by these ligands triggers release of inflammatory cytokines and upregulates cell surface RAGE. Despite such observation, there are currently no therapeutics that target RAGE for treatment of AD-associated neuroinflammation. Peptoids, a novel class of potential AD therapeutics, display low toxicity, facile blood-brain barrier permeability, and resistance to proteolytic degradation. In the current study, peptoids were designed to mimic Aβ, a ligand that binds the V-domain of RAGE, and curtail RAGE inflammatory activation. We reveal the nanomolar binding capability of peptoids JPT1 and JPT1a to RAGE and demonstrate their ability to attenuate lipopolysaccharide-induced pro-inflammatory cytokine production as well as upregulation of RAGE cell surface expression. These results support RAGE antagonist peptoid-based mimics as a prospective therapeutic strategy to counter neuroinflammation in AD and other neurodegenerative diseases.

Development and Characterization of a Cancer Cachexia Rat Model Transplanted with Cells of the Rat Lung Adenocarcinoma Cell Line Sato Lung Cancer (SLC)

Cancer cachexia is a complex malnutrition syndrome that causes progressive dysfunction. This syndrome is accompanied by protein and energy losses caused by reduced nutrient intake and the development of metabolic disorders. As many as 80% of patients with advanced cancer develop cancer cachexia; however, an effective targeted treatment remains to be developed. In this study, we developed a novel rat model that mimics the human pathology during cancer cachexia to elucidate the mechanism underlying the onset and progression of this syndrome. We subcutaneously transplanted rats with SLC cells, a rat lung adenocarcinoma cell line, and evaluated the rats' pathophysiological characteristics. To ensure that our observations were not attributable to simple starvation, we evaluated the characteristics under tube feeding. We observed that SLC-transplanted rats exhibited severe anorexia, weight loss, muscle atrophy, and weakness. Furthermore, they showed obvious signs of cachexia, such as anemia, inflammation, and low serum albumin. The rats also exhibited weight and muscle losses despite sufficient nutrition delivered by tube feeding. Our novel cancer cachexia rat model is a promising tool to elucidate the pathogenesis of cancer cachexia and to conduct further research on the development of treatments and supportive care for patients with this disease.

Soluble RAGE and skeletal muscle tissue RAGE expression profiles in lean and obese young adults across differential aerobic exercise intensities

Nearly 40% of Americans have obesity and are at increased risk for developing type 2 diabetes. Skeletal muscle is responsible for >80% of insulin-stimulated glucose uptake that is attenuated by the inflammatory milieu of obesity and augmented by aerobic exercise. The receptor for advanced glycation endproducts (RAGE) is an inflammatory receptor directly linking metabolic dysfunction with inflammation. Circulating soluble isoforms of RAGE (sRAGE) formed either by proteolytic cleavage (cRAGE) or alternative splicing (esRAGE) act as decoys for RAGE ligands, thereby counteracting RAGE-mediated inflammation. We aimed to determine if RAGE expression or alternative splicing of RAGE is altered by obesity in muscle, and whether acute aerobic exercise (AE) modifies RAGE and sRAGE. Young (20-34 yr) participants without [n = 17; body mass index (BMI): 22.6 ± 2.6 kg/m2] and with obesity (n = 7; BMI: 32.8 ± 2.9 kg/m2) performed acute aerobic exercise (AE) at 40%, 65%, or 80% of maximal aerobic capacity (V̇o2max; mL/kg/min) on separate visits. Blood was taken before and 30 min after each AE bout. Muscle biopsy samples were taken before, 30 min, and 3 h after the 80% V̇o2max AE bout. Individuals with obesity had higher total RAGE and esRAGE mRNA and RAGE protein (P < 0.0001). In addition, RAGE and esRAGE transcripts correlated to transcripts of the NF-κB subunit P65 (P < 0.05). There was no effect of AE on total RAGE or esRAGE transcripts, or RAGE protein (P > 0.05), and AE tended to decrease circulating sRAGE in particular at lower intensities of exercise. RAGE expression is exacerbated in skeletal muscle with obesity, which may contribute to muscle inflammation via NF-κB. Future work should investigate the consequences of increased skeletal muscle RAGE on the development of obesity-related metabolic dysfunction and potential mitigating strategies.NEW & NOTEWORTHY This study is the first to investigate the effects of aerobic exercise intensity on circulating sRAGE isoforms, muscle RAGE protein, and muscle RAGE splicing. sRAGE isoforms tended to diminish with exercise, although this effect was attenuated with increasing exercise intensity. Muscle RAGE protein and gene expression were unaffected by exercise. However, individuals with obesity displayed nearly twofold higher muscle RAGE protein and gene expression, which positively correlated with expression of the P65 subunit of NF-κB.

Shared gene expression signatures between visceral adipose and skeletal muscle tissues are associated with cardiometabolic traits in children with obesity

Obesity in children is related to the development of cardiometabolic complications later in life, where molecular changes of visceral adipose tissue (VAT) and skeletal muscle tissue (SMT) have been proven to be fundamental. The aim of this study is to unveil the gene expression architecture of both tissues in a cohort of Spanish boys with obesity, using a clustering method known as weighted gene co-expression network analysis. For this purpose, we have followed a multi-objective analytic pipeline consisting of three main approaches; identification of gene co-expression clusters associated with childhood obesity, individually in VAT and SMT (intra-tissue, approach I); identification of gene co-expression clusters associated with obesity-metabolic alterations, individually in VAT and SMT (intra-tissue, approach II); and identification of gene co-expression clusters associated with obesity-metabolic alterations simultaneously in VAT and SMT (inter-tissue, approach III). In both tissues, we identified independent and inter-tissue gene co-expression signatures associated with obesity and cardiovascular risk, some of which exceeded multiple-test correction filters. In these signatures, we could identify some central hub genes (e.g., NDUFB8, GUCY1B1, KCNMA1, NPR2, PPP3CC) participating in relevant metabolic pathways exceeding multiple-testing correction filters. We identified the central hub genes PIK3R2, PPP3C and PTPN5 associated with MAPK signaling and insulin resistance terms. This is the first time that these genes have been associated with childhood obesity in both tissues. Therefore, they could be potential novel molecular targets for drugs and health interventions, opening new lines of research on the personalized care in this pathology. This work generates interesting hypotheses about the transcriptomics alterations underlying metabolic health alterations in obesity in the pediatric population.

Implications of receptor for advanced glycation end products for progression from obesity to diabetes and from diabetes to cancer

Obesity and type 2 diabetes mellitus (T2DM) are chronic pathologies with a high incidence worldwide. They share some pathological mechanisms, including hyperinsulinemia, the production and release of hormones, and hyperglycemia. The above, over time, affects other systems of the human body by causing tissue hypoxia, low-grade inflammation, and oxidative stress, which lay the pathophysiological groundwork for cancer. The leading causes of death globally are T2DM and cancer. Other main alterations of this pathological triad include the accumulation of advanced glycation end products and the release of endogenous alarmins due to cell death (i.e., damage-associated molecular patterns) such as the intracellular proteins high-mobility group box protein 1 and protein S100 that bind to the receptor for advanced glycation products (RAGE) - a multiligand receptor involved in inflammatory and metabolic and neoplastic processes. This review analyzes the latest advanced reports on the role of RAGE in the development of obesity, T2DM, and cancer, with an aim to understand the intracellular signaling mechanisms linked with cancer initiation. This review also explores inflammation, oxidative stress, hypoxia, cellular senescence, RAGE ligands, tumor microenvironment changes, and the “cancer hallmarks” of the leading tumors associated with T2DM. The assimilation of this information could aid in the development of diagnostic and therapeutic approaches to lower the morbidity and mortality associated with these diseases.

Post-translational regulation of muscle growth, muscle aging and sarcopenia

Skeletal muscle makes up 30-40% of the total body mass. It is of great significance in maintaining digestion, inhaling and exhaling, sustaining body posture, exercising, protecting joints and many other aspects. Moreover, muscle is also an important metabolic organ that helps to maintain the balance of sugar and fat. Defective skeletal muscle function not only limits the daily activities of the elderly but also increases the risk of disability, hospitalization and death, placing a huge burden on society and the healthcare system. Sarcopenia is a progressive decline in muscle mass, muscle strength and muscle function with age caused by environmental and genetic factors, such as the abnormal regulation of protein post-translational modifications (PTMs). To date, many studies have shown that numerous PTMs, such as phosphorylation, acetylation, ubiquitination, SUMOylation, glycosylation, glycation, methylation, S-nitrosylation, carbonylation and S-glutathionylation, are involved in the regulation of muscle health and diseases. This article systematically summarizes the post-translational regulation of muscle growth and muscle atrophy and helps to understand the pathophysiology of muscle aging and develop effective strategies for diagnosing, preventing and treating sarcopenia.

COVID-19 infection with complicated fulminant myocarditis: a case report

Herein, we report the case of a young female patient who suffered from myositis and heart failure due to fulminant myocarditis induced by the 2019 coronavirus disease (COVID-19). After receiving intra-aortic balloon pump (IABP) and immunomodulatory treatment, her vital signs gradually stabilized and the IABP was removed. Cardiac and muscle magnetic resonance imaging confirmed extensive myocardial and skeletal muscle edema. Though it is not uncommon for COVID-19 infection to be complicated by myocarditis and myositis, such serious muscle injury warrants clinical vigilance.

Advanced glycation end products in skeletal muscle health and sarcopenia: A systematic review of observational studies

BACKGROUND

Advanced glycation end products (AGEs) and AGEs receptor (RAGE) may play a role in sarcopenia. This systematic review evaluated the associations between AGEs measured in tissues (skin) by autofluorescence (SAF) and/or circulation (blood, urine) and muscle health outcomes (strength, mass, function) and sarcopenia in observational studies.

METHODS

MEDLINE, Embase, Scopus and Web of Science were searched for studies reporting associations between AGEs and muscle-related outcomes in community-dwelling adults aged ≥ 30 years (until March 2022).

RESULTS

Fourteen cross-sectional and one prospective study were included in the narrative summary. SAF was negatively associated with muscle strength, mass, and physical functioning in adults aged ≥ 30 years (four studies), and muscle mass (three studies), strength, and sarcopenia (one study) in adults aged ≥ 65 years. Circulating AGEs were negatively associated with muscle strength and physical functioning (four studies) and predicted the risk of walking disability (one prospective study), and sarcopenia (one study) in older adults. The role of RAGE in muscle health was inconclusive.

CONCLUSIONS

SAF and circulating AGEs were negatively associated with muscle-related outcomes in adults aged ≥ 30 years in cross-sectional studies. This finding should be confirmed in well-designed prospective studies investigating sarcopenia, as AGEs represent a potentially modifiable target for intervention.

Role of advanced glycation end products in the longitudinal association between muscular strength and psychotic symptoms among adolescents

Muscular strength, assessed by handgrip, is a risk indicator for psychiatric disorders, including psychosis. However, the biological mechanisms underlying this association remain unclear. Since advanced glycation end products (AGEs) play a key role in skeletal muscle underdevelopment and psychosis, we examined the role of AGEs in the longitudinal association between muscular strength and psychotic symptoms among adolescents. We first evaluated the direction of the relationship between handgrip strength and urine levels of pentosidine, a representative AGEs in a population-based birth cohort of 1,542 adolescents at ages 12 and 14. Then, we examined the role of AGEs in the longitudinal association between handgrip strength and thought problems (TP), as a psychotic symptom indicator, in a subsample of 256 adolescents at ages 13 and 14. An autoregressive cross-lagged model revealed that handgrip strength at age 12 negatively predicted pentosidine levels at age 14 (β = −0.20, p < 0.001), whereas pentosidine levels at age 12 did not predict handgrip strength at age 14 (β = 0.04, p = 0.062). Moreover, pentosidine levels had a significant indirect effect on the relationship between handgrip strength and TP (standard indirect effect = −0.051, p = 0.012), which remained significant after adjusting for gender and preceded TP and pentosidine levels. Thus, adolescents with low muscular strength are at a high risk of developing psychotic symptoms, which could be mediated by AGEs. Future studies need to investigate whether interventions focused on muscular strength prevent the accumulation of AGEs and thereby prevent the development of psychosis.

Dietary advanced glycation end-products (dAGEs) intake and its relation to sarcopenia and frailty - The Rotterdam Study

Studies on mice have shown a relationship between dietary intake of advanced glycation end-products (dAGEs) and deterioration of musculoskeletal health, but human studies are absent. We investigated the relationship between dietary intake of carboxymethyllysine (dCML) - an AGE prototype - and risk of sarcopenia at baseline and after 5 years of follow-up and a single evaluation of physical frailty in participants from the population-based Rotterdam Study. Appendicular lean mass (ALM) was obtained using insight dual-energy X-ray absorptiometry and hand grip strength (HGS) using a hydraulic hand dynamometer. Subjects with both low ALM and weak HGS were classified as having sarcopenia. Frailty (yes/no) was defined by presence of ≥3 and pre-frailty by presence of 1 or 2 components namely, exhaustion, weakness, slowness, weight loss or low physical activity. dCML was calculated using a food frequency questionnaire and dAGE databases. Logistic regression analysis was used to evaluate the odds of physical frailty and prevalent sarcopenia at baseline and follow-up and incident sarcopenia. 2782 participants with an age 66.4 ± 9.9 years and dCML intake 3.3 ± 1.3 mg/day, had data on sarcopenia at both time points. Of whom 84 had sarcopenia at baseline and 73 developed sarcopenia at follow-up. We observed an association of one SD increase in dCML intake with prevalent sarcopenia at baseline [odds ratio, OR = 1.27 (1.01-1.59)] and no association of dCML with incident sarcopenia at 5-year follow-up [OR = 1.12 (0.86-1.44)]. For frailty we analyzed 3577 participants, of whom 1972 were pre-frail and 158 were frail. We observed no association of dCML with either pre-frailty [OR = 0.99 (0.91-1.07)] or frailty [OR = 1.01 (0.83-1.22)] when non-frail subjects were used as reference. Our results show an association of dAGEs with sarcopenia cross-sectionally but not longitudinally where inconclusive findings are observed possibly due to a very low incidence of sarcopenia. There was no association with frailty cross-sectionally.

Methylglyoxal and Its Adducts: Induction, Repair, and Association with Disease

Metabolism is an essential part of life that provides energy for cell growth. During metabolic flux, reactive electrophiles are produced that covalently modify macromolecules, leading to detrimental cellular effects. Methylglyoxal (MG) is an abundant electrophile formed from lipid, protein, and glucose metabolism at intracellular levels of 1-4 μM. MG covalently modifies DNA, RNA, and protein, forming advanced glycation end products (MG-AGEs). MG and MG-AGEs are associated with the onset and progression of many pathologies including diabetes, cancer, and liver and kidney disease. Regulating MG and MG-AGEs is a potential strategy to prevent disease, and they may also have utility as biomarkers to predict disease risk, onset, and progression. Here, we review recent advances and knowledge surrounding MG, including its production and elimination, mechanisms of MG-AGEs formation, the physiological impact of MG and MG-AGEs in disease onset and progression, and the latter in the context of its receptor RAGE. We also discuss methods for measuring MG and MG-AGEs and their clinical application as prognostic biomarkers to allow for early detection and intervention prior to disease onset. Finally, we consider relevant clinical applications and current therapeutic strategies aimed at targeting MG, MG-AGEs, and RAGE to ultimately improve patient outcomes.

Role of RAGE in the Pathogenesis of Neurological Disorders

This review reflects upon our own as well as other investigators' studies on the role of receptor for advanced glycation end-products (RAGE), bringing up the latest information on RAGE in physiology and pathology of the nervous system. Over the last ten years, major progress has been made in uncovering many of RAGE-ligand interactions and signaling pathways in nervous tissue; however, the translation of these discoveries into clinical practice has not come to fruition yet. This is likely, in part to be the result of our incomplete understanding of this crucial signaling pathway. Clinical trials examining the therapeutic efficacy of blocking RAGE-external ligand interactions by genetically engineered soluble RAGE or an endogenous RAGE antagonist, has not stood up to its promise; however, other trials with different blocking agents are being considered with hope for therapeutic success in diseases of the nervous system.

Human Adipose-Derived Stromal Cells Delivered on Decellularized Muscle Improve Muscle Regeneration and Regulate RAGE and P38 MAPK

Volumetric muscle loss (VML) is the acute loss of muscle mass due to trauma. Such injuries occur primarily in the extremities and are debilitating, as there is no clinical treatment to restore muscle function. Pro-inflammatory advanced glycation end-products (AGEs) and the soluble receptor for advanced glycation end-products (RAGE) are known to increase in acute trauma patient’s serum and are correlated with increased injury severity. However, it is unclear whether AGEs and RAGE increase in muscle post-trauma. To test this, we used decellularized muscle matrix (DMM), a pro-myogenic, non-immunogenic extracellular matrix biomaterial derived from skeletal muscle. We delivered adipose-derived stromal cells (ASCs) and primary myoblasts to support myogenesis and immunomodulation (N = 8 rats/group). DMM non-seeded and seeded grafts were compared to empty defect and sham controls. Then, 56 days after surgery muscle force was assessed, histology characterized, and protein levels for AGEs, RAGE, p38 MAPK, and myosin heavy chains were measured. Overall, our data showed improved muscle regeneration in ASC-treated injury sites and a regulation of RAGE and p38 MAPK signaling, while myoblast-treated injuries resulted in minor improvements. Taken together, these results suggested that ASCs combined with DMM provides a pro-myogenic microenvironment with immunomodulatory capabilities and indicates further exploration of RAGE signaling in VML.

The Role of Obesity, Body Composition, and Nutrition in COVID-19 Pandemia: A Narrative Review

The coronavirus disease 2019 (COVID-19) pandemic has spread worldwide, infecting nearly 500 million people, with more than 6 million deaths recorded globally. Obesity leads people to be more vulnerable, developing worse outcomes that can require hospitalization in intensive care units (ICU). This review focused on the available findings that investigated the link between COVID-19, body composition, and nutritional status. Most studies showed that not only body fat quantity but also its distribution seems to play a crucial role in COVID-19 severity. Compared to the body mass index (BMI), visceral adipose tissue and intrathoracic fat are better predictors of COVID-19 severity and indicate the need for hospitalization in ICU and invasive mechanical ventilation. High volumes of epicardial adipose tissue and its thickness can cause an infection located in the myocardial tissue, thereby enhancing severe COVID-related myocardial damage with impairments in coronary flow reserve and thromboembolism. Other important components such as sarcopenia and intermuscular fat augment the vulnerability in contracting COVID-19 and increase mortality, inflammation, and muscle damage. Malnutrition is prevalent in this population, but a lack of knowledge remains regarding the beneficial effects aimed at optimizing nutritional status to limit catabolism and preserve muscle mass. Finally, with the increase in patients recovering from COVID-19, evaluation and treatment in those with Long COVID syndrome may become highly relevant.

Soluble RAGE as a Prognostic Marker of Worsening in Patients Admitted to the ICU for COVID-19 Pneumonia: A Prospective Cohort Study

Background: The different waves of SARS-CoV-2 infection have strained hospital resources and, notably, intensive care units (ICUs). Identifying patients at risk of developing a critical condition is essential to correctly refer patients to the appropriate structure and to spare limited resources. The soluble form of RAGE (sRAGE), the endoplasmic stress response and its surrogates, GRP78 and VEGF-A, may be interesting markers. Methods: This was a prospective monocenter cohort study of adult patients admitted to the ICU for severe COVID-19 pneumonia. The plasma levels of sRAGE, GRP78 and VEGF-A were measured within the first 24 h. Patients were classified as critical if they further needed vasopressor therapy, renal replacement therapy, or invasive mechanical ventilation, or died during their ICU stay, and were otherwise classified as not critical. Results: A total of 98 patients were included and 39 developed a critical condition. Critical patients presented higher sRAGE (626 [450−1043] vs. 227 [137−404] pg/mL, p < 0.0001), interleukin-6 (43 [15−112] vs. 11 [5−20] pg/mL, p < 0.0001), troponin T (17 [9−39] vs. 10 [6−18] pg/mL, p = 0.003) and NT-pro-BNP (321 [118−446] vs. 169 [63−366] pg/mL, p = 0.009) plasma levels. No difference was observed for VEGF-A and GRP78. The variables independently associated with worsening in the ICU were sRAGE (1.03 [1.01−1.05] per 10 pg/mL) and age (1.7 [1.2−2.4] per 5 years). An sRAGE value of 449.5 pg/mL predicted worsening with a sensitivity of 77% and a specificity of 80%. Conclusion: sRAGE may allow the identification of patients at risk of developing a critical form of COVID-19 pneumonia, and thus may be useful to correctly refer patients to the appropriate structure of care.

Involvement of phosphatidylserine receptors in the skeletal muscle regeneration: therapeutic implications

Sarcopenia is a progressive loss of muscle mass and strength with a risk of adverse outcomes such as disability, poor quality of life, and death. Increasing evidence indicates that diminished ability of the muscle to activate satellite cell-dependent regeneration is one of the factors that might contribute to its development. Skeletal muscle regeneration following myogenic cell death results from the proliferation and differentiation of myogenic stem cells, called satellite cells, located beneath the basal lamina of the muscle fibres. Satellite cell differentiation is not a satellite cell-autonomous process but depends on signals provided by the surrounding cells. Infiltrating macrophages play a key role in the process partly by clearing the necrotic cell debris, partly by producing cytokines and growth factors that guide myogenesis. At the beginning of the muscle regeneration process, macrophages are pro-inflammatory, and the cytokines produced by them trigger the proliferation and differentiation of satellite cells. Following the uptake of dead cells, however, a transcriptionally regulated phenotypic change (macrophage polarization) is induced in them resulting in their transformation into healing macrophages that guide resolution of inflammation, completion of myoblast differentiation, myoblast fusion and growth, and return to homeostasis. Impaired efferocytosis results in delayed cell death clearance, delayed macrophage polarization, prolonged inflammation, and impaired muscle regeneration. Thus, proper efferocytosis by macrophages is a determining factor during muscle repair. Here we review that both efferocytosis and myogenesis are dependent on the cell surface phosphatidylserine (PS), and surprisingly, these two processes share a number of common PS receptors and signalling pathways. Based on these findings, we propose that stimulating the function of PS receptors for facilitating muscle repair following injury could be a successful approach, as it would enhance efferocytosis and myogenesis simultaneously. Because increasing evidence indicates a pathophysiological role of impaired efferocytosis in the development of chronic inflammatory conditions, as well as in impaired muscle regeneration both contributing to the development of sarcopenia, improving efferocytosis should be considered also in its management. Again applying or combining those treatments that target PS receptors would be expected to be the most effective, because they would also promote myogenesis. A potential PS receptor-triggering candidate molecule is milk fat globule-EGF-factor 8 (MFG-E8), which not only stimulates PS-dependent efferocytosis and myoblast fusion but also promotes extracellular signal-regulated kinase (ERK) and Akt activation-mediated cell proliferation and cell cycle progression in myoblasts.

Skeletal Muscle Transcriptomic Comparison Between Men and Women in Response to Acute Sprint Exercise

Background: Acute sprint exercise is a time-efficient physical activity that improves cardiorespiratory fitness in younger and middle-aged adults. Growing evidence has demonstrated that acute sprint exercise provides equal to or superior health benefits compared with moderate-intensity continuous training, which will dramatically increase aerobic capacity, insulin sensitivity, and muscle capillarization. Although the beneficial effects of acute sprint exercise are well documented, the mechanisms behind how acute sprint exercise prevents disease and benefits health are less understood.

Method: We obtained differentially expressed genes in muscle (vastus lateralis) from men and women before and after an acute sprint exercise. Then, we identified hub genes from the protein–protein interaction (PPI) network of differentially expressed genes (DEGs) and key transcription factors in men and women related to acute sprint exercise. Finally, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analyses are performed on DEGs and sex-biased genes, respectively.

Results: First, we identified 127 sexually dimorphic genes in men (90 upregulated and 37 downregulated) and 75 genes in women (90 upregulated and 37 downregulated) in response to acute sprint exercise. Second, CEBPB, SMAD3, and CDKN1A are identified as the top three hub genes related to men-biased genes. Accordingly, the top three hub genes related to women-biased genes are JUN, ACTB, and SMAD7. In addition, CLOCK, ZNF217, and KDM2B are the top three enriched transcriptional factors in men-biased genes, while XLR, SOX2, JUND, and KLF4 are transcription factors enriched most in women-biased genes. Furthermore, based on GO and KEGG enrichment analyses, we identified potential key pathways in regulating the exercise-related response in men and women, respectively.

Conclusion: In this study, we found the difference in gene expression and enrichment pathways in muscle in men and women in response to acute sprint exercise. These results will shed new light on the mechanism underlying sex-based differences in skeletal muscle remodeling and metabolism related to acute sprint exercise, which may illustrate the mechanisms behind how acute sprint exercise prevents disease and benefits health.

Intracellular Protein S-Nitrosylation—A Cells Response to Extracellular S100B and RAGE Receptor

Human S100B is a small, multifunctional protein. Its activity, inside and outside cells, contributes to the biology of the brain, muscle, skin, and adipocyte tissues. Overexpression of S100B occurs in Down Syndrome, Alzheimer’s disease, Creutzfeldt–Jakob disease, schizophrenia, multiple sclerosis, brain tumors, epilepsy, melanoma, myocardial infarction, muscle disorders, and sarcopenia. Modulating the activities of S100B, related to human diseases, without disturbing its physiological functions, is vital for drug and therapy design. This work focuses on the extracellular activity of S100B and one of its receptors, the Receptor for Advanced Glycation End products (RAGE). The functional outcome of extracellular S100B, partially, depends on the activation of intracellular signaling pathways. Here, we used Biotin Switch Technique enrichment and mass-spectrometry-based proteomics to show that the appearance of the S100B protein in the extracellular milieu of the mammalian Chinese Hamster Ovary (CHO) cells, and expression of the membrane-bound RAGE receptor, lead to changes in the intracellular S-nitrosylation of, at least, more than a hundred proteins. Treatment of the wild-type CHO cells with nanomolar or micromolar concentrations of extracellular S100B modulates the sets of S-nitrosylation targets inside cells. The cellular S-nitrosome is tuned differently, depending on the presence or absence of stable RAGE receptor expression. The presented results are a proof-of-concept study, suggesting that S-nitrosylation, like other post-translational modifications, should be considered in future research, and in developing tailored therapies for S100B and RAGE receptor-related diseases.

Methylglyoxal Induces Inflammation, Metabolic Modulation and Oxidative Stress in Myoblast Cells

Uremic sarcopenia is a serious clinical problem associated with physical disability and increased morbidity and mortality. Methylglyoxal (MG) is a highly reactive, dicarbonyl uremic toxin that accumulates in the circulatory system in patients with chronic kidney disease (CKD) and is related to the pathology of uremic sarcopenia. The pathophysiology of uremic sarcopenia is multifactorial; however, the details remain unknown. We investigated the mechanisms of MG-induced muscle atrophy using mouse myoblast C2C12 cells, focusing on intracellular metabolism and mitochondrial injury. We found that one of the causative pathological mechanisms of uremic sarcopenia is metabolic flow change to fatty acid synthesis with MG-induced ATP shortage in myoblasts. Evaluation of cell viability revealed that MG showed toxic effects only in myoblast cells, but not in myotube cells. Expression of mRNA or protein analysis revealed that MG induces muscle atrophy, inflammation, fibrosis, and oxidative stress in myoblast cells. Target metabolomics revealed that MG induces metabolic alterations, such as a reduction in tricarboxylic acid cycle metabolites. In addition, MG induces mitochondrial morphological abnormalities in myoblasts. These changes resulted in the reduction of ATP derived from the mitochondria of myoblast cells. Our results indicate that MG is a pathogenic factor in sarcopenia in CKD.

AGE-TXNIP axis drives inflammation in Alzheimer's by targeting Aβ to mitochondria in microglia

Alzheimer's disease (AD) is the most common form of dementia characterized by progressive memory loss and cognitive decline. Although neuroinflammation and oxidative stress are well-recognized features of AD, their correlations with the early molecular events characterizing the pathology are not yet well clarified. Here, we characterize the role of RAGE-TXNIP axis in neuroinflammation in relation to amyloid-beta (Aβ) burden in both in vivo and in vitro models. In the hippocampus of 5xFAD mice microglial activation, cytokine secretion, and glial fibrillary acidic protein-enhanced expression are paralleled with increased TXNIP expression. TXNIP silencing or its pharmacological inhibition prevents neuroinflammation in those mice. TXNIP is also associated with RAGE and Aβ. In particular, RAGE-TXNIP axis is required for targeting Aβ in mitochondria, leading to mitochondrial dysfunction and oxidative stress. Silencing of TXNIP or inhibition of RAGE activation reduces Aβ transport from the cellular surface to mitochondria, restores mitochondrial functionality, and mitigates Aβ toxicity. Furthermore, Aβ shuttling into mitochondria promotes Drp1 activation and exacerbates mitochondrial dysfunction, which induces NLRP3 inflammasome activation, leading to secretion of IL-1β and activation of the pyroptosis-associated protein Gasdermin D (GSDMD). Downregulation of RAGE-TXNIP axis inhibits Aβ-induced mitochondria dysfunction, inflammation, and induction of GSDMD. Herein we unveil a new pathway driven by TXNIP that links the mitochondrial transport of Aβ to the activation of Drp1 and the NLRP3 inflammasome, promoting the secretion of IL-1β and the pyroptosis pathway associated with GSDMD cleavage. Altogether these data shed new light on a novel mechanism of action of RAGE-TXNIP axis in microglia, which is intertwined with Aβ and ultimately causes mitochondria dysfunction and NLRP3 inflammasome cascade activation, suggesting TXNIP as a druggable target to be better deepened for AD.

Skin Autofluorescence, a Noninvasive Biomarker for Advanced Glycation End-products, Is Associated With Sarcopenia

BACKGROUND

Accumulation of advanced glycation end-products (AGEs) in skeletal muscle has been implicated in development of sarcopenia.

AIM

To obtain further insight in the pathophysiology of sarcopenia, we studied its relationship with skin AGEs in the general population.

METHODS

In a cross-sectional analysis, 2744 participants of northern European background, mean age 74.1 years, were included from the Rotterdam Study. Skin AGEs were measured as skin autofluorescence (SAF) using AGE ReaderTM, appendicular skeletal mass index (ASMI) using insight dual-energy X-ray absorptiometry, hand grip strength (HGS) using a hydraulic hand dynamometer, and, in a subgroup, gait speed (GS) measured on an electronic walkway (n = 2080). We defined probable sarcopenia (low HGS) and confirmed sarcopenia (low HGS and low ASMI) based on the European Working Group on Sarcopenia in Older People (EWGSOP2) revised criteria cutoffs. Multivariate linear and logistic regression were performed adjusting for age, sex, body fat percentage, height, renal function, diabetes, and smoking status.

RESULTS

The prevalence of low ASMI was 7.7%; probable sarcopenia, 24%, slow GS, 3%; and confirmed sarcopenia, 3.5%. SAF was inversely associated with ASMI [β -0.062 (95% CI -0.092, -0.032)], HGS [β -0.051 (95% CI -0.075, -0.026)], and GS [β -0.074 (95% CI -0.116, -0.033)]. A 1-unit increase in SAF was associated with higher odds of probable sarcopenia [odds ratio (OR) 1.36 (95% CI 1.09, 1.68)] and confirmed sarcopenia [OR 2.01 (95% CI 1.33, 3.06)].

CONCLUSION

Higher skin AGEs are associated with higher sarcopenia prevalence. We call for future longitudinal studies to explore the role of SAF as a potential biomarker of sarcopenia.

Methylglyoxal reduces molecular responsiveness to 4 weeks of endurance exercise in mouse plantaris muscle

Endurance exercise triggers skeletal muscle adaptations, including enhanced insulin signaling, glucose metabolism, and mitochondrial biogenesis. However, exercise-induced skeletal muscle adaptations may not occur in some cases, a condition known as exercise-resistance. Methylglyoxal (MG) is a highly reactive dicarbonyl metabolite and has detrimental effects on the body such as causing diabetic complications, mitochondrial dysfunction, and inflammation. This study aimed to clarify the effect of methylglyoxal on skeletal muscle molecular adaptations following endurance exercise. Mice were randomly divided into 4 groups (n = 12 per group): sedentary control group, voluntary exercise group, MG-treated group, and MG-treated with voluntary exercise group. Mice in the voluntary exercise group were housed in a cage with a running wheel, while mice in the MG-treated groups received drinking water containing 1% MG. Four weeks of voluntary exercise induced several molecular adaptations in the plantaris muscle, including increased expression of peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC1α), mitochondria complex proteins, toll-like receptor 4 (TLR4), 72-kDa heat shock protein (HSP72), hexokinase II, and glyoxalase 1; this also enhanced insulin-stimulated Akt Ser⁴⁷³ phosphorylation and citrate synthase activity. However, these adaptations were suppressed with MG treatment. In the soleus muscle, the exercise-induced increases in the expression of TLR4, HSP72, and advanced glycation end products receptor 1 were inhibited with MG treatment. These findings suggest that MG is a factor that inhibits endurance exercise-induced molecular responses including mitochondrial adaptations, insulin signaling activation, and the upregulation of several proteins related to mitochondrial biogenesis, glucose handling, and glycation in primarily fast-twitch skeletal muscle.

Efferocytosis in the Central Nervous System

The effective clearance of apoptotic cells is essential for maintaining central nervous system (CNS) homeostasis and restoring homeostasis after injury. In most cases of physiological apoptotic cell death, efferocytosis prevents inflammation and other pathological conditions. When apoptotic cells are not effectively cleared, destruction of the integrity of the apoptotic cell membrane integrity, leakage of intracellular contents, and secondary necrosis may occur. Efferocytosis is the mechanism by which efferocytes quickly remove apoptotic cells from tissues before they undergo secondary necrosis. Cells with efferocytosis functions, mainly microglia, help to eliminate apoptotic cells from the CNS. Here, we discuss the impacts of efferocytosis on homeostasis, the mechanism of efferocytosis, the associations of efferocytosis failure and CNS diseases, and the current clinical applications of efferocytosis. We also identify efferocytosis as a novel potential target for exploring the causes and treatments of CNS diseases.

Advanced Glycation End-Products in Skeletal Muscle Aging

Advanced age causes skeletal muscle to undergo deleterious changes including muscle atrophy, fast-to-slow muscle fiber transition, and an increase in collagenous material that culminates in the age-dependent muscle wasting disease known as sarcopenia. Advanced glycation end-products (AGEs) non-enzymatically accumulate on the muscular collagens in old age via the Maillard reaction, potentiating the accumulation of intramuscular collagen and stiffening the microenvironment through collagen cross-linking. This review contextualizes known aspects of skeletal muscle extracellular matrix (ECM) aging, especially the role of collagens and AGE cross-linking, and underpins the motor nerve’s role in this aging process. Specific directions for future research are also discussed, with the understudied role of AGEs in skeletal muscle aging highlighted. Despite more than a half century of research, the role that intramuscular collagen aggregation and cross-linking plays in sarcopenia is well accepted yet not well integrated with current knowledge of AGE’s effects on muscle physiology. Furthermore, the possible impact that motor nerve aging has on intramuscular cross-linking and muscular AGE levels is posited.

Elevated level of the soluble receptor for advanced glycation end-products involved in sarcopenia: an observational study

BACKGROUND

The soluble receptor for advanced glycation end products (sRAGE) has been proposed to serve as a marker for disease severity, but its role in sarcopenia, an age-related progressive loss of muscle mass and function, remains elusive. This study examines the association between sRAGE and sarcopenia.

METHODS

A total of 314 community-dwelling elderly adults who had their health examination at Tri-Service General Hospital from 2017 to 2019 underwent protein analysis with enzyme-linked immunosorbent assay. The relationship with sarcopenia and its detailed information, including components and diagnosis status, were examined using linear and logistic regressions.

RESULTS

As for sarcopenia components, low muscle mass (β = 162.8, p = 0.012) and strength (β = 181.31, p = 0.011) were significantly correlated with sRAGE, but not low gait speed (p = 0.066). With regard to disease status, confirmed sarcopenia (β = 436.93, p < 0.001), but not probable (p = 0.448) or severe sarcopenia (p = 0.488), was significantly correlated with sRAGE. In addition, females revealed a stronger association with sRAGE level by showing significant correlations with low muscle mass (β = 221.72, p = 0.014) and low muscle strength (β = 208.68, p = 0.043).

CONCLUSIONS

sRAGE level showed a positive association with sarcopenia, illustrating its involvement in the evolution of sarcopenia. This association is more evident in female groups, which may be attributed to the loss of protection from estrogen in postmenopausal women. Utilizing sRAGE level as a prospective marker for sarcopenia deserves further investigation in future studies.

Fermented rice bran supplementation attenuates chronic colitis-associated extraintestinal manifestations in female C57BL/6N mice

Patients with inflammatory bowel disease (IBD) have higher incidence of extraintestinal manifestations (EIM), including liver disorders, sarcopenia, and neuroinflammation. Fermented rice bran (FRB), generated from rice bran (RB), is rich in bioactive compounds, and exhibits anti-colitis activity. However, its role in EIM prevention is still unclear. Here, for the first time, we investigated whether EIM in female C57Bl/6N mice is attenuated by FRB supplementation. EIM was induced by repeated administration of 1.5% dextran sulfate sodium (DSS) in drinking water (4 d) followed by drinking water (12 d). Mice were divided into 3 groups-control (AIN93M), 10% RB, and 10% FRB. FRB ameliorated relapsing colitis and inflammation in muscle by significantly lowering proinflammatory cytokines Tnf-α and Il-6 in serum and advanced glycation end product-specific receptor (Ager) in serum and muscle when compared with the RB and control groups. As FRB reduced aspartate aminotransferase levels and oxidative stress, it might prevent liver disorders. FRB downregulated proinflammatory cytokine and chemokine transcripts responsible for neuroinflammation in the hippocampus and upregulated mRNA expression of G protein coupled receptors (GPRs), Gpr41 and Gpr43, in small and large intestines, which may explain the FRB-mediated protective mechanism. Hence, FRB can be used as a supplement to prevent IBD-associated EIM.

Advanced Glycation End Products Are Retained in Decellularized Muscle Matrix Derived from Aged Skeletal Muscle

Decellularized tissues are biocompatible materials that engraft well, but the age of their source has not been explored for clinical translation. Advanced glycation end products (AGEs) are chemical cross-links that accrue on skeletal muscle collagen in old age, stiffening the matrix and increasing inflammation. Whether decellularized biomaterials derived from aged muscle would suffer from increased AGE collagen cross-links is unknown. We characterized gastrocnemii of 1-, 2-, and 20-month-old C57BL/6J mice before and after decellularization to determine age-dependent changes to collagen stiffness and AGE cross-linking. Total and soluble collagen was measured to assess if age-dependent increases in collagen and cross-linking persisted in decellularized muscle matrix (DMM). Stiffness of aged DMM was determined using atomic force microscopy. AGE levels and the effect of an AGE cross-link breaker, ALT-711, were tested in DMM samples. Our results show that age-dependent increases in collagen amount, cross-linking, and general stiffness were observed in DMM. Notably, we measured increased AGE-specific cross-links within old muscle, and observed that old DMM retained AGE cross-links using ALT-711 to reduce AGE levels. In conclusion, deleterious age-dependent modifications to collagen are present in DMM from old muscle, implying that age matters when sourcing skeletal muscle extracellular matrix as a biomaterial.

Insulin Signal Transduction Perturbations in Insulin Resistance

Type 2 diabetes mellitus is a widespread medical condition, characterized by high blood glucose and inadequate insulin action, which leads to insulin resistance. Insulin resistance in insulin-responsive tissues precedes the onset of pancreatic β-cell dysfunction. Multiple molecular and pathophysiological mechanisms are involved in insulin resistance. Insulin resistance is a consequence of a complex combination of metabolic disorders, lipotoxicity, glucotoxicity, and inflammation. There is ample evidence linking different mechanistic approaches as the cause of insulin resistance, but no central mechanism is yet described as an underlying reason behind this condition. This review combines and interlinks the defects in the insulin signal transduction pathway of the insulin resistance state with special emphasis on the AGE-RAGE-NF-κB axis. Here, we describe important factors that play a crucial role in the pathogenesis of insulin resistance to provide directionality for the events. The interplay of inflammation and oxidative stress that leads to β-cell decline through the IAPP-RAGE induced β-cell toxicity is also addressed. Overall, by generating a comprehensive overview of the plethora of mechanisms involved in insulin resistance, we focus on the establishment of unifying mechanisms to provide new insights for the future interventions of type 2 diabetes mellitus.

Biological Aspects of Selected Myokines in Skeletal Muscle: Focus on Aging

In the last decade, clear evidence has emerged that the cellular components of skeletal muscle are important sites for the release of proteins and peptides called "myokines", suggesting that skeletal muscle plays the role of a secretory organ. After their secretion by muscles, these factors serve many biological functions, including the exertion of complex autocrine, paracrine and/or endocrine effects. In sum, myokines affect complex multi-organ processes, such as skeletal muscle trophism, metabolism, angiogenesis and immunological response to different physiological (physical activity, aging, etc.) or pathological states (cachexia, dysmetabolic conditions, chronic inflammation, etc.). The aim of this review is to describe in detail a number of myokines that are, to varying degrees, involved in skeletal muscle aging processes and belong to the group of proteins present in the functional environment surrounding the muscle cell known as the "Niche". The particular myokines described are those that, acting both from within the cell and in an autocrine manner, have a defined relationship with the modulation of oxidative stress in muscle cells (mature or stem) involved in the regulatory (metabolic or regenerative) processes of muscle aging. Myostatin, IGF-1, NGF, S100 and irisin are examples of specific myokines that have peculiar features in their mechanisms of action. In particular, the potential role of one of the most recently characterized myokines-irisin, directly linked to an active lifestyle-in reducing if not reversing senescence-induced oxidative damage is discussed in terms of its possible application as an agent able to counteract the deleterious effects of muscle aging.

Plasma HMGB1 levels and physical performance in ICU survivors

PURPOSE

Physical impairment after critical illness is recognized as a part of the post-intensive care syndrome (PICS). About one third of intensive care unit (ICU) survivors suffer from long-term physical disability, yet the underlying pathophysiological mechanisms remain poorly understood. The pro-inflammatory alarmin, high mobility group box 1 (HMGB1), promotes muscle dysfunction in experimental models, and HMGB1 stays elevated in some patients after ICU discharge. Accordingly, we investigated the relationship between HMGB1 plasma levels and physical performance in ICU survivors.

METHODS

Prospective cohort study of 100 ICU survivors from the general ICU at the Karolinska University Hospital, Sweden. Patients returned for follow up at 3 (58 patients) and 6 months (51 patients) after ICU discharge. Blood samples were collected, and a 6-minute walk test (6-MWT), a handgrip-strength test (HST), and a timed-stands test (TST) were performed.

RESULTS

Compared to reference values of the different physical tests, 16% of patients underperformed at all tests at 3 months and 12% at 6 months. All test results, except hand-grip strength left, improved significantly over the follow-up period (P < .05). There was no significant association between plasma HMGB1 levels at 3 and 6 months and scores on the three tests (6-MWT, TST, and HST) (P = .50-0.69).

CONCLUSION

In this follow-up study of ICU survivors, we found no significant association between plasma HMGB1 levels and physical performance. Additional follow-up studies of HMGB1 plasma levels and muscle function in ICU survivors are still warranted.

EDITORIAL COMMENT

HMGB-1, a marker of cell damage and activation, is known to increase in ICU patients. In study participants at 3- to 6-month post-ICU stay, HMGB-1 levels were still elevated, although no association to the primary outcome, physical performance, was found. Mechanisms for failure to recover physical performance post-ICU remain unclear, and investigations into cause of post-intensive care syndrome need to continue.

TRIAL REGISTRATIONS

ClinicalTrials.gov identifier NCT02914756.

Dieckol Attenuated Glucocorticoid-Induced Muscle Atrophy by Decreasing NLRP3 Inflammasome and Pyroptosis

Dexamethasone (Dexa), frequently used as an anti-inflammatory agent, paradoxically leads to muscle inflammation and muscle atrophy. Receptor for advanced glycation end products (RAGE) and Toll-like receptor 4 (TLR4) lead to nucleotide-binding oligomerization domain-like receptor pyrin domain containing 3 (NLRP3) inflammasome formation through nuclear factor-κB (NF-κB) upregulation. NLRP3 inflammasome results in pyroptosis and is associated with the Murf-1 and atrogin-1 upregulation involved in protein degradation and muscle atrophy. The effects of Ecklonia cava extract (ECE) and dieckol (DK) on attenuating Dexa-induced muscle atrophy were evaluated by decreasing NLRP3 inflammasome formation in the muscles of Dexa-treated animals. The binding of AGE or high mobility group protein 1 to RAGE or TLR4 was increased by Dexa but significantly decreased by ECE or DK. The downstream signaling pathways of RAGE (c-Jun N-terminal kinase or p38) were increased by Dexa but decreased by ECE or DK. NF-κB, downstream of RAGE or TLR4, was increased by Dexa but decreased by ECE or DK. The NLRP3 inflammasome component (NLRP3 and apoptosis-associated speck-like), cleaved caspase -1, and cleaved gasdermin D, markers of pyroptosis, were increased by Dexa but decreased by ECE and DK. Interleukin-1β/Murf-1/atrogin-1 expression was increased by Dexa but restored by ECE or DK. The mean muscle fiber cross-sectional area and grip strength were decreased by Dexa but restored by ECE or DK. In conclusion, ECE or DK attenuated Dexa-induced muscle atrophy by decreasing NLRP3 inflammasome formation and pyroptosis.

Effects of omega-7 palmitoleic acids on skeletal muscle differentiation in a hyperglycemic condition

Maternal obesity and diabetes are known to be involved in fetal myogenesis, but the later stages of myogenesis are not well understood. In this study, we investigated the influence of a hyperglycemic environment on L6 skeletal myoblast differentiation and the function of omega-7 palmitoleic acids. Exposure to a high concentration of glucose (25 mM) in high-glucose culture medium (HG) increased the expression of myogenic genes (MyoD, Myogenin, MRF4, Myhc2x, and Myhc2a) and the synthesis of myosin. HG also activated the PI3K/AKT pathway revealed muscle cell differentiation. Furthermore, the levels of reactive oxygen species (ROS) and an inflammatory cytokine (Tnfaip3; tumor necrosis factor alpha-induced protein 3), which are crucial for the growth and differentiation of skeletal muscle, were increased by HG. Palmitoleic acids suppressed the expression levels of myogenic regulatory genes and increased the expression level of a cell proliferation-related gene (Pax3). Trans-palmitoleic acid and eicosapentaenoic acid (TPA and EPA) increased the phosphorylation level of MAPK/ERK1/2 and downregulated ROS generation and Tnfaip3 expression. In contrast, cis-palmitoleic acid inactivated MAPK/ERK1/2, leading to increased ROS generation. In conclusion, a hyperglycemic environment mediated by HG induced excessive muscle differentiation. Palmitoleic acids inhibited myoblast differentiation by downregulating muscle-specific genes. Moreover, trans-palmitoleic acids may have beneficial antioxidant and/or anti-inflammatory effects in cells.

Hyperactivated RAGE in Comorbidities as a Risk Factor for Severe COVID-19-The Role of RAGE-RAS Crosstalk

The receptor for advanced glycation-end products (RAGE) is a multiligand receptor with a role in inflammatory and pulmonary pathologies. Hyperactivation of RAGE by its ligands has been reported to sustain inflammation and oxidative stress in common comorbidities of severe COVID-19. RAGE is essential to the deleterious effects of the renin-angiotensin system (RAS), which participates in infection and multiorgan injury in COVID-19 patients. Thus, RAGE might be a major player in severe COVID-19, and appears to be a useful therapeutic molecular target in infections by SARS-CoV-2. The role of RAGE gene polymorphisms in predisposing patients to severe COVID-19 is discussed.&nbsp.

Targeting RAGE to prevent SARS-CoV-2-mediated multiple organ failure: Hypotheses and perspectives

A novel infectious disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), was detected in December 2019 and declared as a global pandemic by the World Health. Approximately 15% of patients with COVID-19 progress to severe pneumonia and eventually develop acute respiratory distress syndrome (ARDS), septic shock and/or multiple organ failure with high morbidity and mortality. Evidence points towards a determinant pathogenic role of members of the renin-angiotensin system (RAS) in mediating the susceptibility, infection, inflammatory response and parenchymal injury in lungs and other organs of COVID-19 patients. The receptor for advanced glycation end-products (RAGE), a member of the immunoglobulin superfamily, has important roles in pulmonary pathological states, including fibrosis, pneumonia and ARDS. RAGE overexpression/hyperactivation is essential to the deleterious effects of RAS in several pathological processes, including hypertension, chronic kidney and cardiovascular diseases, and diabetes, all of which are major comorbidities of SARS-CoV-2 infection. We propose RAGE as an additional molecular target in COVID-19 patients for ameliorating the multi-organ pathology induced by the virus and improving survival, also in the perspective of future infections by other coronaviruses.

Skeletal Muscle Damage in COVID-19: A Call for Action

Both laboratory investigations and body composition quantification measures (e.g., computed tomography, CT) portray muscle loss in symptomatic Coronavirus disease 2019 (COVID-19) patients. Muscle loss is associated with a poor prognosis of the disease. The exact mechanism of muscle damage in COVID-19 patients, as well as the long-term consequences of muscle injury in disease survivors, are unclear. The current review briefly summarizes the literature for mechanisms, assessment measures, and interventions relevant to skeletal muscle insult in COVID-19 patients. Muscle injury is likely to be attributed to the cytokine storm, disease severity, malnutrition, prolonged physical inactivity during intensive care unit (ICU) stays, mechanical ventilation, and myotoxic drugs (e.g., dexamethasone). It has been assessed by imaging and non-imaging techniques (e.g., CT and electromyography), physical performance tests (e.g., six-minute walk test), anthropometric measures (e.g., calf circumference), and biomarkers of muscle dystrophy (e.g., creatine kinase). Interventions directed toward minimizing muscle loss among COVID-19 patients are lacking. However, limited evidence shows that respiratory rehabilitation improves respiratory function, muscle strength, quality of life, and anxiety symptoms in recovering older COVID-19 patients. Neuromuscular electrical stimulation may restore muscle condition in ICU-admitted patients, albeit empirical evidence is needed. Given the contribution of malnutrition to disease severity and muscle damage, providing proper nutritional management for emaciated patients may be one of the key issues to achieve a better prognosis and prevent the after-effects of the disease. Considerable attention to longer-term consequences of muscle injury in recovering COVID-19 patients is necessary.

Inhibition of the Receptor for Advanced Glycation End Products Enhances the Cytotoxic Effect of Gemcitabine in Murine Pancreatic Tumors

Pancreatic ductal adenocarcinoma (PDAC) remains a very difficult cancer to treat. Recent in vitro and in vivo studies suggest that the activation of the receptor for advanced glycation end products (RAGE) by its ligands stimulates pancreatic cancer cell proliferation and tumor growth. Additional studies show that, in the RAGE ligand, the high mobility group box 1 (HMGB1) protein plays an important role in chemoresistance against the cytotoxic agent gemcitabine by promoting cell survival through increased autophagy. We hypothesized that blocking the RAGE/HMGB1 interaction would enhance the cytotoxic effect of gemcitabine by reducing cell survival and autophagy. Using a preclinical mouse model of PDAC and a monoclonal antibody (IgG 2A11) as a RAGE inhibitor, we demonstrate that RAGE inhibition concurrent with gemcitabine treatment enhanced the cytotoxic effect of gemcitabine. The combination of IgG 2A11 and gemcitabine resulted in decreased autophagy compared to treatment with gemcitabine combined with control antibodies. Notably, we also observed that RAGE inhibition protected against excessive weight loss during treatment with gemcitabine. Our data suggest that the combination of gemcitabine with a RAGE inhibitor could be a promising therapeutic approach for the treatment of pancreatic cancer and needs to be further investigated.

The use of the soluble receptor for advanced glycation-end products (sRAGE) as a potential biomarker of disease risk and adverse outcomes

The soluble receptor for advanced glycation end-products (sRAGE) has been classically considered a sink for pro-inflammatory RAGE ligands and as such has been associated with protection from inflammatory stress and disease. An alternative, though not mutually exclusive view is that high levels of sRAGE in circulation reflect the overstimulation of cell surface RAGE which if persistent, lead to the amplification of pro-inflammatory processes and the exacerbation of pathological states. With these two scenarios in mind this review focuses on the potential role of sRAGE as a prospective biomarker of disease risk and adverse outcomes.

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The prognostic value of measuring sRAGE levels in blood is subjected to debate.

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Raised sRAGE levels may result from the overstimulation of cell surface RAGE.

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Raised sRAGE may reflect chronic inflammation and multimorbidity rather than a healthy state.

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sRAGE is a promising biomarker of disease risk and adverse outcomes.

Increase of α-dicarbonyls in liver and receptor for advanced glycation end products on immune cells are linked to nonalcoholic fatty liver disease and liver cancer

Hepatocellular carcinoma (HCC) is the most common primary malignancy of the liver with a very poor prognosis and constantly growing incidence. Among other primary risks of HCC, metabolic disorders and obesity have been extensively investigated over recent decades. The latter can promote nonalcoholic fatty liver disease (NAFLD) leading to the inflammatory form of nonalcoholic steatohepatitis (NASH), that, in turn, promotes HCC. Molecular determinants of this pathogenic progression, however, remain largely undefined. In this study, we have focussed on the investigation of α-dicarbonyl compounds (α-dC), highly reactive and tightly associated with overweight-induced metabolic disorders, and studied their potential role in NAFLD and progression toward HCC using murine models. NAFLD was induced using high-fat diet (HFD). Autochthonous HCC was induced using transposon-based stable intrahepatic overexpression of oncogenic NRAS^G12V in mice lacking p19^Arf tumor suppressor. Our study demonstrates that the HFD regimen and HCC resulted in strong upregulation of α-dC in the liver, heart, and muscles. In addition, an increase in α-dC was confirmed in sera of NAFLD and NASH patients. Furthermore, higher expression of the receptor for advanced glycation products (RAGE) was detected exclusively on immune cells and not on stroma cells in livers of mice with liver cancer progression. Our work confirms astable interplay of liver inflammation, carbonyl stress mediated by α-dC, and upregulated RAGE expression on CD8⁺ Tand natural killer (NK) cells in situ in NAFLD and HCC, as key factors/determinants in liver disease progression. The obtained findings underline the role of α-dC and RAGE⁺CD8⁺ Tand RAGE⁺ NK cells as biomarkers and candidates for a local therapeutic intervention in NAFLD and malignant liver disease.

Advances in cell membrane chromatography

Cell membrane chromatography (CMC) is a biomimetic chromatographic method based on the ability of membrane receptors to selectively interact with their ligands in vivo. Using membrane receptors as a stationary phase, the CMC method helps in determining the binding characteristics between ligands and membrane receptors and in efficiently identifying specific target components in a complex sample that produce the cellular biological effects of ligands (drugs, antibodies, enzymes, cytokines, etc.). CMC is an analytical tool for revealing characteristics of ligand-receptor interactions, screening and discovering target substances, and accurately controlling the quality of drugs. Since establishment of CMC in the early 1990s, with the rapid development of cell biology, significant progress has been made in the development of high-expression receptors, engineered cell cultures, and standardized preparations, which allowed in vitro immobilization of cell membrane receptors and miniaturization of binding assays. A variety of CMC models have been established using different membrane receptors as a stationary phase, and many new methods have been developed by combining CMC with high-performance liquid chromatography (HPLC)/mass spectrometry or HPLC-IT-TOF technologies. CMC methods have been widely used to study drug-receptor interactions and to screen complex samples for effective or harmful components.

Higher sRAGE Levels Predict Mortality in Frail Older Adults with Cardiovascular Disease

INTRODUCTION

The evidence that blood levels of the soluble receptor for advanced glycation end products (sRAGE) predict mortality in people with cardiovascular diseases (CVD) is inconsistent. To clarify this matter, we investigated if frailty status influences this association.

METHODS

We analysed data of 1,016 individuals (median age, 75 years) from 3 population-based European cohorts, enrolled in the FRAILOMIC project. Participants were stratified by history of CVD and frailty status. Mortality was recorded during 8 years of follow-up.

RESULTS

In adjusted Cox regression models, baseline serum sRAGE was positively associated with an increased risk of mortality in participants with CVD (HR 1.64, 95% CI 1.09-2.49, p = 0.019) but not in non-CVD. Within the CVD group, the risk of death was markedly enhanced in the frail subgroup (CVD-F, HR 1.97, 95% CI 1.18-3.29, p = 0.009), compared to the non-frail subgroup (CVD-NF, HR 1.50, 95% CI 0.71-3.15, p = 0.287). Kaplan-Meier analysis showed that the median survival time of CVD-F with high sRAGE (>1,554 pg/mL) was 2.9 years shorter than that of CVD-F with low sRAGE, whereas no survival difference was seen for CVD-NF. Area under the ROC curve analysis demonstrated that for CVD-F, addition of sRAGE to the prediction model increased its prognostic value.

CONCLUSIONS

Frailty status influences the relationship between sRAGE and mortality in older adults with CVD. sRAGE could be used as a prognostic marker of mortality for these individuals, particularly if they are also frail.

From mitochondria to sarcopenia: Role of inflammaging and RAGE-ligand axis implication

Sarcopenia is characterized by a loss of muscle mass and function that reduces mobility, diminishes quality of life, and can lead to fall-related injuries. At the intracellular level, mitochondrial population alterations are considered as key contributors to the complex etiology of sarcopenia. Mitochondrial dysfunctions lead to reactive oxygen species production, altered cellular proteostasis, and promotes inflammation. Interestingly, the receptor for advanced glycation end-products (RAGE) is a pro-inflammatory receptor involved in inflammaging. In this review, after a brief description of sarcopenia, we will describe how mitochondria and the pathways controlling mitochondrial population quality could participate to age-induced muscle mass and force loss. Finally, we will discuss the RAGE-ligand axis during aging and its possible connection with mitochondria to control inflammaging and sarcopenia.

Calcium-Dependent Translocation of S100B Is Facilitated by Neurocalcin Delta

S100B is a calcium-binding protein that governs calcium-mediated responses in a variety of cells—especially neuronal and glial cells. It is also extensively investigated as a potential biomarker for several disease conditions, especially neurodegenerative ones. In order to establish S100B as a viable pharmaceutical target, it is critical to understand its mechanistic role in signaling pathways and its interacting partners. In this report, we provide evidence to support a calcium-regulated interaction between S100B and the neuronal calcium sensor protein, neurocalcin delta both in vitro and in living cells. Membrane overlay assays were used to test the interaction between purified proteins in vitro and bimolecular fluorescence complementation assays, for interactions in living cells. Added calcium is essential for interaction in vitro; however, in living cells, calcium elevation causes translocation of the NCALD-S100B complex to the membrane-rich, perinuclear trans-Golgi network in COS7 cells, suggesting that the response is independent of specialized structures/molecules found in neuronal/glial cells. Similar results are also observed with hippocalcin, a closely related paralog; however, the interaction appears less robust in vitro. The N-terminal region of NCALD and HPCA appear to be critical for interaction with S100B based on in vitro experiments. The possible physiological significance of this interaction is discussed.

RAGE Signaling in Melanoma Tumors

Despite recent progresses in its treatment, malignant cutaneous melanoma remains a cancer with very poor prognosis. Emerging evidences suggest that the receptor for advance glycation end products (RAGE) plays a key role in melanoma progression through its activation in both cancer and stromal cells. In tumors, RAGE activation is fueled by numerous ligands, S100B and HMGB1 being the most notable, but the role of many other ligands is not well understood and should not be underappreciated. Here, we provide a review of the current role of RAGE in melanoma and conclude that targeting RAGE in melanoma could be an approach to improve the outcomes of melanoma patients.