Collagen, cross-linking, and advanced glycation end products in aging human skeletal muscle

Assessing Muscle Protein Synthesis Rates In Vivo in Humans: The Deuterated Water (2H2O) Method

Skeletal muscle tissue is in a constant state of turnover, with muscle tissue protein synthesis and breakdown rates ranging between 1% and 2% across the day in vivo in humans. Muscle tissue remodeling is largely controlled by the up- and down-regulation of muscle tissue protein synthesis rates. Research studies generally apply stable isotope-labeled amino acids to assess muscle protein synthesis rates in vivo in humans. Following labeled amino acid administration in a laboratory setting, muscle tissue samples are collected over several hours to assess the incorporation rate of these labeled amino acids in muscle tissue protein. To allow quantification of bulk muscle protein synthesis rates over more prolonged periods, the use of deuterated water methodology has regained much interest. Ingestion of daily boluses of deuterium oxide results in 2H enrichment of the body water pool. The available 2H-atoms become incorporated into endogenously synthesized alanine primarily through transamination of pyruvate in the liver. With 2H-alanine widely available to all tissues, it becomes incorporated into de novo synthesized tissue proteins. Assessing the increase in tissue protein-bound 2H-alanine enrichment in muscle biopsy samples over time allows for the calculation of muscle protein synthesis rates over several days or even weeks. As the deuterated water method allows for the assessment of muscle tissue protein synthesis rates under free-living conditions in nonlaboratory settings, there is an increasing interest in its application. This manuscript describes the theoretical background of the deuterated water method and offers a comprehensive tutorial to correctly apply the method to determine bulk muscle protein synthesis rates in vivo in humans.

Strain-dependent dynamic re-alignment of collagen fibers in skeletal muscle extracellular matrix

Collagen fiber architecture within the skeletal muscle extracellular matrix (ECM) is significant to passive muscle mechanics. While it is thought that collagen fibers re-orient themselves in response to changes in muscle length, this has not been dynamically visualized and quantified within a muscle. The goal of this study was to measure changes in collagen alignment across a range of muscle lengths and compare the corresponding alignment to muscle mechanics. We hypothesized that collagen fibers dynamically increase alignment in response to muscle stretching, and this change in alignment is related to passive muscle stiffness. Further, we hypothesized that digesting collagen fibers with collagenase would reduce the re-alignment response to muscle stretching. Using DBA/2J and D2.mdx mice, we isolated extensor digitorum longus (EDL), soleus, and diaphragm muscles for collagenase or sham treatment and decellularization to isolate intact or collagenase-digested decellularized muscles (DCMs). These DCMs were mechanically tested and imaged using second harmonic generation microscopy to measure collagen alignment across a range of strains. We found that collagen alignment increased in a strain-dependent fashion, but collagenase did not significantly affect the strain-dependent change in alignment. We also saw that the collagen fibers in the diaphragm epimysium (surface ECM) and perimysium (deep ECM) started at different angles, but still re-oriented in the same direction in response to stretching. These robust changes in collagen alignment were weakly related to passive DCM stiffness. Overall, we demonstrated that the architecture of muscle ECM is dynamic in response to strain and is related to passive muscle mechanics. STATEMENT OF SIGNIFICANCE: Our study presents a unique visualization and quantification of strain-induced changes in muscle collagen fiber alignment as they relate to passive mechanics. Using dynamic imaging of collagen in skeletal muscle we demonstrate that as skeletal muscle is stretched, collagen fibers re-orient themselves along the axis of stretch and increase their alignment. The degree of alignment and the increase in alignment are each weakly related to passive muscle stiffness. Collagenase treatments further demonstrate that the basis for muscle Extracellular matrix stiffness is dependent on factors beyond collagen crosslinking and alignment. Together the study contributes to the knowledge of the structure-function relationships of muscle extracellular matrix to tissue stiffness relevant to conditions of fibrosis and aberrant stiffness.

Muscle aging and sarcopenia: The pathology, etiology, and most promising therapeutic targets

Sarcopenia is a progressive muscle wasting disorder that severely impacts the quality of life of elderly individuals. Although the natural aging process primarily causes sarcopenia, it can develop in response to other conditions. Because muscle function is influenced by numerous changes that occur with age, the etiology of sarcopenia remains unclear. However, recent characterizations of the aging muscle transcriptional landscape, signaling pathway disruptions, fiber and extracellular matrix compositions, systemic metabolomic and inflammatory responses, mitochondrial function, and neurological inputs offer insights and hope for future treatments. This review will discuss age-related changes in healthy muscle and our current understanding of how this can deteriorate into sarcopenia. As our elderly population continues to grow, we must understand sarcopenia and find treatments that allow individuals to maintain independence and dignity throughout an extended lifespan.

New Glycotoxin Inhibitor from Sesuvium sesuvioides Mitigates Symptoms of Insulin Resistance and Diabetes by Suppressing AGE-RAGE Axis in Skeletal Muscle

The current study intended to investigate the role of new natural compounds derived from the Sesuvium sesuvioides plant in mitigating symptoms of diabetes and insulin resistance in the diabetic mice model. Anti-advanced glycation activity, insulin, and adiponectin were quantified by enzyme-linked immunosorbent assay (ELISA). Glucose uptake was performed using enzymatic fluorescence assay, and glycogen synthesis was measured using PAS staining. Gene and protein expression was assessed using real time PCR (RT-PCR), and immunoblotting and fluorescent microscopy, respectively. The new flavonoid glycoside eupalitin 3-O-α-L-rhamnopyranosyl-(1→2)-β-D-glucopyranoside 1 isolated from S. sesuvioides exhibited anti-AGE activity by reducing human glycated albumin in liver cells. In a diabetic mouse model treated with compound 1, we observed improved glucose tolerance, increased adiponectin levels, and decreased insulin resistance. We also observed alleviated AGEs induced reduction in glucose uptake and restored glycogen synthesis in the compound 1-treated diabetic mice muscles. Exploring the molecular mechanism of action in skeletal muscle tissue of diabetic mice, we found that 1 reduced AGE-induced reactive oxygen species and the inflammatory gene in the muscle of diabetic mice. Additionally, 1 exhibited these effects by reducing the gene and protein expression of receptor for advanced glycation end products (RAGE) and inhibiting protein kinase C (PKC) delta activation. This further led us to demonstrate that compound 1 reduced serine phosphorylation of IRS-1, thereby restoring insulin sensitivity. We conclude that a new flavonoid glycoside from S. sesuvioides could be a therapeutic target for the treatment of symptoms of insulin resistance and diabetes.

A Comparative Study of the Effects of Different Crosslinking Methods on the Physicochemical Properties of Collagen Multifilament Bundles

Crosslinking is usually required to improve the mechanical properties and stability of collagen-based scaffolds. Introducing exogenous crosslinks into collagen may however affect the collagen structure. Since the architecture of collagen is tied to its functionality, it is important to study the effect of crosslinking and to select a crosslinking method that preserves both the collagen structure and mechanical properties. The objective of this study is to compare the effect of various crosslinking methods on the structure and mechanical properties of bioartificial tendon-like materials (collagen multifilament bundles) fabricated by contact drawing. We examine both physical (ultraviolet light, UVC) and chemical (genipin, carbodiimide (EDC), and glutaraldehyde) crosslinking methods. The presence of collagen and the formation of well-ordered collagen structures are confirmed by attenuated total reflectance Fourier-transform infrared spectromicroscopy and wide-angle X-ray scattering for all crosslinking methods. The morphology of the collagen multifilament bundles is similar across crosslinking methods. Swelling of the multifilament bundles is dramatically reduced following crosslinking and varies by crosslinking method, with genipin- and carbodiimide-crosslinked specimens swelling the least. Ultimate tensile strength (UTS) and Young's modulus significantly improve for all crosslinked specimens compared to non-crosslinked specimens. Glutaraldehyde crosslinked collagen multifilament bundles display the highest UTS values ranging from 33.82±0.0 MPa to 45.59±0.76 MPa.

Shoulder muscle weakness and proprioceptive impairments in type 2 diabetes mellitus: exploring correlations for improved clinical management

Background

Type 2 diabetes mellitus (T2DM) is a prevalent metabolic disorder with systemic implications, potentially affecting musculoskeletal health. This study aimed to assess shoulder muscle strength and joint repositioning accuracy in individuals with T2DM, exploring potential correlations and shedding light on the musculoskeletal consequences of the condition. The objectives were two-fold: (1) to assess and compare shoulder strength and joint repositioning accuracy between individuals with T2DM and asymptomatic counterparts, and (2) to examine the correlation between shoulder strength and joint repositioning accuracy in individuals with T2DM.

Methods

A cross-sectional study enrolled 172 participants using the convenience sampling method, including 86 individuals with T2DM and an age-matched asymptomatic group (n = 86). Shoulder strength was assessed using a handheld dynamometer, while joint repositioning accuracy was evaluated with an electronic digital inclinometer.

Results

Individuals with T2DM exhibited reduced shoulder muscle strength compared to asymptomatic individuals (p < 0.001). Additionally, joint repositioning accuracy was significantly lower in the T2DM group (p < 0.001). Negative correlations were observed between shoulder strength and joint repositioning accuracy in various directions (ranging from -0.29 to -0.46, p < 0.001), indicating that higher muscle strength was associated with improved joint repositioning accuracy in individuals with T2DM.

Conclusion

This study highlights the significant impact of T2DM on shoulder muscle strength and joint repositioning accuracy. Reduced strength and impaired accuracy are evident in individuals with T2DM, emphasizing the importance of addressing musculoskeletal aspects in diabetes management. The negative correlations suggest that enhancing shoulder muscle strength may lead to improved joint repositioning accuracy, potentially contributing to enhanced physical functioning in this population.

Tracking of Nascent Matrix Deposition during Muscle Stem Cell Activation across Lifespan Using Engineered Hydrogels

Adult stem cells occupy a niche that contributes to their function, but how stem cells rebuild their microenvironment after injury remains an open-ended question. Herein, biomaterial-based systems and metabolic labeling are utilized to evaluate how skeletal muscle stem cells deposit extracellular matrix. Muscle stem cells and committed myoblasts are observed to generate less nascent matrix than muscle resident fibro-adipogenic progenitors. When cultured on substrates that matched the stiffness of physiological uninjured and injured muscles, muscle stem cells increased nascent matrix deposition with activation kinetics. Reducing the ability to deposit nascent matrix by an inhibitor of vesicle trafficking (Exo-1) attenuated muscle stem cell function and mimicked impairments observed from muscle stem cells isolated from old muscles. Old muscle stem cells are observed to deposit less nascent matrix than young muscle stem cells, which is rescued with therapeutic supplementation of insulin-like growth factors. These results highlight the role of nascent matrix production with muscle stem cell activation.

Stretch-shortening cycles protect against the age-related loss of power generation in rat single muscle fibres

Aging is associated with impaired strength and power during isometric and shortening contractions, however, during lengthening (i.e., eccentric) contractions, strength is maintained. During daily movements, muscles undergo stretch-shortening cycles (SSCs). It is unclear whether the age-related maintenance of eccentric strength offsets age-related impairments in power generation during SSCs owing to the utilization of elastic energy or other cross-bridge based mechanisms. Here we investigated how aging influences SSC performance at the single muscle fibre level and whether performing active lengthening prior to shortening protects against age-related impairments in power generation. Single muscle fibres from the psoas major of young (∼8 months; n = 31 fibres) and old (∼32 months; n = 41 fibres) male F344BN rats were dissected and chemically permeabilized. Fibres were mounted between a force transducer and length controller and maximally activated (pCa 4.5). For SSCs, fibres were lengthened from average sarcomere lengths of 2.5 to 3.0 μm and immediately shortened back to 2.5 μm at both fast and slow (0.15 and 0.60 Lo/s) lengthening and shortening speeds. The magnitude of the SSC effect was calculated by comparing work and power during shortening to an active shortening contraction not preceded by active lengthening. Absolute isometric force was ∼37 % lower in old compared to young rat single muscle fibres, however, when normalized to cross-sectional area (CSA), there was no longer a significant difference in isometric force between age groups, meanwhile there was an ∼50 % reduction in absolute power in old as compared with young. We demonstrated that SSCs significantly increased power production (75-110 %) in both young and old fibres when shortening occurred at a fast speed and provided protection against power-loss with aging. Therefore, in older adults during everyday movements, power is likely 'protected' in part due to the stretch-shortening cycle as compared with isolated shortening contractions.

Current research trends on the effect of diabetes mellitus on rotator cuff tendon healing/tendinopathy

Rotator cuff tendon tears are a leading cause of shoulder pain. They are challenging to treat, and tendon-bone healing has a high failure rate despite successful surgery. Tendons connect the muscles and bones, which make them important for the body's overall mobility and stability. Metabolic diseases, including diabetes or high blood pressure, can affect the healing process after repair of a damaged tendon. With a global incidence of 9.3%, diabetes is considered as a significant risk factor for rotator cuff tendon healing because it causes structural, inflammatory, and vascular changes in the tendon. However, the mechanisms of how diabetes affects tendon healing remain unknown. Several factors have been suggested, including glycation product accumulation, adipokine dysregulation, increased levels of reactive oxygen species, apoptosis, inflammatory cytokines, imbalanced matrix-metalloproteinase-to-tissue-inhibitor ratio, and impaired angiogenesis and differentiation of the tendon sheath. Despite the effects of diabetes on tendon function and healing, few treatments are available to improve recovery in these patients. This review summarizes the current literature on the pathophysiological changes of the tendon in diabetes and hyperlipidemia. Preclinical and clinical evidence regarding the association between diabetes and tendon healing is presented. Moreover, current approaches to improve tendon healing in patients with diabetes are reviewed.

Age-related blunting of serial sarcomerogenesis and mechanical adaptations following 4 wk of maximal eccentric resistance training

During aging, muscles undergo atrophy, which is partly accounted for by a loss of sarcomeres in series. Serial sarcomere number (SSN) is associated with aspects of muscle mechanical function including the force-length and force-velocity-power relationships; hence, the age-related loss of SSN contributes to declining performance. Training emphasizing eccentric contractions increases SSN in young healthy rodents; however, the ability for eccentric training to increase SSN in old age is unknown. Ten young (8 mo) and 11 old (32 mo) male Fisher344/BN rats completed 4 wk of unilateral eccentric plantar flexion training. Pre- and posttraining, the plantar flexors were assessed for the torque-frequency, passive torque-angle, and torque-velocity-power relationships. The soleus, lateral gastrocnemius (LG), and medial gastrocnemius (MG) were harvested for SSN assessment via laser diffraction, with the untrained leg used as a control. In the untrained leg/pretraining, old rats had lower SSN in the soleus, LG, and MG, lower maximum torque, power, and shortening velocity, and greater passive torque than young. Young showed increased soleus and MG SSN following training. In contrast, old had no change in soleus SSN and experienced SSN loss in the LG. Pre- to posttraining, young experienced an increase in maximum isometric torque, whereas old had reductions in maximum torque, shortening velocity, and power, and increased passive torque. Our results show that although young muscle has the ability to add sarcomeres in response to maximal eccentric training, this stimulus could be not only ineffective, but also detrimental to aged muscle leading to dysfunctional remodeling.NEW & NOTEWORTHY The loss of sarcomeres in series with age contributes to declining muscle performance. The present study investigated whether eccentric training could improve performance via serial sarcomere addition in old muscle, like in young muscle. Four weeks of maximal eccentric training induced serial sarcomere addition in the young rat plantar flexors and improved in vivo performance, however, led to dysfunctional remodeling accompanied by further impaired performance in old rats.

Reliability of Ultrasound Shear Wave Elastography for Evaluating Psoas Major and Quadratus Lumborum Stiffness: Gender and Physical Activity Effects

OBJECTIVE

We aimed to assess the reliability of quantifying psoas major (PM) and quadratus lumborum (QL) stiffness with ultrasound shear wave elastography (SWE), and to explore the effects of gender and physical activity on muscle stiffness.

METHODS

Fifty-two healthy participants (18-32 y) were recruited. To determine reliability, 29 of them underwent repeated SWE measurements of PM and QL stiffness by an operator on the same day. The intra-class correlation coefficients (ICC3,1), standard error of measurement (SEM) and minimal detectable change with 95% confidence interval (MDC95) were calculated. The rest participants underwent a single measurement. Two-way MANCOVA was conducted for the effects of gender and physical activity on muscle stiffness.

RESULTS

The observed reliability for PM (ICC3,1 = 0.89-0.92) and QL (ICC3,1 = 0.79-0.82) were good-to-excellent and good, respectively. The SEM (kPa) was 0.79-1.03 and 1.23-1.28, and the MDC95 (kPa) was 2.20-2.85 and 3.41-3.56 for PM and QL, respectively. After BMI adjustment, both gender (PM: F = 10.15, p = 0.003; QL: F = 18.07, p < 0.001) and activity level (PM: F = 5.90, p = 0.005; QL: F = 6.33, p = 0.004) influenced muscle stiffness. The female and inactive groups exhibited higher stiffness in both muscles.

CONCLUSION

SWE is reliable for quantifying the stiffness of PM and QL. Female and physical inactivity may elevate PM and QL stiffness, underscoring the importance of accounting for these factors in muscle stiffness investigations. Larger prospective studies are needed to further elucidate their effects.

One Week of Single-Leg Immobilization Lowers Muscle Connective Protein Synthesis Rates in Healthy, Young Adults

PURPOSE

Short periods of limb immobilization lower myofibrillar protein synthesis rates. Within skeletal muscle, the extracellular matrix of connective proteins is recognized as an important factor determining the capacity to transmit contractile force. Little is known regarding the impact of immobilization and subsequent recovery on muscle connective protein synthesis rates. This study examined the impact of 1 wk of leg immobilization and 2 wk of subsequent ambulant recovery on daily muscle connective protein synthesis rates.

METHODS

Thirty healthy, young (24 ± 5 yr) men were subjected to 7 d of one-legged knee immobilization followed by 14 d of ambulant recovery. Deuterium oxide ingestion was applied over the entire period, and muscle biopsy samples were collected before immobilization, after immobilization, and after recovery to measure muscle connective protein synthesis rates and mRNA expression of key extracellular matrix proteins (collagen I, collagen III), glycoproteins (fibronectin, tenascin-C), and proteoglycans (fibromodulin, and decorin). A two-way repeated-measures (time-leg) ANOVA was used to compare changes in muscle connective protein synthesis rates during immobilization and recovery.

RESULTS

During immobilization, muscle connective protein synthesis rates were lower in the immobilized (1.07 ± 0.30%·d -1 ) compared with the nonimmobilized (1.48 ± 0.44%·d -1 ; P < 0.01) leg. When compared with the immobilization period, connective protein synthesis rates in the immobilized leg increased during subsequent recovery (1.48 ± 0.64%·d -1 ; P < 0.01). After recovery, skeletal muscle collagen I, collagen III, fibronectin, fibromodulin, and decorin mRNA expression increased when compared with the postimmobilization time point (all P < 0.001).

CONCLUSIONS

One week of leg immobilization lowers muscle connective protein synthesis rates. Muscle connective protein synthesis rates increase during subsequent ambulant recovery, which is accompanied by increased mRNA expression of key extracellular matrix proteins.

An overview on glycation: molecular mechanisms, impact on proteins, pathogenesis, and inhibition

The formation of a heterogeneous set of advanced glycation end products (AGEs) is the final outcome of a non-enzymatic process that occurs in vivo on long-life biomolecules. This process, known as glycation, starts with the reaction between reducing sugars, or their autoxidation products, with the amino groups of proteins, DNA, or lipids, thus gaining relevance under hyperglycemic conditions. Once AGEs are formed, they might affect the biological function of the biomacromolecule and, therefore, induce the development of pathophysiological events. In fact, the accumulation of AGEs has been pointed as a triggering factor of obesity, diabetes-related diseases, coronary artery disease, neurological disorders, or chronic renal failure, among others. Given the deleterious consequences of glycation, evolution has designed endogenous mechanisms to undo glycation or to prevent it. In addition, many exogenous molecules have also emerged as powerful glycation inhibitors. This review aims to provide an overview on what glycation is. It starts by explaining the similarities and differences between glycation and glycosylation. Then, it describes in detail the molecular mechanism underlying glycation reactions, and the bio-molecular targets with higher propensity to be glycated. Next, it discusses the precise effects of glycation on protein structure, function, and aggregation, and how computational chemistry has provided insights on these aspects. Finally, it reports the most prevalent diseases induced by glycation, and the endogenous mechanisms and the current therapeutic interventions against it.

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.

Pathophysiological interactions between sarcopenia and type 2 diabetes: A two-way street influencing diagnosis and therapeutic options

This review will try to elucidate the interconnected pathophysiology of sarcopenia and type 2 diabetes (T2D) and will try to identify a common pathway to explain their development. To this end, the PubMed and Scopus databases were searched for articles published about the underlying pathophysiology, diagnosis and treatment of both sarcopenia and T2D. The medical subject heading (MeSH) terms 'sarcopenia' AND 'diabetes mellitus' AND ('physiopathology' OR 'diagnosis' OR 'therapeutics' OR 'aetiology' OR 'causality') were used. After screening, 32 papers were included. It was evident that sarcopenia and T2D share multiple pathophysiological mechanisms. Common changes in muscle architecture consist of a shift in myocyte composition, increased myosteatosis and a decreased capacity for muscle regeneration. Further, both diseases are linked to an imbalance in myokine and sex hormone production. Chronic low-grade inflammation and increased levels of oxidative stress are also known pathophysiological contributors. In the future, research efforts should be directed towards discovering common checkpoints in the development of T2D and sarcopenia as possible shared therapeutic targets for both diseases. Current treatment for T2D with biguanides, incretins and insulin may already convey a protective effect on the development of sarcopenia. Furthermore, attention should be given to early diagnosis of sarcopenia within the population of people with T2D, given the sizeable physical and medical burden it encompasses. A combination of simple diagnostic techniques could be used at regular diabetes check-ups to identify sarcopenia at an early stage and start lifestyle modifications and treatment as soon as possible.

Association between Osteoporosis and Skeletal Muscle Mass in Men

STUDY DESIGN

Cross-sectional study.

PURPOSE

This cross-sectional study aimed to investigate the risk factors for osteoporosis in men by assessing bone mineral density (BMD), skeletal muscle mass, body fat mass, grip strength, and advanced glycation end products (AGEs).

OVERVIEW OF LITERATURE

Fewer studies have reported the correlation between BMD and skeletal muscle mass in women. Moreover, a few studies have examined the relationship between osteoporosis and skeletal muscle mass.

METHODS

This study included 99 men (mean age, 74.9 years; range, 28-93 years) who visited Qiball Clinic for BMD and body composition examinations. The osteoporosis group consisted of 24 patients (mean age, 72.5 years; range, 44-92 years), and the control group consisted of 75 individuals (mean age, 74.9 years; range, 28-93 years). Whole-body skeletal muscle mass was measured using a bioelectrical impedance analyzer. BMD was measured by dual X-ray absorptiometry. Skin autofluorescence (SAF), a marker of dermal AGE accumulation, was measured using a spectroscope. Osteoporosis was defined as a bone density T score of -2.5 or less. Physical findings, skeletal muscle mass, BMD, grip strength, and SAF were compared between the osteoporosis and control groups.

RESULTS

The osteoporosis group had significantly lower trunk muscle mass (23.1 kg vs. 24.9 kg), lower leg muscle mass (14.4 kg vs. 13.0 kg), and skeletal mass index (7.1 kg/m2 vs. 6.7 kg/m2) than the control group (all p<0.05). Lower limb muscle mass was identified as a risk factor for osteoporosis in men (odds ratio, 0.64; p=0.03).

CONCLUSIONS

Conservative treatment of osteoporosis in men will require an effective approach that facilitates the maintenance or strengthening of skeletal muscle mass, including exercise therapy with a focus on lower extremities and nutritional supplementation.

Age-Associated Differences in Recovery from Exercise-Induced Muscle Damage

Understanding the intricate mechanisms governing the cellular response to resistance exercise is paramount for promoting healthy aging. This narrative review explored the age-related alterations in recovery from resistance exercise, focusing on the nuanced aspects of exercise-induced muscle damage in older adults. Due to the limited number of studies in older adults that attempt to delineate age differences in muscle discovery, we delve into the multifaceted cellular influences of chronic low-grade inflammation, modifications in the extracellular matrix, and the role of lipid mediators in shaping the recovery landscape in aging skeletal muscle. From our literature search, it is evident that aged muscle displays delayed, prolonged, and inefficient recovery. These changes can be attributed to anabolic resistance, the stiffening of the extracellular matrix, mitochondrial dysfunction, and unresolved inflammation as well as alterations in satellite cell function. Collectively, these age-related impairments may impact subsequent adaptations to resistance exercise. Insights gleaned from this exploration may inform targeted interventions aimed at enhancing the efficacy of resistance training programs tailored to the specific needs of older adults, ultimately fostering healthy aging and preserving functional independence.

Quantification of local matrix deposition during muscle stem cell activation using engineered hydrogels

Adult stem cells occupy a niche that contributes to their function, but how stem cells remodel their microenvironment remains an open-ended question. Herein, biomaterials-based systems and metabolic labeling were utilized to evaluate how skeletal muscle stem cells deposit extracellular matrix. Muscle stem cells and committed myoblasts were observed to generate less nascent matrix than muscle resident fibro-adipogenic progenitors. When cultured on substrates that matched the stiffness of physiological uninjured and injured muscles, the increased nascent matrix deposition was associated with stem cell activation. Reducing the ability to deposit nascent matrix in muscle stem cells attenuated function and mimicked impairments observed from muscle stem cells isolated from old aged muscles, which could be rescued with therapeutic supplementation of insulin-like growth factors. These results highlight how nascent matrix production is critical for maintaining healthy stem cell function.

Leveraging Biomaterial Platforms to Study Aging-Related Neural and Muscular Degeneration

Aging is a complex multifactorial process that results in tissue function impairment across the whole organism. One of the common consequences of this process is the loss of muscle mass and the associated decline in muscle function, known as sarcopenia. Aging also presents with an increased risk of developing other pathological conditions such as neurodegeneration. Muscular and neuronal degeneration cause mobility issues and cognitive impairment, hence having a major impact on the quality of life of the older population. The development of novel therapies that can ameliorate the effects of aging is currently hindered by our limited knowledge of the underlying mechanisms and the use of models that fail to recapitulate the structure and composition of the cell microenvironment. The emergence of bioengineering techniques based on the use of biomimetic materials and biofabrication methods has opened the possibility of generating 3D models of muscular and nervous tissues that better mimic the native extracellular matrix. These platforms are particularly advantageous for drug testing and mechanistic studies. In this review, we discuss the developments made in the creation of 3D models of aging-related neuronal and muscular degeneration and we provide a perspective on the future directions for the field.

Effects of aging and diabetes on the deformation mechanisms and molecular structural characteristics of collagen fibrils under daily activity

Crosslinking plays an important role in collagen-based tissues since it affects mechanical behavior and tissue metabolism. Aging and diabetes affect the type and density of crosslinking, effectively altering tissue properties. However, most studies focus on these effects under large stress rather than daily activities. We focus on the deformation mechanisms and structural change at the binding sites for integrins, proteoglycans, and collagenase in collagen fibrils using a fully atomistic model. We show that high-connectivity enzymatic crosslinking (our "HC" model, representing normal tissues) and advanced-glycation end-products (our "Glucosepane" model, which increase in diabetes) result in uniform deformation under daily activity, but low-connectivity enzymatic crosslinking (our "LC" model, representing aging tissues) does not. In particular, the HC model displays more sliding, which may explain the ability of healthy tissues to absorb more strain energy. In contrast, AGEs induce instability in the structures near the binding sites, which would affect the tissue metabolism of the collagen molecule. Our results provide important insights into the molecular mechanisms of collagen and a possible explanation for the role of crosslinking in tissues undergoing daily activity.

Sulfonamides stimulate ROS formation upon glycation of human carbonic anhydrase II

Advanced glycation end products are the most important species of glycation pathway, and cause disorders such as oxidative stress and diabetes. Sulfonamide compounds, which are generally known as widespread inhibitors, are potential agents used in different drug products, which can readily enter biological matrices. In the present work, the structure and activity of human carbonic anhydrase II studied in the presence of glucose as well as four sulfonamide agents from different views. These included enzyme kinetics, free lysine content, fluorescence spectroscopy, circular dichroism, and ROS measurement. Our results indicated that upon glycation, the structure of HCA II collapses and 8 to 13 lysine residues will be more available based on ligand incubation. Secondary and tertiary structural changes were also observed in the presence and absence of sulfonamide agents using fluorescence and circular dichroism methods, respectively. These spectroscopic data also showed a remarkable increase in hydrophobicity and decrease in α-helix contents during glycation, especially after 35 days of incubation. ROS assay was studied in the presence of glucose and sulfonamide compounds, that demonstrated the role of sulfonamide compounds in ROS formation in the presence of glucose in a synergistic manner. Overall, our data indicated that sulfonamides act as a stimulant factor upon prolonged interaction with HCA II and may intensify the complications of some disorders, such as diabetes and other conformational diseases.

Effects of foot and ankle mobilisations combined with home stretches in people with diabetic peripheral neuropathy: a proof-of-concept RCT

INTRODUCTION

People with diabetic peripheral neuropathy (DPN) and limited joint mobility syndrome (LJMS) can experience increased forefoot peak plantar pressures (PPPs), a known risk factor for ulceration. The aim of this study was to investigate whether ankle and 1st metatarsophalangeal (MTP) joint mobilisations and home-based stretches in people with DPN improve joint range of motion (ROM) and reduce forefoot PPPs.

DESIGN AND METHODS

Sixty-one people with DPN (IWGDF risk 2), were randomly assigned to a 6-week programme of ankle and 1st MTP joint mobilisations (n = 31) and home-based stretches or standard care only (n = 30). At baseline (T0); 6-week post intervention (T1) and at 3 months follow-up (T2), a blinded assessor recorded dynamic ankle dorsiflexion range using 3D (Codamotion) motion analysis and the weight bearing lunge test, static 1st MTP joint dorsiflexion ROM, dynamic plantar pressure and balance.

RESULTS

At T1 and T2 there was no difference between both groups in ankle dorsiflexion in stance phase, plantar pressure and balance. Compared to the control group, the intervention group showed a statistically significant increase in static ankle dorsiflexion range (Left 1.52 cm and 2.9cms, Right 1.62 cm and 2.7 cm) at 6 (T1) and 18 weeks (T2) respectively p < 0.01). Between group differences were also seen in left hallux dorsiflexion (2.75°, p < 0.05) at T1 and in right hallux dorsiflexion ROM (4.9°, p < 0.01) at T2 follow up. Further, functional reach showed a significant increase in the intervention group (T1 = 3.13 cm p < 0.05 and T2 = 3.9 cm p < 0.01). Intervention adherence was high (80%).

CONCLUSIONS

Combining ankle and 1st MTP joint mobilisations with home-based stretches in a 6-week programme in people with DPN is effective in increasing static measures of range. This intervention may be useful for improving ankle, hallux joint mobility and anteroposterior stability limits in people with diabetes and neuropathy but not for reducing PPP or foot ulcer risk.

TRIAL REGISTRATION

https://classic.

CLINICALTRIALS

gov/ct2/show/NCT03195855 .

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.

Prevalence of Sarcopenia and Dynapenia and Related Clinical Outcomes in Patients with Type 1 Diabetes Mellitus

BACKGROUND

Sarcopenia has recently been recognized as a complication of diabetes. However, there are few results about the prevalence of sarcopenia and dynapenia and the related clinical outcomes in type 1 diabetes mellitus (T1DM). Our objectives were to evaluate the prevalence of sarcopenia and dynapenia and to determine whether there are any associations with disease-related factors in people with T1DM.

METHODS

A cross-sectional study was conducted in people with T1DM. We assessed appendicular skeletal mass index (ASMI) using bioimpedance 50 Hz (Nutrilab Akern). Muscle function was assessed through handgrip strength (HGS) using a Jamar dynamometer. Sarcopenia was defined as a low HGS with low ASMI, whereas dynapenia was defined as low HGS with a normal ASMI. We used HGS data from the Spanish population percentile table and a cut-off point at p5 as dynapenia. The association of clinical, metabolic, and lifestyle variables with sarcopenia and dynapenia was studied.

RESULTS

This study included 62 T1DM patients (66% females, mean age of 38 ± 14 years, body mass index (BMI) of 24.9 ± 4.7 kg/m2). The prevalence of sarcopenia and dynapenia was 8% and 23%, respectively. In our sample, there were more men in the sarcopenic and dynapenic groups. The sarcopenic group showed a significantly higher mean HbA1c value. Lower diabetes duration, PREDIMED score, BMI, and muscle mass measures (fat-free mass index (FFMI), ASMI, and body cell mass index (BCMI)) were significantly associated with sarcopenia. Decreased diabetes duration, PREDIMED score, phase angle (PhA), and HGS values showed a significant association with dynapenia.

CONCLUSIONS

The prevalence of sarcopenia and dynapenia was high in people with T1DM in our study. Specifically, the proportion of dynapenia was quite high. HGS and ASMI are practical tools for the assessment of muscle health status in T1DM, and low values are associated with poor glycemic control, underweight, and low adherence to the Mediterranean diet. Thus, dynapenia may predict accelerated muscle aging in T1DM.

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.

Protein Turnover in Skeletal Muscle: Looking at Molecular Regulation towards an Active Lifestyle

Skeletal muscle is a highly plastic tissue, able to change its mass and functional properties in response to several stimuli. Skeletal muscle mass is influenced by the balance between protein synthesis and breakdown, which is regulated by several signaling pathways. The relative contribution of Akt/mTOR signaling, ubiquitin-proteasome pathway, autophagy among other signaling pathways to protein turnover and, therefore, to skeletal muscle mass, differs depending on the wasting or loading condition and muscle type. By modulating mitochondria biogenesis, PGC-1α has a major role in the cell's bioenergetic status and, thus, on protein turnover. In fact, rates of protein turnover regulate differently the levels of distinct protein classes in response to atrophic or hypertrophic stimuli. Mitochondrial protein turnover rates may be enhanced in wasting conditions, whereas the increased turnover of myofibrillar proteins triggers muscle mass gain. The present review aims to update the knowledge on the molecular pathways implicated in the regulation of protein turnover in skeletal muscle, focusing on how distinct muscle proteins may be modulated by lifestyle interventions with emphasis on exercise training. The comprehensive analysis of the anabolic effects of exercise programs will pave the way to the tailored management of muscle wasting conditions.

Vertical stiffness and lower limb inter-joint coordination in older versus younger runners

Older runners (OR) are increasing their participation in races. Aging may impact the adopted running pattern. Hence, the analysis of stiffness and the inter-joint lower limb coordination in the sagittal plane could contribute to investigating this impact. This study aimed to compare the vertical stiffness (Kvert) and the inter-joint lower limb coordination in the sagittal plane between younger runners (YR) and OR. This cross-sectional study recruited 15 YR males and 15 OR males. The pelvis and lower limb motions were assessed while running on a treadmill at self-selected (range OR: 1.94-3.75 m.s-1, YR: 2.08-4.17 m.s-1) and fixed speeds (3.33 m.s-1). Hip-ankle, knee-ankle, and hip-knee coupling angle (CA) and its variability (CAV) were extracted using the vector coding method. Mann-Whitney U tests compared Kvert between groups at each running speed. Watson's U2 tests compared the mean CA between groups in three intervals of the contact phase at each running speed. Statistical Parametric Mapping independent t-test compared the CAV curve between groups at each running speed. OR showed greater Kvert than YR at both speeds. Hip-ankle CA pattern differed between groups during the early stance at both speed conditions. OR showed in-phase, distal dominancy in hip-ankle CA, whereas YR showed anti-phase, proximal dominancy. Knee-ankle CA was distinct only at self-selected speed, in which OR showed in-phase, proximal dominancy, while YR exhibited anti-phase, proximal dominancy. CAV did not differ between groups. The findings showed that OR adopted a stiffer pattern characterized by distinct inter-joint lower limb CA, at early stance, during self-selected and fixed speeds.

Research on the anti-ageing mechanism of Prunella vulgaris L

Prunella vulgaris L. (P. vulgaris) has long been considered to have antipyretic, analgesic and anti-inflammatory effects, lowering blood lipids and pressure. Many studies show that in addition to the traditional telomere attrition, DNA damage and epigenetic changes, immunosenescence is also a new possibility to explore the mechanism of ageing. Therefore, this herb may have potential anti-ageing effects. Typically, there are a series of markers that identify senescent cells, such as superoxide dismutase (SOD)2, an inhibitor of CDK4 (p16^INK4A), tumor necrosis factor (TNF)-α, immune cells number, proliferation, and nuclear abnormalities. These changes rarely present in young tissues, while greatly increasing in response to ageing. Firstly, the ageing model of the Institute of Cancer Research (ICR) mouse was established by D-galactose subcutaneous injection. Then, SOD2, p16^INK4A and TNF-α were detected by quantitative Real-time PCR (qPCR), Western Blot (WB) and Enzyme-Linked Immunosorbent Assay (ELISA). Simultaneously, senescent cells in livers were stained by hematoxylin and eosin (HE). The viability of splenocytes was detected by Cell Counting Kit-8(CCK-8). The difference in specific immune cells (NK cells, B lymphocytes and T lymphocytes) was detected by flow cytometry. Both low (100 mg/kg) and high (300 mg/kg) concentrations of P. vulgaris treated ageing ICR mice show anti-ageing alterations, such as p16^INK4A decreased approximately 1/2 and SOD2 tripled in livers, TNF-α decreased from 1 to 0.6 in plasma, and T cells increased from 0.09 to 0.19%. Compared with the ageing group, the spleen cells in the Prunella-treated group had stronger proliferation ability. Thus, P. vulgaris could have an anti-ageing effect. This is the first study to demonstrate the anti-ageing effect of P. vulgaris. It may also be capable of preventing a variety of age-related diseases.

Dietary advanced glycation end products (dAGEs): An insight between modern diet and health

Advanced glycation end products (AGEs) are formed by a series of chemical reactions of amino acids, peptides, proteins, and ketones at normal temperature or heated non-enzymatic conditions. A large amount of AGEs derived from Maillard Reaction (MR) during the process of food heat-processing. After oral intake, dietary AGEs are converted into biological AGEs through digestion and absorption, and accumulated in almost all organs. The safety and health risk of dietary AGEs have attracted wide attention. Increasing evidence have shown that uptake of dietary AGEs is closely related to the occurrence of many chronic diseases, such as diabetes, chronic kidney disease, osteoporosis, and Alzheimer's disease. This review summarized the most updated information of production, bio-transport in vivo, detection technologies, and physiological toxicity of dietary AGEs, and also discussed approaches to inhibit dietary AGEs generation. Impressively, the future opportunities and challenges on the detection, toxicity, and inhibition of dietary AGEs are raised.

Therapeutic effects of human umbilical cord mesenchymal stem cell-derived extracellular vesicles on ovarian functions through the PI3K/Akt cascade in mice with premature ovarian failure

Premature ovarian failure (POF) mainly refers to ovarian dysfunction in females younger than forty. Mesenchymal stem cells (MSCs) are considered an increasingly promising therapy for POF. This study intended to uncover the therapeutic effects of human umbilical cord MSC-derived extracellular vesicles (hucMSCEVs) on POF. hucMSCs were identified by observing morphology and examining differentiation capabilities. EVs were extracted from hucMSCs and later identified utilizing nanoparticle tracking analysis, transmission electron microscopy, and Western blotting. POF mouse models were established by injecting D-galactose (Dgal). The estrous cycles were assessed through vaginal cytology, and serum levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), anti-mullerian hormone (AMH), estradiol (E2), and progesterone (P) were measured by ELISA. The human ovarian granulosa cell line KGN was used for in vitro experiments. The uptake of hucMSC-EVs by KGN cells was detected. After D-gal treatment, cell proliferation and apoptosis were assessed via CCK-8 assay and flow cytometry. The PI3K/Akt pathway-related proteins were determined by Western blotting. Our results revealed that POF mice had prolonged estrous cycles, increased FSH and LH levels, and decreased AMH, E2, and P levels. Treatment with hucMSC-EVs partially counteracted the above changes. D-gal treatment reduced proliferation and raised apoptosis in KGN cells, while hucMSC-EV treatment annulled the changes. D-gal-treated cells exhibited downregulated p-PI3K/PI3K and p-Akt/Akt levels, while hucMSC-EVs activated the PI3K/Akt pathway. LY294002 suppressed the roles of hucMSC-EVs in promoting KGN cell proliferation and lowering apoptosis. Collectively, hucMSC-EVs facilitate proliferation and suppress apoptosis of ovarian granulosa cells by activating the PI3K/Akt pathway, thereby alleviating POF.

Repurposing Drugs for Diabetes Mellitus as Potential Pharmacological Treatments for Sarcopenia - A Narrative Review

Sarcopenia, the age-related loss of muscle strength and mass or quality, is a common condition with major adverse consequences. Although the pathophysiology is incompletely understood, there are common mechanisms between sarcopenia and the phenomenon of accelerated ageing seen in diabetes mellitus. Drugs currently used to treat type 2 diabetes mellitus may have mechanisms of action that are relevant to the prevention and treatment of sarcopenia, for those with type 2 diabetes and those without diabetes. This review summarises shared pathophysiology between sarcopenia and diabetes mellitus, including the effects of advanced glycation end products, mitochondrial dysfunction, chronic inflammation and changes to the insulin signalling pathway. Cellular and animal models have generated intriguing, albeit mixed, evidence that supports possible beneficial effects on skeletal muscle function for some classes of drugs used to treat diabetes, including metformin and SGLT2 inhibitors. Most human observational and intervention evidence for the effects of these drugs has been derived from populations with type 2 diabetes mellitus, and there is a need for intervention studies for older people with, and at risk of, sarcopenia to further investigate the balance of benefit and risk in these target populations. Not all diabetes treatments will be safe to use in those without diabetes because of variable side effects across classes. However, some agents [including glucagon-like peptide (GLP)-1 receptor agonists and SGLT2 inhibitors] have already demonstrated benefits in populations without diabetes, and it is these agents, along with metformin, that hold out the most promise for further investigation in sarcopenia.

Osteosarcopenia in the Spine Beyond Bone Mineral Density: Association Between Paraspinal Muscle Impairment and Advanced Glycation Endproducts

STUDY DESIGN

Prospective cross-sectional study.

OBJECTIVE

To determine if an accumulation of advanced glycation endproducts (AGEs) is associated with impaired paraspinal muscle composition.

BACKGROUND

Impaired bone integrity and muscle function are described as osteosarcopenia. Osteosarcopenia is associated with falls, fragility fractures, and reduced quality of life. Bone integrity is influenced by bone quantity (bone mineral density) and quality (microarchitecture and collagen). The accumulation of AGEs stiffens collagen fibers and increases bone fragility. The relationship between paraspinal muscle composition and bone collagen properties has not been evaluated.

METHODS

Intraoperative bone biopsies from the posterior superior iliac spine were obtained and evaluated with multiphoton microscopy for fluorescent AGE cross-link density (fAGEs). Preoperative magnetic resonance imaging measurements at level L4 included the musculus (m.) psoas and combined m. multifidus and m. erector spinae (posterior paraspinal musculature, PPM). Muscle segmentation on axial images (cross-sectional area, CSA) and calculation of a pixel intensity threshold method to differentiate muscle (functional cross-sectional area, fCSA) and intramuscular fat (FAT). Quantitative computed tomography was performed at the lumbar spine. Univariate and multivariable regression models were used to investigate associations between fAGEs and paraspinal musculature.

RESULTS

One hundred seven prospectively enrolled patients (50.5% female, age 60.7 y, BMI 28.9 kg/m 2 ) were analyzed. In all, 41.1% and 15.0% of the patients demonstrated osteopenia and osteoporosis, respectively. Univariate linear regression analysis demonstrated a significant association between cortical fAGEs and CSA in the psoas (ρ=0.220, P =0.039) but not in the PPM. Trabecular fAGEs revealed no significant associations to PPM or psoas musculature. In the multivariable analysis, higher cortical fAGEs were associated with increased FAT (β=1.556; P =0.002) and CSA (β=1.305; P =0.005) in the PPM after adjusting for covariates.

CONCLUSION

This is the first investigation demonstrating that an accumulation of nonenzymatic collagen cross-linking product fAGEs in cortical bone is associated with increased intramuscular fat in the lumbar paraspinal musculature.

Contribution of intramuscular connective tissue and its structural components on meat tenderness-revisited: a review

The tenderness of meat influences consumers' perceptions of its quality. Meat tenderness is a key quality characteristic that influences consumer satisfaction, repeat purchases, and willingness to pay higher prices for meat. Muscle fibers, connective tissues, and adipocytes are the main structural components of meat that contribute to its tenderness and texture. In the present review, we have focused on the role of connective tissue and its components in meat tenderness, specifically perimysial intramuscular connective tissue (IMCT) and its concept as an immutable "background toughness." The collagen contribution to cooked meat toughness can be altered by animal diet, compensatory growth, slaughter age, aging, and cooking. As well, progressive thickening of the perimysium leads to a progressive increase in shear force values in beef, pork, chicken, and this may occur prior to adipocyte formation as cattle finish in feedlots. Conversely, adipocyte accumulation in the perimysium can decrease cooked meat shear force, suggesting that the contribution of IMCT to meat toughness is complex and driven by both collagen structure and content. This review provides a theoretical foundation of information to modify IMCT components to improve meat tenderness.

The AGE-RAGE Axis and the Pathophysiology of Multimorbidity in COPD

Chronic obstructive pulmonary disease (COPD) is a disease of the airways and lungs due to an enhanced inflammatory response, commonly caused by cigarette smoking. Patients with COPD are often multimorbid, as they commonly suffer from multiple chronic (inflammatory) conditions. This intensifies the burden of individual diseases, negatively affects quality of life, and complicates disease management. COPD and comorbidities share genetic and lifestyle-related risk factors and pathobiological mechanisms, including chronic inflammation and oxidative stress. The receptor for advanced glycation end products (RAGE) is an important driver of chronic inflammation. Advanced glycation end products (AGEs) are RAGE ligands that accumulate due to aging, inflammation, oxidative stress, and carbohydrate metabolism. AGEs cause further inflammation and oxidative stress through RAGE, but also through RAGE-independent mechanisms. This review describes the complexity of RAGE signaling and the causes of AGE accumulation, followed by a comprehensive overview of alterations reported on AGEs and RAGE in COPD and in important co-morbidities. Furthermore, it describes the mechanisms by which AGEs and RAGE contribute to the pathophysiology of individual disease conditions and how they execute crosstalk between organ systems. A section on therapeutic strategies that target AGEs and RAGE and could alleviate patients from multimorbid conditions using single therapeutics concludes this review.

Exercise builds the scaffold of life: muscle extracellular matrix biomarker responses to physical activity, inactivity, and aging

Skeletal muscle extracellular matrix (ECM) is critical for muscle force production and the regulation of important physiological processes during growth, regeneration, and remodelling. ECM remodelling is a tightly orchestrated process, sensitive to multi-directional tensile and compressive stresses and damaging stimuli, and its assessment can convey important information on rehabilitation effectiveness, injury, and disease. Despite its profound importance, ECM biomarkers are underused in studies examining the effects of exercise, disuse, or aging on muscle function, growth, and structure. This review examines patterns of short- and long-term changes in the synthesis and concentrations of ECM markers in biofluids and tissues, which may be useful for describing the time course of ECM remodelling following physical activity and disuse. Forces imposed on the ECM during physical activity critically affect cell signalling while disuse causes non-optimal adaptations, including connective tissue proliferation. The goal of this review is to inform researchers, and rehabilitation, medical, and exercise practitioners better about the role of ECM biomarkers in research and clinical environments to accelerate the development of targeted physical activity treatments, improve ECM status assessment, and enhance function in aging, injury, and disease.

Human skeletal muscle-specific atrophy with aging: a comprehensive review

Age-related skeletal muscle atrophy appears to be a muscle group-specific process, yet only a few specific muscles have been investigated and our understanding in this area is limited. This review provides a comprehensive summary of the available information on age-related skeletal muscle atrophy in a muscle-specific manner, nearly half of which comes from the quadriceps. Decline in muscle-specific size over ∼50 yr of aging was determined from 47 cross-sectional studies of 982 young (∼25 yr) and 1,003 old (∼75 yr) individuals and nine muscle groups: elbow extensors (-20%, -0.39%/yr), elbow flexors (-19%, -0.38%/yr), paraspinals (-24%, -0.47%/yr), psoas (-29%, -0.58%/yr), hip adductors (-13%, -0.27%/yr), hamstrings (-19%, -0.39%/yr), quadriceps (-27%, -0.53%/yr), dorsiflexors (-9%, -0.19%/yr), and triceps surae (-14%, -0.28%/yr). Muscle-specific atrophy rate was also determined for each of the subcomponent muscles in the hamstrings, quadriceps, and triceps surae. Of all the muscles included in this review, there was more than a fivefold difference between the least (-6%, -0.13%/yr, soleus) to the most (-33%, -0.66%/yr, rectus femoris) atrophying muscles. Muscle activity level, muscle fiber type, sex, and timeline of the aging process all appeared to have some influence on muscle-specific atrophy. Given the large range of muscle-specific atrophy and the large number of muscles that have not been investigated, more muscle-specific information could expand our understanding of functional deficits that develop with aging and help guide muscle-specific interventions to improve the quality of life of aging women and men.

Muscle group-specific skeletal muscle aging: a 5-yr longitudinal study in septuagenarians

There is some evidence that the age-associated change in skeletal muscle mass is muscle specific, yet the number of specific muscles that have been studied to form our understanding in this area is limited. In addition, few aging investigations have examined multiple muscles in the same individuals. This longitudinal investigation compared changes in skeletal muscle size via computed tomography of the quadriceps (rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius), hamstrings (biceps femoris short and long heads, semitendinosus, and semimembranosus), psoas, rectus abdominis, lateral abdominals (obliques and transversus abdominis), and paraspinal muscles (erector spinae and multifidi) of older individuals from the Health, Aging, and Body Composition (Health ABC) study at baseline and 5.0 ± 0.1 years later (n = 469, 73 ± 3 yr and 78 ± 3 yr, 49% women, 33% black). Skeletal muscle size decreased (P < 0.05) in quadriceps (-3.3%), hamstrings (-5.9%), psoas (-0.4%), and rectus abdominis (-7.0%). The hamstrings and rectus abdominis atrophied approximately twice as much as the quadriceps (P < 0.05), whereas the quadriceps atrophied substantially more than the psoas (P < 0.05). The lateral abdominals (+5.9%) and paraspinals (+4.3%) hypertrophied (P < 0.05) to a similar degree (P > 0.05) over the 5 years. These data suggest that older individuals experience skeletal muscle atrophy and hypertrophy in a muscle group-specific fashion in the eighth decade, a critical time period in the aging process. A broader understanding of muscle group-specific skeletal muscle aging is needed to better guide exercise programs and other interventions that mitigate decrements in physical function with aging.NEW & NOTEWORTHY These longitudinal analyses of six muscle groups in septuagenarians provide novel information on the muscle group-specific aging process. Although the quadriceps, hamstrings, psoas, and rectus abdominis atrophied with different magnitudes, the lateral abdominals and paraspinals hypertrophied over the 5 years. These findings contribute to a better understanding of the skeletal muscle aging process and highlight the need to complete studies in this area with a muscle-specific focus.

Propolis Ethanolic Extract Attenuates D-gal-induced C2C12 Cell Injury by Modulating Nrf2/HO-1 and p38/p53 Signaling Pathways

Previous study has shown that propolis ethanolic extract (PEE) has a protective effect on aging skeletal muscle atrophy. However, the exact molecular mechanism remains unclear. This study aimed to investigate the effect of PEE on D-galactose (D-gal)-induced damage in mouse C2C12 cells. The results revealed that PEE increased the viability of senescent C2C12 cells, decreased the number of senescence-associated β-galactosidase (SA-β-Gal)-positive cells and promoted the differentiation of C2C12 cells. PEE resisted oxidative stress caused by D-gal by activating the Nrf2/HO-1 signaling pathway and maintained the differentiation ability of C2C12 cells. PEE inhibited apoptosis by suppressing p38 phosphorylation and reducing p53 expression. In summary, our findings reveal the molecular mechanism by which PEE protects D-gal-induced C2C12 cells, providing a theoretical basis for the development of PEE for the alleviation of muscle atrophy.

Advanced Glycation End Products and Bone Metabolism in Patients with Chronic Kidney Disease

Advanced glycation end products (AGEs) accumulation may be involved in the progression of CKD-bone disorders. We sought to determine the relationship between AGEs measured in the blood, skin, and bone with histomorphometry parameters, bone protein, gene expression, and serum biomarkers of bone metabolism in patients with CKD stages 3 to 5D patients. Serum levels of AGEs were estimated by pentosidine, glycated hemoglobin (A1c), and N-carboxymethyl lysine (CML). The accumulation of AGEs in the skin was estimated from skin autofluorescence (SAF). Bone AGEs accumulation and multiligand receptor for AGEs (RAGEs) expression were evaluated by immunohistochemistry; bone samples were used to evaluate protein and gene expression and histomorphometric analysis. Data are from 86 patients (age: 51 ± 13 years; 60 [70%] on dialysis). Median serum levels of pentosidine, CML, A1c, and SAF were 71.6 pmol/mL, 15.2 ng/mL, 5.4%, and 3.05 arbitrary units, respectively. AGEs covered 3.92% of trabecular bone and 5.42% of the cortical bone surface, whereas RAGEs were expressed in 0.7% and 0.83% of trabecular and cortical bone surfaces, respectively. AGEs accumulation in bone was inversely related to serum receptor activator of NF-κB ligand/parathyroid hormone (PTH) ratio (R = -0.25; p = 0.03), and RAGE expression was negatively related to serum tartrate-resistant acid phosphatase-5b/PTH (R = -0.31; p = 0.01). Patients with higher AGEs accumulation presented decreased bone protein expression (sclerostin [1.96 (0.11-40.3) vs. 89.3 (2.88-401) ng/mg; p = 0.004]; Dickkopf-related protein 1 [0.064 (0.03-0.46) vs. 1.36 (0.39-5.87) ng/mg; p = 0.0001]; FGF-23 [1.07 (0.4-32.6) vs. 44.1 (6-162) ng/mg; p = 0.01]; and osteoprotegerin [0.16 (0.08-2.4) vs. 6.5 (1.1-23.7) ng/mg; p = 0.001]), upregulation of the p53 gene, and downregulation of Dickkopf-1 gene expression. Patients with high serum A1c levels presented greater cortical porosity and Mlt and reduced osteoblast surface/bone surface, eroded surface/bone surface, osteoclast surface/bone surface, mineral apposition rate, and adjusted area. Cortical thickness was negatively correlated with serum A1c (R = -0.28; p = 0.02) and pentosidine levels (R = -0.27; p = 0.02). AGEs accumulation in the bone of CKD patients was related to decreased bone protein expression, gene expression changes, and increased skeletal resistance to PTH; A1c and pentosidine levels were related to decreased cortical thickness; and A1c levels were related to increased cortical porosity and Mlt. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

The impact of age-related increase in passive muscle stiffness on simulated upper limb reaching

Ageing changes the musculoskeletal and neural systems, potentially affecting a person's ability to perform daily living activities. One of these changes is increased passive stiffness of muscles, but its contribution to performance is difficult to separate experimentally from other ageing effects such as loss of muscle strength or cognitive function. A computational upper limb model was used to study the effects of increasing passive muscle stiffness on reaching performance across the model's workspace (all points reachable with a given model geometry). The simulations indicated that increased muscle stiffness alone caused deterioration of reaching accuracy, starting from the edges of the workspace. Re-tuning the model's control parameters to match the ageing muscle properties does not fully reverse ageing effects but can improve accuracy in selected regions of the workspace. The results suggest that age-related muscle stiffening, isolated from other ageing effects, impairs reaching performance. The model also exhibited oscillatory instability in a few simulations when the controller was tuned to the presence of passive muscle stiffness. This instability is not observed in humans, implying the presence of natural stabilizing strategies, thus pointing to the adaptive capacity of neural control systems as a potential area of future investigation in age-related muscle stiffening.

Association of Autofluorescent Advanced Glycation End Products (AGEs) with Frailty Components in Chronic Kidney Disease (CKD): Data from a Single-Center Cohort Study

BACKGROUND

Chronic kidney disease (CKD) is characterized by an overproduction and accumulation of advanced glycation end products (AGEs). Because AGEs may play a role in the development of malnutrition and sarcopenia, two essential components of frailty, we evaluated whether they may also contribute to the onset of frailty in CKD patients.

METHODS

We performed a cross-sectional analysis of 117 patients. AGEs were quantified using a fluorescence spectrophotometer and soluble receptor for AGE (sRAGE) isoforms by ELISA. We defined frailty according to the frailty phenotype (FP) proposed by Fried.

RESULTS

The average age of patients was 80 ± 11 years, 70% were male, and the mean eGFR was 25 + 11 mL/min/1.73m². Frailty was diagnosed in 51 patients, and 40 patients were classified as pre-frail. AGEs and RAGE isoforms seem not to correlate with overall frailty. Instead, AGEs were associated with specific frailty domains, inversely associated with BMI (R = -0.22, p = 0.016) and directly associated with gait test time (R = 0.17, p = 0.049). AGEs were also associated with involuntary weight loss (OR 1.84 p = 0.027), independent of age and sex.

CONCLUSIONS

AGEs are associated with some pivotal components of the frailty phenotype, although they are not associated with frailty overall.

Characteristics of Postoperative Patients with Breast Cancer Aged 65 Years and Older

Objective: This study aimed to compare postoperative patients with breast cancer aged ≥65 years with those aged <65 years and clarify the characteristics of postoperative patients with breast cancer aged ≥65. Methods: In total, 376 patients in whom we were able to evaluate survey items one month after surgery were included in the study. Comorbidity, including diabetes mellitus and hypertension, shoulder range of motion (ROM), upper-limb function, and psychological problems, was evaluated. Results: Hypertension and diabetes mellitus were significantly higher in patients aged ≥65 years (the elderly group) than in those aged <65 years (the non-elderly group) (p < 0.05). Preoperative shoulder flexion ROM was significantly restricted in the elderly group compared with the non-elderly group (p < 0.05). Preoperative shoulder abduction ROM was significantly restricted in the elderly group compared with the non-elderly group (p < 0.05). At one month after surgery, upper-limb function was more impaired in the non-elderly group than in the elderly group (p < 0.05). In both groups, both ROM and upper-limb function were significantly impaired one month after surgery compared with before surgery (p < 0.05). Conclusions: Postoperative patients with breast cancer aged ≥65 years should be careful about risk management and intervention during rehabilitation. Preoperative evaluation of shoulder ROM should be performed because patients aged ≥65 years have limited ROM before surgery.

Advanced Glycation End Products and Inflammatory Cytokine Profiles in Maintenance Hemodialysis Patients After the Ingestion of a Protein-Dense Meal

OBJECTIVE

The goal of this investigation was to evaluate circulating and skeletal muscle inflammatory biomarkers between maintenance hemodialysis (MHD) and demographic-matched control subjects (CON) before and after ingestion of a protein-rich meal.

DESIGN AND METHODS

CON (n = 8; 50 ± 2 years; 31 ± 1 kg/m2) and MHD patients (n = 8; 56 ± 5 years; 32 ± 2 kg/m2) underwent a basal blood draw and muscle biopsy and serial blood draws after the ingestion of a mixed meal on a nondialysis day. Plasma advanced glycation end products (AGEs) and markers of oxidation were assessed via liquid chromatography-tandem mass spectrometry before and after the meal (+240 min). Circulating inflammatory cytokines and soluble receptors for AGE (sRAGE) isoforms (endogenous secretory RAGEs and cleaved RAGEs) were determined before and after the meal (+240 min). Basal muscle was probed for inflammatory cytokines and protein expression of related signaling components (RAGE, Toll-like receptor 4, oligosaccharyltransferase subunit 48, TIR-domain-containing adapter-inducing interferon-β, total IκBα, and pIκBα).

RESULTS

Basal circulating AGEs were 7- to 343-fold higher (P < .001) in MHD than those in CON, but only MG-H1 increased in CON after the meal (P < .001). There was a group effect (MHD > CON) for total sRAGEs (P = .02) and endogenous secretory RAGEs (P < .001) and a trend for cleaved RAGEs (P=.09), with no meal effect. In addition, there was a group effect (MHD < CON; P < .05) for circulating fractalkine, interleukin (IL)10, IL17A, and IL1β and a trend (P < .10) for IL6 and macrophage inflammatory protein 1 alpha, whereas tumor necrosis factor alpha was higher in MHD (P < .001). In muscle, Toll-like receptor 4 (P = .03), TIR-domain-containing adapter-inducing interferon-β (P = .002), and oligosaccharyltransferase subunit 48 (P = .02) expression was lower in MHD than that in CON, whereas IL6 was higher (P = .01) and IL8 (P = .08) tended to be higher in MHD.

CONCLUSION

Overall, MHD exhibited an exaggerated, circulating, and skeletal muscle inflammatory biomarker environment, and the meal did not appreciably affect the inflammatory status.

Ageing of skeletal muscle extracellular matrix and mitochondria: finding a potential link

Aim: To discuss the progress of extracellular matrix (ECM) characteristics, mitochondrial homeostasis, and their potential crosstalk in the pathogenesis of sarcopenia, a geriatric syndrome characterized by a generalized and progressive reduction in muscle mass, strength, and physical performance.Methods: This review focuses on the anatomy and physiology of skeletal muscle, alterations of ECM and mitochondria during ageing, and the role of the interplay between ECM and mitochondria in the pathogenesis of sarcopenia.Results: Emerging evidence points to a clear interplay between mitochondria and ECM in various tissues and organs. Under the ageing process, the ECM undergoes changes in composition and physical properties that may mediate mitochondrial changes via the systematic metabolism, ROS, SPARC pathway, and AMPK/PGC-1α signalling, which in turn exacerbate muscle degeneration. However, the precise effects of such crosstalk on the pathobiology of ageing, particularly in skeletal muscle, have not yet been fully understood.Conclusion: The changes in skeletal muscle ECM and mitochondria are partially responsible for the worsened muscle function during the ageing process. A deeper understanding of their alterations and interactions in sarcopenic patients can help prevent sarcopenia and improve its prognoses.

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.

Age-Related Changes in Extracellular Matrix

Extracellular matrix (ECM) is an extracellular tissue structure that, in addition to mechanical support to the cell, is involved in regulation of many cellular processes, including chemical transport, growth, migration, differentiation, and cell senescence. Age-related changes in the structure and composition of the matrix and increase of ECM stiffness with age affect functioning of many tissues and contribute to the development of various pathological conditions. This review considers age-related changes of ECM in various tissues and organs, in particular, effect of ECM changes on aging is discussed.

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.

Phytochemicals as Potential Inhibitors of Advanced Glycation End Products: Health Aspects and Patent Survey

BACKGROUND

The glycation of proteins and lipids synthesizes the advanced glycation end products (AGEs), i.e., substances that irreversibly damage macromolecules present in tissues and organs, which contribute to the impairment of biological functions. For instance, the accumulation of AGEs induces oxidative stress, the inflammatory responses, and consequently the on set/worsening of diseases, including obesity, asthma, cognitive impairment, and cancer. There is a current demand on natural and low-cost sources of anti-AGE agents. As a result, food phytochemicals presented promising results to inhibit glycation and consequently, the formation of AGEs.

OBJECTIVE

Here we describe how the AGEs are present in food via Maillard reaction and in organs via natural aging, as well as the effects of AGEs on the worsening of diseases. Also we described the methods used to detect AGEs in samples, and the current findings on the use of phytochemicals (phenolic compounds, phytosterols, carotenoids, terpenes and vitamins) as natural therapeuticals to inhibit health damages via inhibition of AGEs in vitro and in vivo.

METHODS

This manuscript reviewed publications available in the PubMed and Science Direct databases dated from the last 20 years on the uses of phytochemicals for the inhibition of AGEs. Recent patents on the use of anti-AGEs drugs were reviewed with the use of Google Advanced Patents database.

RESULTS AND DISCUSSION

There is no consensus about which concentration of AGEs in blood serum should not be hazardous to the health of individuals. Food phytochemicals derived from agroindustry wastes, including peanut skins, and the bagasses derived from citrus and grapes are promising anti-AGEs agents via scavenging of free radicals, metal ions, the suppression of metabolic pathways that induces inflammation, the activation of pathways that promote antioxidant defense, and the blocking of AGE connection with the receptor for advanced glycation endproducts (RAGE).

CONCLUSION

Phytochemicals derived from agroindustry are promising anti-AGEs, which can be included to replace synthetic drugs to inhibit AGE formation, and consequently to act as therapeutical strategy to prevent and treat diseases caused by AGEs, including diabetes, ovarian cancer, osteoporosis, and Alzheimer's disease.

Myeloid cell-specific mutation of Spi1 selectively reduces M2-biased macrophage numbers in skeletal muscle, reduces age-related muscle fibrosis and prevents sarcopenia

Intramuscular macrophages play key regulatory roles in determining the response of skeletal muscle to injury and disease. Recent investigations showed that the numbers and phenotype of intramuscular macrophages change during aging, suggesting that those changes could influence the aging process. We tested that hypothesis by generating a mouse model that harbors a myeloid cell-specific mutation of Spi1, which is a transcription factor that is essential for myeloid cell development. The mutation reduced the numbers of macrophages biased to the CD163+/CD206+ M2 phenotype in muscles of aging mice without affecting the numbers of CD68-expressing macrophages and reduced the expression of transcripts associated with the M2-biased phenotype. The mutation did not affect the colony-forming ability or the frequency of specific subpopulations of bone marrow hematopoietic cells and did not affect myeloid/lymphoid cell ratios in peripheral blood leukocyte populations. Cellularity of most myeloid lineage cells was not influenced by the mutation. The Spi1 mutation in bone marrow-derived macrophages in vitro also did not affect expression of transcripts that indicate the M2-biased phenotype. Thus, myeloid cell-targeted mutation of Spi1 influences macrophage phenotype in muscle but did not affect earlier stages of differentiation of cells in the macrophage lineage. The mutation reduced age-related muscle fibrosis, which is consistent with the reduction of M2-biased macrophages, and reduced expression of the pro-fibrotic enzyme arginase. Most importantly, the mutation prevented sarcopenia. Together, our observations indicate that intramuscular, M2-biased macrophages play significant roles in promoting detrimental, age-related changes in muscle.

The Effects of Aging on the Intramuscular Connective Tissue

The intramuscular connective tissue plays a critical role in maintaining the structural integrity of the muscle and in providing mechanical support. The current study investigates age-related changes that may contribute to passive stiffness and functional impairment of skeletal muscles. Variations in the extracellular matrix in human quadriceps femoris muscles in 10 young men, 12 elderly males and 16 elderly females, and in the hindlimb muscles of 6 week old, 8 month old and 2 year old C57BL/6J male mice, were evaluated. Picrosirius red, Alcian blue and Weigert Van Gieson stainings were performed to evaluate collagen, glycosamynoglycans and elastic fibers. Immunohistochemistry analyses were carried out to assess collagen I, collagen III and hyaluronan. The percentage area of collagen was significantly higher with aging (p < 0.01 in humans, p < 0.001 in mice), mainly due to an increase in collagen I, with no differences in collagen III (p > 0.05). The percentage area of elastic fibers in the perimysium was significantly lower (p < 0.01) in elderly men, together with a significant decrease in hyaluronan content both in humans and in mice. No significant differences were detected according to gender. The accumulation of collagen I and the lower levels of hyaluronan and elastic fibers with aging could cause a stiffening of the muscles and a reduction of their adaptability.