Muscle Weakness in Rheumatoid Arthritis: The Role of Ca2+ and Free Radical Signaling

Immunomodulatory roles of metalloproteinases in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic, autoimmune pathology characterized by persistent synovial inflammation and gradually advancing bone destruction. Matrix metalloproteinases (MMPs), as a family of zinc-containing enzymes, have been found to play an important role in degradation and remodeling of extracellular matrix (ECM). MMPs participate in processes of cell proliferation, migration, inflammation, and cell metabolism. A growing number of persons have paid attention to their function in inflammatory and immune diseases. In this review, the details of regulation of MMPs expression and its expression in RA are summarized. The role of MMPs in ECM remodeling, angiogenesis, oxidative and nitrosative stress, cell migration and invasion, cytokine and chemokine production, PANoptosis and bone destruction in RA disease are discussed. Additionally, the review summarizes clinical trials targeting MMPs in inflammatory disease and discusses the potential of MMP inhibition in the therapeutic context of RA. MMPs may serve as biomarkers for drug response, pathology stratification, and precision medicine to improve clinical management of rheumatoid arthritis.

Funcionality assessed by the core set of the international classification of functionality and health for rheumatoid arthritis: A cohort study

OBJECTIVE

The aim of this study was to evaluate the function of a cohort of patients with rheumatoid arthritis (RA) from the core set of the International Classification of Functioning and Health (ICF) for RA over 12 months.

METHODS

We used prospective longitudinal data to conduct a cohort study among a well-characterized group of RA patients. Ninety RA patients aged between 40 and 70 years were included in the study. Patients were evaluated at baseline and after 12 months. Age, disease duration, current smoking, erosions, disease activity, functional test, disability and physical activity were evaluated. Then, the ICF core set classification for RA was applied.

RESULTS

81 patients completed the assessments, the majority of patients were female (88.9%) and the mean age was 56.5 ± 7.3 years. At baseline, the median disease activity was 3.0. There was a statistically significant (p < 0.02) improvement in "Exercise tolerance functions" over 12 months and also a statistically significant (p < 0.001) decrease in "Muscle strength functions" over 12 months. The activity and participation domain showed a weak correlation with the clinical data of the DAS28-PCR (p<0.02).

CONCLUSION

We conclude that relevant aspects of the ICF Core Set for RA were able to adequately express the physical and functional factors of the RA cohort. This tool provides a common language for the interdisciplinary team, which can enhance the use of timely interventions to prevent physical disability in clinical practice.

Identification of Plasma Biomarkers from Rheumatoid Arthritis Patients Using an Optimized Sequential Window Acquisition of All THeoretical Mass Spectra (SWATH) Proteomics Workflow

Rheumatoid arthritis (RA) is a systemic autoimmune and inflammatory disease. Plasma biomarkers are critical for understanding disease mechanisms, treatment effects, and diagnosis. Mass spectrometry-based proteomics is a powerful tool for unbiased biomarker discovery. However, plasma proteomics is significantly hampered by signal interference from high-abundance proteins, low overall protein coverage, and high levels of missing data from data-dependent acquisition (DDA). To achieve quantitative proteomics analysis for plasma samples with a balance of throughput, performance, and cost, we developed a workflow incorporating plate-based high abundance protein depletion and sample preparation, comprehensive peptide spectral library building, and data-independent acquisition (DIA) SWATH mass spectrometry-based methodology. In this study, we analyzed plasma samples from both RA patients and healthy donors. The results showed that the new workflow performance exceeded that of the current state-of-the-art depletion-based plasma proteomic platforms in terms of both data quality and proteome coverage. Proteins from biological processes related to the activation of systemic inflammation, suppression of platelet function, and loss of muscle mass were enriched and differentially expressed in RA. Some plasma proteins, particularly acute-phase reactant proteins, showed great power to distinguish between RA patients and healthy donors. Moreover, protein isoforms in the plasma were also analyzed, providing even deeper proteome coverage. This workflow can serve as a basis for further application in discovering plasma biomarkers of other diseases.

Changes in passive stiffness and length of the semitendinosus muscles in rats with arthritis-induced knee flexion contracture

BACKGROUND

Arthritis-induced joint contracture is caused by arthrogenic and myogenic factors. The arthrogenic factor, localized within the joint, is naturally accepted as the cause of contracture. However, the detailed mechanisms underlying arthritis-induced myogenic contracture are largely unknown. We aimed to elucidate the mechanisms of arthritis-induced myogenic contracture by examining the muscle mechanical properties.

METHODS

Knee arthritis was induced in rats by injecting complete Freund's adjuvant into the right knees, while the untreated contralateral knees were used as controls. After one or four weeks of injection, passive stiffness, length, and collagen content of the semitendinosus muscles were assessed, along with passive knee extension range of motion.

FINDINGS

After one week of injection, flexion contracture formation was confirmed by a decreased range of motion. Range of motion restriction was partially relieved by myotomy, but still remained even after myotomy, indicating the contribution of both myogenic and arthrogenic factors to contracture formation. After one week of injection, the stiffness of the semitendinosus muscle was significantly higher in the injected side than in the contralateral side. After four weeks of injection, the stiffness of the semitendinosus muscle in the injected side returned to levels comparable to the contralateral side, parallel to partial improvement of flexion contracture. Muscle length and collagen content did not change due to arthritis at both time points.

INTERPRETATION

Our results suggest that increased muscle stiffness, rather than muscle shortening, contributes to myogenic contracture detected during the early stage of arthritis. The increased muscle stiffness cannot be explained by excess collagen.

Novel aspects of muscle involvement in immune-mediated inflammatory arthropathies and connective tissue diseases

Myalgia, myopathy and myositis are the most important types of muscle impairment in immune-mediated inflammatory arthropathies and connective tissue diseases. Multiple pathogenetic and histological changes occur in the striated muscles of these patients. Clinically, the most important muscle involvement is the one that causes complaints to the patients. In everyday practice, insidious symptoms present a serious problem for the clinician; in many cases, it is difficult to decide when and how to treat the muscle symptoms that are often present only subclinically. In this work, authors review the international literature on the types of muscle problems in autoimmune diseases. In scleroderma histopathological picture of muscle shows a very heterogeneous picture, necrosis and atrophy are common. In rheumatoid arthritis and systemic lupus erythematosus, myopathy is a much less defined concept, further studies are needed to describe it. According to our view, overlap myositis should be recognized as a separate entity, preferably with distinct histological and serological characteristics. More studies are needed to describe muscle impairment in autoimmune diseases which may help to explore this topic more in depth and be of clinical use.

Conservative Management of Low Back Pain and Scoliosis in a Patient With Rheumatoid Arthritis: Eight Years Follow-Up

Scoliosis in patients with rheumatoid arthritis (RA) can cause significant pain and disability. RA has been extensively studied in relation to the cervical spine, yet the pathology of the thoracic and lumbar spine in RA patients has been largely overlooked. A 66-year-old woman, with longstanding RA and severe scoliosis, presented to the chiropractic clinic with a five-month history of exacerbated low back pain radiating to the right lower limb. The patient was treated with a combination of full-spine mechanical spinal distraction, spinal manipulative therapy, mechanical distraction of the cervical spine, and soft tissue treatment (scraping therapy). Thereafter, the patient recovered from the pain and radiculopathy and showed improvements in the radiological parameters, walking gait, and postural balance. Radiography was performed at the 12-month, four-year, and eight-year follow-up appointments and revealed improvements in symptoms, posture, and scoliosis. Although the treatment for RA-related scoliosis is similar to that for other types of scoliosis, due to the nature of RA, treatment should be tailored to individual patients. This case report highlights the importance of considering chiropractic therapy for the management of lumbar scoliosis in patients with RA, as a comprehensive treatment plan resulted in improved spinal balance, mobility, gait, posture, and quality of life.

An Apriori Algorithm-Based Association Analysis of Analgesic Drugs in Chinese Medicine Prescriptions Recorded From Patients With Rheumatoid Arthritis Pain

Chronic pain, a common symptom of people with rheumatoid arthritis, usually behaves as persistent polyarthralgia pain and causes serious damage to patients' physical and mental health. Opioid analgesics can lead to a series of side effects like drug tolerance and addiction. Thus, seeking an alternative therapy and screening out the corresponding analgesic drugs is the key to solving the current dilemma. Traditional Chinese Medicine (TCM) therapy has been recognized internationally for its unique guiding theory and definite curative effect. In this study, we used the Apriori Algorithm to screen out potential analgesics from 311 cases that were treated with compounded medication prescription and collected from “Second Affiliated Hospital of Zhejiang Chinese Medical University” in Hangzhou, China. Data on 18 kinds of clinical symptoms and 16 kinds of Chinese herbs were extracted based on this data mining. We also found 17 association rules and screened out four potential analgesic drugs—“Jinyinhua,” “Wugong,” “Yiyiren,” and “Qingfengteng,” which were promised to help in the clinical treatment. Besides, combined with System Cluster Analysis, we provided several different herbal combinations for clinical references.

Maximal strength training in patients with inflammatory rheumatic disease: implications for physical function and quality of life

PURPOSE

Patients with inflammatory rheumatic disease (IRD) have attenuated muscle strength in the lower extremities, resulting in impaired physical function and quality of life. Although maximal strength training (MST), applying heavy resistance, is documented to be a potent countermeasure for such attenuation, it is uncertain if it is feasible in IRD given the pain, stiffness, and joint swelling that characterize the population.

METHODS

23 patients with IRD (49 ± 13 years; 20 females/3 males), diagnosed with spondyloarthritis, rheumatoid arthritis, or systemic lupus erythematosus, were randomized to MST or a control group (CG). The MST group performed four × four repetitions dynamic leg press two times per week for 10 weeks at ~ 90% of one repetition maximum (1RM). Before and after training 1RM, rate of force development (RFD), and health-related quality of life (HRQoL) were measured.

RESULTS

Session attendance in the MST group was 95%, of which 95% conducted according to MST protocol. Furthermore, MST increased 1RM (29 ± 12%, p = 0.001) and early and late phase RFD (33-76%, p < 0.05). All improvements were different from the CG (p < 0.05). MST also resulted in HRQoL improvements in the dimensions; physical functioning, general health, and vitality (p < 0.05). Physical functioning was associated with 1RM (rho = 0.55, p < 0.01) and early phase RFD (rho = 0.53-0.71, p < 0.01; different from CG p < 0.05).

CONCLUSIONS

Despite being characterized by pain, stiffness, and joint swelling, patients with IRD appear to tolerate MST well. Given the improvements in 1RM, RFD, and HRQoL MST should be considered as a treatment strategy to counteract attenuated muscle strength, physical function, and HRQoL.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT04998955, retrospectively registered.

Interaction effect of systemic inflammation and modifiable rheumatoid cachexia risk factors on resting energy expenditure in patients with rheumatoid arthritis

Background

In rheumatoid cachexia (RC), high resting energy expenditure (REE) is associated with loss of muscle mass driven by proinflammatory cytokines. The objectives of this study were to investigate parameters associated with RC, and the interaction between systemic inflammation and modifiable risk factors for RC on REE.

Methods

Thirty-five rheumatoid arthritis (RA) and nineteen non-RA controls comparable in age, sex, race and BMI underwent measures of REE by indirect calorimetry. Clinical, dietary, body composition and physical function data were collected. Homeostasis model assessment for insulin resistance (HOMA-IR) and serum interleukin-6 (IL-6) were used as parameters of IR and systemic inflammation, respectively. Regression models tested association between REE and dependent variables, including pre-specified interaction tests involving HOMA-IR and IL-6 and dietary intake of protein per weight (PPW) and IL-6.

Results

RA subjects were mostly women (94%) and had a median age of 54 years (50.5, 70) and BMI of 30.5 kg/m2 (26.1, 36.9). We observed a significant interaction effect between PPW and serum IL-6 on REE among RA subjects in the multiple regression model among RA. The upper tertile of PPW demonstrated a significant negative correlation between REE and IL-6 (β=-19.97, 95% CI [-35.41, -4.54], p=0.01). The lower tertile of PPW demonstrated a significant positive correlation between REE and IL-6 (β=42.24, 95% CI [4.25, 80.23], p=0.03).

Conclusions

While IR can lead to muscle catabolism, IR was not significantly associated with REE in RA individuals. Higher dietary protein intake could attenuate the effect of systemic inflammation on REE in RA patients.

Muscle function following testosterone replacement in men on opioid therapy for chronic non-cancer pain: A randomized controlled trial

BACKGROUND

Chronic pain and opioid treatment are associated with increased risk of male hypogonadism and subsequently decreased muscle function. A diagnosis of hypogonadism is based on the presence of low total testosterone and associated symptoms. The effect of testosterone replacement therapy on muscle function in men with chronic pain and low total testosterone remains to be investigated.

OBJECTIVES

To investigate the effects of testosterone replacement therapy on muscle function and gait performance in men treated with opioids for chronic non-cancer pain.

MATERIALS AND METHODS

A double-blind, placebo-controlled study. Forty-one men (>18 years) with opioid-treated chronic pain and serum total testosterone < 12 nmol/L were randomized to 24 weeks testosterone replacement therapy (testosterone undecanoate injection three times/6 months, n  = 20) or placebo injections (n  = 21). Muscle function was measured as leg press maximal voluntary contraction, leg extension power using the Nottingham power rig and handgrip strength using a handheld dynameter. Gait performance was measured at usual and maximal gait speed on a 10-m track. Body composition (lean body mass and fat mass) was determined by dual-energy X-ray absorptiometry. Mann-Whitney tests were performed on ∆-values (24-0 weeks) between testosterone replacement therapy and placebo.

RESULTS

At baseline, median (interquartile range) age was 55 ± 13 years and BMI was 30.7 ± 5.2 kg/m² . ∆-muscle function and ∆-gait performance were similar between testosterone replacement therapy and placebo. Median ∆-leg press maximal voluntary contraction was 174.2 ± 406.7 Newton, following testosterone replacement therapy, and 7.6 ± 419.1 Newton, after placebo, p = 0.091. ∆-lean body mass was significantly higher following testosterone replacement therapy compared to placebo, 3.6 ± 2.7 versus 0.1 ± 3.5 kg, respectively (p < 0.001).

DISCUSSION

Testosterone replacement therapy, compared to placebo, did not improve muscle function or gait performance despite increased lean body mass. Changes in body composition did not infer any changes in muscle function.

CONCLUSION

24 weeks testosterone replacement therapy in opioid-treated men with pain-related male hypogonadism did not improve muscle function.

Skeletal muscle redox signaling in rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory disease characterized by synovitis and the presence of serum autoantibodies. In addition, skeletal muscle weakness is a common comorbidity that contributes to inability to work and reduced quality of life. Loss in muscle mass cannot alone account for the muscle weakness induced by RA, but instead intramuscular dysfunction appears as a critical factor underlying the decreased force generating capacity for patients afflicted by arthritis. Oxidative stress and associated oxidative post-translational modifications have been shown to contribute to RA-induced muscle weakness in animal models of arthritis and patients with RA. However, it is still unclear how and which sources of reactive oxygen and nitrogen species (ROS/RNS) that are involved in the oxidative stress that drives the progression toward decreased muscle function in RA. Nevertheless, mitochondria, NADPH oxidases (NOX), nitric oxide synthases (NOS) and phospholipases (PLA) have all been associated with increased ROS/RNS production in RA-induced muscle weakness. In this review, we aim to cover potential ROS sources and underlying mechanisms of oxidative stress and loss of force production in RA. We also addressed the use of antioxidants and exercise as potential tools to counteract oxidative stress and skeletal muscle weakness.

Conversion of Fused Hip to Total Hip Arthroplasty: Long-Term Clinical and Radiological Outcomes

BACKGROUND

Despite promising results at the mid-term followup, several aspects of conversion of the fused hip to total hip arthroplasty (THA) remain controversial. The aim of this study was to evaluate clinical and radiological outcomes with a minimum 5-year followup in patients who underwent conversion of the fused hip to THA.

METHODS

Fifty-seven patients (59 hips) were evaluated. The Harris Hip Score (HHS), range of motion (ROM), and the Visual Analogue Scale (VAS) were used to assess hip function and low back pain. Subjective satisfaction with surgery and the presence of the Trendelenburg sign was also evaluated. Radiological assessment was performed pre- and postoperatively to evaluate loosening and heterotopic ossification (HO).

RESULTS

After a mean followup of 13.0 ± 6.2 years, HHS and VAS significantly improved from 46.0 ± 16.7 to 80.8 ± 18.8 and from 4.4 ± 1.5 to 2.1 ± 1.4 (both P < .001), respectively. Twenty-three patients (40.4%) had a positive Trendelenburg sign, and HOs were found in 29 cases (49.1%). An overall 29.8% complication rate was noted. Smoking habits and rheumatoid arthritis were predictive of Trendelenburg sign (P = .046 and P = .038, respectively). Implant survival rate as the end point was 98.7 ± 1.3% at 5 years, 92.4 ± 3.3% at 10 years, 82.1 ± 5.7% at 15 years, and 73.4 ± 8.0% at 20 and 25 years. A worse cumulative implant survival rate was noted in patients who underwent previous hip surgery, defined as any hip operation before fusion (P = .005).

CONCLUSION

Conversion of the fused hip to hip arthroplasty provides high levels of hip functionality and satisfaction with surgery at long-term followup. An implant survival rate higher than 70% can be expected 25 years postoperatively.

Identification of differentially expressed genes, signaling pathways and immune infiltration in rheumatoid arthritis by integrated bioinformatics analysis

Background

The disability rate associated with rheumatoid arthritis (RA) ranks high among inflammatory joint diseases. However, the cause and potential molecular events are as yet not clear. Here, we aimed to identify differentially expressed genes (DEGs), pathways and immune infiltration involved in RA utilizing integrated bioinformatics analysis and investigating potential molecular mechanisms.

Materials and methods

The expression profiles of GSE55235, GSE55457, GSE55584 and GSE77298 were downloaded from the Gene Expression Omnibus database, which contained 76 synovial membrane samples, including 49 RA samples and 27 normal controls. The microarray datasets were consolidated and DEGs were acquired and further analyzed by bioinformatics techniques. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of DEGs were performed using R (version 3.6.1) software, respectively. The protein-protein interaction (PPI) network of DEGs were developed utilizing the STRING database. Finally, the CIBERSORT was used to evaluate the infiltration of immune cells in RA.

Results

A total of 828 DEGs were recognized, with 758 up-regulated and 70 down-regulated. GO and KEGG pathway analyses demonstrated that these DEGs focused primarily on cytokine receptor activity and relevant signaling pathways. The 30 most firmly related genes among DEGs were identified from the PPI network. The principal component analysis showed that there was a significant difference between the two tissues in infiltration immune.

Conclusion

This study shows that screening for DEGs, pathways and immune infiltration utilizing integrated bioinformatics analyses could aid in the comprehension of the molecular mechanisms involved in RA development. Besides, our study provides valuable data related to DEGs, pathways and immune infiltration of RA and may provide new insight into the understanding of molecular mechanisms.

Fast skeletal muscle troponin activator CK-2066260 mitigates skeletal muscle weakness independently of the underlying cause

BACKGROUND

Muscle weakness is a common symptom in numerous diseases and a regularly occurring problem associated with ageing. Prolonged low-frequency force depression (PLFFD) is a form of exercise-induced skeletal muscle weakness observed after exercise. Three different intramuscular mechanisms underlying PLFFD have been identified: decreased sarcoplasmic reticulum Ca²⁺ release, decreased myofibrillar Ca²⁺ sensitivity, and myofibrillar dysfunction. We here used these three forms of PLFFD as models to study the effectiveness of a fast skeletal muscle troponin activator, CK-2066260, to mitigate muscle weakness.

METHODS

Experiments were performed on intact single muscle fibres or fibre bundles from mouse flexor digitorum brevis, which were stimulated with electrical current pulses, while force and the free cytosolic [Ca²⁺ ] ([Ca²⁺ ]_i ) were measured. PLFFD was induced by three different stimulation protocols: (i) repeated isometric contractions at low intensity (350 ms tetani given every 5 s for 100 contractions); (ii) repeated isometric contractions at high intensity (250 ms tetani given every 0.5 s for 300 contractions); and (iii) repeated eccentric contractions (350 ms tetani with 20% length increase given every 20 s for 10 contractions). The extent and cause of PLFFD were assessed by comparing the force-[Ca²⁺ ]_i relationship at low (30 Hz) and high (120 Hz) stimulation frequencies before (control) and 30 min after induction of PLFFD, and after an additional 5 min of rest in the presence of CK-2066260 (10 μM).

RESULTS

Prolonged low-frequency force depression following low-intensity and high-intensity fatiguing contractions was predominantly due to decreased sarcoplasmic reticulum Ca²⁺ release and decreased myofibrillar Ca²⁺ sensitivity, respectively. CK-2066260 exposure resulted in marked increases in 30 Hz force from 52 ± 16% to 151 ± 13% and from 6 ± 4% to 98 ± 40% of controls with low-intensity and high-intensity contractions, respectively. Following repeated eccentric contractions, PLFFD was mainly due to myofibrillar dysfunction, and it was not fully reversed by CK-2066260 with 30 Hz force increasing from 48 ± 8% to 76 ± 6% of the control.

CONCLUSIONS

The fast skeletal muscle troponin activator CK-2066260 effectively mitigates muscle weakness, especially when it is caused by impaired activation of the myofibrillar contractile machinery due to either decreased sarcoplasmic reticulum Ca²⁺ release or reduced myofibrillar Ca²⁺ sensitivity.

The Role of Nonmedical Therapeutic Approaches in the Rehabilitation of Complex Regional Pain Syndrome

Purpose of the Review

Nonmedical therapeutic approaches are fundamental to the management of of Complex Regional Pain Syndrome (CRPS) in order to promote the best outcome for patients. This review focuses on three key approaches underpinning CRPS rehabilitation, namely, physiotherapy and occupational therapy, psychological approaches and education and self-management.

Recent Findings

Recently published European standards outline the quality of therapeutic care that people with CRPS must receive. Early initiated therapy is essential to optimise outcomes, underpinned by patient education. Therapists should promote early movement of the affected limb and encourage re-engagement with usual activities as immobilisation is known to have negative outcomes. There is evidence to support the possible long-term benefit of graded motor imagery and mirror therapy. Psychological assessment should include identification of depression and post-traumatic stress disorder, as treatment of these conditions may improve the trajectory of CRPS. Novel therapies include neurocognitive approaches and those addressing spatial bias, both of which should provide a focus for future research.

Summary

There exists a broad range of nonmedical therapeutic approaches to rehabilitation for CPRS that are thought to be important. However, the evidence for their efficacy is limited. Further research using standardised outcomes would be helpful in developing targeted therapies for the future.

Finding possible pharmacological effects of identified organic compounds in medicinal waters (BTEX and phenolic compounds)

Medicinal thermal waters consist of a mixture of different organic and inorganic compounds. Traditionally, these waters are only characterized and classified by their inorganic composition; however, the bioavailability of the majority of these inorganic compounds is limited. Many authors investigate the organic fractions of thermal waters. These authors propose that these compounds have a potential effect on health. To elucidate the underlying mechanisms, it is crucial to know the composition of the organic fractions. The absorption of these compounds on intact skin or mucosa is notable. Some of them have local anaesthetic effect or affect receptors in the central nervous system. In the knowledge of the chemical composition, we are able to estimate the possible pharmacological effect or might be able to assess possible toxicity risks. In the present article, we aim to review possible health effects of two of the identified organic fractions: benzene and alkylbenzenes and phenolic compounds that might correlate with the therapeutic effect on rheumatological or other diseases.

Intramuscular mechanisms of overtraining

Strenuous exercise is a potent stimulus to induce beneficial skeletal muscle adaptations, ranging from increased endurance due to mitochondrial biogenesis and angiogenesis, to increased strength from hypertrophy. While exercise is necessary to trigger and stimulate muscle adaptations, the post-exercise recovery period is equally critical in providing sufficient time for metabolic and structural adaptations to occur within skeletal muscle. These cyclical periods between exhausting exercise and recovery form the basis of any effective exercise training prescription to improve muscle endurance and strength. However, imbalance between the fatigue induced from intense training/competitions, and inadequate post-exercise/competition recovery periods can lead to a decline in physical performance. In fact, prolonged periods of this imbalance may eventually lead to extended periods of performance impairment, referred to as the state of overreaching that may progress into overtraining syndrome (OTS). OTS may have devastating implications on an athlete's career and the purpose of this review is to discuss potential underlying mechanisms that may contribute to exercise-induced OTS in skeletal muscle. First, we discuss the conditions that lead to OTS, and their potential contributions to impaired skeletal muscle function. Then we assess the evidence to support or refute the major proposed mechanisms underlying skeletal muscle weakness in OTS: 1) glycogen depletion hypothesis, 2) muscle damage hypothesis, 3) inflammation hypothesis, and 4) the oxidative stress hypothesis. Current data implicates reactive oxygen and nitrogen species (ROS) and inflammatory pathways as the most likely mechanisms contributing to OTS in skeletal muscle. Finally, we allude to potential interventions that can mitigate OTS in skeletal muscle.

Interleukin-6 affects pacsin3, ephrinA4 expression and cytoskeletal proteins in differentiating primary skeletal myoblasts through transcriptional and post-transcriptional mechanisms

Interleukin (IL)-6 is a proinflammatory cytokine released in injured and contracting skeletal muscles. In this study, we examined cellular expression of proteins associated with cytoskeleton organization and cell migration, chosen on the basis of microRNA profiling, in rat primary skeletal muscle cells (RSkMC) treated with IL-6 (1 ng/ml) for 11 days. MiRNA microarray analysis and qRT-PCR revealed increased expression of miR-154-3p and miR-338-3p in muscle cells treated with IL-6. Pacsin3 was downregulated post-transcriptionally by IL-6, but not by IGF-I. Ephrin4A protein was increased both in IL-6- and IGF-I-treated myocytes. IL-6, but not IGF-I, stimulated migratory ability of RSkMC, examined in wound healing assay. Alpha-actinin protein was slightly augmented in RSKMC treated with IL-6, similarly to IGF-I. IL-6, but not IGF-I, upregulated desmin in differentiating RSkMC. IL-6 supplementation caused accumulation of alpha-actinin and desmin in near-nuclear area of muscle cells, which was manifested by increased ratio: mean near-nuclear fluorescence/mean peripheral cytoplasm fluorescence of these proteins. We concluded that IL-6, a known proinflammatory cytokine and a physical activity-associated myokine, acting during differentiation of primary skeletal muscle cells, alters expression of nonmuscle-specific miRNAs. This cytokine causes differential effects on pacsin-3 and ephrinA4, through post-transcriptional inhibition and stimulation, respectively. IL-6-exerted modifications of cytoskeletal proteins in muscle cells include both transcriptional (desmin and dynein heavy chain 5) and post-transcriptional activation (alpha-actinin). Moreover, IL-6 augments near-nuclear distribution of cytoskeletal proteins, alpha-actinin and desmin and promotes migration of myocytes. Such effects suggest that IL-6 plays a role during skeletal muscle regeneration, acting through mechanisms independent of regulation of myogenic program.

Force generated by myosin cross-bridges is reduced in myofibrils exposed to ROS/RNS

Skeletal muscle weakness is associated with oxidative stress and oxidative posttranslational modifications on contractile proteins. There is indirect evidence that reactive oxygen/nitrogen species (ROS/RNS) affect skeletal muscle myofibrillar function, although the details of the acute effects of ROS/RNS on myosin-actin interactions are not known. In this study, we examined the effects of peroxynitrite (ONOO−) on the contractile properties of individual skeletal muscle myofibrils by monitoring myofibril-induced displacements of an atomic force cantilever upon activation and relaxation. The isometric force decreased by ~50% in myofibrils treated with the ONOO− donor (SIN-1) or directly with ONOO−, which was independent of the cross-bridge abundancy condition (i.e., rigor or relaxing condition) during SIN-1 or ONOO− treatment. The force decrease was attributed to an increase in the cross-bridge detachment rate ( gapp) in combination with a conservation of the force redevelopment rate (kTr) and hence, an increase in the population of cross-bridges transitioning from force-generating to non-force-generating cross-bridges during steady-state. Taken together, the results of this study provide important information on how ROS/RNS affect myofibrillar force production which may be of importance for conditions where increased oxidative stress is part of the pathophysiology.

miR‑760 regulates skeletal muscle proliferation in rheumatoid arthritis by targeting Myo18b

MicroRNAs serve an important role in the development of several diseases. Numerous genes regulate the skeletal muscle differentiation of C2C12 myoblasts. The role of miR-760 in rheumatoid arthritis (RA) has not been reported, to the best of our knowledge. Therefore, the aim of the present study was to examine the role of miR-760 in regulating skeletal muscle proliferation in RA. Potential genes functionally involved in the tarsal joint of a collagen-induced RA model were identified using Gene Expression Omnibus. Reverse transcription-quantitative PCR and western blot analyses were performed to determine the mRNA and protein expression levels. The proliferation, cell cycle progression and migration of C2C12 myoblasts were detected using Cell Counting Kit-8, flow cytometry and wound-healing assays, respectively. TargetScan was used to predict the potential target genes of miR-760, and this was verified using a dual-luciferase reporter assay. In the present study, myosin-18b (Myo18b) expression was determined to be downregulated in the RA model. Silencing Myo18b decreased the proliferation, abrogated the cell cycle progression, and reduced the migration and differentiation of C2C12 myoblasts. Expression levels of cyclin-dependent kinase 2, cyclin D1, matrix metalloproteinase (MMP)-2, MMP-9, myogenin and myosin heavy chain 6 were all decreased when Myo18b was silenced. Furthermore, overexpression of Myo18b induced opposing effects on C2C12 myoblasts. It was shown that Myo18b was a target gene of miRNA-760. Overexpression of miR-760 decreased proliferation, cell cycle progression, migration and differentiation in C2C12 myoblasts, and decreased the expression of Myo18b. The opposite results were observed when miR-760 was downregulated. In conclusion, miR-760 inhibited proliferation and differentiation by targeting Myo18b in C2C12 myoblasts. The results of the present study may contribute to understanding the mechanisms underlying RA skeletal muscle proliferation, and miR-760/Myo18b may serve as potential targets for treating patients with RA.

Systemic effects of IL-17 in inflammatory arthritis

Inflammatory arthritis occurs in many diseases and is characterized by joint inflammation and damage. However, the inflammatory state in arthritis is commonly associated with systemic manifestations, which are generally linked to a poor prognosis. The pro-inflammatory cytokine IL-17 functions within a complex network of cytokines and contributes to the pathogenesis of various inflammatory diseases. Three IL-17 inhibitors have already been approved for the treatment of psoriasis, psoriatic arthritis, and ankylosing spondylitis. After a brief description of IL-17 and its local effects on joints, this Review focuses on the systemic effects of IL-17 in inflammatory arthritis. Increased circulating concentrations of bioactive IL-17 mediate changes in blood vessels, liver and cardiac and skeletal muscles. The effects of IL-17 on vascular and cardiac cells might contribute to the increased risk of cardiovascular events that occurs in all patients with inflammatory disorders. In the liver, IL-17 contributes to the high circulating concentrations of acute-phase proteins, such as C-reactive protein, and the appearance of liver lesions. In skeletal muscle, IL-17 contributes to muscle contractibility defects and weakness. Thus, targeting IL-17 might have beneficial effects at both local and systemic levels, and could also be proposed for the treatment of a wider range of inflammatory diseases.

Oxidative hotspots on actin promote skeletal muscle weakness in rheumatoid arthritis

Skeletal muscle weakness in patients suffering from rheumatoid arthritis (RA) adds to their impaired working abilities and reduced quality of life. However, little molecular insight is available on muscle weakness associated with RA. Oxidative stress has been implicated in the disease pathogenesis of RA. Here we show that oxidative post-translational modifications of the contractile machinery targeted to actin result in impaired actin polymerization and reduced force production. Using mass spectrometry, we identified the actin residues targeted by oxidative 3-nitrotyrosine (3-NT) or malondialdehyde adduct (MDA) modifications in weakened skeletal muscle from mice with arthritis and patients afflicted by RA. The residues were primarily located to three distinct regions positioned at matching surface areas of the skeletal muscle actin molecule from arthritis mice and RA patients. Moreover, molecular dynamic simulations revealed that these areas, here coined "hotspots", are important for the stability of the actin molecule and its capacity to generate filaments and interact with myosin. Together, these data demonstrate how oxidative modifications on actin promote muscle weakness in RA patients and provide novel leads for targeted therapeutic treatment to improve muscle function.

Redox Status and Muscle Pathology in Rheumatoid Arthritis: Insights from Various Rat Hindlimb Muscles

Due to atrophy, muscle weakness is a common occurrence in rheumatoid arthritis (RA). The majority of human studies are conducted on the vastus lateralis muscle—a muscle with mixed fiber type—but little comparative data between multiple muscles in either rodent or human models are available. The current study therefore assessed both muscle ultrastructure and selected redox indicators across various muscles in a model of collagen-induced rheumatoid arthritis in female Sprague-Dawley rats. Only three muscles, the gastrocnemius, extensor digitorum longus (EDL), and soleus, had lower muscle mass (38%, 27%, and 25% loss of muscle mass, respectively; all at least P < 0.01), while the vastus lateralis muscle mass was increased by 35% (P < 0.01) in RA animals when compared to non-RA controls. However, all four muscles exhibited signs of deterioration indicative of rheumatoid cachexia. Cross-sectional area was similarly reduced in gastrocnemius, EDL, and soleus (60%, 58%, and 64%, respectively; all P < 0.001), but vastus lateralis (22% smaller, P < 0.05) was less affected, while collagen deposition was significantly increased in muscles. This pathology was associated with significant increases in tissue levels of reactive oxygen species (ROS) in all muscles except the vastus lateralis, while only the gastrocnemius had significantly increased levels of lipid peroxidation (TBARS) and antioxidant activity (FRAP). Current data illustrates the differential responses of different skeletal muscles of the hindlimb to a chronic inflammatory challenge both in terms of redox changes and resistance to cachexia.

Relation of Moderate Physical Activity to Blood Markers of Oxidative Stress and Antioxidant Defense in the Elderly

The aim of the present study was to establish whether markers of oxidative stress and the enzymatic defense system of the blood are related to moderate physical activity in younger old and the oldest old men. They were divided into four groups according to the age and level of physical activity (groups YN and YA—inactive and active younger old men aged 65-74 years, groups ON and OA—inactive and active oldest old men aged 90-99 years). Venous blood was collected from the subjects in the morning before breakfast. MDA concentration and antioxidant enzyme activities (SOD, CAT, GPx, and GR) in erythrocyte hemolysates were assayed. The concentration of isoprostanes (8-iso-PGF2α) and carbonyl groups in protein (CP) was measured in plasma and serum. All assayed antioxidant enzyme activities and the SOD/GPx ratios were significantly higher in the active younger old males than in all the inactive ones. In the group of oldest old active participants, only the GPx activity was significantly higher compared to the inactive oldest old males. The activity of CAT and GPx in the younger old inactive men was significantly lower than that in the oldest old inactive subjects. However, SOD, CAT, and GR activities and SOD/GPx ratio were significantly higher in the younger old active men compared to the oldest old active participants. The concentrations of isoprostanes, protein carbonyls, and MDA were significantly lower in both active and inactive younger old males than in the respective groups of the oldest old men and in both groups of active men, independently of age, compared to the respective inactive subjects. The present study confirmed that oxidative stress is related to age. Physical activity caused a decrease of oxidative stress markers independently of age and resulted in an increase of GPx activity in both younger old and the oldest old active groups.

Comparison of Chlorantraniliprole and Flubendiamide Activity Toward Wild-Type and Malignant Hyperthermia-Susceptible Ryanodine Receptors and Heat Stress Intolerance

Chlorantraniliprole (CP) and flubendiamide (FD) are widely used in agriculture globally to control lepidopteran pests. Both insecticides target ryanodine receptors (RyRs) and promote Ca2+ leak from sarcoplasmic reticulum (SR) within insect skeletal muscle yet are purportedly devoid of activity toward mammalian RyR1 and muscle. RyRs are ion channels that regulate intracellular Ca2+ release from SR during physiological excitation-contraction coupling. Mutations in RYR1 genes confer malignant hyperthermia susceptibility (MHS), a potentially lethal pharmacogenetic disorder in humans and animals. Compared with vehicle control, CP (10 µM) triggers a 65-fold higher rate of Ca2+ efflux from Ca2+-loaded mammalian WT-RyR1 SR vesicles, whereas FD (10 µM) produces negligible influence on Ca2+ leak. We, therefore, compared whether CP or FD differentially influence patterns of high-affinity [3H]ryanodine ([3H]Ry) binding to RyR1 isolated from muscle SR membranes prepared from adult C57BL/6J mice expressing WT, homozygous C-terminal MHS mutation T4826I, or heterozygous N-terminal MHS mutation R163C. Basal [3H]Ry binding differed among genotypes with rank order T4826I ≫R163C∼WT, regardless of [Ca2+] in the assay medium. Both CP and FD (0.01-100 µM) elicited concentration-dependent increase in [3H]Ry binding, although CP showed greater efficacy regardless of genotype or [Ca2+]. Exposure to CP (500 mg/kg; p.o) failed to shift intolerance to heat stress (38°C) characteristic of R163C and T4826I MHS mice, nor cause lethality in WT mice. Although nM-µM of either diamide is capable of differentially altering WT and MHS RyR1 conformation in vitro, human RyR1 mutations within putative diamide N- and C-terminal interaction domains do not alter heat stress intolerance (HSI) in vivo.