Rheumatoid arthritis (RA) is associated with loss of muscle quality and strength, but accessible quantitative tools for detecting these changes remain limited. We evaluated whether shear wave viscoelastic imaging (SWVI), acoustic attenuation imaging (AAI), and isokinetic strength testing could characterize rectus femoris muscle involvement in RA, and used public synovial transcriptomic data to provide hypothesis-generating biological context. Twenty-nine patients with RA (early RA, n = 7; active RA, n = 11; treated low/moderate-activity RA, n = 11) and 27 healthy controls underwent rectus femoris ultrasound and knee isokinetic strength testing. The main ultrasound variables were rectus femoris thickness and cross-sectional area, mean Young’s modulus (Emean), viscosity (Vimean), speed of sound (SoS), and AAI. Group differences, Spearman correlations, receiver-operating-characteristic (ROC) curves, and exploratory logistic models were analyzed. Because the RA cohort was small and diabetes was more common in RA than in controls, ROC, nomogram, and multivariable results were interpreted as exploratory rather than confirmatory. Public GSE55235 synovial transcriptome data were reanalyzed to identify inflammatory and extracellular-matrix pathways that may plausibly link synovitis with systemic muscle impairment. Rectus femoris thickness and cross-sectional area showed limited between-group separation, whereas Emean, Vimean, SoS, AAI, and isokinetic strength differed across groups (all p < 0.001). AAI increased from controls to early, active, and treated low/moderate-activity RA groups and correlated with disease duration in the full cohort (Spearman rho = 0.864); this association remained strong in RA-only adjusted sensitivity analyses. SoS decreased across the same gradient (rho = − 0.875 with duration in the full cohort), whereas Vimean was highest in active RA and correlated with DAS28 in the full cohort (rho = 0.643). Extensor peak torque was lower in RA and correlated inversely with DAS28 in the full cohort (rho = − 0.844); the corresponding RA-only association was more moderate but remained significant (rho = − 0.642). In exploratory ROC analyses, AAI, SoS, and extensor peak torque showed high apparent discrimination between RA and controls; however, the small overall and subgroup samples, baseline differences in diabetes and height, and absence of external validation make these estimates potentially unstable and preclude conclusions about clinical applicability. Synovial transcriptomic analysis showed enrichment of TNF, NF-κB, JAK-STAT, cytokine-receptor, and extracellular-matrix remodeling pathways in RA synovium, supporting a plausible inflammatory background rather than direct evidence of muscle pathology. In this exploratory clinical-transcriptomic study, SWVI/AAI and isokinetic strength testing detected rectus femoris muscle-quality and functional differences associated with RA. AAI and SoS may be candidate ultrasound parameters for RA-associated muscle involvement, but their disease specificity, independence from diabetes, and tissue-level interpretation require confirmation in larger, externally validated studies with reference-standard muscle-composition assessment and reliability testing. • This study integrates meta-analysis, Mendelian randomization, and single-cell RNA sequencing to comprehensively evaluate treatment efficacy, genetic influences, and immune alterations in late-onset rheumatoid arthritis (LORA). • LORA patients exhibit distinct treatment responses compared with younger-onset RA, including lower clinical remission rates with biologics/tsDMARDs and higher residual disease activity (DAS28). • Genetic variants in the IL-6R and TYK2 pathways are identified as key modifiers of drug response and disease susceptibility in LORA. • The findings underscore the need for age- and genetics-informed personalized treatment strategies in elderly patients with rheumatoid arthritis.

Purpose This study investigated how differential macrophage polarization dynamics drive the severity of post-traumatic joint contracture (PTJC) compared to non-traumatic joint contracture (NTJC). Methods We first performed a bioinformatic analysis intersecting the human dataset GSE135854 with macrophage polarization gene sets to identify core pathogenic targets. Subsequently, rat models of surgically-induced post-traumatic contracture and immobilization-only non-traumatic contracture were established. This study assessed temporal changes in joint range of motion, histopathological fibrosis, macrophage polarization dynamics, and molecular pathways including TLR4/MyD88/NF-κB signaling and fibrotic mediators. Results Bioinformatic profiling identified 1,137 core genes linking macrophage polarization to arthrofibrosis, which were enriched in immune-related biological processes and the NF-kappa B signaling pathway. Clinically, TLR4 and MYD88 were downregulated in end-stage human fibrosis, suggesting a temporal resolution of early inflammatory signals. In rat models, PTJC exhibited significantly more severe contracture and aggressive fibroproliferative remodeling compared to NTJC. Mechanistically, PTJC induced a robust early surge in M1 macrophages via TLR4/MyD88/NF-κB pathway activation, followed by a delayed, pathological M2 response. In contrast, NTJC showed milder macrophage dynamics. The discrepancy between early-stage rat models (upregulation) and end-stage clinical samples (downregulation) underscores the TLR4 axis as an early initiator of the fibrotic cascade. Conclusion Trauma drives severe contracture via a specific, aggressive fibroproliferative cascade involving dysregulated macrophage plasticity and regional tissue crosstalk. Effective management of PTJC requires phase-specific strategies: targeting the early TLR4-mediated M1 surge and modulating the late-stage pathological M2 response, distinct from the prophylactic needs of NTJC.

To investigate the intervention effect of extracorporeal shock wave combined with manual traction on fixation-induced knee contracture and its influence on PTEN-PI3K/AKT signaling pathway. Thirty-six SD male rats were randomly divided into six groups. The left knee joints were not fixed in the control group (C group). Rats in other groups underwent brace fixation in the extended position of the left knee. After 4 weeks of bracing, it is randomly divided into five groups: Model group (M group), natural recovery group (NR group), extracorporeal shock wave treatment group ( ET group), manual traction group (MT group), and extracorporeal shock wave combined with manual traction group (CT group). Joint range of motion (ROM) of left knee was carried out to assess joint function. Hematoxylin and eosin (HE) staining and Masson staining were respectively used to assess the cell number and collagen deposition expression. Immunohistochemical staining and Western blot were used to assess protein levels of phosphatase and tensin homolog ( PTEN), phosphatidylinositol 3-kinase (PI3K), and protein kinase B (AKT). The combined therapy was more effective than extracorporeal shock wave therapy or manual traction alone against the joint ROM, cell number and the collagen deposition, low- expression of PTEN, and overexpression of PI3K/AKT in the anterior joint capsule of rats with knee extension contracture. Extracorporeal shock wave combined with manual traction can promote the histopathological changes of anterior joint capsule fibrosis, upregulate the protein expression of PTEN and downregulate the protein expression of PI3K/AKT in the fibrotic joint capsule in a rat joint contracture model.

Joint contracture is one of the common diseases clinically, and joint capsule fibrosis is considered to be one of the most important pathological changes of joint contracture. However, the underlying mechanism of joint capsule fibrosis is still controversial. The present study aims to establish an animal model of knee extending joint contracture in rats, and to investigate the role of hypoxia-mediated pyroptosis in the progression of joint contracture using this animal model. 36 male SD rats were selected, 6 of which were not immobilized and were used as control group, while 30 rats were divided into I-1 group (immobilized for 1 week following 7 weeks of free movement), I-2 group (immobilized for 2 weeks following 6 weeks of free movement), I-4 group (immobilized for 4 weeks following 4 weeks of free movement), I-6 group (immobilized for 6 weeks following 2 weeks of free movement) and I-8 group (immobilized for 8 weeks) according to different immobilizing time. The progression of joint contracture was assessed by the measurement of knee joint range of motion, collagen deposition in joint capsule was examined with Masson staining, protein expression levels of HIF-1α, NLRP3, Caspase-1, GSDMD-N, TGF-β1, α-SMA and p-Smad3 in joint capsule were assessed using western blotting, and the morphological changes of fibroblasts were observed by transmission electron microscopy. The degree of total and arthrogenic contracture progressed from the first week and lasted until the first eight weeks after immobilization. The degree of total and arthrogenic contracture progressed rapidly in the first four weeks after immobilization and then progressed slowly. Masson staining indicated that collagen deposition in joint capsule gradually increased in the first 8 weeks following immobilization. Western blotting analysis showed that the protein levels of HIF-1α continued to increase during the first 8 weeks of immobilization, and the protein levels of pyroptosis-related proteins NLRP3, Caspase-1, GSDMD-N continued to increase in the first 4 weeks after immobilization and then decreased. The protein levels of fibrosis-related proteins TGF-β1, p-Smad3 and α-SMA continued to increase in the first 8 weeks after immobilization. Transmission electron microscopy showed that 4 weeks of immobilization induced cell membrane rupture and cell contents overflow, which further indicated the activation of pyroptosis. Knee extending joint contracture animal model can be established by external immobilization orthosis in rats, and the activation of hypoxia-mediated pyroptosis may play a stimulating role in the process of joint capsule fibrosis and joint contracture.

Recent studies have shown that immobilization enhances reactive oxygen species (ROS) production and mitophagy activity in atrophic skeletal muscle. However, there are relatively few studies examining the biological changes and underlying mechanisms of skeletal muscle during remobilization. In this study, we aimed to investigate the effects of remobilization on skeletal muscle and explore the role of BNIP3-dependent mitophagy in this process. Thirty rats were randomly divided into six groups based on immobilization and remobilization time: control (C), immobilization for two weeks (I-2w), and remobilization for one day (R-1d), three days (R-3d), seven days (R-7d), and two weeks (R-2w). At the end of the experimental period, the rectus femoris muscles were removed and weighed, and the measurements were expressed as the ratio of muscle wet weight to body weight (MWW/BW). Sirius Red staining was performed to calculate the values of cross-sectional area (CSA) of rectus femoris. Oxidative fluorescent dihydroethidium was used to evaluate the production of ROS, and the levels of superoxide dismutase (SOD) were also detected. The morphological changes of mitochondria and the formation of mitophagosomes in rectus femoris were examined and evaluated by transmission electron microscope. Immunofluorescence was employed to detect the co-localization of BNIP3 and LC3B, while Western blot analysis was performed to quantify the levels of proteins associated with mitophagy and mitochondrial biogenesis. The total ATP content of the rectus femoris was determined to assess mitochondrial function. Within the first three days of remobilization, the rats demonstrated decreased MWW/BW, CSA, and ATP concentration, along with increased ROS production and HIF-1α protein levels in the rectus femoris. Results also indicated that remobilization triggered BNIP3-dependent mitophagy, supported by the accumulation of mitophagosomes, the degradation of mitochondrial proteins (including HSP60 and COX IV), the elevation of BNIP3-dependent mitophagy protein markers (including BNIP3, LC3B-II/LC3B-I, and Beclin-1), and the accumulation of puncta representing co-localization of BNIP3 with LC3B. Additionally, PGC-1α, which is involved in the regulation of mitochondrial biogenesis, was upregulated within the first seven days of remobilization to counteract this adverse effect. Our findings suggested that BNIP3-denpendent mitophagy was sustained activated at the early stages of remobilization, and it might contribute to the worsening of skeletal muscle atrophy.

The study aimed to observe the therapeutic effect of static progressive stretching (SPS) combined with extracorporeal shock wave therapy (ESWT) on extension knee joint contracture in rats and the effect on the mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway in the development of joint capsule fibrosis. Thirty-six Sprague Dawley rats were randomly divided into blank control group, immobilization model group, natural recovery group, ESWT intervention group, SPS intervention group, and SPS combined with ESWT intervention group. The left knee joints of the rats, except for the control group, were fixed with an external fixation brace for four weeks at full extension to form joint contractures. The therapeutic effect of each intervention was assessed by evaluating total and arthrogenic contracture, the number of total cells and collagen deposition in the anterior joint capsule, the protein levels of TGF-β1, FGF-2, and ERK2 in the anterior joint capsule, the mean optical density of upstream RAS and downstream ERK2 positive expression in the MAPK/ERK pathway. SPS in combination with ESWT was more effective in relieving joint contracture, improving the histopathological changes in the anterior joint capsule, and suppressing the high expression of target proteins and the overactivated MAPK/ERK pathway. The overactivated MAPK/ERK pathway was involved in the formation of extension knee joint contracture in rats. SPS in combination with ESWT was effective in relieving joint contracture and fibrosis of joint capsule. Moreover, the inhibition of the overactivated MAPK/ERK pathway may be the potential molecular mechanism for its therapeutic effect.

OBJECTIVES:The aims of the study are to investigate the effect of electrical stimulation on disuse muscular atrophy induced by immobilization (IM) and to explore the role of PERK signal and Parkin-dependent mitophagy in this process.DESIGN:In the first subexperiment, 24 rabbits were divided into four groups, which underwent different periods of IM. In the second subexperiment, 24 rabbits were divided into four groups on average in accordance with different kinds of interventions. To test the time-dependent changes of rectus femoris after IM, and to evaluate the effect of electrical stimulation, the wet weights, cross-sectional area and fat deposition of rectus femoris were assessed in this study, along with the protein levels of atrogin-1, p-PERK, Parkin, and COXIV.RESULTS:The wet weights and cross-sectional area decreased, and the fat deposition increased in rectus femoris after IM, along with the elevated protein levels of atrogin-1, p-PERK, Parkin, and decreased protein levels of COXIV. The above histomorphological and molecular changes can be partially ameliorated by electrical stimulation.CONCLUSIONS:Immobilization of unilateral lower limb could induce rectus femoris atrophy, which can be partially rectified by electrical stimulation. PERK signal and Parkin-mediated mitophagy may be the mechanisms by which electrical stimulation can play a significant role.

Joint capsule fibrosis, a common complication of joint immobilization, is mainly characterized by abnormal collagen deposition. The present study aimed to investigate the effect of extracorporeal shock wave therapy (ESWT) on reduced collagen deposition in the joint capsule during immobilization-induced joint capsule fibrosis. Additionally, the potential involvement of the adenosine A(2)A receptor (A2AR)-Neurotrophic factor e2-related factor 2 (Nrf2)/Haem oxygenase-1 (HO-1) pathway was explored. Thirty 3-month-old male Sprague-Dawley rats were randomly assigned to five groups: control (C), immobilization model (IM), natural recovery (NR), ESWT intervention (EI), and ESWT combined with A(2)AR antagonist SCH 58261 intervention (CI). After the left knee joints of rats in the IM, NR, EI and CI groups were immobilized using a full-extension fixation brace for 4 weeks, the EI and CI groups received ESWT twice a week for 4 weeks. The CI group was also treated with ESWT following intraperitoneal injection of SCH 58261 (0.01 mg/kg) for 4 weeks. The range of motion of the left knee joint was measured, and the protein levels of collagens I and III, A(2)AR, phosphorylated-protein kinase A/protein kinase A (p-PKA/PKA), p-Nrf2/Nrf2, and HO-1 were analysed by Western blotting. The IM and NR groups showed significantly greater arthrogenic contracture than the C group (P < 0.05). Compared to the NR group, the EI and CI groups exhibited significant improvement in arthrogenic contracture (P < 0.05). Conversely, the EI group showed lower contracture than the CI group (P < 0.05). Similar results were observed for collagen deposition and the protein levels of collagens I and III. The intervention groups (EI and CI groups) showed higher levels of p-Nrf2/Nrf2 and HO-1 than the NR group (P < 0.05). Moreover, the EI group exhibited higher levels of p-PKA/PKA, p-Nrf2/Nrf2, and HO-1 than the CI group (P < 0.05). However, no significant difference was found in the A(2)AR levels among the five groups (P > 0.05). ESWT may activate A(2)AR, leading to the phosphorylation of PKA. Subsequently, Nrf2 may be activated, resulting in the upregulation of HO-1, which then reduces collagen deposition and alleviates immobilization-induced joint capsule fibrosis.

Objective: The aim of the work described here was to investigate the efficacy and potential mechanisms of low intensity pulsed ultrasound (LIPUS) for the treatment of arthrogenic contracture induced by immobilization in rabbits.Methods: The left knee joint of rabbits was immobilized for 6 wk to establish the model of extending knee joint contracture. The rabbits were divided into a control group (C), a group immobilized for 6 wk (IM-6w), a group remobilized for 1 wk (RM-1w), a group subjected to LIPUS intervention for 1 wk (LIPUS-1w), a group remobilized for 2 wk (RM-2w) and a group subjected to LIPUS intervention for 2 wk (LIPUS-2w). The degrees of arthrogenic contracture and joint capsule fibrosis were assessed, as were the levels of reactive oxygen species (ROS) and the activation status of the TGF-fl1/Smad signaling pathway in the joint capsule.Results: After immobilization for 6 wk, the degrees of arthrogenic contracture and joint capsule fibrosis increased. The ROS level increased, as evidenced by an increase in malondialdehyde content and a decrease in superoxide dismutase content. In addition, the TGF-fl1/Smad signaling pathway was significantly activated. The degrees of knee joint contracture increased in the first week after remobilization and decreased in the second week. Furthermore, joint capsule fibrosis continued to develop during the 2 wk of remobilization, and the ROS level increased, while the TGF-fl1/Smad signaling pathway was significantly activated. LIPUS effectively reduced the level of ROS in the joint capsule, which further inhibited activation of the TGF-fl1/Smad signaling pathway, thereby improving joint capsule fibrosis and reducing arthrogenic contracture.Conclusion: The high ROS levels and overactivation of the TGF-fl1/Smad signaling pathway may be reasons why immobilization induces knee joint capsule fibrosis. LIPUS can alleviate the degree of knee joint capsule fibrosis induced by immobilization by inhibiting the production of ROS and the activation of the TGF-fl1/Smad signaling pathway.

Joint capsule fibrosis, a common complication of joint immobilization, is mainly characterized by abnormal collagen deposition. The present study aimed to investigate the effect of extracorporeal shock wave therapy (ESWT) on reduced collagen deposition in the joint capsule during immobilization-induced joint capsule fibrosis. Additionally, the potential involvement of the adenosine A 2 A receptor (A 2 AR)-Neurotrophic factor e2-related factor 2 (Nrf2)/Haem oxygenase-1 (HO-1) pathway was explored. Thirty 3-month-old male Sprague–Dawley rats were randomly assigned to five groups: control (C), immobilization model (IM), natural recovery (NR), ESWT intervention (EI), and ESWT combined with A 2 AR antagonist SCH 58261 intervention (CI). After the left knee joints of rats in the IM, NR, EI and CI groups were immobilized using a full-extension fixation brace for 4 weeks, the EI and CI groups received ESWT twice a week for 4 weeks. The CI group was also treated with ESWT following intraperitoneal injection of SCH 58261 (0.01 mg/kg) for 4 weeks. The range of motion of the left knee joint was measured, and the protein levels of collagens I and III, A 2 AR, phosphorylated-protein kinase A/protein kinase A (p-PKA/PKA), p-Nrf2/Nrf2, and HO-1 were analysed by Western blotting. The IM and NR groups showed significantly greater arthrogenic contracture than the C group ( P < 0.05). Compared to the NR group, the EI and CI groups exhibited significant improvement in arthrogenic contracture ( P < 0.05). Conversely, the EI group showed lower contracture than the CI group ( P < 0.05). Similar results were observed for collagen deposition and the protein levels of collagens I and III. The intervention groups (EI and CI groups) showed higher levels of p-Nrf2/Nrf2 and HO-1 than the NR group ( P < 0.05). Moreover, the EI group exhibited higher levels of p-PKA/PKA, p-Nrf2/Nrf2, and HO-1 than the CI group ( P < 0.05). However, no significant difference was found in the A 2 AR levels among the five groups ( P > 0.05). ESWT may activate A 2 AR, leading to the phosphorylation of PKA. Subsequently, Nrf2 may be activated, resulting in the upregulation of HO-1, which then reduces collagen deposition and alleviates immobilization-induced joint capsule fibrosis.

The purpose of this study was to observe the therapeutic effect of extracorporeal shock wave (ESW) on extensional joint contracture of knee joint in rats and its mechanism on articular capsule fibrosis. Thirty-two SD rats were randomly divided into blank control, immobilization, natural recovery, and ESW intervention groups. Except for the control group, the left knee joints of other rats were fixed with external fixation brace for 4 weeks when they were fully extended to form joint contracture. The effect of intervention was assessed by evaluating joint contracture, total cell count and collagen deposition in joint capsule, and protein expression levels of TGF-β1, p-Smad2/3, Smad2/3, p-JNK, JNK, I and III collagen in joint capsule. ESW can effectively reduce arthrogenic contracture, improve the histopathological changes of anterior joint capsule, inhibit the high expression of target protein and the excessive activation of TGF-β1/Smad2/3/JNK signal pathway. Inhibition of excessive activation of TGF-β1/Smad2/3/JNK pathway may be one of the potential molecular mechanisms by which extracorporeal shock wave can play a role.

As one of main causes of athrogenic contracture, joint capsule fibrosis which is described as a condition with excessive deposition of collagen components and extracellular matrix (ECM) in joint capsule, is a response to long-time immobilization. The purpose of this study was to explore the effect and the underlying mechanism of low-intensity pulsed ultrasound (LIPUS) in treating knee joint capsule fibrosis. A rabbit model of knee joint capsule fibrosis induced by 6w-immobilization was employed in this study. The degree of knee joint capsule fibrosis was assessed by measurement of arthrogenic contracture and Masson-staining. Furthermore, malondialdehyde (MDA) and superoxide dismutase (SOD) were measured to assess the level of reactive oxygen species (ROS). Apart from these, the activation of TGF-β1/Smad signaling pathway was determined through western blot analysis contained TGF-β1, Smad2, p-Smad2, Smad3, p-Smad3 and Smad4, and immunohistochemical staining for p-Smad2/3 positive cells. After 6 wk-immobilization, the degree of arthrogenic contracture and the collagen density were increased. Moreover, the activity of MDA was upregulated and the content of SOD was downregulated. Correspondingly, the TGF-β1/Smad signaling pathway was significantly activated. After 2 wk-LIPUS treatment, the degree of arthrogenic contracture and the collagen density were lower than 2 wk-remobilizaiton. Relatively, the activity of MDA was decresed and the content of SOD was increased compared with 2 wk-remobilizaiton. Importantly,the TGF-β1/Smad signaling pathway was significantly inhibited compared with 2 wk-remobilizaiton. Our findings thus conclude that high level ROS and hyperactive TGF-β1/Smad signaling pathway might be one of the causes of knee joint capsule fibrosis induced by immobilization and LIPUS attenuated the severity of immobilization-induced knee joint capsule fibrosis through inhibition of the production of ROS and the activation of TGF-β1/Smad signaling pathway. Our findings might provide a theoretical basis for knee joint capsule fibrosis after immobilization and provide the potential therapeutic target.

BACKGROUND:Current research lacks a model of knee extension contracture in rats.AIM:To elucidate the formation process of knee extension contracture.METHODS:We developed a rat model using an aluminum external fixator. Sixty male Sprague-Dawley rats with mature bones were divided into the control group (n = 6) and groups that had the left knee immobilized with an aluminum external fixator for 1, 2, and 3 d, and 1, 2, 3, 4, 6, and 8 wk (n = 6 in each group). The passive extension range of motion, histology, and expression of fibrosis-related proteins were compared between the control group and the immobilization groups.RESULTS:Myogenic contracture progressed very quickly during the initial 2 wk of immobilization. After 2 wk, the contracture gradually changed from myogenic to arthrogenic. The arthrogenic contracture progressed slowly during the 1st week, rapidly progressed until the 3rd week, and then showed a steady progression until the 4rd week. Histological analyses confirmed that the anterior joint capsule of the extended fixed knee became increasingly thicker over time. Correspondingly, the level of transforming growth factor beta 1 (TGF-β1) and phosphorylated mothers against decapentaplegic homolog 2 (p-Smad2) in the anterior joint capsule also increased with the immobilization time. Over time, the cross-sectional area of muscle fibers gradually decreased, while the amount of intermuscular collagen and TGF-β1, p-Smad2, and p-Smad3 was increased. Unexpectedly, the amount of intermuscular collagen and TGF-β1, p-Smad2, and p-Smad3 was decreased during the late stage of immobilization (6-8 wk). The myogenic contracture was stabilized after 2 wk of immobilization, whereas the arthrogenic contracture was stabilized after 3 wk of immobilization and completely stable in 4 wk.CONCLUSION:This rat model may be a useful tool to study the etiology of joint contracture and establish therapeutic approaches.

As an important exercise and energy metabolism organ of the human body, the normal maintenance of skeletal muscle mass is essential for the body to perform normal physiological functions. The autophagy-lysosome (AL) pathway is a physiological or pathological mechanism that is ubiquitous in normal and diseased cells. It plays a key role in the maintaining of protein balance, removing damaged organelles, and the stability of internal environment. The smooth progress of the autophagy process needs to go through multiple steps, which are completed under the coordinated action of multiple factors. Autophagy maintains the muscle homeostasis of a healthy body by removing cell components such as damaged myofibrils and isolated cytoplasmic proteins. Autophagy could also provide the initial energy required for cell proliferation, promote muscle regeneration and remodeling after injury. At the same time, autophagy disorder is also an important cause of age-related skeletal muscle atrophy. Autophagy could affect the response of skeletal muscle to exercise, and increasing the level of basic autophagy is beneficial to improve the adaptive response of skeletal muscle to exercise. This article summarizes the role and pathways of autophagy in the maintenance of skeletal muscle quality, in order to provide effective rehabilitation strategies for clinical prevention and treatment of muscle atrophy.

Abstract Background: The study aimed to elucidate the formation process and therapeutic strategies of knee extension contracture, we developed a novel rat model using an aluminum external fixator.Methods: Sixty male SD rats with mature bones were divided into the control group (n=6) and groups that had the left knee immobilized with an aluminum external fixator for 1, 2, and 3 days, and 1, 2, 3, 4, 6, and 8 weeks (n=6 in each group). The passive extension range of motion, histology, and expression of fibrosis-related proteins were compared between the control group and the immobilization groups.Results: Myogenic contracture progressed very quickly during the initial 2 weeks of immobilization; after 2 weeks, the contracture gradually changed from myogenic to arthrogenic. The arthrogenic contracture progressed slowly during the first week, rapidly progressed until the third week, and then showed a steady progression. Histological analysis confirmed that the anterior joint capsule of the extended fixed knee became increasingly thicker over time. Correspondingly, the level of TGFβ-1 in the anterior joint capsule also increased with the immobilization time. Over time, the cross-sectional area of muscle fibers gradually decreased, while the amount of intermuscular collagen and TGFβ-1 increased. Unexpectedly, the amount of intermuscular collagen and TGFβ-1 decreased during the late stage of immobilization (6–8 weeks).Conclusion: Myogenic contracture is stabilized after 2 weeks of immobilization, while arthrogenic contracture is stabilized after 3 weeks of immobilization. This novel rat model may be a useful tool to study the etiology of joint contracture and establish new therapeutic approaches.

The study aimed to investigate the effect of low-frequency electrical stimulation (LFES) on disuse muscle atrophy and its mechanism in a rabbit model of knee extension contracture. This study involved two experiments. In the time-point experiment, 24 rabbits were randomly divided into 4 groups: Control 1 (Ctrl1 group), immobilization for 2 weeks (I-2 group), immobilization for 4 weeks (I-4 group), and immobilization for 6 weeks (I-6 group). In the intervention experiment, 24 rabbits were randomly divided into 4 groups: Control 2 (Ctrl2 group), electrical stimulation (ESG group), natural recovery (NRG group), and electrical stimulation treatment (ESTG group). All intervention effects were assessed by evaluating the knee joint range of motion (ROM), cross-sectional area (CSA) of the rectus femoris muscle, and expression of autophagy-related proteins. The time-point experiment showed that immobilization reduced the knee ROM, reduced the rectus femoris muscle CSA, and activated autophagy in skeletal muscle. The levels of five autophagy-related proteins [mammalian target of rapamycin (mTOR), phosphorylated mTOR (p-mTOR), autophagy-related protein 7 (Atg7), p62, and microtubule-associated protein light chain 3B-II (LC3B-II)] were significantly elevated in the skeletal muscle of the I-4 group. The intervention experiment further showed that LFES significantly improved the immobilization-induced reductions in ROM and CSA. Additionally, LFES resulted in a significant decrease in the protein expression of mTOR, p-mTOR, Atg7, p62, and LC3B-II in the rectus femoris muscle. LFES alleviates immobilization-evoked disuse muscle atrophy possibly by inhibiting autophagy in the skeletal muscle of rabbits.

Background: The aim of this study was to investigate the therapeutic effect of electrical stimulation on disuse muscular atrophy in a rabbit model of knee joint contracture and explore the role of endoplasmic reticulum stress-induced Parkin-dependent mitophagy in this process.Methods: Two sub-experiments were carried out successively in our study. In the first sub-experiment, 24 rabbits were divided into four groups on average based on the immobilization time: Ctrl 1, I-2, I-4, and I-6 groups. In the second sub-experiment, 24 rabbits were also divided into four groups on average in accordance with the process mode: Ctrl2, ES, NR, and EST groups. To test the time-dependent changes of the rectus femoris muscles after immobilization in rabbits, and to evaluate the effect of electrical stimulation on the atrophic rectus femoris muscles, the wet weights of rectus femoris muscles were assessed in this study, along with the protein levels of atrogin-1, p-PERK, Parkin and COXIV.Results: The wet weights of rectus femoris muscles, the protein levels of atrogin-1, p-PERK and Parkin increased after immobilization. It was also revealed that the protein levels of COXIV decreased after immobilization. Electrical stimulation was effective against muscle atrophy, the elevated expression of atrogin-1, p-PERK, Parkin, and the decreased expression of COXIV.Conclusions: Immobilization of unilateral lower limb could induce rectus femoris muscle atrophy, endoplasmic reticulum stress and Parkin mediated mitophagy. Endoplasmic reticulum stress-induced Parkin-dependent mitophagy may be one of the mechanisms by which electrical stimulation can play a significant role.

Purpose The two structural components contributing to joint contracture formation are myogenic and arthrogenic contracture, and myofibrosis is an important part of myogenic contracture. Myofibrosis is a response to long-time immobilization and is described as a condition with excessive deposition of endomysial and perimysial connective tissue components in skeletal muscle. The purpose of this study was to confirm whether metformin can attenuate the formation of myogenic contracture and myofibrosis through the phosphorylation level of adenosine monophosphate-activated protein kinase (AMPK) and inhabitation of subsequent transforming growth factor beta (TGF-β) 1/Smad signaling pathway.Materials and Methods An immobilized rat model was used to determine whether metformin could inhibit myogenic contracture and myofibrosis. The contents of myogenic contracture of knee joint was calculated by measuring instrument of range of motion (ROM), and myofibrosis of rectus femoris were determined by ultrasound shear wave elastography and Masson staining. Protein expression of AMPK and subsequent TGF-β1/Smad signaling pathway were determined by western blot. Subsequently, Compound C, a specific AMPK inhibitor, was used to further clarify the role of the AMPK-mediated inhibition of TGF-β1/Smad signaling pathway.Results We revealed that the levels of myogenic contracture and myofibrosis were gradually increased during immobilization, and overexpression of TGF-β1-induced formation of myofibrosis by activating Smad2/3 phosphorylation. Activation of AMPK by metformin suppressed overexpression of TGF-β1 and TGF-β1-induced Smad2/3 phosphorylation, further reducing myogenic contracture and myofibrosis during immobilization. In contrast, inhibition of AMPK by Compound C partially counteracted the inhibitory effect of TGF-β1/Smad signaling pathway by metformin.Conclusion Notably, we first illustrated the therapeutic effect of metformin through AMPK-mediated inhibition of TGF-β1/Smad signaling pathway in myofibrosis, which may provide a new therapeutic strategy for myogenic contracture.

目的 观察早期低频电刺激对兔伸直型膝关节挛缩的治疗作用,并探讨其可能的干预机制.方法 将24只新西兰白兔随机分成对照(C)组、单纯电刺激(E)组、自然恢复(NR)组和电刺激治疗(EST)组,每组6只.C组自由活动7周;E组先自由活动4周,随后对左后肢股四头肌给予3周的低频电刺激;NR组先将左膝关节伸直固定4周,随后解除固定自然恢复3周;EST组先将左膝关节伸直固定4周,随后对左后肢股四头肌给予3周的低频电刺激.每组干预结束后,分别测量兔左膝关节剔除肌肉前后的活动范围(ROM),对股直肌进行HE和Masson染色,Western blot检测股直肌和关节囊中转化生长因子-β1(TGF-β1)和α-平滑肌肌动蛋白(α-SMA)的蛋白表达量.结果 与NR组相比,EST组膝关节的总挛缩和肌源性挛缩减轻(P＜0.01),关节源性挛缩未见改善;股直肌HE染色显示EST组肌纤维的形状和肌膜完整性较NR组改善,Masson染色的定量分析显示EST组股直肌纤维化的改善程度高于NR组(P＜0.01).此外,EST组股直肌中TGF-β1和α-SMA的表达量较NR组减低(P＜0.05),EST组关节囊中TGF-β1和o-SMA的蛋白表达量较NR组关节囊相比差异无统计学意义.结论 早期低频电刺激可通过降低骨骼肌纤维化水平来改善兔膝关节伸直型挛缩;且对骨骼肌纤维化的抑制作用大于对关节囊纤维化的抑制作用.

Purpose: We investigate the underlying biological effects and mechanisms of rESWT on myogenic contracture and muscle atrophy in a rabbit model of extending knee joint contracture. Materials and Methods: In group control, the knee joint was not fixed. In group I-4w, the knee joint was only fixed for 4 weeks. In groups SR-1 w, SR-2 w, and SR-4 w, the knee joint was fixed for 4 weeks before the rabbits underwent 1, 2, and 4 weeks of self-recovery, respectively. In groups rESWT-1 w, rESWT 2 w, and rESWT-4 w, the knee joint was fixed for 4 weeks before the rabbits underwent 1, 2, and 4 weeks of rESWT, respectively. The myogenic contracture was measured, the cross-sectional area and key protein levels for NF-kappa B/HIF-1 alpha signaling pathway and myogenic regulatory factors were evaluated. Results: During the recovery period, biological findings showed that the levels of myogenic contracture and muscle atrophy were milder in group rESWT by compared with group SR after 2 weeks. Molecular biological analysis showed that MyoD protein levels in the group rESWT was significantly higher than those in the group SR, and importantly, phospho-NF-kappa B p65 and HIF-1 alpha protein levels in the group rESWT were significantly lower than those in the group SR at the same time point. Conclusions: This is the first study demonstrated that rESWT has the potential to reduce myogenic contracture and muscle atrophy after long-term immobilization in animal model. It is a possible mechanism that changing the low oxygen environment in skeletal muscle through rESWT may inhibit activation of NF-kappa B/HIF-1 alpha signaling pathway.