Mechanical stress protects against osteoarthritis via regulation of the AMPK/NF-κB signaling pathway

Effects of different combinations of mechanical loading intensity, duration, and frequency on the articular cartilage in mice

BACKGROUND

Understanding how healthy articular cartilage responds to mechanical loading is critical. Moderate mechanical loading has positive effects on the cartilage, such as maintaining cartilage homeostasis. The degree of mechanical loading is determined by a combination of intensity, frequency, and duration; however, the best combination of these parameters for knee cartilage remains unclear. This study aimed to determine which combination of intensity, frequency, and duration provides the best mechanical loading on healthy knee articular cartilage in vitro and in vivo.

METHODS AND RESULTS

In this study, 33 male mice were used. Chondrocytes isolated from mouse knee joints were subjected to different cyclic tensile strains (CTSs) and assessed by measuring the expression of cartilage matrix-related genes. Furthermore, the histological characteristics of mouse tibial cartilages were quantified using different treadmill exercises. Chondrocytes and mice were divided into the control group and eight intervention groups: high-intensity, high-frequency, and long-duration; high-intensity, high-frequency, and short-duration; high-intensity, low-frequency, and long-duration; high-intensity, low-frequency, and short-duration; low-intensity, high-frequency, and long-duration; low-intensity, high-frequency, and short-duration; low-intensity, low-frequency, and long-duration; low-intensity, low-frequency, and short-duration. In low-intensity CTSs, chondrocytes showed anabolic responses by altering the mRNA expression of COL2A1 in short durations and SOX9 in long durations. Furthermore, low-intensity, low-frequency, and long-duration treadmill exercises minimized chondrocyte hypertrophy and enhanced aggrecan synthesis in tibial cartilages.

CONCLUSION

Low-intensity, low-frequency, and long-duration mechanical loading is the best combination for healthy knee cartilage to maintain homeostasis and activate anabolic responses. Our findings provide a significant scientific basis for exercise and lifestyle instructions.

Global burden and socioeconomic impact of knee osteoarthritis: a comprehensive analysis

Objective

To report the trend changes of the prevalence, incidence, and disability-adjusted life years (DALYs) of knee osteoarthritis (KOA) according to age, sex, sociodemographic index (SDI), and income.

Methods

This analysis used estimates from the broader Global Burden of Disease (GBD) study 2019, which covered 201 countries from 1990 to 2019. National prevalence, incidence, and DALYs were shown by using ggplot2 and maps packages. Five-year intervals were used for age groupings. The Commonwealth and the World Bank income classifications were used for income grouping.

Results

Globally, there were ~364.58 million prevalent cases (females: 225.16 million), 29.51 million incident cases (females: 17.53 million), and 11.53 million DALYs (females: 7.09 million) due to KOA in 2019. The Western Pacific Region had a high endemicity of ~7,319.87 cases per 100,000 people (7.64%). Japan's prevalence rate (12,610.12 cases per 100,000 population) was 10 times that of Somalia (1,178.23) in 2019. In 200 countries (except the United Arab Emirates), the prevalence, incidence, and DALY rates of KOA in 2019 were higher among females than among males and increased with age up to the oldest age group. The prevalence was highest in the high-middle SDI countries, and the incidence and DALYs were highest in the middle SDI countries.

Conclusion

There was a large burden of KOA worldwide, with some notable intercountry variation. Some countries had 10 times the burden of other countries. Increasing population awareness regarding the prevalence, incidence, and DALYs of KOA with a focus on the population in the Western Pacific Region is needed, particularly for older females. informs health policy development, and contributes to improving the efficiency, equity, and effectiveness of healthcare systems.

Moderate mechanical stress suppresses chondrocyte ferroptosis in osteoarthritis by regulating NF-κB p65/GPX4 signaling pathway

Ferroptosis is a recently identified form of programmed cell death that plays an important role in the pathophysiological process of osteoarthritis (OA). Herein, we investigated the protective effect of moderate mechanical stress on chondrocyte ferroptosis and further revealed the internal molecular mechanism. Intra-articular injection of sodium iodoacetate (MIA) was conducted to induce the rat model of OA in vivo, meanwhile, interleukin-1 beta (IL-1β) was treated to chondrocytes to induce the OA cell model in vitro. The OA phenotype was analyzed by histology and microcomputed tomography, the ferroptosis was analyzed by transmission electron microscope and immunofluorescence. The expression of ferroptosis and cartilage metabolism-related factors was analyzed by immunohistochemical and Western blot. Animal experiments revealed that moderate-intensity treadmill exercise could effectively reduce chondrocyte ferroptosis and cartilage matrix degradation in MIA-induced OA rats. Cell experiments showed that 4-h cyclic tensile strain intervention could activate Nrf2 and inhibit the NF-κB signaling pathway, increase the expression of Col2a1, GPX4, and SLC7A11, decrease the expression of MMP13 and P53, thereby restraining IL-1β-induced chondrocyte ferroptosis and degeneration. Inhibition of NF-κB signaling pathway relieved the chondrocyte ferroptosis and degeneration. Meanwhile, overexpression of NF-κB by recombinant lentivirus reversed the positive effect of CTS on chondrocytes. Moderate mechanical stress could activate the Nrf2 antioxidant system, inhibit the NF-κB p65 signaling pathway, and inhibit chondrocyte ferroptosis and cartilage matrix degradation by regulating P53, SLC7A11, and GPX4.

Association between lipid accumulation products and osteoarthritis among adults in the United States: A cross-sectional study, NHANES 2017-2020

OBJECTIVE

Using cross-sectional data from the 2017-2020 National Health and Nutrition Examination Survey (NHANES) for American, the aim of this research is to investigate the potential association between Lipid Accumulation Products (LAP) and the risk of osteoarthritis (OA).

METHODS

Data from the NHANES (2017-2020) were downloaded and further analyzed. The participants between 20 and 80 years reported having OA, and other relevant variables and information on LAP were included. The linear and non-linear associations between LAP and OA were evaluated using multivariable logistic regression analysis and smoothed curve fitting methods. A two-part linear regression model was also used to estimate threshold effects.

RESULTS

The increased risk of OA was shown to have a nonlinear relationship with higher LAP, showing a solid threshold impact with a saturation value of 120.00 cm × mmol/L, according to our data. The two variables showed a positive relationship to the left of the saturation point but no significant association to the right, pointing to a complicated nonlinear relationship between OA prevalence and LAP.

CONCLUSIONS

Our findings revealed that LAP was an independent risk factor for OA when it was <120.00 cm × mmol/L. The LAP index may serve as a valuable method for predicting and diagnosed OA. To validate our results, further large-scale prospective research are required.

Exerkines and osteoarthritis

Osteoarthritis (OA) is the most prevalent chronic joint disease, with physical exercise being a widely endorsed strategy in its management guidelines. Exerkines, defined as cytokines secreted in response to acute and chronic exercise, function through endocrine, paracrine, and/or autocrine pathways. Various tissue-specific exerkines, encompassing exercise-induced myokines (muscle), cardiokines (heart), and adipokines (adipose tissue), have been linked to exercise therapy in OA. Exerkines are derived from these kines, but unlike them, only kines regulated by exercise can be called exerkines. Some of these exerkines serve a therapeutic role in OA, such as irisin, metrnl, lactate, secreted frizzled-related protein (SFRP), neuregulin, and adiponectin. While others may exacerbate the condition, such as IL-6, IL-7, IL-15, IL-33, myostatin, fractalkine, follistatin-like 1 (FSTL1), visfatin, activin A, migration inhibitory factor (MIF), apelin and growth differentiation factor (GDF)-15. They exerts anti-/pro-apoptosis/pyroptosis/inflammation, chondrogenic differentiation and cell senescence effect in chondrocyte, synoviocyte and mesenchymal stem cell. The modulation of adipokine effects on diverse cell types within the intra-articular joint emerges as a promising avenue for future OA interventions. This paper reviews recent findings that underscore the significant role of tissue-specific exerkines in OA, delving into the underlying cellular and molecular mechanisms involved.

RNF125, transcriptionally regulated by NFATC2, alleviates osteoarthritis via inhibiting the Wnt/β-catenin signaling pathway through degrading TRIM14

Osteoarthritis (OA) is a chronic joint disease characterized by the progressive degradation of articular cartilage. In this study, as determined by histological staining, the cartilage surface of the OA rats was damaged, defective and broken, and chondrocytes and proteoglycan were reduced. While moderate physical exercise showed protective effects on the cartilage. Besides, RNA-seq was performed to select a target protein and RNF125 (an E3 ubiquitin ligase) was decreased in the cartilage tissues of OA rats and increased after physiological exercise. However, the precise role of RNF125 in OA is still unknown. This work aimed to investigate the involvement and underlying mechanism of RNF125 in OA pathogenesis. Our results defined that adenovirus-mediated overexpression of RNF125 inhibited the degradation of extracellular matrix of chondrocytes induced by IL-1β, as revealed by increased chondrocyte viability, upregulated COL2A1 and ACAN levels, and downregulated MMP1, MMP13 and ADAMTS5 levels, which was abrogated by NR4A2 knockdown. In vivo, RNF125 relieved OA, manifested as reduced cartilage injury and increased chondrocytes. Mechanically, NFATC2 bound to the RNF125 promoter and directly regulated RNF125 transcription, as illustrated by luciferase reporter, Ch-IP and DNA pull-down assays. Furthermore, RNF125 overexpression inhibited the nuclear translocation of β-catenin, thus suppressing activation of the Wnt/β-catenin signaling pathway. Also, RNF125 as E3 ubiquitin ligase led to the ubiquitination and degradation of TRIM14 protein, and TRIM14 overexpression efficiently reversed the effects of RNF125 overexpression on OA progression. Totally, this study provides new insights into OA pathogenesis regulated by RNF125. RNF125 may be a novel biomarker for OA therapy.

Double-edged role of mechanical stimuli and underlying mechanisms in cartilage tissue engineering

Mechanical stimuli regulate the chondrogenic differentiation of mesenchymal stem cells and the homeostasis of chondrocytes, thus affecting implant success in cartilage tissue engineering. The mechanical microenvironment plays fundamental roles in the maturation and maintenance of natural articular cartilage, and the progression of osteoarthritis Hence, cartilage tissue engineering attempts to mimic this environment in vivo to obtain implants that enable a superior regeneration process. However, the specific type of mechanical loading, its optimal regime, and the underlying molecular mechanisms are still under investigation. First, this review delineates the composition and structure of articular cartilage, indicating that the morphology of chondrocytes and components of the extracellular matrix differ from each other to resist forces in three top-to-bottom overlapping zones. Moreover, results from research experiments and clinical trials focusing on the effect of compression, fluid shear stress, hydrostatic pressure, and osmotic pressure are presented and critically evaluated. As a key direction, the latest advances in mechanisms involved in the transduction of external mechanical signals into biological signals are discussed. These mechanical signals are sensed by receptors in the cell membrane, such as primary cilia, integrins, and ion channels, which next activate downstream pathways. Finally, biomaterials with various modifications to mimic the mechanical properties of natural cartilage and the self-designed bioreactors for experiment in vitro are outlined. An improved understanding of biomechanically driven cartilage tissue engineering and the underlying mechanisms is expected to lead to efficient articular cartilage repair for cartilage degeneration and disease.

Intermittent cyclic mechanical compression promotes endplate chondrocytes degeneration by disturbing Nrf2/PINK1 signaling pathway-dependent mitophagy

An abnormal mechanical load is a pivotal inducer of endplate cartilage degeneration, which subsequently promotes intervertebral disc degeneration. Our previous study indicated that intermittent cyclic mechanical compression (ICMC) promotes endplate chondrocyte degeneration, but the mechanism underlying this effect is unclear. In this study, we investigated PTEN-induced kinase 1(PINK1) dependent mitophagy during ICMC-induced endplate chondrocyte degeneration. Furthermore, we determined whether NF-E2-related factor 2 (Nrf2) activation correlated with PINK1-dependent mitophagy regulation and increased oxidation resistance of endplate chondrocytes under ICMC application. First, we generated a mechanical compression-induced endplate chondrocyte degeneration model in vitro and in vivo. ICMC was found to promote endplate chondrocyte extracellular matrix degradation. PINK1-mediated mitophagy was suppressed in the ICMC-stimulated endplate chondrocytes, while increased mitochondrial reactive oxygen species generation suggested that mitophagy is involved in the protective effect of mechanical strain on endplate chondrocytes. Moreover, Nrf2 expression, interaction with Kelch-like ECH-associated protein (Keap1), and nuclear translocation were inhibited by ICMC. Nrf2 overexpression inhibited reactive oxygen species production and reversed ICMC-induced endplate chondrocyte degeneration. Transfection with PINK1 shRNA abolished this effect and partially blocked Nrf2-induced mitophagy. Our findings suggested that ICMC could inhibit the Nrf2/PINK1 signaling pathway to reduce the mitophagy levels which significantly promote oxidative stress and thereby endplate chondrocyte degeneration. Therapeutic regulation of the Nrf2/PINK1 signaling pathway may be an efficient anabolic strategy for inhibiting this process.

Mitochondrial Dynamics: Working with the Cytoskeleton and Intracellular Organelles to Mediate Mechanotransduction

Cells are constantly exposed to various mechanical environments; therefore, it is important that they are able to sense and adapt to changes. It is known that the cytoskeleton plays a critical role in mediating and generating extra- and intracellular forces and that mitochondrial dynamics are crucial for maintaining energy homeostasis. Nevertheless, the mechanisms by which cells integrate mechanosensing, mechanotransduction, and metabolic reprogramming remain poorly understood. In this review, we first discuss the interaction between mitochondrial dynamics and cytoskeletal components, followed by the annotation of membranous organelles intimately related to mitochondrial dynamic events. Finally, we discuss the evidence supporting the participation of mitochondria in mechanotransduction and corresponding alterations in cellular energy conditions. Notable advances in bioenergetics and biomechanics suggest that the mechanotransduction system composed of mitochondria, the cytoskeletal system, and membranous organelles is regulated through mitochondrial dynamics, which may be a promising target for further investigation and precision therapies.

Integrin αVβ3 Signaling in the Progression of Osteoarthritis Induced by Excessive Mechanical Stress

Osteoarthritis (OA) is believed to be linked with cartilage degeneration, subchondral bone sclerosis, and synovial inflammation that lead to joint failure, and yet treatment that can effectively reverse the pathological process of the disease still not exists. Recent evidence suggests excessive mechanical stress (eMS) as an essential role in the pathogenesis of OA. Increased levels of integrin αVβ3 have been detected in osteoarthritic cartilage and were previously implicated in OA pathogenesis. However, the role of integrin αVβ3 in the process of eMS-induced OA remains unclear. Here, histologic and proteomic analyses of osteoarthritic cartilage in a rat destabilization of the medial meniscus model demonstrated elevated expression of integrin αVβ3 as well as more serious cartilage degeneration in the medial weight-bearing area. Furthermore, results of in vitro study demonstrated that eMS led to a significant increase of integrin αVβ3 expression and phosphorylation of downstream signaling molecules such as FAK and ERK, as well as upregulated expressions of inflammatory and degradative mediators. In addition, we found that inhibition of integrin αVβ3 could alleviate chondrocyte inflammation triggered by eMS both in vivo and in vitro. Our findings suggest a central role for upregulation of integrin αVβ3 signaling in OA pathogenesis and demonstrate that activation of integrin αVβ3 signaling in cartilage contributes to inflammation and joint destruction in eMS-induced OA. Taken together, our data presented here provide a possibility for targeting integrin αVβ3 signaling pathway as a disease-modifying therapy.

Mechanotransduction pathways in articular chondrocytes and the emerging role of estrogen receptor-α

In the synovial joint, mechanical force creates an important signal that influences chondrocyte behavior. The conversion of mechanical signals into biochemical cues relies on different elements in mechanotransduction pathways and culminates in changes in chondrocyte phenotype and extracellular matrix composition/structure. Recently, several mechanosensors, the first responders to mechanical force, have been discovered. However, we still have limited knowledge about the downstream molecules that enact alterations in the gene expression profile during mechanotransduction signaling. Recently, estrogen receptor α (ERα) has been shown to modulate the chondrocyte response to mechanical loading through a ligand-independent mechanism, in line with previous research showing that ERα exerts important mechanotransduction effects on other cell types, such as osteoblasts. In consideration of these recent discoveries, the goal of this review is to position ERα into the mechanotransduction pathways known to date. Specifically, we first summarize our most recent understanding of the mechanotransduction pathways in chondrocytes on the basis of three categories of actors, namely mechanosensors, mechanotransducers, and mechanoimpactors. Then, the specific roles played by ERα in mediating the chondrocyte response to mechanical loading are discussed, and the potential interactions of ERα with other molecules in mechanotransduction pathways are explored. Finally, we propose several future research directions that may advance our understanding of the roles played by ERα in mediating biomechanical cues under physiological and pathological conditions.

Exercise induced meteorin-like protects chondrocytes against inflammation and pyroptosis in osteoarthritis by inhibiting PI3K/Akt/NF-κB and NLRP3/caspase-1/GSDMD signaling

The production of metrnl, a novel adipomyokine, is induced upon exercise in adipose tissue and skeletal muscle. In this study, we investigated the anti-inflammatory and antipyroptotic effects of exercise-induced metrnl producted in rats in vitro and in vivo. Forty Sprague-Dawley rats were divided randomly into five groups: control (CG), osteoarthritis (OA) with sedentary lifestyle (OAG), OA with low intensity exercise (OAL), OA with moderate intensity exercise (OAM), and OA with high intensity exercise (OAH). The correlation between the level of metrnl and OA degree was detected using ELISA, X-ray imaging, histology, and immunohistochemistry in vivo. Primary chondrocytes were preincubated with recombinant metrnl before interleukin-1β administration to verify the anti-inflammatory and antipyroptotic effects of metrnl. Western blotting and quantitative reverse transcription (qRT)-PCR were used to evaluate the differences in protein and mRNA expression between groups, respectively. Reactive oxygen species (ROS) assay, immunofluorescence, transmission electron microscopy (TEM), and flow cytometry were used to evaluate morphological changes and pyroptosis in chondrocytes. In the moderate-intensity treadmill exercise group, the severity of OA showed maximum relief and the metrnl levels had the most significant increase. Metrnl exerted its anti-inflammatory effect through the suppression of the PI3K/Akt/NF-κB pathway in IL-1β-induced OA chondrocytes, which was accompanied with the recovery of collagen II expression and the attenuation of MMP13 and ADAMTS5. Moreover, metrnl ameliorated chondrocyte pyroptosis by inhibiting the activation of the nod-like receptor protein-3/caspase-1/gasdermin D cascade. In conclusion, moderate-intensity exercise improves inflammation and pyroptosis by increasing metrnl release, which inhibits the PI3K/Akt/NF-κB and further NLRP3/caspase-1/GSDMD signaling pathways.

Ginsenoside Compound K Ameliorates Osteoarthritis by Inhibiting the Chondrocyte Endoplasmic Reticulum Stress-Mediated IRE1α-TXNIP-NLRP3 Axis and Pyroptosis

Osteoarthritis (OA) is a common joint disease, and studies have reported that the endoplasmic reticulum stress (ERS) in chondrocytes caused by the cartilage tissue damage could mediate the activation of Nod-like receptor protein 3 (NLRP3) inflammasomes through inositol-requiring enzyme 1 alpha (IRE1α) and thioredoxin interacting protein (TXNIP). Ginsenoside compound K (CK) has an inhibitory effect on IRE1α activation. However, the role of IRE1α-TXNIP and its interaction with CK are still unclear. In this study, we examined the role and mechanism of action of CK in OA. We found that CK ameliorated OA and ERS in IL-1β-treated chondrocytes and a monoiodoacetate-induced rat OA model. The effect of CK on inflammation, pyroptosis, and ERS was blocked by the ERS inducer tunicamycin. In conclusion, CK hindered OA progression by inhibiting the ERS-IRE1α-TXNIP-NLRP3 axis. Overall, our data indicate that CK could be useful in the treatment of OA and other chronic inflammatory diseases.

Therapeutic exercise interventions in rat models of arthritis

Arthritis is the leading cause of musculoskeletal pain and disability worldwide. Nearly 50% of individuals over the age of 65 have arthritis, which contributes to limited function, articular pain, physical inactivity, and diminished quality of life. Therapeutic exercise is often recommended in clinical settings for patients experiencing arthritic pain, however, there is little practical guidance regarding the use of therapeutic exercise to alleviate arthritic musculoskeletal pain. Rodent models of arthritis allow researchers to control experimental variables, which cannot be done with human participants, providing an opportunity to test therapeutic approaches in preclinical models. This literature review provides a summary of published findings in therapeutic exercise interventions in rat models of arthritis as well as gaps in the existing literature. We reveal that preclinical research in this field has yet to adequately investigate the impact of experimental variables in therapeutic exercise including their modality, intensity, duration, and frequency on joint pathophysiology and pain outcomes.

The effectiveness of treadmill and swimming exercise in an animal model of osteoarthritis

Introduction: Osteoarthritis (OA) is considered an inflammatory and degenerative joint disease, characterized by loss of hyaline joint cartilage and adjacent bone remodeling with the formation of osteophytes, accompanied by various degrees of functional limitation and reduction in the quality of life of individuals. The objective of this work was to investigate the effects of treatment with physical exercise on the treadmill and swimming in an animal model of osteoarthritis. Methods: Forty-eight male Wistar rats were divided (n=12 per group): Sham (S); Osteoarthritis (OA); Osteoarthritis + Treadmill (OA + T); Osteoarthritis + Swimming (OA + S). The mechanical model of OA was induced by median meniscectomy. Thirty days later, the animals started the physical exercise protocols. Both protocols were performed at moderate intensity. Forty-eight hours after the end of the exercise protocols, all animals were anesthetized and euthanized for histological, molecular, and biochemical parameters analysis. Results: Physical exercise performed on a treadmill was more effective in attenuating the action of pro-inflammatory cytokines (IFN-γ, TNF-α, IL1-β, and IL6) and positively regulating anti-inflammatories such as IL4, IL10, and TGF-β in relation to other groups. Discussion: In addition to maintaining a more balanced oxi-reductive environment within the joint, treadmill exercise provided a more satisfactory morphological outcome regarding the number of chondrocytes in the histological evaluation. As an outcome, better results were found in groups submitted to exercise, mostly treadmill exercise.

Unraveling the Mechanobiology Underlying Traumatic Brain Injury with Advanced Technologies and Biomaterials

Traumatic brain injury (TBI) is a worldwide health and socioeconomic problem, associated with prolonged and complex neurological aftermaths, including a variety of functional deficits and neurodegenerative disorders. Research on the long-term effects has highlighted that TBI shall be regarded as a chronic health condition. The initiation and exacerbation of TBI involve a series of mechanical stimulations and perturbations, accompanied by mechanotransduction events within the brain tissues. Mechanobiology thus offers a unique perspective and likely promising approach to unravel the underlying molecular and biochemical mechanisms leading to neural cells dysfunction after TBI, which may contribute to the discovery of novel targets for future clinical treatment. This article investigates TBI and the subsequent brain dysfunction from a lens of neuromechanobiology. Following an introduction, the mechanobiological insights are examined into the molecular pathology of TBI, and then an overview is given of the latest research technologies to explore neuromechanobiology, with particular focus on microfluidics and biomaterials. Challenges and prospects in the current field are also discussed. Through this article, it is hoped that extensive technical innovation in biomedical devices and materials can be encouraged to advance the field of neuromechanobiology, paving potential ways for the research and rehabilitation of neurotrauma and neurological diseases.

Exercise for Osteoarthritis: A Literature Review of Pathology and Mechanism

Osteoarthritis (OA) has a very high incidence worldwide and has become a very common joint disease in the elderly. Currently, the treatment methods for OA include surgery, drug therapy, and exercise therapy. In recent years, the treatment of certain diseases by exercise has received increasing research and attention. Proper exercise can improve the physiological function of various organs of the body. At present, the treatment of OA is usually symptomatic. Limited methods are available for the treatment of OA according to its pathogenesis, and effective intervention has not been developed to slow down the progress of OA from the molecular level. Only by clarifying the mechanism of exercise treatment of OA and the influence of different exercise intensities on OA patients can we choose the appropriate exercise prescription to prevent and treat OA. This review mainly expounds the mechanism that exercise alleviates the pathological changes of OA by affecting the degradation of the ECM, apoptosis, inflammatory response, autophagy, and changes of ncRNA, and summarizes the effects of different exercise types on OA patients. Finally, it is found that different exercise types, exercise intensity, exercise time and exercise frequency have different effects on OA patients. At the same time, suitable exercise prescriptions are recommended for OA patients.

Mechanical Stimulation Protects Against Chondrocyte Pyroptosis Through Irisin-Induced Suppression of PI3K/Akt/NF-κB Signal Pathway in Osteoarthritis

Irisin, a myokine secreted by muscle during physical exercise, is known to have biological activities in different cell types. Chondrocyte inflammation and pyroptosis have been shown to play important roles in osteoarthritis (OA). In this study, we investigated the effects of exercise-induced irisin during different intensities of treadmill exercise in a rat OA model and the anti-inflammatory and antipyroptosis mechanism of irisin in OA chondrocytes. Forty-eight SD rats (n = 8) were randomly assigned to control (CG), OA (OAG), OA groups under different intensities of treadmill exercise (OAL, OAM, and OAH), OAM + irisin neutralizing antibodies group (OAM + irisin (NA)). The levels of irisin and the severity of OA between groups were detected using ELISA, histology, immunohistochemistry, X-ray and computed tomography and magnetic resonance imaging. The anti-inflammatory and antipyroptosis mechanisms of irisin were investigated in vitro in OA chondrocytes preincubated with recombinant irisin (0, 5, or 10 ng/ml) for 1 h before treatment with interleukin-1β (IL-1β) for 24 h mRNA and protein expression levels were determined using quantitative reverse transcription polymerase chain reaction, and western blot analyses. Morphological changes and cell death associated with pyroptosis were examined using transmission electron microscopy, flow cytometry and immunofluorescence. Moderate-intensity treadmill exercise increased the levels of irisin, exhibiting the best therapeutic effects on OA which could be suppressed by irisin neutralizing antibodies. Irisin not only recovered the expression of collagen II and attenuated that of MMP-13 and ADAMTS-5 in IL-1β-induced OA chondrocytes by inhibiting the PI3K/Akt/NF-κB signaling pathway, but also inhibited the activity of nod-like receptor protein-3 (NLRP3)/caspase-1, thus ameliorating pyroptosis in chondrocytes. In conclusion, moderate mechanical stimulation protects against chondrocyte pyroptosis through irisin-induced suppression of PI3K/Akt/NF-κB signal pathway in osteoarthritis.

Acupuncture Delays Cartilage Degeneration through Upregulating SIRT1 Expression in Rats with Osteoarthritis

Silent mating type information regulation 2 homolog 1 (SIRT1) has been reported to inhibit osteoarthritic gene expression in chondrocytes. Here, efforts in this study were made to unveil the specific role of SIRT1 in the therapy of acupuncture on cartilage degeneration in osteoarthritis (OA). Specifically, OA was established by the anterior cruciate ligament transection method in the right knee joint of rats, subsequent to which acupuncture was performed on two acupoints. Injection with shSIRT1 sequence–inserted lentiviruses was conducted to investigate the role of SIRT1 in acupuncture-mediated OA. Morphological changes and cell apoptosis in rat OA cartilages were examined by safranin-O staining and terminal deoxynucleotidyl transferase-mediated nick-end labeling (TUNEL) assay, respectively. The serum levels of tumor necrosis factor (TNF)-α and interleukin (IL)-2 in OA rats were assessed by enzyme-linked immunosorbent assay (ELISA). The expressions of SIRT1, cartilage matrix degradation-related proteins (matrix metalloproteinase (MMP)-9 and ADAMTS5), NF-κB signaling-related markers (p-p65/p65 and p-IκBα/IκBα), and cartilage matrix synthesis-related proteins (collagen II and aggrecan) in the OA cartilage were analyzed by western blot. As a result, acupuncture counteracted OA-associated upregulation of TNF-α, IL-2, cartilage matrix degradation-related proteins, and NF-κB signaling-related markers, morphological damage, apoptosis, SIRT1 downregulation, and loss of cartilage matrix synthesis-related proteins in rat articular cartilages. SIRT1 silencing reversed acupuncture-induced counteractive effects on the aforementioned OA-associated phenomena (except apoptosis, the experiment regarding which under SIRT1 silencing was not performed). Collectively, acupuncture inhibited chondrocyte apoptosis, inflammation, NF-κB signaling activation, and cartilage matrix degradation by upregulating SIRT1 expression to delay OA-associated cartilage degeneration.

Mechanosignalling in cartilage: an emerging target for the treatment of osteoarthritis

Mechanical stimuli have fundamental roles in articular cartilage during health and disease. Chondrocytes respond to the physical properties of the cartilage extracellular matrix (ECM) and the mechanical forces exerted on them during joint loading. In osteoarthritis (OA), catabolic processes degrade the functional ECM and the composition and viscoelastic properties of the ECM produced by chondrocytes are altered. The abnormal loading environment created by these alterations propagates cell dysfunction and inflammation. Chondrocytes sense their physical environment via an array of mechanosensitive receptors and channels that activate a complex network of downstream signalling pathways to regulate several cell processes central to OA pathology. Advances in understanding the complex roles of specific mechanosignalling mechanisms in healthy and OA cartilage have highlighted molecular processes that can be therapeutically targeted to interrupt pathological feedback loops. The potential for combining these mechanosignalling targets with the rapidly expanding field of smart mechanoresponsive biomaterials and delivery systems is an emerging paradigm in OA treatment. The continued advances in this field have the potential to enable restoration of healthy mechanical microenvironments and signalling through the development of precision therapeutics, mechanoregulated biomaterials and drug systems in the near future.

Enhancement of DUSP14 (dual specificity phosphatase 14) limits osteoarthritis progression by alleviating chondrocyte injury, inflammation and metabolic homeostasis

Osteoarthritis (OA) is a proverbial inflammatory degenerative joint disease associated with the acceleration of the aging process and is characterized by chondrocyte injury and articular cartilage degradation. Dual-specificity phosphatase 14 (Dusp14), a common member of the DUSP family, has been implicated in multiple inflammatory diseases and bone loss. Nevertheless, the function of DUSP14 in OA remains unclear. In the present study, down-regulation of DUSP14 was corroborated in anterior cruciate ligament transection (ACLT)-induced OA rats and interleukin-1β (IL-1β)-stimulated chondrocytes. Additionally, the gain of DUSP14 reversed IL-1β-induced inhibition of chondrocyte viability but attenuated cell apoptosis. Concomitantly, DUSP14 overexpression muted IL-1β-induced release of pro-inflammatory mediators NO and prostaglandin E2 (PGE2), as well as pro-inflammatory cytokine levels (IL-6 and TNF-α). Furthermore, up-regulation of DUSP14 overturned the effects of IL-1β on the inhibition of collagen II and aggrecan expression, and enhancement of A Disintegrin and Metalloproteinase with Thrombospondin Motifs 5 (ADAMTS5) and matrix metalloproteinases (MMPs; MMP3 and MMP-13). Mechanistically, DUSP14 elevation increased the p-Adenosine 5ʹ-monophosphate-activated protein activated protein kinase(AMPK), inhibitor of NF-κB (IκB) expression and decreased p-p65 NF-κB expression, indicating that DUSP14 might restore the AMPK-IκB pathway to restrain NF-κB signaling under IL-1β exposure. Notably, blockage of AMPK signaling muted the protective efficacy of DUSP14 elevation against IL-1β-induced inflammatory injury and metabolism disturbance in chondrocytes. Interestingly, histological evaluation substantiated that DUSP14 injection alleviated cartilage degradation in OA rats. Together, DUSP14 may ameliorate OA progression by affecting chondrocyte injury, inflammatory response and cartilage metabolism homeostasis, implying a promising therapeutic strategy against OA.

8-Methoxypsoralen has Anti-inflammatory and Antioxidant Roles in Osteoarthritis Through SIRT1/NF-κB Pathway

Osteoarthritis (OA) is mainly manifested by joint pain, stiffness and mobility disorder, which is the main cause of pain and disability in middle-aged and elderly people. In this study, we aimed to explore the role and mechanism of 8-Methoxypsoralen (8-MOP) in the OA model both in vitro and in vivo. The rat chondrocytes were treated with IL-1β, and the proliferation, apoptosis, inflammatory reactions and oxidative stress responses were determined after treatment with different concentrations of 8-MOP. Real-time quantitative polymerase chain reaction (qRT-PCR) and/or Western blot were implemented to check the AMPK/SIRT1/NF-κB expression in chondrocytes. The NF-κB activity was determined by dual luciferase experiment. The pain threshold of OA rat model dealt with 8-MOP and/or the SIRT1 inhibitor EX527 was measured. Our results revealed that 8-MOP evidently reduced IL-1β-mediated apoptosis and inhibition of proliferation, and mitigated the expression of inflammatory cytokines and oxidative stress factors in chondrocytes. Additionally, 8-MOP promoted phosphorylated level of AMPKα, enhanced SIRT1 expression and inhibited the phosphorylation of NF-κB. After treatment with EX527, 8-MOP-mediated protective effects on chondrocytes were mostly reversed. In vivo, 8-MOP obviously improved the pain threshold in the OA rat model and reduced the injury and apoptosis of chondrocytes in the joints. In addition, 8-MOP relieved inflammatory and oxidative stress responses in the articular cartilage via enhancing SIRT1 and repressing NF-κB activation. After the treatment with EX527, the 8-MOP-mediated protective effects were distinctly weakened. In summary, our study testified that 8-MOP alleviates pain, inflammatory and oxidative stress responses in OA rats through the SIRT1/NF-κB pathway, which is expected to become a new reagent for clinical treatment of OA.

Maresin-1 suppresses IL-1β-induced MMP-13 secretion by activating the PI3K/AKT pathway and inhibiting the NF-κB pathway in synovioblasts of an osteoarthritis rat model with treadmill exercise

Aim: Maresin-1 is a metabolite of docosahexaenoic acid (DHA) that has potential anti-inflammatory effects. To explore whether maresin-1 changes and has a therapeutic effect in osteoarthritis (OA) model rats undergoing treadmill exercise, we examined endogenous maresin-1 in a single-session treadmill experiment and OA model rats were treated with maresin-1, moreover, we examined the effects of maresin-1 on IL-1β induced rat fibroblast-like synoviocytes (FLSs) and possible mechanisms.Methods: In single-session treadmill experiment, 48 rats were randomly divided into 3 groups and performed three different intensities of exercise (15.2 m/min, 0°; 19.3 m/min, 5°; 26.8 m/min, 10°) for 60 min. Intra-articular lavage fluid (IALF) samples were harvested after 0, 2, and 4 h from each group (n = 4) and maresin-1 levels were evaluated by ELISA. Another 30 rats were treated with monosodium iodoacetate (MIA) to induce osteoarthritis and exogenous maresin-1 (MaR-1) and were divided into three groups (n = 10, OA: MIA, OAM: MIA+MaR1, and CG: control group). The level of injury was evaluated by OARSI and Mankin scores, and the levels of type II collagen and MMP13 were evaluated by immunohistochemistry. FLSs were obtained from the knee joint of SD rats, and the expression of MMP13 and activation of the PI3k/Akt and NF-κB p65 pathways in IL-1β-induced FLSs were evaluated by western blotting.Results: Maresin-1 levels were increased in IALF at 4 h after exercise, and type II collagen increased in cartilage and MMP13 decreased in the synovium after treatment with maresin-1 in MIA-induced osteoarthritis. The results of vitro experiment showed decreased MMP13, activation of the PI3k/Akt pathway, and suppression of the NF-κB p65 pathway upon treatment with maresin-1 in IL-1β-induced FLSs.Conclusions: The changes in maresin-1 in IALF, as seen in our single-section treadmill exercise, provides an explanation for the therapeutic effect of appropriate-strength treadmill exercise on osteoarthritis, and our experiments confirmed the therapeutic effect of maresin-1 both in vivo and in vitro.

Activation of transient receptor potential vanilloid 4 protects articular cartilage against inflammatory responses via CaMKK/AMPK/NF-κB signaling pathway

Transient receptor potential vanilloid 4 (TRPV4) plays an important role in chondrocytes via Ca²⁺ signaling. However, its role in the progression of osteoarthritis is unclear. This study aimed to evaluate the effects of TRPV4 activation on articular cartilage and chondrocytes stimulated with interleukin (IL)-1β. Bovine and human articular chondrocytes were stimulated with various agents, including IL-1β, GSK1016790A (GSK101; a TRPV4 agonist), Compound C (an AMP-activated protein kinase (AMPK) inhibitor), and STO-609 (a calmodulin-dependent protein kinase kinase (CaMKK) inhibitor), and were processed for Western blot analysis and real-time PCR. The dimethylmethylene blue (DMMB) assay and Safranin O staining were also performed. GSK101 reversed the IL-1β-induced increase in expression of matrix metalloproteinase (MMP)-13 and decrease in expression of aggrecan. GSK101 also decreased proteoglycan release in the DMMB assay and retained Safranin O staining of articular cartilage tissue. Furthermore, GSK101 increased AMPK phosphorylation and decreased IL-1β-induced nuclear factor kappa B (NF-κB) phosphorylation. Compound C and STO-609 reversed the suppressive effects of GSK101 on NF-κB activation and MMP-13 expression. In conclusion, TRPV4 activation had chondroprotective effects on articular cartilage stimulated with IL-1β by activating CaMKK/AMPK and suppressing the NF-κB pathway. TRPV4 activators may offer a promising therapeutic option for preventing the progression of osteoarthritis.

AMPK Signaling in Energy Control, Cartilage Biology, and Osteoarthritis

The adenosine monophosphate (AMP)-activated protein kinase (AMPK) was initially identified as an enzyme acting as an "energy sensor" in maintaining energy homeostasis via serine/threonine phosphorylation when low cellular adenosine triphosphate (ATP) level was sensed. AMPK participates in catabolic and anabolic processes at the molecular and cellular levels and is involved in appetite-regulating circuit in the hypothalamus. AMPK signaling also modulates energy metabolism in organs such as adipose tissue, brain, muscle, and heart, which are highly dependent on energy consumption via adjusting the AMP/ADP:ATP ratio. In clinics, biguanides and thiazolidinediones are prescribed to patients with metabolic disorders through activating AMPK signaling and inhibiting complex I in the mitochondria, leading to a reduction in mitochondrial respiration and elevated ATP production. The role of AMPK in mediating skeletal development and related diseases remains obscure. In this review, in addition to discuss the emerging advances of AMPK studies in energy control, we will also illustrate current discoveries of AMPK in chondrocyte homeostasis, osteoarthritis (OA) development, and the signaling interaction of AMPK with other pathways, such as mTOR (mechanistic target of rapamycin), Wnt, and NF-κB (nuclear factor κB) under OA condition.

Mechanical stimulation of chondrocytes regulates HIF-1α under hypoxic conditions

We investigated the effects of hypoxia-inducible factor (HIF)-1α on articular cartilage under mechanical stimulation and the associated mechanisms. Chondrocytes, isolated from articular cartilage from the knee, hip, and shoulder joints of Wistar rats, were subjected to 20 % tensile stress under hypoxic (5% O₂) conditions for 24 h. HIF-1α and aggrecan expression was significantly enhanced with mechanical stimulation under hypoxia but not significantly altered with mechanical stimulation under normoxia. The nuclear translocation of HIF-1α was enhanced by mechanical stress under hypoxia. Under both normoxia and hypoxia, a disintegrin and metalloproteinase with thrombospondin motifs (ADAM-TS) 5 expression was significantly reduced with mechanical stimulation compared to that in the group without mechanical stimulation. However, HIF-1α knockdown mitigated changes in aggrecan and ADAM-TS5 expression mediated by mechanical stimulation under hypoxia. The effects of treadmill running on HIF-1α production in the articular cartilage of rat knee joints were also analyzed. HIF-1α production increased in the moderate running group and decreased to the same levels as those in the control group in the excessive running group. This suggests that HIF-1α regulates aggrecan and ADAM-TS5 expression in response to mechanical stimulation under hypoxia and general mechanical stimulation in articular cartilage under hypoxia, while controlling cartilage homeostasis.

Synovial Fibrosis Involvement in Osteoarthritis

Bone changes have always been the focus of research on osteoarthritis, but the number of studies on synovitis has increased only over the last 10 years. Our current understanding is that the mechanism of osteoarthritis involves all the tissues that make up the joints, including nerve sprouting, pannus formation, and extracellular matrix environmental changes in the synovium. These factors together determine synovial fibrosis and may be closely associated with the clinical symptoms of pain, hyperalgesia, and stiffness in osteoarthritis. In this review, we summarize the consensus of clinical work, the potential pathological mechanisms, the possible therapeutic targets, and the available therapeutic strategies for synovial fibrosis in osteoarthritis to gain insight and provide a foundation for further study.

miR-137 targets the inhibition of TCF4 to reverse the progression of osteoarthritis through the AMPK/NF-κB signaling pathway

Purpose: To explore the regulatory mechanism of miR-137 and transcription factor 4 (TCF4) in the progression of osteoarthritis (OA).

Patients and Methods: The expressions of miR-137 and TCF4 were detected in OA cartilage tissue, chondrocytes and OA rat cartilage tissue. miR-137 and TCF4 were up-regulated or down-regulated and transfected into chondrocytes and OA rat cartilage tissue. The gene expression, protein level, cell proliferation, apoptosis and inflammatory factors were detected, respectively. LPS and anterior cruciate ligament transection (ACLT) on the right knee were used to induce chondrocyte inflammation and establish rat OA model, respectively.

Results: miR-137 was low expressed in cartilage tissue of OA group, while TCF4 expression and protein level were significantly higher, showing significant negative correlation. In LPS group, chondrocyte activity was significantly inhibited, cell apoptosis ability was significantly enhanced, and the levels of inflammatory factors TNF-α, IL-1β, IL-6 were significantly increased. However, the above results were significantly improved after the up-regulation of miR-137 or down-regulation of TCF4. Double luciferase report revealed that miR-137 and TCF4 had targeted relationship. LPS induced activation of AMPK/NF-κB pathway and higher level of apoptosis. AMPK/NF-κB pathway inhibitor C could inhibit activation of this pathway, and up-regulation of miR-137 or down-regulation of TCF4 could significantly weaken the regulation of LPS on the pathway and apoptosis. Analysis of OA rat model showed that over-expression of miR-137 could inhibit up-regulation of inflammatory factors and activation of AMPK/NF-κB pathway.

Conclusion: miR-137 targets the inhibition of TCF4 to reverse the progression of OA through the AMPK/NF-κB signaling pathway.

d-Mannose suppresses osteoarthritis development in vivo and delays IL-1β-induced degeneration in vitro by enhancing autophagy activated via the AMPK pathway

Osteoarthritis (OA) is a heterogeneous disease that is consistently difficult to treat due to the complexity of the regulatory network involved in OA pathogenesis, especially in terms of cartilage degeneration. As a C-2 epimer of glucose, d-mannose can alleviate bone loss and repress immunopathology by upregulating regulatory T cells; however, the role of d-mannose in OA-related cartilage degeneration remains unknown. In this study, we investigated the chondroprotective effect of d-mannose in vitro and in vivo on OA. We found that incubating interleukin (IL)-1β-treated rat chondrocytes with d-mannose restrained OA degeneration by elevating cell proliferation, strongly activating autophagy, reducing apoptosis, and downregulating catabolism. Additionally, oral gavage administration of d-mannose to monosodium iodoacetate (MIA)-treated rats revealed that a median (1.25 g/kg/day) rather than high or low dose of d-mannose suppressed OA progression and attenuated OA development based on lower macroscopic scores for cartilage, decreased histological scores for cartilage and synovium, strongly activated autophagy, and downregulated catabolism. In terms of a downstream mechanism, we showed that d-mannose might attenuate OA degeneration by activating autophagy in IL-1β-treated rat chondrocytes by promoting the phosphorylation of 5' AMP-activated protein kinase (AMPK). Our in vitro findings revealed that d-mannose delayed IL-1β-induced OA degeneration in rat chondrocytes by enhancing autophagy activation through the AMPK pathway. Furthermore, the in vivo results indicated that a median dose of d-mannose suppressed MIA-induced OA development. These results suggested that d-mannose exhibits chondroprotective effects and represents a potential disease-modifying drug and novel therapeutic agent for OA.

Molecular mechanisms of mechanical load-induced osteoarthritis

INTRODUCTION

Mechanical loading enhances the progression of osteoarthritis. However, its molecular mechanisms have not been established.

OBJECTIVE

The aim of this review was to summarize the probable mechanisms of mechanical load-induced osteoarthritis.

METHODS

A comprehensive search strategy was used to search PubMed and EMBASE databases (from the 15th of January 2015 to the 20th of October 2020). Search terms included "osteoarthritis", "mechanical load", and "mechanism".

RESULTS

Abnormal mechanical loading activates the interleukin-1β, tumour necrosis factor-α, nuclear factor kappa-B, Wnt, transforming growth factor-β, microRNAs pathways, and the oxidative stress pathway. These pathways induce the pathological progression of osteoarthritis. Mechanical stress signal receptors such as integrin, ion channel receptors, hydrogen peroxide-inducible clone-5, Gremlin-1, and transient receptor potential channel 4 are present in the articular cartilages.

CONCLUSION

This review highlights the molecular mechanisms of mechanical loading in inducing chondrocyte apoptosis and extracellular matrix degradation. These mechanisms provide potential targets for osteoarthritis prevention and treatment.

Moderate Mechanical Stimulation Protects Rats against Osteoarthritis through the Regulation of TRAIL via the NF-κB/NLRP3 Pathway

The aim of this study was to examine exercise-related genes in articular cartilage identified through bioinformatics analysis to dissect the potential signaling pathway involved in mechanical stimulation in osteoarthritis (OA). To this end, we evaluated the GSE74898 dataset from the Gene Expression Omnibus database for exercise-related differentially expressed miRNAs (DE-miRNAs) using the R software package and predicted potential target genes for these miRNAs using miRTarBase. Functional annotation and pathway enrichment analysis were performed for these potential DE-miRNA targets. The effects of mechanical stimulation on the tumor necrosis factor-related apoptosis-induced ligand (TRAIL)/nuclear factor-kappa B (NF-κB)/nucleotide-binding and oligomerization domain-like receptor containing protein 3 (NLRP3) signaling pathway were evaluated in articular cartilage and chondrocytes. A total of 394 DE-miRNAs were identified (103 upregulated miRNAs; 291 downregulated miRNAs) in the cartilage of rats following treadmill exercise compared to the cartilage of unexercised control rats. Thus, mechanical stimulation could modulate the TRAIL/NF-κB/NLRP3 signaling pathway on OA. Histological and protein analysis demonstrated that moderate-intensity treadmill exercise could ameliorate OA through the downregulation of TRAIL. Furthermore, moderate cyclic tensile strain (CTS) could rescue chondrocytes from the effects of TRAIL via the inhibition of the nuclear translocation of NF-κB p65 and formation of NLRP3. Our findings indicate that moderate mechanical stimulation could ameliorate the degeneration of cartilage and chondrocyte damage through the inhibition of the TRAIL/NF-κB/NLRP3 pathway.

Protectin DX attenuates IL-1β-induced inflammation via the AMPK/NF-κB pathway in chondrocytes and ameliorates osteoarthritis progression in a rat model

Protectin DX (PDX) has been reported to have extensive anti-inflammatory effects. However, it is unknown whether PDX acts as an anti-inflammatory agent in the context of osteoarthritis (OA). This study aimed to evaluate the anti-inflammatory activity of PDX in vitro and in vivo in a model of OA. Primary rat chondrocytes were preincubated with PDX 1 h prior to IL-1β treatment for 24 h. We found that PDX was nontoxic, and pretreatment with PDX increased cell viability in IL-1β-induced chondrocytes. Preincubation with PDX also efficiently inhibited the degradation of type II collagen dose-dependently. Additionally, the expression of MMP-3, MMP-13, ADAMTS4, iNOS, COX-2, NO, and PGE2 decreased after IL-1β stimulation when cells were preincubated with PDX. Moreover, PDX inhibited the increase in phosphorylated NF-κB p65 and IκBα upon IL-1β stimulation, and the negative effects of IL-1β on chondrocytes were partially blocked by treatment with pyrrolidine dithiocarbamate (PDTC), a selective NF-κB inhibitor. In addition, we found that PDX increased AMPK phosphorylation in IL-1β-mediated chondrocytes. The phosphorylation of AMPK could be inhibited by compound C, a classic AMPK inhibitor. Compound C also remarkably reversed the decrease in p65 phosphorylation and MMP-13 expression caused by PDX. Furthermore, nuclear translocation of NF-κB was visible by immunofluorescence after PDX-induced AMPK activation. Additionally, we verified that PDX ameliorated cartilage degradation in monosodium iodoacetate (MIA)-induced OA rats through histological evaluation and ELISA of TNF-α in the serum and intra-articular lavage fluid. In conclusion, we have shown that PDX suppresses inflammation in chondrocytes in vitro and in vivo, likely through the AMPK/NF-κB signaling pathway. Our results suggest that PDX could be a useful novel therapeutic agent for OA treatment.

MicroRNA-365 functions as a mechanosensitive microRNA to inhibit end plate chondrocyte degeneration by targeting histone deacetylase 4

End plate chondrocyte degeneration is a major cause of intervertebral disc degeneration. Mechanical biophysical forces, including intermittent cyclic mechanical tension (ICMT), exacerbate end plate chondrocyte degeneration. However, the underlying molecular mechanism of mechanical stretch-induced end plate chondrocyte degeneration is still unclear. This study sought to determine whether microRNAs (miRNAs) respond to mechanical stretch and play a role in regulating mechanically-induced end plate chondrocyte degeneration. We identified miR-365 as a mechanoresponsive miRNA in primary human end plate chondrocytes after ICMT application by miRNA microarray analysis. The expression of miR-365 was down-regulated in the disc samples obtained from patients with disc degeneration. We also found that the miR-365 stimulates chondrocyte proliferation but does not promote end plate chondrocyte death. Using bioinformatic analyses and subsequent confirmation by real-time RT-PCR, we identified multiple candidate target genes of miR-365 that responded to in vitro mechanical stimulation; among them, HDAC4 was fully characterized. Mutation of putative miR-365 binding sites in HDAC4 mRNA abolished miR-365 mediated repression of HDAC4 3'-untranslated region (3'UTR) luciferase reporter activity, suggesting that miR-365 binds to the HDAC4 3'UTR. Overexpression of miR-365 significantly decreased the HDAC4 protein level, suggesting that miR-365 acts as an endogenous attenuator of HDAC4 in human end plate chondrocytes. Further, perturbation of miR-365 expression also had a significant effect on the expression of COL2A and ACAN and on matrix degeneration. Overexpression of HDAC4 abolished miR-365 rescued end plate chondrocyte degeneration during ICMT application. Furthermore, we found that the wnt/β-catenin signal pathway was related to HDAC4 and promoted end plate chondrocyte degeneration. Overall, our results suggest that miR-365 is a mechanosensitive miRNA that regulates human chondrocyte degeneration by directly targeting HDAC4. We propose that therapeutic regulation of miR-365 may be an efficient anabolic strategy for inhibiting end plate chondrocyte degeneration.

Catalpol Attenuates IL-1β Induced Matrix Catabolism, Apoptosis and Inflammation in Rat Chondrocytes and Inhibits Cartilage Degeneration

BACKGROUND Chondrocyte dysfunction and apoptosis are 2 major features during the progression of osteoarthritis. Catalpol, an iridoid glycoside isolated from the root of Rehmannia, is a valuable medication with anti-inflammatory, anti-oxidative, and anti-apoptotic effects in various diseases. However, whether catalpol protects against osteoarthritis has not been investigated. MATERIAL AND METHODS To assess the role of catalpol in osteoarthritis and the potential mechanism of action, chondrocytes were treated with interleukin (IL)-1ß and various concentrations of catalpol. Catabolic metabolism, apoptotic level and relative signaling pathway were measured by western blot, real-time polymerase chain reaction and immunofluorescence staining. Meanwhile, we assess the cartilage degeneration in an experimental rat model using Safranin O fast green staining and cartilage was graded according to the Osteoarthritis Research Society International (OARSI) system. RESULTS The results showed that catalpol prevented chondrocyte apoptotic level triggered by IL-1ß, suppressed the release of catabolic enzymes, and inhibited the degradation of extracellular matrix induced by IL-1ß. Catalpol also inhibited the nuclear factor kappa B (NF-kappaB) pathway, reduced the production of inflammatory cytokines (IL-6, tumor necrosis factor-alpha) in IL-1ß-treated chondrocytes, and partially reversed cartilage degeneration in the knee joint in animal model of osteoarthritis. CONCLUSIONS Our work suggested that catalpol treatment attenuates IL-1ß-induced inflammatory response and catabolism in rat chondrocytes by inhibiting the NF-kappaB pathway, suggesting the therapeutic potential of catalpol for the treatment of osteoarthritis.

Cyclic tensile strain promotes the ECM synthesis of cranial base synchondrosis chondrocytes by upregulating miR-140-5p

OBJECTIVE

This study aimed to explore the role of miR-140-5p in cranial base synchondrosis chondrocytes (CBSCs) under cyclic tensile strain (CTS).

SETTING AND SAMPLE POPULATION

A total of 25 1-week-old Sprague Dawley rats from Shanghai Laboratory Animal Center, Chinese Academy of Sciences, were used.

MATERIAL AND METHODS

The second passage of CBSCs was applied with CTS at 10% elongation (1 Hz) for 24 hours. MiR-140-5p levels in CBSCs were detected by qRT-PCR. The role of miR-140-5p in CBSCs was evaluated by transfection of mimics and inhibitor. RNA sequencing and online search of miRNA databases (TargetScan, miRDB and miRanda) were used in prediction of miR-140-5p targets. A luciferase reporter assay was applied to identify the target gene of miR-140-5p.

RESULTS

Compared with the control, the expression of Col2a1 and Sox9 was significantly higher after CTS (P < .05). Also, CBSCs demonstrated higher expression of miR-140-5p after CTS loading for 24 hours (P < .05). Overexpression of miR-140-5p promoted ECM synthesis under CTS loading environment, while suppression of miR-140-5p inhibited the effect. Bloc1s2 was a putative target gene of miR-140-5p.

CONCLUSIONS

The expression of ECM in CBSCs could be promoted by CTS and miR-140-5p might play a role in this process through targeting Bloc1s2.

The Therapeutic Effects of Treadmill Exercise on Osteoarthritis in Rats by Inhibiting the HDAC3/NF-KappaB Pathway in vivo and in vitro

Osteoarthritis (OA) is a disease characterized by non-bacterial inflammation. Histone deacetylase 3 (HDAC3) is a crucial positive regulator in the inflammation that leads to the development of non-OA inflammatory disease. However, the precise involvement of HDAC3 in OA is still unknown, and the underlying mechanism of exercise therapy in OA requires more research. We investigated the involvement of HDAC3 in exercise therapy-treated OA. Expression levels of HDAC3, a disintegrin and metalloproteinase with thrombospondin motifs-5 (ADAMTS-5), matrix metalloproteinase-13 (MMP-13), HDAC3 and nuclear factor-kappaB (NF-kappaB) were measured by western blotting, reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry. Cartilage damage and OA evaluation were measured by hematoxylin and eosin staining and Toluidine blue O staining according to the Mankin score and OARSI score, respectively. We found that moderate-intensity treadmill exercise could relieve OA. Meanwhile, the expression of HDAC3, MMP-13, ADAMTS-5 and NF-kappaB decreased, and collagen II increased in the OA + moderate-intensity treadmill exercise group (OAM) compared with the OA group (OAG) or OA + high- or low-intensity treadmill exercise groups (OAH or OAL). Furthermore, we found the selective HDAC3 inhibitor RGFP966 could also alleviate inflammation in OA rat model through inhibition of nuclear translocation of NF-kappaB. To further explore the relationship between HDAC3 and NF-kappaB, we investigated the change of NF-kappaB relocation in IL-1β-treated chondrocytes under the stimulation of RGFP966. We found that RGFP966 could inhibit the expression of inflammatory markers of OA via regulation of HDAC3/NF-kappaB pathway. These investigations revealed that RGFP966 is therefore a promising new drug for treating OA.

Mechanical strain attenuates cytokine-induced ADAMTS9 expression via transient receptor potential vanilloid type 1

The synovial fluids of patients with osteoarthritis (OA) contain elevated levels of inflammatory cytokines, which induce the expression of a disintegrin and metalloproteinase with thrombospondin motifs (ADAMTS) and of the matrix metalloproteinase (MMP) in chondrocytes. Mechanical strain has varying effects on organisms depending on the strength, cycle, and duration of the stressor; however, it is unclear under inflammatory stimulation how mechanical strain act on. Here, we show that mechanical strain attenuates inflammatory cytokine-induced expression of matrix-degrading enzymes. Cyclic tensile strain (CTS), as a mechanical stressor, attenuated interleukin (IL)-1β and tumor necrosis factor (TNF)-α-induced mRNA expression of ADAMTS4, ADAMTS9, and MMP-13 in normal chondrocytes (NHAC-kn) and in a chondrocytic cell line (OUMS-27). This effect was abolished by treating cells with mechano-gated channel inhibitors, such as gadolinium, transient receptor potential (TRP) family inhibitor, ruthenium red, and with pharmacological and small interfering RNA-mediated TRPV1 inhibition. Furthermore, nuclear factor κB (NF-κB) translocation from the cytoplasm to the nucleus resulting from cytokine stimulation was also abolished by CTS. These findings suggest that mechanosensors such as the TRPV protein are potential therapeutic targets in treating OA.

The Emerging Role of Glucose Metabolism in Cartilage Development

PURPOSE OF REVIEW

Proper cartilage development is critical to bone formation during endochondral ossification. This review highlights the current understanding of various aspects of glucose metabolism in chondrocytes during cartilage development.

RECENT FINDINGS

Recent studies indicate that chondrocytes transdifferentiate into osteoblasts and bone marrow stromal cells during endochondral ossification. In cartilage development, signaling molecules, including IGF2 and BMP2, tightly control glucose uptake and utilization in a stage-specific manner. Perturbation of glucose metabolism alters the course of chondrocyte maturation, suggesting a key role for glucose metabolism during endochondral ossification. During prenatal and postnatal growth, chondrocytes experience bursts of nutrient availability and energy expenditure, which demand sophisticated control of the glucose-dependent processes of cartilage matrix production, cell proliferation, and hypertrophy. Investigating the regulation of glucose metabolism may therefore lead to a unifying mechanism for signaling events in cartilage development and provide insight into causes of skeletal growth abnormalities.

Mechanical stress protects against osteoarthritis via regulation of the AMPK/NF-κB signaling pathway

Mechanical stress plays a key role in regulating cartilage degradation in osteoarthritis (OA). The aim of this study was to evaluate the effects and mechanisms of mechanical stress on articular cartilage. A total of 80 male Sprague‐Dawley rats were randomly divided into eight groups (n = 10 for each group): control group (CG), OA group (OAG), and CG or OAG subjected to low‐, moderate‐, or high‐intensity treadmill exercise (CL, CM, CH, OAL, OAM, and OAH, respectively). Chondrocytes were obtained from the knee joints of rats; they were cultured on Bioflex 6‐well culture plates and subjected to different durations of cyclic tensile strain (CTS) with or without exposure to interleukin‐1β (IL‐1β). The results of the histological score, immunohistochemistry, enzyme‐linked immunosorbent assay, and western‐blot analyses indicated that there were no differences between CM and CG, but OAM showed therapeutic effects compared with OAG. However, CH and OAH experienced more cartilage damage than CG and OAG, respectively. CTS had no therapeutic effects on collagen II of normal chondrocytes, which is consistent with findings after treadmill exercise. However, CTS for 4 hr could alleviate the chondrocyte damage induced by IL‐1β by activating AMP‐activated protein kinase (AMPK) phosphorylation and suppressing nuclear translocation of nuclear factor (NF)‐κB p65. Our findings indicate that mechanical stress had no therapeutic effects on normal articular cartilage and chondrocytes; mechanical stress only caused damage with excessive stimulation. Still, moderate biomechanical stress could reduce sensitization to the inflammatory response of articular cartilage and chondrocytes through the AMPK/NF‐κB signaling pathway.