Moderate-intensity exercise alleviates pyroptosis by promoting autophagy in osteoarthritis via the P2X7/AMPK/mTOR axis

New insights into the function of the NLRP3 inflammasome in sarcopenia: mechanism and therapeutic strategies

Sarcopenia is one of the most common skeletal muscle disorders and is characterized by infirmity and disability. While extensive research has focused on elucidating the mechanisms underlying the progression of sarcopenia, further comprehensive insights into its pathogenesis are necessary to identify new preventive and therapeutic approaches. The involvement of inflammasomes in sarcopenia is widely recognized, with particular emphasis on the NLRP3 (NLR family pyrin domain containing 3) inflammasome. In this review, we aim to elucidate the underlying mechanisms of the NLRP3 inflammasome and its relevance in sarcopenia of various etiologies. Furthermore, we highlight interventions targeting the NLRP3 inflammasome in the context of sarcopenia and discuss the current limitations of our knowledge in this area.

Miao medicine Gu Yan Xiao tincture inhibits mTOR to stimulate chondrocyte autophagy in a rabbit model of osteoarthritis

ETHNOPHARMACOLOGICAL RELEVANCE

The Gu Yan Xiao tincture, a blend of traditional Chinese herbs, is traditionally used for osteoarthritis and related pain. This study investigated its mechanism of action in order to rationalize and validate its therapeutic use.

AIM OF THE STUDY

This study analyzed, in a rabbit model of knee osteoarthritis, whether and how Gu Yan Xiao tincture exerts therapeutic benefits by modulating chondrocyte autophagy.

MATERIALS AND METHODS

The active constituents within the GYX tincture were identified using liquid chromatography-mass spectrometry. The rabbit model was established by injecting animals with type II collagenase intra-articularly, and the effects of topically applied tincture were examined on osteoarthritis lesions of the knee using histopathology, micro-computed tomography and x-ray imaging. Effects of the tincture were also evaluated on levels of inflammatory cytokines, matrix metalloproteases, and autophagy in chondrocytes. As a positive control, animals were treated with sodium diclofenac.

RESULTS

The tincture mitigated the reduction in joint space, hyperplasia of the synovium and matrix metalloproteases in serum that occurred after injection of type II collagenase in rabbits. These therapeutic effects were associated with inhibition of mTOR and activation of autophagy in articular chondrocytes. Inhibiting mTOR with rapamycin potentiated the therapeutic effects of the tincture, while inhibiting autophagy with 3-methyladenine antagonized them.

CONCLUSIONS

Gu Yan Xiao tincture mitigates tissue injury in a rabbit model of osteoarthritis, at least in part by inhibiting mTOR and thereby promoting autophagy in chondrocytes. These results rationalize the use of the tincture not only against osteoarthritis but also potentially other diseases involving inhibition of autophagy in bones and joints.

Pyroptosis: A spoiler of peaceful coexistence between cells in degenerative bone and joint diseases

BACKGROUND

As people age, degenerative bone and joint diseases (DBJDs) become more prevalent. When middle-aged and elderly people are diagnosed with one or more disorders such as osteoporosis (OP), osteoarthritis (OA), and intervertebral disc degeneration (IVDD), it often signals the onset of prolonged pain and reduced functionality. Chronic inflammation has been identified as the underlying cause of various degenerative diseases, including DBJDs. Recently, excessive activation of pyroptosis, a form of programed cell death (PCD) mediated by inflammasomes, has emerged as a primary driver of harmful chronic inflammation. Consequently, pyroptosis has become a potential target for preventing and treating DBJDs.

AIM OF REVIEW

This review explored the physiological and pathological roles of the pyroptosis pathway in bone and joint development and its relation to DBJDs. Meanwhile, it elaborated the molecular mechanisms of pyroptosis within individual cell types in the bone marrow and joints, as well as the interplay among different cell types in the context of DBJDs. Furthermore, this review presented the latest compelling evidence supporting the idea of regulating the pyroptosis pathway for DBJDs treatment, and discussed the potential, limitations, and challenges of various therapeutic strategies involving pyroptosis regulation.

KEY SCIENTIFIC CONCEPTS OF REVIEW

In summary, an interesting identity for the unregulated pyroptosis pathway in the context of DBJDs was proposed in this review, which was undertaken as a spoiler of peaceful coexistence between cells in a degenerative environment. Over the extended course of DBJDs, pyroptosis pathway perpetuated its activity through crosstalk among pyroptosis cascades in different cell types, thus exacerbating the inflammatory environment throughout the entire bone marrow and joint degeneration environment. Correspondingly, pyroptosis regulation therapy emerged as a promising option for clinical treatment of DBJDs.

Endurance exercise preconditioning alleviates ferroptosis induced by doxorubicin-induced cardiotoxicity through mitochondrial superoxide-dependent AMPKα2 activation

Doxorubicin-induced cardiotoxicity (DIC) adversely impacts patients' long-term health and quality of life. Its underlying mechanism is complex, involving regulatory cell death mechanisms, such as ferroptosis and autophagy. Moreover, it is a challenge faced by patients undergoing cardiac rehabilitation. Endurance exercise (E-Exe) preconditioning effectively counters DIC injury, potentially through the adenosine monophosphate-activated protein kinase (AMPK) pathway. However, detailed studies on this process's mechanisms are scarce. Here, E-Exe preconditioning and DIC models were established using mice and primary cultured adult mouse cardiomyocytes (PAMCs). Akin to ferrostatin-1 (ferroptosis inhibitor), rapamycin (autophagic inducer), and MitoTEMPO (mitochondrial free-radical scavenger), E-Exe preconditioning effectively alleviated Fe2+ accumulation and oxidative stress and improved energy metabolism and mitochondrial dysfunction in DIC injury, as demonstrated by multifunctional, enzymatic, and morphological indices. However, erastin (ferroptosis inducer), 3-methyladenine (autophagic inhibitor), adenovirus-mediated AMPKα2 downregulation, and AMPKα2 inhibition by compound C significantly diminished these effects, both in vivo and in vitro. The results suggest a non-traditional mechanism where E-Exe preconditioning, under mild mitochondrial reactive oxygen species generation, upregulates and phosphorylates AMPKα2, thereby enhancing mitochondrial complex I activity, activating adaptive autophagy, and improving myocardial tolerance to DIC injury. Overall, this study highlighted the pivotal role of mitochondria in myocardial DIC-induced ferroptosis and shows how E-Exe preconditioning activated AMPKα2 against myocardial DIC injury. This suggests that E-Exe preconditioning could be a viable strategy for patients undergoing cardiac rehabilitation.

The dysregulated autophagy in osteoarthritis: Revisiting molecular profile

The risk factors of osteoarthritis (OA) are different and obesity, lifestyle, inflammation, cell death mechanisms and diabetes mellitus are among them. The changes in the biological mechanisms are considered as main regulators of OA pathogenesis. The dysregulation of autophagy is observed in different human diseases. During the pathogenesis of OA, the autophagy levels (induction or inhibition) change. The supportive and pro-survival function of autophagy can retard the progression of OA. The protective autophagy prevents the cartilage degeneration. Moreover, autophagy demonstrates interactions with cell death mechanisms and through inhibition of apoptosis and necroptosis, it improves OA. The non-coding RNA molecules can regulate autophagy and through direct and indirect control of autophagy, they dually delay/increase OA pathogenesis. The mitochondrial integrity can be regulated by autophagy to alleviate OA. Furthermore, therapeutic compounds, especially phytochemicals, stimulate protective autophagy in chondrocytes to prevent cell death. The protective autophagy has ability of reducing inflammation and oxidative damage, as two key players in the pathogenesis of OA.

FOXQ1 inhibits the progression of osteoarthritis by regulating pyroptosis

BACKGROUND

Osteoarthritis (OA) is the most common age-related joint disease, and the NLRP3-induced pyroptosis has been demonstrated in its progression. The upstream molecules or specific mechanisms controlling NLRP3 and pyroptosis in OA remain unclear.

METHODS

Transcriptome sequencing was performed in the OA mice model, and the expression levels of differentially expressed genes were assessed by qRT-PCR. The cell model was constructed by IL-1β-induced ATDC5 cells. The cell proliferation was examined using CCK-8 assay, and apoptosis was tested using flow cytometry. Western blot was used in protein inspection, and ELISA was used in inflammatory response evaluation.

RESULTS

Compared with the control group, there were 229 up-regulated and 32 down-regulated genes in model group. We detected that FOXQ1 was down-regulated in the OA mice model, improved proliferation, and restrained apoptosis of chondrocytes. Over-expression of FOXQ1 could inhibit pyroptosis-related proteins and inflammatory cytokines, containing NLRP3, Caspase-1, GSDMD, IL-6, IL-18, and TNF-α, and in contrast, FOXQ1 silencing exerted the opposite trend.

CONCLUSIONS

FOXQ1 may inhibit OA progression via down-regulating NLRP3-induced pyroptosis in the present study.

MiR-29a-3p mediates phosphatase and tensin homolog and inhibits osteoarthritis progression

Despite substantial progress in clinical trials of osteoarthritis (OA) gene therapy, the prevalence of OA is still on the rise. MiRNAs have a potential biomarker and therapeutic target for OA. OA cartilage and chondrosarcoma cells were studied to determine the role of miR-29a-3p and PTEN. OA cartilage and human chondrosarcoma cells (SW1353) were obtained. miR-29a-3p and PTEN signature expression was determined by RT-qPCR. The binding relationship between miR-29a-3p and PTEN was investigated by dual-luciferase reporter gene and western blot assay. TUNEL, immunohistochemistry, CCK-8, and flow cytometry were utilized to determine the proliferation and apoptosis of SW1353 cells. This study indicated downregulation of miR-29a-3p expression and upregulation of PTEN expression in human OA primary chondrocytes or OA tissue samples, compared with the normal cartilage cells or tissues. PTEN expression was negatively correlated with miR-29a-3p expression, and miR-29a-3p targeted PTEN mechanistically. miR-29a-3p reduced SW1353 cell activity and proliferation and promoted cell apoptosis. However, the aforementioned effects could be reversed by downregulating PTEN. miR-29a-3p can stimulate chondrocyte proliferation and inhibit apoptosis by inhibiting PTEN expression.

PPAR γ activation in chondrocytes alleviates glucocorticoid-induced oxidative stress, mitochondrial impairment, and pyroptosis via autophagic flow enhancement

Osteoarthritis (OA) is a progressive age-related disease characterised by pathological changes in the synovium, articular cartilage, and subchondral bone, significantly reducing the patients' quality of life. This study investigated the role of glucocorticoids, specifically dexamethasone, in OA progression, with a particular focus on their effects on chondrocytes. Although glucocorticoids are commonly used for OA pain relief, our research demonstrated that high concentrations of dexamethasone may accelerate OA progression by enhancing the ability of reactive oxygen species to inhibit chondrocyte autophagy, resulting in cell death and accelerated cartilage degeneration. Despite reports on the acceleration of pathogenesis and cartilage damage in some patients of OA taking corticosteroids, the mechanism behind the same has not been investigated. This necessitates an investigation of the concentration-dependent changes in the cartilage cells upon dexamethasone administration. In addition, the protective effect of PPAR γ on chondrocytes can prevent the decrease in chondrocyte autophagy and delay cartilage degeneration. Therefore, our study suggests that the therapeutic use of glucocorticoids in OA treatment should be more nuanced considering their potential detrimental effects. Future investigations should focus on the mechanisms underlying the glucocorticoid-mediated modulation of cell death processes, which could provide insights into new therapeutic strategies for OA treatment.

Lei's formula attenuates osteoarthritis mediated by suppression of chondrocyte senescence via the mTOR axis: in vitro and in vivo experiments

Lei's formula (LSF), a traditional Chinese herbal remedy, is recognized for its remarkable clinical effectiveness in treating osteoarthritis (OA). Despite its therapeutic potential, the exact molecular mechanisms underlying LSF's action in OA have remained enigmatic. Existing research has shed light on the role of the mTOR signaling pathway in promoting chondrocyte senescence, a central factor in OA-related cartilage degeneration. Consequently, targeting mTOR to mitigate chondrocyte senescence presents a promising avenue for OA treatment. The primary objective of this study is to establish LSF's chondroprotective potential and confirm its anti-osteoarthritic efficacy through mTOR inhibition. In vivo assessments using an OA mouse model reveal substantial articular cartilage degeneration. However, LSF serves as an effective guardian of articular cartilage, evidenced by reduced subchondral osteosclerosis, increased cartilage thickness, improved surface smoothness, decreased OARSI scores, elevated expression of cartilage anabolic markers (Col2 and Aggrecan), reduced expression of catabolic markers (Adamts5 and MMP13), increased expression of the chondrocyte hypertrophy marker (Col10), and decreased expression of chondrocyte senescence markers (P16 and P21). In vitro findings demonstrate that LSF shields chondrocytes from H2O2-induced apoptosis, inhibits senescence, enhances chondrocyte differentiation, promotes the synthesis of type II collagen and proteoglycans, and reduces cartilage degradation. Mechanistically, LSF suppresses chondrocyte senescence through the mTOR axis, orchestrating the equilibrium between chondrocyte anabolism and catabolism, ultimately leading to reduced apoptosis and decelerated OA cartilage degradation. LSF holds significant promise as a therapeutic approach for OA treatment, offering new insights into potential treatments for this prevalent age-related condition.

Pharmacological inhibition of ICOS attenuates the protective effect of exercise on cardiac fibrosis induced by isoproterenol

AIMS

To investigate the cardioprotective mechanism of exercise or exercise combined with inducible costimulatory molecules (ICOS) monoclonal antibody (mAb) therapy against isoproterenol (ISO)-induced cardiac remodeling.

MAIN METHODS

Totally 24 male C57BL/6J mice were randomly divided into four groups: the control group (normal saline treatment), ISO group (subcutaneous injection of isoproterenol, 10 mg/kg/day, once daily for 5 consecutive days), the exercise with subcutaneous ISO injection group (EPI), and the exercise with injected with ISO and ICOS mAb group (EPII). The mice in EPI and EPII group were trained on a small animal treadmill for 4 weeks (13 m/min, 0% grade, 60min/day).

KEY FINDINGS

Exercise significantly attenuated CD45+, Mac-2 inflammatory cell infiltration, cardiac fibrosis and inhibited the RIPK1/RIPK3/MLKL/CaMKII and cardiomyocyte pyroptosis pathways to counter ISO-induced severe cardiac injury. The administration of the ICOS mAb may inhibit the cardioprotection of exercise against ISO-induced heart damage. Compared to those in EPI, our data showed that the increasing levels of myocardial fibrosis, the leukocyte infiltration of cardiac tissue and proteins expression of cardiac myocyte necrosis and pyroptosis signaling pathways in the EPII group.

SIGNIFICANCE

Our results demonstrated that exercise decreased leukocyte infiltration in heart, inhibited the cardiomyocyte pyroptosis and necroptosis signaling pathways, and attenuated inflammatory responses to alleviate ISO-induced cardiac fibrosis. However, the antifibrotic effects of combined treatment with exercise and ICOS mAb intervention did not exhibit synergistic enhancement.

Exercise, Spinal Microglia and Neuropathic Pain: Potential Molecular Mechanisms

As one of the most common neuropathic disorders, neuropathic pain often has a negative impact on patients with persistent pain, mood disorders and sleep disturbances. Currently, neuropathic pain is not treated with any specific drug, instead, drugs for other diseases are used as replacements in clinics, but most have adverse effects. In recent years, the role of spinal cord microglia in the pathogenesis of neuropathic pain has been widely recognized, and they are being explored as potential therapeutic targets. Spinal microglia are known to be involved in the pathogenic mechanisms of neuropathic pain through purine signaling, fractalkine signaling, and p38 MAPK signaling. Exercise is a safe and effective treatment, and numerous studies have demonstrated its effectiveness in improving neurological symptoms. Nevertheless, it remains unclear what the exact molecular mechanism is. This review summarized the specific molecular mechanisms of exercise in alleviating neuropathic pain by mediating the activity of spinal microglia and maintaining the phenotypic homeostasis of spinal microglia through purine signaling, fractalkine signaling and p38 MAPK signaling. In addition, it has been proposed that different intensities and types of exercise affect the regulation of the above-mentioned signaling pathways differently, providing a theoretical basis for the improvement of neuropathic pain through exercise.

Recent advances in caspase-3, breast cancer, and traditional Chinese medicine: a review

Caspases (cysteinyl aspartate-specific proteinases) are a group of structurally similar proteases in the cytoplasm that can be involved in cell differentiation, programmed death, proliferation, and inflammatory generation. Experts have found that caspase-3 can serve as a terminal splicing enzyme in apoptosis and participate in the mechanism by which cytotoxic drugs kill cancer cells. Breast cancer (BC) has become the most common cancer among women worldwide, posing a severe threat to their lives. Finding new therapeutic targets for BC is the primary task of contemporary physicians. Numerous studies have revealed the close association between caspase-3 expression and BC. Caspase-3 is essential in BC's occurrence, invasion, and metastasis. In addition, Caspase-3 exerts anticancer effects by regulating cell death mechanisms. Traditional Chinese medicine acting through caspase-3 expression is increasingly used in clinical treatment. This review summarizes the biological mechanism of caspase-3 and research progress on BC. It introduces a variety of traditional Chinese medicine related to caspase-3 to provide new ideas for the clinical treatment of BC.

Advances in understanding effects of miRNAs on apoptosis, autophagy, and pyroptosis in knee osteoarthritis

MicroRNAs (miRNAs) are a class of endogenous small non-coding RNAs. MicroRNAs-mediated signaling pathways play a critical regulatory role in inducing apoptosis, autophagy, and pyroptosis in developing knee osteoarthritis (KOA). Given this, we searched databases, such as PubMed, using keywords including "miRNA," "knee osteoarthritis," "apoptosis," "autophagy," "pyroptosis", and their combinations. Through an extensive literature review, we conclude that miRNAs can be modulated through various signaling pathways, such as Wnt/β-catenin, TGF-β, PI3K/AKT/mTOR, and NLRP3/Caspase-1, to regulate apoptosis, autophagy, and pyroptosis in KOA. Furthermore, we note that P2X7R and HMGB1 may be crucial regulatory molecules involved in the interconnected regulation of apoptosis, autophagy, and pyroptosis in KOA. Additionally, we describe that miR-140-5p and miR-107 can modulate the advancement of KOA chondrocytes by targeting distinct molecules involved in apoptosis, autophagy, and pyroptosis, respectively. Therefore, we conclude that miRNAs may be potential biomarkers and therapeutic targets for the early prediction, diagnosis, and effective therapeutic approaches of KOA.

METTL3 Regulates the m6A Modification of NEK7 to Inhibit the Formation of Osteoarthritis

OBJECTIVE

Osteoarthritis (OA) is a common degenerative joint disease. The occurrence of OA slowly destroys the soft tissue structure of the patient's joint. Severe cases could lead to disability. Current studies had shown that inhibition of chondrocytes pyroptosis could slow down the progression of OA. Our work aimed to explore the specific mechanisms and ways of regulating this process.

DESIGN

In this work, the level of N6-methyladenosine (m6A) in clinical tissues was detected by ribonucleic acid (RNA) m6A dot blot. qRT-PCR (quantitative real-time polymerase chain reaction) was used to detect the messenger RNA (mRNA) expression level of m6A modified enzyme in clinical tissues. MTT (3-(4,5)-dimethylthiahiazo(-z-y1)-3,5-di-phenytetrazoliumromid) and flow cytometry were used to detect the effect of sh-METTL3 (methyltransferase like 3) and NIMA-related kinase 7 (NEK7) transfection on chondrocytes pyroptosis in OA. Western blot was used to detect the protein expression levels of pyroptosis-related proteins. ELISA (enzyme-linked immunosorbent assay) was used to measure the protein concentration of inflammatory cytokines. The SRAMP online database was used to predict the m6A site of NEK7. HE staining was used to assess the progression of OA in mice.

RESULTS

The level of m6A in clinical samples of OA patients was higher, and METTL3 was significantly higher expressed in clinical samples of OA patients. We provided evidence that low expression of METTL3 inhibited chondrocytes pyroptosis. In addition, Rescue experiments and in vivo experiments had shown that METTL3 in combination with NEK7 inhibited the progression of OA by promoting chondrocytes pyroptosis.

CONCLUSIONS

METTL3 regulates m6A modification of NEK7 and inhibits OA progression.

SNORC knockdown alleviates inflammation, autophagy defect and matrix degradation of chondrocytes in osteoarthritis development

Excessive inflammation and autophagy defect of chondrocytes play important roles in the pathological process of osteoarthritis (OA). The present study aimed to clarify the roles of small novel rich in cartilage (SNORC) in these pathological changes of chondrocytes in OA. Bioinformatics analysis of GEO dataset GSE207881 displayed that SNORC was a potential biomarker for OA. As confirmed by quantitative real-time PCR, immunohistochemical staining and western blotting, SNORC was significantly up-regulated in cartilage of OA rat model and interleukin (IL)-1β-stimulated primary rat articular chondrocytes in contrast to their corresponding normal control. Knocking down SNORC in IL-1β-induced chondrocytes obviously suppressed the production of nitric oxide (NO), IL-6, tumor necrosis factor (TNF)-α and prostaglandin E2 (PGE2) to alleviate inflammation, and reduced the protein levels of a disintegrin and metalloproteinase with thrombospondin 5 (ADAMTS5) and matrix metallopeptidase (MMP)13 and elevated collagen type 2 alpha 1 (COL2A1) level to improve matrix degradation. Down-regulation of SNORC increased Beclin1 expression and LC3II/LC3I ratio, but suppressed p62 expression to restore impaired autophagy in IL-1β-induced chondrocytes. Moreover, down-regulating SNORC mitigated mitochondrial dysfunction and apoptosis in IL-1β-stimulated chondrocytes. Mechanically, SNORC simultaneously activated the phosphatidylinositol-3-kinase/serine threonine kinase (PI3K/AKT) and c-Jun N-terminal kinase (JNK)/c-Jun signaling pathway in the IL-1β-induced chondrocyte, while re-activating the PI3K and JNK signals abolished the suppressive effect of down-regulating SNORC on IL-1β-induced chondrocyte damage. In a word, SNORC knockdown alleviates inflammation, matrix degradation, autophagy defect and excessive apoptosis of chondrocytes during OA development via suppressing the PI3K and JNK signaling pathway.

Isoflurane Enhances Autophagy by Activating AMPK/ULK1, Inhibits NLRP3, and Reduces Cognitive Impairment After Cerebral Ischemia-Reperfusion Injury in Rats

Cerebral ischemic stroke (CIS) has become the second leading cause of death worldwide, which is largely related to cerebral ischemia reperfusion injury (CIRI). Surgical intervention is a reliable treatment for CIS, which predictably causes cerebral reperfusion. Therefore, the choice of anesthetic drugs has important clinical significance. Isoflurane (ISO), one of the most used anesthetics, attenuates cognitive impairment and has brain protective effects. However, the role of isoflurane in regulating autophagy and its regulatory mechanism on inflammation in CIRI are still unclear. The middle cerebral artery occlusion (MCAO) method was used to establish a rat model of CIRI. After 24 h of reperfusion, all rats were evaluated by mNSS scoring and dark avoidance experiment. Western blotting and immunofluorescence were used to examine the expression of key proteins. Compared with the sham group, the MCAO group showed increased neurobehavioral scores and decreased cognitive memory function (P < 0.05). As for the ISO-treated MCAO rats, the neurobehavioral score was significantly decreased, the expression of AMPK, ULK1, Beclin1, and LC3B was significantly increased, and the cognitive and memory functions were also significantly improved (P < 0.05). After inhibition of autophagy pathway or key protein AMPK in autophagy, neurobehavioral scores and protein expression of NLRP3, IL-1β, and IL-18 were significantly increased (P < 0.05). Isoflurane post-treatment may enhance autophagy by activating the AMPK/ULK1 signaling pathway and further inhibit the release of inflammatory factors from NLRP3 inflammasomes, thereby ameliorating neurological function and cognitive impairment and exerting a protective effect on the brain in CIRI rats.

Intervertebral disc degeneration and osteoarthritis: a common molecular disease spectrum

Intervertebral disc degeneration (IDD) and osteoarthritis (OA) affecting the facet joint of the spine are biomechanically interdependent, typically occur in tandem, and have considerable epidemiological and pathophysiological overlap. Historically, the distinctions between these degenerative diseases have been emphasized. Therefore, research in the two fields often occurs independently without adequate consideration of the co-dependence of the two sites, which reside within the same functional spinal unit. Emerging evidence from animal models of spine degeneration highlight the interdependence of IDD and facet joint OA, warranting a review of the parallels between these two degenerative phenomena for the benefit of both clinicians and research scientists. This Review discusses the pathophysiological aspects of IDD and OA, with an emphasis on tissue, cellular and molecular pathways of degeneration. Although the intervertebral disc and synovial facet joint are biologically distinct structures that are amenable to reductive scientific consideration, substantial overlap exists between the molecular pathways and processes of degeneration (including cartilage destruction, extracellular matrix degeneration and osteophyte formation) that occur at these sites. Thus, researchers, clinicians, advocates and policy-makers should consider viewing the burden and management of spinal degeneration holistically as part of the OA disease continuum.

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.

Autophagy in the pathogenesis and therapeutic potential of post-traumatic osteoarthritis

Autophagy, as a fundamental mechanism for cellular homeostasis, is generally involved in the occurrence and progression of various diseases. Osteoarthritis (OA) is the most common musculoskeletal disease that often leads to pain, disability and economic loss in patients. Post-traumatic OA (PTOA) is a subtype of OA, accounting for >12% of the overall burden of OA. PTOA is often caused by joint injuries including anterior cruciate ligament rupture, meniscus tear and intra-articular fracture. Although a variety of methods have been developed to treat acute joint injury, the current measures have limited success in effectively reducing the incidence and delaying the progression of PTOA. Therefore, the pathogenesis and intervention strategy of PTOA need further study. In the past decade, the roles and mechanisms of autophagy in PTOA have aroused great interest in the field. It was revealed that autophagy could maintain the homeostasis of chondrocytes, reduce joint inflammatory level, prevent chondrocyte death and matrix degradation, which accordingly improved joint symptoms and delayed the progression of PTOA. Moreover, many strategies that target PTOA have been revealed to promote autophagy. In this review,  we summarize the roles and mechanisms of autophagy in PTOA and the current strategies for PTOA treatment that depend on autophagy regulation, which may be beneficial for PTOA patients in the future.

A20 ameliorates disc degeneration by suppressing mTOR/BNIP3 axis-mediated mitophagy

BACKGROUND

The pathological mechanism of intervertebral disc degeneration (IDD) is an unanswered question that we are committed to exploring. A20 is an anti-inflammatory protein of nucleus pulposus (NP) cells and plays a protective role in intervertebral disc degeneration.

OBJECTIVE

This study aims to investigate the molecular mechanism by which A20 attenuates disc degeneration.

METHODS

The proteins of interest were measured by immunoblotting, immunofluorescence, ELISA assay, and immunohistochemical technique to conduct related experiments. Immunofluorescence assays and mitochondrial membrane potential (JC-1) were used to assess mitophagy and mitochondrial fitness, respectively.

RESULTS

Here, we demonstrated that A20 promoted mitophagy, attenuated pyroptosis, and inhibited the degradation of the extracellular matrix, consequently significantly ameliorating disc degeneration. Mechanistically, A20 reduces pyroptosis and further suppresses cellular mTOR activity. On the one hand, A20-induced mTOR inhibition triggers BNIP3-mediated mitophagy to ensure mitochondrial fitness under LPS stimulation, as a result of mitigating mitochondrial dysfunction induced by LPS. On the other hand, A20-induced mTOR inhibition reduces the loss of mitochondrial membrane potential and the generation of Mitochondrial ROS.

CONCLUSION

The study revealed that A20 promotes BNIP3-mediated mitophagy by suppressing mTOR pathway activation against LPS-induced pyroptosis.

Targeting inflammasome-dependent mechanisms as an emerging pharmacological approach for osteoarthritis therapy

Arthritic diseases have attracted enormous scientific interest because of increased worldwide prevalence and represent a significant socioeconomic burden. Osteoarthritis (OA) is the most prevalent form of arthritis. It is a disorder of the diarthrodial joints, characterized by degeneration and loss of articular cartilage associated with adjacent subchondral bone changes. Chronic and unresolving inflammation has been identified as a critical factor driving joint degeneration and pain in OA. Despite numerous attempts at therapeutic intervention, no effective disease-modifying agents targeting OA inflammation are available to the patients. Inflammasomes are protein complexes known to play a critical role in the inflammatory pathology of several diseases, and their roles in OA pathogenesis have become evident over the last decade. In this sense, it is relevant to evaluate the vital role of inflammasomes as potential modulators of pathogenic features in OA. This review will provide an overview and perspectives on why understanding inflammasome activation is critical for identifying effective OA therapies. We elaborate on the contribution of extracellular mediators from the circulatory system and synovial fluid as well as intracellular activators within the synovial fibroblasts and articular chondrocytes toward invoking the inflammasome in OA. We further discuss the merits of emerging inflammasome targeting therapies and speculate on the potential strategies for inflammasome blockade for OA therapy.

The regulatory role and therapeutic application of pyroptosis in musculoskeletal diseases

Pyroptosis is a controlled form of inflammatory cell death characterized by inflammasome activation, pore formation, and cell lysis. According to different caspases, pyroptosis can be divided into canonical, non-canonical, and other pathways. The role of pyroptosis in disease development has been paid more attention in recent years. The trigger factors of pyroptosis are often related to oxidative stress and proinflammatory substances, which coincide with the pathological mechanism of some diseases. Pyroptosis directly leads to cell lysis and death, and the release of cytosolic components and proinflammatory cytokines affects cell activity and amplifies the inflammatory response. All the above are involved in a series of basic pathological processes, such as matrix degradation, fibrosis, and angiogenesis. Since these pathological changes are also common in musculoskeletal diseases (MSDs), emerging studies have focused on the correlations between pyroptosis and MSDs in recent years. In this review, we first summarized the molecular mechanism of pyroptosis and extensively discussed the differences and crosstalk between pyroptosis, apoptosis, and necrosis. Next, we elaborated on the role of pyroptosis in some MSDs, including osteoarthritis, rheumatoid arthritis, osteoporosis, gout arthritis, ankylosing spondylitis, intervertebral disc degeneration, and several muscle disorders. The regulation of pyroptosis could offer potential therapeutic targets in MSDs treatment. Herein, the existing drugs and therapeutic strategies that directly or indirectly target pyroptosis pathway components have been discussed in order to shed light on the novel treatment for MSDs.

Pyroptosis and Intervertebral Disc Degeneration: Mechanistic Insights and Therapeutic Implications

Low back pain (LBP) is a common problem worldwide, resulting in great patient suffering and great challenges for the social health system. Intervertebral disc (IVD) degeneration (IVDD) is widely acknowledged as one of the key causes of LBP. Accumulating evidence suggests that aberrant pyroptosis of IVD cells is involved in the pathogenesis of IVDD progression, however, the comprehensive roles of pyroptosis in IVDD have not been fully established, leaving attempts to treat IVDD with anti-pyroptosis approaches questionable. In this review, we summarize the characteristics of pyroptosis and emphasize the effects of IVD cell pyroptosis on the pathological progression of IVDD, including secretion of cytokines, nucleus pulposus cell apoptosis and autophagy, accelerated extracellular matrix degradation, annulus fibrosus rupture, cartilage endplate calcification, vascularization, sensory and sympathetic fiber neoinnervation, and infiltrating lymphatic vessels. Finally, we discuss several interventions used to treat IVDD by targeting pyroptosis. This review provides novel insights into the crucial role of IVD cell pyroptosis in IVDD pathogenesis, and could be informative for developing novel therapeutic approaches for IVDD and LBP.

tRNA-Derived Fragment tRF-5009A Regulates Autophagy and Degeneration of Cartilage in Osteoarthritis via Targeting mTOR

tRNA-derived fragments (tRFs) have been reported to have critical regulatory roles in osteoarthritis (OA). Recent studies have suggested that autophagy promotes the homeostasis of the extracellular matrix of chondrocytes in OA. However, the role of tRFs in posttranscriptional gene regulation during autophagy in OA is unknown. Therefore, we explored the role of tRF-5009A in the posttranscriptional gene regulation of autophagy and cartilage degeneration in OA. Using RNA sequencing, we identified tRF-5009A, the tRNA^ValCAC-derived fragment, in OA tissues and explored its expression by quantitative reverse transcription PCR and fluorescence in situ hybridization. We further investigated the relationship between the expression of tRF-5009A and clinical factors in OA. Chondrocytes were transfected with a tRF-5009A inhibitor or mimic to determine their functions, including in relation to autophagy and the cartilage phenotype. A rescue experiment and dual-luciferase reporter assay were conducted to determine whether the 3′-untranslated region (UTR) of mTOR contains a tRF-5009A-binding site. tRF-5009A was downregulated in the cartilage of OA knees, especially in damaged areas. mTOR was highly expressed in damaged cartilage and negatively correlated with the expression of tRF-5009A; transfection with a tRF-5009A inhibitor promoted the expression of mTOR and suppressed autophagy, whereas transfection with a tRF-5009A mimic had the opposite effect. A dual-luciferase reporter assay showed that tRF-5009A silenced the expression of mTOR by binding to its 3′-UTR. Thus, tRF-5009A regulates autophagy and cartilage degeneration in OA by targeting mTOR. In summary, these findings provide an additional tool for the clinical diagnosis and novel targeted therapy of OA.

Circular RNA triple functional domain promotes osteoarthritis' development by modulating the microRNA-136-5p/Nicotinamide phosphoribosyltransferase axis

Numerous studies have affirmed the participation of circular RNA (circRNA) in osteoarthritis (OA)’ development. Previous studies have exposed the elevation of the circRNA triple functional domain (TRIO) in OA, while the molecular mechanism of its effect on OA remains ambiguous. During the study, it was discovered the up-regulation of circTRIO in OA rats and interleukin-1β-treated chondrocytes. Knockdown circTRIO facilitates chondrocyte viability, but suppresses the inflammation, the apoptosis, and matrix metalloproteinases (MMP)-3 and MMP-13 expression, whereas up-regulation aggravates OA. The effect of up-regulation or under-expression of circTRIO on chondrocytes was reversed via the knockdown of Nicotinamide phosphoribosyltransferase (NAMPT) or microRNA (miR)-136-5p separately. Mechanically speaking, circTRIO competitively adsorbing miR-136-5p to target NAMPT influences OA. Briefly, the results of this study inform that the circTRIO/miR-136-5p/NAMPT axis is momentous in OA progression and is supposed to be a promising therapeutic target for some time.

Chloride Channel and Inflammation-Mediated Pathogenesis of Osteoarthritis

Articular cartilage allows the human body to buffer and absorb stress during normal exercise. It is mainly composed of cartilage cells and the extracellular matrix and is surrounded by the extracellular microenvironment formed by synovial fluid and various factors in it. Studies have shown that chondrocytes are the metabolic center of articular cartilage. Under physiological conditions, the extracellular matrix is in a dynamic balance of anabolism and catabolism, and various factors and physical and chemical conditions in the extracellular microenvironment are also in a steady state. This homeostasis depends on the normal function of proteins represented by various ion channels on chondrocytes. In mammalian chondrocyte species, ion channels are mainly divided into two categories: cation channels and anion channels. Anion channels such as chloride channels have become hot research topics in recent years. These channels play an extremely important role in various physiological processes. Recently, a growing body of evidence has shown that many pathological processes, abnormal concentration of mechanical stress and chloride channel dysfunction in articular cartilage lead to microenvironment disorders, matrix and bone metabolism imbalances, which cause partial aseptic inflammation. These pathological processes initiate extracellular matrix degradation, abnormal chondrocyte death, hyperplasia of inflammatory synovium and bony. Osteoarthritis (OA) is a common clinical disease in orthopedics. Its typical manifestations are joint inflammation and pain caused by articular cartilage degeneration, but its pathogenesis has not been fully elucidated. Focusing on the physiological functions and pathological changes of chloride channels and pathophysiology of aseptic inflammation furthers the understanding of OA pathogenesis and provides possible targets for subsequent medication development.