An Emerging Target in the Battle against Osteoarthritis: Macrophage Polarization

The role of macrophage polarization in rheumatoid arthritis and osteoarthritis: Pathogenesis and therapeutic strategies

Rheumatoid arthritis (RA) and osteoarthritis (OA) are common and debilitating joint disorders affecting millions of individuals worldwide. Despite their distinct pathological features, both conditions share a crucial role of macrophages in disease progression. Macrophages exhibit remarkable plasticity, polarizing into pro-inflammatory M1 or anti-inflammatory M2 phenotypes in response to environmental cues. An imbalance in macrophage polarization, particularly a shift towards the M1 phenotype, contributes to chronic inflammation and joint damage in RA and OA. This review explores the complex interplay between macrophages and various cell types, including T cells, B cells, synovial fibroblasts, osteoclasts, chondrocytes, and adipocytes, in the pathogenesis of these diseases. We discuss the current understanding of macrophage polarization in RA and OA, highlighting the molecular mechanisms involved. Furthermore, we provide an overview of potential therapeutic strategies targeting macrophage polarization, such as disease-modifying anti-rheumatic drugs, traditional Chinese medicine, nanomedicines, proteins, chemical compounds, and physical therapies. By elucidating the precise mechanisms governing macrophage polarization and its interactions with other cells in the joint microenvironment, researchers can identify novel therapeutic targets and develop targeted interventions to alleviate disease progression and improve patient outcomes in RA and OA.

Synovial microenvironment in temporomandibular joint osteoarthritis: crosstalk with chondrocytes and potential therapeutic targets

Temporomandibular joint osteoarthritis (TMJOA) is considered to be a low-grade inflammatory disease involving multiple joint tissues. The crosstalk between synovium and cartilage plays an important role in TMJOA. Synovial cells are a group of heterogeneous cells and synovial microenvironment is mainly composed of synovial fibroblasts (SF) and synovial macrophages. In TMJOA, SF and synovial macrophages release a large number of inflammatory cytokines and extracellular vesicles and promote cartilage destruction. Cartilage wear particles stimulate SF proliferation and macrophages activation and exacerbate synovitis. In TMJOA, chondrocytes and synovial cells exhibit increased glycolytic activity and lactate secretion, leading to impaired chondrocyte matrix synthesis. Additionally, the synovium contains mesenchymal stem cells, which are the seed cells for cartilage repair in TMJOA. Co-culture of chondrocytes and synovial mesenchymal stem cells enhances the chondrogenic differentiation of stem cells. This review discusses the pathological changes of synovium in TMJOA, the means of crosstalk between synovium and cartilage, and their influence on each other. Based on the crosstalk between synovium and cartilage in TMJOA, we illustrate the treatment strategies for improving synovial microenvironment, including reducing cell adhesion, utilizing extracellular vesicles to deliver biomolecules, regulating cellular metabolism and targeting inflammatory cytokines.

Human uncultured adipose-derived stromal vascular fraction shows therapeutic potential against osteoarthritis in immunodeficient rats via direct effects of transplanted M2 macrophages

BACKGROUND

The uncultured adipose-derived stromal vascular fraction (SVF), consisting of adipose-derived stromal cells (ADSCs), M2 macrophages (M2Φ) and others, has shown therapeutic potential against osteoarthritis (OA), however, the mechanisms underlying its therapeutic effects remain unclear. Therefore, this study investigated the effects of the SVF on OA in a human-immunodeficient rat xenotransplantation model.

METHODS

OA model was induced in the knees of female immunodeficient rats by destabilization of the medial meniscus. Immediately after the surgery, human SVF (1 × 105), ADSCs (1 × 104), or phosphate buffered saline as a control group were transplanted into the knees. At 4 and 8 weeks postoperatively, OA progression and synovitis were analyzed by macroscopic and histological analyses, and the expression of collagen II, SOX9, MMP-13, ADAMTS-5, F4/80, CD86 (M1), CD163 (M2), and human nuclear antigen (hNA) were evaluated immunohistochemically. In vitro, flow cytometry was performed to collect CD163-positive cells as M2Φ from the SVF. Chondrocyte pellets (1 × 105) were co-cultured with SVF (1 × 105), M2Φ (1 × 104), and ADSCs (1 × 104) or alone as a control group, and the pellet size was compared. TGF-β, IL-10 and MMP-13 concentrations in the medium were evaluated using enzyme-linked immunosorbent assay.

RESULTS

In comparison with the control and ADSC groups, the SVF group showed significantly slower OA progression and less synovitis with higher expression of collagen II and SOX9, lower expression of MMP-13 and ADAMTS-5, and lower F4/80 and M1/M2 ratio in the synovium. Only the SVF group showed partial expression of hNA-, CD163-, and F4/80-positive cells in the rat synovium. In vitro, the SVF, M2Φ, ADSC and control groups, in that order, showed larger pellet sizes, higher TGF-β and IL-10, and lower MMP-13 concentrations.

CONCLUSIONS

The M2Φ in the transplanted SVF directly affected recipient tissue, enhancing the secretion of growth factors and chondrocyte-protecting cytokines, and partially improving chondrocytes and joint homeostasis. These findings indicate that the SVF is as an effective option for regenerative therapy for OA, with mechanisms different from those of ADSCs.

Primed IFN-γ-Umbilical Cord Stem Cells Ameliorate Temporomandibular Joint Osteoarthritis

Temporomandibular joint osteoarthritis (TMJOA) is a degenerative disorder affecting the temporomandibular joint (TMJ), marked by persistent inflammation and structural damage to the joint. Only symptomatic treatment is available for managing TMJOA. Human umbilical cord mesenchymal stem cells (hUC-MSCs) show potential for treating TMJOA via their immune-modulating actions in the disease area. In addition, stimulation of inflammatory cytokines such as interferon-gamma in hUC-MSCs improves the therapeutic activity of naïve stem cells. Emerging evidence indicates that macrophages play significant roles in regulating joint inflammation through diverse secreted mediators in the pathogenesis of TMJOA. This study was conducted to evaluate the effects of inflammatory cytokine-stimulated hUC-MSCs in repairing TMJOA-induced cartilage lesions and the role of macrophages in the disease. Our in vitro data showed that stimulated hUC-MSCs induce M2 polarization of macrophages and enhance the expression of anti-inflammatory molecules. These effects were subsequently validated in vivo. In a rat model of TMJOA, stimulated hUC-MSCs ameliorated inflammation and increased M2 macrophages ratio. Our results indicate that hUC-MSCs stimulated by inflammatory cytokines modulate the activation of M2 macrophages, thereby shifting the local osteoarthritis microenvironment toward a prochondrogenic state and facilitating cartilage repair in inflammatory conditions. Stimulating hUC-MSCs with inflammatory cytokines could potentially offer an effective therapeutic approach for TMJOA, with macrophages playing a pivotal role in immune modulation.

The Implications of Brain-Derived Neurotrophic Factor in the Biological Activities of Platelet-Rich Plasma

Platelet-rich plasma (PRP) is a biological blood-derived therapeutic obtained from whole blood that contains higher levels of platelets. PRP has been primarily used to mitigate joint degeneration and chronic pain in osteoarthritis (OA). This clinical applicability is based mechanistically on the release of several proteins by platelets that can restore joint homeostasis. Platelets are the primary source of brain-derived neurotrophic factor (BDNF) outside the central nervous system. Interestingly, BDNF and PRP share key biological activities with clinical applicability for OA management, such as anti-inflammatory, anti-apoptotic, and antioxidant. However, the role of BDNF in PRP therapeutic activities is still unknown. Thus, this work aimed to investigate the implications of BDNF in therapeutic outcomes provided by PRP therapy in vitro and in-vivo, using the MIA-OA animal model in male Wistar rats. Initially, the PRP was characterized, obtaining a leukocyte-poor-platelet-rich plasma (LP-PRP). Our assays indicated that platelets activated by Calcium release BDNF, and suppression of M1 macrophage polarization induced by LP-PRP depends on BDNF full-length receptor, Tropomyosin Kinase-B (TrkB). OA animals were given LP-PRP intra-articular and showed functional recovery in gait, joint pain, inflammation, and tissue damage caused by MIA. Immunohistochemistry for activating transcriptional factor-3 (ATF-3) on L4/L5 dorsal root ganglia showed the LP-PRP decreased the nerve injury induced by MIA. All these LP-PRP therapeutic activities were reversed in the presence of TrkB receptor antagonist. Our results suggest that the therapeutic effects of LP-PRP in alleviating OA symptoms in rats depend on BDNF/TrkB activity.

Baicalin nanodelivery system based on functionalized metal-organic framework for targeted therapy of osteoarthritis by modulating macrophage polarization

Intra-articular drugs used to treat osteoarthritis (OA) often suffer from poor pharmacokinetics and stability. Nano-platforms as drug delivery systems for drug delivery are promising for OA therapy. In this study, we reported an M1 macrophage-targeted delivery system Bai@FA-UIO-66-NH2 based on folic acid (FA) -modified metal-organic framework (MOF) loaded with baicalin (Bai) as antioxidant agent for OA therapy. With outstanding biocompatibility and high drug loading efficiency, Bai@FA-UIO-66-NH2 could be specifically uptaken by LPS-induced macrophages to serve as a potent ROS scavenger, gradually releasing Bai at the subcellular level to reduce ROS production, modulate macrophage polarization to M2, leading to alleviation of synovial inflammation in OA joints. The synergistic effect of Bai@FA-UIO-66-NH2 on macrophage polarization and ROS scavenging significantly improved the therapeutic efficacy of OA, which may provide a new insight into the design of OA precision therapy.

Role of crosstalk between synovial cells and chondrocytes in osteoarthritis (Review)

Osteoarthritis (OA) is a low-grade, nonspecific inflammatory disease that affects the entire joint. This condition is characterized by synovitis, cartilage erosion, subchondral bone defects, and subpatellar fat pad damage. There is mounting evidence demonstrating the significance of crosstalk between synovitis and cartilage destruction in the development of OA. To comprehensively explore the phenotypic alterations of synovitis and cartilage destruction, it is important to elucidate the crosstalk mechanisms between chondrocytes and synovial cells. Furthermore, the updated iteration of single-cell sequencing technology reveals the interaction between chondrocyte and synovial cells. In the present review, the histological and pathological alterations between cartilage and synovium during OA progression are described, and the mode of interaction and molecular mechanisms between synovial cells and chondrocytes in OA, both of which affect the OA process mainly by altering the inflammatory environment and cellular state, are elucidated. Finally, the current OA therapeutic approaches are summarized and emerging therapeutic targets are reviewed in an attempt to provide potential insights into OA treatment.

BMSC-Derived Exosomes Attenuate Rat Osteoarthritis by Regulating Macrophage Polarization through PINK1/Parkin Signaling Pathway

OBJECTIVE

Exosomes derived from bone marrow mesenchymal stem cells (BMSC-Exos) may modulate the M1/M2 polarization of macrophages during osteoarthritis (OA). However, the underlying mechanisms of BMSC-Exos in this process still need to be elucidated. In this study, we explored the role of BMSC-Exos in the polarization of macrophages in vitro and the OA rats in vivo.

METHODS

The effects of BMSC-Exos on RAW264.7 cells were determined, including the production of reactive oxygen species (ROS) and the protein expression of Akt, PINK1, and Parkin. We prepared an OA model by resecting the anterior cruciate ligament and medial meniscus of Sprague-Dawley (SD) rats. Hematoxylin-eosin (H&E) and safranin O-fast green staining, immunohistochemistry and immunofluorescence analyses, and the examination of interleukin 6 (IL-6), interleukin 1β (IL-1β), tumor necrosis factor alpha (TNF-α), and interleukin 10 (IL-10) were performed to assess changes in cartilage and synovium.

RESULTS

BMSC-Exos inhibited mitochondrial membrane damage, ROS production, and the protein expression of PINK1 and Parkin. Akt phosphorylation was downregulated under lipopolysaccharide (LPS) induction but significantly recovered after treatment with BMSC-Exos. BMSC-Exos alleviated cartilage damage, inhibited M1 polarization, and promoted M2 polarization in the synovium in OA rats. The expression of PINK1 and Parkin in the synovium and the levels of IL-6, IL-1β, and TNF-α in the serum decreased, but the level of IL-10 increased when BMSC-Exos were used in OA rats.

CONCLUSION

BMSC-Exos ameliorate OA development by regulating synovial macrophage polarization, and one of the underlying mechanisms may be through inhibiting PINK1/Parkin signaling.

Conditioned Medium From Stem Cells of Human Exfoliated Deciduous Teeth Alleviates Mouse Osteoarthritis by Inducing sFRP1-Expressing M2 Macrophages

Intravenous administration of conditioned medium from stem cells of human exfoliated deciduous teeth (SHED-CM) regenerates mechanically injured osteochondral tissues in mouse temporomandibular joint osteoarthritis (TMJOA). However, the underlying therapeutic mechanisms remain unclear. Here, we showed that SHED-CM alleviated injured TMJ by inducing anti-inflammatory M2 macrophages in the synovium. Depletion of M2 by Mannosylated Clodrosome abolished the osteochondral repair activities of SHED-CM. Administration of CM from M2-induced by SHED-CM (M2-CM) effectively ameliorated mouse TMJOA by inhibiting chondrocyte inflammation and matrix degradation while enhancing chondrocyte proliferation and matrix formation. Notably, in vitro, M2-CM directly suppressed the catabolic activities while enhancing the anabolic activities of interleukin-1β-stimulated mouse primary chondrocytes. M2-CM also inhibited receptor activator of nuclear factor NF-κB ligand-induced osteoclastogenesis in RAW264.7 cells. Secretome analysis of M2-CM and M0-CM revealed that 5 proteins related to anti-inflammation and/or osteochondrogenesis were enriched in M2-CM. Of these proteins, the Wnt signal antagonist, secreted frizzled-related protein 1 (sFRP1), was the most abundant and played an essential role in the shift to anabolic chondrocytes, suggesting that M2 ameliorated TMJOA partly through sFRP1. This study suggests that secretome from SHED exerted remarkable osteochondral regeneration activities in TMJOA through the induction of sFRP1-expressing tissue-repair M2 macrophages.

Implantable celecoxib nanofibers made by electrospinning: fabrication and characterization

Background: Osteoarthritis causes tremendous damage to the joints, reducing the quality of life and imposing significant financial burden. An implantable drug-delivery system can improve the symptomatic manifestations with low doses and frequencies. However, the free drug has short retention in the joint cavity. Materials & methods: This study used electrostatic spinning technology to create an implantable drug-delivery system loaded with celecoxib (celecoxib nanofibers [Cel-NFs]) to improve retention and bioavailability. Results: Cel-NFs exhibited good formability, hydrophilicity and tensile properties. Cel-NFs were able to continuously release drugs for 2 weeks and increase the uptake capacity of Raw 264.7 cells, ultimately ameliorating symptoms in osteoarthritis rats. Conclusion: These results suggest that Cel-NFs can effectively ameliorate cartilage damage, reduce joint pain and alleviate osteoarthritis progression.

Apoptotic body-inspired nanotherapeutics efficiently attenuate osteoarthritis by targeting BRD4-regulated synovial macrophage polarization

Bromodomain-containing protein 4 (BRD4) is the most well-studied BET protein that is important for the innate immune response. We recently revealed that targeting BRD4 triggers apoptosis in tumor-associated macrophages, but its role in synovial macrophages and joint inflammation is largely unknown. Herein, we demonstrated that BRD4 was highly expressed in the iNOS-positive M1 macrophages in the human and mouse osteoarthritis (OA) synovium, and conditional knockout of BRD4 in the myeloid lineage using Lyz2-cre; BRD4flox/flox mice significantly abolished anterior cruciate ligament transection (ACLT)-induced M1 macrophage accumulation and synovial inflammation. Accordingly, we successfully constructed apoptotic body-inspired phosphatidylserine-containing nanoliposomes (PSLs) loaded with the BRD4 inhibitor JQ1 to regulate inflammatory macrophages. JQ1-loaded PSLs (JQ1@PSLs) exhibited a higher cellular uptake by macrophages than fibroblast-like synoviocytes (FLSs) in vitro and in vivo, as well as the reduction in proinflammatory M1 macrophage polarization. Intra-articular injections of JQ1@PSLs showed prolonged retention within the joint, and remarkably reduced synovial inflammation and joint pain via suppressing M1 polarization accompanied by reduced TRPA1 expression by targeted inhibition of BRD4 in the macrophages, thus attenuating cartilage degradation during OA development. The results show that BRD4-inhibiting JQ1@PSLs can targeted-modulate macrophage polarization, which opens a new avenue for efficient OA therapy via a "Trojan horse".

Spermidine ameliorates osteoarthritis via altering macrophage polarization

OBJECTIVE

Spermidine (SPD) is an anti-aging natural substance, and it exerts effects through anti-apoptosis and anti-inflammation. However, the specific protective mechanism of SPD in osteoarthritis (OA) remains unclear. Here, we explored the role of SPD on the articular cartilage and the synovial tissue, and tested whether the drug would regulate the polarization of synovial macrophages by in vivo and in vitro experiments.

METHODS

By constructing an OA model in mice, we preliminarily explored the protective effect of SPD on the articular cartilage and the synovial tissue. Meanwhile, we isolated and cultured human primary chondrocytes and bone marrow-derived macrophages (BMDMs), and prepared a conditioned medium (CM) to explore the specific protective effect of SPD in vitro.

RESULTS

We found that SPD alleviated cartilage degeneration and synovitis, increased M2 polarization and decreased M1 polarization in synovial macrophages. In vitro experiments, SPD inhibited ERK MAPK and p65/NF-κB signaling in macrophages, and transformed macrophages from M1 to M2 subtypes. Interestingly, SPD had no direct protective effect on chondrocytes in vitro; however, the conditioned medium (CM) from M1 macrophages treated with SPD promoted the anabolism and inhibited the catabolism of chondrocytes. Moreover, this CM markedly suppressed IL-1β-induced p38/JNK MAPK signaling pathway activation in chondrocytes.

CONCLUSIONS

This work provides new perspectives on the role of SPD in OA. SPD does not directly target chondrocytes, but can ameliorate the degradation of articular cartilage through regulating M1/M2 polarization of synovial macrophages. Hence, SPD is expected to be the potential therapy for OA.

Efficacy and immune-inflammatory mechanism of acupuncture-related therapy in animal models of knee osteoarthritis: a preclinical systematic review and network meta-analysis

BACKGROUND

Many KOA patients have not reached indications for surgery, thus we need to find effective non-surgical treatments. Acupuncture is thought to have the potential to modulate inflammation and cytokines in KOA through the immune system. However, the mechanisms have not been elucidated, and there is no network Meta-analysis of acupuncture on KOA animals. So we evaluate the effect and mechanism of acupuncture-related therapy in KOA animals.

METHODS

A comprehensive search was conducted in multiple databases including PubMed, Web of Science, Embase, CBM, CNKI, WanFang, and VIP Database to identify relevant animal studies focusing on acupuncture therapy for KOA. The included studies were assessed for risk of bias using SYRCLE's Risk of Bias tool. Subsequently, pair-wise meta-analysis and network meta-analysis were performed using Stata 15.0 software, evaluating outcomes such as Lequesne index scale, Mankin score, IL-1β, TNF-α, MMP3, and MMP13.

RESULTS

56 RCTs with 2394 animals were included. Meta-analysis showed that among the 6 outcomes, there were significant differences between acupuncture and model group; the overall results of network meta-analysis showed that the normal group or sham operation group performed the best, followed by the acupotomy, acupuncture, and medicine group, and the model group had the worst effect, and there were significant differences between 6 interventions.

CONCLUSIONS

Acupuncture-related therapy can be a possible treatment for KOA. The mechanism involves many immune-inflammatory pathways, which may be mediated by DAMPs/TLR/NF-κB/MAPK,PI3K/Akt/NF-κB pathway, or IFN-γ/JAK-STAT pathway. It needs to be further confirmed by more high-quality animal experiments or meta-analysis.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO identifier: CRD42023377228.

Emerging Roles of Macrophage Polarization in Osteoarthritis: Mechanisms and Therapeutic Strategies

Osteoarthritis (OA) is the most common chronic degenerative joint disease in middle-aged and elderly people, characterized by joint pain and dysfunction. Macrophages are key players in OA pathology, and their activation state has been studied extensively. Various studies have suggested that macrophages might respond to stimuli in their microenvironment by changing their phenotypes to pro-inflammatory or anti-inflammatory phenotypes, which is called macrophage polarization. Macrophages accumulate and become polarized (M1 or M2) in many tissues, such as synovium, adipose tissue, bone marrow, and bone mesenchymal tissues in joints, while resident macrophages as well as other stromal cells, including fibroblasts, chondrocytes, and osteoblasts, form the joint and function as an integrated unit. In this study, we focus exclusively on synovial macrophages, adipose tissue macrophages, and osteoclasts, to investigate their roles in the development of OA. We review recent key findings related to macrophage polarization and OA, including pathogenesis, molecular pathways, and therapeutics. We summarize several signaling pathways in macrophage reprogramming related to OA, including NF-κB, MAPK, TGF-β, JAK/STAT, PI3K/Akt/mTOR, and NLRP3. Of note, despite the increasing availability of treatments for osteoarthritis, like intra-articular injections, surgery, and cellular therapy, the demand for more effective clinical therapies has remained steady. Therefore, we also describe the current prospective therapeutic methods that deem macrophage polarization to be a therapeutic target, including physical stimulus, chemical compounds, and biological molecules, to enhance cartilage repair and alleviate the progression of OA.

Reprogramming Macrophage Polarization, Depleting ROS by Astaxanthin and Thioketal-Containing Polymers Delivering Rapamycin for Osteoarthritis Treatment

Osteoarthritis (OA) is a chronic joint disease characterized by synovitis and joint cartilage destruction. The severity of OA is highly associated with the imbalance between M1 and M2 synovial macrophages. In this study, a novel strategy is designed to modulate macrophage polarization by reducing intracellular reactive oxygen species (ROS) levels and regulating mitochondrial function. A ROS-responsive polymer is synthesized to self-assemble with astaxanthin and autophagy activator rapamycin to form nanoparticles (NP@PolyRHAPM ). In vitro experiments show that NP@PolyRHAPM significantly reduced intracellular ROS levels. Furthermore, NP@PolyRHAPM restored mitochondrial membrane potential, increased glutathione (GSH) levels, and promoted intracellular autophagy, hence successfully repolarizing M1 macrophages into the M2 phenotype. This repolarization enhanced chondrocyte proliferation and vitality while inhibiting apoptosis. In vivo experiments utilizing an anterior cruciate ligament transection (ACLT)-induced OA mouse model revealed the anti-inflammatory and cartilage-protective effects of NP@PolyRHAPM , effectively mitigating OA progression. Consequently, the findings suggest that intra-articular delivery of ROS-responsive nanocarrier systems holds significant promise as a potential and effective therapeutic strategy for OA treatment.

Carveol alleviates osteoarthritis progression by acting on synovial macrophage polarization transformation: An in vitro and in vivo study

Osteoarthritis (OA) is a heterogeneous disease that affects the entire joint. Its pathogenesis involves hypertrophy and hyperplasia of synovial cells and polarization infiltration of macrophages, in which macrophages, as a potential target, can delay the progression of the disease by improving the immune microenvironment in OA. To investigate the role and regulatory mechanism of Carveol in cartilage and synovial macrophage reprogramming and crosstalk during the development of OA. RAW264.7 mouse macrophage cell line was mainly used to stimulate macrophages to polarization towards M1 and M2 by LPS, IL4+IL13, respectively. Different concentrations of Carveol were given to intervene, and macrophage culture medium was collected to intervene mouse C57BL6J chondrocytes. ROS assay kit, western blotting, cellular immunofluorescence, scanning microscope and section histology were used to evaluate the effect of Carveol on anti-M1-polarization, M2-polarization promotion and cartilage protection. The mouse destabilization of medial meniscus (DMM) model was observed by micro-CT scan and histology. We found that CA could inhibit the increase of macrophage inflammation level under the intervention of LPS and promote the production of M2 anti-inflammatory substances under the intervention of IL-4+IL13. In addition, Carveol activated NRF2/HO-1/NQO1 pathway and enhanced ROS clearance in chondrocytes under the intervention of macrophage culture medium. The phosphorylation of I-κBα is inhibited, which further reduces the phosphorylation of P65 downstream of nuclear factor-κB (NF-κB) signaling pathway. In addition, Carveol inhibits mitogen activated protein kinase (MAPK) signaling molecules P-JNK, P-ERK and P-P38, and inhibits the production of inflammatory mediators. In vivo, Carveol can reduce osteophytes and bone spurs induced by DMM, reduce hypertrophy of synovial cells, reduce infiltration of macrophages, inhibit subchondral bone destruction, and reduce articular cartilage erosion. Our study suggests that synovial macrophages are potential targets for OA treatment, and Carveol is an effective candidate for OA treatment.

The Diagnostic Features of Peripheral Blood Biomarkers in Identifying Osteoarthritis Individuals: Machine Learning Strategies and Clinical Evidence

BACKGROUND

People with osteoarthritis place a huge burden on society. Early diagnosis is essential to prevent disease progression and to select the best treatment strategy more effectively. In this study, the aim was to examine the diagnostic features and clinical value of peripheral blood biomarkers for osteoarthritis.

OBJECTIVE

The goal of this project was to investigate the diagnostic features of peripheral blood and immune cell infiltration in osteoarthritis (OA).

METHODS

Two eligible datasets (GSE63359 and GSE48556) were obtained from the GEO database to discern differentially expressed genes (DEGs). The machine learning strategy was employed to filtrate diagnostic biomarkers for OA. Additional verification was implemented by collecting clinical samples of OA. The CIBERSORT website estimated relative subsets of RNA transcripts to evaluate the immune-inflammatory states of OA. The link between specific DEGs and clinical immune-inflammatory markers was found by correlation analysis.

RESULTS

Overall, 67 robust DEGs were identified. The nuclear receptor subfamily 2 group C member 2 (NR2C2), transcription factor 4 (TCF4), stromal antigen 1 (STAG1), and interleukin 18 receptor accessory protein (IL18RAP) were identified as effective diagnostic markers of OA in peripheral blood. All four diagnostic markers showed significant increases in expression in OA. Analysis of immune cell infiltration revealed that macrophages are involved in the occurrence of OA. Candidate diagnostic markers were correlated with clinical immune-inflammatory indicators of OA patients.

CONCLUSION

We highlight that DEGs associated with immune inflammation (NR2C2, TCF4, STAG1, and IL18RAP) may be potential biomarkers for peripheral blood in OA, which are also associated with clinical immune-inflammatory indicators.

Silencing of STUB1 relieves osteoarthritis via inducing NRF2-mediated M2 macrophage polarization

OBJECTIVES

Shifting macrophages towards an anti-inflammatory state is key in treating osteoarthritis (OA) by reducing inflammation and tissue damage. However, the underlying mechanisms guiding this shift remain largely undefined. STUB1, an E3 ubiquitin ligase, known for its regulatory role in macrophage polarization. This study aims to explore the function and underlying action mechanisms of STUB1 in OA.

METHODS

An in vivo OA model was established in rats. Hematoxylin-Eosin and safranin O-fast green staining were performed to reveal the hispathological injuries in knee-joint tissues. Immunohistochemistry and flow cytometry were performed to detect the distribution of M1 and M2 macrophages. The inflammatory response (TNF-α and IL-6 levels) was evaluated by ELISA. In vitro, the interaction between STUB1 and NFR2 was determined by CO-IP and pull-down assays. After treated with LPS (an in vitro model of OA), the viability and apoptosis of chondrocytes were measured by CCK-8 and flow cytometry, respectively.

RESULTS

Silencing STUB1 alleviated OA in rats, as indicated by reduced subchondral bone thickness, knee synovitis score, histopathological damages, and inflammatory response. STUB1 silencing also decreased M1 macrophages and increased M2 macrophages in both in vivo and in vitro settings. NRF2 was identified as a target of STUB1, with STUB1 mediating its ubiquitination. Silencing NRF2 reversed the effects of STUB1 silencing on inducing M2 macrophage polarization. Furthermore, silencing STUB1 upregulated NRF2 expression in LPS-treated chondrocytes, promoting cell viability and inhibiting apoptosis.

CONCLUSION

Silencing STUB1 induces M2 macrophage polarization by inhibiting NRF2 ubiquitination, thereby contributing to the mitigation of OA.

Targeting WNT signalling pathways as new therapeutic strategies for osteoarthritis

Osteoarthritis (OA) is a highly prevalent chronic joint disease and the leading cause of disability. Currently, no drugs are available to control joint damage or ease the associated pain. The wingless-type (WNT) signalling pathway is vital in OA progression. Excessive activation of the WNT signalling pathway is pertinent to OA progression and severity. Therefore, agonists and antagonists of the WNT pathway are considered potential drug candidates for OA treatment. For example, SM04690, a novel small molecule inhibitor of WNT signalling, has demonstrated its potential in a recent phase III clinical trial as a disease-modifying osteoarthritis drug (DMOAD). Therefore, targeting the WNT signalling pathway may be a distinctive approach to developing particular agents helpful in treating OA. This review aims to update the most recent progress in OA drug development by targeting the WNT pathway. In this, we introduce WNT pathways and their crosstalk with other signalling pathways in OA development and highlight the role of the WNT signalling pathway as a key regulator in OA development. Several articles have reviewed the Wnt pathway from different aspects. This candid review provides an introduction to WNT pathways and their crosstalk with other signalling pathways in OA development, highlighting the role of the WNT signalling pathway as a key regulator in OA development with the latest research. Particularly, we emphasise the state-of-the-art in targeting the WNT pathway as a promising therapeutic approach for OA and challenges in their development and the nanocarrier-based delivery of WNT modulators for treating OA.

An in vitro model for osteoarthritis using long-cultured inflammatory human macrophages repeatedly stimulated with TLR agonists

Osteoarthritis (OA) is characterized by an abundance of inflammatory M1-like macrophages damaging local tissues. The search for new potential drugs for OA suffers from the lack of appropriate methods of long-lasting inflammation. Here we developed and characterized an in vitro protocol of long-lasting culture of primary human monocyte-derived macrophages differentiated with a combination of M-CSF+GM-CSF that optimally supported long-cultured macrophages (LC-Mϕs) for up to 15 days, unlike their single use. Macrophages repeatedly stimulated for 15 days with the TLR2 ligand Pam3CSK4 (LCS-Mϕs), showed sustained levels over time of IL-6, CCL2, and CXCL8, inflammatory mediators that were also detected in the synovial fluids of OA patients. Furthermore, macrophages isolated from the synovia of two OA patients showed an expression profile of inflammation-related genes similar to that of LCS-Mϕs, validating our protocol as a model of chronically activated inflammatory macrophages. Next, to confirm that these LCS-Mϕs could be modulated by anti-inflammatory compounds, we employed dexamethasone and/or celecoxib, two drugs widely used in OA treatment, that significantly inhibited the production of inflammatory mediators. This easy-to-use in vitro protocol of long-lasting inflammation with primary human macrophages could be useful for the screening of new compounds to improve the therapy of inflammatory disorders.

Fe-doped carbon dots: a novel biocompatible nanoplatform for multi-level cancer therapy

BACKGROUND

Tumor treatment still remains a clinical challenge, requiring the development of biocompatible and efficient anti-tumor nanodrugs. Carbon dots (CDs) has become promising nanomedicines for cancer therapy due to its low cytotoxicity and easy customization.

RESULTS

Herein, we introduced a novel type of "green" nanodrug for multi-level cancer therapy utilizing Fe-doped carbon dots (Fe-CDs) derived from iron nutrient supplement. With no requirement for target moieties or external stimuli, the sole intravenous administration of Fe-CDs demonstrated unexpected anti-tumor activity, completely suppressing tumor growth in mice. Continuous administration of Fe-CDs for several weeks showed no toxic effects in vivo, highlighting its exceptional biocompatibility. The as-synthesized Fe-CDs could selectively induce tumor cells apoptosis by BAX/Caspase 9/Caspase 3/PARP signal pathways and activate antitumoral macrophages by inhibiting the IL-10/Arg-1 axis, contributing to its significant tumor immunotherapy effect. Additionally, the epithelial-mesenchymal transition (EMT) process was inhibited under the treatment of Fe-CDs by MAPK/Snail pathways, indicating the capacity of Fe-CDs to inhibit tumor recurrence and metastasis.

CONCLUSIONS

A three-level tumor treatment strategy from direct killing to activating immunity to inhibiting metastasis was achieved based on "green" Fe-CDs. Our findings reveal the broad clinical potential of Fe-CDs as a novel candidate for anti-tumor nanodrugs and nanoplatform.

Heterogeneous Cells as well as Adipose-Derived Stromal Cells in Stromal Vascular Fraction Contribute to Enhance Anabolic and Inhibit Catabolic Factors in Osteoarthritis

The stromal-vascular fraction (SVF), comprising heterogeneous cell populations and adipose-derived stromal cells (ADSCs), has therapeutic potential against osteoarthritis (OA); however, the underlying mechanism remains elusive. This study aimed to investigate the therapeutic effects of heterogeneous cells in rabbit SVF on rabbit chondrocytes. Rabbit SVF and ADSCs were autografted into knees at OA onset. The SVF (1 × 105) and low-dose ADSCs (lADSC; 1 × 104) groups adjusted for their stromal cell content were compared. Animals were euthanized 8 and 12 weeks after OA onset for macroscopic and histological analyses of OA progression and synovitis. Immunohistochemical and real-time polymerase chain reaction assessments were conducted. In vitro, immune-fluorescent double staining was performed for SVF to stain macrophages with F4/80, CD86(M1), and CD163(M2). OA progression was markedly suppressed, and synovitis was reduced in the SVF groups (OARSI histological score 8 W: 6.8 ± 0.75 vs. 3.8 ± 0.75, p = 0.001; 12 W: 8.8 ± 0.4 vs. 5.4 ± 0.49, p = 0.0002). The SVF groups had higher expression of collagen II and SOX9 in cartilage and TGF-β and IL-10 in the synovium, lower expression of MMP-13, and lower macrophage M1/M2 ratio than the lADSC groups. Immunofluorescent double staining revealed a markedly higher number of M2 than that of M1 macrophages in the SVF. The therapeutic effects of SVF on chondrocytes were superior than those of lADSCs, with enhanced anabolic and inhibited catabolic factors. Heterogeneous cells, mainly M2 macrophages in the SVF, enhanced growth factor secretion and chondrocyte-protective cytokines, thus benefiting chondrocytes and knee joint homeostasis. Overall, the SVF is a safe, relatively simple, and a useful treatment option for OA.

IL-38 suppresses macrophage M1 polarization to ameliorate synovial inflammation in the TMJ via GLUT-1 inhibition

OBJECTIVES

Interleukin (IL)-38 was discovered as an anti-inflammatory factor. However, IL-38's role in M1 macrophage polarization in the temporomandibular joint (TMJ) and the related mechanism are still unclear. We aimed to explore the effect and the mechanism of IL-38 on synovial inflammation in the TMJ in this study.

METHODS

The expression of IL-38 in the TMJ synovium and macrophages was determined using immunohistochemistry (IHC) and Western blotting (WB). M1 macrophage polarization was induced by LPS, the macrophages were pre-treated with IL-38, and the levels of inflammatory markers associated with M1 macrophages were measured. To assess the mechanism of IL-38, small-interfering RNA (siRNA)-GLUT-1 and STF31 were administered to macrophages, and the affected pathways were identified by WB. The effect of macrophage-conditioned medium (CM) on chondrocyte function was also determined. Finally, a mouse model of CFA-induced TMJ inflammation was established. Histological staining and IHC were used to determine the effect of IL-38.

RESULTS

IL-38 was detected at high levels in macrophages after lipopolysaccharide (LPS)challenge, and IL-38 downregulated M1 macrophage-related proinflammatory markers (iNOS, IL-6, TNF-α, and COX-2) in vitro. IL-38 suppressed M1 polarization by inhibiting GLUT-1 expression, NF-κB signaling, and MAPK signaling. Intriguingly, CM from macrophages that were pretreated with IL-38 and STF31 decreased inflammatory protein expression in chondrocytes. In addition, intra-articular injection of recombinant IL-38 ameliorated synovial inflammation in the TMJ by inhibiting M1 macrophage polarization and suppressing cartilage inflammation in vivo.

CONCLUSIONS

IL-38 is a novel anti-inflammatory factor that contributes to alleviating TMJ inflammation by inhibiting macrophage M1 polarization, thereby ameliorating chondrocyte inflammation and restoring TMJ homeostasis.

M2 macrophage polarization: a potential target in pain relief

Pain imposes a significant urden on patients, affecting them physically, psychologically, and economically. Despite numerous studies on the pathogenesis of pain, its clinical management remains suboptimal, leading to the under-treatment of many pain patients. Recently, research on the role of macrophages in pain processes has been increasing, offering potential for novel therapeutic approaches. Macrophages, being indispensable immune cells in the innate immune system, exhibit remarkable diversity and plasticity. However, the majority of research has primarily focused on the contributions of M1 macrophages in promoting pain. During the late stage of tissue damage or inflammatory invasion, M1 macrophages typically transition into M2 macrophages. In recent years, growing evidence has highlighted the role of M2 macrophages in pain relief. In this review, we summarize the mechanisms involved in M2 macrophage polarization and discuss their emerging roles in pain relief. Notably, M2 macrophages appear to be key players in multiple endogenous pathways that promote pain relief. We further analyze potential pathways through which M2 macrophages may alleviate pain.

Dexamethasone Liposomes Alleviate Osteoarthritis in miR-204/-211-Deficient Mice by Repolarizing Synovial Macrophages to M2 Phenotypes

We undertook this study to investigate the effects and mechanisms of dexamethasone liposome (Dex-Lips) on alleviating destabilization of the medial meniscus (DMM)-induced osteoarthritis (OA) in miR-204/-211-deficient mice. Dex-Lips was prepared by the thin-film hydration method. The characterization of Dex-Lips was identified by the mean size, zeta potential, drug loading, and encapsulation efficiencies. Experimental OA was established by DMM surgery in miR-204/-211-deficient mice, and then Dex-Lips was treated once a week for 3 months. Von Frey filaments was used to perform the pain test. The inflammation level was evaluated with quantitative real-time polymerase chain reaction and enzyme-linked immunosorbent assay. Polarization of macrophages was evaluated by immunofluorescent staining. X-ray, micro-CT scanning, and histological observations were conducted in vivo on DMM mice to describe the OA phenotype. We found that miR-204/-211-deficient mice displayed more severe OA symptoms than WT mice after DMM surgery. Dex-Lips ameliorated DMM-induced OA phenotype and suppressed pain and inflammatory cytokine expressions. Dex-Lips could attenuate pain by regulating PGE2. Dex-Lips treatments reduced the expression of TNF-α, IL-1β, and IL-6 in DRG. Moreover, Dex-Lips could reduce inflammation in the cartilage and serum. Additionally, Dex-Lips repolarize synovial macrophages to M2 phenotypes in miR-204/-211-deficient mice. In conclusion, Dex-Lips inhibited the inflammatory response and alleviated the pain symptoms of OA by affecting the polarization of macrophages.

Expression pattern analysis of m6A regulators reveals IGF2BP3 as a key modulator in osteoarthritis synovial macrophages

BACKGROUND

Disruption of N6 methyl adenosine (m6A) modulation hampers gene expression and cellular functions, leading to various illnesses. However, the role of m6A modification in osteoarthritis (OA) synovitis remains unclear. This study aimed to explore the expression patterns of m6A regulators in OA synovial cell clusters and identify key m6A regulators that mediate synovial macrophage phenotypes.

METHODS

The expression patterns of m6A regulators in the OA synovium were illustrated by analyzing bulk RNA-seq data. Next, we built an OA LASSO-Cox regression prediction model to identify the core m6A regulators. Potential target genes of these m6A regulators were identified by analyzing data from the RM2target database. A molecular functional network based on core m6A regulators and their target genes was constructed using the STRING database. Single-cell RNA-seq data were collected to verify the effects of m6A regulators on synovial cell clusters. Conjoint analyses of bulk and single-cell RNA-seq data were performed to validate the correlation between m6A regulators, synovial clusters, and disease conditions. After IGF2BP3 was screened as a potential modulator in OA macrophages, the IGF2BP3 expression level was tested in OA synovium and macrophages, and its functions were further tested by overexpression and knockdown in vitro.

RESULTS

OA synovium showed aberrant expression patterns of m6A regulators. Based on these regulators, we constructed a well-fitting OA prediction model comprising six factors (FTO, YTHDC1, METTL5, IGF2BP3, ZC3H13, and HNRNPC). The functional network indicated that these factors were closely associated with OA synovial phenotypic alterations. Among these regulators, the m6A reader IGF2BP3 was identified as a potential macrophage mediator. Finally, IGF2BP3 upregulation was verified in the OA synovium, which promoted macrophage M1 polarization and inflammation.

CONCLUSIONS

Our findings revealed the functions of m6A regulators in OA synovium and highlighted the association between IGF2BP3 and enhanced M1 polarization and inflammation in OA macrophages, providing novel molecular targets for OA diagnosis and treatment.

Human Salivary Histatin-1 Attenuates Osteoarthritis through Promoting M1/M2 Macrophage Transition

Osteoarthritis (OA) is an inflammation-driven degenerative joint disease. Human salivary peptide histatin-1 (Hst1) shows pro-healing and immunomodulatory properties. but its role in OA treatment is not fully understood. In this study, we investigated the efficacy of Hst1 in the inflammation modulation-mediated attenuation of bone and cartilage damage in OA. Hst1 was intra-articularly injected into a rat knee joint in a monosodium iodoacetate (MIA)-induced OA model. Micro-CT, histological, and immunohistochemical analyses showed that Hst1 significantly attenuates cartilage and bone deconstruction as well as macrophage infiltration. In the lipopolysaccharide-induced air pouch model, Hst1 significantly reduced inflammatory cell infiltration and inflammation. Enzyme-linked immunosorbent assay (ELISA), RT-qPCR, Western blot, immunofluorescence staining, flow cytometry (FCM), metabolic energy analysis, and high-throughput gene sequencing showed that Hst1 significantly triggers M1-to-M2 macrophage phenotype switching, during which it significantly downregulated nuclear factor kappa-B (NF-κB) and mitogen-activated protein kinases (MAPK) signaling pathways. Furthermore, cell migration assay, Alcian blue, Safranin O staining, RT-qPCR, Western blot, and FCM showed that Hst1 not only attenuates M1-macrophage-CM-induced apoptosis and matrix metalloproteinase expression in chondrogenic cells, but it also restores their metabolic activity, migration, and chondrogenic differentiation. These findings show the promising potential of Hst1 in treating OA.

Nanomedicines Reprogram Synovial Macrophages by Scavenging Nitric Oxide and Silencing CA9 in Progressive Osteoarthritis

Osteoarthritis (OA) is a progressive joint disease characterized by inflammation and cartilage destruction, and its progression is closely related to imbalances in the M1/M2 synovial macrophages. A two-pronged strategy for the regulation of intracellular/extracellular nitric oxide (NO) and hydrogen protons for reprogramming M1/M2 synovial macrophages is proposed. The combination of carbonic anhydrase IX (CA9) siRNA and NO scavenger in "two-in-one" nanocarriers (NAHA-CaP/siRNA nanoparticles) is developed for progressive OA therapy by scavenging NO and inhibiting CA9 expression in synovial macrophages. In vitro experiments demonstrate that these NPs can significantly scavenge intracellular NO similar to the levels as those in the normal group and downregulate the expression levels of CA9 mRNA (≈90%), thereby repolarizing the M1 macrophages into the M2 phenotype and increasing the expression levels of pro-chondrogenic TGF-β1 mRNA (≈1.3-fold), and inhibiting chondrocyte apoptosis. Furthermore, in vivo experiments show that the NPs have great anti-inflammation, cartilage protection and repair effects, thereby effectively alleviating OA progression in both monoiodoacetic acid-induced early and late OA mouse models and a surgical destabilization of medial meniscus-induced OA rat model. Therefore, the siCA9 and NO scavenger "two-in-one" delivery system is a potential and efficient strategy for progressive OA treatment.

Inhibition of miR-182-5p Targets FGF9 to Alleviate Osteoarthritis

Background. The pathogenesis of osteoarthritis (OA) is complex and there is no specific drug for treatment. The aim of this study was to identify the molecular targets of OA therapy, focusing on the expression and biological functions of miR-182-5p and its target genes in OA. Methods. miR-182-5p and fibroblast growth factor 9 (FGF9) were overexpressed or knocked down in IL-1β-induced chondrocytes. An OA knee model was performed by surgically destroying the medial meniscus. The gene expression of miR-182-5p and FGF9 was calculated. The protein FGF9 was tested by western blotting. Cell counting kit-8 (CCK8), plate cloning assay, and flow cytometry were conducted to evaluate cell proliferation and apoptosis. The expression of inflammatory factors, tumor necrosis factor-alpha (TNF-α), interleukin (IL)-6, and interleukin (IL)-8, was evaluated using enzyme-linked immunosorbent assay (ELISA). Dual-luciferase reporter assays validated the targeting relationship between miR-182-5p and FGF9. Hematoxylin–eosin (HE) and safranin O-fast Green (S–O) staining were utilized to access cartilage damage. Ki67 expression in cartilage was detected using immunohistochemistry (IHC). TdT-mediated dUTP nick-end labeling (TUNEL) assays were used to calculate the apoptosis rate of cartilage. Results. The expression of miR-182-5p was upregulated, and FGF9 was downregulated in the IL-1β-induced chondrocytes. OA chondrocytes proliferation ability in the miR-182-5p mimics group was decreased, and the apoptosis rate and inflammatory factor were increased. Transfection with miR-182-5p inhibitor increased the proliferative ability and decreased the apoptosis rate in the IL-1β-induced chondrocytes. Transfection with miR-182-5p inhibitor reversed IL-1β-induced inflammatory factor release in chondrocytes. Targeted binding sites existed between miR-182-5p and FGF9. After overexpression of FGF9, the miR-182-5p effect on OA chondrocytes was reversed. The hyaline cartilage thickness and proteoglycan content decreased in OA rats, and this was reversed by miR-182-5p inhibitor treatment. Conclusions. miR-182-5p expression levels were increased in OA chondrocytes and regulated chondrocyte proliferation, apoptosis, and inflammation by targeting FGF9. miR-182-5p is a potential gene for OA treatment.

Apigenin Inhibits the Progression of Osteoarthritis by Mediating Macrophage Polarization

OBJECTIVE

The overall purpose of this study was to investigate the mechanism of macrophage polarization on chondrocyte injury in osteoarthritis and the protective effect of apigenin on chondrocytes in osteoarthritis.

METHOD

Primary chondrocytes were isolated from the knee cartilage of three-day-old mice, and cells positive for Alsine blue staining and type II collagen immunocytochemical staining were identified and used in followup experiments. Transwell coculture was performed. Chondrocytes were inoculated in the inferior compartment, and macrophages were inoculated in the upper compartment. The experimental groups were the N group, LPS group, and LPS+ apigenin group. The effect of macrophage polarization on chondrocyte inflammation and the protective effect of apigenin on chondrocytes were verified by the drug administration. Real-time quantitative PCR (qPCR) and Western blot were used to detect the expression of RNA and protein. Experimental OA was induced by modified Hulth surgery in mice. Modified Hulth surgery was performed on the mouse's right knee to induce experimental osteoarthritis in mice, with the nonoperative right knee serving as an ipsilateral control. The mice were randomly assigned to three groups (six mice per group): the sham group, the modified Hulth group, and the modified Hulth + apigenin group. Animals were given gavage for four weeks. The protective effect of apigenin on articular cartilage was verified by histological staining and immunohistochemical analysis.

RESULTS

Histological staining showed that apigenin had a protective effect on cartilage degeneration induced by modified Hulth surgery. The PCR results showed that apigenin significantly reduced the expression levels of IL-1, IL-6, MMP3, and MMP13 in the articular cartilage of OA mice, and it had a protective effect on articular cartilage. Apigenin reduced the levels of IL-1, IL-6, TNF-α, and IL-12 in macrophages and increased the levels of MG-L1, MG-L2, ARG-1, and IL-10, which can inhibit the M1 polarization of macrophages and promote M2 polarization. In the coculture system, apigenin decreased the protein levels of TRPM7, P-mTOR, BAX, and c-caspase3 in macrophages, while significantly increasing the protein levels of Bcl2. The levels of IL-1, IL-6, MMP13, TNF-α, P38, JNK, and ERK phosphorylation were reduced in chondrocytes.

CONCLUSION

Apigenin alleviates cartilage injury in OA mice induced by modified Hulth. Apigenin inhibits chondrocyte inflammation through the MAPK pathway. Apigenin alleviates macrophage-polarization-induced inflammatory response and chondrocyte apoptosis in the macrophage-chondrocyte coculture system through the TRPM7-mTOR pathway.

Metformin Attenuates the Inflammatory Response via the Regulation of Synovial M1 Macrophage in Osteoarthritis

Osteoarthritis (OA), the most common chronic inflammatory joint disease, is characterized by progressive cartilage degeneration, subchondral bone sclerosis, synovitis, and osteophyte formation. Metformin, a hypoglycemic agent used in the treatment of type 2 diabetes, has been evidenced to have anti-inflammatory properties to treat OA. It hampers the M1 polarization of synovial sublining macrophages, which promotes synovitis and exacerbates OA, thus lessening cartilage loss. In this study, metformin prevented the pro-inflammatory cytokines secreted by M1 macrophages, suppressed the inflammatory response of chondrocytes cultured with conditional medium (CM) from M1 macrophages, and mitigated the migration of M1 macrophages induced by interleukin-1ß (IL-1ß)-treated chondrocytes in vitro. In the meantime, metformin reduced the invasion of M1 macrophages in synovial regions brought about by the destabilization of medial meniscus (DMM) surgery in mice, and alleviated cartilage degeneration. Mechanistically, metformin regulated PI3K/AKT and downstream pathways in M1 macrophages. Overall, we demonstrated the therapeutic potential of metformin targeting synovial M1 macrophages in OA.

Role of M2 macrophages-derived extracellular vesicles in IL-1β-stimulated chondrocyte proliferation and inflammatory responses

M2 macrophages-derived extracellular vesicles (M2-EVs) serve as a tool for the delivery of miRNAs and play an anti-inflammatory role in diseases. This study sought to explore the role of (M2-EVs) in the proliferation and inflammatory responses of IL-1β-stimulated chondrocytes. M2 macrophages were induced and characterized, followed by isolation and characterization of M2-EVs. Chondrocytes were treated with 10 ng/mL IL-1β and co-cultured with M2 macrophages transfected with Cy3-labeled miR-370-3p. Cell viability, TNF (tumor necrosis factor)-α, IL(Interleukin)-18, IL-10, miR-370-3p, and sex-determining region Y-related high-mobility-group box transcription factor 11 (SOX11) mRNA were determined via cell counting assay kit, colony formation, ELISA, and qRT-PCR. The binding relationship between miR-370-3p and SOX11 was testified via the dual-luciferase assay. The functional rescue experiment was designed to confirm the role of SOX11. M2-EVs improved chondrocyte viability and colony formation, lowered TNF-α and IL-18, and elevated IL-10. M2-EVs delivered miR-370-3p into chondrocytes to upregulate miR-370-3p. Upregulation of miR-370-3p in M2-EVs enhanced the protective role of M2-EVs in chondrocytes. miR-370-3p inhibited SOX11 transcription. SOX11 overexpression attenuated the protective role of M2-EVs in chondrocytes. Overall, our findings suggested that M2-EVs promote proliferation and suppress inflammatory responses in IL-1β-stimulated chondrocytes via the miR-370-3p/SOX11 axis.

Targeting macrophage polarization as a promising therapeutic strategy for the treatment of osteoarthritis

Osteoarthritis (OA) is a chronic osteoarthropathy characterized by the progressive degeneration of articular cartilage and synovial inflammation. Early OA clinical treatments involve intra-articular injection of glucocorticoids, oral acetaminophen and non-steroidal anti-inflammatory drugs (NSAIDs), which are used for anti-inflammation and pain relief. However, long-term use of these agents will lead to inevitable side effects, even aggravate cartilage loss. At present, there are no disease-modifying OA drugs (DMOADs) yet approved by regulatory agencies. Polarization regulation of synovial macrophages is a new target for OA treatment. Inhibiting M1 polarization and promoting M2 polarization of synovial macrophages can alleviate synovial inflammation, relieve joint pain and inhibit articular cartilage degradation, which is a promising strategy for OA treatment. In this study, we describe the molecular mechanisms of macrophage polarization and its key role in the development of OA. Subsequently, we summarize the latest progress of strategies for OA treatment through macrophage reprogramming, including small molecule compounds (conventional western medicine and synthetic compounds, monomer compounds of traditional Chinese medicine), biomacromolecules, metal/metal oxides, cells, and cell derivatives, and interprets the molecular mechanisms, hoping to provide some information for DMOADs development.

Effective Reversal of Macrophage Polarization by Inhibitory Combinations Predicted by a Boolean Protein–Protein Interaction Model

Background: The function and polarization of macrophages has a significant impact on the outcome of many diseases. Targeting tumor-associated macrophages (TAMs) is among the greatest challenges to solve because of the low in vitro reproducibility of the heterogeneous tumor microenvironment (TME). To create a more comprehensive model and to understand the inner workings of the macrophage and its dependence on extracellular signals driving polarization, we propose an in silico approach. Methods: A Boolean control network was built based on systematic manual curation of the scientific literature to model the early response events of macrophages by connecting extracellular signals (input) with gene transcription (output). The network consists of 106 nodes, classified as 9 input, 75 inner and 22 output nodes, that are connected by 217 edges. The direction and polarity of edges were manually verified and only included in the model if the literature plainly supported these parameters. Single or combinatory inhibitions were simulated mimicking therapeutic interventions, and output patterns were analyzed to interpret changes in polarization and cell function. Results: We show that inhibiting a single target is inadequate to modify an established polarization, and that in combination therapy, inhibiting numerous targets with individually small effects is frequently required. Our findings show the importance of JAK1, JAK3 and STAT6, and to a lesser extent STK4, Sp1 and Tyk2, in establishing an M1-like pro-inflammatory polarization, and NFAT5 in creating an anti-inflammatory M2-like phenotype. Conclusions: Here, we demonstrate a protein–protein interaction (PPI) network modeling the intracellular signalization driving macrophage polarization, offering the possibility of therapeutic repolarization and demonstrating evidence for multi-target methods.

Distinct differences in immunological properties of equine orthobiologics revealed by functional and transcriptomic analysis using an activated macrophage readout system

Introduction

Multiple biological therapies for orthopedic injuries are marketed to veterinarians, despite a lack of rigorous comparative biological activity data to guide informed decisions in selecting a most effective compound. Therefore, the goal of this study was to use relevant bioassay systems to directly compare the anti-inflammatory and immunomodulatory activity of three commonly used orthobiological therapies (OTs): mesenchymal stromal cells (MSC), autologous conditioned serum (ACS), and platelet rich plasma (PRP).

Methods

Equine monocyte-derived macrophages were used as the readout system to compare therapies, including cytokine production and transcriptomic responses. Macrophages were stimulated with IL-1ß and treated 24 h with OTs, washed and cultured an additional 24 h to generate supernatants. Secreted cytokines were measured by multiplex immunoassay and ELISA. To assess global transcriptomic responses to treatments, RNA was extracted from macrophages and subjected to full RNA sequencing, using an Illumina-based platform. Data analysis included comparison of differentially expressed genes and pathway analysis in treated vs. untreated macrophages.

Results

All treatments reduced production of IL-1ß by macrophages. Secretion of IL-10 was highest in MSC-CM treated macrophages, while PRP lysate and ACS resulted in greater downregulation of IL-6 and IP-10. Transcriptomic analysis revealed that ACS triggered multiple inflammatory response pathways in macrophages based on GSEA, while MSC generated significant downregulation of inflammatory pathways, and PRP lysate induced a mixed immune response profile. Key downregulated genes in MSC-treated cultures included type 1 and type 2 interferon response, TNF-α and IL-6. PRP lysate cultures demonstrated downregulation of inflammation-related genes IL-1RA, SLAMF9, ENSECAG00000022247 but concurrent upregulation of TNF-α, IL-2 signaling, and Myc targets. ACS induced upregulation of inflammatory IL-2 signaling, TNFα and KRAS signaling and hypoxia, but downregulation of MTOR signaling and type 1 interferon signaling.

Discussion

These findings, representing the first comprehensive look at immune response pathways for popular equine OTs, reveal distinct differences between therapies. These studies address a critical gap in our understanding of the relative immunomodulatory properties of regenerative therapies commonly used in equine practice to treat musculoskeletal disease and will serve as a platform from which further in vivo comparisons may build.

Sotetsuflavone ameliorates Crohn's disease-like colitis by inhibiting M1 macrophage-induced intestinal barrier damage via JNK and MAPK signalling

OBJECTIVES

Intestinal inflammation and intestinal barrier dysfunction are two important pathological changes in Crohn's disease (CD). Sotetsuflavone (SF) is a natural monomeric herbal compound with anti-inflammatory and cytoprotective effects that is mostly nontoxic. The effect of SF on CD-like spontaneous colitis was investigated in this study.

METHODS

Il-10^-/- mice were used as a CD model and were administered different doses of SF. Lipopolysaccharide (LPS) plus IFN-γ-induced macrophages (RAW264.7) and a coculture system (RAW264.7 and organoids) were used in vitro. The protective effects of SF against CD-like colitis and macrophage differentiation and the mechanisms were evaluated.

RESULTS

SF treatment markedly improved spontaneous colitis in the CD model, as shown by the following evidence: reductions in the DAI, macroscopic scores (3.63 ± 1.30), colonic tissue inflammatory scores (2 ± 0.76) and proinflammatory factor levels and the attenuation of colon shortening (8 ± 0.93 cm) and weight loss (1.75 ± 1.83 g). Decreased intestinal permeability and intestinal bacterial translocation rates provided evidence of the protective effect of SF on intestinal barrier function. We also found that SF suppressed M1 macrophage-induced inflammatory responses. In the coculture system of mouse colonic organoids and RAW264.7 cells, SF significantly ameliorated M1 macrophage-induced intestinal epithelial damage. In addition, SF inhibited JNK and MAPK (p38) signalling in both Il-10^-/- mice and LPS plus IFN-γ-induced macrophages (RAW264.7).

CONCLUSIONS

The protective effects of SF against CD-like colitis may be achieved partially by inhibiting M1 macrophage-induced intestinal barrier damage via JNK and p38 signalling. SF may have therapeutic potential for treating CD, especially considering its safety.

Analyzing network pharmacology and molecular docking to clarify Duhuo Jisheng decoction potential mechanism of osteoarthritis mitigation

As a classic remedy for treating Osteoarthritis (OA), Duhuo Jisheng decoction has successfully treated countless patients. Nevertheless, its specific mechanism is unknown. This study explored the active constituents of Duhuo Jisheng decoction and the potential molecular mechanisms for treating OA using a Network Pharmacology approaches. Screening active components and corresponding targets of Duhuo parasite decoction by traditional Chinese medicine systems pharmacology database and analysis platform database. Combining the following databases yielded OA disease targets: GeneCards, DrugBank, PharmGkb, Online Mendelian Inheritance in Man, and therapeutic target database. The interaction analysis of the herb-active ingredient-core target network and protein-protein interaction protein network was constructed by STRING platform and Cytoscape software. Gene ontology functional enrichment analysis and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis were carried out. PyMOL and other software were used to verify the molecular docking between the essential active components and the core target. 262 active ingredients were screened, and their main components were quercetin, kaempferol, wogonin, baicalein, and beta-carotene. 108 intersection targets of disease and drug were identified, and their main components were RELA, FOS, STAT3, MAPK14, MAPK1, JUN, and ESR1. Gene ontology analysis showed that the key targets were mainly involved in biological processes such as response to lipopolysaccharide, response to xenobiotic stimulus, and response to nutrient levels. The results of Kyoto Encyclopedia of Genes and Genomes analysis show that the signal pathways include the AGE - RAGE signaling pathway, IL - 17 signaling pathway, TNF signaling pathway, and Toll - like receptor signaling pathway. Molecular docking showed that the main active components of Duhuo parasitic decoction had a good bonding activity with the key targets in treating OA. Duhuo Jisheng decoction can reduce the immune-inflammatory reaction, inhibit apoptosis of chondrocytes, strengthen proliferation and repair of chondrocytes and reduce the inflammatory response in a multi-component-multi-target-multi-pathway way to play a role in the treatment of OA.

Engineered M2a macrophages for the treatment of osteoarthritis

Background

Macrophage is a central regulator of innate immunity. Its M2 subsets, such as interstitial synovial macrophages, have been found to play critical roles in suppressing chronic inflammation and maintaining homeostasis within the joint. These macrophages have great potential as a disease-modifying cell therapy for osteoarthritis (OA). However, this has not yet been studied.

Methods

Macrophages were isolated from the bone marrow of rats. We constructed a stable macrophage that "locked" in anti-inflammatory and pro-regenerative M2a polarity (L-M2a) by simultaneously knocking out tumor necrosis factor receptor 1 (TNFR1) and overexpressing IL-4 using Cas9-ribonuclear proteins (Cas9-RNP) and electroporation. In vitro, these L-M2a macrophages were treated with OA synovial fluid or co-cultured with OA chondrocytes or fibroblast-like synoviocytes (FLS). In vivo, L-M2a macrophages were injected intra-articularly to evaluate their homing and engrafting abilities and therapeutic effects on OA progression using a rat model.

Results

L-M2a macrophages displayed a typical anti-inflammatory phenotype similar to that of M2 macrophages in vitro. In OA microenvironment, L-M2a macrophages maintained a stable anti-inflammatory phenotype, whereas unmodified M2 macrophages lost their phenotype and switched to M1 polarity. L-M2a macrophages demonstrated a potent anti-inflammatory effect in crosstalk with OA-FLSs and an anti-degenerative effect in crosstalk with senescent OA chondrocytes. In vivo, compared with M2 macrophages and exosomes, L-M2a macrophages exhibited significantly superior therapeutic effects in OA by successfully resolving inflammation, restoring tissue homeostasis, and promoting cartilage regeneration.

Conclusion

The engineered L-M2a macrophages maintained a superior anti-inflammatory and pro-regenerative capacity in the inflammatory OA microenvironment and represents an ideal new strategy for the disease-modifying therapy of OA.

Overview of Anti-Inflammatory and Anti-Nociceptive Effects of Polyphenols to Halt Osteoarthritis: From Preclinical Studies to New Clinical Insights

Knee osteoarthritis (OA) is one of the most multifactorial joint disorders in adults. It is characterized by degenerative and inflammatory processes that are responsible for joint destruction, pain and stiffness. Despite therapeutic advances, the search for alternative strategies to target inflammation and pain is still very challenging. In this regard, there is a growing body of evidence for the role of several bioactive dietary molecules (BDMs) in targeting inflammation and pain, with promising clinical results. BDMs may be valuable non-pharmaceutical solutions to treat and prevent the evolution of early OA to more severe phenotypes, overcoming the side effects of anti-inflammatory drugs. Among BDMs, polyphenols (PPs) are widely studied due to their abundance in several plants, together with their benefits in halting inflammation and pain. Despite their biological relevance, there are still many questionable aspects (biosafety, bioavailability, etc.) that hinder their clinical application. This review highlights the mechanisms of action and biological targets modulated by PPs, summarizes the data on their anti-inflammatory and anti-nociceptive effects in different preclinical in vitro and in vivo models of OA and underlines the gaps in the knowledge. Furthermore, this work reports the preliminary promising results of clinical studies on OA patients treated with PPs and discusses new perspectives to accelerate the translation of PPs treatment into the clinics.

Identification of crucial salivary proteins/genes and pathways involved in pathogenesis of temporomandibular disorders

Temporomandibular disorder (TMD) is a collective term for a group of conditions that lead to impairment of the function of the temporomandibular joint. The proteins/genes and signaling pathways associated with TMD are still poorly understood. The aim of this study was to identify key differentially expressed salivary proteins/genes (DEGs) associated with TMD progression using LC-MS/MS coupled with a bioinformatics approach. The protein–protein interaction network was obtained from the STRING database and the hub genes were identified using Cytoscape including cytoHubba and MCODE plug-ins. In addition, enrichment of gene ontology functions and the Reactome signaling pathway was performed. A total of 140 proteins/genes were differentially expressed. From cluster analysis, a set of 20 hub genes were significantly modulated: ALB, APOA1, B2M, C3, CAT, CLU, CTSD, ENO1, GSN, HBB, HP, HSPA8, LTF, LYZ, MMP9, S100A9, SERPINA1, TF, TPI1, and TXN. Two enriched signaling pathways, glycolysis and gluconeogenesis, and tryptophan signaling pathway involving the hub genes CAT, ENO1, and TPI1 have been identified. The rest of the hub genes were mainly enriched in the innate immune system and antimicrobial peptides signaling pathways. In summary, hub DEGs and the signaling pathways identified here have elucidated the molecular mechanisms of TMD pathogenesis.

Blocking TRPV4 Ameliorates Osteoarthritis by Inhibiting M1 Macrophage Polarization via the ROS/NLRP3 Signaling Pathway

Osteoarthritis (OA) is a low-level inflammatory disease in which synovial macrophage M1 polarization exacerbates the progression of synovitis and OA. Notedly, the ROS (reactive oxygen species) level in macrophages is intimately implicated in macrophage M1 polarization. TRPV4 (transient receptor potential channel subfamily V member 4), as an ion channel, plays a pivotal role in oxidative stress and inflammation. In this study, we investigated the role of TRPV4 in OA progression and M1 macrophage polarization. Male adult Sprague-Dawley (SD) rats underwent a medial meniscus radial transection operation to create an OA model in vivo and RAW 264.7 cells were intervened with 100 ng/mL LPS (lipopolysaccharide) to induce M1-polarized macrophages in vitro. We demonstrated that the infiltration of M1 synovial macrophages and the expression of TRPV4 were increased significantly in OA synovium. In addition, intra-articular injection of HC067074 (a specific inhibitor of TRPV4) alleviated the progression of rat OA and significantly decreased synovial macrophage M1 polarization. Further mechanisms suggested that ROS production by M1 macrophages was decreased after TRPV4 inhibition. In addition, NLRP3 (pyrin domain containing protein 3) as a downstream effector of ROS in M1-polarized macrophage, was significantly suppressed following TRPV4 inhibition. In conclusion, this study discovered that inhibition of TRPV4 delays OA progression by inhibiting M1 synovial macrophage polarization through the ROS/NLRP3 pathway.

Cutting-Edge Approaches in Arthroplasty: Before, during and after Surgery

Personalised medicine was introduced in arthroplasty a long time ago with the aim of respecting each individual person for their unique personal characteristics in order to further improve outcomes [...].

Advances in the therapeutic application and pharmacological properties of kinsenoside against inflammation and oxidative stress-induced disorders

Extensive research has implicated inflammation and oxidative stress in the development of multiple diseases, such as diabetes, hepatitis, and arthritis. Kinsenoside (KD), a bioactive glycoside component extracted from the medicinal plant Anoectochilus roxburghii, has been shown to exhibit potent anti-inflammatory and anti-oxidative abilities. In this review, we summarize multiple effects of KD, including hepatoprotection, pro-osteogenesis, anti-hyperglycemia, vascular protection, immune regulation, vision protection, and infection inhibition, which are partly responsible for suppressing inflammation signaling and oxidative stress. The protective action of KD against dysfunctional lipid metabolism is also associated with limiting inflammatory signals, due to the crosstalk between inflammation and lipid metabolism. Ferroptosis, a process involved in both inflammation and oxidative damage, is potentially regulated by KD. In addition, we discuss the physicochemical properties and pharmacokinetic profiles of KD. Advances in cultivation and artificial synthesis techniques are promising evidence that the shortage in raw materials required for KD production can be overcome. In addition, novel drug delivery systems can improve the in vivo rapid clearance and poor bioavailability of KD. In this integrated review, we aim to offer novel insights into the molecular mechanisms underlying the therapeutic role of KD and lay solid foundations for the utilization of KD in clinical practice.

Exosomes from dysfunctional chondrocytes affect osteoarthritis in Sprague-Dawley rats through FTO-dependent regulation of PIK3R5 mRNA stability

Aims

Exosomes (exo) are involved in the progression of osteoarthritis (OA). This study aimed to investigate the function of dysfunctional chondrocyte-derived exo (DC-exo) on OA in rats and rat macrophages.

Methods

Rat-derived chondrocytes were isolated, and DCs induced with interleukin (IL)-1β were used for exo isolation. Rats with OA (n = 36) or macrophages were treated with DC-exo or phosphate-buffered saline (PBS). Macrophage polarization and autophagy, and degradation and chondrocyte activity of cartilage tissues, were examined. RNA sequencing was used to detect genes differentially expressed in DC-exo, followed by RNA pull-down and ribonucleoprotein immunoprecipitation (RIP). Long non-coding RNA osteoarthritis non-coding transcript (OANCT) and phosphoinositide-3-kinase regulatory subunit 5 (PIK3R5) were depleted in DC-exo-treated macrophages and OA rats, in order to observe macrophage polarization and cartilage degradation. The PI3K/AKT/mammalian target of rapamycin (mTOR) pathway activity in cells and tissues was measured using western blot.

Results

DC-exo inhibited macrophage autophagy (p = 0.002) and promoted M1 macrophage polarization (p = 0.002). DC-exo at 20 μg/ml induced collagen degradation (p < 0.001) and inflammatory cell infiltration (p = 0.023) in rats. OANCT was elevated in DC (p < 0.001) and in cartilage tissues of OA patients (p < 0.001), and positively correlated with patients’ Kellgren-Lawrence grade (p < 0.001). PIK3R5 was increased in DC-exo-treated cartilage tissues (p < 0.001), and OANCT bound to fat mass and obesity-associated protein (FTO) (p < 0.001). FTO bound to PIK3R5 (p < 0.001) to inhibit the stability of PIK3R5 messenger RNA (mRNA) (p < 0.001) and disrupt the PI3K/AKT/mTOR pathway (p < 0.001).

Conclusion

Exosomal OANCT from DC could bind to FTO protein, thereby maintaining the mRNA stability of PIK3R5, further activating the PI3K/AKT/mTOR pathway to exacerbate OA.

Cite this article: Bone Joint Res 2022;11(9):652–668.

Omega-3 Fatty Acids for the Management of Osteoarthritis: A Narrative Review

Osteoarthritis (OA) is a disease which results in degeneration of cartilage within joints and affects approximately 13.6% of adults over 20 years of age in Canada and the United States of America. OA is characterized by a state of low-grade inflammation which leads to a greater state of cellular catabolism disrupting the homeostasis of cartilage synthesis and degradation. Omega-3 polyunsaturated fatty acids (PUFAs) have been postulated as a potential therapeutic treatment option for individuals with OA. Omega-3 PUFAs are recognized for their anti-inflammatory properties, which could be beneficial in the context of OA to moderate pro-inflammatory markers and cartilage loss. The purpose of this narrative review is to outline recent pre-clinical and clinical evidence for the use of omega-3 in the management of OA.

Nrf2-mediated anti-inflammatory polarization of macrophages as therapeutic targets for osteoarthritis

Macrophages are the most abundant immune cells within the synovial joints, and also the main innate immune effector cells triggering the initial inflammatory responses in the pathological process of osteoarthritis (OA). The transition of synovial macrophages between pro-inflammatory and anti-inflammatory phenotypes can play a key role in building the intra-articular microenvironment. The pro-inflammatory cascade induced by TNF-α, IL-1β, and IL-6 is closely related to M1 macrophages, resulting in the production of pro-chondrolytic mediators. However, IL-10, IL1RA, CCL-18, IGF, and TGF are closely related to M2 macrophages, leading to the protection of cartilage and the promoted regeneration. The inhibition of NF-κB signaling pathway is central in OA treatment via controlling inflammatory responses in macrophages, while the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway appears not to attract widespread attention in the field. Nrf2 is a transcription factor encoding a large number of antioxidant enzymes. The activation of Nrf2 can have antioxidant and anti-inflammatory effects, which can also have complex crosstalk with NF-κB signaling pathway. The activation of Nrf2 can inhibit the M1 polarization and promote the M2 polarization through potential signaling transductions including TGF-β/SMAD, TLR/NF-κB, and JAK/STAT signaling pathways, with the regulation or cooperation of Notch, NLRP3, PI3K/Akt, and MAPK signaling. And the expression of heme oxygenase-1 (HO-1) and the negative regulation of Nrf2 for NF-κB can be the main mechanisms for promotion. Furthermore, the candidates of OA treatment by activating Nrf2 to promote M2 phenotype macrophages in OA are also reviewed in this work, such as itaconate and fumarate derivatives, curcumin, quercetin, melatonin, mesenchymal stem cells, and low-intensity pulsed ultrasound.

Exosomes rewire the cartilage microenvironment in osteoarthritis: from intercellular communication to therapeutic strategies

Osteoarthritis (OA) is a prevalent degenerative joint disease characterized by cartilage loss and accounts for a major source of pain and disability worldwide. However, effective strategies for cartilage repair are lacking, and patients with advanced OA usually need joint replacement. Better comprehending OA pathogenesis may lead to transformative therapeutics. Recently studies have reported that exosomes act as a new means of cell-to-cell communication by delivering multiple bioactive molecules to create a particular microenvironment that tunes cartilage behavior. Specifically, exosome cargos, such as noncoding RNAs (ncRNAs) and proteins, play a crucial role in OA progression by regulating the proliferation, apoptosis, autophagy, and inflammatory response of joint cells, rendering them promising candidates for OA monitoring and treatment. This review systematically summarizes the current insight regarding the biogenesis and function of exosomes and their potential as therapeutic tools targeting cell-to-cell communication in OA, suggesting new realms to improve OA management.

Reprogramming Mitochondrial Metabolism in Synovial Macrophages of Early Osteoarthritis by a Camouflaged Meta-Defensome

Osteoarthritis (OA) is a low-grade inflammatory and progressive joint disease, and its progression is closely associated with an imbalance in M1/M2 synovial macrophages. Repolarizing pro-inflammatory M1 macrophages into the anti-inflammatory M2 phenotype is emerging as a strategy to alleviate OA progression but is compromised by unsatisfactory efficiency. In this study, the reprogramming of mitochondrial dysfunction is pioneered with a camouflaged meta-Defensome, which can transform M1 synovial macrophages into the M2 phenotype with a high efficiency of 82.3%. The meta-Defensome recognizes activated macrophages via receptor-ligand interactions and accumulates in the mitochondria through electrostatic attractions. These meta-Defensomes are macrophage-membrane-coated polymeric nanoparticles decorated with dual ligands and co-loaded with S-methylisothiourea and MnO₂ . Meta-Defensomes are demonstrated to successfully reprogram the mitochondrial metabolism of M1 macrophages by scavenging mitochondrial reactive oxygen species and inhibiting mitochondrial NO synthase, thereby increasing mitochondrial transcription factor A expression and restoring aerobic respiration. Furthermore, meta-Defensomes are intravenously injected into collagenase-induced osteoarthritis mice and effectively suppress synovial inflammation and progression of early OA, as evident from the Osteoarthritis Research Society International score. Therefore, reprogramming the mitochondrial metabolism can serve as a novel and practical approach to repolarize M1 synovial macrophages. The camouflaged meta-Defensomes are a promising therapeutic agent for impeding OA progression in tclinic.

Low-Grade Inflammation in the Pathogenesis of Osteoarthritis: Cellular and Molecular Mechanisms and Strategies for Future Therapeutic Intervention

Osteoarthritis (OA) is a musculoskeletal disease characterized by cartilage degeneration and stiffness, with chronic pain in the affected joint. It has been proposed that OA progression is associated with the development of low-grade inflammation (LGI) in the joint. In support of this principle, LGI is now recognized as the major contributor to the pathogenesis of obesity, aging, and metabolic syndromes, which have been documented as among the most significant risk factors for developing OA. These discoveries have led to a new definition of the disease, and OA has recently been recognized as a low-grade inflammatory disease of the joint. Damage-associated molecular patterns (DAMPs)/alarmin molecules, the major cellular components that facilitate the interplay between cells in the cartilage and synovium, activate various molecular pathways involved in the initiation and maintenance of LGI in the joint, which, in turn, drives OA progression. A better understanding of the pathological mechanisms initiated by LGI in the joint represents a decisive step toward discovering therapeutic strategies for the treatment of OA. Recent findings and discoveries regarding the involvement of LGI mediated by DAMPs in OA pathogenesis are discussed. Modulating communication between cells in the joint to decrease inflammation represents an attractive approach for the treatment of OA.