Role of TLR2 and TLR4 in regulation of articular chondrocyte homeostasis

Mechanistic insights into EIF6 as a target of Apigenin in alleviating chondrocyte senescence

PURPOSE

Apigenin, a flavonoid found in edible plants, has demonstrated therapeutic potential in various diseases, but its role in knee osteoarthritis (KOA) remains unclear. This study aimed to identify the potential targets and mechanisms of Apigenin in KOA.

METHODS

Network pharmacology analysis identified 80 targets of Apigenin, of which 48 overlapped with KOA-related targets. Summary-data-based Mendelian randomization (SMR) analysis and molecular docking were utilized to explore key target genes. Single-cell RNA sequencing data from human cartilage tissue and in vitro studies using SW1353 cells treated with 3 % hydrogen peroxide (H2O2) were analyzed to validate findings.

RESULTS

SMR analysis identified EIF6 as a potential target of Apigenin in KOA, negatively associated with disease progression. Molecular docking revealed strong binding affinity between Apigenin and EIF6. Single-cell analysis suggested downregulation of EIF6 may contribute to chondrocyte senescence. In vitro, Apigenin (20 μM) reversed H2O2-induced senescence and increased EIF6 expression in SW1353 cells, improving cell viability.

CONCLUSION

Apigenin upregulates EIF6 expression and mitigates H2O2-induced chondrocyte senescence, highlighting its potential as a therapeutic agent for KOA. These findings provide insights into the nutritional health benefits of Apigenin and its implications for KOA treatment.

Chondrocyte Mitochondrial Quality Control: A Novel Insight into Osteoarthritis and Cartilage Regeneration

Significance: Osteoarthritis (OA), one of the most prevalent joint diseases affecting more than 240 million people, strongly influences human health and reduces life quality. This review aims to fill the current research gap regarding the application and potential of mitochondrial quality control (MQC) based therapies in the treatment of OA, thereby providing guidance for future research and clinical practice. Recent Advances: Chondrocytes respond to the inflammatory microenvironment via an array of signaling pathways and thus are critical in cartilage degeneration and OA progression. Mitochondria, as an important metabolic center in chondrocytes, play a vital role in responding to inflammatory stimuli. Multiple MQC mechanisms, including mitochondrial antioxidant defense, mitochondrial protein quality control, mitochondrial DNA repair, mitochondrial dynamics, mitophagy, and mitochondrial biogenesis, sustain mitochondrial homeostasis under pathological conditions. Critical Issues: Despite extensive OA research, effective therapies remain limited. Elucidating MQC mechanisms in disease progression and post-traumatic cartilage repair is crucial. While preclinical studies demonstrate potential, clinical translation requires addressing protocol standardization, patient stratification, and long-term efficacy, as well as safety validation. Future Directions: Future research should focus on developing personalized MQC-based OA therapies guided by biomarker profiling and signaling pathway modulation. However, translational challenges persist, particularly regarding pervasive off-target effects, inadequate OA-specific targeting capacity, interpatient heterogeneity, and reliable evaluation of long-term therapeutic efficacy. Strategic prioritization of OA-specific MQC targets coupled with delivery system optimization may significantly improve both clinical translatability and therapeutic outcomes.

Enhanced collagen deposition in chondrogenic inflammation with Ibuprofen-specifically loaded chitosan/poly-gamma-glutamic acid nanoparticles

Osteoarthritis (OA) is characterized by degeneration of articular cartilage, related to a pro-inflammatory environment. Different anti-inflammatory drugs have been proposed to treat OA symptoms, namely those from the group of non-steroidal anti-inflammatory drugs (NSAID), but they carry several drawbacks and are not able to repair/regenerate cartilage tissues. In this study, Chitosan (Ch) and Poly-Glutamic acid (PGA) were combined with Ibuprofen, a NSAID widely used in OA, for drug delivery. Ibuprofen-Ch/PGA nanoparticles (Ibuf-NPs) were produced by co-acervation method, and ability to control inflammation and promote chondrogenesis under a pro-inflammatory setting, was evaluated in vitro. To model OA, human bone marrow-derived mesenchymal stem/stromal cells (MSCs) were cultured in 3D pellets for up to 14 days in chondrogenic medium supplemented with pro-inflammatory IL-1β (10 ng/mL). Physicochemical characterization of Ibuf-Ch/PGA NPs, drug release, and anti-inflammatory potential of the Ibuf-NPs were evaluated in IL-1β-supplemented MSC pellets. Cartilage ECM was then characterized by histology/immunohistochemistry (IHC). Ibuf-Ch/PGA NPs (200 nm, 0.2 PdI, 20 mV charge) were obtained, with high drug entrapment efficiency (>90 %), and fast release at physiological pH. Both free drug and Ibuf-Ch/PGA NPs significantly reduce PGE2 in IL-1β-stimulated MSC pellets, but only Ibuf-NPs significantly stimulated collagen deposition, specifically collagen type 2. Overall, this study emphasizes a synergic potential of the NSAID Ibuprofen and Ch/PGA NPs to promote collagen deposition during chondrogenesis under pro-inflammatory conditions, opening new horizons in NSAID-based therapies to modulate inflammation in the context of OA.

Transcriptomic analysis of human cartilage identified potential therapeutic targets for hip osteoarthritis

Cartilage degradation is the hallmark of osteoarthritis (OA). The purpose of this study was to identify and validate differentially expressed genes (DEGs) in human articular cartilage that could serve as potential therapeutic targets for hip OA. We performed transcriptomic profiling in a discovery cohort (12 OA-free and 72 hip OA-affected cartilage) and identified 179 DEGs between OA-free and OA-affected cartilage after correcting for multiple testing (P < 2.97 × 10-6). Pathway and network analyses found eight hub genes to be associated with hip OA (ASPN, COL1A2, MXRA5, P3H1, PCOLCE, SDC1, SPARC, and TLR2), which were all confirmed using qPCR in a validation cohort (36 OA-free and 62 hip OA-affected cartilage) (P < 6.25 × 10-3). Our data showed that dysregulation of extracellular matrix formation and imbalance in the proportion of collagen chains may contribute to the development of hip OA, and SDC1 could be a promising potential therapeutic target. These findings provided a better understanding of the molecular mechanisms for hip OA and may assist in developing targeted treatment strategies.

The Potential Role of Bone Morphogenetic Protein-2/-4 in Excessive Mechanical Overloading-Initiated Joint Degeneration

Excessive mechanical overloading of articular cartilage caused by excessive exercise or severe trauma is considered a critical trigger in the development of osteoarthritis (OA). However, the available clinical theranostic molecular targets and underlying mechanisms still require more elucidation. Here, we aimed to examine the possibility that bone morphogenetic proteins (BMPs) serve as molecular targets in rat cartilages and human chondrocytes under conditions of excessive mechanical overloading. Two rat models involving high-intensity running training and surgery for destabilization of medial meniscus, along with a cell model subjected to cyclic tensile strain, were established to simulate and investigate excessive mechanical overloading effects on cartilages/chondrocytes. We employed various methods, including immunohistochemistry, real-time polymerase chain reaction, western blot analysis, and enzyme-linked immunosorbent assay, to evaluate the expression, secretion, phosphorylation, and nuclear translocation of mRNA/proteins in cartilages and chondrocytes. Our findings revealed a simultaneous upregulation of BMP-2 and downregulation of BMP-4 in degenerated and inflamed cartilages and chondrocytes under excessive mechanical overloading. Furthermore, toll-like receptor 2 and nuclear factor kappa B-p50/p65 subunits signaling were identified as regulators governing this distinct expression pattern. Treatment with recombinant BMP-2 and/or BMP-4 proteins significantly ameliorated cartilage degeneration and chondrocyte inflammation induced by excessive mechanical overloading. These results strongly suggest that BMP-2 upregulation and BMP-4 downregulation might represent mechanisms for self-rescue and degeneration in damaged cartilage/chondrocytes, respectively. Our findings advance new insights that BMP-2/-4 might be potential molecular targets for excessive mechanical overloading-caused OA development and should be taken into account in future clinical applications.

The crosstalk between DNA-damage responses and innate immunity

DNA damage is typically caused during cell growth by DNA replication stress or exposure to endogenous or external toxins. The accumulation of damaged DNA causes genomic instability, which is the root cause of many serious disorders. Multiple cellular organisms utilize sophisticated signaling pathways against DNA damage, collectively known as DNA damage response (DDR) networks. Innate immune responses are activated following cellular abnormalities, including DNA damage. Interestingly, recent studies have indicated that there is an intimate relationship between the DDR network and innate immune responses. Diverse kinds of cytosolic DNA sensors, such as cGAS and STING, recognize damaged DNA and induce signals related to innate immune responses, which link defective DDR to innate immunity. Moreover, DDR components operate in immune signaling pathways to induce IFNs and/or a cascade of inflammatory cytokines via direct interactions with innate immune modulators. Consistently, defective DDR factors exacerbate the innate immune imbalance, resulting in severe diseases, including autoimmune disorders and tumorigenesis. Here, the latest progress in understanding crosstalk between the DDR network and innate immune responses is reviewed. Notably, the dual function of innate immune modulators in the DDR network may provide novel insights into understanding and developing targeted immunotherapies for DNA damage-related diseases, even carcinomas.

Zwitterion-Lubricated Hydrogel Microspheres Encapsulated with Metformin Ameliorate Age-Associated Osteoarthritis

Chondrocyte senescence and reduced lubrication play pivotal roles in the pathogenesis of age-related osteoarthritis (OA). In the present study, highly lubricated and drug-loaded hydrogel microspheres are designed and fabricated through the radical polymerization of sulfobetaine (SB)-modified hyaluronic acid methacrylate using microfluidic technology. The copolymer contains a large number of SB and carboxyl groups that can provide a high degree of lubrication through hydration and form electrostatic loading interactions with metformin (Met@SBHA), producing a high drug load for anti-chondrocyte senescence. Mechanical, tribological, and drug release analyses demonstrated enhanced lubricative properties and prolonged drug dissemination of the Met@SBHA microspheres. RNA sequencing (RNA-seq) analysis, network pharmacology, and in vitro assays revealed the extraordinary capacity of Met@SBHA to combat chondrocyte senescence. Additionally, inducible nitric oxide synthase (iNOS) has been identified as a promising protein modulated by Met in senescent chondrocytes, thereby exerting a significant influence on the iNOS/ONOO-/P53 pathway. Notably, the intra-articular administration of Met@SBHA in aged mice ameliorated cartilage senescence and OA pathogenesis. Based on the findings of this study, Met@SBHA emerges as an innovative and promising strategy in tackling age-related OA serving the dual function of enhancing joint lubrication and mitigating cartilage senescence.

Mechanisms of chondrocyte regulated cell death in osteoarthritis: Focus on ROS-triggered ferroptosis, parthanatos, and oxeiptosis

Osteoarthritis (OA) is a common chronic inflammatory degenerative disease. Since chondrocytes are the only type of cells in cartilage, their survival is critical for maintaining cartilage morphology. This review offers a comprehensive analysis of how reactive oxygen species (ROS), including superoxide anions, hydrogen peroxide, hydroxyl radicals, nitric oxide, and their derivatives, affect cartilage homeostasis and trigger several novel modes of regulated cell death, including ferroptosis, parthanatos, and oxeiptosis, which may play roles in chondrocyte death and OA development. Moreover, we discuss potential therapeutic strategies to alleviate OA by scavenging ROS and provide new insight into the research and treatment of the role of regulated cell death in OA.

When DNA-damage responses meet innate and adaptive immunity

When cells proliferate, stress on DNA replication or exposure to endogenous or external insults frequently results in DNA damage. DNA-Damage Response (DDR) networks are complex signaling pathways used by multicellular organisms to prevent DNA damage. Depending on the type of broken DNA, the various pathways, Base-Excision Repair (BER), Nucleotide Excision Repair (NER), Mismatch Repair (MMR), Homologous Recombination (HR), Non-Homologous End-Joining (NHEJ), Interstrand Crosslink (ICL) repair, and other direct repair pathways, can be activated separately or in combination to repair DNA damage. To preserve homeostasis, innate and adaptive immune responses are effective defenses against endogenous mutation or invasion by external pathogens. It is interesting to note that new research keeps showing how closely DDR components and the immune system are related. DDR and immunological response are linked by immune effectors such as the cyclic GMP-AMP synthase (cGAS)-Stimulator of Interferon Genes (STING) pathway. These effectors act as sensors of DNA damage-caused immune response. Furthermore, DDR components themselves function in immune responses to trigger the generation of inflammatory cytokines in a cascade or even trigger programmed cell death. Defective DDR components are known to disrupt genomic stability and compromise immunological responses, aggravating immune imbalance and leading to serious diseases such as cancer and autoimmune disorders. This study examines the most recent developments in the interaction between DDR elements and immunological responses. The DDR network's immune modulators' dual roles may offer new perspectives on treating infectious disorders linked to DNA damage, including cancer, and on the development of target immunotherapy.

The experimental study of mir-99a-5p negative regulation of TLR8 receptor mediated-mediated innate immune response in rabbit knee cartilage injury

BACKGROUND

Traumatic cartilage injury is an important cause of osteoarthritis (OA) and limb disability, and toll-like receptors (TLRs) mediated innate immune response has been confirmed to play a crucial role in cartilage injury. In the previous study, we found that the activation of TLR8 molecules in injured articular cartilage was more obvious than other TLRs by establishing an animal model of knee impact injury in rabbits, and the changes of TLR8 molecules could significantly affect the process of articular cartilage injury and repair.

OBJECTIVE

To verify how mir-99a-5p regulates TLR8 receptor mediated innate immune response to treat traumatic cartilage injury.

METHODS

The impact of a heavy object on the medial condyle of the rabbit's knee joint caused damage to the medial condylar cartilage. Through pathological and imaging analysis, it was demonstrated whether the establishment of an animal model of traumatic cartilage injury was successful. Establishing a cell model by virus transfection of chondrocytes to demonstrate the role of TLR8 in the innate immune response to impact cartilage injury. Through transcriptome sequencing, potential targets of TLR8, mir-99a-5p, were predicted, and basic experiments were conducted to demonstrate how they interact with innate immune responses to impact cartilage damage.

RESULTS

TLR8 is a receptor protein of the immune system, which is widely expressed in immune cells. In our study, we found that TLR8 expression is localized in lysosomes and endosomes. Mir-99a-5p can negatively regulate TLR8 to activate PI3K-AKT molecular pathway and aggravate cartilage damage. Inhibiting TLR8 expression can effectively reduce the incidence of articular cartilage damage.

CONCLUSION

Based on the results from this study, mir-99a-5p may be an effective molecular marker for predicting traumatic cartilage injury and targeting TLR8 is a novel and promising approach for the prevention or early treatment of cartilage damage.

Biomaterial-Based Gene Delivery: Advanced Tools for Enhanced Cartilage Regeneration

Gene therapy has emerged as a promising and innovative approach in cartilage regeneration. Integrating biomaterials into gene therapy offers a unique opportunity to enhance gene delivery efficiency, optimize gene expression dynamics, modulate immune responses, and promote tissue regeneration. Despite the rapid progress in biomaterial-based gene delivery, there remains a deficiency of comprehensive discussions on recent advances and their specific application in cartilage regeneration. Therefore, this review aims to provide a thorough overview of various categories of biomaterials employed in gene delivery, including both viral and non-viral vectors, with discussing their distinct advantages and limitations. Furthermore, the diverse strategies employed in gene therapy are discussed and summarized, such as the utilization of growth factors, anti-inflammatory cytokines, and chondrogenic genes. Additionally, we highlights the significant challenges that hinder biomaterial-based gene delivery in cartilage regeneration, including immune response modulation, gene delivery efficiency, and the sustainability of long-term gene expression. By elucidating the functional properties of biomaterials-based gene therapy and their pivotal roles in cartilage regeneration, this review aims to enhance further advances in the design of sophisticated gene delivery systems for improved cartilage regeneration outcomes.

NOS inhibition reverses TLR2-induced chondrocyte dysfunction and attenuates age-related osteoarthritis

Osteoarthritis (OA) is a joint disease featuring cartilage breakdown and chronic pain. Although age and joint trauma are prominently associated with OA occurrence, the trigger and signaling pathways propagating their pathogenic aspects are ill defined. Following long-term catabolic activity and traumatic cartilage breakdown, debris accumulates and can trigger Toll-like receptors (TLRs). Here we show that TLR2 stimulation suppressed the expression of matrix proteins and induced an inflammatory phenotype in human chondrocytes. Further, TLR2 stimulation impaired chondrocyte mitochondrial function, resulting in severely reduced adenosine triphosphate (ATP) production. RNA-sequencing analysis revealed that TLR2 stimulation upregulated nitric oxide synthase 2 (NOS2) expression and downregulated mitochondria function-associated genes. NOS inhibition partially restored the expression of these genes, and rescued mitochondrial function and ATP production. Correspondingly, Nos2-/- mice were protected from age-related OA development. Taken together, the TLR2-NOS axis promotes human chondrocyte dysfunction and murine OA development, and targeted interventions may provide therapeutic and preventive approaches in OA.

The Nrf2/HMGB1/NF-κB axis modulates chondrocyte apoptosis and extracellular matrix degradation in osteoarthritis

Osteoarthritis (OA) is a degenerative or posttraumatic condition of the joints. In OA chondrocytes, Nrf2 functions as a stress response regulator with antioxidant and anti-inflammatory effects. This study aims to investigate the role of Nrf2 and its downstream pathway in the development of osteoarthritis. IL-1β treatment suppresses Nrf2, aggrecan, and COL2A1 levels and cell viability but promotes apoptosis in chondrocytes. IL-1β stimulation induces cell apoptosis, upregulates the mRNA expression of inflammatory factors, decreases aggrecan, COL2A1, and Bcl-2 levels but increases ADAMTS-5, ADAMTS-4, MMP13, cleaved caspase 3, and BAX levels, and promotes p65 phosphorylation. Nrf2 overexpression exerts opposite effects on IL-1β-treated chondrocytes, as demonstrated by the significant attenuation of IL-1β-induced changes in chondrocytes. By binding to the HMGB1 promoter region, Nrf2 suppresses HMGB1 expression. Similar to Nrf2 overexpression, HMGB1 knockdown also attenuates IL-1β-induced changes in chondrocytes. Notably, under IL-1β stimulation, the effects of Nrf2 overexpression or tert-butylhydroquinone (TBHQ, an activator of Nrf2) on apoptosis, inflammatory factor expression, ECM and apoptosis, and NF-κB pathway activity in chondrocytes are remarkably reversed by HMGB1 overexpression or recombinant HMGB1 (rHMGB1). Similarly, rHMGB1 could partially counteract the curative effect of TBHQ on OA damage in mice. In OA cartilage tissue samples, the level of Nrf2 is lower, while the levels of HMGB1, apoptotic, and inflammatory factors are increased compared to normal cartilage tissue samples. In conclusion, for the first time, the Nrf2/HMGB1 axis was found to modulate apoptosis, ECM degradation, inflammation and activation of NF-κB signaling in chondrocytes and OA mice.

Preparation of Melatonin-Loaded Nanoparticles with Targeting and Sustained Release Function and Their Application in Osteoarthritis

(1) The vicious cycle of innate immune response and reactive oxygen species (ROS) generation is an important pathological process of osteoarthritis (OA). Melatonin may be a new hope for the treatment of OA because of its antioxidant capacity. However, the mechanism of melatonin in the treatment of OA is still not completely clear, and the physiological characteristics of articular cartilage make melatonin unable to play a long-term role in OA. (2) The effects of melatonin on ROS and the innate immune response system in OA chondrocytes and the therapeutic effect in vivo were evaluated. Then, a melatonin-loaded nano-delivery system (MT@PLGA-COLBP) was prepared and characterized. Finally, the behavior of MT@PLGA-COLPB in cartilage and the therapeutic effect in OA mice were evaluated. (3) Melatonin can inhibit the activation of the innate immune system by inhibiting the TLR2/4-MyD88-NFκB signal pathway and scavenging ROS, thus improving cartilage matrix metabolism and delaying the progression of OA in vivo. MT@PLGA-COLBP can reach the interior of cartilage and complete the accumulation in OA knee joints. At the same time, it can reduce the number of intra-articular injections and improve the utilization rate of melatonin in vivo. (4) This work provides a new idea for the treatment of osteoarthritis, updates the mechanism of melatonin in the treatment of osteoarthritis, and highlights the application prospect of PLGA@MT-COLBP nanoparticles in preventing OA.

MRI-visible mesoporous polydopamine nanoparticles with enhanced antioxidant capacity for osteoarthritis therapy

Since the progression of osteoarthritis (OA) is closely associated with synovitis and cartilage destruction, the inhibition of inflammatory responses in synovial macrophages and reactive oxygen species (ROS) induced apoptosis in chondrocytes is crucial for OA amelioration. However, most of the current anti-inflammatory and antioxidant drugs are small molecules apt to be eliminated in vivo. Herein, mesoporous polydopamine nanoparticles (DAMM NPs) doped with arginine and manganese (Mn) ions were prepared to load dexamethasone (DEX) for OA intervention. A series of in vitro studies showed that the sustained release of DEX from DAMM NPs suppressed synovial inflammation and simultaneously inhibited toll-like receptor 3 (TLR-3) production in chondrocytes, contributing to prevention of chondrocyte apoptosis through the inflammatory factor-dependent TLR-3/NF-κB signaling pathway via modulation of macrophage-chondrocyte crosstalk. In addition, DAMM NPs exerted a predominant role in removal of ROS generated in chondrocytes. Therefore, the DEX-loaded DAMM NPs significantly attenuated OA development in mice model. Importantly, the T1-T2 magnetic contrast capabilities of DAMM NPs allowed an MRI-trackable delivery, manifesting a distinct feature widely regarded to boost the potential of nanomedicines for clinical applications. Together, our developed antioxidant-enhanced DAMM NPs with MRI-visible signals may serve as a novel multifunctional nanocarriers for prevention of OA progression.

NOTCH1: A Novel Player in the Molecular Crosstalk Underlying Articular Chondrocyte Protection by Oleuropein and Hydroxytyrosol

Osteoarthritis (OA) is the most common joint disease, but no effective and safe disease-modifying treatment is available. Risk factors such as age, sex, genetics, injuries and obesity can concur to the onset of the disease, variably triggering the loss of maturational arrest of chondrocytes further sustained by oxidative stress, inflammation and catabolism. Different types of nutraceuticals have been studied for their anti-oxidative and anti-inflammatory properties. Olive-derived polyphenols draw particular interest due to their ability to dampen the activation of pivotal signaling pathways in OA. Our study aims to investigate the effects of oleuropein (OE) and hydroxytyrosol (HT) in in vitro OA models and elucidate their possible effects on NOTCH1, a novel therapeutic target for OA. Chondrocytes were cultured and exposed to lipopolysaccharide (LPS). Detailed analysis was carried out about the OE/HT mitigating effects on the release of ROS (DCHF-DA), the increased gene expression of catabolic and inflammatory markers (real time RT-PCR), the release of MMP-13 (ELISA and Western blot) and the activation of underlying signaling pathways (Western blot). Our findings show that HT/OE efficiently attenuates LPS-induced effects by firstly reducing the activation of JNK and of the NOTCH1 pathway downstream. In conclusion, our study provides molecular bases supporting the dietary supplementation of olive-derived polyphenols to revert/delay the progression of OA.

Lipopolysaccharides and hydrogen peroxide induce contrasting pathological conditions in dental pulpal cells

AIM

To determine the effects of lipopolysaccharides (LPS), hydrogen peroxide (H₂ O₂ ), and both combined on cell proliferation/differentiation, inflammation, mitochondrial dynamics as indicated by mitochondrial fission/fusion, antioxidants as indicated by superoxide dismutase 2 (SOD2), and apoptosis of human dental pulpal cells (HDPCs).

METHODOLOGY

Pulpal tissues from eight healthy subjects (n = 8) were collected from Faculty of Dentistry, Chiang Mai University. Isolated HDPCs from healthy donors were divided into four experimental groups: vehicle, 20 μg/ml LPS, 400 μM H₂ O₂ , and the two combined. All experimental groups were investigated to assess cell proliferation, mineralization, differentiation, inflammation, mitochondrial dynamics, antioxidants, and apoptosis.

RESULTS

H₂ O₂ and combined agents decreased cell proliferation of HDPCs equally. LPS, H₂ O_2, and both combined decreased mineralization and differentiation with an increase in tumour necrosis factor-alpha (TNF-α) levels. Surprisingly, LPS and combined agents increased SOD2 expression and caused an imbalance in mitochondrial dynamics. A significant increase in apoptosis was observed in the case of H₂ O₂ and combined agents.

CONCLUSIONS

These findings suggest that LPS induced inflammation, imbalanced mitochondrial dynamics, and reduced cell differentiation without altering apoptosis and cell proliferation. However, H₂ O₂ decreased cell proliferation, and differentiation, and increased inflammation, and apoptosis without interfering with mitochondrial dynamics. Based on our findings, combining LPS and H₂ O₂ could be potentially used as the inducers in in vitro study to mimic the clinical pulpitis.

A single-cell mass cytometry platform to map the effects of preclinical drugs on cartilage homeostasis

No disease-modifying drug exists for osteoarthritis (OA). Despite success in animal models, candidate drugs continue to fail in clinical trials owing to the unmapped interpatient heterogeneity and disease complexity. We used a single-cell platform based on cytometry by time-of-flight (cyTOF) to precisely outline the effects of candidate drugs on human OA chondrocytes. OA chondrocytes harvested from patients undergoing total knee arthroplasty were treated with 2 drugs, an NF-κB pathway inhibitor, BMS-345541, and a chondroinductive small molecule, kartogenin, that showed preclinical success in animal models for OA. cyTOF conducted with 30 metal isotope-labeled antibodies parsed the effects of the drugs on inflammatory, senescent, and chondroprogenitor cell populations. The NF-κB pathway inhibition decreased the expression of p-NF-κB, HIF2A, and inducible NOS in multiple chondrocyte clusters and significantly depleted 4 p16ink4a-expressing senescent populations, including NOTCH1+STRO1+ chondroprogenitor cells. While kartogenin also affected select p16ink4a-expressing senescent clusters, there was a less discernible effect on chondroprogenitor cell populations. Overall, BMS-345541 elicited a uniform drug response in all patients, while only a few responded to kartogenin. These studies demonstrate that a single-cell cyTOF-based drug screening platform can provide insights into patient response assessment and patient stratification.

CircKMT2E Participates in Osteoarthritis through Promotes Apoptosis of Chondrocytes Via Sponging miR-140-5p to Activate TLR4

Objective

To explore the latent pathogenesis of circRNAs in osteoarthritis (OA), as well as their function mechanism.

Methods

The murine chondrocytes with and without OA were involved and used for in-depth sequencing. Herein, we carried out subsequent bioinformatics analysis to disclose the expression pattern, characteristics of circRNAs based on gene ontology, and the KEGG pathway analyses. Then sequencing data were used to deduce the interaction between circRNA and miRNA. The potential miRNA response elements for the annotated circRNAs and relevant target genes were forecasted on the basis of TargetScan and miRanda. For chondrocytes, the effect of the overexpression of the screened circRNA for apoptosis was spotted by flow cytometry as well as Western Blot.

Results

466 diverse circRNAs in the 23,787 spotted circRNAs were both significantly and differentially transcribed. CircKMT2E was upregulated more than two folds in chondrocytes with OA compared with normal tissues, exhibiting an expression trend opposite to miR-140-5p. We disclosed that circKMT2E could possess mutual effect with miR-140-5p by way of AGO proteins. Thus, circKMT2E was verified to have functioned as a molecular sponge targeting miR-140-5p. Therefore, circKMT2E may be at work in the pathogenesis of OA. Further, the sponge connection between circKMT2E and miR-140-5p was proved on the basis of a dual-luciferase reporter assay. Besides, miR-140-5p was speculated can bind TLR4 by bioinformatics analysis. Further PCR analysis found the relative expression level of TLR4, caspase-3, and Bax in the OA groups presented significant upregulation. Overexpression of circKMT2E can promote apoptosis of chondrocytes.

Conclusion

The upregulation of circKMT2E is involved in the chondrocyte apoptosis of the pathogenesis of OA through activation of TLR4 by the sponge function of miR-140-5p.

Nitidine Chloride Alleviates Inflammation and Cellular Senescence in Murine Osteoarthritis Through Scavenging ROS

Osteoarthritis (OA) is one of the most common chronic musculoskeletal disorder worldwide, representing a major source of disability, pain and socioeconomic burden. Yet the effective pharmaceutical treatments applied in the clinical works are merely symptomatic management with uncertainty around their long-term safety and efficacy, namely no drugs currently are capable of modulating the biological progression of OA. Here, we identified the potent anti-inflammatory as well as anti-oxidative properties of Nitidine Chloride (NitC), a bioactive phytochemical alkaloid extracted from natural herbs, in IL-1β-treated rat articular chondrocytes (RACs), LPS-stimulated RAW 264.7 and rat osteoarthritic models in vivo. We demonstrated NitC remarkably inhibited the production of inflammatory mediators including COX2 and iNOS, suppressed the activation of MAPK and NF-κB cell signaling pathway and reduced the expression of extracellular matrix (ECM) degrading enzymes including MMP3, MMP9 and MMP13 in IL-1β-treated RACs. Several emerging bioinformatics tools were performed to predict the underlying mechanism, the result of which indicated the potential reactive oxygen species (ROS) clearance potential of NitC. Further, NitC exhibited its anti-oxidative potential through ameliorating cellular senescence in IL-1β-treated RACs and decreasing NLRP3 inflammasomes activation in LPS-stimulated RAW 264.7 via scavenging ROS. Additionally, X-ray, micro-CT and other experiments in vivo demonstrated that intra-articular injection of NitC significantly alleviated the cartilage erosion, ECM degradation and subchondral alterations in OA progression. In conclusion, the present study reported the potent anti-inflammatory and anti-oxidative potential of NitC in OA biological process, providing a promising therapeutic agent for OA management.

Innate/Inflammatory Bioregulation of Surfactant Protein D Alleviates Rat Osteoarthritis by Inhibiting Toll-Like Receptor 4 Signaling

Osteoarthritis (OA) is a deteriorating disease of cartilage tissues mainly characterized as low-grade inflammation of the joint. Innate immune molecule surfactant protein D (SP-D) is a member of collectin family of collagenous Ca²⁺-dependent defense lectins and plays a vital role in the inflammatory and innate immune responses. The present study investigated the SP-D-mediated innate/inflammatory bioregulation in OA and explored the underlying molecular mechanism. Transcriptome analysis revealed that SP-D regulated genes were strongly enriched in the inflammatory response, immune response, cellular response to lipopolysaccharide (LPS), PI3K-Akt signaling, Toll-like receptor (TLR) signaling, and extracellular matrix (ECM)-receptor interaction pathways. Knockdown of the SP-D gene by the recombinant adeno-associated virus promoted the macrophage specific markers of CD68, F4/80 and TLR4 in the articular cartilage in vivo. SP-D alleviated the infiltration of synovial macrophages and neutrophils, and inhibited TLR4, TNF-α and the phosphorylation of PI3K, Akt and NF-κB p65 in cartilage. SP-D suppressed cartilage degeneration, inflammatory and immune responses in the rat OA model, whilst TAK-242 strengthened this improvement. In in vitro conditions, SP-D pre-treatment inhibited LPS-induced overproduction of inflammation-correlated cytokines such as IL-1β and TNF-α, and suppressed the overexpression of TLR4, MD-2 and NLRP3. SP-D prevented the LPS-induced degradation of ECM by down-regulating MMP-13 and up-regulating collagen II. Blocking of TLR4 by TAK-242 further enhanced these manifestations. We also demonstrated that SP-D binds to the TLR4/MD-2 complex to suppress TLR4-mediated PI3K/Akt and NF-κB signaling activation in chondrocytes. Taken together, these findings indicate that SP-D has chondroprotective properties dependent on TLR4-mediated PI3K/Akt and NF-κB signaling and that SP-D has an optimal bioregulatory effect on the inflammatory and innate responses in OA.

Small extracellular vesicles from hypoxic mesenchymal stem cells alleviate intervertebral disc degeneration by delivering miR-17-5p

Minimally invasive repair strategies are a very promising approach for the treatment of intervertebral disc degeneration (IDD). In recent years, small extracellular vesicles (sEVs) secreted from mesenchymal stem cells (MSCs) have been shown great potential in alleviating IDD. However, in vitro experiments, MSCs are usually exposed to a normoxic micro-environment, which differs greatly from the hypoxic micro-environment in vivo. The primary purpose of our research was to determine whether sEVs isolated from MSCs under hypoxic status (H-sEVs) exhibit a more beneficial effect on protecting IDD compared with sEVs derived from MSCs under normoxic status (N-sEVs). A tail IDD rat model and a series of experiments in vitro were conducted to compare the beneficial effects of PBS, N-sEVs, and H-sEVs treatment. Then, to validate the role of sEVs miRNAs in IDD, a miRNA microarray sequencing analysis and a series of rescue experiments were conducted. Luciferase activity, RNA-ChIP and western blot were performed to explore the potential mechanisms. The results indicate that sEVs alleviate IDD by ameliorating the homeostatic imbalance between anabolism and catabolism in vivo and in vitro. Microarray sequencing result shows that miR-17-5p is maximally enriched in H-sEVs. Toll-like receptor 4 (TLR4) was determined to be a target downstream gene of miR-17-5p. Finally, it was found that H-sEVs miR-17-5p may modulate proliferation and synthesis of human nucleus pulposus cells (HNPCs) matrix via TLR4 pathway. In conclusion, H-sEVs miR-17-5p alleviate IDD via promoting HNPCs matrix proliferation and synthesis, providing new therapeutic targets for IDD. STATEMENT OF SIGNIFICANCE: Intervertebral disc degeneration (IDD) is the primary cause of low back pain (LBP), which is a huge burden to society. Our research demonstrates for the first time that hypoxic pretreatment of small extracellular vesicles (H-sEVs) effectively alleviated the progress of IDD. In short, in the present research, we found that H-sEVs miR-17-5p could modulate proliferation and synthesis of nucleus pulposus cells (NPCs) matrix via TLR4/PI3K/AKT pathway. Therefore, hypoxic pre-treatment is a prospective and efficient method to optimize the therapeutic effect of MSCs-derived sEVs. miRNA and MSCs-derived sEVs combination may be a promising therapeutic approach for IDD.

Enhancing extracellular vesicles for therapeutic treatment of arthritic joints

Extracellular vesicles are small membrane-derived packages of information that are released from virtually all cell types. These nano-packages contain regulatory material including proteins, lipids, mRNA and microRNA and are a key mechanism of paracellular communication within a given microenvironment. Encompassed with a lipid bilayer, these organelles have been attributed numerous roles in regulating both physiological and pathological functions. Herein, we describe the role of EVs in the context of Rheumatoid and Osteoarthritis and explore how they could be harnessed to treat inflammatory and degenerative joint conditions. These structures offer a promising therapeutic strategy for treating musculoskeletal diseases due to their bioactive content, stability, small size and intrinsic ability to enter the avascular cartilage, a notoriously challenging tissue to target. We also discuss how EVs can be manipulated to load therapeutic cargo or present additional targeting moieties to enhance their beneficial actions and tissue regenerative properties.

Roles of mechanosensitive channel Piezo1/2 proteins in skeleton and other tissues

Mechanotransduction is a fundamental ability that allows living organisms to receive and respond to physical signals from both the external and internal environments. The mechanotransduction process requires a range of special proteins termed mechanotransducers to convert mechanical forces into biochemical signals in cells. The Piezo proteins are mechanically activated nonselective cation channels and the largest plasma membrane ion channels reported thus far. The regulation of two family members, Piezo1 and Piezo2, has been reported to have essential functions in mechanosensation and transduction in different organs and tissues. Recently, the predominant contributions of the Piezo family were reported to occur in the skeletal system, especially in bone development and mechano-stimulated bone homeostasis. Here we review current studies focused on the tissue-specific functions of Piezo1 and Piezo2 in various backgrounds with special highlights on their importance in regulating skeletal cell mechanotransduction. In this review, we emphasize the diverse functions of Piezo1 and Piezo2 and related signaling pathways in osteoblast lineage cells and chondrocytes. We also summarize our current understanding of Piezo channel structures and the key findings about PIEZO gene mutations in human diseases.

TLR4 Antagonism Reduces Movement-Induced Nociception and ATF-3 Expression in Experimental Osteoarthritis

Introduction

Toll-like receptor 4 (TLR4) is a pattern recognition receptor involved in the detection of pathogen-associated molecular patterns (PAMPs), but also a "danger-sensing" receptor that recognizes host-derived endogenous molecules called damage-associated molecular patterns (DAMPs). The involvement of TLR4 in rheumatic diseases is becoming evident, as well as its potential role as a target for therapeutic intervention. Moreover, increasing evidence also suggests that TLR4 is implicated in chronic pain states. Thus, in this study, we evaluated whether a systemic administration of a synthetic antagonist of TLR4 (TLR4-A1) could decrease nociception and cartilage degradation in experimental osteoarthritis (OA). Furthermore, as the activation transcription factor (ATF)-3 serves as a negative regulator for TLR4-stimulated inflammatory response, we also evaluated the effect of TLR4 inhibition on ATF-3 expression in primary afferent neurons at the dorsal root ganglia (DRG).

Methods

OA was induced in adult male Wistar rats through an intra-articular injection of 2 mg of sodium mono-iodoacetate (MIA) into the left knee. From days 14 to 28 after OA induction, animals received an intraperitoneal injection of either TLR4-A1 (10 mg/kg) or vehicle. Movement- and loading-induced nociception was evaluated in all animals, by the Knee-Bend and CatWalk tests, before and at several time-points after TLR4-A1/vehicle administration. Immunofluorescence for TLR4 and ATF-3 was performed in L3-L5 DRG. Knee joints were processed for histopathological evaluation.

Results

Administration of TLR4-A1 markedly reduced movement-induced nociception in OA animals, particularly in the Knee-Bend test. Moreover, the increase of ATF-3 expression observed in DRG of OA animals was significantly reduced by TLR4-A1. However, no effect was observed in cartilage loss nor in the neuronal cytoplasmic expression of TLR4 upon antagonist administration.

Conclusion

The TLR4 antagonist administration possibly interrupts the TLR4 signalling cascade, thus decreasing the neurotoxic environment at the joint, which leads to a reduction in ATF-3 expression and in nociception associated with experimental OA.

Effects of Extracellular Vesicles from Blood-Derived Products on Osteoarthritic Chondrocytes within an Inflammation Model

Osteoarthritis (OA) is hallmarked by a progressive degradation of articular cartilage. One major driver of OA is inflammation, in which cytokines such as IL-6, TNF-α and IL-1β are secreted by activated chondrocytes, as well as synovial cells—including macrophages. Intra-articular injection of blood products—such as citrate-anticoagulated plasma (CPRP), hyperacute serum (hypACT), and extracellular vesicles (EVs) isolated from blood products—is gaining increasing importance in regenerative medicine for the treatment of OA. A co-culture system of primary OA chondrocytes and activated M1 macrophages was developed to model an OA joint in order to observe the effects of EVs in modulating the inflammatory environment. Primary OA chondrocytes were obtained from patients undergoing total knee replacement. Primary monocytes obtained from voluntary healthy donors and the monocytic cell line THP-1 were differentiated and activated into proinflammatory M1 macrophages. EVs were isolated by ultracentrifugation and characterized by nanoparticle tracking analysis and Western blot. Gene expression analysis of chondrocytes by RT-qPCR revealed increased type II collagen expression, while cytokine profiling via ELISA showed lower TNF-α and IL-1β levels associated with EV treatment. In conclusion, the inflammation model provides an accessible tool to investigate the effects of blood products and EVs in the inflammatory context of OA.

Functional repertoire of EV-associated miRNA profiles after lipoprotein depletion via ultracentrifugation and size exclusion chromatography from autologous blood products

Cartilage breakdown, inflammation and pain are hallmark symptoms of osteoarthritis, and autologous blood products such as citrate-anticoagulated platelet-rich plasma (CPRP) or hyperacute serum (hypACT) have been developed as a regenerative approach to rebuild cartilage, inhibit inflammation and reduce pain. However, mechanisms of action of these blood derivatives are still not fully understood, in part due to the large number of components present in these medical products. In addition, the discovery of extracellular vesicles (EVs) and their involvement in intercellular communication mediated by cargo molecules like microRNAs (miRNAs) opened up a whole new level of complexity in understanding blood products. In this study we focused on the development of an isolation protocol for EVs from CPRP and hypACT that can also deplete lipoproteins, which are often co-isolated in EV research due to shared physical properties. Several isolation methods were compared in terms of particle yield from CPRP and hypACT. To gain insights into the functional repertoire conveyed via EV-associated miRNAs, we performed functional enrichment analysis and identified NFκB signaling strongly targeted by CPRP EV miRNAs, whereas hypACT EV miRNAs affect IL6- and TGFβ/SMAD signaling.

Lipopolysaccharide Binding Protein and CD14, Cofactors of Toll-like Receptors, Are Essential for Low-Grade Inflammation-Induced Exacerbation of Cartilage Damage in Mouse Models of Posttraumatic Osteoarthritis

Objective

Osteoarthritis (OA) is initiated by pathogenic factors produced by multiple stimuli, including mechanical stress, metabolic stress, and/or inflammaging. This study was undertaken to identify novel low‐grade inflammation–associated pathogenic mediators of OA.

Methods

Candidate pathogenic molecules were screened using microarray data obtained from chondrocytes exposed to OA‐associated catabolic factors. In mice with OA generated by destabilization of the medial meniscus (DMM), low‐grade inflammation was induced by a high‐fat diet or endotoxemia. Functions of candidate molecules in OA pathogenesis were examined using primary‐culture chondrocytes from mice with DMM‐induced OA, following intraarticular injection of adenovirus expressing the candidate gene. Specific functions of candidate genes were evaluated using whole‐body gene‐knockout mice.

Results

Bioinformatics analysis identified multiple candidate pathogenic factors that were associated with low‐grade inflammation, including components of the Toll‐like receptor (TLR) signaling pathways (e.g., TLR‐2, TLR‐4, lipopolysaccharide binding protein [LBP], and CD14). Overexpression of the individual TLR signaling components in mouse joint tissue did not alter cartilage homeostasis. However, the low‐grade inflammation induced by a high‐fat diet or endotoxemia markedly enhanced posttraumatic OA cartilage destruction in mice, and this exacerbation of cartilage destruction was significantly abrogated in LBP^−/− and CD14^−/− mice. Additionally, LBP and CD14 were found to be necessary for the expression of matrix‐degrading enzymes in mouse chondrocytes treated with proinflammatory cytokines.

Conclusion

LBP and CD14, which are accessory molecules of TLRs, are necessary for the exacerbation of posttraumatic OA cartilage destruction resulting from low‐grade inflammation, such as that triggered by a high‐fat diet or endotoxemia.