PGE2 activates EP4 in subchondral bone osteoclasts to regulate osteoarthritis

The bone marrow lipidomics of mice reveal sex-related differences

Osteoporosis is a common skeletal disorder characterized by an imbalance between bone resorption and formation, exhibiting a higher prevalence in women compared with men. While previous studies have primarily focused on genomics and genetics in osteoporosis susceptibility, there is a lack of systematic exploration of sex-specific differences in lipid levels in mouse bone marrow. Multiple reaction monitoring-based liquid chromatography-trandem mass spectrometry (LC-MS/MS) was used to quantify lipidomic profiles in bone marrow samples from three female mice and three male mice. The LC-MS/MS technique based on the multiple reaction monitoring method identified and quantified 184 lipids from 15 lipid classes. The contents of most lipids in the bone marrow cells of female mice were higher than those in male mice, including four polyunsaturated fatty acids, three phospholipids and four sphingolipids. Among all the lipid molecules, lactosylceramide (d18:0/16:0) showed the highest fold change in female mice, while its precursor lipid, glucosylceramide, was the most up-regulated in male mice. This study, focusing on bone marrow lipidomics, elucidates significant sexual dimorphism in lipid levels within bone marrow cells. It provides novel evidence supporting the higher prevalence of osteoporosis in women and enhances our understanding of the connection between sex-specific lipid levels and the risk of osteoporosis.

Microenvironmental interference with intra-articular stem cell regeneration influences the onset and progression of arthritis

Studies have indicated that the preservation of joint health and the facilitation of damage recovery are predominantly contingent upon the joint's microenvironment, including cell-cell interactions, the extracellular matrix's composition, and the existence of local growth factors. Mesenchymal stem cells (MSCs), which possess the capacity to self-renew and specialize in many directions, respond to cues from the microenvironment, and aid in the regeneration of bone and cartilage, are crucial to this process. Changes in the microenvironment (such as an increase in inflammatory mediators or the breakdown of the extracellular matrix) in the pathological context of arthritis might interfere with stem cell activation and reduce their ability to regenerate. This paper investigates the potential role of joint microenvironmental variables in promoting or inhibiting the development of arthritis by influencing stem cells' ability to regenerate. The present status of research on stem cell activity in the joint microenvironment is also outlined, and potential directions for developing new treatments for arthritis that make use of these intervention techniques to boost stem cell regenerative potential through altering the intra-articular environment are also investigated. This review's objectives are to investigate these processes, offer fresh perspectives, and offer a solid scientific foundation for the creation of arthritic treatment plans in the future.

Effects of Platelet-Rich Plasma Combined with Physical Therapy on IL-1β, TGF-β1, and MMP-3 in Patients with Knee Osteoarthritis

The occurrence of osteoarthritis in the knee joint is regulated by a complex network, and there is currently no specific therapeutic drug available. Functional exercises and treatments targeting inflammatory factors have shown the potential to alleviate knee osteoarthritis to some extent. Therefore, the aim of this study was to assess the intra-articular injection (IAI) of autologous platelet-rich plasma (PRP) combined with physical therapy (PT) in treating knee osteoarthritis. A total of 128 patients with knee osteoarthritis were included in the study, including 64 males and 64 females. A total of 128 patients were divided into sodium hyaluronate group (HA group), PRP group, PRP + PT group, and PT group, with 32 cases in each group. Visual analog scale (VAS), Western Ontario and McMaster University Osteoarthritis Index (WOMAC), and Japanese Orthopaedic Association (JOA) were employed to evaluate the recovery of patients from pain and osteoarthritis. Color Doppler ultrasound imaging technology was utilized to assess joint effusion, synovial membrane thickness, and articular cartilage thickness in patients with knee osteoarthritis. Enzyme-linked immunosorbent assay (ELISA) was employed to detect the levels of interleukin-1β (IL-1β), transforming growth factor-β1 (TGF-β1), and matrix metallopeptidase 3 (MMP-3) in the synovial fluid. Compared to the HA group, the PT group, PRP group, and PRP combined with PT (PRP + PT) group all showed reduced VAS and WOMAC scores, increased JOA scores, decreased joint effusion, synovial membrane thickness, and articular cartilage thickness in the knee joint. Additionally, levels of IL-1β and MMP-3 in the synovial fluid decreased, while TGF-β1 levels increased (P < 0.05). Compared with the PT group, the VAS and WOMAC scores of the knee joint in the PRP group decreased, JOA scores increased, joint effusion, synovial thickness, and articular cartilage thickness decreased, but there was no statistically significant difference (P > 0.05), and the PRP + PT group showed decreased VAS and WOMAC scores, increased JOA scores, reduced joint effusion, synovial membrane thickness, and articular cartilage thickness in the knee joint. Moreover, levels of IL-1β and MMP-3 in the synovial fluid decreased, while TGF-β1 levels increased (P < 0.05). No severe adverse reactions were observed in any of the four groups, but the pain rate in the PRP + TP group was significantly lower than PT group, PRP group, and PRP + PT group (P < 0.05). The efficacy of intra-articular injection of PRP combined with exercise therapy in the treatment of knee osteoarthritis is superior to that of single interventions such as simple interventions of HA, PRP injection, and PT. Furthermore, intra-articular injection of PRP combined with exercise therapy demonstrates enhanced effectiveness in improving the inflammatory levels associated with knee osteoarthritis and facilitating the rehabilitation process.

Gold nanoparticles exhibit anti-osteoarthritic effects via modulating interaction of the "microbiota-gut-joint" axis

Osteoarthritis (OA) is a common degenerative joint disease that can cause severe pain, motor dysfunction, and even disability. A growing body of research indicates that gut microbiota and their associated metabolites are key players in maintaining bone health and in the progression of OA. Short-chain fatty acids (SCFAs) are a series of active metabolites that widely participate in bone homeostasis. Gold nanoparticles (GNPs) with outstanding anti-bacterial and anti-inflammatory properties, have been demonstrated to ameliorate excessive bone loss during the progression of osteoporosis (OP) and rheumatoid arthritis (RA). However, the protective effects of GNPs on OA progression are not clear. Here, we observed that GNPs significantly alleviated anterior cruciate ligament transection (ACLT)-induced OA in a gut microbiota-dependent manner. 16S rDNA gene sequencing showed that GNPs changed gut microbial diversity and structure, which manifested as an increase in the abundance of Akkermansia and Lactobacillus. Additionally, GNPs increased levels of SCFAs (such as butyric acid), which could have improved bone destruction by reducing the inflammatory response. Notably, GNPs modulated the dynamic balance of M1/M2 macrophages, and increased the serum levels of anti-inflammatory cytokines such as IL-10. To sum up, our study indicated that GNPs exhibited anti-osteoarthritis effects via modulating the interaction of "microbiota-gut-joint" axis, which might provide promising therapeutic strategies for OA.

Cause and chondroprotective effects of prostaglandin E2 secretion during mesenchymal stromal cell chondrogenesis

Mesenchymal stromal cells (MSCs) that are promising for cartilage tissue engineering secrete high amounts of prostaglandin E2 (PGE2), an immunoactive mediator involved in endochondral bone development. This study aimed to identify drivers of PGE2 and its role in the inadvertent MSC misdifferentiation into hypertrophic chondrocytes. PGE2 release, which rose in the first three weeks of MSC chondrogenesis, was jointly stimulated by endogenous BMP, WNT, and hedgehog activity that supported the exogenous stimulation by TGF-β1 and insulin to overcome the PGE2 inhibition by dexamethasone. Experiments with PGE2 treatment or the inhibitor celecoxib or specific receptor antagonists demonstrated that PGE2, although driven by prohypertrophic signals, exerted broad autocrine antihypertrophic effects. This chondroprotective effect makes PGE2 not only a promising option for future combinatorial approaches to direct MSC tissue engineering approaches into chondral instead of endochondral development but could potentially have implications for the use of COX-2-selective inhibitors in osteoarthritis pain management.

Pathological progression of osteoarthritis: a perspective on subchondral bone

Osteoarthritis (OA) is a degenerative bone disease associated with aging. The rising global aging population has led to a surge in OA cases, thereby imposing a significant socioeconomic burden. Researchers have been keenly investigating the mechanisms underlying OA. Previous studies have suggested that the disease starts with synovial inflammation and hyperplasia, advancing toward cartilage degradation. Ultimately, subchondral-bone collapse, sclerosis, and osteophyte formation occur. This progression is deemed as "top to bottom." However, recent research is challenging this perspective by indicating that initial changes occur in subchondral bone, precipitating cartilage breakdown. In this review, we elucidate the epidemiology of OA and present an in-depth overview of the subchondral bone's physiological state, functions, and the varied pathological shifts during OA progression. We also introduce the role of multifunctional signal pathways (including osteoprotegerin (OPG)/receptor activator of nuclear factor-kappa B ligand (RANKL)/receptor activator of nuclear factor-kappa B (RANK), and chemokine (CXC motif) ligand 12 (CXCL12)/CXC motif chemokine receptor 4 (CXCR4)) in the pathology of subchondral bone and their role in the "bottom-up" progression of OA. Using vivid pattern maps and clinical images, this review highlights the crucial role of subchondral bone in driving OA progression, illuminating its interplay with the condition.

Skeletal interoception in osteoarthritis

The interoception maintains proper physiological conditions and metabolic homeostasis by releasing regulatory signals after perceving changes in the internal state of the organism. Among its various forms, skeletal interoception specifically regulates the metabolic homeostasis of bones. Osteoarthritis (OA) is a complex joint disorder involving cartilage, subchondral bone, and synovium. The subchondral bone undergoes continuous remodeling to adapt to dynamic joint loads. Recent findings highlight that skeletal interoception mediated by aberrant mechanical loads contributes to pathological remodeling of the subchondral bone, resulting in subchondral bone sclerosis in OA. The skeletal interoception is also a potential mechanism for chronic synovial inflammation in OA. In this review, we offer a general overview of interoception, specifically skeletal interoception, subchondral bone microenviroment and the aberrant subchondral remedeling. We also discuss the role of skeletal interoception in abnormal subchondral bone remodeling and synovial inflammation in OA, as well as the potential prospects and challenges in exploring novel OA therapies that target skeletal interoception.

Gentiopicroside ameliorates the lipopolysaccharide-induced inflammatory response and hypertrophy in chondrocytes

PURPOSE

This study aimed to evaluate the protective effects of gentiopicroside against lipopolysaccharide-induced chondrocyte inflammation.

METHODS

SW 1353 chondrosarcoma cells were stimulated with LPS (5 μg/ml) for 24 h and treated with different concentrations of gentiopicroside (GPS) for 24 h. The toxic effects of GPS on chondrocytes were determined using a CCK-8 assay and EdU staining. Western blotting, qPCR, and immunofluorescence analysis were used to examine the protective effect of GPS against the inflammatory response in chondrocytes induced by lipopolysaccharide (LPS). One-way ANOVA was used to compare the differences between the groups (significance level of 0.05).

RESULTS

The CCK-8 results showed that 10, 20 and 40 μM GPS had no significant toxic effects on chondrocytes; GPS effectively reduced the production of IL-1β and PGE2, reversed LPS-induced extracellular matrix degradation in cartilage by inhibiting the Stat3/Runx2 signaling pathway, and suppressed the hypertrophic transformation of SW 1353 chondrosarcoma cells.

CONCLUSION

Our study demonstrated that GPS significantly inhibited the LPS-induced inflammatory response and hypertrophic cellular degeneration in SW 1353 chondrosarcoma cells and is a valuable traditional Chinese medicine for the treatment of knee osteoarthritis.

Glaucocalyxin A delays the progression of OA by inhibiting NF-κB and MAPK signaling pathways

BACKGROUND

Osteoarthritis (OA) is a common degenerative joint condition marked by inflammation and cartilage breakdown. Currently, there is a dearth of treatment medications that can clearly slow the course of OA. Glaucocalyxin A (GLA) is a diterpene chemical identified and extracted from Rabdosia japonica with antithrombotic, anticoagulant, anti-tumor, anti-inflammatory, anti-oxidant, and other pharmacological properties. Previous research has linked inflammation to abnormalities in the homeostasis of the extracellular matrix (ECM). Although GLA has been shown to have anti-inflammatory qualities, its effects on the progression of OA are unknown. As a result, the goal of this study was to see if GLA could slow the course of OA.

METHODS

ATDC5 cells were stimulated by IL-1β to create an inflammatory chondrocyte damage model. Quantitative polymerase chain reaction, Western Blot, high-density culture, and immunofluorescence were used to detect the expression levels of associated gene phenotypes. We also created a mouse model of OA induced by destabilization of the medial meniscus (DMM) instability, and GLA was administered intraperitoneally once every two days for eight weeks. Mice knee specimens were stained with hematoxylin-eosin, Safranin O/fast green, and immunohistochemical, and the Osteoarthritis Research Society International grade system and Mankin's score were used to assess the protective effect of GLA on cartilage.

RESULTS

In vitro and in vivo, we explored the effects and molecular processes of GLA as a therapy for OA. The findings demonstrated that GLA might reduce the expression of associated inflammatory mediators and protect the ECM by inhibiting the NF-κB and MAPK signaling pathways. Animal research revealed that GLA could protect against the DMM-induced OA model mice by stabilizing ECM.

CONCLUSION

Taken together, our findings show that GLA has a protective impact on cartilage throughout OA progression, implying that GLA could be employed as a possible therapeutic agent for OA, thus giving a new therapeutic method for the treatment of OA.

Revisiting prostaglandin E2: A promising therapeutic target for osteoarthritis

Osteoarthritis (OA) is a complex disease characterized by cartilage degeneration and persistent pain. Prostaglandin E2 (PGE2) plays a significant role in OA inflammation and pain. Recent studies have revealed the significant role of PGE2-mediated skeletal interoception in the progression of OA, providing new insights into the pathogenesis and treatment of OA. This aspect also deserves special attention in this review. Additionally, PGE2 is directly involved in pathologic processes including aberrant subchondral bone remodeling, cartilage degeneration, and synovial inflammation. Therefore, celecoxib, a commonly used drug to alleviate inflammatory pain through inhibiting PGE2, serves not only as an analgesic for OA but also as a potential disease-modifying drug. This review provides a comprehensive overview of the discovery history, synthesis and release pathways, and common physiological roles of PGE2. We discuss the roles of PGE2 and celecoxib in OA and pain from skeletal interoception and multiple perspectives. The purpose of this review is to highlight PGE2-mediated skeletal interoception and refresh our understanding of celecoxib in the pathogenesis and treatment of OA.

Tanshinone IIA attenuates osteoarthritis via inhibiting aberrant angiogenesis in subchondral bone

Excessive angiogenesis in subchondral bone is a pathological feature of osteoarthritis (OA). Tanshinone IIA (TIIA), an active compound found in Salvia miltiorrhiza, demonstrates significant anti-angiogenic properties. However, the effect of TIIA on abnormal subchondral angiogenesis in OA is still unclear. This study aims to investigate the mechanism of TIIA in modulating subchondral bone angiogenesis during OA and assess its therapeutic potential in OA. Our findings demonstrate that TIIA attenuated articular cartilage degeneration, normalized subchondral bone remodeling, and effectively suppressed aberrant angiogenesis within subchondral bone in monosodium iodoacetate (MIA)-induced OA mice. Additionally, the angiogenesis capacity of primary CD31hiEmcnhi endothelial cells was observed to be significantly reduced after treatment with TIIA in vitro. Mechanically, TIIA diminished the proportion of hypertrophic chondrocytes, ultimately leading to a substantial reduction in the secretion of vascular endothelial growth factor A (VEGFA). The supernatant of hypertrophic chondrocytes promoted the tube formation of CD31hiEMCNhi endothelial cells, whereas TIIA inhibited this process. Furthermore, TIIA effectively suppressed the expression of vascular endothelial growth factor receptor 2 (VEGFR2) along with its downstream MAPK pathway in CD31hiEmcnhi endothelial cells. In conclusion, our data indicated that TIIA could effectively inhibit the abnormal angiogenesis in subchondral bone during the progression of OA by suppressing the VEGFA/VEFGR2/MAPK pathway. These findings significantly contribute to our understanding of the abnormal angiogenesis in OA and offer a promising therapeutic target for OA treatment.

Machine learning-mediated identification of ferroptosis-related genes in osteonecrosis of the femoral head

Osteonecrosis of the femoral head (ONFH) is a condition caused by a disruption or damage to the femoral head's blood supply, which causes the death of bone cells and bone marrow components and prevents future regeneration. Ferroptosis, a type of controlled cell death, is caused by iron-dependent lipid peroxidation. Here, we identified ferroptosis-related genes and infiltrating immune cells involved in ONFH and predicted the underlying molecular mechanisms. The GSE123568 dataset was subjected to differential expression analysis to identify genes related to ferroptosis. Subsequently, GO and KEGG pathway enrichment analyses, as well as protein-protein interaction (PPI) network analysis, were conducted. Hub genes involved in ferroptosis were identified using machine learning and other techniques. Additionally, immune infiltration analysis and lncRNA-miRNA-mRNA network prediction analysis were performed. Finally, we determined whether ferroptosis occurred by measuring iron content. The hub genes were validated by ROC curve analysis and qRT-PCR. Four ferroptosis-related hub genes (MAPK3, PTGS2, STK11, and SLC2A1) were identified. Additionally, immune infiltration analysis revealed a strong correlation among ONFH, hub genes, and various immune cells. Finally, we predicted the network relationship between differentially expressed lncRNAs and hub genes in the lncRNA-miRNA-mRNA network. MAPK3, PTGS2, STK11, and SLC2A1 have been identified as potential ferroptosis-related biomarkers and drug targets for the diagnosis and prognosis of ONFH, while some immune cells, as well as the interaction between lncRNA, miRNA, and mRNA, have also been identified as potential pathogenesis markers and therapeutic targets.

Periplogenin attenuates LPS-mediated inflammatory osteolysis through the suppression of osteoclastogenesis via reducing the NF-κB and MAPK signaling pathways

The key target for treating inflammatory osteolysis is osteoclasts. In an inflammatory environment, osteoclast differentiation increases, and bone resorption is enhanced. Periplogenin (Ppg) is a traditional Chinese medicine. It has anti-inflammatory and antitumor effects, but its impact on inflammatory osteolysis is unknown. This study found that Ppg prevented LPS-induced skull osteolysis by inhibiting the expression of inflammatory cytokines and osteoclast production. In vitro, Ppg blocked the RANKL-induced generation of osteoclasts, the development of pseudopodia bands, and bone resorption. Ppg also attenuated the expression of NFATc1, c-Fos, CTSK, and Atp6v0d2 proteins by inhibiting the NFATc1 signaling pathway. In addition, Ppg inhibited the expression of osteoclast-specific genes, including NFATc1, c-Fos, CTSK, Atp6v0d2, and Mmp9. Moreover, Ppg also inhibited NF-κB and MAPK pathways. In vivo, Ppg reduced the number of osteoclasts on the surface of the bone and suppressed LPS-induced osteolysis of the skull. These outcomes suggest that Ppg can serve as a new alternative therapy for treating inflammatory osteolysis by inhibiting inflammation and osteoclasts.

Osteoarthritis year in review 2023: Biology

Great progress continues to be made in our understanding of the multiple facets of osteoarthritis (OA) biology. Here, we review the major advances in this field and progress towards therapy development over the past year, highlighting a selection of relevant published literature from a PubMed search covering the year from the end of April 2022 to the end of April 2023. The selected articles have been arranged in themes. These include 1) molecular regulation of articular cartilage and implications for OA, 2) mechanisms of subchondral bone remodelling, 3) role of synovium and inflammation, 4) role of age-related changes including cartilage matrix stiffening, cellular senescence, mitochondrial dysfunction, metabolic dysfunction, and impaired autophagy, and 5) peripheral mechanisms of OA pain. Progress in the understanding of the cellular and molecular mechanisms responsible for the multiple aspects of OA biology is unravelling novel therapeutic targets for disease modification.

Regulating Chondro-Bone Metabolism for Treatment of Osteoarthritis via High-Permeability Micro/Nano Hydrogel Microspheres

Destruction of cartilage due to the abnormal remodeling of subchondral bone (SB) leads to osteoarthritis (OA), and restoring chondro-bone metabolic homeostasis is the key to the treatment of OA. However, traditional intra-articular injections for the treatment of OA cannot directly break through the cartilage barrier to reach SB. In this study, the hydrothermal method is used to synthesize ultra-small size (≈5 nm) selenium-doped carbon quantum dots (Se-CQDs, SC), which conjugated with triphenylphosphine (TPP) to create TPP-Se-CQDs (SCT). Further, SCT is dynamically complexed with hyaluronic acid modified with aldehyde and methacrylic anhydride (AHAMA) to construct highly permeable micro/nano hydrogel microspheres (SCT@AHAMA) for restoring chondro-bone metabolic homeostasis. In vitro experiments confirmed that the selenium atoms scavenged reactive oxygen species (ROS) from the mitochondria of mononuclear macrophages, inhibited osteoclast differentiation and function, and suppressed early chondrocyte apoptosis to maintain a balance between cartilage matrix synthesis and catabolism. In vivo experiments further demonstrated that the delivery system inhibited osteoclastogenesis and H-vessel invasion, thereby regulating the initiation and process of abnormal bone remodeling and inhibiting cartilage degeneration in SB. In conclusion, the micro/nano hydrogel microspheres based on ultra-small quantum dots facilitate the efficient penetration of articular SB and regulate chondro-bone metabolism for OA treatment.

α-Solanine attenuates chondrocyte pyroptosis to improve osteoarthritis via suppressing NF-κB pathway

α-Solanine has been shown to exhibit anti-inflammatory and anti-tumour properties; however, its efficacy in treating osteoarthritis (OA) remains ambiguous. The study aimed to evaluate the therapeutic effects of α-solanine on OA development in a mouse OA model. The OA mice were subjected to varying concentrations of α-solanine, and various assessments were implemented to assess OA progression. We found that α-solanine significantly reduced osteophyte formation, subchondral sclerosis and OARSI score. And it decreased proteoglycan loss and calcification in articular cartilage. Specifically, α-solanine inhibited extracellular matrix degradation by downregulating collagen 10, matrix metalloproteinase 3 and 13, and upregulating collagen 2. Importantly, α-solanine reversed chondrocyte pyroptosis phenotype in articular cartilage of OA mice by inhibiting the elevated expressions of Caspase-1, Gsdmd and IL-1β, while also mitigating aberrant angiogenesis and sensory innervation in subchondral bone. Mechanistically, α-solanine notably hindered the early stages of OA progression by reducing I-κB phosphorylation and nuclear translocation of p65, thereby inactivating NF-κB signalling. Our findings demonstrate the capability of α-solanine to disrupt chondrocyte pyroptosis and sensory innervation, thereby improving osteoarthritic pathological progress by inhibiting NF-κB signalling. These results suggest that α-solanine could serve as a promising therapeutic agent for OA treatment.

The antidepressive mechanism of Longya Lilium combined with Fluoxetine in mice with depression-like behaviors

Traditional Chinese medicine is one of the most commonly used complementary and alternative medicine therapies for depression. Integrated Chinese-western therapies have been extensively applied in numerous diseases due to their superior efficiency in individual treatment. We used the meta-analysis, network pharmacology, and bioinformatics studies to identify the putative role of Longya Lilium combined with Fluoxetine in depression. Depression-like behaviors were mimicked in mice after exposure to the chronic unpredictable mild stress (CUMS). The underlying potential mechanism of this combination therapy was further explored based on in vitro and in vivo experiments to analyze the expression of COX-2, PGE2, and IL-22, activation of microglial cells, and neuron viability and apoptosis in the hippocampus. The antidepressant effect was noted for the combination of Longya Lilium with Fluoxetine in mice compared to a single treatment. COX-2 was mainly expressed in hippocampal CA1 areas. Longya Lilium combined with Fluoxetine reduced the expression of COX-2 and thus alleviated depression-like behavior and neuroinflammation in mice. A decrease of COX-2 curtailed BV-2 microglial cell activation, inflammation, and neuron apoptosis by blunting the PGE2/IL-22 axis. Therefore, a combination of Longya Lilium with Fluoxetine inactivates the COX-2/PGE2/IL-22 axis, consequently relieving the neuroinflammatory response and the resultant depression.

Crosstalk Between the Neuroendocrine System and Bone Homeostasis

The homeostasis of bone microenvironment is the foundation of bone health and comprises 2 concerted events: bone formation by osteoblasts and bone resorption by osteoclasts. In the early 21st century, leptin, an adipocytes-derived hormone, was found to affect bone homeostasis through hypothalamic relay and the sympathetic nervous system, involving neurotransmitters like serotonin and norepinephrine. This discovery has provided a new perspective regarding the synergistic effects of endocrine and nervous systems on skeletal homeostasis. Since then, more studies have been conducted, gradually uncovering the complex neuroendocrine regulation underlying bone homeostasis. Intriguingly, bone is also considered as an endocrine organ that can produce regulatory factors that in turn exert effects on neuroendocrine activities. After decades of exploration into bone regulation mechanisms, separate bioactive factors have been extensively investigated, whereas few studies have systematically shown a global view of bone homeostasis regulation. Therefore, we summarized the previously studied regulatory patterns from the nervous system and endocrine system to bone. This review will provide readers with a panoramic view of the intimate relationship between the neuroendocrine system and bone, compensating for the current understanding of the regulation patterns of bone homeostasis, and probably developing new therapeutic strategies for its related disorders.

IgSF11 deficiency alleviates osteoarthritis in mice by suppressing early subchondral bone changes

Osteoarthritis (OA) is a degenerative joint disease. While it is classically characterized by articular cartilage destruction, OA affects all tissues in the joints and is thus also accompanied by local inflammation, subchondral bone changes, and persistent pain. However, our understanding of the underlying subchondral bone dynamics during OA progression is poor. Here, we demonstrate the contribution of immunoglobulin superfamily 11 (IgSF11) to OA subchondral bone remodeling by using a murine model. In particular, IgSF11 was quickly expressed by differentiating osteoclasts and upregulated in subchondral bone soon after destabilization-of-the-medial-meniscus (DMM)-induced OA. In mice, IgSF11 deficiency not only suppressed subchondral bone changes in OA but also blocked cartilage destruction. The IgSF11-expressing cells in OA subchondral bone were found to be involved in osteoclast maturation and bone resorption and colocalized with receptor-activator of nuclear-factor κ-B (RANK), the key osteoclast differentiation factor. Thus, our study shows that blocking early subchondral bone changes in OA can ameliorate articular cartilage destruction in OA.

Inflammatory mechanisms in post-traumatic osteoarthritis: a role for CaMKK2

Post-traumatic osteoarthritis (PTOA) is a multifactorial disease of the cartilage, synovium, and subchondral bone resulting from direct joint trauma and altered joint mechanics after traumatic injury. There are no current disease-modifying therapies for PTOA, and early surgical interventions focused on stabilizing the joint do not halt disease progression. Chronic pain and functional disability negatively affect the quality of life and take an economic toll on affected patients. While multiple mechanisms are at play in disease progression, joint inflammation is a key contributor. Impact-induced mitochondrial dysfunction and cell death or altered joint mechanics after trauma culminate in inflammatory cytokine release from synoviocytes and chondrocytes, cartilage catabolism, suppression of cartilage anabolism, synovitis, and subchondral bone disease, highlighting the complexity of the disease. Current understanding of the cellular and molecular mechanisms underlying the disease pathology has allowed for the investigation of a variety of therapeutic strategies that target unique apoptotic and/or inflammatory processes in the joint. This review provides a concise overview of the inflammatory and apoptotic mechanisms underlying PTOA pathogenesis and identifies potential therapeutic targets to mitigate disease progression. We highlight Ca2+/calmodulin-dependent protein kinase kinase 2 (CaMKK2), a serine/threonine protein kinase that was recently identified to play a role in murine and human osteoarthritis pathogenesis by coordinating chondrocyte inflammatory responses and apoptosis. Given its additional effects in regulating macrophage inflammatory signaling and bone remodeling, CaMKK2 emerges as a promising disease-modifying therapeutic target against PTOA.

Arachidonic acid metabolism in health and disease

Arachidonic acid (AA), an n-6 essential fatty acid, is a major component of mammalian cells and can be released by phospholipase A2. Accumulating evidence indicates that AA plays essential biochemical roles, as it is the direct precursor of bioactive lipid metabolites of eicosanoids such as prostaglandins, leukotrienes, and epoxyeicosatrienoic acid obtained from three distinct enzymatic metabolic pathways: the cyclooxygenase pathway, lipoxygenase pathway, and cytochrome P450 pathway. AA metabolism is involved not only in cell differentiation, tissue development, and organ function but also in the progression of diseases, such as hepatic fibrosis, neurodegeneration, obesity, diabetes, and cancers. These eicosanoids are generally considered proinflammatory molecules, as they can trigger oxidative stress and stimulate the immune response. Therefore, interventions in AA metabolic pathways are effective ways to manage inflammatory-related diseases in the clinic. Currently, inhibitors targeting enzymes related to AA metabolic pathways are an important area of drug discovery. Moreover, many advances have also been made in clinical studies of AA metabolic inhibitors in combination with chemotherapy and immunotherapy. Herein, we review the discovery of AA and focus on AA metabolism in relation to health and diseases. Furthermore, inhibitors targeting AA metabolism are summarized, and potential clinical applications are discussed.

Human osteoarthritic articular cartilage stem cells suppress osteoclasts and improve subchondral bone remodeling in experimental knee osteoarthritis partially by releasing TNFAIP3

BACKGROUND

Though articular cartilage stem cell (ACSC)-based therapies have been demonstrated to be a promising option in the treatment of diseased joints, the wide variety of cell isolation, the unknown therapeutic targets, and the incomplete understanding of the interactions of ACSCs with diseased microenvironments have limited the applications of ACSCs.

METHODS

In this study, the human ACSCs have been isolated from osteoarthritic articular cartilage by advantage of selection of anatomical location, the migratory property of the cells, and the combination of traumatic injury, mechanical stimuli and enzymatic digestion. The protective effects of ACSC infusion into osteoarthritis (OA) rat knees on osteochondral tissues were evaluated using micro-CT and pathological analyses. Moreover, the regulation of ACSCs on osteoarthritic osteoclasts and the underlying mechanisms in vivo and in vitro were explored by RNA-sequencing, pathological analyses and functional gain and loss experiments. The one-way ANOVA was used in multiple group data analysis.

RESULTS

The ACSCs showed typical stem cell-like characteristics including colony formation and committed osteo-chondrogenic capacity. In addition, intra-articular injection into knee joints yielded significant improvement on the abnormal subchondral bone remodeling of osteoarthritic rats. Bioinformatic and functional analysis showed that ACSCs suppressed osteoarthritic osteoclasts formation, and inflammatory joint microenvironment augmented the inhibitory effects. Further explorations demonstrated that ACSC-derived tumor necrosis factor alpha-induced protein 3 (TNFAIP3) remarkably contributed to the inhibition on osteoarhtritic osteoclasts and the improvement of abnormal subchondral bone remodeling.

CONCLUSION

In summary, we have reported an easy and reproducible human ACSC isolation strategy and revealed their effects on subchondral bone remodeling in OA rats by releasing TNFAIP3 and suppressing osteoclasts in a diseased microenvironment responsive manner.

Effect of Extracellular Ribonucleic Acids on Neurovascularization in Osteoarthritis

Osteoarthritis is a degenerative disease characterized by abnormal neurovascularization at the osteochondral junctions, the regulatory mechanisms of which remain poorly understood. In the present study, a murine osteoarthritic model with augmented neurovascularization at the osteochondral junction is used to examine this under-evaluated facet of degenerative joint dysfunction. Increased extracellular RNA (exRNA) content is identified in neurovascularized osteoarthritic joints. It is found that the amount of exRNA is positively correlated with the extent of neurovascularization and the expression of vascular endothelial growth factor (VEGF). In vitro binding assay and molecular docking demonstrate that synthetic RNAs bind to VEGF via electrostatic interactions. The RNA-VEGF complex promotes the migration and function of endothelial progenitor cells and trigeminal ganglion cells. The use of VEGF and VEGFR2 inhibitors significantly inhibits the amplification of the RNA-VEGF complex. Disruption of the RNA-VEGF complex by RNase and polyethyleneimine reduces its in vitro activities, as well as prevents excessive neurovascularization and osteochondral deterioration in vivo. The results of the present study suggest that exRNAs may be potential targets for regulating nerve and blood vessel ingrowth under physiological and pathological joint conditions.

Identification of polyunsaturated fatty acids as potential biomarkers of osteoarthritis after sodium hyaluronate and mesenchymal stem cell treatment through metabolomics

Introduction: Osteoarthritis (OA) is a prevalent joint disorder worldwide. Sodium hyaluronate (SH) and mesenchymal stem cells (MSCs) are promising therapeutic strategies for OA. Previous studies showed they could improve knee function and clinical symptoms of OA. However, the mechanism of the therapeutic effects on the improvement of OA has not been clearly explained. Methods: In our study, we used a technique called 5-(diisopropylamino)amylamine derivatization liquid chromatography coupled with mass spectrometry to find the metabolites in OA synovial fluid under different treatments. Results and Discussion: After looking into the metabolomics, we discovered that SH and MSC treatment led to the downregulation of ω-6 polyunsaturated fatty acids (PUFAs) and the upregulation of ω-3 PUFAs. Significantly, the contents of 5(S)-HETE, PGA2, PGB2, and PGJ2 were lower in the MSC group than in the SH group after quantification using 5-(diisopropylamino)amylamine derivatization-UHPLC-QQQ-MS. This is the first report on the relationship of 11(S)-HETE, PGA2, PGB2, PGF2β, 11β-PGF2α, and DK-PGE2 with OA. Moreover, the correlation analysis of metabolites and inflammation factors showed the positive association of ω-6 PUFAs with pro-inflammation cytokines, and of ω-3 PUFAs with anti-inflammation cytokines. Our results indicated the therapeutic effect of SH and MSCs in patients with OA. In addition, this reliable metabolic approach could uncover novel biomarkers to treat OA.

NFATc1-mediated expression of SLC7A11 drives sensitivity to TXNRD1 inhibitors in osteoclast precursors

Excess osteoclast activity is found in many bone metabolic diseases, and inhibiting osteoclast differentiation has proven to be an effective strategy. Here, we revealed that osteoclast precursors (pre-OCs) were more susceptible to thioredoxin reductase 1 (TXNRD1) inhibitors than bone marrow-derived monocytes (BMDMs) during receptor activator of nuclear factor kappa B ligand (RANKL)-mediated osteoclastogenesis. Mechanistically, we found that nuclear factor of activated T-cells 1 (NFATc1) upregulated solute carrier family 7 member 11 (SLC7A11) expression through transcriptional regulation during RANKL-induced osteoclastogenesis. During TXNRD1 inhibition, the rate of intracellular disulfide reduction is significantly reduced. Increased cystine transport leads to increased cystine accumulation, which leads to increased cellular disulfide stress and disulfidptosis. We further demonstrated that SLC7A11 inhibitors and treatments that prevent disulphide accumulation could rescue this type of cell death, but not the ferroptosis inhibitors (DFO, Ferro-1), the ROS scavengers (Trolox, Tempol), the apoptosis inhibitor (Z-VAD), the necroptosis inhibitor (Nec-1), or the autophagy inhibitor (CQ). An in vivo study indicated that TXNRD1 inhibitors increased bone cystine content, reduced the number of osteoclasts, and alleviated bone loss in an ovariectomized (OVX) mouse model. Together, our findings demonstrate that NFATc1-mediated upregulation of SLC7A11 induces targetable metabolic sensitivity to TXNRD1 inhibitors during osteoclast differentiation. Moreover, we innovatively suggest that TXNRD1 inhibitors, a classic drug for osteoclast-related diseases, selectively kill pre-OCs by inducing intracellular cystine accumulation and subsequent disulfidptosis.

Connexin 43 hemichannels and prostaglandin E2 release in anabolic function of the skeletal tissue to mechanical stimulation

Bone adapts to changes in the physical environment by modulating remodeling through bone resorption and formation to maintain optimal bone mass. As the most abundant connexin subtype in bone tissue, connexin 43 (Cx43)-forming hemichannels are highly responsive to mechanical stimulation by permitting the exchange of small molecules (<1.2 kDa) between bone cells and the extracellular environment. Upon mechanical stimulation, Cx43 hemichannels facilitate the release of prostaglandins E2 (PGE2), a vital bone anabolic factor from osteocytes. Although most bone cells are involved in mechanosensing, osteocytes are the principal mechanosensitive cells, and PGE2 biosynthesis is greatly enhanced by mechanical stimulation. Mechanical stimulation-induced PGE2 released from osteocytic Cx43 hemichannels acts as autocrine effects that promote β-catenin nuclear accumulation, Cx43 expression, gap junction function, and protects osteocytes against glucocorticoid-induced osteoporosis in cultured osteocytes. In vivo, Cx43 hemichannels with PGE2 release promote bone formation and anabolism in response to mechanical loading. This review summarizes current in vitro and in vivo understanding of Cx43 hemichannels and extracellular PGE2 release, and their roles in bone function and mechanical responses. Cx43 hemichannels could be a significant potential new therapeutic target for treating bone loss and osteoporosis.

Cardamonin alleviates chondrocytes inflammation and cartilage degradation of osteoarthritis by inhibiting ferroptosis via p53 pathway

Osteoarthritis (OA) is a common degenerative joint disease, mainly presented by the deterioration of articular cartilage. Amounts of data demonstrated this deterioration is composed of oxidative stress, pro-inflammation and chondrocyte death events. Ferroptosis is a novel form of cell death that differs from apoptosis and autophagy, recent studies have shown that chondrocyte ferroptosis contributes to the development of osteoarthritis. Cardamonin (CAD) has been demonstrated to possess antioxidant and anti-inflammatory properties in several diseases, whether CAD may influence the OA progression is still obscure. Therefore, we aimed to determine whether CAD alleviates chondrocyte ferroptosis and its effect on OA with potential mechanism. In this study, we found that inflammation, cartilage degradation and ferroptosis induced by interleukin-1β (IL-1β) were significantly alleviated by CAD. Moreover, the administration of the ferroptosis inhibitor, Deferoxamine (DFO) reversed the inflammatory and cartilage degradation effects of IL-1β as well. Chondrocyte mitochondrial morphology and function were alleviated by both CAD and DFO. We found that CAD increased collagen II, p53, SLC7A11 GPX4 expression and decreased MMP13, iNOS, COX2 expression in chondrocytes, further investigation showed that the P53 signaling pathway was involved. In vivo, intra-articular injection of CAD significantly ameliorated cartilage damage in a rat OA model, induced collagen II and SLC7A11 expression by immunohistochemistry. Our study proves that CAD ameliorated OA cartilage degradation by regulating ferroptosis via P53 signaling pathway, suggesting a potential role of CAD in OA treatment.

The role of non-steroidal anti-inflammatory drugs as adjuncts to periodontal treatment and in periodontal regeneration

Periodontitis is the sixth most prevalent chronic disease globally and places significant burdens on societies and economies worldwide. Behavioral modification, risk factor control, coupled with cause-related therapy have been the "gold standard" treatment for managing periodontitis. Given that host inflammatory and immunological responses play critical roles in the pathogenesis of periodontitis and impact treatment responses, several adjunctive strategies aimed at modulating host responses and improving the results of periodontal therapy and maintenance have been proposed. Of the many pharmacological host modulators, we focused on non-steroidal anti-inflammatory drugs (NSAIDs), due to their long history and extensive use in relieving inflammation and pain and reducing platelet aggregation. NSAIDs have been routinely indicated for treating rheumatic fever and osteoarthritis and utilized for the prevention of cardiovascular events. Although several efforts have been made to incorporate NSAIDs into the treatment of periodontitis, their effects on periodontal health remain poorly characterized, and concerns over the risk-benefit ratio were also raised. Moreover, there is emerging evidence highlighting the potential of NSAIDs, especially aspirin, for use in periodontal regeneration. This review summarizes and discusses the use of NSAIDs in various aspects of periodontal therapy and regeneration, demonstrating that the benefits of NSAIDs as adjuncts to conventional periodontal therapy remain controversial. More recent evidence suggests a promising role for NSAIDs in periodontal tissue engineering and regeneration.

Functional Loss of Terminal Complement Complex Protects Rabbits from Injury-Induced Osteoarthritis on Structural and Cellular Level

The terminal complement complex (TCC) has been described as a potential driver in the pathogenesis of posttraumatic osteoarthritis (PTOA). However, sublytic TCC deposition might also play a crucial role in bone development and regeneration. Therefore, we elucidated the effects of TCC on joint-related tissues using a rabbit PTOA model. In brief, a C6-deficient rabbit breed was characterized on genetic, protein, and functional levels. Anterior cruciate ligament transection (ACLT) was performed in C6-deficient (C6^-/-) and C6-sufficient (C6^+/-) rabbits. After eight weeks, the progression of PTOA was determined histologically. Moreover, the structure of the subchondral bone was evaluated by µCT analysis. C6 deficiency could be attributed to a homozygous 3.6 kb deletion within the C6 gene and subsequent loss of the C5b binding site. Serum from C6^-/- animals revealed no hemolytic activity. After ACLT surgery, joints of C6^-/- rabbits exhibited significantly lower OA scores, including reduced cartilage damage, hypocellularity, cluster formation, and osteophyte number, as well as lower chondrocyte apoptosis rates and synovial prostaglandin E2 levels. Moreover, ACLT surgery significantly decreased the trabecular number in the subchondral bone of C6^-/- rabbits. Overall, the absence of TCC protected from injury-induced OA progression but had minor effects on the micro-structure of the subchondral bone.

The interplay between the nerves and skeleton: a 30-year bibliometric analysis

Background

The mechanisms and effects of the interplay between the nerves and skeleton remain a popular research topic. This study aimed to analyze and evaluate publications on nerve-bone interactions using bibliometrics and to identify the state of the art of current research, hotspots, and future directions.

Methods

This study included 1989 articles and reviews from the Web of Science Core Collection (WoSCC) published from January 1, 1991, to June 22, 2022. The Bibliometrix package of R 4.2.0 (The R Foundation for Statistical Computing, Vienna, Austria) was used to analyze basic information about the publications, including the annual number of publications, institution analysis, author influence analysis, journal analysis, and the national cooperation network. We also used CiteSpace 5.8.R3 for bibliometric analysis, including co-occurrence, co-citation, and cluster analysis.

Results

We discovered a significant increase in the number of articles on nerve-bone interactions published over the last 10 years. The most active country and institution were the United States and the University of Minnesota, respectively. In terms of journals and cocited journals, Bone was ranked highest with respect to the number of publications, while Journal of Bone and Mineral Research was ranked highest among cited journals. Wang Lei was the author with the most publications, and Bjurholm A was the most cited author. The analysis of references and keywords revealed that the impact of nerve- and neuromodulation-related factors on stem cell differentiation was a persistently hot topic. Osteoarthritis, neuropeptide Y, and osteoclastogenic process are likely to be the next era of research hotspots. The neurovascular crosstalk within bone has received great attention, especially in skeletal diseases, which may provide potential targets for future treatments.

Conclusions

We used a bibliometric method to provide an efficient, objective, and comprehensive assessment of existing research about the interplay between the skeletal and nervous systems and to accurately identify hotspots and research frontiers, providing valuable information for future research.

Potential Anti-Inflammatory and Chondroprotective Effect of Luzula sylvatica

(1) Interest in the Juncaceae family has risen as some members have shown anti-inflammatory properties and interesting compounds. In this regard, we decided to investigate the antioxidant and anti-inflammatory properties of Luzula sylvatica, a Juncaceae not yet extensively studied, in the context of osteoarthritis. (2) The Luzula sylvatica Ethanol extract (LS-E) was used to test the production of reactive oxygen species (ROS) by leucocytes, the IL1β and PGE2 production by peripheral blood mononuclear cells (PBMCs), the production of EP4, and the activation of NFκB in THP-1, as well as the IL1β-activated normal human knee articular chondrocytes (NHAC-Kn) gene expression, grown in monolayers or maintained in alginate beads. (3) Organic acids, caffeoylquinic acids, quercetin and luteolin, compounds frequently found in this family were identified. The LS-E exhibited inhibited ROS formation. The LS-E did not affect NFκB activation and IL1β secretion but dampened the secretion of PGE2 by PBMCs and the presence of EP4 in THP-1. It also modulated the expression of NHAC-Kn in both models and inhibited the expression of several proteases and inflammatory mediators. (4) Luzula sylvatica might supply interesting antioxidant protection against cartilage damages and lessen joint inflammation, notably by decreasing PGE2 secretion in the synovial fluid. Moreover, it could act directly on chondrocytes by decreasing the expression of proteases and, thus, preventing the degradation of the extracellular matrix.

Skeletal interoception in bone homeostasis and pain

Accumulating evidence indicates that interoception maintains proper physiological status and orchestrates metabolic homeostasis by regulating feeding behaviors, glucose balance, and lipid metabolism. Continuous skeletal remodeling consumes a tremendous amount of energy to provide skeletal scaffolding, support muscle movement, store vital minerals, and maintain a niche for hematopoiesis, which are processes that also contribute to overall metabolic balance. Although skeletal innervation has been described for centuries, recent work has shown that skeletal metabolism is tightly regulated by the nervous system and that skeletal interoception regulates bone homeostasis. Here, we provide a general discussion of interoception and its effects on the skeleton and whole-body metabolism. We also discuss skeletal interoception-mediated regulation in the context of pathological conditions and skeletal pain as well as future challenges to our understanding of these process and how they can be leveraged for more effective therapy.

Immune mechanism of low bone mineral density caused by ankylosing spondylitis based on bioinformatics and machine learning

Background and Objective: This study aims to find the key immune genes and mechanisms of low bone mineral density (LBMD) in ankylosing spondylitis (AS) patients.

Methods: AS and LBMD datasets were downloaded from the GEO database, and differential expression gene analysis was performed to obtain DEGs. Immune-related genes (IRGs) were obtained from ImmPort. Overlapping DEGs and IRGs got I-DEGs. Pearson coefficients were used to calculate DEGs and IRGs correlations in the AS and LBMD datasets. Louvain community discovery was used to cluster the co-expression network to get gene modules. The module most related to the immune module was defined as the key module. Metascape was used for enrichment analysis of key modules. Further, I-DEGs with the same trend in AS and LBMD were considered key I-DEGs. Multiple machine learning methods were used to construct diagnostic models based on key I-DEGs. IID database was used to find the context of I-DEGs, especially in the skeletal system. Gene–biological process and gene-pathway networks were constructed based on key I-DEGs. In addition, immune infiltration was analyzed on the AS dataset using the CIBERSORT algorithm.

Results: A total of 19 genes were identified I-DEGs, of which IFNAR1, PIK3CG, PTGER2, TNF, and CCL3 were considered the key I-DEGs. These key I-DEGs had a good relationship with the hub genes of key modules. Multiple machine learning showed that key I-DEGs, as a signature, had an excellent diagnostic performance in both AS and LBMD, and the SVM model had the highest AUC value. Key I-DEGs were closely linked through bridge genes, especially in the skeletal system. Pathway analysis showed that PIK3CG, IFNAR1, CCL3, and TNF participated in NETs formation through pathways such as the MAPK signaling pathway. Immune infiltration analysis showed neutrophils had the most significant differences between case and control groups and a good correlation with key I-DEG.

Conclusion: The key I-DEGs, TNF, CCL3, PIK3CG, PTGER2, and IFNAR1, can be utilized as biomarkers to determine the risk of LBMD in AS patients. They may affect neutrophil infiltration and NETs formation to influence the bone remodeling process in AS.

α-Chaconine Facilitates Chondrocyte Pyroptosis and Nerve Ingrowth to Aggravate Osteoarthritis Progression by Activating NF-κB Signaling

BACKGROUND

With the rapid growth of the elderly population, the incidence of osteoarthritis (OA) increases annually, which has attracted extensive attention in public health. The roles of dietary intake in controlling joint disorders are perhaps one of the most frequently posed questions by OA patients, while the information about the interaction between dietary intake and OA based on scientific research is limited. α-Chaconine is the richest glycoalkaloid in eggplants such as potatoes. Previous evidence suggests that α-Chaconine is a toxic compound to nervous and digestive systems with potentially severe and fatal consequences for humans and farm animals, but its effect on OA development remains obscure.

OBJECTIVE

To determine whether α-Chaconine deteriorates OA progression through sensory innervation and chondrocyte pyroptosis via regulating nuclear factor-κB (NF-κB) signaling, providing evidence for a possible linkage between α-Chaconine and OA progression.

METHODS

We established a mouse OA model by destabilization of medial meniscus (DMM) surgery and then intra-articular injection of 20 or 100 μM α-Chaconine into the OA mice for 8 and 12 weeks. The severity of OA progression was evaluated by histological staining and radiographic analyses. The expressions of matrix metabolic indicators, Col2, Mmp3, and Mmp13, as well as pyroptosis-related proteins, Nlrp3, Caspase-1, Gsdmd, IL-1β, IL-18, were determined by immunohistochemistry. And the changes in sensory nerve ingrowth and activity of NF-κB signaling were determined by immunofluorescence.

RESULTS

We found that α-Chaconine could exacerbate mouse OA progression, resulting in subchondral sclerosis, osteophyte formation, and higher OARSI scores. Specifically, α-Chaconine could augment cartilage matrix degradation and induce chondrocyte pyroptosis and nerve ingrowth. Mechanistical analysis revealed that α-Chaconine stimulated NF-κB signaling by promoting I-κB α phosphorylation and p65 nuclear translocation.

CONCLUSION

Collectively, our findings raise the possibility that α-Chaconine intake can boost chondrocyte pyroptosis and nerve ingrowth to potentiate OA progression by activating NF-κB signaling.

miR-210-3p protects against osteoarthritis through inhibiting subchondral angiogenesis by targeting the expression of TGFBR1 and ID4

Excessive subchondral angiogenesis is a key pathological feature of osteoarthritis (OA), as it alters the balance of subchondral bone remodeling and causes progressive cartilage degradation. We previously found that miR-210-3p correlates negatively with angiogenesis, though the specific mechanism of miR-210-3p-related angiogenesis in subchondral bone during OA progression remains unclear. This study was conducted to identify the miR-210-3p-modulating subchondral angiogenesis mechanism in OA and investigate its therapeutic effect. We found that miR-210-3p expression correlated negatively with subchondral endomucin positive (Emcn+) vasculature in the knee joints of OA mice. miR-210-3p overexpression regulated the angiogenic ability of endothelial cells (ECs) under hypoxic conditions in vitro. Mechanistically, miR-210-3p inhibited ECs angiogenesis by suppressing transforming growth factor beta receptor 1 (TGFBR1) mRNA translation and degrading DNA-binding inhibitor 4 (ID4) mRNA. In addition, TGFBR1 downregulated the expression of ID4. Reduced ID4 levels led to a negative feedback regulation of TGFBR1, enhancing the inhibitory effect of miR-210-3p on angiogenesis. In OA mice, miR-210-3p overexpression in ECs via adeno-associated virus (AAV) alleviated cartilage degradation, suppressed the type 17 immune response and relieved symptoms by attenuating subchondral Emcn+ vasculature and subchondral bone remodeling. In conclusion, we identified a miR-210-3p/TGFBR1/ID4 axis in subchondral ECs that modulates OA progression via subchondral angiogenesis, representing a potential OA therapy target.

Inhibition of PGE2 in Subchondral Bone Attenuates Osteoarthritis

Aberrant subchondral bone architecture is a crucial driver of the pathological progression of osteoarthritis, coupled with increased sensory innervation. The sensory PGE2/EP4 pathway is involved in the regulation of bone mass accrual by the induction of differentiation of mesenchymal stromal cells. This study aimed to clarify whether the sensory PGE2/EP4 pathway induces aberrant structural alteration of subchondral bone in osteoarthritis. Destabilization of the medial meniscus (DMM) using a mouse model was combined with three approaches: the treatment of celecoxib, capsaicin, and sensory nerve-specific prostaglandin E2 receptor 4 (EP4)-knockout mice. Cartilage degeneration, subchondral bone architecture, PGE2 levels, distribution of sensory nerves, the number of osteoprogenitors, and pain-related behavior in DMM mice were assessed. Serum and tissue PGE2 levels and subchondral bone architecture in a human sample were measured. Increased PGE2 is closely related to subchondral bone’s abnormal microstructure in humans and mice. Elevated PGE2 concentration in subchondral bone that is mainly derived from osteoblasts occurs in early-stage osteoarthritis, preceding articular cartilage degeneration in mice. The decreased PGE2 levels by the celecoxib or sensory denervation by capsaicin attenuate the aberrant alteration of subchondral bone architecture, joint degeneration, and pain. Selective EP4 receptor knockout of the sensory nerve attenuates the aberrant formation of subchondral bone and facilitates the prevention of cartilage degeneration in DMM mice. Excessive PGE2 in subchondral bone caused a pathological alteration to subchondral bone in osteoarthritis and maintaining the physiological level of PGE2 could potentially be used as an osteoarthritis treatment.

Natural Compounds Affecting Inflammatory Pathways of Osteoarthritis

Osteoarthritis (OA) is the most common type of arthritis and chronic joint disease, affecting more than 240 million people worldwide. Although there are numerous advances in using drugs in treating OA, the use of natural compounds has aroused much interest among researchers due to their safety margin. Recent discovery shows that natural compounds play an extensive role in the oxidative stress signaling pathway in treating OA. Thus, this review summarizes the commonly used natural compounds for treating OA focusing on the oxidative stress signaling pathway and its downstream mediators. Selected databases—such as Scopus, Web of Science, Nature, and PubMed—were used to search for potentially relevant articles. The search is limited to the last 15 years and the search was completed using the Boolean operator’s guideline using the keywords of natural product AND oxidative stress AND osteoarthritis OR natural extract AND ROS AND degenerative arthritis OR natural plant AND free radicals AND degenerative joint disease. In total, 37 articles were selected for further review. Different downstream mechanisms of oxidative stress involved in the usage of natural compounds for OA treatment and anabolic and catabolic effects of natural compounds that exhibit chondroprotective effects have been discussed with the evidence of in vitro and in vivo trials in this review.

Dynamics of action of a Lys-49 and an Asp-49 PLA2s on inflammasome NLRP3 activation in murine macrophages

Phospholipases A₂ (PLA₂s) are proteins found in snake venoms with hemolytic, anticoagulant, myotoxic, edematogenic, bactericidal and inflammatory actions. In Bothrops jararacussu snake venom were isolated a Lys49-PLA₂ (BthTX-I) and an Asp49-PLA₂ (BthTX-II) with myotoxic and inflammatory actions. Both PLA₂s can activate the NLRP3 inflammasome, an intracytoplasmic platform that recognizes molecules released when tissue is damaged liberating IL-1β that contributes to the inflammatory response observed in envenoming. The dynamic of action of BthTX-I and BthTX-II in both thioglycollate (TG)-elicited macrophages and C2C12 myoblasts and the involvement of EP1 and EP2 receptors, and PGE₂ in NLRP3 inflammasome activation were evaluated. Both toxins induced PGE₂ liberation and inflammasome components (NLRP3, Caspase-1, ASC, IL-1β, and IL18), IL-6, P2X7, COX-1, COX-2, EP2 and EP4 gene expression in TG-elicited macrophages but not in C2C12 myoblasts. EP2 (PF04418948) and EP4 (GW627368X) inhibitors abolished this effect. Both PLA₂s also induced NLRP3 inflammasome protein expression that was abolished with the inhibitors used. Immunofluorescence and IL-1β assays confirmed the NLRP3 activation in TG-elicited macrophages with the participation of both EP2 and EP4 receptors confirming their involvement in this effect. All in all, BthTX-I and BthTX-II activate macrophages and induce the NLRP3 inflammasome complex activation with the participation of the PGE₂ via COX pathway and EP2 and EP4, both PGE₂ receptors, contributing to the local inflammatory effects observed in envenoming.

Osteomyelitis, Oxidative Stress and Related Biomarkers

Bone is a very dynamic tissue, subject to continuous renewal to maintain homeostasis through bone remodeling, a process promoted by two cell types: osteoblasts, of mesenchymal derivation, are responsible for the deposition of new material, and osteoclasts, which are hematopoietic cells, responsible for bone resorption. Osteomyelitis (OM) is an invasive infectious process, with several etiological agents, the most common being Staphylococcus aureus, affecting bone or bone marrow, and severely impairing bone homeostasis, resulting in osteolysis. One of the characteristic features of OM is a strong state of oxidative stress (OS) with severe consequences on the delicate balance between osteoblastogenesis and osteoclastogenesis. Here we describe this, analyzing the effects of OS in bone remodeling and discussing the need for new, easy-to-measure and widely available OS biomarkers that will provide valid support in the management of the disease.