Autophagic LC3+ calcified extracellular vesicles initiate cartilage calcification in osteoarthritis

Nano-zinc oxide (nZnO) targets the AMPK-ULK1 pathway to promote bone regeneration

BACKGROUND

Nano-zinc oxide (nZnO) has attracted significant attention in bone tissue engineering due to its antibacterial properties, anti-inflammatory effects, biocompatibility, and chemical stability. Although numerous studies have demonstrated the enhancement of osteogenic differentiation by nZnO-modified tissue engineering materials, the underlying mechanisms remain poorly characterized.

METHODS

This study aimed to identify the molecular mechanisms how nZnO promoted osteogenic differentiation and bone regeneration using transcriptome analysis, drug intervention, and shRNA knockdown techniques, etc. First, the study evaluated the in vivo effects of gelatin methacryloyl (GelMA) containing nZnO on bone regeneration using a mouse calvarial defect model. The impact of nZnO exposure on the osteogenic differentiation of mesenchymal stem cells (MSCs) was then assessed. The combined treatment of nZnO and MSCs in GelMA for bone regeneration was assessed in the mouse calvarial defect model thereafter.

RESULTS

nZnO induced osteoblastic differentiation to promote bone regeneration. nZnO activated the AMP-dependent protein kinase (AMPK)-ULK1 signals to stimulate autophagosomes formation and facilitate autophagy flow, which was the essential pathway to induce osteogenic differentiation. The combined treatment of MSCs and nZnO significantly enhanced bone regeneration in calvarial defect mice. Conversely, AMPK inhibitor Compound C (C.C) reversed the effects on autophagy flow and osteogenic potentiality induced by nZnO.

CONCLUSIONS

These results highlight that nZnO can regulate bone regeneration by activating autophagy through the AMPK/ULK1 signaling pathway, which may provide a novel therapeutic strategy for addressing bone defects using nZnO.

Anoctamin-5 deficiency enhances ATG9A-dependent autophagy, inducing osteogenesis and gnathodiaphyseal dysplasia-like bone formation

Mutations in the anoctamin-5 (ANO5) gene can lead to musculoskeletal disorders, with monoallelic (autosomal dominant) mutations typically presenting as skeletal abnormalities known as gnathodiaphyseal dysplasia (GDD). Clinically, GDD is characterized by thickened cortices of long bones and mandibles, narrowed medullary cavities, and increased bone fragility. While autophagy is necessary in regulating bone formation, the specific relationship between ANO5 and autophagy remains poorly understood. In this study, we demonstrated that Ano5 deficiency activates autophagy in mouse cranial osteoblasts (mCOBs), leading to enhanced osteogenic capacity in Ano5-/- mCOBs. The application of 3-methyladenine (3-MA) and chloroquine (CQ) reversed the excessive osteogenesis observed in Ano5-/- mCOBs. Further analysis revealed that Ano5 deficiency upregulated the expression of ATG9A, and silencing ATG9A significantly reduced both autophagy and osteogenic activity in Ano5-/- mCOBs. Additionally, AMP-activated protein kinase (AMPK) was found to positively regulate ATG9A, and inhibiting AMPK reduced ATG9A expression, which in turn mitigated excessive osteogenesis of Ano5-/- mCOBs. Moreover, in vivo experiments confirmed that treatment with 3-MA alleviated the bone phenotype abnormalities in Ano5-/- mice. These findings suggest that Ano5 negatively regulates autophagy, contributing to illuminate pathogenesis of GDD. Meanwhile, this research highlights potential therapeutic strategies targeting autophagy to pave the way for the clinical manifestations of GDD.

Identification of osteoarthritis-associated chondrocyte subpopulations and key gene-regulating drugs based on multi-omics analysis

The mechanism by which chondrocytes respond to mechanical stress in joints significantly affects the balance and function of cartilage. This study aims to characterize osteoarthritis-associated chondrocyte subpopulations and key gene targets for regulatory drugs. To begin, single-cell and transcriptome datasets were obtained from the Gene Expression Omnibus (GEO) database. Cell communication and pseudo-temporal analysis, as well as High-dimensional Weighted Gene Co-expression Network Analysis (hdWGCNA), were conducted on the single-cell data to identify key chondrocyte subtypes and module genes. Subsequently, Consensus Cluster Plus analysis was utilized to identify distinct disease subgroups within the osteoarthritis (OA) training dataset based on the key module genes. Furthermore, differential gene expression analysis and GO/KEGG pathway enrichment analysis were performed on the identified subgroups. To screen for hub genes associated with OA, a combination of 10 machine learning algorithms and 113 algorithm compositions was integrated. Additionally, the immune and pathway scores of the training dataset samples were evaluated using the ESTIMATE, MCP-counter, and ssGSEA algorithms to establish the relationship between the hub genes and immune and pathways. Following this, a network depicting the interaction between the hub genes and transcription factors was constructed based on the Network Analyst database. Moreover, the hub genes were subjected to drug prediction and molecular docking using the RNAactDrug database and AutoDockTools. Finally, real-time fluorescence quantitative PCR (RT-qPCR) was employed to detect the expression of hub genes in the plasma samples collected from osteoarthritis patients and healthy adults. In the OA sample, there is a significant increase in the proportion of prehypertrophic chondrocytes (preHTC), particularly in subgroups 6, 7, and 9. We defined these subgroups as OA_PreHTC subgroups. The OA_PreHTC subgroup exhibits a higher communication intensity with proliferative-related pathways such as ANGPTL and TGF-β. Furthermore, two OA disease subgroups were identified in the training set samples. This led to the identification of 411 differentially expressed genes (DEGs) related to osteoarthritis, 2485 DEGs among subgroups, as well as 238 intersecting genes and 5 hub genes (MMP13, FAM26F, CHI3L1, TAC1, and CKS2). RT-qPCR results indicate significant differences in the expression levels of five hub genes and their related TFs in the clinical blood samples of OA patients compared to the healthy control group (NC). Moreover, these five hub genes are positively associated with inflammatory pathways such as TNF-α, JAK-STAT3, and inflammatory response, while being negatively associated with proliferation pathways like WNT and KRAS. Additionally, the five hub genes are positively associated with neutrophils, activated CD4 T cell, gamma delta T cell, and regulatory T cell, while being negatively associated with CD56dim natural killer cell and Type 17T helper cell. Molecular docking results reveal that CAY10603, Tenulin, T0901317, and Nonactin exhibit high binding activity to CHI3L1, suggesting their potential as therapeutic drugs for OA. The OA_PreHTC subgroups plays a crucial role in the occurrence and development of osteoarthritis (OA). Five hub genes may exert their effects on OA through interactions with PreHTC cells, other chondrocytes, and immune cells, playing a role in inhibiting cell proliferation and stimulating inflammation, thus having high diagnostic value for OA. Additionally, CAY10603, Tenulin, T0901317, and Nonactin have potential therapeutic effects for OA patients.

Building a digital library on research into mineralizing vesicles: a systematic review-based approach

This systematic review consolidates current research on mineralizing extracellular vesicles, or matrix vesicles (MVs), including their isolation, characterization, and role in physiological and pathological calcification. We searched PubMed/Medline, Scopus, and Web of Knowledge by employing the keywords "matrix vesicles" or "collagenase-released matrix vesicles" or "mineralizing vesicles" and publishing years from 2000 to 2023. Seventy-one studies met the inclusion criteria. The studies described different experimental protocols, especially with respect to methods for isolating MVs, wherein digestion with collagenase combined with centrifugation was the most used. The studies employed characterization techniques, including the determination of alkaline phosphatase (ALP) and transmission electron microscopy (TEM), to assess the functionality, size, and morphology of MVs. MVs contain key proteins such as ALP, annexins, and osteocalcin, along with calcium and phosphate ions, which are all critical for precipitating apatite. In the studies, evaluation of ALP activity revealed that MVs are more effective for mineralization than their parent cells and, hence, a valuable tool to regenerate bone and to engineer tissues. On the other hand, MVs play an essential role in pathologies, and the studies showed how they contribute to vascular calcification. Despite the therapeutic potential of MVs, isolation methods and characterization protocols vary across the studies, so standardized methods are needed. We have consolidated the data resulting from this systematic review in an open digital library on MVs with free access to all researchers. The users of the digital library can apply filters and taxonomy to find and interconnect the data resulting from the review.

β-Diketone Functionalized Microspheres Chelate Reactive Iron via Metal Coordination for Cartilage Repair

Excessive intracellular iron accumulation can induce mitochondrial dysfunction, leading to chondrocyte ferroptosis, a key contributor to cartilage damage in osteoarthritis (OA). Here, micelle-microfluidic hydrogel microspheres, featuring keto-enol-thiol bridged nano-sized secondary structures that disintegrate within the intracellular peroxidative environment to reveal β-diketone groups with metal chelation capabilities, are utilized for the in situ removal of reactive iron, thereby facilitating cartilage repair through the restoration of mitochondrial homeostasis. The relevant experiments demonstrate that the microspheres reduce iron influx by downregulating transferrin receptor (TfR1) expression and decrease mitochondrial iron uptake by upregulating mitochondrial outer membrane iron-sulfur cluster protein (CISD1), thus restoring intracellular mitochondrial iron homeostasis. Furthermore, the antioxidant properties of the ketone-thioether segments synergistically mitigate chondrocyte phospholipid peroxidation via Nrf2/SLC7A11/GPX4 axis, inhibiting ferroptosis and slowing OA progression. In summary, this system that in situ sustainably chelates reactive iron via metal coordination exhibits great potential in the minimally invasive treatment of OA and other ferroptosis-mediated diseases.

LIPUS Promotes Calcium Oscillation and Enhances Calcium Dependent Autophagy of Chondrocytes to Alleviate Osteoarthritis

Osteoarthritis (OA) is a degenerative disease which places an enormous burden on society, effective treatments are still limited. As a non-invasive and safe physical therapy, low-intensity pulsed ultrasound (LIPUS) can alleviate OA progression, but the underlying mechanism is not fully understood, especially the mechanical transduction between LIPUS and the organism. In this pioneering study, the biomechanical effects of LIPUS on living mice chondrocytes and living body zebrafish are investigate by using fluorescence imaging technology, to dynamically "visualize" its invisible mechanical stimuli in the form of calcium oscillations. It is also confirmed that LIPUS maintains cartilage homeostasis by promoting chondrocyte autophagy in a calcium-dependent manner. In addition, chondrocyte ion channels are screened by scRNA-seq and confirm that the mechanosensitive ion channel transient receptor potential vanilloid 4 (TRPV4) mediated the biological effects of LIPUS on chondrocytes. Finally, it is found that a combination of pharmacologically induced and LIPUS-induced Ca2+ influx in chondrocytes enhances the cartilage-protective effect of LIPUS, which may provide new insights for optimizing LIPUS in the treatment of OA.

The communication role of extracellular vesicles in the osteoarthritis microenvironment

Osteoarthritis (OA) is the most common degenerative joint disease worldwide, characterized by synovial inflammation, cartilage loss, and reactive hyperplasia of subchondral bone, affecting the quality of life of hundreds of millions of people. However, the molecular mechanisms underlying the occurrence and progression of OA remain unclear, and there is no therapy can substantially interrupt or reverse the destructive process of OA. More insight into the pathogenesis of OA may result in innovative therapeutics. The OA microenvironment plays a pivotal role in the development and progression of OA, which encompasses chondrocytes, adipocytes, synovial fibroblasts, endothelial cells, and immune cells. Extracellular vesicles (EVs) have emerged as a novel form of intercellular communication, mediating the transfer of a range of bioactive molecules to create a specific microenvironment. Recent studies have reported that the cargos of EVs play a crucial role in the pathogenesis of OA, including noncoding RNAs (ncRNAs), proteins, and lipids. This review systematically analyzes and summarizes the biological characteristics and functionalities of EVs derived from diverse cellular sources, especially how EVs mediate communication between different cells in the OA microenvironment, with a view to providing new insights into the pathogenesis of OA.

M6A Demethyltransferase FTO Attenuates Meniscus Degeneration and Osteoarthritis via Orchestrating Autophagy and Energetic Metabolism

Impaired autophagy is reported to promote osteoarthritis (OA). However, the mechanism by which autophagy in regulating meniscus degeneration and OA remains unclear. Here, unconvered aberrant energetic metabolism pattern in meniscus cells with OA is uncovered first, which results in lower adenosine triphosphate (ATP) production. And these phenomena are induced by impaired autophagy in meniscus cells with OA. It is further revealed that the suppression of m6A demethylase fat mass and obesity-associated protein (FTO) inhibits autophagy and causing lower ATP production by reducing oxidative phosphorylation. Specific deletion of FTO in meniscus cells by generating FTOflox/flox; COL1A1-CreERT2 (FTOcko) mice impair autophagy and promote meniscus degeneration and OA, while intra-articular injection of adeno-associated virus of FTO (AAV-FTO) restores autophagy and alleviates meniscus degeneration and OA. Mechanistically, FTO regulates the mRNA stability of ATG16L1 by targeting the m6A methylation sites on ATG16L1 in a YTHDF2-dependent manner, thereby inhibiting the formation of autophagosomes and causing an imbalance in energetic metabolism. Intra-articular injection of AAV-FTO reverses the catabolic phenotype of meniscus degeneration and OA in FTOcko mice. In summary, these findings reveal FTO orchestrates autophagy and energetic metabolism by regulating ATG16L1 in a m6A-dependent manner. Therefore, targeting FTO might be a potential therapeutic strategy for meniscus degeneration and early-stage OA.

Potential and challenges of utilizing exosomes in osteoarthritis therapy (Review)

Exosomes are integral to the pathophysiology of osteoarthritis (OA) due to their roles in mediating intercellular communication and regulating inflammatory processes. Exosomes are integral to the transport of bioactive molecules, such as proteins, lipids and nucleic acids, which can influence chondrocyte behavior and joint homeostasis. Given their properties of regeneration and ability to target damaged tissues, exosomes represent a promising therapeutic avenue for OA treatment. Exosomes have potential in promoting cartilage repair, reducing inflammation and improving overall joint function. However, several challenges remain, including the need for standardized isolation and characterization methods, variability in exosomal content, and regulatory hurdles. The present review aims to provide a comprehensive overview of the current understanding of exosome mechanisms in OA and their therapeutic potential, while also addressing the ongoing challenges faced in translating these findings into clinical practice. By consolidating existing research, the present review aims to pave the way for future studies aimed at optimizing exosome‑based therapies for effective OA management.

Neurovascularization inhibiting dual responsive hydrogel for alleviating the progression of osteoarthritis

Treating osteoarthritis (OA) associated pain is a challenge with the potential to significantly improve patients lives. Here, we report on a hydrogel for extracellular RNA scavenging and releasing bevacizumab to block neurovascularization at the osteochondral interface, thereby mitigating OA pain and disease progression. The hydrogel is formed by cross-linking aldehyde-phenylboronic acid-modified sodium alginate/polyethyleneimine-grafted protocatechuic acid (OSAP/PPCA) and bevacizumab sustained-release nanoparticles (BGN@Be), termed OSPPB. The dynamic Schiff base bonds and boronic ester bonds allow for injectability, self-healing, and pH/reactive oxygen species dual responsiveness. The OSPPB hydrogel can significantly inhibit angiogenesis and neurogenesis in vitro. In an in vivo OA model, intraarticular injection of OSPPB accelerates the healing process of condyles and alleviates chronic pain by inhibiting neurovascularization at the osteochondral interface. The injectable hydrogel represents a promising technique to treat OA and OA associated pain.

Peripheral Lysosomal Positioning in Inflamed Odontoblasts Facilitates Mineralization

INTRODUCTION

Odontoblasts, terminally differentiated dentin-producing cells, critically rely on lysosomal functions for intracellular recycling and renewal. Beyond their traditional degradative role, lysosomes actively orchestrate cellular responses to external stimuli through precise and rapid intracellular trafficking and positioning. This study aimed to explore the influence of lysosomal positioning on odontoblast mineralization and the underlying mechanisms implicated in carious inflammation.

METHODS

Human dental pulp stem cells were induced to differentiate into human odontoblast-like cells (hOBLCs). hOBLCs were treated with various doses of LPS (0.1, 1, 5 μg/mL) to mimic carious inflammation. Lysosomal positioning was examined by immunofluorescence staining of lysosomal associated membrane protein 1 in healthy and carious human teeth, LPS-treated hOBLCs, mouse lower incisors at postnatal day 2.5, and mineralization medium cultured human dental pulp stem cells. Lysosomal positioning was manipulated by knockdown or overexpression of SNAPIN or ARL8B. Mineralization was assessed by ARS staining and expression of DSPP and DMP1. Lysosomal exocytosis was examined by detection of lysosomal-plasma membrane fusion, surface exposure of lysosomal associated membrane protein 1 luminal epitopes (1D4B), and extracellularly released lysosomal enzymes.

RESULTS

Peripheral lysosomal positioning was markedly increased in odontoblasts within moderate and extensive carious lesions (P < .001) and in hOBLCs following LPS treatment. Increased peripheral dispersion of lysosomes was similarly observed during odontoblastic differentiation in vivo and in vitro. Moreover, peripheral lysosomal positioning promoted mineralization in inflamed hOBLCs, potentially via mTORC1 signaling pathway and lysosomal exocytosis.

CONCLUSION

Inflammatory stimuli prompted a relocation of lysosomes in odontoblasts, redistributing them from perinuclear location toward the cell periphery, which in turn facilitated mineralization, potentially via mTORC1 signaling and lysosomal exocytosis.

Matrix vesicle-inspired delivery system based on nanofibrous chitosan microspheres for enhanced bone regeneration

Inspired by the initial mineralization process with bone matrix vesicles (MVs), this study innovatively developed a delivery system to mediate mineralization during bone regeneration. The system comprises nanofibrous chitosan microspheres (NCM) and poly (allylamine hydrochloride)-stabilized amorphous calcium phosphate (PAH-ACP), which is thereafter referred to as NCMP. NCM is synthesized through the thermal induction of chitosan molecular chains, serving as the carrier, while PAH-ACP functions as the mineralization precursor. Additionally, the nanofibrous network of NCMP mimics the architecture of natural extracellular matrix (ECM), creating an optimal niche for the active adhesion of stem cells to its surface, exhibiting good biocompatibility, immunoregulation, and osteogenic performance. In vivo, NCMP effectively recruits cells and mineralizes collagen, modulates cell behavior and differentiation, and promotes in situ biomineralization in rat calvarial defects. These results underscore the dual efficacy of NCMP not only as an effective delivery system for mineralization precursors but also as ECM-mimicking bio-blocks, offering a promising avenue for enhancing the repair and regeneration of bone defects.

Fasting activates optineurin-mediated mitophagy in chondrocytes to protect against osteoarthritis

Mitochondrial homeostasis plays a crucial role in the pathogenesis of osteoarthritis (OA), a chronic musculoskeletal disorder characterized by articular cartilage degeneration and chondrocyte apoptosis. However, molecular mechanisms underlying the association between mitophagy and OA remain unclear. Here, we aimed to investigate the role of the autophagy receptor protein optineurin (OPTN) in OA, and explore the effects of dietary intervention on OA symptoms and its relationship with OPTN-mediated mitophagy. Our findings showed the downregulation of OPTN in patients with OA. Using an Optn-knockout mouse model, we demonstrated that OPTN deficiency leads to impaired mitophagy, resulting in the accumulation of damaged mitochondria, increased production of reactive oxygen species, and chondrocyte apoptosis. Furthermore, fasting prevented OA progression by activating OPTN-mediated mitophagy and maintaining mitochondrial homeostasis in mice. The present study revealed a novel mechanism by which OPTN-mediated mitophagy influences chondrocytes and the OA phenotype in Optn-knockout mice, suggesting that OPTN-mediated mitophagy plays a crucial role in OA development and progression. This study provides new insights into the pathogenesis of OA and offers a potential avenue for the development of novel drugs targeting OPTN to mitigate OA progression.

Effect of regional crosstalk between sympathetic nerves and sensory nerves on temporomandibular joint osteoarthritic pain

Temporomandibular joint osteoarthritis (TMJ-OA) is a common disease often accompanied by pain, seriously affecting physical and mental health of patients. Abnormal innervation at the osteochondral junction has been considered as a predominant origin of arthralgia, while the specific mechanism mediating pain remains unclear. To investigate the underlying mechanism of TMJ-OA pain, an abnormal joint loading model was used to induce TMJ-OA pain. We found that during the development of TMJ-OA, the increased innervation of sympathetic nerve of subchondral bone precedes that of sensory nerves. Furthermore, these two types of nerves are spatially closely associated. Additionally, it was discovered that activation of sympathetic neural signals promotes osteoarthritic pain in mice, whereas blocking these signals effectively alleviates pain. In vitro experiments also confirmed that norepinephrine released by sympathetic neurons promotes the activation and axonal growth of sensory neurons. Moreover, we also discovered that through releasing norepinephrine, regional sympathetic nerves of subchondral bone were found to regulate growth and activation of local sensory nerves synergistically with other pain regulators. This study identified the role of regional sympathetic nerves in mediating pain in TMJ-OA. It sheds light on a new mechanism of abnormal innervation at the osteochondral junction and the regional crosstalk between peripheral nerves, providing a potential target for treating TMJ-OA pain.

Exploration of the mechanism of tetramethoxyflavone in treating osteoarthritis based on network pharmacology and molecular docking

Objectives

This study aimed to explore the potential mechanisms of TMF (5,7,3',4'-tetramethoxyflavone) in treating osteoarthritis (OA) using network pharmacology and molecular docking.

Materials and Methods

Databases including SwissTargetPrediction, BATMAN-TCM, PharmMapper, TargetNet, SuperPred, and SEA were utilized to screen the targets of TMF. "OA" was used as the disease keyword to predict OA-related genes through GeneCards, Therapeutic Target Database, PharmGKB, Online Mendelian Inheritance in Man, and Comparative Toxicogenomics Database. The Venn diagram was employed to identify the intersection of predicted targets between TMF and OA as potential targets for TMF in treating OA. The intersection targets were input into the STRING 12.0 online database to construct a protein-protein interaction (PPI) network and identify core targets. Subsequently, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were performed using the Metascape V3.5 online database platform. Finally, molecular docking between TMF and core targets was conducted using AutoDockTools 1.5.6.

Results

A total of 228 intersection targets for TMF treating OA were obtained, and PPI network analysis identified 5 core targets: STAT3, SRC, CTNNB1, EGFR, and AKT1. GO enrichment analysis yielded 2736 results, while KEGG analysis identified 203 pathways. Most elated GO and KEGG items of TMF in treating OA may include hormonal responses, antiviral and anticancer effects, anti-inflammation, phosphorus metabolism, phosphate metabolism, nitrogen compound responses, cancer-related pathways, PI3K-Akt signaling pathway, and MAPK signaling pathway. Molecular docking revealed good binding affinities between TMF and all core targets except STAT3.

Conclusion

TMF might act on multiple targets and activate diverse pathways to intervene in OA, revealing the molecular processes involved in TMF treatment of OA.

Single-Cell Transcriptomic Analysis Reveals Biomechanical Loading-Induced Imbalance in Bone and Fat, Leading to Ossification in Lumbar Intervertebral Disc Nucleus Pulposus Degeneration

In this study, we explored the impact of different biomechanical loadings on lumbar spine motion segments, particularly concerning intervertebral disc degeneration (IVDD). We aimed to uncover the cellular milieu and mechanisms driving ossification in the nucleus pulposus (NP) during IVDD, a process whose underlying mechanisms have remained elusive. The study involved the examination of fresh NP tissue from the L3-S1 segment of five individuals, either with IVDD or healthy. The analysis consisted of histopathological evaluation and single-cell RNA sequencing. To further validate the impact of biomechanical loading on IVDD, particularly on the CITED4 + METRN + NP chondrocytes and the bone-fat balance mechanism, a retrospective analysis was conducted using paraffin-embedded NP samples from patients. A distinct subset of CITED4 + METRN+ chondrocytes in the degenerated NP that were influenced by biomechanical loading was identified. These cells were evaluated for their potential as diagnostic biomarkers. Pseudotemporal analysis indicated that inflammation and repair processes were integral to NP ossification. Notably, the L4/5 and L5/S1 segments with severe IVDD showed pronounced ossification and heightened lipogenic metabolism. Cell communication analysis sheds light on the roles of bone-fat balance proteins and various ossification genes. Additionally, immunohistochemistry and immunofluorescence confirmed that biomechanical loading intensified IVDD by fostering osteogenic differentiation, mediated by macrophage migration inhibitory factor (MIF)-regulated bone-fat balance. This research reveals the microenvironmental factors of IVDD NP ossification under biomechanical loading, highlighting the role of bone-fat imbalance. These insights significantly enhance the understanding of IVDD pathogenesis and pave the way for innovative therapeutic approaches.

Modulating Autophagy in Osteoarthritis: Exploring Emerging Therapeutic Drug Targets

Osteoarthritis (OA) is a degenerative joint disease characterized by the breakdown of cartilage and the subsequent inflammation of joint tissues, leading to pain and reduced mobility. Despite advancements in symptomatic treatments, disease-modifying therapies for OA remain limited. This narrative review examines the dual role of autophagy in OA, emphasizing its protective functions during the early stages and its potential to contribute to cartilage degeneration in later stages. By delving into the molecular pathways that regulate autophagy, this review highlights its intricate interplay with oxidative stress and inflammation, key drivers of OA progression. Emerging therapeutic strategies aimed at modulating autophagy are explored, including pharmacological agents such as AMP kinase activators, and microRNA-based therapies. Preclinical studies reveal encouraging results, demonstrating that enhancing autophagy can reduce inflammation and decelerate cartilage degradation. However, the therapeutic benefits of autophagy modulation depend on precise, stage-specific approaches. Excessive or dysregulated autophagy in advanced OA may lead to chondrocyte apoptosis, exacerbating joint damage. This review underscores the promise of autophagy-based interventions in bridging the gap between experimental research and clinical application. By advancing our understanding of autophagy's role in OA, these findings pave the way for innovative and effective therapies. Nonetheless, further research is essential to optimize these strategies, address potential off-target effects, and develop safe, targeted treatments that improve outcomes for OA patients.

Identification of mitophagy-related biomarkers in osteoarthritis

BACKGROUND

Osteoarthritis (OA) is a common joint disease, and existing drugs cannot cure OA, so there is an urgent need to identify new targets. Mitophagy plays an important role in OA; however, the role of mitophagy in the OA immune system is not yet clear.

METHODS

In this study, differential analysis and enrichment analysis were used to identify mitophagy-related genes (MRGs) with differential expression in OA and the functional pathways involved in OA. Subsequently, two machine learning methods, RF and LASSO, were used to screen MRGs with diagnostic value and construct nomograms. At the same time, the relationship between mitophagy and OA immune response was explored by immunoinfiltration analysis.

RESULTS

Forty-three differentially MRGs were identified in OA, of which six MRGs (GABARAPL2, PARL, GABARAPL1, JUN, RRAS, and SNX7) were associated with the diagnosis of OA. The ROC analysis results show that these 6 MRGs have high predictive accuracy in the diagnosis of OA. In immune infiltration analysis, we found that the abundance of significantly different immune cells in OA was mostly upregulated. In addition, the expression of diagnostic-related MRGs is correlated with changes in the abundance of immune cells in OA.

CONCLUSION

This study demonstrates that six MRGs can be used as diagnostic biomarkers. The expression of diagnostic-related MRGs is correlated with changes in the abundance of immune cells in OA. At the same time, mitophagy may affect the immune microenvironment of OA by regulating immune cells, ultimately leading to the progression of OA.

Bone and Joint-on-Chip Platforms: Construction Strategies and Applications

Organ-on-a-chip, also known as "tissue chip," is an advanced platform based on microfluidic systems for constructing miniature organ models in vitro. They can replicate the complex physiological and pathological responses of human organs. In recent years, the development of bone and joint-on-chip platforms aims to simulate the complex physiological and pathological processes occurring in human bones and joints, including cell-cell interactions, the interplay of various biochemical factors, the effects of mechanical stimuli, and the intricate connections between multiple organs. In the future, bone and joint-on-chip platforms will integrate the advantages of multiple disciplines, bringing more possibilities for exploring disease mechanisms, drug screening, and personalized medicine. This review explores the construction and application of Organ-on-a-chip technology in bone and joint disease research, proposes a modular construction concept, and discusses the new opportunities and future challenges in the construction and application of bone and joint-on-chip platforms.

Extracellular Vesicles Derived from Ligament Tissue Transport Interleukin-17A to Mediate Ligament-To-Bone Crosstalk in Ankylosing Spondylitis

Pathological new bone formation is a critical feature of the progression of ankylosing spondylitis (AS), and spine ankylosis is a distinctive feature of this condition. Ligaments are the primary regions of pathological new bone formation in AS. Here, it is demonstrated that ligament tissue-derived extracellular vesicles (EVs) and their interleukin-17A (IL-17A) cargo mediate the communication between the tissue and other cells. The investigation revealed that IL-17A in EVs can activate the JAK-STAT3 pathway, thereby stimulating the expression of MMP14 in AS ligament. Overexpression of MMP14 can lead to changes in the cytoskeleton and mechanical signaling of mesenchymal stem cells and other cells. These alterations in cellular cytoskeleton and mechanical signaling at ligament sites in patients with AS or in stem cells treated with EVs can result in pathological new bone formation. Finally, inhibiting IL-17A activity and EV endocytosis effectively controlled inflammation and pathological new bone formation. Overall, these data suggest that ligament-derived EVs and the enclosed IL-17A have a potential role in driving pathological new bone formation in AS, and targeting EVs may therefore emerge as a novel approach to delaying ectopic ossification in AS.

Identification of key biomarkers related to fibrocartilage chondrocytes for osteoarthritis based on bulk, single-cell transcriptomic data

Introduction

Osteoarthritis (OA) is a prevalent joint disease that severely impacts patients' quality of life. Due to its unclear pathogenesis and lack of effective therapeutic targets, discovering new biomarkers for OA is essential. Recently, the role of chondrocyte subpopulations in OA progression has gained significant attention, offering potential insights into the disease. This study aimed to explore the role of fibrocartilage chondrocytes (FC) in the progression of OA and identify key biomarkers related to FC.

Methods

We analyzed single-cell ribonucleic acid sequencing (scRNA-seq) data from samples of OA and normal cartilage, focusing on FC. Microarray data were integrated to identify differentially expressed genes (DEGs). We conducted functional-enrichment analyses, including Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO), and used weighted gene co-expression network analysis (WGCNA) and the least absolute shrinkage and selection operator (LASSO) algorithm to select biomarkers. A novel risk model for OA was constructed using these biomarkers. We then built a transcription factor (TF)-gene interaction network and performed immunohistochemistry (IHC) to validate protein expression levels of these biomarkers in cartilage samples.

Results

The study identified 545 marker genes associated with FC in OA. GO and KEGG analyses revealed their biological functions; microarray analysis identified 243 DEGs on which functional-enrichment analysis were conducted. Using WGCNA and LASSO, we identified six hub genes, on the basis of which we constructed a risk model for OA. In addition, correlation analysis revealed a close association between Forkhead Box (FoxO)-mediated transcription and these these biomarkers. IHC showed significantly lower protein levels of ABCA5, ABCA6 and SLC7A8 in OA samples than in normal samples.

Conclusion

This study used a multi-omics approach to identify six FC-related OA biomarkers (BCL6, ABCA5, ABCA6, CITED2, NR1D1, and SLC7A8) and developed an exploratory risk model. Functional enrichment analysis revealed that the FoxO pathway may be linked to these markers, particularly implicating ABCA5 and ABCA6 in cholesterol homeostasis within chondrocytes. These findings highlight ABCA family members as novel contributors to OA pathogenesis and suggest new therapeutic targets.

A switch from lysosomal degradation to secretory autophagy initiates osteogenic bone metastasis in prostate cancer

The identification of both autophagy-related material degradation and unconventional secretion has paved the way for significant breakthroughs linking autophagy to a plethora of physiological processes and disease conditions. However, the mechanisms that coordinate these two pathways remain elusive. Here, we demonstrate that a switch from the lysosomal degradation to a secretory autophagy pathway is governed by protein tyrosine phosphatase 1B (PTP1B, encoded by PTPN1). Dephosphorylation at two tyrosine residues of syntaxin17 (STX17) by PTP1B reduces autophagosome-lysosome fusion while switching the cells to a secretory autophagy pathway. Both PTP1B overexpression and tumour-derived extracellular vesicles (EVs) can activate the secretory autophagy pathway in osteoblasts. Moreover, we demonstrate that osteoblastic LC3+ EVs, generated via the secretory autophagy pathway, are the primary contributor to tumour-associated bone remodelling in prostate cancer. Depletion of tumour-derived EVs secretion or genetic ablation of osteoblastic PTP1B rescues aberrant bone remodelling and lesions, highlighting the relevance between LC3+ EVs and the formation of bone metastatic niche. Our results reveal the significance of tumour-regulated PTP1B in the fate decision of autophagosomes, and propose a role ofLC3+ EVs in shaping the bone metastatic niche.

Development and validation of a robotic system for milling individualized jawbone cavities in oral and maxillofacial surgery

OBJECTIVES

This study aimed to develop and validate a robotic system capable of performing accurate and minimally invasive jawbone milling procedures in oral and maxillofacial surgery.

METHODS

The robotic hardware system mainly includes a UR5E arm (Universal Robots, Denmark) and the binocular positioning system (FusionTrack 250, Atracsys LLC, Switzerland). The robotic software (Dental Navi 3.0.0, Yakebot Technology Ltd., China) is capable of generating cutting tool paths based on three-dimensional shape description files, typically in the stereolithography format, and selected cutting tool parameters, as well as designing surgical accessories. Fully impacted supernumerary tooth models in the maxilla were fabricated using software and three-dimensional printing. Following the planning of a customized cavity to fully expose the tooth, maxillary bone milling was performed on both the robot and static guide groups (n = 8). After milling, all models underwent scanning for assessment.

RESULTS

In the experiment with fully buried supernumerary tooth models in the maxilla, the root mean square, translation error, over-removal rate, and maximum distance were significantly smaller in the robot group compared to the static guide group. Moreover, the overlap ratio and Dice coefficient were significantly greater in the robot group. No statistically significant differences were observed between the two groups in terms of the rotation error (P = 0.80) or under-removal rate (P = 0.92).

CONCLUSIONS

This study has developed a robotic system for milling individualized jawbone cavities in oral and maxillofacial surgery, and its accuracy has been preliminarily verified to meet clinical requirements.

CLINICAL SIGNIFICANCE

The robotic system can achieve precise, minimally invasive, individualized jawbone milling in a variety of oral and maxillofacial surgeries, including tooth autotransplantation, surgical reshaping for zygomatic fibrous dysplasia, removal of fully impacted supernumerary or impacted teeth, and endodontic microsurgery, among other relevant clinical applications.

Transplanted MSCs promote alveolar bone repair via hypoxia-induced extracellular vesicle secretion

OBJECT

Mesenchymal stem cell (MSC) therapy is a potential strategy for promoting alveolar bone regeneration. This study evaluated the effects and mechanisms of transplanted MSCs on alveolar bone repair.

METHODS

Mouse alveolar bone defect model was treated using mouse bone marrow mesenchymal stem cell (BMSC) transplantation. The bone repair was evaluated by micro-CT and Masson staining. The conditioned medium of hypoxia-treated BMSCs was co-cultured with normal BMSCs in vitro to detect the regulatory effect of transplanted MSCs on the chemotactic and migratory functions of host cells. The mechanisms were investigated using Becn siRNA transfection and western blotting.

RESULTS

BMSC transplantation promoted bone defect regeneration. The hypoxic microenvironment induces BMSCs to release multiple extracellular vesicle (EV)-mediated regulatory proteins that promote the migration of host stem cells. Protein array analysis, western blotting, GFP-LC3 detection, and Becn siRNA transfection confirmed that autophagy activation in BMSCs plays a key role during this process.

CONCLUSION

The local hypoxic microenvironment induces transplanted MSCs to secrete a large number of EV-mediated regulatory proteins, thereby upregulating the migration function of the host stem cells and promoting alveolar bone defect regeneration. This process depends on the autophagy-related mechanism of the transplanted MSCs.

Adipose tissue-derived extracellular vesicles aggravate temporomandibular joint osteoarthritis associated with obesity

INTRODUCTION

Temporomandibular joint osteoarthritis (TMJ OA) is a major disease that affects maxillofacial health and is characterised by cartilage degeneration and subchondral bone remodelling. Obesity is associated with the exacerbation of pathological manifestations of TMJ OA. However, the underlying mechanism between adipose tissue and the TMJ axis remains limited.

OBJECTIVES

To evaluate the effects of obesity and the adipose tissue on the development of TMJ OA.

METHODS

The obesity-related metabolic changes in TMJ OA patients were detected by physical signs and plasma metabolites. The effects of adipose tissue-derived EVs (Ad-EVs) on TMJ OA was investigated through histological and cytological experiments as well as gene editing technology. Alterations of Ad-EVs in obese state were identified by microRNA-seq analysis and the mechanism by which EVs affect TMJ OA was explored in vitro and in vivo.

RESULTS

Obesity and the related metabolic changes were important influencing factors for TMJ OA. Ad-EVs from obese mice induced marked chondrocyte apoptosis, cartilage matrix degradation and subchondral bone remodelling, which exacerbated the development of TMJ OA. Depletion of Ad-EVs secretion by knocking out the geranylgeranyl diphosphate synthase (Ggpps) gene in adipose tissue significantly inhibited the obesity-induced aggravation of TMJ OA. MiR-3074-5p played an important role in this process .

CONCLUSIONS

Our work unveils an unknown link between obese adipose tissue and TMJ OA. Targeting the Ad-EVs and the miR-3074-5p may represent a promising therapeutic strategy for obesity-related TMJ OA.

KEY POINTS

High-fat-diet-induced obesity aggravate the progression of TMJ OA in mice. Obese adipose tissue participates in cartilage damage through the altered miRNA in extracellular vesicles. Inhibition of miR-3074-5p/SMAD4 pathway in chondrocyte alleviated the effect of HFD-EVs on TMJ OA.

Poly(p-coumaric acid) nanoparticles alleviate temporomandibular joint osteoarthritis by inhibiting chondrocyte ferroptosis

Oxidative stress and inflammation are key drivers of osteoarthritis (OA) pathogenesis and disease progression. Herein we report the synthesis of poly(p-coumaric) nanoparticles (PCA NPs) from p-courmaic acid (p-CA), a naturally occurring phytophenolic acid, to be a multifunctional and drug-free therapeutic for temporomandibular joint osteoarthritis (TMJOA). Compared to hyaluronic acid (HA) that is clinically given as viscosupplementation, PCA NPs exhibited long-term efficacy, superior anti-oxidant and anti-inflammatory properties in alleviating TMJOA and repairing the TMJ cartilage and subchondral bone in a rat model of TMJOA. Notably, TMJ repair mediated by PCA NPs could be attributed to their anti-oxidant and anti-inflammatory properties in enhancing cell proliferation and matrix synthesis, while reducing inflammation, oxidative stress, matrix degradation, and chondrocyte ferroptosis. Overall, our study demonstrates a multifunctional nanoparticle, synthesized from natural p-coumaric acid, that is stable and possess potent antioxidant, anti-inflammatory properties and ferroptosis inhibition, beneficial for treatment of TMJOA.

Yin-Yang: two sides of extracellular vesicles in inflammatory diseases

The concept of Yin-Yang, originating in ancient Chinese philosophy, symbolizes two opposing but complementary forces or principles found in all aspects of life. This concept can be quite fitting in the context of extracellular vehicles (EVs) and inflammatory diseases. Over the past decades, numerous studies have revealed that EVs can exhibit dual sides, acting as both pro- and anti-inflammatory agents, akin to the concept of Yin-Yang theory (i.e., two sides of a coin). This has enabled EVs to serve as potential indicators of pathogenesis or be manipulated for therapeutic purposes by influencing immune and inflammatory pathways. This review delves into the recent advances in understanding the Yin-Yang sides of EVs and their regulation in specific inflammatory diseases. We shed light on the current prospects of engineering EVs for treating inflammatory conditions. The Yin-Yang principle of EVs bestows upon them great potential as, therapeutic, and preventive agents for inflammatory diseases.

Matrix stiffness aggravates osteoarthritis progression through H3K27me3 demethylation induced by mitochondrial damage

Abnormal epigenetics is the initial factor of the occurrence and development of osteoarthritis (OA), and abnormal mechanical load is a key pathogenic factor of OA. However, how abnormal mechanical load affects chondrocyte epigenetics is unclear. Chondrocytes reportedly respond to mechanics through the extracellular matrix (ECM), which has a role in regulating epigenetics in various diseases, and mitochondria are potential mediators of communication between mechanics and epigenetics. Therefore, it is hypothesized that the matrix mechanics of cartilage regulates their epigenetics through mitochondria and leads to OA. The matrix stiffness of OA cartilage on the stress-concentrated side increases, mitochondrial damage of chondrocyte is severe, and the chondrocyte H3K27me3 is demethylated. Moreover, mitochondrial permeability transition pore (mPTP) opens to increase the translocation of plant homeodomain finger protein 8 (Phf8) into the nucleus to catalyze H3K27me3 demethylation. This provides a new perspective for us to understand the mechanism of OA based on mechanobiology.

The C5AR1/TNFSF13B axis alleviates osteoarthritis by activating the PI3K/Akt/GSK3β/Nrf2/HO-1 pathway to inhibit ferroptosis

Chondrocyte ferroptosis induces the occurrence of osteoarthritis (OA). As a key gene of OA, C5a receptor 1 (C5AR1) is related to ferroptosis. Here, we investigated whether C5AR1 interferes with chondrocyte ferroptosis during OA occurrence. C5AR1 was downregulated in PA-treated chondrocytes. Overexpression of C5AR1 increased the cell viability and decreased ferroptosis in chondrocytes. Moreover, Tumor necrosis factor superfamily member 13B (TNFSF13B) was downregulated in PA-treated chondrocytes, and knockdown of TNFSF13B eliminated the inhibitory effect of C5AR1 on ferroptosis in chondrocytes. More importantly, the PI3K/Akt/GSK3β/Nrf2/HO-1 pathway inhibitor LY294002 reversed the inhibition of C5AR1 or TNFSF13B on ferroptosis in chondrocytes. Finally, we found that C5AR1 alleviated joint tissue lesions and ferroptosis in rats and inhibited the progression of OA in the rat OA model constructed by anterior cruciate ligament transection (ACLT), which was reversed by interfering with TNFSF13B. This study shows that C5AR1 reduces the progression of OA by upregulating TNFSF13B to activate the PI3K/Akt/GSK3β/Nrf2/HO-1 pathway and thereby inhibiting chondrocyte sensitivity to ferroptosis, indicating that C5AR1 may be a potential therapeutic target for ferroptosis-related diseases.

Critical signaling molecules in the temporomandibular joint osteoarthritis under different magnitudes of mechanical stimulation

The mechanical stress environment in the temporomandibular joint (TMJ) is constantly changing due to daily mandibular movements. Therefore, TMJ tissues, such as condylar cartilage, the synovial membrane and discs, are influenced by different magnitudes of mechanical stimulation. Moderate mechanical stimulation is beneficial for maintaining homeostasis, whereas abnormal mechanical stimulation leads to degeneration and ultimately contributes to the development of temporomandibular joint osteoarthritis (TMJOA), which involves changes in critical signaling molecules. Under abnormal mechanical stimulation, compensatory molecules may prevent degenerative changes while decompensatory molecules aggravate. In this review, we summarize the critical signaling molecules that are stimulated by moderate or abnormal mechanical loading in TMJ tissues, mainly in condylar cartilage. Furthermore, we classify abnormal mechanical stimulation-induced molecules into compensatory or decompensatory molecules. Our aim is to understand the pathophysiological mechanism of TMJ dysfunction more deeply in the ever-changing mechanical environment, and then provide new ideas for discovering effective diagnostic and therapeutic targets in TMJOA.

Therapeutics of the future: Navigating the pitfalls of extracellular vesicles research from an osteoarthritis perspective

Extracellular vesicles have gained wide momentum as potential therapeutics for osteoarthritis, a highly prevalent chronic disease that still lacks an approved treatment. The membrane-bound vesicles are secreted by all cells carrying different cargos that can serve as both disease biomarkers and disease modifiers. Nonetheless, despite a significant peak in research regarding EVs as OA therapeutics, clinical implementation seems distant. In addition to scalability and standardization challenges, researchers often omit to focus on and consider the proper tropism of the vesicles, the practicality and relevance of their source, their low native therapeutic efficacy, and whether they address the disease as a whole. These considerations are necessary to better understand EVs in a clinical light and have been comprehensively discussed and ultimately summarized in this review into a conceptualized framework termed the nanodiamond concept. Future perspectives are also discussed, and alternatives are presented to address some of the challenges and concerns.

Exploring the Link Between Autophagy-Lysosomal Dysfunction and Early Heterotopic Ossification in Tendons

Heterotopic ossification (HO), the pathological formation of bone within soft tissues such as tendon and muscle, is a notable complication resulting from severe injury. While soft tissue injury is necessary for HO development, the specific molecular pathology responsible for trauma-induced HO remains a mystery. The previous study detected abnormal autophagy function in the early stages of tendon HO. Nevertheless, it remains to be determined whether autophagy governs the process of HO generation. Here, trauma-induced tendon HO model is used to investigate the relationship between autophagy and tendon calcification. In the early stages of tenotomy, it is observed that autophagic flux is significantly impaired and that blocking autophagic flux promoted the development of more rampant calcification. Moreover, Gt(ROSA)26sor transgenic mouse model experiments disclosed lysosomal acid dysfunction as chief reason behind impaired autophagic flux. Stimulating V-ATPase activity reinstated both lysosomal acid functioning and autophagic flux, thereby reversing tendon HO. This present study demonstrates that autophagy-lysosomal dysfunction triggers HO in the stages of tendon injury, with potential therapeutic targeting implications for HO.

Microarray analysis of signalling interactions between inflammation and angiogenesis in subchondral bone in temporomandibular joint osteoarthritis

Inflammation and angiogenesis, the major pathological changes of osteoarthritis (OA), are closely associated with joint pain; however, pertinent signalling interactions within subchondral bone of osteoarthritic joints and potential contribution to the peripheral origin of OA pain remain to be elucidated. Herein we developed a unilateral anterior crossbite mouse model with osteoarthritic changes in the temporomandibular joint. Microarray-based transcriptome analysis, besides quantitative real-time polymerase chain reaction, was performed to identify differentially expressed genes (DEGs). Overall, 182 DEGs (fold change ≥ 2, P < 0.05) were identified between the control and unilateral anterior crossbite groups: 168 were upregulated and 14 were downregulated. On subjecting significant DEGs to enrichment analyses, inflammation and angiogenesis were identified as the most affected. Inflammation-related DEGs were mainly enriched in T cell activation and differentiation and in the mammalian target of rapamycin/nuclear factor-κB/tumour necrosis factor signalling. Furthermore, angiogenesis-related DEGs were mainly enriched in the Gene Ontology terms angiogenesis regulation and vasculature development and in the KEGG pathways of phosphoinositide 3-kinase-protein kinase B/vascular endothelial growth factor/hypoxia-inducible factor 1 signalling. Protein-protein interaction analysis revealed a close interaction between inflammation- and angiogenesis-related DEGs, suggesting that phosphatidylinositol-4,5-bisphosphate 3-kinase catalytic subunit delta (Pi3kcd), cathelicidin antimicrobial peptide (Camp), C-X-C motif chemokine receptor 4 (Cxcr4), and MYB proto-oncogene transcription factor (Myb) play a central role in their interaction. To summarize, our findings reveal that in subchondral bone of osteoarthritic joints, signal interaction is interrelated between inflammation and angiogenesis and associated with the peripheral origin of OA pain; moreover, our data highlight potential targets for the inhibition of OA pain.

Proteomic characterization of extracellular vesicles in programmed cell death

Programmed cell death (PCD) is a fundamental biological process that plays a critical role in cell development, differentiation, and homeostasis. The secretion and uptake of extracellular vesicles (EVs) is one of the important regulatory mechanisms for PCD. EVs are natural membrane structures secreted by cells that contain a variety of proteins, lipids, nucleic acids, and other bioactive molecules. Due to their important roles in intercellular communication and disease progression, there is great interest in studying EVs and their cargo. Different protein components are sorted and packaged in EVs, allowing EVs to perform their functions. The study of EV proteomics helps us understand the role of PCD in the development of diseases. Meanwhile, proteomics is a powerful tool for studying the composition and function of EVs, which assists in the identification, quantification, and profiling of protein components of EVs, and provides insight into the molecular mechanisms involved in PCD and related diseases. In this review, we summarize the characteristics of EV proteomics in different types of PCD, compare different proteomic profiling strategies for EVs, and discuss the impact of EV proteomics on cell function and regulation during PCD, to understand its role in the pathogenesis of related diseases.

Calcified apoptotic vesicles from PROCR+ fibroblasts initiate heterotopic ossification

Heterotopic ossification (HO) comprises the abnormal formation of ectopic bone in extraskeletal soft tissue. The factors that initiate HO remain elusive. Herein, we found that calcified apoptotic vesicles (apoVs) led to increased calcification and stiffness of tendon extracellular matrix (ECM), which initiated M2 macrophage polarization and HO progression. Specifically, single-cell transcriptome analyses of different stages of HO revealed that calcified apoVs were primarily secreted by a PROCR+ fibroblast population. In addition, calcified apoVs enriched calcium by annexin channels, absorbed to collagen I via electrostatic interaction, and aggregated to produce calcifying nodules in the ECM, leading to tendon calcification and stiffening. More importantly, apoV-releasing inhibition or macrophage deletion both successfully reversed HO development. Thus, we are the first to identify calcified apoVs from PROCR+ fibroblasts as the initiating factor of HO, and might serve as the therapeutic target for inhibiting pathological calcification.

Lysosomal destabilization: A missing link between pathological calcification and osteoarthritis

Calcification of cartilage by hydroxyapatite is a hallmark of osteoarthritis and its deposition strongly correlates with the severity of osteoarthritis. However, no effective strategies are available to date on the prevention of hydroxyapatite deposition within the osteoarthritic cartilage and its role in the pathogenesis of this degenerative condition is still controversial. Therefore, the present work aims at uncovering the pathogenic mechanism of intra-cartilaginous hydroxyapatite in osteoarthritis and developing feasible strategies to counter its detrimental effects. With the use of in vitro and in vivo models of osteoarthritis, hydroxyapatite crystallites deposited in the cartilage are found to be phagocytized by resident chondrocytes and processed by the lysosomes of those cells. This results in lysosomal membrane permeabilization (LMP) and release of cathepsin B (CTSB) into the cytosol. The cytosolic CTSB, in turn, activates NOD-like receptor protein-3 (NLRP3) inflammasomes and subsequently instigates chondrocyte pyroptosis. Inhibition of LMP and CTSB in vivo are effective in managing the progression of osteoarthritis. The present work provides a conceptual therapeutic solution for the prevention of osteoarthritis via alleviation of lysosomal destabilization.

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.

The Role of Extracellular Vesicles in the Pathogenesis and Treatment of Rheumatoid Arthritis and Osteoarthritis

Cells can communicate with each other through extracellular vesicles (EVs), which are membrane-bound structures that transport proteins, lipids and nucleic acids. These structures have been found to mediate cellular differentiation and proliferation apoptosis, as well as inflammatory responses and senescence, among others. The cargo of these vesicles may include immunomodulatory molecules, which can then contribute to the pathogenesis of various diseases. By contrast, EVs secreted by mesenchymal stem cells (MSCs) have shown important immunosuppressive and regenerative properties. Moreover, EVs can be modified and used as drug carriers to precisely deliver therapeutic agents. In this review, we aim to summarize the current evidence on the roles of EVs in the progression and treatment of rheumatoid arthritis (RA) and osteoarthritis (OA), which are important and prevalent joint diseases with a significant global burden.

The role of exosomes and their enhancement strategies in the treatment of osteoarthritis

With the increasingly prominent problem of population aging, osteoarthritis (OA), which is closely related to aging, has become a serious illness affecting the lives and health of elderly individuals. However, effective treatments are still lacking. OA is typically considered a low-grade inflammatory state. The inflammatory infiltration of macrophages, neutrophils, T cells, and other cells is common in diseased joints. These cells create the inflammatory environment of OA and are involved in the onset and progression of the disease. Exosomes, a type of complex vesicle containing abundant RNA molecules and proteins, play a crucial role in the physiological and pathological processes of an organism. In comparison to other therapeutic methods such as stem cells, exosomes have distinct advantages of precise targeting and low immunogenicity. Moreover, research and techniques related to exosomes are more mature, indicating a promising future in disease treatment. Many studies have shown that the impact of exosomes on the inflammatory microenvironment directly or indirectly leads to the occurrence of various diseases. Furthermore, exosomes can be helpful in the management of illnesses. This article provides a comprehensive review and update on the research of exosomes, a type of extracellular vesicle, in the treatment of OA by modulating the inflammatory microenvironment. It also combines innovative studies on the modification of exosomes. In general, the application of exosomes in the treatment of OA has been validated, and the introduction of modified exosome technology holds potential for enhancing its therapeutic efficacy.

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.

Intercellular mitochondrial component transfer triggers ischemic cardiac fibrosis

Myocardial fibrosis is the villain of sudden cardiac death. Myocardial ischemia/reperfusion (MI/R) injury induces cardiomyocyte damage or even death, which in turn stimulates fibroblast activation and fibrosis, but the intercellular communication mechanism remains unknown. Recent studies have shown that small extracellular vesicles (sEVs) significantly contribute to intercellular communication. Whether and how sEV might mediate post-MI/R cardiomyocyte/fibroblasts communication remain unknown. Here, in vivo and in vitro MI/R models were established. We demonstrate that sEVs derived from cardiomyocyte (Myo-sEVs) carry mitochondrial components, which enter fibroblasts to initiate myocardial fibrosis. Based on bioinformatics screening and experimental verification, the activating molecule in Beclin1-regulated autophagy protein 1 (autophagy/beclin-1 regulator 1, Ambra1) was found to be a critical component of these sEV and might be a new marker for Myo-sEVs. Interestingly, release of Ambra1+-Myo-sEVs was caused by secretory rather than canonical autophagy after MI/R injury and thereby escaped degradation. In ischemic and peripheral areas, Ambra1+-Myo-sEVs were internalized by fibroblasts, and the delivered mtDNA components to activate the fibroblast cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway to promote fibroblast activation and proliferation. In addition, our data show that Ambra1 is expressed on the EV surface and cardiac-specific Ambra1 down regulation inhibits the Ambra1+-Myo-sEVs release and fibroblast uptake, effectively inhibiting ischemic myocardial fibrosis. This finding newly provides the evidence that myocardial secretory autophagy plays a role in intercellular communication during cardiac fibrosis. Ambra1 is a newly characterized molecule with bioactivity and might be a marker for Myo-sEVs, providing new therapeutic targets for cardiac remodeling.

Identification of basement membrane-related biomarkers associated with the diagnosis of osteoarthritis based on machine learning

BACKGROUND

Osteoarthritis is a very common clinical disease in middle-aged and elderly individuals, and with the advent of ageing, the incidence of this disease is gradually increasing. There are few studies on the role of basement membrane (BM)-related genes in OA.

METHOD

We used bioinformatics and machine learning methods to identify important genes related to BMs in OA patients and performed immune infiltration analysis, lncRNA‒miRNA-mRNA network prediction, ROC analysis, and qRT‒PCR.

RESULT

Based on the results of machine learning, we determined that LAMA2 and NID2 were the key diagnostic genes of OA, which were confirmed by ROC and qRT‒PCR analyses. Immune analysis showed that LAMA2 and NID2 were closely related to resting memory CD4 T cells, mast cells and plasma cells. Two lncRNAs, XIST and TTTY15, were simultaneously identified, and lncRNA‒miRNA‒mRNA network prediction was performed.

CONCLUSION

LAMA2 and NID2 are important potential targets for the diagnosis and treatment of OA.

Stage-specific and location-specific cartilage calcification in osteoarthritis development

OBJECTIVES

This study investigated the stage-specific and location-specific deposition and characteristics of minerals in human osteoarthritis (OA) cartilages via multiple nano-analytical technologies.

METHODS

Normal and OA cartilages were serially sectioned for micro-CT, scanning electron microscopy with energy dispersive X-ray spectroscopy, micro-Raman spectroscopy, focused ion beam scanning electron microscopy, high-resolution electron energy loss spectrometry with transmission electron microscopy, nanoindentation and atomic force microscopy to analyse the structural, compositional and mechanical properties of cartilage in OA progression.

RESULTS

We found that OA progressed by both top-down calcification at the joint surface and bottom-up calcification at the osteochondral interface. The top-down calcification process started with spherical mineral particle formation in the joint surface during early-stage OA (OA-E), followed by fibre formation and densely packed material transformation deep into the cartilage during advanced-stage OA (OA-A). The bottom-up calcification in OA-E started when an excessive layer of calcified tissue formed above the original calcified cartilage, exhibiting a calcified sandwich structure. Over time, the original and upper layers of calcified cartilage fused, which thickened the calcified cartilage region and disrupted the cartilage structure. During OA-E, the calcified cartilage was hypermineralised, containing stiffer carbonated hydroxyapatite (HAp). During OA-A, it was hypomineralised and contained softer HAp. This discrepancy may be attributed to matrix vesicle nucleation during OA-E and carbonate cores during OA-A.

CONCLUSIONS

This work refines our current understanding of the mechanism underlying OA progression and provides the foothold for potential therapeutic targeting strategies once the location-specific cartilage calcification features in OA are established.

Breakthrough of extracellular vesicles in pathogenesis, diagnosis and treatment of osteoarthritis

Osteoarthritis (OA) is a highly prevalent whole-joint disease that causes disability and pain and affects a patient's quality of life. However, currently, there is a lack of effective early diagnosis and treatment. Although stem cells can promote cartilage repair and treat OA, problems such as immune rejection and tumorigenicity persist. Extracellular vesicles (EVs) can transmit genetic information from donor cells and mediate intercellular communication, which is considered a functional paracrine factor of stem cells. Increasing evidences suggest that EVs may play an essential and complex role in the pathogenesis, diagnosis, and treatment of OA. Here, we introduced the role of EVs in OA progression by influencing inflammation, metabolism, and aging. Next, we discussed EVs from the blood, synovial fluid, and joint-related cells for diagnosis. Moreover, we outlined the potential of modified and unmodified EVs and their combination with biomaterials for OA therapy. Finally, we discuss the deficiencies and put forward the prospects and challenges related to the application of EVs in the field of OA.