Pathological calcification in osteoarthritis: an outcome or a disease initiator?

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.

Unraveling the Mechanisms of Hypertrophy-Induced Matrix Mineralization and Modifications in Articular Chondrocytes

Chondrocyte hypertrophic differentiation is a main event leading to articular cartilage degradation in osteoarthritis. It is associated with matrix remodeling and mineralization, the dynamics of which is not well characterized during chondrocyte hypertrophic differentiation in articular cartilage. Based on an in vitro model of progressive differentiation of immature murine articular chondrocytes (iMACs) into prehypertrophic (Prehyp) and hypertrophic (Hyp) chondrocytes, we performed kinetics of chondrocyte differentiation from Prehyp to Hyp to follow matrix mineralization and remodeling by immunofluorescence, biochemical, molecular, and physicochemical approaches, including atomic force microscopy, scanning electron microscopy associated with energy-dispersive X-ray spectroscopy (SEM-EDS), attenuated total reflection infrared analyses, and X-ray diffraction. Chondrocyte apoptosis was determined by TUNEL assay. The results show the formation of a mineral phase 7 days after Hyp induction, which spreads within the matrices to form poorly crystalline carbonate-substituted hydroxyapatite after 14 days, then the proportions of crystalline relative to amorphous content increases over time. Hyp differentiation also induced a matrix turnover that occurs over the first 7 days, characterized by a decrease in type II collagen and aggrecan and the concomitant appearance of type X collagen. This is accompanied by an increase in the enzymatic activity of MMP-13, the main collagenase in cartilage. The number of apoptotic chondrocytes slightly increased with Hyp differentiation and SEM-EDS analyses detected phosphorus-rich structures that could correspond to apoptotic bodies. Our findings highlight the mechanisms of matrix remodeling events leading to the mineralization of articular cartilage that may occur in osteoarthritis.

Prevalence and classification of meniscal calcifications in the human knee

OBJECTIVE

To investigate the occurrence of meniscal calcifications in individuals with and without knee osteoarthritis (OA). Additionally, we aim to identify the specific types of calcifications: basic calcium phosphate (BCP) and calcium pyrophosphate dihydrate (CPP).

METHOD

We analyzed 82 meniscal posterior horn samples (medial and lateral) collected from 41 human subjects. Among them, 20 individuals underwent total knee replacement due to medial compartment OA, while 21 deceased donors had no known knee OA. The assessment of meniscal calcifications and Pauli's histopathological scoring was conducted using histological sections. Furthermore, adjacent sections underwent measurement using Raman spectroscopy to characterize BCP and CPP calcifications based on their distinct spectral fingerprints.

RESULTS

All OA individuals exhibited calcifications in at least one meniscus, compared to 9.5% (95%CI 1%, 30%) of donors. Among 35 OA menisci with calcifications, 28(80%) had BCP, 5(14%) had CPP and 2(6%) had both types. In 4 donor menisci, 3(75%) had CPP while 1(25%) had both types. We estimated the association between Pauli score and presence of BCP in OA individuals, yielding an odds ratio of 2.1 (95%CI 0.8, 5.3) per 1 Pauli score. The association between Pauli score and presence of CPP (in whole study sample) seemed weaker, with odds ratio of 1.3 (95%CI 1.1, 1.7).

CONCLUSION

The presence of BCP was predominant in menisci of OA individuals, whereas CPP exhibited similar prevalence in individuals with and without OA. The formation of BCP crystals in menisci may represent an important and specific characteristic of OA disease process that warrants further attention.

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.

Unveiling a foreign body masquerading as periarticular calcification: a case report

INTRODUCTION

Evaluating isolated extremity discomfort can be challenging when initial imaging and exams provide limited information. Though subtle patient history hints often underlie occult pathologies, benign symptoms are frequently miscategorized as idiopathic.

CASE PRESENTATION

We present a case of retained glass obscuring as acute calcific periarthritis on imaging. A 48-year-old White male with vague fifth metacarpophalangeal joint pain had unrevealing exams, but radiographs showed periarticular calcification concerning inflammation. Surgical exploration unexpectedly revealed an encapsulated glass fragment eroding bone. Further history uncovered a forgotten glass laceration decade prior. The foreign body was removed, resolving symptoms.

DISCUSSION

This case reveals two imperative diagnostic principles for nonspecific extremity pain: (1) advanced imaging lacks specificity to differentiate inflammatory arthropathies from alternate intra-articular processes such as foreign bodies, and (2) obscure patient history questions unearth causal subtleties that direct accurate diagnosis. Though initial scans suggested acute calcific periarthritis, exhaustive revisiting of the patient's subtle decade-old glass cut proved pivotal in illuminating the underlying driver of symptoms.

CONCLUSION

Our findings underscore the critical limitations of imaging and the vital role that meticulous history-taking plays in clarifying ambiguous chronic limb presentations. They spotlight the imperative of probing even distant trauma when symptoms seem disconnected from causative events. This case reinforces the comprehensive evaluation of all subtle patient clues as key in illuminating elusive extremity pain etiologies.

Koumine inhibits IL-1β-induced chondrocyte inflammation and ameliorates extracellular matrix degradation in osteoarthritic cartilage through activation of PINK1/Parkin-mediated mitochondrial autophagy

Osteoarthritis (OA) is a degenerative joint disease, Increasingly, mitochondrial autophagy has been found to play an important regulatory role in the prevention and treatment of osteoarthritis. Koumine is a bioactive alkaloid extracted from the plant Gelsemium elegans. In previous research, Koumine was found to have potential in improving the progression of OA in rats. However, the specific mechanism of its action has not been fully explained. Therefore, the aim of this study was to investigate whether Koumine can alleviate OA in rats by influencing mitochondrial autophagy. In the in vitro study, rat chondrocytes (RCCS-1) were induced with IL-1β (10 ng/mL) to induce inflammation, and Koumine (50 μg/mL) was co-treated. In the in vivo study, a rat OA model was established by intra-articular injection of 2% papain, and Koumine was administered orally (1 mg/kg, once daily for two weeks). It was found that Koumine effectively reduced cartilage erosion in rats with osteoarthritis. Additionally, it decreased the levels of inflammatory factors such as IL-1β, IL-6, and extracellular matrix (ECM) components MMP13 and ADAMTS5 in chondrocytes and articular cartilage tissue, while increasing the level of Collagen II.Koumine inhibited the production of reactive oxygen species (ROS) in cartilage tissue and increased the number of autophagosomes in chondrocytes and articular cartilage tissue. Additionally, it upregulated the expression of mitochondrial autophagy proteins LC3Ⅱ/Ⅰ, PINK1, Parkin, and Drp1. The administration of Mdivi-1 (50 μM) reversed the enhanced effect of Koumine on mitochondrial autophagy, as well as its anti-inflammatory and anti-ECM degradation effects in rats with OA. These findings suggest that Koumine can alleviate chondrocyte inflammation and improve the progression of OA in rats by activating PINK1/Parkin-mediated mitochondrial autophagy.

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.

Advanced glycation end products promote meniscal calcification by activating the mTOR-ATF4 positive feedback loop

The meniscus is vital for maintaining knee homeostasis and function. Meniscal calcification is one of the earliest radiological indicators of knee osteoarthritis (KOA), and meniscal calcification is associated with alterations in biomechanical properties. Meniscal calcification originates from a biochemical process similar to vascular calcification. Advanced glycation end products (AGEs) and their receptors (RAGEs) reportedly play critical roles in vascular calcification. Herein, we investigated whether targeting AGE-RAGE is a potential treatment for meniscal calcification. In our study, we demonstrated that AGE-RAGE promotes the osteogenesis of meniscal cells and exacerbates meniscal calcification. Mechanistically, AGE-RAGE activates mTOR and simultaneously promotes ATF4 accumulation, thereby facilitating the ATF4-mTOR positive feedback loop that enhances the osteogenic capacity of meniscal cells. In this regard, mTOR inhibits ATF4 degradation by reducing its ubiquitination, while ATF4 activates mTOR by increasing arginine uptake. Our findings substantiate the unique role of AGE-RAGE in the meniscus and reveal the role of the ATF4-mTOR positive feedback loop during the osteogenesis of meniscal cells; these results provide potential therapeutic targets for KOA.

Klf10 is involved in extracellular matrix calcification of chondrocytes alleviating chondrocyte senescence

Osteoarthritis (OA) is a chronic degenerative disease resulting joint disability and pain. Accumulating evidences suggest that chondrocyte extracellular matrix calcification plays an important role in the development of OA. Here, we showed that Krüppel-like factor 10 (Klf10) was involved in the regulation of chondrocyte extracellular matrix calcification by regulating the expression of Frizzled9. Knockdown of Klf10 attenuated TBHP induced calcification and reduced calcium content in chondrocytes. Restoring extracellular matrix calcification of chondrocytes could aggravate chondrocyte senescence. Destabilization of a medial meniscus (DMM) mouse model of OA, in vivo experiments revealed that knockdown Klf10 improved the calcification of articular cartilage and ameliorated articular cartilage degeneration. These findings suggested that knockdown Klf10 inhibited extracellular matrix calcification-related changes in chondrocytes and alleviated chondrocyte senescence.

Searching for Essential Genes and Targeted Drugs Common to Breast Cancer and Osteoarthritis

BACKGROUND

It is documented that osteoarthritis can promote the progression of breast cancer (BC).

OBJECTIVE

This study aims to search for the essential genes associated with breast cancer (BC) and osteoarthritis (OA), explore the relationship between epithelial-mesenchymal transition (EMT)- related genes and the two diseases, and identify the candidate drugs.

METHODS

The genes related to both BC and OA were determined by text mining. Protein-protein Interaction (PPI) analysis was carried out, and as a result, the exported genes were found to be related to EMT. PPI and the correlation of mRNA of these genes were also analyzed. Different kinds of enrichment analyses were performed on these genes. A prognostic analysis was performed on these genes for examining their expression levels at different pathological stages, in different tissues, and in different immune cells. Drug-gene interaction database was employed for potential drug discovery.

RESULTS

A total number of 1422 genes were identified as common to BC and OA and 58 genes were found to be related to EMT. We found that HDAC2 and TGFBR1 were significantly poor in overall survival. High expression of HDAC2 plays a vital role in the increase of pathological stages. Four immune cells might play a role in this process. Fifty-seven drugs were identified that could potentially have therapeutic effects.

CONCLUSION

EMT may be one of the mechanisms by which OA affects BC. Using the drugs can have potential therapeutic effects, which may benefit patients with both diseases and broaden the indications for drug use.

MMP13 promotes the osteogenic potential of BMP9 by enhancing Wnt/β-catenin signaling via HIF-1α upregulation in mouse embryonic fibroblasts

Bone morphogenetic protein 9 (BMP9) has been validated as one of the most potent osteoinduction factors, but its underlying mechanism remains unclear. As a member of the matrix metalloproteinase (MMP) family, MMP13 may be involved in regulating the lineage-specific differentiation of mouse embryonic fibroblasts (MEFs). The goal of this study was to determine whether MMP13 regulates the osteoinduction potential of BMP9 in MEFs, which are multipotent progenitor cells widely used for stem cell biology research. In vitro and in vivo experiments showed that BMP9-induced osteogenic markers and/or bone were enhanced by exogenous MMP13 in MEFs, but were reduced by MMP13 knockdown or inhibition. The expression of hypoxia inducible factor 1 alpha (HIF-1α) was induced by BMP9, which was enhanced by MMP13. The protein expression of β-catenin and phosphorylation level of glycogen synthase kinase-3 beta (GSK-3β) were increased by BMP9 in MEFs, as was the translocation of β-catenin from the cytoplasm to the nucleus; all these effects of BMP9 were enhanced by MMP13. Furthermore, the MMP13 effects of increasing BMP9-induced β-catenin protein expression and GSK-3β phosphorylation level were partially reversed by HIF-1α knockdown. These results suggest that MMP13 can enhance the osteoinduction potential of BMP9, which may be mediated, at least in part, through the HIF-1α/β-catenin axis. Our findings demonstrate a novel role of MMP13 in the lineage decision of progenitor cells and provide a promising strategy to speed up bone regeneration.

Isoorientin ameliorates H2O2-induced apoptosis and oxidative stress in chondrocytes by regulating MAPK and PI3K/Akt pathways

Osteoarthritis (OA) is a chronic and complicated degenerative disease for which there is currently no effective treatment. Isoorientin (ISO) is a natural plant extract that has antioxidant activity and could be used to treat OA. However, due to a lack of research, it has not been widely used. In this study, we investigated the protective effects and molecular mechanisms of ISO on H₂O₂-induced chondrocytes, a widely used cell model for OA. Based on RNA-seq and bioinformatics, we discovered that ISO significantly increased the activity of chondrocytes induced by H₂O₂, which was associated with apoptosis and oxidative stress. Furthermore, the combination of ISO and H₂O₂ significantly reduced apoptosis and restored mitochondrial membrane potential (MMP), which may be achieved by inhibiting apoptosis and mitogen-activated protein kinase (MAPK) signaling pathways. Moreover, ISO increased superoxide dismutase (SOD), heme oxygenase 1 (HO-1) and quinone oxidoreductase 1 (NQO-1) and reduced malondialdehyde (MDA) levels. Finally, ISO inhibited H₂O₂-induced intracellular reactive oxygen species (ROS) in chondrocytes by activating the nuclear factor erythroid 2-related factor 2 (Nrf2) and phosphatidylinositol 3 kinase/protein kinase B (PI3K/Akt) signaling pathways. This study establishes a theoretical framework for ISO's ability to inhibit OA in vitro models.

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.

Temporomandibular Joint Osteoarthritis: Pathogenic Mechanisms Involving the Cartilage and Subchondral Bone, and Potential Therapeutic Strategies for Joint Regeneration

The temporomandibular joint (TMJ) is a specialized synovial joint that is crucial for the movement and function of the jaw. TMJ osteoarthritis (TMJ OA) is the result of disc dislocation, trauma, functional overburden, and developmental anomalies. TMJ OA affects all joint structures, including the articular cartilage, synovium, subchondral bone, capsule, ligaments, periarticular muscles, and sensory nerves that innervate the tissues. The present review aimed to illustrate the main pathomechanisms involving cartilage and bone changes in TMJ OA and some therapeutic options that have shown potential restorative properties regarding these joint structures in vivo. Chondrocyte loss, extracellular matrix (ECM) degradation, and subchondral bone remodeling are important factors in TMJ OA. The subchondral bone actively participates in TMJ OA through an abnormal bone remodeling initially characterized by a loss of bone mass, followed by reparative mechanisms that lead to stiffness and thickening of the condylar osteochondral interface. In recent years, such therapies as intraarticular platelet-rich plasma (PRP), hyaluronic acid (HA), and mesenchymal stem cell-based treatment (MSCs) have shown promising results with respect to the regeneration of joint structures or the protection against further damage in TMJ OA. Nevertheless, PRP and MSCs are more frequently associated with cartilage and/or bone repair than HA. According to recent findings, the latter could enhance the restorative potential of other therapies (PRP, MSCs) when used in combination, rather than repair TMJ structures by itself. TMJ OA is a complex disease in which degenerative changes in the cartilage and bone develop through intricate mechanisms. The regenerative potential of such therapies as PRP, MSCs, and HA regarding the cartilage and subchondral bone (alone or in various combinations) in TMJ OA remains a matter of further research, with studies sometimes obtaining discrepant results.

Bibliometric and visualization analysis of macrophages associated with osteoarthritis from 1991 to 2021

Background

Macrophages significantly contributes to symptomology and structural progression of osteoarthritis (OA) and raise increasing attention in the relative research field. Recent studies have shown that tremendous progress has been made in the research of macrophages associated with osteoarthritis. However, a comprehensive bibliometric analysis is lacking in this research field. This study aimed to introduce the research status as well as hotspots and explore the field of macrophages research in OA from a bibliometric perspective.

Methods

This study collected 1481 records of macrophages associated with osteoarthritis from 1991 to 2021 in the web of science core collection (WoSCC) database. CiteSpace, VOSviewer, and R package “bibliometrix” software were used to analyze regions, institutions, journals, authors, and keywords to predict the latest trends in macrophages associated with osteoarthritis research.

Results

The number of publications related to macrophages associated with osteoarthritis is increasing annually. China and the USA, contributing more than 44% of publications, were the main drivers for research in this field. League of European Research Universities was the most active institution and contributed the most publications. Arthritis and Rheumatism is the most popular journal in this field with the largest publications, while Osteoarthritis and Cartilage is the most co-cited journal. Koch AE was the most prolific writer, while Bondeson J was the most commonly co-cited author. “Rheumatology”, “Orthopedics”, and “Immunology” were the most widely well-represented research areas of OA associated macrophages. “Rheumatoid arthritis research”, “clinical symptoms”, “regeneration research”, “mechanism research”, “pathological features”, and “surgery research” are the primary keywords clusters in this field.

Conclusion

This is the first bibliometric study comprehensively mapped out the knowledge structure and development trends in the research field of macrophages associated with osteoarthritis in recent 30 years. The results comprehensively summarize and identify the research frontiers which will provide a reference for scholars studying macrophages associated with osteoarthritis.

Relationship Amongst Vitamin K Status, Vitamin K Antagonist Use and Osteoarthritis: A Review

Vitamin K is essential for the carboxylation of the vitamin K-dependent proteins that are responsible for the suppression of matrix calcification. The use of vitamin K antagonists (VKAs) in patients with cardiovascular diseases could affect protein carboxylation and lead to the development of osteoarthritis (OA). This review aims to summarise the current evidence for the relationship between VKAs and OA. The literature search revealed that in observation studies, good vitamin K status, as reflected by the circulating level or protein carboxylation status of vitamin K, is associated positively with improved joint structural and functional indices and negatively associated with OA incidence. By contrast, in limited retrospective and prospective studies, the use of VKAs is associated positively with OA occurrence and knee/hip replacement. Pharmacological interactions between VKAs and various OA therapeutic agents exist and require careful monitoring and dosing. In conclusion, further epidemiological studies are warranted to verify the relationship between VKA use and OA to strengthen the evidence. Given that VKA use exerts potentially negative effects on joint health, intervention is required to protect the quality of life and mobility of patients.

Autophagic LC3+ calcified extracellular vesicles initiate cartilage calcification in osteoarthritis

Pathological cartilage calcification plays an important role in osteoarthritis progression but in which the origin of calcified extracellular vesicles (EVs) and their effects remain unknown. Here, we demonstrate that pathological cartilage calcification occurs in the early stage of the osteoarthritis in which the calcified EVs are closely involved. Autophagosomes carrying the minerals are released in EVs, and calcification is induced by those autophagy-regulated calcified EVs. Autophagy-derived microtubule-associated proteins 1A/1B light chain 3B (LC3)-positive EVs are the major population of calcified EVs that initiate pathological calcification. Release of LC3-positive calcified EVs is caused by blockage of the autophagy flux resulted from histone deacetylase 6 (HDAC6)-mediated microtubule destabilization. Inhibition of HDAC6 activity blocks the release of the LC3-positive calcified EVs by chondrocytes and effectively reverses the pathological calcification and degradation of cartilage. The present work discovers that calcified EVs derived from autophagosomes initiate pathological cartilage calcification in osteoarthritis, with potential therapeutic targeting implication.

MiR-20a-5p facilitates cartilage repair in osteoarthritis via suppressing mitogen-activated protein kinase kinase kinase 2

Bone marrow mesenchymal stem cell (BMSC) chondrogenic differentiation contributes to the treatment of osteoarthritis (OA). Numerous studies have indicated that microRNAs (miRNAs) regulate the pathogenesis and development of multiple disorders, including OA. Nevertheless, the role of miR-20a-5p in OA remains obscure. Forty male C57BL/6 mice were divided into four groups and were surgically induced OA or underwent sham surgery in the presence or absence of miR-20a-5p. Flow cytometry was implemented to detect surface markers of BMSCs. Reverse transcription quantitative polymerase chain reaction revealed the upregulation of miR-20a-5p during BMSC chondrogenic differentiation. Western blotting displayed that miR-20a-5p inhibition decreased protein levels of cartilage matrix markers but enhanced those of catabolic and hypertrophic chondrocyte markers in BMSCs. Alcian blue staining, hematoxylin‑eosin staining and micro-CT revealed that miR-20a-5p inhibition restrained chondrogenic differentiation and miR-20a-5p overexpression promoted the repair of damaged cartilage and subchondral bone, respectively. Luciferase reporter assay identified that mitogen activated protein kinase kinase kinase 2 (Map3k2) was a target of miR-20a-5p in BMSCs. Moreover, the expression of miR-20a-5p and Map3k2 was negatively correlated in murine cartilage tissues. Knocking down Map3k2 could rescue the suppressive influence of miR-20a-5p inhibition on chondrogenic differentiation of BMSCs. In conclusion, miR-20a-5p facilitates BMSC chondrogenic differentiation and contributes to cartilage repair in OA by suppressing Map3k2.

Effects of vitamin D with or without calcium on pathological ossification: A retrospective clinical study

Vitamin D protects against the development and severity of several rheumatic diseases. However, the effect of vitamin D on the pathological ossification associated with rheumatic diseases remains unknown. The present retrospective study analyzed the clinical outcomes of vitamin D without calcium compared with vitamin D with calcium on pathological ossification in joints and ligaments. Data were collected from patients who were diagnosed with osteoarthritis, rheumatoid arthritis or spondylarthritis, and the presence of pathological ossification in joints or ligaments was confirmed by X-ray, computed tomography or magnetic resonance imaging examination. A total of 2,965 patients aged 18-75 years old were included, among who, 1,725 were included in the vitamin D alone group and 1,240 in the vitamin D with calcium group. Vitamin D was administered intramuscularly (300,000 IU) once every 7-10 days, 4-6 times in total. Patients who ingested an oral calcium supplement (1,000 mg/day; ≥5 days/week) were considered the vitamin D with calcium group. The clinical outcome was evaluated based on the imaging changes of pathological ossification, which were classified as alleviation, aggravation and unchanged. The bone mineral density (BMD) was determined, and the calcium concentration in the serum and urine was measured. The results revealed that vitamin D alone alleviated pathological ossification, while vitamin D combined with calcium aggravated pathological ossification in the majority of patients (P<0.0001) independent of disease type and patient age. BMD measurements demonstrated a decreasing trend in the vitamin D alone group, whereas they exhibited an increasing trend in the vitamin D combined with calcium group. The urine calcium concentration increased after vitamin D treatment alone. Therefore, it was concluded that vitamin D exerted both pro-resorptive and anti-resorptive actions on pathological ossification. The bidirectional action of vitamin D on bone metabolism may depend on exogenous calcium supplementation.

Amorphous-mediated crystallization of calcium pyrophosphate tetrahydrate: the role of alkaline earth metal ions

Although calcium pyrophosphates are commonly involved in crystal arthropathies, their formation mechanisms remain largely underexplored. Here, we investigated the crystallization pathway of calcium pyrophosphate tetrahydrate in the absence and presence...

Unraveling an Innate Mechanism of Pathological Mineralization-Regulated Inflammation by a Nanobiomimetic System

Pathological mineralization (PTM) often occurs under inflammation and affects the prognosis of diseases, such as atherosclerosis and cancers. However, how the PTM impacts inflammation has not been well explored. Herein, poly lactic-co-glycolic acid (PLGA)/gelatin/hydroxyapatite (HA) electrospun nanofibers are rationally designed as an ideal PTM microenvironment biomimetic system for unraveling the role of PTM on inflammation. The results demonstrate that the inflammatory response decreases continuously during the process of mineralization. When mature macromineralization forms, the inflammation almost completely disappears. Mechanistically, the PTM formation is mediated by matrix proteins, local high calcium, and cell debris (nuclei), or actively regulated by the lysosomal/plasma membrane components secreted by macrophages. These inflammatory inducible factors (calcium, cell debris, etc.) can be "buried" through PTM process, resulting in reduced immune responses. Overall, the present study demonstrates that PTM is an innate mechanism of inflammation subsidence, providing valuable insight into understanding the action of mineralization on inflammation.

The Gasotransmitter Hydrogen Sulfide (H2S) Prevents Pathologic Calcification (PC) in Cartilage

Pathologic calcification (PC) is a painful and disabling condition whereby calcium-containing crystals deposit in tissues that do not physiologically calcify: cartilage, tendons, muscle, vessels and skin. In cartilage, compression and inflammation triggered by PC leads to cartilage degradation typical of osteoarthritis (OA). The PC process is poorly understood and treatments able to target the underlying mechanisms of the disease are lacking. Here we show a crucial role of the gasotransmitter hydrogen sulfide (H₂S) and, in particular, of the H₂S-producing enzyme cystathionine γ-lyase (CSE), in regulating PC in cartilage. Cse deficiency (Cse KO mice) exacerbated calcification in both surgically-induced (menisectomy) and spontaneous (aging) murine models of cartilage PC, and augmented PC was closely associated with cartilage degradation (OA). On the contrary, Cse overexpression (Cse tg mice) protected from these features. In vitro, Cse KO chondrocytes showed increased calcification, potentially via enhanced alkaline phosphatase (Alpl) expression and activity and increased IL-6 production. The opposite results were obtained in Cse tg chondrocytes. In cartilage samples from patients with OA, CSE expression inversely correlated with the degree of tissue calcification and disease severity. Increased cartilage degradation in murine and human tissues lacking or expressing low CSE levels may be accounted for by dysregulated catabolism. We found higher levels of matrix-degrading metalloproteases Mmp-3 and -13 in Cse KO chondrocytes, whereas the opposite results were obtained in Cse tg cells. Finally, by high-throughput screening, we identified a novel small molecule CSE positive allosteric modulator (PAM), and demonstrated that it was able to increase cellular H₂S production, and decrease murine and human chondrocyte calcification and IL-6 secretion. Together, these data implicate impaired CSE-dependent H₂S production by chondrocytes in the etiology of cartilage PC and worsening of secondary outcomes (OA). In this context, enhancing CSE expression and/or activity in chondrocytes could represent a potential strategy to inhibit PC.

Stimuli-Sensitive Nanotherapies for the Treatment of Osteoarthritis

Osteoarthritis (OA) is a common chronic inflammatory disease in the joints. It is one of the leading causes of disability with increasing morbidity, which has become one of the serious clinical issues. Current treatments would only provide temporary relief due to the lack of early diagnosis and effective therapy, and thus the replacement of joints may be needed when the OA deteriorates. Although the intra-articular injection and oral administration of drugs are helpful for OA treatment, they are suffering from systemic toxicity, short retention time in joint, and insufficient bioavailability. Nanomedicine is potential to improve the drug delivery efficiency and targeting ability. In this focused progress review, the particle-based drug loading systems that can achieve targeted and triggered release are summarized. Stimuli-responsive nanocarriers that are sensitive to endogenous microenvironmental signals such as reactive oxygen species, enzymes, pH, and temperature, as well as external stimuli such as light for OA therapy are introduced in this review. Furthermore, the nanocarriers associated with targeted therapy and imaging for OA treatment are summarized. The potential applications of nanotherapies for OA treatment are finally discussed.

Pathological mechanism of chondrocytes and the surrounding environment during osteoarthritis of temporomandibular joint

Temporomandibular joint (TMJ) osteoarthritis is a common chronic degenerative disease of the TMJ. In order to explore its aetiology and pathological mechanism, many animal models and cell models have been constructed to simulate the pathological process of TMJ osteoarthritis. The main pathological features of TMJ osteoarthritis include chondrocyte death, extracellular matrix (ECM) degradation and subchondral bone remodelling. Chondrocyte apoptosis accelerates the destruction of cartilage. However, autophagy has a protective effect on condylar chondrocytes. Degradation of ECM not only changes the properties of cartilage but also affects the phenotype of chondrocytes. The loss of subchondral bone in the early stages of TMJ osteoarthritis plays an aetiological role in the onset of osteoarthritis. In recent years, increasing evidence has suggested that chondrocyte hypertrophy and endochondral angiogenesis promote TMJ osteoarthritis. Hypertrophic chondrocytes secrete many factors that promote cartilage degeneration. These chondrocytes can further differentiate into osteoblasts and osteocytes and accelerate cartilage ossification. Intrachondral angiogenesis and neoneurogenesis are considered to be important triggers of arthralgia in TMJ osteoarthritis. Many molecular signalling pathways in endochondral osteogenesis are responsible for TMJ osteoarthritis. These latest discoveries in TMJ osteoarthritis have further enhanced the understanding of this disease and contributed to the development of molecular therapies. This paper summarizes recent cognition on the pathogenesis of TMJ osteoarthritis, focusing on the role of chondrocyte hypertrophy degeneration and cartilage angiogenesis.

Optical Biomarkers for the Diagnosis of Osteoarthritis through Raman Spectroscopy: Radiological and Biochemical Validation Using Ex Vivo Human Cartilage Samples

Osteoarthritis (OA) is the most common rheumatic disease, characterized by progressive articular cartilage degradation. Raman spectroscopy (RS) has been recently proposed as a label-free tool to detect molecular changes in musculoskeletal tissues. We used cartilage samples derived from human femoral heads to perform an ex vivo study of different Raman signals and ratios, related to major and minor molecular components of articular cartilage, hereby proposed as candidate optical biomarkers for OA. Validation was performed against the radiological Kellgren-Lawrence (K-L) grading system, as a gold standard, and cross-validated against sulfated glycosaminoglycans (sGAGs) and total collagens (Hyp) biochemical contents. Our results showed a significant decrease in sGAGs (SGAGs, A1063 cm^-1/A1004 cm^-1) and proteoglycans (PGs, A1375 cm^-1/A1004 cm^-1) and a significant increase in collagen disorganization (ColD/F, A1245 cm^-1/A1270 cm^-1), with OA severity. These were correlated with sGAGs or Hyp contents, respectively. Moreover, the SGAGs/HA ratio (A1063 cm^-1/A960 cm^-1), representing a functional matrix, rich in proteoglycans, to a mineralized matrix-hydroxyapatite (HA), was significantly lower in OA cartilage (K-L I vs. III-IV, p < 0.05), whilst the mineralized to collagenous matrix ratio (HA/Col, A960 cm^-1/A920 cm^-1) increased, being correlated with K-L. OA samples showed signs of tissue mineralization, supported by the presence of calcium crystals-related signals, such as phosphate, carbonate, and calcium pyrophosphate dihydrate (MGP, A960 cm^-1/A1004 cm^-1, MGC, A1070 cm^-1/A1004 cm^-1 and A1050 cm^-1/A1004 cm^-1). Finally, we observed an increase in lipids ratio (IL, A1450 cm^-1/A1670 cm^-1) with OA severity. As a conclusion, we have described the molecular fingerprint of hip cartilage, validating a panel of optical biomarkers and the potential of RS as a complementary diagnostic tool for OA.

Xanthine Oxidoreductase Is Involved in Chondrocyte Mineralization and Expressed in Osteoarthritic Damaged Cartilage

Pathologic calcification of cartilage consists of the formation of basic calcium phosphate (BCP) and/or calcium pyrophosphate dihydrate (CPPD) containing calcium crystals in mature hyaline or articular cartilage and is associated with aging, cartilage injury and likely plays a role in accelerating the pathology of osteoarthritis (OA). The pathways regulating joint calcification, in particular cartilage calcification, are not completely understood, but inflammation and the formation of reactive oxygen species (ROS) are contributory factors. The xanthine oxidase (XO) form of xanthine oxidoreductase (XOR), the key enzyme in xanthine and uric acid metabolism, is a major cellular source of superoxide. We hypothesized that XOR could be implicated in chondrocyte mineralization and cartilage calcification and degradation in OA. We showed both in murine primary chondrocyte and chondrogenic ATDC5 cells, that mineralization was inhibited by two different XOR inhibitors, febuxostat and allopurinol. In addition, XOR inhibition reduced the expression of the pro-mineralizing cytokine interleukin-6 (IL-6). We next generated XOR knock-out chondrocyte cell lines with undetectable XOR expression and XO activity. XOR knock-out chondrocyte cells showed decreased mineralization and reduced alkaline phosphatase (Alp) activity. To assess the precise form of XOR involved, primary chondrocytes of XOR mutant mice expressing either the XDH form (XDH ki) or the XO form (XO ki) were studied. We found that XO ki chondrocytes exhibited increased mineralization compared to XDH ki chondrocytes, and this was associated with enhanced Alp activity, ROS generation and IL-6 secretion. Finally, we found increased XOR expression in damaged vs. undamaged cartilage obtained from OA patients and XOR expression partially co-localized with areas showing pathologic calcification. Altogether, our results suggest that XOR, via its XO form, contribute to chondrocyte mineralization and pathological calcification in OA cartilage.

CD11b Signaling Prevents Chondrocyte Mineralization and Attenuates the Severity of Osteoarthritis

Osteoarthritis (OA) is a progressive joint disease that is strongly associated with calcium-containing crystal formation (mineralization) by chondrocytes leading ultimately to cartilage calcification. However, this calcification process is poorly understood and treatments targeting the underlying disease mechanisms are lacking. The CD11b/CD18 integrin (Mac-1 or αMβ2), a member of the beta 2 integrin family of adhesion receptors, is critically involved in the development of several inflammatory diseases, including rheumatoid arthritis and systemic lupus erythematosus. We found that in a collagen-induced arthritis, CD11b-deficient mice exhibited increased cartilage degradation compared to WT control animals. However, the functional significance of CD11b integrin signaling in the pathophysiology of chondrocytes remains unknown. CD11b expression was found in the extracellular matrix and in chondrocytes in both healthy and damaged human and murine articular cartilage. Primary murine CD11b KO chondrocytes showed increased mineralization when induced in vitro by secondary calciprotein particles (CPP) and quantified by Alizarin Red staining. This increased propensity to mineralize was associated with an increased alkaline phosphatase (Alp) expression (measured by qRT-PCR and activity assay) and an enhanced secretion of the pro-mineralizing IL-6 cytokine compared to control wild-type cells (measured by ELISA). Accordingly, addition of an anti-IL-6 receptor antibody to CD11b KO chondrocytes reduced significantly the calcification and identified IL-6 as a pro-mineralizing factor in these cells. In the same conditions, the ratio of qRT-PCR expression of collagen X over collagen II, and that of Runx2 over Sox9 (both ratio being indexes of chondrocyte hypertrophy) were increased in CD11b-deficient cells. Conversely, the CD11b activator LA1 reduced chondrocyte mineralization, Alp expression, IL-6 production and collagen X expression. In the meniscectomy (MNX) model of murine knee osteoarthritis, deficiency of CD11b led to more severe OA (OARSI scoring of medial cartilage damage in CD11b: 5.6 ± 1.8, in WT: 1.2 ± 0.5, p < 0.05, inflammation in CD11b: 2.8 ± 0.2, in WT: 1.4 ± 0.5). In conclusion, these data demonstrate that CD11b signaling prevents chondrocyte hypertrophy and chondrocyte mineralization in vitro and has a protective role in models of OA in vivo.

Molecular analysis of the destruction of articular joint tissues by Raman spectroscopy

INTRODUCTION

Osteoarthritis (OA) is a highly heterogenous disease influenced by different molecular, anatomic, and physiologic imbalances. Some of the bottlenecks for enhanced diagnosis and therapeutic assessment are the lack of validated biomarkers and early diagnosis tools. In this narrative review, we analyze the potential of Raman spectroscopy (RS) as a label-free optical tool for the characterization of articular joint tissues and its application as a diagnosis tool for OA.

AREAS COVERED

Raman spectra produce a unique 'molecular fingerprint' providing rotational and vibrational molecular information, allowing the identification and follow-up of molecular changes associated with OA pathological mechanisms. Focusing on multiple joint tissues (cartilage, synovium, bone, tendons, ligaments, and meniscus) and their contribution in disease incidence and progression, this review highlights the current knowledge on the application of RS in the characterization of organic and inorganic molecules present at these tissues and alterations that occur in the onset of OA.

EXPERT OPINION

Vibrational spectroscopy techniques, such as RS, are low cost, rapid and minimally invasive approaches that offer high specificity in the assessment of the molecular composition of complex tissues. Combined with multivariate statistical methods, RS offers great potential for optical biomarkers discovery or disease diagnosis applications, and we hereby discuss clinical translational progresses on the field.