Calcium-phosphate complex increased during subchondral bone remodeling affects earlystage osteoarthritis

Bioceramic-mediated chondrocyte hypertrophy promotes calcified cartilage formation for rabbit osteochondral defect repair

Osteochondral tissue is a highly specialized and complex tissue composed of articular cartilage and subchondral bone that are separated by a calcified cartilage interface. Multilayered or gradient scaffolds, often in conjunction with stem cells and growth factors, have been developed to mimic the respective layers for osteochondral defect repair. In this study, we designed a hyaline cartilage-hypertrophic cartilage bilayer graft (RGD/RGDW) with chondrocytes. Previously, we demonstrated that RGD peptide-modified chondroitin sulfate cryogel (RGD group) is chondro-conductive and capable of hyaline cartilage formation. Here, we incorporated whitlockite (WH), a Mg2+-containing calcium phosphate, into RGD cryogel (RGDW group) to induce chondrocyte hypertrophy and form collagen X-rich hypertrophic cartilage. This is the first study to use WH to produce hypertrophic cartilage. Chondrocytes-laden RGDW cryogel exhibited significantly upregulated expression of hypertrophy markers in vitro and formed ectopic hypertrophic cartilage in vivo, which mineralized into calcified cartilage in bone microenvironment. Subsequently, RGD cryogel and RGDW cryogel were combined into bilayer (RGD/RGDW group) and implanted into rabbit osteochondral defect, where RGD layer supports hyaline cartilage regeneration and bioceramic-containing RGDW layer promotes calcified cartilage formation. While the RGD group (monolayer) formed hyaline-like neotissue that extends into the subchondral bone, the RGD/RGDW group (bilayer) regenerated hyaline cartilage tissue confined to its respective layer and promoted osseointegration for integrative defect repair.

Amorphous calcium carbonate as a novel potential treatment for osteoarthritis in dogs: a pilot clinical study

Background

Amorphous calcium carbonate (ACC) is a potential new treatment for canine osteoarthritis (OA) with novel mechanisms based on local pH modulation and targeting bone remodeling, inflammation, and pain. The aim of this pilot exploratory clinical study was to obtain initial data on the potential efficacy and safety of ACC in OA dogs and to determine if further investigation was appropriate using similar assessment methods.

Materials and methods

In this prospective, randomized, double-blind, controlled pilot study, 41 client-owned dogs were allocated in a 2:1 ratio to ACC: placebo given orally for 56 days. Efficacy assessments included improvements in pain and mobility using owner questionnaires [Canine Brief Pain Inventory (CBPI), Client Specific Outcome Measure (CSOM), and Veterinary Orthopedic Scores (VOS)]. Safety in the study population was monitored by veterinary examinations, clinical pathology, and adverse events.

Results

Fifty-three dogs were screened, of which 41 enrolled and served for the safety assessment. Thirty-six dogs were found evaluable for initial efficacy assessment. Three dogs given placebo (21.4%) and one given ACC (4.5%) were removed before day 56 due to owner-perceived pain and were considered treatment failures. There were no serious adverse events or clinically significant treatment-related effects in the study. Overall, ACC was found safe in the small study population. On day 56, proportionally more ACC than placebo dogs were treatment successes based on CBPI (45.5% vs. 21.4%) and CSOM (63.6% vs. 30.8%, respectively); however, these differences were not statistically significant (p = 0.15 and 0.06, respectively). On day 56, within the ACC group but not the placebo group, the CBPI, CSOM, and VOS assessments were lower compared to day 0 and day 14 (p < 0.05).

Limitations

The relatively small number of dogs limited the statistical power of the pilot study in evaluating the efficacy and safety of ACC.

Conclusion

Study results support the conduct of larger, appropriately powered studies using similar assessments to confirm whether ACC may be a safe and effective treatment for OA in dogs.

Pathological progression of osteoarthritis: a perspective on subchondral bone

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

Spatial analysis of the osteoarthritis microenvironment: techniques, insights, and applications

Osteoarthritis (OA) is a debilitating degenerative disease affecting multiple joint tissues, including cartilage, bone, synovium, and adipose tissues. OA presents diverse clinical phenotypes and distinct molecular endotypes, including inflammatory, metabolic, mechanical, genetic, and synovial variants. Consequently, innovative technologies are needed to support the development of effective diagnostic and precision therapeutic approaches. Traditional analysis of bulk OA tissue extracts has limitations due to technical constraints, causing challenges in the differentiation between various physiological and pathological phenotypes in joint tissues. This issue has led to standardization difficulties and hindered the success of clinical trials. Gaining insights into the spatial variations of the cellular and molecular structures in OA tissues, encompassing DNA, RNA, metabolites, and proteins, as well as their chemical properties, elemental composition, and mechanical attributes, can contribute to a more comprehensive understanding of the disease subtypes. Spatially resolved biology enables biologists to investigate cells within the context of their tissue microenvironment, providing a more holistic view of cellular function. Recent advances in innovative spatial biology techniques now allow intact tissue sections to be examined using various -omics lenses, such as genomics, transcriptomics, proteomics, and metabolomics, with spatial data. This fusion of approaches provides researchers with critical insights into the molecular composition and functions of the cells and tissues at precise spatial coordinates. Furthermore, advanced imaging techniques, including high-resolution microscopy, hyperspectral imaging, and mass spectrometry imaging, enable the visualization and analysis of the spatial distribution of biomolecules, cells, and tissues. Linking these molecular imaging outputs to conventional tissue histology can facilitate a more comprehensive characterization of disease phenotypes. This review summarizes the recent advancements in the molecular imaging modalities and methodologies for in-depth spatial analysis. It explores their applications, challenges, and potential opportunities in the field of OA. Additionally, this review provides a perspective on the potential research directions for these contemporary approaches that can meet the requirements of clinical diagnoses and the establishment of therapeutic targets for OA.

Curculigoside inhibits osteoarthritis <em>via</em> the regulation of NLRP3 pathway

Osteoarthritis (OA) is characterized by degenerative articular cartilage. Nucleotide-binding oligomerization domain-like receptor containing pyrin domain 3 (NLRP3) plays an important role in inflammation. This study aims to investigate whether protective effects of curculigoside on OA are medicated by the regulation of NLRP3 pathway. Destabilization of the medial meniscus (DMM) was performed to build an OA mouse model. After surgery, OA mice were treated with curculigoside. Immunohistochemistry was conducted to evaluate OA cartilage. In addition, human chondrocytes were isolated and treated with curculigoside. The mRNA and protein expression of iNOS, MMP-9, NLRP3 was detected by PCR and Western blot analysis. Curculigoside inhibited mRNA and protein levels of iNOS and MMP-9 induced by DMM surgery in a dose-dependent manner. Furthermore, the expression of NLRP3, NF-κB and PKR was downregulated after curculigoside administration. Moreover, curculigoside reversed the effects of IL-1β on MMP-9, iNOS and type II collagen expression at mRNA and protein levels in human chondrocytes in a dose-dependent manner. In conclusion, curculigoside exhibits beneficial effect on cartilage via the inhibition of NLRP3 pathway.

Surface-Modified Nano-Hydroxyapatite Uniformly Dispersed on High-Porous GelMA Scaffold Surfaces for Enhanced Osteochondral Regeneration

Purpose

This study aims to investigate the impact of enhancing subchondral bone repair on the efficacy of articular cartilage restoration, thereby achieving improved osteochondral regeneration outcomes.

Methods

In this study, we modified the surface of nano-hydroxyapatite (n-HAp) through alkylation reactions to prepare n-HApMA. Characterization techniques, including X-ray diffraction, infrared spectroscopy scanning, thermogravimetric analysis, particle size analysis, and electron microscopy, were employed to analyze n-HApMA. Bioinks were prepared using n-HApMA, high porosity GelMA hydrogel, and adipose tissue derived stromal cells (ADSCs). The rheological properties of the bioinks during photocuring were investigated using a rheometer. Based on these bioinks, a biphasic scaffold was constructed. The viability of cells within the scaffold was observed using live-dead cell staining, while the internal morphology was examined using scanning electron microscopy. The stiffness of the scaffold was evaluated through compression testing. Scaffolds were implanted into the osteochondral defects of New Zealand rabbit knees, and microCT was utilized to observe the subchondral bone repair. Hematoxylin and eosin (H&E) staining, Masson's trichrome staining, and Safranin O/Fast Green staining were performed to assess the regeneration of subchondral bone and cartilage. Furthermore, immunohistochemical staining was employed to detect the expression of osteogenic and chondrogenic-related molecules.

Results

Scaffold characterization revealed that surface modification enables the uniform distribution of n-HApMA within the GelMA matrix. The incorporation of 5% n-HApMA notably enhanced the elastic modulus and stiffness of the 6% high-porosity GelMA in comparison to n-HAp. Moreover, in-vivo study showed that the homogeneous dispersion of n-HApMA on the GelMA matrix facilitated the osteogenic differentiation of adipose-derived stem cells (ADSCs) and promoted osteochondral tissue regeneration.

Conclusion

These findings suggest potential applications of the n-HApMA/GelMA composite in the field of tissue engineering and regenerative medicine.

Suppressing Chondrocyte Hypertrophy to Build Better Cartilage

Current clinical strategies for restoring cartilage defects do not adequately consider taking the necessary steps to prevent the formation of hypertrophic tissue at injury sites. Chondrocyte hypertrophy inevitably causes both macroscopic and microscopic level changes in cartilage, resulting in adverse long-term outcomes following attempted restoration. Repairing/restoring articular cartilage while minimizing the risk of hypertrophic neo tissue formation represents an unmet clinical challenge. Previous investigations have extensively identified and characterized the biological mechanisms that regulate cartilage hypertrophy with preclinical studies now beginning to leverage this knowledge to help build better cartilage. In this comprehensive article, we will provide a summary of these biological mechanisms and systematically review the most cutting-edge strategies for circumventing this pathological hallmark of osteoarthritis.

Bone marrow lesions in osteoarthritis: From basic science to clinical implications

Osteoarthritis (OA) is the most prevalent musculoskeletal disease characterized by multiple joint structure damages, including articular cartilage, subchondral bone and synovium, resulting in disability and economic burden. Bone marrow lesions (BMLs) are common and important magnetic resonance imaging (MRI) features in OA patients. Basic and clinical research on subchondral BMLs in the pathogenesis of OA has been a hotspot. New evidence shows that subchondral bone degeneration, including BML and angiogenesis, occurs not only at or after cartilage degeneration, but even earlier than cartilage degeneration. Although BMLs are recognized as important biomarkers for OA, their exact roles in the pathogenesis of OA are still unclear, and disputes about the clinical impact and treatment of BMLs remain. This review summarizes the current basic and clinical research progress of BMLs. We particularly focus on molecular pathways, cellular abnormalities and microenvironmental changes of subchondral bone that contributed to the formation of BMLs, and emphasize the crosstalk between subchondral bone and cartilage in OA development. Finally, potential therapeutic strategies targeting BMLs in OA are discussed, which provides novel strategies for OA treatment.

Contrast-enhanced micro-computed tomography of compartment and time-dependent changes in femoral cartilage and subchondral plate in a murine model of osteoarthritis

A lack of understanding of the mechanisms underlying osteoarthritis (OA) progression limits the development of effective long-term treatments. Quantitatively tracking spatiotemporal patterns of cartilage and bone degeneration is critical for assessment of more appropriately targeted OA therapies. In this study, we use contrast-enhanced micro-computed tomography (μCT) to establish a timeline of subchondral plate (SCP) and cartilage changes in the murine femur after destabilization of the medial meniscus (DMM). We performed DMM or sham surgery in 10-12-week-old male C57Bl/6J mice. Femora were imaged using μCT after 0, 2, 4, or 8 weeks. Cartilage-optimized scans were performed after immersion in contrast agent CA4+. Bone mineral density distribution (BMDD), cartilage attenuation, SCP, and cartilage thickness and volume were measured, including lateral and medial femoral condyle and patellar groove compartments. As early as 2 weeks post-DMM, cartilage thickness significantly increased and cartilage attenuation, SCP volume, and BMDD mean significantly decreased. Trends in cartilage and SCP metrics within each joint compartment reflected those seen in global measurements, and both BMDD and SCP thickness were consistently greater in the lateral and medial condyles than the patellar groove. Sham surgery also resulted in significant changes to SCP and cartilage metrics, highlighting a potential limitation of using surgical models to study tissue morphology or composition changes during OA progression. Contrast-enhanced μCT analysis is an effective tool to monitor changes in morphology and composition of cartilage, and when combined with bone-optimized μCT, can be used to assess the progression of degenerative changes after joint injury.

Arctiin-reinforced antioxidant microcarrier antagonizes osteoarthritis progression

Loss of extracellular matrix (ECM) of cartilage due to oxidative stress injury is one of the main characteristics of osteoarthritis (OA). As a bioactive molecule derived from the traditional Chinese Burdock, arctiin exerts robust antioxidant properties to modulate redox balance. However, the potential therapeutic effects of arctiin on OA and the underlying mechanisms involved are still unknown. Based on the Traditional Chinese Medicine Systems Pharmacology Database and Analysis Platform (TCMSP) tool, Burdock-extracted small molecule arctiin was identified as a potential anti-arthritic component. In vitro, treatment using arctiin rescued the interleukin (IL)-1β-induced activation of proteinases and promoted the cartilage ECM synthesis in human chondrocytes. In vivo, intraperitoneal injection of arctiin ameliorated cartilage erosion and encountered subchondral bone sclerosis in the post-traumatic OA mice. Transcriptome sequencing uncovered that arctiin-enhanced cartilage matrix deposition was associated with restricted oxidative stress. Mechanistically, inhibition of nuclear factor erythroid 2-related factor 2 (NRF2) abolished arctiin-mediated anti-oxidative and anti-arthritic functions. To further broaden the application prospects, a gellan gum (GG)-based bioactive gel (GG-CD@ARC) encapsulated with arctiin was made to achieve long-term and sustained drug release. Intra-articular injection of GG-CD@ARC counteracted cartilage degeneration in the severe (12 weeks) OA mice model. These findings indicate that arctiin may be a promising anti-arthritic agent. Furthermore, GG-modified bioactive glue loaded with arctiin provides a unique strategy for treating moderate to severe OA.

The immune microenvironment in cartilage injury and repair

The ability of articular cartilage to repair itself is limited because it lacks blood vessels, nerves, and lymph tissue. Once damaged, it can lead to joint swelling and pain, accelerating the progression of osteoarthritis. To date, complete regeneration of hyaline cartilage exhibiting mechanical properties remains an elusive goal, despite the many available technologies. The inflammatory milieu created by cartilage damage is critical for chondrocyte death and hypertrophy, extracellular matrix breakdown, ectopic bone formation, and progression of cartilage injury to osteoarthritis. In the inflammatory microenvironment, mesenchymal stem cells (MSCs) undergo aberrant differentiation, and chondrocytes begin to convert or dedifferentiate into cells with a fibroblast phenotype, thereby resulting in fibrocartilage with poor mechanical qualities. All these factors suggest that inflammatory problems may be a major stumbling block to cartilage repair. To produce a milieu conducive to cartilage repair, multi-dimensional management of the joint inflammatory microenvironment in place and time is required. Therefore, this calls for elucidation of the immune microenvironment of cartilage repair after injury. This review provides a brief overview of: (1) the pathogenesis of cartilage injury; (2) immune cells in cartilage injury and repair; (3) effects of inflammatory cytokines on cartilage repair; (4) clinical strategies for treating cartilage defects; and (5) strategies for targeted immunoregulation in cartilage repair. STATEMENT OF SIGNIFICANCE: Immune response is increasingly considered the key factor affecting cartilage repair. It has both negative and positive regulatory effects on the process of regeneration and repair. Proinflammatory factors are secreted in large numbers, and necrotic cartilage is removed. During the repair period, immune cells can secrete anti-inflammatory factors and chondrogenic cytokines, which can inhibit inflammation and promote cartilage repair. However, inflammatory factors persist, which accelerate the degradation of the cartilage matrix. Furthermore, in an inflammatory microenvironment, MSCs undergo abnormal differentiation, and chondrocytes begin to transform or dedifferentiate into fibroblast-like cells, forming fibrocartilage with poor mechanical properties. Consequently, cartilage regeneration requires multi-dimensional regulation of the joint inflammatory microenvironment in space and time to make it conducive to cartilage regeneration.

[The Role of Platelet-Derived Growth Factor-AA in the Pathogenesis and Development of Osteoarthritis]

Osteoarthritis (OA) is a chronic degenerative disease involving the entire joint. The pathogenesis and progression of OA bear close connection to the destruction and the abnormal metabolism of cartilage, subchondral bones and synovium. Platelet derived growth factor-AA (PDGF-AA) is a critical mitogenic and chemotactic factor for a variety of cells, including chondrocytes, mesenchymal stem cells, osteoclasts and osteoblasts, and PDGF-AA promotes effective wound repair. This paper reviewed the pathological changes of cartilage, subchondral bones and synovium in the process of OA development, and summarized research progress regarding the effect of PDGF-AA on the tissues and related cells mentioned above. Current studies have basically clarified the pathological changes of cartilage, subchondral bones and synovium in OA patients, and have shown that PDGF-AA serves critical regulatory function in the tissues or cells involved in OA, the internal mechanism of which remains unclear, though. More studies should be done to find ways to apply PDGF-AA for clinic purpose and to diagnose and treat OA on the cellular basis.

Senescent skeletal cells cross-talk with synovial cells plays a key role in the pathogenesis of osteoarthritis

Osteoarthritis (OA) has been recognized as an age-related degenerative disease commonly seen in the elderly that affects the whole “organ” including cartilage, subchondral bone, synovium, and muscles. An increasing number of studies have suggested that the accumulation of senescent cells triggering by various stresses in the local joint contributes to the pathogenesis of age-related diseases including OA. In this review, we mainly focus on the role of the senescent skeletal cells (chondrocytes, osteoblasts, osteoclasts, osteocyte, and muscle cells) in initiating the development and progression of OA alone or through cross-talk with the macrophages/synovial cells. Accordingly, we summarize the current OA-targeted therapies based on the abovementioned theory, e.g., by eliminating senescent skeletal cells and/or inhibiting the senescence-associated secretory phenotype (SASP) that drives senescence. Furthermore, the existing animal models for the study of OA from the perspective of senescence are highlighted to fill the gap between basic research and clinical applications. Overall, in this review, we systematically assess the current understanding of cellular senescence in OA, which in turn might shed light on the stratified OA treatments.

The collagenases: are they tractable targets for preventing cartilage destruction in osteoarthritis?

INTRODUCTION

The etiology and pathogenesis of osteoarthritis (OA) have been intensely investigated; however, the disease course and progression are not completely understood. A prominent role for interstitial collagenases is recognized in this degenerative process, hence strategies to target them are of major interest.

AREAS COVERED

The pathogenesis of OA, the role of interstitial collagenases (MMP-1, -8 and -13) and collagenase modifying drugs are examined and discussed. We reviewed relevant papers from PubMed and Google Scholar.

EXPERT OPINION

There is strong evidence for the therapeutic potential of MMP inhibitors in OA; however, they are not expected to impact the inflammatory process. Therefore, there is a need for a relative inhibitor of MMP-13 collagenase which possesses anti-inflammatory properties. The identification of novel broad-spectrum relative multiple peptidase inhibitors could provide desirable tools for the prophylaxis, cure, or treatment of diseases involving articular cartilage (AC) degradation, in particular OA.

Cell Interplay in Osteoarthritis

Osteoarthritis (OA) is a common chronic disease and a significant health concern that needs to be urgently solved. OA affects the cartilage and entire joint tissues, including the subchondral bone, synovium, and infrapatellar fat pads. The physiological and pathological changes in these tissues affect the occurrence and development of OA. Understanding complex crosstalk among different joint tissues and their roles in OA initiation and progression is critical in elucidating the pathogenic mechanism of OA. In this review, we begin with an overview of the role of chondrocytes, synovial cells (synovial fibroblasts and macrophages), mast cells, osteoblasts, osteoclasts, various stem cells, and engineered cells (induced pluripotent stem cells) in OA pathogenesis. Then, we discuss the various mechanisms by which these cells communicate, including paracrine signaling, local microenvironment, co-culture, extracellular vesicles (exosomes), and cell tissue engineering. We particularly focus on the therapeutic potential and clinical applications of stem cell-derived extracellular vesicles, which serve as modulators of cell-to-cell communication, in the field of regenerative medicine, such as cartilage repair. Finally, the challenges and limitations related to exosome-based treatment for OA are discussed. This article provides a comprehensive summary of key cells that might be targets of future therapies for OA.

Exosomes Isolated From Bone Marrow Mesenchymal Stem Cells Exert a Protective Effect on Osteoarthritis via lncRNA LYRM4-AS1-GRPR-miR-6515-5p

Objectives

The aim of this study was to investigate the effects of exosomes isolated from human bone marrow mesenchymal stem cells (BMSCs) on osteoarthritis (OA) and a competitive endogenous RNA (ceRNA) network.

Methods

Exosomes were isolated from human BMSCs and characterized by transmission electron microscopy (TEM), Nanosight (NTA), and western blotting. Chondrocytes were treated with interleukin-1β (IL-1β) and then transfected with exosomes. Cell viability and apoptosis were determined using Cell Counting Kit-8 (CCK-8) and flow cytometry, respectively. Cells with IL-1β and exosomes were sequenced, and differentially expressed lncRNAs (DE-lncRNAs) and miRNAs (DE-miRNAs) were identified. Thereafter, a ceRNA network (LYRM4-AS1-GRPR-miR-6515-5p) was chosen for further validation.

Results

TEM, NTA, and western blotting showed that exosomes were successfully isolated, and PKH67 staining showed that exosomes could be taken up by IL-1β-induced chondrocytes. Compared with the control group, IL-1β significantly decreased cell viability and promoted apoptosis (P < 0.05), while exosomes reversed the changes induced by IL-1β. For MMP3, AKT, and GRPR, IL-1β upregulated their expression, while exosomes downregulated their expression. For PTEN, there was no significant difference in PTEN expression between the control and IL-1β groups; however, exosomes markedly upregulated PTEN expression. By sequencing, 907 DE-lncRNAs and 25 DE-miRNAs were identified, and a ceRNA network was constructed. The dual-luciferase reporter gene indicated that LYRM4-AS1, miR-6515-5, and GRPR interacted with each other. The results of cell experiments showed that LYRM4-AS1 regulated the growth of IL-1β-induced chondrocytes by GRPR/miR-6515-5p.

Conclusion

Exosomes may alleviate OA inflammation by regulating the LYRM4-AS1/GRPR/miR-6515-5p signaling pathway.

Microenvironment in subchondral bone: predominant regulator for the treatment of osteoarthritis

Osteoarthritis (OA) is a degenerative joint disease in the elderly. Although OA has been considered as primarily a disease of the articular cartilage, the participation of subchondral bone in the pathogenesis of OA has attracted increasing attention. This review summarises the microstructural and histopathological changes in subchondral bone during OA progression that are due, at the cellular level, to changes in the interactions among osteocytes, osteoblasts, osteoclasts (OCs), endothelial cells and sensory neurons. Therefore, we focus on how pathological cellular interactions in the subchondral bone microenvironment promote subchondral bone destruction at different stages of OA progression. In addition, the limited amount of research on the communication between OCs in subchondral bone and chondrocytes (CCs) in articular cartilage during OA progression is reviewed. We propose the concept of 'OC-CC crosstalk' and describe the various pathways by which the two cell types might interact. Based on the 'OC-CC crosstalk', we elaborate potential therapeutic strategies for the treatment of OA, including restoring abnormal subchondral bone remodelling and blocking the bridge-subchondral type H vessels. Finally, the review summarises the current understanding of how the subchondral bone microenvironment is related to OA pain and describes potential interventions to reduce OA pain by targeting the subchondral bone microenvironment.

From Pathogenesis to Therapy in Knee Osteoarthritis: Bench-to-Bedside

Osteoarthritis (OA) is currently the most widespread musculoskeletal condition and primarily affects weight-bearing joints such as the knees and hips. Importantly, knee OA remains a multifactorial whole-joint disease, the appearance and progression of which involves the alteration of articular cartilage as well as the synovium, subchondral bone, ligaments, and muscles through intricate pathomechanisms. Whereas it was initially depicted as a predominantly aging-related and mechanically driven condition given its clear association with old age, high body mass index (BMI), and joint malalignment, more recent research identified and described a plethora of further factors contributing to knee OA pathogenesis. However, the pathogenic intricacies between the molecular pathways involved in OA prompted the study of certain drugs for more than one therapeutic target (amelioration of cartilage and bone changes, and synovial inflammation). Most clinical studies regarding knee OA focus mainly on improvement in pain and joint function and thus do not provide sufficient evidence on the possible disease-modifying properties of the tested drugs. Currently, there is an unmet need for further research regarding OA pathogenesis as well as the introduction and exhaustive testing of potential disease-modifying pharmacotherapies in order to structure an effective treatment plan for these patients.

Impact of the 25-Hydroxycholecalciferol Concentration and Vitamin D Deficiency Treatment on Changes in the Bone Level at the Implant Site during the Process of Osseointegration: A Prospective, Randomized, Controlled Clinical Trial

INTRODUCTION

The most important factor which is responsible for the positive course of implant treatment is the process of osseointegration between the implant structure and the host's bone tissue. The aim of this study was to assess what effect the 25-hydroxycholecalciferol concentration and vitamin D deficiency treatment have on changes in the bone level at the implant site during the process of osseointegration in the mandible.

MATERIALS AND METHODS

The study was with 122 people qualified for implant surgery, who were assigned to three research groups (A, B, and C). Laboratory, clinical, and radiological tests were performed on the day of surgery, and after 6 and 12 weeks. The bone level in the immediate proximity of the implant was determined by radiovisiography (RVG).

RESULTS

The bone level after 12 weeks in Groups B and C was significantly higher than after 6 weeks. The bone level in the study Group B was significantly higher than in Group A. The study showed that the higher the levels of 25-hydroxycholecalciferol were observed on the day of surgery, the higher was the level of bone surrounding the implant after 6 and 12 after surgery.

CONCLUSION

The correct level of 25-hydroxycholecalciferol on the day of surgery and vitamin D deficiency treatment significantly increase the bone level at the implant site in the process of radiologically assessed osseointegration.

Amentadione from the Alga Cystoseira usneoides as a Novel Osteoarthritis Protective Agent in an Ex Vivo Co-Culture OA Model

Osteoarthritis (OA) remains a prevalent chronic disease without effective prevention and treatment. Amentadione (YP), a meroditerpenoid purified from the alga Cystoseira usneoides, has demonstrated anti-inflammatory activity. Here, we investigated the YP anti-osteoarthritic potential, by using a novel OA preclinical drug development pipeline designed to evaluate the anti-inflammatory and anti-mineralizing activities of potential OA-protective compounds. The workflow was based on in vitro primary cell cultures followed by human cartilage explants assays and a new OA co-culture model, combining cartilage explants with synoviocytes under interleukin-1β (IL-1β) or hydroxyapatite (HAP) stimulation. A combination of gene expression analysis and measurement of inflammatory mediators showed that the proposed model mimicked early disease stages, while YP counteracted inflammatory responses by downregulation of COX-2 and IL-6, improved cartilage homeostasis by downregulation of MMP3 and the chondrocytes hypertrophic differentiation factors Col10 and Runx2. Importantly, YP downregulated NF-κB gene expression and decreased phosphorylated IkBα/total IkBα ratio in chondrocytes. These results indicate the co-culture as a relevant pre-clinical OA model, and strongly suggest YP as a cartilage protective factor by inhibiting inflammatory, mineralizing, catabolic and differentiation processes during OA development, through inhibition of NF-κB signaling pathways, with high therapeutic potential.

Transglutaminase-2 regulates Wnt and FoxO3a signaling to determine the severity of osteoarthritis

Transglutaminase 2 (TG2), also known as tissue transglutaminase, is a calcium-dependent enzyme that has a variety of intracellular and extracellular substrates. TG2 not only increases in osteoarthritis (OA) tissue but also affects the progression of OA. However, it is still unclear how TG2 affects cartilage degradation in OA at the molecular level. Surgically induced OA lead to an increase of TG2 in the articular cartilage and growth plate, and it was dependent on TGFβ1 in primary chondrocytes. The inhibition of TG2 enzymatic activity with intra-articular injection of ZDON, the peptide-based specific TG2 inhibitor, ameliorated the severity of surgically induced OA as well as the expression of MMP-3 and MMP-13. ZDON attenuated MMP-3 and MMP-13 expression in TGFβ- and calcium ionophore-treated chondrocytes in a Runx2-independent manner. TG2 inhibition with ZDON suppressed canonical Wnt signaling through a reduction of β-catenin, which was mediated by ubiquitination-dependent proteasomal degradation. In addition, TG2 activation by a calcium ionophore enhanced the phosphorylation of AMPK and FoxO3a and the nuclear translocation of FoxO3a, which was responsible for the increase in MMP-13. In conclusion, TG2 plays an important role in the pathogenesis of OA as a major catabolic mediator that affects the stability of β-catenin and FoxO3a-mediated MMP-13 production.

NF-κB promotes osteoclast differentiation by overexpressing MITF via down regulating microRNA-1276 expression

BACKGROUND

Nuclear factor-kappa B (NF-κB) is an important nuclear transcription factor in cells, involving in a series of processes such as cell proliferation, apoptosis, and differentiation. In this study, we explored the specific mechanism of NF-κB on the differentiation of osteoclasts.

METHODS

MicroRNAs (miRNAs) expression microarray data GSE105027 related to osteoarthritis was obtained to screen out the differentially expressed miRNA. Phorbol-12-myristate-13-acetate (PMA) was used to induce THP-1 cells to differentiate into macrophages, followed by induction to osteoclasts using macrophage colony-stimulating factor (M-CSF) and receptor activator of NF-κB ligand (RANKL). ELISA and RT-qPCR were conducted to examine IL-6 and IL-1β expression. The binding of NF-κB to the miR-1276 promoter region was demonstrated by ChIP assay, and targeting relationship between miR-1276 and MITF was verified by dual luciferase reporter assay. KK, iKBα, NF-kB, p-IKK, p-iKBα, p-NF-kB expression was analyzed by western blot. NF-κB and miR-1276 expression in osteoclasts was examined later. After gain- and less-of-function study, the effects on osteoclast differentiation were detected by TRAP-positive osteoclasts, TRAP activity, TRAP-5b content, F-Actin expression, as well as osteoclast differentiation marker genes expression.

RESULTS

NF-κB was activated in osteoclasts, and down-regulation of NF-κB inhibited osteoclast differentiation. Next, miR-1276 was downregulated in osteoclasts after differentiation from monocytes. Meanwhile, NF-κB decreased the expression of miR-1276 by binding to the miR-1276 promoter, thereby elevating MITF expression, thereby promoting osteoclast differentiation.

CONCLUSION

In summary, NF-κB promoted osteoclast differentiation through downregulating miR-1276 to upregulate MITF.

Degrading products of chondroitin sulfate can induce hypertrophy-like changes and MMP-13/ADAMTS5 production in chondrocytes

Chondroitin sulfate (CS) is the most abundant glycosaminoglycan (GAG) in articular cartilage and the loss of CS-GAG occurs early in OA. As a major component of perichondral matrix interacting directly with chondrocytes, the active turnover of CS can affect to break the homeostasis of chondrocytes. Here we employ CS-based 3-dimensional (3D) hydrogel scaffold system to investigate how the degradation products of CS affect the catabolic phenotype of chondrocytes. The breakdown of CS-based ECM by the chondroitinase ABC (ChABC) resulted in a hypertrophy-like morphologic change in chondrocytes, which was accompanied by catabolic phenotypes, including increased MMP-13 and ADAMTS5 expression, nitric oxide (NO) production and oxidative stress. The inhibition of Toll-like receptor 2 (TLR2) or TLR4 with OxPAPC (TLR2 and TLR4 dual inhibitor) and LPS-RS (TLR4-MD2 inhibitor) ameliorated these catabolic phenotypes of chondrocytes by CS-ECM degradation, suggesting a role of CS breakdown products as damage-associated molecular patterns (DAMPs). As downstream signals of TLRs, MAP kinases, NF-kB, NO and STAT3-related signals were responsible for the catabolic phenotypes of chondrocytes associated with ECM degradation. NO in turn reinforced the activation of MAP kinases as well as NFkB signaling pathway. Thus, these results propose that the breakdown product of CS-GAG can recapitulate the catabolic phenotypes of OA.

Nephronectin Expression is Inhibited by Inorganic Phosphate in Osteoblasts

Nephronectin (Npnt), an extracellular matrix protein, is known to be a ligand of integrin α8β1, and it has also been known to play critical roles as various organs. In the present study, elevated extracellular inorganic phosphate (Pi) strongly inhibited the expression of Npnt in MC3T3-E1 cells, while the existence of extracellular calcium (Ca) was indispensable for its effect. Furthermore, Pi-induced inhibition of Npnt gene expression was recovered by inhibitors of both sodium-dependent Pi transporter (Pit) and fibroblast growth factor receptors (Fgfrs). These results demonstrated that Npnt gene expression is regulated by extracellular Pi via Pit and Fgfrs.