Synovial mesenchymal progenitor derived aggrecan regulates cartilage homeostasis and endogenous repair capacity

α2-Macroglobulin Promotes Chondrocyte Proliferation and Cartilage Matrix Synthesis via Inducing PCNA

Objectivesα2-Macroglobulin (A2M) can prevent cartilage degeneration by blocking many types of cartilage-degrading enzymes, but the mechanism remains to be clarified. This study aimed to test that A2M protects against cartilage degeneration by promoting chondrocyte proliferation and cartilage matrix synthesis via inducing proliferating cell nuclear antigen (PCNA).DesignThe cartilage degeneration of the anterior cruciate ligament transection (ACLT) model was evaluated by Safranin O-fast green staining, and articular cartilage degeneration was graded using the Osteoarthritis Research Society International (OARSI)-modified Mankin criteria. The chondrocyte proliferation was detected by 5-Bromodeoxyuridinc (BrdU), MTT, and Cell Counting Kit-8 (CCK8) methods. The chondrocyte apoptosis was detected by lactate dehydrogenase (LDH) assay and Annexin PI staining with the flow cytometer. The glycosaminoglycan (sGAG) and aggrecan in culture supernatant were measured by enzyme-linked immunosorbent assay (ELISA). Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was used to analyze the type II collagen and aggrecan mRNA expression. The PCNA protein expression was analyzed by western blot and immunofluorescent staining.ResultsA2M can attenuate cartilage degeneration in ACLT rats. The OARSI scores for cartilage degeneration in the A2M group were lower than those in the phosphate-buffered saline (PBS) group. A2M can promote chondrocyte proliferation and inhibit chondrocyte apoptosis, promote the cartilage matrix synthesis in chondrocytes (type II collagen and aggrecan), and culture supernatant (sGAG and aggrecan). At the same time, it also up-regulated the PCNA protein expression in chondrocytes.ConclusionsA2M can promote chondrocyte proliferation and cartilage matrix synthesis via inducing PCNA expression.

Metformin exhibits inhibitory effects on ferroptosis and alleviates chondrocyte metabolic imbalance in osteoarthritis models, as well as Erastin-induced ferroptosis, through the modulation of the P53/SLC7A11 pathway

Osteoarthritis (OA) is a prevalent degenerative disease, and metformin, the first-line treatment for type 2 diabetes, has shown potential in slowing the progression of OA, although its mechanism of action is not fully understood. This study aims to explore the role of ferroptosis in OA and evaluate the therapeutic effects and mechanisms of metformin on ferroptosis. We identified gene differences associated with OA through RNA-Seq data analysis and predicted potential targets using network pharmacology and molecular docking techniques. In vivo experimental methods, including histological examination, immunofluorescence, Western blotting, real-time quantitative PCR, biochemical analysis, and ELISA, were used to study the effects of metformin in the modified Hulth method and Erastin-induced OA models. The study found that metformin significantly inhibits chondrocyte ferroptosis by upregulating SLC7A11 and downregulating P53 expression, maintaining the balance of synthesis and catabolism in chondrocytes, and effectively slowing down the degeneration of knee joint cartilage in rats. Overall, this study not only provides further evidence for the anti-OA effects of metformin but also identifies its direct targets in the inhibition of ferroptosis in OA.

Curdlan/chitosan NIR-responsive in situ forming gel: An injectable scaffold for the treatment of epiphyseal plate injury

Premature closure of the epiphyseal plate inducing by the formation of bone bridges after epiphyseal plate injury, can lead to limb shortening and angular deformity, causing adverse effects on the growth and development of adolescents. Therefore, preventing the formation of bone bridges has become the primary task for children with epiphyseal plate fractures. In our study, a novel near-infrared (NIR)-responsive bone repair scaffold (CGCB), namely black phosphorus (BP)-loaded in-situ gel based on curdlan (CUD), β-glycerophosphate (GP) and chitosan (CS), was developed. In vitro studies confirmed that the CGCB can promote the differentiation and migration of chondrocytes and has potential cartilage repair ability. A drilled model of epiphyseal plate injury further confirmed that CGCB can promote the repair of epiphyseal plate injury and NIR irradiation combined with CGCB significantly repaired the injury site by increasing expression of Sox9 and Aggrecan. The above findings indicate that the near-infrared (NIR) responsive bone repair scaffold (CGCB) can effectively inhibit bone bridge formation, prevent early closure of the epiphyseal plate, and provide new ideas for repairing epiphyseal plate defects in children.

Therapeutic targets in aging-related osteoarthritis: A focus on the extracellular matrix homeostasis

Osteoarthritis (OA) represents a globally prevalent degenerative bone diseases and is the primary contributors to pain and disability among middle-aged and elderly people, thereby imposing significant social and economic burdens. When articular cartilage is in the aging environment, epigenetic modifications, DNA damage and mitochondrial dysfunction lead to cell senescence. Chondrocyte senescence has been identified as a pivotal event in this metabolic dysregulation of the extracellular matrix (ECM). It can affect the composition and structure of ECM, and the mechanical and biological signals transmitted by ECM to senescent chondrocytes affect their physiology and pathology. Over the past few decades, the role of ECM in aging-related OA has received increasing attention. In this review, we summarize the changes of cartilage's major ECM (type II collagen and aggrecan) and the interaction between aging and ECM in OA, and explore therapeutic strategies targeting cartilagae ECM, such as noncoding RNAs, small-molecule drugs, and mesenchymal stem cell (MSC)-derived extracellular vesicles for OA. The aim of this study was to elucidate the potential benefits of ECM-based therapies as novel strategies for the management of OA diseases.

Defining the extracellular matrix in non-cartilage soft-tissues in osteoarthritis: a systematic review

Aims

Extracellular matrix (ECM) is a critical determinant of tissue mechanobiology, yet remains poorly characterized in joint tissues beyond cartilage in osteoarthritis (OA). This review aimed to define the composition and architecture of non-cartilage soft joint tissue structural ECM in human OA, and to compare the changes observed in humans with those seen in animal models of the disease.

Methods

A systematic search strategy, devised using relevant matrix, tissue, and disease nomenclature, was run through the MEDLINE, Embase, and Scopus databases. Demographic, clinical, and biological data were extracted from eligible studies. Bias analysis was performed.

Results

A total of 161 studies were included, which covered capsule, ligaments, meniscus, skeletal muscle, synovium, and tendon in both humans and animals, and fat pad and intervertebral disc in humans only. These studies covered a wide variety of ECM features, including individual ECM components (i.e. collagens, proteoglycans, and glycoproteins), ECM architecture (i.e. collagen fibre organization and diameter), and viscoelastic properties (i.e. elastic and compressive modulus). Some ECM changes, notably calcification and the loss of collagen fibre organization, have been extensively studied across osteoarthritic tissues. However, most ECM features were only studied by one or a few papers in each tissue. When comparisons were possible, the results from animal experiments largely concurred with those from human studies, although some findings were contradictory.

Conclusion

Changes in ECM composition and architecture occur throughout non-cartilage soft tissues in the osteoarthritic joint, but most of these remain poorly defined due to the low number of studies and lack of healthy comparator groups.

Proteoglycans Enhance the Therapeutic Effect of BMSC Transplantation on Osteoarthritis

BACKGROUND

The injection of bone mesenchymal stem cells (BMSCs) for osteoarthritis (OA) treatment fails to address the disrupted extracellular microenvironment, limiting the differentiation and paracrine functions of BMSCs and resulting in suboptimal therapeutic outcomes. Proteoglycans (PGs) promote cell differentiation, tissue repair, and microenvironment remodeling. This study investigated the potential of combining PGs with BMSCs to increase the efficacy of OA treatment.

METHODS

We evaluated the effects of PG on BMSC and chondrocyte functions by adding various PG concentrations to the culture media. Additionally, a Transwell system was used to assess the impact of PG on the communication between BMSCs and chondrocytes. The results of the in vitro experiment were verified by tissue staining and immunohistochemistry following the treatment of OA model rats.

RESULTS

Our findings indicate that PG effectively induces Col II expression in BMSCs and enhances the paracrine secretion of TGF-β1, thereby activating the TGF-β signaling pathway in chondrocytes and increasing PRG4 gene expression. Compared with the other groups, the BMSC/PG treatment group presented a smoother articular surface and more robust extracellular matrix than the other groups in vivo, with significantly increased expression and distribution of Smad2/3 and PRG4.

CONCLUSIONS

PG enhances BMSC differentiation into chondrocytes and stimulates paracrine TGF-β1 secretion. Proteoglycans not only promote chondrocyte differentiation and paracrine TGF-β1 signaling in BMSCs but also increase the sensitivity of chondrocytes to TGF-β1 secreted from BMSCs, leading to PRG4 expression through the TGFR/Smad2/3 pathway. Proteoglycans can enhance the therapeutic effect of BMSC treatment on OA and have the potential to delay the degeneration of OA cartilage.

The Presentation, Clinical Diagnosis, Risk Factors, and Management of Rapidly Progressive Hip Osteoarthritis: A Narrative Literature Review

Rapidly progressive hip osteoarthritis (RPOH) is a rare and severe form of osteoarthritis (OA), marked by the rapid degeneration and destruction of the femoral head, often within months. Despite its unclear etiology, several factors such as subchondral fractures and immune responses have been proposed as possible contributors. This narrative review aims to synthesize current knowledge on the pathogenesis, risk factors, clinical presentation, imaging features, and grading systems of RPOH. Predominantly affecting elderly females, RPOH presents distinctive challenges in both diagnosis and management due to its abrupt onset and severity. Known risk factors include advanced age, female gender, obesity, intra-articular corticosteroids use, and long-term hemodialysis. Clinically, RPOH is characterized by severe pain during active weight-bearing movements, despite patients presenting a normal range of motion during passive examination in the early stages. While several classification systems exist, there is no universal standard, complicating differential diagnosis and clinical approaches. This review emphasizes the necessity for early diagnostic methods utilizing specific biomarkers, rapid differential diagnosis, and targeted, personalized interventions based on individual risk factors.

Protective Effects of Vitamin D on Proteoglycans of Human Articular Chondrocytes through TGF-β1 Signaling

The extracellular matrix of cartilage primarily constitutes of collagen and aggrecan. Cartilage degradation starts with aggrecan loss in osteoarthritis (OA). Vitamin D (VD) plays an essential role in several inflammation-related diseases and can protect the collagen in cartilage during OA. The present study focused on the role of VD in aggrecan turnover of human articular chondrocytes treated with tumor necrosis factor α (TNF-α) and the possible mechanism. Treatment with different doses of VD and different periods of intervention with TNF-α and TGF-β1 receptor (TGFβR1) inhibitor SB525334 were investigated. The viability of human chondrocytes and extracellular secretion of TGF-β1 were measured. The expression of intracellular TGFβR1 and VD receptor was examined. Transcriptional and translational levels of aggrecan and the related metabolic factors were analyzed. The results showed that TNF-α markedly reduced the viability, TGFβR1 expressions and aggrecan levels of human chondrocytes, and increased disintegrin and metalloproteinase with thrombospondin motifs. The alterations were partially inhibited by VD treatment. Furthermore, the effects of VD were blocked by the TGFβR1 inhibitor SB525334 in TNF-α-treated cells. VD may prevent proteoglycan loss due to TNF-α via TGF-β1 signaling in human chondrocytes.

Proteomics in orthopedic research: Recent studies and their translational implications

Proteomics is a growing field that offers insights into various aspects of disease processes and therapy responses. Within the field of orthopedics, there are a variety of diseases that have a poor prognosis due to a lack of targeted curative therapy or disease modifying therapy. Other diseases have been difficult to manage in part due to lack of clinical biomarkers that offer meaningful insight into disease progression or severity. As an emerging technology, proteomics has been increasingly applied in studying bone biology and an assortment of orthopedics related diseases, such as osteoarthritis, osteosarcoma and bone tumors, osteoporosis, traumatic bone injury, spinal cord injury, hip and knee arthroplasty, and fragile healing. These efforts range from mechanistic studies for elucidating novel insights in tissue activity and metabolism to identification of candidate biomarkers for diagnosis, prognosis, and targeted treatment. The knowledge gained from these proteomic and functional studies has provided unique perspectives in studying orthopedic diseases. In this review, we seek to report on the current state of the proteomic study in the field of orthopedics, overview the advances in clinically applicable discoveries, and discuss the opportunities that may guide us for future research.

Articular cartilage repair biomaterials: strategies and applications

Articular cartilage injury is a frequent worldwide disease, while effective treatment is urgently needed. Due to lack of blood vessels and nerves, the ability of cartilage to self-repair is limited. Despite the availability of various clinical treatments, unfavorable prognoses and complications remain prevalent. However, the advent of tissue engineering and regenerative medicine has generated considerable interests in using biomaterials for articular cartilage repair. Nevertheless, there remains a notable scarcity of comprehensive reviews that provide an in-depth exploration of the various strategies and applications. Herein, we present an overview of the primary biomaterials and bioactive substances from the tissue engineering perspective to repair articular cartilage. The strategies include regeneration, substitution, and immunization. We comprehensively delineate the influence of mechanically supportive scaffolds on cellular behavior, shedding light on emerging scaffold technologies, including stimuli-responsive smart scaffolds, 3D-printed scaffolds, and cartilage bionic scaffolds. Biologically active substances, including bioactive factors, stem cells, extracellular vesicles (EVs), and cartilage organoids, are elucidated for their roles in regulating the activity of chondrocytes. Furthermore, the composite bioactive scaffolds produced industrially to put into clinical use, are also explicitly presented. This review offers innovative solutions for treating articular cartilage ailments and emphasizes the potential of biomaterials for articular cartilage repair in clinical translation.

Long Non-coding RNA DLEU1 Promotes Progression of Osteoarthritis via miR-492/TLR8 Axis

BACKGROUND

Long non-coding RNAs (LncRNAs) are generally reported to participate in the development of Osteoarthritis (OA) by acting as competing endogenous RNAs (ceRNAs). However, the molecular mechanism is largely unknown. This study aimed to investigate the possible mechanisms contributing to osteoarthritis (OA).

METHODS

Four gene expression profiles from patients with OA were downloaded from a public database and integrated to screen important RNAs associated with OA. Differentially expressed (DE) lncRNAs, microRNAs (miRNAs), and mRNAs were filtered, and a ceRNA network was constructed. An in vitro OA model was established by treating chondrocytes with IL-1β. The expression levels of MMP-13, COL2A1, aggrecan, and RUNX2 were detected by qRT-PCR and western blot. Cell proliferation ability was detected by CCK-8 assay. Flow cytometry was used for apoptosis assay. A dual luciferase reporter gene was used to confirm the relationship between DLEU1, miR-492, and TLR8.

RESULTS

An OA-related ceRNA network, including 11 pathways, 3 miRNAs, 7 lncRNAs, and 16 mRNAs, was constructed. DLEU1 and TLR8 were upregulated, and miR-492 was downregulated in IL-1β-induced chondrocytes. Overexpression of DLEU1 suppressed viability and promoted apoptosis and extracellular matrix (ECM) degradation in IL-1β induced chondrocytes. Luciferase reporter assay validated the regulatory relations among DLEU1, miR-492, and TLR8. Further study revealed that the effects of DLEU1 on chondrocytes could be reversed by miR-492.

CONCLUSION

DLEU1 may be responsible for the viability, apoptosis, and ECM degradation in OA via miR-492/TLR8 axis.

PG545 Prevents Osteoarthritis Development by Regulating PI3K/AKT/mTOR Signaling and Activating Chondrocyte Autophagy

INTRODUCTION

Osteoarthritis (OA) is a degenerative disease common in the elderly and is characterized by joint pain, swelling, and restricted movement. In recent years, heparanase has been reported to play an important role in the development of osteoarthritic cartilage. PG545 is a heparan sulfate mimetic with heparanase inhibitory activity. In this study, the therapeutic effects and possible mechanisms of PG545 were investigated in a chondrocyte injury model induced by interleukin-1β (IL -1β).

METHODS

Following treatment with PG545 or the autophagy inhibitor 3-methyladenine (3-MA), chondrocyte viability was detected using Cell Counting Kit-8 and fluorescein diacetate/propidium iodide double staining. The apoptosis rate of chondrocytes was determined by flow cytometry. Expression of light chain 3 and P62 was monitored by immunofluorescence labeling. Western blot, lentivirus infection with red fluorescent protein and green fluorescent protein, and quantitative real-time polymerase chain reaction were used to determine the expression levels of chondrocyte markers, apoptosis-related factors, autophagy proteins, and key proteins of the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway. The expression and activity of stress-specific enzymes such as malondialdehyde, superoxide dismutase, and catalase (CAT) were investigated. Chondrocytes with ATG5 knockdown were used to investigate the relationship between the therapeutic effect of PG545 and autophagy. The therapeutic effect of PG545 was verified in vivo.

RESULTS

PG545 had a significant protective effect on chondrocytes by reducing oxidative stress, apoptosis, and degradation of chondrocytes and increasing chondrocyte proliferation. PG545 was effective in inducing autophagy in IL-1β-treated cells, while 3-MA attenuated the effect. The PI3K/Akt/mTOR pathway may be involved in the promotion of autophagy and OA treatment by PG545.

CONCLUSION

PG545 was able to restore impaired autophagy and autophagic flux via the PI3K/Akt/mTOR pathway, thereby delaying the progression of OA, suggesting that PG545 may be a novel therapeutic approach for OA.

Mesenchymal progenitor cells from non-inflamed versus inflamed synovium post-ACL injury present with distinct phenotypes and cartilage regeneration capacity

BACKGROUND

Osteoarthritis (OA) is a chronic debilitating disease impacting a significant percentage of the global population. While there are numerous surgical and non-invasive interventions that can postpone joint replacement, there are no current treatments which can reverse the joint damage occurring during the pathogenesis of the disease. While many groups are investigating the use of stem cell therapies in the treatment of OA, we still don't have a clear understanding of the role of these cells in the body, including heterogeneity of tissue resident adult mesenchymal progenitor cells (MPCs).

METHODS

In the current study, we examined MPCs from the synovium and individuals with or without a traumatic knee joint injury and explored the chondrogenic differentiation capacity of these MPCs in vitro and in vivo.

RESULTS

We found that there is heterogeneity of MPCs with the adult synovium and distinct sub-populations of MPCs and the abundancy of these sub-populations change with joint injury. Furthermore, only some of these sub-populations have the ability to effect cartilage repair in vivo. Using an unbiased proteomics approach, we were able to identify cell surface markers that identify this pro-chondrogenic MPC population in normal and injured joints, specifically CD82^LowCD59⁺ synovial MPCs have robust cartilage regenerative properties in vivo.

CONCLUSIONS

The results of this study clearly show that cells within the adult human joint can impact cartilage repair and that these sub-populations exist within joints that have undergone a traumatic joint injury. Therefore, these populations can be exploited for the treatment of cartilage injuries and OA in future clinical trials.