Osteoarthritis as an organ disease: from the cradle to the grave

Gene expression and immune infiltration analysis comparing lesioned and preserved subchondral bone in osteoarthritis

Background

Osteoarthritis (OA) is a degenerative disease requiring additional research. This study compared gene expression and immune infiltration between lesioned and preserved subchondral bone. The results were validated using multiple tissue datasets and experiments.

Methods

Differentially expressed genes (DEGs) between the lesioned and preserved tibial plateaus of OA patients were identified in the GSE51588 dataset. Moreover, functional annotation and protein-protein interaction (PPI) network analyses were performed on the lesioned and preserved sides to explore potential therapeutic targets in OA subchondral bones. In addition, multiple tissues were used to screen coexpressed genes, and the expression levels of identified candidate DEGs in OA were measured by quantitative real-time polymerase chain reaction. Finally, an immune infiltration analysis was conducted.

Results

A total of 1,010 DEGs were identified, 423 upregulated and 587 downregulated. The biological process (BP) terms enriched in the upregulated genes included "skeletal system development", "sister chromatid cohesion", and "ossification". Pathways were enriched in "Wnt signaling pathway" and "proteoglycans in cancer". The BP terms enriched in the downregulated genes included "inflammatory response", "xenobiotic metabolic process", and "positive regulation of inflammatory response". The enriched pathways included "neuroactive ligand-receptor interaction" and "AMP-activated protein kinase signaling". JUN, tumor necrosis factor α, and interleukin-1β were the hub genes in the PPI network. Collagen XI A1 and leucine-rich repeat-containing 15 were screened from multiple datasets and experimentally validated. Immune infiltration analyses showed fewer infiltrating adipocytes and endothelial cells in the lesioned versus preserved samples.

Conclusion

Our findings provide valuable information for future studies on the pathogenic mechanism of OA and potential therapeutic and diagnostic targets.

Human Umbilical Cord Mesenchymal Stem Cells Alleviate Rat Knee Osteoarthritis via Activating Wnt/ β-catenin Signaling Pathway

BACKGROUND

Osteoarthritis (OA) is a chronic disease characterized by joint cartilage degeneration, destruction, and osteogenic hyperplasia. Human umbilical cord mesenchymal stem cells (hUCMSCs) have attracted increasing research interest due to their high clonogenic, proliferative, and migratory potential, as well as their improved secretion of relevant chondrogenic factors. This study evaluated the therapeutic potential and underlying mechanism of hUC-MSCs in alleviating pathological symptoms of OA.

METHODS

For the in vivo study, OA rats were established by the Hulth method to observe the therapeutic effect of intra-articular injection of hUC-MSCs. X-ray tests, gross observations, and histological and immunohistochemical assessments were conducted in rats. Levels of interleukin-1 beta (IL-1β), IL-6, matrix metalloproteinase-13 (MMP-13), and tissue inhibitor matrix metalloproteinase-1 in rats' synovial fluid were measured using enzyme-linked immunosorbent assay kits. For the in vitro study, hUC-MSCs and chondrocytes were cultured to explore the effect and underlying mechanisms of hUC-MSCs on OA. Apoptosis, proliferation, and glycosaminoglycan (GAG) were measured in the chondrocytes. The relative expression of aggrecan, COL-2, and SOX-9 mRNA was quantified by real-time polymerase chain reaction. Expressions of Wnt/β-catenin signaling molecules were measured by Western blot.

RESULTS

We found that intra-articular injection of hUC-MSCs reduced the combined score, increased the expression of collagen II, and decreased the expression of MMP-13, IL-1β, and IL-6 in rat knee joints. Additionally, hUC-MSCs increased the content of GAGs, inhibited chondrocyte apoptosis, and promoted chondrocyte proliferation. The expression of aggrecan, COL-2, and SOX-9 mRNA in chondrocytes was promoted by hUC-MSCs via activation of the Wnt/β-catenin signaling pathway.

CONCLUSION

Overall, this study demonstrated that hUC-MSCs induce the secretion of some cytokines via the paracrine function to activate the Wnt/β-catenin signaling pathway to reduce the pathological condition of OA and maintain the proper expression of cytokines and extracellular matrix proteins.

A Zebrafish Mutant in the Extracellular Matrix Protein Gene efemp1 as a Model for Spinal Osteoarthritis

Osteoarthritis is a degenerative articular disease affecting mainly aging animals and people. The extracellular matrix protein Efemp1 was previously shown to have higher turn-over and increased secretion in the blood serum, urine, and subchondral bone of knee joints in osteoarthritic patients. Here, we use the zebrafish as a model system to investigate the function of Efemp1 in vertebrate skeletal development and homeostasis. Using in situ hybridization, we show that the efemp1 gene is expressed in the brain, the pharyngeal arches, and in the chordoblasts surrounding the notochord at 48 hours post-fertilization. We generated an efemp1 mutant line, using the CRISPR/Cas9 method, that produces a severely truncated Efemp1 protein. These mutant larvae presented a medially narrower chondrocranium at 5 days, which normalized later at day 10. At age 1.5 years, µCT analysis revealed an increased tissue mineral density and thickness of the vertebral bodies, as well as a decreased distance between individual vertebrae and ruffled borders of the vertebral centra. This novel defect, which has, to our knowledge, never been described before, suggests that the efemp1 mutant represents the first zebrafish model for spinal osteoarthritis.

CaSR modulates proliferation of the superficial zone cells in temporomandibular joint cartilage via the PTHrP nuclear localization sequence

The superficial zone cells in mandibular condylar cartilage are proliferative. The present purpose was to delineate the relation of calcium-sensing receptor (CaSR) and parathyroid hormone-related peptide nuclear localization sequence (PTHrP87-139 ), and their role in the proliferation behaviors of the superficial zone cells. A gain- and loss-of-function strategy were used in an in vitro fluid flow shear stress (FFSS) model and an in vivo bilateral elevation bite model which showed mandibular condylar cartilage thickening. CaSR and PTHrP87-139 were modulated through treating the isolated superficial zone cells with activator/SiRNA and via deleting CaSR or parathyroid hormone-related peptide (PTHrP) gene in mice with the promoter gene of proteoglycan 4 (Prg4-CreERT2 ) in the tamoxifen-inducible pattern with or without additional injection of Cinacalcet, the CaSR agonist, or PTHrP87-139 peptide. FFSS stimulated CaSR and PTHrP expression, and accelerated proliferation of the Prg4-expressing superficial zone cells, in which process CaSR acted as an up-streamer of PTHrP. Proteoglycan 4 specific knockout of CaSR or PTHrP reduced the cartilage thickness, suppressed the proliferation and early differentiation of the superficial zone cells, and inhibited cartilage thickening and matrix production promoted by bilateral elevation bite. Injections of CaSR agonist Cinacalcet could not improve the phenotype caused by PTHrP mutation. Injections of PTHrP87-139 peptide rescued the cartilage from knockout of CaSR gene. CaSR modulates proliferation of the superficial zone cells in mandibular condylar cartilage through activation of PTHrP nuclear localization sequence. Our data support the therapeutic target of CaSR in promoting PTHrP production in superficial zone cartilage.

Mediation of the Same Epigenetic and Transcriptional Effect by Independent Osteoarthritis Risk-Conferring Alleles on a Shared Target Gene, COLGALT2

OBJECTIVE

Over 100 DNA variants have been associated with osteoarthritis (OA), including rs1046934, located within a linkage disequilibrium block encompassing part of COLGALT2 and TSEN15. The present study was undertaken to determine the target gene(s) and the mechanism of action of the OA locus using human fetal cartilage, cartilage from OA and femoral neck fracture arthroplasty patients, and a chondrocyte cell model.

METHODS

Genotyping and methylation array data of DNA from human OA cartilage samples (n = 87) were used to determine whether the rs1046934 genotype is associated with differential DNA methylation at proximal CpGs. Results were replicated in DNA from human arthroplasty (n = 132) and fetal (n = 77) cartilage samples using pyrosequencing. Allelic expression imbalance (AEI) measured the effects of genotype on COLGALT2 and TSEN15 expression. Reporter gene assays and epigenetic editing determined the functional role of regions harboring differentially methylated CpGs. In silico analyses complemented these experiments.

RESULTS

Three differentially methylated CpGs residing within regulatory regions were detected in the human OA cartilage array data, and 2 of these were replicated in human arthroplasty and fetal cartilage. AEI was detected for COLGALT2 and TSEN15, with associations between expression and methylation for COLGALT2. Reporter gene assays confirmed that the CpGs are in chondrocyte enhancers, with epigenetic editing results directly linking methylation with COLGALT2 expression.

CONCLUSION

COLGALT2 is a target of this OA locus. We previously characterized another OA locus, marked by rs11583641, that independently targets COLGALT2. The genotype of rs1046934, like rs11583641, mediates its effect by modulating expression of COLGALT2 via methylation changes to CpGs located in enhancers. Although the single-nucleotide polymorphisms, CpGs, and enhancers are distinct between the 2 independent OA risk loci, their effect on COLGALT2 is the same. COLGALT2 is the target of independent OA risk loci sharing a common mechanism of action.

Exosomal miR-429 derived from adipose-derived stem cells ameliorated chondral injury in osteoarthritis via autophagy by targeting FEZ2

BACKGROUND

Osteoarthritis (OA) is the most prevalent musculoskeletal disease, imposing a significant public health burden. Exosomes might be an effective means of treating OA.

PURPOSE

To investigate the role of exosomes from adipose tissue-derived stromal cells (ADSCs) in OA. We explored whether exosomes from ADSCs could be absorbed by OA chondrocytes, whether there were differences in miR-429 expression in the exosomes of ADSCs and chondrocytes, and whether ADSC exosomal miR-429 could enhance chondrocyte proliferation to exert therapeutic effects in OA.

STUDY DESIGN

Controlled laboratory study.

METHODS

ADSCs were isolated and cultured from 4-week-old Sprague-Dawley rats. ADSCs and chondrocytes were identified by flow cytometry assay and fluorescent staining, respectively. The exosomes were extracted and identified. Exosome transport was verified by cell staining and co-culture. Beclin 1, collagen II, LC3-II/I, miR-429, and FEZ2 mRNA and protein expression were investigated with real-time PCR and western blotting, respectively. Chondrocyte proliferation was investigated with Cell Counting Kit-8 (CCK-8) assay. The association between miR-429 and FEZ2 was verified with luciferase assay. A rat OA model was established and rat knee joint cartilage tissue was examined with hematoxylin-eosin and toluidine blue staining.

RESULTS

Both ADSCs and chondrocytes secreted exosomes and ADSC-derived exosomes could be absorbed by the chondrocytes. ADCS exosomes contained higher miR-429 levels than chondrocyte exosomes. The luciferase assay demonstrated that miR-429 directly targeted FEZ2. Compared with the OA group, miR-429 promoted chondrocyte proliferation while FEZ2 decreased it. miR-429 promoted autophagy by targeting FEZ2 to ameliorate cartilage injury. In vivo, miR-429 promoted autophagy to alleviate OA by targeting FEZ2.

CONCLUSION

ADSC exosomes could be beneficial for OA and could be absorbed by chondrocytes to promote chondrocyte proliferation through miR-429. miR-429 ameliorated cartilage injury in OA by targeting FEZ2 and promoting autophagy.

Kartogenin Induced Adipose-Derived Stem Cell Exosomes Enhance the Chondrogenic Differentiation Ability of Adipose-Derived Stem Cells

Objective

The objective of this study is to explore the effect of kartogenin (KGN-)-pretreated adipose-derived stem cell-derived exosomes (ADSC-EXOs) on the chondrogenic differentiation ability of ADSCs.

Methods

Adipose-derived stem cells (ADSCs) were treated with different doses of KGN, and exosomes (EXOs) were extracted. EXOs were then identified using an electron microscope (EM), nanoparticle tracking analyzer, nanoparticle tracking analysis software, and exosomal protein markers. EXOs were labeled with the fluorescent dye PKH67 and their uptake by cells was evaluated. A cell counting kit-8 (CCK-8) assay, flow cytometry, clonogenic assay, and a cell scratch assay were used to detect the abilities of proliferation, apoptosis, clone formation, and migration of ADSCs, respectively. Subsequently, Alcian blue staining and toluidine blue staining were used to detect the chondrogenic differentiation ability of ADSCs in each group. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot (WB) techniques were used to detect the expression of chondrogenic differentiation-related genes.

Results

In this study, ADSCs and KGN-induced ADSC-EXOs were successfully extracted and isolated. EXOs and ADSCs coculturing results showed that KGN-induced ADSC-EXOs can significantly promote proliferation, clone formation, migration, and chondrogenic differentiation of ADSCs and inhibit apoptosis. In addition, KGN-induced ADSC-EXOs can increase the expression of chondrogenic-related genes in ADSCs (Aggrecan, Collagen III, Collagen II, and SOX9), and can significantly decrease the expression of chondrolysis-related genes (MMP-3, ADAMTS4, and ADAMTS5).

Conclusion

KGN-induced ADSC-EXOs can enhance the chondrogenic differentiation ability of ADSCs by promoting cell proliferation and migration while inhibiting cell apoptosis. KGN treatment can also increase the expression of chondrogenic differentiation-related genes and decrease the expression of chondrolysis-related genes. These results provide a new approach to cartilage repair and regeneration.

Translating osteoarthritis genetics research: challenging times ahead

The ultimate goal of molecular genetic studies of human diseases is to translate the discoveries for patient benefit. For diseases that lack licensed disease-modifying therapeutics, such as osteoarthritis (OA), the need is acute. OA is polygenic and affects older individuals, with a recent genome-wide study of over 800 000 individuals adding 52 novel association signals to those already reported on for this common arthritis. Many of the predicted effector genes of these signals encode proteins that are targets of drugs for other indications, highlighting repurposing opportunities. Here, the potential for OA genetic data to translate is discussed, including whether the developmental origin of OA will limit the application of genetic risk data for disease-modification purposes.

Temporal extracellular vesicle protein changes following intraarticular treatment with integrin α10β1-selected mesenchymal stem cells in equine osteoarthritis

Introduction

Equine osteoarthritis (OA) is a heterogeneous, degenerative disease of the musculoskeletal system with multifactorial causation, characterized by a joint metabolic imbalance. Extracellular vesicles are nanoparticles involved in intracellular communication. Mesenchymal stem cell (MSC) therapy is a form of regenerative medicine that utilizes their properties to repair damaged tissues. Despite its wide use in veterinary practice, the exact mechanism of action of MSCs is not fully understood. The aim of this study was to determine the synovial fluid extracellular vesicle protein cargo following integrin α10β1-selected mesenchymal stem cell (integrin α10-MSC) treatment in an experimental model of equine osteoarthritis with longitudinal sampling.

Methods

Adipose tissue derived, integrin α10-MSCs were injected intraarticularly in six horses 18 days after experimental induction of OA. Synovial fluid samples were collected at day 0, 18, 21, 28, 35, and 70. Synovial fluid was processed and extracellular vesicles were isolated and characterized. Extracellular vesicle cargo was then analyzed using data independent acquisition mass spectrometry proteomics.

Results

A total of 442 proteins were identified across all samples, with 48 proteins differentially expressed (FDR ≤ 0.05) between sham-operated control joint without MSC treatment and OA joint treated with MSCs. The most significant pathways following functional enrichment analysis of the differentially abundant protein dataset were serine endopeptidase activity (p = 0.023), complement activation (classical pathway) (p = 0.023), and collagen containing extracellular matrix (p = 0.034). Due to the lack of an OA group without MSC treatment, findings cannot be directly correlated to only MSCs.

Discussion

To date this is the first study to quantify the global extracellular vesicle proteome in synovial fluid following MSC treatment of osteoarthritis. Changes in the proteome of the synovial fluid-derived EVs following MSC injection suggest EVs may play a role in mediating the effect of cell therapy through altered joint homeostasis. This is an important step toward understanding the potential therapeutic mechanisms of MSC therapy, ultimately enabling the improvement of therapeutic efficacy.

The relationship between common variants in the DPEP1 gene and the susceptibility and clinical severity of osteoarthritis

AIM

Previous studies have provided evidence linking the DPEP1 gene to the risk of osteoarthritis (OA) in Europeans. In this study, we aimed to examine the relationship between DPEP1 gene and the susceptibility and clinical severity of OA in a Chinese Han population.

METHODS

This study comprised two independent samples. For the discovery stage, 1022 patients with knee OA and 1864 controls were recruited. Fourteen tag single nucleotide polymorphisms (SNPs) covering the DPEP1 gene were selected and genotyped. Associated SNPs in the discovery data set were subsequently genotyped in the replication data set consisting of 826 hip OA cases and 1662 controls. Both genotypic and allelic genetic associations were tested. The relationship of significant SNPs to the expression of DPEP1 and its neighboring genes was examined using the GTEx database.

RESULTS

A nonsynonymous SNP, rs1126464, was determined to be associated with the disease status of OA in both the discovery and replication stages (odds ratio [OR] 0.75, 95% confidence interval [95% CI] 0.68-0.82, P = 7.16 × 10^-11 ). This SNP was further characterized as being significantly related to a higher Kellgren-Lawrence grade in OA patients (OR 0.64, 95% CI 0.55-0.74, P = 2.53 × 10^-9 ). According to the GTEx data, SNP rs1126464 was significantly related to the gene expression of 15 genes in multiple types of human tissues.

CONCLUSION

We reported a common DNA variant in the DPEP1 gene that contributes to the risk of OA, providing additional evidence that the DPEP1 gene plays a significant role in the pathological mechanisms of OA.

Recapitulating monocyte extravasation to the synovium in an organotypic microfluidic model of the articular joint

The synovium of osteoarthritis (OA) patients can be characterized by an abnormal accumulation of macrophages originating from extravasated monocytes. Since targeting monocyte extravasation may represent a promising therapeutic strategy, our aim was to develop an organotypic microfluidic model recapitulating this process. Synovium and cartilage were modeled by hydrogel-embedded OA synovial fibroblasts and articular chondrocytes separated by a synovial fluid channel. The synovium compartment included a perfusable endothelialized channel dedicated to monocyte injection. Monocyte extravasation in response to chemokines and OA synovial fluid was quantified. The efficacy of chemokine receptor antagonists, RS-504393 (CCR2 antagonist) and Cenicriviroc (CCR2/CCR5 antagonist) in inhibiting extravasation was tested pre-incubating monocytes with the antagonists before injection. After designing and fabricating the chip, culture conditions were optimized to achieve an organotypic model including synovial fibroblasts, articular chondrocytes, and a continuous endothelial monolayer expressing intercellular adhesion molecule-1 and vascular cell adhesion molecule-1. A significantly higher number of monocytes extravasated in response to the chemokine mix (p< 0.01) and OA synovial fluid (p< 0.01), compared to a control condition. In both cases, endothelium pre-activation enhanced monocyte extravasation. The simultaneous blocking of CCR2 and CCR5 proved to be more effective (p< 0.001) in inhibiting monocyte extravasation in response to OA synovial fluid than blocking of CCR2 only (p< 0.01). The study of extravasation in the model provided direct evidence that OA synovial fluid induces monocytes to cross the endothelium and invade the synovial compartment. The model can be exploited either to test molecules antagonizing this process or to investigate the effect of extravasated monocytes on synovium and cartilage cells.

Primary culture of chondrocytes after collagenase IA or II treatment of articular cartilage from elderly patients undergoing arthroplasty

Background

Joint replacement surgery provides articular cartilage samples for chondrocyte isolation. To our knowledge, the effect of the collagenase type on releasing of chondrocytes from the extracellular matrix of cartilage is not reported.

Objectives

To determine whether cartilage digested with collagenase IA yielded more chondrocytes than that digested with collagenase II and determine whether chondrocytes isolated with collagenase IA could be cultured in vitro.

Methods

Cartilage slices collected from 18 elderly patients who received joint replacement surgery (16 hips, 2 knees) were digested sequentially with 0.4% pronase E and 0.02% collagenase IA, or with 0.15% collagenase II alone, or sequentially with 0.4% pronase E and 0.02% collagenase II. We compared cell yield from each method. Cell viability by the most effective method was calculated and plotted. The morphology of cultured monolayer chondrocytes was recorded with a light microscope.

Results

Sequential digestion with pronase E and collagenase IA yielded 2566 ± 873 chondrocytes per mg wet cartilage, which was more effective than the other isolation methods (P = 0.018). The average chondrocyte viability could reach 84% ± 8% (n = 11). Light microscopic images showed typical chondrocyte morphology in monolayer cultures.

Conclusion

Sequential digestion of human articular cartilage with pronase E and collagenase IA was more effective than collagenase II alone or collagenase II combined with pronase E for releasing chondrocytes from extracellular matrix of cartilage. Chondrocytes isolated with this method could be maintained in monolayer cultures for at least 2 passages with unaltered morphology.

Progress in the use of mesenchymal stromal cells for osteoarthritis treatment

LITERATURE REVIEW OF MSCS IN THE TREATMENT OF OSTEOARTHRITIS IN THE PAST FIVE YEARS: Osteoarthritis (OA) is one of the most common chronic joint diseases, with prominent symptoms caused by many factors. However, current medical interventions for OA have resulted in poor clinical outcomes, demonstrating that there are huge unmet medical needs in this area. Cell therapy has opened new avenues of OA treatment. Different sources of mesenchymal stromal cells (MSCs) may have different phenotypes and cellular functions. Pre-clinical and clinical studies have demonstrated the feasibility, safety and efficacy of MSC therapy. Mitogen-activated protein kinase, Wnt and Notch signaling pathways are involved in the chondrogenesis of MSC-mediated treatments. MSCs may also exert effective immunoregulatory and paracrine effects to stimulate tissue repair. Therapy with extracellular vesicles containing cytokines, which are secreted by MSCs, might be a potential treatment for OA.

Exosomes from Kartogenin-Pretreated Infrapatellar Fat Pad Mesenchymal Stem Cells Enhance Chondrocyte Anabolism and Articular Cartilage Regeneration

Objective

To evaluate the effect of Kartogenin-pretreated exosomes derived from infrapatellar fat pad mesenchymal stem cells on chondrocyte in vitro and articular cartilage regeneration in vivo.

Methods

Infrapatellar fat pad mesenchymal stem cells (IPFP-MSCs) were isolated from rabbits to harvest exosomes. After identification of mesenchymal stem cells and exosomes, rabbit chondrocytes were divided into three groups for further treatment: the EXO group (chondrocytes treated with exosomes isolated from infrapatellar fat pad mesenchymal stem cells), KGN-EXO group (chondrocytes treated with exosomes isolated from infrapatellar fat pad mesenchymal stem cells pretreated with KGN), and control group. After processing and proliferation, phenotypic changes of chondrocytes were measured. In the in vivo study, 4 groups of rabbits with articular cartilage injury were treated with KGN-EXO, EXO, IPFP-MSCs, and control. Macroscopic evaluation and histological evaluation were made to figure out the different effects of the 4 groups on cartilage regeneration in vivo.

Results

The proliferation rate of chondrocytes in the EXO or KGN-EXO group was significantly higher than that in the control group (P < 0.05). The qRT-PCR results showed that the expression of Sox-9, Aggrecan, and Col II was the highest in the KGN-EXO group compared with the EXO group and the control group (P < 0.05). The results of Western blot were consistent with the results of qRT-PCR. In vivo, the cartilage defects in the KGN-EXO group showed better gross appearance and improved histological score than those in IPFP-MSC groups, EXO groups, and control groups (P < 0.05). At 12 weeks, the defect site in the KGN-EXO group was almost completely repaired with a flat and smooth surface, while a large amount of hyaline cartilage-like structures and no obvious cracks were observed.

Conclusion

Our study demonstrates that the exosomes isolated from infrapatellar fat pad mesenchymal stem cells pretreated with KGN have potent ability to induce chondrogenic differentiation of stem cells, effectively promoting the proliferation and the expression of chondrogenic proteins and genes of chondrocytes. The KGN-EXO can also promote the repair of articular cartilage defects more effectively, which can be used as a potential therapeutic method in the future.

Potential of Exosomes for Diagnosis and Treatment of Joint Disease: Towards a Point-of-Care Therapy for Osteoarthritis of the Knee

In the knee joint, articular cartilage injury can often lead to osteoarthritis of the knee (OAK). Currently, no point-of-care treatment can completely address OAK symptoms and regenerate articular cartilage to restore original functions. While various cell-based therapies are being developed to address OAK, exosomes containing various components derived from their cells of origin have attracted attention as a cell-free alternative. The potential for exosomes as a novel point-of-care treatment for OAK has been studied extensively, especially in the context of intra-articular treatments. Specific exosomal microRNAs have been identified as possibly effective in treating cartilage defects. Additionally, exosomes have been studied as biomarkers through their differences in body fluid composition between joint disease patients and healthy subjects. Exosomes themselves can be utilized as a drug delivery system through their manipulation and encapsulation of specific contents to be delivered to specific cells. Through the combination of exosomes with tissue engineering, novel sustained release drug delivery systems are being developed. On the other hand, many of the functions and activities of exosomes are unknown and challenges remain for clinical applications. In this review, the possibilities of intra-articular treatments utilizing exosomes and the challenges in using exosomes in therapy are discussed.

Fraxetin inhibits interleukin-1β-induced apoptosis, inflammation, and matrix degradation in chondrocytes and protects rat cartilage in vivo

Osteoarthritis (OA) is a disease characterized by degeneration of the joint complex due to cartilage destruction. Fraxetin, a widely used and studied coumarin compound extracted from a traditional Chinese herb (Qin Pi), has shown anti-inflammatory and antioxidant properties, but its effects on OA have not been studied. In the present study, western blotting, immunofluorescence, and terminal deoxynucleotidyl transferase (TdT) dUTP nick-end labeling (TUNEL) were used to evaluate the effects of fraxetin on IL-1β-induced apoptotic activity, inflammatory responses, and catabolism in rat chondrocytes. The results showed that fraxetin prevented IL-1β-induced apoptosis of chondrocytes and inhibited inflammatory mediator release by regulating the Toll-like receptor 4 (TLR4)/myeloid differentiation primary response 88 (MyD88)/nuclear factor (NF)-κB pathway in chondrocytes. Additionally, fraxetin suppressed the upregulation of matrix metalloproteinase 13 (MMP13) and degradation of collagen II in the extracellular matrix (ECM). Moreover, the effects of fraxetin in vivo were assessed in a monosodium iodoacetate (MIA)-induced rat model of OA using hematoxylin and eosin (H&E) and Safranin O-fast green staining and magnetic resonance imaging (MRI). The results showed that fraxetin protected the cartilage against destruction. In conclusion, fraxetin could be a potential therapeutic for OA.

Immunomodulation of MSCs and MSC-Derived Extracellular Vesicles in Osteoarthritis

Osteoarthritis (OA) has become recognized as a low-grade inflammatory state. Inflammatory infiltration of the synovium by macrophages, T cells, B cells, and other immune cells is often observed in OA patients and plays a key role in the pathogenesis of OA. Hence, orchestrating the local inflammatory microenvironment and tissue regeneration microenvironment is important for the treatment of OA. Mesenchymal stem cells (MSCs) offer the potential for cartilage regeneration owing to their effective immunomodulatory properties and anti-inflammatory abilities. The paracrine effect, mediated by MSC-derived extracellular vehicles (EVs), has recently been suggested as a mechanism for their therapeutic properties. In this review, we summarize the interactions between MSCs or MSC-derived EVs and OA-related immune cells and discuss their therapeutic effects in OA. Additionally, we discuss the potential of MSC-derived EVs as a novel cell-free therapy approach for the clinical treatment of OA.

[The role of Wnt signaling pathway in osteoarthritis via the dual-targeted regulation of cartilage and subchondral bone]

Objective

To summarize the active changes of Wnt signaling pathway in osteoarthritis (OA) as well as the influence and mechanism of dual-targeted regulation on cartilage and subchondral bone and the role of crosstalk between them on OA process.

Methods

The relevant literature concerning the articular cartilage, subchondral bone, and crosstalk between them in OA and non-OA states by Wnt signaling pathway in vivo and vitro experimental studies and clinical studies in recent years was reviewed, and the mechanism was analyzed and summarized.

Results

Wnt signaling can regulate the differentiation and function of chondrocytes and osteoblasts through the classic β-catenin-dependent or non-classical β-catenin-independent Wnt signaling pathway and its cross-linking with other signaling pathways, thereby affecting the cartilage and bone metabolism. Moreover, Wnt signaling pathway can activate the downstream protein Wnt1-inducible-signaling pathway protein 1 to regulate the progress of OA and it also can be established gap junctions between different cells in cartilage and subchondral bone to communicate molecules directly to regulate OA occurrence and development. Intra-articular injection of Wnt signaling inhibitor SM04690 can inhibit the progress of OA, and overexpression of Wnt signaling pathway inhibitor Dickkopf in osteoblasts can antagonize the role of vascular endothelial growth factor work on chondrocytes and inhibit the catabolism of its matrix.

Conclusion

The regulation of metabolism and function of cartilage and subchondral bone and crosstalk between them is through interactions among Wnt signaling pathway and molecules of other signaling. Therefore, it plays an vital role in the occurrence and development of OA and is expected to become a new target of OA treatment through intervention and regulation of Wnt signaling pathway.

Interplay between genetics and epigenetics in osteoarthritis

Research into the molecular genetics of osteoarthritis (OA) has been substantially bolstered in the past few years by the implementation of powerful genome-wide scans that have revealed a large number of novel risk loci associated with the disease. This refreshing wave of discovery has occurred concurrently with epigenetic studies of joint tissues that have examined DNA methylation, histone modifications and regulatory RNAs. These epigenetic analyses have involved investigations of joint development, homeostasis and disease and have used both human samples and animal models. What has become apparent from a comparison of these two complementary approaches is that many OA genetic risk signals interact with, map to or correlate with epigenetic mediators. This discovery implies that epigenetic mechanisms, and their effect on gene expression, are a major conduit through which OA genetic risk polymorphisms exert their functional effects. This observation is particularly exciting as it provides mechanistic insight into OA susceptibility. Furthermore, this knowledge reveals avenues for attenuating the negative effect of risk-conferring alleles by exposing the epigenome as an exploitable target for therapeutic intervention in OA.

miR-148a/LDLR mediates hypercholesterolemia induced by prenatal dexamethasone exposure in male offspring rats

Epidemiology suggests that adverse environmental exposure during pregnancy may predispose children to hypercholesterolemia in adulthood. This study aimed to demonstrate hypercholesterolemia induced by prenatal dexamethasone exposure (PDE) in adult male offspring rats and explore the intrauterine programming mechanisms. Pregnant Wistar rats were injected subcutaneously with dexamethasone (0, 0.1, 0.2, and 0.4 mg/kg∙d) from gestational days (GD) 9 to 21, and the serum and liver of the male offsprings were collected at GD21, postnatal week (PW) 12 and 28. Furthermore, the effects of dexamethasone on the expression of low-density lipoprotein receptor (LDLR) and its epigenetic mechanism was confirmed in the bone marrow mesenchymal stem cells (BMSCs) hepatoid differentiated cells and continuous hepatocyte line. PDE could reduce the birth weight of male offsprings, increase the serum total cholesterol (TCH) level in adult rats, and decrease the liver low-density lipoprotein receptor (LDLR) expression. Serum TCH level and liver LDLR expression were decreased in PDE male fetuses in utero (GD21). Moreover, PDE increased the translocation of the glucocorticoid receptor (GR) in the fetal liver, the expression of DiGeorge syndrome critical region 8 gene (DGCR8), the pre- and post-natal expression of miR-148a. The results of PDE offspring in vivo and in vitro exhibited similar changes. These changes could be reversed by overexpressing LDLR, inhibiting miR-148a or GR. PDE caused hypercholesterolemia in male adult offspring rats, which was mediated via dexamethasone activated intrauterine hepatic GR, enhanced the expression of DGCR8 and miR-148a, thereby reducing the expression of LDLR, leading to impaired liver cholesterol reverse transport function, and finally causing hypercholesterolemia in adult rats.

Zebrafish Models of Human Skeletal Disorders: Embryo and Adult Swimming Together

Danio rerio (zebrafish) is an elective model organism for the study of vertebrate development because of its high degree of homology with human genes and organs, including bone. Zebrafish embryos, because of the optical clarity, small size, and fast development, can be easily used in large-scale mutagenesis experiments to isolate mutants with developmental skeletal defects and in high-throughput screenings to find new chemical compounds for the ability to revert the pathological phenotype. On the other hand, the adult zebrafish represents another powerful resource for pathogenic and therapeutic studies about adult human bone diseases. In fish, some characteristics such as bone turnover, reparation, and remodeling of the adult bone tissue cannot be found at the embryonic stage. Several pathological models have been established in adult zebrafish such as bone injury models, osteoporosis, and genetic diseases such as osteogenesis imperfecta. Given the growing interest for metabolic diseases and their complications, adult zebrafish models of type 2 diabetes and obesity have been recently generated and analyzed for bone complications using scales as model system. Interestingly, an osteoporosis-like phenotype has been found to be associated with metabolic alterations suggesting that bone complications share the same mechanisms in humans and fish. Embryo and adult represent powerful resources in rapid development to study bone physiology and pathology from different points of view.

Intraarticular Ligament Degeneration Is Interrelated with Cartilage and Bone Destruction in Osteoarthritis

Osteoarthritis (OA) induces inflammation and degeneration of all joint components including cartilage, joint capsule, bone and bone marrow, and ligaments. Particularly intraarticular ligaments, which connect the articulating bones such as the anterior cruciate ligament (ACL) and meniscotibial ligaments, fixing the fibrocartilaginous menisci to the tibial bone, are prone to the inflamed joint milieu in OA. However, the pathogenesis of ligament degeneration on the cellular level, most likely triggered by OA associated inflammation, remains poorly understood. Hence, this review sheds light into the intimate interrelation between ligament degeneration, synovitis, joint cartilage degradation, and dysbalanced subchondral bone remodeling. Various features of ligament degeneration accompanying joint cartilage degradation have been reported including chondroid metaplasia, cyst formation, heterotopic ossification, and mucoid and fatty degenerations. The entheses of ligaments, fixing ligaments to the subchondral bone, possibly influence the localization of subchondral bone lesions. The transforming growth factor (TGF)β/bone morphogenetic (BMP) pathway could present a link between degeneration of the osteochondral unit and ligaments with misrouted stem cell differentiation as one likely reason for ligament degeneration, but less studied pathways such as complement activation could also contribute to inflammation. Facilitation of OA progression by changed biomechanics of degenerated ligaments should be addressed in more detail in the future.