Suitability of porcine chondrocyte micromass culture to model osteoarthritis in vitro

Quantitatively measuring the cytotoxicity of viscous hydrogels with direct cell sampling in a micro scale format "MicroDrop" and its comparison to CCK8

Tissue engineering holds promise for developing therapeutic applications using viscous materials e.g. hydrogels. However, assessing the cytotoxicity of such materials with conventional assays can be challenging due to non-specific interactions. To address this, we optimized a live/dead staining method for quantitative evaluation and compared it with the conventional CCK8 assay. Our MicroDrop method involved seeding droplets containing 5000 cells in 10 µl medium on 12-well plates. After allowing them to adhere for 4 h, various viscous samples were applied to the cells and measurements were conducted using a fluorescence microscope immediately and at daily intervals up to 72 h. A sodium dodecyl sulfate (SDS) dilution series compared the MicroDrop with the CCK8 assay. The findings revealed a cell-type specific pattern for 10 mg/ml hyaluronic acid (HA), wherein MC3T3-E1 cells maintained 95% viability until 72 h, while L929 cells experienced a gradual decline to 17%. 2 mg/ml HA exhibited consistent viability above 90% across all time points and cell lines. Similarly, fibrin demonstrated 90% viability across dilutions and time points, except for undiluted samples showing a decrease from 85% to 20%. Gelatin-methacrylol sustained viability above 70% across all time points at both 5% and 10% concentrations. The comparison of the SDS dilution series between viability (MicroDrop) and metabolic activity (CCK8) assay showed a correlation coefficient of 0.95. The study validates the feasibility of the established assay, providing researchers with an efficient tool for assessing cytotoxicity in viscous materials. Additionally, it holds the potential to yield more precise data on well-known hydrogels.

Wheatgrass extract has chondroprotective and anti-inflammatory effects on porcine cartilage

Lameness is a commonly observed disorder in sows and negatively impacts both animal welfare and the profitability of the pig sector. The purpose of this study was to determine anti-inflammatory and/or chondroprotective effects of wheatgrass (WG) on porcine cartilage explants stimulated with lipopolysaccharide (LPS). Explants were aseptically prepared from the intercarpal joints of nine market-weight pigs and placed in culture at 37°C for a total of 120 hours. For the final 96 hours, explants were conditioned with an aqueous extract of WG (0, 5 or 15 μg/mL), and for the final 48 hours explants were stimulated with LPS (0 or 10 µg/mL). Media was removed and replaced every 24 hours. Samples from the final 48 hours were analyzed for biomarkers of cartilage inflammation [prostaglandin E2 (PGE2) and nitric oxide (NO)] and cartilage structure [glycosaminoglycan (GAG)], and cartilage explants were stained for an estimate of cell viability. Stimulation of explants with LPS significantly increased media concentrations of PGE2, GAG and NO compared with that from unstimulated explants. LPS stimulation did not significantly affect cell viability. Conditioning of explants with WG (5 μg/mL) significantly reduced LPS-stimulated cartilage release of PGE2, NO, and GAG (5 and 15 μg/mL), without impairing chondrocyte viability. These data provide evidence for a non-cytotoxic chondroprotective and anti-inflammatory effect of WG extract in cartilage and suggest a role of WG in protection against cartilage breakdown, inflammation, and pain associated with osteoarthritis.

Significance of m6A regulatory factor in gene expression and immune function of osteoarthritis

One of the most prevalent posttranscriptional modifications of eukaryotic mRNA is the RNA N6-methyladenosine (m⁶A) regulator, which plays a significant role in various illnesses. The involvement of m⁶A regulators in osteoarthritis (OA) is not fully known. By comparing nonosteoarthritic and osteoarthritic patients, 26 important m⁶A regulators were identified from the gene expression omnibus GSE48556 dataset. Seven candidate m⁶A regulators (IGFBP3, WTAP, IGFBP1, HNRNPC, RBM15B, YTHDC1, and METTL3) were screened using a random forest model to assess the likelihood of OA. A column line graph model founded on seven m⁶A modulator candidates was created. According to decision curve analysis, patients might profit from the column line graph model. Based on chosen relevant m⁶A modifiers, a consensus clustering approach was utilized to categorize OA into two m⁶A categories (group A and group B). To measure the m⁶A pattern, a principal component analysis technique was created to generate the m⁶A score for every sample. Cluster A patients exhibited more excellent m⁶A scores than cluster B patients. Furthermore, we discovered that patients with lower and higher m⁶A scores had varied immunological responses using the m⁶A type. At last, m⁶A regulators contribute significantly to the progression of OA. Our research on m⁶A patterns might help to guide further OA immunotherapeutic techniques.

Similarities and differences between rat and mouse chondrocyte gene expression induced by IL-1β

Background

Osteoarthritis (OA) is the most prevalent degenerative joint disease. In vitro experiments are an intuitive method used to investigate its early pathogenesis. Chondrocyte inflammation models in rats and mice are often used as in vitro models of OA. However, similarities and differences between them in the early stages of inflammation have not been reported.

Objective

This paper seeks to compare the chondrocyte phenotype of rats and mice in the early inflammatory state and identify chondrocytes suitable for the study of early OA.

Methods

Under similar conditions, chondrocytes from rats and mice were stimulated using the same IL-1β concentration for a short period of time. The phenotypic changes of chondrocytes were observed under a microscope. The treated chondrocytes were subjected to RNA-seq to identify similarities and differences in gene expression. Chondrocytes were labelled with EdU for proliferation analysis. Cell proliferation-associated proteins, including minichromosome maintenance 2 (MCM2), minichromosome maintenance 5 (MCM5), Lamin B1, proliferating cell nuclear antigen (PCNA), and Cyclin D1, were analysed by immunocytochemical staining, cell immunofluorescence, and Western blots to verify the RNA-seq results.

Results

RNA-seq revealed that the expression patterns of cytokines, chemokines, matrix metalloproteinases, and collagen were similar between the rat and mouse chondrocyte inflammation models. Nonetheless, the expression of proliferation-related genes showed the opposite pattern. The RNA-seq results were further verified by subsequent experiments. The expression levels of MCM2, MCM5, Lamin B1, PCNA, and Cyclin D1 were significantly upregulated in rat chondrocytes (P < 0.05) and mouse chondrocytes (P < 0.05).

Conclusions

Based on the findings, the rat chondrocyte inflammation model may help in the study of the early pathological mechanism of OA.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13018-021-02889-2.

A Novel Method Facilitating the Simple and Low-Cost Preparation of Human Osteochondral Slice Explants for Large-Scale Native Tissue Analysis

For in vitro modeling of human joints, osteochondral explants represent an acceptable compromise between conventional cell culture and animal models. However, the scarcity of native human joint tissue poses a challenge for experiments requiring high numbers of samples and makes the method rather unsuitable for toxicity analyses and dosing studies. To scale their application, we developed a novel method that allows the preparation of up to 100 explant cultures from a single human sample with a simple setup. Explants were cultured for 21 days, stimulated with TNF-α or TGF-β3, and analyzed for cell viability, gene expression and histological changes. Tissue cell viability remained stable at >90% for three weeks. Proteoglycan levels and gene expression of COL2A1, ACAN and COMP were maintained for 14 days before decreasing. TNF-α and TGF-β3 caused dose-dependent changes in cartilage marker gene expression as early as 7 days. Histologically, cultures under TNF-α stimulation showed a 32% reduction in proteoglycans, detachment of collagen fibers and cell swelling after 7 days. In conclusion, thin osteochondral slice cultures behaved analogously to conventional punch explants despite cell stress exerted during fabrication. In pharmacological testing, both the shorter diffusion distance and the lack of need for serum in the culture suggest a positive effect on sensitivity. The ease of fabrication and the scalability of the sample number make this manufacturing method a promising platform for large-scale preclinical testing in joint research.

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.

Promoted Viability and Differentiated Phenotype of Cultured Chondrocytes With Low Level Laser Irradiation Potentiate Efficacious Cells for Therapeutics

Effective clinical treatments of cartilage lesions in affected joints require large numbers of viable chondrogenic cells generated through in vivo stimulation or ex vivo expansion of chondrocytes isolated from small biopsy specimens. Conventional passaging of chondrocytes in culture provides sufficient cells for treatments but these cells usually lose their differentiated phenotype. This leads to the formation of fibrocartilaginous tissue due to a malfunctioning repair process. Biostimulation of passaging chondrocytes with low level laser irradiation (LLLI) may theoretically produce more functional chondrocytes for cell-based repair of cartilage defects. Molecular and cellular analyses, cytochemistry, cell cultivation, and microscopy showed that LLLI treatments were found to (1) increase chondrocyte viability, (2) promote secretion of matrix proteins, (3) upregulate expression of chondrogenic genes, and (4) downregulate gene expression of cell destructive proteases and genes coding for mediators involved in the extrinsic apoptosis signaling pathway. Furthermore, LLLI attenuated induction of genes associated with cell death and matrix breakdown induced by IL-1β, some of which was seen at the protein level, with verification of effects on gene expression in the C28/I2 human chondrocyte line. LLLI treatments during culture generated larger numbers of viable chondrocytes compared to untreated cultures. Moreover, LLLI-treated chondrocytes in culture also rectified and simultaneously maintained their differentiated phenotype. Cultured chondrocytes treated with LLLI are a promising cell source for repairing cartilage lesions in vivo and restoration of articular function using tissue engineering strategies.

Photopolymerizable gelatin and hyaluronic acid for stereolithographic 3D bioprinting of tissue-engineered cartilage

To create artificial cartilage in vitro, mimicking the function of native extracellular matrix (ECM) and morphological cartilage-like shape is essential. The interplay of cell patterning and matrix concentration has high impact on the phenotype and viability of the printed cells. To advance the capabilities of cartilage bioprinting, we investigated different ECMs to create an in vitro chondrocyte niche. Therefore, we used methacrylated gelatin (GelMA) and methacrylated hyaluronic acid (HAMA) in a stereolithographic bioprinting approach. Both materials have been shown to support cartilage ECM formation and recovery of chondrocyte phenotype. We used these materials as bioinks to create cartilage models with varying chondrocyte densities. The models maintained shape, viability, and homogenous cell distribution over 14 days in culture. Chondrogenic differentiation was demonstrated by cartilage-typical proteoglycan and type II collagen deposition and gene expression (COL2A1, ACAN) after 14 days of culture. The differentiation pattern was influenced by cell density. A high cell density print (25 × 106  cells/mL) led to enhanced cartilage-typical zonal segmentation compared to cultures with lower cell density (5 × 106  cells/mL). Compared to HAMA, GelMA resulted in a higher expression of COL1A1, typical for a more premature chondrocyte phenotype. Both bioinks are feasible for printing in vitro cartilage with varying differentiation patterns and ECM organization depending on starting cell density and chosen bioink. The presented technique could find application in the creation of cartilage models and in the treatment of articular cartilage defects using autologous material and adjusting the bioprinted constructs size and shape to the patient. © 2019 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B:2649-2657, 2019.

Scaffoldless tissue-engineered cartilage for studying transforming growth factor beta-mediated cartilage formation

Reduced transforming growth factor beta (TGF-β) signaling is associated with osteoarthritis (OA). TGF-β is thought to act as a chondroprotective agent and provide anabolic cues to cartilage, thus acting as an OA suppressor in young, healthy cartilage. A potential approach for treating OA is to identify the factors that act downstream of TGF-β's anabolic pathway and target those factors to promote cartilage regeneration or repair. The aims of the present study were to (a) develop a scaffoldless tissue-engineered cartilage model with reduced TGF-β signaling and disrupted cartilage formation and (b) validate the system for identifying the downstream effectors of TGF-β that promote cartilage formation. Sox9 was used to validate the model because Sox9 is known to promote cartilage formation and TGF-β regulates Sox9 activity. Primary bovine articular chondrocytes were grown in Transwell supports to form cartilage tissues. An Alk5/TGF-β type I receptor inhibitor, SB431542, was used to attenuate TGF-β signaling, and an adenovirus encoding FLAG-Sox9 was used to drive the expression of Sox9 in the in vitro-generated cartilage. SB431542-treated tissues exhibited reduced cartilage formation including reduced thicknesses and reduced proteoglycan staining compared with control tissue. Expression of FLAG-Sox9 in SB431542-treated cartilage allowed the formation of cartilage despite antagonism of the TGF-β receptor. In summary, we developed a three-dimensional in vitro cartilage model with attenuated TGF-β signaling. Sox9 was used to validate the model for identification of anabolic agents that counteract loss of TGF-β signaling. This model has the potential to identify additional anabolic factors that could be used to repair or regenerate damaged cartilage.

RIPK1 suppresses apoptosis mediated by TNF and caspase-3 in intervertebral discs

BACKGROUND

Low back pain has become a serious social and economic burden and the leading cause of disability worldwide. Among a variety of pathophysiological triggers, intervertebral disc (IVD) degeneration plays a primary underlying role in causing such pain. Specifically, multiple independent endplate changes have been implicated in the initiation and progression of IVD degeneration.

METHODS

In this study, we built a signaling network comprising both well-characterized IVD pathology-associated proteins as well as some potentially correlated proteins that have been associated with one or more of the currently known pathology-associated proteins. We then screened for the potential IVD degeneration-associated proteins using patients' normal and degenerative endplate specimens. Short hairpin RNAs for receptor interacting serine/threonine kinase 1 (RIPK1) were constructed to examine the effects of RIPK1 knockdown in primary chondrocyte cells and in animal models of caudal vertebra intervertebral disc degeneration in vivo.

RESULTS

RIPK1 was identified as a potential IVD degeneration-associated protein based on IVD pathology-associated signaling networks and the patients' degenerated endplate specimens. Construction of the short hairpin RNAs was successful, with short-term RIPK1 knockdown triggering inflammation in the primary chondrocytes, while long-term knockdown triggered apoptosis through cleavage of the caspase 3 pathway, down-regulated NF-κB and mitogen-activating protein kinase (MAPK)s cascades, and decreased cell survival and inflammation. Animal models of caudal vertebra intervertebral disc degeneration further demonstrated that apoptosis was induced by up-regulation of tumor necrosis factor (TNF) accompanied by down-regulation of NF-κB and MAPKs cascades that are dependent on caspase and RIPK1.

CONCLUSIONS

These results provide proof-of-concept for developing novel therapies to combat IVD degeneration through interfering with RIPK1-mediated apoptosis signaling pathways especially in patients with RIPK1 abnormality.

Dose-Dependent Effect of Mesenchymal Stromal Cell Recruiting Chemokine CCL25 on Porcine Tissue-Engineered Healthy and Osteoarthritic Cartilage

Thymus-expressed chemokine (CCL25) is a potent cell attractant for mesenchymal stromal cells, and therefore it is a candidate for in situ cartilage repair approaches focusing on the recruitment of endogenous repair cells. However, the influence of CCL25 on cartilage is unknown. Accordingly, in this study, we investigated the effect of CCL25 on tissue-engineered healthy and osteoarthritic cartilage. Porcine chondrocytes were cultured in a three-dimensional (3D) micromass model that has been proven to mimic key-aspects of human cartilage and osteoarthritic alterations upon stimulation with tumor necrosis factor-α (TNF-α). Micromass cultures were stimulated with CCL25 (0, 0.05, 0.5, 5, 50, 500 nmol/L) alone or in combination with 0.6 nmol/L TNF-α for seven days. Effects were evaluated by life/dead staining, safranin O staining, histomorphometrical analysis of glycosaminoglycans (GAGs), collagen type II (COL2A1) real-time RT-PCR and Porcine Genome Array analysis. 500 nmol/L CCL25 led to a significant reduction of GAGs and COL2A1 expression and induced the expression of matrix metallopeptidases (MMP) 1, MMP3, early growth response protein 1 (EGR1), and superoxide dismutase 2 (SOD2). In concentrations lower than 500 nmol/L, CCL25 seems to be a candidate for in situ cartilage repair therapy approaches.

Transcriptional Profiling of Leucocyte Count Variation from Porcine Peripheral Blood Reveals Differential Gene Expression

Leucocytes have tremendous health-check importance related to the individual antiviral capacity of pigs and other mammals. However, the molecular mechanism of the immune response of blood leucocytes in pigs is not completely known. This study investigated the leucocyte-count variation before and after poly I:C stimulation in a Duroc–Erhualian F2 population. Pigs with increased and decreased differences in leucocyte counts were coded as increased responder (IR) and decreased responder (DR), respectively. Then, we used microarray technology to compare the gene-expression profiles of both groups of pigs. Transcriptomic analysis identified 129 differentially expressed genes (DEGs) in IR pigs and 136 DEGs in DR pigs. Forty-one common DEGs showed that both groups had similar expression patterns of immune responses. These results illustrated a differential expression in both groups. Furthermore, qPCR experiment was performed to verify the differential-expression profile. Functional annotation of the DEGs indicated that both IR and DR pigs were similar in several biological processes, including innate immune response, and also exhibited distinct differences in biological processes, molecular function, and pathways. These results provided insights into the mechanism underlying the antiviral capacity of pigs. Trial registration number is CAS Registry Number 24939-03-5.

The effectiveness of allogeneic mesenchymal stem cells therapy for knee osteoarthritis in pigs

Background

Intraarticular injection of the mesenchymal stem cells (MSCs) has shown to be successful for treating osteoarthritis (OA). Nevertheless, many studies have been focusing on autologous MSCs. The following study investigates the safety and effectiveness of intraarticular injection of allogenic MSCs in a pig OA model.

Methods

Superparamagnetic iron oxide (SPIO) nanoparticles were labelled with bone marrow-derived mesenchymal stem cells (BM-MSCs) to allow cells tracking using magnetic resonance imaging (MRI). A pig OA model was established by bilateral medial meniscectomy. Next, SPIO-BM-MSCs were injected into the right knee, while the left knee was left untreated. MRI and radiography were used to assess the degree of OA and to evaluate the effectiveness of allogenic MSCs. Hematoxylin and eosin (H&E), safranin-o fast green staining, toluidine blue, and immunohistochemical staining were used to evaluate the therapeutic effect of the injections.

Results

At concentration of ≤20 µg/mL, SPIO caused no toxicity to BM-MSCs. Four weeks after surgery, OA changes were observed on MRI scan. The SPIO labeled BM-MSCs were found moving towards the impaired part of the cartilage 8 to 24 h after injections. In addition, no significant differences between the right side (therapeutic side) and the left side (untreated side) were observed following histological and immunohistochemistry analysis.

Conclusions

The suitable concentration of SPIO for labelling BMSCs was 20 µg/mL, while the allogenic MSCs could move towards and accumulate around the impaired cartilage. No significant difference was found between treatment and control group.

Chemokine CCL25 Induces Migration and Extracellular Matrix Production of Anulus Fibrosus-Derived Cells

Intervertebral disc degeneration is a major source of back pain. For intervertebral disc regeneration after herniation a fast closure of anulus fibrosus (AF) defects is crucial. Here, the use of the C-C motif chemokine ligand 25 (CCL)25 in comparison to differentiation factors such as transforming growth factor (TGF)β3, bone morphogenetic protein (BMP)2, BMP7, BMP12, and BMP14 (all in concentrations of 10, 50 and 100 ng/mL) was tested in an in vitro micro mass pellet model with isolated and cultivated human AF-cells (n = 3) to induce and enhance AF-matrix formation. The pellets were differentiated (serum-free) with supplementation of the factors. After 28 days all used factors induced proteoglycan production (safranin O staining) and collagen type I production (immunohistochemical staining) in at least one of the tested concentrations. Histomorphometric scoring revealed that TGFβ3 delivered the strongest induction of proteoglycan production in all three concentrations. Furthermore, it was the only factor able to facilitate collagen type II production, even higher than in native tissue samples. CCL25 was also able to induce proteoglycan and collagen type I production comparable to several BMPs. CCL25 could additionally induce migration of AF-cells in a chemotaxis assay and therefore possibly aid in regeneration processes after disc herniation by recruiting AF-cells.

Hyaluronic Acid Influence on Normal and Osteoarthritic Tissue-Engineered Cartilage

The aim of this study is to identify gene expression profiles associated with hyaluronic acid (HA) treatment of normal and osteoarthritis (OA)-like tissue-engineered cartilage. 3D cartilage micromasses were treated with tumour necrosis factor-α (TNF-α) (OA-inducer) and/or HA for 7 days. Viability was examined by PI/FDA staining. To document extracellular matrix (ECM) formation, glycosaminoglycans (GAG) were stained with Safranin-O and cartilage-specific type II collagen was detected immunohistochemically. Genome-wide gene expression was determined using microarray analysis. Normal and OA-like micromasses remained vital and showed a spherical morphology and homogenous cell distribution regardless of the treatment. There was no distinct difference in immunolabeling for type II collagen. Safranin-O staining demonstrated a typical depletion of GAG in TNF-α-treated micromasses (−73%), although the extent was limited in the presence of HA (−39%). The microarray data showed that HA can influence the cartilage metabolism via upregulation of TIMP3 in OA-like condition. The upregulation of VEGFA and ANKRD37 genes implies a supportive role of HA in cartilage maturation and survival. The results of this study validate the feasibility of the in vitro OA model for the investigation of HA. On the cellular level, no inhibiting or activating effect of HA was shown. Microarray data demonstrated a minor impact of HA on gene expression level.

Comprehensive Genome-Wide Transcriptomic Analysis of Immature Articular Cartilage following Ischemic Osteonecrosis of the Femoral Head in Piglets

OBJECTIVE

Ischemic osteonecrosis of the femoral head (ONFH) in piglets results in an ischemic injury to the immature articular cartilage. The molecular changes in the articular cartilage in response to ONFH have not been investigated using a transcriptomic approach. The purpose of this study was to perform a genome-wide transcriptomic analysis to identify genes that are upregulated in the immature articular cartilage following ONFH.

METHODS

ONFH was induced in the right femoral head of 6-week old piglets. The unoperated femoral head was used as the normal control. At 24 hours (acute ischemic-hypoxic injury), 2 weeks (avascular necrosis in the femoral head) and 4 weeks (early repair) after surgery (n = 4 piglets/time point), RNA was isolated from the articular cartilage of the femoral head. A microarray analysis was performed using Affymetrix Porcine GeneChip Array. An enrichment analysis and functional clustering of the genes upregulated due to ONFH were performed using DAVID and STRING software, respectively. The increased expression of selected genes was confirmed by a real-time qRTPCR analysis.

RESULTS

Induction of ONFH resulted in the upregulation of 383 genes at 24 hours, 122 genes at 2 weeks and 124 genes at 4 weeks compared to the normal controls. At 24 hours, the genes involved in oxidoreductive, cell-survival, and angiogenic responses were significantly enriched among the upregulated genes. These genes were involved in HIF-1, PI3K-Akt, and MAPK signaling pathways. At 2 weeks, secretory and signaling proteins involved in angiogenic and inflammatory responses, PI3K-Akt and matrix-remodeling pathways were significantly enriched. At 4 weeks, genes that represent inflammatory cytokines and chemokine signaling pathways were significantly enriched. Several index genes (genes that are upregulated at more than one time point following ONFH and are known to be important in various biological processes) including HIF-1A, VEGFA, IL-6, IL6R, IL-8, CCL2, FGF2, TGFB2, MMP1, MMP3, ITGA5, FN and Col6A1 were upregulated in the immature articular cartilage following ONFH. A qRTPCR analysis of selected genes confirmed the upregulated expression observed in the microarray analysis.

CONCLUSION

Immature articular cartilage responds to ONFH by the upregulation of genes involved in hypoxic stress response, angiogenesis, matrix remodeling and inflammation. This study provides novel insights into the multi-faceted role of immature articular cartilage, with inflammation as a key component, following ONFH in piglets.

Menisectomized miniature Vietnamese pigs develop articular cartilage pathology resembling osteoarthritis

Animal models have been used to understand the basic biology of osteoarthritis (OA) and have helped to identify new candidate biomarkers for the early diagnosis and treatment of this condition. Small animals cannot sufficiently mimic human diseases; therefore, large animal models are needed. Pigs have been used as models for human diseases because they are similar to humans in terms of their anatomy, physiology and genome. Hence, we analyzed articular cartilage and synovial membrane pathology in miniature Vietnamese pigs after a unilateral partial menisectomy and 20-day exercise regimen to determine if the pigs developed pathological characteristics similar to human OA. Histological and protein expression analysis of articular cartilage from menisectomized pigs revealed the following pathologic changes resembling OA: fibrillation, fissures, chondrocyte cluster formation, decrease in proteoglycan content and upregulation of the OA-associated proteins MMP-3, MMP-13, procaspase-3 and IL-1β. Moreover, histological analysis of synovial membrane revealed mild synovitis, characterized by hyperplasia, cell infiltration and neoangiogenesis. Pathological changes were not observed in the contralateral joints or the joints of sham-operated pigs. Further studies are required to validate such an OA model; however, our results can encourage the use of pigs to study early stages of OA physiopathology. Based on their similarities to humans, pigs may be useful for preclinical studies to identify new candidate biomarkers and novel treatments for OA.

Association of reduced type IX collagen gene expression in human osteoarthritic chondrocytes with epigenetic silencing by DNA hypermethylation

OBJECTIVE

To investigate whether the changes in collagen gene expression in osteoarthritic (OA) human chondrocytes are associated with changes in the DNA methylation status in the COL2A1 enhancer and COL9A1 promoter.

METHODS

Expression levels were determined using quantitative reverse transcription-polymerase chain reaction, and the percentage of DNA methylation was quantified by pyrosequencing. The effect of CpG methylation on COL9A1 promoter activity was determined using a CpG-free vector; cotransfections with expression vectors encoding SOX9, hypoxia-inducible factor 1α (HIF-1α), and HIF-2α were carried out to analyze COL9A1 promoter activities in response to changes in the methylation status. Chromatin immunoprecipitation assays were carried out to validate SOX9 binding to the COL9A1 promoter and the influence of DNA methylation.

RESULTS

Although COL2A1 messenger RNA (mRNA) levels in OA chondrocytes were 19-fold higher than those in the controls, all of the CpG sites in the COL2A1 enhancer were totally demethylated in both samples. The levels of COL9A1 mRNA in OA chondrocytes were 6,000-fold lower than those in controls; 6 CpG sites of the COL9A1 promoter were significantly hypermethylated in OA patients as compared with controls. Treatment with 5-azadeoxycitidine enhanced COL9A1 gene expression and prevented culture-induced hypermethylation. In vitro methylation decreased COL9A1 promoter activity. Mutations in the 5 CpG sites proximal to the transcription start site decreased COL9A1 promoter activity. Cotransfection with SOX9 enhanced COL9A1 promoter activity; CpG methylation attenuated SOX9 binding to the COL9A1 promoter.

CONCLUSION

This first demonstration that hypermethylation is associated with down-regulation of COL9A1 expression in OA cartilage highlights the pivotal role of epigenetics in OA, involving not only hypomethylation, but also hypermethylation, with important therapeutic implications for OA treatment.