In vitro chondrocyte differentiation using costochondral chondrocytes as a source of primary rat chondrocyte cultures: an improved isolation and cryopreservation method

Cell-recruited microspheres for OA treatment by dual-modulating inflammatory and chondrocyte metabolism

Osteoarthritis (OA) is a degenerative disease potentially exacerbated due to inflammation, cartilage degeneration, and increased friction. Both mesenchymal stem cells (MSCs) and pro-inflammatory macrophages play important roles in OA. A promising approach to treating OA is to modify multi-functional hydrogel microspheres to target the OA microenvironment and structure. Arginyl-glycyl-aspartic acid (RGD) is a peptide widely used in bioengineering owing to its cell adhesion properties, which can recruit BMSCs and macrophages. We developed TLC-R, a microsphere loaded with TGF-β1-containing liposomes. The recruitment effect of TLC-R on macrophages and BMSCs was verified by in vitro experiments, along with its function of promoting chondrogenic differentiation of BMSCs. And we evaluated the effect of TLC-R in balancing OA metabolism in vitro and in vivo. When TLC-R was co-cultured with BMSCs and lipopolysaccharide (LPS)-treated macrophages, it showed the ability to recruit both cells in substantial numbers. As the microspheres degraded, TGF-β1 and chondroitin sulfate (ChS) were released to promote chondrogenic differentiation of the recruited BMSCs, modulate chondrocyte metabolism and inhibit inflammation induced by the macrophages. Furthermore, in vivo analysis showed that TLC-R restored the narrowed space, reduced osteophyte volume, and improved cartilage metabolic homeostasis in OA rats. Altogether, TLC-R provides a comprehensive and novel solution for OA treatment by dual-modulating inflammatory and chondrocyte metabolism.

Chromatin profiling identifies chondrocyte-specific Sox9 enhancers important for skeletal development

The transcription factor SRY-related HMG box 9 (Sox9) is essential for chondrogenesis. Mutations in and around SOX9 cause campomelic dysplasia (CD) characterized by skeletal malformations. Although the function of Sox9 in this context is well studied, the mechanisms that regulate Sox9 expression in chondrocytes remain to be elucidated. Here, we have used genome-wide profiling to identify 2 Sox9 enhancers located in a proximal breakpoint cluster responsible for CD. Enhancer activity of E308 (located 308 kb 5' upstream) and E160 (located 160 kb 5' upstream) correlated with Sox9 expression levels, and both enhancers showed a synergistic effect in vitro. While single deletions in mice had no apparent effect, simultaneous deletion of both E308 and E160 caused a dwarf phenotype, concomitant with a reduction of Sox9 expression in chondrocytes. Moreover, bone morphogenetic protein 2-dependent chondrocyte differentiation of limb bud mesenchymal cells was severely attenuated in E308/E160 deletion mice. Finally, we found that an open chromatin region upstream of the Sox9 gene was reorganized in the E308/E160 deletion mice to partially compensate for the loss of E308 and E160. In conclusion, our findings reveal a mechanism of Sox9 gene regulation in chondrocytes that might aid in our understanding of the pathophysiology of skeletal disorders.

Strontium/Silicon/Calcium-Releasing Hierarchically Structured 3D-Printed Scaffolds Accelerate Osteochondral Defect Repair

Articular cartilage defects are a global challenge, causing substantial disability. Repairing large defects is problematic, often exceeding cartilage's self-healing capacity and damaging bone structures. To tackle this problem, a scaffold-mediated therapeutic ion delivery system is developed. These scaffolds are constructed from poly(ε-caprolactone) and strontium (Sr)-doped bioactive nanoglasses (SrBGn), creating a unique hierarchical structure featuring macropores from 3D printing, micropores, and nanotopologies due to SrBGn integration. The SrBGn-embedded scaffolds (SrBGn-µCh) release Sr, silicon (Si), and calcium (Ca) ions, which improve chondrocyte activation, adhesion, proliferation, and maturation-related gene expression. This multiple ion delivery significantly affects metabolic activity and maturation of chondrocytes. Importantly, Sr ions may play a role in chondrocyte regulation through the Notch signaling pathway. Notably, the scaffold's structure and topological cues expedite the recruitment, adhesion, spreading, and proliferation of chondrocytes and bone marrow-derived mesenchymal stem cells. Si and Ca ions accelerate osteogenic differentiation and blood vessel formation, while Sr ions enhance the polarization of M2 macrophages. The findings show that SrBGn-µCh scaffolds accelerate osteochondral defect repair by delivering multiple ions and providing structural/topological cues, ultimately supporting host cell functions and defect healing. This scaffold holds great promise for osteochondral repair applications.

Oxymatrine Protects Chondrocytes against IL-1β-triggered Apoptosis in Vitro and Inhibits Osteoarthritis in Mice Model

Background

Osteoarthritis (OA) is a multifactorial disease with various risk factors, resulting in the degeneration of articular cartilage and whole joints. However, to date, no effective disease-modifying therapy for OA has been developed. Oxymatrine (OMT) is associated with many pharmacological effects, including anti-inflammatory, antiapoptotic, and antioxidative properties. However, the role of OMT in OA remains unclear.

Materials and Methods

An IL-1β-induced chondrocyte model and anterior cruciate ligament transection (ACLT)-induced murine model of OA were constructed. The effect of OMT on chondrocyte viability was assessed using the CCK-8 assay. The protein level was assessed by Western blot analysis, and the apoptosis rate was assessed by flow cytometry in vitro and TUNEL staining in OA model mice. The effect of OMT on the degradation of articular cartilage in ACLT-induced OA mice was assessed by histological analysis.

Results

OMT at 0–2 mg/mL showed no conspicuous cytotoxicity on chondrocytes after 24 hours of incubation. OMT at 0.5, 1, and 2 mg/mL inhibited IL-1β-triggered apoptosis, upregulated MMP13, MMP9, and Col X, and upregulated Col II in chondrocytes in vitro. OMT represses the NF-κB signaling cascade in IL-1β-triggered chondrocytes in vitro. In an in vivo study, OMT decreased the apoptosis rate of chondrocytes and exerted a protective effect against the degradation of articular cartilage in ACLT-triggered OA mice.

Conclusion

OMT plays a protective role against chondrocyte injury induced by IL-1β in vitro or ACLT in vivo. OMT may play a role in chondrocytes during OA by inhibiting NF-κB signaling by decreasing the phosphorylation of p65 and IκB. OMT treatment may be a promising chondroprotective approach to delay OA cartilage progression.

Exogenous growth hormone functionally alleviates glucocorticoid-induced longitudinal bone growth retardation in male rats by activating the Ihh/PTHrP signaling pathway

Glucocorticoid (GC)-induced longitudinal bone growth retardation is a common and severe adverse effect in pediatric patients receiving GC immunosuppressive therapy. Molecular mechanisms underlying GC-induced growth inhibition are unclear. GC withdrawal following short-term high-dose use is common, including in the immediate post-transplant period. However, whether skeleton growth recovery is sufficient or whether growth-promoting therapy is required following GC withdrawal is unknown. The aim of this study was to investigate the effect of exogenous growth hormone (GH) on growth plate impairment in GC-induced longitudinal bone growth retardation. Here, apoptotic chondrocytes in the hypertrophic layer of growth plates increased whereas Indian Hedgehog (Ihh) and Parathyroid Hormone Related Peptide (PTHrP) protein levels in the growth plate decreased following GC exposure. The hypertrophic zone of the growth plate expanded following GC withdrawal. Subcutaneously injected GH penetrated the growth plate and modified its organization in rats following GC withdrawal. Ihh and PTHrP expression in GC-induced apoptotic chondrocytes decreased in vitro. GH promoted chondrocyte proliferation by activating Ihh/PTHrP signaling. Downregulating Ihh using specific siRNAs increased chondrocyte apoptosis and inhibited PTHrP, Sox9, and type II collagen (Col2a1) protein expression. GH inhibited apoptosis of Ihh-deficient growth plate chondrocytes by upregulating PTHrP, Sox9, and Col2a1 expression. Thus, reversal of the effect of GC on growth plate impairment following its withdrawal is insufficient, and exogenous GH provides growth plate chondral protection and improved longitudinal growth following GC withdrawal by acting on the Ihh/PTHrP pathway.

The Technique of Thyroid Cartilage Scaffold Support Formation for Extrusion-Based Bioprinting

During biofabrication, a tissue scaffold may require temporary support. The aim of this study was to develop an approach of human thyroid cartilage scaffold temporal support formation. The scaffold 3D-model was based on DICOM images. XY plane projections were used to form scaffold supporting part. To verify the technique, collagen hydrogel was chosen as the main scaffold component. Gelatin was applied for the supporting part. To test the applicability of the approach, a model of thyroid cartilage scaffold with the support was printed. The scaffold corresponded to a given model, although some discrepancy in geometry was observed during verification by computed tomography.

Dmrt2 promotes transition of endochondral bone formation by linking Sox9 and Runx2

Endochondral bone formation is fundamental for skeletal development. During this process, chondrocytes undergo multiple steps of differentiation and coordinated transition from a proliferating to a hypertrophic stage, which is critical to advance skeletal development. Here, we identified the transcription factor Dmrt2 (double-sex and mab-3 related transcription factor 2) as a Sox9-inducible gene that promotes chondrocyte hypertrophy in pre-hypertrophic chondrocytes. Epigenetic analysis further demonstrated that Sox9 regulates Dmrt2 expression through an active enhancer located 18 kb upstream of the Dmrt2 gene and that this enhancer's chromatin status is progressively activated through chondrocyte differentiation. Dmrt2-knockout mice exhibited a dwarf phenotype with delayed initiation of chondrocyte hypertrophy. Dmrt2 augmented hypertrophic chondrocyte gene expression including Ihh through physical and functional interaction with Runx2. Furthermore, Dmrt2 deficiency reduced Runx2-dependent Ihh expression. Our findings suggest that Dmrt2 is critical for sequential chondrocyte differentiation during endochondral bone formation and coordinates the transcriptional network between Sox9 and Runx2.

Bone marrow mesenchymal stem cell-derived exosomes protect cartilage damage and relieve knee osteoarthritis pain in a rat model of osteoarthritis

Background

This study aimed to investigate the effect of bone marrow mesenchymal stem cell (BMSC)-derived exosome injection on cartilage damage and pain relief in both in vitro and in vivo models of osteoarthritis (OA).

Methods

The BMSCs were extracted from rat bone marrow of the femur and tibia. Chondrocytes were treated with IL-1β to establish the in vitro model of OA. Chondrocyte proliferation and migration were assessed by CCK-8 and transwell assay, respectively. A rat model of OA was established by injection of sodium iodoacetate. At 6 weeks after the model was established, the knee joint specimens and dorsal root ganglion (DRG) of rats were collected for histologic analyses. For pain assessment, paw withdrawal threshold (PWT) and paw withdrawal latency (PWL) were evaluated before model establishment and at 1, 2, 4, and 6 weeks after model establishment.

Results

Exosomes can be endocytosed with the chondrocytes in vitro. Exosome treatment significantly attenuated the inhibitory effect of IL-1β on the proliferation and migration of chondrocytes. Exosome pre-treatment significantly attenuated IL-1β-induced downregulation of COL2A1 and ACAN and upregulation of MMP13 and ADAMTS5. In the animal study, exosome treatment significantly upregulated COL2A1 protein and downregulated MMP13 protein in the cartilage tissue of the OA rat. At weeks 2, 4, and 6, the PWL value was significantly improved in the exosome-treated OA rats as compared with the untreated OA animals. Moreover, exosome treatment significantly alleviated the upregulation of CGRP and iNOS in the DRG tissue of OA rats.

Conclusion

BMSC-derived exosomes can effectively promote cartilage repair and extracellular matrix synthesis, as well as alleviate knee pain in the OA rats.

Alterations in characteristics of canine articular chondrocytes in non-passaged long-term monolayer culture: Matter of differentiation, dedifferentiation and redifferentiation

This study investigated the effects of culture time on phenotype stability of canine articular chondrocytes (CACs) in non-passaged long-term monolayer culture. Third passage (P3) CACs isolated from four cartilage samples were seeded at three different initial seeding densities (0.2 × 10⁴, 1.0 × 10⁴ and 5.0 × 10⁴ cells/cm²) and maintained in monolayer condition up to 8 weeks without undergoing subculture after confluence. The characteristic changes of chondrocytes during the culture period were evaluated based on the cell morphology, cell proliferation, glycosaminoglycans (GAGs) content, DNA quantification, mRNA expression and ultrastructure of chondrocytes. Chondrocytes maintained under post-confluence condition exhibited a capability to grow and proliferate up to 4 weeks. Alcian blue staining and Dimethylmethylene blue (DMMB) assay revealed that the extracellular matrix (ECM) synthesis was increased in a time-dependent manner from 2 to 8 weeks. The chondrocyte mRNA expression profile was dramatically affected by prolonged culture time, with a significant downregulation of collagen type I, whereas the expression of collagen type II, aggrecan, Sox9 and matrix metalloproteinase 13 (MMP-13) were significantly upregulated. In addition, transmission electron microscopy (TEM) result indicated dilation of rough endoplasmic reticulum (RER) in these long-term monolayer cultured chondrocytes. These findings demonstrate that the chondrocytes phenotype could be partially redifferentiated through the spontaneous redifferentiation process in long-term cultures using standard culture medium without the addition of chondrogenic supplements or tissue-culture scaffolds.

miR-106a mimics the nuclear factor-κB signalling pathway by targeting DR6 in rats with osteoarthritis

Introduction

Osteoarthritis (OA) is a common inflammatory joint disease characterised by progressive cartilage destruction. Management of this condition remains a significant challenge, and new therapies are required. We investigated the protective effects of miR-106a mimics in a murine model of OA.

Material and methods

This study was performed using both in vitro and in vivo OA models. Primary chondrocytes were isolated from female rats, with inflammation induced via treatment with lipopolysaccharide (LPS). Then the effects of a miR-106a mimic were examined based on the level of inflammatory cytokine production and apoptotic signalling following LPS stimulation. An in vivo rat model of OA was generated by injecting LPS into the anterior cruciate ligament, followed by treatment with miR-106a mimics. Then, inflammatory and apoptotic protein expression was assessed in the cartilage tissue.

Results

Treatment with miR-106a mimic reduced the levels of inflammatory cytokines and apoptotic proteins in cartilage tissues following LPS-induced inflammation. Furthermore, the mimic ameliorated the expression of DR-6 mRNA and DR6, IκBα, and p65 proteins in chondrocytes. Similar effects were seen in the in vivo model, with the mimic attenuating expression of NF-κB, p65, IκBα, and DR6 proteins and improving histopathological outcomes in the chondrocytes of OA rats.

Conclusions

Treatment with miR-106a mimic ameliorates inflammation in cartilage tissues of OA subjects by activating death receptor 6 via the NF-κB signalling pathway.

Enhancement of autophagy flux by isopsoralen ameliorates interleukin-1β-stimulated apoptosis in rat chondrocytes

Chondrocyte apoptosis contributes to the pathogenesis of cartilage degeneration in osteoarthritis (OA). We found that isopsoralen pretreatment significantly reversed the increase in DNA fragmentation and apoptosis rate, and significantly decreased the caspase-3 activity and PARP cleavage in IL-1β-treated chondrocytes. Isopsoralen pretreatment markedly inhibited disruption of matrix proteins. Moreover, the expressions of LC3-II and LAMP-1 were markedly increased but the expression of p62/SQSTM1 was remarkably decreased by isopsoralen pretreatment. Importantly, the protective effects of isopsoralen against IL-1β were blocked by pretreatment with autophagy inhibitor 3-MA and bafilomycin A1. These results suggest that isopsoralen ameliorates chondrocyte apoptosis by promoting autophagy flux.[Formula: see text].

Dissection of the molecular targets and signaling pathways of Guzhi Zengsheng Zhitongwan based on the analysis of serum proteomics

Background

Guzhi Zengsheng Zhitongwan (GZZSZTW) is an effective formula of traditional Chinese herbal medicine and has been widely applied in the treatment of joint diseases for many years. The aim of this study was to dissect the molecular targets and signaling pathways of Guzhi Zengsheng Zhitongwan based on the analysis of serum proteomics.

Methods

The Chinese herbs of GZZSZTW were immersed in 5 l distilled water and boiled with reflux extraction method. The extract was filtered, concentrated and freeze-dried. The chemical profile of GZZSZTW extract was determined by high-performance lipid chromatography (HPLC). The 7-week old Sprague-Dawley (SD) rats in GZZSZTW groups were received oral administration at doses of 0.8, 1.05, and 1.3 g/kg per day and the rats in blank group were fed with drinking water. Serum samples were collected from the jugular veins. Primary chondrocyte viability was evaluated by CCK-8 assay. A full spectrum of the molecular targets and signaling pathways of GZZSZTW were investigated by isobaric tags for relative and absolute quantitation (iTRAQ) analysis and a systematic bioinformatics analysis accompanied with parallel reaction monitoring (PRM) and siRNA validation.

Results

GZZSZTW regulated a series of functional proteins and signaling pathways responsible for cartilage development, growth and repair. Functional classification analysis indicated that these proteins were mainly involved in the process of cell surface dynamics. Pathway analysis mapped these proteins into several signalling pathways involved in chondrogenesis, chondrocyte proliferation and differentiation, and cartilage repair, including hippo signaling pathway, cGMP-PKG signaling pathway, cell cycle and calcium signaling pathway. Protein–protein interaction analysis and siRNA knockdown assay identified an interaction network consisting of TGFB1, RHO GTPases, ILK, FLNA, LYN, DHX15, PKM, RAB15, RAB1B and GIPC1.

Conclusions

Our results suggest that the effects of GZZSZTW on treating joint diseases might be achieved through the TGFB1/RHO interaction network coupled with other proteins and signaling pathways responsible for cartilage development, growth and repair. Therefore, the present study has greatly expanded our knowledge and provided scientific support for the underlying therapeutic mechanisms of GZZSZTW on treating joint diseases. It also provided possible alternative strategies for the prevention and treatment for joint diseases by using traditional Chinese herbal formulas.

Alteration of the Total Cellular Glycome during Late Differentiation of Chondrocytes

In normal articular cartilage, chondrocytes do not readily proliferate or terminally differentiate, and exhibit a low level of metabolism. Hypertrophy-like changes of chondrocytes have been proposed to play a role in the pathogenesis of osteoarthritis by inducing protease-mediated cartilage degradation and calcification; however, the molecular mechanisms underlying these changes are unclear. Glycans are located on the outermost cell surface. Dynamic cellular differentiation can be monitored and quantitatively characterized by profiling the glycan structures of total cellular glycoproteins. This study aimed to clarify the alterations in glycans upon late differentiation of chondrocytes, during which hypertrophy-like changes occur. Primary mouse chondrocytes were differentiated using an insulin-induced chondro-osteogenic differentiation model. Comprehensive glycomics, including N-glycans, O-glycans, free oligosaccharides, glycosaminoglycan, and glycosphingolipid, were analyzed for the chondrocytes after 0-, 10- and 20-days cultivation. The comparison and clustering of the alteration of glycans upon hypertrophy-like changes of primary chondrocytes were performed. Comprehensive glycomic analyses provided complementary alterations in the levels of various glycans derived from glycoconjugates during hypertrophic differentiation. In addition, expression of genes related to glycan biosynthesis and metabolic processes was significantly correlated with glycan alterations. Our results indicate that total cellular glycan alterations are closely associated with chondrocyte hypertrophy and help to describe the glycophenotype by chondrocytes and their hypertrophic differentiation. our results will assist the identification of diagnostic and differentiation biomarkers in the future.

Adenovirus-mediated transduction with Histone Deacetylase 4 ameliorates disease progression in an osteoarthritis rat model

BACKGROUND

Downregulation of histone deacetylase-4 (HDAC4) contributes to cartilage degeneration in osteoarthritis (OA) because it promotes upregulation of runt-related transcription factor-2 (Runx-2) and osteoarthritis-related genes. The effect of HDAC4 upregulation on cartilage damage in OA remains unknown.

METHODS

Rat chondrocytes were infected with Ad-GFP or Ad-HDAC4-GFP for 48 h, stimulated with interleukin-1β (IL-1β, 10 ng/mL) for 24 h, and then harvested for RT-qPCR. Male Sprague-Dawley rats in 3 groups were given anterior cruciate ligament transection (ACLT) or sham operation, and knee injections with different adenovirus (Ad) vectors at 48 h after surgery and every 3 weeks thereafter: ACLT+Ad-GFP (n = 17); ACLT+Ad-HDAC4-GFP (n = 20); and sham+Ad-GFP (n = 15). Three ACLT-Ad-HDAC4-GFP rats were sacrificed at different times to examine the expression of HDAC4. Two ACLT-Ad-GFP rats and two ACLT-Ad-HDAC4-GFP rats were euthanized at week-2; articular cartilage was harvested and expression of HDAC4 was determined by RT-qPCR. All other rats were euthanized at week-8. Cartilage damage and OA progression was assessed using radiography, fluorescence molecular tomography (FMT), histology, immunohistochemistry (IHC), ELISA, and RT-qPCR.

RESULTS

Overexpression of HDAC4 in chondrocytes stimulated by IL-1β reduced the levels of Runx-2, MMP-13, and Collagen X, but increased the levels of Collagen II and Aggrecan. Upregulation of HDAC4 reduced osteophyte formation and cartilage damage, and increased articular cartilage anabolism.

CONCLUSION

HDAC4 attenuated articular cartilage damage by repression of Runx-2, MMP-13, and collagen X and induction of collagen II and ACAN in this rat model of OA. Upregulation of HDAC4 may provide chondroprotection in OA patients.

Simvastatin With PRP Promotes Chondrogenesis of Bone Marrow Stem Cells In Vitro and Wounded Rat Achilles Tendon-Bone Interface Healing In Vivo

BACKGROUND

Tendons and ligaments are joined to bone in a specialized interface that transmits force from muscle to bone and permits body movement. Tendon/ligament injuries always occur in the interface areas, and injured tendons/ligaments have a limited healing response because the insertion site is composed of a fibrocartilaginous zone.

PURPOSE

To study the effect of simvastatin with platelet-rich plasma (PRP) on chondrogenesis of rat bone marrow stem cells (BMSCs) in vitro and wounded rat Achilles tendon-bone interface healing in vivo.

STUDY DESIGN

Controlled laboratory study.

METHODS

The in vitro model was performed by the culture of rat BMSCs with various concentrations of simvastatin (0, 10, 50, 100 nM) for 2 weeks. The effect of simvastatin on the chondrogenic differentiation of the BMSCs was examined by histochemical analysis and real-time quantitative reverse transcription polymerase chain reaction. The in vivo model was carried out by testing the healing effect of simvastatin with PRP on 12 wounded rat Achilles tendon-bone interfaces.

RESULTS

Simvastatin induced chondrogenic differentiation of rat BMSCs in a concentration-dependent manner as evidenced by histological staining and real-time quantitative reverse transcription polymerase chain reaction. The wounds treated with simvastatin alone or with simvastatin-containing PRP gel healed much faster than the wounds treated with saline alone or PRP alone. Histological analysis showed that higher percentages of healed tissues were positively stained with safranin O and fast green in wounds treated with simvastatin-containing PRP gel than in the other 3 groups. Immunohistochemical analysis further demonstrated these findings, as evidenced by more positively stained healed tissues with collagen I and II antibodies in the wound areas treated with simvastatin-containing PRP gel than the other 3 groups.

CONCLUSION

The combination of simvastatin with PRP induced chondrogenesis of BMSCs in vitro and enhanced fibrocartilage formation in vivo. The simvastatin-PRP gel treatment promotes wounded tendon-bone interface healing in clinical treatment.

CLINICAL RELEVANCE

The combination of simvastatin with PRP may be a good clinical treatment for wounded tendon/ligament junction healing, especially for acute sports-related tendon/ligament injuries.

Differential chondro- and osteo-stimulation in three-dimensional porous scaffolds with different topological surfaces provides a design strategy for biphasic osteochondral engineering

Bone/cartilage interfacial tissue engineering needs to satisfy the differential properties and architectures of the osteochondral region. Therefore, biphasic or multiphasic scaffolds that aim to mimic the gradient hierarchy are widely used. Here, we find that two differently structured (topographically) three-dimensional scaffolds, namely, "dense" and "nanofibrous" surfaces, show differential stimulation in osteo- and chondro-responses of cells. While the nanofibrous scaffolds accelerate the osteogenesis of mesenchymal stem cells, the dense scaffolds are better in preserving the phenotypes of chondrocytes. Two types of porous scaffolds, generated by a salt-leaching method combined with a phase-separation process using the poly(lactic acid) composition, had a similar level of porosity (~90%) and pore size (~150 μm). The major difference in the surface nanostructure led to substantial changes in the surface area and water hydrophilicity (nanofibrous ≫ dense); as a result, the nanofibrous scaffolds increased the cell-to-matrix adhesion of mesenchymal stem cells significantly while decreasing the cell-to-cell contracts. Importantly, the chondrocytes, when cultured on nanofibrous scaffolds, were prone to lose their phenotype, including reduced chondrogenic expressions (SOX-9, collagen type II, and Aggrecan) and glycosaminoglycan content, which was ascribed to the enhanced cell-matrix adhesion with reduced cell-cell contacts. On the contrary, the osteogenesis of mesenchymal stem cells was significantly accelerated by the improved cell-to-matrix adhesion, as evidenced in the enhanced osteogenic expressions (RUNX2, bone sialoprotein, and osteopontin) and cellular mineralization. Based on these findings, we consider that the dense scaffold is preferentially used for the chondral-part, whereas the nanofibrous structure is suitable for osteo-part, to provide an optimal biphasic matrix environment for osteochondral tissue engineering.

Methionine attenuates the intensity of rheumatoid arthritis by downregulating NF-κB and iNOS expression in neonatal rats

The present study investigated the anti-arthritic effects of methionine in neonatal rats. Rats were divided into four groups, with six rats in each group. The rats were administered methionine (150- or 300-mg/kg body weight) orally for 45 consecutive days. The expression levels of catalase, superoxide dismutase (SOD), reduced glutathione (GSH), lipid peroxidation, glutathione peroxidase (Gpx), prostaglandin E₂ (PGE₂), matrix metalloproteinase-3, uric acid, nitric oxide (NO), ceruloplasmin, inducible nitric oxide synthase (iNOS), and nuclear factor (NF)-κB were determined in rheumatoid arthritis-induced neonatal rats. The levels of SOD, catalase, Gpx, and GSH were substantially reduced in control rats, while the levels of other parameters were increased in control neonatal rats. However, methionine supplementation significantly increased (more than 40%) the levels of SOD, catalase, Gpx, and GSH in neonatal rats. The levels of lipid peroxidation, uric acid, ceruloplasmin, NO, and PGE₂ were significantly reduced following methionine supplementation. Furthermore, NF-κB mRNA expression was substantially reduced up to 51.7% in the 300-mg/kg methionine group, whereas the mRNA expression of iNOS was reduced up to 43.5% in the 300-mg/kg methionine group. NF-κB protein expression was substantially reduced up to 45.8% in the 300-mg/kg methionine group, whereas the protein expression of iNOS was reduced up to 45.4% in the 300-mg/kg methionine group. Taken together, these data suggest that methionine supplementation was effective against rheumatoid arthritis.

Co-culture of dedifferentiated and primary human chondrocytes obtained from cadaveric donor enhance the histological quality of repair tissue: an in-vivo animal study

To compare the quality of the repair tissue in three-dimensional co-culture of human chondrocytes implanted in an in vivo model. Six cadaveric and five live human donors were included. Osteochondral biopsies from the donor knees were harvested for chondrocyte isolation. Fifty percent of cadaveric chondrocytes were expanded until passage-2 (P2) while the remaining cells were cryopreserved in passage-0 (P0). Fresh primary chondrocytes (P0f) obtained from live human donors were co-cultured. Three-dimensional constructs were prepared with a monolayer of passage-2 chondrocytes, collagen membrane (Geistlich Bio-Gide^®), and pellet of non-co-cultured (P2) or co-cultured chondrocytes (P2 + P0c, P2 + P0f). Constructs were implanted in the subcutaneous tissue of athymic mice and left for 3 months growth. Safranin-O and Alcian blue staining were used to glycosaminoglycan content assessment. Aggrecan and type-II collagen were evaluated by immunohistochemistry. New-formed tissue quality was evaluated with an adaptation of the modified O'Driscoll score. Histological quality of non-co-cultured group was 4.37 (SD ±4.71), while co-cultured groups had a mean score of 8.71 (SD ±3.98) for the fresh primary chondrocytes and 9.57 (SD ±1.27) in the cryopreserved chondrocytes. In immunohistochemistry, Co-culture groups were strongly stained for type-II and aggrecan not seen in the non-co-cultured group. It is possible to isolate viable chondrocytes from cadaveric human donors in samples processed in the first 48-h of dead. There is non-significant difference between the numbers of chondrocytes isolated from live or cadaveric donors. Cryopreservation of cadaveric primary chondrocytes does not alter the capability to form cartilage like tissue. Co-culture of primary and passaged chondrocytes enhances the histological quality of new-formed tissue compared to non-co-cultured cells.

Expression of the semicarbazide-sensitive amine oxidase in articular cartilage: its role in terminal differentiation of chondrocytes in rat and human

OBJECTIVE

Semicarbazide-sensitive amine oxidase (SSAO) catalyzes the oxidation of primary amines into ammonia and reactive species (hydrogen peroxide, aldehydes). It is highly expressed in mammalian tissues, especially in vascular smooth muscle cells and adipocytes, where it plays a role in cell differentiation and glucose transport. The study aims at characterizing the expression and the activity of SSAO in rat and human articular cartilage of the knee, and to investigate its potential role in chondrocyte terminal differentiation.

DESIGN

SSAO expression was examined by immunohistochemistry and western blot. Enzyme activity was measured using radiolabeled benzylamine as a substrate. Primary cell cultures of rat chondrocytes were treated for 21 days by a specific SSAO inhibitor, LJP 1586. Terminal chondrocyte differentiation markers were quantified by RT-qPCR. The basal and IL1β-stimulated glucose transport was monitored by the entrance of (3)[H]2-deoxyglucose in chondrocytes.

RESULTS

SSAO was expressed in chondrocytes of rat and human articular cartilage. SSAO expression was significantly enhanced during the hypertrophic differentiation of chondrocytes characterized by an increase in MMP13 and in alkaline phosphatase (ALP) expressions. SSAO inhibition delayed the late stage of chondrocyte differentiation without cell survival alteration and diminished the basal and IL1β-stimulated glucose transport. Interestingly, SSAO activity was strongly increased in human osteoarthritic cartilage.

CONCLUSIONS

SSAO was expressed as an active form in rat and human cartilage. The results suggest the involvement of SSAO in rat chondrocyte terminal differentiation via a modulation of the glucose transport. In man, the increased SSAO activity detected in osteoarthritic patients may trigger hypertrophy and cartilage degeneration.

TGF-β Suppresses Ift88 Expression in Chondrocytic ATDC5 Cells

Ift88 is an intraflagella transport protein, critical for the cilium, and has been shown to be required for the maintenance of chondrocytes and cartilage. However, how Ift88 is controlled by cytokines that play a role in osteoarthritis is not well understood. Therefore, we examined the effects of TGF-β on the expression of Ift88. We used ATDC5 cells as chondrocytes and analyzed the effects of TGF-β on gene expression. TGF-β treatment suppresses the levels of Ift88 mRNA in a dose-dependent manner starting from as low as 0.5 ng/mL and reaching the nadir at around 2 ng/mL. TGF-β treatment also suppresses the protein levels of Ift88. TGF-β suppression of Ift88 is still observed when the cells are cultured in the presence of a transcriptional inhibitor while the TGF-β suppression is weakened in the presence of a protein synthesis inhibitor, cycloheximide. TGF-β treatment suppresses the levels of Ift88 mRNA stability suggesting the presence of posttranscriptional regulation. TGF-β treatment reduces the number of cilia positive cells and suppresses average length of cilia. Knockdown of Ift88 by siRNA enhances TGF-β-induced increase in type II collagen mRNA expression in ATDC5 cells revealing the suppressive role of Ift88 on TGF-β-induced regulation of extracellular matrix protein expression. TGF-β also suppresses Ift88 mRNA expression in primary culture of rib chondrocytes. These data indicate that TGF-β regulates Ift88 gene expression at least in part via posttrascriptional manner.

Isolation and culture of murine primary chondrocytes

To identify factors that are necessary and sufficient for chondrocyte hypertrophic differentiation and cartilage matrix mineralization, primary chondrocyte culture models have been developed. Here we describe the isolation, short-term and long-term culture, and analysis of primary costal chondrocytes from the mouse. Briefly, sternae and rib cages from neonatal pups are dissected, and chondrocytes are isolated via enzymatic digestions. Chondrocytes are then plated at high density and cultured in the presence of ascorbic acid and beta-glycerophosphate as well as various recombinant proteins to promote or inhibit hypertrophic differentiation. We also describe the use of adenoviruses to recombine floxed alleles and over-express genes within these cultures. Finally, we detail methods for alkaline phosphatase and alizarin red staining that are used to visualize chondrocyte maturation and cartilage matrix mineralization.

Protective effects of C-type natriuretic peptide on linear growth and articular cartilage integrity in a mouse model of inflammatory arthritis

Objective

The C-type natriuretic peptide (CNP) signaling pathway is a major contributor to postnatal skeletal growth in humans. This study was undertaken to investigate whether CNP signaling could prevent growth delay and cartilage damage in an animal model of inflammatory arthritis.

Methods

We generated transgenic mice that overexpress CNP (B6.SJL-Col2a1-NPPC) in chondrocytes. We introduced the CNP transgene into mice with experimental systemic inflammatory arthritis (K/BxN T cell receptor [TCR]) and determined the effect of CNP overexpression in chondrocytes on the severity of arthritis, cartilage damage, and linear growth. We also examined primary chondrocyte cultures for changes in gene and protein expression resulting from CNP overexpression.

Results

K/BxN TCR mice exhibited linear growth delay (P < 0.01) compared to controls, and this growth delay was correlated with the severity of arthritis. Diminished chondrocyte proliferation and matrix production was also seen in K/BxN TCR mice. Compared to non–CNP-transgenic mice, K/BxN TCR mice with overexpressed CNP had milder arthritis, no growth delay, and less cartilage damage. Primary chondrocytes from mice overexpressing CNP were less sensitive to inflammatory cytokines than wild-type mouse chondrocytes.

Conclusion

CNP overexpression in chondrocytes can prevent endochondral growth delay and protect against cartilage damage in a mouse model of inflammatory arthritis. Pharmacologic or biologic modulation of the CNP signaling pathway may prevent growth retardation and protect cartilage in patients with inflammatory joint diseases, such as juvenile idiopathic arthritis.

The ras-GTPase activity of neurofibromin restrains ERK-dependent FGFR signaling during endochondral bone formation

The severe defects in growth plate development caused by chondrocyte extracellular signal-regulated protein kinases 1 and 2 (ERK1/2) gain or loss-of-function suggest that tight spatial and temporal regulation of mitogen-activated protein kinase signaling is necessary to achieve harmonious growth plate elongation and structure. We provide here evidence that neurofibromin, via its Ras guanosine triphosphatase -activating activity, controls ERK1/2-dependent fibroblast growth factor receptor (FGFR) signaling in chondrocytes. We show first that neurofibromin is expressed in FGFR-positive prehypertrophic and hypertrophic chondrocytes during growth plate endochondral ossification. Using mice lacking neurofibromin 1 (Nf1) in type II collagen-expressing cells, (Nf1col2(-/-) mutant mice), we then show that lack of neurofibromin in post-mitotic chondrocytes triggers a number of phenotypes reminiscent of the ones observed in mice characterized by FGFR gain-of-function mutations. Those include dwarfism, constitutive ERK1/2 activation, strongly reduced Ihh expression and decreased chondrocyte proliferation and maturation, increased chondrocytic expression of Rankl, matrix metalloproteinase 9 (Mmp9) and Mmp13 and enhanced growth plate osteoclastogenesis, as well as increased sensitivity to caspase-9 mediated apoptosis. Using wildtype (WT) and Nf1(-/-) chondrocyte cultures in vitro, we show that FGF2 pulse-stimulation triggers rapid ERK1/2 phosphorylation in both genotypes, but that return to the basal level is delayed in Nf1(-/-) chondrocytes. Importantly, in vivo ERK1/2 inhibition by daily injection of a recombinant form of C-type natriuretic peptide to post-natal pups for 18 days was able to correct the short stature of Nf1col2(-/-) mice. Together, these results underscore the requirement of neurofibromin and ERK1/2 for normal endochondral bone formation and support the notion that neurofibromin, by restraining RAS-ERK1/2 signaling, is a negative regulator of FGFR signaling in differentiating chondrocytes.

Effect of melatonin on the proliferation and differentiation of chondrocytes from rat vertebral body growth plate in vitro

PURPOSE

Abnormal growth of vertebral body growth plate (VBGP) is considered as one of the etiologic factors in the adolescent idiopathic scoliosis (AIS). It was well-known that melatonin was correlated with the emergence and development of AIS. This study aimed to investigate the effect of melatonin on rat VBGP chondrocytes in vitro.

METHODS

Chondrocytes were isolated from rat VBGP, and treated with or without melatonin. Cell proliferation was measured by the Alamar Blue assay. Gene expression of collagen type II and aggrecan were evaluated by real-time PCR. Expression of the melatonin receptors (MT1, MT2), proliferating cell nuclear antigen (PCNA, a cell proliferation marker), Sox9 (a chondrocytic differentiation marker) and Smad4 (a common mediator in regulating the proliferation and differentiation of chondrocytes) were detected by Western blotting.

RESULTS

Expression of melatonin receptors (MT1, MT2) were detected in the rat VBGP chondrocytes. Melatonin, at 10 and 100 µg/mL concentration, significantly inhibited the proliferation of VBGP-chondrocytes and the gene expression of collagen type II and aggrecan, and down-regulated the protein expression of PCNA, Sox9 and Smad4. In addition, the inhibitory effect of melatonin was reversed by luzindole, a melatonin receptor antagonist.

CONCLUSIONS

These results suggest that melatonin at high concentrations can inhibit the proliferation and differentiation of VBGP chondrocytes, which might give some new insight into the pathogenic mechanism of AIS.

A method of isolating viable chondrocytes with proliferative capacity from cryopreserved human articular cartilage

This study aimed to optimise methods of cryopreserving human articular cartilage (AC) tissue for the isolation of late chondrocytes. Human AC specimens from osteoarthritis patients who had undergone total knee replacement were used to optimise the chondrocyte isolation process and the choice of cryoprotective agent (CPA). For AC tissue cryopreservation, intact cored cartilage discs (5 mm diameter) and diced cartilage (0.2-1 mm cubes) from the same sized discs were step cooled and stored in liquid nitrogen for up to 48 h before chondrocyte isolation and in vitro assay of cell viability and proliferative potential. The results showed that 10 % dimethyl sulphoxide in 90 % foetal bovine serum was a successful CPA for chondrocyte cryopreservation. Compared with intact cored discs, dicing of AC tissue into 0.2-1 mm cubes significantly increased the viability and proliferative capacity of surviving chondrocytes after cryopreservation. In situ cross-section imaging using focused ion beam microscopy revealed that dicing of cored AC discs into small cubes reduced the cryo-damage to cartilage tissue matrix. In conclusion, modification of appropriate factors, such as the size of the tissue, cryoprotective agent, and isolation protocol, can allow successful isolation of viable chondrocytes with high proliferative capacity from cryopreserved human articular cartilage tissue. Further studies are required to determine whether these cells may retain cartilage differentiation capacity and provide sufficient chondrocytes for use as implants in clinical applications.

In vivo chondrocyte and transforming growth factor-β1 delivery using the thermosensitive chitosan/starch/β-glycerol phosphate hydrogel

In present study, the chitosan/starch/β-glycerol phosphate hydrogel was investigated as an effective carrier for chondrocytes and delivery of transforming growth factor-β1. In vitro study indicated that transforming growth factor-β1 was released sustainably for 14 days with its biological activity to stimulate chondrocyte functions, as indicated by the strong expression of type II collagen protein. Subcutaneous implantation to rats revealed the strong expressions of type II collagen and aggrecan messenger ribonucleic acids, and also type II collagen protein was observed in the hydrogel in combination with transforming growth factor-β1 within 2 weeks. Our collective results showed the potential of chitosan/starch/β-glycerol phosphate hydrogel for effective delivery of chondrocytes and transforming growth factor-β1, and preserve chondrocytes’ phenotype and functions in vitro.

Arid5a cooperates with Sox9 to stimulate chondrocyte-specific transcription

SRY-box-containing gene 9 (Sox9) is an essential transcription factor in chondrocyte lineage determination and differentiation. Recent studies demonstrated that Sox9 controls the transcription of chondrocyte-specific genes in association with several other transcriptional regulators. To further understand the molecular mechanisms by which Sox9 influences transcriptional events during chondrocyte differentiation, we attempted to identify transcriptional partners of Sox9 and to examine their roles in chondrocyte differentiation. We isolated AT-rich interactive domain-containing protein 5a (Arid5a; also known as Mrf1) as an activator of the Col2a1 gene promoter from an ATDC5 cDNA library. Arid5a was highly expressed in cartilage and induced during chondrocyte differentiation. Furthermore, Arid5a physically interacted with Sox9 in nuclei and up-regulated the chondrocyte-specific action of Sox9. Overexpression of Arid5a stimulated chondrocyte differentiation in vitro and in an organ culture system. In contrast, Arid5a knockdown inhibited Col2a1 expression in chondrocytes. In addition, Arid5a binds directly to the promoter region of the Col2a1 gene and stimulates acetylation of histone 3 in the region. Our results suggest that Arid5a may directly interact with Sox9 and thereby enhance its chondrocyte-specific action.

Osteogenic potential of rat stromal cells derived from periodontal ligament

Various mesenchymal stromal cells (MSCs) have been applied to regenerative medicine. MSCs derived from periodontal tissue could also be a useful cell source for alveolar bone regeneration. However, only a few attempts of direct comparisons have been made between MSCs from periodontal tissues and those from other somatic tissues. The purpose of this study was to clarify the osteogenic characteristics of mesenchymal stromal cells derived from bone marrow (BMSCs), adipose tissue (ASCs) and periodontal ligament (PDLSCs). BMSCs, ASCs and PDLSCs were isolated from Fisher 344 rats. After 1 week of primary culture, stromal cells were subjected to cell surface analysis and osteogenic differentiation. The cells were subcultured for 2 weeks with and without osteogenic supplements (OS), followed by biochemical and histological analyses. With regard to cell surface antigens, all MSCs were positive for CD29 and CD90 and negative for CD45. With regard to osteogenic differentiation, BMSCs with OS had the highest ALP activity, calcium uptake and osteocalcin content. Without OS, PDLSCs had the highest levels of these bone differentiation markers. RT-PCR analysis and histological analysis showed similar trends. These results indicate that PDLSCs are an ideal candidate for alveolar bone regeneration.

The transcription factor Znf219 regulates chondrocyte differentiation by assembling a transcription factory with Sox9

Sox9 is an essential transcription factor for chondrogenesis by regulating the expression of chondrogenic genes. However, its regulatory mechanism is not fully understood. To address this, we attempted to identify the transcriptional partners of Sox9 by screening the cDNA library of the chondrogenic cell line ATDC5 using the collagen 2α1 (Col2α1) gene promoter fused to a luciferase reporter gene. One of the positive clones encoded the Znf219 gene. Whole mount in situ hybridization experiments indicated that Znf219 mRNA was specifically expressed in the developing limb buds where Col2α1 and Sox9 were strongly expressed. Znf219 markedly enhanced the transcriptional activity of Sox9 on the Col2a1 gene promoter. In addition, Znf219 is physically associated with Sox9 and is colocalized with Sox9 in the nucleus. We also found that overexpression of Znf219 profoundly increased Sox9-induced mRNA expression of Col2a1, aggrecan and Col11a2. Consistently, knockdown of Znf219 decreased the Sox9-induced mRNA expression of these genes. Furthermore, a dominant-negative mutant Znf219 inhibited Bmp2-induced chondrocyte differentiation. Our results suggest that Znf219 plays an important role in the regulation of chondrocyte differentiation as a transcriptional partner of Sox9.

Sox9 family members negatively regulate maturation and calcification of chondrocytes through up-regulation of parathyroid hormone-related protein

Sox9 is a transcription factor that plays an essential role in chondrogenesis and has been proposed to inhibit the late stages of endochondral ossification. However, the molecular mechanisms underlying the regulation of chondrocyte maturation and calcification by Sox9 remain unknown. In this study, we attempted to clarify roles of Sox9 in the late stages of chondrocyte differentiation. We found that overexpression of Sox9 alone or Sox9 together with Sox5 and Sox6 (Sox5/6/9) inhibited the maturation and calcification of murine primary chondrocytes and up-regulated parathyroid hormone-related protein (PTHrP) expression in primary chondrocytes and the mesenchymal cell line C3H10T1/2. Sox5/6/9 stimulated the early stages of chondrocyte proliferation and development. In contrast, Sox5/6/9 inhibited maturation and calcification of chondrocytes in organ culture. The inhibitory effects of Sox5/6/9 were rescued by treating with anti-PTHrP antibody. Moreover, Sox5/6/9 bound to the promoter region of the PTHrP gene and up-regulated PTHrP gene promoter activity. Interestingly, we also found that the Sox9 family members functionally collaborated with Ihh/Gli2 signaling to regulate PTHrP expression and chondrocyte differentiation. Our results provide novel evidence that Sox9 family members mediate endochondral ossification by up-regulating PTHrP expression in association with Ihh/Gli2 signaling.

Assessment of the suitability of chitosan/polybutylene succinate scaffolds seeded with mouse mesenchymal progenitor cells for a cartilage tissue engineering approach

In this work, scaffolds derived from a new biomaterial originated from the combination of a natural material and a synthetic material were tested for assessing their suitability for cartilage tissue engineering applications. In order to obtain a better outcome result in terms of scaffolds' overall properties, different blends of natural and synthetic materials were created. Chitosan and polybutylene succinate (C-PBS) 50/50 (wt%) were melt blended using a twin-screw extruder and processed into 5 x 5 x 5 mm scaffolds by compression moulding with salt leaching. Micro-computed tomography analysis calculated an average of 66.29% porosity and 92.78% interconnectivity degree for the presented scaffolds. The salt particles used ranged in size between 63 and 125 mum, retrieving an average pore size of 251.28 mum. Regarding the mechanical properties, the compressive modulus was of 1.73 +/- 0.4 MPa (E(sec) 1%). Cytotoxicity evaluation revealed that the leachables released by the developed porous structures were not harmful to the cells and hence were noncytotoxic. Direct contact assays were carried out using a mouse bone marrow-derived mesenchymal progenitor cell line (BMC9). Cells were seeded at a density of 5 x 10(5) cells/scaffold and allowed to grow for periods up to 3 weeks under chondrogenic differentiating conditions. Scanning electron microscopy analysis revealed that the cells were able to proliferate and colonize the scaffold structure, and MTS test demonstrated cell viability during the time of the experiment. Finally, Western blot performed for collagen type II, a natural cartilage extracellular matrix component, showed that this protein was being expressed by the end of 3 weeks, which seems to indicate that the BMC9 cells were being differentiated toward the chondrogenic pathway. These results indicate the adequacy of these newly developed C-PBS scaffolds for supporting cell growth and differentiation toward the chondrogenic pathway, suggesting that they should be considered for further studies in the cartilage tissue engineering field.

MSX2 stimulates chondrocyte maturation by controlling Ihh expression

Several studies indicated that a homeobox gene, Msx2, is implicated in regulation of skeletal development by controlling enchondral ossification as well as membranous ossification. However, the molecular basis by which Msx2 conducts chondrogenesis is currently unclear. In this study, we examined the role of Msx2 in chondrocyte differentiation using mouse primary chondrocytes and embryonic metatarsal explants. Treatment with BMP2 up-regulated the expression of Msx2 mRNA along with chondrocyte differentiation in murine primary chondrocytes. Overexpression of wild-type Msx2 stimulated calcification of primary chondrocytes in the presence of BMP2. We also found that constitutively active Msx2 (caMsx2) enhanced BMP2-dependent calcification more efficiently than wild-type Msx2. Consistently, caMsx2 overexpression up-regulated the expression of alkaline phosphatase and collagen type X induced by BMP2. Furthermore, organ culture experiments using mouse embryonic metatarsals indicated that caMsx2 clearly stimulated the maturation of chondrocytes into the prehypertrophic and hypertrophic stages in the presence of BMP2. In contrast, knockdown of Msx2 inhibited maturation of primary chondrocytes. The stimulatory effect of Msx2 on chondrocyte maturation was enhanced by overexpression of Smad1 and Smad4 but inhibited by Smad6, an inhibitory Smad for BMP2 signaling. These data suggest that Msx2 requires BMP2/Smad signaling for its chondrogenic action. In addition, caMsx2 overexpression induced Ihh (Indian hedgehog) expression in mouse primary chondrocytes. Importantly, treatment with cyclopamine, a specific inhibitor for hedgehogs, blocked Msx2-induced chondrogenesis. Collectively, our results indicated that Msx2 promotes the maturation of chondrocytes, at least in part, through up-regulating Ihh expression.

Cell Distribution in a Scaffold with Random Architectures under the Influence of Fluid Dynamics

Fluid dynamic environment and scaffold architectures have an important influence on cell growth and distribution inside the scaffold. A porous cylindrical scaffold with a central channel is seeded with the sheep mesenchymal stem cells (MSCs) in this study. Then the cell seeded scaffold is continuously perfused with α-MEM medium by a peristaltic pump for 7, 14, and 28 days. Histological study shows that the cell proliferation rates are different throughout the whole scaffolds. The different cell coverage is shown in various positions of the scaffold. A computational fluid dynamics (CFD) modeling is used to simulate the flow conditions within perfused cell-seeded scaffolds to give insight into the mechanisms of these cell growth phenomena. Relating the simulation results to perfusion experiments, the even fluid velocity (~0.26—0.64 mm/s) and shear stress (~0.0029—0.027 Pa) are found to correspond to increased cell proliferation within the cell-scaffold constructs. This method exhibits novel capabilities to compare results obtained for different perfusion rates or different scaffold microarchitectures and may allow specific fluid velocities and shear stresses to be determined that optimize the perfusion flow rate, porous scaffold architecture, and distribution of in vitro tissue growth.

Murine and chicken chondrocytes regulate osteoclastogenesis by producing RANKL in response to BMP2

Chondrocytes express RANKL, but their role in osteoclastogenesis is not clear. We report that hypertrophic chondrocytes induce osteoclast formation through RANKL production stimulated by BMP2 and Runx2/Smad1 and thus they may regulate resorption of calcified matrix by osteoclasts at growth plates.

INTRODUCTION

Bone morphogenetic protein (BMP) signaling and Runx2 regulate chondrogenesis during bone development and fracture repair and RANKL expression by osteoblast/stromal cells. Chondrocytes express RANKL, and this expression is stimulated by vitamin D3, but it is not known if chondrocytes directly support osteoclast formation or if BMPs or Runx2 is involved in this potential regulation of osteoclastogenesis.

MATERIAL AND METHODS

The chondrocyte cell line, ATDC5, primary mouse sternal chondrocytes, and chick sternal chondrocytes were used. Cells were treated with BMP2, and expression of RANKL and chondrocyte marker genes was determined by real-time RT-PCR and Western blot. Chondrocytes and spleen-derived osteoclast precursors +/- BMP2 were co-cultured to examine the effect of chondrocyte-produced RANKL on osteoclast formation. A reporter assay was used to determine whether BMP2-induced RANKL production is through transcriptional regulation of the RANKL promoter and whether it is mediated by Runx2.

RESULTS

BMP2 significantly increased expression of RANKL mRNA and protein in all three types of chondrocytes, particularly by Col X-expressing and upper sternal chondrocytes. Chondrocytes constitutively induced osteoclast formation. This effect was increased significantly by BMP2 and prevented by RANK:Fc. BMP2 significantly increased luciferase activity of the RANKL-luc reporter, and Smad1 increased this effect. Deletion or mutation of Runx2 binding sites within the RANKL promoter or overexpression of a dominant negative Runx2 abolished BMP2- and Smad1-mediated activation of RANKL promoter activity.

CONCLUSIONS

Hypertrophic chondrocytes may regulate osteoclastogenesis at growth plates to remove calcified matrix through BMP-induced RANKL expression.

BMP-5 expression increases during chondrocyte differentiation in vivo and in vitro and promotes proliferation and cartilage matrix synthesis in primary chondrocyte cultures

Bone morphogenetic proteins (BMPs) play pivotal roles in bone and cartilage growth and repair. Through phenotypes of short-ear (se) mice, which have BMP-5 mutations, a role for BMP-5 in some specific aspects of skeletogenesis and cartilage growth is known. This report examines BMP-5 expression in the growth plate and in differentiating cultures of primary chondrocytes, and the effects of addition of BMP-5 or its inhibition by anti-BMP-5 antibody in chondrocyte cultures. By laser capture microdissection and immunohistochemistry, we found that BMP-5 is expressed in proliferating zone (PZ) chondrocytes and that the expression increases sharply with hypertrophic differentiation. A similar pattern was observed in differentiating cultures of primary chondrocytes, with BMP-5 expression increasing as cells differentiated, in contrast to other BMPs. BMP-5 added to cultures increased cell proliferation early in the culture period and also stimulated cartilage matrix synthesis. Also, BMP-5 addition to the cultures activated phosphorylation of Smad 1/5/8 and p38 MAP kinase and caused increased nuclear accumulation of phospho-Smads. Anti-BMP-5 antibody inhibited the endogenous BMP-5, reducing cell proliferation and phospho-Smad nuclear accumulation. Together, the results demonstrate that BMP-5 is normally an important regulator of chondrocyte proliferation and differentiation. Whether other BMPs may compensate in BMP-5 loss-of-function mutations is discussed.

The effect of chondrocyte cryopreservation on cartilage engineering

Chondrocytes were collected from the stifle joints of four pigs to study the effect of cryopreservation on the chondrogenic potential of chondrocytes. Half of the cells were cryopreserved for 3months. Polyglycolic acid scaffolds were cultured with fresh or cryopreserved chondrocytes for 4weeks. Cell morphology and the quality of engineered tissue were evaluated by scanning electron microscopy, histopathology and biochemical methods. More cells attached to scaffolds at 48h when fresh chondrocytes were seeded. At 4weeks, the numbers of cells, DNA and collagen II were greater in constructs engineered by fresh cells. However, the collagen II/DNA ratio did not differ between the two groups. More matrix was identified on a scanning electron microscope and by histopathology in the fresh group. Cartilage engineered with cryopreserved chondrocytes may contain less matrix and fewer cells. These findings most likely resulted from a lack of cell attachment on the matrix secondary to cryopreservation. Future studies are needed to further evaluate the mechanism by which cryopreservation may affect chondrocyte attachment.