Enhanced hyaline cartilage matrix synthesis in collagen sponge scaffolds by using siRNA to stabilize chondrocytes phenotype cultured with bone morphogenetic protein-2 under hypoxia

Propolis as a Potential Therapeutic Agent to Counteract Age-Related Changes in Cartilage: An In Vivo Study

Aging is intricately linked to chronic low-grade systemic inflammation, which plays a significant role in various age-related conditions, including osteoarthritis (OA). The aging process significantly influences the development of OA due to alterations in cartilage composition, reduced proteoglycan content, dysregulation of growth factor signaling, and heightened oxidative stress. Propolis, a natural product renowned for its potent antioxidant and anti-inflammatory properties, has the potential to mitigate age-induced changes in cartilage. The primary objective of this study was to rigorously assess the impact of in vivo propolis treatment on the histopathological characteristics of knee articular cartilage in senescent rats. This study involved a cohort of twenty male Sprague-Dawley rats, randomly allocated into four distinct groups for comparative analysis: YR (control group consisting of young rats), SR (senescent rats), SR-EEP (senescent rats treated with an ethanolic extract of propolis, EEP), and SR-V (senescent rats administered with a control vehicle). This study employed comprehensive histological and stereological analyses of knee articular cartilage. Propolis treatment exhibited a significant capacity to alleviate the severity of osteoarthritis, enhance the structural integrity of cartilage, and augment chondrocyte density. These promising findings underscore the potential of propolis as a compelling therapeutic agent to counteract age-related alterations in cartilage and, importantly, to potentially forestall the onset of osteoarthritis.

Bone Marrow MSC Secretome Increases Equine Articular Chondrocyte Collagen Accumulation and Their Migratory Capacities

Equine osteoarthritis (OA) leads to cartilage degradation with impaired animal well-being, premature cessation of sport activity, and financial losses. Mesenchymal stem cell (MSC)-based therapies are promising for cartilage repair, but face limitations inherent to the cell itself. Soluble mediators and extracellular vesicles (EVs) secreted by MSCs are the alternatives to overcome those limitations while preserving MSC restorative properties. The effect of equine bone marrow MSC secretome on equine articular chondrocytes (eACs) was analyzed with indirect co-culture and/or MSC-conditioned media (CM). The expression of healthy cartilage/OA and proliferation markers was evaluated in eACs (monolayers or organoids). In vitro repair experiments with MSC-CM were made to evaluate the proliferation and migration of eACs. The presence of nanosized EVs in MSC-CM was appraised with nanoparticle tracking assay and transmission electron microscopy. Our results demonstrated that the MSC secretome influences eAC phenotype by increasing cartilage functionality markers and cell migration in a greater way than MSCs, which could delay OA final outcomes. This study makes acellular therapy an appealing strategy to improve equine OA treatments. However, the MSC secretome contains a wide variety of soluble mediators and small EVs, such as exosomes, and further investigation must be performed to understand the mechanisms occurring behind these promising effects.

Autophagy and Polyphenols in Osteoarthritis: A Focus on Epigenetic Regulation

Autophagy is an intracellular mechanism that maintains cellular homeostasis in different tissues. This process declines in cartilage due to aging, which is correlated with osteoarthritis (OA), a multifactorial and degenerative joint disease. Several studies show that microRNAs regulate different steps of autophagy but only a few of them participate in OA. Therefore, epigenetic modifications could represent a therapeutic opportunity during the development of OA. Besides, polyphenols are bioactive components with great potential to counteract diseases, which could reverse altered epigenetic regulation and modify autophagy in cartilage. This review aims to analyze epigenetic mechanisms that are currently associated with autophagy in OA, and to evaluate whether polyphenols are used to reverse the epigenetic alterations generated by aging in the autophagy pathway.

Articular cartilage and osteochondral tissue engineering techniques: Recent advances and challenges

In spite of the considerable achievements in the field of regenerative medicine in the past several decades, osteochondral defect regeneration remains a challenging issue among diseases in the musculoskeletal system because of the spatial complexity of osteochondral units in composition, structure and functions. In order to repair the hierarchical tissue involving different layers of articular cartilage, cartilage-bone interface and subchondral bone, traditional clinical treatments including palliative and reparative methods have showed certain improvement in pain relief and defect filling. It is the development of tissue engineering that has provided more promising results in regenerating neo-tissues with comparable compositional, structural and functional characteristics to the native osteochondral tissues. Here in this review, some basic knowledge of the osteochondral units including the anatomical structure and composition, the defect classification and clinical treatments will be first introduced. Then we will highlight the recent progress in osteochondral tissue engineering from perspectives of scaffold design, cell encapsulation and signaling factor incorporation including bioreactor application. Clinical products for osteochondral defect repair will be analyzed and summarized later. Moreover, we will discuss the current obstacles and future directions to regenerate the damaged osteochondral tissues.

Tumor Suppressive Role of miR-342-5p in Human Chondrosarcoma Cells and 3D Organoids

Chondrosarcomas are malignant bone tumors. Their abundant cartilage-like extracellular matrix and their hypoxic microenvironment contribute to their resistance to chemotherapy and radiotherapy, and no effective therapy is currently available. MicroRNAs (miRNAs) may be an interesting alternative in the development of therapeutic options. Here, for the first time in chondrosarcoma cells, we carried out high-throughput functional screening using impedancemetry, and identified five miRNAs with potential antiproliferative or chemosensitive effects on SW1353 chondrosarcoma cells. The cytotoxic effects of miR-342-5p and miR-491-5p were confirmed on three chondrosarcoma cell lines, using functional validation under normoxia and hypoxia. Both miRNAs induced apoptosis and miR-342-5p also induced autophagy. Western blots and luciferase reporter assays identified for the first time Bcl-2 as a direct target of miR-342-5p, and also Bcl-xL as a direct target of both miR-342-5p and miR-491-5p in chondrosarcoma cells. MiR-491-5p also inhibited EGFR expression. Finally, only miR-342-5p induced cell death on a relevant 3D chondrosarcoma organoid model under hypoxia that mimics the in vivo microenvironment. Altogether, our results revealed the tumor suppressive activity of miR-342-5p, and to a lesser extent of miR-491-5p, on chondrosarcoma lines. Through this study, we also confirmed the potential of Bcl-2 family members as therapeutic targets in chondrosarcomas.

Silk fibroin hydrogel scaffolds incorporated with chitosan nanoparticles repair articular cartilage defects by regulating TGF-β1 and BMP-2

Cartilage defects frequently occur around the knee joint yet cartilage has limited self-repair abilities. Hydrogel scaffolds have excellent potential for use in tissue engineering. Therefore, the aim of the present study was to assess the ability of silk fibroin (SF) hydrogel scaffolds incorporated with chitosan (CS) nanoparticles (NPs) to repair knee joint cartilage defects. In the present study, composite systems of CS NPs incorporated with transforming growth factor-β1 (TGF-β1; TGF-β1@CS) and SF incorporated with bone morphogenetic protein-2 (BMP-2; TGF-β1@CS/BMP-2@SF) were developed and characterized with respect to their size distribution, zeta potential, morphology, and release of TGF-β1 and BMP-2. Bone marrow stromal cells (BMSCs) were co-cultured with TGF-β1@CS/BMP-2@SF extracts to assess chondrogenesis in vitro using a cell counting kit-8 assay, which was followed by in vivo evaluations in a rabbit model of knee joint cartilage defects. The constructed TGF-β1@CS/BMP-2@SF composite system was successfully characterized and showed favorable biocompatibility. In the presence of TGF-β1@CS/BMP-2@SF extracts, BMSCs exhibited normal cell morphology and enhanced chondrogenic ability both in vitro and in vivo, as evidenced by the promotion of cell viability and the alleviation of cartilage defects. Thus, the TGF-β1@CS/BMP-2@SF hydrogel developed in the present study promoted chondrogenic ability of BMSCs both in vivo and in vitro by releasing TGF-β1 and BMP-2, thereby offering a novel therapeutic strategy for repairing articular cartilage defects in knee joints.

Validation of the 1,4-butanediol thermoplastic polyurethane as a novel material for 3D bioprinting applications

Tissue engineering (TE) seeks to fabricate implants that mimic the mechanical strength, structure, and composition of native tissues. Cartilage TE requires the development of functional personalized implants with cartilage-like mechanical properties capable of sustaining high load-bearing environments to integrate into the surrounding tissue of the cartilage defect. In this study, we evaluated the novel 1,4-butanediol thermoplastic polyurethane elastomer (b-TPUe) derivative filament as a 3D bioprinting material with application in cartilage TE. The mechanical behavior of b-TPUe in terms of friction and elasticity were examined and compared with human articular cartilage, PCL, and PLA. Moreover, infrapatellar fat pad-derived human mesenchymal stem cells (MSCs) were bioprinted together with scaffolds. in vitro cytotoxicity, proliferative potential, cell viability, and chondrogenic differentiation were analyzed by Alamar blue assay, SEM, confocal microscopy, and RT-qPCR. Moreover, in vivo biocompatibility and host integration were analyzed. b-TPUe demonstrated a much closer compression and shear behavior to native cartilage than PCL and PLA, as well as closer tribological properties to cartilage. Moreover, b-TPUe bioprinted scaffolds were able to maintain proper proliferative potential, cell viability, and supported MSCs chondrogenesis. Finally, in vivo studies revealed no toxic effects 21 days after scaffolds implantation, extracellular matrix deposition and integration within the surrounding tissue. This is the first study that validates the biocompatibility of b-TPUe for 3D bioprinting. Our findings indicate that this biomaterial can be exploited for the automated biofabrication of artificial tissues with tailorable mechanical properties including the great potential for cartilage TE applications.

Histological Evaluation and Gene Expression Profiling of Autophagy-Related Genes for Cartilage of Young and Senescent Rats

Autophagy is a cellular mechanism that protects cells from stress by digesting non-functional cellular components. In the cartilage, chondrocytes depend on autophagy as a principal mechanism to maintain cellular homeostasis. This protective role diminishes prior to the structural damage that normally occurs during aging. Considering that aging is the main risk factor for osteoarthritis, evaluating the expression of genes associated with autophagy in senescent cartilage might allow for the identification of potential therapeutic targets for treatment. Thus, we studied two groups of young and senescent rats. A histological analysis of cartilage and gene expression quantification for autophagy-related genes were performed. In aged cartilage, morphological changes were observed, such as an increase in cartilage degeneration as measured by the modified Mankin score, a decrease in the number of chondrocytes and collagen II (Col2a1), and an increase in matrix metalloproteinase 13 (Mmp13). Moreover, 84 genes associated with autophagy were evaluated by a PCR array analysis, and 15 of them were found to be significantly decreased with aging. Furthermore, an in silico analysis based on by two different bioinformatics software tools revealed that several processes including cellular homeostasis, autophagosome assembly, and aging—as well as several biological pathways such as autophagy, insulin-like growth factor 1 (IGF-1) signaling, PI3K (phosphoinositide 3-kinase)/AKT (serine/threonine kinase) signaling, and mammalian target of rapamycin (mTOR) signaling—were enriched. In conclusion, the analysis identified some potential targets for osteoarthritis treatment that would allow for the development of new therapeutic strategies for this chronic disease.

Electrospun Polymers in Cartilage Engineering-State of Play

Articular cartilage defects remain a clinical challenge. Articular cartilage defects progress to osteoarthritis, which negatively (e.g., remarkable pain, decreased mobility, distress) affects millions of people worldwide and is associated with excessive healthcare costs. Surgical procedures and cell-based therapies have failed to deliver a functional therapy. To this end, tissue engineering therapies provide a promise to deliver a functional cartilage substitute. Among the various scaffold fabrication technologies available, electrospinning is continuously gaining pace, as it can produce nano- to micro- fibrous scaffolds that imitate architectural features of native extracellular matrix supramolecular assemblies and can deliver variable cell populations and bioactive molecules. Herein, we comprehensively review advancements and shortfalls of various electrospun scaffolds in cartilage engineering.

Scaffold-Based Delivery of Nucleic Acid Therapeutics for Enhanced Bone and Cartilage Repair

Recent advances in tissue engineering have made progress toward the development of biomaterials capable of the delivery of growth factors, such as bone morphogenetic proteins, in order to promote enhanced tissue repair. However, controlling the release of these growth factors on demand and within the desired localized area is a significant challenge and the associated high costs and side effects of uncontrolled delivery have proven increasingly problematic in clinical orthopedics. Gene therapy may be a valuable tool to avoid the limitations of local delivery of growth factors. Following a series of setbacks in the 1990s, the field of gene therapy is now seeing improvements in safety and efficacy resulting in substantial clinical progress and a resurgence in confidence. Biomaterial scaffold-mediated gene therapy provides a template for cell infiltration and tissue formation while promoting transfection of cells to engineer therapeutic proteins in a sustained but ultimately transient fashion. Additionally, scaffold-mediated delivery of RNA-based therapeutics can silence specific genes associated with orthopedic pathological states. This review will provide an overview of the current state-of-the-art in the field of gene-activated scaffolds and their use within orthopedic tissue engineering applications. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1671-1680, 2019.

Propolis Reduces the Expression of Autophagy-Related Proteins in Chondrocytes under Interleukin-1β Stimulus

Background: Osteoarthritis (OA) is a progressive and multifactorial disease that is associated with aging. A number of changes occur in aged cartilage, such as increased oxidative stress, decreased markers of healthy cartilage, and alterations in the autophagy pathway. Propolis extracts contain a mixture of polyphenols and it has been proved that they have high antioxidant capacity and could regulate the autophagic pathway. Our objective was to evaluate the effect of ethanolic extract of propolis (EEP) on chondrocytes that were stimulated with IL-1β. Methods: Rabbit chondrocytes were isolated and stimulated with IL-1β and treated with EEP. We evaluated cell viability, nitric oxide production, healthy cartilage, and OA markers, and the expression of three proteins associated with the autophagy pathway LC3, ATG5, and AKT1. Results: The EEP treatment reduces the expression of LC3, ATG5, and AKT1, reduces the production of nitric oxide, increases the expression of healthy markers, and reduces OA markers. Conclusions: These results suggest that treatment with EEP in chondrocytes that were stimulated with IL-1β has beneficial effects, such as a decrease in the expression of proteins associated with autophagy, MMP13, and production of nitric oxide, and also increased collagen II.

Characterization of the Proliferating Layer Chondrocytes of Growth Plate for Cartilage Regeneration

IMPACT STATEMENT

In recent years, cell-based therapy is a promising strategy for repairing defect cartilage. However, in vitro expansion of articular chondrocytes (ACs) for collecting enough cell numbers eventually develops cell de-differentiation. In the present study, we choose the proliferative layer chondroctytes (PLCs) of growth plate as new candidate. The novel findings include (1) the higher proliferation potential of PLCs in comparison with the ACs, (2) PLCs produced more GAG than ACs, (3) the increased in GAG matrix production, (4) and lower senescence in PLCs. From these results, we found PLCs might be suitable as cell source for cartilage regeneration.

Regulation of Extracellular Matrix Synthesis by Shell Extracts from the Marine Bivalve Pecten maximus in Human Articular Chondrocytes- Application for Cartilage Engineering

The shells of the bivalve mollusks are organo-mineral structures predominantly composed of calcium carbonate, but also of a minor organic matrix, a mixture of proteins, glycoproteins, and polysaccharides. These proteins are involved in mineral deposition and, more generally, in the spatial organization of the shell crystallites in well-defined microstructures. In this work, we extracted different organic shell extracts (acid-soluble matrix, acid-insoluble matrix, water-soluble matrix, guanidine HCl/EDTA-extracted matrix, referred as ASM, AIM, WSM, and EDTAM, respectively) from the shell of the scallop Pecten maximus and studied their biological activities on human articular chondrocytes (HACs). We found that these extracts differentially modulate the biological activities of HACs, depending on the type of extraction and the concentration used. Furthermore, we showed that, unlike ASM and AIM, WSM promotes maintenance of the chondrocyte phenotype in monolayer culture. WSM increased the expression of chondrocyte-specific markers (aggrecan and type II collagen), without enhancing that of the main chondrocyte dedifferentiation marker (type I collagen). We also demonstrated that WSM could favor redifferentiation of chondrocyte in collagen sponge scaffold in hypoxia. Thus, this study suggests that the organic matrix of Pecten maximus, particularly WSM, may contain interesting molecules with chondrogenic effects. Our research emphasizes the potential use of WSM of Pecten maximus for cell therapy of cartilage.

Characterization and use of Equine Bone Marrow Mesenchymal Stem Cells in Equine Cartilage Engineering. Study of their Hyaline Cartilage Forming Potential when Cultured under Hypoxia within a Biomaterial in the Presence of BMP-2 and TGF-ß1

Articular cartilage presents a poor capacity for self-repair. Its structure-function are frequently disrupted or damaged upon physical trauma or osteoarthritis in humans. Similar musculoskeletal disorders also affect horses and are the leading cause of poor performance or early retirement of sport- and racehorses. To develop a therapeutic solution for horses, we tested the autologous chondrocyte implantation technique developed on human bone marrow (BM) mesenchymal stem cells (MSCs) on horse BM-MSCs. This technique involves BM-MSC chondrogenesis using a combinatory approach based on the association of 3D-culture in collagen sponges, under hypoxia in the presence of chondrogenic factors (BMP-2 + TGF-β₁) and siRNA to knockdown collagen I and HtrA1. Horse BM-MSCs were characterized before being cultured in chondrogenic conditions to find the best combination to enhance, stabilize, the chondrocyte phenotype. Our results show a very high proliferation of MSCs and these cells satisfy the criteria defining stem cells (pluripotency-surface markers expression). The combination of BMP-2 + TGF-β₁ strongly induces the chondrogenic differentiation of MSCs and prevents HtrA1 expression. siRNAs targeting Col1a1 and Htra1 were functionally validated. Ultimately, the combined use of specific culture conditions defined here with specific growth factors and a Col1a1 siRNAs (50 nM) association leads to the in vitro synthesis of a hyaline-type neocartilage whose chondrocytes present an optimal phenotypic index similar to that of healthy, differentiated chondrocytes. Our results lead the way to setting up pre-clinical trials in horses to better understand the reaction of neocartilage substitute and to carry out a proof-of-concept of this therapeutic strategy on a large animal model.

Chondrogenic Differentiation of Defined Equine Mesenchymal Stem Cells Derived from Umbilical Cord Blood for Use in Cartilage Repair Therapy

Cartilage engineering is a new strategy for the treatment of cartilage damage due to osteoarthritis or trauma in humans. Racehorses are exposed to the same type of cartilage damage and the anatomical, cellular, and biochemical properties of their cartilage are comparable to those of human cartilage, making the horse an excellent model for the development of cartilage engineering. Human mesenchymal stem cells (MSCs) differentiated into chondrocytes with chondrogenic factors in a biomaterial appears to be a promising therapeutic approach for direct implantation and cartilage repair. Here, we characterized equine umbilical cord blood-derived MSCs (eUCB-MSCs) and evaluated their potential for chondrocyte differentiation for use in cartilage repair therapy. Our results show that isolated eUCB-MSCs had high proliferative capacity and differentiated easily into osteoblasts and chondrocytes, but not into adipocytes. A three-dimensional (3D) culture approach with the chondrogenic factors BMP-2 and TGF-β1 potentiated chondrogenic differentiation with a significant increase in cartilage-specific markers at the mRNA level (Col2a1, Acan, Snorc) and the protein level (type II and IIB collagen) without an increase in hypertrophic chondrocyte markers (Col10a1 and Mmp13) in normoxia and in hypoxia. However, these chondrogenic factors caused an increase in type I collagen, which can be reduced using small interfering RNA targeting Col1a2. This study provides robust data on MSCs characterization and demonstrates that eUCB-MSCs have a great potential for cartilage tissue engineering.

Improvement of the Chondrocyte-Specific Phenotype upon Equine Bone Marrow Mesenchymal Stem Cell Differentiation: Influence of Culture Time, Transforming Growth Factors and Type I Collagen siRNAs on the Differentiation Index

Articular cartilage is a tissue characterized by its poor intrinsic capacity for self-repair. This tissue is frequently altered upon trauma or in osteoarthritis (OA), a degenerative disease that is currently incurable. Similar musculoskeletal disorders also affect horses and OA incurs considerable economic loss for the equine sector. In the view to develop new therapies for humans and horses, significant progress in tissue engineering has led to the emergence of new generations of cartilage therapy. Matrix-associated autologous chondrocyte implantation is an advanced 3D cell-based therapy that holds promise for cartilage repair. This study aims to improve the autologous chondrocyte implantation technique by using equine mesenchymal stem cells (MSCs) from bone marrow differentiated into chondrocytes that can be implanted in the chondral lesion. The optimized protocol relies on culture under hypoxia within type I/III collagen sponges. Here, we explored three parameters that influence MSC differentiation: culture times, growth factors and RNA interference strategies. Our results suggest first that an increase in culture time from 14 to 28 or 42 days lead to a sharp increase in the expression of chondrocyte markers, notably type II collagen (especially the IIB isoform), along with a concomitant decrease in HtrA1 expression. Nevertheless, the expression of type I collagen also increased with longer culture times. Second, regarding the growth factor cocktail, TGF-β3 alone showed promising result but the previously tested association of BMP-2 and TGF-β1 better limits the expression of type I collagen. Third, RNA interference targeting Col1a2 as well as Col1a1 mRNA led to a more significant knockdown, compared with a conventional strategy targeting Col1a1 alone. This chondrogenic differentiation strategy showed a strong increase in the Col2a1:Col1a1 mRNA ratio in the chondrocytes derived from equine bone marrow MSCs, this ratio being considered as an index of the functionality of cartilage. These data provide evidence of a more stable chondrocyte phenotype when combining Col1a1 and Col1a2 siRNAs associated to a longer culture time in the presence of BMP-2 and TGF-β1, opening new opportunities for preclinical trials in the horse. In addition, because the horse is an excellent model for human articular cartilage disorders, the equine therapeutic approach developed here can also serve as a preclinical step for human medicine.

Small non-coding RNAs-based bone regulation and targeting therapeutic strategies

Small non-coding RNAs, which are 20-25 nucleotide ribonucleic acids, have emerged as an important transformation in the biological evolution over almost three decades. microRNAs (miRNAs) and short interfering RNAs (siRNAs) are two significant categories of the small RNAs that exert important effects on bone endocrinology and skeletology. Therefore, clarifying the expression and function of these important molecules in bone endocrine physiology and pathology is of great significance for improving their potential therapeutic value for metabolism-associated bone diseases. In the present review, we highlight the recent advances made in understanding the function and molecular mechanism of these small non-coding RNAs in bone metabolism, especially their potentially therapeutic values in bone-related diseases.

Hypoxia Is a Critical Parameter for Chondrogenic Differentiation of Human Umbilical Cord Blood Mesenchymal Stem Cells in Type I/III Collagen Sponges

Umbilical cord blood (UCB) is an attractive alternative to bone marrow for isolation of mesenchymal stem cells (MSCs) to treat articular cartilage defects. Here, we set out to determine the growth factors (bone morphogenetic protein 2 (BMP-2) and transforming growth factor-β (TGF-β1)) and oxygen tension effects during chondrogenesis of human UCB-MSCs for cartilage engineering. Chondrogenic differentiation was induced using 3D cultures in type I/III collagen sponges with chondrogenic factors in normoxia (21% O₂) or hypoxia (<5% O₂) for 7, 14 and 21 days. Our results show that UCB-MSCs can be committed to chondrogenesis in the presence of BMP-2+TGF-β1. Normoxia induced the highest levels of chondrocyte-specific markers. However, hypoxia exerted more benefit by decreasing collagen X and matrix metalloproteinase-13 (MMP13) expression, two chondrocyte hypertrophy markers. However, a better chondrogenesis was obtained by switching oxygen conditions, with seven days in normoxia followed by 14 days in hypoxia, since these conditions avoid hypertrophy of hUCB-MSC-derived chondrocytes while maintaining the expression of chondrocyte-specific markers observed in normoxia. Our study demonstrates that oxygen tension is a key factor for chondrogenesis and suggests that UBC-MSCs 3D-culture should begin in normoxia to obtain a more efficient chondrocyte differentiation before placing them in hypoxia for chondrocyte phenotype stabilization. UCB-MSCs are therefore a reliable source for cartilage engineering.

RNA Interference and BMP-2 Stimulation Allows Equine Chondrocytes Redifferentiation in 3D-Hypoxia Cell Culture Model: Application for Matrix-Induced Autologous Chondrocyte Implantation

As in humans, osteoarthritis (OA) causes considerable economic loss to the equine industry. New hopes for cartilage repair have emerged with the matrix-associated autologous chondrocyte implantation (MACI). Nevertheless, its limitation is due to the dedifferentiation occurring during the chondrocyte amplification phase, leading to the loss of its capacity to produce a hyaline extracellular matrix (ECM). To enhance the MACI therapy efficiency, we have developed a strategy for chondrocyte redifferentiation, and demonstrated its feasibility in the equine model. Thus, to mimic the cartilage microenvironment, the equine dedifferentiated chondrocytes were cultured in type I/III collagen sponges for 7 days under hypoxia in the presence of BMP-2. In addition, chondrocytes were transfected by siRNA targeting Col1a1 and Htra1 mRNAs, which are overexpressed during dedifferentiation and OA. To investigate the quality of the neo-synthesized ECM, specific and atypical cartilage markers were evaluated by RT-qPCR and Western blot. Our results show that the combination of 3D hypoxia cell culture, BMP-2 (Bone morphogenetic protein-2), and RNA interference, increases the chondrocytes functional indexes (Col2a1/Col1a1, Acan/Col1a1), leading to an effective chondrocyte redifferentiation. These data represent a proof of concept for this process of application, in vitro, in the equine model, and will lead to the improvement of the MACI efficiency for cartilage tissue engineering therapy in preclinical/clinical trials, both in equine and human medicine.

Improved Chondrogenic Potential and Proteomic Phenotype of Porcine Chondrocytes Grown in Optimized Culture Conditions

For successful cartilage tissue engineering, the ability to generate a high number of chondrocytes in vitro while avoiding terminal differentiation or de-differentiation is critical. The ability to accomplish this by using the abundant and easily sampled costal cartilage could provide a practical alternative to the use of articular cartilage and mesenchymal stem cells. Chondrocytes isolated from pig costal cartilage were expanded in either serum-free medium with FGF2 (SFM) or fetal bovine serum-containing medium (SCM), under either high (21%) or low (5%) oxygen conditions. Overall, chondrocytes cultured in SFM and low oxygen (Low-SFM) demonstrated the highest cell growth rate (p < 0.05). The effect of passage number on the differentiation status of the chondrocytes was analyzed by alkaline phosphatase (AP) staining and real-time PCR for known chondrocyte quality markers. AP staining indicated that chondrocytes grown in SCM had a higher proportion of terminally differentiated (hypertrophic) chondrocytes (p < 0.05). At the mRNA level, expression ratios of ACAN/VCAN and COL2/COL1 were significantly higher (p < 0.05) in cells expanded in Low-SFM, indicating reduced de-differentiation. In vitro re-differentiation capacity was assessed after a 6-week induction, and chondrocytes grown in Low-SFM showed similar expression ratios of COL2/COL1 and ACAN/VCAN to native cartilage. Proteomic analysis of in vitro produced cartilage indicated that the Low-SFM condition most closely matched the proteomic profile of native costal and articular cartilage. In conclusion, Low-SFM culture conditions resulted in improved cell growth rates, reduced levels of de-differentiation during expansion, greater ability to re-differentiate into cartilage on induction, and an improved proteomic profile that resembles that of in vivo cartilage.

Enhanced chondrogenesis of bone marrow-derived stem cells by using a combinatory cell therapy strategy with BMP-2/TGF-β1, hypoxia, and COL1A1/HtrA1 siRNAs

Mesenchymal stem cells (MSCs) hold promise for cartilage engineering. Here, we aimed to determine the best culture conditions to induce chondrogenesis of MSCs isolated from bone marrow (BM) of aged osteoarthritis (OA) patients. We showed that these BM-MSCs proliferate slowly, are not uniformly positive for stem cell markers, and maintain their multilineage potential throughout multiple passages. The chondrogenic lineage of BM-MSCs was induced in collagen scaffolds, under normoxia or hypoxia, by BMP-2 and/or TGF-β1. The best chondrogenic induction, with the least hypertrophic induction, was obtained with the combination of BMP-2 and TGF-β1 under hypoxia. Differentiated BM-MSCs were then transfected with siRNAs targeting two markers overexpressed in OA chondrocytes, type I collagen and/or HtrA1 protease. siRNAs significantly decreased mRNA and protein levels of type I collagen and HtrA1, resulting in a more typical chondrocyte phenotype, but with frequent calcification of the subcutaneously implanted constructs in a nude mouse model. Our 3D culture model with BMP-2/TGF-β1 and COL1A1/HtrA1 siRNAs was not effective in producing a cartilage-like matrix in vivo. Further optimization is needed to stabilize the chondrocyte phenotype of differentiated BM-MSCs. Nevertheless, this study offers the opportunity to develop a combinatory cellular therapy strategy for cartilage tissue engineering.

A 5-mC Dot Blot Assay Quantifying the DNA Methylation Level of Chondrocyte Dedifferentiation In Vitro

The dedifferentiation of hyaline chondrocytes into fibroblastic chondrocytes often accompanies monolayer expansion of chondrocytes in vitro. The global DNA methylation level of chondrocytes is considered to be a suitable biomarker for the loss of the chondrocyte phenotype. However, results based on different experimental methods can be inconsistent. Therefore, it is important to establish a precise, simple, and rapid method to quantify global DNA methylation levels during chondrocyte dedifferentiation. Current genome-wide methylation analysis techniques largely rely on bisulfite genomic sequencing. Due to DNA degradation during bisulfite conversion, these methods typically require a large sample volume. Other methods used to quantify global DNA methylation levels include high-performance liquid chromatography (HPLC). However, HPLC requires complete digestion of genomic DNA. Additionally, the prohibitively high cost of HPLC instruments limits HPLC's wider application. In this study, genomic DNA (gDNA) was extracted from human chondrocytes cultured with varying number of passages. The gDNA methylation level was detected using a methylation-specific dot blot assay. In this dot blot approach, a gDNA mixture containing the methylated DNA to be detected was spotted directly onto an N⁺ membrane as a dot inside a previously drawn circular template pattern. Compared with other gel electrophoresis-based blotting approaches and other complex blotting procedures, the dot blot method saves significant time. In addition, dot blots can detect overall DNA methylation level using a commercially available 5-mC antibody. We found that the DNA methylation level differed between the monolayer subcultures, and therefore could play a key role in chondrocyte dedifferentiation. The 5-mC dot blot is a reliable, simple, and rapid method to detect the general DNA methylation level to evaluate chondrocyte phenotype.

DNA Methylation Profiling in Chondrocyte Dedifferentiation In Vitro

DNA methylation has emerged as a crucial regulator of chondrocyte dedifferentiation, which severely compromises the outcome of autologous chondrocyte implantation (ACI) treatment for cartilage defects. However, the full-scale DNA methylation profiling in chondrocyte dedifferentiation remains to be determined. Here, we performed a genome-wide DNA methylation profiling of dedifferentiated chondrocytes in monolayer culture and chondrocytes treated with DNA methylation inhibitor 5-azacytidine (5-AzaC). This research revealed that the general methylation level of CpG was increased while the COL-1A1 promoter methylation level was decreased during the chondrocyte dedifferentiation. 5-AzaC could reduce general methylation levels and reverse the chondrocyte dedifferentiation. Surprisingly, the DNA methylation level of COL-1A1 promoter was increased after 5-AzaC treatment. The COL-1A1 expression level was increased while that of SOX-9 was decreased during the chondrocyte dedifferentiation. 5-AzaC treatment up-regulated the SOX-9 expression while down-regulated the COL-1A1 promoter activity and gene expression. Taken together, these results suggested that differential regulation of the DNA methylation level of cartilage-specific genes might contribute to the chondrocyte dedifferentiation. Thus, the epigenetic manipulation of these genes could be a potential strategy to counteract the chondrocyte dedifferentiation accompanying in vitro propagation. J. Cell. Physiol. 232: 1708-1716, 2017. © 2016 Wiley Periodicals, Inc.

Chondrogenic commitment of human umbilical cord blood-derived mesenchymal stem cells in collagen matrices for cartilage engineering

Umbilical cord blood (UCB) is a promising alternative source of mesenchymal stem cells (MSCs), because UCB-MSCs are abundant and harvesting them is a painless non-invasive procedure. Potential clinical applications of UCB-MSCs have been identified, but their ability for chondrogenic differentiation has not yet been fully evaluated. The aim of our work was to characterize and determine the chondrogenic differentiation potential of human UCB-MSCs (hUCB-MSCs) for cartilage tissue engineering using an approach combining 3D culture in type I/III collagen sponges and chondrogenic factors. Our results showed that UCB-MSCs have a high proliferative capacity. These cells differentiated easily into an osteoblast lineage but not into an adipocyte lineage. Furthermore, BMP-2 and TGF-β1 potentiated chondrogenic differentiation, as revealed by a strong increase in mature chondrocyte-specific mRNA (COL2A1, COL2B, ACAN) and protein (type II collagen) markers. Although growth factors increased the transcription of hypertrophic chondrocyte markers such as COL10A1 and MMP13, the cells present in the neo-tissue maintained their phenotype and did not progress to terminal differentiation and mineralization of the extracellular matrix after subcutaneous implantation in nude mice. Our study demonstrates that our culture model has efficient chondrogenic differentiation, and that hUCB-MSCs can be a reliable source for cartilage tissue engineering.

Interstitial Perfusion Culture with Specific Soluble Factors Inhibits Type I Collagen Production from Human Osteoarthritic Chondrocytes in Clinical-Grade Collagen Sponges

Articular cartilage has poor healing ability and cartilage injuries often evolve to osteoarthritis. Cell-based strategies aiming to engineer cartilaginous tissue through the combination of biocompatible scaffolds and articular chondrocytes represent an alternative to standard surgical techniques. In this context, perfusion bioreactors have been introduced to enhance cellular access to oxygen and nutrients, hence overcoming the limitations of static culture and improving matrix deposition. Here, we combined an optimized cocktail of soluble factors, the BIT (BMP-2, Insulin, Thyroxin), and clinical-grade collagen sponges with a bidirectional perfusion bioreactor, namely the oscillating perfusion bioreactor (OPB), to engineer in vitro articular cartilage by human articular chondrocytes (HACs) obtained from osteoarthritic patients. After amplification, HACs were seeded and cultivated in collagen sponges either in static or dynamic conditions. Chondrocyte phenotype and the nature of the matrix synthesized by HACs were assessed using western blotting and immunohistochemistry analyses. Finally, the stability of the cartilaginous tissue produced by HACs was evaluated in vivo by subcutaneous implantation in nude mice. Our results showed that perfusion improved the distribution and quality of cartilaginous matrix deposited within the sponges, compared to static conditions. Specifically, dynamic culture in the OPB, in combination with the BIT cocktail, resulted in the homogeneous production of extracellular matrix rich in type II collagen. Remarkably, the production of type I collagen, a marker of fibrous tissues, was also inhibited, indicating that the association of the OPB with the BIT cocktail limits fibrocartilage formation, favoring the reconstruction of hyaline cartilage.

Disparate response of articular- and auricular-derived chondrocytes to oxygen tension

PURPOSE/AIM

To determine the effect of reduced (5%) oxygen tension on chondrogenesis of auricular-derived chondrocytes. Currently, many cell and tissue culture experiments are performed at 20% oxygen with 5% carbon dioxide. Few cells in the body are subjected to this supra-physiological oxygen tension. Chondrocytes and their mesenchymal progenitors are widely reported to have greater chondrogenic expression when cultured at low, more physiological, oxygen tension (1-7%). Although generally accepted, there is still some controversy, and different culture methods, species, and outcome metrics cloud the field. These results are, however, articular chondrocyte biased and have not been reported for auricular-derived chondrocytes.

MATERIALS AND METHODS

Auricular and articular chondrocytes were isolated from skeletally mature New Zealand White rabbits, expanded in culture and differentiated in high density cultures with serum-free chondrogenic media. Cartilage tissue derived from aggregate cultures or from the tissue engineered sheets were assessed for biomechanical, glycosaminoglycan, collagen, collagen cross-links, and lysyl oxidase activity and expression.

RESULTS

Our studies show increased proliferation rates for both auricular and articular chondrocytes at low (5%) O2 versus standard (20%) O2. In our scaffold-free chondrogenic cultures, low O2 was found to increase articular chondrocyte accumulation of glycosaminoglycan, but not cross-linked type II collagen, or total collagen. Conversely, auricular chondrocytes accumulated less glycosaminoglycan, cross-linked type II collagen and total collagen under low oxygen tension.

CONCLUSIONS

This study highlights the dramatic difference in response to low O2 of chondrocytes isolated from different anatomical sites. Low O2 is beneficial for articular-derived chondrogenesis but detrimental for auricular-derived chondrogenesis.

Hypoxia potentiates the BMP-2 driven COL2A1 stimulation in human articular chondrocytes via p38 MAPK

OBJECTIVE

Since the biological effect of cartilage mediators is generally studied in a non-physiologic environment of 21% O2, we investigated the effects of a chronic hypoxia on the capability of articular chondrocytes to respond to one anabolic stimulation.

DESIGN

Human Articular Chondrocytes (HACs) were cultured under hypoxia and stimulated with the chondrogenic growth factor BMP-2. The phenotype of the chondrocytes was studied by RT-PCR, and the cartilage-specific type II collagen production and deposition were also examined by western immunoblot and immunofluorescence. The Bone Morphogenetic protein (BMP) signalling pathway was also analysed.

RESULTS

BMP-2 is much more efficient to stimulate the expression of the cartilage-specific gene COL2A1 by HACs when cultured under hypoxia (1%O2) compared to normoxia (21%O2). Analysis of the BMP-activated signalling shows that the Smad pathway is inhibited under hypoxia, whereas p38 MAPK is activated, and is involved in a synergy between hypoxia and BMP signalling, thus contributing to the enhanced anabolic response.

CONCLUSIONS

Our study shows that hypoxia interplays with a chondrogenic factor and enhances the overall anabolic activity of the HACs. Alternatively to Hypoxia-Inducible Factor (HIF) signalling, and through a cross-talk with the BMP signalling which involves the p38 pathway, hypoxic stimulation markedly increases the capability of chondrocytes to produce the cartilage-specific type II collagen. Therefore our study provides new evidences of the multilayered effects of hypoxia in the anabolic functions of chondrocytes. This understanding may help promoting the anabolic function of articular chondrocytes, and thus improving their manipulation for cell therapy.

Jellyfish collagen and alginate: Combined marine materials for superior chondrogenesis of hMSC

Marine, hybrid constructs of porous scaffolds from fibrillized jellyfish collagen and alginate hydrogel are mimicking both of the main tissue components of cartilage, thus being a promising approach for chondrogenic differentiation of human mesenchymal stem cells (hMSC). Investigating their potential for articular cartilage repair, the present study examined scaffolds being either infiltrated with an alginate-cell-suspension (ACS) or seeded with hMSC and embedded in alginate after cell adhesion (EAS). Hybrid constructs with 2×10(5) and 4.5×10(5)hMSC/scaffold were compared to hMSC encapsulated in pure alginate discs, both chondrogenically stimulated for 21days. Typical round, chondrocyte-like morphology was observed in pure alginate gels and ACS scaffolds, while cells in EAS were elongated and tightly attached to the collagen pores. Col 2 gene expression was comparable in all scaffold types examined. However, the Col 2/Col 1 ratio was higher for pure alginate discs and ACS scaffolds compared to EAS. In contrast, cells in EAS scaffolds displayed higher gene expression of Sox 9, Col 11 and ACAN compared to ACS and pure alginate. Secretion of sulfated glycosaminoglycans (sGAG) was comparable for ACS and EAS scaffolds. In conclusion hybrid constructs of jellyfish collagen and alginate support hMSC chondrogenic differentiation and provide more stable and constructs compared to pure hydrogels.

Articular cartilage: from formation to tissue engineering

Hyaline cartilage is the nonlinear, inhomogeneous, anisotropic, poro-viscoelastic connective tissue that serves as friction-reducing and load-bearing cushion in synovial joints and is vital for mammalian skeletal movements. Due to its avascular nature, low cell density, low proliferative activity and the tendency of chondrocytes to de-differentiate, cartilage cannot regenerate after injury, wear and tear, or degeneration through common diseases such as osteoarthritis. Therefore severe damage usually requires surgical intervention. Current clinical strategies to generate new tissue include debridement, microfracture, autologous chondrocyte transplantation, and mosaicplasty. While articular cartilage was predicted to be one of the first tissues to be successfully engineered, it proved to be challenging to reproduce the complex architecture and biomechanical properties of the native tissue. Despite significant research efforts, only a limited number of studies have evolved up to the clinical trial stage. This review article summarizes the current state of cartilage tissue engineering in the context of relevant biological aspects, such as the formation and growth of hyaline cartilage, its composition, structure and biomechanical properties. Special attention is given to materials development, scaffold designs, fabrication methods, and template-cell interactions, which are of great importance to the structure and functionality of the engineered tissue.

In vitro engineering of human 3D chondrosarcoma: a preclinical model relevant for investigations of radiation quality impact

Background

The benefit of better ballistic and higher efficiency of carbon ions for cancer treatment (hadron-therapy) is asserted since decades, especially for unresectable or resistant tumors like sarcomas. However, hadron-therapy with carbon ions stays underused and raises some concerns about potential side effects for patients. Chondrosarcoma is a cartilaginous tumor, chemo- and radiation-resistant, that lacks reference models for basic and pre-clinical studies in radiation-biology. Most studies about cellular effects of ionizing radiation, including hadrons, were performed under growth conditions dramatically different from human homeostasis. Tridimensional in vitro models are a fair alternative to animal models to approach tissue and tumors microenvironment.

Methods

By using a collagen matrix, standardized culture conditions, physiological oxygen tension and a well defined chondrosarcoma cell line, we developed a pertinent in vitro 3D model for hadron-biology studies. Low- and high-Linear Energy Transfer (LET) ionizing radiations from GANIL facilities of ~1 keV/μm and 103 ± 4 keV/μm were used respectively, at 2 Gy single dose. The impact of radiation quality on chondrosarcoma cells cultivated in 3D was analyzed on cell death, cell proliferation and DNA repair.

Results

A fair distribution of chondrosarcoma cells was observed in the whole 3D scaffold. Moreover, LET distribution in depth, for ions, was calculated and found acceptable for radiation-biology studies using this kind of scaffold. No difference in cell toxicity was observed between low- and high-LET radiations but a higher rate of proliferation was displayed following high-LET irradiation. Furthermore, 3D models presented a higher and longer induction of H2AX phosphorylation after 2 Gy of high-LET compared to low-LET radiations.

Conclusions

The presented results show the feasibility and usefulness of our 3D chondrosarcoma model in the study of the impact of radiation quality on cell fate. The observed changes in our tissue-like model after ionizing radiation exposure may explain some discrepancies between radiation-biology studies and clinical data.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1590-5) contains supplementary material, which is available to authorized users.

Synoviocyte Derived-Extracellular Matrix Enhances Human Articular Chondrocyte Proliferation and Maintains Re-Differentiation Capacity at Both Low and Atmospheric Oxygen Tensions

Background

Current tissue engineering methods are insufficient for total joint resurfacing, and chondrocytes undergo de-differentiation when expanded on tissue culture plastic. De-differentiated chondrocytes show poor re-differentiation in culture, giving reduced glycosaminoglycan (GAG) and collagen matrix accumulation. To address this, porcine synoviocyte-derived extracellular matrix and low (5%) oxygen tension were assessed for their ability to enhance human articular chondrocyte expansion and maintain re-differentiation potential.

Methods

Porcine synoviocyte matrices were devitalized using 3 non-detergent methods. These devitalized synoviocyte matrices were compared against tissue culture plastic for their ability to support human chondrocyte expansion. Expansion was further compared at both low (5%), and atmospheric (20%) oxygen tension on all surfaces. Expanded cells then underwent chondrogenic re-differentiation in aggregate culture at both low and atmospheric oxygen tension. Aggregates were assessed for their GAG and collagen content both biochemically and histologically.

Results

Human chondrocytes expanded twice as fast on devitalized synoviocyte matrix vs. tissue culture plastic, and cells retained their re-differentiation capacity for twice the number of population doublings. There was no significant difference in growth rate between low and atmospheric oxygen tension. There was significantly less collagen type I, collagen type II, aggrecan and more MMP13 expression in cells expanded on synoviocyte matrix vs. tissue culture plastic. There were also significant effects due to oxygen tension on gene expression, wherein there was greater collagen type I, collagen type II, SOX9 and less MMP13 expression on tissue culture plastic compared to synoviocyte matrix. There was a significant increase in GAG, but not collagen, accumulation in chondrocyte aggregates re-differentiated at low oxygen tension over that achieved in atmospheric oxygen conditions.

Conclusions

Synoviocyte-derived matrix supports enhanced expansion of human chondrocytes such that the chondrocytes are maintained in a state from which they can re-differentiate into a cartilage phenotype after significantly more population doublings. Also, low oxygen tension supports GAG, but not collagen, accumulation. These findings are a step towards the production of a more functional, tissue engineered cartilage.

Radiation-induced alterations of osteogenic and chondrogenic differentiation of human mesenchymal stem cells

While human mesenchymal stem cells (hMSCs), either in the bone marrow or in tumour microenvironment could be targeted by radiotherapy, their response is poorly understood. The oxic effects on radiosensitivity, cell cycle progression are largely unknown, and the radiation effects on hMSCs differentiation capacities remained unexplored. Here we analysed hMSCs viability and cell cycle progression in 21% O₂ and 3% O₂ conditions after medical X-rays irradiation. Differentiation towards osteogenesis and chondrogenesis after irradiation was evaluated through an analysis of differentiation specific genes. Finally, a 3D culture model in hypoxia was used to evaluate chondrogenesis in conditions mimicking the natural hMSCs microenvironment. The hMSCs radiosensitivity was not affected by O₂ tension. A decreased number of cells in S phase and an increase in G2/M were observed in both O₂ tensions after 16 hours but hMSCs released from the G2/M arrest and proliferated at day 7. Osteogenesis was increased after irradiation with an enhancement of mRNA expression of specific osteogenic genes (alkaline phosphatase, osteopontin). Osteoblastic differentiation was altered since matrix deposition was impaired with a decreased expression of collagen I, probably through an increase of its degradation by MMP-3. After induction in monolayers, chondrogenesis was altered after irradiation with an increase in COL1A1 and a decrease in both SOX9 and ACAN mRNA expression. After induction in a 3D culture in hypoxia, chondrogenesis was altered after irradiation with a decrease in COL2A1, ACAN and SOX9 mRNA amounts associated with a RUNX2 increase. Together with collagens I and II proteins decrease, associated to a MMP-13 expression increase, these data show a radiation-induced impairment of chondrogenesis. Finally, a radiation-induced impairment of both osteogenesis and chondrogenesis was characterised by a matrix composition alteration, through inhibition of synthesis and/or increased degradation. Alteration of osteogenesis and chondrogenesis in hMSCs could potentially explain bone/joints defects observed after radiotherapy.

Preclinical study of SZ2080 material 3D microstructured scaffolds for cartilage tissue engineering made by femtosecond direct laser writing lithography

Over the last decade DLW employing ultrafast pulsed lasers has become a well-established technique for the creation of custom-made free-form three-dimensional (3D) microscaffolds out of a variety of materials ranging from proteins to biocompatible glasses. Its potential applications for manufacturing a patient's specific scaffold seem unlimited in terms of spatial resolution and geometry complexity. However, despite few exceptions in which live cells or primitive organisms were encapsulated into a polymer matrix, no demonstration of an in vivo study case of scaffolds generated with the use of such a method was performed. Here, we report a preclinical study of 3D artificial microstructured scaffolds out of hybrid organic-inorganic (HOI) material SZ2080 fabricated using the DLW technique. The created 2.1 × 2.1 × 0.21 mm(3) membrane constructs are tested both in vitro by growing isolated allogeneic rabbit chondrocytes (Cho) and in vivo by implanting them into rabbit organisms for one, three and six months. An ex vivo histological examination shows that certain pore geometry and the pre-growing of Cho prior to implantation significantly improves the performance of the created 3D scaffolds. The achieved biocompatibility is comparable to the commercially available collagen membranes. The successful outcome of this study supports the idea that hexagonal-pore-shaped HOI microstructured scaffolds in combination with Cho seeding may be successfully implemented for cartilage tissue engineering.

BMP-2, hypoxia, and COL1A1/HtrA1 siRNAs favor neo-cartilage hyaline matrix formation in chondrocytes

Osteoarthritis (OA) is an irreversible pathology that causes a decrease in articular cartilage thickness, leading finally to the complete degradation of the affected joint. The low spontaneous repair capacity of cartilage prevents any restoration of the joint surface, making OA a major public health issue. Here, we developed an innovative combination of treatment conditions to improve the human chondrocyte phenotype before autologous chondrocyte implantation. First, we seeded human dedifferentiated chondrocytes into a collagen sponge as a scaffold, cultured them in hypoxia in the presence of a bone morphogenetic protein (BMP), BMP-2, and transfected them with small interfering RNAs targeting two markers overexpressed in OA dedifferentiated chondrocytes, that is, type I collagen and/or HtrA1 serine protease. This strategy significantly decreased mRNA and protein expression of type I collagen and HtrA1, and led to an improvement in the chondrocyte phenotype index of differentiation. The effectiveness of our in vitro culture process was also demonstrated in the nude mouse model in vivo after subcutaneous implantation. We, thus, provide here a new protocol able to favor human hyaline chondrocyte phenotype in primarily dedifferentiated cells, both in vitro and in vivo. Our study also offers an innovative strategy for chondrocyte redifferentiation and opens new opportunities for developing therapeutic targets.

Extracellular matrix production in vitro in cartilage tissue engineering

Cartilage tissue engineering is arising as a technique for the repair of cartilage lesions in clinical applications. However, fibrocartilage formation weakened the mechanical functions of the articular, which compromises the clinical outcomes. Due to the low proliferation ability, dedifferentiation property and low production of cartilage-specific extracellular matrix (ECM) of the chondrocytes, the cartilage synthesis in vitro has been one of the major limitations for obtaining high-quality engineered cartilage constructs. This review discusses cells, biomaterial scaffolds and stimulating factors that can facilitate the cartilage-specific ECM production and accumulation in the in vitro culture system. Special emphasis has been put on the factors that affect the production of ECM macromolecules such as collagen type II and proteoglycans in the review, aiming at providing new strategies to improve the quality of tissue-engineered cartilage.

Cartilage tissue engineering: molecular control of chondrocyte differentiation for proper cartilage matrix reconstruction

BACKGROUND

Articular cartilage defects are a veritable therapeutic problem because therapeutic options are very scarce. Due to the poor self-regeneration capacity of cartilage, minor cartilage defects often lead to osteoarthritis. Several surgical strategies have been developed to repair damaged cartilage. Autologous chondrocyte implantation (ACI) gives encouraging results, but this cell-based therapy involves a step of chondrocyte expansion in a monolayer, which results in the loss in the differentiated phenotype. Thus, despite improvement in the quality of life for patients, reconstructed cartilage is in fact fibrocartilage. Successful ACI, according to the particular physiology of chondrocytes in vitro, requires active and phenotypically stabilized chondrocytes.

SCOPE OF REVIEW

This review describes the unique physiology of cartilage, with the factors involved in its formation, stabilization and degradation. Then, we focus on some of the most recent advances in cell therapy and tissue engineering that open up interesting perspectives for maintaining or obtaining the chondrogenic character of cells in order to treat cartilage lesions.

MAJOR CONCLUSIONS

Current research involves the use of chondrocytes or progenitor stem cells, associated with "smart" biomaterials and growth factors. Other influential factors, such as cell sources, oxygen pressure and mechanical strain are considered, as are recent developments in gene therapy to control the chondrocyte differentiation/dedifferentiation process.

GENERAL SIGNIFICANCE

This review provides new information on the mechanisms regulating the state of differentiation of chondrocytes and the chondrogenesis of mesenchymal stem cells that will lead to the development of new restorative cell therapy approaches in humans. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.