Articular chondrocyte redifferentiation in 3D co-cultures with mesenchymal stem cells

Culture-expanded mesenchymal stromal cell therapy: does it work in knee osteoarthritis? A pathway to clinical success

Osteoarthritis (OA) is a degenerative multifactorial disease with concomitant structural, inflammatory, and metabolic changes that fluctuate in a temporal and patient-specific manner. This complexity has contributed to refractory responses to various treatments. MSCs have shown promise as multimodal therapeutics in mitigating OA symptoms and disease progression. Here, we evaluated 15 randomized controlled clinical trials (RCTs) and 11 nonrandomized RCTs using culture-expanded MSCs in the treatment of knee OA, and we found net positive effects of MSCs on mitigating pain and symptoms (improving function in 12/15 RCTs relative to baseline and in 11/15 RCTs relative to control groups at study endpoints) and on cartilage protection and/or repair (18/21 clinical studies). We examined MSC dose, tissue of origin, and autologous vs. allogeneic origins as well as patient clinical phenotype, endotype, age, sex and level of OA severity as key parameters in parsing MSC clinical effectiveness. The relatively small sample size of 610 patients limited the drawing of definitive conclusions. Nonetheless, we noted trends toward moderate to higher doses of MSCs in select OA patient clinical phenotypes mitigating pain and leading to structural improvements or cartilage preservation. Evidence from preclinical studies is supportive of MSC anti-inflammatory and immunomodulatory effects, but additional investigations on immunomodulatory, chondroprotective and other clinical mechanisms of action are needed. We hypothesize that MSC basal immunomodulatory "fitness" correlates with OA treatment efficacy, but this hypothesis needs to be validated in future studies. We conclude with a roadmap articulating the need to match an OA patient subset defined by molecular endotype and clinical phenotype with basally immunomodulatory "fit" or engineered-to-be-fit-for-OA MSCs in well-designed, data-intensive clinical trials to advance the field.

The synergistic regulation of chondrogenesis by collagen-based hydrogels and cell co-culture

The suitable seeding cells and scaffolds are very important for tissue engineering to create functional cartilage. Although the physicochemical properties of scaffold and co-culture system of mesenchymal stem cells (MSCs) and chondrocytes could affect functional properties of engineered cartilage tissues respectively, the combined effects of them on chondrogenesis is currently unknown. Herein, methacrylated collagen (CMA30 and CMA80) hydrogels with different degradation rate and stiffness were prepared. The MSCs and chondrocytes were co-cultured or monocultured in collagen, CMA30 and CMA80 hydrogels in vitro or in vivo. The results demonstrated that cell spreading and proliferation was regulated by degradation rate and stiffness of hydrogels. Compared to single MSCs culture, co-culture cells in all collagen-based hydrogels significantly improved chondrogenesis. CMA30 hydrogel with moderate degradation rate and low storage modulus was the most effective for co-culture system to promote chondrogenesis compared to Col and CMA80 hydrogel in vitro culture, while there was no obvious difference between CMA30 and CMA80 hydrogel in vivo. Furthermore, the intercellular substance exchange was very important for co-culture system to maintain the positive effect on chondrogenesis. Overall, the current study highlights the synergistic effects of the physicochemical properties of collagen-based hydrogel and co-culture system on cartilage formation. STATEMENT OF SIGNIFICANCE: Scaffolds and cells play a key role in cartilage tissue engineering. The combined effects of physicochemical properties of collagen hydrogels and co-culture system (MSCs and chondrocytes) on chondrogenesis is unknown. In contrast to the studies that investigated the effect of single factor (scaffolds or cells) on cartilage formation, this manuscript explored the synergistic regulation of both scaffold properties and biological factors on chondrogenesis, and provided a promising strategy for cartilage tissue engineering.

Biodegradable Poly(D-L-lactide-co-glycolide) (PLGA)-Infiltrated Bioactive Glass (CAR12N) Scaffolds Maintain Mesenchymal Stem Cell Chondrogenesis for Cartilage Tissue Engineering

Regeneration of articular cartilage remains challenging. The aim of this study was to increase the stability of pure bioactive glass (BG) scaffolds by means of solvent phase polymer infiltration and to maintain cell adherence on the glass struts. Therefore, BG scaffolds either pure or enhanced with three different amounts of poly(D-L-lactide-co-glycolide) (PLGA) were characterized in detail. Scaffolds were seeded with primary porcine articular chondrocytes (pACs) and human mesenchymal stem cells (hMSCs) in a dynamic long-term culture (35 days). Light microscopy evaluations showed that PLGA was detectable in every region of the scaffold. Porosity was greater than 70%. The biomechanical stability was increased by polymer infiltration. PLGA infiltration did not result in a decrease in viability of both cell types, but increased DNA and sulfated glycosaminoglycan (sGAG) contents of hMSCs-colonized scaffolds. Successful chondrogenesis of hMSC-colonized scaffolds was demonstrated by immunocytochemical staining of collagen type II, cartilage proteoglycans and the transcription factor SOX9. PLGA-infiltrated scaffolds showed a higher relative expression of cartilage related genes not only of pAC-, but also of hMSC-colonized scaffolds in comparison to the pure BG. Based on the novel data, our recommendation is BG scaffolds with single infiltrated PLGA for cartilage tissue engineering.

Application of Alginate Hydrogels for Next-Generation Articular Cartilage Regeneration

The articular cartilage has insufficient intrinsic healing abilities, and articular cartilage injuries often progress to osteoarthritis. Alginate-based scaffolds are attractive biomaterials for cartilage repair and regeneration, allowing for the delivery of cells and therapeutic drugs and gene sequences. In light of the heterogeneity of findings reporting the benefits of using alginate for cartilage regeneration, a better understanding of alginate-based systems is needed in order to improve the approaches aiming to enhance cartilage regeneration with this compound. This review provides an in-depth evaluation of the literature, focusing on the manipulation of alginate as a tool to support the processes involved in cartilage healing in order to demonstrate how such a material, used as a direct compound or combined with cell and gene therapy and with scaffold-guided gene transfer procedures, may assist cartilage regeneration in an optimal manner for future applications in patients.

Chondrogenic Characteristics of Auricular Chondrocytes Cocultured With Adipose-Derived Stem Cells are Superior to Stromal Vascular Fraction of Adipose Tissue

ABSTRACT

Reconstruction of craniofacial cartilage defects is among the most challenging operations in facial plastic surgery. The co-culture system of partial replacement of chondrocytes by stem cells has been confirmed effective in the repair of cartilaginous defects. The aim of this study is to compare chondrogenic properties of expanded adipose-derived stem cells (ADSCs) and stromal vascular fraction (SVF), including ADSCs/SVF monoculture and coculture with rabbit auricular chondrocytes (ACs). Analysis of morphology, histology, real-time polymerase chain reaction and glycosaminoglycans (GAG) quantification were performed to characterize the chondrogenesis of pellets. The triple differentiation potential of ADSCs had been confirmed. Further, using flow cytometry, the authors demonstrated that ADSCs and SVF have different characteristics in cell surface markers, and ADSCs are more enriched in cells from the mesenchymal lineage than SVF. GAG production of ADSCs is significantly higher than that of SVF in pellet monoculture, and pellet coculture of ADSCs and ACs are better in depositing cartilage matrix than the mixture of SVF and ACs. Our study suggests that ADSCs may be more suitable seed cells for craniofacial cartilage defect or deformity repair.

Crosstalk Between Mesenchymal Stromal Cells and Chondrocytes: The Hidden Therapeutic Potential for Cartilage Regeneration

Cartilage injuries following trauma create a puzzling clinical scenario. The finite reparative potential of articular cartilage is well known, and injuries are associated with an increased risk of osteoarthritis. Cell-based therapies have spotlighted chondrocytes and mesenchymal stromal cells (MSCs) as the functional unit of articular cartilage and the progenitor cells, respectively. The available clinical treatments cannot reproduce the biomechanical properties of articular cartilage and call for continuous investigations into alternative approaches. Co-cultures of chondrocytes and MSCs are an attractive in vitro system to step closer to the in vivo multicellular environment's complexity. Research on the mechanisms of interaction between both cell types will reveal essential cues to understand cartilage regeneration. This review describes the latest discoveries on these interactions, along with advantages and main challenges in vitro and in vivo. The successful clinical translation of in vitro studies requires establishing rigorous standards and clinically relevant research models and an organ-targeting therapeutic strategy.

Improving In Vitro Cartilage Generation by Co-Culturing Adipose-Derived Stem Cells and Chondrocytes on an Allograft Adipose Matrix Framework

BACKGROUND

Microtia is an inherited condition that results in varying degrees of external ear deformities; the most extreme form is anotia. Effective surgical reconstruction techniques have been developed. However, these usually require multistage procedures and have other inherent disadvantages. Tissue engineering technologies offer new approaches in the field of external ear reconstruction. In this setting, chondrocytes are cultured in the laboratory with the aim of creating bioengineered cartilage matrices. However, cartilage engineering has many challenges, including difficulty in culturing sufficient chondrocytes. To overcome these hurdles, the authors propose a novel model of cartilage engineering that involves co-culturing chondrocytes and adipose-derived stem cells on an allograft adipose-derived extracellular matrix scaffold.

METHODS

Auricular chondrocytes from porcine ear were characterized. Adipose-derived stem cells were isolated and expanded from human lipoaspirate. Then, the auricular chondrocytes were cultured on the allograft adipose matrix either alone or with the adipose-derived stem cells at different ratios and examined histologically.

RESULTS

Cartilage induction was most prominent when the cells were co-cultured on the allograft adipose matrix at a ratio of 1:9 (auricular chondrocyte-to-adipose-derived stem cell ratio). Furthermore, because of the xenogeneic nature of the experiment, the authors were able to determine that the adipose-derived stem cells contributed to chondrogenesis by means of a paracrine stimulation of the chondrocytes.

CONCLUSIONS

In this situation, adipose-derived stem cells provide sufficient support to induce the formation of cartilage when the number of auricular chondrocytes available is limited. This novel model of cartilage engineering provides a setting for using the patient's own chondrocytes and adipose tissue to create a customized ear framework that could be further used for surgical reconstruction.

Biocompatibility assessment of resin-based cements on vascularized dentin/pulp tissue-engineered analogues

OBJECTIVES

A three-dimensional (3D) dentin/pulp tissue analogue, resembling the human natural tissue has been engineered in an in vitro setup, aiming to assess the cytocompatibility of resin-based dental restorative cements.

METHODS

Stem Cells from Apical Papilla (SCAP) and Human Umbilical Vein Endothelial Cells (HUVEC) were embedded in Collagen-I/Fibrin hydrogels at 1:3 ratio within 24-well plates. Hanging culture inserts were placed over the hydrogels, housing an odontoblast-like cell layer and a human treated-dentin barrier. Shear modulus of the hydrogels at 3.5 and 5 mg/ml was evaluated by dynamic mechanical analysis. Eluates of two resin-based cements, a dual-cure- (Breeze™, Pentron: Cement-1/C1), and a self-adhesive cement (SpeedCEMplus™, Ivoclar-Vivadent: Cement-2/C2) were applied into the dentin/pulp tissue analogue after pre-stimulation with LPS. Cytocompatibility was assessed by MTT assay, live/dead staining and real-time PCR analysis.

RESULTS

Both hydrogel concentrations showed similar shear moduli to the natural pulp until day (D) 7, while the 5 mg/ml-hydrogel substantially increased stiffness by D14. Both cements caused no significant toxicity to the dentin/pulp tissue analogue. C1 induced stimulation (p < 0.01) of cell viability (158 ± 3%, 72 h), while pre-stimulation with LPS attenuated this effect. C2 (±LPS) caused minor reduction of viability (15-20%, 24 h) that recovered at 72 h for the LPS+ group. Both cements caused upregulation of VEGF, ANGP-1, and downregulation of the respective receptors VEGFR-2 and Tie-1.

SIGNIFICANCE

Both resin-based cements showed good cytocompatibility and triggered angiogenic response within the dentin/pulp tissue analogue, indicating initiation of pulp repair responses to the released xenobiotics.

An Evidence-Based Systematic Review of Human Knee Post-Traumatic Osteoarthritis (PTOA): Timeline of Clinical Presentation and Disease Markers, Comparison of Knee Joint PTOA Models and Early Disease Implications

Understanding the causality of the post-traumatic osteoarthritis (PTOA) disease process of the knee joint is important for diagnosing early disease and developing new and effective preventions or treatments. The aim of this review was to provide detailed clinical data on inflammatory and other biomarkers obtained from patients after acute knee trauma in order to (i) present a timeline of events that occur in the acute, subacute, and chronic post-traumatic phases and in PTOA, and (ii) to identify key factors present in the synovial fluid, serum/plasma and urine, leading to PTOA of the knee in 23-50% of individuals who had acute knee trauma. In this context, we additionally discuss methods of simulating knee trauma and inflammation in in vivo, ex vivo articular cartilage explant and in vitro chondrocyte models, and answer whether these models are representative of the clinical inflammatory stages following knee trauma. Moreover, we compare the pro-inflammatory cytokine concentrations used in such models and demonstrate that, compared to concentrations in the synovial fluid after knee trauma, they are exceedingly high. We then used the Bradford Hill Framework to present evidence that TNF-α and IL-6 cytokines are causal factors, while IL-1β and IL-17 are credible factors in inducing knee PTOA disease progresssion. Lastly, we discuss beneficial infrastructure for future studies to dissect the role of local vs. systemic inflammation in PTOA progression with an emphasis on early disease.

Feasibility of Human Platelet Lysate as an Alternative to Foetal Bovine Serum for In Vitro Expansion of Chondrocytes

Osteoarthritis (OA) is a degenerative joint disease that affects a lot of people worldwide. Current treatment for OA mainly focuses on halting or slowing down the disease progress and to improve the patient’s quality of life and functionality. Autologous chondrocyte implantation (ACI) is a new treatment modality with the potential to promote regeneration of worn cartilage. Traditionally, foetal bovine serum (FBS) is used to expand the chondrocytes. However, the use of FBS is not ideal for the expansion of cells mean for clinical applications as it possesses the risk of animal pathogen transmission and animal protein transfer to host. Human platelet lysate (HPL) appears to be a suitable alternative to FBS as it is rich in biological factors that enhance cell proliferation. Thus far, HPL has been found to be superior in promoting chondrocyte proliferation compared to FBS. However, both HPL and FBS cannot prevent chondrocyte dedifferentiation. Discrepant results have been reported for the maintenance of chondrocyte redifferentiation potential by HPL. These differences are likely due to the diversity in the HPL preparation methods. In the future, more studies on HPL need to be performed to develop a standardized technique which is capable of producing HPL that can maintain the chondrocyte redifferentiation potential reproducibly. This review discusses the in vitro expansion of chondrocytes with FBS and HPL, focusing on its capability to promote the proliferation and maintain the chondrogenic characteristics of chondrocytes.

Engineered-extracellular vesicles as an optimistic tool for microRNA delivery for osteoarthritis treatment

Worldwide, osteoarthritis (OA) is one of the most common chronic diseases. In OA, profiling gene expression changes occur and cartilage tissue homeostasis is lost. Suggestions for OA treatment include regulation of gene expressions via the use of microRNAs (miRNAs). However, problems exist with the use of miRNAs, the most important of which is the delivery of sufficient amounts of effective miRNAs to save cartilage tissue. The engineering of extracellular vesicles (EVs) with the use of advanced techniques would be an efficient OA treatment. Therefore, we discuss the importance of miRNAs in terms of cartilage tissue regeneration and review recent advances in production of enriched EVs and miRNA delivery by EVs for future clinical applications.

Utility of direct 3D co-culture model for chondrogenic differentiation of mesenchymal stem cells on hyaluronan scaffold (Hyaff-11)

This study presents direct 2D and 3D co-culture model of mesenchymal stem cells (MSCs) line with chondrocytes isolated from patients with osteoarthritis (unaffected area). MSCs differentiation into chondrocytes after 14, 17 days was checked by estimation of collagen I, II, X, aggrecan expression using immunohistochemistry. Visualization, localization of cells on Hyaff-11 was performed using enzymatic technique and THUNDER Imaging Systems. Results showed, that MSCs/chondrocytes 3D co-culture induced suitable conditions for chondrocytes grow and MSCs differentiation than 2D monoculture. Despite that differentiated cells on Hyaff-11 expressed collagen X, they showed high collagen II (80%) and aggrecan (60%) expression with simultaneous decrease of collagen I expression (10%). The high concentration of differentiated cells on Hyaff-11, indicate that this structure has an impact on cells cooperation and communication. In conclusion, we suggest that high expression of collagen II and aggrecan in 3D co-culture model, indicate that cooperation between different subpopulations may have synergistic impact on MSCs chondrogenic potential. Revealed the high concentration and localization of cells growing in deeper layers of membrane in 3D co-culture, indicate that induced microenvironmental enhance cell migration within scaffold. Additionally, we suggest that co-culture model might be useful for construction a bioactive structure for cartilage tissue regeneration.

Co-culture and Mechanical Stimulation on Mesenchymal Stem Cells and Chondrocytes for Cartilage Tissue Engineering

Defects in articular cartilage injury and chronic osteoarthritis are very widespread and common, and the ability of injured cartilage to repair itself is limited. Stem cell-based cartilage tissue engineering provides a promising therapeutic option for articular cartilage damage. However, the application of the technique is limited by the number, source, proliferation, and differentiation of stem cells. The co-culture of mesenchymal stem cells and chondrocytes is available for cartilage tissue engineering, and mechanical stimulation is an important factor that should not be ignored. A combination of these two approaches, i.e., co-culture of mesenchymal stem cells and chondrocytes under mechanical stimulation, can provide sufficient quantity and quality of cells for cartilage tissue engineering, and when combined with scaffold materials and cytokines, this approach ultimately achieves the purpose of cartilage repair and reconstruction. In this review, we focus on the effects of co-culture and mechanical stimulation on mesenchymal stem cells and chondrocytes for articular cartilage tissue engineering. An in-depth understanding of the impact of co-culture and mechanical stimulation of mesenchymal stem cells and chondrocytes can facilitate the development of additional strategies for articular cartilage tissue engineering.

Mechanotransduction and Stiffness-Sensing: Mechanisms and Opportunities to Control Multiple Molecular Aspects of Cell Phenotype as a Design Cornerstone of Cell-Instructive Biomaterials for Articular Cartilage Repair

Since material stiffness controls many cell functions, we reviewed the currently available knowledge on stiffness sensing and elucidated what is known in the context of clinical and experimental articular cartilage (AC) repair. Remarkably, no stiffness information on the various biomaterials for clinical AC repair was accessible. Using mRNA expression profiles and morphology as surrogate markers of stiffness-related effects, we deduced that the various clinically available biomaterials control chondrocyte (CH) phenotype well, but not to equal extents, and only in non-degenerative settings. Ample evidence demonstrates that multiple molecular aspects of CH and mesenchymal stromal cell (MSC) phenotype are susceptible to material stiffness, because proliferation, migration, lineage determination, shape, cytoskeletal properties, expression profiles, cell surface receptor composition, integrin subunit expression, and nuclear shape and composition of CHs and/or MSCs are stiffness-regulated. Moreover, material stiffness modulates MSC immuno-modulatory and angiogenic properties, transforming growth factor beta 1 (TGF-β1)-induced lineage determination, and CH re-differentiation/de-differentiation, collagen type II fragment production, and TGF-β1- and interleukin 1 beta (IL-1β)-induced changes in cell stiffness and traction force. We then integrated the available molecular signaling data into a stiffness-regulated CH phenotype model. Overall, we recommend using material stiffness for controlling cell phenotype, as this would be a promising design cornerstone for novel future-oriented, cell-instructive biomaterials for clinical high-quality AC repair tissue.

Coculturing of mesenchymal stem cells of different sources improved regenerative capability of osteochondral defect in the mature rabbit: An in vivo study

PURPOSE

Choosing a therapeutic cell source for osteochondral repair remains a challenge. The present study investigated coculturing mesenchymal stem cells (MSCs) from different sources to provide an improved therapeutic cell option for osteochondral repair.

METHODS

Dutch and Japanese white rabbits were used in this study, the first for isolating MSCs and the second for creating an osteochondral model in the medial femoral condyle. The 26 rabbit knees were divided randomly into four groups: control ( n = 6), bone marrow-derived MSCs (BMSCs) ( n = 7), synovial tissue MSCs (SMSCs) ( n = 7), and cocultured MSCs ( n = 6). Tissue repair was assessed using the Fortier scale, and colony-forming assay was performed.

RESULTS

At different cell densities, cocultured and SMSCs formed larger colonies than BMSCs, indicating their high proliferative potential. After 2 months, complete filling of the defect with smooth surface regularity was detected in the cocultured MSC group, although there was no significant difference among the therapeutic groups macroscopically. Also, tissue repair was histologically better in the cocultured MSC group than in the control and SMSC groups, due to repair of the subchondral bone and coverage with hyaline cartilage. Additionally, toluidine blue and collagen-II staining intensity in the repaired tissue was better in the cocultured MSC group than in the remaining groups.

CONCLUSION

Our results suggest that cocultured MSCs are a suitable option for the regeneration capability of osteochondral defects due to their enhanced osteochondrogenic potential.

Effects of culture conditions on the mechanical and biological properties of engineered cartilage constructed with collagen hybrid scaffold and human mesenchymal stem cells

Mesenchymal stem cells (MSCs) has been used as one of the new cell sources in osteochondral tissue engineering. It has been well known that control of their differentiation into chondrocytes plays a key role in developing engineered cartilages. Therefore, this study aims to develop a fundamental protocol to control the differentiation and proliferation of MSCs to construct an engineered cartilage. We compared the effects of three different culture conditions on cell proliferation, extracellular matrix formation and the mechanical response of engineered cartilage constructed using a collagen-based hybrid scaffold and human MSCs. The experimental results clearly showed that the combined culture condition of the chondrogenic differentiation culture and the chondrocyte growth culture exhibited statistically significant cell proliferation, ECM formation and stiffness responses as compared to the other two combinations. It is thus concluded that the combination of the differentiation culture with the subsequent growth culture is recommended as the culture condition for chondrogenic tissue engineering using hMSCs.

Tissue Specific Differentiation of Human Chondrocytes Depends on Cell Microenvironment and Serum Selection

Therapeutic options to cure osteoarthritis (OA) are not yet available, although cell-based therapies for the treatment of traumatic defects of cartilage have already been developed using, e.g., articular chondrocytes. In order to adapt cell-based therapies to treat OA, appropriate cell culture conditions are necessary. Chondrocytes require a 3-dimensional (3D) environment for redifferentiation after 2-dimensional (2D) expansion. Fetal bovine serum (FBS) is commonly used as a medium supplement, although the usage of a xenogeneic serum could mask the intrinsic behavior of human cells in vitro. The aim of this study was to compare human articular chondrocytes cultivated as monolayers (2D) and the development of microtissues (3D) in the presence of FBS with those cultivated with human serum (HS). Evaluation of the expression of various markers via immunocytochemistry on monolayer cells revealed a higher dedifferentiation degree of chondrocytes cultivated with HS. Scaffold-free microtissues were generated using the agar overlay technique, and their differentiation level was evaluated via histochemistry and immunohistochemistry. Microtissues cultivated in the medium with FBS showed a higher redifferentiation level. This was evidenced by bigger microtissues and a more cartilage-like composition of the matrix with not any/less positivity for cartilage-specific markers in HS versus moderate-to-high positivity in FBS-cultured microtissues. The present study showed that the differentiation degree of chondrocytes depends both on the microenvironment of the cells and the serum type with FBS achieving the best results. However, HS should be preferred for the engineering of cartilage-like microtissues, as it rather enables a "human-based" situation in vitro. Hence, cultivation conditions might be further optimized to gain an even more adequate and donor-independent redifferentiation of chondrocytes in microtissues, e.g., designing a suitable chemically-defined serum supplement.

Mechanical stimulation promotes the proliferation and the cartilage phenotype of mesenchymal stem cells and chondrocytes co-cultured in vitro

Mesenchymal stem cells and chondrocytes are an important source of the cells for cartilage tissue engineering. Therefore, the culture and expansion methods of these cells need to be improved to overcome the aging of chondrocytes and induced chondrogenic differentiation of mesenchymal stem cells. The aim of this study was to expand the cells for cartilage tissue engineering by combining the advantages of growing cells in co-culture and under a mechanically-stimulated environment. Rabbit chondrocytes and co-cultured cells (bone mesenchymal stem cells and chondrocytes) were subjected to cyclic sinusoidal dynamic tensile mechanical stimulationusing the FX-4000 tension system. Chondrocyte proliferation was assayed by flow cytometry and CFSE labeling. The cell cartilage phenotype was determined by detecting GAG, collagen II and TGF-β1 protein expression by ELISA and the Col2α1, TGF-β1 and Sox9 gene expression by RT-PCR. The results show that the co-culture improved both the proliferation ability of chondrocytes and the cartilage phenotype of co-cultured cells. A proper cyclic sinusoidal dynamic tensile mechanical stimulation improved the proliferation ability and cartilage phenotype of chondrocytes and co-cultured cells. These results suggest that the co-culture of mesenchymal stem cells with chondrocytes and proper mechanical stimulation may be an appropriate way to rapidly expand the cells that have an improved cartilage phenotype for cartilage tissue engineering.

Progress of co-culture systems in cartilage regeneration

INTRODUCTION

Cartilage tissue engineering has rapidly developed in recent decades, exhibiting promising potential to regenerate and repair cartilage. However, the origin of a large amount of a suitable seed cell source is the major bottleneck for the further clinical application of cartilage tissue engineering. The use of a monoculture of passaged chondrocytes or mesenchymal stem cells results in undesired outcomes, such as fibrocartilage formation and hypertrophy. In the last two decades, co-cultures of chondrocytes and a variety of mesenchymal stem cells have been intensively investigated in vitro and in vivo, shedding light on the perspective of co-culture in cartilage tissue engineering.

AREAS COVERED

We summarize the recent literature on the application of heterologous cell co-culture systems in cartilage tissue engineering and compare the differences between direct and indirect co-culture systems as well as discuss the underlying mechanisms.

EXPERT OPINION

Co-culture system is proven to address many issues encountered by monocultures in cartilage tissue engineering, including reducing the number of chondrocytes needed and alleviating the dedifferentiation of chondrocytes. With the further development and knowledge of biomaterials, cartilage tissue engineering that combines the co-culture system and advanced biomaterials is expected to solve the difficult problem regarding the regeneration of functional cartilage.

Human osteochondritis dissecans fragment-derived chondrocyte characteristics ex vivo, after monolayer expansion-induced de-differentiation, and after re-differentiation in alginate bead culture

BACKGROUND

Autologous chondrocyte implantation (ACI) is a therapy for articular cartilage and osteochondral lesions that relies on notch- or trochlea-derived primary chondrocytes. An alternative cell source for ACI could be osteochondritis dissecans (OCD) fragment-derived chondrocytes. Assessing the potential of these cells, we investigated their characteristics ex vivo and after monolayer expansion, as monolayer expansion is an integral step of ACI. However, as monolayer expansion can induce de-differentiation, we asked whether monolayer-induced de-differentiation can be reverted through successive alginate bead culture.

METHODS

Chondrocytes were isolated from the OCD fragments of 15 patient knees with ICRS grades 3-4 lesions for ex vivo analyses, primary alginate bead culture, monolayer expansion, and alginate bead culture following monolayer expansion for attempting re-differentiation. We determined yield, viability, and the mRNA expression of aggrecan and type I, II, and X collagen.

RESULTS

OCD fragment-derived chondrocyte isolation yielded high numbers of viable cells with a low type I:II collagen expression ratio (< 1) and a relatively high aggrecan and type II and X collagen mRNA expression, indicating chondrogenic and hypertrophic characteristics. As expected, monolayer expansion induced de-differentiation. Alginate bead culture of monolayer-expanded cells significantly improved the expression profile of all genes investigated, being most successful in decreasing the hypertrophy marker type X collagen to 1.5% of its ex vivo value. However, the chondrogenic phenotype was not fully restored, as the collagen type I:II expression ratio decreased significantly but remained > 1.

CONCLUSION

OCD fragment derived human chondrocytes may hold not yet utilized clinical potential for cartilage repair.

Co-implantation of bone marrow mesenchymal stem cells and chondrocytes increase the viability of chondrocytes in rat osteo-chondral defects

Replacement of chondrocytes by adult stem cells was believed to improve the performance of autologous chondrocytes transplantation, since less chondrocytes were needed. Previous studies have demonstrated that the increased cartilage production in pellet co-cultures of chondrocytes and bone marrow mesenchymal stem cells (BMSCs) is due to the trophic effects of the MSC by stimulating chondrocyte proliferation and matrix production. However, the destination of MSCs or chondrocytes after implanted in osteo-chondral defects is not clear. The aim of the present study is to investigate the viability of MSCs and chondrocytes after co-implantation into a rat osteo-chondral defect model. MSCs were isolated from bone marrow and chondrocytes were extracted from knee joints of neonatal rats. Results of sulfated glycosaminoglycans (GAG) and collagen quantification demonstrated that co-culture pellets of BMSCs and chondrocytes have more GAG deposition than that of BMSCs or chondrocytes alone. Tracking cells with fluorescence protein demonstrated that MSCs disappeared following co-culture. In a rat knee injury model, co-implantation of BMSCs and chondrocytes contained more viable chondrocytes than chondrocytes implanted alone. To conclude, BMSCs were replaced by chondrocytes in pellet co-culture and BMSCs increased the viability of chondrocytes following co-implantation in a osteo-chondral defects model. Co-implantation of BMSCs and chondrocytes may be a promising approach to repairing osteo-chondral defects in the clinical setting.

Trophic effects of adipose-tissue-derived and bone-marrow-derived mesenchymal stem cells enhance cartilage generation by chondrocytes in co-culture

AIMS

Combining mesenchymal stem cells (MSCs) and chondrocytes has great potential for cell-based cartilage repair. However, there is much debate regarding the mechanisms behind this concept. We aimed to clarify the mechanisms that lead to chondrogenesis (chondrocyte driven MSC-differentiation versus MSC driven chondroinduction) and whether their effect was dependent on MSC-origin. Therefore, chondrogenesis of human adipose-tissue-derived MSCs (hAMSCs) and bone-marrow-derived MSCs (hBMSCs) combined with bovine articular chondrocytes (bACs) was compared.

METHODS

hAMSCs or hBMSCs were combined with bACs in alginate and cultured in vitro or implanted subcutaneously in mice. Cartilage formation was evaluated with biochemical, histological and biomechanical analyses. To further investigate the interactions between bACs and hMSCs, (1) co-culture, (2) pellet, (3) Transwell® and (4) conditioned media studies were conducted.

RESULTS

The presence of hMSCs-either hAMSCs or hBMSCs-increased chondrogenesis in culture; deposition of GAG was most evidently enhanced in hBMSC/bACs. This effect was similar when hMSCs and bAC were combined in pellet culture, in alginate culture or when conditioned media of hMSCs were used on bAC. Species-specific gene-expression analyses demonstrated that aggrecan was expressed by bACs only, indicating a predominantly trophic role for hMSCs. Collagen-10-gene expression of bACs was not affected by hBMSCs, but slightly enhanced by hAMSCs. After in-vivo implantation, hAMSC/bACs and hBMSC/bACs had similar cartilage matrix production, both appeared stable and did not calcify.

CONCLUSIONS

This study demonstrates that replacing 80% of bACs by either hAMSCs or hBMSCs does not influence cartilage matrix production or stability. The remaining chondrocytes produce more matrix due to trophic factors produced by hMSCs.

Multilineage Constructs for Scaffold-Based Tissue Engineering: A Review of Tissue-Specific Challenges

There is a growing interest in the regeneration of tissue in interfacial regions, where biological, physical, and chemical attributes vary across tissue type. The simultaneous use of distinct cell lineages can help in developing in vitro structures, analogous to native composite tissues. This literature review gathers the recent reports that have investigated multiple cell types of various sources and lineages in a coculture system for tissue-engineered constructs. Such studies aim at mimicking the native organization of tissues and their interfaces, and/or to improve the development of complex tissue substitutes. This paper thus distinguishes itself from those focusing on technical aspects of coculturing for a single specific tissue. The first part of this review is dedicated to variables of cocultured tissue engineering such as scaffold, cells, and in vitro culture environment. Next, tissue-specific coculture methods and approaches are covered for the most studied tissues. Finally, cross-analysis is performed to highlight emerging trends in coculture principles and to discuss how tissue-specific challenges can inspire new approaches for regeneration of different interfaces to improve the outcomes of various tissue engineering strategies.

Recent advances in 3D bioprinting for the regeneration of functional cartilage

The field of regeneration for functional cartilage has progressed tremendously. Conventional approaches for regenerating the damaged tissue based on integrated manufacturing are limited by their inability to produce precise and customized biomimetic tissues. On the other hand, 3D bioprinting is a promising technique with increased versatility because it can co-deliver cells and biomaterials with proper compositions and spatial distributions. In the present article, we review recent progress in the complete 3D printing process involved in functional cartilage regeneration, including printing techniques, biomaterials and cells. We also discuss the combination of 3D in vivo hybrid bioprinting with spheroids, gene delivery strategies and zonal cartilage design as a future direction of cartilage regeneration research.

Mixed cell therapy of bone marrow-derived mesenchymal stem cells and articular cartilage chondrocytes ameliorates osteoarthritis development

Of the many cell-based treatments that have been tested in an effort to regenerate osteoarthritic articular cartilage, none have ever produced cartilage that compare with native hyaline cartilage. Studies show that different cell types lead to inconsistent results and for cartilage regeneration to be considered successful, there must be an absence of fibrotic tissue. Here we report of a series of experiments in which bone marrow-derived stem cells (BMSCs) and articular cartilage chondrocytes (ACCs) were mixed in a 1:1 ratio and tested for their ability to enhance cartilage regeneration in three different conditions: (1) in an in vitro differentiation model; (2) in an ex vivo cartilage defect model implanted subcutaneously in mice; and (3) as an intra-articular injection in a meniscectomy-induced OA model in rats. The mixed cells were compared with monocultures of BMSCs and ACCs. In all three experimental models there was significantly enhanced cartilage regeneration and decreased fibrosis in the mixed BMSCs+ACCs group compared with the monocultures. Molecular analysis showed a reduction in vascularization and hypertrophy, coupled with higher chondrogenic gene expression resulting from the BMSCs+ACCs treatment. Together, our data suggest that mixed BMSCs+ACCs treatment is highly chondro-protective and is more effective in regenerating damaged cartilage in both the ex vivo cartilage defect and post-trauma OA disease models. The results from this approach could potentially be used for regeneration of cartilage in OA patients.

Honing Cell and Tissue Culture Conditions for Bone and Cartilage Tissue Engineering

An avenue of tremendous interest and need in health care encompasses the regeneration of bone and cartilage. Over the years, numerous tissue engineering strategies have contributed substantial progress toward the realization of clinically relevant therapies. Cell and tissue culture protocols, however, show many variations that make experimental results among different publications challenging to compare. This collection surveys prevalent cell sources, soluble factors, culture medium formulations, environmental factors, and genetic modification approaches in the literature. The intent of consolidating this information is to provide a starting resource for scientists considering how to optimize the parameters for cell differentiation and tissue culture procedures within the context of bone and cartilage tissue engineering.

Direct Coculture of Human Chondrocytes and Synovium-Derived Stem Cells Enhances In Vitro Chondrogenesis

Objective

Coculture of chondrocytes and mesenchymal stem cells (MSCs) has been developed as a strategy to overcome the dedifferentiation of chondrocytes during in vitro expansion in autologous chondrocyte transplantation. Synovium-derived stem cells (SDSCs) can be a promising cell source for coculture due to their superior chondrogenic potential compared to other MSCs and easy accessibility without donor site morbidity. However, studies on coculture of chondrocytes and SDSCs are very limited. The aim of this study was to investigate whether direct coculture of human chondrocytes and SDSCs could enhance chondrogenesis compared to monoculture of each cell.

Materials and Methods

In this experimental study, passage 2 chondrocytes and SDSCs were directly cocultured using different ratios of chondrocytes to SDSCs (3:1, 1:1, or 1:3). glycosaminoglycan (GAG) synthetic activity was assessed using GAG assays and Safranin-O staining. Expression of chondrogenesis-related genes (collagen types I, II, X, Aggrecan, and Sox-9) were analyzed by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and immunohistochemistry staining.

Results

GAG/DNA ratios in 1:1 and 1:3 coculture groups were significantly increased compared to those in the chondrocyte and SDSC monoculture groups. Type II collagen and SOX-9 were significantly upregulated in the 1:1 coculture group compared to those in the chondrocyte and SDSC monoculture groups. On the other hand, osteogenic marker (type I collagen) and hypertrophic marker (type X collagen) were significantly downregulated in the coculture groups compared to those in the SDSC monoculture group.

Conclusion

Direct coculture of human chondrocytes and SDSCs significantly enhanced chondrogenic potential, especially at a ratio of 1:1, compared to chondrocyte or SDSC monocultures.

The Use of Cocultured Mesenchymal Stem Cells with Tendon-Derived Stem Cells as a Better Cell Source for Tendon Repair

The management of tendon tissue injury presents a significant clinical challenge due to the unique properties of tendons. Cell-based therapy provides a new alternative for regenerating functional tendons, such as in tendon rupture repair, but largely remains at the preclinical research stage. A cell source for graft preparation is essential for successful clinic application. In this study, a novel cell coculture system of bone marrow mesenchymal stem cells (BMSCs) and tendon-derived stem cells (TDSCs) was developed and investigated. BMSCs and TDSCs were cultured separately or in combination at ratios of 20:1, 10:1, 5:1, and 1:1 in vitro, and the cocultured cells showed an enhanced proliferation and collagenous protein production. The coculture system promoted tenogenic differentiation with enhanced tenogenic marker gene expression and collagen matrix production, particularly in the groups with a ratio of 1:1. Using a rat patellar tendon window injury model, we demonstrated that the cell sheets formed by cocultured cells promoted tendon healing significantly, compared to those with a single-cell source. Our study suggests that BMSCs and TDSCs cocultured at the 1:1 ratio may be an improved cell source/preparation for tendon tissue engineering.

Tissue engineering-relevant characteristics of ex vivo and monolayer-expanded chondrocytes from the notch versus trochlea of human knee joints

PURPOSE

The aim was to analyse the biological characteristics of chondrocytes from the two biopsy sites notch vs. trochlea of human knee joints. The question was whether tissue engineering-relevant characteristics such as viability and mRNA expression profile would be comparable ex vivo and after monolayer expansion, as these are parts of routine autologous chondrocyte implantation (ACI).

METHODS

Biopsies from the intercondylar notch and the lateral aspect of the trochlea from 20 patients with ICRS grades 3 and 4 cartilage defects were harvested during arthroscopy. Collagen types 1, 2, and 10 mRNA were quantified by polymerase chain reaction.

RESULTS

Compared with notch chondrocytes, ex vivo trochlea chondrocytes had comparable cell numbers, vitality and aggrecan, collagen types 1, -2 and -10 mRNA expression. After monolayer expansion both notch and trochlea chondrocyte characteristics were comparably altered, regardless of their biopsy origin, and no significant differences in viability and mRNA expression were noted.

CONCLUSIONS

Collectively, these findings suggest that tissue engineering-relevant characteristics of notch and trochlea chondrocytes are comparable ex vivo and after monolayer expansion. Thus, trochlea chondrocytes promise clinical potential and chondrocytes for ACI could potentially be generated from both notch and trochlea biopsy sites.

Co-culture of chondrons and mesenchymal stromal cells reduces the loss of collagen VI and improves extracellular matrix production

Adult articular chondrocytes are surrounded by a pericellular matrix (PCM) to form a chondron. The PCM is rich in hyaluronan, proteoglycans, and collagen II, and it is the exclusive location of collagen VI in articular cartilage. Collagen VI anchors the chondrocyte to the PCM. It has been suggested that co-culture of chondrons with mesenchymal stromal cells (MSCs) might enhance extracellular matrix (ECM) production. This co-culture study investigates whether MSCs help to preserve the PCM and increase ECM production. Primary bovine chondrons or chondrocytes or rat MSCs were cultured alone to establish a baseline level for ECM production. A xenogeneic co-culture monolayer model using rat MSCs (20, 50, and 80%) was established. PCM maintenance and ECM production were assessed by biochemical assays, immunofluorescence, and histological staining. Co-culture of MSCs with chondrons enhanced ECM matrix production, as compared to chondrocyte or chondron only cultures. The ratio 50:50 co-culture of MSCs and chondrons resulted in the highest increase in GAG production (18.5 ± 0.54 pg/cell at day 1 and 11 ± 0.38 pg/cell at day 7 in 50:50 co-culture versus 16.8 ± 0.61 pg/cell at day 1 and 10 ± 0.45 pg/cell at day 7 in chondron monoculture). The co-culture of MSCs with chondrons appeared to decelerate the loss of the PCM as determined by collagen VI expression, whilst the expression of high-temperature requirement serine protease A1 (HtrA1) demonstrated an inverse relationship to that of the collagen VI. Together, this implies that MSCs directly or indirectly inhibited HtrA1 activity and the co-culture of MSCs with chondrons enhanced ECM synthesis and the preservation of the PCM.

Induced Redifferentiation of Human Chondrocytes from Articular Cartilage Lesion in Alginate Bead Culture After Monolayer Dedifferentiation: An Alternative Cell Source for Cell-Based Therapies?

Human chondrocytes isolated from articular cartilage (AC) lesions as an alternative cell source to the standard nonweight-bearing notch biopsy site may hold clinical potential for cell-based therapies. The aim was to characterize human AC lesion site chondrocytes, compare them to notch chondrocytes, and evaluate their redifferentiation potential after monolayer expansion and subsequent three-dimensional (3D) alginate bead culture. Lesion chondrocytes from knee joints of 20 patients with International Cartilage Repair Society (ICRS) grade 3 and 4 cartilage defects were analyzed ex vivo or cultured in primary alginate bead culture, monolayer expansion, or redifferentiated in alginate culture following monolayer expansion. The mRNA expression of the types I, II, and X collagen, and the proteoglycan aggrecan was compared between the four groups. In addition, notch chondrocytes of nine patients were compared to lesion chondrocytes ex vivo. AC lesion chondrocytes displayed ex vivo a nondegenerative phenotype, characterized by a relatively high mRNA expression of aggrecan and type II and X collagen, but a low type I collagen expression and a low ratio of type I to II collagen mRNA expression. Compared to notch chondrocytes, the mRNA expression of aggrecan and type II collagen was comparable and the ratio of type I to II collagen mRNA expression was below 1 in both groups, indicating a functional chondrocyte phenotype. Dedifferentiation led to a significantly altered degenerative mRNA expression profile. Induced redifferentiation in alginate beads after monolayer expansion significantly improved the mRNA expression of aggrecan, the type I and II collagen, and the type I to II collagen ratio, compared to monolayer expansion only. These data suggested that redifferentiating lesion chondrocytes after monolayer expansion in alginate beads resulted in a pool of cells with greater chondrogenic potential, compared to expanded dedifferentiated chondrocytes. Collectively, these data suggest that ex vivo and redifferentiated lesion chondrocytes may hold nonutilized clinical potential for the tissue engineering of AC.

Applications of Tissue Engineering in Joint Arthroplasty: Current Concepts Update

Research in tissue engineering has undoubtedly achieved significant milestones in recent years. Although it is being applied in several disciplines, tissue engineering's application is particularly advanced in orthopedic surgery and in degenerative joint diseases. The literature is full of remarkable findings and trials using tissue engineering in articular cartilage disease. With the vast and expanding knowledge, and with the variety of techniques available at hand, the authors aimed to review the current concepts and advances in the use of cell sources in articular cartilage tissue engineering.

Redifferentiation of High-Throughput Generated Fibrochondrocyte Micro-Aggregates: Impact of Low Oxygen Tension

In meniscus tissue engineering strategies, enhancing the matrix quality of the neomeniscal tissue is important. When the differentiated phenotype of fibrochondrocytes is lost, the quality of the matrix becomes compromised. The objective of this study was to produce uniform fibrochondrocyte micro-aggregates with desirable phenotype and tissue homogeneity in large quantities using a simple and reproducible method. Furthermore, we investigated if hypoxia could enhance the matrix quality. Porcine fibrochondrocytes were expanded at 21% oxygen until passage 3 (P3) and a gene expression profile was determined. P3 fibrochondrocytes were cultivated in chondrogenic medium at 5 and 21% oxygen in high-throughput agarose chips containing 2,865 microwells 200 µm in diameter. Evaluation included live/dead staining, histological examination, immunohistochemistry, dimethylmethylene blue assay and real-time reverse transcriptase quantitative polymerase chain reaction of the micro-aggregates. Gene expression analysis showed a drastic decline in collagen II and high expression of collagen I during monolayer culture. After 4 days, uniform and stable micro-aggregates could be produced. The redifferentiation and matrix quality of the hypoxic cultured micro-aggregates were enhanced relative to the normoxic cultures. Sulfated glycosaminoglycan synthesis was significantly higher, and collagen II expression and the collagen II/collagen I ratio were significantly upregulated in the hypoxic cultures. High-throughput production of uniform microtissues holds promise for the generation of larger-scale tissue engineering constructs or optimization of redifferentiation mechanisms for clinical applications.

The Effect of Cell Dose on the Early Magnetic Resonance Morphological Outcomes of Autologous Cell Implantation for Articular Cartilage Defects in the Knee: A Randomized Clinical Trial

BACKGROUND

Although autologous chondrocyte implantation (ACI) has been established as a standard treatment for large full-thickness cartilage defects, the effect of different doses of autologous chondrocyte products on structural outcomes has never been examined.

HYPOTHESIS

In ACI, the dose level may have an influence on medium-term magnetic resonance morphological findings after treatment.

STUDY DESIGN

Randomized controlled trial; Level of evidence, 1.

METHODS

A total of 75 patients who underwent ACI using a pure, autologous, third-generation matrix-associated ACI product were divided into 3 groups representing different doses: 3 to 7 spheroids/cm(2), 10 to 30 spheroids/cm(2), and 40 to 70 spheroids/cm(2). Magnetic resonance imaging was performed at 1.5, 3, 6, and 12 months after ACI and was evaluated by the magnetic resonance observation of cartilage repair tissue (MOCART) score and the Knee injury and Osteoarthritis Outcome Score (KOOS).

RESULTS

MOCART scores showed improvements after 3 months, with slight dose dependence, and further improvement after 12 months, although without significant dose dependence. The mean MOCART scores after 3 months (0 = worst, 100 = best) were 59.8, 64.5, and 64.7 for the low-, medium-, and high-dose groups, respectively, and 62.9 for all patients; at 12 months, these were 74.1, 74.5, and 68.8 for the respective dose groups and 72.4 for all patients. Several MOCART items (surface of repair tissue, structure of repair tissue, signal intensity of repair tissue, subchondral bone, and synovitis) showed a more rapid response with the medium and high doses than with the low dose, suggesting a potential dose relationship. No significant correlation between the MOCART (overall and subscores) with clinical outcomes as assessed by the overall KOOS was detected at 3- and 12-month assessments.

CONCLUSION

This study reveals a trend toward earlier recovery after treatment with higher spheroid doses in terms of better defect filling for full-thickness cartilage defects of the knee, while outcomes after 12 months were similar in all dose groups. However, a correlation with clinical outcomes or the failure rate at 1 year after ACI was not found. A longer follow-up will be required for more definite conclusions on the clinical relevance of ACI cell density to be drawn.

REGISTRATION

NCT01225575 (ClinicalTrials.gov identifier); 2009-016816-20 (EudraCT number).

Fibroblast growth factor 18 increases the trophic effects of bone marrow mesenchymal stem cells on chondrocytes isolated from late stage osteoarthritic patients

Coculture of mesenchymal stem cells with chondrocytes increases production of cartilaginous matrix. Chondrocytes isolated from late stage osteoarthritic patients usually lost their phenotype of producing cartilaginous matrix. Fibroblast growth factor 18 is believed to redifferentiate OA chondrocyte into functionally active chondrocytes. The aim of this study is to investigate the supportive effects of MSCs on OA chondrocytes and test if FGF18 could enhance the responsiveness of OA chondrocytes to the support of MSCs in a coculture system. Both pellet and transwell co-cultures were used. GAG quantification, hydroxyproline assay, and qPCR were performed. An ectopic models of cartilage formation was also applied. Our data indicated that, in pellets coculture of MSCs and OA chondrocytes, matrix production was increased in the presence of FGF18, comparing to the monoculture of chondrocytes. Results from transwell coculture study showed that expression of matrix producing genes in OA chondrocytes increased when cocultured with MSCs with FGF18 in culture medium, while hypertrophic genes were not changed by coculture. Finally, coimplantation of MSCs with OA chondrocytes produces more matrix than chondrocytes only. In conclusion, FGF18 can restore the responsiveness of OA chondrocytes to the trophic effects of MSCs. Coimplantation of MSCs and OA chondrocytes treated with FGF18 may be a good alternative cell source for regenerating cartilage tissue that is degraded during OA pathological changes.

Enhancing chondrogenic phenotype for cartilage tissue engineering: monoculture and coculture of articular chondrocytes and mesenchymal stem cells

Articular cartilage exhibits an inherently low rate of regeneration. Consequently, damage to articular cartilage often requires surgical intervention. However, existing treatments generally result in the formation of fibrocartilage tissue, which is inferior to native articular cartilage. As a result, cartilage engineering strategies seek to repair or replace damaged cartilage with an engineered tissue that restores full functionality to the impaired joint. These strategies often involve the use of chondrocytes, yet in vitro expansion and culture can lead to undesirable changes in chondrocyte phenotype. This review focuses on the use of articular chondrocytes and mesenchymal stem cells (MSCs) in either monoculture or coculture for the enhancement of chondrogenesis. Coculture strategies increasingly outperform their monoculture counterparts with regard to chondrogenesis and present unique opportunities to attain chondrocyte phenotype stability in vitro. Methods to prevent chondrocyte dedifferentiation and promote chondrocyte redifferentiation as well as to promote the chondrogenic differentiation of MSCs while preventing MSC hypertrophy are discussed.

Articular chondrocytes and mesenchymal stem cells seeded on biodegradable scaffolds for the repair of cartilage in a rat osteochondral defect model

This work investigated the ability of co-cultures of articular chondrocytes and mesenchymal stem cells (MSCs) to repair articular cartilage in osteochondral defects. Bovine articular chondrocytes and rat MSCs were seeded in isolation or in co-culture onto electrospun poly(ɛ-caprolactone) (PCL) scaffolds and implanted into an osteochondral defect in the trochlear groove of 12-week old Lewis rats. Additionally, a blank PCL scaffold and untreated defect were investigated. After 12 weeks, the extent of cartilage repair was analyzed through histological analysis, and the extent of bone healing was assessed by quantifying the total volume of mineralized bone in the defect through microcomputed tomography. Histological analysis revealed that the articular chondrocytes and co-cultures led to repair tissue that consisted of more hyaline-like cartilage tissue that was thicker and possessed more intense Safranin O staining. The MSC, blank PCL scaffold, and empty treatment groups generally led to the formation of fibrocartilage repair tissue. Microcomputed tomography revealed that while there was an equivalent amount of mineralized bone formation in the MSC, blank PCL, and empty treatment groups, the defects treated with chondrocytes or co-cultures had negligible mineralized bone formation. Overall, even with a reduced number of chondrocytes, co-cultures led to an equal level of cartilage repair compared to the chondrocyte samples, thus demonstrating the potential for the use of co-cultures of articular chondrocytes and MSCs for the in vivo repair of cartilage defects.

Chondrogenic phenotype of articular chondrocytes in monoculture and co-culture with mesenchymal stem cells in flow perfusion

This work investigated the effect of flow perfusion bioreactor culture with and without transforming growth factor-β3 (TGF-β3) supplementation on the proliferation, extracellular matrix (ECM) production, and chondrogenic gene expression of chondrocytes both in monoculture and in co-culture with bone marrow-derived mesenchymal stem cells (MSCs). Both cell populations were cultured on electrospun poly(ɛ-caprolactone) scaffolds for 2 weeks in static or flow perfusion culture with and without TGF-β3. Overall, it was observed that without growth factors, flow perfusion culture resulted in increased cell proliferation and ECM with a more cartilage-like composition. While with TGF-β3 induction, flow perfusion constructs generally had lower chondrogenic gene expression than the corresponding static cultures, the growth factor still had an inductive effect on the cells with enhanced gene expression compared with the corresponding noninduced cultures. In addition, while flow perfusion cultures generally had reduced overall ECM content, the ECM distribution was more homogenous compared with the corresponding static cultures. These results are significant in that they indicate that while flow perfusion culture has some beneficial effects on the chondrogenic phenotype of articular chondrocytes, flow perfusion alone is not sufficient to maintain the chondrogenic phenotype of chondrocytes in either monoculture or co-culture, thus demonstrating the advantages of using exogenously added growth factors in flow perfusion culture. Furthermore, the results demonstrate the advantages of flow perfusion culture for the creation of large tissue engineered constructs and the potential of co-cultures of articular chondrocytes and MSCs to be used in flow perfusion culture.