Chondrogenic differentiation of mesenchymal stem cells: challenges and unfulfilled expectations

Effect of Cyclic Dynamic Compressive Loading on Chondrocytes and Adipose-Derived Stem Cells Co-Cultured in Highly Elastic Cryogel Scaffolds

In this study, we first used gelatin/chondroitin-6-sulfate/hyaluronan/chitosan highly elastic cryogels, which showed total recovery from large strains during repeated compression cycles, as 3D scaffolds to study the effects of cyclic dynamic compressive loading on chondrocyte gene expression and extracellular matrix (ECM) production. Dynamic culture of porcine chondrocytes was studied at 1 Hz, 10% to 40% strain and 1 to 9 h/day stimulation duration, in a mechanical-driven multi-chamber bioreactor for 14 days. From the experimental results, we could identify the optimum dynamic culture condition (20% and 3 h/day) to enhance the chondrocytic phenotype of chondrocytes from the expression of marker (Col I, Col II, Col X, TNF-α, TGF-β1 and IGF-1) genes by quantitative real-time polymerase chain reactions (qRT-PCR) and production of ECM (GAGs and Col II) by biochemical analysis and immunofluorescence staining. With up-regulated growth factor (TGF-β1 and IGF-1) genes, co-culture of chondrocytes with porcine adipose-derived stem cells (ASCs) was employed to facilitate chondrogenic differentiation of ASCs during dynamic culture in cryogel scaffolds. By replacing half of the chondrocytes with ASCs during co-culture, we could obtain similar production of ECM (GAGs and Col II) and expression of Col II, but reduced expression of Col I, Col X and TNF-α. Subcutaneous implantation of cells/scaffold constructs in nude mice after mono-culture (chondrocytes or ASCs) or co-culture (chondrocytes + ASCs) and subject to static or dynamic culture condition in vitro for 14 days was tested for tissue-engineering applications. The constructs were retrieved 8 weeks post-implantation for histological analysis by Alcian blue, Safranin O and Col II immunohistochemical staining. The most abundant ectopic cartilage tissue was found for the chondrocytes and chondrocytes + ASCs groups using dynamic culture, which showed similar neo-cartilage formation capability with half of the chondrocytes replaced by ASCs for co-culture. This combined co-culture/dynamic culture strategy is expected to cut down the amount of donor chondrocytes needed for cartilage-tissue engineering.

Modulating the oxidative environment during mesenchymal stem cells chondrogenesis with serum increases collagen accumulation in agarose culture

Chondrogenesis of mesenchymal stem cells (MSCs) is induced in culture conditions that have been associated with oxidative stress, although the extent to which the oxidative environment affects differentiation and extracellular matrix (ECM) accumulation is not known. The objectives of this study were to evaluate the oxidative environment during MSCs chondrogenesis in conventional serum-free medium, and the effect of serum-supplementation on intracellular reactive oxygen species (ROS) and chondrogenesis. Young adult equine MSCs were seeded into agarose and cultured in chondrogenic medium, with or without 5% fetal bovine serum (FBS), for up to 15 days. Samples were evaluated for intracellular ROS, the antioxidant glutathione, ECM and gene expression measures of chondrogenesis, and carbonylation as an indicator of oxidative damage. Intracellular ROS increased with time in culture, and was lower in medium supplemented with FBS. Glutathione decreased ∼12-fold during early chondrogenesis (p < 0.0001), and was not affected by FBS (p = 0.25). After 15 days of culture, FBS supplementation increased hydroxyproline accumulation ∼80% (p = 0.0002); otherwise, measures of chondrogenesis were largely unaffected. Protein carbonylation in chondrogenic MSCs cultures was not significantly different between serum-free and FBS cultures (p = 0.72). Supplementation with adult equine serum increased hydroxyproline accumulation by 45% over serum-free culture (p = 0.0006). In conclusion, this study characterized changes in the oxidative environment during MSC chondrogenesis, and suggested that lowering ROS may be an effective approach to increase collagen accumulation. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:506-514, 2018.

Joint diseases: from connexins to gap junctions

Connexons form the basis of hemichannels and gap junctions. They are composed of six tetraspan proteins called connexins. Connexons can function as individual hemichannels, releasing cytosolic factors (such as ATP) into the pericellular environment. Alternatively, two hemichannel connexons from neighbouring cells can come together to form gap junctions, membrane-spanning channels that facilitate cell-cell communication by enabling signalling molecules of approximately 1 kDa to pass from one cell to an adjacent cell. Connexins are expressed in joint tissues including bone, cartilage, skeletal muscle and the synovium. Indicative of their importance as gap junction components, connexins are also known as gap junction proteins, but individual connexin proteins are gaining recognition for their channel-independent roles, which include scaffolding and signalling functions. Considerable evidence indicates that connexons contribute to the function of bone and muscle, but less is known about the function of connexons in other joint tissues. However, the implication that connexins and gap junctional channels might be involved in joint disease, including age-related bone loss, osteoarthritis and rheumatoid arthritis, emphasizes the need for further research into these areas and highlights the therapeutic potential of connexins.

Successful Low-Cost Scaffold-Free Cartilage Tissue Engineering Using Human Cartilage Progenitor Cell Spheroids Formed by Micromolded Nonadhesive Hydrogel

The scaffold-free tissue engineering using spheroids is pointed out as an approach for optimizing the delivery system of cartilage construct. In this study, we aimed to evaluate the micromolded nonadhesive hydrogel (MicroTissues®) for spheroid compaction (2-day culture) and spontaneous chondrogenesis (21-day culture) using cartilage progenitors cells (CPCs) from human nasal septum without chondrogenic stimulus. CPC spheroids showed diameter stability (486 μm ± 65), high percentage of viable cells (88.1 ± 2.1), and low percentage of apoptotic cells (2.3%). After spheroid compaction, the synthesis of TGF-β1, TGF-β2, and TGF-β3 was significantly higher compared to monolayer (p < 0.005). Biomechanical assay revealed that the maximum forces applied to spheroids after chondrogenesis were 2.6 times higher than for those cultured for 2 days. After spontaneous chondrogenesis, CPC spheroids were entirely positive for N-cadherin, collagen type II and type VI, and aggrecan and chondroitin sulfate. Comparing to monolayer, the expression of SOX5 and SOX6 genes analyzed by qPCR was significantly upregulated (p < 0.01). Finally, we observed the capacity of CPC spheroids starting to fuse. To the best of our knowledge, this is the first time in the scientific literature that human CPC spheroids were formed by micromolded nonadhesive hydrogel, achieving a successful scaffold-free cartilage engineering without chondrogenic stimulus (low cost).

Role of the protease corin in chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells

Mesenchymal stem cells (MSCs) have the potency to differentiate into chondrocytes, osteocytes and adipocytes. Corin is a cardiac protease that activates the natriuretic peptides, thereby regulating blood volume and pressure. In addition to the heart, corin gene upregulation was reported in bone marrow- and adipose tissue-derived MSCs that underwent osteogenic differentiation. To date, the biological significance of corin expression in MSC differentiation remains unknown. In this study we isolated and cultured human bone marrow-derived MSCs that were capable of undergoing chondrogenic, osteogenic and adipogenic lineage differentiation. By reverse transcription polymerase chain reaction (RT-PCR) and immunostaining, we found that corin expression was upregulated when these MSCs underwent chondrogenic, osteogenic and adipogenic differentiation. The upregulation of corin expression was most significant in the cells undergoing chondrogenic lineage differentiation. Silencing corin gene expression by small hairpin RNA in the MSCs inhibited chondrogenic, but not osteogenic and adipogenic, differentiation. These results suggest a novel function of corin in MSC differentiation and chondrocyte development.

Comparison of in vitro-cultivation of human mesenchymal stroma/stem cells derived from bone marrow and umbilical cord

Cell-mediated therapy is currently considered as a novel approach for many human diseases. Potential uses range from topic applications with the regeneration of confined tissue areas to systemic applications. Stem cells including mesenchymal stroma/stem cells (MSCs) represent a highly attractive option. Their potential to cure or alleviate human diseases is investigated in a number of clinical trials. A wide variety of methods has been established in the past years for isolation, cultivation and characterization of human MSCs as expansion is presently deemed a prerequisite for clinical application with high numbers of cells carrying reproducible properties. MSCs have been retrieved from various tissues and used in a multitude of settings whereby numerous experimental protocols are available for expansion of MSCs in vitro. Accordingly, different isolation, culture and upscaling techniques contribute to the heterogeneity of MSC characteristics and the, sometimes, controversial results. Therefore, this review discusses and summarizes certain experimental conditions for MSC in vitro culture focusing on adult bone marrow-derived and neonatal umbilical cord-derived MSCs in order to enhance our understanding for MSC tissue sources and to stratify different procedures. Copyright © 2016 John Wiley & Sons, Ltd.

Using Costal Chondrocytes to Engineer Articular Cartilage with Applications of Passive Axial Compression and Bioactive Stimuli

Generating neocartilage with suitable mechanical integrity from a cell source that can circumvent chondrocyte scarcity is indispensable for articular cartilage regeneration strategies. Costal chondrocytes of the rib eliminate donor site morbidity in the articular joint, but it remains unclear how neocartilage formed from these cells responds to mechanical loading, especially if the intent is to use it in a load-bearing joint. In a series of three experiments, this study sought to determine efficacious parameters of passive axial compressive stimulation that would enable costal chondrocytes to synthesize mechanically robust cartilage. Experiment 1 determined a suitable time window for stimulation by its application during either the matrix synthesis phase, the maturation phase, or during both phases of the self-assembling process. The results showed that compressive stimulation at either time was effective in increasing instantaneous moduli by 92% and 87% in the synthesis and maturation phases, respectively. Compressive stimulation during both phases did not further improve properties beyond a one-time stimulation. The magnitude of passive axial compression was examined in Experiment 2 by applying 0, 3.3, 5.0, or 6.7 kPa stresses to the neocartilage. Unlike 6.7 kPa, both 3.3 and 5.0 kPa significantly increased neocartilage compressive properties by 42% and 48% over untreated controls, respectively. Experiment 3 examined how the passive axial compression regimen developed from the previous phases interacted with a bioactive regimen (transforming growth factor [TGF]-β1, chondroitinase ABC, and lysyl oxidase-like 2). Passive axial compression significantly improved the relaxation modulus compared with bioactive treatment alone. Furthermore, a combined treatment of compressive and bioactive stimulation improved the tensile properties of neocartilage 2.6-fold compared with untreated control. The ability to create robust articular cartilage from passaged costal chondrocytes through appropriate mechanical and bioactive stimuli will greatly extend the clinical applicability of tissue-engineered products to a wider patient population.

Progenitor Cells from Cartilage: Grade Specific Differences in Stem Cell Marker Expression

Recent research has confirmed the presence of Mesenchymal stem cell (MSC)-like progenitors (MPC) in both normal and osteoarthritic cartilage. However, there is only limited information concerning how MPC markers are expressed with osteoarthritis (OA) progression. The purpose of this study was to compare the prevalence of various MPC markers in different OA grades. Human osteoarthritic tibial plateaus were obtained from ten patients undergoing total knee replacement. Each sample had been classified into a mild or severe group according to OARSI scoring. Tissue was taken from each specimen and mRNA expression levels of CD105, CD166, Notch 1, Sox9, Acan and Col II A1 were measured at day 0 and day 14 (2 weeks in vitro). Furthermore, MSC markers: Nucleostemin, CD90, CD73, CD166, CD105 and Notch 1 were studied by immunofluorescence. mRNA levels of MSC markers did not differ between mild and severe OA at day 0. At day 14, protein analysis showed that proliferated cells from both sources expressed all 6 MSC markers. Only cells from the mild OA subjects resulted in a significant increase of mRNA CD105 and CD166 after in vitro expansion. Moreover, cells from the mild OA subjects showed significantly higher levels of CD105, Sox9 and Acan compared with those from severe OA specimens. Results confirmed the presence of MSC markers in mild and severe OA tissue at both mRNA and protein levels. We found significant differences between cells obtained from mild compared to severe OA specimens suggests that mild OA derived cells may have a greater MSC potential.

Transcriptome-Wide Analyses of Human Neonatal Articular Cartilage and Human Mesenchymal Stem Cell-Derived Cartilage Provide a New Molecular Target for Evaluating Engineered Cartilage

Cellular differentiation comprises a progressive, multistep program that drives cells to fabricate a tissue with specific and site distinctive structural and functional properties. Cartilage constitutes one of the potential differentiation lineages that mesenchymal stem cells (MSCs) can follow under the guidance of specific bioactive agents. Single agents such as transforming growth factor beta (TGF-β) and bone morphogenetic protein 2 in unchanging culture conditions have been historically used to induce in vitro chondrogenic differentiation of MSCs. Despite the expression of traditional chondrogenic biomarkers such as type II collagen and aggrecan, the resulting tissue represents a transient cartilage rather than an in vivo articular cartilage (AC), differing significantly in structure, chemical composition, cellular phenotypes, and mechanical properties. Moreover, there have been no comprehensive, multicomponent parameters to define high-quality and functional engineered hyaline AC. To address these issues, we have taken an innovative approach based on the molecular interrogation of human neonatal articular cartilage (hNAC), dissected from the knees of 1-month-old cadaveric specimens. Subsequently, we compared hNAC-specific transcriptional regulatory elements and differentially expressed genes with adult human bone marrow (hBM) MSC-derived three-dimensional cartilage structures formed in vitro. Using microarray analysis, the transcriptome of hNAC was found to be globally distinct from the transient, cartilage-like tissue formed by hBM-MSCs in vitro. Specifically, over 500 genes that are highly expressed in hNAC were not expressed at any time point during in vitro human MSC chondrogenesis. The analysis also showed that the differences were less variant during the initial stages (first 7 days) of the in vitro chondrogenic differentiation program. These observations suggest that the endochondral fate of hBM-MSC-derived cartilage may be rerouted at earlier stages of the TGF-β-stimulated chondrogenic differentiation program. Based on these analyses, several key molecular differences (transcription factors and coded cartilage-related proteins) were identified in hNAC that will be useful as molecular inductors and identifiers of the in vivo AC phenotype. Our findings provide a new gold standard of a molecularly defined AC phenotype that will serve as a platform to generate novel approaches for AC tissue engineering.

The role of laminins in cartilaginous tissues: from development to regeneration

As a key molecule of the extracellular matrix, laminin provides a delicate microenvironment for cell functions. Recent findings suggest that laminins expressed by cartilage-forming cells (chondrocytes, progenitor cells and stem cells) could promote chondrogenesis. However, few papers outline the effect of laminins on providing a favorable matrix microenvironment for cartilage regeneration. In this review, we delineated the expression of laminins in hyaline cartilage, fibrocartilage and cartilage-like tissue (nucleus pulposus) throughout several developmental stages. We also examined the effect of laminins on the biological activities of chondrocytes, including adhesion, migration and survival. Furthermore, we scrutinized the potential influence of various laminin isoforms on cartilage-forming cells' proliferation and chondrogenic differentiation. With this information, we hope to facilitate the understanding of the spatial and temporal interactions between cartilage-forming cells and laminin microenvironment to eventually advance cell-based cartilage engineering and regeneration.

Core-shell microparticles for protein sequestration and controlled release of a protein-laden core

Development of multifunctional biomaterials that sequester, isolate, and redeliver cell-secreted proteins at a specific timepoint may be required to achieve the level of temporal control needed to more fully regulate tissue regeneration and repair. In response, we fabricated core-shell heparin-poly(ethylene-glycol) (PEG) microparticles (MPs) with a degradable PEG-based shell that can temporally control delivery of protein-laden heparin MPs. Core-shell MPs were fabricated via a re-emulsification technique and the number of heparin MPs per PEG-based shell could be tuned by varying the mass of heparin MPs in the precursor PEG phase. When heparin MPs were loaded with bone morphogenetic protein-2 (BMP-2) and then encapsulated into core-shell MPs, degradable core-shell MPs initiated similar C2C12 cell alkaline phosphatase (ALP) activity as the soluble control, while non-degradable core-shell MPs initiated a significantly lower response (85+19% vs. 9.0+4.8% of the soluble control, respectively). Similarly, when degradable core-shell MPs were formed and then loaded with BMP-2, they induced a ∼7-fold higher C2C12 ALP activity than the soluble control. As C2C12 ALP activity was enhanced by BMP-2, these studies indicated that degradable core-shell MPs were able to deliver a bioactive, BMP-2-laden heparin MP core. Overall, these dynamic core-shell MPs have the potential to sequester, isolate, and then redeliver proteins attached to a heparin core to initiate a cell response, which could be of great benefit to tissue regeneration applications requiring tight temporal control over protein presentation.

STATEMENT OF SIGNIFICANCE

Tissue repair requires temporally controlled presentation of potent proteins. Recently, biomaterial-mediated binding (sequestration) of cell-secreted proteins has emerged as a strategy to harness the regenerative potential of naturally produced proteins, but this strategy currently only allows immediate amplification and re-delivery of these signals. The multifunctional, dynamic core-shell heparin-PEG microparticles presented here overcome this limitation by sequestering proteins through a PEG-based shell onto a protein-protective heparin core, temporarily isolating bound proteins from the cellular microenvironment, and re-delivering proteins only after degradation of the PEG-based shell. Thus, these core-shell microparticles have potential to be a novel tool to harness and isolate proteins produced in the cellular environment and then control when proteins are re-introduced for the most effective tissue regeneration and repair.

Platelet Rich Plasma and Culture Configuration Affect the Matrix Forming Phenotype of Bone Marrow Stromal Cells

We aim to examine the influence of platelet rich plasma (PRP) and spatial cues in cartilage/bone matrix forming proteins, and to evaluate the mitotic and chemotactic potential of PRP on human mesenchymal stem cells (hMSCs). Directed cell migration towards PRP gradients was assessed in chemotactic chambers, and recorded by time-lapse microscopy. hMSCs cultured in three-dimensional (3D) scaffolds were visualized by scanning electron microscopy; Hoechst dye was used to confirm cell confluence in 3D-constructs and monolayers before experimental treatment. MSCs were treated with 10% PRP lysate or 10% PRP lysate supplemented with TGF-β-based differentiation medium. The expression of cartilage (COL2A1, Sox9, ACAN, COMP), and bone (COL1A1, VEGF, COL10A1, Runx2) fundamental genes was assessed by real time PCR in monolayers and 3D-constructs. PRP had mitotic (p < 0.001), and chemotactic effect on hMSCs, Ralyleigh test p = 1.02E - 10. Two and three-week exposure of MSCs to PRP secretome in 3D-constructs or monolayers decreased Sox9 expression (p < 0.001 and p = 0.050) and COL2A1, (p = 0.011 and p = 0.019). MSCs in monolayers exposed to PRP showed increased ACAN (p = 0.050) and COMP (p < 0.001). Adding TGF-β-based differentiation medium to PRP increased COMP, and COL2A1 expression at gene and protein level, but merely in 3D-constructs, p < 0.001. TGF-β addition to monolayers reduced Sox9 (p < 0.001), aggrecan (p = 0.004), and VEGF (p = 0.004). Cells exposed to PRP showed no changes in hypertrophy associated genes in either monolayers or 3D-constructs. Our study suggests hMSCs have high-degree of plasticity having the potential to change their matrix-forming phenotype when exposed to PRP and according to spatial configuration.

Mesenchymal Stem Cell-Based Cartilage Regeneration Approach and Cell Senescence: Can We Manipulate Cell Aging and Function?

Aging is the most prominent risk factor triggering several degenerative diseases, such as osteoarthritis (OA). Due to its poor self-healing capacity, once injured cartilage needs to be reestablished. This process might be approached through resorting to cell-based therapies and/or tissue engineering. Human mesenchymal stem cells (MSCs) represent a promising approach due to their chondrogenic differentiation potential. Presently, in vitro chondrogenic differentiation of MSCs is limited by two main reasons as follows: aging of MSCs, which determines the loss of cell proliferative and differentiation capacity and MSC-derived chondrocyte hypertrophic differentiation, which limits the use of these cells in cartilage tissue regeneration approach. The effect of aging on MSCs is fundamental for stem cell-based therapy development, especially in older subjects. In the present review we focus on homeostasis alterations occurring in MSC-derived chondrocytes during in vitro aging. Moreover, we deal with potential cell aging regulation approaches, such as cell stimulation through telomerase activators, mechanical strain, and epigenetic regulation. Future investigations in this field might provide new insights into innovative strategies for cartilage regeneration and potentially inspire novel therapeutic approaches for OA treatment.

The Good the Bad and the Ugly of Glycosaminoglycans in Tissue Engineering Applications

High sulfation, low cost, and the status of heparin as an already FDA- and EMA- approved product, mean that its inclusion in tissue engineering (TE) strategies is becoming increasingly popular. However, the use of heparin may represent a naïve approach. This is because tissue formation is a highly orchestrated process, involving the temporal expression of numerous growth factors and complex signaling networks. While heparin may enhance the retention and activity of certain growth factors under particular conditions, its binding 'promiscuity' means that it may also inhibit other factors that, for example, play an important role in tissue maintenance and repair. Within this review we focus on articular cartilage, highlighting the complexities and highly regulated processes that are involved in its formation, and the challenges that exist in trying to effectively engineer this tissue. Here we discuss the opportunities that glycosaminoglycans (GAGs) may provide in advancing this important area of regenerative medicine, placing emphasis on the need to move away from the common use of heparin, and instead focus research towards the utility of specific GAG preparations that are able to modulate the activity of growth factors in a more controlled and defined manner, with less off-target effects.

Tissue-specific bioactivity of soluble tendon-derived and cartilage-derived extracellular matrices on adult mesenchymal stem cells

BACKGROUND

Biological scaffolds composed of tissue-derived extracellular matrix (ECM) can promote homologous (i.e., tissue-specific) cell differentiation through preservation of biophysical and biochemical motifs found in native tissues. Solubilized ECMs derived from decellularized tendon and cartilage have recently been promoted as tissue-specific biomaterials, but whether tissue-specific bioactivity is preserved following solubilization is unknown. This study explored the tissue-specific bioactivity of soluble decellularized tendon and cartilage ECMs on human bone marrow-derived mesenchymal stem cells (MSCs) presented across different culture microenvironments, including two-dimensional (2D) tissue culture plastic, aligned electrospun nanofibers, cell pellets, and cell-seeded photocrosslinkable hydrogels.

METHODS

Tendon and cartilage ECMs were decellularized using established methods and solubilized either via pepsin digestion or urea extraction. The effect of soluble ECMs on cell proliferation and differentiation was initially explored by supplementing basal medium of human MSCs cultured on 2D tissue culture plastic. In subsequent experiments, MSCs were cultured on aligned electrospun nanofibers, ascell pellets, or encapsulated within photocrosslinkable methacrylated gelatin (GelMA) hydrogels. Urea-extracted tendon and cartilage ECMs were added as supplements.

RESULTS

Pepsin-digested ECMs did not promote homologous differentiation in human MSCs, whether provided as a medium supplement or three-dimensional (3D) hydrogels. In contrast, urea-extracted ECMs tended to promote tissue-specific differentiation of MSCs cultured in 2D and 3D microenvironments. The application of the small molecule TGF-β signaling inhibitor SB-431542 largely negated the tissue-specific gene expression patterns mediated by tendon and cartilage ECMs. This suggests that the action of endogenous TGF-β was required, but was not sufficient, to impart tissue-specific bioactivity of urea-extracted ECMs. When urea-extracted cartilage ECM was incorporated within a photocurable GelMA hydrogel it independently enhanced chondrogenesis in encapsulated MSCs, and showed additive prochondrogenesis upon TGF-β supplementation in the medium.

CONCLUSIONS

Urea-extracted ECM fractions of decellularized tendon and cartilage are soluble supplements capable of enhancing tissue-specific differentiation of adult stem cells.

A consistent and potentially exploitable response during chondrogenesis of mesenchymal stem cells from osteoarthritis patients to the protein encoded by the susceptibility gene GDF5

Osteoarthritis (OA) is a common joint disease characterised by the focal loss of the protective cartilage layer at the ends of the bones. It is painful, disabling, multifactorial and polygenic. The growth differentiation factor 5 gene GDF5 was one of the first reported OA susceptibility signals that showed consistent association to OA, with the transcript single nucleotide polymorphism (SNP) rs143383 demonstrating association in Asians and Europeans. The functional effect of the signal is reduced expression of the gene. The GDF5 protein is an extracellular matrix signalling molecule that is active during chondrogenesis and in mature chondrocytes. Due to the functional impact of the susceptibility, we previously assessed the effect of supplementing chondrocytes from OA patients with exogenous GDF5. Their response was highly discordant, precluding the application of GDF5 as a simple means of attenuating the genetic deficit. Since GDF5 is also active during development, we have now assessed the effect of exogenous GDF5 on bone marrow derived mesenchymal stem cells (MSCs) that are undergoing chondrogenesis during cartilage disc formation. MSCs from healthy donors and OA patients were studied and the effect of GDF5 was assessed by measuring the wet mass of the discs, by histological staining, and by monitoring the change in expression of anabolic, catabolic and hypertrophic protein-coding genes. The MSCs expressed the three principal GDF5 receptor genes and responded in a significantly anabolic manner (increase in wet mass, p = 0.0022; Bonferroni corrected p = 0.018) to a variant form of GDF5 that targets the most abundantly expressed receptor, BMPR-IA. GDF5 elicited significant (p < 0.05) changes in the expression of anabolic, catabolic and hypertrophic genes with several consistent effects in healthy donors and in OA patients. Our data implies that, unlike OA chondrocytes, OA MSCs do respond in a predictable, anabolic manner to GDF5, which could therefore provide a route to modulate the genetic deficit mediated by the rs143383 association signal.

Cartilage repair by mesenchymal stem cells: Clinical trial update and perspectives

Osteoarthritis is a degenerative disease of joints with destruction of articular cartilage associated with subchondral bone hypertrophy and inflammation. OA is the leading cause of joint pain resulting in significant worsening of the quality-of-life in the elderly. Numerous efforts have been spent to overcome the inherently poor healing ability of articular cartilage. Mesenchymal stem cells (MSCs) have been in the limelight of cell-based therapies to promote cartilage repair. Despite progressive advancements in MSC manipulation and the introduction of various bioactive scaffolds and growth factors in preclinical studies, current clinical trials are still at early stages with preliminary aims to evaluate safety, feasibility and efficacy. This review summarises recently reported MSC-based clinical trials and discusses new research directions with particular focus on the potential application of MSC-derived extracellular vehicles, miRNAs and advanced gene editing techniques which may shed light on the development of novel treatment strategies. The translational potential of this article: This review summarises recent MSC-related clinical research that focuses on cartilage repair. We also propose a novel possible translational direction for hyaline cartilage formation and a new paradigm making use of extra-cellular signalling and epigenetic regulation in the application of MSCs for cartilage repair.

Combination of Collagen-Based Scaffold and Bioactive Factors Induces Adipose-Derived Mesenchymal Stem Cells Chondrogenic Differentiation In vitro

Recently, multipotent mesenchymal stem cells (MSCs) have attracted much attention in the field of regenerative medicine due to their ability to give rise to different cell types, including chondrocytes. Damaged articular cartilage repair is one of the most challenging issues for regenerative medicine, due to the intrinsic limited capability of cartilage to heal because of its avascular nature. While surgical approaches like chondral autografts and allografts provide symptoms and function improvement only for a short period, MSC based stimulation therapies, like microfracture surgery or autologous matrix-induced chondrogenesis demonstrate to be more effective. The use of adult chondrocytes, which are the main cellular constituent of cartilage, in medical practice, is indeed limited due to their instability in monolayer culture and difficulty to collect donor tissue (articular and nasal cartilage). The most recent cartilage engineering approaches combine cells, biomaterial scaffold and bioactive factors to promote functional tissue replacements. Many recent evidences demonstrate that scaffolds providing specific microenvironmental conditions can promote MSCs differentiation toward a functional phenotype. In the present work, the chondrogenic potential of a new Collagen I based 3D scaffold has been assessed in vitro, in combination with human adipose-derived MSCs which possess a higher chondrogenic potential compared to MSCs isolated from other tissues. Our data indicate that the scaffold was able to promote the early stages of chondrogenic commitment and that supplementation of specific soluble factors was able to induce the complete differentiation of MSCs in chondrocytes as demonstrated by the appearance of cartilage distinctive markers (Sox 9, Aggrecan, Matrilin-1, and Collagen II), as well as by the cartilage-specific Alcian Blue staining and by the acquisition of typical cellular morphology. Such evidences suggest that the investigated scaffold formulation could be suitable for the production of medical devices that can be beneficial in the field of articular cartilage engineering, thus improving the efficacy and durability of the current therapeutic options.

Advances and Prospects in Stem Cells for Cartilage Regeneration

The histological features of cartilage call attention to the fact that cartilage has a little capacity to repair itself owing to the lack of a blood supply, nerves, or lymphangion. Stem cells have emerged as a promising option in the field of cartilage tissue engineering and regenerative medicine and could lead to cartilage repair. Much research has examined cartilage regeneration utilizing stem cells. However, both the potential and the limitations of this procedure remain controversial. This review presents a summary of emerging trends with regard to using stem cells in cartilage tissue engineering and regenerative medicine. In particular, it focuses on the characterization of cartilage stem cells, the chondrogenic differentiation of stem cells, and the various strategies and approaches involving stem cells that have been used in cartilage repair and clinical studies. Based on the research into chondrocyte and stem cell technologies, this review discusses the damage and repair of cartilage and the clinical application of stem cells, with a view to increasing our systematic understanding of the application of stem cells in cartilage regeneration; additionally, several advanced strategies for cartilage repair are discussed.

Cell therapy for cartilage defects of the hip

BACKGROUND

Chondral injuries are commonly related to poor clinical outcome, but recent data showed some improvements in function and pain after hip arthroscopy. Cell-based therapies represent an appealing alternative strategy for cartilage regeneration, and interesting results have been recently reported after intra-articular injections of mesenchymal stem cells (MSCs). The results of hip arthroscopy for femoroacetabular impingement (FAI) and intra-articular injections of autologous expanded bone marrow - MSCs (BM-MSCs) are reported in this retrospective study.

MATERIALS AND METHODS

Twenty patients (29 hips) received hip arthroscopy for FAI and focal cartilage injuries or mild to moderate osteoarthrosis (OA). Three intra-articular injections of 20×10⁶ BM-MSCs were injected from 4 to 6 weeks postoperative. The modified Harris Hip score (mHHS), the WOMAC score, the VAIL score and VAS score were administered to all patients.

RESULTS

The mean age of the patients was 51.8 years, and the mean follow-up was 24 months. The median preoperative mHHS, WOMAC and VAIL scores were 64.3, 73 and 56.5 respectively, and they increased to 91, 97 and 83 at final follow up (p<0.05). The VAS score also improved from a median of 6 to 2. Four patients received a THA (13% of the hips) at the median of 9 months post intervention (range 6-36 months). Six patients referred pain after the injection of MSCs, which improved with oral pain killers. No major complications were reported.

CONCLUSION

BM-MSCc injections in combination with hip arthroscopy may improve the quality of life and functional score in patient with FAI and cartilage injuries which are still not candidate to a THA.

LEVEL OF EVIDENCE

IV case series.

Joint sparing treatments in early ankle osteoarthritis: current procedures and future perspectives

Ankle osteoarthritis (AOA) is a severe pathology, mostly affecting a post-traumatic young population. Arthroscopic debridement, arthrodiastasis, osteotomy are the current joint sparing procedures, but, in the available studies, controversial results were achieved, with better outcomes in case of limited degeneration. Only osteotomy in case of malalignment is universally accepted as a joint sparing procedure in case of partial AOA. Recently, the biological mechanism of osteoarthritis has been intensively studied: it is a whole joint pathology, affecting cartilage, bone and synovial membrane. In particular, the first stage is characterized by a reversible catabolic activity with a state of chondropenia. Thus, biological procedures for early AOA were proposed in order to delay or to avoid end stage procedures. Mesenchymal stem cells (MSCs) may be a good solution to prevent or reverse degeneration, due to their immunomodulatory features (able to control the catabolic joint environment) and their regenerative osteochondral capabilities (able to treat the chondral defects). In fact, MSCs may regulate the cytokine cascade and the metalloproteinases release, restoring the osteochondral tissue as well. After interesting reports of mesenchymal stem cells seeded on scaffold and applied to cartilage defects in non-degenerated joints, bone marrow derived cells transplantation appears to be a promising technique in order to control the degenerative pathway and restore the osteochondral defects.

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.

Microsphere-based scaffolds encapsulating chondroitin sulfate or decellularized cartilage

Extracellular matrix materials such as decellularized cartilage (DCC) and chondroitin sulfate (CS) may be attractive chondrogenic materials for cartilage regeneration. The goal of the current study was to investigate the effects of encapsulation of DCC and CS in homogeneous microsphere-based scaffolds, and to test the hypothesis that encapsulation of these extracellular matrix materials would induce chondrogenesis of rat bone marrow stromal cells. Four different types of homogeneous scaffolds were fabricated from microspheres of poly(D,L-lactic-co-glycolic acid): Blank (poly(D,L-lactic-co-glycolic acid) only; negative control), transforming growth factor-β3 encapsulated (positive control), DCC encapsulated, and CS encapsulated. These scaffolds were then seeded with rat bone marrow stromal cells and cultured for 6 weeks. The DCC and CS encapsulation altered the morphological features of the microspheres, resulting in higher porosities in these groups. Moreover, the mechanical properties of the scaffolds were impacted due to differences in the degree of sintering, with the CS group exhibiting the highest compressive modulus. Biochemical evidence suggested a mitogenic effect of DCC and CS encapsulation on rat bone marrow stromal cells with the matrix synthesis boosted primarily by the inherently present extracellular matrix components. An important finding was that the cell seeded CS and DCC groups at week 6 had up to an order of magnitude higher glycosaminoglycan contents than their acellular counterparts. Gene expression results indicated a suppressive effect of DCC and CS encapsulation on rat bone marrow stromal cell chondrogenesis with differences in gene expression patterns existing between the DCC and CS groups. Overall, DCC and CS were easily included in microsphere-based scaffolds; however, there is a requirement to further refine their concentrations to achieve the differentiation profiles we seek in vitro.

Disc-type hyaline cartilage reconstruction using 3D-cell sheet culture of human bone marrow stromal cells and human costal chondrocytes and maintenance of its shape and phenotype after transplantation

In this study, we developed the disc-type bio-cartilage reconstruction strategies for transplantable hyaline cartilage for reconstructive surgery using 3D-cell sheet culture of human bone marrow stromal cells and human costal chondrocytes. We compared chondrogenesis efficiency between different chondrogenic-induction methods such as micromass culture, pellet culture, and 3D-cell sheet culture. Among them, the 3D-cell sheet culture resulted in the best chondrogenesis with the disc-type bio-cartilage (>12 mm diameter in size) in vitro, but sometimes spontaneous curling and contraction of 3D-cell sheet culture resulted in the formation of bead-type cartilage, which was prevented by type I collagen coating or by culturing on amniotic membrane. Previously, it was reported that tissue-engineered cartilage reconstructed in vitro does not maintain its cartilage phenotype after transplantation but tends to transform to other tissue type such as bone or connective tissue. However, the disc-type bio-cartilage of 3D-cell sheet culture maintained its hyaline cartilage phenotype even after exposure to the osteogenic-induction condition in vitro for 3 weeks or after the transplantation for 4 weeks in mouse subcutaneous. Collectively, the disc-type bio-cartilage with 12 mm diameter can be reproducibly reconstructed by the 3D-cell sheet culture, whose hyaline cartilage phenotype and shape can be maintained under the osteogenic-induction condition as well as after the transplantation. This disc-type bio-cartilage can be proposed for the application to reconstructive surgery and repair of disc-type cartilage such as mandibular cartilage and digits.

Electronic Supplementary Material

Supplementary material is available for this article at 10.1007/s13770-016-9065-6 and is accessible for authorized users.

3D bioprinting of BM-MSCs-loaded ECM biomimetic hydrogels for in vitro neocartilage formation

In this work we demonstrate how to print 3D biomimetic hydrogel scaffolds for cartilage tissue engineering with high cell density (>10(7) cells ml(-1)), high cell viability (85 ÷ 90%) and high printing resolution (≈100 μm) through a two coaxial-needles system. The scaffolds were composed of modified biopolymers present in the extracellular matrix (ECM) of cartilage, namely gelatin methacrylamide (GelMA), chondroitin sulfate amino ethyl methacrylate (CS-AEMA) and hyaluronic acid methacrylate (HAMA). The polymers were used to prepare three photocurable bioinks with increasing degree of biomimicry: (i) GelMA, (ii) GelMA + CS-AEMA and (iii) GelMA + CS-AEMA + HAMA. Alginate was added to the bioinks as templating agent to form stable fibers during 3D printing. In all cases, bioink solutions were loaded with bone marrow-derived human mesenchymal stem cells (BM-MSCs). After printing, the samples were cultured in expansion (negative control) and chondrogenic media to evaluate the possible differentiating effect exerted by the biomimetic matrix or the synergistic effect of the matrix and chondrogenic supplements. After 7, 14, and 21 days, gene expression of the chondrogenic markers (COL2A1 and aggrecan), marker of osteogenesis (COL1A1) and marker of hypertrophy (COL10A1) were evaluated qualitatively by means of fluorescence immunocytochemistry and quantitatively by means of RT-qPCR. The observed enhanced viability and chondrogenic differentiation of BM-MSCs, as well as high robustness and accuracy of the employed deposition method, make the presented approach a valid candidate for advanced engineering of cartilage tissue.

Articular cartilage repair: Current needs, methods and research directions

Articular cartilage is a highly specialized tissue whose remarkable properties of deformability, resistance to mechanical loading, and low-friction gliding are essential to joint function. Due to its role as a cushion in bone articulation, articular cartilage is subject to many types of damaging insults, including decades of wear and tear, and acute joint injuries. However, this built-for-life tissue has a very poor intrinsic ability in adulthood to durably heal defects created by damaging insults. Consequently, articular cartilage progressively deteriorates and is eventually eroded, exposing the subchondral bone to the joint space, triggering inflammation and osteophyte development, and generating severe pain and joint incapacitation. The disease is called osteoarthritis (OA) and is today the leading cause of pain and disability in the human population. Researchers and clinicians have worked for decades to develop strategies to treat OA and restore joint function, but they are still far from being able to offer patients effective preventive or restorative treatments. Novel ideas, knowledge and technologies that nurture hope for major new breakthroughs are therefore sought. In this review, we first outline the composition, structure, and functional properties of normal human adult articular cartilage, as a reference for tissue conservation and regenerative strategies. We then describe current options that have been used clinically and in pre-clinical trials to treat osteoarthritic patients, and we discuss the benefits and inadequacies of these treatment options. Next, we review research efforts that are currently ongoing to try and achieve durable repair of functional cartilage tissue. Methods include engineering of tissue implants and we discuss the needs and options for tissue scaffolds, cell sources, and growth and differentiation factors to generate de novo or repair bona fide articular cartilage.

Biological Therapies for Cartilage Lesions in the Hip: A New Horizon

Treatment of hip cartilage disease is challenging, and there is no clear algorithm to address this entity. Biomarkers are arising as promising diagnostic tools because they could play a role in the early assessment of the prearthritic joint and as a prognostic factor before and after treatment. The potential effect of biomarkers may be used to categorize individuals at risk of evolving to severe osteoarthritis, to develop new measures for clinical progression of the disease, and to develop new treatment options for the prevention of osteoarthritis progression. A trend toward a less invasive biological treatment will usher in a new treatment era. With the growth of surgical skills in hip arthroscopy, cartilage restoration techniques are evolving in a fast and exponential manner. Biological and surgical treatments have been proposed to treat these pathologies. Biological treatments include platelet-rich plasma, stem cells or bone marrow aspirate concentration, hyaluronic acid, losartan, and fish oil. Surgical treatments include microfracture alone or augmented, direct repair, autologous chondrocyte implantation, matrix-induced chondrocyte implantation, autologous matrix-induced chondrogenesis, mosaicplasty, osteochondral allograft transplantation, and stem cells implanted in matrix (stem cells in membranes/expanded stem cells). This article reviews new evidence available on treatment options for chondral lesions and early osteoarthritis of the hip. [Orthopedics. 2016; 39(4):e715-e723.].

Autologous chondrocyte implantation (ACI) for cartilage defects of the knee: A guideline by the working group "Clinical Tissue Regeneration" of the German Society of Orthopaedics and Trauma (DGOU)

BACKGROUND

Autologous chondrocyte implantation (ACI) is an established and well-accepted procedure for the treatment of localised full-thickness cartilage defects of the knee.

METHODS

The present review of the working group "Clinical Tissue Regeneration" of the German Society of Orthopaedics and Trauma (DGOU) describes the biology and function of healthy articular cartilage, the present state of knowledge concerning therapeutic consequences of primary cartilage lesions and the suitable indication for ACI.

RESULTS

Based on best available scientific evidence, an indication for ACI is given for symptomatic cartilage defects starting from defect sizes of more than three to four square centimetres; in the case of young and active sports patients at 2.5cm(2), while advanced degenerative joint disease needs to be considered as the most important contraindication.

CONCLUSION

The present review gives a concise overview on important scientific background and the results of clinical studies and discusses the advantages and disadvantages of ACI.

LEVEL OF EVIDENCE

Non-systematic Review.

Cell-based tissue engineering strategies used in the clinical repair of articular cartilage

One of the most important issues facing cartilage tissue engineering is the inability to move technologies into the clinic. Despite the multitude of current research in the field, it is known that 90% of new drugs that advance past animal studies fail clinical trials. The objective of this review is to provide readers with an understanding of the scientific details of tissue engineered cartilage products that have demonstrated a certain level of efficacy in humans, so that newer technologies may be developed upon this foundation. Compared to existing treatments, such as microfracture or autologous chondrocyte implantation, a tissue engineered product can potentially provide more consistent clinical results in forming hyaline repair tissue and in filling the entirety of the defect. The various tissue engineering strategies (e.g., cell expansion, scaffold material, media formulations, biomimetic stimuli, etc.) used in forming these products, as collected from published literature, company websites, and relevant patents, are critically discussed. The authors note that many details about these products remain proprietary, not all information is made public, and that advancements to the products are continuously made. Nevertheless, by understanding the design and production processes of these emerging technologies, one can gain tremendous insight into how to best use them and also how to design the next generation of tissue engineered cartilage products.

Cell-based tissue engineering strategies used in the clinical repair of articular cartilage

One of the most important issues facing cartilage tissue engineering is the inability to move technologies into the clinic. Despite the multitude of current research in the field, it is known that 90% of new drugs that advance past animal studies fail clinical trials. The objective of this review is to provide readers with an understanding of the scientific details of tissue engineered cartilage products that have demonstrated a certain level of efficacy in humans, so that newer technologies may be developed upon this foundation. Compared to existing treatments, such as microfracture or autologous chondrocyte implantation, a tissue engineered product can potentially provide more consistent clinical results in forming hyaline repair tissue and in filling the entirety of the defect. The various tissue engineering strategies (e.g., cell expansion, scaffold material, media formulations, biomimetic stimuli, etc.) used in forming these products, as collected from published literature, company websites, and relevant patents, are critically discussed. The authors note that many details about these products remain proprietary, not all information is made public, and that advancements to the products are continuously made. Nevertheless, by understanding the design and production processes of these emerging technologies, one can gain tremendous insight into how to best use them and also how to design the next generation of tissue engineered cartilage products.

Expression of CD90 decreases with progression of synovial chondromatosis in the temporomandibular joint

OBJECTIVES

The aim of the present study was to investigate the factors that contribute to the progression of synovial chondromatosis in the temporomandibular joint (TMJ).

METHODS

The authors investigated the expression of CD105 and CD90 in specimens from 17 patients with synovial chondromatosis in the TMJ, using immunohistochemical staining, and expression of CD105 and CD90 in cartilaginous nodules was scored semiquantitatively.

RESULTS

The expression of CD105 and CD90 was found in almost all the cases. In particular, the expression of CD90 in cartilaginous nodules significantly decreased with the progression of synovial chondromatosis.

DISCUSSION

The factors that determine progression of synovial chondromatosis are not fully understood. The results of this study suggest that CD90 may play an important role in the progression of synovial chondromatosis in the TMJ.

Nondestructive Techniques to Evaluate the Characteristics and Development of Engineered Cartilage

In this review, methods for evaluating the properties of tissue engineered (TE) cartilage are described. Many of these have been developed for evaluating properties of native and osteoarthritic articular cartilage. However, with the increasing interest in engineering cartilage, specialized methods are needed for nondestructive evaluation of tissue while it is developing and after it is implanted. Such methods are needed, in part, due to the large inter- and intra-donor variability in the performance of the cellular component of the tissue, which remains a barrier to delivering reliable TE cartilage for implantation. Using conventional destructive tests, such variability makes it near-impossible to predict the timing and outcome of the tissue engineering process at the level of a specific piece of engineered tissue and also makes it difficult to assess the impact of changing tissue engineering regimens. While it is clear that the true test of engineered cartilage is its performance after it is implanted, correlation of pre and post implantation properties determined non-destructively in vitro and/or in vivo with performance should lead to predictive methods to improve quality-control and to minimize the chances of implanting inferior tissue.

Adipose-Derived Mesenchymal Stem Cells for the Treatment of Articular Cartilage: A Systematic Review on Preclinical and Clinical Evidence

Among the current therapeutic approaches for the regeneration of damaged articular cartilage, none has yet proven to offer results comparable to those of native hyaline cartilage. Recently, it has been claimed that the use of mesenchymal stem cells (MSCs) provides greater regenerative potential than differentiated cells, such as chondrocytes. Among the different kinds of MSCs available, adipose-derived mesenchymal stem cells (ADSCs) are emerging due to their abundancy and easiness to harvest. However, their mechanism of action and potential for cartilage regeneration are still under investigation, and many other aspects still need to be clarified. The aim of this systematic review is to give an overview of in vivo studies dealing with ADSCs, by summarizing the main evidence for the treatment of cartilage disease of the knee.

Effect of mesenchymal stromal cells for articular cartilage degeneration treatment: a meta-analysis

BACKGROUND AIMS

Articular cartilage is an avascular tissue that has limited capacity for self-repair. Mesenchymal stromal cells have been considered as potential candidates for cartilage regeneration. However, clinical results of cartilage formation with the use of these cells need evaluation. We aimed to assess the effect of mesenchymal stromal cell treatment on articular cartilage defects.

METHODS

We searched PubMed, Embase and the Cochrane Central Register of Controlled Trials with key words including "cartilage," "clinical trial," "mesenchymal," "stromal" and "stem cell" up to December 3, 2014. We selected the controlled trial that used treatment with mesenchymal stromal cells on cartilage injury compared with other treatment. We assessed the results of the meta-analysis by means of the error matrix approach. The outcome measures were ranked as comprehensive evaluation index, highest relevance; unilateral evaluation index, medial relevance; and single evaluation index, lowest relevance.

RESULTS

Eleven trials assessing 558 patients were included in the meta-analysis. Stem cell treatment significantly improved the American Orthopedic Foot and Ankle Society Scale (Standard Mean Difference, SMD, 0.91; 95% confidence interval [CI], 0.52 to 1.29). The Osteo-Arthritis Outcome Score was also significantly improved in stem cell treatment (SMD, 2.81; 95% CI, 2.02 to 3.60). Other comprehensive evaluation indexes, such as the American Knee Society Knee Score System (SMD -0.12, 95% CI, -1.02 to 0.78), the Hospital for Special Surgery Knee Rating Scale (SMD, 0.24, 95% CI, -0.56 to 1.05) and the International Knee Documentation Committee (SMD, -0.21; 95% CI, -0.77 to 0.34), appeared to have no significant differences by use of stem cell and other treatments. Overall, there was no obvious advantage regarding the application of stem cells to treat cartilage injury, compared with other treatments.

CONCLUSIONS

In conclusion, assessment of the comprehensive evaluation index indicated that there were no significant differences after stem cell treatment. However, assessment of clinical symptoms and cartilage morphology showed significant improvement after stem cell treatment.

From Skeletal Development to Tissue Engineering: Lessons from the Micromass Assay

Damage and degeneration of the skeletal elements due to disease, trauma, and aging lead to a significant health and economical burden. To reduce this burden, skeletal tissue engineering strategies aim to regenerate functional bone and cartilage in the adult body. However, challenges still exist. Such challenges involve the identification of the external cues that determine differentiation, how to control chondrocyte hypertrophy, and how to achieve specific tissue patterns and boundaries. To address these issues, it could be insightful to look at skeletal development, a robust morphogenetic process that takes place during embryonic development and is commonly modeled in vitro by the micromass assay. In this review, we investigate what the tissue engineering field can learn from this assay. By comparing embryonic skeletal precursor cells from different anatomic locations and developmental stages in micromass, the external cues that guide lineage commitment can be identified. The signaling pathways regulating chondrocyte hypertrophy, and the cues required for tissue patterning, can be elucidated by combining the micromass assay with genetic, molecular, and engineering tools. The lessons from the micromass assay are limited by two major differences between developmental and regenerative skeletogenesis: cell type and scale. We highlight an important difference between embryonic and adult skeletal progenitor cells, in that adult progenitors are not able to form mesenchymal condensations spontaneously. Also, the mechanisms of tissue patterning need to be adjusted to the larger tissue engineering constructs. In conclusion, mechanistic insights of skeletal tissue generation gained from the micromass model could lead to improved tissue engineering strategies and constructs.

Cell Therapy and Tissue Engineering Approaches for Cartilage Repair and/or Regeneration

Articular cartilage injuries caused by traumatic, mechanical and/or by progressive degeneration result in pain, swelling, subsequent loss of joint function and finally osteoarthritis. Due to the peculiar structure of the tissue (no blood supply), chondrocytes, the unique cellular phenotype in cartilage, receive their nutrition through diffusion from the synovial fluid and this limits their intrinsic capacity for healing. The first cellular avenue explored for cartilage repair involved the in situ transplantation of isolated chondrocytes. Latterly, an improved alternative for the above reparative strategy involved the infusion of mesenchymal stem cells (MSC), which in addition to a self-renewal capacity exhibit a differentiation potential to chondrocytes, as well as a capability to produce a vast array of growth factors, cytokines and extracellular matrix compounds involved in cartilage development. In addition to the above and foremost reparative options up till now in use, other therapeutic options have been developed, comprising the design of biomaterial substrates (scaffolds) capable of sustaining MSC attachment, proliferation and differentiation. The implantation of these engineered platforms, closely to the site of cartilage damage, may well facilitate the initiation of an ‘in situ’ cartilage reparation process. In this mini-review, we examined the timely and conceptual development of several cell-based methods, designed to repair/regenerate a damaged cartilage. In addition to the above described cartilage reparative options, other therapeutic alternatives still in progress are portrayed.

The microwell-mesh: A novel device and protocol for the high throughput manufacturing of cartilage microtissues

Microwell platforms are frequently described for the efficient and uniform manufacture of 3-dimensional (3D) multicellular microtissues. Multiple partial or complete medium exchanges can displace microtissues from discrete microwells, and this can result in either the loss of microtissues from culture, or microtissue amalgamation when displaced microtissues fall into common microwells. Herein we describe the first microwell platform that incorporates a mesh to retain microtissues within discrete microwells; the microwell-mesh. We show that bonding a nylon mesh with an appropriate pore size over the microwell openings allows single cells to pass through the mesh into the microwells during the seeding process, but subsequently retains assembled microtissues within discrete microwells. To demonstrate the utility of this platform, we used the microwell-mesh to manufacture hundreds of cartilage microtissues, each formed from 5 × 10(3) bone marrow-derived mesenchymal stem/stromal cells (MSC). The microwell-mesh enabled reliable microtissue retention over 21-day cultures that included multiple full medium exchanges. Cartilage-like matrix formation was more rapid and homogeneous in microtissues than in conventional large diameter control cartilage pellets formed from 2 × 10(5) MSC each. The microwell-mesh platform offers an elegant mechanism to retain microtissues in microwells, and we believe that this improvement will make this platform useful in 3D culture protocols that require multiple medium exchanges, such as those that mimic specific developmental processes or complex sequential drug exposures.

Long-term expandable SOX9+ chondrogenic ectomesenchymal cells from human pluripotent stem cells

Here we report the successful generation and long-term expansion of SOX9-expressing CD271⁺PDGFRα⁺CD73⁺ chondrogenic ectomesenchymal cells from the PAX3/SOX10/FOXD3-expressing MIXL1⁻CD271^hiPDGFRα^loCD73⁻ neural crest-like progeny of human pluripotent stem cells in a chemically defined medium supplemented with Nodal/Activin/transforming growth factorβ (TGFβ) inhibitor and fibroblast growth factor (FGF). When “primed” with TGFβ, such cells efficiently formed translucent cartilage particles, which were completely mineralized in 12 weeks in immunocompromized mice. The ectomesenchymal cells were expandable without loss of chondrogenic potential for at least 16 passages. They maintained normal karyotype for at least 10 passages and expressed genes representing embryonic progenitors (SOX4/12, LIN28A/B), cranial mesenchyme (ALX1/3/4), and chondroprogenitors (SOX9, COL2A1) of neural crest origin (SOX8/9, NGFR, NES). Ectomesenchyme is a source of many craniofacial bone and cartilage structures. The method we describe for obtaining a large quantity of human ectomesenchymal cells will help to model craniofacial disorders in vitro and potentially provide cells for the repair of craniofacial damage.

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Generation of SOX9⁺ chondrogenic ectomesenchymal cells from hPSCs

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Long-term expandability of the cells without loss of in vitro chondrogenicity

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Need for TGFβ priming for cartilage particle formation

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In vivo ossification capacity of cartilage developed in vitro

Bone marrow mesenchymal stem cells suppress metastatic tumor development in mouse by modulating immune system

Introduction

Bone marrow mesenchymal stem cells (BMSCs) have been studied extensively because of their potential use in clinical therapy, regenerative medicine, and tissue engineering. However, their application in tumor therapy remains yet in preclinical stage because of the distinct results from different researches and vagueness of their functional mechanism. In this study, the influence of BMSCs on tumor growth was observed and the potential mechanism was investigated.

Method

Two animal models, H22 ascitogenous hepatoma in BALb/c mouse and B16-F10 pulmonary metastatic melanoma in C57 mouse, were adopted in experience in vivo and treated with BMSCs by intravenous injection. The percentage of Gr-1⁺CD11b⁺ myeloid-derived suppressor cells (MDSCs) and IFN-γ⁺ T cells were observed in peripheral blood (PB) and bone marrow (BM) by Flow Cytometry. BMSCs were co-cultured in vitro with tumor cells and MDSCs in a tumor conditioned medium separately in order to illustrate the mechanism.

Results

Our results demonstrated that BMSCs treatment caused a delayed tumor growth and a prolonged survival in both tumor models, the homing fraction of BMSCs in BM was 2% - 5% in 24–72 hours after transfusion and the percentage of Gr-1⁺CD11b⁺ MDSCs was downregulated in peripheral blood and BM. Meanwhile, IFN-γ⁺ T lymphocytes in PB increased. In vitro co-culture showed that BMSCs inhibited the induction and proliferation of MDSCs in tumor conditioned medium, whereas they didn’t affect the proliferation of B16-F10 and H22 cells by in vitro co-culture. Both in vivo and in vitro results showed that BMSCs have a systemic suppressive effect on MDSCs.

Conclusion

Our data suggest that BMSCs has suppressive effect on tumor and is feasible to be applied in cancer treatment. BMSCs inhibiting MDSCs induction and proliferation is likely one of the mechanism.

Cell-based articular cartilage repair: the link between development and regeneration

Clinical efforts to repair damaged articular cartilage (AC) currently face major obstacles due to limited intrinsic repair capacity of the tissue and unsuccessful biological interventions. This highlights a need for better therapeutic strategies. This review summarizes the recent advances in the field of cell-based AC repair. In both animals and humans, AC defects that penetrate into the subchondral bone marrow are mainly filled with fibrocartilaginous tissue through the differentiation of bone marrow mesenchymal stem cells (MSCs), followed by degeneration of repaired cartilage and osteoarthritis (OA). Cell therapy and tissue engineering techniques using culture-expanded chondrocytes, bone marrow MSCs, or pluripotent stem cells with chondroinductive growth factors may generate cartilaginous tissue in AC defects but do not form hyaline cartilage-based articular surface because repair cells often lose chondrogenic activity or result in chondrocyte hypertrophy. The new evidence that AC and synovium develop from the same pool of precursors with similar gene profiles and that synovium-derived chondrocytes have stable chondrogenic activity has promoted use of synovium as a new cell source for AC repair. The recent finding that NFAT1 and NFAT2 transcription factors (TFs) inhibit chondrocyte hypertrophy and maintain metabolic balance in AC is a significant advance in the field of AC repair. The use of synovial MSCs and discovery of upstream transcriptional regulators that help maintain the AC phenotype have opened new avenues to improve the outcome of AC regeneration.

Cartilage-derived extracellular matrix extract promotes chondrocytic phenotype in three-dimensional tissue culture

Cell transplantation is a promising regenerative therapy for cartilage degeneration. However, obtaining sufficient numbers of cells for this purpose is a challenge, due a lack of autologous donor tissue and the difficulty of culturing chondrocytes in vitro. Tissue engineering strategies that induce or maintain chondrocytic phenotype may solve these problems by (1) broadening the range of available donor tissue, and (2) facilitating the expansion of these cells while controlling phenotypic drift. In this study, bone marrow-derived mesenchymal stem cells (MSCs) and cartilage-derived cells (CDCs) were cultured on composite hydrogels containing agarose and homogenized cartilage extracellular matrix (ECM). MSCs cultured on agarose-ECM scaffolds did not show significant signs of chondrogenic differentiation in the absence of additional cues. However, CDCs cultured on agarose-ECM scaffolds proliferated more rapidly than their ECM-free counterparts and MSCs, while retaining chondrocytic morphology. These results were corroborated via expression of cartilage marker genes: in autologous constructs, SOX 9 expression was upregulated by 12.6 ± 5.3-fold, and COL II was upregulated by 2.0 ± 0.3-fold. Agarose-ECM composite hydrogels are therefore useful for expanding partially differentiated CDCs for applications in regenerative medicine.

Adult mesenchymal stem cells and women's health

Adult mesenchymal stem cells (MSCs) were previously described as multipotent cells that could differentiate into bone, cartilage, muscle, and other mesenchymal tissues. New information suggests that MSCs can be found in every tissue of the body because they function as perivascular cells--pericytes--found outside all blood vessels. When these vessels break or are inflamed, pericytes are detached and form MSCs, which are activated by their local microenvironment of injury. Such MSCs function to secrete powerful immune-modulatory and regenerative agents; more than 450 clinical trials are now ongoing, covering a huge spectrum of clinical conditions. How such activated MSCs affect menstrual cycle, menopause, or osteotrophic cancers has only recently been studied. This article outlines these issues and challenges the scientific and medical community to use this newfound knowledge to uncover new clinical logics and medial solutions for women.

Cartilage Tissue Engineering: What Have We Learned in Practice?

Many technologies that underpin tissue engineering as a research field were developed with the aim of producing functional human cartilage in vitro. Much of our practical experience with three-dimensional cultures, tissue bioreactors, scaffold materials, stem cells, and differentiation protocols was gained using cartilage as a model system. Despite these advances, however, generation of engineered cartilage matrix with the composition, structure, and mechanical properties of mature articular cartilage has not yet been achieved. Currently, the major obstacles to synthesis of clinically useful cartilage constructs are our inability to control differentiation to the extent needed, and the failure of engineered and host tissues to integrate after construct implantation. The aim of this chapter is to distil from the large available body of literature the seminal approaches and experimental techniques developed for cartilage tissue engineering and to identify those specific areas requiring further research effort.

Chondrogenic potential of human articular chondrocytes and skeletal stem cells: a comparative study

Regenerative medicine strategies have increasingly focused on skeletal stem cells (SSCs), in response to concerns such as donor site morbidity, dedifferentiation and limited lifespan associated with the use of articular chondrocytes for cartilage repair. The suitability of SSCs for cartilage regeneration, however, remains to be fully determined. This study has examined the chondrogenic potential of human STRO-1-immunoselected SSCs (STRO-1⁺ SSCs), in comparison to human articular chondrocytes (HACs), by utilising two bioengineering strategies, namely “scaffold-free” three-dimensional (3-D) pellet culture and culture using commercially available, highly porous, 3-D scaffolds with interconnected pore networks. STRO-1⁺ SSCs were isolated by magnetic-activated cell sorting from bone marrow samples of haematologically normal osteoarthritic individuals following routine hip replacement procedures. Chondrocytes were isolated by sequential enzymatic digestion of deep zone articular cartilage pieces dissected from femoral heads of the same individuals. After expansion in monolayer cultures, the harvested cell populations were centrifuged to form high-density 3-D pellets and also seeded in the 3-D scaffold membranes, followed by culture in serum-free chondrogenic media under static conditions for 21 and 28 days, respectively. Chondrogenic differentiation was determined by gene expression, histological and immunohistochemical analyses. Robust cartilage formation and expression of hyaline cartilage-specific markers were observed in both day-21 pellets and day-28 explants generated using HACs. In comparison, STRO-1⁺ SSCs demonstrated significantly lower chondrogenic differentiation potential and a tendency for hypertrophic differentiation in day-21 pellets. Culture of STRO-1⁺ SSCs in the 3-D scaffolds improved the expression of hyaline cartilage-specific markers in day-28 explants, however, was unable to prevent hypertrophic differentiation of the SSC population. The advantages of application of SSCs in tissue engineering are widely recognised; the results of this study, however, highlight the need for further development of cell culture protocols that may otherwise limit the application of this stem cell population in cartilage bioengineering strategies.