Clonal populations of chondrocytes with progenitor properties identified within human articular cartilage

Mechanism of the Mitogen-Activated Protein Kinases/Mammalian Target of Rapamycin Pathway in the Process of Cartilage Endplate Stem Cell Degeneration Induced by Tension Load

STUDY DESIGN

Basic Research.

OBJECTIVE

Intervertebral disc degeneration (IVDD) is caused by the cartilage endplate (CEP). Cartilage endplate stem cell (CESC) is involved in the recovery of CEP degeneration. Tension load (TL) contributes a lot to the initiation and progression of IVDD. This study aims to investigate the regulatory mechanism of the Mitogen-activated protein kinases/Mammalian target of rapamycin (MAPK/mTOR) pathway during TL-induced CESC degeneration.

METHODS

CESCs were isolated from New Zealand big-eared white female rabbits (6 months old). FX-4000T cell stress loading system was applied to establish a TL-induced degeneration model of CESCs. Western blotting was used to detect the level of mTOR pathway-related proteins and autophagy markers LC3-Ⅱ, Beclin-1, and p62 in degenerative CESCs. The expression of MAPK pathway-related proteins JNK and extracellular signal-regulated kinases (ERK) in degenerated CESCs was inhibited by cell transfection to explore whether JNK and ERK play a regulatory role in TL-induced autophagy in CESCs.

RESULTS

In the CESC degeneration model, the mTOR pathway was activated. After inhibition of mTOR, the autophagy level of CESCs was increased, and the degeneration of CESCs was alleviated. The MAPK pathway was also activated in the CESC degeneration model. Inhibition of JNK expression may alleviate TL-induced CEP degeneration by inhibiting Raptor phosphorylation and activating autophagy. Inhibition of ERK expression may alleviate TL-induced CEP degeneration by inhibiting mTOR phosphorylation and activating autophagy.

CONCLUSION

Inhibition of JNK and ERK in the MAPK signaling family alleviated TL-induced CESC degeneration by inhibiting the phosphorylation of Raptor and mTOR in the mTOR pathway.

The effect of mitochondrial fusion on chondrogenic differentiation of cartilage progenitor/stem cells via Notch2 signal pathway

Background

Osteoarthritis (OA) is a debilitating disease that inflicts intractable pain, a major problem that humanity faces, especially in aging populations. Stem cells have been used in the treatment of many chronic diseases, including OA. Cartilage progenitor/stem cells (CPSCs) are a type of stem cells with the ability to self- renew and differentiate. They hold a promising future for the understanding of the progression of OA and for its treatment. Previous studies have reported the relationship between mitochondrial dynamics and mesenchymal stem cell (MSC) proliferation, differentiation and aging. Mitochondrial dynamic and morphology change during stem cell differentiation.

Methods

This study was performed to access the relationship between mitochondrial dynamics and chondrogenic differentiation of CPSCs. Mitochondrial fusion and fission levels were measured during the chondrogenic differentiation process of CPSCs. After that, we used mitochondrial fusion promoter to induce fusion in CPSCs and then the chondrogenic markers were measured. Transmission electron microscopy (TEM) and confocal microscopy were used to capture the mass and fusion status of mitochondria. Lentiviruses were used to detect the role of mitofusin 2 (Mfn2) in CPSC chondrogenic differentiation. In vivo, Mfn2 was over-expressed in sheets of rat CPSCs, which were then injected intra-articularly into the knees of rats.

Results

Mitochondrial fusion markers were upregulated during the chondrogenic induction process of CPSCs. The mass of mitochondria was higher in differentiated CPSC, and the fusion status was obvious relative to un-differentiated CPSC. Chondrogenesis of CPSCs was upregulated with the induction by mitochondrial fusion promoter. Mfn2 over-expression significantly increased chondrocyte-specific gene expression and reversed OA through NOTCH2 signal pathway.

Conclusions

Our study demonstrated that the mitochondrial fusion promotes chondrogenesis differentiation of CPSCs. Mfn2 accelerates the chondrogenesis differentiation of CPSCs through Notch2. In vivo, Mfn2-OE in sheets of rCPSCs ameliorated OA in the rat model.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-022-02758-7.

The clinical potential of articular cartilage-derived progenitor cells: a systematic review

Over the past two decades, evidence has emerged for the existence of a distinct population of endogenous progenitor cells in adult articular cartilage, predominantly referred to as articular cartilage-derived progenitor cells (ACPCs). This progenitor population can be isolated from articular cartilage of a broad range of species, including human, equine, and bovine cartilage. In vitro, ACPCs possess mesenchymal stromal cell (MSC)-like characteristics, such as colony forming potential, extensive proliferation, and multilineage potential. Contrary to bone marrow-derived MSCs, ACPCs exhibit no signs of hypertrophic differentiation and therefore hold potential for cartilage repair. As no unique cell marker or marker set has been established to specifically identify ACPCs, isolation and characterization protocols vary greatly. This systematic review summarizes the state-of-the-art research on this promising cell type for use in cartilage repair therapies. It provides an overview of the available literature on endogenous progenitor cells in adult articular cartilage and specifically compares identification of these cell populations in healthy and osteoarthritic (OA) cartilage, isolation procedures, in vitro characterization, and advantages over other cell types used for cartilage repair. The methods for the systematic review were prospectively registered in PROSPERO (CRD42020184775).

Innovative Tissue-Engineered Strategies for Osteochondral Defect Repair and Regeneration: Current Progress and Challenges

Clinical treatments for the repair of osteochondral defects (OCD) are merely palliative, not completely curative, and thus enormously unfulfilled challenges. With the in-depth studies of biology, medicine, materials, and engineering technology, the conception of OCD repair and regeneration should be renewed. During the past decades, many innovative tissue-engineered approaches for repairing and regenerating damaged osteochondral units have been widely explored. Various scaffold-free and scaffold-based strategies, such as monophasic, biphasic, and currently fabricated multiphasic and gradient architectures have been proposed and evaluated. Meanwhile, progenitor cells and tissue-specific cells have also been intensively investigated in vivo as well as ex vivo. Concerning bioactive factors and drugs, they have been combined with scaffolds and/or living cells, and even released in a spatiotemporally controlled manner. Although tremendous progress has been achieved, further research and development (R&D) is needed to convert preclinical outcomes into clinical applications. Here, the osteochondral unit structure, its defect classifications, and diagnosis are summarized. Commonly used clinical reparative techniques, tissue-engineered strategies, emerging 3D-bioprinting technologies, and the status of their clinical applications are discussed. Existing challenges to translation are also discussed and potential solutions for future R&D directions are proposed.

Isolation and Characterization of Human Synovial Fluid-Derived Mesenchymal Stromal Cells from Popliteal Cyst

Mesenchymal stem cells (MSCs) are multipotent progenitor cells in adult tissues. The aim of this study is to isolate and identify synovial fluid-derived mesenchymal stromal cells (SF-MSCs) from the popliteal cyst fluid of pediatric patients. SF-MSCs were collected from the popliteal cyst fluid of pediatric patients during cystectomy surgery. After cyst fluid extraction and adherent culturing, in vitro morphology, growth curve, and cell cycle were observed. The expression of stem cell surface markers was analyzed by flow cytometry, and expression of cell marker protein was detected by immunofluorescence. SF-MSCs were cultured in osteogenic, adipogenic, and chondrogenic differentiation medium. The differentiation potential of SF-MSCs was analyzed by alkaline phosphatase (Alizarin Red), Oil Red O, and Alcian blue. Antibody detection of human angiogenesis-related proteins was performed compared with bone marrow mesenchymal stem cells (BM-MSCs). The results show that SF-MSCs from the popliteal cyst fluid of pediatric patients showed a shuttle appearance and logarithmic growth. Flow cytometry analysis revealed that SF-MSCs were negative for hematopoietic lineage markers (CD34, CD45) and positive for MSC markers (CD44, CD73, CD90, and CD105). Interstitial cell marker (vimentin) and myofibroblast-like cell marker alpha-smooth muscle actin (α-SMA) were positive. These cells could differentiate into osteogenic, adipogenic, and chondrogenic lineages, respectively. Several types of human angiogenesis-related proteins were detected in the cell secretory fluid. These results show that we successfully obtained SF-MSCs from the popliteal cyst fluid of pediatric patients, which have the potential to be a valuable source of MSCs.

Meniscus Repair and Regeneration: A Systematic Review from a Basic and Translational Science Perspective

Meniscus injuries are among the most common athletic injuries and result in functional impairment in the knee. Repair is crucial for pain relief and prevention of degenerative joint diseases like osteoarthritis. Current treatments, however, do not produce long-term improvements. Thus, recent research has been investigating new therapeutic options for regenerating injured meniscal tissue. This review comprehensively details the current methodologies being explored in the basic sciences to stimulate better meniscus injury repair. Furthermore, it describes how these preclinical strategies may improve current paradigms of how meniscal injuries are clinically treated through a unique and alternative perspective to traditional clinical methodology.

Reproduction of Characteristics of Extracellular Matrices in Specific Longitudinal Depth Zone Cartilage within Spherical Organoids in Response to Changes in Osmotic Pressure

Articular cartilage is compressed with joint-loading and weight-bearing stresses, followed by a bulging of the tissue during times of off-loading. This loading and off-loading causes changes in water content, and thus alterations in osmotic pressure. Another unique characteristic of articular cartilage is that it has longitudinal depth: surface, middle, and deep zones. Since each zone is composed of unique components of highly negative extracellular matrices, each zone has a different level of osmotic pressure. It was unclear how changes in osmotic pressure affected chondrocyte matrix turnover in specific longitudinal zones. Therefore, we hypothesized that a change in extrinsic osmotic pressure would alter the production of extracellular matrices by zone-specific chondrocytes. We incubated spheroidal cartilage organoids, formed by specific longitudinal depth zone-derived chondrocytes, under different levels of osmotic pressure. We compared the gene expression and the immunohistology of the matrix proteins produced by the zone-specific chondrocytes. We found that high osmotic pressure significantly upregulated the transient expression of aggrecan and collagen type-II by all zone-derived chondrocytes (p < 0.05). At a high osmotic pressure, surface-zone chondrocytes significantly upregulated the expression of collagen type-I (p < 0.05), and middle- and deep-zone chondrocytes significantly upregulated matrix metalloproteinase-13 (p < 0.05). The spheroids, once exposed to high osmotic pressure, accumulated extracellular matrices with empty spaces. Our findings show that chondrocytes have zone-specific turnover of extracellular matrices in response to changes in osmotic pressure.

Use of Limiting Dilution Method for Isolation of Nucleus Pulposus Mesenchymal Stem/Progenitor Cells and Effects of Plating Density on Biological Characteristics and Plasticity

Objectives

To evaluate the effects of the limiting dilution method and plating density in rat nucleus pulposus mesenchymal stem/progenitor cells (NPMSCs).

Materials and Methods

Nucleus pulposus tissues were isolated from 12-week-old male Sprague-Dawley rats and NPMSCs were isolated using limiting dilution method. Cells were then classified into 3 groups according to plating density. Cell morphologies were observed, and colony-forming units, migration abilities, proliferative capacities, cell cycle percentages, multilineage differentiation capacities, stem cell biomarker expression levels, and immunophenotyping were also examined in each group.

Results

Low density group (LD) had higher morphological homogeneity, stronger colony-forming ability, higher cell proliferation capacity, and enhanced cell migration ability relative to the other two groups (p < 0.05). Moreover, LD had more cells entering S phase, with fewer cells arrested in G0/G1 phase (p < 0.05). While all three density groups showed a multilineage differentiation potential, LD showed a higher degree of observed and semiquantified lineage specific staining (p < 0.05). Furthermore, LD displayed higher expression levels of stem cell biomarkers (Nanog, Oct4, and Sox2) and showed higher percentages of CD29+, CD44+, and CD90+ cells (p < 0.05) following flow cytometry analysis.

Conclusions

Limiting dilution method is suggested when isolating NPMSCs as a means of improving cell activity and plasticity.

Spheroidal Organoids Reproduce Characteristics of Longitudinal Depth Zones in Bovine Articular Cartilage

Articular cartilage has multiple histologically distinct longitudinal depth zones. Development and pathogenesis occur throughout these zones. Cartilage explants, monolayer cell culture and reconstituted 3-dimensional cell constructs have been used for investigating mechanisms of pathophysiology in articular cartilage. Such models have been insufficient to reproduce zone-dependent cellular characteristics and extracellular matrix (ECM) upon investigation into cartilage development and pathogenesis. Therefore, we defined a chondrocyte spheroid model consistently formed with isolated chondrocytes from longitudinal depth zones without extrinsic materials. This spheroid showed zone-dependent characteristics of size, cartilage-specific ECM (collagen types I and II, aggrecan and keratan sulfate) and gene expressions of anabolic and catabolic molecules (matrix molecules and matrix metalloproteinase-13). In addition, the spheroid model is small enough to maintain the viability of cells and point symmetry to analyze the gradient of diffusive molecules. This spheroid organoid model will be useful to elucidate the mechanism of histogenesis and pathogenesis in articular cartilage.

From gristle to chondrocyte transplantation: treatment of cartilage injuries

This review addresses the progress in cartilage repair technology over the decades with an emphasis on cartilage regeneration with cell therapy. The most abundant cartilage is the hyaline cartilage that covers the surface of our joints and, due to avascularity, this tissue is unable to repair itself. The cartilage degeneration seen in osteoarthritis causes patient suffering and is a huge burden to society. The surgical approach to cartilage repair was non-existing until the 1950s when new surgical techniques emerged. The use of cultured cells for cell therapy started as experimental studies in the 1970s that developed over the years to a clinical application in 1994 with the introduction of the autologous chondrocyte transplantation technique (ACT). The technology is now spread worldwide and has been further refined by combining arthroscopic techniques with cells cultured on matrix (MACI technology). The non-regenerating hypothesis of cartilage has been revisited and we are now able to demonstrate cell divisions and presence of stem-cell niches in the joint. Furthermore, cartilage derived from human embryonic stem cells and induced pluripotent stem cells could be the base for new broader cell treatments for cartilage injuries and the future technology base for prevention and cure of osteoarthritis.

A genome wide analysis of alternative splicing events during the osteogenic differentiation of human cartilage endplate-derived stem cells

Low back pain is a prevalent disease, which leads to suffering and disabilities in a vast number of individuals. Degenerative disc diseases are usually the underlying causes of low back pain. However, the pathogenesis of degenerative disc diseases is highly complex and difficult to determine. Current therapies for degenerative disc diseases are various. In particular, cell-based therapies have proven to be effective and promising. Our research group has previously isolated and identified the cartilage endplate‑derived stem cells. In addition, alternative splicing is a sophisticated regulatory mechanism, which greatly increases cellular complexity and phenotypic diversity of eukaryotic organisms. The present study continued to investigate alternative splicing events in osteogenic differentiation of cartilage endplate‑derived stem cells. An Affymetrix Human Transcriptome Array 2.0 was used to detect splicing changes between the control and differentiated samples. Additionally, molecular function and pathway analysis were also performed. Following rigorous bioinformatics analysis of the data, 3,802 alternatively spliced genes were identified, and 10 of these were selected for validation by reverse transcription‑polymerase chain reaction. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes pathway analysis also revealed numerous enriched GO terms and signaling pathways. To the best of our knowledge, the present study is the first to investigate alternative splicing mechanisms in osteogenic differentiation of stem cells on a genome‑wide scale. The illumination of molecular mechanisms of stem cell osteogenic differentiation may assist the development novel bioengineered methods to treat degenerative disc diseases.

Distinguishing characteristics of stem cells derived from different anatomical regions of human degenerated intervertebral discs

INTRODUCTION

Several types of stem cells have been successfully demonstrated to exist in the human degenerated intervertebral disc (IVD), which is composed of annulus fibrosus (AF), nucleus pulposus (NP) and cartilage endplate (CEP). However, the differences in the biological characteristics among these and bone marrow derived mesenchymal stem cells (BM-MSCs) remain unclear.

MATERIALS AND METHODS

To investigate this issue, cells were harvested from human AF, NP, CEP, and bone marrow, respectively; passage 2 cells were selected using the agarose suspension culture system to obtain stem cell clones. Following expansion in vitro, stem cells from different anatomical regions were compared regarding the morphology, proliferation ability, immunophenotypic expression, and multi-lineage differentiation capacity. In addition, stem cell-alginate bead compositions were constructed for the comparison of DNA and sGAG content.

RESULTS

There were subtle differences regarding cell morphology, but no significant differences in proliferation ability among the four types of stem cells. For the immunophenotypic analysis, all stem cells basically fulfilled the criteria for mesenchymal stem cells (MSCs), which have been published by the International Society for Cellular Therapy (ISCT), with a significant difference in CD105 expression. A comparison of the osteogenic capacities indicated: cartilage endplate-derived stem cells (CESCs) > annulus fibrosus-derived stem cells (AFSCs) > BM-MSCs > nucleus pulposus-derived stem cells (NPSCs). The chondrogenesis difference was similar to osteogenesis. For adipogenesis: BM-MSCs >NPSCs >CESCs >AFSCs. In the stem cell/alginate composition, the CESCs consistently showed the superior chondrogenic potential among all those cell types.

CONCLUSIONS

Our data indicated that all the four types of stem cells shared some similar biological properties (regarding shape, proliferation ability and immunophenotypic expression). CESCs, which had the strongest osteogenic and chondrogenic potentials, may serve as excellent seed cells for NP/cartilage or bone tissue engineering.

Global Gene Expression Profiling and Alternative Splicing Events during the Chondrogenic Differentiation of Human Cartilage Endplate-Derived Stem Cells

Low back pain (LBP) is a very prevalent disease and degenerative disc diseases (DDDs) usually account for the LBP. However, the pathogenesis of DDDs is complicated and difficult to elucidate. Alternative splicing is a sophisticated regulatory process which greatly increases cellular complexity and phenotypic diversity of eukaryotic organisms. In addition, the cartilage endplate-derived stem cells have been discovered and identified by our research group. In this paper, we continue to investigate gene expression profiling and alternative splicing events during chondrogenic differentiation of cartilage endplate-derived stem cells. We adopted Affymetrix Human Transcriptome Array 2.0 (HTA 2.0) to compare the transcriptional and splicing changes between the control and differentiated samples. RT-PCR and quantitative PCR are used to validate the microarray results. The GO and KEGG pathway analysis was also performed. After bioinformatics analysis of the data, we detected 1953 differentially expressed genes. In terms of alternative splicing, the Splicing Index algorithm was used to select alternatively spliced genes. We detected 4411 alternatively spliced genes. GO and KEGG pathway analysis also revealed several functionally involved biological processes and signaling pathways. To our knowledge, this is the first study to investigate the alternative splicing mechanisms in chondrogenic differentiation of stem cells on a genome-wide scale.

Cartilage issues in football-today's problems and tomorrow's solutions

Articular cartilage injury is prevalent in football players and results from chronic joint stress or acute traumatic injuries. Articular cartilage injury can often result in progressive painful impairment of joint function and limit sports participation. Management of articular cartilage injury in athletes aims to return the player to competition, and requires effective and durable joint surface restoration that resembles normal hyaline articular cartilage that can withstand the high joint stresses of football. Existing articular cartilage repair techniques can return the athlete with articular cartilage injury to high-impact sports, but treatment does not produce normal articular cartilage, and this limits the success rate and durability of current cartilage repair in athletes. Novel scientific concepts and treatment techniques that apply modern tissue engineering technologies promise further advancement in the treatment of these challenging injuries in the high demand athletic population. We review the current knowledge of cartilage injury pathophysiology, epidemiology and aetiology, and outline existing management algorithms, developing treatment options and future strategies to manage articular cartilage injuries in football players.

Articular Chondroprogenitor Cells Maintain Chondrogenic Potential but Fail to Form a Functional Matrix When Implanted Into Muscles of SCID Mice

OBJECTIVE

Articular cartilage is a complex tissue comprising phenotypically distinct zones. Research has identified the presence of a progenitor cell population in the surface zone of immature articular cartilage. The aim of the present study was to determine the in vivo plasticity of articular cartilage progenitor.

DESIGN

Chondropogenitor cells were isolated from bovine metacarpalphalangeal joints by differential adhesion to fibronectin. Cells were labeled with PKH26 and injected into the thigh muscle of severe-combined immunodeficient (SCID) mice. After 2 weeks, the muscles were dissected and cryosectioned. Sections were stained with safranin O and labeled for sox9 and collagen type II. Polymerase chain reaction analysis was carried out to determine plasticity for a number of tissue-specific markers. Full-depth chondrocytes acted as a control.

RESULTS

Fluorescent PKH26 labeled cells were detected after 2 weeks in all samples analyzed. A cartilage pellet was present after injection of freshly isolated chondrocytes. After injection with clonal and enriched populations of chondroprogenitors, no distinct pellet was detected, but diffuse cartilage nodules were found with regions of safranin O staining and Sox9. Low levels of collagen type II were also detected. Polymerase chain reaction analysis identified the presence of the endothelial cell marker PECAM-1 in one clonal cell line, demonstrating phenotypic plasticity into the phenotype of the surrounding host tissues.

CONCLUSIONS

The bovine articular cartilage progenitor cells were able to survive in vivo postimplantation, but failed to create a robust cartilage pellet, despite expressing sox9 and type II collagen. This suggests the cells require further signals for chondrogenic differentiation.

Characterization of colony-forming cells in adult human articular cartilage

Recent studies have shown that adult human articular cartilage contains stem-like cells within the native structure. In this study, we aimed to determine the localization of putative stem cell markers such as CD90, STRO-1, OCT-3/4, CD105 and CD166 in adult human articular cartilage tissue sections and demonstrate the expression of these markers within the expanded surface zone colony-forming (CF) cells and evaluate their differentiation potential. Biopsy samples were either fixed immediately for immunohistochemical analyses or processed for in vitro cell culture. Immunohistochemical and flow cytometry analyses were performed by using CD90, STRO-1, OCT-3/4, CD105 and CD166 antibodies. Isolated colony-forming (CF) cells were further stimulated, by using the appropriate growth factors in their pellet culture, to obtain cartilage, bone and adipose lineages. We observed that the expression of the stem cell markers were in various zones of the human adult cartilage. Flow cytometry results showed that in CF cells the expression of CD90 and CD166 was high, while OCT-3/4 was low. We also determined that CF cells could be stimulated towards cartilage, bone and adipose lineages. The results of this research support the idea that the resident stem-like cells in adult human articular cartilage express these putative stem cell markers, but further experimental investigations are needed to determine the precise localization of these cells.

Utilization of stem cells in alginate for nucleus pulposus tissue engineering

In a general view of anatomy, intervertebral disc is composed of three parts: annulus fibrosus (AF), nucleus pulposus (NP), and cartilage endplate (CEP). Recently, several types of stem cells were successfully isolated from these corresponding regions, but up to now, no research was performed about which kind of stem cells is the most efficient candidate for NP tissue engineering or for stem cell-based disc regeneration therapy. In this study, we compared the regenerative potentials of the above-mentioned three kinds of disc-derived stem cells with that of the classic bone marrow (BM)-mesenchymal stem cells (MSCs) in a rabbit disc degeneration model. By magnetic resonance imaging (MRI), X-ray, histology, etc. evaluations, we found that cartilage endplate-derived stem cells (CESCs) showed superior capacity compared with the annulus fibrosus-derived stem cells (AFSCs), nucleus pulposus-derived stem cells (NPSCs), and BM-MSCs (p<0.05); additionally, when comparing the CESC group with the normal control group, there existed no statistical difference in X-ray (p>0.05). Those results demonstrated that the CESC-seeded alginate construct performed the most powerful ability for NP regeneration, while AFSCs showed the most inferior potency, NPSCs and BM-MSCs had similar regenerative capacity and located in the middle. All in all, our study showed that CESCs might act as an efficient seed cell source for NP tissue engineering, which paved a new way for the biological solution of disc degeneration diseases.

Maintenance of "stem cell" features of cartilage cell sub-populations during in vitro propagation

Background

The discovery of mesenchymal stem cells (MSCs) or MSC-like cells in cartilage tissue does not tie in well with the established view that MSCs derive from a perivascular niche. The presence of MSCs may raise concerns about specificity and application safety, particularly in terms of the regulatory site. The aim of the present study was to investigate the benefits or possible risks of the MSC-like properties of cells isolated from cartilage in the context of autologous chondrocyte implantation.

Methods

Chondrocytic cells were isolated from cartilage or intervertebral disc tissue. Flow cytometry was used to analyze the expression of cell surface antigens. MSC-like cells were either enriched or depleted by means of magnetic cell sorting (MACS) involving the monoclonal antibodies W5C5/SUSD2 and W8B2/MSCA-1. We addressed the issues of prolonged expansion of such cells as well as the influence of culture medium as a trigger for selecting a single cell type. Established protocols were used to study in vitro differentiation. In addition to histological and biochemical assessment, the acquired phenotypes were also evaluated on the mRNA transcript level.

Results

In the studied cells, we found strongly analogous expression of antigens typically expressed on MSCs, including CD49e, CD73, CD90, CD105, CD140b and CD166. The expression of W5C5 and W8B2 antigens in cartilage cell sub-populations did not correlate with multi-potency. We demonstrated that a chondroid precursor, but not a bona fide multipotent mesenchymal, cell type can be obtained under established in vitro culture conditions. The culture media used for expansion influenced the cell phenotype.

Conclusions

The risk of adverse adipose or osseous differentiation is not posed by expanded chondrocyte cultures, even after enrichment of putative MSC-like cell populations by MACS. It is possible that this limited “stemness” in chondrocytes, expanded for use in ACI, may instead be beneficial as it allows re-differentiation under appropriate conditions despite prolonged times in culture.

Similar cellular migration patterns from niches in intervertebral disc and in knee-joint regions detected by in situ labeling: an experimental study in the New Zealand white rabbit

INTRODUCTION

Potential stem cell niches (SNs) were recently reported in intervertebral discs (IVDs) and knee joints (KJs) in different mammals (located adjacent to the epiphyseal plate; EP). The aim here was to examine further possible cellular migration and migration directions of cells originating from niches possibly involved in regeneration of cartilaginous tissues in the IVD and in the KJ regions in adult mammals.

METHODS

In total, 33 rabbits were used in studies A through C. A. IVD cells were sorted; fluorescence-activated cell sorting (FACS) by size (forward scatter; ≤ 10 μm or >10 μm or GDF5+ cells (anti-GDF5 antibody). Sorted cells, labeled with cell tracer (carboxyfluorescein-diacetate-succinimidyl ester; CDFA-SE) were applied on IVD explants in vitro. Migrating cells/distance was evaluated by fluorescence- and confocal-microscopy (FC). B. DNA labeling was performed with BrdU (oral administration). Animals were killed (14 to 56 days), KJs collected, and BrdU+ cells visualized with immunohistochemistry (IHC)/anti-BrdU antibody in SN and articular cartilage (AC). C. Cell tracer: (Fe-nanoparticles: Endorem) were injected into SNs of IVDs (LI-LV) and KJs (tibia). Animals were killed after 2 to 6 weeks. Fe-labeled cells were traced by ferric-iron staining (Prussian blue reaction; Mallory method).

RESULTS

A. GDF5+ cells and ≤ 10-μm cells displayed the best migration capability in IVD explants. GDF5+ cells were detected at a tissue depth of 1,300 μm (16 days). B. BrdU+ cells were observed in early time points in niches of KJs, and at later time points in AC, indicating a gradual migration of cells. C. Fe+ cells were detected in IVDs; in annulus fibrosus (AF) in 11 of 12 animals and in nucleus pulposus (NP) in two of 12 animals. In AC (tibia), Fe+ cells were detected in six of 12 animals. In the potential migration route (PMR), from niches toward the IVD, Fe+ cells (three of 12 animals) and in PMR toward AC (KJs) (six of 12 animals) were detected.

CONCLUSIONS

Results indicate similar cellular migration patterns in cartilage regions (IVD and KJs) with migration from stem cell niche areas into the mature cartilaginous tissues of both the KJs and the IVD. These findings of a cellular migration pattern in mature cartilage are of interest from tissue-repair and engineering perspectives.

Study to determine the presence of progenitor cells in the degenerated human cartilage endplates

INTRODUCTION

Cartilage endplate (CEP) degeneration is usually accompanied by loss of cellularity, and this loss may be a crucial key factor in initiation and development of degenerative disc disease. The study of cell types in degenerated CEP could help in understanding CEP etiopathogenesis, and may help in devising new treatments, especially if the presence of progenitor cells could be demonstrated. The aim of this study was to determine if progenitor cells existed in degenerated human CEP.

MATERIALS AND METHODS

Cells isolated from CEP were cultured in a three-dimensional agarose suspension to screen for proliferative cell clusters. Cell clusters were then expanded in vitro and the populations were analyzed for colony forming unit, immunophenotype, multilineage induction, and expression of stem cell-related genes.

RESULTS

The presence of progenitor cells in degenerated human CEP is indicated by the results of CFU, immunophenotype, multilineage induction, and expression of stem cell-related genes.

CONCLUSIONS

We believe that this is the first study which has conclusively shown the presence of progenitor cells in degenerated CEP. The finding of this study may influence the clinical management of degenerative disc disorder.

Characteristics of stem cells derived from the degenerated human intervertebral disc cartilage endplate

Mesenchymal stem cells (MSCs) derived from adult tissues are an important candidate for cell-based therapies and regenerative medicine due to their multipotential differentiation capability. MSCs have been identified in many adult tissues but have not reported in the human intervertebral disc cartilage endplate (CEP). The initial purpose of this study was to determine whether MSCs exist in the degenerated human CEP. Next, the morphology, proliferation capacity, cell cycle, cell surface epitope profile and differentiation capacity of these CEP-derived stem cells (CESCs) were compared with bone-marrow MSCs (BM-MSCs). Lastly, whether CESCs are a suitable candidate for BM-MSCs was evaluated. Isolated cells from degenerated human CEP were seeded in an agarose suspension culture system to screen the proliferative cell clusters. Cell clusters were chosen and expanded in vitro and were compared with BM-MSCs derived from the same patient. The morphology, proliferation rate, cell cycle, immunophenotype and stem cell gene expression of the CESCs were similar to BM-MSCs. In addition, the CESCs could be induced into osteoblasts, adipocytes, chondrocytes, and are superior to BM-MSCs in terms of osteogenesis and chondrogenesis. This study is first to demonstrate the presence of stem cells in the human degenerated CEP. These results may improve our understanding of intervertebral disc (IVD) pathophysiology and the degeneration process, and could provide cell candidates for cell-based regenerative medicine and tissue engineering.

Using changes in hydrostatic and osmotic pressure to manipulate metabolic function in chondrocytes

Articular cartilage has distinct histological depth zones. In each zone, chondrocytes are subject to different hydrostatic (HP) and osmotic pressure (OP) due to weight-bearing and joint-loading. Previous in vitro studies of regeneration and pathophysiology in cartilage have failed to consider the characteristics of histological heterogeneity and the effects of combinations of changes in HP and OP. Thus, we have constructed molecular, biochemical, and histological profiles of anabolic and catabolic molecules produced by chondrocytes from each depth zone isolated from bovine articular cartilage in response to changes in HP and OP. We cultured the chondrocytes with combinations of loading or off-loading of HP at 0-0.5 MPa, 0.5 Hz, and changes in OP of 300-450 mosM over 1 wk, and evaluated mRNA expression and immunohistology of both anabolic and catabolic molecules and amounts of accumulated sulfated glycosaminoglycan. Any changes in HP and OP upregulated mRNA of anabolic and catabolic molecules in surface-, middle-, and deep-zone cells, in descending order of magnitude. Off-loading HP maintained the anabolic and reduced the catabolic mRNA; high OP retained upregulation of catabolic mRNA. These molecular profiles were consistent with immunohistological and biochemical findings. Changes in HP and OP are essential for simulating chondrocyte physiology and useful for manipulating phenotypes.

Articular cartilage: structure and regeneration

Articular cartilage (AC) has no or very low ability of self-repair, and untreated lesions may lead to the development of osteoarthritis. One method that has been proven to result in long-term repair or isolated lesions is autologous chondrocyte transplantation. However, first generation of these cells' implantation has limitations, and introducing new effective cell sources can improve cartilage repair. AC provides a resilient and compliant articulating surface to the bones in diarthrodial joints. It protects the joint by distributing loads applied to it, so preventing potentially damaging stress concentrations on the bone. At the same time it provides a low-friction-bearing surface to enable free movement of the joint. AC may be considered as a visco- or poro-elastic fiber-composite material. Fibrils of predominantly type II collagen provide tensile reinforcing to a highly hydrated proteoglycan gel. The tissue typically comprises 70% water and it is the structuring and retention of this water by the proteoglycans and collagen that is largely responsible for the remarkable ability of the tissue to support compressive loads.

Plasticity of fetal cartilaginous cells

Tissue-specific stem cells found in adult tissues can participate in the repair process following injury. However, adult tissues, such as articular cartilage and intervertebral disc, have low regeneration capacity, whereas fetal tissues, such as articular cartilage, show high regeneration ability. The presence of fetal stem cells in fetal cartilaginous tissues and their involvement in the regeneration of fetal cartilage is unknown. The aim of the study was to assess the chondrogenic differentiation and the plasticity of fetal cartilaginous cells. We compared the TGF-β3-induced chondrogenic differentiation of human fetal cells isolated from spine and cartilage tissues to that of human bone marrow stromal cells (BMSC). Stem cell surface markers and adipogenic and osteogenic plasticity of the two fetal cell types were also assessed. TGF-β3 stimulation of fetal cells cultured in high cell density led to the production of aggrecan, type I and II collagens, and variable levels of type X collagen. Although fetal cells showed the same pattern of surface stem cell markers as BMSCs, both type of fetal cells had lower adipogenic and osteogenic differentiation capacity than BMSCs. Fetal cells from femoral head showed higher adipogenic differentiation than fetal cells from spine. These results show that fetal cells are already differentiated cells and may be a good compromise between stem cells and adult tissue cells for a cell-based therapy.

Coculture of human embryonic stem cells and human articular chondrocytes results in significantly altered phenotype and improved chondrogenic differentiation

Human embryonic stem (hES) cells have been suggested as a cell source for the repair of cartilage lesions. Here we studied how coculture with human articular chondrocytes affects the expansion potential, morphology, expression of surface markers, and differentiation abilities of hES cells, with special regard to chondrogenic differentiation. Undifferentiated hES cells were cocultured with irradiated neonatal or adult articular chondrocytes in high-density pellet mass cultures for 14 days. Cocultured hES cells were then expanded on plastic and their differentiation potential toward the adipogenic, osteogenic, and chondrogenic lineages was compared with that of undifferentiated hES cells. The expression of different surface markers was investigated using flow cytometry and teratoma formation was studied using injection of the cells under the kidney capsule. Our results demonstrate that although hES cells have to be grown on Matrigel, the cocultured hES cells could be massively expanded on plastic with a morphology and expression of surface markers similar to mesenchymal stem cells. Coculture further resulted in a more homogenous pellet and significantly increased cartilage matrix production, both in high-density pellet mass cultures and hyaluronan-based scaffolds. Moreover, cocultured cells formed colonies in agarose suspension culture, also demonstrating differentiation toward chondroprogenitor cells, whereas no colonies were detected in the hES cell cultures. Coculture further resulted in a significantly decreased osteogenic potential. No teratoma formation was detected. Our results confirm the potential of the culture microenvironment to influence hES cell morphology, expansion potential, and differentiation abilities over several population doublings.

Dysplasia epiphysealis hemimelica: a case report with novel pathophysiologic aspects

Dysplasia epiphysealis hemimelica (DEH) is a rare developmental disorder. The underlying pathophysiology is largely unclear. Its diagnosis is based on clinical findings and may be difficult due to its low incidence and close relationship to other disorders such as osteochondroma. We describe a 13-year-old boy who presented with a unilateral lesion of the left medial femoral condyle and left ankle. In addition to standard diagnostic tools such as radiographs and MRI, arthroscopy-guided biopsy was performed; histologic/immunohistochemical findings from cartilage-bone specimens confirmed the diagnosis and provided novel information toward a disease mechanism. The cellular phenotype of clustered chondrocytes exhibited characteristics of chondroprogenitor cells and terminally differentiated cells, suggesting dysregulation of resident progenitor cells. No other surgery was performed and during a 2 year period, we observed spontaneous ossification of the lesion associated with decreased joint impairment. Immunohistochemical analysis of the lesion provided a more accurate diagnosis and may contribute to unraveling potential novel mechanisms involved in its pathogenesis.

Identification of a stem cell niche in the zone of Ranvier within the knee joint

A superficial lesion of the articular cartilage does not spontaneously self-repair and has been suggested to be partly due to lack of progenitor cells within the joint that can reach the site of injury. To study whether progenitor cells are present within the joint, 3-month-old New Zealand white rabbits were exposed to bromodeoxyuridine (BrdU) for 12 consecutive days and were then sacrificed 4, 6, 10, 14, 28 and 56 days after the first BrdU administration. Presence of BrdU and localization of progenitor markers were detected using immunohistochemistry. After 10 days of BrdU exposure, BrdU-positive cells, i.e. proliferating cells, were abundantly detected in the epiphyseal plate, the perichondrial groove of Ranvier, and in all zones of the articular cartilage. After a wash-out period, BrdU-positive cells were still present, i.e. those considered to be progenitor cells, in these regions of the knee except for the proliferative zone of the epiphyseal plate. Cells in the perichondrial groove of Ranvier were further positive for several markers associated with progenitor cells and stem cell niches, including Stro-1, Jagged1, and BMPr1a. Our results demonstrate that a small population of progenitor cells is present in the perichondrial groove of Ranvier as well as within the articular cartilage in the knee. The perichondrial groove of Ranvier also demonstrates the properties of a stem cell niche.

Clonal chondroprogenitors maintain telomerase activity and Sox9 expression during extended monolayer culture and retain chondrogenic potential

OBJECTIVE

Articular cartilage contains mesenchymally derived chondroprogenitor cells that have the potential to be used for stem cell therapy. The aim of this study was to characterise the growth kinetics and properties of in vitro expanded cloned chondroprogenitors and determine if critical determinants of the progenitor phenotype were maintained or lost in culture.

METHODS

Chondroprogenitors were isolated from immature bovine metacarpalphalangeal joints by differential adhesion to fibronectin. Cloned colonies were expanded in vitro up to 50 population doublings (PD). Growth characteristics were assessed by cell counts, analysis of telomere length, telomerase activity, expression of senescence-associated beta-galactosidase activity and real-time quantitative polymerase chain reaction to analyse the gene expression patterns of sox9 and Notch-1 in chondroprogenitors.

RESULTS

Cloned chondroprogenitors exhibited exponential growth for the first 20 PD, then slower linear growth with evidence of replicative senescence at later passages. Mean telomere lengths of exponentially growing chondroprogenitors were significantly longer than dedifferentiated chondrocytes that had undergone a similar number of PD (P<0.05). Chondroprogenitors also had 2.6-fold greater telomerase activity. Chondroprogenitors maintained similar sox9 and lower Notch-1 mRNA levels compared to non-clonal dedifferentiated chondrocytes. Chondroprogenitors were induced to differentiate into cartilage in 3D pellet cultures, immunological investigation of sox9, Notch-1, aggrecan and proliferating cell nuclear antigen (PCNA) expression showed evidence of co-ordinated growth and differentiation within the cartilage pellet.

CONCLUSION

Clonal chondroprogenitors from immature articular cartilage provide a useful tool to understand progenitor cell biology from the perspective of cartilage repair. Comparisons with more mature progenitor populations may lead to greater understanding in optimising repair strategies.

Human articular chondrocytes--plasticity and differentiation potential

Articular cartilage has no or very low ability of self-repair, and untreated lesions may lead to the development of osteoarthritis. One method which has been proven to result in long-term repair of isolated lesions is autologous chondrocyte transplantation. In this method, culture-expanded chondrocytes isolated from full-thickness biopsies, taken from a non-weight-bearing area at the supromedial edge of the femoral condyle, are transplanted back to the patient under a cover of periosteum. The treatment is able to regenerate hyaline cartilage with long-term durability. Although the repair mechanism behind this treatment has not been fully elucidated, emerging data generated by microarray technologies reveal an interesting regeneration process involving cellular and molecular mechanisms found during fetal development. In hyaline cartilage, the human chondrocyte population is generally considered a homogenous cell population, but recently several investigators have demonstrated that cells isolated from human articular cartilage have stem cell properties and that the superficial layer contains such cells. This paper will discuss these recent data and their implications for future treatment strategies aiming to induce regeneration in articular cartilage surfaces.

In vitro cartilage tissue formation by Co-culture of primary and passaged chondrocytes

Passaging chondrocytes to increase cell number is one way to overcome the major limitation to cartilage tissue engineering, which is obtaining sufficient numbers of chondrocytes to form large amounts of tissue. Because neighboring cells can influence cell phenotype and because passaging induces dedifferentiation, we examined whether coculture of primary and passaged bovine articular chondrocytes in 3-dimensional culture would form cartilage tissue in vitro. Chondrocytes passaged in monolayer culture up to 4 times were mixed with primary (nonpassaged) chondrocytes (5-40% of total cell number) and grown on filter inserts for up to 4 weeks. Passaged cells alone did not form cartilage, but with the addition of increasing numbers of primary chondrocytes, up to 20%, there was an increase in cartilage tissue formation as determined histologically and biochemically and demonstrated by increasing proteoglycan and collagen accumulation. The passaged cells appeared to be undergoing redifferentiation, as indicated by up-regulation of aggrecan, type II collagen, and SOX9 gene expression and decreased type I collagen expression. This switch in collagen type was confirmed using Western blots. Confocal microscopy showed that fluorescently labeled primary cells were distributed throughout the tissue. This coculture approach could provide a new way to solve the problem of limited cell number for cartilage tissue engineering.

Mesenchymal stem cells in bone and cartilage repair: current status

The progression of rheumatoid pathologies, degenerative diseases, traumatologies, and their cortege of increasing medical, social and economical needs, has mandated the development of tissue repair and engineering technologies in orthopedic medicine. Mesenchymal stem cells (MSCs) are multipotent cells that can be extracted from large and relatively easily accessible compartments of the body, especially the bone marrow, and such cells are able to differentiate into adipogenic, chondrogenic and osteogenic precursors. The concept of using MSCs to repair tissues has progressively evolved, and the goal of cell-mediated therapy is to prolong the natural physiological abilities of healing, or substitute them, when these are lacking, failing or progressing too slowly. In recent years, the first clinical trials on the utility of MSCs, with or without scaffolds and/or growth factors, have been initiated. In this review, the authors focus on findings from preclinical research, clinical trials and case reports involving bone and cartilage repairs. New perspectives are considered regarding uses of cell types, cell delivery approaches and growth factors. They also consider the stringent conditions, constraints and considerations necessary to take cell-mediated therapy from bench to bedside.

Future of tissue engineering in rheumatic diseases

Chronic inflammation during rheumatoid arthritis and degenerative processes during osteoarthritis eventually result in joint destruction. Anti-inflammatory therapies facilitate the inhibition or delay of progressing joint cartilage and bone loss, but do not regenerate these tissues. Surgical procedures are quite unsatisfactory in long-term evaluation and often lead to endoprothetic joint replacement. Present tissue engineering technologies offer new strategies for the treatment of cartilage and bone defects. Here, beyond implantation of cell suspensions, biomaterials combined with tissue-specific cells or mesenchymal stem cells are clinically applied. This review focuses on state-of-the-art and future in situ mesenchymal stem cell-based tissue engineering approaches for joint repair in patients with rheumatic diseases.

Three-dimensional (3-D) imaging of chondrocytes in articular cartilage: growth-associated changes in cell organization

Three-dimensional (3-D) imaging and analysis techniques can be used to assess the organization of cells in biological tissues, providing key insights into the role of cell arrangement in growth, homeostasis, and degeneration. The objective of the present study was to use such methods to assess the growth-related changes in cell organization of articular cartilage from different sites in the bovine knee. Three-dimensional images of fetal, calf, and adult cartilage were obtained and processed to identify cell nuclei. The density of cells was lower with growth and with increasing depth from the articular surface. The cell organization, assessed by the angle to the nearest neighboring cell, also varied with growth, and reflected the classical organization of cells in adult tissue, with neighboring cells arranged horizontally in the superficial zone (average angle of 20 degrees) and vertically in the deep zone (60 degrees). In all other regions and growth stages of cartilage, the angle was approximately 32 degrees, indicative of an isotropic organization. On the contrary, the nearest neighbor distance did not vary significantly with growth or depth. Together, these results indicate that cartilage growth is associated with distinctive 3-D arrangements of groups of chondrocytes.