Clonal growth of human articular cartilage and the functional role of the periosteum in chondrogenesis

Identifying the key genes regulating mesenchymal stem cells chondrogenic differentiation: an in vitro study

Background

Mesenchymal stem cells (MSCs) possess the potential to differentiate into chondrocytes, which makes them an ideal source for healing cartilage defects. Here, we seek to identify the essential genes participating in MSCs chondrogenesis.

Methods

Human MSCs were induced for chondrogenesis for 7, 14, and 21 days using a high-density micromass culture system, and RNA was extracted for RNA-seq.

Results

A total of 6247 differentially expressed genes (DEGs) were identified on day 7, and 85 DEGs were identified on day 14. However, no significant DEGs was identified on day 21. The top 30 DEGs at day 7, including COL9A3, COL10A1, and CILP2, are closely related to extracellular matrix organization. While the top 30 DEGs at day 14 revealed that inflammation-related genes were enriched, including CXCL8, TLR2, and CCL20. We also conducted protein–protein interaction (PPI) networks analysis using the search tool for the retrieval of interacting genes (STRING) database and identified key hub genes, including CXCL8, TLR2, CCL20, and MMP3. The transcriptional factors were also analyzed, identifying the top 5 TFs: LEF1, FOXO1, RORA, BHLHE41, and SOX5. We demonstrated one particular TF, RORA, in promoting early MSCs chondrogenesis.

Conclusions

Taken together, our results suggested that these DEGs may have a complex effect on MSCs chondrogenesis both synergistically and solitarily.

A low dose cell therapy system for treating osteoarthritis: In vivo study and in vitro mechanistic investigations

Mesenchymal stem cells (MSCs) can be effective in alleviating the progression of osteoarthritis (OA). However, low MSC retention and survival at the injection site frequently require high doses of cells and/or repeated injections, which are not economically viable and create additional risks of complications. In this study, we produced MSC-laden microcarriers in spinner flask culture as cell delivery vehicles. These microcarriers containing a low initial dose of MSCs administered through a single injection in a rat anterior cruciate ligament (ACL) transection model of OA achieved similar reparative effects as repeated high doses of MSCs, as evaluated through imaging and histological analyses. Mechanistic investigations were conducted using a co-culture model involving human primary chondrocytes grown in monolayer, together with MSCs grown either within 3D constructs or as a monolayer. Co-culture supernatants subjected to secretome analysis showed significant decrease of inflammatory factors in the 3D group. RNA-seq of co-cultured MSCs and chondrocytes using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis revealed processes relating to early chondrogenesis and increased extracellular matrix interactions in MSCs of the 3D group, as well as phenotypic maintenance in the co-cultured chondrocytes. The cell delivery platform we investigated may be effective in reducing the cell dose and injection frequency required for therapeutic applications.

Optimization of Protocol for Isolation of Chondrocytes from Human Articular Cartilage

OBJECTIVE

Cartilage tissue engineering has evolved as one of the therapeutic strategies for cartilage defect, which relies on a large number of viable chondrocytes. Because of limited availability of cartilage and low chondrocytes yield from cartilage, the need for an improve isolation protocol for maximum yield of viable cells is a key to achieving successful clinical constructs. This study optimizes and compares different protocols for isolation of chondrocytes from cartilage.

DESIGN

We employed enzymatic digestion of cartilage using collagenase II and trypsin. The chondrocytes yield, growth kinetics, aggrecan, and collagen type 2 (COL2) expression were evaluated. Collagen type 1 (COL1) mRNA expression was assessed to monitor the possibility of chondrocytes dedifferentiation.

RESULTS

Chondrocyte yield per gram of cartilage was significantly higher (P < 0.05) using collagenase II in Hank's balanced salt solution (HBSS) compared with 0.25% trypsin. The number of chondrocyte yield per gram was higher in cartilage digested with collagenase in HBSS compared with Dulbecco's modified Eagle medium/F12; however, the difference was not statistically significant. Chondrocytes seeded at lower densities had shorter population doubling time compared to those seeded at higher density. Protein and gene expression of chondrocyte phenotype indicates the expression of aggrecan and COL2. The expression of COL1 was significantly increased (P < 0.05) in passage 3 compared with primary chondrocytes. The mRNA expression of chondrocyte phenotype was similar in primary and passaged one cells.

CONCLUSIONS

Collagenase in HBSS yield the highest number of viable chondrocytes and the isolated cells expressed chondrocyte phenotype. This protocol can be employed to generate large number of viable chondrocytes, particularly with limited cartilage biopsies.

Osteogenic and Chondrogenic Potential of Periosteum-Derived Mesenchymal Stromal Cells: Do They Hold the Key to the Future?

The periosteum, with its outer fibrous and inner cambium layer, lies in a dynamic environment with a niche of pluripotent stem cells for their reparative needs. The inner cambium layer is rich in mesenchymal progenitors, osteogenic progenitors, osteoblasts, and fibroblasts in a scant collagen matrix environment. Their role in union and remodeling of fracture is well known. However, the periosteum as a source of mesenchymal stem cells has not been explored in detail. Moreover, with the continuous expansion of techniques, newer insights have been acquired into the roles and regulation of these periosteal cells. From a therapeutic standpoint, the periosteum as a source of tissue engineering has gained much attraction. Apart from its role in bone repair, analysis of the bone-forming potential of periosteum-derived stem cells is lacking. Hence, this article elucidates the role of the periosteum as a potential source of mesenchymal stem cells along with their capacity for osteogenic and chondrogenic differentiation for therapeutic application in the future.

Translating Periosteum's Regenerative Power: Insights From Quantitative Analysis of Tissue Genesis With a Periosteum Substitute Implant

: An abundance of surgical studies during the past 2 centuries provide empirical evidence of periosteum's regenerative power for reconstructing tissues as diverse as trachea and bone. This study aimed to develop quantitative, efficacy-based measures, thereby providing translational guidelines for the use of periosteum to harness the body's own healing potential and generate target tissues. The current study quantitatively and qualitatively demonstrated tissue generation modulated by a periosteum substitute membrane that replicates the structural constituents of native periosteum (elastin, collagen, progenitor cells) and its barrier, extracellular, and cellular properties. It shows the potentiation of the periosteum's regenerative capacity through the progenitor cells that inhabit the tissue, biological factors intrinsic to the extracellular matrix of periosteum, and mechanobiological factors related to implant design and implementation. In contrast to the direct intramembranous bone generated in defects surrounded by patent periosteum in situ, tissue generation in bone defects bounded by the periosteum substitute implant occurred primarily via endochondral mechanisms whereby cartilage was first generated and then converted to bone. In addition, in defects treated with the periosteum substitute, tissue generation was highest along the major centroidal axis, which is most resistant to prevailing bending loads. Taken together, these data indicate the possibility of designing modular periosteum substitute implants that can be tuned for vectorial and spatiotemporal delivery of biological agents and facilitation of target tissue genesis for diverse surgical scenarios and regenerative medicine approaches. It also underscores the potential to develop physical therapy protocols to maximize tissue genesis via the implant's mechanoactive properties.

SIGNIFICANCE

In the past 2 centuries, the periosteum, a niche for stem cells and super-smart biological material, has been used empirically in surgery to repair tissues as diverse as trachea and bone. In the past 25 years, the number of articles indexed in PubMed for the keywords "periosteum and tissue engineering" and "periosteum and regenerative medicine" has burgeoned. Yet the biggest limitation to the prescriptive use of periosteum is lack of easy access, giving impetus to the development of periosteum substitutes. Recent studies have opened up the possibility to bank periosteal tissues (e.g., from the femoral neck during routine resection for implantation of hip replacements). This study used an interdisciplinary, quantitative approach to assess tissue genesis in modular periosteum substitute implants, with the aim to provide translational strategies for regenerative medicine and tissue engineering.

Cellular and Acellular Approaches for Cartilage Repair: A Philosophical Analysis

There are several choices of cells to use for cartilage repair. Cells are used as internal or external sources and sometimes in combination. In this article, an analysis of the different cell choices and their use and potential is provided. Embryonic cartilage formation is of importance when finding more about how to be able to perfect cartilage repair. Some suggestions for near future research based on up-to-date knowledge on chondrogenic cells are given to hopefully stimulate more studies on the final goal of cartilage regeneration.

The study of the frequency effect of dynamic compressive loading on primary articular chondrocyte functions using a microcell culture system

Compressive stimulation can modulate articular chondrocyte functions. Nevertheless, the relevant studies are not comprehensive. This is primarily due to the lack of cell culture apparatuses capable of conducting the experiments in a high throughput, precise, and cost-effective manner. To address the issue, we demonstrated the use of a perfusion microcell culture system to investigate the stimulating frequency (0.5, 1.0, and 2.0 Hz) effect of compressive loading (20% and 40% strain) on the functions of articular chondrocytes. The system mainly integrates the functions of continuous culture medium perfusion and the generation of pneumatically-driven compressive stimulation in a high-throughput micro cell culture system. Results showed that the compressive stimulations explored did not have a significant impact on chondrocyte viability and proliferation. However, the metabolic activity of chondrocytes was significantly affected by the stimulating frequency at the higher compressive strain of 40% (2 Hz, 40% strain). Under the two compressive strains studied, the glycosaminoglycans (GAGs) synthesis was upregulated when the stimulating frequency was set at 1 Hz and 2 Hz. However, the stimulating frequencies explored had no influence on the collagen production. The results of this study provide useful fundamental insights that will be helpful for cartilage tissue engineering and cartilage rehabilitation.

Human cartilage fragments in a composite scaffold for single-stage cartilage repair: an in vitro study of the chondrocyte migration and the influence of TGF-β1 and G-CSF

PURPOSE

Minced chondral fragments are becoming popular as a source of cells for cartilage repair, as a growing interest is developing towards one-stage procedures to treat cartilage lesions. The purpose of this study is to (A) compare cell outgrowth from cartilage fragments of adult and young donors using two different types of scaffolds and (B) evaluate the influence of transforming-growth-factor-β1 (TGF-β1) and granulocyte colony-stimulating factor (G-CSF) on chondrocyte behaviour.

METHODS

In part (A) cartilage fragments from adult and young donors were either loaded onto an HA-derivative injectable paste scaffold or onto an HA-derivative membrane scaffold. Construct sections were then examined for cell counting after 1, 2 and 3 months. In part (B) only membrane scaffolds were prepared using cartilage fragments from young donors. Constructs were cultured either in standard growth medium or in the presence of specific growth factors, such as TGF-β1 or G-CSF or TGF-β1 + G-CSF. After 1 month, construct sections were examined for cell counting. Expression of chondrocyte markers (SOX9, CD151, CD49c) and proliferative markers (β-catenin, PCNA) was assessed using immunofluorescence techniques, both in unstimulated construct sections and in cells from unstimulated and stimulated construct cultures.

RESULTS

Part (A): histological analysis showed age-dependent and time-dependent chondrocyte migration. A significant difference (p < 0.05) was observed between young and older donors at the same time point. No difference was detected between the two types of scaffolds within the same group at the same time point. Part (B): after 1 month, the number of migrating cells/area significantly increased due to exposure to TGF-β1 and/or G-CSF (p < 0.05). Immunofluorescence revealed that outgrowing cells from unstimulated scaffold sections were positive for SOX9, CD151, CD49c and G-CSF receptor. Immunofluorescence of cells from construct cultures showed an increase in β-catenin in all stimulated groups and an increased PCNA expression in G-CSF-exposed cultures (p < 0.05).

CONCLUSION

Outgrowing cells may represent a subset of chondrocytes undergoing a phenotypic shift towards a proliferative state. TGF-β1, and to a greater extent G-CSF, may accelerate this outgrowth. The clinical relevance of this study may involve a potential future clinical application of scaffolds preloaded with growth factors as an additional coating for chondral fragments. Indeed, a controlled delivery of G-CSF, widely employed in various clinical settings, might improve the repair process driven by minced human cartilage fragments during one-stage cartilage repair.

Enhanced chondrocyte proliferation and mesenchymal stromal cells chondrogenesis in coculture pellets mediate improved cartilage formation

In this study, we aimed at investigating the interactions between primary chondrocytes and mesenchymal stem/stromal cells (MSC) accounting for improved chondrogenesis in coculture systems. Expanded MSC from human bone marrow (BM-MSC) or adipose tissue (AT-MSC) were cultured in pellets alone (monoculture) or with primary human chondrocytes from articular (AC) or nasal (NC) cartilage (coculture). In order to determine the reached cell number and phenotype, selected pellets were generated by combining: (i) human BM-MSC with bovine AC, (ii) BM-MSC from HLA-A2+ with AC from HLA-A2- donors, or (iii) human green fluorescent protein transduced BM-MSC with AC. Human BM-MSC and AC were also cultured separately in transwells. Resulting tissues and/or isolated cells were assessed immunohistologically, biochemically, cytofluorimetrically, and by RT-PCR. Coculture of NC or AC (25%) with BM-MSC or AT-MSC (75%) in pellets resulted in up to 1.6-fold higher glycosaminoglycan content than what would be expected based on the relative percentages of the different cell types. This effect was not observed in the transwell model. BM-MSC decreased in number (about fivefold) over time and, if cocultured with chondrocytes, increased type II collagen and decreased type X collagen expression. Instead, AC increased in number (4.2-fold) if cocultured with BM-MSC and maintained a differentiated phenotype. Chondro-induction in MSC-chondrocyte coculture is a robust process mediated by two concomitant effects: MSC-induced chondrocyte proliferation and chondrocyte-enhanced MSC chondrogenesis. The identified interactions between progenitor and mature cell populations may lead to the efficient use of freshly harvested chondrocytes for ex vivo cartilage engineering or in situ cartilage repair.

Periosteum as a source of mesenchymal stem cells: the effects of TGF-β3 on chondrogenesis

INTRODUCTION

Numerous experimental efforts have been undertaken to induce the healing of lesions within articular cartilage by re-establishing competent repair tissue. Adult mesenchymal stem cells have attracted attention as a source of cells for cartilage tissue engineering. The purpose of this study was to investigate chondrogenesis employing periosteal mesenchymal cells.

METHODS

Periosteum was harvested from patients who underwent orthopedic surgeries. Mesenchymal stem cells were characterized through flow cytometry using specific antibodies. The stem cells were divided into four groups. Two groups were stimulated with transforming growth factor β3 (TGF-β3), of which one group was cultivated in a monolayer culture and the other was cultured in a micromass culture. The remaining two groups were cultivated in monolayer or micromass cultures in the absence of TGF-β3. Cell differentiation was verified through quantitative reverse transcription-polymerase chain reaction (RT-PCR) and using western blot analysis.

RESULT

In the groups cultured without TGF-β3, only the cells maintained in the micromass culture expressed type II collagen. Both the monolayer and the micromass groups that were stimulated with TGF-β3 expressed type II collagen, which was observed in both quantitative RT-PCR and western blot analysis. The expression of type II collagen was significantly greater in the micromass system than in the monolayer system.

CONCLUSION

The results of this study demonstrate that the interactions between the cells in the micromass culture system can regulate the proliferation and differentiation of periosteal mesenchymal cells during chondrogenesis and that this effect is enhanced by TGF-β3.

Influence of cyclic bending loading on in vivo skeletal tissue regeneration from periosteal origin

INTRODUCTION

Periosteum osteogenic and chondrogenic properties stimulate the proliferation then differentiation of mesenchymal precursor cells originating from its deeper layers and from neighboring host tissues. The local mechanical environment plays a role in regulating this differentiation of cells into lineages involved in the skeletal regeneration process.

HYPOTHESIS

The aim of this experimental animal study is to explore the influence of cyclic high amplitude bending-loading on skeletal tissue regeneration. The hypothesis is that this mechanical loading modality can orient the skeletogenesis process towards the development of anatomical and histological articular structures.

MATERIAL AND METHODS

A vascularised periosteal flap was transferred in close proximity to each knee joint line in 17 rabbits. On one side, the tibiofemoral joint space was bridged and loading occurred when the animal bent its knee during spontaneous locomotion. On the other side, the flap was placed 12 mm distal to the joint line producing no loading during bending. Tissue regeneration was chronologically analyzed on histologic samples taken from the 4th day to the 6th month.

RESULTS

The structure and mechanical behavior of regenerating tissue evolved over time. As a result of the cyclic bending-loading regimen, cartilage tissue was maintained in specific areas of the regenerating tissue. When loading was discontinued, final osteogenic and fibrogenic differentiation occurred in the neoformed cartilage. Fissures developed in the cartilage aggregates resulting in pseudo-gaps suggesting similar processes to embryonic articular development. Ongoing mesenchymal stem cells stimulation was identified in the host tissues contiguous to the periosteal transfer.

DISCUSSION

These results suggest that the pseudarthrosis concept should be reconsidered within the context of motion induced articular histogenesis.

Interaction of periosteal explants with articular chondrocytes alters expression profile of matrix metalloproteinases

Periosteal tissue is a source of growth factors and of osteochondral progenitor cells which makes it suitable for implantation in chondral defects as known in autologous chondrocyte implantation. The aim of this study was to determine the interaction between periosteal tissue and articular chondrocytes with respect to catabolic effectors such as matrix metalloproteinases (MMPs) and IL-6. Human articular chondrocytes were cultured for up to 28 days as micromass pellets in coculture either with physical contact to periosteal explants or allowing paracrine interactions only. Expression, secretion, and activation of MMPs and IL-6 were analyzed in chondrocytes, periosteum, and culture supernatants. Both coculture conditions influence gene expression levels of MMPs and IL-6 in a time-, culture-, and tissue-dependent manner. Coculturing of periosteum with chondrocytes promotes gene expression and secretion of IL-6. In periosteum, physical contact inhibits MMP-2 and MMP-13 gene expression while paracrine coculture induces expression of IL-6, MMP-2, -7, and -13. Pro-MMP-2, -7, and -13 were detected in supernatants of all culture regimens whereas pro-MMP-9 was secreted from periosteum only. As a balanced amount of MMP activity is likely required to achieve sufficient integration of the regenerate tissue with the surrounding healthy cartilage, an exceeding expression of proteinases might result in degradation, hypertrophy or rejection of the graft.

[Vascularized periosteum and bone regeneration]

The osteogenic potential of periosteum is widely recognized. During development, it plays a prominent role in the radial growth of long bones. Similarly, it has a key role in the consolidation of fractures. The physiological function of periosteum in the healthy, mature skeleton remains relatively subtle; however, its detachment from the bone surface reactivates its potential for fibrogenic and osteochondrogenic regeneration. This discreet anatomical structure is actually a reservoir of mesenchymal progenitor cells capable of proliferating and differentiating, by reinitializing cellular and molecular cascades of embryogenesis in mesenchymal tissues. However, given the hitherto limited knowledge of the quantitative potential of periosteum and of the pathways regulating tissue differentiation during regeneration, human applications have remained anecdotal. The findings of several in vivo and in vitro experiments indicate that the maintenance of the periosteum's vascularization stimulates its quantitative potential. The structural organization of the regenerated material in vivo is governed by locoregional biological and mechanical regulatory mechanisms that serve to make it capable of performing its new functions. The increasing awareness of periosteum's potential is stimulating active research in the fields of cellular biology and tissue engineering. The demonstration of its regenerative potential in animals gives reason to believe that strips of vascularized periosteum could become part of the developing armamentarium of regenerative medicine.

Autologous chondrocyte implantation: a long-term follow-up

BACKGROUND

The medium-term results of autologous chondrocyte implantation (ACI) have shown good to excellent outcomes for the majority of patients. However, no long-term results 10 to 20 years after the surgery have been reported.

HYPOTHESIS

Autologous chondrocyte implantation provides a durable solution to the treatment of full-thickness cartilage lesions of the knee, maintaining good clinical results even 10 to 20 years after implantation.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

In this uncontrolled study, questionnaires with the Lysholm, Tegner-Wallgren, Brittberg-Peterson, modified Cincinnati (Noyes), and Knee Injury and Osteoarthritis Outcome Score (KOOS) scores were sent to 341 patients. Preoperative Lysholm, Tegner-Wallgren, and Brittberg-Peterson scores were also retrieved when possible from patients' files. The patients were asked to grade their status during the past 10 years as better, worse, or unchanged. Finally, they were asked if they would do the operation again.

RESULTS

There were 224 of 341 patients who replied to our posted questionnaires and were assessed. The mean cartilage lesion size was 5.3 cm(2). Ten to 20 years after the implantation (mean, 12.8 years), 74% of the patients reported their status as better or the same as the previous years. There were 92% who were satisfied and would have the ACI again. The Lysholm, Tegner-Wallgren, and Brittberg-Peterson scores were improved compared with the preoperative values. The average Lysholm score improved from 60.3 preoperatively to 69.5 postoperatively, the Tegner from 7.2 to 8.2, and the Brittberg-Peterson from 59.4 to 40.9. At the final measurement, the KOOS score was on average 74.8 for pain, 63 for symptoms, 81 for activities of daily living (ADL), 41.5 for sports, and 49.3 for quality of life (QOL). The average Noyes score was 5.4. Patients with bipolar lesions had a worse final outcome than patients with multiple unipolar lesions. The presence of meniscal injuries before ACI or history of bone marrow procedures before the implantation did not appear to affect the final outcomes. The age at the time of the operation or the size of lesion did not seem to correlate with the final outcome.

CONCLUSION

Autologous chondrocyte implantation has emerged as an effective and durable solution for the treatment of large full-thickness cartilage and osteochondral lesions of the knee joint. Our study suggests that the clinical and functional outcomes remain high even 10 to 20 years after the implantation.

Coculture between periosteal explants and articular chondrocytes induces expression of TGF-beta1 and collagen I

OBJECTIVE

Repair of focal articular cartilage lesions is usually performed by employing cell-based therapeutic strategies such as autologous chondrocyte implantation (ACI). The aim of this study was to determine whether periosteum exerts pro-chondrogenic effects on the transplanted cells beyond its biomechanical role in ACI.

METHODS

Micromass pellets of human articular chondrocytes were cocultured for up to 28 days with human periosteal explants either with physical contact or separated by a membrane allowing paracrine interactions only. Quantitative reverse transcription (RT)-PCR, ELISA, immunohistochemistry and collagen isolation were used to analyse the expression and secretion of TGF-beta1, collagens I and II and chondrogenic differentiation markers such as MIA (CD-RAP) and aggrecan.

RESULTS

TGF-beta1 gene expression was induced significantly in paracrine cocultures in periosteum, whereas it was repressed in physical contact cocultures. However, a higher TGF-beta1 secretion rate was observed in physical contact cocultures compared with periosteal monocultures. The expression of COL2A1, melanoma inhibitory activity (cartilage-derived retinoic acid-sensitive protein) [MIA (CD-RAP)] and aggrecan was mainly unaffected by culture conditions, whereas COL1A1 gene expression was increased in periosteal paracrine cocultures. Collagen I staining was induced in micromass pellets from paracrine cocultures, whereas it was repressed in chondrocytes from physical contact cocultures.

CONCLUSIONS

We found evidence for a bidirectional regulating system with paracrine signalling pathways between periosteum and articular chondrocytes. Stimulation of TGF-beta1 and COL1A1 gene expression in periosteal paracrine cocultures and the increased release of TGF-beta1 protein in physical contact conditions indicate an anabolic, and not merely chondrogenic micro-environment in this in vitro model for periosteal-based ACI.

Transplanted chondrocytes inhibit endochondral ossification within cartilage repair tissue

The aim of this study was to investigate the effect of transplanted chondrocytes on endochondral bone formation in cartilage repair tissue. In the knee joint of miniature pigs, cartilage lesions were treated by microfracturing and were then either left empty, covered with a collagen membrane, or treated by matrix-associated autologous chondrocyte transplantation. In control lesions, the subchondral bone plate was left intact (partial-thickness lesion). The repair tissues were analyzed after 12 weeks by histological methods focusing on bone formation and vascularization. The effect of chondrocytes on angiogenesis was assessed by in vitro assays. The presence of antiangiogenic proteins in cartilage repair tissue, including thrombospondin-1 (TSP-1) and chondromodulin-I (ChM-I), was detected immunohistochemically and their expression in chondrocytes and bone marrow stromal cells was measured by quantitative RT-PCR. Significant outgrowths of subchondral bone and excessive endochondral ossification within the repair tissue were regularly observed in lesions with an exposed or microfractured subchondral bone plate. In contrast, such excessive bone formation was significantly inhibited by the additional transplantation of chondrocytes. Cartilaginous repair tissue that resisted ossification was strongly positive for the antiangiogenic proteins, TSP-1 and ChM-I, which were, however, not detectable in vascularized osseous outgrowths. Chondrocytes were identified to be the major source of TSP-1- and ChM-I expression and were shown to counteract the angiogenic activity of endothelial cells. These data suggest that the resistance of cartilaginous repair tissue against endochondral ossification following the transplantation of chondrocytes is associated with the presence of antiangiogenic proteins whose individual relevance has yet to be further explored.

Treatment of cartilage defects in the knee using alginate beads containing human mature allogenic chondrocytes

BACKGROUND

The repair of osteochondral lesions is imperfect and transient; chondral lesions do not heal in mature cartilage. Attempts have been made to restore cartilage lesions by filling the defects with a temporary artificial biocompatible matrix.

PURPOSE

To determine whether the implantation of alginate beads containing human mature allogenic chondrocytes is feasible and safe for the treatment of symptomatic cartilage defects in the knee.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

A biodegradable, alginate-based, biocompatible scaffold containing human mature allogenic chondrocytes was used for the treatment of chondral and osteochondral lesions in the knee. Twenty-one patients were clinically and prospectively evaluated with use of the Western Ontario and McMaster Universities Osteoarthritis Index and a visual analog scale for pain preoperatively and at 3, 6, 9, 12, 18, and 24 months of follow-up. Of the 21 patients, 13 consented to having a biopsy sample taken for investigative purposes from the area of implantation at 12 months of follow-up, allowing histologic assessment of the repair tissue.

RESULTS

A statistically significant clinical improvement became apparent after 6 months, and patients improved during the 24 months of follow-up. Adverse reactions to the alginate/fibrin matrix seeded with the allogenic cartilage cells were not observed. Histologic analysis of the biopsy specimens rated the repair tissue as hyaline-like in 15.3% of the samples, as mixed tissue in 46.2%, as fibrocartilage in 30.8%, and as fibrous in 7.7%.

CONCLUSION

The results of this short-term pilot study show that the alginate-based scaffold containing human mature allogenic chondrocytes is feasible and safe for the treatment of symptomatic cartilage defects of the knee. The described technique provides clinical and histologic outcomes that are equal but not superior to those of other cartilage repair techniques.

Paracrine effect of transplanted rib chondrocyte spheroids supports formation of secondary cartilage repair tissue

The study's objective was to investigate if transplanted chondrocyte or periosteal cell spheroids have influence on ingrowing bone marrow-derived cells in a novel cartilage repair approach in miniature pigs. Autologous rib chondrocytes or periosteal cells were cultured as spheroids and press-fitted into cavities that were milled into large, superficial chondral lesions of the patellar joint surface. Within the milled cavities, the subchondral bone plate was either penetrated or left intact (full-thickness or partial-thickness cavities). The transplantation of chondrocyte spheroids into full-thickness cavities induced the formation of additional secondary repair cartilage that exceeded the original volume of the transplanted spheroids. The resulting continuous tissue was rich in proteoglycans and stained positive for type II collagen. Cell labeling revealed that secondarily invading repair cells did not originate from transplanted spheroids, but rather from arroded bone marrow. However, secondary invasion of repair cells was less pronounced following transplantation of periosteal cells and absent in partial-thickness cavities. According to in vitro analyses, these observations could be ascribed to the ability of chondrocyte spheroids to secrete relevant amounts of bone morphogenetic protein-2, which was not detected for periosteal cells. Transplanted chondrocyte spheroids exert a dual function: they provide cells for the repair tissue and have a stimulatory paracrine activity, which promotes ingrowth and chondrogenesis of bone marrow-derived cells.

Immature porcine knee cartilage lesions show good healing with or without autologous chondrocyte transplantation

OBJECTIVE

The purpose of this study was to find out how deep chondral lesions heal in growing animals spontaneously and after autologous chondrocyte transplantation.

METHODS

A 6mm deep chondral lesion was created in the knee joints of 57 immature pigs and repaired with autologous chondrocyte transplantation covered with periosteum or muscle fascia, with periosteum only, or left untreated. After 3 and 12 months, the repair tissue was evaluated with International Cartilage Repair Society (ICRS) macroscopic grading, modified O'Driscoll histological scoring, and staining for collagen type II and hyaluronan, and with toluidine blue and safranin-O staining for glycosaminoglycans. The repair tissue structure was also examined with quantitative polarized light microscopy and indentation analysis of the cartilage stiffness.

RESULTS

The ICRS grading indicated nearly normal repair tissue in 65% (10/17) after the autologous chondrocyte transplantation and 86% (7/8) after no repair at 3 months. At 1 year, the repair tissue was nearly normal in all cases in the spontaneous repair group and in 38% (3/8) in the chondrocyte transplantation group. In most cases, the cartilage repair tissue stained intensely for glycosaminoglycans and collagen type II indicating repair tissue with true constituents of articular cartilage. There was a statistical difference in the total histological scores at 3 months (P=0.028) with the best repair in the spontaneous repair group. A marked subchondral bone reaction, staining with toluidine blue and collagen type II, was seen in 65% of all animals.

CONCLUSIONS

The spontaneous repair ability of full thickness cartilage defects of immature pigs is significant and periosteum or autologous chondrocytes do not bring any additional benefits to the repair.

A peek into the possible future of management of articular cartilage injuries: gene therapy and scaffolds for cartilage repair

Two rapidly progressing areas of research will likely contribute to cartilage repair procedures in the foreseeable future: gene therapy and synthetic scaffolds. Gene therapy refers to the transfer of new genetic information to cells that contribute to the cartilage repair process. This approach allows for manipulation of cartilage repair at the cellular and molecular level. Scaffolds are the core technology for the next generation of autologous cartilage implantation procedures in which synthetic matrices are used in conjunction with chondrocytes. This approach can be improved further using bioreactor technologies to enhance the production of extracellular matrix proteins by chondrocytes seeded onto a scaffold. The resulting "neo-cartilage implant" matures within the bioreactor, and can then be used to fill cartilage defects.

The Chondrocyte: Biology and Clinical Application

Chondrocyte is a unique cell type in articular cartilage tissue and is essential for cartilage formation and functionality. It arises from mesenchymal stem cells (MSCs) and is regulated by a series of cytokine and transcription factor interactions, including the transforming growth factor-beta super family, fibroblast growth factors, and insulin-like growth factor-1. To understand the biomechanisms of the chondrocyte differentiation process, various cellular model systems have been employed, such as primary chondrocyte culture, clonal normal cell lines (HCS-2/8, Ch-1, ATDC5, CFK-2, and RCJ3.1C5.18), and transformed clonal cell lines (T/C-28a2, T/C-28a4, C-28/I2, tsT/AC62, and HPV-16 E6/E7). Additionally, cell culture methods, including conventional monolayer culture, three-dimensional scaffold culture, bioreactor culture, pellet culture, and organ culture, have been established to create stable environments for the expansion, phenotypic maintenance, and subsequent biological study of chondrocytes for clinical application. Knowledge gained through these study systems has allowed for the use of chondrocytes in orthopedics for the treatment of cartilage injury and epiphyseal growth plate defects using tissue-engineering approaches. Furthermore, the potential of chondrocyte implantation for facial reconstruction, the treatment of long segmental tracheal defects, and urinary incontinence and vesicoureteral reflux are being investigated. This review summarizes the present study of chondrocyte biology and the potential uses of this cell in orthopedics and other disciplines.

The healing potential of the periosteum molecular aspects

The presence of pluripotential mesenchymal cells in the under surface of the periosteum in combination with growth factors regularly produced or released after injury, provide this unique tissue with an important role in the healing of bone and cartilage. The periosteum contributes in the secondary callus formation with cells and growth factors and should always be preserved and protected when surgery is performed for the management of a fracture. The current evidence about the cellular interactions, the stimulants and the signalling pathways related to osteogenesis and chondrogenesis is described. An essential knowledge of the basics related to the contribution of the periosteum in the healing of fractures, osteotomies, during the process of distraction osteogenesis and in some degree in the repair of cartilagenous defects, provides the surgeons with a better insight to understand the upcoming "biological" interventions in the management of skeletal injuries.

Cartilage repair: generations of autologous chondrocyte transplantation

Articular cartilage in adults has a limited capacity for self-repair after a substantial injury. Surgical therapeutic efforts to treat cartilage defects have focused on delivering new cells capable of chondrogenesis into the lesions. Autologous chondrocyte transplantation (ACT) is an advanced cell-based orthobiologic technology used for the treatment of chondral defects of the knee that has been in clinical use since 1987 and has been performed on 12,000 patients internationally. With ACT, good to excellent clinical results are seen in isolated post-traumatic lesions of the knee joint in the younger patient, with the formation of hyaline or hyaline-like repair tissue. In the classic ACT technique, chondrocytes are isolated from small slices of cartilage harvested arthroscopically from a minor weight-bearing area of the injured knee. The extracellular matrix is removed by enzymatic digestion, and the cells are then expanded in monolayer culture. Once a sufficient number of cells has been obtained, the chondrocytes are implanted into the cartilage defect, using a periosteal patch over the defect as a method of cell containment. The major complications are periosteal hypertrophy, delamination of the transplant, arthrofibrosis and transplant failure. Further improvements in tissue engineering have contributed to the next generation of ACT techniques, where cells are combined with resorbable biomaterials, as in matrix-associated autologous chondrocyte transplantation (MACT). These biomaterials secure the cells in the defect area and enhance their proliferation and differentiation.