Plasticity of clonal populations of dedifferentiated adult human articular chondrocytes

Tissue engineering strategies to study cartilage development, degeneration and regeneration

Cartilage tissue engineering has primarily focused on the generation of grafts to repair cartilage defects due to traumatic injury and disease. However engineered cartilage tissues have also a strong scientific value as advanced 3D culture models. Here we first describe key aspects of embryonic chondrogenesis and possible cell sources/culture systems for in vitro cartilage generation. We then review how a tissue engineering approach has been and could be further exploited to investigate different aspects of cartilage development and degeneration. The generated knowledge is expected to inform new cartilage regeneration strategies, beyond a classical tissue engineering paradigm.

Knockdown of the cell cycle inhibitor p21 enhances cartilage formation by induced pluripotent stem cells

The limited regenerative capacity of articular cartilage contributes to progressive joint dysfunction associated with cartilage injury or osteoarthritis. Cartilage tissue engineering seeks to provide a biological substitute for repairing damaged or diseased cartilage, but requires a cell source with the capacity for extensive expansion without loss of chondrogenic potential. In this study, we hypothesized that decreased expression of the cell cycle inhibitor p21 would enhance the proliferative and chondrogenic potential of differentiated induced pluripotent stem cells (iPSCs). Murine iPSCs were directed to differentiate toward the chondrogenic lineage with an established protocol and then engineered to express a short hairpin RNA (shRNA) to reduce the expression of p21. Cells expressing the p21 shRNA demonstrated higher proliferative potential during monolayer expansion and increased synthesis of glycosaminoglycans (GAGs) in pellet cultures. Furthermore, these cells could be expanded ∼150-fold over three additional passages without a reduction in the subsequent production of GAGs, while control cells showed reduced potential for GAG synthesis with three additional passages. In pellets from extensively passaged cells, knockdown of p21 attenuated the sharp decrease in cell number that occurred in control cells, and immunohistochemical analysis showed that p21 knockdown limited the production of type I and type X collagen while maintaining synthesis of cartilage-specific type II collagen. These findings suggest that manipulating the cell cycle can augment the monolayer expansion and preserve the chondrogenic capacity of differentiated iPSCs, providing a strategy for enhancing iPSC-based cartilage tissue engineering.

Bone-forming capacity of adult human nasal chondrocytes

Nasal chondrocytes (NC) derive from the same multipotent embryological segment that gives rise to the majority of the maxillofacial bone and have been reported to differentiate into osteoblast-like cells in vitro. In this study, we assessed the capacity of adult human NC, appropriately primed towards hypertrophic or osteoblastic differentiation, to form bone tissue in vivo. Hypertrophic induction of NC-based micromass pellets formed mineralized cartilaginous tissues rich in type X collagen, but upon implantation into subcutaneous pockets of nude mice remained avascular and reverted to stable hyaline-cartilage. In the same ectopic environment, NC embedded into ceramic scaffolds and primed with osteogenic medium only sporadically formed intramembranous bone tissue. A clonal study could not demonstrate that the low bone formation efficiency was related to a possibly small proportion of cells competent to become fully functional osteoblasts. We next tested whether the cues present in an orthotopic environment could induce a more efficient direct osteoblastic transformation of NC. Using a nude rat calvarial defect model, we demonstrated that (i) NC directly participated in frank bone formation and (ii) the efficiency of survival and bone formation by NC was significantly higher than that of reference osteogenic cells, namely bone marrow-derived mesenchymal stromal cells. This study provides a proof-of-principle that NC have the plasticity to convert into bone cells and thereby represent an easily available cell source to be further investigated for craniofacial bone regeneration.

Novel Perfused Compression Bioreactor System as an in vitro Model to Investigate Fracture Healing

Secondary bone fracture healing is a physiological process that leads to functional tissue regeneration via endochondral bone formation. In vivo studies have demonstrated that early mobilization and the application of mechanical loads enhances the process of fracture healing. However, the influence of specific mechanical stimuli and particular effects during specific phases of fracture healing remain to be elucidated. In this work, we have developed and provided proof-of-concept of an in vitro human organotypic model of physiological loading of a cartilage callus, based on a novel perfused compression bioreactor (PCB) system. We then used the fracture callus model to investigate the regulatory role of dynamic mechanical loading. Our findings provide a proof-of-principle that dynamic mechanical loading applied by the PCB can enhance the maturation process of mesenchymal stromal cells toward late hypertrophic chondrocytes and the mineralization of the deposited extracellular matrix. The PCB provides a promising tool to study fracture healing and for the in vitro assessment of alternative fracture treatments based on engineered tissue grafts or pharmaceutical compounds, allowing for the reduction of animal experiments.

Isolation and characterization of human mesenchymal stem cells derived from synovial fluid in patients with osteochondral lesion of the talus

BACKGROUND

Recently, mesenchymal stem cells (MSCs) have been suggested as a source for cell-based treatment of cartilage lesions based on the ability of these cells to differentiate into chondrocytes.

PURPOSE

To characterize MSCs derived from the synovial fluid in ankle joints with osteochondral lesion of the talus (OLT).

STUDY DESIGN

Controlled laboratory study.

METHODS

Synovial fluid was collected from the ankle joints of 28 patients with OLT who underwent arthroscopic marrow stimulation between September 2011 and April 2012. Epitope profiles and multilineage differentiation were assessed to characterize the synovial fluid MSCs. To clarify the origin of synovial fluid MSCs, we assessed gene profiles of MSCs derived from various mesenchymal tissues by reverse transcription-polymerase chain reaction (RT-PCR) analysis.

RESULTS

Synovial fluid MSCs expressed CD90 and CD105, showed low expression of CD14 and CD34, and underwent multilineage differentiation in vitro. The RT-PCR revealed strong expression of CD90, CD44, and CD73, whereas CD45 and CD133 were not detected. The colony number of synovial fluid MSCs from OLT significantly increased in stages C and D, as defined by arthroscopic classification. Gene expression profiles indicated that synovial fluid MSCs derived from the patients with OLT were more similar to MSCs from synovium than to MSCs from bone marrow and adipose tissue.

CONCLUSION

This study confirmed that human synovial fluid is a good source of MSCs, with the capacity to differentiate toward several cell lineages. Further study with matched controls of synovial fluid MSCs derived from ankle joints without OLT is required for a more accurate evaluation of synovial fluid MSCs.

CLINICAL RELEVANCE

The findings of this study provide a platform for exploring the potential role of synovial fluid MSCs in OLT and their therapeutic potential in novel joint regeneration strategies.

Origin and function of cartilage stem/progenitor cells in osteoarthritis

Articular cartilage is a physiologically non-self-renewing avascular tissue with a singular cell type, the chondrocyte, which functions as the load-bearing surface of the arthrodial joint. Injury to cartilage often progresses spatiotemporally from the articular surface to the subchondral bone, leading to development of degenerative joint diseases such as osteoarthritis (OA). Although lacking intrinsic reparative ability, articular cartilage has been shown to contain a population of stem cells or progenitor cells, similar to those found in many other adult tissues, that are thought to be involved in the maintenance of tissue homeostasis. These so-called cartilage-derived stem/progenitor cells (CSPCs) have been observed in human, equine and bovine articular cartilage, and have been identified, isolated and characterized on the basis of expression of stem-cell-related surface markers, clonogenicity and multilineage differentiation ability. However, the origin and functions of CSPCs are incompletely understood. We review here the current status of CSPC research and discuss the possible origin of these cells, what role they might have in cartilage repair, and their therapeutic potential in OA.

3D dynamic culture of rabbit articular chondrocytes encapsulated in alginate gel beads using spinner flasks for cartilage tissue regeneration

Cell-based therapy using chondrocytes for cartilage repair suffers from chondrocyte dedifferentiation. In the present study, the effects of an integrated three-dimensional and dynamic culture on rabbit articular chondrocytes were investigated. Cells (passages 1 and 4) were encapsulated in alginate gel beads and cultured in spinner flasks in chondrogenic and chondrocyte growth media. Subcutaneous implantation of the cell-laden beads was performed to evaluate the ectopic chondrogenesis. It was found that cells remained viable after 35 days in the three-dimensional dynamic culture. Passage 1 cells demonstrated a proliferative growth in both media. Passage 4 cells showed a gradual reduction in DNA content in growth medium, which was attenuated in chondrogenic medium. Deposition of glycosaminoglycans (GAG) was found in all cultures. While passage 1 cells generally produced higher amounts of GAG than passage 4 cells, GAG/DNA became similar on day 35 for both cells in growth media. Interestingly, GAG/DNA in growth medium was greater than that in chondrogenic medium for both cells. Based on GAG quantification and gene expression analysis, encapsulated passage 1 cells cultured in growth medium displayed the best ectopic chondrogenesis. Taken together, the three-dimensional and dynamic culture for chondrocytes holds great potential in cartilage regeneration.

An improved cartilage digestion method for research and clinical applications

Enzymatic isolation of chondrocytes from a cartilage biopsy is the first step to establish in vitro models of chondrogenesis or to generate cell-based grafts for cartilage repair. Such process is based on manually operated procedures and typically results in yields lower than 20% of the total available cells. In this study, we hypothesized that, as compared to conventionally used protocols, the enzymatic digestion of human articular cartilage in the presence of ascorbic acid 2-phosphate (AscA2P) or of sodium chloride (NaCl), in combination with the use of a perfusion bioreactor system, leads to a higher and more reproducible yield of cell populations with high proliferation and chondrogenic capacity. The addition of AscA2P within the enzymatic digestion medium did not significantly increase the cell yield, but resulted in a significant decrease of the intradonor variability in cell yield (-17.8% ± 10.7%, p = 0.0247) and in a significant increase of the proliferation rate of the isolated chondrocytes (+19.0% ± 1.4%, p < 0.05) with respect to the control group. The addition of NaCl during cartilage digestion did not modulate cell yield. When the cartilage digestion was further performed under direct perfusion flow, beneficial synergistic effects were achieved, with an overall increase of 34.7% ± 6.8% (p < 0.001) in the cell yield and an average decrease of 57.8% ± 11.2% (p < 0.01) in the coefficient of variation with respect to the control group. Importantly, by implementing this strategy it was possible to retrieve clonal subpopulations more efficiently capable of undergoing chondrogenesis, both in vitro and in vivo. Our findings bear relevance for the preparation of human chondrocytes for laboratory investigations, and in the perspective of efficient and streamlined manufacturing of cell/tissue grafts for articular cartilage repair.

Single cell sorting identifies progenitor cell population from full thickness bovine articular cartilage

OBJECTIVE

To date, no approved clinical intervention successfully prevents the progressive degradation of injured articular cartilage that leads to osteoarthritis (OA). Stem/progenitor cell populations within tissues of diarthrodial joint have shown their therapeutic potential in treating OA. However, this potential has not been fully realized due in part to the heterogeneity of these subpopulations. Characterization of clonal populations derived from a single cell may help identify more homogenous stem/progenitor populations within articular cartilage. Moreover, chondrogenic potential of clonal populations from different zones could be further examined to elucidate their differential roles in maintaining articular cartilage homeostasis.

METHOD

We combined Fluorescence-activated cell sorting (FACS) and clonogenicity screening to identify stem/progenitor cells cloned from single cells. High-efficiency colony-forming cells (HCCs) were isolated, and evaluated for stem/progenitor cell characteristics. HCCs were also isolated from different zones of articular cartilage. Their function was compared by lineage-specific gene expression, and differentiation potential.

RESULTS

A difference in colony-forming efficiency was observed in terms of colony sizes. HCCs were highly clonogenic and multipotent, and overexpressed stem/progenitor cell markers. Also, proliferation and migration associated genes were over-expressed in HCCs. HCCs showed zonal differences with deep HCCs more chondrogenic and osteogenic than superficial HCCs.

CONCLUSION

Our approach is a simple yet practical way to identify homogeneous stem/progenitor cell populations with clonal origin. The discovery of progenitor cells demonstrates the intrinsic self-repairing potential of articular cartilage. Differences in differentiation potential may represent the distinct roles of superficial and deep zone stem/progenitor cells in the maintenance of articular cartilage homeostasis.

Interleukin-1 beta and tumor necrosis factor alpha inhibit migration activity of chondrogenic progenitor cells from non-fibrillated osteoarthritic cartilage

Introduction

The repair capability of traumatized articular cartilage is highly limited so that joint injuries often lead to osteoarthritis. Migratory chondrogenic progenitor cells (CPC) might represent a target cell population for in situ regeneration. This study aims to clarify, whether 1) CPC are present in regions of macroscopically intact cartilage from human osteoarthritic joints, 2) CPC migration is stimulated by single growth factors and the cocktail of factors released from traumatized cartilage and 3) CPC migration is influenced by cytokines present in traumatized joints.

Methods

We characterized the cells growing out from macroscopically intact human osteoarthritic cartilage using a panel of positive and negative surface markers and analyzed their differentiation capacity. The migratory response to platelet-derived growth factor (PDGF)-BB, insulin-like growth factor 1 (IGF-1), supernatants obtained from in vitro traumatized cartilage and interleukin-1 beta (IL-1β) as well as tumor necrosis factor alpha (TNF-α) were tested with a modified Boyden chamber assay. The influence of IL-1β and TNF-α was additionally examined by scratch assays and outgrowth experiments.

Results

A comparison of 25 quadruplicate marker combinations in CPC and bone-marrow derived mesenchymal stromal cells showed a similar expression profile. CPC cultures had the potential for adipogenic, osteogenic and chondrogenic differentiation. PDGF-BB and IGF-1, such as the supernatant from traumatized cartilage, induced a significant site-directed migratory response. IL-1β and TNF-α significantly reduced basal cell migration and abrogated the stimulative effect of the growth factors and the trauma supernatant. Both cytokines also inhibited cell migration in the scratch assay and primary outgrowth of CPC from cartilage tissue. In contrast, the cytokine IL-6, which is present in trauma supernatant, did not affect growth factor induced migration of CPC.

Conclusion

These results indicate that traumatized cartilage releases chemoattractive factors for CPC but IL-1β and TNF-α inhibit their migratory activity which might contribute to the low regenerative potential of cartilage in vivo.

Expansion of human mesenchymal stromal cells from fresh bone marrow in a 3D scaffold-based system under direct perfusion

Mesenchymal stromal/stem cell (MSC) expansion in conventional monolayer culture on plastic dishes (2D) leads to progressive loss of functionality and thus challenges fundamental studies on the physiology of skeletal progenitors, as well as translational applications for cellular therapy and molecular medicine. Here we demonstrate that 2D MSC expansion can be entirely bypassed by culturing freshly isolated bone marrow nucleated cells within 3D porous scaffolds in a perfusion-based bioreactor system. The 3D-perfusion system generated a stromal tissue that could be enzymatically treated to yield CD45- MSC. As compared to 2D-expanded MSC (control), those derived from 3D-perfusion culture after the same time (3 weeks) or a similar extent of proliferation (7-8 doublings) better maintained their progenitor properties, as assessed by a 4.3-fold higher clonogenicity and the superior differentiation capacity towards all typical mesenchymal lineages. Transcriptomic analysis of MSC from 5 donors validated the robustness of the process and indicated a reduced inter-donor variability and a significant upregulation of multipotency-related gene clusters following 3D-perfusion--as compared to 2D-expansion. Interestingly, the differences in functionality and transcriptomics between MSC expanded in 2D or under 3D-perfusion were only partially captured by cytofluorimetric analysis using conventional surface markers. The described system offers a multidisciplinary approach to study how factors of a 3D engineered niche regulate MSC function and, by streamlining conventional labor-intensive processes, is prone to automation and scalability within closed bioreactor systems.

Rapid prototyped porous nickel-titanium scaffolds as bone substitutes

While calcium phosphate–based ceramics are currently the most widely used materials in bone repair, they generally lack tensile strength for initial load bearing. Bulk titanium is the gold standard of metallic implant materials, but does not match the mechanical properties of the surrounding bone, potentially leading to problems of fixation and bone resorption. As an alternative, nickel–titanium alloys possess a unique combination of mechanical properties including a relatively low elastic modulus, pseudoelasticity, and high damping capacity, matching the properties of bone better than any other metallic material. With the ultimate goal of fabricating porous implants for spinal, orthopedic and dental applications, nickel–titanium substrates were fabricated by means of selective laser melting. The response of human mesenchymal stromal cells to the nickel–titanium substrates was compared to mesenchymal stromal cells cultured on clinically used titanium. Selective laser melted titanium as well as surface-treated nickel–titanium and titanium served as controls. Mesenchymal stromal cells had similar proliferation rates when cultured on selective laser melted nickel–titanium, clinically used titanium, or controls. Osteogenic differentiation was similar for mesenchymal stromal cells cultured on the selected materials, as indicated by similar gene expression levels of bone sialoprotein and osteocalcin. Mesenchymal stromal cells seeded and cultured on porous three-dimensional selective laser melted nickel–titanium scaffolds homogeneously colonized the scaffold, and following osteogenic induction, filled the scaffold’s pore volume with extracellular matrix. The combination of bone-related mechanical properties of selective laser melted nickel–titanium with its cytocompatibility and support of osteogenic differentiation of mesenchymal stromal cells highlights its potential as a superior bone substitute as compared to clinically used titanium.

Chondrocyte and mesenchymal stem cell-based therapies for cartilage repair in osteoarthritis and related orthopaedic conditions

Osteoarthritis (OA) represents a final and common pathway for all major traumatic insults to synovial joints. OA is the most common form of degenerative joint disease and a major cause of pain and disability. Despite the global increase in the incidence of OA, there are no effective pharmacotherapies capable of restoring the original structure and function of damaged articular cartilage. Consequently cell-based and biological therapies for osteoarthritis (OA) and related orthopaedic disorders have become thriving areas of research and development. Autologous chondrocyte implantation (ACI) has been used for treatment of osteoarticular lesions for over two decades. Although chondrocyte-based therapy has the capacity to slow down the progression of OA and delay partial or total joint replacement surgery, currently used procedures are associated with the risk of serious adverse events. Complications of ACI include hypertrophy, disturbed fusion, delamination, and graft failure. Therefore there is significant interest in improving the success rate of ACI by improving surgical techniques and preserving the phenotype of the primary chondrocytes used in the procedure. Future tissue-engineering approaches for cartilage repair will also benefit from advances in chondrocyte-based repair strategies. This review article focuses on the structure and function of articular cartilage and the pathogenesis of OA in the context of the rising global burden of musculoskeletal disease. We explore the challenges associated with cartilage repair and regeneration using cell-based therapies that use chondrocytes and mesenchymal stem cells (MSCs). This paper also explores common misconceptions associated with cell-based therapy and highlights a few areas for future investigation.

Sonic hedgehog improves redifferentiation of dedifferentiated chondrocytes for articular cartilage repair

Sonic hedgehog (Shh) is involved in the induction of early cartilaginous differentiation of mesenchymal cells in the limb. We investigated whether Shh could promote redifferentiation of dedifferentiated chondrocytes and have a favorable effect on the regeneration of cartilage. Articular chondrocytes of rats were separated and cultured. The redifferentiation of dedifferentiated chondrocytes transfected with Shh was evaluated using monolayer and pellet culture system. The signaling molecules (Ptc 1, Gli 1 and Sox9) of the hedgehog pathway were investigated. A rat model of articular cartilage defect was used to evaluate cartilage repair after transplantation with dedifferentiated chondrocytes. After Shh gene transfer, the hedgehog pathway was upregulated in dedifferentiated chondrocytes. Real time-PCR and western blot analysis verified the stronger expression of Ptc1, Gli1 and Sox9 in Shh transfected cells. Shh upregulates the Shh signaling pathway and multiple cytokines (bone morphogenetic protein 2 and insulin-like growth factor 1) in dedifferentiated chondrocytes. After transplantation in the joint, histologic analysis of the regenerative tissues revealed that significantly better cartilage repair in rats transplanted with Shh transfected cells. These data suggest that Shh could induce redifferentiation of dedifferentiated chondrocytes through up-regulating Shh signaling pathway, and have considerable therapeutic potential in cartilage repair.

Growth factor priming differentially modulates components of the extracellular matrix proteome in chondrocytes and synovium-derived stem cells

To make progress in cartilage repair it is essential to optimize protocols for two-dimensional cell expansion. Chondrocytes and SDSCs are promising cell sources for cartilage repair. We previously observed that priming with a specific growth factor cocktail (1 ng/mL transforming growth factor-β1, 5 ng/mL basic fibroblast growth factor, and 10 ng/mL platelet-derived growth factor-BB) in two-dimensional culture, led to significant improvement in mechanical and biochemical properties of synovium-derived stem cell (SDSC)-seeded constructs. The current study assessed the effect of growth factor priming on the proteome of canine chondrocytes and SDSCs. In particular, growth factor priming modulated the proteins associated with the extracellular matrix in two-dimensional cultures of chondrocytes and SDSCs, inducing a partial dedifferentiation of chondrocytes (most proteins associated with cartilage were down-regulated in primed chondrocytes) and a partial differentiation of SDSCs (some collagen-related proteins were up-regulated in primed SDSCs). However, when chondrocytes and SDSCs were grown in pellet culture, growth factor-primed cells maintained their chondrogenic potential with respect to glycosaminoglycan and collagen production. In conclusion, the strength of the label-free proteomics technique is that it allows for the determination of changes in components of the extracellular matrix proteome in chondrocytes and SDSCs in response to growth factor priming, which could help in future tissue engineering strategies.

Matrix forming characteristics of inner and outer human meniscus cells on 3D collagen scaffolds under normal and low oxygen tensions

Background

Limited intrinsic healing potential of the meniscus and a strong correlation between meniscal injury and osteoarthritis have prompted investigation of surgical repair options, including the implantation of functional bioengineered constructs. Cell-based constructs appear promising, however the generation of meniscal constructs is complicated by the presence of diverse cell populations within this heterogeneous tissue and gaps in the information concerning their response to manipulation of oxygen tension during cell culture.

Methods

Four human lateral menisci were harvested from patients undergoing total knee replacement. Inner and outer meniscal fibrochondrocytes (MFCs) were expanded to passage 3 in growth medium supplemented with basic fibroblast growth factor (FGF-2), then embedded in porous collagen type I scaffolds and chondrogenically stimulated with transforming growth factor β3 (TGF-β3) under 21% (normal or normoxic) or 3% (hypoxic) oxygen tension for 21 days. Following scaffold culture, constructs were analyzed biochemically for glycosaminoglycan production, histologically for deposition of extracellular matrix (ECM), as well as at the molecular level for expression of characteristic mRNA transcripts.

Results

Constructs cultured under normal oxygen tension expressed higher levels of collagen type II (p = 0.05), aggrecan (p < 0.05) and cartilage oligomeric matrix protein, (COMP) (p < 0.05) compared to hypoxic expanded and cultured constructs. Accumulation of ECM rich in collagen type II and sulfated proteoglycan was evident in normoxic cultured scaffolds compared to those under low oxygen tension. There was no significant difference in expression of these genes between scaffolds seeded with MFCs isolated from inner or outer regions of the tissue following 21 days chondrogenic stimulation (p > 0.05).

Conclusions

Cells isolated from inner and outer regions of the human meniscus demonstrated equivalent differentiation potential toward chondrogenic phenotype and ECM production. Oxygen tension played a key role in modulating the redifferentiation of meniscal fibrochondrocytes on a 3D collagen scaffold in vitro.

Non-adherent mesenchymal progenitors from adipose tissue stromal vascular fraction

In primary human bone marrow cultures, the initial adherent cell fraction has been shown to provide a microenvironment for self-renewal of primitive non-adherent mesenchymal progenitors (non-adherent progenitors of bone marrow stroma [BM-NAMP]), with increased differentiation potential compared to adherent colony-forming units-fibroblast (CFU-f). The present study investigates whether NAMP exist also in cultures of stromal vascular fraction (SVF) cells derived from human adipose tissue. Adipose-tissue NAMP (AT-NAMP) were shown to be stably non-adherent and their number correlated with the number of the initial adhering CFU-f. Unlike BM-NAMP, AT-NAMP did not propagate in suspension in serial replating experiments and the number of colonies steadily decreased with each replating step. However, when AT-NAMP were kept on the initially adhering SVF cells, they could significantly expand without loss of clonogenic, proliferation, and differentiation potential. Although AT-NAMP progeny differentiated into mesodermal lineages similar to that of adherent CFU-f, it was enriched in early mesenchymal progenitor populations, characterized by increased expression of SSEA-4 and CD146. Furthermore, FGF-2 supported AT-NAMP survival and could not be replaced by another mitogenic factor, such as platelet derived growth factor BB. In conclusion, these data suggest that the SVF adherent fraction provides niche signals that regulate the expansion of adipose non-adherent mesenchymal progenitors with the maintenance of their potency. The biological differences described between BM- and AT-NAMP further qualify the properties of the stroma from different tissues and will be relevant for the selection of a cell source for specific regeneration strategies.

Retropatellar fat pad-derived stem cells from older osteoarthritic patients have lesser differentiation capacity and expression of stemness genes

BACKGROUND AIMS

The use of retropatellar fat pad-derived mesenchymal stromal cells (RFMSCs) for cell-based therapy, particularly for cartilage repair, has been reported by several investigators in recent years. However, the effects of the donor's age and medical condition on the characteristics of RFMSCs have not been well established. The aim of this study was to determine whether age and medical condition can reduce the multipotential of stem cells isolated from the retropatellar fat pad.

METHODS

The RFMSCs were isolated from patients with osteoarthritic knee cartilage (degenerative group; 40-60 years old) and compared with patients without degenerative knee disease (young group; <40 years old) in terms of their growth kinetics, immunophenotype, differentiation ability and stemness gene expression.

RESULTS

Data showed that RFMSCs from both groups have similar growth kinetics and immunophenotype profile at passage 3. However, RFMSCs from the degenerative group showed lower adipogenic, osteogenic and chondrogenic differentiation ability compared with RFMSCs derived from the young group. The stemness gene expression level of RFMSCs derived from the degenerative group was lower than that in the young group. RFMSCs from both groups met the minimum criteria of mesenchymal stromal cells and have the potential for cartilage regeneration. However, RFMSCs from the degenerative group showed lower regeneration capability.

CONCLUSIONS

These results indicate that older age and osteoarthritic condition did affect the multipotential of stem cells derived from the retropatellar fat pad under the current prescribed condition. More studies will be conducted to clarify whether the age or medical condition contributed more to the loss of differentiation capacity and stemness gene expression of RFMSCs.

Influence of cartilage extracellular matrix molecules on cell phenotype and neocartilage formation

Interaction between chondrocytes and the cartilage extracellular matrix (ECM) is essential for maintaining the cartilage's role as a low-friction and load-bearing tissue. In this study, we examined the influence of cartilage zone-specific ECM on human articular chondrocytes (HAC) in two-dimensional and three-dimensional (3D) environments. Two culture systems were used. SYSTEM 1: HAC were cultured on cell-culture plates that had been precoated with the following ECM molecules for 7 days: decorin, biglycan, tenascin C (superficial zone), collagen type II, hyaluronan (HA) (middle and deep zones), and osteopontin (deep zone). Uncoated standard culture plates were used as controls. Expanded cells were examined for phenotypic changes using real-time polymerase chain reaction. In addition, expanded cells were placed into high-density pellet cultures for 14 days. Neocartilage formation was assessed via gene expression and histology evaluations. SYSTEM 2: HAC that were cultured on untreated plates and encapsulated in a 3D alginate scaffold were mixed with one of the zone-specific ECM molecules. Cell viability, gene expression, and histology assessments were conducted on 14-day-old tissues. In HAC monolayer culture, exposure to decorin, HA, and osteopontin increased COL2A1 and aggrecan messenger RNA (mRNA) levels compared with controls. Biglycan up-regulated aggrecan without a significant impact on COL2A1 expression; Tenascin C reduced COL2A1 expression. Neocartilage formed after preculture on tenascin C and collagen type II expressed higher COL2A1 mRNA compared with control pellets. Preculture of HAC on HA decreased both COL2A1 and aggrecan expression levels compared with controls, which was consistent with histology. Reduced proteoglycan 4 (PRG4) mRNA levels were observed in HAC pellets that had been precultured with biglycan and collagen type II. Exposing HAC to HA directly in 3D-alginate culture most effectively induced neocartilage formation, showing increased COL2A1 and aggrecan, and reduced COL1A1 compared with controls. Decorin treatments increased HAC COL2A1 mRNA levels. These data indicate that an appropriate exposure to cartilage-specific ECM proteins could be used to enhance cartilage formation and to even induce the formation of zone-specific phenotypes to improve cartilage regeneration.

Beneficial effects of autologous bone marrow-derived mesenchymal stem cells in naturally occurring tendinopathy

Tendon injuries are a common age-related degenerative condition where current treatment strategies fail to restore functionality and normal quality of life. This disease also occurs naturally in horses, with many similarities to human tendinopathy making it an ideal large animal model for human disease. Regenerative approaches are increasingly used to improve outcome involving mesenchymal stem cells (MSCs), supported by clinical data where injection of autologous bone marrow derived MSCs (BM-MSCs) suspended in marrow supernatant into injured tendons has halved the re-injury rate in racehorses. We hypothesized that stem cell therapy induces a matrix more closely resembling normal tendon than the fibrous scar tissue formed by natural repair. Twelve horses with career-ending naturally-occurring superficial digital flexor tendon injury were allocated randomly to treatment and control groups. 1X10(7) autologous BM-MSCs suspended in 2 ml of marrow supernatant were implanted into the damaged tendon of the treated group. The control group received the same volume of saline. Following a 6 month exercise programme horses were euthanized and tendons assessed for structural stiffness by non-destructive mechanical testing and for morphological and molecular composition. BM-MSC treated tendons exhibited statistically significant improvements in key parameters compared to saline-injected control tendons towards that of normal tendons and those in the contralateral limbs. Specifically, treated tendons had lower structural stiffness (p<0.05) although no significant difference in calculated modulus of elasticity, lower (improved) histological scoring of organisation (p<0.003) and crimp pattern (p<0.05), lower cellularity (p<0.007), DNA content (p<0.05), vascularity (p<0.03), water content (p<0.05), GAG content (p<0.05), and MMP-13 activity (p<0.02). Treatment with autologous MSCs in marrow supernatant therefore provides significant benefits compared to untreated tendon repair in enhancing normalisation of biomechanical, morphological, and compositional parameters. These data in natural disease, with no adverse findings, support the use of this treatment for human tendon injuries.

Articular cartilage-derived cells hold a strong osteogenic differentiation potential in comparison to mesenchymal stem cells in vitro

Cartilaginous matrix-degenerative diseases like osteoarthritis (OA) are characterized by gradual cartilage erosion, and also by increased presence of cells with mesenchymal stem cell (MSC) character within the affected tissues. Moreover, primary chondrocytes long since are known to de-differentiate in vitro and to be chondrogenically re-differentiable. Since both findings appear to conflict with each other, we quantitatively assessed the mesenchymal differentiation potential of OA patient cartilage-derived cells (CDC) towards the osteogenic and adipogenic lineage in vitro and compared it to that of MSC isolated from adipose tissue (adMSC) of healthy donors. We analyzed expression of MSC markers CD29, CD44, CD105, and CD166, and, following osteogenic and adipogenic induction in vitro, quantified their expression of osteogenic and adipogenic differentiation markers. Furthermore, CDC phenotype and proliferation were monitored. We found that CDC exhibit an MSC CD marker expression pattern similar to adMSC and a similar increase in proliferation rate during osteogenic differentiation. In contrast, the marked reduction of proliferation observed during adipogenic differentiation of adMSC was absent in CDC. Quantification of differentiation markers revealed a strong osteogenic differentiation potential for CDC, however almost no capacity for adipogenic differentiation. Since in the pathogenesis of OA, cartilage degeneration coincides with high bone turnover rates, the high osteogenic differentiation potential of OA patient-derived CDC may affect clinical therapeutic regimens aiming at autologous cartilage regeneration in these patients.

Applied osmotic loading for promoting development of engineered cartilage

This study investigated the potential use of static osmotic loading as a cartilage tissue engineering strategy for growing clinically relevant grafts from either synovium-derived stem cells (SDSCs) or chondrocytes. Bovine SDSCs and chondrocytes were individually encapsulated in 2% w/v agarose and divided into chondrogenic media of osmolarities 300 (hypotonic), 330 (isotonic), and 400 (hypertonic, physiologic) mOsM for up to 7 weeks. The application of hypertonic media to constructs comprised of SDSCs or chondrocytes led to increased mechanical properties as compared to hypotonic (300mOsM) or isotonic (330mOsM) media (p<0.05). Constant exposure of SDSC-seeded constructs to 400mOsM media from day 0 to day 49 yielded a Young's modulus of 513±89kPa and GAG content of 7.39±0.52%ww on day 49, well within the range of values of native, immature bovine cartilage. Primary chondrocyte-seeded constructs achieved almost as high a Young's modulus, reaching 487±187kPa and 6.77±0.54%ww (GAG) for the 400mOsM condition (day 42). These findings suggest hypertonic loading as a straightforward strategy for 3D cultivation with significant benefits for cartilage tissue engineering strategies. In an effort to understand potential mechanisms responsible for the observed response, cell volume measurements in response to varying osmotic conditions were evaluated in relation to the Boyle-van't Hoff (BVH) law. Results confirmed that chondrocytes behave as perfect osmometers; however SDSCs deviated from the BVH relation.

Mesenchymal stem cells and their chondrogenic differentiated and dedifferentiated progeny express chemokine receptor CCR9 and chemotactically migrate toward CCL25 or serum

INTRODUCTION

Guided migration of chondrogenically differentiated cells has not been well studied, even though it may be critical for growth, repair, and regenerative processes. The chemokine CCL25 is believed to play a critical role in the directional migration of leukocytes and stem cells. To investigate the motility effect of serum- or CCL25-mediated chemotaxis on chondrogenically differentiated cells, mesenchymal stem cells (MSCs) were induced to chondrogenic lineage cells.

METHODS

MSC-derived chondrogenically differentiated cells were characterized for morphology, histology, immunohistochemistry, quantitative polymerase chain reaction (qPCR), surface profile, and serum- or CCL25-mediated cell migration. Additionally, the chemokine receptor, CCR9, was examined in different states of MSCs.

RESULTS

The chondrogenic differentiated state of MSCs was positive for collagen type II and Alcian blue staining, and showed significantly upregulated expression of COL2A1and SOX9, and downregulated expression of CD44, CD73, CD90, CD105 and CD166, in contrast to the undifferentiated and dedifferentiated states of MSCs. For the chondrogenic differentiated, undifferentiated, and dedifferentiated states of MSCs, the serum-mediated chemotaxis was in a percentage ratio of 33%:84%:85%, and CCL25-mediated chemotaxis was in percentage ratio of 12%:14%:13%, respectively. On the protein level, CCR9, receptor of CCL25, was expressed in the form of extracellular and intracellular domains. On the gene level, qPCR confirmed the expression of CCR9 in different states of MSCs.

CONCLUSIONS

CCL25 is an effective cue to guide migration in a directional way. In CCL25-mediated chemotaxis, the cell-migration rate was almost the same for different states of MSCs. In serum-mediated chemotaxis, the cell-migration rate of chondrogenically differentiated cells was significantly lower than that in undifferentiated or dedifferentiated cells. Current knowledge of the surface CD profile and cell migration could be beneficial for regenerative cellular therapies.

The potential for stem cells in cerebral palsy--piecing together the puzzle

The substantial socioeconomic burden of a diagnosis of cerebral palsy, coupled with a positive anecdotal and media spin on stem cell treatments, drives many affected families to seek information and treatment outside of the current clinical and scientific realm. Preclinical studies using several types of stem and adult cells--including mesenchymal stem cells, neural precursor cells, olfactory ensheathing glia and Schwann cells--have demonstrated some regenerative and functional efficacy in neurologic paradigms. This paper describes the most common cell types investigated for transplant in vivo and summarizes the current state of early-phase clinical trials. It investigates the most relevant and promising coadministered therapies, including rehabilitation, drug targeting, magnetic stimulation, and bioengineering approaches. We highlight the need for adjunctive combinatorial strategies to successfully transfer stem cell treatments from bench to bedside.

Enhancing post-expansion chondrogenic potential of costochondral cells in self-assembled neocartilage

The insufficient healing capacity of articular cartilage necessitates mechanically functional biologic tissue replacements. Using cells to form biomimetic cartilage implants is met with the challenges of cell scarcity and donor site morbidity, requiring expanded cells that possess the ability to generate robust neocartilage. To address this, this study assesses the effects of expansion medium supplementation (bFGF, TFP, FBS) and self-assembled construct seeding density (2, 3, 4 million cells/5 mm dia. construct) on the ability of costochondral cells to generate biochemically and biomechanically robust neocartilage. Results show TFP (1 ng/mL TGF-β1, 5 ng/mL bFGF, 10 ng/mL PDGF) supplementation of serum-free chondrogenic expansion medium enhances the post-expansion chondrogenic potential of costochondral cells, evidenced by increased glycosaminoglycan content, decreased type I/II collagen ratio, and enhanced compressive properties. Low density (2 million cells/construct) enhances matrix synthesis and tensile and compressive mechanical properties. Combined, TFP and Low density interact to further enhance construct properties. That is, with TFP, Low density increases type II collagen content by over 100%, tensile stiffness by over 300%, and compressive moduli by over 140%, compared with High density. In conclusion, the interaction of TFP and Low density seeding enhances construct material properties, allowing for a mechanically functional, biomimetic cartilage to be formed using clinically relevant costochondral cells.

Stage-specific embryonic antigen-4 is not a marker for chondrogenic and osteogenic potential in cultured chondrocytes and mesenchymal progenitor cells

One important challenge for regenerative medicine is to produce a clinically relevant number of cells with consistent tissue-forming potential. Isolation and expansion of cells from skeletal tissues results in a heterogeneous population of cells with variable regenerative potential. A more consistent tissue formation could be achieved by identification and selection of potent progenitors based on cell surface molecules. In this study, we assessed the expression of stage-specific embryonic antigen-4 (SSEA-4), a classic marker of undifferentiated stem cells, and other surface markers in human articular chondrocytes (hACs), osteoblasts, and bone marrow-derived mesenchymal stromal cells (bmMSCs) and characterized their differentiation potential. Further, we sorted SSEA-4-expressing hACs and followed their potential to proliferate and to form cartilage in vitro. Cells isolated from cartilage and bone exhibited remarkably heterogeneous SSEA-4 expression profiles in expansion cultures. SSEA-4 expression levels increased up to ∼5 population doublings, but decreased following further expansion and differentiation cultures; levels were not related to the proliferation state of the cells. Although SSEA-4-sorted chondrocytes showed a slightly better chondrogenic potential than their SSEA-4-negative counterparts, differences were insufficient to establish a link between SSEA-4 expression and chondrogenic potential. SSEA-4 levels in bmMSCs also did not correlate to the cells' chondrogenic and osteogenic potential in vitro. SSEA-4 is clearly expressed by subpopulations of proliferating somatic cells with a MSC-like phenotype. However, the predictive value of SSEA-4 as a specific marker of superior differentiation capacity in progenitor cell populations from adult human tissue and even its usefulness as a stem cell marker appears questionable.

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.

Mesenchymal stem cell: keystone of the hematopoietic stem cell niche and a stepping-stone for regenerative medicine

Mesenchymal stem cells (MSCs) are self-renewing precursor cells that can differentiate into bone, fat, cartilage, and stromal cells of the bone marrow. Recent studies suggest that MSCs themselves are critical for forming a niche that maintains hematopoietic stem cells (HSCs). The ease by which human MSC-like and stromal progenitor cells can be isolated from the bone marrow and other tissues has led to the rapid development of clinical investigations exploring their anti-inflammatory properties, tissue preservation capabilities, and regenerative potential. However, the identity of genuine MSCs and their specific contributions to these various beneficial effects have remained enigmatic. In this article, we examine the definition of MSCs and discuss the importance of rigorously characterizing their stem cell activity. We review their role and that of other putative niche constituents in the regulation of bone marrow HSCs. Additionally, how MSCs and their stromal progeny alter immune function is discussed, as well as potential therapeutic implications.

Generation of Scaffold Free 3-D Cartilage-Like Microtissues from Human Chondrocytes

Since our society is characterized by an increasing age of its people on the one hand and a high number of persons dealing with sports on the other hand, the number of patients suffering from traumatic defects or osteoarthritis is growing. In combination with the articular cartilage specific limited capacity to regenerate, a need for suitable therapies is obvious. Thereby, cell-based therapies are of major interest. This type of clinical intervention was introduced to patients at the beginning of the 1990s. During the last years, a technological shift from simple cell suspensions to more complex 3D structures was performed. In order to optimize the scaffold free generation of cartilage, such as microtissues from human chondrocytes, the authors examine the influence of a static or spinner flask culture with respect to differentiation and architecture of the engineered microtissues. Additionally, the impact of the soluble factors TGF-ß2 and ascorbic acid on this process are investigated. The results demonstrate a positive impact of TGF-ß2 and ascorbic acid supplementation with respect to general Type II Collagen and proteoglycan expression for both the static and spinner flask culture.

A reliable protocol for the isolation of viable, chondrogenically differentiated human mesenchymal stem cells from high-density pellet cultures

Administration of chondrogenically differentiated mesenchymal stem cells (MSC) is discussed as a promising approach for the regenerative treatment of injured or diseased cartilage. The high-density pellet culture is the standard culture for chondrogenic differentiation, but cells in pellets secrete extracellular matrix (ECM) that they become entrapped in. Protocols for cell isolation from pellets often result in cell damage and dedifferentiation towards less differentiated MSC. Therefore, our aim was to develop a reliable protocol for the isolation of viable, chondrogenically differentiated MSC from high-density pellet cultures. Human bone marrow MSC were chondrogenically stimulated with transforming growth factor-β3, and the cartilaginous structure of the pellets was verified by alcian blue staining of cartilage proteoglycans, antibody staining of cartilage collagen type II, and quantitative real-time reverse-transcription polymerase chain reaction of the marker genes COL2A1 and SOX9. Trypsin and collagenases II and P were tested alone or in combination, and for different concentrations and times, to find a protocol for optimized pellet digestion. Whereas trypsin was not able to release viable cells, 90-min digestion with 300 U of collagenase II, 20 U of collagenase P, and 2 mM CaCl2 worked quite well and resulted in about 2.5×10(5) cells/pellet. The protocol was further optimized for the separation of released cells and ECM from each other. Cells were alcian blue and collagen type II positive and expressed COL2A1 and SOX9, verifying a chondrogenic character. However, they had different morphological shapes. The ECM was also uniformly alcian blue and collagen type II positive but showed different organizational and structural forms. To conclude, our protocol allows the reliable isolation of a defined number of viable, chondrogenically differentiated MSC from high-density pellet cultures. Such cells, as well as the ECM components, are of interest as research tools and for cartilage tissue engineering.

Increased adipogenesis in cultured embryonic chondrocytes and in adult bone marrow of dominant negative Erg transgenic mice

In monolayer culture, primary articular chondrocytes have an intrinsic tendency to lose their phenotype during expansion. The molecular events underlying this chondrocyte dedifferentiation are still largely unknown. Several transcription factors are important for chondrocyte differentiation. The Ets transcription factor family may be involved in skeletal development. One family member, the Erg gene, is mainly expressed during cartilage formation. To further investigate the potential role of Erg in the maintenance of the chondrocyte phenotype, we isolated and cultured chondrocytes from the rib cartilage of embryos of transgenic mice that express a dominant negative form of Erg (DN-Erg) during cartilage formation. DN-Erg expression in chondrocytes cultured for up to 20 days did not affect the early dedifferentiation usually observed in cultured chondrocytes. However, lipid droplets accumulated in DN-Erg chondrocytes, suggesting adipocyte emergence. Transcriptomic analysis using a DNA microarray, validated by quantitative RT-PCR, revealed strong differential gene expression, with a decrease in chondrogenesis-related markers and an increase in adipogenesis-related gene expression in cultured DN-Erg chondrocytes. These results indicate that Erg is involved in either maintaining the chondrogenic phenotype in vitro or in cell fate orientation. Along with the in vitro studies, we compared adipocyte presence in wild-type and transgenic mice skeletons. Histological investigations revealed an increase in the number of adipocytes in the bone marrow of adult DN-Erg mice even though no adipocytes were detected in embryonic cartilage or bone. These findings suggest that the Ets transcription factor family may contribute to the homeostatic balance in skeleton cell plasticity.

Cell sources for the regeneration of articular cartilage: the past, the horizon and the future

Avascular, aneural articular cartilage has a low capacity for self-repair and as a consequence is highly susceptible to degradative diseases such as osteoarthritis. Thus the development of cell-based therapies that repair focal defects in otherwise healthy articular cartilage is an important research target, aiming both to delay the onset of degradative diseases and to decrease the need for joint replacement surgery. This review will discuss the cell sources which are currently being investigated for the generation of chondrogenic cells. Autologous chondrocyte implantation using chondrocytes expanded ex vivo was the first chondrogenic cellular therapy to be used clinically. However, limitations in expansion potential have led to the investigation of adult mesenchymal stem cells as an alternative cell source and these therapies are beginning to enter clinical trials. The chondrogenic potential of human embryonic stem cells will also be discussed as a developmentally relevant cell source, which has the potential to generate chondrocytes with phenotype closer to that of articular cartilage. The clinical application of these chondrogenic cells is much further away as protocols and tissue engineering strategies require additional optimization. The efficacy of these cell types in the regeneration of articular cartilage tissue that is capable of withstanding biomechanical loading will be evaluated according to the developing regulatory framework to determine the most appropriate cellular therapy for adoption across an expanding patient population.

TGFβ inhibition during expansion phase increases the chondrogenic re-differentiation capacity of human articular chondrocytes

OBJECTIVE

Autologous chondrocyte implantation is a cell-based treatment to repair articular cartilage defects, relying on the availability of expanded (de-differentiated) chondrocytes. Unfortunately, the expansion process causes several phenotypical changes, requiring re-establishment of the native chondrogenic phenotype to sustain proper repair. Among other proteins, transforming growth factor-β (TGFβ) is known to influence the chondrogenic re-differentiation of human articular chondrocytes (HACs) and their matrix deposition. Thus we investigated the effects of TGFβ-depletion during the expansion phase.

DESIGN

HACs were isolated from articular cartilage and expanded in the canonical serum-supplemented medium [fetal calf serum (FCS)] or in a chemically-defined (CD) medium, with or without anti-TGFβ antibody administration. The re-differentiation potential of the cells was assessed by pellet cultures, gene expression analysis and histology.

RESULTS

Cell proliferation proceeded more rapidly in CD-medium than in FCS-medium; it was not affected by the use of anti-TGFβ antibody but was further increased by addition of exogenous TGFβ1, via increased p-Smad1/5/8. Conversely, in FCS-medium, addition of anti-TGFβ antibody decreased both proliferation and p-Smad1/5/8 level. Challenging either FCS- or CD-medium with anti-TGFβ antibody during expansion enhanced chondrogenesis in the subsequent pellet cultures. Moreover, TGFβ-depletion during expansion in CD-medium inhibited mRNA expression of hypertrophic markers, collagen type-X (COL10) and matrix metalloproteinase-13 (MMP-13). Interestingly, the TGFβ1 level detected by enzyme-linked immunosorbent sandwich assay (ELISA) during cell expansion was correlated with COL10 mRNA expression after re-differentiation.

CONCLUSION

TGFβ-depletion during expansion improves the re-differentiation capacity of chondrocytes and inhibits hypertrophy. These results indicate the importance of the expansion medium composition to improve chondrogenic re-differentiation and to inhibit hypertrophy.

Effect of collagen type I or type II on chondrogenesis by cultured human articular chondrocytes

INTRODUCTION

Current cartilage repair procedures using autologous chondrocytes rely on a variety of carriers for implantation. Collagen types I and II are frequently used and valuable properties of both were shown earlier in vitro, although a preference for either was not demonstrated. Recently, however, fibrillar collagens were shown to promote cartilage degradation. The goal of this study was to evaluate the effects of collagen type I and type II coating on chondrogenic properties of in vitro cultured human chondrocytes, and to investigate if collagen-mediated cartilage degradation occurs.

METHODS

Human chondrocytes of eight healthy cartilage donors were isolated, expanded, and cultured on culture well inserts coated with either collagen type I, type II, or no coating (control). After 28 days of redifferentiation culture, safranin O and immunohistochemical staining for collagen types I, II, X, and Runx2/Cbfa1 were performed and glycosaminoglycan (GAG) and DNA content and release were examined. Further, expression of collagen type I, type II, type X, MMP13, Runx2/Cbfa1, DDR2, α2 and β1 integrin were examined by reverse transcriptase-polymerase chain reaction.

RESULTS

The matrix, created by chondrocytes grown on collagen type I- and II-coated membranes, resembled cartilage more than when grown on noncoated membranes as reflected by histological scoring. Immunohistochemical staining did not differ between the conditions. GAG content as well as GAG/DNA were higher for collagen type II-coated cartilage constructs than control. GAG release was also higher on collagen type I- and II-coated constructs. Expression of collagen type X was higher of chondrocytes grown on collagen type II compared to controls, but no collagen X protein could be demonstrated by immunohistochemistry. No effects of collagen coating on DDR2 nor MMP-13 gene expression were found. No differences were observed between collagen types I and II.

CONCLUSION

Chondrocyte culture on collagen type I or II promotes more active matrix production and turnover. No significant differences between collagen types I and II were observed, nor were hypertrophic changes more evident in either condition. The use of collagen type I or II coating for in vitro models, thus, seems a sound basis for in vivo repair procedures.

[Cell-based therapy options for osteochondral defects. Autologous mesenchymal stem cells compared to autologous chondrocytes]

Cartilage defects are multifactorial and site-specific and therefore need a clear analysis of the underlying pathology as well as an individualized therapy so that cartilage repair lacks a one-for-all therapy. The results of comparative clinical studies using cultured chondrocytes in autologous chondrocyte implantation (ACI) have shown some superiority over conventional microfracturing under defined conditions, especially for medium or large defects and in long-term durability. Adult mesenchymal stem cells can be isolated from bone marrow, have the potency to proliferate in culture and are capable of differentiating into the chondrogenic pathway. They represent a promising versatile cell source for cartilage repair but the ideal conditions for cultivation and application in cartilage repair are not yet known or have not yet been characterized. Adding a scaffold offers mechanical stability and advances chondrogenic differentiation for both possible cell sources.

Oriented lamellar silk fibrous scaffolds to drive cartilage matrix orientation: towards annulus fibrosus tissue engineering

A novel design of silk-based scaffold is developed using a custom-made winding machine, with fiber alignment resembling the anatomical criss-cross lamellar fibrous orientation features of the annulus fibrosus of the intervertebral disc. Crosslinking of silk fibroin fibers with chondroitin sulphate (CS) was introduced to impart superior biological functionality. The scaffolds, with or without CS, instructed alignment of expanded human chondrocytes and of the deposited extracellular matrix while supporting their chondrogenic redifferentiation. The presence of CS crosslinking could not induce statistically significant changes in the measured collagen or glycosaminoglycan content, but resulted in an increased construct stiffness. By offering the combined effect of cell/matrix alignment and chondrogenic support, the silk fibroin scaffolds developed with precise fiber orientation in lamellar form represent a suitable substrate for tissue engineering of the annulus fibrosus part of the intervertebral disc.

BLOOD-DERIVED, TISSUE ENGINEERING BIOMATERIALS

Fibrin sealant and platelet gels are human blood-derived, biodegradable, non toxic, surgical products obtained by mixing a fibrinogen concentrate or a platelet rich plasma with thrombin, respectively. Fibrin sealant is now a well known surgical tool increasingly used to stop or control bleeding, or to provide air and fluid tightness in many surgical situations. Platelet gels are newly developed preparations that are of specific interest because they contain numerous physiological growth factors and cytikines that are released upon the activation of blood platelets by thrombin. These growth factors, including PDGF, TGF-β 1, BMP, and VEGF have been shown to stimulate cell growth and differentiation with special clinical benefits for soft and bony tissue healing and regeneration. Platelet gels allow surgeons to manipulate the cellular environment of surgical sites and to guide tissue regeneration. A specific interest of such products is observed for the induction of osteogenesis and chondrogenesis. Advances in the preparation, clinical use, and safety of these two important classes of blood-derived biomaterials are reviewed.

Enhancing the biological performance of synthetic polymeric materials by decoration with engineered, decellularized extracellular matrix

Materials based on synthetic polymers can be extensively tailored in their physical properties but often suffer from limited biological functionality. Here we tested the hypothesis that the biological performance of 3D synthetic polymer-based scaffolds can be enhanced by extracellular matrix (ECM) deposited by cells in vitro and subsequently decellularized. The hypothesis was tested in the context of bone graft substitutes, using polyesterurethane (PEU) foams and mineralized ECM laid by human mesenchymal stromal cells (hMSC). A perfusion-based bioreactor system was critically employed to uniformly seed and culture hMSC in the scaffolds and to efficiently decellularize (94% DNA reduction) the resulting ECM while preserving its main organic and inorganic components. As compared to plain PEU, the decellularized ECM-polymer hybrids supported the osteoblastic differentiation of newly seeded hMSC by up-regulating the mRNA expression of typical osteoblastic genes (6-fold higher bone sialoprotein; 4-fold higher osteocalcin and osteopontin) and increasing calcium deposition (6-fold higher), approaching the performance of ceramic-based materials. After ectopic implantation in nude mice, the decellularized hybrids induced the formation of a mineralized matrix positively immunostained for bone sialoprotein and resembling an immature osteoid tissue. Our findings consolidate the perspective of bioreactor-based production of ECM-decorated polymeric scaffolds as off-the-shelf materials combining tunable physical properties with the physiological presentation of instructive biological signals.

Validation of an automated procedure to isolate human adipose tissue-derived cells by using the Sepax® technology

The stromal vascular fraction of adipose tissue has gained popularity as a source of autologous progenitor cells for tissue engineering and regenerative medicine applications. The aim of this study was to validate a newly developed, automated procedure to isolate adipose-derived mesenchymal stem/stromal cells (ASCs) from adult human lipoaspirates in a closed and clinical-grade device, based on the Sepax(®) technology. Using a total of 11 donors, this procedure was compared with the standard operator-based manual separation in terms of isolation yield, clonogenic fraction, phenotype, and differentiation potential of ASCs. As compared with the manual process, automation resulted in a 62% higher isolation yield, with 2.6±1.2×10(5) nucleated cells per mL of liposuction, and a 24% higher frequency of clonogenic progenitors. The variability in the isolation yield and clonogenicity across different preparations was reduced by 18% and 50%, respectively. The cytofluorimetric profile and in vitro differentiation capacity into mesenchymal lineages were comparable in the cells isolated using the two procedures. The new Sepax-based process thus allows an efficient isolation of ASCs with higher and more reproducible yields than the standard manual procedure, along with minimal operator intervention. These results are expected to facilitate the use of ASCs for clinical purposes, either within an intraoperative setting or in combination with further in vitro cell expansion/cultivation.