Micromass co-culture of human articular chondrocytes and human bone marrow mesenchymal stem cells to investigate stable neocartilage tissue formation in vitro

Sesamin encouraging effects on chondrogenic differentiation of human amniotic fluid-derived mesenchymal stem cells

Worldwide, the most recognized musculoskeletal degenerative disease is osteoarthritis (OA). Sesamin, a major abundant lignan compound present in Sesamun Indicum Linn, has been described for its various pharmacological effects and health benefits. However, the promoting effects of sesamin on chondrogenic differentiation have not yet been observed. Herein, the aim of this study was to investigate the effects of sesamin on cell cytotoxicity and the potent supporting effects on chondrogenic differentiation of human amniotic fluid-derived mesenchymal stem cells (hAF-MSCs). The results indicated that sesamin was not toxic to hAF-MSCs after sesamin treatment. When treating the cells with a combination of sesamin and inducing factors, sesamin was able to up-regulate the expression level of specific genes which play an essential role during the cartilage development process, including SOX9, AGC, COL2A1, COL11A1, and COMP and also simultaneously promote the cartilage extracellular protein synthesis, aggrecan and type II collagen. Additionally, histological analysis revealed a high amount of accumulated sGAG staining inside the porous scaffold in the sesamin co-treating group. In conclusion, the results of this study have indicated that sesamin can be considered a chondrogenic inducing factor and a beneficial dietary supplement for cartilage repair.

Microfluidic Technology for the Generation of Cell Spheroids and Their Applications

A three-dimensional (3D) tissue model has significant advantages over the conventional two-dimensional (2D) model. A 3D model mimics the relevant in-vivo physiological conditions, allowing a cell culture to serve as an effective tool for drug discovery, tissue engineering, and the investigation of disease pathology. The present reviews highlight the recent advances and the development of microfluidics based methods for the generation of cell spheroids. The paper emphasizes on the application of microfluidic technology for tissue engineering including the formation of multicellular spheroids (MCS). Further, the paper discusses the recent technical advances in the integration of microfluidic devices for MCS-based high-throughput drug screening. The review compares the various microfluidic techniques and finally provides a perspective for the future opportunities in this research area.

Endochondral Priming: A Developmental Engineering Strategy for Bone Tissue Regeneration

Tissue engineering and regenerative medicine have significant potential to treat bone pathologies by exploiting the capacity for bone progenitors to grow and produce tissue constituents under specific biochemical and physical conditions. However, conventional tissue engineering approaches, which combine stem cells with biomaterial scaffolds, are limited as the constructs often degrade, due to a lack of vascularization, and lack the mechanical integrity to fulfill load bearing functions, and as such are not yet widely used for clinical treatment of large bone defects. Recent studies have proposed that in vitro tissue engineering approaches should strive to simulate in vivo bone developmental processes and, thereby, imitate natural factors governing cell differentiation and matrix production, following the paradigm recently defined as "developmental engineering." Although developmental engineering strategies have been recently developed that mimic specific aspects of the endochondral ossification bone formation process, these findings are not widely understood. Moreover, a critical comparison of these approaches to standard biomaterial-based bone tissue engineering has not yet been undertaken. For that reason, this article presents noteworthy experimental findings from researchers focusing on developing an endochondral-based developmental engineering strategy for bone tissue regeneration. These studies have established that in vitro approaches, which mimic certain aspects of the endochondral ossification process, namely the formation of the cartilage template and the vascularization of the cartilage template, can promote mineralization and vascularization to a certain extent both in vitro and in vivo. Finally, this article outlines specific experimental challenges that must be overcome to further exploit the biology of endochondral ossification and provide a tissue engineering construct for clinical treatment of large bone/nonunion defects and obviate the need for bone tissue graft.

Repair of cartilage defects in osteoarthritis rats with induced pluripotent stem cell derived chondrocytes

Background

The incapacity of articular cartilage (AC) for self-repair after damage ultimately leads to the development of osteoarthritis. Stem cell-based therapy has been proposed for the treatment of osteoarthritis (OA) and induced pluripotent stem cells (iPSCs) are becoming a promising stem cell source.

Results

Three steps were developed to differentiate human iPSCs into chondrocytes which were transplanted into rat OA models induced by monosodium iodoacetate (MIA). After 6 days embryonic body (EB) formation and 2 weeks differentiation, the gene and protein expression of Col2A1, GAG and Sox9 has significantly increased compare to undifferentiated hiPSCs. After 15 weeks transplantation, no immune responses were observed, micro-CT showed gradual engraftment and the improvement of subchondrol plate integrity, and histological examinations demonstrated articular cartilage matrix production.

Conclusions

hiPSC could be an efficient and clinically translatable approach for cartilage tissue regeneration in OA cartilages.

Effect of Transplanting Various Concentrations of a Composite of Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells and Hyaluronic Acid Hydrogel on Articular Cartilage Repair in a Rabbit Model

Background

Mesenchymal stem cells (MSCs) are known to have therapeutic potential for cartilage repair. However, the optimal concentration of MSCs for cartilage repair remains unclear. Therefore, we aimed to explore the feasibility of cartilage repair by human umbilical cord blood-derived MSCs (hUCB-MSCs) and to determine the optimal concentrations of the MSCs in a rabbit model.

Methods

Osteochondral defects were created in the trochlear groove of femur in 55 rabbits. Four experimental groups (11 rabbits/group) were treated by transplanting the composite of hUCB-MSCs and HA with various MSCs concentrations (0.1, 0.5, 1.0, and 1.5 x 10⁷ cells/ml). One control group was left untreated. At 4, 8, and 16 weeks post-transplantation, the degree of cartilage repair was evaluated grossly and histologically.

Findings

Overall, transplanting hUCB-MSCs and HA hydrogel resulted in cartilage repair tissue with better quality than the control without transplantation (P = 0.015 in 0.1, P = 0.004 in 0.5, P = 0.004 in 1.0, P = 0.132 in 1.5 x 10⁷ cells/ml). Interestingly, high cell concentration of hUCB-MSCs (1.5×10⁷ cells/ml) was inferior to low cell concentrations (0.1, 0.5, and 1.0 x 10⁷ cells/ml) in cartilage repair (P = 0.394,P = 0.041, P = 0.699, respectively). The 0.5 x 10⁷ cells/ml group showed the highest cartilage repair score at 4, 8 and 16 weeks post transplantation, and followed by 0.1x10⁷ cells/ml group or 1.0 x 10⁷ cell/ml group.

Conclusions

The results of this study suggest that transplantation of the composite of hUCB-MSCs and HA is beneficial for cartilage repair. In addition, this study shows that optimal MSC concentration needs to be determined for better cartilage repair.

Osteogenic Differentiation of Mesenchymal Stem Cells by Mimicking the Cellular Niche of the Endochondral Template

In vitro bone regeneration strategies that prime mesenchymal stem cells (MSCs) with chondrogenic factors, to mimic aspects of the endochondral ossification process, have been shown to promote mineralization and vascularization by MSCs both in vitro and when implanted in vivo. However, these approaches required the use of osteogenic supplements, namely dexamethasone, ascorbic acid, and β-glycerophosphate, none of which are endogenous mediators of bone formation in vivo. Rather MSCs, endothelial progenitor cells, and chondrocytes all reside in proximity within the cartilage template and might paracrineally regulate osteogenic differentiation. Thus, this study tests the hypothesis that an in vitro bone regeneration approach that mimics the cellular niche existing during endochondral ossification, through coculture of MSCs, endothelial cells, and chondrocytes, will obviate the need for extraneous osteogenic supplements and provide an alternative strategy to elicit osteogenic differentiation of MSCs and mineral production. The specific objectives of this study were to (1) mimic the cellular niche existing during endochondral ossification and (2) investigate whether osteogenic differentiation could be induced without the use of any external growth factors. To test the hypothesis, we evaluated the mineralization and vessel formation potential of (a) a novel methodology involving both chondrogenic priming and the coculture of human umbilical vein endothelial cells (HUVECs) and MSCs compared with (b) chondrogenic priming of MSCs alone, (c) addition of HUVECs to chondrogenically primed MSC aggregates, (d-f) the same experimental groups cultured in the presence of osteogenic supplements and (g) a noncoculture group cultured in the presence of osteogenic growth factors alone. Biochemical (DNA, alkaline phosphatase [ALP], calcium, CD31⁺, vascular endothelial growth factor [VEGF]), histological (alcian blue, alizarin red), and immunohistological (CD31⁺) analyses were conducted to investigate osteogenic differentiation and vascularization at various time points (1, 2, and 3 weeks). The coculture methodology enhanced both osteogenesis and vasculogenesis compared with osteogenic differentiation alone, whereas osteogenic supplements inhibited the osteogenesis and vascularization (ALP, calcium, and VEGF) induced through coculture alone. Taken together, these results suggest that chondrogenic and vascular priming can obviate the need for osteogenic supplements to induce osteogenesis of human MSCs in vitro, while allowing for the formation of rudimentary vessels.

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

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

Mesenchymal Stem Cells Reshape and Provoke Proliferation of Articular Chondrocytes by Paracrine Secretion

Coculture between mesenchymal stem cells (MSCs) and articular chondrocytes (ACs) represents a promising strategy for cartilage regeneration. This study aimed at elaborating how ACs were regulated by MSCs. Rabbit ACs (rACs) and rabbit MSCs (rMSCs) were seeded separately in a Transwell system to initiate non-contact coculture in growth medium without chondrogenic factors. Cell morphology, cell proliferation, production of extracellular matrix (ECM), and gene expression of rACs were characterized. Upon coculture, rACs underwent a morphological transition from a rounded or polygonal shape into a fibroblast-like one and proliferation was provoked simultaneously. Such effects were dependent on the amount of rMSCs. Along with these changes, ECM production and gene expression of rACs were also perturbed. Importantly, when a ROCK inhibitor (Y27632) was supplemented to coculture, the effects except that on cell proliferation were inhibited, suggesting the involvement of RhoA/ROCK signaling. By applying an inhibitor (BIBF1120) of VEGFR1/2/3, FGFR1/2/3 and PDGFRα/β in coculture, or supplementing FGF-1, VEGF-A and PDGFbb in monoculture, it was confirmed that the paracrine factors by rMSCs mediated the compounding effects on rACs. These findings shed light on MSCs-ACs interactions and might confer an insight view on cell-based cartilage regeneration.

Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells Contribute to Chondrogenesis in Coculture with Chondrocytes

Human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) have been shown as the most potential stem cell source for articular cartilage repair. In this study, we aimed to develop a method for long-term coculture of human articular chondrocytes (hACs) and hUCB-MSCs at low density in vitro to determine if the low density of hACs could enhance the hUCB-MSC chondrogenic differentiation as well as to determine the optimal ratio of the two cell types. Also, we compared the difference between direct coculture and indirect coculture at low density. Monolayer cultures of hUCB-MSCs and hACs were investigated at different ratios, at direct cell-cell contact groups for 21 days. Compared to direct coculture, hUCB-MSCs and hACs indirect contact culture significantly increased type II collagen (COL2) and decreased type I collagen (COL1) protein expression levels. SRY-box 9 (SOX9) mRNA levels and protein expression were highest in indirect coculture. Overall, these results indicate that low density direct coculture induces fibrocartilage. However, indirect coculture in conditioned chondrocyte cell culture medium can increase expression of chondrogenic markers and induce hUCB-MSCs differentiation into mature chondrocytes. This work demonstrates that it is possible to promote chondrogenesis of hUCB-MSCs in combination with hACs, further supporting the concept of novel coculture strategies for tissue engineering.

Chondrocytes, Mesenchymal Stem Cells, and Their Combination in Articular Cartilage Regenerative Medicine

Articular cartilage (AC) is a highly organized connective tissue lining, covering the ends of bones within articulating joints. Its highly ordered structure is essential for stable motion and provides a frictionless surface easing load transfer. AC is vulnerable to lesions and, because it is aneural and avascular, it has limited self-repair potential which often leads to osteoarthritis. To date, no fully successful treatment for osteoarthritis has been reported. Thus, the development of innovative therapeutic approaches is desperately needed. Autologous chondrocyte implantation, the only cell-based surgical intervention approved in the United States for treating cartilage defects, has limitations because of de-differentiation of articular chondrocytes (AChs) upon in vitro expansion. De-differentiation can be abated if initial populations of AChs are co-cultured with mesenchymal stem cells (MSCs), which not only undergo chondrogenesis themselves but also support chondrocyte vitality. In this review we summarize studies utilizing AChs, non-AChs, and MSCs and compare associated outcomes. Moreover, a comprehensive set of recent human studies using chondrocytes to direct MSC differentiation, MSCs to support chondrocyte re-differentiation and proliferation in co-culture environments, and exploratory animal intra- and inter-species studies are systematically reviewed and discussed in an innovative manner allowing side-by-side comparisons of protocols and outcomes. Finally, a comprehensive set of recommendations are made for future studies.

Modulating stem cell–chondrocyte interactions for cartilage repair using combinatorial extracellular matrix-containing hydrogels

Combinatorial ECM-containing hydrogels with decoupled mechanical and biochemical cues modulate cartilage formation by a stem cell and chondrocyte co-culture in 3D.

Generation of three-dimensional multiple spheroid model of olfactory ensheathing cells using floating liquid marbles

We describe a novel protocol for three-dimensional culturing of olfactory ensheathing cells (OECs), which can be used to understand how OECs interact with other cells in three dimensions. Transplantation of OECs is being trialled for repair of the paralysed spinal cord, with promising but variable results and thus the therapy needs improving. To date, studies of OEC behaviour in a multicellular environment have been hampered by the lack of suitable three-dimensional cell culture models. Here, we exploit the floating liquid marble, a liquid droplet coated with hydrophobic powder and placed on a liquid bath. The presence of the liquid bath increases the humidity and minimises the effect of evaporation. Floating liquid marbles allow the OECs to freely associate and interact to produce OEC spheroids with uniform shapes and sizes. In contrast, a sessile liquid marble on a solid surface suffers from evaporation and the cells aggregate with irregular shapes. We used floating liquid marbles to co-culture OECs with Schwann cells and astrocytes which formed natural structures without the confines of gels or bounding layers. This protocol can be used to determine how OECs and other cell types associate and interact while forming complex cell structures.

Direct Cell-Cell Contact with Chondrocytes Is a Key Mechanism in Multipotent Mesenchymal Stromal Cell-Mediated Chondrogenesis

Using a combination of articular chondrocytes (ACs) and mesenchymal stromal cells (MSCs) has shown to be a viable option for a single-stage cell-based treatment of focal cartilage defects. However, there is still considerable debate whether MSCs differentiate or have a chondroinductive role through trophic factors. In addition, it remains unclear whether direct cell-cell contact is necessary for chondrogenesis. Therefore, the aim of this study was to investigate whether direct or indirect cell-cell contact between ACs and MSCs is essential for increased cartilage production in different cellular environments and elucidate the mechanisms behind these cellular interactions. Human ACs and MSCs were cultured in a 10:90 ratio in alginate beads, fibrin scaffolds, and pellets. Cells were mixed in direct cocultures, separated by a Transwell filter (indirect cocultures), or cultured with conditioned medium. Short tandem repeat analysis revealed that the percentages of ACs increased during culture, while those of MSCs decreased, with the biggest change in fibrin glue scaffolds. For alginate, where the lack of cell-cell contact could be confirmed by histological analysis, no difference was found in matrix production between direct and indirect cocultures. For fibrin scaffolds and pellet cultures, an increased glycosaminoglycan production and type II collagen deposition were found in direct cocultures compared with indirect cocultures and conditioned medium. Positive connexin 43 staining and transfer of cytosolic calcein indicated communication through gap junctions in direct cocultures. Taken together, these results suggest that MSCs stimulate cartilage formation when placed in close proximity to chondrocytes and that direct cell-cell contact and communication through gap junctions are essential in this chondroinductive interplay.

Cartilage Repair Using Composites of Human Umbilical Cord Blood-Derived Mesenchymal Stem Cells and Hyaluronic Acid Hydrogel in a Minipig Model

The cartilage regeneration potential of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs) with a hyaluronic acid (HA) hydrogel composite has shown remarkable results in rat and rabbit models. The purpose of the present study was to confirm the consistent regenerative potential in a pig model using three different cell lines. A full-thickness chondral injury was intentionally created in the trochlear groove of each knee in 6 minipigs. Three weeks later, an osteochondral defect, 5 mm wide by 10 mm deep, was created, followed by an 8-mm-wide and 5-mm-deep reaming. A mixture (1.5 ml) of hUCB-MSCs (0.5×10(7) cells per milliliter) and 4% HA hydrogel composite was then transplanted into the defect on the right knee. Each cell line was used in two minipigs. The osteochondral defect created in the same manner on the left knee was untreated to act as the control. At 12 weeks postoperatively, the pigs were sacrificed, and the degree of subsequent cartilage regeneration was evaluated by gross and histological analysis. The transplanted knee resulted in superior and more complete hyaline cartilage regeneration compared with the control knee. The cellular characteristics (e.g., cellular proliferation and chondrogenic differentiation capacity) of the hUCB-MSCs influenced the degree of cartilage regeneration potential. This evidence of consistent cartilage regeneration using composites of hUCB-MSCs and HA hydrogel in a large animal model could be a stepping stone to a human clinical trial in the future.

SIGNIFICANCE

To date, several studies have investigated the chondrogenic potential of human umbilical cord blood-derived mesenchymal stem cells (hUCB-MSCs); however, the preclinical studies are still limited in numbers with various results. In parallel, in the past several years, the cartilage regeneration potential of hUCB-MSCs with a hyaluronic acid (HA) hydrogel composite have been investigated and remarkable results in rat and rabbit models have been attained. (These experimental results are currently in preparation for publication.) Before applying the cartilage regeneration technique in a human clinical trial, it seemed necessary to confirm the consistent result in a larger animal model. At 12 weeks postoperatively, the minipigs were sacrificed, and the degree of subsequent cartilage regeneration was evaluated by gross and histological analysis. The transplanted knee resulted in superior and more complete hyaline cartilage regeneration compared with the control knee. This evidence of consistent cartilage regeneration with composites of hUCB-MSCs and HA hydrogel in a large animal model could be a stepping stone to a human clinical trial in the future.

Study on viability and chondrogenic differentiation of cryopreserved adipose tissue-derived mesenchymal stromal cells for future use in regenerative medicine

Adipose-derived mesenchymal stromal cells are promising as a regenerative therapy tool for defective tissues in mesenchymal lineage, including fat, bone, cartilage, and blood vessels. In potential future clinical applications, adipose-derived stem cell cryopreservation is an essential fundamental technology. The aim of this study is to define an adequate protocol for the cryopreservation of adipose-derived mesenchymal stromal cells, by comparing various protocols so as to determine the effects of cryopreservation on viability and chondrogenic differentiation potential of adipose-derived stem cells upon freeze-thawing of AT-MSCs colonies cryopreserved with standard and modified protocols, using flow cytometry and confocal microscopy. The study concludes that adipose-derived mesenchymal stromal cells could be long-term cryopreserved without any loss of their proliferative or differentiation potential.

Platelet-rich concentrates differentially release growth factors and induce cell migration in vitro

BACKGROUND

Platelet-rich concentrates are used as a source of growth factors to improve the healing process. The diverse preparation protocols and the gaps in knowledge of their biological properties complicate the interpretation of clinical results.

QUESTIONS/PURPOSES

In this study we aimed to (1) analyze the concentration and kinetics of growth factors released from leukocyte- and platelet-rich fibrin (L-PRF), leukocyte- and platelet-rich plasma (L-PRP), and natural blood clot during in vitro culture; (2) investigate the migration of mesenchymal stem cells (MSCs) and human umbilical vein endothelial cells (HUVECs) as a functional response to the factors released; and (3) uncover correlations between individual growth factors with the initial platelet/leukocyte counts or the induced cell migration.

METHODS

L-PRF, L-PRP, and natural blood clot prepared from 11 donors were cultured in vitro for 28 days and media supernatants collected after 8 hours and 1, 3, 7, 14, and 28 days. Released transforming growth factor β1 (TGF-β1), vascular endothelial growth factor (VEGF), insulin growth factor (IGF-1), platelet-derived growth factor AB (PDGF-AB), and interleukin-1β (IL-1β) were measured in the supernatants with enzyme-linked immunosorbent assay. Migration of MSC and HUVEC induced by the supernatants was evaluated in Boyden chambers.

RESULTS

More TGF-ß1 was released (mean ± SD in pg/mL of blood) from L-PRF (37,796 ± 5492) compared with L-PRP (23,738 ± 6848; p < 0.001) and blood clot (3739 ± 4690; p < 0.001), whereas more VEGF and IL-1ß were released from blood clot (1933 ± 704 and 2053 ± 908, respectively) compared with both L-PRP (642 ± 208; p < 0.001 and 273 ± 386; p < 0.001, respectively) and L-PRF (852 ± 376; p < 0.001 and 65 ± 56, p < 0.001, respectively). No differences were observed in IGF-1 and PDGF-AB released from any of the concentrates. TGF-β1 release peaked at Day 7 in L-PRF and at 8 hours and Day 7 in L-PRP and 8 hours and Day 14 in blood clot. In all concentrates, main release of VEGF occurred between 3 and 7 days and of IL-1β between Days 1 and 7. IGF-1 and PDGF-AB were released until Day 1 in L-PRP and blood clot, in contrast to sustained release over the first 3 days in L-PRF. The strongest migration of MSC occurred in response to L-PRF, and more HUVEC migration was seen in L-PRF and blood clot compared with L-PRP. TGF-β1 correlated with initial platelet counts in L-PRF (Pearson r = 0.66, p = 0.0273) and initial leukocyte counts in L-PRP (Pearson r = 0.83, p = 0.0016). A positive correlation of IL-1β on migration of MSC and HUVEC was revealed (Pearson r = 0.16, p = 0.0208; Pearson r = 0.31, p < 0.001).

CONCLUSIONS

In comparison to L-PRP, L-PRF had higher amounts of released TGF-β1, a long-term release of growth factors, and stronger induction of cell migration. Future preclinical studies should confirm these data in a defined injury model.

CLINICAL RELEVANCE

By characterizing the biologic properties of different platelet concentrates in vitro, we may gain a better understanding of their clinical effects and develop guidelines for specific future applications.

Poly(γ-Glutamic Acid) as an Exogenous Promoter of Chondrogenic Differentiation of Human Mesenchymal Stem/Stromal Cells

Cartilage damage and/or aging effects can cause constant pain, which limits the patient's quality of life. Although different strategies have been proposed to enhance the limited regenerative capacity of cartilage tissue, the full production of native and functional cartilaginous extracellular matrix (ECM) has not yet been achieved. Poly(γ-glutamic acid) (γ-PGA), a naturally occurring polyamino acid, biodegradable into glutamate residues, has been explored for tissue regeneration. In this work, γ-PGA's ability to support the production of cartilaginous ECM by human bone marrow mesenchymal stem/stromal cells (MSCs) and nasal chondrocytes (NCs) was investigated. MSC and NC pellets were cultured in basal medium (BM), chondrogenic medium (CM), and CM-γ-PGA-supplemented medium (CM+γ-PGA) over a period of 21 days. Pellet size/shape was monitored with time. At 14 and 21 days of culture, the presence of sulfated glycosaminoglycans (sGAGs), type II collagen (Col II), Sox-9, aggrecan, type XI collagen (Col XI), type X collagen (Col X), calcium deposits, and type I collagen (Col I) was analyzed. After excluding γ-PGA's cytotoxicity, earlier cell condensation, higher sGAG content, Col II, Sox-9 (day 14), aggrecan, and Col X (day 14) production was observed in γ-PGA-supplemented MSC cultures, with no signs of mineralization or Col I. These effects were not evident with NCs. However, Sox-9 (at day 14) and Col X (at days 14 and 21) were increased, decreased, or absent, respectively. Overall, γ-PGA improved chondrogenic differentiation of MSCs, increasing ECM production earlier in culture. It is proposed that γ-PGA incorporation in novel biomaterials has a beneficial impact on future approaches for cartilage regeneration.

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.

Fabrication of multi-well chips for spheroid cultures and implantable constructs through rapid prototyping techniques

Three-dimensional (3D) culture models are widely used in basic and translational research. In this study, to generate and culture multiple 3D cell spheroids, we exploited laser ablation and replica molding for the fabrication of polydimethylsiloxane (PDMS) multi-well chips, which were validated using articular chondrocytes (ACs). Multi-well ACs spheroids were comparable or superior to standard spheroids, as revealed by glycosaminoglycan and type-II collagen deposition. Moreover, the use of our multi-well chips significantly reduced the operation time for cell seeding and medium refresh. Exploiting a similar approach, we used clinical-grade fibrin to generate implantable multi-well constructs allowing for the precise distribution of multiple cell types. Multi-well fibrin constructs were seeded with ACs generating high cell density regions, as shown by histology and cell fluorescent staining. Multi-well constructs were compared to standard constructs with homogeneously distributed ACs. After 7 days in vitro, expression of SOX9, ACAN, COL2A1, and COMP was increased in both constructs, with multi-well constructs expressing significantly higher levels of chondrogenic genes than standard constructs. After 5 weeks in vivo, we found that despite a dramatic size reduction, the cell distribution pattern was maintained and glycosaminoglycan content per wet weight was significantly increased respect to pre-implantation samples. In conclusion, multi-well chips for the generation and culture of multiple cell spheroids can be fabricated by low-cost rapid prototyping techniques. Furthermore, these techniques can be used to generate implantable constructs with defined architecture and controlled cell distribution, allowing for in vitro and in vivo investigation of cell interactions in a 3D environment.

Subcutaneous Adipose Tissue-Derived Stem Cell Utility Is Independent of Anatomical Harvest Site

One of the challenges for tissue engineering and regenerative medicine is to obtain suitably large cell numbers for therapy. Mesenchymal stem cells (MSCs) can easily be expanded in vitro to obtain large numbers of cells, but this approach may induce cellular senescence. The characteristics of cells are dependent on variables like age, body mass index (BMI), and disease conditions, however, and in the case of adipose tissue-derived stem cells (ASCs), anatomical harvest site is also an important variable that can affect the regenerative potential of isolated cells. We therefore had kept the parameters (age, BMI, disease conditions) constant in this study to specifically assess influence of anatomical sites of individual donors on utility of ASCs. Adipose tissue was obtained from multiple anatomical sites in individual donors, and viability and nucleated cell yield were determined. MSC frequency was enumerated using colony forming unit assay and cells were characterized by flow cytometry. Growth characteristics were determined by long-term population doubling analysis of each sample. Finally, MSCs were induced to undergo adipogenic, osteogenic, and chondrogenic differentiation. To validate the findings, these results were compared with similar single harvest sites from multiple individual patients. The results of the current study indicated that MSCs obtained from multiple harvest sites in a single donor have similar morphology and phenotype. All adipose depots in a single donor exhibited similar MSC yield, viability, frequency, and growth characteristics. Equivalent differentiation capacity into osteocytes, adipocytes, and chondrocytes was also observed. On the basis of results, we conclude that it is acceptable to combine MSCs obtained from various anatomical locations in a single donor to obtain suitably large cell numbers required for therapy, avoiding in vitro senescence and lengthy and expensive in vitro culturing and expansion steps.

In vivo tracking and fate of intra-articularly injected superparamagnetic iron oxide particle-labeled multipotent stromal cells in an ovine model of osteoarthritis

In this study, superparamagnetic iron oxide (SPIO) particle-labeled mesenchymal stromal cells (MSCs) were injected intra-articularly into osteoarthritic knee joints. Their fate and distribution were evaluated using magnetic resonance imaging (MRI) and macroscopic and histologic postmortem examination. Osteoarthritis was induced in 12 sheep by bilateral meniscectomy. After 6 weeks, one knee joint received 10 × 10(6) SPIO-labeled MSCs (Molday Ion Rhodamine B). Contralateral knees received a control injection of a) PBS, b) SPIO in PBS, c) 10 × 10(6) nonvital SPIO-labeled MSCs in PBS, or d) no injection. MR images were acquired immediately after injection and 1, 4, 8, and 12 weeks thereafter using a 0.5-T unit and a T2* sequence. Signal intensity of synovial fluid and synovial lining was assessed semiquantitatively using a scoring system. Viable SPIO-labeled MSCs produced a strong hypointense signal in the synovial fluid immediately after injection, but normal signal intensity of the synovial fluid was observed 1 week later. Synovial lining maintained its hypointensity throughout the study period. Nonvital SPIO-labeled MSCs induced hypointense signals of the synovial fluid; synovial lining appeared weak and inconsistently hypointense in the following weeks. Pure SPIO produced a strong hyperintense signal in the synovial fluid at the time of injection only. Histologically, in all knee joints receiving viable SPIO-labeled MSCs, SPIO particles were detected (Prussian blue) within the synovial lining, dorsal fat pad, and neomeniscus tissue, but not in osteochondral samples. Few SPIO particles were detected in joints injected with nonvital SPIO-labeled MSCs. Immunohistologically, no increased cell death (TUNEL) was observed in the area of detected SPIO particles, but we did observe potential chondrogenic cell differentiation (Safranin O or S100β). We conclude that viable SPIO-labeled MSCs remain detectable within the joint for 12 weeks and attach themselves to some but not all diseased joint structures.

Enhanced cell-induced articular cartilage regeneration by chondrons; the influence of joint damage and harvest site

OBJECTIVE

Interactions between chondrocytes and their native pericellular matrix provide optimal circumstances for regeneration of cartilage. However, cartilage diseases such as osteoarthritis change the pericellular matrix, causing doubt to them as a cell source for autologous cell therapy.

METHODS

Chondrons and chondrocytes were isolated from stifle joints of goats in which cartilage damage was surgically induced in the right knee. After 4 weeks of regeneration culture, DNA content and proteoglycan and collagen content and release were determined.

RESULTS

The cartilage regenerated by chondrons isolated from the damaged joint contained less proteoglycans and collagen compared to chondrons from the same harvest site in the nonoperated knee (P < 0.01). Besides, chondrons still reflected whether they were isolated from a damaged joint, even if they where isolated from the opposing or adjacent condyle. Although chondrocytes did not reflect this diseased status of the joint, chondrons always outperformed chondrocytes, even when isolated from the damaged joints (P < 0.0001). Besides increased cartilage production, the chondrons showed less collagenase activity compared to the chondrocytes.

CONCLUSION

Chondrons still outperform chondrocytes when they were isolated from a damaged joint and they might be a superior cell source for articular cartilage repair and cell-induced cartilage formation.

Icariin promotes directed chondrogenic differentiation of bone marrow mesenchymal stem cells but not hypertrophy in vitro

Icariin (ICA), a Traditional Chinese Medicine, has been demonstrated to be a promoting compound for extracellular matrix synthesis and gene expression of chondrocytes. However, whether ICA can act as a substitute for or cooperate with growth factors to directly promote stable chondrogenesis of bone marrow mesenchymal stem cells (BMSCs) remains unknown. In the present study, rat BMSCs were cultivated in monolayer cultures with a chondrogenic medium containing transforming growth factor-β3 for 14 days; ICA was added to the same chondrogenic medium throughout the culture period at a concentration of 1×10⁻⁶ M. Cell morphology was observed using an inverted microscope, and chondrogenic differentiation markers, including collagen II, aggrecan and SRY (sex determining region Y)-box 9 (SOX9), were detected by immunofluorescence, reverse transcription-quantitative polymerase chain reaction and western blot analysis. Hypertrophic differentiation was also analyzed using collagen I gene expression and alkaline phosphatase (ALP) activity. The results revealed that ICA was effective at forming an increased number of and larger aggregates, and significantly upregulated the mRNA expression levels and protein synthesis of collagen II, aggrecan and SOX9. Furthermore, the chondrogenic medium alone caused hypertrophic differentiation through the upregulation of collagen I gene expression and ALP activity, which was not potentiated by the presence of ICA. Thus, ICA promoted directed chondrogenic differentiation of BMSCs, but had no effect on hypertrophic differentiation. The present results also suggested that ICA may be an effective accelerant of growth factors for cartilage tissue engineering by promoting their chondrogenic differentiating effects but reducing the effect of hypertrophic differentiation.

Tailored PVA/ECM scaffolds for cartilage regeneration

Articular cartilage lesions are a particular challenge for regenerative medicine due to cartilage low self-ability repair in case of damage. Hence, a significant goal of musculoskeletal tissue engineering is the development of suitable structures in virtue of their matrix composition and biomechanical properties. The objective of our study was to design in vitro a supporting structure for autologous chondrocyte growth. We realized a biohybrid composite scaffold combining a novel and nonspecific extracellular matrix (ECM), which is decellularized Wharton's jelly ECM, with the biomechanical properties of the synthetic hydrogel polyvinyl alcohol (PVA). Wharton's jelly ECM was tested for its ability in promoting scaffold colonization by chondrocytes and compared with polyvinyl alcohol itself and the more specific decellularized cartilage matrix. Our preliminary evidences highlighted the chance of using Wharton's jelly ECM in combination with PVA hydrogels as an innovative and easily available scaffold for cartilage restoration.

Three-dimensional osteogenic and chondrogenic systems to model osteochondral physiology and degenerative joint diseases

Tissue engineered constructs have the potential to function as in vitro pre-clinical models of normal tissue function and disease pathogenesis for drug screening and toxicity assessment. Effective high throughput assays demand minimal systems with clearly defined performance parameters. These systems must accurately model the structure and function of the human organs and their physiological response to different stimuli. Musculoskeletal tissues present unique challenges in this respect, as they are load-bearing, matrix-rich tissues whose functionality is intimately connected to the extracellular matrix and its organization. Of particular clinical importance is the osteochondral junction, the target tissue affected in degenerative joint diseases, such as osteoarthritis (OA), which consists of hyaline articular cartilage in close interaction with subchondral bone. In this review, we present an overview of currently available in vitro three-dimensional systems for bone and cartilage tissue engineering that mimic native physiology, and the utility and limitations of these systems. Specifically, we address the need to combine bone, cartilage and other tissues to form an interactive microphysiological system (MPS) to fully capture the biological complexity and mechanical functions of the osteochondral junction of the articular joint. The potential applications of three-dimensional MPSs for musculoskeletal biology and medicine are highlighted.

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

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

Osteoarthritic cartilage explants affect extracellular matrix production and composition in cocultured bone marrow-derived mesenchymal stem cells and articular chondrocytes

Introduction

In the present study, we established a novel in vitro coculture model to evaluate the influence of osteoarthritis (OA) cartilage explants on the composition of newly produced matrix and chondrogenic differentiation of human bone marrow-derived mesenchymal stem cells (BMSCs) and the phenotype of OA chondrocytes. In addition, we included a “tri-culture” model, whereby a mixture of BMSCs and chondrocytes was cultured on the surface of OA cartilage explants.

Methods

Gene expression analysis, protein and glycosaminoglycan (GAG) assays, dot-blot, immunofluorescence, and biomechanical tests were used to characterize the properties of newly generated extracellular matrix (ECM) from chondrocytes and chondrogenically differentiated BMSCs and a mix thereof. We compared articular cartilage explant cocultures with BMSCs, chondrocytes, and mixed cultures (chondrocytes and BMSCs 1:1) embedded in fibrin gels with fibrin gel-embedded cells cultured without cartilage explants (monocultures).

Results

In general, co- and tri-cultured cell regimens exhibited reduced mRNA and protein levels of collagens I, II, III, and X in comparison with monocultures, whereas no changes in GAG synthesis were observed. All co- and tri-culture regimens tended to exhibit lower Young’s and equilibrium modulus compared with monocultures. In contrast, aggregate modulus and hydraulic permeability seemed to be higher in co- and tri-cultures. Supernatants of cocultures contained significant higher levels of interleukin-1 beta (IL-1β), IL-6, and IL-8. Stimulation of monocultures with IL-1β and IL-6 reduced collagen gene expression in BMSCs and mixed cultures in general but was often upregulated in chondrocytes at late culture time points. IL-8 stimulation affected BMSCs only.

Conclusions

Our results suggest an inhibitory effect of OA cartilage on the production of collagens. This indicates a distinct modulatory influence that affects the collagen composition of the de novo-produced ECM from co- and tri-cultured cells and leads to impaired mechanical and biochemical properties of the matrix because of an altered fibrillar network. We suggest that soluble factors, including IL-1β and IL-6, released from OA cartilage partly mediate these effects. Thus, neighbored OA cartilage provides inhibitory signals with respect to BMSCs’ chondrogenic differentiation and matrix composition, which need to be accounted for in future cell-based OA treatment strategies.

Chondrogenic differentiation of mesenchymal stem cells: challenges and unfulfilled expectations

Articular cartilage repair and regeneration provides a substantial challenge in Regenerative Medicine because of the high degree of morphological and mechanical complexity intrinsic to hyaline cartilage due, in part, to its extracellular matrix. Cartilage remains one of the most difficult tissues to heal; even state-of-the-art regenerative medicine technology cannot yet provide authentic cartilage resurfacing. Mesenchymal stem cells (MSCs) were once believed to be the panacea for cartilage repair and regeneration, but despite years of research, they have not fulfilled these expectations. It has been observed that MSCs have an intrinsic differentiation program reminiscent of endochondral bone formation, which they follow after exposure to specific reagents as a part of current differentiation protocols. Efforts have been made to avoid the resulting hypertrophic fate of MSCs; however, so far, none of these has recreated a fully functional articular hyaline cartilage without chondrocytes exhibiting a hypertrophic phenotype. We reviewed the current literature in an attempt to understand why MSCs have failed to regenerate articular cartilage. The challenges that must be overcome before MSC-based tissue engineering can become a front-line technology for successful articular cartilage regeneration are highlighted.

Immortalised human mesenchymal stem cells undergo chondrogenic differentiation in alginate and PGA/PLLA scaffolds

Adult mesenchymal stem cells (MSCs) are a promising cell source in tissue engineering due to their availability, ease of isolation and high proliferative activity. This study was undertaken to investigate whether immortalised human MSC are able to undergo chondrogenic differentiation when cultured in alginate or in resorbable scaffolds. We directly compared chondrogenesis MSCs with that of human nasoseptal chondrocytes. Two previously established human stem cell lines L87/4 and V54-2 immortalised using the SV40 large T-antigen were either cultured in alginate or in polyglycolic acid/poly-L-lactic acid (PGA/PLLA) (90/10) copolymer scaffolds. TGF-β1 was added for induction of chondrogenesis. Human nasoseptal chondrocytes and human fibroblasts were used as controls. Cultures were analysed for sulfated glycosaminoglycans (alcian blue staining) and for the presence of collagen type I, II and X (immunolabelling). SV40 large T-antigen immortalised human MSCs have the potential to undergo chondrogenic differentiation: After 21 days, cartilage-specific type II collagen was present in alginate and PGA/PLLA scaffolds, independent of the addition of TGF-β1. Collagen type X was present in monolayer cultures as well as in alginate and PGA/PLLA scaffolds. Collagen type I was produced in marginal amounts only. Immortalised human MSCs are a suitable tool to study chondrogenesis in vitro and to screen biomaterials for cartilage tissue engineering applications.

Concise review: unraveling stem cell cocultures in regenerative medicine: which cell interactions steer cartilage regeneration and how?

Cartilage damage and osteoarthritis (OA) impose an important burden on society, leaving both young, active patients and older patients disabled and affecting quality of life. In particular, cartilage injury not only imparts acute loss of function but also predisposes to OA. The increase in knowledge of the consequences of these diseases and the exponential growth in research of regenerative medicine have given rise to different treatment types. Of these, cell-based treatments are increasingly applied because they have the potential to regenerate cartilage, treat symptoms, and ultimately prevent or delay OA. Although these approaches give promising results, they require a costly in vitro cell culture procedure. The answer may lie in single-stage procedures that, by using cell combinations, render in vitro expansion redundant. In the last two decades, cocultures of cartilage cells and a variety of (mesenchymal) stem cells have shown promising results as different studies report cartilage regeneration in vitro and in vivo. However, there is considerable debate regarding the mechanisms and cellular interactions that lead to chondrogenesis in these models. This review, which included 52 papers, provides a systematic overview of the data presented in the literature and tries to elucidate the mechanisms that lead to chondrogenesis in stem cell cocultures with cartilage cells. It could serve as a basis for research groups and clinicians aiming at designing and implementing combined cellular technologies for single-stage cartilage repair and treatment or prevention of OA.

Concise review: unraveling stem cell cocultures in regenerative medicine: which cell interactions steer cartilage regeneration and how?

Cartilage damage and osteoarthritis (OA) impose an important burden on society, leaving both young, active patients and older patients disabled and affecting quality of life. In particular, cartilage injury not only imparts acute loss of function but also predisposes to OA. The increase in knowledge of the consequences of these diseases and the exponential growth in research of regenerative medicine have given rise to different treatment types. Of these, cell-based treatments are increasingly applied because they have the potential to regenerate cartilage, treat symptoms, and ultimately prevent or delay OA. Although these approaches give promising results, they require a costly in vitro cell culture procedure. The answer may lie in single-stage procedures that, by using cell combinations, render in vitro expansion redundant. In the last two decades, cocultures of cartilage cells and a variety of (mesenchymal) stem cells have shown promising results as different studies report cartilage regeneration in vitro and in vivo. However, there is considerable debate regarding the mechanisms and cellular interactions that lead to chondrogenesis in these models. This review, which included 52 papers, provides a systematic overview of the data presented in the literature and tries to elucidate the mechanisms that lead to chondrogenesis in stem cell cocultures with cartilage cells. It could serve as a basis for research groups and clinicians aiming at designing and implementing combined cellular technologies for single-stage cartilage repair and treatment or prevention of OA.

Comparison of articular cartilage repair with different hydrogel-human umbilical cord blood-derived mesenchymal stem cell composites in a rat model

Introduction

The present work was designed to explore the feasibility and efficacy of articular cartilage repair using composites of human umbilical cord blood derived mesenchymal stem cells (hUCB-MSCs) and four different hydrogels in a rat model.

Methods

Full-thickness articular cartilage defects were created at the trochlear groove of femur in both knees of rats. Composites of hUCB-MSCs and four different hydrogels (group A, 4% hyaluronic acid; group B, 3% alginate:30% pluronic (1:1, v/v); group C, 4% hyaluronic acid: 3% alginate: 20% pluronic (2:1:1, v/v}; and group D, 4% hyaluronic acid:3% alginate:20% pluronic;chitosan (4:1:1:2, v/v).) were then transplanted into right knee defect in each study group (five rats/group). Left knees were transplanted with corresponding hydrogels without hUCB-MSCs as controls. At 16 weeks post-transplantation, degrees of cartilage repair were evaluated macroscopically and histologically using Masson’s Trichrome, safranin-O, Sirius red staining, and type-II collagen immunostaining.

Results

Overall, group A with 4% hyaluronic acid hydrogel resulted in superior cartilage repair grossly and histologically and achieved a cellular arrangement and collagen organization pattern mimicking adjacent uninjured articular cartilage. Immunostaining and safranin-O staining also revealed that group A displayed the largest areas of type II collagen staining. Sirius red staining revealed that the organization pattern of collagen bundles was more similar to normal cartilage in group A. No evidence of rejection was found.

Conclusions

The results of this study suggest that hUCB-MSCs could be used to repair articular cartilage defects in vivo and that hyaluronic acid is an attractive hydrogel candidate for use in combination with hUCB-MSCs.

Cartilage tissue engineering: molecular control of chondrocyte differentiation for proper cartilage matrix reconstruction

BACKGROUND

Articular cartilage defects are a veritable therapeutic problem because therapeutic options are very scarce. Due to the poor self-regeneration capacity of cartilage, minor cartilage defects often lead to osteoarthritis. Several surgical strategies have been developed to repair damaged cartilage. Autologous chondrocyte implantation (ACI) gives encouraging results, but this cell-based therapy involves a step of chondrocyte expansion in a monolayer, which results in the loss in the differentiated phenotype. Thus, despite improvement in the quality of life for patients, reconstructed cartilage is in fact fibrocartilage. Successful ACI, according to the particular physiology of chondrocytes in vitro, requires active and phenotypically stabilized chondrocytes.

SCOPE OF REVIEW

This review describes the unique physiology of cartilage, with the factors involved in its formation, stabilization and degradation. Then, we focus on some of the most recent advances in cell therapy and tissue engineering that open up interesting perspectives for maintaining or obtaining the chondrogenic character of cells in order to treat cartilage lesions.

MAJOR CONCLUSIONS

Current research involves the use of chondrocytes or progenitor stem cells, associated with "smart" biomaterials and growth factors. Other influential factors, such as cell sources, oxygen pressure and mechanical strain are considered, as are recent developments in gene therapy to control the chondrocyte differentiation/dedifferentiation process.

GENERAL SIGNIFICANCE

This review provides new information on the mechanisms regulating the state of differentiation of chondrocytes and the chondrogenesis of mesenchymal stem cells that will lead to the development of new restorative cell therapy approaches in humans. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties.

Cryopreservation of whole adipose tissue for future use in regenerative medicine

BACKGROUND

Human adipose tissue (AT) is an ideal stem cell source for autologous cell-based therapies. The preferred setting for tissue engineering and regenerative medicine applications is the availability of clinically acceptable off-the-shelf cells and cell products. As AT is not always available for use, cryopreserved tissue represents an alternative approach. The aim of the present study was to compare the different properties of mesenchymal stem cells (MSCs) isolated from cryopreserved AT. We have measured cell recovery, viability, phenotype, proliferative potential, and differentiation into mesenchymal (adipogenic, osteogenic, chondrogenic) and nonmesenchymal (neuron-like cells) lineages.

MATERIALS AND METHODS

AT (n = 10) was harvested from donors and either processed fresh or cryopreserved in liquid nitrogen dewars. Both fresh and thawed tissues were enzymatically digested. MSCs were analyzed by fluorescence-activated cell sorting for CD3, CD14, CD19, CD34, CD44, CD45, CD73, CD90, and CD105 expression. Growth characteristics of both groups were investigated for population doublings, doubling time, saturation density, and plating efficiency. MSCs derived from fresh and thawed tissues were assessed for differentiation potential both qualitatively and quantitatively.

RESULTS

Adherent cells from fresh and thawed tissues displayed similar fibroblastic morphology. Cryopreservation did not alter expression of phenotypic markers. Similarly, the proliferative potential of MSCs was not compromised by cryopreservation. Furthermore, cryopreservation did not alter the differentiation capability of MSCs as determined with histochemistry, immunofluorescence, and real time reverse transcriptase-polymerase chain reaction.

CONCLUSIONS

We conclude that human AT could be successfully cryopreserved for future clinical application and the recovered MSCs were equivalent in functionality to the freshly processed MSCs.

Engineering superficial zone chondrocytes from mesenchymal stem cells

Recent cartilage engineering efforts have focused on development of zonally organized tissue. However, there remains a need for protocols that differentiate progenitor populations into chondrocytes of zonal phenotype. Here, we evaluate the potential of coculture of bovine mesenchymal stem cells (MSCs) and zonal explants of bovine cartilage tissue to drive MSC differentiation to chondrocytes with the superficial zone phenotype. Two coculture systems were set up: one between alginate encapsulated MSCs and superficial zone cartilage explants, and one between MSCs and middle/deep zone cartilage explants. Chondrogenic and superficial zone markers were monitored over a 21-day differentiation period via gene and protein expression. A control conditioned media study was used to determine the impact of communication via soluble factors between cell populations during differentiation. At day 21, results show superficial zone explant coculture without transforming-growth factor β3 supplementation induces upregulation of chondrogenic gene expression markers SOX9 and type II collagen 3.4-fold and 11.4-fold, respectively, over standard chondrogenic control media. Further, coculture of MSCs and superficial zone explants can be used to upregulate mRNA expression of the superficial zone marker proteoglycan-4 in MSCs (1.75-fold over chondrogenic control at day 21), indicating the superficial zone chondrocyte phenotype. Gene expression data show middle/deep zone explant and MSC coculture did not induce the chondrogenesis observed in superficial zone explant coculture. Likewise, poor chondrogenesis was observed in all conditioned media groups. Results highlight the importance of superficial zone cartilage and cells in guiding stem cell fate and regulating differentiation of MSCs to chondrocytes of the superficial zone type.

Donor age negatively impacts adipose tissue-derived mesenchymal stem cell expansion and differentiation

BACKGROUND

Human adipose tissue is an ideal autologous source of mesenchymal stem cells (MSCs) for various regenerative medicine and tissue engineering strategies. Aged patients are one of the primary target populations for many promising applications. It has long been known that advanced age is negatively correlated with an organism's reparative and regenerative potential, but little and conflicting information is available about the effects of age on the quality of human adipose tissue derived MSCs (hAT-MSCs).

METHODS

To study the influence of age, the expansion and in vitro differentiation potential of hAT-MSCs from young (<30 years), adult (35-50 years) and aged (>60 years) individuals were investigated. MSCs were characterized for expression of the genes p16(INK4a) and p21 along with measurements of population doublings (PD), superoxide dismutase (SOD) activity, cellular senescence and differentiation potential.

RESULTS

Aged MSCs displayed senescent features when compared with cells isolated from young donors, concomitant with reduced viability and proliferation. These features were also associated with significantly reduced differentiation potential in aged MSCs compared to young MSCs.

CONCLUSIONS

In conclusion, advancing age negatively impacts stem cell function and such age related alterations may be detrimental for successful stem cell therapies.

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

In this work, we evaluated the ability of 3D co-cultures with mesenchymal stem cells (MSCs) to redifferentiate monolayer expanded articular chondrocytes (ACs) and produce cartilaginous extracellular matrix at varying stages of the dedifferentiation process and further examined the dependency of this effect on the culture medium composition. Primary bovine ACs were expanded in monolayers for up to nine population doublings to obtain seven cell stocks with gradually increasing levels of dedifferentiation. Culture expanded ACs were then seeded as monocultures and co-cultures with rabbit bone marrow-derived MSCs (30:70 ratio of ACs-to-MSCs) on porous scaffolds. Parallel cultures were established for each cell population in serum-containing growth medium and serum-free induction medium supplemented with dexamethasone and TGF-β3. After 3 weeks, all groups were analyzed for DNA content, glycosaminoglycan (GAG) and hydroxyproline (HYP) production, and chondrogenic gene expression. Significant enhancements in cellularity, GAG content and GAG/HYP ratio, and chondrogenic phenotype were observed in the induction medium compared to growth medium at all levels of AC expansion. Furthermore, primary co-cultures showed similarly enhanced chondrogenesis compared to monocultures in both culture media, whereas passaged ACs benefitted from co-culturing only in the induction medium. We conclude that co-cultures of ACs and MSCs can produce superior in vitro engineered cartilage in comparison to pure AC cultures, due to both heterotypic cellular interactions and decreased need for monolayer expansion of biopsied chondrocytes. While the initial level of AC dedifferentiation affected the quality of the engineered constructs, co-culture benefits were realized at all stages of AC expansion when suitable chondroinductive culture medium was used.

Trophic stimulation of articular chondrocytes by late-passage mesenchymal stem cells in coculture

Coculture of mesenchymal stem cells (MSCs) with articular chondrocytes (ACs) increases glycosaminoglycan (GAG) accumulation compared to monoculture. MSCs might (1) differentiate into ACs (progenitor role) and/or (2) stimulate AC matrix metabolism (trophic role). MSCs lose the ability to undergo chondrogenesis after extended passaging. We hypothesized that MSCs act predominantly as progenitors, and that late-passage MSCs without chondrogenic potential would be unable to increase GAG in coculture. Early- and late-passage human MSCs (hMSCs) were grown in pellet monoculture under chondrogenic conditions and in pellet coculture with bovine ACs. Chondrogenesis was assessed with GAG quantification, safranin-O staining, and quantitative PCR (qPCR). Contributions of human and bovine cells were assessed with species-specific qPCR and human-specific immunostaining. Late-passage hMSCs did not undergo chondrogenesis in monoculture with chondrogenic stimuli or in coculture with ACs. Early-passage hMSCs underwent chondrogenesis only in response to chondrogenic stimuli. Coculture pellets in both cases accumulated as much GAG/DNA as monoculture AC pellets. Aggrecan transcription was not increased in coculture. Late-passage hMSCs that do not undergo chondrogenesis are capable of stimulating GAG accumulation in coculture with ACs. This supports a trophic effect of hMSCs on ACs. hMSCs may have therapeutic utility even after prolonged passaging.

Cell-derived polymer/extracellular matrix composite scaffolds for cartilage regeneration, Part 1: investigation of cocultures and seeding densities for improved extracellular matrix deposition

This study investigated the coculture of chondrocytes and mesenchymal stem cells (MSCs) on electrospun fibrous polymer scaffolds to produce polymer/extracellular matrix (ECM) hybrid constructs with the objective of reducing the number of chondrocytes necessary to produce ample cartilage-like ECM within the scaffolds. To generate these hybrid constructs, electrospun poly(ɛ-caprolactone) fibrous scaffolds were seeded at both high and low initial densities with five different ratios of chondrocytes to MSCs: 1:0, 1:1, 1:3, 1:5, and 0:1, and cultured for 7, 14, and 21 days. Glycosaminoglycan production and distribution within the three coculture groups was similar to quantities generated by chondrocyte-only controls. Conversely, as the concentration of chondrocytes was increased, the collagen content of the constructs also increased at each time point, with a 1:1 chondrocyte to MSC ratio approximating the collagen production of chondrocytes alone. Histological staining suggested that cocultured constructs mimicked the well-distributed ECM patterns of chondrocyte generated constructs, while improving greatly over the restricted distribution of matrix within MSC-only constructs. These results support the capacity of cocultures of chondrocytes and MSCs to generate cartilaginous matrix within a polymeric scaffold. Further, the inclusion of MSCs in these cocultures enables the reduction of chondrocytes needed to produce cell-generated ECM.

TGF-β3-induced chondrogenesis in co-cultures of chondrocytes and mesenchymal stem cells on biodegradable scaffolds

In this work, it was hypothesized that co-cultures of articular chondrocytes (ACs) and mesenchymal stem cells (MSCs) would exhibit enhanced sensitivity to chondrogenic stimuli, such as TGF-β3, and would require a reduced concentration of TGF-β3 to achieve an equivalent level of chondrogenesis compared to monocultures of each cell type. Furthermore, it was hypothesized that compared to monocultures, the chondrogenic phenotype of AC/MSC co-cultures would be more stable upon the removal of TGF-β3 from the culture medium. These hypotheses were investigated by culturing ACs and MSCs alone and in a 1:3 ratio on electrospun poly(ε-caprolactone) scaffolds. All cell populations were cultured for two weeks with 0, 1, 3, or 10 ng/ml of TGF-β3. After two weeks growth factor supplementation was removed, and the constructs were cultured for two additional weeks. Cell proliferation, extracellular matrix production, and chondrogenic gene expression were evaluated after two and four weeks. The results demonstrated that co-cultures of ACs and MSCs require a reduced concentration and duration of TGF-β3 exposure to achieve an equivalent level of chondrogenesis compared to AC or MSC monocultures. Thus, the present work implicates that the promise of co-cultures for cartilage engineering is enhanced by their robust phenotype and heightened sensitivity to TGF-β3.

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.

Adipose mesenchymal stem cells protect chondrocytes from degeneration associated with osteoarthritis

Our work aimed at evaluating the role of adipose stem cells (ASC) on chondrocytes from osteoarthritic (OA) patients and identifying the mediators involved. We used primary chondrocytes, ASCs from different sources and bone marrow mesenchymal stromal cells (MSC) from OA donors. ASCs or MSCs were co-cultured with chondrocytes in a minimal medium and using cell culture inserts. Under these conditions, ASCs did not affect the proliferation of chondrocytes but significantly decreased camptothecin-induced apoptosis. Both MSCs and ASCs from different sources allowed chondrocytes in the cocultures maintaining a stable expression of markers specific for a mature phenotype, while expression of hypertrophic and fibrotic markers was decreased. A number of factors known to regulate the chondrocyte phenotype (IL-1β, IL-1RA, TNF-α) and matrix remodeling (TIMP-1 and -2, MMP-1 and -9, TSP-1) were not affected. However, a significant decrease of TGF-β1 secretion by chondrocytes and induction of HGF secretion by ASCs was observed. Addition of a neutralizing anti-HGF antibody reversed the anti-fibrotic effect of ASCs whereas hypertrophic markers were not modulated. In summary, ASCs are an interesting source of stem cells for efficiently reducing hypertrophy and dedifferentiation of chondrocytes, at least partly via the secretion of HGF. This supports the interest of using these cells in therapies for osteo-articular diseases.

Cell sources for trachea tissue engineering: past, present and future

Trachea tissue engineering has been one of the most promising approaches to providing a potential clinical application for the treatment of long-segment tracheal stenosis. The sources of the cells are particularly important as the primary factor for tissue engineering. The use of appropriate cells seeded onto scaffolds holds huge promise as a means of engineering the trachea. Furthermore, appropriate cells would accelerate the regeneration of the tissue even without scaffolds. Besides autologous mature cells, various stem cells, including bone marrow-derived mesenchymal stem cells, adipose tissue-derived stem cells, umbilical cord blood-derived mesenchymal stem cells, amniotic fluid stem cells, embryonic stem cells and induced pluripotent stem cells, have received extensive attention in the field of trachea tissue engineering. Therefore, this article reviews the progress on different cell sources for engineering tracheal cartilage and epithelium, which can lead to a better selection and strategy for engineering the trachea.