Effect of dynamic compressive loading and its combination with a growth factor on the chondrocytic phenotype of 3-dimensional scaffold-embedded chondrocytes

Cellular and molecular changes to chondrocytes in an in vitro model of developmental dysplasia of the hip‑an experimental model of DDH with swaddling position

The aim of the present study was to assess the cellular and molecular changes to chondrocytes in a developmental dysplasia of the hip (DDH) model and to investigate the early metabolism of chondrocytes in DDH. Neonatal Wistar rats were used for the DDH model with swaddling position. Primary cultures of chondrocytes were prepared at serial interval stages (2, 4, 6 and 8 weeks) to investigate cellular proliferation. The expression of collagen II and aggrecan mRNA was detected to assess the anabolic ability of chondrocytes. The expression of matrix metallopeptidase (MMP)-13 and ADAM metallopeptidase with thrombospondin type 1 motif 5 (ADAMTS-5) mRNA was measured to investigate the degradation of collagen II and aggrecan, respectively. Morphological changes were observed in coronal dissection samples after the removal of fixation. Primary chondrocytes at serial intervals were assessed using a Cell Counting Kit-8 assay and the results revealed that DDH chondrocytes had more proliferative activity. The expression of collagen II mRNA was upregulated at 2 weeks and was more sensitive to mechanical loading compared with aggrecan. Similar changes occurred at 6 weeks. Furthermore, MMP-13 and ADAMTS-5 mRNA expression levels were upregulated at 2 weeks. It was also demonstrated that DDH chondrocytes exhibited high proliferative activity at the early stages and degeneration later.

Dynamic Mechanical Compression of Chondrocytes for Tissue Engineering: A Critical Review

Articular cartilage functions to transmit and translate loads. In a classical structure-function relationship, the tissue resides in a dynamic mechanical environment that drives the formation of a highly organized tissue architecture suited to its biomechanical role. The dynamic mechanical environment includes multiaxial compressive and shear strains as well as hydrostatic and osmotic pressures. As the mechanical environment is known to modulate cell fate and influence tissue development toward a defined architecture in situ, dynamic mechanical loading has been hypothesized to induce the structure-function relationship during attempts at in vitro regeneration of articular cartilage. Researchers have designed increasingly sophisticated bioreactors with dynamic mechanical regimes, but the response of chondrocytes to dynamic compression and shear loading remains poorly characterized due to wide variation in study design, system variables, and outcome measurements. We assessed the literature pertaining to the use of dynamic compressive bioreactors for in vitro generation of cartilaginous tissue from primary and expanded chondrocytes. We used specific search terms to identify relevant publications from the PubMed database and manually sorted the data. It was very challenging to find consensus between studies because of species, age, cell source, and culture differences, coupled with the many loading regimes and the types of analyses used. Early studies that evaluated the response of primary bovine chondrocytes within hydrogels, and that employed dynamic single-axis compression with physiologic loading parameters, reported consistently favorable responses at the tissue level, with upregulation of biochemical synthesis and biomechanical properties. However, they rarely assessed the cellular response with gene expression or mechanotransduction pathway analyses. Later studies that employed increasingly sophisticated biomaterial-based systems, cells derived from different species, and complex loading regimes, did not necessarily corroborate prior positive results. These studies report positive results with respect to very specific conditions for cellular responses to dynamic load but fail to consistently achieve significant positive changes in relevant tissue engineering parameters, particularly collagen content and stiffness. There is a need for standardized methods and analyses of dynamic mechanical loading systems to guide the field of tissue engineering toward building cartilaginous implants that meet the goal of regenerating articular cartilage.

Hypoxia Potentiates Anabolic Effects of Exogenous Hyaluronic Acid in Rat Articular Cartilage

Hyaluronic acid (HA) is used clinically to treat osteoarthritis (OA), but its pharmacological effects under hypoxic conditions remain unclear. Articular chondrocytes in patients with OA are exposed to a hypoxic environment. This study investigated whether hypoxia could potentiate the anabolic effects of exogenous HA in rat articular cartilage and whether these mechanisms involved HA receptors. HA under hypoxic conditions significantly enhanced the expression of extracellular matrix genes and proteins in explant culture, as shown by real-time reverse transcription-polymerase chain reaction (RT-PCR), Western blotting, and dimethylmethylene blue (DMMB) assays. Staining with Safranin-O and immunohistochemical staining with antibody to type II collagen were also enhanced in pellet culture. The expression of CD44 was increased by hypoxia and significantly suppressed by transfection with siRNAs targeting hypoxia-inducible factor 1 alpha (siHIF-1α). These findings indicate that hypoxia potentiates the anabolic effects of exogenous HA by a mechanism in which HIF-1α positively regulates the expression of CD44, enhancing the binding affinity for exogenous HA. The anabolic effects of exogenous HA may increase as OA progresses.

BM-MSCs and Bio-Oss complexes enhanced new bone formation during maxillary sinus floor augmentation by promoting differentiation of BM-MSCs

Bone marrow-derived mesenchymal stem cells (BM-MSCs) have been recognized as a new strategy for maxillary sinus floor elevation. However, little is known concerning the effect of the biomechanical pressure (i.e., sinus pressure, masticatory pressure, and respiration) on the differentiation of BM-MSCs and the formation of new bone during maxillary sinus floor elevation. The differentiation of BM-MSCs into osteoblasts was examined in vitro under cyclic compressive pressure using the Flexcell® pressure system, and by immunohistochemical analysis, qRT-PCR, and Western blot. Micro-CT was used to detect bone formation and allow image reconstruction of the entire maxillary sinus floor elevation area. Differentiation of BM-MSCs into osteoblasts was significantly increased under cyclic compressive pressure. The formation of new bone was enhanced after implantation of the pressured complex of BM-MSCs and Bio-Oss during maxillary sinus floor elevation. The pressured complex of BM-MSCs and Bio-Oss promoted new bone formation and maturation in the rabbit maxillary sinus. Stem cell therapy combined with this tissue engineering technique could be effectively used in maxillary sinus elevation and bone regeneration.

Mechanostimulation changes the catabolic phenotype of human dedifferentiated osteoarthritic chondrocytes

PURPOSE

The treatment of cartilage defects with matrix-embedded autologous chondrocytes is a promising method to support the repair process and to foster reconstitution of full functionality of the joint.

METHODS

Human osteoarthritic chondrocytes were harvest from nine different patients (mean ± SD age 68 ± 8 years) who underwent total knee replacement. The chondrocytes were embedded after a precultivation phase into a collagen I hydrogel. Mid-term intermitted mechanostimulation on matrix-embedded dedifferentiated human osteoarthritic chondrocytes was performed by intermittently applying a cyclic sinusoid compression regime for 4 days (cycles of 1 h of sinusoidal stimulation (1 Hz) and 4 h of break; maximum compression 2.5%). Stimulated (Flex) and non-stimulated (No Flex) cell matrix constructs were analysed concerning the expression of genes involved in tissue metabolism, the content of sulphated glycosaminoglycans (sGAG) and the morphology of the chondrocytes.

RESULTS

Gene expression analysis showed a high significant increase in collagen type II expression (p < 0.001), a significant increase in aggrecan expression (p < 0.04) and a high significant decrease in MMP-13 expression (p < 0.001) under stimulation condition compared with unstimulated controls. No significant changes were found in the gene expression rate of MMP-3. This positive effect of the mechanostimulation was confirmed by the analyses of sGAG. Mechanically stimulated cell-matrix constructs had nearly tripled sGAG content than the non-stimulated control (p < 0.002). In addition, histological examination showed that morphology of chondrocytes was altered from a spindle-shaped to a chondrocyte-characteristic rounded phenotype.

CONCLUSION

Mid-term intermitted mechanical stimulation in vitro has the potential to improve the cell quality of cell matrix constructs prepared from dedifferentiated osteoarthritic chondrocytes. This observation may extend the inclusion criteria for matrix-assisted autologous chondrocyte implantation (MACI) and confirms the importance of moderate dynamic compression in clinical rehabilitation after MACI.

Extracellular and intracellular mechanisms of mechanotransduction in three-dimensionally embedded rat chondrocytes

Purpose

Articular cartilage homeostasis involves modulation of chondrocyte matrix synthesis in response to mechanical stress (MS). We studied extracellular and intracellular mechanotransduction pathways mediating this response.

Methods

We first confirmed rapid up-regulation of the putative chondro-protective cytokine, interleukin (IL)-4, as an immediate response to MS. We then studied the role of IL-4 by investigating responses to exogenous IL-4 or a specific IL-4 inhibitor, combined with MS. Next we investigated the intracellular second messengers. Since chondrocyte phenotype alters according to the extracellular environment, we characterized the response to mechanotransduction in 3-dimensionally embedded chondrocytes.

Results

Expression of aggrecan and type II collagen was significantly up-regulated by exogenous IL-4 whereas MS-induced matrix synthesis was inhibited by an IL-4 blocker. Further, MS-induced matrix synthesis was completely blocked by a p38 MAPK inhibitor, while it was only partially blocked by inhibitors of other putative second messengers.

Conclusion

IL-4 mediates an extracellular pathway of mechanotransduction, perhaps via an autocrine/paracrine loop, while p38 mediates an intracellular pathway prevalent only in a 3-dimensional environment.

Biocomposites reinforced by fibers or tubes as scaffolds for tissue engineering or regenerative medicine

As a dynamic and hierarchically organized composite, native extracellular matrix (ECM) not only supplies mechanical support, which the embedded cells need, but also regulates various cellular activities through interaction with them. On the basis of the ECM-mimetic principle, good biocompatibility and appropriate mechanical properties are the two basic requirements that the ideal scaffolds for the tissue engineering or regenerative medicine need. Some fibers and tubes have been shown effective to reinforce scaffolds for tissue engineering or regenerative medicine. In this review, three parts, namely properties affected by the addition of fibers or tubes, scaffolds reinforced by fibers or tubes for soft tissue repair, and scaffolds reinforced by fibers or tubes for hard tissue repair are stated, which shows that tissue repair or regeneration efficacy was enhanced significantly by fiber or tube reinforcement. In addition, it indicates that these reinforcing agents can improve the biocompatibility and biodegradation of the scaffolds in most cases. However, there are still some concerns, such as the homogeneousness in structure or composition throughout the reinforced scaffolds, the adhesive strength between the matrix and the fibers or tubes, cytotoxicity of nanoscaled reinforcing agents, etc., which were also discussed in the conclusion and perspectives part.

Effects of platelet-rich plasma on cartilage grafts in rabbits as an animal model

BACKGROUND

Cartilage tissue has limited regenerative capacity and the management of cartilage defects has always been a challenging issue. Platelet-rich plasma (PRP) has been recently been used to improve healing of cartilage defects. In the present experiment, we aimed to investigate the effects of PRP on regeneration capacity as well as survival of the cartilage grafts in a rabbit model.

METHODS

In 15 white New Zealand rabbits, auricular cartilage was used to produce 4 pieces of cartilage (each about 2×2 cm). Two samples were diced to small pieces and 2 samples left intact. PRP was prepared using 5 ml of auricular blood. After measuring of the weight and volume of cartilages, they mixed with either normal saline or PRP and then implanted on the back of the rabbit. After 12 weeks, the implants were removed and the weight and volume were measured and the numbers of nucleated lacunae were counted on H & E staining.

RESULTS

Histological findings showed that in both the intact and diced cartilages, adding PRP resulted in increasing regeneration of chondrocytes. Moreover, adding PRP to intact cartilages had a significant effect in maintaining the grafts 'weight and volume (p<0.05) but in diced cartilages, this effect was not significant.

CONCLUSION

Our findings yielded valuable information on the effect of PRP on survival and regeneration of autologous cartilage grafts as the extent of angiogenesis and the diameters of vessels were more pronounced in the side using PRP and markedly lesser reduction of weight and volume were visible in this group. PRP was effective in increasing survival and regeneration capacity of cartilage grafts in rabbit model.

Platelet lysate 3D scaffold supports mesenchymal stem cell chondrogenesis: an improved approach in cartilage tissue engineering

Articular lesions are still a major challenge in orthopedics because of cartilage's poor healing properties. A major improvement in therapeutics was the development of autologous chondrocytes implantation (ACI), a biotechnology-derived technique that delivers healthy autologous chondrocytes after in vitro expansion. To obtain cartilage-like tissue, 3D scaffolds are essential to maintain chondrocyte differentiated status. Currently, bioactive 3D scaffolds are promising as they can deliver growth factors, cytokines, and hormones to the cells, giving them a boost to attach, proliferate, induce protein synthesis, and differentiate. Using mesenchymal stem cells (MSCs) differentiated into chondrocytes, one can avoid cartilage harvesting. Thus, we investigated the potential use of a platelet-lysate-based 3D bioactive scaffold to support chondrogenic differentiation and maintenance of MSCs. The MSCs from adult rabbit bone marrow (n = 5) were cultivated and characterized using three antibodies by flow cytometry. MSCs (1 × 10(5)) were than encapsulated inside 60 µl of a rabbit platelet-lysate clot scaffold and maintained in Dulbecco's Modified Eagle Medium Nutrient Mixture F-12 supplemented with chondrogenic inductors. After 21 days, the MSCs-seeded scaffolds were processed for histological analysis and stained with toluidine blue. This scaffold was able to maintain round-shaped cells, typical chondrocyte metachromatic extracellular matrix deposition, and isogenous group formation. Cells accumulated inside lacunae and cytoplasm lipid droplets were other observed typical chondrocyte features. In conclusion, the usage of a platelet-lysate bioactive scaffold, associated with a suitable chondrogenic culture medium, supports MSCs chondrogenesis. As such, it offers an alternative tool for cartilage engineering research and ACI.

Cartilage restoration in haemophilia: advanced therapies

Current treatment of joint cartilage lesions is based either on conventional techniques (bone marrow stimulation, osteochondral autograft or allograft transplantation) or on newly developed techniques (chondrocyte implantation and those based on cell therapy that use bioreactors, growth factors, mesenchymal stem cells [MSCs] and genetically modified cells). The aim of this article is to review the therapeutic strategies above mentioned and to determine whether the chondral damage seen in haemophilia could benefit from any of them. The different conventional techniques have shown similar results whereas autologous chondrocyte implantation, which is in common use at the present time, has not been shown to produce any conclusive results or to lead to the formation of hyaline cartilage. MSCs hold promise for the repair of joint cartilage given their differentiation capacity and the therapeutic effect. The use of bioreactors and growth factors, which stimulate cartilage formation, may optimize such strategies in the context of reimplantation of chondrocytes, differentiated MSCs and cartilage progenitor cells. The aim of cell therapy is restoration of function through the repair of damaged tissue or the stimulation of growth factor synthesis. Implantation of autologous chondrocytes or MSCs was up to now able to address only highly localized chondral lesions. Adequate control of the differentiation process as well as the use of growth factors and appropriate bioreactors could transform cell-based therapies into a more efficient and longer term treatment even for patients with haemophilia. Nevertheless, raising false expectations in these patients should be avoided. There are a number of approaches to cartilage restoration in haemophilic arthropathy, which are currently being explored for other joint related degenerative disorders. If it can be proven to be effective for the disorders in which clinical trials are ongoing and costs could be limited, it might be an useful palliative approach to haemophilic arthropathy. However, we still have a long way to go for use in haemophilic arthropathy.

Platelet-rich plasma loaded hydrogel scaffold enhances chondrogenic differentiation and maturation with up-regulation of CB1 and CB2

Three-dimensional scaffolds like hydrogels can be used for cell and drug delivery and have become a major research focus in tissue engineering. Presently, we investigated the regenerative potency of platelet-rich plasma (PRP) combined with a chondrocyte/hydrogel composite scaffold in the repair of articular cartilage defects using a rabbit model. Primary isolated joint chondrocytes from the trachlear groove of rabbit were cultured in hydrogels as follows; hydrogel (2900 Pa or 5900 Pa)+chondrocytes and hydrogel+chondrocytes+PRP for in vitro analysis and in vivo implantation. The 5900 Pa hydrogel markedly increased cellular viability and development in a time-dependent manner. Furthermore, the hydrogels attenuated the expression of SOX-9, aggrecan, and type II collagen. PRP-containing hydrogels produced an immediate increase in mRNA levels of cannabinoid receptor (CB)1 and CB2, compared with control and PRP-free hydrogels. Osteochondral defects were enhanced recovery with formation of cartilage and perichondrium in the 5900 Pa hydrogel+chondrocytes+PRP. Hydrogel may provide a suitable environment for proliferation and maturation of joint chondrocytes in relation to the gelation density and bioactive sources like PRP resulting in improvement for cartilage regeneration.

Chondrocyte source for cartilage regeneration in an immature animal: Is iliac apophysis a good alternative?

BACKGROUND

Autologous articular cartilage at present forms the main source of chondrocytes for cartilage tissue engineering. In children, iliac apophysis is a rich and readily accessible source of chondrocytes. This study compares the growth characteristics and phenotype maintenance of goat iliac apophysis growth plate chondrocytes with those sourced from goat articular cartilage, and thereby assesses their suitability for autologous chondrocyte transplantation in immature animals for growth plate and articular cartilage regeneration.

MATERIALS AND METHODS

Four sets of experiments were carried out. Cartilage samples were harvested under aseptic conditions from goat iliac apophysis and knee articular cartilage. The chondrocytes were isolated in each set and viable cells were counted and subsequently cultured as a monolayer in tissue culture flasks containing chondrogenic media at 2.5 × 10(3)cells/cm(2). The growth was periodically assessed with phase contrast microcopy and the cells were harvested on 8(th) and 15(th) days for morphology, cell yield, and phenotype assessment. Student's t-test was used for comparison of the means.

RESULTS

Confluence was reached in the iliac apophysis growth plate chondrocytes flasks on the 10(th) day and the articular cartilage chondrocytes flasks on the 14(th) day. Mean cell count of growth plate chondrocytes on the 8(th) day was 3.64 × 10(5) (SD = 0.601) and that of articular cartilage chondrocytes was 1.40 × 10(5) (SD = 0.758) per flask. The difference in the means was statistically significant (P = 0.003). On the 15(th) day, the mean cell number had increased to 1.35 × 10(6)(SD = 0.20) and 1.19 × 10(6) (SD = 0.064) per flask, respectively. This difference was not statistically significant (P = 0.26). The population doubling time on the 8(th) day of cell culture was 3.18 and 6.24 days respectively, for iliac apophyseal and articular cartilage chondrocytes, which was altered to 3.59 and 3.1 days, respectively, on the 15(th) day. The immunocytochemistry showed 100% retention of collagen 2 positive and collagen 1 negative cells in both sets of cultures in all samples.

CONCLUSION

Iliac apophysis is a rich source of chondrocytes with a high growth rate and ability to retain phenotype when compared to articular cartilage derived chondrocytes. Further in vivo studies may determine the efficacy of physeal and articular repair in children with apophyseal chondrocytes.

Effects of intermittent hydrostatic pressure and BMP-2 on osteoarthritic human chondrocyte metabolism in vitro

PURPOSE

This study examined effects of intermittent hydrostatic pressure (IHP) and a chondrogenic growth factor, bone morphogenetic protein-2 (BMP-2), on anabolic, catabolic, and other metabolic markers in human osteoarthritic (OA) chondrocytes in vitro.

METHODS

Articular chondrocytes, isolated from femoral OA cartilage and maintained in high-density monolayer culture, were examined for effects of BMP-2 and IHP on gene expression of matrix-associated proteins (aggrecan, type II collagen, and SOX9) and catabolic matrix metalloproteinases (MMP-2 and MMP-3) and culture medium levels of the metabolic markers MMP-2, nitric oxide (NO), and glycosaminoglycan (GAG). The results were analyzed using a mixed linear regression model to investigate the effects of load and growth factor concentration.

RESULTS

IHP and BMP-2 modulated OA chondrocyte metabolism in accordance with growth factor concentration independently, without evidence of synergism or antagonism. Each type of stimulus acted independently on anabolic matrix gene expression. Type II collagen and SOX9 gene expression were stimulated by both IHP and BMP-2 whereas aggrecan was increased only by BMP-2. IHP exhibited a trend to decrease MMP-2 gene expression as a catabolic marker whereas BMP-2 did not. NO production was increased by addition of BMP-2 and IHP exhibited a trend for increased levels. GAG production was increased by BMP-2.

CONCLUSIONS

This study confirmed the hypothesis that human OA chondrocytes respond to a specific type of mechanical load, IHP, through enhanced articular cartilage macromolecule gene expression and that IHP, in combination with a chondrogenic growth factor BMP-2, additively enhanced matrix gene expression without interactive effects.

The role of tissue engineering in articular cartilage repair and regeneration

Articular cartilage repair and regeneration continue to be largely intractable because of the poor regenerative properties of this tissue. The field of articular cartilage tissue engineering, which aims to repair, regenerate, and/or improve injured or diseased articular cartilage functionality, has evoked intense interest and holds great potential for improving articular cartilage therapy. This review provides an overall description of the current state of and progress in articular cartilage repair and regeneration. Traditional therapies and related problems are introduced. More importantly, a variety of promising cell sources, biocompatible tissue engineered scaffolds, scaffoldless techniques, growth factors, and mechanical stimuli used in current articular cartilage tissue engineering are reviewed. Finally, the technical and regulatory challenges of articular cartilage tissue engineering and possible future directions are also discussed.