Phenotypic changes in proliferation, differentiation, and migration of chondrocytes: 3D in vitro models for joint wound healing

Effects of collagen matrix and bioreactor cultivation on cartilage regeneration of a full-thickness critical-size knee joint cartilage defects with subchondral bone damage in a rabbit model

Cartilage has limited self-repair ability. The purpose of this study was to investigate the effects of different species of collagen-engineered neocartilage for the treatment of critical-size defects in the articular joint in a rabbit model. Type II and I collagen obtained from rabbits and rats was mixed to form a scaffold. The type II/I collagen scaffold was then mixed with rabbit chondrocytes to biofabricate neocartilage constructs using a rotating cell culture system [three-dimensional (3D)-bioreactor]. The rabbit chondrocytes were mixed with rabbit collagen scaffold and rat collagen scaffold to form neoRBT (neo-rabbit cartilage) and neoRAT (neo-rat cartilage) constructs, respectively. The neocartilage matrix constructs were implanted into surgically created defects in rabbit knee chondyles, and histological examinations were performed after 2 and 3 months. Cartilage-like lacunae formation surrounding the chondrocytes was noted in the cell cultures. After 3 months, both the neoRBT and neoRAT groups showed cartilage-like repair tissue covering the 5-mm circular, 4-mm-deep defects that were created in the rabbit condyle and filled with neocartilage plugs. Reparative chondrocytes were aligned as apparent clusters in both the neoRAT and neoRBT groups. Both neoRBT and neoRAT cartilage repair demonstrated integration with healthy adjacent tissue; however, more integration was obtained using the neoRAT cartilage. Our data indicate that different species of type II/I collagen matrix and 3D bioreactor cultivation can facilitate cartilage engineering in vitro for the repair of critical-size defect.

Effects of insulin-like growth factor 1 and basic fibroblast growth factor on the morphology and proliferation of chondrocytes embedded in Matrigel in a microfluidic platform

An integrated microfluidic device was utilized in the present study to investigate the morphology and proliferation of rabbit articular chondrocytes embedded in Matrigel in the presence of insulin-like growth factor 1 (IGF-1) and/or basic fibroblast growth factor (bFGF). The microfluidic device was composed of two parallel channels and a central perfusion-based three-dimensional cell culture module. The rabbit chondrocytes were cultured for 2 weeks at series of concentration gradients of IGF-1 and/or bFGF, which were generated through a diffusion process. At the end of the experiment, the morphology and quantity of cells were measured. Since high expression of collagen II is essential to the function of hyaline cartilage, immunofluorescent images of collagen II expression prior to and after the experiments were gathered for each group. The mean fluorescence intensity ratio (MIR) of collagen II in each group was calculated. The MIRs of collagen II in chondrocytes treated with IGF-1 ranged from 0.6-0.81, those in the cells treated with bFGF ranged from 0.47-0.52, and those in cells treated with a combination of IGF-1 and bFGF ranged from 0.63-0.83. Chondrocyte aggregations were observed in the group treated with 75-100 ng/ml IGF-1 (3.46-fold proliferation ratio). Similarly, a 3.83-fold proliferation ratio was identified in chondrocytes treated with 2.5-5.0 ng/ml bFGF. The group treated with 50-75 ng/ml IGF-1 and 2.5-5.0 ng/ml bFGF exhibited the optimum increase in proliferation (4.83-fold proliferation ratio). The microfluidic device used in the present study can be easily adapted to investigate other growth factors at any concentration gradient. In addition, parallel experiments can be performed simultaneously with a small quantity of cells, making it an attractive platform for the high-throughput screening of cell culture parameters. This platform will aid in the optimization of culture conditions for the in vitro expansion of chondrocytes while maintaining their in vivo morphology, which will improve autologous chondrocyte implantation capabilities for the treatment of cartilage injury.

Type II collagen and glycosaminoglycan expression induction in primary human chondrocyte by TGF-β1

Background

A localized non-surgical delivery of allogeneic human chondrocytes (hChonJ) with irradiated genetically modified chondrocytes (hChonJb#7) expressing transforming growth factor-β1 (TGF-β1) showed efficacy in regenerating cartilage tissue in our pre-clinical studies and human Phase I and II clinical trials. These previous observations led us to investigate the molecular mechanisms of the cartilage regeneration.

Methods

Genetically modified TGF-β1preprotein was evaluated by monitoring cell proliferation inhibition activity. The effect of modified TGF-β1 on chondrocytes was evaluated based on the type II collagen mRNA levels and the amount of glycosaminoclycan (GAG) formed around chondrocytes, which are indicative markers of redifferentiated chondrocytes. Among the cartilage matrix components produced by hChonJb#7 cells, type II collagen and proteoglycan, in addition to TGF-β1, were also tested to see if they could induce hChonJ redifferentiation. The ability of chondrocytes to attach to artificially induced defects in rabbit cartilage was tested using fluorescent markers.

Results

Throughout these experiments, the TGF-β1 produced from hChonJb#7 was shown to be equally as active as the recombinant human TGF-β1. Type II collagen and GAG production were induced in hChonJ cells by TGF-β1 secreted from the irradiated hChonJb#7 cells when the cells were co-cultured in micro-masses. Both hChonJ and hChonJb#7 cells could attach efficiently to the defect area in the rabbit cartilage.

Conclusions

This study suggests that the mixture (TG-C) of allogeneic human chondrocytes (hChonJ) and irradiated genetically modified human chondrocytes expressing TGF-β1 (hChonJb#7) attach to the damaged cartilage area to produce type II collagen-GAG matrices by providing a continuous supply of active TGF-β1.