Joint mimicking mechanical load activates TGFβ1 in fibrin-poly(ester-urethane) scaffolds seeded with mesenchymal stem cells

Transforming growth factor‐β1 (TGF‐β1) is widely used in an active recombinant form to stimulate the chondrogenic differentiation of mesenchymal stem cells (MSCs). Recently, it has been shown that the application of multiaxial load, that mimics the loading within diarthrodial joints, to MSCs seeded in to fibrin‐poly(ester‐urethane) scaffolds leads to the endogenous production and secretion of TGF‐β1 by the mechanically stimulated cells, which in turn drives the chondrogenic differentiation of the cells within the scaffold. The work presented in this short communication provides further evidence that the application of joint mimicking multiaxial load induces the secretion of TGF‐β1 by mechanically stimulated MSCs. The results of this work also show that joint‐like multiaxial mechanical load activates latent TGF‐β1 in response to loading in the presence or absence of cells; this activation was not seen in non‐loaded control scaffolds. Despite the application of mechanical load to scaffolds with different distributions/numbers of cells no significant differences were seen in the percentage of active TGF‐β1 quantified in the culture medium of scaffolds from different groups. The similar level of activation in scaffolds containing different numbers of cells, cells at different stages of differentiation or with different distributions of cells suggests that this activation results from the mechanical forces applied to the culture system rather than differences in cellular behaviour. These results are relevant when considering rehabilitation protocols after cell therapy or microfracture, for articular cartilage repair, where increased TGF‐β1 activation in response to joint mobilization may improve the quality of developing cartilaginous repair material

Differences in human mesenchymal stem cell secretomes during chondrogenic induction

Mesenchymal stem cells (MSCs) can be induced towards chondrogenesis through the application of chondrogenic stimuli such as transforming growth factor-β (TGF-β) or by multiaxial mechanical load. Previous work has showed that the chondrogenic effect of multiaxial load on MSCs is mediated by the endogenous production of TGF-β1 by stimulated cells. This work compared the effects of TGF-β1 stimulation and multiaxial mechanical load on the secretomes of stimulated cells. MSCs were seeded into fibrin-poly(ester-urethane) scaffolds and chondrogenically stimulated with either TGF-β1 or mechanical load. The culture media was collected and analysed for 174 proteins using a cytokine antibody array. The results of the secretome analysis were then confirmed at a gene expression level by real-time PCR. As results implicated nitric oxide (NO), the media nitrite content was also determined as an indirect measurement of media NO levels. Results showed that TGF-β1 stimulation and mechanical load lead to similar changes in factors such as BLC, VEGF and MMP13, whilst differences in detected levels were seen for factors including leptin, MDC, MIP3α and LAP. Gene expression analysis confirmed significant changes in four factors: angiopoietin 2, GROα, MMP13 and osteoprotegerin. After one week in culture the media nitrite content was significantly higher in loaded groups than both control and TGF-β1 stimulated groups, suggesting this may be a major therapeutic target. These data show that despite clear similarities, TGF-β1 stimulation and load have distinct effects on MSCs and are not analogous. This study has identified a number of potentially novel targets for tissue engineering, these data may also be useful for improving rehabilitation protocols e.g. after microfracture

Effective repair of articular cartilage using human pluripotent stem cell-derived tissue

In an effort to develop an effective source of clinically relevant cells and tissues for cartilage repair a directed differentiation method was used to generate articular chondrocytes and cartilage tissues from human embryonic stem cells (hESCs). It has previously been demonstrated that chondrocytes derived from hESCs retain a stable cartilage-forming phenotype following subcutaneous implantation in mice. In this report, the potential of hESC-derived articular-like cartilage to repair osteochondral defects created in the rat trochlea was evaluated. Articular cartilage-like tissues were generated from hESCs and implanted into the defects. After 6 and 12 weeks, the defects were evaluated histologically and immunohistochemically, and the quality of repair was assessed using a modified ICRS II scoring system. Following 6 and 12 weeks after implantation, hESC-derived cartilage tissues maintained their proteoglycan and type II collagen-rich matrix and scored significantly higher than control defects, which had been filled with fibrin glue alone. Implants were found to be well integrated with native host tissue at the basal and lateral surfaces, although implanted human cells and host cells remained regionally separated. A subset of implants underwent a process of remodeling similar to endochondral ossification, suggesting the potential for a single cartilaginous implant to promote the generation of new subchondral bone in addition to repair of the articular cartilage. The ability to create cartilage tissues with integrative and reparative properties from an unlimited and robust cell source represents a significant advance for cartilage repair that can be further developed in large animal models before clinicalsetting application

Asymmetrical seeding of MSCs into fibrin–poly(ester‐urethane) scaffolds and its effect on mechanically induced chondrogenesis

Mesenchymal stem cells (MSCs) are currently being investigated as candidate cells for regenerative medicine approaches for the repair of damaged articular cartilage. For these cells to be used clinically, it is important to understand how they will react to the complex loading environment of a joint in vivo. In addition to investigating alternative cell sources, it is also important for the structure of tissue‐engineered constructs and the organization of cells within them to be developed and, if possible, improved. A custom built bioreactor was used to expose human MSCs to a combination of shear and compression loading. The MSCs were either evenly distributed throughout fibrin‐poly(ester‐urethane) scaffolds or asymmetrically seeded with a small proportion seeded on the surface of the scaffold. The effect of cell distribution on the production and deposition of cartilage‐like matrix in response to mechanical load mimicking in vivo joint loading was then investigated. The results show that asymmetrically seeding the scaffold led to markedly improved tissue development based on histologically detectable matrix deposition. Consideration of cell location, therefore, is an important aspect in the development of regenerative medicine approaches for cartilage repair. This is particularly relevant when considering the natural biomechanical environment of the joint in vivo and patient rehabilitation protocols