Stem cell-derived chondrocytes for regenerative medicine

Expansion and Chondrogenic Differentiation of Human Mesenchymal Stem Cells

The potential of human mesenchymal stem cells (hMSC) to differentiate into various types of mesenchymal tissue, such as chondrocytes, makes them a potential cell source in cartilage tissue engineering. Because of the requirement of high cell amounts for the generation of cartilage implants or for the extensive experimental studies to investigate the culture parameters, the initial cells have to be expanded, which leads to high population doubling numbers. It is known that hMSC can differentiate into chondrocytes at least up to the 15th population doubling. To monitor the differentiation status, the protein MIA (melanoma inhibitory activity), which is only synthesized by malignant melanomas and chondrocytes, can be used. In this study the chondrogenic differentiation potential of hMSC beyond the 15th population doubling was investigated using MIA as a chondrocyte marker. A chondrogenic potential of hMSC at higher population doubling numbers may be of interest due to the requirement of less frequent isolations of cells. Therefore hMSC were cultured in a monolayer until the 37th population doubling. Cells of different passages were cultured as pellets for two weeks in transforming growth factor (TGF)-β3 containing differentiation medium. The MIA contents in medium on the last three cultivation days were measured for each case using an MIA-ELISA-kit. A significant difference between MIA content in medium of the pellet and non-stimulated monolayer reference cultures was detectable until the 32nd population doubling. In addition, the hMSC were seeded at lower densities to investigate whether the cells may be expanded faster and with less amount of work due to higher population doubling numbers per passage. The reduced inoculation density led to an increased growth rate. (Int J Artif Organs 2007; 30: 611–8)

Skeletal tissue engineering using embryonic stem cells

Various cell types have been investigated as candidate cell sources for cartilage and bone tissue engineering. In this review, we focused on chondrogenic and osteogenic differentiation of mouse and human embryonic stem cells (ESCs) and their potential in cartilage and bone tissue engineering. A decade ago, mouse ESCs were first used as a model to study cartilage and bone development and essential genes, factors and conditions for chondrogenesis and osteogenesis were unravelled. This knowledge, combined with data from the differentiation of adult stem cells, led to successful chondrogenic and osteogenic differentiation of mouse ESCs and later also human ESCs. Next, researchers focused on the use of ESCs for skeletal tissue engineering. Cartilage and bone tissue was formed in vivo using ESCs. However, the amount, homogeneity and stability of the cartilage and bone formed were still insufficient for clinical application. The current protocols require improvement not only in differentiation efficiency but also in ESC-specific hurdles, such as tumourigenicity and immunorejection. In addition, some of the general tissue engineering challenges, such as cell seeding and nutrient limitation in larger constructs, will also apply for ESCs. In conclusion, there are still many challenges, but there is potential for ESCs in skeletal tissue engineering.

Enhancing osteogenic differentiation of mouse embryonic stem cells by nanofibers

Controlled differentiation of embryonic stem cells (ESC) is necessary to their use as a cell source for tissue engineering or regeneration. To date, most studies have concentrated on chemical cues to direct ESC differentiation. However, during normal embryonic development, multiple factors beyond chemical cues play a role, including the extracellular matrix (ECM) in bone development. In this study, we use nanofibrous (NF) matrices to mimic the morphology of the ECM to examine the contribution of the ECM morphology to the differentiation of mouse ESC. After 12 h of differentiation culture, mouse ESC form protrusions interacting with NF matrices, while they appear not to interact with flat films. Immunofluorescence staining after 26 days of differentiation culture indicates a greater degree of differentiation for mouse ESC on NF matrices compared to flat films. Polymerase chain reaction results, also, show greater degree of osteogenic differentiation on NF matrices compared to flat films when osteogenic supplements are added to the culture. Overall, these results demonstrate that NF morphology contributes to the controlled differentiation of mouse ESC.

Stem cells for tissue engineering of articular cartilage

Articular cartilage injuries are one of the most common disorders in the musculo-skeletal system. Injured cartilage tissue cannot spontaneously heal and, if not treated, can lead to osteoarthritis of the affected joints. Although a variety of procedures are being employed to repair cartilage damage, methods that result in consistent durable repair tissue are not yet available. Tissue engineering is a recently developed science that merges the fields of cell biology, engineering, material science, and surgery to regenerate new functional tissue. Three critical components in tissue engineering of cartilage are as follows: first, sufficient cell numbers within the defect, such as chondrocytes or multipotent stem cells capable of differentiating into chondrocytes; second, access to growth and differentiation factors that modulate these cells to differentiate through the chondrogenic lineage; third, a cell carrier or matrix that fills the defect, delivers the appropriate cells, and supports cell proliferation and differentiation. Stem cells that exist in the embyro or in adult somatic tissues are able to renew themselves through cell division without changing their phenotype and are able to differentiate into multiple lineages including the chondrogenic lineage under certain physiological or experimental conditions. Here the application of stem cells as a cell source for cartilage tissue engineering is reviewed.