Usefulness of Agarose Mold as a Storage Container for Three-Dimensional Tissue-Engineered Cartilage

The efficiency of substance exchange may be decreased when the thickness and volume of such a tissue-engineered cartilage that is composed of cultured cells and porous scaffold increase. Moreover, during the transport of this construct with complicated shapes, excessive and focal mechanical loading may cause deformation. The establishment of incubation and transport methods is necessary for the three-dimensional tissue-engineered cartilage. Therefore, we investigated the preparation of an agarose mold with a concavity similar to the shape of 3-dimensional tissue-engineered cartilage to prevent excessive and focal concentration of stress, while avoiding interference with substance exchange as much as possible. Firstly, we investigated the preparation at 1% - 4% agarose concentrations. Since the mechanical strength was insufficient at 1%, 2% was regarded as appropriate. Using 2% agarose, we prepared a mold with a 5 × 5 × 5 mm concavity to accommodate tissue-engineered cartilage (5 × 5 × 5 mm mixture of 1.5 × 107 cells and collagen gel), and stored the regenerative cartilage in it for 2 and 24 hours. On comparison with storage in a plastic mold with the same shape in which substance exchanged from side and bottom was impossible, although no significant differences were noted in the number or viability of cells after 2 hours, these were markedly reduced in the plastic mold after 24 hours. It was confirmed that favorable cell numbers and viability were maintained by immediately retaining the regenerative cartilage in the culture medium in the agarose mold and keeping the temperature at 37°C. Since this agarose mold also buffers against mechanical forces loaded on the three-dimensional regenerative tissue, it may be useful as a container for storage and transport of large-sized three-dimensional regenerative tissue.

Roles and regulation of bone morphogenetic protein-7 in kidney development and diseases

The gene encoding bone morphogenetic protein-7(BMP7) is expressed in the developing kidney in embryos and also in the mature organ in adults. During kidney development, expression of BMP7 is essential to determine the final number of nephrons in and proper size of the organ. The secreted BMP7 acts on the nephron progenitor cells to exert its dual functions: To maintain and expand the progenitor population and to provide them with competence to respond to differentiation cues, each relying on distinct signaling pathways. Intriguingly, in the adult organ, BMP7 has been implicated in protection against and regeneration from injury. Exogenous administration of recombinant BMP7 to animal models of kidney diseases has shown promising effects in counteracting inflammation, apoptosis and fibrosis evoked upon injury. Although the expression pattern of BMP7 has been well described, the mechanisms by which it is regulated have remained elusive and the processes by which the secretion sites of BMP7 impinge upon its functions in kidney development and diseases have not yet been assessed. Understanding the regulatory mechanisms will pave the way towards gaining better insight into the roles of BMP7, and to achieving desired control of the gene expression as a therapeutic strategy for kidney diseases.

Hollow Fiber Module Applied for Effective Proliferation and Harvest of Cultured Chondrocytes

Steady and useful culture for chondrocytes is essential for cartilage regenerative medicine. However, in conventional plate culture, the chondrocytes become dedifferentiated and lose their ability to make cartilage matrices. Three-dimensional culture mimicking the physiological environment in native chondrocytes is useful to maintain the chondrocyte properties during the proliferation culture. However, the three-dimensional culture is practically a hard task due to difficult harvest of the cells. Thus, we attempted to apply porous materials, hollow fibers for the three-dimensional culture, and developed their module to realize the effective harvest of the cells. Polyethersulfone-based hollow fibers, whose safety and cell affinity were confirmed by the experiment of the coculture with human chondrocytes, were collected to fabricate a module. The hollow fiber module was installed with screw ends, and enabled the easy removal of chondrocytes from the inner unit. Cultured human chondrocytes embedded within collagen hydrogel were put into the outer lumen of the hollow fiber module, while chondrocyte prolfieration medium was perfused through the inner lumen at 0 to 30 mL/min. After 2 weeks’ culture, the flow rate of 3 to 10 mL/min effectively supported the chondrocyte proliferation. Then, long-term culture using the hollow fiber module at flow rate of 5 mL/min was performed, revealing that the cell growth in this module at 3 weeks was approximately twice larger than that in static culture. The numbers of viable cells could be maintained by week 7. The hollow fiber module installed with screw ends can effectively culture and harvest the chondrocytes.