Combination of baculovirus-expressed BMP-2 and rotating-shaft bioreactor culture synergistically enhances cartilage formation

Baculovirus is an emerging gene delivery vector, thanks to a number of unique advantages. Herein, we genetically modified the rabbit articular chondrocytes with a recombinant baculovirus (Bac-CB) encoding bone morphogenetic protein-2 (BMP-2), which conferred high level BMP-2 expression and triggered the re-differentiation of dedifferentiated third passage (P3) chondrocytes in the monolayer culture. The transduced and mock-transduced P3 cells were seeded into porous scaffolds and cultured in either the dishes or the rotating-shaft bioreactor (RSB), a novel bioreactor imparting a dynamic, two-phase culture environment. Neither mock-transduced constructs in the RSB culture nor the Bac-CB-transduced constructs in the static culture grew into uniform cartilaginous tissues. Only the Bac-CB-transduced constructs cultured in the RSB for 3 weeks resulted in cartilaginous tissues with hyaline appearance, uniform cell distribution, cartilage-specific gene expression and considerably enhanced cartilage-specific extracellular matrix deposition, as determined by histological staining, reverse transcription-PCR analyses and biochemical assays. This is the first study demonstrating that combination of baculovirus-mediated growth factor expression and RSB culture synergistically enhanced in vitro creation of cartilaginous tissues from dedifferentiated chondrocytes. Since baculovirus transduction is generally considered safe, this approach represents a viable alternative to stimulate the formation of engineered cartilage in a more cost-effective way than the growth factor supplementation.