Interplay Between Local Versus Soluble Transforming Growth Factor-Beta and Fibrin Scaffolds: Role of Cells and Impact on Human Mesenchymal Stem Cell Chondrogenesis

Structural extracellular matrix molecules gain increasing attention as scaffolds for cartilage tissue engineering owing to their natural role as a growth factor repository. We recently observed that a collagen-type I/III (Col-I/III) matrix, human recombinant transforming growth factor-beta (TGF-beta) protein, and fibrin hydrogel (FG) combined to a biphasic construct provided sufficient long-term TGF-beta support to drive in vitro chondrogenesis of human mesenchymal stem cells (hMSC). Here we ask whether FG and Col-I/III can both retain TGF-beta, describe the influence of cell seeding on TGF-beta release, and compare the molecular path of hMSC chondrogenic differentiation under soluble versus local TGF-beta supply. Release of growth factor from scaffolds augmented with increasing amounts of TGF-beta was analyzed over 7 days and chondrogenesis was assessed over 42 days. Low TGF-beta release rates from Col-I/III as opposed to higher release from FG indicated that both molecules retained TGF-beta, with Col-I/III being the superior storage component. Cell seeding enhanced TGF-beta retention in FG by about threefold and almost stopped release beyond 24 h. TGF-beta remained bioactive and supported MSC chondrogenesis without impairing the amount of proteoglycan and collagen-type II deposition per cell and per construct compared to standard scaffold-free MSC pellets supplied with soluble TGF-beta. Local TGF-beta, however, mediated lower cell content, less collagen-type X relative to collagen-type II deposition and no matrix metalloproteinase-13 up-regulation. In conclusion, cells quickly halted release of local TGF-beta from FG, turning FG and Col-I/III into attractive TGF-beta repositories capable to drive full hMSC chondrogenesis, but via a modulated differentiation pathway. Since only part of the changes was reproduced by transient soluble TGF-beta supply, release kinetics alone could not explain the molecular differences, suggesting that local TGF-beta acts distinct from its soluble counterpart.