Angiostatin-functionalized collagen scaffolds suppress angiogenesis but do not induce chondrogenesis by mesenchymal stromal cells in vivo.

Tissue engineering for fibrocartilage regeneration using mesenchymal stromal cells (MSC) and biomaterial scaffolds is emerging as a promising strategy, but inhibiting vascularization to prevent endochondral ossification is important to develop stable implants. The objective of this study was to investigate the effect of angiostatin on inhibition of angiogenesis and promotion of chondrogenesis by collagen scaffolds with or without MSC implanted subcutaneously in rats. One scaffold from the following groups was implanted in each animal: Collagen scaffolds only, scaffolds functionalized with angiostatin, scaffolds loaded with MSC and scaffolds functionalized with angiostatin and loaded with MSC. The various scaffolds were harvested after 2 and 8 weeks for histological analysis, Real-time quantitative polymerase chain reaction (RT-qPCR) and immunofluorescence quantification. Results demonstrated significantly decreased expression of inflammatory (interleukin 1 alpha and beta) and angiogenic genes (platelet and endothelial cell adhesion molecule 1) in scaffolds functionalized with angiostatin after 2 weeks in vivo. Histologically, after 8 weeks, the scaffolds with angiostatin had less inflammatory cells and more collagen matrix formation, but no fibrocartilage formation was detected. Thus, although angiostatin suppressed angiogenesis, it did not stimulate ectopic chondrogenesis in tissue engineered constructs in vivo.