Collagen-targeting parathyroid hormone-related peptide promotes collagen binding and in vitro chondrogenesis in bone marrow-derived MSCs

Parathyroid hormone-related peptide (PTHrP) is an important inductive factor during chondrogenesis of mesenchymal stem cells (MSCs). PTHrP induces chondrogenesis and suppresses hypertrophy, yet the lack of an efficient delivery system limits its use for cartilage tissue engineering in clinical application. In this study, a peptide of 7 amino acids was first used to engineer PTHrP to construct a collagen-targeting system. This peptide functioned as a collagen-binding domain (CBD) to specially target the PTHrP to collagen. ELISA assay was used to determine the collagen-binding ability of CBD-PTHrP. The effect of CBD-PTHrP on chondrogenesis was measured by an in vitro pellet assay in bone marrow-derived MSCs (BM-MSCs). As expected, the CBD peptide promoted the binding of CBD-PTHrP to collagen when compared to NAT-PTHrP. Furthermore, the recombinant protein CBD-PTHrP induced the expression of COL2A1 and Sox-9, inhibited the expression of COL1A1 at the mRNA and protein levels as effectively as NAT-PTHrP. Safranin-O and immunohistochemistry for collagen types I, II, X and Sox-9 generally paralleled qRT-PCR and western blotting findings with minor variations. In conclusion, our study demonstrated that CBD-PTHrP is a collagen-targeting system and promotes in vitro chondrogenesis in BM-MSCs. We suggest that this is an efficient delivery system for cartilage tissue engineering in clinical application.