Insertion of gallic acid onto chitosan promotes the differentiation of osteoblasts from murine bone marrow-derived mesenchymal stem cells

Chitosan, a naturally occurring biodegradable and biocompatible polymer, has found use as a food additive, nutraceuticals, and functional foods in recent years. In this study, gallic acid-g-chitosan (GAC) was prepared by the insertion of GA onto plain chitosan (PC) via free radical-mediated grafting and its osteogenic effects were investigated in murine bone marrow-derived mesenchymal stem cells (mBMMSCs). Structural characterization of PC and GAC was performed using 1H NMR and FT-IR spectroscopy. The amount of GA successfully grafted onto PC was 111 mg GA/g GAC via the Folin-Ciocalteu's method. While PC and GAC promoted the increase in alkaline phosphatase activity and mineralization, GAC increased these factors significantly more than PC, indicating that the grafting of GA onto chitosan increased its osteogenic potential. Mechanistic study revealed that GAC activated Wnt1 and Wnt3a mRNA and protein expression as well as increased the translocation of β-catenin into the nucleus and upregulated the expression of β-catenin targeted genes including Runx2, osterix, type I collagen and cyclin D1. In addition, DKK-1, a Wnt antagonist, decreased GAC-mediated osteoblast differentiation in mBMMSCs through blocking the Wnt/β-catenin signaling pathway.