Affinity-selected polysaccharide for rhBMP-2-induced osteogenesis via BMP receptor activation

Abstract

Bone morphogenetic protein-2 (BMP-2) is a key regulator of osteogenesis and always involved in bone regeneration and repair. However, supraphysiological BMP-2 doses are always associated with complications such as heterotopic ossification and inflammation, which leads to pain and impaired mobility. Polysaccharides have been widely used to bind BMP-2 and up-regulate its osteoinduction. Here, we developed a semi-synthetic polysaccharide, 2-N, 6-O-sulafted chitosan (26SCS), and compared its enhancement on recombinant human BMP-2 (rhBMP-2) induced osteogenesis with that of natural sulfated polysaccharide heparin and non-sulfated polysaccharide dextran. We found that both 26SCS and heparin amplified the signaling of rhBMP-2 on rat bone marrow stromal cells (RBMSCs) via enhancing the binding between rhBMP-2 and BMP-2 receptors (BMPRs) and activating the phosphorylation of Smad pathway, which lowered the effective dosage of rhBMP-2 on RBMSCs differentiation. By contrast, dextran had no effect on rhBMP-2-induced osteogenic differentiation. In addition, the pro-osteogenic potential of 26SCS and heparin combined with rhBMP-2 was confirmed in vivo using a mouse ectopic bone model. Micro-computed tomography and histological evaluation revealed more mature trabecular bone in the new ossified tissue with the treatment of 26SCS and low dose of rhBMP-2 than that with the treatment of high dose of rhBMP-2 alone. The addition of 26SCS did not activate osteoclast that led to bone resorption like heparin, but significantly promoted the angiogenesis. These findings suggested that 26SCS retained the advantages of heparin and amplified the regenerative capacity of rhBMP-2, which might provide a new strategy for growth factors correlated bone regeneration.