Human plasma fibronectin potentialization of the in vitro and in vivo osteogenic activity of BMPs onto hydroxyapatite coatings with a focus on BMP-6
Résumé
Design of new osteoinductive biomaterials to recapitulate an optimized physiological environment capable of recruiting stem cells and instructing their fate towards the osteoblastic lineage has become a priority in orthopedic surgery. This work aims at evaluating the bioactivity of BMP combined with human plasma fibronectin (FN/BMP) delivered in solution or coated onto titanium-hydroxyapatite (TiHA) surfaces prepared by pulsed laser deposition (PLD) technique. Herein, we focus on the comparison of in vitro osteogenic efficacy in mouse C2C12 pre-osteoblasts of three BMP members, namely: BMP-2, BMP-6 and BMP-7. In parallel, we evaluated the molecular binding strength between each BMP with FN using the Surface Plasmon Resonance (SPR) technology. The affinity of BMPs for FN fundamentally differs depending on the BMP considered. Indeed, combining FN with BMP-2 on TiHA surfaces potentiates the burst of gene-mediated osteogenic induction, while it prolongs the osteogenic activity of BMP-6 and surprisingly annihilates the BMP-7 one. These results correlate with FN/BMP affinity for TiHA, since BMP-6 > BMP-2 > BMP-7. Finally, by analyzing the osteogenic activity in the peri-implant environment, we showed that osteoinductive paracrine effects were significantly decreased upon (FN/BMP-6), as opposed to (FN/BMP-2) coatings. Altogether, our in vitro results support the use of FN/BMP-6 to develop a biomimetic microenvironment capable to induce osteogenic activity under physiological conditions, with minimum side effects. Results of in vivo experiments in an intra-muscular ectopic model and in a critical-size radial defect in rabbit for validating the osteogenic capacity of FN/BMP-6 adsorbed on TiHA surfaces will be presented.