Facilitated receptor-recognition and enhanced bioactivity of bone morphogenetic protein-2 on magnesium-substituted hydroxyapatite surface.

Baolin Huang,Tong Li,Sai Ding,Changsheng Liu,Yuan Yuan,Wenjing Zhang

doi:10.1038/srep24323

Abstract

Biomaterial surface functionalized with bone morphogenetic protein-2 (BMP-2) is a promising approach to fabricating successful orthopedic implants/scaffolds. However, the bioactivity of BMP-2 on material surfaces is still far from satisfactory and the mechanism of related protein-surface interaction remains elusive. Based on the most widely used bone-implants/scaffolds material, hydroxyapatite (HAP), we developed a matrix of magnesium-substituted HAP (Mg-HAP, 2.2 at% substitution) to address these issues. Further, we investigated the adsorption dynamics, BMPRs-recruitment, and bioactivity of recombinant human BMP-2 (rhBMP-2) on the HAP and Mg-HAP surfaces. To elucidate the mechanism, molecular dynamic simulations were performed to calculate the preferred orientations, conformation changes, and cysteine-knot stabilities of adsorbed BMP-2 molecules. The results showed that rhBMP-2 on the Mg-HAP surface exhibited greater bioactivity, evidenced by more facilitated BMPRs-recognition and higher ALP activity than on the HAP surface. Moreover, molecular simulations indicated that BMP-2 favoured distinct side-on orientations on the HAP and Mg-HAP surfaces. Intriguingly, BMP-2 on the Mg-HAP surface largely preserved the active protein structure evidenced by more stable cysteine-knots than on the HAP surface. These findings explicitly clarify the mechanism of BMP-2-HAP/Mg-HAP interactions and highlight the promising application of Mg-HAP/BMP-2 matrixes in bone regeneration implants/scaffolds.

Highlights

An urgent need to understand and tailor the adsorption and bioactivity of bone morphogenetic protein-2 (BMP-2) upon orthopedic implants/ scaffolds
Despite all these molecular dynamics (MD) and steered molecular dynamics (SMD) simulations for bone morphogenetic proteins (BMPs)-2 adsorption, up to date, relatively little knowledge has been obtained about the bone morphogenetic protein receptors (BMPRs)-recruitment and bioactivity of BMP-2 upon the HAP and Mg-substituted HAP (Mg-HAP) model surfaces
In the present study we both experimentally and numerically investigated the adsorption, BMPRs-recruitment, and bioactivity of recombinant human BMP-2 (rhBMP-2) on the HAP and Mg-HAP surfaces. With these typical matrixes as material models, the results indicated that the BMPR-IA binding capacity and bioactivity of adsorbed rhBMP-2 were significantly up-regulated on the Mg-HAP surface compared to the HAP surface, even though the adsorption amount of rhBMP-2 was slightly decreased

Summary

Introduction

An urgent need to understand and tailor the adsorption and bioactivity of BMP-2 upon orthopedic implants/ scaffolds. A series of MD and SMD simulations showed a shield effect in the adsorption processes of leucine-rich amelogenin protein onto silicon-doped HAP surfaces[37] In another recent study using MD and SMD, it has found that the interfacial mechanical behavior is governed by the electrostatic attraction between an osteopontin and a HAP surface[38]. It was proven that proteins could show different adsorption mechanisms on the HAP surface, such as the adsorption formed with electrostatic interaction and water-bridged H-bonds[36,39] These works clearly explained the conformational changes of the protein during the adsorption/desorption processes, but they lack in vitro/vivo validation of the bioactivity of the adsorbed proteins. The detailed mechanism was elucidated by the experimental results and numerical simulations

Methods

Results

Discussion

Conclusion