Macrophage-derived small extracellular vesicles promote biomimetic mineralized collagen-mediated endogenous bone regeneration

Anqi Liu,Yan Liu,Ting Zhang,Lisha Zhu,Nan Jiang,Steve G F Shen,Cuicui Fu,Shengji Cui,Yu Wang,Shanshan Jin

doi:10.1038/s41368-020-00100-6

Abstract

Macrophages play an important role in material-related immune responses and bone formation, but the functionality of macrophage-derived extracellular vesicles (EVs) in material-mediated bone regeneration is still unclear. Here, we evaluated intracellular communication through small extracellular vesicles (sEVs) and its effects on endogenous bone regeneration mediated by biomimetic intrafibrillarly mineralized collagen (IMC). After implantation in the bone defect area, IMC generated more neobone and recruited more mesenchymal stem cells (MSCs) than did extrafibrillarly mineralized collagen (EMC). More CD63+CD90+ and CD63+CD163+ cells were detected in the defect area in the IMC group than in the EMC group. To determine the functional roles of sEVs, extracellular vesicles from macrophages cultured on different mineralized collagen were isolated, and they showed no morphological differences. However, macrophage-derived sEVs in the IMC group showed an enhanced Young’s modulus and exerted beneficial effects on the osteogenic differentiation of bone marrow MSCs by increasing the expression of the osteoblastic differentiation markers BMP2, BGLAP, COL1, and OSX and calcium nodule formation. Mechanistically, sEVs from IMC-treated macrophages facilitated MSC osteogenesis through the BMP2/Smad5 pathway, and blocking sEV secretion with GW4869 significantly impaired MSC proliferative, immunomodulative and osteogenic potential. Taken together, these findings show that macrophage-derived sEVs may serve as an emerging functional tool in biomaterial-mediated endogenous bone regeneration.

Highlights

Immune homeostasis is essential for successful bone regeneration driven by biomaterial scaffolds.[1]
Promoting endogenous bone regeneration and mesenchymal stem cells (MSCs) recruitment with biomimetic mineralized collagen Biomimetic mineralized collagen was fabricated according to our previously published procedures,[18,19] and its typical microstructure and element content were observed by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) (Fig. 1a)
The distribution of Ca and C was opposite in extrafibrillarly mineralized collagen (EMC), with an area of elevated Ca concentration corresponding to an area of reduced C concentration

Summary

Introduction

Immune homeostasis is essential for successful bone regeneration driven by biomaterial scaffolds.[1] Host-biomaterial reactions were previously associated with rejection; to date, innate immune effector cells, most notably macrophages, have been identified as important mediators and instructors during scaffold remodeling and tissue regeneration.[2,3,4] Immunoengineering via the development of ‘immune-interactive’ smart biomaterials has emerged as an effective strategy to improve bone regenerative outcomes This strategy utilizes biomaterial physicochemical modifications, including surface topography and chemistry, inorganic components and biomimetic bone architecture, to offer an appropriate microenvironment for immune responses, host cell recruitment and differentiation.[5,6,7,8]. Monocyte/macrophage depletion impairs osteoblastic differentiation and bone regeneration.[5,11]

Methods

Results

Conclusion