Macrophage Effects on Mesenchymal Stem Cell Osteogenesis in a Three-DimensionalIn VitroBone Model

Abstract

As musculoskeletal (MSK) disorders continue to increase globally, there is an increased need for novel, in vitro models to efficiently study human bone physiology in the context of both healthy and diseased conditions. For these models, the inclusion of innate immune cells is critical. Specifically, signaling factors generated from macrophages play key roles in the pathogenesis of many MSK processes and diseases, including fracture, osteoarthritis, infection etc. In this study, we aim to engineer three-dimensional (3D) and macrophage-encapsulated bone tissues in vitro, to model cell behavior, signaling, and other biological activities in vivo, in comparison to current two-dimensional models. We first investigated and optimized 3D culture conditions for macrophages, and then co-cultured macrophages with mesenchymal stem cells (MSCs), which were induced to undergo osteogenic differentiation to examine the effect of macrophage on new bone formation. Seeded within a 3D hydrogel scaffold fabricated from photocrosslinked methacrylated gelatin, macrophages maintained high viability and were polarized toward an M1 or M2 phenotype. In co-cultures of macrophages and human MSCs, MSCs displayed immunomodulatory activities by suppressing M1 and enhancing M2 macrophage phenotypes. Lastly, addition of macrophages, regardless of polarization state, increased MSC osteogenic differentiation, compared with MSCs alone, with proinflammatory M1 macrophages enhancing new bone formation most effectively. In summary, this study illustrates the important roles that macrophage signaling and inflammation play in bone tissue formation.

Macrophage-Derived Exosomes Promote Bone Mesenchymal Stem Cells Towards Osteoblastic Fate Through microRNA-21a-5p

“…A recent study found that co-cultured macrophages and mesenchymal stem cells can be induced to undergo osteogenic differentiation, with M2 macrophages being the most successful at promoting the generation of new bone tissue ( Loi et al, 2016 ; Zhang et al, 2017 ; Nathan et al, 2019 ). Furthermore, quite a few studies have shown that an initial proinflammatory phase modulated by M1 macrophages promotes osteogenesis in BMSCs ( Tu et al, 2015 ; Lu et al, 2017 ; Romero-López et al, 2020 ; Xia et al, 2020 ). However, the mechanism of M1 macrophages promoting osteogenic differentiation at the early stage of inflammation is still rather ambiguous.…”

The Effects of Macrophage Phenotype on Osteogenic Differentiation of MSCs in the Presence of Polyethylene Particles

“…These 3D constructs were then cultured in a custom-designed, dual-flow microphysiological system. Figure 1 a shows the loading process of the scaffold-based 3D cultures [ 13 ]. The medium was perfused into the scaffold chamber from both the upper and lower inlets, as shown in Figure 1 b.…”

Modeling Immunity In Vitro: Slices, Chips, and Engineered Tissues

“…Here we discuss in more detail models of the gut, brain, lungs, and vasculature with an integrated immune element. The role of macrophages has also been examined in models of osteogenesis and muscle repair (113)(114)(115)(116)(117) but is outside the scope of this review.…”