Bone Abstracts

Bone-tissue engineering approaches involve culturing mesenchymal stem cells (MSCs) on 3D scaffolds designed to mimic the composition, structure, and biomechanics of the native bone matrix. One of the key challenges in bone–tissue engineering is to understand the host response to implantable engineered constructs. Macrophages play an important role in fracture healing and tissue repair and are mainly involved in the inflammatory response at the early stage upon scaffold implantation and during its degradation. Growing evidence suggests that MSCs regulate inflammatory response mediated by macrophages through the secretion of soluble factors. 3D tissue scaffold structures drive MSCs into spatial dispositions that may regulate their immunomodulatory properties. The objective of this study was to determine the role of 3D scaffold geometry in regulating paracrine factors secreted by MSC in a co-culture model with macrophages. To this aim, MSCs were seeded on highly porous polystyrene scaffolds, which provide a 3D spatial environment, and co-cultured with TPA-differentiated THP1 cells using a transwell insert system. As controls, MSC were co-cultured with macrophages in 2D conditions. 3D growth of MSCs modulated the secretion patterns of PGE₂, TSG6, MCP1, and RANKL. Compared to isolated MSCs, the presence of macrophages induced an increase in PGE₂, TSG6, and MCP1 levels. Scaffolding structure of co-cultured MSCs further increased PGE₂ and TSG6 secretion but led to a decrease in MCP1 levels. Secretion of RANTES, MIP1α, RANKL, MCSF, and GM–CSF to the co-culture medium was attenuated when MSCs were cultured on 3D scaffolds. Monocyte migration rate was lower when assayed using conditioned medium from 3D than 2D co-cultures. Taking together, these data suggest that MSCs sense and respond to 3D environment modulating secretion profiles of chemokines and anti-inflammatory molecules that regulate their cross-talk with macrophages. Spatial arrangement of MSCs on 3D scaffolds may be responsible of their inhibitory action on monocyte migration.