3D Cocultures of Osteoblasts and Staphylococcus aureus on Biomimetic Bone Scaffolds as a Tool to Investigate the Host–Pathogen Interface in Osteomyelitis

Abstract

Osteomyelitis (OM) is an infectious disease of the bone primarily caused by the opportunistic pathogen Staphylococcus aureus (SA). This Gram-positive bacterium has evolved a number of strategies to evade the immune response and subvert bone homeostasis, yet the underlying mechanisms remain poorly understood. OM has been modeled in vitro to challenge pathogenetic hypotheses in controlled conditions, thus providing guidance and support to animal experimentation. In this regard, traditional 2D models of OM inherently lack the spatial complexity of bone architecture. Three-dimensional models of the disease overcome this limitation; however, they poorly reproduce composition and texture of the natural bone. Here, we developed a new 3D model of OM based on cocultures of SA and murine osteoblastic MC3T3-E1 cells on magnesium-doped hydroxyapatite/collagen I (MgHA/Col) scaffolds that closely recapitulate the bone extracellular matrix. In this model, matrix-dependent effects were observed in proliferation, gene transcription, protein expression, and cell–matrix interactions both of the osteoblastic cell line and of bacterium. Additionally, these had distinct metabolic and gene expression profiles, compared to conventional 2D settings, when grown on MgHA/Col scaffolds in separate monocultures. Our study points to MgHA/Col scaffolds as biocompatible and bioactive matrices and provides a novel and close-to-physiology tool to address the pathogenetic mechanisms of OM at the host–pathogen interface.

The osteoblast secretome in Staphylococcus aureus osteomyelitis

“…On the contrary, Tgf-β (a reported repressor of Ptx3 transcription) decreased over time. In the conditioned medium of the 3D cocultures, TNF-α was not detected, while PTX3 and OPG levels were stable over time ( 79 ). Importantly, the expression of selected osteogenic (Bmp2, Alp, Spp1), and antioxidant (Nrf-2, Ho-1) genes were substantially affected by the applied 3D setting, indicating matrix-dependent effects on osteoblasts during an S. aureus infection ( 79 ).…”

“…3D models that closely resemble the in vivo conditions have been implemented ( 79 , 102 , 103 ). In this regard, manufacturing of bioactive bone mimetic scaffolds that recapitulate texture and chemistry of the natural bone matrix provide unique experimental tools to study the interface between pathogens (including S. aureus ) and both skeletal and immune cells in a tightly controlled setting.…”

Bacterial Infection-Mimicking Three-Dimensional Phagocytosis and Chemotaxis in Electrospun Poly(ε-caprolactone) Nanofibrous Membrane

“…A number of 3D in vitro culture systems have been developed to study the interactions between bacteria and cells [ 14 ]. S. aureus infection in skin tissue and bone has been studied using 3D co-culture models [ 15 , 16 ]. Ding et al demonstrated that macrophages can transmigrate across a polyethylene terephthalate membrane to reach the epithelial cell layer cultured with S. aureus [ 17 ].…”

Host–Pathogen Interactions: Organotypic Cultures to Unravel the Mysteries of the Primordial Hostility among Organisms

“…Chronic and prolonged infections with S. aureus represent the highest burden of disease, with decreasing likelihood of treatment success as the infection becomes established [ 23 ]. In this Special Issue, two different publications [ 24 , 25 ] showed the potential of 3D models in gaining more insight towards controlling the burden caused by such a threatening pathogen. Hofstee et al [ 24 ] showed that staphylococcal abscess communities cause myeloid-derived suppressor cell (MDSC) expansion from bone marrow cells and identified possible mediators to be targeted as an additional strategy for treating chronic S. aureus infections.…”

“…Hofstee et al [ 24 ] showed that staphylococcal abscess communities cause myeloid-derived suppressor cell (MDSC) expansion from bone marrow cells and identified possible mediators to be targeted as an additional strategy for treating chronic S. aureus infections. Parente et al [ 25 ] developed a 3D model of osteomyelitis (OM), a bone condition primarily induced by S. aureus infections, based on co-cultures of S. aureus and murine osteoblastic MC3T3-E1 cells on magnesium-doped hydroxyapatite/collagen I (MgHA/Col) scaffolds that closely recapitulate the bone extracellular matrix. This model shows great potential for the study of OM caused by S. aureus infections.…”