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

Raffaella Parente ¹ , Valentina Possetti ¹ , Maria Lucia Schiavone ^{1 2} , Elisabetta Campodoni ³ , Ciro Menale ^{2 4} , Mattia Loppini ^{1 5} , Andrea Doni ¹ , Barbara Bottazzi ¹ , Alberto Mantovani ^{1 5 6} , Monica Sandri ³ , Anna Tampieri ^{3 7} , Cristina Sobacchi ^{1 2} , Antonio Inforzato ^{1 5}

1. IRCCS Humanitas Research Hospital, 20089 Rozzano, Italy.
2. National Research Council-Institute for Genetic and Biomedical Research (CNR-IRGB), Milan Unit, 20089 Rozzano, Italy.
3. National Research Council-Institute of Science and Technology for Ceramics (CNR-ISTEC), 48018 Faenza, Italy.
4. Department of Clinical Medicine and Surgery, University of Naples “Federico II”, 80131 Naples, Italy.
5. Department of Biomedical Sciences, Humanitas University, 20072 Pieve Emanuele, Italy.
6. The William Harvey Research Institute, Queen Mary University of London, London E1 4NS, UK.
7. National Research Council-Institute of Nanostructured Material (CNR-ISMN), 40129 Bologna, Italy.

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.

Keywords: 3D models; Staphylococcus aureus; biomimetic bone scaffolds; host–pathogen interface; osteoblast-like cells; osteomyelitis.

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