The Extracellular Matrix for Bone Regeneration: Interplay between mesenchymal stromal cells and the bone microenvironment

Bone is a very dynamic tissue composed of bone extracellular matrix (ECM) in a tight interplay with bone cells. Extracellular signaling molecules and the ECM with its biochemical and biophysical cues continuously influence bone cell behaviour, tightly regulating bone formation and quality. Bone tissue is continuously undergoing remodelling and can self-repair after fracture healing. However, major challenges remain in case of large skeletal defects or age-related bone fragility. Bone tissue engineering has recently emerged as therapeutic strategy in alternative to bone grafts. Understanding how bone ECM and signaling molecules influence cell behaviour is crucial to ameliorate mesenchymal stromal cell (MSC) properties and to develop optimal bone grafts that reproduce the physiological bone microenvironment for tissue engineering applications. Cell-derived ECMs have been proposed as a good alternative to native decellularized organs in the context of tissue engineering, in combination with scaffolds, to reproduce the physiological architectural complexity of ECM.
In this thesis, we studied how the extracellular microenvironment influences osteoblast behavior and how we can manipulate it for regenerative purposes. We created three osteoblast-derived ECMs and we investigated how the protein composition studied by mass spectrometry affects MSC osteogenic differentiation and mineralization, to ameliorate MSC properties for bone regeneration. We employed a kinase array to disentangle MSC adhesion to the osteoblast-derived ECM, for the rational design of novel cell-instructive scaffolds for tissue engineering. Moreover, we studied how the extracellular environment with signaling molecules, such as Activin-A, affects osteoblast gene expression and miRNA profile to regulate ECM mineralization, thereby modulating bone tissue quality. Overall this study contributes to a better understanding of the physiology of tissue microenvironment, but also to identify regulatory candidates that could be possibly used to ameliorate in vitro cultures, to improve the promising properties of MSCs in regenerative medicine.