Thesis defence by Valia KHODR

Mots-clés:

Abstract

    Bone morphogenetic factors (BMPs) are growth factors with several physiological and pathological roles. As their name suggest, they are osteoinductive as they promote stem cells differentiation into osteoblasts, in addition, they are involved in a large panel of physiological and pathological processes, including angiogenesis, adipogenesis, muscle differentiation and embryonic development and cancers. In vivo, BMPs bind two types of BMP receptors (BMPR); type –I and type-II. In this thesis, we focused on the early steps of bone tissue formation starting at the molecular scale with the BMP/BMPR interaction. The large number of BMPs associated to a low number of BMPR leads to a phenomenon of promiscuity, where a BMP can bind different BMPRs with various affinities. In the thesis, the binding affinities and kinetic properties of four BMPs: BMP-2, BMP-4, BMP-7 and BMP-9 with five type-I BMPR (ALK1, ALK2, ALK3, ALK5, ALK6) and three type-II BMPRs (BMPR-II, ACTR-IIA, ACTR-IIB) were first studied using biolayer interferometry (BLI) and surface plasmon resonance (SPR). In a second part, biomaterials in the form of polyelectrolytes biomimetic films were used to present BMP to cells in a matrix-bound manner, and to study the combined effect of film stiffness and BMP-2 presentation (for BMP-2, BMP-4, BMP-7 and BMP-9). C2C12 skeletal myoblasts and human periosteum-derived stem cells (hPDSCs) were used as cellular models of BMP-responsive cells. High content screening (HCS) of cellular responses was done to quantify cell adhesion evaluated by cell number and cell spreading area, and cell differentiation in bone by quantifying Smad and alkaline phosphatase (ALP) activities. Using RNA silencing of BMP receptors and of the adhesion receptors integrins enabled to reveal the specific roles of each receptors. In a third part, a HCS assay to quantify phosphorylated Smad was developed and a proof-of-concept of drug assays on biomaterials was realized, using commercial inhibitors of ALK2, ALK5 inhibitors.