Seminar LMGP - 24/09/2015 - Anne VALAT - Kinetics of BMP-2 induced transdifferentiation of C2C12 myoblasts

Orthopedic surgeons seek to obtain an optimal osteointegration of prosthetic devices in order to minimize implant rejects and avoid corrective surgeries. One of the actual challenges in the field of biomaterials thus consists in developing osteoinductive materials and surface coatings. The Bone Morphogenetic Protein 2 (BMP-2) is a bioactive molecule widely used to induce osteogenic differentiation in vitro as well as in vivo, especially to help bone formation in long bones non-union and spinal surgery. However, BMP-2 is usually loaded in porous collagen sponges, which leads to non-physiological delivery of the protein and side effects such as ectopic bone formation. A further understanding of BMP-2 effects on bone tissue formation is crucial to a better control of bone regeneration in vivo.
To address these issues, our group has developed a surface coating based on layer-by-layer technique that allows a precise and controlled delivery of BMP-2. This thin films made of the biopolymers hyaluronan and poly(L-Lysine) can be coated on almost any kind of surface and, interestingly, can trap BMP-2, deliver it precisely and present it in a “matrix-bound” manner to the cells, mimicking the in vivo extracellular environment. Skeletal muscle cells can respond to these bioactive coatings by trans-differentiating into bone tissue instead of forming muscle tissue. Each type of tissue is associated with the presence of specific components in the extra-cellular matrix and of specific adhesion receptors, which are involved in the cell/ECM interactions (integrins) and in the cell/cell interactions (cadherins).

My PhD project, supported by CEMAM, aims at analyzing and quantifying the kinetic of differentiation of muscle progenitors in response to BMP-2 (bone differentiation) in comparison to myogenic differentiation in the absence of BMP-2. First, we compared the ability of the LbL films to induce early bone or muscle tissue formation, in the presence or absence of matrix-bound BMP-2, to that of conventional plastic substrates with BMP-2 added in solution. Early trans-differentiation is characterized by the appearance of muscle and bone transcription factors and by the production of proteins to form an extracellular matrix. . Secondly, using databases, we analyzed the potential repertoire of integrins and of cadherins associated to the myogenic and osteogenic differentiation pathways. Using quantitative gene expression (qPCR) and protein expression, we quantified the process of differentiation and trans-differentiation over time and identified the key adhesion receptors involved. Our results highlight the specificity of the phenotypic switch associated with the presence or absence of BMP-2. . Finally, using receptor knock-down and inhibitors of signaling pathways, we will validate the specific role of these key receptors on the osteogenic differentiation. Our results will help to propose new therapies in order to boost regeneration of diseased bones.