Integros

The present project aims to assess a novel approach to promote the osteogenic differentiation of mesenchymal stem cells for bone healing and regeneration in patients with large bone defects and those with reduced number of osteocompetent cells. Although these cells are considered as a valuable source for bone tissue regeneration, their capacity to differentiate along functional bone forming osteoblasts remains relatively limited in vivo. An important issue for efficient bone regeneration is therefore to target hMSCs to promote their osteogenic potential. P. Marie’s team has recently shown that forced expression of the a5 integrin subunit (ITGA5) or priming ITGA5 integrin using specific agonists induces osteoblast gene expression and osteogenic differentiation of cultured human MSCs (hMSCs). We also showed that forced expression of ITGA5 in hMSCs results in a marked increase in de novo osteogenesis in vivo, trevealing a critical role for ITGA5 in osteogenic differentiation of adult human mesenchymal stromal cells. In this project, we will evaluate the potential of promoting the osteogenic potential of mesenchymal stem cells in vitro and in vivo by targeting ITGA5. To this goal, Partner 1 (Institut de Recherches Servier) will first use chemical and molecular modeling methods based on structural homology models to develop new non-peptidic entities that can mimic the existing ITGA5 agonist, the cyclic CRRETAWAC peptide. Partner 1 will also be in charge of the identification of novel analogues (peptidomimetics and heterocyclic compounds) that activate ITGA5, through SAR (structure-activity relationship) studies on the cyclic CRRETAWAC peptide, in silico modeling of its interaction with the alpha5beta1 integrin, and in silico screening of selected chemical libraries and evaluation of hits in molecular assays. Partner 2 (P. Marie’s Team, Inserm U606) will be in charge of testing ITGA5 agonists developed by partner 1 in functional tests in hMSCs. To this goal, partner 2 will select ITGA5 agonists having the most positive stimulatory effect on FAK/ERK/PI3K signaling that activates MSC osteogenic differentiation and that promote markers of osteoblast differentiation and osteogenic differentiation in murine and human MSCs in vitro. A limited number of these molecules will be then tested for their capacity to promote bone formation in vivo using two models, a standard ectopic model in the mouse and an animal model of senile osteoporosis which exhibits low bone mass, impaired bone formation and decreased osteoblastogenesis. These animals will be treated with appropriate amount of ITGA5 agonists delivered locally or systematically and the effects on osteogenesis will be assessed by quantitative histomorphometry and microCT analysis. The success of the project will be based on the tight coordination between various disciplines (chemistry, modelisation, pharmacology, biology, histology) and on the combined expertise of one recognised academic laboratory in bone biology (MSCs and osteogenesis) and a pharmaceutical company that has a strong expertise in pharmacology of integrins and has developed a successful therapeutic strategy in osteoporosis.