Osteoporosis is a common age-related disorder characterized by low bone mass and deterioration in bone microarchitecture, leading to increased skeletal fragility and fracture risk. Age-related osteoporosis fractures are increasing in link with the proportion of elderly population is increasing, thus resulting in human burden for the health system. Beside the efficacy of antiresorbing drugs at stopping bone loss, the major question arising now is how is it possible to restore lost bone? For this aim, there is a crucial need for identifying new targets especially on bone forming cells (osteoblasts). Our project will focus on the lysophosphatidic acid (LPA)-producing enzyme Autotaxin (ATX) because LPA has an anabolic action on bone by activating osteoblasts. However, LPA also promotes osteoclastic bone resorption. Thus, specific therapeutic blocking of LPA’s catabolic activity could promote its anabolic action on bone tissue. ATX is the main producer of LPA in the organism. Remarkably, global deletion of ATX gene (Enpp2) is lethal at the embryonic stage making impossible the use of mice for bone study. Nevertheless, the choice of ATX was supported because of our recent observations in MC3T3 cell line and calvaria primary osteoblasts that express high levels of ATX making osteoblasts a potent source of LPA at the bone site. The first objective of the project is to elucidate the role of ATX/LPA axis during bone mass acquisition in youth and bone loss in aging and to determine its impact on osteoblast function and bone quality. For this aim we will analyze ATXdeltaOb mice already generated by crossing Enpp2flox/flox mice with Osx:GFP-Cre/+ animals allowing specific invalidation of ATX expression in osteoblast progenitors and hypertrophic chondrocytes. These animals present a remarkable low bone mass phenotype. Animal bone phenotype will be characterized based on technics used in routine in partners’ laboratories such as microCT, histology, immunohistochemistry, fluorescence imaging. The second objective of the project is to characterize novel signaling pathways that control the anabolic activity of osteoblasts and that connect osteoblast to osteoclast functions. Our project will decipher in primary mouse and human osteoblasts the molecular connections between Wnt/beta-catenin and ATX/LPA signaling pathways that have recently been revealed in malignant cells allowing the identification of potential new therapeutic targets. The third objective of the project is to develop new therapeutic tools promoting bone gain. To this aim we will characterize at molecular levels domains of ATX that bind to cell surface of osteoblasts and osteoclasts because of ATX new role emerging as a docking molecule required for the proper presentation of LPA to the cell surface, leading to the activation of specific LPA receptors. We and other have shown that ATX binds to beta-1, beta-3 integrins and heparan sulfate proteoglycans. We have demonstrated that ATX controls osteoclastic bone erosion in inflammatory conditions. Because of the paramount role of beta-3 integrin in osteoclast function, we will develop a unique strategy in the field by performing in silico proteochemometrics studies based on artificial intelligence followed by co-crystallography and biochemical analyses of ATX with identified beta-3 integrins interactants that will be validated both in osteoclast activity and osteoblast/osteoclast coculture assays. Functionally active peptides will be PEGylated to increase stability in vivo and used in our preclinical animal models of osteoporosis as a proof of concept in the development of new therapies against bone loss. Altogether, based on animal whole body bone characterization, histology, osteoblast and osteoclast cell biology, in silico proteochemometrics and crystallography analyses, the project will fully characterize the molecular of actions of ATX on bone cells and will develop new tools dedicated to bone regeneration therapies.