The functional role of the Calcium Activated Nucleotidase 1 (CANT1) gene in the skeleton: an in vivo study with a mouse model of Desbuquois dysplasia

Desbuquois dysplasia (DBQD) is a severe autosomal recessive chondrodysplasia characterized by severe prenatal and postnatal growth retardation, joint laxity and progressive scoliosis. It is caused by mutations in the Calcium Activated Nucleotidase 1 (CANT1) gene, encoding for a calcium activated nucleotidase that preferentially hydrolyses UDP. Two different forms of the enzyme have been characterized, but their functions remain to be elucidated: i) a membrane bound form in the endoplasmic reticulum and Golgi. The subcellular location and the substrate preference, UDP, suggest CANT1 involvement in protein glycosylation. In particular, since the disorder affects mainly cartilage, it might be involved in proteoglycan synthesis, the main cartilage glycoprotein; ii) a soluble secreted form that can be involved in pyrimidinergic signaling by modulating the availability of extracellular UDP to P2Y receptors, a group of G protein coupled receptors. The objectives of the project are to define the physiological function of CANT1 and its role in the etiology of DBQD. We plan to address these overall objectives through the following specific aims: a) to generate a mouse model of DBQD; b) to define the physiological function of the membrane bound form of CANT1 and its role in DBQD by biochemical analysis of cartilage proteoglycans and histological studies of cartilage in the mouse model; c) to define the physiological function of the soluble secreted form of CANT1 and its role in DBQD by studying UDP signaling in chondrocyte cultures from the mouse model. All studies will be performed on the mouse model of DBQD we will generate since they cannot be done in human patients for ethical reasons. These studies are designed to yield a deeper understanding of the function of CANT1 and of the pathogenesis of inherited forms of osteoarthropathy, so that effective therapies can be developed.