Enzymes of the ADAMTS family are closely related to MMPs and ADAMs. They further contain specific domains, such as a variable number of a domain known as « ThromboSPondin type I repeats » (TSP I).
Amongs this family, ADAMTS2, 3 and 14 share a strong homology of sequence and structure. The primary function of ADAMTS2, 3 and 14, also known as aminoprocollagen peptidases, is to process fibrillar procollagen into mature molecules by excising the amino-propeptide. The lack of activity of ADAMTS2 is responsible for a inherited disease in human and in animal (Ehlers Danlos syndrom type VII C or dermatosparaxis) characterized by an extreme skin fragility. Analysis of ADAMTS-2 knock-out mice (Adamts2-/-) has shown also that male are sterile, suggesting that ADAMTS-2 have functions independent of its aminoprocollagen peptidase activity.
In the first part of the results, we demonstrate that ADAMTS-2 inhibits angiogenesis, independently of its catalytic activity. ADAMTS-2 is able to reduce proliferation of endothelial cells, and to induce their retraction and detachment from the substrate resulting in apoptosis. Dephosphorylation of Erk1/2 and MLC largely precedes the ADAMTS-2 induced morphological alterations. In 3-D culture models, ADAMTS-2 strongly reduced branching of capillary-like structures formed by endothelial cells and their long-term maintenance and inhibited vessels formation in embryoid bodies (EB). Growth and vascularization of tumors formed in nude mice by HEK 293-EBNA cells expressing ADAMTS-2 were drastically reduced. A similar anti-tumoral activity was observed when using cells expressing recombinant deleted forms of ADAMTS-2, including catalytically inactive enzyme. Nucleolin, a nuclear protein also found to be associated with the cell membrane, was identified as a potential receptor mediating the antiangiogenic properties of ADAMTS-2.
In following parts of results, we studied the functions of ADAMTS2, 3 and 14 in two different models: zebrafish models and mice models without expression of one of the aminoprocollagen peptidases.
Zebrafish models: Four orthologues for ADAMTS2, 3 and 14 were identified in zebrafish (two orthologues for ADAMTS-2, one for ADAMTS3 and one for ADAMTS14). These enzymes present each a specific expression profil in RT-PCR and in situ hybridization studies. ADAMTS3 is the most expressed during the embryonic period. In situ hybridization demonstrate a strong expression of ADAMTS3 in the neural tube and in specific parts of the brains, suggesting a function during brain development. Repression of ADAMTS-3 expression by specific morpholinos induces lethality at an early stage of development.
Mice models: Constitutive knock-out of Adamts3 lead to embryonic lethality around 15 dpc. Histological studies of 12.5 dpc, 13.5 dpc and 14.5 dpc Adamts3-/- embryos demonstrated an implication of Adamts3 in development of the brain, the liver and most probably of the heart.
Constitutive knock-out of Adamts14 lead to a reduction of body size and of ear size. Histological studies of Adamts14-/- bones and ears suggested an implication of Adamts14 in growth regulation of bones and/or cartilage.