ADAMTS-1 increases the three-dimensional growth of osteoblasts through type I collagen processing

The multi-domain neutral endopeptidase, ADAMTS-1 (a disintegrin and metalloprotease with thrombospondin repeats) is induced by parathyroid hormone (PTH) in rat osteoblasts and has therefore been suggested to be involved in initiation of bone remodeling. However, its function(s) in bone cells have not been studied. Here, we first establish that ADAMTS-1 protein is rapidly and transiently produced by human primary osteoblasts in response to PTH (1–34). We also show that ADAMTS-1 is specifically in close proximity to collagen fibrils in bone tissue using ultrastructural immunolabeling. To study the consequence(s) of ADAMTS-1 metalloprotease production in osteoblastic cells, human osteosarcoma cells (SaOS-2), were forced to express either wild-type (wtATS) or a point-mutated (pmATS) metalloprotease dead ADAMTS-1. SaOS-2 cells expressing wtATS had a growth advantage and increased collagenolytic activity when seeded inside a collagen type I gel but exhibited a reduced migration in a scratch wound assay. Immunolabeling of moving cells shows ADAMTS-1 to be located towards the direction of cellular migration. Finally, Western analysis demonstrated excess accumulation of mature collagen type I α1 species in the extracellular matrix together with increased release of distinct small collagen fragments into the conditioned media, by cultures of wtATS cells compared to pmATS cells. These results show that ADAMTS-1 has both the opportunity in bone and capability in vitro to induce collagen type I processing, together with a positive influence on osteoblastic three-dimensional growth. Although it is not clear at present if ADAMTS-1 promotes collagen degradation directly or indirectly, it shows that ADAMTS-1 activity can have a profound influence on the osteoblast phenotype, inhibiting migration on a planar substrate but enhancing growth in a collagen scaffold. These findings further establish ADAMTS-1 as a potentially important protein in PTH induced bone remodeling.