A disintegrin and metalloproteinase with thrombospondin motifs 18 (ADAMTS18) cleaves fibronectin and negatively regulates its fibrillogenesis

Remodeling of the extracellular matrix (ECM) plays a crucial role in the development, maintenance, and repair of all tissues. Therefore, identifying the regulators of this process is essential. Among these, A disintegrin and metalloproteinase with thrombospondin motifs 18 (ADAMTS18) has been implicated in fibronectin (FN) matrix regulation. Knockout of ADAMTS18, either in mouse models or in vitro, was shown to lead to FN accumulation, mutation in epithelial branching, and reduction in endothelial sprouting. However, the mechanisms by which ADAMTS18 influences endothelial-specific functions and the ECM, particularly in the regulation of FN fibrils, remain unclear. In this study, using both siRNA-mediated knockdown and overexpression of ADAMTS18 in primary endothelial cells (ECs), we delineated some of these mechanisms. Using global RNA-Seq of ECs, we demonstrated differential gene regulation of vessel development and endothelial adhesion genes with ADAMTS18 siRNA knockdown, whereas cell matrix- and cell cycle-associated genes were affected by overexpression of ADAMTS18. Consistent with the latter, we observed reduced EC proliferation and altered cell cycle with ADAMTS18 overexpression. Using mass spectrometry, we identified two sites in FN that are proteolytically cleaved by ADAMTS18, including a cleavage site in the linker FN-I_5-6. Cleavage at this site generated FN molecules lacking the N-terminal FN-I_1-5 (29 kDa) fragment that is known to be essential for FN fibrillogenesis. Accordingly, ADAMTS18 overexpression greatly impaired FN fibrillogenesis in endothelial cultures and in coculture with fibroblasts. Our results implicate ADAMTS18 in FN-associated ECM remodeling and suggest an important role for ADAMTS18 in endothelium biology.