ADAMTS9-Mediated Extracellular Matrix Dynamics Regulates Umbilical Cord Vascular Smooth Muscle Differentiation and Rotation.

Despite the significance for fetal nourishment in mammals, mechanisms of umbilical cord vascular growth remain poorly understood. Here, the secreted metalloprotease ADAMTS9 is shown to be necessary for murine umbilical cord vascular development. Restricting it to the cell surface using a gene trap allele, Adamts9(Gt), impaired umbilical vessel elongation and radial growth via reduced versican proteolysis and accumulation of extracellular matrix (ECM). Both Adamts9(Gt) and conditional Adamts9 deletion revealed that ADAMTS9 produced by mesenchymal cells acted non-autonomously to regulate smooth muscle cell (SMC) proliferation, differentiation, and orthogonal reorientation during growth of the umbilical vasculature. In Adamts9(Gt/Gt), we observed interference with PDGFRβ signaling via the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway, which regulates cytoskeletal dynamics during SMC rotation. In addition, we observed disrupted Shh signaling and perturbed orientation of the mesenchymal primary cilium. Thus, ECM dynamics is a major influence on umbilical vascular SMC fate, with ADAMTS9 acting as its principal mediator.