The endothelial protective factors, BMP9 and BMP10, inhibit CCL2 release by human vascular endothelial cells.

Bone morphogenetic protein (BMP)-9 and BMP10 are circulating ligands that mediate endothelial cell (EC) protection via complexes of the type I receptor, ALK1, and the type II receptors, the activin type-IIA and bone morphogenetic type II receptors. We previously demonstrated that BMP9 induces the expression of interleukin-6, interleukin-8 and E-selectin in ECs and may influence their interactions with monocytes and neutrophils. We asked whether BMP9 and BMP10 regulate the expression of Chemokine (C-C motif) ligand 2 (CCL2), a key chemokine involved in monocyte-macrophage chemoattraction. Here, we show that BMP9 and BMP10 repress basal CCL2 expression and release from human pulmonary artery ECs and aortic ECs. This was dependent on ALK1 and co-dependent on ACTR-IIA and BMPR-II. Assessment of canonical Smad signalling indicated a reliance of this response on Smad4. Of note, Smad1/5 signalling contributed only at BMP9 concentrations similar to those in the circulation. In the context of inflammation, BMP9 did not alter the induction of CCL2 by TNF-α. As CCL2 promotes monocyte/macrophage chemotaxis and endothelial permeability, these data support the concept that BMP9 preserves basal endothelial integrity.