Abstract 16812: Bone Morphogenetic Protein Signaling is Required for Vascular Calcification in a Murine Model of Matrix GLA Protein Deficiency

Abstract

Introduction: Matrix GLA protein (MGP) is a mineral-binding extracellular matrix protein that is thought to prevent vessel calcification by sequestration of calcium ions. However, MGP also inhibits bone morphogenetic protein (BMP) signaling. MGP -/- mice exhibit severe medial arterial calcification by 2 wks and die by 6 wks from aortic aneurysm and rupture. We hypothesized that MGP prevents vascular calcification via its effects on BMP signaling. Methods: MGP -/- mice were treated with either vehicle or the small molecule BMP type I receptor inhibitor LDN-193189 (LDN, 2.5 mg/kg once daily IP) from day 1 to 28. Whole aortas were harvested for phospho-Smad 1/5/8 (P-Smad) immunohistochemistry, a marker of BMP signaling, and for Alizarin Red staining of calcium. Osteogenic activity in aortas was visualized ex vivo by the uptake of a fluorescent bisphosphonate imaging probe. MGP -/- mice were also treated with vehicle or LDN to ascertain if inhibition of BMP signaling could impact survival, using Kaplan-Meier and Cox regression analysis. Results: MGP -/- aortas demonstrated increased P-Smad compared to wild-type mice. LDN treatment of MGP -/- mice reduced aortic P-Smad levels and was associated with a reduction in tissue calcium levels (Fig. A & B). Pharmacologic inhibition of BMP signaling in MGP -/- mice resulted in an 81% reduction in aortic osteogenic activity compared to vehicle-treated controls (Fig. C; n=6 in each group; normalized average intensity ± SEM, 0.19 ± 0.05 vs 1.0 ± 0.10, P<0.0001), with similar reductions observed at the aortic arch and the abdominal aorta. LDN treated mice exhibited improved survival compared to vehicle-treated controls (n=10 in each group; Cox hazard ratio 0.04, 95% CI 0.01-0.17, P<0.001). Conclusions: MGP prevents vascular calcification primarily via its impact on BMP signaling. Pharmacologic BMP inhibition improves survival in MGP -/- mice and may represent an important therapeutic target in the treatment of human vascular disease.