Rapamycin Reduces Arterial Mineral Density and Promotes Beneficial Vascular Remodeling in a Murine Model of Severe Medial Arterial Calcification.

Abstract

Peripheral artery disease (PAD) is the narrowing of the arteries that carry blood to the lower extremities. PAD has been traditionally associated with atherosclerosis. However, recent studies have found that thrombotic events triggered by medial arterial calcification (MAC) is the primary cause of chronic limb ischemia below the knee. MAC is localized around the elastic fibers surrounding smooth muscle cells (SMCs) in arteries. Matrix GLA protein (MGP) binds circulating calcium and prevents hydroxyapatite mineral deposition, while also modulating pro-osteogenic signaling by attenuating BMP-2-mediated activation of Runx2 gene expression. Mgp^-/- mice develop severe MAC and die around 8 weeks after birth due to aortic rupture or heart failure. We previously discovered a rare genetic disease Arterial Calcification due to Deficiency of CD73 (ACDC), in which patients present with extensive MAC in their lower extremity arteries. Using a patient-specific induced pluripotent stem cell model, we found that rapamycin inhibited calcification. Here we investigated whether rapamycin could reduce MAC in vivo using the Mgp^-/- murine model. Mgp^+/+ and Mgp^-/- mice received 5mg/kg rapamycin or vehicle. Calcification content was assessed via microCT, and vascular morphology and extracellular matrix content were assessed histologically. Immunostaining and western blot analysis were used to examine SMC phenotype and extracellular matrix content. Rapamycin prolonged Mgp^-/- mice lifespan, decreased mineral density in the arteries, maintained SMC contractile phenotype, and improved vessel structure, however, calcification volume was unchanged. Mgp^-/- mice with SMC-specific deletion of Raptor or Rictor did not recapitulate treatment with rapamycin. These findings suggest rapamycin promotes beneficial vascular remodeling in vessels with MAC.