Abstract 14726: Sortilin 1 is a Novel Inducer of Vascular Calcification via a Phosphate-Dependent Mechanism
Background. Vascular calcification is a prominent feature of chronic inflammatory disorders such as chronic renal disease (CRD) and atherosclerosis, and has no medical therapies. Human genome wide association studies linked the SORT1 gene, encoding sortilin 1, with increased risk of cardiovascular diseases and coronary artery calcification; however, the underlying mechanisms are unknown. We hypothesized that sortilin 1 contributes to the osteogenic transition of vascular smooth muscle cells (SMC).
Methods and Results. In calcified regions of human atherosclerotic plaques (n=20), cells coexpressed sortilin 1 and activated RUNX2, a regulator of osteoblast differentiation. In human SMC osteogenic phosphate-rich media induced an osteoblast phenotype, coinciding with 22-fold increased expression of sortilin 1 mRNA/protein. Silencing of sortilin 1 by siRNA significantly reduced alkaline phosphatase activity (TNAP) (-30%; p=0.009) and matrix mineralization (-33%; p=0.004) in calcified SMC. In contrast, increased endogenous or exogenous sortilin 1 promoted TNAP activity by 37% (p=0.016) and matrix mineralization by up to 77% (p=0.002). PCR array revealed a significant inverse correlation between phosphate-regulating endopeptidase (PHEX) and sortilin 1. Sortilin 1 siRNA induced PHEX by 1.5-fold, whereas increased sortilin 1 diminished PHEX expression by 77%. In silico analysis suggested that sortilin 1 is a target for microRNA-125b. We verified miR-125b indeed binds to 3’UTR of SORT1, repressing its expression. Analysis of the sortilin 1 co-immunoprecipitated proteome identified candidate binding proteins that could be differentially regulated as a function of SMC calcification. Induction of CRD by 5/6 nephrectomy in Apoe-/- mice increased phosphate and sortilin 1 serum levels by 2.8-fold and 3.3-fold, respectively, and showed a significant correlation between these two factors (p=0.001). Moreover, CRD dramatically increased sortilin 1 expression in medial SMC (+667%; p=0.024).
Conclusion. We demonstrated for the first time a direct role of sortilin 1 in vascular calcification. Sortilin 1 may be a therapeutic target for vascular calcification in patients with CRD.
- © 2012 by American Heart Association, Inc.