The role of vascular peroxidase 1 in ox-LDL-induced vascular smooth muscle cell calcification

Reactive oxygen species (ROS)-induced osteogenic differentiation of vascular smooth muscle cells (VSMCs) is associated with the pathogenesis of vascular calcification. Vascular peroxidase 1 (VPO1), a peroxidase in the cardiovascular system, utilizes the hydrogen peroxide (H2O2) produced by co-expressed NADPH oxidases to produce hypochlorous acid (HOCl) and catalyze peroxidative reactions. The aim of this study was to determine whether VPO1 plays a role in the osteogenic differentiation of VSMCs in the setting of the vascular calcification induced by oxidized low-density lipoprotein (ox-LDL). In cultured primary rat VSMCs, we observed that the expression of VPO1 was significantly increased in combination with increases in calcification, as demonstrated via increased mineralization, as well as increased alkaline phosphatase (ALP) activity and up-regulated runt-related transcription factor 2 (Runx2) expression in ox-LDL-treated cells. Ox-LDL-induced VSMC calcification and Runx2 expression were both inhibited by knockdown of VPO1 using a small interfering RNA or by an NADPH oxidase inhibitor. Moreover, the knockdown of VPO1 in VSMCs suppressed the production of HOCl and the phosphorylation of AKT, ERK and P38 MAPK. Furthermore, HOCl treatment facilitated the phosphorylation of AKT, ERK1/2 and P38 MAPK and the expression of Runx2, whereas LY294002 (a specific inhibitor of PI3K), U0126 (a specific inhibitor of ERK1/2) and SB203580 (a specific inhibitor of P38 MAPK) significantly attenuated the HOCl-induced up-regulation of Runx2. Collectively, these results demonstrated that VPO1 promotes ox-LDL-induced VSMC calcification via the VPO1/HOCl/PI3K/AKT, ERK1/2, and P38 MAPK/Runx2 signaling pathways.