Oxidized low-density lipoprotein increases bone sialoprotein expression in vascular smooth muscle cells via runt-related transcription factor 2.

BACKGROUND: Vascular calcification is a pivotal stage in atherosclerosis. During vascular calcification, vascular smooth muscle cells (VSMCs) synthesize many osteogenic factors such as bone sialoprotein (BSP). Oxidative stress plays a critical role in progression of atherosclerosis and also increases extracellular matrix proteins expression. BSP overexpression has been observed during vascular calcification by oxidative stress. However, the regulatory mechanism of oxidized low-density lipoprotein (oxLDL)-mediated vascular calcification has not yet been fully defined. In this study, we aimed to investigate whether runt-related transcription factor 2 (Runx2) affects the oxLDL-induced BSP expression or not.
METHODS: In this experimental study, we cultured VSMCs in F12K media and then treated them with oxLDL. The expression of Runx2 and BSP genes was determined by real-time polymerase chain reaction method. Protein level of each gene was investigated by Western blotting technique. To determine whether Runx2 regulates BSP gene expression at VSMCs induced by oxLDL, we suppressed Runx2 mRNA using siRNA. Transfected cells then were treated with oxLDL and expression of Runx2 and BSP genes was determined again.
RESULTS: oxLDL increased Runx2 and BSP expression (4.8 ± 0.47-fold and 4.91 ± 0.56-fold, respectively) after 48 hours. Western blotting method confirmed the increased levels of Runx2 and BSP proteins after 48 hours. Runx2 overexpression alone induced BSP expression, whereas knockdown of Runx2 with small interfering siRNA blocked oxLDL-induced BSP expression.
CONCLUSIONS: Our results showed that oxLDL-induced BSP expression was dependent on Runx2 expression, suggesting that Runx2 is required for oxLDL-induced BSP expression.