Osteopontin plays a key role in vascular smooth muscle cell proliferation via EGFR-mediated activation of AP-1 and C/EBPβ pathways

Abstract

Osteopontin (OPN) is known as an active player in the progression of vascular remodeling diseases, however, the precise role in the proliferation of vascular smooth muscle cells (VSMC) is unclear. Thus, this study investigated the role of OPN in VSMC proliferation induced by 4-hydroxynonenal (HNE), and identified the intracellular signaling pathways involved in 4-HNE-induced OPN production. In VSMC primary cultured from rat thoracic aorta as well as in VSMC in the media of aorta, HNE enhanced OPN expression in concentration-dependent manners. Both the proliferation of cultured VSMC and PCNA positive cells in aortic tissues were also increased by HNE, which were attenuated in OPN-deficient cells and aortic tissues isolated from OPN-deficient mice, indicating a pivotal role of OPN in HNE-induced VSMC proliferation. In the promoter assay, HNE increased OPN promoter activity, which was attenuated when the regions harboring AP-1 and C/EBPβ binding sites were mutated. The increased bindings of AP-1 and C/EBPβ to the OPN promoter were also demonstrated by ChIP analysis. In addition, the increases in both OPN expression and the activities of AP-1 and C/EBPβ by HNE were attenuated by AG1478, an EGFR antagonist. Based on these results, it was suggested that HNE induced OPN expression in VSMC via signaling pathways involving AP-1 and C/EBPβ, leading to increases in VSMC proliferation and subsequent vascular remodeling.