Upregulation of vascular angiotensin II receptor gene expression by low-density lipoprotein in vascular smooth muscle cells

Because LDL and the angiotensin II type 1 (AT1) receptor are thought to be involved in the pathogenesis of chronic vascular disease, we studied possible interactions between these two biological systems in cultured rat vascular smooth muscle cells. Incubation of vascular smooth muscle cells with 100 micrograms/mL LDL profoundly increased AT1 receptor mRNA to approximately 250% of control levels as assessed by Northern hybridization analysis. This effect is maximal 12 hours after addition of LDL to the culture medium and is sustained for up to 24 hours. The LDL-induced upregulation is dose dependent, with a maximal effect obtained with 100 micrograms/mL LDL. There is a correlative increase of cell surface-associated AT1 receptors as assessed by saturation radioligand binding assays. The half-life of AT1 receptor mRNA is increased substantially by LDL compared with that of cells treated only with 5,6-dichlorobenzimidazole to block transcription. Angiotensin II-induced elevation of cytosolic calcium concentration is significantly increased in vascular smooth muscle cells pretreated with LDL to 368 +/- 41 nmol/L compared with control cells pretreated with vehicle (248 +/- 33 nmol/L). Moreover, angiotensin II-induced DNA synthesis is markedly enhanced when cells are coincubated with 100 micrograms/mL LDL. These data reveal a significant upregulation of AT1 receptor gene expression by LDL in vascular smooth muscle cells through mechanisms that involve posttranscriptional mRNA stabilization. Ultimately, this AT1 receptor upregulation leads to an elevated functional response of vascular smooth muscle cells on angiotensin II stimulation.