Abstract 580: Regulation of Inflammatory Gene Expression by Angiotensin II-induced KLF4 in Vascular Smooth Muscle Cells

Abstract

Angiotensin II (Ang II)-mediated vascular smooth muscle cell (VSMC) dysfunction plays a critical role in the pathogenesis of Cardiovascular Diseases (CVDs). However, the role of Ang II-induced transcription factors in the diverse effects of Ang II remains unclear. We profiled Ang II induced gene expression by microarray analysis of RNA isolated from Ang II-treated and control VSMC. Our results identified numerous differentially regulated genes including several key transcription factors in Ang II-stimulated VSMC compared with controls. Ingenuity Pathway Analysis indicated that Ang II-regulated genes are involved in VSMC dysfunction highly relevant to CVDs. We validated the expression of several genes by RT-qPCR and further characterized the functions of the most differentially regulated gene, KLF4, known to regulate growth factor induced VSMC phenotypic switching. We demonstrated that Ang II induced the expression of KLF4 in cultured VSMC in vitro , in mice aortas cultured ex vivo , and in aortas isolated from Ang II-infused mice in vivo . Ang II-induced KLF4 expression was inhibited by Losartan, demonstrating regulation via the AT1 receptor. Transfection experiments using WT and mutant KLF4 promoter constructs revealed the key role of cis -elements with consensus binding sites for p53, SP1 and YY1 in Ang II-induced KLF4 promoter activation. Next, we performed gene expression profiling by Affymetrix gene arrays after siRNA mediated KLF4 knockdown in VSMC. The differentially expressed genes were subsequently analyzed by DAVID to obtain enriched biological processes and potential pathways relevant to cardiovascular functions. Results showed that KLF4 knockdown upregulated the expression of several genes related to cell proliferation and hypertrophy. Interestingly, KLF4 knockdown also enhanced the expression of multiple pro-inflammatory genes including IL-6 and downregulated several anti-inflammatory genes including Thrombomodulin, suggesting an anti-inflammatory role for KLF4 in VSMC. Together, these results suggest that KLF4 may act as a novel molecular brake to modulate Ang II actions that, when disrupted, can further augment Ang II mediated VSMC dysfunction associated with vascular diseases.