Abstract 188: I X2 X2

Abstract

Background: An increase in aortic stiffness is a fundamental component of hypertension. However, the molecular mechanism involved is unclear. Our hypothesis is that the increased aortic stiffness in hypertension is partially due to the activation of serum response factor (SRF) /myocardin in vascular smooth muscle cells (VSMCs). Methods: 4 months old male spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats were studied. Aortic pressure and stiffness were measured by a Millar catheter and by Doppler imaging echocardiography, respectively. VSMCs were isolated from thoracic aorta (TA), then cultured and tested at passages 2 to 4. Real time PCR and western blot were used to detect the gene and protein expression. Results: Aortic pressure was higher in SHR than WKY (mean arterial pressure (MAP) 138.7±11.8 vs 102.7±7 mmHg, p <0.01). Aorta stiffness reflected by arterial stiffness index (ASI) was 2.5-fold higher in SHR vs WKY ( p <0.01). Compared to WKY, VSMCs from SHR TA showed a 12-fold increase in SRF, a nuclear transcriptional factor, and 2.7-fold increase in myocardin, a smooth muscle specific coactivator of SRF, at both mRNA and protein levels (All, p <0.01 vs. WKY TA VSMCs). Myocardin nuclear translocation was also markedly increased in TA VSMCs from SHR by 12-fold versus WKY, ( p <0.01). SRF/myocardin downstream target genes, α-smooth muscle actin (α-SMA) and SM22 were increased by 3-fold in TA VSMCs in SHR vs WKY ( p <0.01). In vitro , CCG-100602, a specific inhibitor of SRF/myocardin interaction, not only strikingly repressed the increase of the expression in SRF, myocardin and the downstream targets α-SMA and SM22, but also blocked the nuclear translocation of myocardin in TA VSMCs from SHR ( p <0.01 vs untreated SHR VSMCs). However, such effects were not observed on WKY TA VSMCs. In vivo , 2-week treatment with CCG-100602 significantly reduced MAP and ASI by 19% and 63% in SHR, respectively ( p <0.01 vs untreated SHR), while aortic MAP and ASI in WKY rats remain unchanged upon the treatments. Conclusion: The activation of myocardin/SRF in aortic VSMCs presents a novel mechanism of increased aortic stiffness in SHR.