Phenotypic Modulation of Vascular Smooth Muscle Cells and Its Contribution to Leukocyte Recruitment to Endothelial Cells under Disturbed Flow

• Main Authors: Chen Cheng-Nan, 陳政男
• Other Authors: Chiu Jeng-Jiann
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/86188710112377690816

博士 === 國防醫學院 === 生命科學研究所 === 94 === The early stage of atherogenesis develops at regions of arterial tree exposed to disturbed flow and involves adhesion of leukocytes (WBCs) to and their transmigration across endothelial cells (ECs), which are located in close proximity to smooth muscle cells (SMCs). SMCs located in normal arterial media exhibit a contractile phenotype, whereas SMCs in atherosclerotic plaques show a synthetic phenotype. Growth factor platelet-derived growth factor (PDGF)-BB and cytokine interleukin (IL)-1 contribute to progression of atherosclerotic lesions, where medial vascular SMCs change from their contractile to synthetic phenotype. The aims of this study were (1) to elucidate the role of PDGF-BB and IL-1 in phenotypic modulation of SMCs, and (2) to investigate the effects of disturbed flow and SMCs on the recruitment of three different types of WBCs [neutrophils, peripheral blood lymphocytes (PBLs), and monocytes] to ECs using our newly developed EC/SMC co-culture flow system. Human aortic SMCs grown on polymerized collagen showed time-dependent increases in the expression of contractile protein markers, including smooth muscle (SM)-actin, myosin heavy chain (SM-MHC), and calponin. Co-stimulation of these SMCs with PDGF-BB and IL-1 induced a sustained phosphorylation of their PDGF receptor (PDGFR)-, Akt and, p70S6K and down-regulated the expression of SM-actin, SM-MHC, and calponin. In contrast, the mTOR inhibitor rapamycin inhibited the PDGF-BB/IL-1-induced p70S6K phosphorylation and elevated these marker protein expressions. While adenoviruses expressing dominant-negative Akt eliminated the PDGF-BB/IL-1 effect on SM- actin, SM-MHC, and calponin expressions, constitutively active Akt mimicked the PDGF-BB/IL-1 effect. PDGF-BB/IL-1 co-stimulation induced a sustained association between PDGFR- and IL-1 receptor (IL-1R1). This receptor association was blocked by a PDGFR- neutralizing antibody (AF385), an IL-1R1 antagonist (IL-1ra), or a specific inhibitor of PDGFR- phosphorylation (AG1295), which consequently eliminated the PDGF-BB/IL-1-induced activation of PDGFR-/Akt/p70S6K and down-regulation of SMC marker protein expressions. When ECs were co-cultured with synthetic SMCs embedded in the collagen gel, the adhesion and transmigration of neutrophils, PBLs, and monocytes were increased in comparison to the monoculture ECs. Disturbed flow enhanced WBC recruitment to the EC/SMC, particularly in the reattachment area, where the rolling velocity of WBCs and their transmigration time were decreased, as compared with the other areas. Neutrophils, PBLs, and monocytes showed different subendothelial migration patterns under disturbed flow. Their movements were more random and shorter in distance in the reattachment area. Co-culture of ECs and SMCs induced their expressions of adhesion molecules and chemokines, which contributed to the increased WBC adhesion and transmigration. Our findings indicate that ECM components play an important role in the control of phenotypic properties of cultured SMCs. The findings also provide insights into the mechanisms contributing to phenotypic change of SMCs from contractile to synthetic state. Since SMCs in the plaques exert significant effects on ECs, the results from the use of our newly developed EC/SMC co-culture model may provide data for the understanding of the interaction between WBCs and the vessel wall (composed of ECs and SMCs) under the complex flow environments found in regions of prevalence of atherosclerotic lesions.