Mourani Peter M, Garl Pamela J, Wenzlau Janet M, Carpenter Todd C, Stenmark Kurt R, Weiser-Evans Mary C M
Department of Pediatrics, University of Colorado Health Sciences Center, Denver, Colo 80262, USA.
Circulation. 2004 Mar 16;109(10):1299-306. doi: 10.1161/01.CIR.0000118462.22970.BE. Epub 2004 Mar 1.
At distinct times during embryonic development and after vascular injury, smooth muscle cells (SMCs) exhibit a highly proliferative, serum-independent growth phenotype. The aim of the present study was to evaluate the functional role of S6 ribosomal protein (S6RP) and upstream positive and negative regulators in the control of SMC serum-independent growth.
We previously reported increased expression of S6RP mRNA was associated with this unique growth phenotype. Using immunohistochemistry and Western blot analysis, we report high levels of total and phospho-S6RP and increased levels of Akt and p70S6K phosphorylation, upstream positive regulators of S6RP, in rat embryonic aortas and adult balloon-injured carotid arteries compared with quiescent adult aortas and uninjured carotid arteries. Western blot analysis demonstrated that cultured embryonic and neointimal SMCs that exhibited serum-independent growth capabilities expressed high levels of S6RP and constitutively active Akt, mTOR, and p70S6K. Pharmacological and molecular inhibition of phosphatidylinositol 3-kinase (PI3K) signaling pathways, using PI3K inhibitors, rapamycin, or dominant-negative Akt adenovirus, suppressed embryonic and neointimal SMC serum-independent growth. Finally, decreased activity of PTEN, an endogenous negative regulator of PI3K signaling, was associated with high in vivo SMC growth rates, and morpholino-mediated loss of endogenous PTEN induced a serum-independent growth phenotype in cultured serum-dependent SMCs.
The possibility exists that cells that exhibit a distinct embryonic-like growth phenotype different from traditional SMCs are major contributors to intimal thickening. Growth of SMCs that exhibit this phenotype is dependent on constitutive Akt and mTOR/p70S6K signaling and is actively inhibited through the timed acquisition of the endogenously produced growth suppressor PTEN.
在胚胎发育的不同时期以及血管损伤后，平滑肌细胞（SMC）呈现出高度增殖、血清非依赖性生长表型。本研究的目的是评估S6核糖体蛋白（S6RP）及其上游正负调节因子在控制SMC血清非依赖性生长中的功能作用。
我们之前报道S6RP mRNA表达增加与这种独特的生长表型相关。使用免疫组织化学和蛋白质印迹分析，我们发现与静止的成年主动脉和未损伤的颈动脉相比，大鼠胚胎主动脉和成年球囊损伤颈动脉中总S6RP和磷酸化S6RP水平较高，且Akt和p70S6K磷酸化水平增加，它们是S6RP的上游正调节因子。蛋白质印迹分析表明，具有血清非依赖性生长能力的培养胚胎和新生内膜SMC表达高水平的S6RP以及组成型激活的Akt、mTOR和p70S6K。使用PI3K抑制剂、雷帕霉素或显性负性Akt腺病毒对磷脂酰肌醇3激酶（PI3K）信号通路进行药理学和分子抑制，可抑制胚胎和新生内膜SMC的血清非依赖性生长。最后，PI3K信号的内源性负调节因子PTEN活性降低与体内SMC高生长速率相关，吗啉代介导的内源性PTEN缺失在培养的血清依赖性SMC中诱导出血清非依赖性生长表型。
存在这样一种可能性，即表现出与传统SMC不同的独特胚胎样生长表型的细胞是内膜增厚的主要促成因素。表现出这种表型的SMC生长依赖于组成型Akt和mTOR/p70S6K信号传导，并通过内源性产生的生长抑制因子PTEN的适时获得而受到积极抑制。
