加州大学：细胞表型新分子机制

　　

加州大学：细胞表型新分子机制

生物通报道：来自美国加州大学圣地牙哥分校生物工程学系等处的研究人员首次阐明高血流剪切力影响血管平滑肌细胞表型，进而提供维持血管稳定保护作用的分子机制。这一研究成果公布在国际知名刊物《Circulation Research》杂志上。

血管平滑肌细胞表型调控（Phenotypic modulation）是影响血管功能及病理发展的重要因素。在正常状态下，平滑肌细胞维持收缩表型（contractile phenotype），来调控血管弹性及功能。在疾病发展过程中，平滑肌细胞表型转变为合成表型（synthetic phenotype），此时细胞开始增生与发炎，并转移至内皮细胞（endothelial cells）处，造成血管壁增厚且逐渐阻塞，此为形成动脉硬化症的重要细胞病理机制。而临床医学证据显示，动脉硬化常发生于血管分歧处的扰流（disturbed flow）区域，在较直血管的层流（laminar flow）区域，高血流剪切力（shear stress）具有保护作用，较少动脉硬化症的形成。然而，血流剪切力对于调控血管平滑肌细胞表型的影响及分子机制，迄今尚未有文献报导。

在这篇文章中，研究人员利用自行研发建构的血管内皮与平滑肌细胞共培养（co-culture）血液动力系统，发现高血流剪切力（12 dynes/cm2）可促使内皮细胞调节平滑肌细胞的表型，由病理的合成型转变为生理的收缩型，此时平滑肌细胞收缩型结构蛋白（如SMα-actin、SM-MHC、calponin、h-caldesmon及SM22α）的表达量增加，并抑制平滑肌细胞增生及发炎因子的表达。收集内皮细胞经由高剪切力刺激24小时后的培养液，发现可诱发平滑肌细胞内过氧化体增生剂活化受体（peroxisome proliferator-activated receptor）alpha、delta与gamma配位体结合活性（ligand binding activity）的增加。

利用小分子RNA（small interfering RNA）抑制平滑肌细胞内过氧化体增生剂活化受体alpha与delta的表达后，发现可抑制血流剪切力所诱发的平滑肌细胞表型改变。高血流剪切力可促使内皮细胞释放前列环素（prostacyclin），此为高血流剪其力诱发平滑肌细胞过氧化体增生剂活化受体的活化及收缩表型表达的主要原因。

此外，利用过氧化体增生剂活化受体alpha的基因剔除（knockout）小鼠进行活体动物实验发现，相较于野生型（wild-type）小鼠，过氧化体增生剂活化受体alpha基因剔除鼠的胸主动脉平滑肌细胞会明显呈现病理的合成型，而此种小鼠对于血管收缩剂，例如第二型血管张力素（angiotension II）的刺激，也会引发明显的血管收缩作用。此研究结果发现高血流剪其力可促使血管内皮细胞释放前列环素，诱使平滑肌细胞内过氧化体增生剂活化受体alpha、delta的活化，进而诱导平滑肌细胞由合成型转变为收缩型。

（生物通：万纹）

原文摘要：

Shear stress induces synthetic-to-contractile phenotypic modulation in smooth muscle cells via peroxisome proliferator-activated receptor α/δ activations by prostacyclin released by sheared endothelial cells

Rationale: Phenotypic modulation of smooth muscle cells (SMCs), which are located in close proximity to endothelial cells (ECs), is critical in regulating vascular function. The role of flow-induced shear stress in the modulation of SMC phenotype has not been well defined. Objective: The objective was to elucidate the role of shear stress on ECs in modulating SMC phenotype and its underlying mechanism. Methods and Results: Application of shear stress (12 dyn/cm2) to ECs cocultured with SMCs modulated SMC phenotype from synthetic to contractile state, with upregulation of contractile markers, downregulation of proinflammatory genes, and decreased percentage of cells in the synthetic phase. Treating SMCs with media from sheared ECs induced peroxisome proliferator-activated receptor (PPAR)-α, -δ, and -γ ligand binding activities; transfecting SMCs with specific small interfering (si)RNAs of PPAR-α and -δ, but not -γ, inhibited shear induction of contractile markers. ECs exposed to shear stress released prostacyclin (PGI2). Transfecting ECs with PGI2 synthase-specific siRNA inhibited shear-induced activation of PPAR-α/δ, upregulation of contractile markers, downregulation of proinflammatory genes, and decrease in percentage of SMCs in synthetic phase. Mice with PPAR-α deficiency (compared with control littermates) showed altered SMC phenotype oward a synthetic state, with increased arterial contractility in response to angiotensin II. Conclusions: These results indicate that laminar shear stress induces synthetic-to-contractile phenotypic modulation in SMCs through the activation of PPAR-α/δ by the EC-released PGI2. Our findings provide insights into the mechanisms underlying the EC-SMC interplays and the protective homeostatic function of laminar shear stress in modulating SMC phenotype.