Role of lysophosphatidic acid in fluid flow-response in vascular endothelial cells

机械转导在维持细胞稳态中起着重要作用。在内皮细胞中，它可能是局部血流动力学控制所必需的。细胞内Ca^<2+>浓度升高（[Ca^<2+>]_i）是机械接受的重要信号，但分子机制尚不清楚。我们证明了溶血磷脂酸（LPA, 0.3-10 μM）是一种生物活性磷脂，在几种细胞类型中使[Ca^<2+>]_i对机械应力的反应增敏。在LPA存在的情况下，培养的牛晶状体上皮细胞和主动脉内皮细胞在机械应力作用下可见[Ca^<2+>]_i的局部增加。这种现象被称为“Ca^<2+>斑点”。药理研究表明，Ca^<2+>点是通过机械敏感通道发生的初级Ca^<2+>内流事件。在小鼠主动脉和肾动脉原位观察LPA的增敏作用。内皮细胞[Ca^<2+>]_i升高引起主动脉平滑肌细胞随后的[Ca^<2+>]_i瞬态和收缩。然后我们研究了lpa诱导内皮依赖性血管收缩的机制。多光子激光扫描显微镜观察内皮细胞Ca^<2+>反应和血管收缩。血栓素A_2 (TXA2)/前列腺素H_2 （PGH2）受体拮抗剂SQ-29548可抑制LPA诱导的血管收缩。此外，这种收缩被OKY-046 （ozagrel）部分抑制，一种TXA2合成酶抑制剂。这些结果表明，在流体诱导血管收缩的情况下，LPA受到内皮源性TXA2/PGH2的调节。我们假设LPA作为内皮细胞的机械增敏剂

The mechanotransduction plays an important role in maintenance of cellular homeostasis. In endothelial cells, it may be essential for local hemodynamic control. Increase in intracellular Ca^<2+> concentration ([Ca^<2+>]_i) is an important signal for mechanoreception, however, the molecular mechanisms remain unclear. We demonstrated that lysophosphatidic acid (LPA, 0.3-10 μM), a bioactive phospholipid, sensitizes response of [Ca^<2+>]_i to mechanical stress in several cell types. Local increases in [Ca^<2+>]_i within the cell subjected to mechanical stress were visualized in cultured bovine lens epithelial and aortic endothelial cells in the presence of LPA. The phenomenon was termed "Ca^<2+> spots". Pharmacological studies revealed that Ca^<2+> spot is an elementary Ca^<2+>-influx event through mechanosensitive channels. The sensitizing effect of LPA was observed in mouse aorta and renal artery in situ. The increase in endothelial [Ca^<2+>]_i caused subsequent [Ca^<2+>]_i transients and contraction in smooth muscle cells in aorta. We then examined the mechanism of LPA-induced endothelium-dependent vascular contraction. Endothelial Ca^<2+> response and vascular contraction were observed with multi photon laser scanning microscopy. The vascular contraction induced by LPA was inhibited by SQ-29548, an antagonist of thromboxane A_2 (TXA2)/prostagrandin H_2 (PGH2) receptor. Moreover, this contraction was partly inhibited by OKY-046 (ozagrel), an inhibitor of TXA2 synthetase. These results suggest that LPA in the presence of fluid flow induced vascular contraction was regulated by endothelium-derived TXA2/PGH2. We hypothesize that LPA acts as a mechanosensitizer in endothelial