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

在内皮细胞中，机械应力可能是局部血流动力学控制所必需的。细胞内Ca^2+浓度（[Ca^2+] i）升高是机械感受的重要信号，但其分子机制尚不清楚。我们证明溶血磷脂酸（LPA，0.3-10 μM）是一种生物活性磷脂，它能使几种细胞类型的胞内Ca^<2+>浓度（[Ca^<2+>]_i）对机械应力的反应敏感。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的增加引起随后的[Ca^<2+>]_i瞬变和主动脉平滑肌细胞的收缩。然后，我们研究了LPA诱导的内皮依赖性血管收缩的机制。用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（TXA_2）/前列腺素H_2（PGH_2）受体拮抗剂SQ-29548可抑制LPA引起的血管收缩。TXA 2合成酶抑制剂OKY-046（奥扎格雷）可部分抑制这种收缩。这些结果表明，LPA在流体流动诱导的血管收缩的存在下由内皮源性TXA 2/PGH 2调节。我们还证实了LPA在肾动脉切应力依赖性Ca^2+反应中的增敏作用具有区域特异性，并且是通过LPA-1、-2和-3以外的其他受体诱导的。我们假设LPA在内皮细胞中作为机械敏化剂。

In endothelial cells, mechanical stress 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 in intracellular Ca^<2+> concentration ([Ca^<2+>]_i) to mechanical stress in several cell types. 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 also demonstrated that sensitizing effect of LPA in shear stress-dependent Ca^<2+> response has region-specific property in renal artery and is induced through other receptor than LPA-1,-2 and -3. We hypothesize that LPA acts as a mechanosensitizer in endothelial cells.