Department of Intensive Care, Institute for Cardiovascular Research, VU University Medical Centre, Amsterdam, The Netherlands.
PLoS One. 2011;6(8):e23448. doi: 10.1371/journal.pone.0023448. Epub 2011 Aug 15.
Angiopoietin-2 (Ang-2) is associated with lung injury in ALI/ARDS. As endothelial activation by thrombin plays a role in the permeability of acute lung injury and Ang-2 may modulate the kinetics of thrombin-induced permeability by impairing the organization of vascular endothelial (VE-)cadherin, and affecting small Rho GTPases in human pulmonary microvascular endothelial cells (HPMVECs), we hypothesized that Ang-2 acts as a sensitizer of thrombin-induced hyperpermeability of HPMVECs, opposed by Ang-1.
METHODOLOGY/PRINCIPAL FINDINGS: Permeability was assessed by measuring macromolecule passage and transendothelial electrical resistance (TEER). Angiopoietins did not affect basal permeability. Nevertheless, they had opposing effects on the thrombin-induced permeability, in particular in the initial phase. Ang-2 enhanced the initial permeability increase (passage, P = 0.010; TEER, P = 0.021) in parallel with impairment of VE-cadherin organization without affecting VE-cadherin Tyr685 phosphorylation or increasing RhoA activity. Ang-2 also increased intercellular gap formation. Ang-1 preincubation increased Rac1 activity, enforced the VE-cadherin organization, reduced the initial thrombin-induced permeability (TEER, P = 0.027), while Rac1 activity simultaneously normalized, and reduced RhoA activity at 15 min thrombin exposure (P = 0.039), but not at earlier time points. The simultaneous presence of Ang-2 largely prevented the effect of Ang-1 on TEER and macromolecule passage.
CONCLUSIONS/SIGNIFICANCE: Ang-1 attenuated thrombin-induced permeability, which involved initial Rac1 activation-enforced cell-cell junctions, and later RhoA inhibition. In addition to antagonizing Ang-1, Ang-2 had also a direct effect itself. Ang-2 sensitized the initial thrombin-induced permeability accompanied by destabilization of VE-cadherin junctions and increased gap formation, in the absence of increased RhoA activity.
血管生成素-2（Ang-2）与 ALI/ARDS 中的肺损伤有关。由于凝血酶激活内皮在急性肺损伤的通透性中起作用，并且 Ang-2 可能通过损害血管内皮（VE）-钙粘蛋白的组织并影响人肺微血管内皮细胞（HPMVEC）中的小 Rho GTPases，来调节凝血酶诱导的通透性动力学，我们假设 Ang-2 作为凝血酶诱导的 HPMVEC 高通透性的敏化剂起作用，而 Ang-1 则相反。
方法/主要发现：通过测量大分子通透性和跨内皮电阻（TEER）来评估通透性。Angiopoietins 不影响基础通透性。然而，它们对凝血酶诱导的通透性具有相反的影响，特别是在初始阶段。Ang-2 增强了初始通透性增加（通透性，P = 0.010；TEER，P = 0.021），同时损害了 VE-钙粘蛋白的组织，而不影响 VE-钙粘蛋白 Tyr685 磷酸化或增加 RhoA 活性。Ang-2 还增加了细胞间间隙的形成。Ang-1 预孵育增加了 Rac1 活性，增强了 VE-钙粘蛋白的组织，减少了初始凝血酶诱导的通透性（TEER，P = 0.027），同时在 15 分钟凝血酶暴露时使 Rac1 活性正常化并降低了 RhoA 活性（P = 0.039），但在更早的时间点则不然。Ang-2 的同时存在在很大程度上阻止了 Ang-1 对 TEER 和大分子通透性的影响。
结论/意义：Ang-1 减弱了凝血酶诱导的通透性，这涉及初始 Rac1 激活增强的细胞-细胞连接，以及随后的 RhoA 抑制。除了拮抗 Ang-1 外，Ang-2 本身也有直接作用。Ang-2 敏化了初始凝血酶诱导的通透性，同时破坏了 VE-钙粘蛋白连接，并增加了间隙形成，而没有增加 RhoA 活性。
