Garcia J G, Schaphorst K L
Indiana University School of Medicine, Indianapolis, USA.
J Investig Med. 1995 Apr;43(2):117-26.
Investigation of the regulation of permeability properties of the endothelium has yielded evidence to support the concept of a dual regulation of EC gap formation and barrier function. In this model, the primary determinants of EC permeability are tethering/adhesive properties (Figure 1) and tensile centripetal force generation (Figure 2). The importance of actin-myosin interactions and active cellular contraction and force generation has been reviewed. In the model of thrombin-induced EC barrier dysfunction, there is a strong shift in the MLC species from the unphosphorylated to the diphosphorylated form, indicating activation of MLCK, a key enzyme whose importance in EC contraction has been well established. Although important differences between EC and SMC exist, endothelial cell gap formation involves actomyosin-dependent contractile mechanisms similar to SMC, a cellular system in which MLC phosphorylation correlates with the initial rate of tension development. The increase in MLC phosphorylation and isometric tension is consistent with the hypothesis that activation of signal transduction mediates an increase in isometric tension to a new level of "latch state" through the cytoskeleton. Thus, the available evidence implicates a strong role for cellular force generation and contraction in the evolution of thrombin-induced barrier dysfunction. Accumulating evidence also indicates that modulation of tethering properties, primarily those involving cell-matrix and cell-cell adhesion, is also a key determinant of basal EC barrier properties as well as agonist-mediated barrier dysfunction. Because each of these focal adhesion constituents may be involved in establishing tethering properties in endothelium, they each may be involved in determining barrier permeability and may be involved in the evolution of agonist-mediated barrier dysfunction. Therefore, in addition to MLCK-dependent active tensile force generation, agonist-induced barrier dysfunction may occur via MLCK-independent pathways that rely on basal levels of MLC phosphorylation or by affecting proteins involved in tethering properties of endothelium that contribute to barrier function. Further examination of tethering force properties, combined with elucidation of EC relaxation via MLC dephosphorylation may yield clues as to how this important vascular barrier is maintained and restored after vascular insult.
对内皮细胞通透性特性调节的研究已获得证据，支持内皮细胞间隙形成和屏障功能双重调节的概念。在该模型中，内皮细胞通透性的主要决定因素是拴系/黏附特性（图1）和向心拉伸力的产生（图2）。肌动蛋白-肌球蛋白相互作用以及细胞主动收缩和力产生的重要性已得到综述。在凝血酶诱导的内皮细胞屏障功能障碍模型中，肌球蛋白轻链（MLC）种类从非磷酸化形式向双磷酸化形式发生了强烈转变，表明肌球蛋白轻链激酶（MLCK）被激活，MLCK是一种关键酶，其在内皮细胞收缩中的重要性已得到充分证实。尽管内皮细胞和平滑肌细胞之间存在重要差异，但内皮细胞间隙形成涉及与平滑肌细胞类似的肌动球蛋白依赖性收缩机制，在平滑肌细胞这个细胞系统中，MLC磷酸化与张力发展的初始速率相关。MLC磷酸化和等长张力的增加与以下假设一致，即信号转导的激活通过细胞骨架将等长张力增加到新的“闩锁状态”水平。因此，现有证据表明细胞力的产生和收缩在凝血酶诱导的屏障功能障碍演变中起重要作用。越来越多的证据还表明，拴系特性的调节，主要是那些涉及细胞-基质和细胞-细胞黏附的特性，也是基础内皮细胞屏障特性以及激动剂介导的屏障功能障碍的关键决定因素。由于这些黏着斑成分中的每一种都可能参与在内皮细胞中建立拴系特性，它们各自可能参与决定屏障通透性，并可能参与激动剂介导的屏障功能障碍的演变。因此，除了依赖MLCK的主动拉伸力产生外，激动剂诱导的屏障功能障碍可能通过依赖MLC磷酸化基础水平的非MLCK依赖性途径发生，或者通过影响参与内皮细胞拴系特性且有助于屏障功能的蛋白质发生。进一步研究拴系力特性，结合通过MLC去磷酸化阐明内皮细胞舒张，可能会揭示在血管损伤后这个重要的血管屏障是如何维持和恢复的线索。
