Stolwijk Judith A, Zhang Xuexin, Gueguinou Maxime, Zhang Wei, Matrougui Khalid, Renken Christian, Trebak Mohamed
From the Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, Pennsylvania 17033.
the Applied Biophysics Inc., Troy, New York 12180.
J Biol Chem. 2016 Oct 28;291(44):22894-22912. doi: 10.1074/jbc.M116.756114. Epub 2016 Sep 13.
Endothelial barrier function is tightly regulated by plasma membrane receptors and is crucial for tissue fluid homeostasis; its dysfunction causes disease, including sepsis and inflammation. The ubiquitous activation of Ca signaling upon phospholipase C-coupled receptor ligation leads quite naturally to the assumption that Ca signaling is required for receptor-regulated endothelial barrier function. This widespread hypothesis draws analogy from smooth muscle and proposes the requirement of G protein-coupled receptor (GPCR)-generated Ca signaling in activating the endothelial contractile apparatus and generating interendothelial gaps. Notwithstanding endothelia being non-excitable in nature, the hypothesis of Ca-induced endothelial contraction has been invoked to explain actions of GPCR agonists that either disrupt or stabilize endothelial barrier function. Here, we challenge this correlative hypothesis by showing a lack of causal link between GPCR-generated Ca signaling and changes in human microvascular endothelial barrier function. We used three endogenous GPCR agonists: thrombin and histamine, which disrupt endothelial barrier function, and sphingosine-1-phosphate, which stabilizes barrier function. The qualitatively different effects of these three agonists on endothelial barrier function occur independently of Ca entry through the ubiquitous store-operated Ca entry channel Orai1, global Ca entry across the plasma membrane, and Ca release from internal stores. However, disruption of endothelial barrier function by thrombin and histamine requires the Ca sensor stromal interacting molecule-1 (STIM1), whereas sphingosine-1-phosphate-mediated enhancement of endothelial barrier function occurs independently of STIM1. We conclude that although STIM1 is required for GPCR-mediated disruption of barrier function, a causal link between GPCR-induced cytoplasmic Ca increases and acute changes in barrier function is missing. Thus, the cytosolic Ca-induced endothelial contraction is a cum hoc fallacy that should be abandoned.
内皮屏障功能受质膜受体严格调控，对组织液稳态至关重要；其功能障碍会引发包括败血症和炎症在内的疾病。磷脂酶C偶联受体连接后钙信号的普遍激活自然而然地让人认为，钙信号是受体调节的内皮屏障功能所必需的。这一广泛的假说借鉴了平滑肌的情况，并提出G蛋白偶联受体（GPCR）产生的钙信号在激活内皮收缩装置和产生内皮间隙方面的必要性。尽管内皮本质上是不可兴奋的，但钙诱导的内皮收缩假说已被用来解释GPCR激动剂破坏或稳定内皮屏障功能的作用。在这里，我们通过表明GPCR产生的钙信号与人类微血管内皮屏障功能变化之间缺乏因果联系，对这一相关假说提出了挑战。我们使用了三种内源性GPCR激动剂：凝血酶和组胺，它们会破坏内皮屏障功能；以及1-磷酸鞘氨醇，它能稳定屏障功能。这三种激动剂对内皮屏障功能的定性不同影响独立于通过普遍存在的储存-操作性钙内流通道Orai1的钙内流、跨质膜的整体钙内流以及从内部储存释放的钙。然而，凝血酶和组胺对内皮屏障功能的破坏需要钙传感器基质相互作用分子1（STIM1），而1-磷酸鞘氨醇介导的内皮屏障功能增强独立于STIM1发生。我们得出结论，虽然STIM1是GPCR介导的屏障功能破坏所必需的，但GPCR诱导的细胞质钙增加与屏障功能急性变化之间的因果联系并不存在。因此，胞质钙诱导的内皮收缩是一种应该摒弃的相关谬误。
