Calcium Signaling Is Dispensable for Receptor Regulation of Endothelial Barrier Function.
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 Ca2+signaling upon phospholipase C-coupled receptor ligation leads quite naturally to the assumption that Ca2+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 Ca2+signaling in activating the endothelial contractile apparatus and generating interendothelial gaps. Notwithstanding endothelia being non-excitable in nature, the hypothesis of Ca2+-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 Ca2+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 Ca2+entry through the ubiquitous store-operated Ca2+entry channel Orai1, global Ca2+entry across the plasma membrane, and Ca2+release from internal stores. However, disruption of endothelial barrier function by thrombin and histamine requires the Ca2+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 Ca2+increases and acute changes in barrier function is missing. Thus, the cytosolic Ca2+-induced endothelial contraction is a cum hoc fallacy that should be abandoned.
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.
Judith A
JA
Stolwijk
From the Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, Pennsylvania 17033.
Xuexin
X
Zhang
From the Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, Pennsylvania 17033.
Maxime
M
Gueguinou
From the Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, Pennsylvania 17033.
Wei
W
Zhang
the Department of Physiological Sciences, East Virginia Medical School, Norfolk, Virginia 23507, and.
Khalid
K
Matrougui
the Applied Biophysics Inc., Troy, New York 12180.
Christian
C
Renken
From the Department of Cellular and Molecular Physiology, Penn State University College of Medicine, Hershey, Pennsylvania 17033, mtrebak@hmc.psu.edu.
Mohamed
M
Trebak
D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000378:metabolism*; D006801:Humans; D008246:Lysophospholipids / Q000378:metabolism; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D000071740:ORAI1 Protein / Q000235:genetics / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives / Q000378:metabolism; D000071737:Stromal Interaction Molecule 1 / Q000235:genetics / Q000378:metabolism; D013917:Thrombin / Q000235:genetics / Q000378:metabolism
D008246:Lysophospholipids; D009363:Neoplasm Proteins; D000071740:ORAI1 Protein; C103530:STIM1 protein, human; D000071737:Stromal Interaction Molecule 1; C060506:sphingosine 1-phosphate; D013917:Thrombin; D013110:Sphingosine; D002118:Calcium
G protein-coupled receptor (GPCR); calcium release-activated calcium channel protein 1 (ORAI1); calcium signaling; endothelial cell; endothelial dysfunction; stromal interaction molecule 1 (STIM1)