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. 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. tension generated by smooth muscle cells during contraction (8). Nevertheless, Propacetamol hydrochloride during the past three decades Ca2+-dependent endothelial contraction, a concept extrapolated from studies on muscle cells, has been invoked to explain changes in endothelial barrier function downstream GPCR agonists. Barrier disrupting GPCR agonists such as thrombin and histamine activate Gq,11 protein and induce the production of inositol 1,4,5-trisphosphate (IP3) through the action of phospholipase C. This will result in Ca2+ release from the IP3-sensitive internal stores of the endoplasmic reticulum (ER) and activation of Ca2+ entry across the plasma membrane through the ubiquitous store-operated Ca2+ entry (SOCE) pathway activated by ER store depletion (9). It is now appreciated that ER store depletion causes the ER-resident Ca2+ sensor stromal-interacting molecule 1 (STIM1) to move toward ER-plasma membrane junctional spaces to trap and directly activate Orai1 Ca2+ entry channels (10,C17). According to the Ca2+-dependent model, the sustained Ca2+ entry signal thus generated (but not Ca2+ release) activates a key Ca2+- and calmodulin-dependent kinase, the myosin light chain kinase (MLCK) leading to MLC phosphorylation, formation of actin stress materials, and endothelial contraction resulting in formation of intercellular gaps (3, 18,C21). For the barrier-stabilizing agonist S1P, Ca2+ launch from internal stores, but not Ca2+ access, was proposed to induce Rac activation, therefore promoting assembly of adherens junctions and conditioning of endothelial barrier function (22). Early studies from our group while others shown that in endothelial cells from numerous vascular mattresses (human being pulmonary artery, human being dermal microvasculature, and human being umbilical vein) thrombin, VEGF, and the store-depleting drug thapsigargin activate SOCE encoded by STIM1 and Orai1 (11, 23,C25). In a recent study, we Propacetamol hydrochloride have challenged the hypothesis that SOCE is required for endothelial contraction in response to the Propacetamol hydrochloride powerful barrier-disrupting agonist thrombin (23). We shown using molecular tools that thrombin-mediated endothelial barrier disruption Rabbit Polyclonal to CPB2 required the ER-resident STIM1 protein but occur individually of SOCE, Orai1, and MLCK (23). We also showed that STIM1 is required for RhoA activation, MLC phosphorylation, actin reorganization, and disruption of intercellular adhesions (23). In the current study, we set out to determine whether these findings are unique to thrombin or shared by additional barrier-altering or barrier-enhancing GPCR agonists and whether Ca2+ launch from your ER is required for agonist-mediated effects on endothelial barrier function. We therefore used high throughput impedance measurements to determine the part of Ca2+ launch and Ca2+ access mechanisms in regulating endothelial barrier function downstream of three GPCR agonists, namely thrombin, histamine, and S1P. Thrombin and histamine are two standard inflammatory agonists that cause transient barrier disruption, whereas the platelet-derived agonist S1P enhances endothelial barrier function. These three agonists are of major relevance to vascular pathologies such as swelling, allergy, and atherosclerosis. We compared side by side the effects of these three agonists on endothelial barrier function using electrical measurements and fluorescence microscopy. We also monitored the Ca2+ launch from stores and Ca2+ access across the plasma membrane induced by these agonists. We statement that although Ca2+ signaling in response Propacetamol hydrochloride to these agonists coincides with changes in barrier function, neither Ca2+ access nor Ca2+ launch are necessary for GPCR-mediated disruption or enhancement of barrier function. We display that Orai1 takes on no significant part in thrombin-, histamine-, and S1P-induced changes in endothelial barrier function. However, STIM1 is required for disruption of endothelial barrier function by thrombin and histamine but is not involved in S1P-mediated enhancement of endothelial barrier function. Results Thrombin, Histamine, and S1P Evoke Distinct Impedance Response.
- 4 EGFR-targeted nanobodyCPS conjugates localize in tumors specifically
- Similarly, during acute VL, human PBMCs failed to develop IL-1 in response to the stimulation of the antigen (Elliott et?al
- FITC- and Cy3-conjugated supplementary antibodies were utilized to visualize the tagged ORF65 and TGN46 protein, respectively
- Dedication of CIV-DP To measure CIV-DP concentrations, a sandwich ELISA was used
- (D) (Left) Schematic representation of the apoptotic signal induced by Fas-Ab and the antiapoptotic signal induced by Met activation