Endothelial Barrier Protection by Activated Protein C Through PAR1-dependent Sphingosine 1-phosphate receptor-1 Crossactivation

Blood. 2005 Apr 15;105(8):3178-84. doi: 10.1182/blood-2004-10-3985. Epub 2004 Dec 30.


Endothelial cells normally form a dynamically regulated barrier at the blood-tissue interface, and breakdown of this barrier is a key pathogenic factor in inflammatory disorders such as sepsis. Pro-inflammatory signaling by the blood coagulation protease thrombin through protease activated receptor-1 (PAR1) can disrupt endothelial barrier integrity, whereas the bioactive lipid sphingosine 1-phosphate (S1P) recently has been demonstrated to have potent barrier protective effects. Activated protein C (APC) inhibits thrombin generation and has potent anti-inflammatory effects. Here, we show that APC enhanced endothelial barrier integrity in a dual-chamber system dependent on binding to endothelial protein C receptor, activation of PAR1, and activity of cellular sphingosine kinase. Small interfering RNA that targets sphingosine kinase-1 or S1P receptor-1 blocked this protective signaling by APC. Incubation of cells with PAR1 agonist peptide or low concentrations of thrombin (approximately 40 pM) had a similar barrier-enhancing effect. These results demonstrate that PAR1 activation on endothelial cells can have opposite biologic effects, reveal a role for cross-communication between the prototypical barrier-protective S1P and barrier-disruptive PAR1 pathway, and suggest that S1P receptor-1 mediates protective effects of APC in systemic inflammation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antibodies / pharmacology
  • Capillary Permeability / physiology*
  • Endothelium, Vascular / metabolism
  • Humans
  • Inflammation / metabolism
  • Protein C / immunology
  • Protein C / metabolism*
  • RNA, Small Interfering
  • Receptor Cross-Talk / physiology*
  • Receptor, PAR-1 / metabolism*
  • Receptors, Lysosphingolipid / genetics
  • Receptors, Lysosphingolipid / metabolism*
  • Signal Transduction / physiology


  • Antibodies
  • Protein C
  • RNA, Small Interfering
  • Receptor, PAR-1
  • Receptors, Lysosphingolipid