Induction of endothelial barrier dysfunction by serum factors in rats subjected to traumatic brain injury and hemorrhagic shock

Abstract

Traumatic brain injury (TBI) has been associated with the development of indirect acute respiratory distress syndrome (ARDS). However, the causative relationship between TBI and lung injury remains unclear. To explore potential mechanisms linking TBI with the development of ARDS, we characterized the effects of serum factors released following TBI and hemorrhagic shock (HS) in a rat model on the pulmonary endothelial cell (EC) barrier dysfunction, a key feature of ARDS. We found that serum samples from animals exposed to both controlled cortical impact (CCI) and HS, but not from sham-operated rats induced significant barrier dysfunction in human pulmonary artery EC monolayers at 2 days post injury. Thrombin inhibitor and thrombin receptor antagonist attenuated the acute phase of the serum-induced trans-endothelial resistance (TER) decline caused by CCI-HS serum, but not in later time points. However, both the early and late phases of CCI-HS-induced EC permeability were inhibited by heparin. The barrier disruptive effects of CCI-HS serum were also prevented by serum preincubation with heparin-sepharose. Pulmonary EC treated for 3 h with serum from CCI-HS rats demonstrated a significant decline in expression of EC junctional protein, VE-Cadherin, and disassembly of peripheral EC adherens junction complexes monitored by immunostaining with VE-cadherin antibody.These results suggest that exposure to CCI-HS causes early and late-phase barrier disruptive effects in vascular endothelium. While thrombin-PAR1 signaling has been identified as a mechanism of acute EC permeability increase by CCI-HS serum, the factor(s) defining long-term EC barrier disruption in CCI-HS model remains to be determined.

The neuro-endothelial axis in traumatic brain injury: mechanisms of multi-organ dysfunction, novel therapies, and future directions

“…Traumatic brain injury is associated with an upregulation of the coagulation cascade and decreased fibrinolysis, contributing to the mechanism of acute lung injury (4,36,37). The procoagulant protein and protease, thrombin, can disrupt the endothelial actin cytoskeleton resulting in increased endothelial leak (4,24). Ke et al (24) examined the relationship of TBI to acute lung injury by incubating serum obtained from rats subjected to controlled cortical injury and hemorrhagic shock with human pulmonary artery ECs.…”

“…The procoagulant protein and protease, thrombin, can disrupt the endothelial actin cytoskeleton resulting in increased endothelial leak (4,24). Ke et al (24) examined the relationship of TBI to acute lung injury by incubating serum obtained from rats subjected to controlled cortical injury and hemorrhagic shock with human pulmonary artery ECs. Incubation with injured serum led to endothelial barrier dysfunction, increased permeability, and decreased VE-cadherin (24).…”

“…Ke et al (24) examined the relationship of TBI to acute lung injury by incubating serum obtained from rats subjected to controlled cortical injury and hemorrhagic shock with human pulmonary artery ECs. Incubation with injured serum led to endothelial barrier dysfunction, increased permeability, and decreased VE-cadherin (24). The EC disruption was hypothesized to be mediated by thrombin due to the known increase in thrombin after injury.…”

“…Treatment with both anticoagulants decreased permeability and improved barrier dysfunction in the early phase (24). In addition, inhibition of protease-activated receptor 1 (PAR1), a G protein–coupled receptor for thrombin, also led to similar improvements in EC dysfunction (24). While this study contributes to our understanding of the role of thrombin in TBI-induced lung EC injury, the downstream pathway initiated by PAR1 activation remains unknown.…”

“…Severe TBI has been associated with acute lung injury, with a reported incidence rate as high as 30% (21). Acute lung injury in patients with severe TBI is associated with a 30% to 40% mortality rate, likely affected by pulmonary EC injury leading to vascular hyperpermeability (22)(23)(24). Two major mechanisms have been proposed as explanations for TBI-associated pulmonary insult: the receptor for advanced glycation end products (RAGE) pathway and coagulation-associated lung endothelial injury.…”