Phosphorylated ERM Mediates Lipopolysaccharide Induced Pulmonary Microvascular Endothelial Cells Permeability Through Negatively Regulating Rac1 Activity.

[INTRODUCTION] The endotoxin lipopolysaccharide (LPS)-induced pulmonary endothelial barrier disruption is a key pathogenesis of acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). However, the molecular mechanisms underlying LPS-impaired permeability of pulmonary microvascular endothelial cells (PMVECs) are not fully understood.

[METHODS] Rat PMVECs were isolated and monolayered cultured, then challenged with different doses of LPS (0.1mg/L, 1mg/L, and 10mg/L). Trans-endothelial electrical resistance (TER) was utilized to measure the integrity of the endothelial barrier. Ras-related C3 botulinum toxin substrate 1 (Rac1) activity and the phosphorylation of Ezrin/Radixin/Moesin proteins (ERM) were assessed by pulldown assay and Western Blotting. Small interfering RNA (siRNA) inhibition of Rac1 and Moesin were applied to evaluate the effect of PMVEs permeability and related pathway.

[RESULTS] LPS induced dose and time-dependent decreases in TER and increase in ERM threonine phosphorylation, while inactivated Rac1 activity in PMVEC. siRNA study demonstrated that both Rac1 and Moesin were involved in the mediation of the LPS-induced hyperpermeability in PMVECs monolayers, and Rac1 and Moesin could regulate each other.

[CONCLUSION] Phosphorylated ERM mediates LPS induced PMVECs permeability through negatively regulating Rac1 activity.