Activation of Epac alleviates inflammation and vascular leakage in LPS-induced acute murine lung injury

Abstract

Exchange protein directly activated by cAMP (Epac) is an important molecule in cAMP signal transduction, but the effect of Epac on lipopolysaccharide (LPS)-induced acute lung injury (ALI) is unclear. In this study, we treated in vitro and in vivo models with the Epac activator 8CPT to determine the effect and related mechanisms of Epac. The in vitro results indicate that 8CPT inhibits lipopolysaccharide (LPS)-induced tumor necrosis factor-α (TNF-α) release from mouse macrophages (MH-S), whereas the protein kinase A (PKA) activator 6BnZ has no effect. Furthermore, Epac over-expression can significantly suppress TNF-α release from LPS induced MH-S cell, while Epac siRNA can slightly increase TNF-α release. Moreover, 8CPT reduces LPS-induced microvascular permeability in human pulmonary microvascular endothelial cells (HPMVECs), whereas the PKA activator 6BnZ has no effect. In mice with LPS-induced ALI, 8CPT significantly reduces LPS-induced inflammatory cytokine release, neutrophil recruitment, and albumin leakage. LPS simultaneously decreases the Epac but not the PKA levels. However, 8CPT reverses the decreased Epac levels. Furthermore, the mechanism involves the small GTPase Rac1/2 but not the mitogen-activated protein kinase (MAPK) pathway. Thus, Epac activation reduces inflammation and microvascular permeability in LPS-induced lung injury and an Epac activator represents a novel choice for the early therapy of ALI.

Keywords: Acute lung injury; Epac; LPS; PKA; cAMP.