Abstract 15266: Inhibiting Endothelial Mammalian Sterile 20-Like Kinase 1 Attenuates Acute Lung Injury in Mice

Abstract

Introduction: Lung endothelium plays a pivotal role in the orchestration of inflammatory and injury responses to acute pulmonary insults. Mammalian sterile 20-like kinase 1 (Mst1), a mammalian homolog of Hippo, is a serine/threonine kinase that is ubiquitously expressed in many tissues and has been shown to play an important role in the regulation of complex biological processes, such as apoptosis, oncogenesis and organ growth. While Mst1 is highly expressed in the lung, its role in the endothelial response to pulmonary insults is largely unknown. Hypothesis: Mst1 regulates inflammatory responses in acute lung injury. Methods: Mst1 activity was assessed in lung endothelium by western blot and immunofluorescent staining. EC activation was measured by nuclear factor kappa B (NF-κB) dependent luciferase assay and the electrophoresis mobility shift assay. Mst1 knockout mice and pharmacological inhibitor were employed to assess the effects of Mst1 on homeostatic and lipopolysaccharide (LPS)-induced endothelial inflammation. Results: In this study, we found that Mst1 activation, as determined by Mst1 phosphorylation and nuclear translocation, was significantly increased in lung ECs after exposure to tumor necrosis factor-alpha (TNF-α) and in lungs of LPS-instilled mice as compared to the vehicle control. Overexpression of either full length Mst1 or its kinase domain promoted NF-κB activation by approximately 6.5-fold and 8-fold, respectively, whereas overexpression of the dominant negative forms of Mst1 attenuated endothelial inflammatory responses to both TNF-α and interleukin-1β stimulation. Consistent with these observations, endothelial specific deletion of Mst1 markedly attenuated LPS-induced acute lung injury in mice. Furthermore, we found that treatment of wild-type mice with Mst1 specific pharmacological inhibitor significantly prevented LPS-induced lung injury. Conclusion: Our findings identified Mst1 kinase as a key regulator in promoting lung EC activation and vascular inflammation, and suggest that therapeutic strategies aimed at inhibiting Mst1 activation might be effective for preventing inflammatory vascular diseases of the lung.