SIRT2 stabilizes endothelial adherens junctions
Authors: Yang Deying , Lee Jonathan , Yang Xiaoyan , Komarova Yulia 
Published: June 2021

Endothelial barrier functional is essential for maintenance of tissue‐fluid homeostasis in lung. Disruption of the endothelial barrier leads to pulmonary edema, acute lung injury, and respiratory failure. Adherens junction (AJ) protein complex, and associated cytoskeleton are the major components regulating barrier integrity. Post‐translational protein modifications of AJ constituents, such as phosphorylation, nitration, and nitrosylation, have been well known to regulate endothelial barrier function. More recently, lysine acetylation/deacetylation has emerged as an important and physiologically significant posttranslational protein modification involved in pathogenesis of human diseases. Sirtuins (SIRTs) are NAD+‐dependent deacetylases, and critical regulators of energy metabolism and oxidative stress response in different cell types. Here, we studied the function of SIRT2, the only cytosolic sirtuin family member, in regulating endothelial barrier function in the context of inflammatory lung disease. We have showed that SIRT2 is the most abundant sirtuin in human lung endothelial cells. Importantly, SIRT2 protein level is significantly increased in lung endothelial cells upon challenging mice with a sublethal dose of lipopolysaccharides, a gram‐negative bacteria endotoxin which causes systemic inflammatory responses resulting in acute lung injury. Increase in SIRT2 protein level was also observed in human lung microvascular endothelial cells (HLMVEC) upon challenge with permeability‐increasing agents such as human α‐thrombin and TNF‐α, further emphasizing the potentially important role of SIRT2 in regulating adaptation of endothelial cells to inflammatory responses. Furthermore, depletion of SIRT2 in HLMVECs monolayers led to destabilization of VE‐cadherin junctions suggesting that SIRT2 regulates integrity of endothelial barrier. SIRT2 depleted monolayers also demonstrated an increased gap area following TNF‐α treatment whereas cells overexpressing human SIRT2 attenuated TNF‐α‐induced disruption of VE‐cadherin junctions. Our data suggest that SIRT2 plays a critical role in the maintenance of endothelial barrier function under basal conditions and upon inflammatory response. In order to explore the underlying mechanism by which SIRT2 regulates endothelial barrier integrity, we performed mass‐spectrometry analysis of acetylated proteins in HLMVECs treated with control siRNA or depleted of SIRT2. Interestingly, we found that acetylation of BORG5, a Cdc42 effector protein 1, was markedly increased after SIRT2 knockdown as well as in cells treated with hTNF‐α. We observed that human SIRT2‐FLAG interacted with BORG5‐V5 overexpressed in HEK293T cells and the level of acetyl‐BORG5 was increased in cells depleted of SIRT2. Furthermore, knockdown BORG5 reversed gap formation in endothelial cell with SIRT2 knockdown suggesting that SIRT2 stabilizes AJs through deacetylation of BORG5. Overall, our studies describe the novel role of SIRT2 in the mechanisms regulating the endothall barrier integrity through deacetylation of BORG5 allowing the assembly of stable AJs.Support or Funding InformationXiaoyan Yang is supported by AHA Award #17SDG33410608This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.