Increased Kindlin-2 via SMURF1 Inhibition Attenuates Endothelial Permeability and Acute Lung Injury

Integrin β4 (ITGB4) mediates lung endothelial cell (EC) inflammation attenuated by simvastatin, an HMG CoA-reductase inhibitor. The cytoplasmic domain of ITGB4 is predicted to bind kindlin-2. Kindlin-2 expression is mediated by SMURF1, an E3 ubiquitin ligase that promotes kindlin-2 ubiquitination and degradation. We hypothesized that increased kindlin-2 expression via the inhibition of SMURF1 mediates EC inflammatory responses relevant to acute lung injury (ALI). To investigate this, human lung ECs were treated with simvastatin (5 µM, 16 h) prior to the immunoprecipitation of kindlin-2 and Western blotting for ITGB4. Next, ECs were treated with a SMURF1 inhibitor, A01, and increased kindlin-2 expression was confirmed. In assays of barrier function, kindlin-2 was silenced (siRNA) in ECs prior to thrombin and measurements of transendothelial resistance (TER) and FITC-dextran transwell flux. Repeat assessments of barrier function were performed in A01-treated ECs. Finally, mice were pretreated with A01 prior to LPS; bronchoalveolar lavage (BAL) fluid was collected, and their lungs were used for histology. Simvastatin increased ITGB4:kindlin-2 association, while A01 increased kindlin-2 expression. Thrombin-induced EC barrier disruption was both increased after kindlin-2 silencing and decreased by A01. Finally, murine ALI was significantly attenuated by A01. Our findings suggest that the augmentation of kindlin-2 may serve as a novel ALI therapeutic strategy.