Downregulation of a tumor suppressor gene LKB1 in lung transplantation as a biomarker for chronic murine lung allograft rejection

Background: We recently demonstrated decreased tumor suppressor gene liver kinase B1 (LKB1) level in lung transplant recipients diagnosed with bronchiolitis obliterans syndrome. STE20-related adaptor alpha (STRAD alpha) functions as a pseudokinase that binds and regulates LKB1 activity.Methods: A murine model of chronic lung allograft rejection in which a single lung from a B6D2F1 mouse was orthotopically transplanted into a DBA/2J mouse was employed. We examined the effect of LKB1 knockdown using CRISPR-CAS9 in vitro culture system.Results: Significant downregulation of LKB1 and STRAD alpha expression was found in donor lung compared to recipient lung. STRAD alpha knockdown significantly inhibited LKB1, pAMPK expression but induced phosphorylated mammalian target of rapamycin (mTOR), fibronectin, and Collagen-I, expression in BEAS-2B cells. LKB1 overexpression decreased fibronectin, Collagen-I, and phosphorylated mTOR expression in A549 cells.Conclusions: We demonstrated that downregulation of LKB1-STRAD alpha pathway accompanied with increased fibrosis, results in development of chronic rejection following murine lung transplantation.