Gene expression of SOAT1, a key enzyme for cholesteryl ester biosynthesis, is regulated by LPS and correlates with the antibacterial activity of human bronchial epithelial cell secretions against Pseudomonas aeruginosa (P1249)

Abstract

Airway epithelial cells contribute to the first line of mucosal defense by secretion of antimicrobial peptides and antimicrobial lipids, including the cholesteryl ester (CE) cholesteryl arachidonate. Sterol O-acyltransferase 1 (SOAT1) is a key enzyme for CE biosynthesis. However, little is known about the regulation of the lipid-mediated arm of innate host defense. Polarized human bronchial epithelial cells (HBE) were incubated for 6 h with 100 ng/mL LPS, 10 μg/mL peptidoglycan (PG), 25 μg/mL PamCys3, and solvent control. SOAT1 mRNA was quantified by qRT-PCR with duplexing and RPLP0α as housekeeping gene. Lipid content of apical HBE secretions was analyzed by rpHPLC. SOAT1 expression was blocked with siRNA/lipofection. Antibacterial activity of HBE secretions was assessed by a 3 h colony forming unit assay with Pseudomonas aeruginosa (PA). SOAT1 gene expression was significantly increased by LPS (14.6 ±11.4, means ± SD, n=4, p=0.037). Stimulation with PG and PamCys3 increased SOAT1 expression by ~ 4- and 2-fold, respectively. Secretions from LPS-stimulated HBE showed an increase of total lipids including CA by ~30-50%. Selective inhibition of SOAT1 mRNA expression by 80% reduced the antibacterial activity of HBE whereby PA showed enhanced bacterial growth reaching >170% of the controls. These data suggest that SOAT1 is regulated by conserved innate immunity pathways and further support the role of antimicrobial lipids as effector molecules in mucosal airway defense.