Gram-negative bacterial lipopolysaccharide and antimicrobial LL-37 enhance ICAM-1 expression and NF-κB activation in senescent endothelial cells

Abstract

 Cellular senescence is associated with the induction of a proinflammatory phenotype. Previous studies revealed that senescent endothelial cells are localized at the sites of atherosclerotic lesions, suggesting the involvement of endothelial cell senescence in atherogenesis. Importantly, bacterial infection has been speculated to contribute to the pathogenesis of atherosclerosis ; however the effect of bacterial components or host-derived antimicrobial substances on senescent endothelial cells has not fully understood. Here, we investigated the effects of Gram-negative bacterial lipopolysaccharide (LPS) and antimicrobial peptide LL-37, which is deposited at the atherosclerotic loci, on senescent endothelial cells using serially passaged human umbilical vein endothelial cells (HUVECs). The results indicated that senescent endothelial cells basally exhibited proinflammatory phenotype, as evidenced by increased expression of intercellular adhesion molecule-1 (ICAM-1) and activation of NF-κB (phosphorylation of p65), compared with non-senescent cells. Of note, senescent endothelial cells more potently responded to the stimulation of LPS or LL-37, as evidenced by further enhanced ICAM-1 expression and NF-κB activation, compared with non-senescent cells. Moreover, expression levels of the receptors for LPS (TLR4) and LL-37 (purinergic receptor P2X7) were upregulated in senescent endothelial cells, suggesting that both LPS and LL-37 enhance the ICAM-1 expression and NF-κB activation in senescent endothelial cells possibly via the upregulated TLR4 and P2X7. Together these observations indicate that senescent endothelial cells may contribute to the pathogenesis of atherosclerosis via the basal proinflammatory phenotype and the enhanced inflammatory responses against atherogenic factors including bacterial LPS and host-derived antimicrobial LL-37.