Molecular Mechanisms in Peptidoglycan-Induced Human Umbilical Vascular Endothelial Cell Apoptosis

Peptidoglycan (PGN), a component of the outer membrane of Gram-positive bacteria has been implicated in the pathological process of sepsis. However, the molecular mechanism of PGN-induced vascular endothelium dysfunction has not been fully elucidated. Apoptosis signal regulating kinase 1 (ASK I) has been recently reported to play a crucial role in cell apoptosis under various cellular stresses. The purpose of this study was thus to investigate whether PUN-activated ASK1 results in cell apoptosis in human umbilical vascular endothelial cells (HUVECs). PUN was shown to cause a decrease in cell viability in a concentration-dependent manner. Flow cytometric analysis demonstrated that PGN increased the percentage of apoptotic cells. PUN induced ASK1 activation was accompanied by the increased phosphorylation of p38MAPK, a major downstream signaling molecule of ASK1. In addition, PUN was shown to increase apoptotic protein, Bax, expression in HUVECs. Inhibitor of p38MAPK signaling abrogated the PUN-increased DNA fragmentation and Bax expression, suggesting functional crosstalk. The toll-like receptor 2 (TLR2) agonist, Pam3CSK4, was also shown to induce ASK1 activation and p38MAPK phosphorylation, and subsequent cell apoptosis in HUVECs. Our data suggest that ASK1-p38MAPK cascade activation, followed by Bax expression, contributes to PUN-induced cell apoptosis.