Molecular Mechanisms in Peptidoglycan-Induced Human Umbilical Vascular Endothelial Cell Apoptosis
TSRANG-NENG JANG1, PEI-TING CHIU2, WEI-CHUAN CHEN3 AND MING-JEN HSU2*
1, Department of Internal Medicine, Shin Kong Wu Ho-Su Memorial Hospital, Taipei, Taiwan, R.O.C.
2, Department of Pharmacology, School of Medicine, College of Medicine, Taipei Medical University, Taipei, Taiwan, R.O.C.
3, Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei, Taiwan, R.O.C.
(Received: September 10, 2010; Accepted: April 15, 2011)
ABSTRACT
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 (ASK1) 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 PGN-activated ASK1 results in cell apoptosis in human umbilical vascular endothelial cells (HUVECs). PGN 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. PGN induced ASK1 activation was accompanied by the increased phosphorylation of p38MAPK, a major downstream signaling molecule of ASK1. In addition, PGN was shown to increase apoptotic protein, Bax, expression in HUVECs. Inhibitor of p38MAPK signaling abrogated the PGN-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 PGN-induced cell apoptosis.
Key words: sepsis, vascular leak syndromes, peptidoglycan (PGN), ASK1 (Apoptosis signal regulating kinase 1)