Native low density lipoproteins (n-LDL) and oxidized low density lipoproteins (Ox-LDL) play a central role in atherogenesis and possess a wide variety of biological properties. We investigated whether n-LDL or Ox-LDL modulate cyclooxygenase-1 and -2 (Cox-1 and Cox-2) expression and prostaglandins release in human endothelial cells via an MAPK-dependent pathway. HUVECs were incubated in the presence of n-LDL or Ox-LDL (30 µg/ml for both) for 2-15 h. Real-time PCR, western blotting and immunocytochemistry were used to investigate Cox-1 and Cox-2 expression. N-LDL and Ox-LDL induced Cox-2 expression in a time- and dose-dependent manner. The Cox-2 protein was strongly induced 2 h after exposure to n-LDL or Ox-LDL, the induction was maximal after 4 h and sustained for at least 8 h. The effect was specific for Cox-2, as Cox-1 expression was not modulated either by n-LDL or by Ox-LDL. The induction of Cox-2 expression was mainly dependent on the activation of p38 MAPK. Transient transfection analysis using a Cox-2 promoter showed that n-LDL and Ox-LDL exert their effects at the transcriptional level via NF-κB and CREB activation. N-LDL and Ox-LDL increased PGE2 release in a Cox-2-dependent manner while TXA2 and PGI2 release were not affected either by n-LDL or Ox-LDL. The finding that n-LDL and Ox-LDL induces Cox-2 in human endothelial cells through a p38 MAPK, NF-κB, CREB dependent pathway thus modulating PGE2 release, suggests a new mechanism by which these lipoproteins induce endothelial dysfunction, sustaining inflammatory processes in the arterial wall.

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