Lysophosphatidylcholine in phospholipase A-modified LDL triggers secretion of angiopoietin 2.

BACKGROUND AND AIMS

Secretory phospholipase A (PLA) hydrolyzes LDL phospholipids generating modified LDL particles (PLA-LDL) with increased atherogenic properties. Exocytosis of Weibel-Palade bodies (WPB) releases angiopoietin 2 (Ang2) and externalizes P-selectin, which both play important roles in vascular inflammation. Here, we investigated the effects of PLA-LDL on exocytosis of WPBs.

METHODS

Human coronary artery endothelial cells (HCAECs) were stimulated with PLA- LDL, and its uptake and effect on Ang2 release, leukocyte adhesion, and intracellular calcium levels were measured. The effects of PLA-LDL on Ang2 release and WPB exocytosis were measured in and ex vivo in mice.

RESULTS

Exposure of HCAECs to PLA-LDL triggered Ang2 secretion and promoted leukocyte-HCAEC interaction. Lysophosphatidylcholine was identified as a critical component of PLA-LDL regulating the WPB exocytosis, which was mediated by cell-surface proteoglycans, phospholipase C, intracellular calcium, and cytoskeletal remodeling. PLA-LDL also induced murine endothelial WPB exocytosis in blood vessels in and ex vivo, as evidenced by secretion of Ang2 in vivo, P-selectin translocation to plasma membrane in intact endothelial cells in thoracic artery and tracheal vessels, and reduced Ang2 staining in tracheal endothelial cells. Finally, in contrast to normal human coronary arteries, in which Ang2 was present only in the endothelial layer, at sites of advanced atherosclerotic lesions, Ang2 was detected also in the intima, media, and adventitia.

CONCLUSIONS

Our studies reveal PLA-LDL as a potent agonist of endothelial WPB exocytosis, resulting in increased secretion of Ang2 and translocation of P-selectin. The results provide mechanistic insight into PLA-LDL-dependent promotion of vascular inflammation and atherosclerosis.