Role of endothelial nitric oxide synthase in endothelial activation: insights from eNOS knockout endothelial cells

1 Department of Medicine, University of Würzburg, D97080 Würzburg, Germany; 2 Cardiovascular Research Center, Division of Cardiology, Massachusetts General Hospital, 3 Department of Pathology, Massachusetts General Hospital and Harvard Medical School, and 4 Vascular Research Division, Brigham and Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115; and 5 Department of Pharmacology and Molecular Cardiobiology Program, Yale University School of Medicine, New Haven, Connecticut 06536 Submitted 25 November 2002 ; accepted in final form 13 January 2004 The objective of this study was to determine whether absence of endothelial nitric oxide synthase (eNOS) affects the expression of cell surface adhesion molecules in endothelial cells. Murine lung endothelial cells (MLECs) were prepared by immunomagnetic bead selection from wild-type and eNOS knockout mice. Wild-type cells expressed eNOS, but eNOS knockout cells did not. Expression of neuronal NOS and inducible NOS was not detectable in cells of either genotype. Upon stimulation, confluent wild-type MLECs produced significant amounts of NO compared with N -monomethyl- L -arginine-treated wild-type cells. eNOS knockout and wild-type cells showed no difference in the expression of E-selectin, P-selectin, intracellular adhesion molecule-1, and vascular cell adhesion molecule-1 as measured by flow cytometry on the surface of platelet endothelial cell adhesion molecule-1 (PECAM-1/CD31)-positive cells. Both eNOS knockout and wild-type cells displayed the characteristics of resting endothelium. Adhesion studies in a parallel plate laminar flow chamber showed no difference in leukocyte-endothelial cell interactions between the two genotypes. Cytokine treatment induced endothelial cell adhesion molecule expression and increased leukocyte-endothelial cell interactions in both genotypes. We conclude that in resting murine endothelial cells, absence of endothelial production of NO by itself does not initiate endothelial cell activation or promote leukocyte-endothelial cell interactions. We propose that eNOS derived NO does not chronically suppress endothelial cell activation in an autocrine fashion but serves to counterbalance signals that mediate activation. vascular biology; atherosclerosis; mouse models Address for reprint requests and other correspondence: P. L. Huang, Cardiovascular Research Center, Massachusetts General Hospital-East, 149 East 13th St., Charlestown, MA 02129 (E-mail: huangp{at}heli