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In the present study, we investigated whether low shear (LS, 2 dyn/cm2) favors high glucose (HG, 30 mM) induced nuclear factor kappa B (NF-kappaB) activity by regulating NO release in human aortic endothelial cells (HAEC). The results show that (i) under LS, the NF-kappaB activity of HAEC exposed to HG was significantly higher than HAEC in normal glucose (NG, 5.5mM) (P < 0.05). In contrast, under HS, the activation of NF-kappaB in HAEC exposed to HG showed no significant difference compared to that of NG. (ii) The NF-kappaB activity induced by HG is suppressed by high shear (HS) in the absence of a NO synthase inhibitor, Nomega-nitro-L-arginine methyl ester (L-NAME) but restored in its presence, while LS + HG induced NF-kappaB activity remains the same in the presence or absence of L-NAME. (iii) Endothelial nitric oxide synthase (eNOS) protein expression and quantitative detection of NO indicated that high shear stress significantly induced higher eNOS expression and NO production compared to low shear stress condition. Collectively, these data suggest that HS exerts a protective effect on HG induced NF-kappaB activity through NO mediated signaling. LS, on the other hand, may down-regulate eNOS expression resulting in reduced NO release, and thereby maintain high glucose induced NF-kappaB DNA-binding activity. These observations explain, in part, the mechanism by means of which hyperglycemia accelerates the focal development of atherosclerotic lesions in low shear (lesion prone) areas of the arterial tree., (Copyright 2003 Elsevier Ireland Ltd.)

Shear stress stimulates NO production involving the Ca2+-independent mechanisms in endothelial cells. We have shown that exposure of bovine aortic endothelial cells (BAEC) to shear stress stimulates phosphorylation of eNOS at S635 and S1179 by the protein kinase A- (PKA-) dependent mechanisms. We examined whether phosphorylation of S635 of eNOS induced by PKA stimulates NO production in a calcium-independent manner. Expression of a constitutively active catalytic subunit of PKA (Cqr) in BAEC induced phosphorylation of S635 and S1179 residues and dephosphorylation of T497. Additionally, Cqr expression stimulated NO production, which could not be prevented by treating cells with the intracellular calcium chelator BAPTA-AM. To determine the role of each eNOS phosphorylation site in NO production, HEK-293 cells transfected with eNOS point mutants whereby S116, T497, S635, and S1179 were mutated to either A or D. Maximum NO production from S635D-expressing cells was significantly higher than that of either wild type or S635A in both basal and elevated [Ca2+]i conditions. More interestingly, S635D cells produced NO even when [Ca2+]i was nearly depleted by BAPTA-AM. We confirmed these results obtained in HEK-293 cells in BAEC transfected with S635D, S635A, or wild-type eNOS vector. These findings suggest that, once phosphorylated at S635 residue, eNOS produces NO without requiring any changes in [Ca2+]i. PKA-dependent phosphorylation of eNOS S635 and subsequent basal NO production in a Ca2+-independent manner may play an important role in regulating vascular biology and pathophysiology.

We have investigated the role of inhibitor kappaBalpha (IkappaBalpha) in the activation of nuclear factor kappaB (NF-kappaB) observed in human aortic endothelial cells (HAEC) undergoing a low shear stress of 2 dynes/cm(2). Low shear for 6 h resulted in a reduction of IkappaBalpha levels, an activation of NF-kappaB, and an increase in kappaB-dependent vascular cell adhesion molecule 1 (VCAM-1) mRNA expression and endothelial-monocyte adhesion. Overexpression of IkappaBalpha in HAEC attenuated all of these shear-induced responses. These results suggest that downregulation of IkappaBalpha is the major factor in the low shear-induced activation of NF-kappaB in HAEC. We then investigated the role of nitric oxide (NO) in the regulation of IkappaBalpha/NF-kappaB. Overexpression of endothelial nitric oxide synthase (eNOS) inhibited NF-kappaB activation in HAEC exposed to 6 h of low shear stress. Addition of the structurally unrelated NO donors S-nitrosoglutathione (300 microM) or sodium nitroprusside (1 mM) before low shear stress significantly increased cytoplasmic IkappaBalpha and concomitantly reduced NF-kappaB binding activity and kappaB-dependent VCAM-1 promoter activity. Together, these data suggest that NO may play a major role in the regulation of IkappaBalpha levels in HAEC and that the application of low shear flow increases NF-kappaB activity by attenuating NO generation and thus IkappaBalpha levels.