Constitutive nitric oxide synthase protein and mrna levels are
elevated in cultured human and bovine endothelial cells exposed to
fluid shear stress.
Ranjan, Vibhu, Zeshuai Xiao, Scott L. Diamond.
Bioengineering Laboratory, Department of Chemical Engineering, The
State University of New York, Buffalo, NY 14260, Tel (716) 645-2911
ext. 2205, Fax (716) 645-3822
APStracts 2:0064H, 1995.
Flow induced activation of nitric oxide synthase (NOS) in endothelial
cells causes vasodilation due to a burst in NO production,
particularly when prevailing flows change acutely. The role of
chronic fluid shear stress exposures on endothelial constitutive
nitric oxide synthase (cNOS) levels may also have an important role
in vessel diameter control. To test the role of sustained flow
exposures, we subjected primary human umbilical vein endothelial
cells (HUVEC) or bovine aortic endothelial cells (BAEC, passage 2-14)
to steady laminar shear stress using a parallel-plate flow apparatus.
In both endothelial cell types, the intracellular level of cNOS was
elevated within 3 hr of flow exposure at 25 dynes/cm2 and remained
elevated at 6 and 12 hours of flow exposure, compared to stationary
controls, as indicated by digital immunofluorescence microscopy.
Shear stress exposure for 6 hr caused a 2.2 +/- 0.3 and 2.8 +/- 0.3
-fold elevation of cNOS proteins levels in BAEC (n = 3, p<0.01) and
HUVEC (n = 3, p<0.01), respectively, in the presence or absence of
1 [mu]M dexamethasone. Dexamethasone suppresses induction of the
inducible NOS gene, indicating that constitutive NOS was elevated by
fluid shear stress. Flow exposure at 4 dynes/cm2 caused no
enhancement of cNOS levels in either cell type. The flow induction of
the cNOS protein levels was not blocked by preincubation of BAEC with
100 to 400 [mu]M of NG-nitro-L-arginine methyl ester, indicating that
a positive feedback loop for flow induced NO (or cGMP) was not
involved in the elevation of cNOS levels. Also the protein kinase C
inhibitor, H7 (10 [mu]M) had no effect on induction of NOS protein in
BAEC exposed to 25 dynes/cm2. The cNOS mRNA levels were found to be
elevated by 2 to 3-fold in BAEC after 6 or 12 hours of flow exposure
at either 4 or 25 dynes/cm2, and this induction of NOS mRNA occurred
in the presence of dexamethasone. The rapid and sustained elevation
of endothelial NOS levels by chronic flow exposure in coordination
with the sustained suppression of endothelin-1 gene expression by
arterial levels of shear stress may provide a mechanism at the level
of gene expression for chronic regulation of vessel diameter by
endothelial response to prevailing blood flow.
Received 18 November 1994; accepted in final form 15 February
1995.
APS Manuscript Number H1031-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 March 1995.