Regulation of endothelial nitric oxide synthase expression by laminar shear stress

The endothelial nitric oxide synthase (eNOS) produces nitric oxide from L-arginine. One of the most physiologically important stimuli of eNOS expression is unidirectional shear stress. Areas of the vasculature exposed to high shear seem protected from the development of atherosclerosis, while areas exposed to low shear are prone to atherosclerotic lesions. It is thought that shear regulation of eNOS may contribute to this phenomenon.; Unidirectional shear stress results in a 4–5-fold increase in eNOS mRNA after 6 hours. We found that increased steady state mRNA is a result of a transient increase in transcription, followed by prolonged message stabilization. We identified two separate pathways controlling transcription and stability. We found that eNOS transcription was controlled by a c-Src-dependent, Ras/Raf/MEK/ERK dependent pathway, whereas mRNA stability was also c-Src-dependent, but Ras/Raf/MEK/ERK independent.; Unidirectional shear stress causes a transient increase in eNOS transcription. Using chimeric eNOS-CAT promoter constructs, we identified a 25 base pair region in the eNOS promoter that is responsive to shear stress. Furthermore, we found that NFκB translocated to the nucleus and bound to this region in response to shear. We confirmed these data using a dominant negative IκB construct, which inhibited eNOS promoter activity in response to shear.; We have shown that c-Src plays a role in shear stress stimulation of eNOS expression in cultured cells. To examine the role of c-Src in vivo, we exercised C57Blk/6 and c-Src heterozygous (c-Src+/−) mice for 3 weeks. Exercise increased eNOS protein >2-fold in the aorta and 1.7-fold in the hearts of C57Blk/6 mice while having no effect on eNOS in c-Src+/− mice. Training also increased aortic ecSOD protein expression, which is regulated by NO•, only in C57Blk/6 mice while having no effect in c-Src+/− mice.; These studies describe the pathway by which unidirectional shear stress increases eNOS expression, and the physiological role of this pathway during exercise training. There are several diseases in which decreased eNOS expression contributes to endothelial dysfunction. Thus, understanding the mechanisms by which shear stress and exercise increase the expression of this beneficial factor may aid in the creation of novel therapeutics targeting vascular disease.