Role of arginase pathway in response to shear stress: new potential therapeutic targets for atherosclerosis?

Introduction: Alterations of wall shear stress can predispose the endothelium to the development of atherosclerotic plaques. Ample evidence indicates that arginase expression and/or activity correlates with several risk factors for cardiovascular disease including atherosclerosis. However, the role of arginase pathway in response to shear stress has never been investigated. Methods: To evaluate the regulation of arginases by different shear stress patterns without neuroendocrine factors, we perfused carotid arterial segments to the following hemodynamic conditions: unidirectional high and low shear stress, and oscillatory shear stress. After 3 days of flow exposure, vascular function was analyzed by diameter measurements, arginase expression and localization by western blot and immunohistochemistry, respectively. We compared these well-controlled measurements to an in vivo model of shear stress-induced atherogenesis. In brief, the carotid artery of ApoE-/- mice, fed with high cholesterol diet, was exposed to high, low and oscillatory shear stress values by the placement of a shear stress modifier for 9 weeks. Immunohistochemistry was used to determine the expression of arginase I and II and to characterize the arginase expression in different cell types encountered in atherosclerotic plaques. Results: Our preliminary results from ex vivo perfusion arteries showed for the first time that exposure of carotid segments to high shear stress conditions (athero-protective) significantly decrease arginase II protein expression as compared to both low and oscillatory flow conditions. Immunohistochemisty analysis confirmed a pronounced decrease in the expression of arginase II on ECs and SMCs exposed to this high shear stress. Our preliminary data suggest that arginase I and II are also regulated by shear stress in vivo. Arginases were up-regulated on EC, SMC and macrophages of carotid segments exposed either to low stress or to oscillatory shear stress conditions. Conclusions: The present study demonstrates that arginase expression is already modulated by 3 days exposure to different shear stress patterns in carotid arteries perfused ex vivo. Similar findings are also observed in a model of shear stress-induced atherogenesis in vivo. Histopathological analysis of carotid lesions in ApoE-/- mice exposed to shear stress and chronically treated with arginase inhibitors may further elucidate the role of arginases in modulating both plaque size and vulnerability

Modulation of arginase pathway by hemodynamic forces

Fabienne Riche

It is well recognized that alterations on wall shear stress plays an important role on the development of atherosclerosis disease. It is known that oscillatory shear stress (OSS) flow pattern induces endothelial dysfunction via changes on nitric oxide (NO) pathway. NO is a potent vasodilator molecule and its availability can be evaluated by vasoreactivity organ chamber experiment. Arginase is an enzyme which is implicated in the signaling pathway of NO as it competes with endothelium nitric oxide synthase (eNOS) for the use of arginine. Increase in arginase expression and activity has been associated atherosclerosis, however the modulation of arginase by wall shear stress has never been studied before. This project consists of experimental work to better understand the implication of shear stress, NO and arginase expression in endothelial dysfunction of arteries. By using western blot and immunohistochemistry techniques we investigated the expression and localization of arginase in pig carotid arteries (PCA) perfused in an ex vivo arterial support system. While arginase I isoform was not present in PCA, arginase II was constitutively expressed. Its expression was augmented by exposure to high shear stress (HSS) flow and dependent of flow duration. OSS flow significantly increases the expression of arginase as compared to HSS. Inhibition of arginase in PCA perfused under OSS was not able to improve endothelial function neither NO availability. In a second part we characterize the geometry of rabbit carotid bifurcation and investigate if the receptor-mediated endothelial function and NO availability varies in this bifurcation. In the presence of NOS inhibitor, the contraction of the arteries in response to norepinephirne was higher. This difference is significant for segments which have the better endothelial dependant relaxation: the external carotid and the middle part of the common carotid.

2008

Oscillatory shear stress and reduced compliance impair vascular functions

Rafaela Fernandes Da Silva, Veronica Gambillara, Paolo Silacci, Nikolaos Stergiopulos, Tyler Nerton Thacher

Shear stress has been shown to influence endothelial cell gene expression and morphology. In particular, low and bi-directional shear stress, mimicking conditions at plaque-prone areas, down-regulates the expression of several atheroprotective genes, and up-regulates that of other genes considered as pro-inflammatory. Another mechanical situation thought to have a negative influence on vascular functions is arterial stiffness. Loss of arterial compliance occurs during ageing, in diabetic as well as in hypertensive patients. In this work we investigated the effects of these two particular hemodynamic environments (bi-directional shear stress and reduced compliance), using a recently developed perfusion system allowing to expose native arteries in vitro to complex hemodynamic environments. We were able to show that both plaque-prone shear stress and reduced compliance trigger endothelial dysfunction, but via different mechanisms. Only reduced compliance affected vascular contractility, inducing a dedifferentiation of smooth muscle cells and a consequent loss of norepinephrine sensitivity.

2007