Decreased Flow-Dependent Dilation in Carotid Arteries of Tissue Kallikrein–Knockout Mice

Abstract

Flow-dependent dilation is a fundamental mechanism by which large arteries ensure appropriate blood supply to tissues. We investigated whether or not the vascular kallikrein-kinin system, especially tissue kallikrein (TK), contributes to flow-dependent dilation by comparing wild-type and TK-knockout mice in which the presence or absence of TK expression was verified. We examined in vitro changes in the outer diameter of perfused carotid arteries from TK / and TK / mice. In both groups, exogenous bradykinin caused a similar dilation that was abolished by the B 2 receptor antagonist HOE-140, as well as by the NO synthase inhibitor N-nitro-L-arginine methyl ester. However, purified kininogen dilated only TK / arteries, demonstrating the essential role of TK in the vascular formation of kinins. In TK / arteries, increasing intraluminal flow caused a larger endothelium-dependent dilation than that seen in TK /. In both strains the flow response was mediated by NO and by endothelium-derived hyperpolarizing factor, whereas in TK / vasoconstrictor prostanoids participated as well. HOE-140 impaired flow-dependent dilation in TK / arteries while showing no effect in TK /. This compound reduced the flow response in TK / arteries to a level similar to that in TK /. After NO synthase inhibition, HOE-140 no longer affected the response of TK /. Impaired flow-dependent dilation was also observed in arteries from knockout mice lacking bradykinin B 2 receptors as compared with wild-type animals. This study demonstrates the active contribution of the vascular kallikrein-kinin system to one-third of the flow-dependent dilation response via activation of B 2 receptors coupled to endothelial NO release. (Circ Res. 2001;88: 593-599.) Key Words: bradykinin kininogen flow-dependent vasodilation endothelium bradykinin B 2 receptor L arge arteries accommodate changes in blood flow by increasing their diameter via the release of endothelial factors such as NO, prostacyclin, and endothelium-derived hyperpolarizing factor (EDHF). 1-4 This flow-dependent dila-tion (FDD) response represents a fundamental physiological mechanism that acts to oppose vasoconstriction, normalize shear stress, and ensure appropriate blood supply to tissues. Bradykinin modulates vascular smooth muscle tone by stimulating endothelial B 2 receptors and releasing NO and other mediators. 5-7 Bradykinin is a product of the cleavage of high and low molecular weight kininogens resulting from activation of proteases such as plasma and tissue kallikreins (TKs), cathepsins, or calpains. 8-12 The presence in the vessel wall of kininogens and kallikrein-like activities, including TK, suggests the existence of an endogenous vascular kinin-generating system, different from the circulating plasma kallikrein-kinin system. 13-16 However, the physiological role of the vascular kallikrein-kinin system itself has not been fully established because of the possible contribution of preadsorbed plasma kallikrein to vascular kinin formation and the lack of specific inhibitors of TK. 17-19 ...

G protein-coupled receptors sense fluid shear stress in endothelial cells

“…The involvement of B 2 receptor in a flow-dependent response was demonstrated earlier by a number of studies reviewed elsewhere (17,18,41); impaired flow-dependent response was observed in arteries from knockout mice lacking B 2 receptors (17). Because the flow-dependent dilation is a fundamental mechanism by which large arteries ensure adequate supply of blood to the tissues (42,43), our observation that the B 2 receptor can respond to mechanical perturbation of cell membrane without involvement of ligand suggests a molecular mechanism by which fluid shear stress can be sensed.…”

“…Note that an IC 50 that is at least 100-1,000 times lower for ligand-induced response of B2K chameleon (compared with native B 2 receptor, see dose-response of FRET ratio in Fig. 5) makes it rather unlikely that this conformational change is caused by an autocrine pathway (17). Endothelial cells are known to secrete tissue kallikreinin, which remains at the cell membrane and regulates conversion of kininogen into lys-bradykinin, which is equally potent as bradykinin.…”

“…To test the hypothesis that mechanical forces initiate mechanochemical signal transduction by increasing membrane tension and altering physical properties of the cell membrane, we have chosen to study human B 2 bradykinin GPCR, which is known to be involved in a fluid flow-dependent response in endothelial cells (16)(17)(18). Here, we demonstrate that the B 2 receptor changes conformation when stimulated by fluid shear stress, hypotonic shock, and benzyl alcohol in the absence of any ligand.…”

Novel Vascular Biology of Third-Generation L-Type Calcium Channel Antagonists

“…48 This transduction mechanism, from local kinin production to the B 2 -kinin receptor to NO production, was thought to be novel but has recently been implicated as the mechanism of flow-mediated dilation in the rat carotid artery. 59 In that study, flow-mediated dilation was reduced in the carotid artery from tissue kallikreinϪ/Ϫ and B 2 -kininϪ/Ϫ mice, indicating an important role for local kinin formation. Moreover, in the tissue kallikreinϩ/ϩ carotid artery, flowmediated dilation was blocked by an NOS inhibitor and HOE-140.…”

High Blood Pressure Reduction Reverses Angiotensin II Type 2 Receptor–Mediated Vasoconstriction Into Vasodilation in Spontaneously Hypertensive Rats

“…6,7,11,16,17,20,22 This vasodilation may play an important role in the regulation of arterial blood pressure by increasing the diameter of resistance arteries. Vasodilation induced by AT 2 R stimulation has been described in several vascular territories and is usually associated with NO production by endothelial cells and cGMP production by smooth muscle cells.…”