Redox Signaling of the Arteriolar Myogenic Response

Abstract

Arteriolar vascular smooth muscle cells (VSMCs) are mechanosensitive, constricting to elevations in transmural pressure (P TM ). The goal of the present study was to determine using mouse isolated tail arterioles and arteries whether oxidant signaling regulates this myogenic response. In response to P TM elevation, VSMCs of arterioles but not arteries generated constriction and increased reactive oxygen species (ROS) activity (using the H 2 O 2 -sensitive probe dichlorodihydrofluorescein). Arterioles had increased expression of NADPH oxidase components compared with arteries. Inhibition of NADPH oxidase, using mice with targeted impairment of enzyme components (p47 phox or rac1) or diphenyleneiodonium, prevented the pressure-induced generation of ROS. When ROS activity was inhibited, either by inhibiting NADPH oxidase or with N-acetylcysteine, the myogenic constriction was abolished. The myogenic constriction was also inhibited by catalase, which inactivates H 2 O 2 , but was unaffected by a cell-permeant mimic of superoxide dismutase (MnTMPyP). ␣ 1 -Adrenergic constriction was not associated with altered ROS activity and was not affected by inhibition of NADPH oxidase or ROS. Exogenous H 2 O 2 constricted VSMCs of arterioles but not arteries. Thus, NADPH oxidase and ROS, in particular H 2 O 2 , contribute to the myogenic response of arteriolar VSMCs. V ascular smooth muscle cells (VSMCs) of arterioles, but not arteries, are mechanosensitive, constricting to elevations in transmural pressure (P TM ). This myogenic response contributes to blood flow autoregulation and the establishment of basal vascular tone. 1 The response is an inherent property of arteriolar VSMCs involving calcium-dependent actin/myosin interaction, but the more proximal signaling components have not been clearly defined. 1 In cultured cells, mechanical stress initiates integrin-dependent activation of rho GTPases (rho, rac1, and CDC42), leading to reorganization of the cytoskeleton. 2,3 Cytoskeleton reorganization by rac1 is mediated by NADPH oxidase and generation of reactive oxygen species (ROS). 4 This enzyme complex, comprising Nox1, p47 phox , p67 phox , p22 phox , and rac1, is a key signaling system in cultured, noncontractile VSMCs. 5,6 The aim of the present study was to determine whether the rac1/NADPH oxidase/ROS signaling pathway regulates the myogenic response of arteriolar VSMCs. Materials and Methods Vasomotor ResponsesMouse-tail arterioles and arteries were cannulated in a microperfusion chamber (Living Systems) and studied in the absence of flow as described. 7 Unless stated otherwise, arterioles with intact endothelium were analyzed. Involvement of animals in the study was approved by the Ohio State University Animal Care and Use Committee. ROS DeterminationEndothelium-denuded vessels 7 were incubated with the H 2 O 2 -sensitive probe 5-(and 6)-chloromethyl-2Ј,7Ј-dichlorodihydro-fluorescein diacetate (DCF), 5 g/mL, for 30 minutes (37°C, P TM of 10 mm Hg). Because activation of DCF fluorescence is irreversible, fluorescent im...

Control and Coordination of Vasomotor Tone in the Microcirculation

“…In any case, the involvement of Cx43-based channels in the control of vasomotor tone is consistent with the finding that tensile stretch increased the expression of this connexin as well as gap junction intercellular communication in vascular smooth muscle cells (Cowan et al, 1998). Interestingly, this response was mediated by the formation of reactive oxygen species (Cowan et al, 1998;Cowan et al, 2003), which has been reported to contribute to the initiation of the myogenic constriction in mouse-tail arterioles (Nowicki et al, 2001). …”

Regulation of Bone Morphogenetic Protein-2 Expression in Endothelial Cells

“…The data presented in Figure 2 indicated that H 2 O 2 production is an important mediator of NF-〉 activation in endothelial cells. Importantly, we found that high pressure can elicit significant increases in vascular H 2 O 2 generation, 34 likely by activation of NAD(P)H oxidase ( Figure 4F). 15 The view that high pressureinduced NAD(P)H oxidase may initiate NF-〉 activation in endothelial cells even in the absence of proinflammatory cytokines is supported by the finding that high pressure-induced activation of NF-〉 was decreased significantly by DPI ( Figure 4G).…”

l -Arginine Reverses p47phox and gp91phox Expression Induced by High Salt in Dahl Rats

“…Rac1, which belongs to the small GTPase protein superfamily, participates in the regulation of NADPH oxidase in numerous cell types. 44 We were surprised to find that L-arginine decreases Rac1 at the levels of mRNA as well as protein in renal cortex of DS rats ( Figures 4D and 5C). Taken together, these actions of L-arginine, which appear to interfere with translocation of p47phox to the membrane fraction and to downregulate total expression levels of gp91phox as well as Rac1, may contribute to decrease overall enzyme activity of renal NADPH oxidase in high salt-loaded animals.…”