Redox Signaling via Oxidative Inactivation of PTEN Modulates Pressure-Dependent Myogenic Tone in Rat Middle Cerebral Arteries

Abstract

The present study examined the level of generation of reactive oxygen species (ROS) and roles of inactivation of the phosphatase PTEN and the PI3K/Akt signaling pathway in response to an increase in intramural pressure-induced myogenic cerebral arterial constriction. Step increases in intraluminal pressure of cannulated cerebral arteries induced myogenic constriction and concomitant formation of superoxide (O2 .−) and its dismutation product hydrogen peroxide (H2O2) as determined by fluorescent HPLC analysis, microscopic analysis of intensity of dihydroethidium fluorescence and attenuation of pressure-induced myogenic constriction by pretreatment with the ROS scavenger 4,hydroxyl-2,2,6,6-tetramethylpiperidine1-oxyl (tempol) or Mito-tempol or MitoQ in the presence or absence of PEG-catalase. An increase in intraluminal pressure induced oxidation of PTEN and activation of Akt. Pharmacological inhibition of endogenous PTEN activity potentiated pressure-dependent myogenic constriction and caused a reduction in NPo of a 238 pS arterial KCa channel current and an increase in [Ca2+]i level in freshly isolated cerebral arterial muscle cells (CAMCs), responses that were attenuated by Inhibition of the PI3K/Akt pathway. These findings demonstrate an increase in intraluminal pressure induced increase in ROS production triggered redox-sensitive signaling mechanism emanating from the cross-talk between oxidative inactivation of PTEN and activation of the PI3K/Akt signaling pathway that involves in the regulation of pressure-dependent myogenic cerebral arterial constriction.

Modulation of the myogenic mechanism: concordant effects of NO synthesis inhibition and O2− dismutation on renal autoregulation in the time and frequency domains

“…Similar observations have been made on the cerebral circulation. Increased luminal pressure in rat middle cerebral arteries increased O 2 Ϫ and H 2 O 2 generation that resulted in augmentation of myogenic constriction (26). The potentiation was inhibited by tempol in the presence or absence of polyethylene glycol catalase (26), indicating a primary action of O 2 Ϫ rather than H 2 O 2 .…”

“…Increased luminal pressure in rat middle cerebral arteries increased O 2 Ϫ and H 2 O 2 generation that resulted in augmentation of myogenic constriction (26). The potentiation was inhibited by tempol in the presence or absence of polyethylene glycol catalase (26), indicating a primary action of O 2 Ϫ rather than H 2 O 2 . Moreover, H 2 O 2 commonly acts as vasodilator in circulatory beds, such as cerebral, coronary, mesenteric, and skeletal muscle, and may function as an endotheliumdependent hyperpolarization factor and an activator of potassium channels (10,14,47,55,64,70); both dilator and hyperpolarizing actions are expected to blunt rather than potentiate pressure-induced myogenic constriction.…”

“…However, we believe that the renal hemodynamic actions of tempol are primarily due to dismutation of O 2 Ϫ and the removal of its vasoconstrictor influence rather than increased H 2 O 2 levels. This conclusion is based on the published work of other investigators showing that the potentiating action of O 2 Ϫ on myogenic vasoconstriction in arteries and arterioles during increased intraluminal pressure is inhibited by tempol, but not by catalase (26,50). Also, the enhanced myogenic response of afferent arterioles of SHR is normalized by the O 2 Ϫ scavenger tempol or by the Nox2 inhibitor gp91ds, findings that led to the conclusion that Nox2-derived O 2 Ϫ may contribute to the enhanced myogenic response (76).…”

“…Increased luminal pressure rapidly increased NA-DPH oxidase production of ROS in isolated mouse tail arterioles (66), hamster gracilis muscle arteries (44), carotid arteries (84), cerebral arteries (26), and mouse afferent arterioles (50,53). This was associated with enhanced myogenic vasoconstriction, perhaps by promoting Ca 2ϩ entry or sensitivity of the VSMC contractile apparatus (26,66 (49,53) and in the steady-state myogenic response to increased intraluminal pressure (49,50,53). O 2 Ϫ is thought to enhance in vitro renal myogenic contraction largely independent of NO (50), although its actions in modulating MD-TGF appear to be either by limiting bioavailability of NO (54,93) or a direct action on the afferent arteriole (54).…”

Extravascular Blood Augments Myogenic Constriction of Cerebral Arterioles: Implications for Hemorrhage‐Induced Vasospasm

“…To this end, we hypothesized that short‐term exposure of isolated cerebral arterioles to extravascular hemolyzed blood (EHB) or extravascular erythrocyte lysate (EEL) augments the myogenic constrictor response of cerebral arterioles at a given intraluminal pressure. In addition, we addressed the potential involvement of reactive oxygen species (ROS) in EHB/EEL‐induced enhanced myogenic constriction, inspired by previous findings showing that augmentation of myogenic response was mediated by ROS in various pathologic conditions 5. To test our hypothesis, mouse cerebral arterioles branching off from the middle cerebral artery (MCA arterioles) were isolated and cannulated.…”