Angiotensin II potentiates zinc-induced cortical neuronal death by acting on angiotensin II type 2 receptor

Mi-Ha Park,Jae-Young Koh,Ha Na Kim,Joon Seo Lim,Jae-Sung Ahn

doi:10.1186/1756-6606-6-50

Mi-Ha Park, Jae-Young Koh + Show 3 more

Open Access

https://doi.org/10.1186/1756-6606-6-50

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Abstract

BackgroundThe angiotensin system has several non-vascular functions in the central nervous system. For instance, inhibition of the brain angiotensin system results in a reduction in neuronal death following acute brain injury such as ischemia and intracerebral hemorrhage, even under conditions of constant blood pressure. Since endogenous zinc has been implicated as a key mediator of ischemic neuronal death, we investigated the possibility that the angiotensin system affects the outcome of zinc-triggered neuronal death in cortical cell cultures.ResultsExposure of cortical cultures containing neurons and astrocytes to 300 μM zinc for 15 min induced submaximal death in both types of cells. Interestingly, addition of angiotensin II significantly enhanced the zinc-triggered neuronal death, while leaving astrocytic cell death relatively unchanged. Both type 1 and 2 angiotensin II receptors (AT1R and AT2R, respectively) were expressed in neurons as well as astrocytes. Zinc neurotoxicity was substantially attenuated by PD123319, a specific inhibitor of AT2R, and augmented by CGP42112, a selective activator of AT2R, indicating a critical role for this receptor subtype in the augmentation of neuronal cell death.Because zinc toxicity occurs largely through oxidative stress, the levels of superoxides in zinc-treated neurons were assessed by DCF fluorescence microscopy. Combined treatment with zinc and angiotensin II substantially increased the levels of superoxides in neurons compared to those induced by zinc alone. This increase in oxidative stress by angiotensin II was completely blocked by the addition of PD123319. Finally, since zinc-induced oxidative stress may be caused by induction and/or activation of NADPH oxidase, the activation status of Rac and the level of the NADPH oxidase subunit p67phox were measured. Angiotensin II markedly increased Rac activity and the levels of p67phox in zinc-treated neurons and astrocytes in a PD123319-dependent manner.ConclusionThe present study shows that the angiotensin system, especially that involving AT2R, may have an oxidative injury-potentiating effect via augmentation of the activity of NADPH oxidase. Hence, blockade of angiotensin signaling cascades in the brain may prove useful in protecting against the oxidative neuronal death that is likely to occur in acute brain injury.

Highlights

The angiotensin system has several non-vascular functions in the central nervous system
Addition of angiotensin II (0.5–50 μM) significantly enhanced zincinduced cell death in a concentration-dependent manner (Figure 1B). This potentiating effect was specific for zinc, since addition of 1 μM angiotensin II did not alter the submaximal calcium-overload excitotoxicity induced by 24-h exposure to 60 μM glutamate, 20 μM NMDA, or 200 nM ionomycin (Figure 1C)
Since zinc can injure both neurons and astrocytes, we examined whether the potentiation of zinc-induced cortical cell death by angiotensin II exhibited specificity toward neurons

Summary

Introduction

The angiotensin system has several non-vascular functions in the central nervous system. Inhibition of the brain angiotensin system results in a reduction in neuronal death following acute brain injury such as ischemia and intracerebral hemorrhage, even under conditions of constant blood pressure. Calcium overload induced by glutamate was considered a common mechanism for neuronal death in a wide variety of neurological conditions [4]. Recent evidence indicates that multiple mechanisms, including glutamate toxicity, oxidative stress and apoptosis, may act in concert to cause neuronal death in acute brain injury. Glutamate neurotoxicity induces calcium overload [6], which activates oxidative stress [7]. Reperfusion injury enhances the production of reactive oxygen species (ROS) [8,9] In both cases, the resulting increase in oxidative stress causes further glutamate release [10] and excitotoxicity. Calcium-induced apoptosis, inflammation, and autophagy contribute to neuronal death under certain circumstances [3,11]

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