Mitochondrial Redox Systems in Neurogenic Hypertension

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DESCRIPTION (provided by applicant): Dysregulation of brain angiotensin II (AngII) signaling is implicated in the pathogenesis of cardiovascular diseases, including heart failure and hypertension. Increased circulating levels of AngII can lead to the development of neurogenic hypertension by acting on blood-brain-barrier deficient brain regions, known as circumventricular organs (CVOs). Activation of the CVOs can alter central cardiovascular outputs including sympatho-excitation. To better understand the central actions of AngII in the development of neurogenic hypertension and to identify novel therapeutic targets of the disease, it is essential to investigate the intra- neuronal signaling mechanisms of AngII in the brain. Previously, we and others identified reactive oxygen species (ROS), particularly superoxide radicals (O2.-), generated by NADPH oxidase as important signaling intermediates in central neurons stimulated with AngII. However, additional sources of O2.-- including mitochondria, which are the primary sites for O2.- generation in most cells, have yet to be investigated. In addition, a potential link between NADPH oxidase and mitochondria-derived O2.- in the intra-neuronal signaling of AngII remains to be elucidated. Herein, we propose a series of molecular, biochemical, and integrative cardiovascular physiological experiments to test our hypothesis that a mitochondria-localized NADPH oxidase in AngII-sensitive neurons contributes to an increase in mitochondrial O2.-, which in turn mediates AngII-dependent hypertension by acting on redox-sensitive proteins known to control neuronal firing and sympatho-excitation. We will test this hypothesis in three Specific Aims. In Specific Aim 1, we will investigate the role of NADPH oxidase in producing mitochondria-localized O2.- in AngII-stimulated neurons. This aim builds upon our preliminary data showing that AngII increases mitochondrial O2.- in cultured neurons and that a NADPH oxidase catalytic subunit (Nox4) is present in mitochondria of neurons. In Specific Aim 2, we will examine the mechanisms by which mitochondrial-produced O2.- regulates AngII- induced neuronal activation. This aim is supported by our new preliminary data indicating that increased scavenging of mitochondrial O2.- via adenoviral-mediated overexpression of manganese superoxide dismutase (MnSOD), the O2.- scavenging enzyme specifically targeted to mitochondria, attenuates AngII- induced inhibition of neuronal potassium current. Finally, in Specific Aim 3, we will expand our previous observation that MnSOD overexpression in the brain inhibits the acute central AngII-induced pressor response by investigating the role of mitochondrial-produced O2.- in the brain in mediating the chronic sympatho-excitation and the development of hypertension in a mouse model of AngII-dependent neurogenic hypertension. These studies will provide new information on the intra-neuronal signaling mechanisms of AngII, and may identify mitochondrial-localized O2.- in neurons as important therapeutic targets in AngII-dependent neuro-cardiovascular diseases, such as hypertension.