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      Within the Brain: The Renin Angiotensin System

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          Abstract

          For many years, modulators of the renin angiotensin system (RAS) have been trusted by clinicians for the control of essential hypertension. It was recently demonstrated that these modulators have other pleiotropic properties independent of their hypotensive effects, such as enhancement of cognition. Within the brain, different components of the RAS have been extensively studied in the context of neuroprotection and cognition. Interestingly, a crosstalk between the RAS and other systems such as cholinergic, dopaminergic and adrenergic systems have been demonstrated. In this review, the preclinical and clinical evidence for the impact of RAS modulators on cognitive impairment of multiple etiologies will be discussed. In addition, the expression and function of different receptor subtypes within the RAS such as: Angiotensin II type I receptor (AT1R), Angiotensin II type II receptor (AT2R), Angiotensin IV receptor (AT4R), Mas receptor (MasR), and Mas-related-G protein-coupled receptor (MrgD), on different cell types within the brain will be presented. We aim to direct the attention of the scientific community to the plethora of evidence on the importance of the RAS on cognition and to the different disease conditions in which these agents can be beneficial.

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          Brain Renin-Angiotensin System and Microglial Polarization: Implications for Aging and Neurodegeneration

          Jose Labandeira-Garcia, Ana I. Rodriguez-Perez, Pablo Garrido-Gil … (2017)
          Microglia can transform into proinflammatory/classically activated (M1) or anti-inflammatory/alternatively activated (M2) phenotypes following environmental signals related to physiological conditions or brain lesions. An adequate transition from the M1 (proinflammatory) to M2 (immunoregulatory) phenotype is necessary to counteract brain damage. Several factors involved in microglial polarization have already been identified. However, the effects of the brain renin-angiotensin system (RAS) on microglial polarization are less known. It is well known that there is a “classical” circulating RAS; however, a second RAS (local or tissue RAS) has been observed in many tissues, including brain. The locally formed angiotensin is involved in local pathological changes of these tissues and modulates immune cells, which are equipped with all the components of the RAS. There are also recent data showing that brain RAS plays a major role in microglial polarization. Level of microglial NADPH-oxidase (Nox) activation is a major regulator of the shift between M1/proinflammatory and M2/immunoregulatory microglial phenotypes so that Nox activation promotes the proinflammatory and inhibits the immunoregulatory phenotype. Angiotensin II (Ang II), via its type 1 receptor (AT1), is a major activator of the NADPH-oxidase complex, leading to pro-oxidative and pro-inflammatory effects. However, these effects are counteracted by a RAS opposite arm constituted by Angiotensin II/AT2 receptor signaling and Angiotensin 1–7/Mas receptor (MasR) signaling. In addition, activation of prorenin-renin receptors may contribute to activation of the proinflammatory phenotype. Aged brains showed upregulation of AT1 and downregulation of AT2 receptor expression, which may contribute to a pro-oxidative pro-inflammatory state and the increase in neuron vulnerability. Several recent studies have shown interactions between the brain RAS and different factors involved in microglial polarization, such as estrogens, Rho kinase (ROCK), insulin-like growth factor-1 (IGF-1), tumor necrosis factor α (TNF)-α, iron, peroxisome proliferator-activated receptor gamma, and toll-like receptors (TLRs). Metabolic reprogramming has recently been involved in the regulation of the neuroinflammatory response. Interestingly, we have recently observed a mitochondrial RAS, which is altered in aged brains. In conclusion, dysregulation of brain RAS plays a major role in aging-related changes and neurodegeneration by exacerbation of oxidative stress (OS) and neuroinflammation, which may be attenuated by pharmacological manipulation of RAS components.
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            The renin angiotensin system, oxidative stress and mitochondrial function in obesity and insulin resistance.

            Latha Ramalingam, Kalhara Menikdiwela, Monique LeMieux … (2017)
            Obesity is a complex disease characterized by excessive expansion of adipose tissue and is an important risk factor for chronic diseases such as cardiovascular disorders, hypertension and type 2 diabetes. Moreover, obesity is a major contributor to inflammation and oxidative stress, all of which are key underlying causes for diabetes and insulin resistance. Specifically, adipose tissue secretes bioactives molecules such as inflammatory hormone angiotensin II, generated in the Renin Angiotensin System (RAS) from its precursor angiotensinogen. Accumulated evidence suggests that RAS may serve as a strong link between obesity and insulin resistance. Dysregulation of RAS also occurs in several other tissues including those involved in regulation of glucose and whole body homeostasis as well as insulin sensitivity such as muscle, liver and pancreas and heart. Here we review the scientific evidence for these interactions and potential roles for oxidative stress, inflammation and mitochondrial dysfunction in these target tissues which may mediate effects of RAS in metabolic diseases. This article is part of a Special Issue entitled: Oxidative Stress and Mitochondrial Quality in Diabetes/Obesity and Critical Illness Spectrum of Diseases - edited by P. Hemachandra Reddy.
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              Brain renin-angiotensin--a new look at an old system.

              David Wright, Joseph W. Harding (2011)
              The classic renin-angiotensin system (RAS) is described as a circulating hormone system focused on cardiovascular and body water regulation, with angiotensin II as its major effector. Detlef Ganten's discovery some years ago of an independent local brain RAS composed of the necessary functional components (angiotensinogen, peptidases, angiotensins and specific receptor proteins) significantly expanded the possible physiological and pharmacological functions of this system. This review first describes the enzymatic pathways resulting in active angiotensin ligands and their interaction with AT(1), AT(2) and AT(4) receptor proteins. We discuss the characterization and distribution of the AT(1) and AT(2) receptor subtypes and the current controversy over the identity of the AT(4) receptor subtype. Research findings favoring the candidates insulin-regulated aminopeptidase (IRAP) and the type 1 tyrosine kinase receptor c-Met, are presented. Next, we summarize current research efforts directed at the use of angiotensin analogues in the treatment of clinical disorders such as memory dysfunction, cerebral blood flow and cerebroprotection, stress, depression, alcohol consumption, seizure, Alzheimer's and Parkinson's diseases, and diabetes. The use of ACE inhibitors, and AT(1) and/or AT(2) receptor blockers, has shown promise in the treatment of several of these pathologies. The development of blood-brain barrier penetrant AT(4) receptor agonists and antagonists is of major importance regarding the continuing evaluation of the efficacy of new treatment approaches. Copyright © 2011 Elsevier Ltd. All rights reserved.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Int J Mol Sci
                Journal ID (iso-abbrev): Int J Mol Sci
                Journal ID (publisher-id): ijms
                Title: International Journal of Molecular Sciences
                Publisher: MDPI
                ISSN (Electronic): 1422-0067
                Publication date (Electronic): 15 March 2018
                Publication date Collection: March 2018
                Volume: 19
                Issue: 3
                Electronic Location Identifier: 876
                Affiliations
                [1 ]Program in Clinical and Experimental Therapeutics, College of Pharmacy, University of Georgia, Augusta, GA 30912, USA; lajackson1@ 123456augusta.edu (L.J.); weldahshan@ 123456augusta.edu (W.E.); sfagan@ 123456augusta.edu (S.C.F.)
                [2 ]Department of Neurology, Medical College of Georgia, Augusta University, Augusta, GA 30912, USA
                [3 ]Department of Physiology, Medical College of Georgia, Augusta University, Augusta, GA 30912, USA
                [4 ]Charlie Norwood Veterans Affairs Medical Center, Augusta, GA 30904, USA
                Author notes
                [* ]Correspondence: aergul@ 123456augusta.edu ; Tel.: +1-706-721-9103
                Article
                Publisher ID: ijms-19-00876
                DOI: 10.3390/ijms19030876
                PMC ID: 5877737
                PubMed ID: 29543776
                SO-VID: 82edbf9b-483c-45b8-8eb5-cfe2849dafec
                Copyright © © 2018 by the authors.
                License:

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                History
                Date received : 21 February 2018
                Date accepted : 11 March 2018
                Categories
                Subject: Review

                ScienceOpen disciplines: Molecular biology
                Keywords: angiotensin,angiotensin at1 receptor,angiotensin at2 receptor,mas receptor,mas-related-g protein coupled mrgd receptor,inflammation,microglia,vascular cognitive impairment (vci),alzhemiers disease (ad),parkinson’s disease (pd),aging
                Data availability:
                ScienceOpen disciplines: Molecular biology
                Keywords: angiotensin, angiotensin at1 receptor, angiotensin at2 receptor, mas receptor, mas-related-g protein coupled mrgd receptor, inflammation, microglia, vascular cognitive impairment (vci), alzhemiers disease (ad), parkinson’s disease (pd), aging

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