Brain Renin-angiotensin System Research Articles

The role of the brain renin-angiotensin system in Parkinson´s disease.

The renin-angiotensin system (RAS) was classically considered a circulating hormonal system that regulates blood pressure. However, different tissues and organs, including the brain, have a local paracrine RAS. Mutual regulation between the dopaminergic system and RAS has been observed in several tissues. Dysregulation of these interactions leads to renal and cardiovascular diseases, as well as progression of dopaminergic neuron degeneration in a major brain center of dopamine/angiotensin interaction such as the nigrostriatal system. A decrease in the dopaminergic function induces upregulation of the angiotensin type-1 (AT1) receptor activity, leading to recovery of dopamine levels. However, AT1 receptor overactivity in dopaminergic neurons and microglial cells upregulates the cellular NADPH-oxidase-superoxide axis and Ca2+ release, which mediate several key events in oxidative stress, neuroinflammation, and α-synuclein aggregation, involved in Parkinson's disease (PD) pathogenesis. An intraneuronal antioxidative/anti-inflammatory RAS counteracts the effects of the pro-oxidative AT1 receptor overactivity. Consistent with this, an imbalance in RAS activity towards the pro-oxidative/pro-inflammatory AT1 receptor axis has been observed in the substantia nigra and striatum of several animal models of high vulnerability to dopaminergic degeneration. Interestingly, autoantibodies against angiotensin-converting enzyme 2 and AT1 receptors are increased in PD models and PD patients and contribute to blood-brain barrier (BBB) dysregulation and nigrostriatal pro-inflammatory RAS upregulation. Therapeutic strategies addressed to the modulation of brain RAS, by AT1 receptor blockers (ARBs) and/or activation of the antioxidative axis (AT2, Mas receptors), may be neuroprotective for individuals with a high risk of developing PD or in prodromal stages of PD to reduce progression of the disease.

Angiotensin type 1 receptor activation promotes neuronal and glial alpha-synuclein aggregation and transmission

The brain renin-angiotensin system (RAS) has been related to dopaminergic degeneration, and high expression of the angiotensin II (AngII) type 1 receptor (AT1) gene is a marker of the most vulnerable neurons in humans. However, it is unknown whether AngII/AT1 overactivation affects α-synuclein aggregation and transmission. In vitro, AngII/AT1 activation increased α-synuclein aggregation in dopaminergic neurons and microglial cells, which was related to AngII-induced NADPH-oxidase activation and intracellular calcium raising. In mice, AngII/AT1 activation was involved in MPTP-induced increase in α-synuclein expression and aggregation, as they significantly decreased in mice treated with the AT1 blocker telmisartan and AT1 knockout mice. Cell co-cultures (transwells) revealed strong transmission of α-synuclein from dopaminergic neurons to astrocytes and microglia. AngII induced a higher α-synuclein uptake by microglial cells and an increase in the transfer of α-synuclein among astroglial cells. However, AngII did not increase the release of α-synuclein by neurons. The results further support brain RAS dysregulation as a major mechanism for the progression of Parkinson’s disease, and AT1 inhibition and RAS modulation as therapeutic targets.

The central renin–angiotensin system: A genetic pathway, functional decoding, and selective target engagement characterization in humans

Accumulating evidence suggests that the brain renin angiotensin system (RAS) plays a pivotal role in the regulation of cognition and behavior as well as in the neuropathology of neurological and mental disorders. The angiotensin II type 1 receptor (AT1R) mediates most functional and neuropathology-relevant actions associated with the central RAS. However, an overarching comprehension to guide translation and utilize the therapeutic potential of the central RAS in humans is currently lacking. We conducted a comprehensive characterization of the RAS using an innovative combination of transcriptomic gene expression mapping, image-based behavioral decoding, and pre-registered randomized controlled discovery-replication pharmacological resting-state functional magnetic resonance imaging (fMRI) trials (N = 132) with a selective AT1R antagonist. The AT1R exhibited a particular dense expression in a subcortical network encompassing the thalamus, striatum, and amygdalo-hippocampal formation. Behavioral decoding of the AT1R gene expression brain map showed an association with memory, stress, reward, and motivational processes. Transient pharmacological blockade of the AT1R further decreased neural activity in subcortical systems characterized by a high AT1R expression, while increasing functional connectivity in the cortico-basal ganglia-thalamo-cortical circuitry. Effects of AT1R blockade on the network level were specifically associated with the transcriptomic signatures of the dopaminergic, opioid, acetylcholine, and corticotropin-releasing hormone signaling systems. The robustness of the results was supported in an independent pharmacological fMRI trial. These findings present a biologically informed comprehensive characterization of the central AT1R pathways and their functional relevance on the neural and behavioral level in humans.

Telmisartan Protects Mitochondrial Function, Gait, and Neuronal Apoptosis by Activating the Akt/GSK3β/PGC1α Pathway in an MPTP-Induced Mouse Model of Parkinson's Disease.

Mitochondrial dysfunction is one of the major hallmarks of Parkinson's disease (PD). Recently, angiotensin II type 1 and type 2 receptors (AT1R, AT2R) were reported to be present on the mitochondrial membrane. Both are crucial players in the brain renin-angiotensin system (RAS). Current evidence indicates that blockade of brain AT1R protects dopaminergic neurons in PD. Thus, the current study was aimed to explore the effects of Telmisartan (Tel), a selective AT1R blocker, on mitochondrial function and a mouse model by exposure to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) [250 mg/kg body weight (10 divided i.p. injections, each 25 mg/kg body weight at 3.5 days interval) + Probenecid 250 mg/kg]. Gait function was assessed by beam walk, and mice were euthanized on the 35th day and their brain tissues isolated for Western blot analysis. Pretreatment with Tel significantly protected motor functions during the beam walk in MPTP-treated mice. Tel attenuated the increased levels of AT1R, α-syn, and inflammatory markers such as inducible nitric oxide synthase (iNOS) and ionized calcium-binding adaptor molecule 1 (IBA1) in MPTP-treated mice. In addition, Tel preserved the expression of AT2R, tyrosine hydroxylase (TH), p-Akt/Akt, and p-GSK3β (Ser-9)/GSK3β, as well as protecting mitofusin protein 1 (MFN1) and Peroxisome proliferator-activated receptor-gamma coactivator-α (PGC1α), a critical activator of mitochondrial biogenesis. These results indicate that Tel protects mitochondrial function and gait in a mouse model of PD by modulating the Akt/GSK3β/PGC1α pathway.

Extracellular Vesicles and Their Renin-Angiotensin Cargo as a Link between Metabolic Syndrome and Parkinson's Disease.

Several studies showed an association between metabolic syndrome (MetS) and Parkinson's disease (PD). The linking mechanisms remain unclear. MetS promotes low-grade peripheral oxidative stress and inflammation and dysregulation of the adipose renin-angiotensin system (RAS). Interestingly, brain RAS dysregulation is involved in the progression of dopaminergic degeneration and PD. Circulating extracellular vesicles (EVs) from MetS fat tissue can cross the brain-blood barrier and may act as linking signals. We isolated and characterized EVs from MetS and control rats and analyzed their mRNA and protein cargo using RT-PCR and the ExoView R200 platform, respectively. Furthermore, cultures of the N27 dopaminergic cell line and the C6 astrocytic cell line were treated with EVs from MetS rats. EVs were highly increased in MetS rat serum, which was inhibited by treatment of the rats with the angiotensin type-1-receptor blocker candesartan. Furthermore, EVs from MetS rats showed increased pro-oxidative/pro-inflammatory and decreased anti-oxidative/anti-inflammatory RAS components, which were inhibited in candesartan-treated MetS rats. In cultures, EVs from MetS rats increased N27 cell death and modulated C6 cell function, upregulating markers of neuroinflammation and oxidative stress, which were inhibited by the pre-treatment of cultures with candesartan. The results from rat models suggest EVs and their RAS cargo as a mechanism linking Mets and PD.

Role of brain renin-angiotensin system in depression: A new perspective.

Depression is a mood disorder characterized by abnormal thoughts. The pathophysiology of depression is related to the deficiency of serotonin (5HT), which is derived from tryptophan (Trp). Mitochondrial dysfunction, oxidative stress, and neuroinflammation are involved in the pathogenesis of depression. Notably, the renin-angiotensin system (RAS) is involved in the pathogenesis of depression, and different findings revealed that angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) may be effective in depression. However, the underlying mechanism for the role of dysregulated brain RAS-induced depression remains speculative. Therefore, this review aimed to revise the conceivable role of ACEIs and ARBs and how these agents ameliorate the pathophysiology of depression. Dysregulation of brain RAS triggers the development and progression of depression through the reduction of brain 5HT and expression of brain-derived neurotrophic factor (BDNF) and the induction of mitochondrial dysfunction, oxidative stress, and neuroinflammation. Therefore, inhibition of central classical RAS by ARBS and ACEIs and activation of non-classical RAS prevent the development of depression by regulating 5HT, BDNF, mitochondrial dysfunction, oxidative stress, and neuroinflammation.

Altered Gene Expression Within the Renin-Angiotensin System in Normal Aging and Dementia.

The renin-angiotensin system (RAS) is dysregulated in Alzheimer's disease (AD). In this study, we have explored the hypothesis that an -age--related imbalance in brain RAS is a trigger for RAS dysregulation in AD. We characterized RAS gene expression in the frontal cortex from (i) a cohort of normal aging (n = 99, age range = 19-96 years) and (ii) a case-control cohort (n = 209) including AD (n = 66), mixed dementia (VaD + AD; n = 50), pure vascular dementia (VaD; n = 42), and age-matched controls (n = 51). The AD, mixed dementia, and age-matched controls were further stratified by Braak tangle stage (BS): BS0-II (n = 48), BSIII-IV (n = 44), and BSV-VI (n = 85). Gene expression was calculated by quantitative PCR (qPCR) for ACE1, AGTR1, AGTR2, ACE2, LNPEP, and MAS1 using the 2-∆∆Cq method, after adjustment for reference genes (RPL13 and UBE2D2) and cell-specific calibrator genes (NEUN, GFAP, PECAM). ACE1 and AGTR1, markers of classical RAS signaling, and AGTR2 gene expression were elevated in normal aging and gene expression in markers of protective downstream regulatory RAS signaling, including ACE2, MAS1, and LNPEP, were unchanged. In AD and mixed dementia, AGTR1 and AGTR2 gene expression were elevated in BSIII-IV and BSV-VI, respectively. MAS1 gene expression was reduced at BSV-VI and was inversely related to parenchymal Aβ and tau load. LNPEP gene expression was specifically elevated in VaD. These data provide novel insights into RAS signaling in normal aging and dementia.

New trials in resistant hypertension: mixed blessing stories.

Resistant hypertension (RH) is linked to an increased risk of cardiovascular and renal complications. Treatment options include non-pharmacological interventions, such as lifestyle modifications, and the use of specific antihypertensive drug combinations, including diuretics. Renal denervation is another option for treatment-resistant hypertension. New compounds targeting different pathways involved in RH-including inhibitors of aminopeptidase A, endothelin antagonists and selective aldosterone synthase inhibitors-have been tested in clinical trials in this condition. The centrally acting drug firibastat, targeting the brain renin-angiotensin system, failed to demonstrate significant effectiveness in reducing blood pressure (BP) in patients with difficult-to-treat and RH in the Firibistat in Resistant Hypertension (FRESH) trial. Aprocitentan, a dual endothelin A and B receptor antagonist, showed a moderate but statistically significant decrease in BP in patients with RH in the Parallel-Group, Phase 3 Study with Aprocitentan in Subjects with Resistant Hypertension (PRECISION) trial. However, concerns remain about potential adverse events, such as fluid retention. The use of baxdrostat, a selective aldosterone synthase inhibitor, showed promising results in reducing BP in patients with treatment-resistant hypertension in the Baxdrostat in Resistant Hypertension (BrigHTN) trial. However, a subsequent trial, HALO, failed to meet its primary endpoint. The unexpected results may be influenced by factors such as patient adherence and white-coat hypertension. Despite the disappointing results from HALO, the potential benefits of inhibiting aldosterone synthesis remain to be fully understood. In conclusion, managing RH remains challenging, and new compounds like firibastat, aprocitentan and baxdrostat have shown varied effectiveness. Further research is needed to improve our understanding and treatment of this condition.

Abstract P430: Primary Neuronal Cilium As A Novel Mediator Of Angiotensin II And Hypertension

Cilia are membrane-bound, microtubular projections emanating from the cell surface and present on virtually all cell types including neurons. Cilia abnormalities (ciliopathies) have been linked to a broad range of diseases including hypertension. Moreover, we previously reported that DOCA-salt hypertension is associated with alterations in cilia in select nuclei involved in cardiovascular regulation and fluid homeostasis such as the supraoptic nucleus, but the underlying mechanisms are not known. Given the well-established role of the brain renin-angiotensin system in DOCA-salt hypertension, we hypothesized that Angiotensin II (Ang II) contribute to neuronal cilia abnormalities in hypertension. We began by examining the effect of Ang II on cilia in two different neuronal cell lines, mouse hypothalamic N47 and Cath.a. Ang II treatment (100 nM for 4 hrs) caused a significant increase in cilia length of N47 cells that were transiently transfected with a Flag-tagged AT1a receptor (AT1aR) compared to non-transfected cells (3.83±0.15 μm vs 2.25±0.06 μm, P<0.05). No change in cilia length was observed in AT1aR positive (2.71±0.09 μm) or negative cells (2.55±0.07 μm) treated with vehicle. Moreover, Ang II had no effect on cilia in N47 cells transfected with a Flag-tagged AT2R. Ang II also significantly increased cilia length in Cath.a cells which express the endogenous AT1aR. Truncation of AT1aR at position 318 resulted in loss of Ang II induced cilia elongation in N47 cells, indicating that the C-terminus of the receptor is important for Ang II regulation of cilia. Next, we evaluated the effect of Ang II infusion with minipumps (480ng/kg/min) on neuronal cilia in C57BL/6 mice. Mice infused with Ang II for 5 days which have elevated blood pressure displayed abnormally elongated cilia in the supraoptic nucleus (8.28±0.12 μm vs 6.37± 0.11 μm, P<0.05). Interestingly, Ang II-induced cilia elongation preceded the development of hypertension as it was observed in mice infused with Ang II for 2 days when no change in blood pressure was detected. These findings point to Ang II as an important regulator of neuronal cilia via AT1aR. This represents a novel mechanism for cardiovascular regulation by the renin-angiotensin system.

Genetic Ablation of Prorenin Receptor in the Rostral Ventrolateral Medulla Influences Blood Pressure and Hydromineral Balance in Deoxycorticosterone-Salt Hypertension.

Non-enzymatic activation of renin via its interaction with prorenin receptor (PRR) has been proposed as a key mechanism of local renin-angiotensin system (RAS) activation. The presence of renin and angiotensinogen has been reported in the rostral ventrolateral medulla (RVLM). Overactivation of bulbospinal neurons in the RVLM is linked to hypertension (HTN). Previous studies have shown that the brain RAS plays a role in the pathogenesis of the deoxycorticosterone (DOCA)-salt HTN model. Thus, we hypothesized that PRR in the RVLM is involved in the local activation of the RAS, facilitating the development of DOCA-salt HTN. Selective PRR ablation targeting the RVLM (PRRRVLM-Null mice) resulted in an unexpected sex-dependent and biphasic phenotype in DOCA-salt HTN. That is, PRRRVLM-Null females (but not males) exhibited a significant delay in achieving maximal pressor responses during the initial stage of DOCA-salt HTN. Female PRRRVLM-Null subsequently showed exacerbated DOCA-salt-induced pressor responses during the "maintenance" phase with a maximal peak at 13 d on DOCA-salt. This exacerbated response was associated with an increased sympathetic drive to the resistance arterioles and the kidney, exacerbated fluid and sodium intake and output in response to DOCA-salt, and induced mobilization of fluids from the intracellular to extracellular space concomitant with elevated vasopressin. Ablation of PRR suppressed genes involved in RAS activation and catecholamine synthesis in the RVLM but also induced expression of genes involved in inflammatory responses. This study illustrates complex and sex-dependent roles of PRR in the neural control of BP and hydromineral balance through autonomic and neuroendocrine systems. Graphical abstract.

Brain Renin-Angiotensin System: From Physiology to Pathology in Neuronal Complications Induced by SARS-CoV-2.

Angiotensin-converting enzyme 2 (ACE2), a key enzyme in the renin-angiotensin system (RAS), is expressed in various tissues and organs, including the central nervous system (CNS). The spike protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for coronavirus disease-2019 (COVID-19), binds to ACE2, which raises concerns about the potential for viral infection in the CNS. There are numerous reports suggesting a link between SARS-CoV-2 infection and neurological manifestations. This study aimed to present an updated review of the role of brain RAS components, especially ACE2, in neurological complications induced by SARS-CoV-2 infection. Several routes of SARS-CoV-2 entry into the brain have been proposed. Because an anosmia condition appeared broadly in COVID-19 patients, the olfactory nerve route was suggested as an early pathway for SARS-CoV-2 entry into the brain. In addition, a hematogenous route via disintegrations in the blood-brain barrier following an increase in systemic cytokine and chemokine levels and retrograde axonal transport, especially via the vagus nerve innervating lungs, have been described. Common nonspecific neurological symptoms in COVID-19 patients are myalgia, headache, anosmia, and dysgeusia. However, more severe outcomes include cerebrovascular diseases, cognitive impairment, anxiety, encephalopathy, and stroke. Alterations in brain RAS components such as angiotensin II (Ang II) and ACE2 mediate neurological manifestations of SARS-CoV-2 infection, at least in part. Downregulation of ACE2 due to SARS-CoV-2 infection, followed by an increase in Ang II levels, leads to hyperinflammation and oxidative stress, which in turn accelerates neurodegeneration in the brain. Furthermore, ACE2 downregulation in the hypothalamus induces stress and anxiety responses by increasing corticotropin-releasing hormone. SARS-CoV-2 infection may also dysregulate the CNS neurotransmission, leading to neurological complications observed in severe cases of COVID-19. It can be concluded that the neurological manifestations of COVID-19 may be partially associated with changes in brain RAS components.

Effects of losartan and enalapril on lithium-pilocarpine-induced status epilepticus, spontaneous convulsive seizures, and cardiac changes in rats

Modulating the brain renin-angiotensin system presents an innovative pathway for exploring newer treatment approaches in epilepsy. The current study aimed to evaluate the influence of losartan (LOS) and enalapril (ENP), which are angiotensin receptor blocker and angiotensin-converting enzyme inhibitor, respectively, on the incidence, initiation, and duration of status epilepticus (SE), spontaneous convulsive seizures (SCS), survival, and cardiac alterations in rats subjected to lithium-pilocarpine (LiP)-induced SE. Lithium (127 mg/kg, i.p.) pretreated male Wistar rats were administered pilocarpine (30 mg/kg, i.p.) after 24 h to induce SE, which was terminated after 90 min of onset. Daily 10-h video monitoring was carried out for examining onset, frequency, duration of SCS, and mortality till 18 days. The administration of LOS (10 mg/kg, i.p.), ENP (20 mg/kg, i.p.) and atenolol (AT; 50 mg/kg, p.o.) was started before lithium in pre-SE protocol and for post-SE protocol these drugs were administered 1 h after terminating SE and continued for 7 days’ post-SE. Cardiac pathology, echocardiography, heart weight/body weight ratio, and histopathology were evaluated. None of the drugs used (LOS/ENP/AT) offered protection against SE. Administration before SE decreased and post-SE administration increased the latency of SCS, and the overall duration of seizures remained short in both cases as compared to untreated rats. The heart weight/body weight ratio decreased in rats that did not survive. No echocardiographic changes were observed in any of the groups. Untreated SE rats showed myocyte ischemic changes, which were not present in any treated rats. In conclusion, LOS may reduce cardiac complications in SE rats. Hence, further evaluation of LOS as an add-on in epilepsy treatment should be performed.

The hypothalamus as a key regulator of glucose homeostasis: emerging roles of the brain renin-angiotensin system.

The regulation of plasma glucose levels is a complex and multifactorial process involving a network of receptors and signaling pathways across numerous organs that act in concert to ensure homeostasis. However, much about the mechanisms and pathways by which the brain regulates glycemic homeostasis remains poorly understood. Understanding the precise mechanisms and circuits employed by the central nervous system to control glucose is critical to resolving the diabetes epidemic. The hypothalamus, a key integrative center within the central nervous system, has recently emerged as a critical site in the regulation of glucose homeostasis. Here, we review the current understanding of the role of the hypothalamus in regulating glucose homeostasis, with an emphasis on the paraventricular nucleus, the arcuate nucleus, the ventromedial hypothalamus, and lateral hypothalamus. In particular, we highlight the emerging role of the brain renin-angiotensin system in the hypothalamus in regulating energy expenditure and metabolic rate, as well as its potential importance in the regulation of glucose homeostasis.

Evaluating the brain renin‐angiotensin system (RAS) and sex differences in pre‐clinical models of Alzheimer’s Disease

AbstractBackgroundHypertension is linked to Alzheimer’s Disease (AD) risk, although the mechanisms remain unclear. The renin angiotensin system (RAS), critical for blood pressure homeostasis, is thought to contribute to AD pathology, and targeted RAS therapies are under current clinical investigation. To further evaluate the neurobiological mechanisms of RAS in AD, the current study leveraged two transgenic AD mouse models to compare the behavioral and cognitive deficits and the brain RAS in male and female mice.MethodsA triple‐transgenic mouse model of AD (3xTg‐AD), which exhibits both amyloid beta and tau pathology, was used for in‐house assays, while an RNA‐sequencing database using a novel mouse model on a genetically diverse background (AD‐BXD) (GEO accession number GSE119215) was used to compare expression levels of hippocampal RAS genes at 6 and 14 mos. Morris water maze (MWM) and Y‐maze alternation tests were performed at early (3‐4 mos) and middle (5‐6 mos) time points on 3xTg‐AD mice (n = 8/sex/age/genotype), followed by collection of plasma and whole brain.ResultsCompared to controls, beginning at 3.5 months, 3xTg‐AD male and female mice exhibited deficits in learning assessed by MWM escape latency (p<0.01). However, beginning at 6 months, only 3xTg‐AD females had deficits in memory assessed by Y‐maze alternation below 50% (i.e. chance) (p<0.05). Sex‐dependent deficits are consistent with variability in phenotype beginning at early time points. Next we assessed hippocampal RNA‐sequencing data from the AD‐BXD database. These data demonstrated a sex‐dependent increase in expression of counter‐regulatory RAS genes ACE (p<0.0001) and ACE2 (p<0.05) and decrease in MasR (p<0.01) when comparing 6 and 14 month females, as compared to males and wild‐type controls. There was no change in classical RAS gene expression, indicating that variation in expression of neuroprotective but not classical RAS genes may be more pronounced in aging female mice.ConclusionOur results demonstrate sex and stage‐specific behavioral deficits in the 3xTg‐AD model, which may be linked to changes in hippocampal regulation of the counter‐regulatory arm of brain RAS. Additional studies are needed to further evaluate underlying mechanisms for the role of the neuroprotective arm of the brain RAS in AD and its biomarker and therapeutic targeting potential.

Interplay between the renin angiotensin system and oxidative stress contributes to alcohol addiction by stimulating dopamine accumulation in the mesolimbic pathway

The brain renin–angiotensin system (RAS) has recently been implicated in the development of substance abuse and addiction. However, the integrative roles of the two counter-regulating RAS arms, including the ACE1/Ang II/AT1R axis and the ACE2/Ang(1–7)/MasR axis, in alcohol addiction remain unclear. Using the 20% ethanol intermittent-access two-bottle-choice (IA2BC) paradigm, we observed significant alcohol preference and addictive behaviors in rats. Additionally, we observed significant disruption in the RAS and redox homeostasis in the ventral tegmental area (VTA), as indicated by upregulation of ACE1 activities, Ang II levels, AT1R expression, and glutathione disulfide contents, as well as downregulation of ACE2 activities, Ang(1–7) levels, MasR expression and glutathione content. Moreover, dopamine accumulated in the VTA and nucleus accumbens of IA2BC rats. Intra-VTA infusion of the antioxidant tempol substantially attenuated RAS imbalance and addictive behaviors. Intra-VTA infusion of the ACE1 inhibitor captopril significantly reduced oxidative stress, alcohol preference, addictive behaviors, and dopamine accumulation, whereas intra-VTA infusion of the ACE2 inhibitor MLN4760 had the opposite effects. The anti-addictive effects of the ACE2/Ang(1–7)/MasR axis were further observed using intra-VTA infusion of Ang(1–7) and a MasR-specific antagonist A779. Therefore, our findings suggest that excessive alcohol intake causes RAS imbalance via oxidative stress, and that a dysregulated RAS in the VTA contributes to alcohol addiction by stimulating oxidative stress and dopaminergic neurotransmission. Breaking the vicious cycle of RAS imbalance and oxidative stress using brain-permeable antioxidants, ACE1 inhibitors, ACE2 activators, or Ang(1–7) mimetics thus represents a promising strategy for combating alcohol addiction.

Angiotensinergic neurotransmission in the bed nucleus of the stria terminalis is involved in cardiovascular responses to acute restraint stress in rats.

The brain angiotensin II acting via AT1 receptors is a prominent mechanism involved in physiological and behavioral responses during aversive situations. The AT2 receptor has also been implicated in stress responses, but its role was less explored. Despite these pieces of evidence, the brain sites related to control of the changes during aversive threats by the brain renin-angiotensin system (RAS) are poorly understood. The bed nucleus of the stria terminalis (BNST) is a limbic structure related to the cardiovascular responses by stress, and components of the RAS system were identified in this forebrain region. Therefore, we investigated the role of angiotensinergic neurotransmission present within the BNST acting via local AT1 and AT2 receptors in cardiovascular responses evoked by an acute session of restraint stress in rats. For this, rats were subjected to bilateral microinjection of either the angiotensin-converting enzyme inhibitor captopril, the selective AT1 receptor antagonist losartan, or the selective AT2 receptor antagonist PD123319 before they underwent the restraint stress session. We observed that BNST treatment with captopril reduced the decrease in tail skin temperature evoked by restraint stress, without affecting the pressor and tachycardic responses. Local AT2 receptor antagonism within the BNST reduced both the tachycardia and the drop in tail skin temperature during restraint. Bilateral microinjection of losartan into the BNST did not affect the restraint-evoked cardiovascular changes. Taken together, these data indicate an involvement of BNST angiotensinergic neurotransmission acting via local AT2 receptors in cardiovascular responses during stressful situations.

JS-ECCR/HBPRCA-4: NEURAL CONTROL OF CARDIOVASCULAR FUNCTION AND ERYTHROPOIESIS BY THE BRAIN RAS

The renin-angiotensin system (RAS) strongly modulates not only cardiovascular homeostasis but also other non-cardiovascular physiological processes like erythropoiesis. The production of the peptide hormone angiotensin II (Ang II) in the circulatory system constitutes the main source of the RAS activity. However, Ang II has also been recognized to be generated locally by various tissues, because RAS components are either locally expressed and/or imported from the circulation. Contrary to peripheral organs, the blood-brain-barrier limits the traffic of all circulating RAS proteins into the brain, thus, brain Ang II formation relies exclusively on locally expressed RAS precursor and enzymes. Several brain cardiovascular centers contain neuronal populations responsive to Ang II that take part in sympathetic nerve outflow, vasopressin secretion, thirst and salt appetite. Angiotensinogen (Agt), the RAS precursor, is mostly produced by astrocytes in the brain. To investigate the role of the brain RAS in cardiovascular control and erythropoiesis, two transgenic rodent models with astrocyte-specific Agt gain- and loss-of-function were phenotyped. In both models, astrocyte-specific transgene expression was delivered using the human GFAP promoter. The gain-of-function model is a transgenic mouse overexpressing rat Agt, and the loss-of-function model is a rat expressing an antisense RNA against the endogenous Agt mRNA. The transgenic mouse line overexpresses the rat Agt mRNA distributed across the brain, including areas containing cardiovascular centers. Overexpression of Agt increased brain Ang II formation but reduced the peripheral Ang II levels. Rats expressing the antisense RNA exhibited a brain-specific decrease of Agt protein by ∼90%. The cardiovascular phenotyping of the two lines demonstrated opposing effects for the brain RAS. Increased brain RAS reactivity was associated with high BP, vascular sympathetic tone and vasopressin secretion, and downregulation of the brain RAS reduced BP and vasopressin secretion. Similarly, the brain RAS modulated erythropoiesis in contrary directions because capillary hematocrit experiments revealed that overproduction of Ang II in the brain correlates with increased erythropoiesis while reduced Ang II production with moderated erythropoiesis. These findings were further validated using detailed blood cell counting with an automated hematology analyzer. Submitting the transgenic mice with increased brain Ang II and respective controls to peripheral sympathectomy with 6-hydroxydopamine revealed that brain Ang II via sympathetic nerve activity increases erythropoiesis in transgenic mice. Altogether, these models confirmed the functionality of the brain RAS, and that baseline BP and erythropoiesis depends on its integrity and reactivity.

Alzheimer's disease: Is there a relationship between brain renin-angiotensin system, estradiol and glucose transporter-4 (GLUT-4)?

<abstract> <p>One of the diseases more related to the continuous aging of the population is Alzheimer's disease, which is a type of dementia currently without either effective diagnosis biomarkers or treatments. Its higher prevalence in women makes it necessary to study pathways/systems that could participate and/or be involved in its development, as well as those that could be affected by hormonal factors, which, in this case, are estradiol levels. In this sense, one of the systems under study that is gaining special relevance in the scientific community is the brain renin-angiotensin system and its regulatory proteolytic enzymes. This system is strongly modulated by estrogens, and it is also connected with the cerebral glucose metabolism through the angiotensin IV receptor, also recognized as the insulin-regulated aminopeptidase (IRAP). Due to the fact that the cerebral glucose metabolism is highly compromised in patients with Alzheimer's disease, it is necessary to know the elements of the systems and their functions in this process, namely, the cerebral renin-angiotensin system, estradiol and IRAP, an enzyme and receptor co-localized in brain tissue with the insulin-dependent glucose transporter 4 (GLUT4). Knowledge of the connection between them could shed light on the molecular mechanisms of this disease and also provide new diagnostic and therapeutic targets.</p> </abstract>

Age-related reduction in brain ACE-2 is not exacerbated by Alzheimer's disease pathology in mouse models of Alzheimer's disease.

An imbalance in the circulatory and organ-specific renin-angiotensin system (RAS) pathways is associated with age-related dysfunction and disease including cardiovascular burden and more recently Alzheimer's disease (AD). It is currently unclear whether an age-associated imbalance in components of the RAS within the brain precedes the onset of AD or whether a RAS imbalance is associated with the onset of disease pathology and cognitive decline. Angiotensin-converting enzyme-1 (ACE-1) and -2 (ACE-2) protein (ELISA) and enzyme activity (FRET assay), markers of the classical and counter-regulatory RAS axis respectively, and Ang-II and Ang-(1-7) peptide levels (ELISA), were measured in the left cortex across four transgenic AD mouse models of amyloid pathology (5xFAD - 2, 6, and 12months of age; Apd9 - 3-4, 12, and 18months of age; Tg2576 - 3-4 and 24months of age; and PDAPP - 3-4, 7, 11, 15, and 18months of age) and littermate wild-type (WT) controls. ACE-1 level, and enzyme activity, was unaltered in relation to age in WT mice and across all four models. In contrast, ACE-2 level and enzyme activity, was reduced and Ang-II increased with ageing in both WT animals and disease models. The changes in ACE-2 and Ang-II in AD models mirrored WT mice, except for the 5xFAD model, when the reduction in ACE-2 (and elevated Ang-II) was observed at a younger age. These data indicate an age-related dysregulation of brain RAS is likely to be driven by a reduction in ACE-2. The reduction in ACE-2 occurs at a young age, coinciding with early pathological changes and the initial deposition of Aβ, and preceding neuronal loss and cognitive decline, in the transgenic AD models. However, the age-related loss was mirrored in WT mice suggesting that the change was independent of pathological Aβ deposition.

AT1 receptor autoantibodies mediate effects of metabolic syndrome on dopaminergic vulnerability

The metabolic syndrome has been associated to chronic peripheral inflammation and related with neuroinflammation and neurodegeneration, including Parkinson’s disease. However, the responsible mechanisms are unclear. Previous studies have involved the brain renin-angiotensin system in progression of Parkinson’s disease and the angiotensin receptor type 1 (AT1) has been recently revealed as a major marker of dopaminergic vulnerability in humans. Dysregulation of tissue renin-angiotensin system is a key common mechanism for all major components of metabolic syndrome. Circulating AT1 agonistic autoantibodies have been observed in several inflammation-related peripheral processes, and activation of AT1 receptors of endothelial cells, dopaminergic neurons and glial cells have been observed to disrupt endothelial blood -brain barrier and induce neurodegeneration, respectively. Using a rat model, we observed that metabolic syndrome induces overactivity of nigral pro-inflammatory renin-angiotensin system axis, leading to increase in oxidative stress and neuroinflammation and enhancing dopaminergic neurodegeneration, which was inhibited by treatment with AT1 receptor blockers (ARBs). In rats, metabolic syndrome induced the increase in circulating levels of LIGHT and other major pro-inflammatory cytokines, and 27-hydroxycholesterol. Furthermore, the rats showed a significant increase in serum levels of proinflammatory AT1 and angiotensin converting enzyme 2 (ACE2) autoantibodies, which correlated with levels of several metabolic syndrome parameters. We also found AT1 and ACE2 autoantibodies in the CSF of these rats. Effects of circulating autoantibodies were confirmed by chronic infusion of AT1 autoantibodies, which induced blood–brain barrier disruption, an increase in the pro-inflammatory renin-angiotensin system activity in the substantia nigra and a significant enhancement in dopaminergic neuron death in two different rat models of Parkinson’s disease. Observations in the rat models, were analyzed in a cohort of parkinsonian and non-parkinsonian patients with or without metabolic syndrome. Non-parkinsonian patients with metabolic syndrome showed significantly higher levels of AT1 autoantibodies than non-parkinsonian patients without metabolic syndrome. However, there was no significant difference between parkinsonian patients with metabolic syndrome or without metabolic syndrome, which showed higher levels of AT1 autoantibodies than non-parkinsonian controls. This is consistent with our recent studies, showing significant increase of AT1 and ACE2 autoantibodies in parkinsonian patients, which was related to dopaminergic degeneration and neuroinflammation. Altogether may lead to a vicious circle enhancing the progression of the disease that may be inhibited by strategies against production of these autoantibodies or AT1 receptor blockers (ARBs).