Angiotensin receptor subtype mediated physiologies and behaviors: new discoveries and clinical targets

Droplet-based microfluidic platform for detecting agonistic peptides that are self-secreted by yeast expressing a G-protein-coupled receptor

BACKGROUND

Single-cell droplet microfluidics is an important platform for high-throughput analyses and screening because it provides an independent and compartmentalized microenvironment for reaction or cultivation by coencapsulating individual cells with various molecules in monodisperse microdroplets. In combination with microbial biosensors, this technology becomes a potent tool for the screening of mutant strains. In this study, we demonstrated that a genetically engineered yeast strain that can fluorescently sense agonist ligands via the heterologous expression of a human G-protein-coupled receptor (GPCR) and concurrently secrete candidate peptides is highly compatible with single-cell droplet microfluidic technology for the high-throughput screening of new agonistically active peptides.

RESULTS

The water-in-oil microdroplets were generated using a flow-focusing microfluidic chip to encapsulate engineered yeast cells coexpressing a human GPCR [i.e., angiotensin II receptor type 1 (AGTR1)] and a secretory agonistic peptide [i.e., angiotensin II (Ang II)]. The single yeast cells cultured in the droplets were then observed under a microscope and analyzed using image processing incorporating machine learning techniques. The AGTR1-mediated signal transduction elicited by the self-secreted Ang II peptide was successfully detected via the expression of a fluorescent reporter in single-cell yeast droplet cultures. The system could also distinguish Ang II analog peptides with different agonistic activities. Notably, we further demonstrated that the microenvironment of the single-cell droplet culture enabled the detection of rarely existing positive (Ang II-secreting) yeast cells in the model mixed cell library, whereas the conventional batch-culture environment using a shake flask failed to do so. Thus, our approach provided compartmentalized microculture environments, which can prevent the diffusion, dilution, and cross-contamination of peptides secreted from individual single yeast cells for the easy identification of GPCR agonists.

CONCLUSIONS

We established a droplet-based microfluidic platform that integrated an engineered yeast biosensor strain that concurrently expressed GPCR and self-secreted the agonistic peptides. This offers individually isolated microenvironments that allow the culture of single yeast cells secreting these peptides and gaging their signaling activities, for the high-throughput screening of agonistic peptides. Our platform base on yeast GPCR biosensors and droplet microfluidics will be widely applicable to metabolic engineering, environmental engineering, and drug discovery.

Role of angiotensin receptor blockers in the context of Alzheimer's disease

As the world's population ages, the prevalence of age-related neurological disorders such as Alzheimer's disease (AD) is increasing. There is currently no treatment for Alzheimer's disease, and the few approved medications have a low success rate in lowering symptoms. As a result, several attempts are underway worldwide to identify new targets for the therapy of Alzheimer's disease. In preclinical studies of Alzheimer's disease, it was recently found that inhibition of angiotensin-converting enzyme (ACE) and blocking of the angiotensin II receptors reduce symptoms of neurodegeneration, Aβ plaque development, and tau hyperphosphorylation. Angiotensin II type I (AT1) blockers, such as telmisartan, candesartan, valsartan, and others, have a wide safety margin and are commonly used to treat hypertension. Renal and cardiovascular failures are reduced due to their vascular protective actions. Inhibition of AT1 receptors in the brain has a neuroprotective impact in humans, reducing the risk of stroke, increasing cognition, and slowing the progression of Alzheimer's disease. The review focuses on the mechanisms via which AT1 blockers may act beneficially in Alzheimer's disease. Although their effect is evident in preclinical studies, clinical trials, on the other hand, are in short supply to validate the strategy. More dose-response experiments with possible AT1 blockers and brain-targeted administration will be needed in the future.

C-Met Receptors Deficiency Was Involved in Absence Seizures Development in WAG/Rij Rats

Background: A variety of receptors may be involved in the pathogenesis of absence seizures. The c-Met receptors have a critical role in modulating the GABAergic interneurons and creating a balance between excitatory and inhibitory neurotransmission, sensorimotor gating, and normal synaptic plasticity. Objectives: This study aimed to assess the changes of the c-Met receptor during the appearance of absence attacks in the experimental model of absence epilepsy. Methods: A total of 48 animals were divided into four groups of two- and six-month-old WAG/Rij and Wistar rats. Epileptic WAG/Rij rats showing SWP in electrocorticogram (ECoG) were included in the epileptic group. The two-month-old WAG/Rij rats as well as two- and six-month-old Wistar rats not exhibiting SWP in ECoG were selected as the non-epileptic. Gene (RT-PCR) and protein expression (western blotting) of c-Met receptors as well as c-Met protein distribution (immunohistochemistry) in the somatosensory cortex and hippocampus were assessed during seizure development of the absence attacks. Results: According to the study findings, a lower c-Met gene and protein expression, as well as a lower protein distribution, were observed in the hippocampus (P < 0.001, P < 0.05, and P < 0.001, respectively) and cortex (P < 0.01, P < 0.001 and P < 0.001, respectively) of the two-month-old WAG/Rij rats compared to the same-age Wistar rats. Moreover, the data revealed a reduction of hippocampal and cortical c-Met protein expression (P < 0.001, for both) in six-month-old WAG/Rij rats compared to two-month-old ones. Six-month-old WAG/Rij rats had a lower cortical c-Met gene (P < 0.05) and protein expression (P < 0.001) as well as lower hippocampal and cortical protein distribution (P < 0.05 and P < 0.001) than the same-age Wistar rats. Conclusions: In sum, the c-Met receptor was found to play a significant role in the development of absence epilepsy. This receptor, therefore, may have been considered as an effective goal for absence seizure inhibition.

Targeting brain Renin-Angiotensin System for the prevention and treatment of Alzheimer's disease: Past, present and future

Alzheimer's disease (AD) is a well-known neurodegenerative disease characterized by the presence of two main hallmarks - Tau hyperphosphorylation and Aβ deposits. Notwithstanding, in the last few years the scientific evidence about the drivers of AD have been changing and nowadays age-related vascular alterations and several cardiovascular risk factors have been shown to trigger the development of AD. In this context, drugs targeting the Renin Angiotensin System (RAS), commonly used for the treatment of hypertension, are evidencing a high potential to delay AD development due to their action on brain RAS. Indeed, the ACE 1/Ang II/AT1R axis is believed to be upregulated in AD and to be responsible for deleterious effects such as increased oxidative stress, neuroinflammation, blood-brain barrier (BBB) hyperpermeability, astrocytes dysfunction and a decrease in cerebral blood flow. In contrast, the alternative axis - ACE 1/Ang II/AT2R; ACE 2/Ang (1-7)/MasR; Ang IV/ AT4R(IRAP) - seems to counterbalance the deleterious effects of the principal axis and to exert beneficial effects on memory and cognition. Accordingly, retrospective studies demonstrate a reduced risk of developing AD among people taking RAS medication as well as several in vitro and in vivo pre-clinical studies as it is herein critically reviewed. In this review, we first revise, at a glance, the pathophysiology of AD focused on its classic hallmarks. Secondly, an overview about the impact of the RAS on the pathophysiology of AD is also provided, focused on their four essential axes ACE 1/Ang II/AT2R; ACE 2/Ang (1-7)/MasR; Ang IV/ AT4R(IRAP) and ACE 1/Ang II/AT1R. Finally, the therapeutic potential of available drugs targeting RAS on AD, namely angiotensin II receptor blockers (ARBs) and angiotensin converting enzyme inhibitors (ACEIs), is highlighted and data supporting this hope will be presented, from in vitro and in vivo pre-clinical to clinical studies.

Captopril and losartan attenuate behavioural sensitization in mice chronically exposed to toluene

Inhalants are consumed worldwide for recreational purposes. The main component found in many inhalants is toluene. One of the most deleterious behavioural effects caused by chronic exposure to inhalants is addiction. This response has been associated with activation of the mesolimbic dopaminergic pathway, and it is known that the renin angiotensin system plays a role in the modulation of this dopaminergic system. In the present work, we hypothesize that blockade of the RAS with angiotensin converting enzyme inhibitors or angiotensin II type 1 receptor blockers is able to attenuate the addictive response induced by toluene. We exposed mice to toluene for four weeks to induce locomotor sensitization. In the second phase of the work, captopril or losartan were administered for 20 days. Subsequently, the expression of behavioural sensitization was evaluated with a toluene challenge. To exclude false associations between the observed responses and treatments, motor coordination and blood pressure were analysed in animals treated with captopril or losartan. At the end of the behavioural studies, animal brains were harvested and Ang II/Ang-(1-7) and Ang-(1-7)/Ang II ratios were analysed in the nucleus accumbens (NAc) and prefrontal cortex (PFCx). The results showed that toluene induced behavioural sensitization, while captopril or losartan treatment attenuated the expression of this response. No significant differences were observed in motor coordination or blood pressure. Repeated toluene administration decreased Ang-(1-7)/Ang II ratio in the PFCx. On the other hand, treatment with captopril or losartan decreased the Ang II/Ang-(1-7) ratio and enhanced the Ang-(1-7)/Ang II ratio in the NAc. This work suggests that blockade of RAS attenuates the toluene-induced behavioural sensitization.

Aβ-accelerated neurodegeneration caused by Alzheimer's-associated ACE variant R1279Q is rescued by angiotensin system inhibition in mice

Recent genome-wide association studies identified the angiotensin-converting enzyme gene (ACE) as an Alzheimer's disease (AD) risk locus. However, the pathogenic mechanism by which ACE causes AD is unknown. Using whole-genome sequencing, we identified rare ACE coding variants in AD families and investigated one, ACE1 R1279Q, in knockin (KI) mice. Similar to AD, ACE1 was increased in neurons, but not microglia or astrocytes, of KI brains, which became elevated further with age. Angiotensin II (angII) and angII receptor AT1R signaling were also increased in KI brains. Autosomal dominant neurodegeneration and neuroinflammation occurred with aging in KI hippocampus, which were absent in the cortex and cerebellum. Female KI mice exhibited greater hippocampal electroencephalograph disruption and memory impairment compared to males. ACE variant effects were more pronounced in female KI mice, suggesting a mechanism for higher AD risk in women. Hippocampal neurodegeneration was completely rescued by treatment with brain-penetrant drugs that inhibit ACE1 and AT1R. Although ACE variant-induced neurodegeneration did not depend on β-amyloid (Aβ) pathology, amyloidosis in 5XFAD mice crossed to KI mice accelerated neurodegeneration and neuroinflammation, whereas Aβ deposition was unchanged. KI mice had normal blood pressure and cerebrovascular functions. Our findings strongly suggest that increased ACE1/angII signaling causes aging-dependent, Aβ-accelerated selective hippocampal neuron vulnerability and female susceptibility, hallmarks of AD that have hitherto been enigmatic. We conclude that repurposed brain-penetrant ACE inhibitors and AT1R blockers may protect against AD.

Inhibition of PLCβ1 signaling pathway regulates methamphetamine self-administration and neurotoxicity in rats

Studies have shown that the central renin-angiotensin system is involved in neurological disorders. Our previous studies have demonstrated that angiotensin II receptor type 1 (AT1R) in the brain could be a potential target against methamphetamine (METH) use disorder. The present study was designed to investigate the underlying mechanisms of the inhibitory effect of AT1R on various behavioural effects of METH. We first examined the effect of AT1R antagonist, candesartan cilexetil (CAN), on behavioural and neurotoxic effects of METH. Furthermore, we studied the role of phospholipase C beta 1 (PLCβ1) blockade behavioural and neurotoxic effects of METH. The results showed that CAN significantly attenuated METH-induced behavioral disorders and neurotoxicity associated with increased oxidative stress. AT1R and PLCβ1 were significantly upregulated in vivo and in vitro. Inhibition of PLCβ1 effectively alleviated METH-induced neurotoxicity and METH self-administration (SA) by central blockade of the PLCβ1 involved signalling pathway. PLCβ1 blockade significantly decreased the reinforcing and motivation effects of METH. PLCβ1 involved signalling pathway, as well as a more specific role of PLCβ1, involved the inhibitory effects of CAN on METH-induced behavioural dysfunction and neurotoxicity. Collectively, our findings reveal a novel role of PLCβ1 in METH-induced neurotoxicity and METH use disorder.

A Narrative Review of the Renin-Angiotensin-Aldosterone System in the Placenta and Placental Bed of HIV Infected Women of African Ancestry with Preeclampsia

PURPOSE OF REVIEW

Both HIV infection and preeclampsia (PE), a pregnancy-specific disorder of hypertension and multi-system organ involvement, have high prevalence rates especially in low-to-middle-income countries. The immunoexpression of specific renin-angiotensin-aldosterone system (RAAS) receptors in the placenta and placental bed interface may forecast the risk of PE.

RECENT FINDINGS

Preeclampsia is a leading risk factor for mortality worldwide and remains a challenge in HIV-infected individuals especially those on antiretroviral therapy (ART). Irregular RAAS stimulation may be linked to the pathophysiology of hypertension in HIV infection and in PE. The AT1 receptor is expressed across all trimesters of pregnancy, within placental tissue, eliciting vasoconstriction. This increased expression is associated with the severity of PE, implying that the increased expression may be involved in the pathogenesis of this pregnancy disorder. The AT2 receptor expression in normotensive pregnancies was shown to be lower as compared to non-pregnant individuals. Furthermore, in the PE placental bed, the AT2 receptor is the predominant receptor subtype and is found in extravillous trophoblast cells where they facilitate vasodilation. However, AT4R in placentae of PE pregnancies are found to be significantly reduced compared to normotensives pregnancies. The data on the role played by the RAAS pathway in pregnancy is conflicting. Investigation into a tissue-based RAAS with emphasis on immune-expression within the placenta and placental bed may help resolve this conundrum.

From Angiotensin IV to Small Peptidemimetics Inhibiting Insulin-Regulated Aminopeptidase

It was reported three decades ago that intracerebroventricular injection of angiotensin IV (Ang IV, Val-Tyr-Ile-His-Pro-Phe) improved memory and learning in the rat. There are several explanations for these positive effects of the hexapeptide and related analogues on cognition available in the literature. In 2001, it was proposed that the insulin-regulated aminopeptidase (IRAP) is a main target for Ang IV and that Ang IV serves as an inhibitor of the enzyme. The focus of this review is the efforts to stepwise transform the hexapeptide into more drug-like Ang IV peptidemimetics serving as IRAP inhibitors. Moreover, the discovery of IRAP inhibitors by virtual and substance library screening and direct design applying knowledge of the structure of IRAP and of related enzymes is briefly presented.

Angiotensin-converting enzyme as a new immunologic target for the new SARS-CoV-2

The coronavirus disease 2019 (COVID-19) pandemic has affected the daily lives of millions of people worldwide and had caused significant mortality; hence, the assessment of therapeutic options is of great interest. The leading cause of death among COVID-19 patients is acute respiratory distress syndrome caused by hyperinflammation secondary to cytokine release syndrome (CRS). Cytokines, such as tumor necrosis factor-α, interleukin-6, interferon-γ and interleukin-10, are the main mediators of CRS. Based on recent evidence, the angiotensin-converting enzyme (ACE) II is known to be the target of the COVID-19 spike protein, which enables the virus to penetrate human cells. ACE II also possesses an anti-inflammatory role in many pathologies such as cardiovascular disease, hypertension, diabetes mellitus and other conditions, which are the main risk factors of poor prognosis in COVID-19 infection. Changes in tissue ACE II levels are associated with many diseases and hyperinflammatory states, and it is assumed that elevated levels of ACE II could aggravate the course of COVID-19 infection. Therefore, the use of renin-angiotensin-aldosterone system inhibitors (RASis) in COVID-19 patients could be hypothetically considered, though sufficient evidence is not presented by the scientific community. In this work, based on the most recent pieces of evidence, the roles of RAS and RASi in immunologic interactions are addressed. Furthermore, the molecular and immunologic aspects of RASi and their potential significance in COVID-19 are discussed.

Contributions by the Brain Renin-Angiotensin System to Memory, Cognition, and Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by progressive neuron losses in memory-associated brain structures that rob patients of their dignity and quality of life. Five drugs have been approved by the FDA to treat AD but none modify or significantly slow disease progression. New therapies are needed to delay the course of this disease with the ultimate goal of preventing neuron losses and preserving memory functioning. In this review we describe the renin-angiotensin II (AngII) system (RAS) with specific regard to its deleterious contributions to hypertension, facilitation of neuroinflammation and oxidative stress, reduced cerebral blood flow, tissue remodeling, and disruption of memory consolidation and retrieval. There is evidence that components of the RAS, AngIV and Ang(1-7), are positioned to counter such damaging influences and these systems are detailed with the goal of drawing attention to their importance as drug development targets. Ang(1-7) binds at the Mas receptor, while AngIV binds at the AT4 receptor subtype, and these receptor numbers are significantly decreased in AD patients, accompanied by declines in brain aminopeptidases A and N, enzymes essential for the synthesis of AngIV. Potent analogs may be useful to counter these changes and facilitate neuronal functioning and reduce apoptosis in memory associated brain structures of AD patients.

Angiotensin III Induces JAK2/STAT3 Leading to IL-6 Production in Rat Vascular Smooth Muscle Cells

The Janus kinase-2/ signal transducer and activators of transcription-3 (JAK2/STAT3) pathway and interleukin-6 (IL-6) are pleiotropic signal transduction systems that are responsible for induction of many cytokines and growth factors. It is unknown whether the renin angiotensin aldosterone system (RAAS) peptide, angiotensin (Ang) III induces JAK2/STAT3 and IL-6 in vascular smooth muscle cells (VSMCs). Thus, the purpose of this study was to investigate whether Ang III induces the JAK2/STAT3 pathway leading to IL-6 production in cultured VSMCs isolated from Wistar rats and determine whether differences exist in spontaneously hypertensive rat (SHR) VSMCs. We gauged Ang III’s effects on this pathway by measuring its action on STAT3 as well as IL-6 production. Ang III behaved similarly as Ang II in stimulation of STAT3 phosphorylation in Wistar and SHR VSMCs. Moreover, there were no differences in this Ang III effect in SHR versus Wistar VSMCs. In Wistar VSMCs, Ang II and Ang III significantly induced IL-6 protein secretion and mRNA expression. However, IL-6 protein secretions mediated by these peptides were significantly greater in SHR VSMCs. Ang III induced the JAK2/STAT3 pathway, leading to IL-6 protein secretion and IL-6 mRNA expression via actions on AT₁Rs. Moreover, the actions of Ang III to induce IL-6 production was dysregulated in SHR VSMCs. These findings suggest that Ang III acts on AT₁Rs to induce JAK2/STAT3, leading to an increase in IL-6 in cultured VSMCs. These findings are important in establishing Ang III as an important physiologically relevant peptide in VSMCs.

The Potential Therapeutic Capacity of Inhibiting the Brain Renin-Angiotensin System in the Treatment of Co-Morbid Conditions in Epilepsy

Epilepsy is one of the most prevalent neurological diseases and although numerous novel anticonvulsants have been approved, the proportion of patients who are refractory to medical treatment of seizures and have progressive co-morbidities such as cognitive impairment and depression remains at about 20-30%. In the last decade, extensive research has identified a therapeutic capacity of the components of the brain renin-angiotensin system (RAS) in seizure- and epilepsy-related phenomena. Alleviating the activity of RAS in the central nervous system is considered to be a potential adjuvant strategy for the treatment of numerous detrimental consequences of epileptogenesis. One of the main advantages of RAS is associated with its modulatory influence on different neurotransmitter systems, thereby exerting a fine-tuning control mechanism for brain excitability. The most recent scientific findings regarding the involvement of the components of brain RAS show that angiotensin II (Ang II), angiotensin-converting enzyme (ACE), Ang II type 1 (AT₁) and type 2 (AT₂) receptors are involved in the control of epilepsy and its accompanying complications, and therefore they are currently of therapeutic interest in the treatment of this disease. However, data on the role of different components of brain RAS on co-morbid conditions in epilepsy, including hypertension, are insufficient. Experimental and clinical findings related to the involvement of Ang II, ACE, AT₁, and AT₂ receptors in the control of epilepsy and accompanying complications may point to new therapeutic opportunities and adjuvants for the treatment of common co-morbid conditions of epilepsy.

The effect of angiotensin AT1A inactivation on innate and learned fear responses in mice and its relationship to blood pressure

Angiotensin AT₁ receptors are implicated in behavioral and physiological processes associated with fear and stress. However, the precise role of AT₁ receptors in modulating fear-related behavior and its relation to their physiological effects remains unclear. Here, we examined innate and learned fear responses and their relationship to cardiovascular arousal in AT_1A receptor knockout (AT_1A^-/-) mice. Using synchronized video and blood pressure telemetry, we found that, in a novel test environment, AT_1A^-/- mice showed reduced neophobia but a similar rise in blood pressure, as compared to AT_1A^+/+ mice. In response to a discrete threat, footshock, both flight behavior and cardiovascular arousal were decreased in AT_1A^-/- mice. Reduced flight behavior was also observed in AT_1A^-/- mice in the elevated T-maze test. During fear conditioning, the immediate freezing response to the first shock, but not the rate of freezing acquisition was decreased in AT_1A^-/- mice. Likewise, AT_1A^-/- mice showed reduced freezing and pressor responses to the first re-exposure, but normal rate of freezing extinction over subsequent trials. Similarly, in the elevated T-maze, the rates of avoidance acquisition and escape learning remained unchanged in AT_1A^-/- mice. Finally, after re-exposure, AT_1A^-/- mice displayed altered c-Fos expression, compared to AT_1A^+/+ mice, in the hypothalamus and periaqueductal gray but not in fear-related limbic-cortical areas, nor in medullary nuclei that convey visceral afferent information. We conclude that AT_1A receptor knockout reduces innate fear responses, without affecting learning efficiency in mice. These effects are dissociable from cardiovascular effects and likely reflect altered neurotransmission in hypothalamic-midbrain defense regions.

Microglial Activation Is Modulated by Captopril: in Vitro and in Vivo Studies

The renin-angiotensin system (RAS) is an important peripheral system involved in homeostasis modulation, with angiotensin II (Ang II) serving as the main effector hormone. The main enzyme involved in Ang II formation is angiotensin-converting enzyme (ACE). ACE inhibitors (ACEIs) such as captopril (Cap) are predominantly used for the management of hypertension. All of the components of the RAS have also been identified in brain. Centrally located hormones such as Ang II can induce glial inflammation. Moreover, in Alzheimer’s disease (AD) models, where glial inflammation occurs and is thought to contribute to the propagation of the disease, increased levels of Ang II and ACE have been detected. Interestingly, ACE overexpression in monocytes, migrating to the brain was shown to prevent AD cognitive decline. However, the specific effects of captopril on glial inflammation and AD remain obscure. In the present study, we investigated the effect of captopril, given at a wide concentration range, on inflammatory mediators released by lipopolysaccharide (LPS)-treated glia. In the current study, both primary glial cells and the BV2 microglial cell line were used. Captopril decreased LPS-induced nitric oxide (NO) release from primary mixed glial cells as well as regulating inducible NO synthase (iNOS) expression, NO, tumor necrosis factor-α (TNF-α) and induced interleukin-10 (IL-10) production by BV2 microglia. We further obtained data regarding intranasal effects of captopril on cortical amyloid β (Aβ) and CD11b expression in 5XFAD cortex over three different time periods. Interestingly, we noted decreases in Aβ burden in captopril-treated mice over time which was paralleled by increased microglial activation. These results thus shed light on the neuroprotective role of captopril in AD which might be related to modulation of microglial activation.

Angiotensin II facilitates GABAergic neurotransmission at postsynaptic sites in rat amygdala neurons

The central nucleus of the amygdala (CeA) is critical in the regulation of sodium appetite. Angiotensin II (Ang II) is important in the generation of sodium appetite and may function as a neurotransmitter or modulator to affect the synaptic transmission and the excitability of neurons. However, the role of Ang II in the CeA remains unclear. In this study, we determined the effects of Ang II on the excitatory and inhibitory synaptic inputs to the CeA neurons in brain slices with whole-cell patch-clamp recordings. Ang II (0.5-5 μM) significantly potentiated the amplitude of spontaneous GABAergic inhibitory postsynaptic currents (IPSCs) in a concentration-dependent manner. Ang II (2 μM) significantly increased the amplitude of miniature GABAergic inhibitory postsynaptic currents (mIPSCs) without affecting the frequency. This effect was blocked by Ang II type 1 (AT₁) receptor antagonist, losartan. One mM guanosine 5'-O-(-2-thiodiphosphate) (GDP-β-s) in the pipette internal solution eliminated the facilitatory effect of Ang II on GABAergic synaptic transmission. In contrast, Ang II had no effect on the spontaneous glutamatergic excitatory postsynaptic currents (EPSCs) and did not alter the frequency and amplitude of miniature EPSCs at concentrations that facilitated IPSCs. Furthermore, Ang II decreased the firing activity of CeA neurons, and this effect was abolished by losartan and GDP-β-s. In addition, Ang II failed to inhibit CeA neurons in the presence of bicuculline. These data provide substantial new evidence that Ang II inhibits the CeA neurons by facilitation of GABAergic synaptic input efficacy through activation of postsynaptic AT₁ receptors.

The Renin-Angiotensin-Aldosterone System as a Therapeutic Target in Late Injury Caused by Ischemia-Reperfusion

Ischemia-reperfusion (I/R) injury is a well-known phenomenon that involves different pathophysiological processes. Connection in diverse systems of survival brings about cellular dysfunction or even apoptosis. One of the survival systems of the cells, to the assault caused by ischemia, is the activation of the renin-angiotensin-aldosterone system (also known as an axis), which is focused on activating diverse signaling pathways to favor adaptation to the decrease in metabolic supports caused by the hypoxia. In trying to adapt to the I/R event, great changes occur that unchain cellular dysfunction with the capacity to lead to cell death, which translates into a poor prognosis due to the progression of dysfunction of the cellular activity. The search for the understanding of the diverse therapeutic alternatives in molecular coupling could favor the prognosis and evolution of patients who are subject to the I/R process.

Losartan suppresses the kainate-induced changes of angiotensin AT1 receptor expression in a model of comorbid hypertension and epilepsy

AIMS

Experimental and clinical studies have demonstrated that components of renin-angiotensin system are elevated in the hippocampus in epileptogenic conditions. In the present work, we explored the changes in the expression of angiotensin II receptor, type 1 (AT₁ receptor) in limbic structures, as well as the effect of the AT1 receptor antagonist losartan in a model of comorbid hypertension and epilepsy.

MAIN METHODS

The expression of AT₁ receptors was compared between spontaneously hypertensive rats (SHRs) and Wistar rats by using immunohistochemistry in the kainate (KA) model of temporal lobe epilepsy (TLE). The effect of losartan was studied on AT₁ receptor expression in epileptic rats that were treated for a period of 4weeks after status epilepticus.

KEY FINDINGS

The naive and epileptic SHRs were characterized by stronger protein expression of AT₁ receptor than normotensive Wistar rats in the CA1, CA3a, CA3b, CA3c field and the hilus of the dentate gyrus of the dorsal hippocampus but fewer cells were immunostained in the piriform cortex. Increased AT₁ immunostaining was observed in the basolateral amygdala of epileptic SHRs but not of epileptic Wistar rats. Losartan exerted stronger and structure-dependent suppression of AT₁ receptor expression in SHRs compared to Wistar rats.

SIGNIFICANCE

Our results confirm the important role of AT₁ receptor in epilepsy and suggest that the AT₁receptor antagonists could be used as a therapeutic strategy for treatment of comorbid hypertension and epilepsy.

Angiotensin AT1 receptors modulate the anxiogenic effects of angiotensin (5-8) injected into the rat ventrolateral periaqueductal gray

Losartan and PD 123,319 are non-peptide angiotensin (Ang) receptor antagonists for the AT1 and AT2 subtypes of Ang II receptors, respectively. The tetrapeptide Ang (5-8) is the smallest Ang-peptide that elicits anxiogenic effects on unconditioned and conditioned experimental models upon injection into the ventrolateral column of the periaqueductal gray (vlPAG), and Ang (5-8) can be synthesized (from Ang II or Ang III) and inactivated in this mesencephalic structure. The vlPAG is also known to play a central role in mechanisms of fear and anxiety. We therefore utilized male Wistar rats to examine the effects of losartan and PD 123,319 injections, selective antagonists of the AT1 and AT2 receptors, respectively, into the vlPAG in the elevated plus-maze, a classic rat model of anxiety, and against the anxiogenic effect of Ang (5-8) (0.4 nmol/0.25μL) upon injection into the same region. The anxiolytic profile was dependent on the dose of intra-vlPAG losartan, whereas no effects on experimental anxiety were observed in the plus-maze following PD 123,319 injection. The anxiogenic effect of Ang (5-8) injection into the vlPAG remained unchanged in the PD 123,319-pretreated rats, but the effect did not occur in losartan-pretreated rats. The results led us to suggest that the anxiogenic effect of Ang (5-8) injection into the vlPAG may depend on the local activation of AT1, but not AT2 receptors. Activation of AT1 receptors in structures nearby vlPAG may be tonically involved in fear and experimental anxiety.

Intranasal telmisartan ameliorates brain pathology in five familial Alzheimer's disease mice

The renin-angiotensin system (RAS) is a major circulative system engaged in homeostasis modulation. Angiotensin II (Ang II) serves as its main effector hormone upon binding to its primary receptor, Ang II receptor type 1 (AT₁R). It is well established that an intrinsic independent brain RAS exists. Abnormal AT₁R activation both in the periphery and in the brain probably contributes to the development of Alzheimer's disease (AD) pathology that is characterized, among others, by brain inflammation. Moreover, treatment with drugs that block AT₁R (AT₁R blockers, ARBs) ameliorates most of the clinical risk factors leading to AD. Previously we showed that short period of intranasal treatment with telmisartan (a brain penetrating ARB) reduced brain inflammation and ameliorated amyloid burden (a component of Alzheimer's plaques) in AD transgenic mouse model. In the present study, we aimed to examine the long-term effect of intranasally administrated telmisartan on brain inflammation features including microglial activation, astrogliosis, neuronal loss and hippocampus-dependent cognition in five-familial AD mouse model (5XFAD). Five month of intranasal treatment with telmisartan significantly reduced amyloid burden in the cortex and hippocampus of 5XFAD mice as compared with the vehicle-treated 5XFAD group. Similar effects were also observed for CD11b staining, which is a marker for microglial accumulation. Telmisartan also significantly reduced astrogliosis and neuronal loss in the cortex of 5XFAD mice compared with the vehicle-treated group. Improved spatial acquisition of the 5XFAD mice following long-term intranasal administration of telmisartan was also observed. Taken together, our data suggest a significant role for AT1R blockage in mediating neuronal loss and cognitive behavior, possibly through regulation of amyloid burden and glial inflammation.

Angiotensin Receptors: Structure, Function, Signaling and Clinical Applications

Angiotensinogen - a serpin family protein predominantly produced by the liver is systematically processed by proteases of the Renin Angiotensin system (RAS) generating hormone peptides. Specific cell surface receptors for at least three distinct angiotensin peptides produce distinct cellular signals that regulate system-wide physiological response to RAS. Two well characterized receptors are angiotensin type 1 receptor (AT1 receptor) and type 2 receptor (AT2 receptor). They respond to the octapeptide hormone angiotensin II. The oncogene product MAS is a putative receptor for Ang (1-7). While these are G-protein coupled receptors (GPCRs), the in vivo angiotensin IV binding sites may be type 2 transmembrane proteins. These four receptors together regulate cardiovascular, hemodynamic, neurological, renal, and endothelial functions; as well as cell proliferation, survival, matrix-cell interactions and inflammation. Angiotensin receptors are important therapeutic targets for several diseases. Thus, researchers and pharmaceutical companies are focusing on drugs targeting AT1 receptor than AT2 receptor, MAS and AngIV binding sites. AT1 receptor blockers are the cornerstone of current treatment for hypertension, heart failure, renal failure and many types of vascular diseases including atherosclerosis, aortic aneurism and Marfan syndrome.

Renin-angiotensin system as a potential therapeutic target in stroke and retinopathy: experimental and clinical evidence

As our knowledge expands, it is now clear that the renin-angiotensin (Ang) system (RAS) mediates functions other than regulating blood pressure (BP). The RAS plays a central role in the pathophysiology of different neurovascular unit disorders including stroke and retinopathy. Moreover, the beneficial actions of RAS modulation in brain and retina have been documented in experimental research, but not yet exploited clinically. The RAS is a complex system with distinct yet interconnected components. Understanding the different RAS components and their functions under brain and retinal pathological conditions is crucial to reap their benefits. The aim of the present review is to provide an experimental and clinical update on the role of RAS in the pathophysiology and treatment of stroke and retinopathy. Combining the evidence from both these disorders allows a unique opportunity to move both fields forward.

Genetic Variants of Angiotensin-Converting Enzyme Are Linked to Autism: A Case-Control Study

Background

Autism is a disease of complex nature with a significant genetic component. The importance of renin-angiotensin system (RAS) elements in cognition and behavior besides the interaction of angiotensin II (Ang II), the main product of angiotensin-converting enzyme (ACE), with neurotransmitters in CNS, especially dopamine, proposes the involvement of RAS in autism. Since the genetic architecture of autism has remained elusive, here we postulated that genetic variations in RAS are associated with autism.

Methods

Considering the relation between the three polymorphisms of ACE (I/D, rs4343 and rs4291) with the level of ACE activity, we have investigated this association with autism, in a case-control study. Genotype and allele frequencies of polymorphisms were determined in DNAs extracted from venous blood of 120 autistic patients and their age and sex-matched healthy controls, using polymerase chain reaction (PCR) and PCR–restriction fragment length polymorphism (PCR–RFLP) methods.

Results

There were strong associations between both DD genotype of ACE I/D and the D allele, with autism (P = 0.006, OR = 2.9, 95% CI = 1.64–5.13 and P = 0.006, OR = 2.18, 95% CI = 1.37–3.48 respectively). Furthermore, a significant association between the G allele of rs4343 and autism was observed (P = 0.006, OR = 1.84, 95%CI = 1.26–2.67). Moreover, haplotype analysis revealed an association between DTG haplotype and autism (P = 0.008).

Conclusion

Our data suggests the involvement of RAS genetic diversity in increasing the risk of autism.

Effects of Blood Pressure Lowering With Different Antihypertensive Agents on Cognitive Function and Plasma Brain-derived Neurotrophic Factor Levels: A Comparative Study

PURPOSE

Hypertension is a risk factor for cognitive impairment (CI). However, the specific effect of antihypertensive therapy on cognitive function is still controversial. We aimed to investigate the effect of antihypertensive agents targeting the renin-angiotensin system (RAS) on CI and brain-derived neurotropic factor (BDNF).

METHODS

We included 62 patients who had been using the same antihypertensive agent for at least 3 months. Patients who had relevant conditions that could contribute to CI were excluded. After subjects were divided into 3 groups according to their current antihypertensive medication, the cognitive status of each patient was assessed by the mini-mental state examination (MMSE). BDNF and plasma renin activity were evaluated.

RESULTS

There was a negative association between systolic blood pressure and MMSE independent of medication (rho = -0.251, P = 0.049). There was no significant correlation between MMSE and BDNF. The MMSE score was slightly higher in the non-RAS group, but the difference did not reach statistical significance (P = 0.09). There was also no significant difference in BDNF levels between study groups (P = 0.32). Mean plasma renin activity levels were significantly lower in the non-RAS group compared with the angiotensin converting enzyme inhibitor and angiotensin receptor blocker groups (P = 0.007).

CONCLUSIONS

We suggest that the essential intervention for CI in hypertensive patients is appropriate for blood pressure control.

Binding to and Inhibition of Insulin-Regulated Aminopeptidase by Macrocyclic Disulfides Enhances Spine Density

Angiotensin IV (Ang IV) and related peptide analogs, as well as nonpeptide inhibitors of insulin-regulated aminopeptidase (IRAP), have previously been shown to enhance memory and cognition in animal models. Furthermore, the endogenous IRAP substrates oxytocin and vasopressin are known to facilitate learning and memory. In this study, the two recently synthesized 13-membered macrocyclic competitive IRAP inhibitors HA08 and HA09, which were designed to mimic the N terminus of oxytocin and vasopressin, were assessed and compared based on their ability to bind to the IRAP active site, and alter dendritic spine density in rat hippocampal primary cultures. The binding modes of the IRAP inhibitors HA08, HA09, and of Ang IV in either the extended or γ-turn conformation at the C terminus to human IRAP were predicted by docking and molecular dynamics simulations. The binding free energies calculated with the linear interaction energy method, which are in excellent agreement with experimental data and simulations, have been used to explain the differences in activities of the IRAP inhibitors, both of which are structurally very similar, but differ only with regard to one stereogenic center. In addition, we show that HA08, which is 100-fold more potent than the epimer HA09, can enhance dendritic spine number and alter morphology, a process associated with memory facilitation. Therefore, HA08, one of the most potent IRAP inhibitors known today, may serve as a suitable starting point for medicinal chemistry programs aided by MD simulations aimed at discovering more drug-like cognitive enhancers acting via augmenting synaptic plasticity.

Renin-angiotensin system-targeting antihypertensive drugs and risk of vascular cognitive impairment: A meta-analysis

OBJECTIVES

To evaluate the effects of renin-angiotensin system (RAS)-targeting antihypertensive drugs and its classes on the incidence of vascular cognitive impairment (VCI).

METHODS

Pubmed, Embase, and Cochrane Library database of selected articles, and previous systematic reviews through May 2015 were searched. Studies that evaluated the association between use of RAS-targeting drugs and VCI were included. Relative risks (RRs) with 95% confidence intervals (CIs) were pooled using fixed effects models or random effects models.

RESULTS

In all studies as a whole, the use of RAS-targeting drugs was significantly associated with a reduced risk of VCI (RR, 0.87; 95% CI, 0.75-0.98) and vascular dementia (VD) (RR, 0.78; 95% CI, 0.64-0.93), compared no use of RAS-targeting drugs. Subgroup analysis showed that subjects with Angiotensin-Converting Enzyme Inhibitors (ACEI) use significantly associated with a reduced incidence of VCI (RR, 0.81; 95% CI 0.70-0.91) and VD (RR, 0.75; 95% CI, 0.57-0.93); however, subjects with Angiotensin Receptor Blockers (ARB) use had not this effect on VCI (RR, 0.94; 95% CI 0.76-1.13) or VD (RR, 0.94; 95% CI, 0.45-1.44). In an analysis of subgroups, case-control studies found that the use of RAS-targeting drugs could effectively decrease the incidence of VCI (RR, 0.77; 95% CI 0.66-0.87) and VD (RR, 0.77; 95% CI, 0.66-0.88); however, the randomized trials alone showed no significant effect on the incidence of VCI (RR, 0.94; 95% CI 0.82-1.07) or VD (RR, 0.94; 95% CI, 0.35-1.53). Meanwhile, in an analysis of cognitive impairment of vascular origin (VaCI), no significant association was found between RAS-targeting drugs, ACEI, or ARB and the incidence of VaCI.

CONCLUSION

RAS-targeting drugs treatment may produce remarkable efficacy on reducing the incidence of VCI and VD. Meanwhile, ACEI use, rather than ARB use, significantly protects against VCI and VD incidence. However, among the classes of RAS-targeting drugs, neither ACEI nor ARB plays protective role in VaCI incidence. Further more RCTs are required to reliably establish whether RAS-targeting drugs use decreases the risk of VCI (VD and VaCI).

Long-Term Treatment with Losartan Attenuates Seizure Activity and Neuronal Damage Without Affecting Behavioral Changes in a Model of Co-morbid Hypertension and Epilepsy

Over the last 10 years, accumulated experimental and clinical evidence has supported the idea that AT1 receptor subtype is involved in epilepsy. Recently, we have shown that the selective AT1 receptor antagonist losartan attenuates epileptogenesis and exerts neuroprotection in the CA1 area of the hippocampus in epileptic Wistar rats. This study aimed to verify the efficacy of long-term treatment with losartan (10 mg/kg) after kainate-induced status epilepticus (SE) on seizure activity, behavioral and biochemical changes, and neuronal damage in a model of co-morbid hypertension and epilepsy. Spontaneous seizures were video- and EEG-monitored in spontaneously hypertensive rats (SHRs) for a 16-week period after SE. The behavior was analyzed by open field, elevated plus maze, sugar preference test, and forced swim test. The levels of serotonin in the hippocampus and neuronal loss were estimated by HPLC and hematoxylin and eosin staining, respectively. The AT1 receptor antagonism delayed the onset of seizures and alleviated their frequency and duration during and after discontinuation of treatment. Losartan showed neuroprotection mostly in the CA3 area of the hippocampus and the septo-temporal hilus of the dentate gyrus in SHRs. However, the AT1 receptor antagonist did not exert a substantial influence on concomitant with epilepsy behavioral changes and decreased 5-HT levels in the hippocampus. Our results suggest that the antihypertensive therapy with an AT1 receptor blocker might be effective against seizure activity and neuronal damage in a co-morbid hypertension and epilepsy.

Long-term intracerebroventricular infusion of angiotensin II after kainate-induced status epilepticus: Effects on epileptogenesis, brain damage, and diurnal behavioral changes

Our previous studies revealed that Angiotensin (Ang) II has anticonvulsant effects in acute seizure models. However, data on its role in experimental models of epilepsy are missing. In the present study, we tested whether posttreatment with Ang II after kainate (KA)-induced status epilepticus (SE) can affect epileptogenesis, concomitant behavioral changes, and brain damage. The Wistar rats were intracerebroventricularly infused via osmotic mini-pumps with Ang II (1.52μg/μl/day for 28days) after SE. Spontaneous motor seizures (SMS) were video-recorded for up to three months. Locomotor activity, anxiety, and depression-like behavior were evaluated during the last week of drug infusion, while spatial memory was assessed during the 3rd month after SE. Angiotensin II decreased the latency for onset of the first SMS and increased the frequency of SMS two months after SE. The continuous peptide infusion exacerbated the KA-induced hyperactivity and caused depression-like behavior. The reduced anxiety of KA-treated rats was alleviated by Ang II exposure. The KA-induced deficit in the hippocampal-dependent spatial memory was not influenced by Ang II. However, Ang II partially prevented the neuronal damage in the hippocampus, specifically in the CA1 area. The role of AT1 and AT2 receptor activation in the effects of the octapeptide is discussed.

International Union of Basic and Clinical Pharmacology. XCIX. Angiotensin Receptors: Interpreters of Pathophysiological Angiotensinergic Stimuli [corrected]

The renin angiotensin system (RAS) produced hormone peptides regulate many vital body functions. Dysfunctional signaling by receptors for RAS peptides leads to pathologic states. Nearly half of humanity today would likely benefit from modern drugs targeting these receptors. The receptors for RAS peptides consist of three G-protein-coupled receptors—the angiotensin II type 1 receptor (AT1 receptor), the angiotensin II type 2 receptor (AT2 receptor), the MAS receptor—and a type II trans-membrane zinc protein—the candidate angiotensin IV receptor (AngIV binding site). The prorenin receptor is a relatively new contender for consideration, but is not included here because the role of prorenin receptor as an independent endocrine mediator is presently unclear. The full spectrum of biologic characteristics of these receptors is still evolving, but there is evidence establishing unique roles of each receptor in cardiovascular, hemodynamic, neurologic, renal, and endothelial functions, as well as in cell proliferation, survival, matrix-cell interaction, and inflammation. Therapeutic agents targeted to these receptors are either in active use in clinical intervention of major common diseases or under evaluation for repurposing in many other disorders. Broad-spectrum influence these receptors produce in complex pathophysiological context in our body highlights their role as precise interpreters of distinctive angiotensinergic peptide cues. This review article summarizes findings published in the last 15 years on the structure, pharmacology, signaling, physiology, and disease states related to angiotensin receptors. We also discuss the challenges the pharmacologist presently faces in formally accepting newer members as established angiotensin receptors and emphasize necessary future developments.

Neuropeptides: metabolism to bioactive fragments and the pharmacology of their receptors

The proteolytic processing of neuropeptides has an important regulatory function and the peptide fragments resulting from the enzymatic degradation often exert essential physiological roles. The proteolytic processing generates, not only biologically inactive fragments, but also bioactive fragments that modulate or even counteract the response of their parent peptides. Frequently, these peptide fragments interact with receptors that are not recognized by the parent peptides. This review discusses tachykinins, opioid peptides, angiotensins, bradykinins, and neuropeptide Y that are present in the central nervous system and their processing to bioactive degradation products. These well-known neuropeptide systems have been selected since they provide illustrative examples that proteolytic degradation of parent peptides can lead to bioactive metabolites with different biological activities as compared to their parent peptides. For example, substance P, dynorphin A, angiotensin I and II, bradykinin, and neuropeptide Y are all degraded to bioactive fragments with pharmacological profiles that differ considerably from those of the parent peptides. The review discusses a selection of the large number of drug-like molecules that act as agonists or antagonists at receptors of neuropeptides. It focuses in particular on the efforts to identify selective drug-like agonists and antagonists mimicking the effects of the endogenous peptide fragments formed. As exemplified in this review, many common neuropeptides are degraded to a variety of smaller fragments but many of the fragments generated have not yet been examined in detail with regard to their potential biological activities. Since these bioactive fragments contain a small number of amino acid residues, they provide an ideal starting point for the development of drug-like substances with ability to mimic the effects of the degradation products. Thus, these substances could provide a rich source of new pharmaceuticals. However, as discussed herein relatively few examples have so far been disclosed of successful attempts to create bioavailable, drug-like agonists or antagonists, starting from the structure of endogenous peptide fragments and applying procedures relying on stepwise manipulations and simplifications of the peptide structures.

Regulation of nonclassical renin-angiotensin system receptor gene expression in the adrenal medulla by acute and repeated immobilization stress

The involvement of the nonclassical renin-angiotensin system (RAS) in the adrenomedullary response to stress is unclear. Therefore, we examined basal and immobilization stress (IMO)-triggered changes in gene expression of the classical and nonclassical RAS receptors in the rat adrenal medulla, specifically the angiotensin II type 2 (AT2) and type 4 (AT4) receptors, (pro)renin receptor [(P)RR], and Mas receptor (MasR). All RAS receptors were identified, with AT2 receptor mRNA levels being the most abundant, followed by the (P)RR, AT1A receptor, AT4 receptor, and MasR. Following a single IMO, AT2 and AT4 receptor mRNA levels decreased by 90 and 50%, respectively. Their mRNA levels were also transiently decreased by repeated IMO. MasR mRNA levels displayed a 75% transient decrease as well. Conversely, (P)RR mRNA levels were increased by 50% following single or repeated IMO. Because of its abundance, the function of the (P)RR was explored in PC-12 cells. Prorenin activation of the (P)RR increased phosphorylation of extracellular signal-regulated kinase 1/2 and tyrosine hydroxylase at Ser31, likely increasing its enzymatic activity and catecholamine biosynthesis. Together, the broad and dynamic changes in gene expression of the nonclassical RAS receptors implicate their role in the intricate response of the adrenomedullary catecholaminergic system to stress.

The development of small molecule angiotensin IV analogs to treat Alzheimer's and Parkinson's diseases

Alzheimer's (AD) and Parkinson's (PD) diseases are neurodegenerative diseases presently without effective drug treatments. AD is characterized by general cognitive impairment, difficulties with memory consolidation and retrieval, and with advanced stages episodes of agitation and anger. AD is increasing in frequency as life expectancy increases. Present FDA approved medications do little to slow disease progression and none address the underlying progressive loss of synaptic connections and neurons. New drug design approaches are needed beyond cholinesterase inhibitors and N-methyl-d-aspartate receptor antagonists. Patients with PD experience the symptomatic triad of bradykinesis, tremor-at-rest, and rigidity with the possibility of additional non-motor symptoms including sleep disturbances, depression, dementia, and autonomic nervous system failure. This review summarizes available information regarding the role of the brain renin-angiotensin system (RAS) in learning and memory and motor functions, with particular emphasis on research results suggesting a link between angiotensin IV (AngIV) interacting with the AT4 receptor subtype. Currently there is controversy over the identity of this AT4 receptor protein. Albiston and colleagues have offered convincing evidence that it is the insulin-regulated aminopeptidase (IRAP). Recently members of our laboratory have presented evidence that the brain AngIV/AT4 receptor system coincides with the brain hepatocyte growth factor/c-Met receptor system. In an effort to resolve this issue we have synthesized a number of small molecule AngIV-based compounds that are metabolically stable, penetrate the blood-brain barrier, and facilitate compromised memory and motor systems. These research efforts are described along with details concerning a recently synthesized molecule, Dihexa that shows promise in overcoming memory and motor dysfunctions by augmenting synaptic connectivity via the formation of new functional synapses.

Memory beyond expression

The idea that memories are not invariable after the consolidation process has led to new perspectives about several mnemonic processes. In this framework, we review our studies on the modulation of memory expression during reconsolidation. We propose that during both memory consolidation and reconsolidation, neuromodulators can determine the probability of the memory trace to guide behavior, i.e. they can either increase or decrease its behavioral expressibility without affecting the potential of persistent memories to be activated and become labile. Our hypothesis is based on the findings that positive modulation of memory expression during reconsolidation occurs even if memories are behaviorally unexpressed. This review discusses the original approach taken in the studies of the crab Neohelice (Chasmagnathus) granulata, which was then successfully applied to test the hypothesis in rodent fear memory. Data presented offers a new way of thinking about both weak trainings and experimental amnesia: memory retrieval can be dissociated from memory expression. Furthermore, the strategy presented here allowed us to show in human declarative memory that the periods in which long-term memory can be activated and become labile during reconsolidation exceeds the periods in which that memory is expressed, providing direct evidence that conscious access to memory is not needed for reconsolidation. Specific controls based on the constraints of reminders to trigger reconsolidation allow us to distinguish between obliterated and unexpressed but activated long-term memories after amnesic treatments, weak trainings and forgetting. In the hypothesis discussed, memory expressibility--the outcome of experience-dependent changes in the potential to behave--is considered as a flexible and modulable attribute of long-term memories. Expression seems to be just one of the possible fates of re-activated memories.

Construction of a yeast-based signaling biosensor for human angiotensin II type 1 receptor via functional coupling between Asn295-mutated receptor and Gpa1/Gi3 chimeric Gα

Angiotensin II (Ang II) type 1 receptor (AGTR1) is a G-protein-coupled receptor (GPCR). Its natural ligand, Ang II, is an important effector molecule controlling blood pressure and volume in the cardiovascular system, and is consequently involved in various diseases such as hypertension and heart failure. Thus, the signaling mediator, AGTR1, is a significant molecular target in medicinal and therapeutic fields. Yeast is a useful organism for sensing GPCR signaling because it provides a simplified version of the complicated machinery used by mammalian cells for signal transduction. Although yeast cells can successfully transmit a signal through a variety of human GPCRs expressed in the cell membrane, there have been no reports of the functional activation of AGTR1-mediated signaling in yeast cells. In the present study, we introduced a single mutation into human AGTR1 and used yeast-human chimeric Gα to exert the functional activation of AGTR1 in yeast cells. The engineered yeast cells expressing AGTR1 mutated at Asn295 and the chimeric Gα successfully transmitted the signal inside the yeast cells in response to Ang II peptide and its analogs (Ang III and Ang IV peptides) added to the assay medium. Further, we demonstrated that the autocrine Ang II peptide and its analog, produced and secreted by the engineered yeast cells, could by themselves promote AGTR1-mediated signaling. This means that screening for agonistic peptides with various sequences from a self-produced genetic library would be a viable strategy. Thus, the constructed yeast biosensor, integrating an Asn295-mutated AGTR1 receptor, will be valuable in the design of drugs to treat AGTR1-related diseases.

Telmisartan protects central neurons against nutrient deprivation-induced apoptosis in vitro through activation of PPARγ and the Akt/GSK-3β pathway

AIM

To determine whether angiotensin II receptor blockers (ARBs) could protect central neurons against nutrient deprivation-induced apoptosis in vitro and to elucidate the underlying mechanisms.

METHODS

Primary rat cerebellar granule cells (CGCs) underwent B27 (a serum substitute) deprivation for 24 h to induce neurotoxicity, and cell viability was analyzed using LDH assay and WST-1 assay. DNA laddering assay and TUNEL assay were used to detect cell apoptosis. The expression of caspase-3 and Bcl-2, and the phosphorylation of Akt and GSK-3β were detected using Western blot analysis. AT1a mRNA expression was determined using RT-PCR analysis.

RESULTS

B27 deprivation significantly increased the apoptosis of CGCs, as demonstrated by LDH release, DNA laddering, caspase-3 activation and positive TUNEL staining. Pretreatment with 10 μmol/L ARBs (telmisartan, candesartan or losartan) partially blocked B27 deprivation-induced apoptosis of CGCs with telmisartan being the most effective one. B27 deprivation markedly increased the expression of AT1a receptor in CGCs, inhibited Akt and GSK-3β activation, decreased Bcl-2 level, and activated caspase-3, which were reversed by pretreatment with 1 μmol/L telmisartan. In addition, pretreatment with 10 μmol/L PPARγ agonist pioglitazone was more effective in protecting CGCs against B27 deprivation-induced apoptosis, whereas pretreatment with 20 μmol/L PPARγ antagonist GW9662 abolished all the effects of telmisartan in CGCs deprived of B27.

CONCLUSION

ARBs, in particular telmisartan, can protect the nutrient deprivation-induced apoptosis of CGCs in vitro through activation of PPARγ and the Akt/GSK-3β pathway.

Comparative study of the effects of free bound and carrier protein angiotensin II in experimental hypoglycemia and hyperglycemia

Experimental hypoglycemia and hyperglycemia eliminated the differences in the regulatory functions of free angiotensin II and its complexes with carrier proteins (transport protein BSA and neurospecific protein S100b) in rats. Under these conditions, free and protein-bound angiotensin II primarily suppressed operant drinking behavior and reduced the hypertensive and tachyarrhythmic effects in comparison with control rats. These changes were most pronounced during acute hyperglycemia. We hypothesized that complexes of angiotensin II with functionally different proteins are differentially and simultaneously involved in not only compensation of behavioral and hemodynamic disturbances during acute and/or chronic hypoglycemia and hyperglycemia, but also their transformation into pathological processes mediated by the so-called metabolic memory mechanisms.

Effects of angiotensin (5-8) microinfusions into the ventrolateral periaqueductal gray on defensive behaviors in rats

Peptides of the renin-angiotensin system modulate blood pressure and hydro-electrolyte composition. Angiotensin (Ang) receptors are localized in brain areas related to the regulation of autonomic and endocrine control and involved in sensory perception, memory process and behavioral responses. Among these areas, the ventrolateral periaqueductal gray (vlPAG) is one of the most important structures of the neuronal circuitry controlling the autonomic and behavioral components of emotional states. Although Ang II metabolism in the vlPAG forms several Ang-peptides including Ang (5-8), the role of this tetrapeptide in the organization of defensive responses has not yet been described. To address this issue, the purpose of the present study was to determine the effects of intra-vlPAG injections of Ang (5-8) (0.2, 0.4 and 0.8 nmol/0.25 μL) in rats submitted to the elevated plus-maze (EPM) test. Additionally, it was evaluated the effects of intra-vlPAG Ang (5-8) on the expression of conditioned fear, assessed by the fear-potentiated startle and contextual conditioned freezing tests. The results showed that Ang (5-8) produced an intense, dose-related reduction in the entries into and time spent in the open arms of the EPM, decreased direct exploration and increased risk assessment behaviors. Moreover, intra-vlPAG injections of Ang (5-8) before the test session promoted pro-aversive effects in the FPS and enhanced contextual freezing. Taken together, these results point out to an important anxiogenic-like action for Ang (5-8) in the mediation of defensive behaviors organized in the vlPAG.

Plasma renin-angiotensin system-regulating aminopeptidase activities are modified in early stage Alzheimer's disease and show gender differences but are not related to apolipoprotein E genotype

Alterations in blood pressure and components of the renin-angiotensin system (RAS) contribute to the development and progression of Alzheimer's disease (AD), resulting in changes that can lead or contribute to cognitive decline. Aspartyl aminopeptidase (ASAP), aminopeptidase A (APA), aminopeptidase N (APN) and aminopeptidase B (APB) catabolise circulating angiotensins, whereas insulin-regulated aminopeptidase (IRAP) has been described as the AT4 receptor. We have found in AD patients a significant decrease of APA activity in men but not in women, and of APN, APB and IRAP in both genders, when compared with control subjects. No changes were found in ASAP activity. Also, APN, APB and IRAP but not APA correlated with the Mini-Mental test, but no relationship with APOE genotype was found. We conclude that several components of the RAS are modified in AD patients, with gender differences. Furthermore, ROC analysis indicates that APN, APB and IRAP activities could be useful non-invasive biomarkers of AD from the earliest stages.

Combined treatment with gabapentin and drugs affecting the renin-angiotensin system against electroconvulsions in mice

Recent experimental data suggest that certain angiotensin-converting enzyme (ACE) inhibitors and angiotensin AT1 receptor antagonists may possess anticonvulsant activity. The purpose of this study was to examine the effects of two ACE inhibitors, captopril and enalapril, and two AT1 receptor antagonists, losartan and telmisartan, on the protective action of gabapentin in the maximal electroshock seizure threshold test in mice. Additionally, the effects of the combined treatment with gabapentin and antihypertensive drugs on memory retention in the passive avoidance task and motor coordination in the chimney test were assessed. All drugs were injected intraperitoneally. Losartan (50mg/kg) significantly increased the convulsive threshold for gabapentin. The other antihypertensive drugs, captopril (50mg/kg), enalapril (30 mg/kg) and telmisartan (30 mg/kg), did not affect the anticonvulsant activity of gabapentin. The observed interaction between gabapentin and losartan could be pharmacokinetic in nature. Losartan increased plasma and total brain concentrations of gabapentin. In the chimney test, losartan (50mg/kg) administered with gabapentin (50mg/kg) caused motor impairment. In the passive avoidance test, memory retention was not affected by the combined treatment with gabapentin and antihypertensive drugs. It is suggested that the use of captopril, enalapril and telmisartan in epileptic patients receiving gabapentin is presumed neutral upon its anticonvulsant action. The utmost caution is advised when combining losartan and gabapentin in clinical practice due to the appearance of pharmacokinetic interactions between losartan and gabapentin as well as motor impairment evoked by these drugs in mice.

The role of the angiotensin AT2 receptor on the diurnal variations of nociception and motor coordination in rats

Phasic pain demonstrates significant diurnal variation in rats. Angiotensin II modulates pain transmission and the diurnal variation in nociception in several rodent pain models. The participation of AT2 receptors in the diurnal regulation of nociception is not yet elucidated. In the present study we investigated the effects of selective peptide AT2 agonist CGP 42112A and the nonpeptide AT2 receptor antagonist PD 123319 on the nociception, motor coordination and arterial blood pressure. Male Wistar 12 weeks old rats were used. CGP 42112A was injected at single doses of 1 and 5 μg/rat intracerebroventricularly (ICV) and infused chronically ICV at a dose of 12 μg/rat/day during 14 days by osmotic minipumps. PD123319 was injected at single doses of 1 and 5 μg/rat, ICV and chronically subcutaneously at a dose of 10 mg/kg/day/14 days. Nociception was assessed by an analgesimeter, arterial blood pressure (ABP) was measured by tail cuff method, and motor coordination by Rota-rod method. Single doses of CGP 42112A (1 and 5 μg/rat) provoked a short lasting antinociception. Unlike acute injection, chronic CGP 42112A infusion increased nociception at the beginning and the end of light phase thus attenuating the diurnal variations observed in the controls. Moreover, it produced an increase of ABP and improved motor coordination. Both acute (1 μg/rat) and chronic PD 123319 treatment resulted in a decrease of pain threshold and chronic treatment attenuated its diurnal fluctuation. Our data support a role for Ang II type 2 receptors in the control of diurnal variations of nociception in rats.