Angiotensin-(1-7) inhibits autophagy in the brain of spontaneously hypertensive rats

Resolution of inflammation, an active process to restore the immune microenvironment balance: A novel drug target for treating arterial hypertension

The resolution of inflammation, the other side of the inflammatory response, is defined as an active and highly coordinated process that promotes the restoration of immune microenvironment balance and tissue repair. Inflammation resolution involves several key processes, including dampening proinflammatory signaling, specialized proresolving lipid mediator (SPM) production, nonlipid proresolving mediator production, efferocytosis and regulatory T-cell (Treg) induction. In recent years, increasing attention has been given to the effects of inflammation resolution on hypertension. Furthermore, our previous studies reported the antihypertensive effects of SPMs. Therefore, in this review, we aim to summarize and discuss the detailed association between arterial hypertension and inflammation resolution. Additional, the association between gut microbe-mediated immune and hypertension is discussed. This findings suggested that accelerating the resolution of inflammation can have beneficial effects on hypertension and its related organ damage. Exploring novel drug targets by focusing on various pathways involved in accelerating inflammation resolution will contribute to the treatment and control of hypertensive diseases in the future.

The role of captopril in leukotriene deficient type 1 diabetic mice

T1D can be associated with metabolic disorders and several impaired pathways, including insulin signaling, and development of insulin resistance through the renin-angiotensin system (RAS). The main precursor of RAS is angiotensinogen (Agt) and this system is often linked to autophagy dysregulation. Dysregulated autophagy has been described in T1D and linked to impairments in both glucose metabolism, and leukotrienes (LTs) production. Here, we have investigated the role of RAS and LTs in both muscle and liver from T1D mice, and its effects on insulin and autophagy pathways. We have chemically induced T1D in 129sve and 129sve 5LO-/- mice (lacking LTs) with streptozotocin (STZ). To further inhibit ACE activity, mice were treated with captopril (Cap). In muscle of T1D mice, treatment with Cap increased the expression of RAS (angiotensinogen and angiotensin II receptor), insulin signaling, and autophagy markers, regardless of the genotype. In the liver of T1D mice, the treatment with Cap increased the expression of RAS and insulin signaling markers, mostly when LTs were absent. 5LO-/- T1D mice showed increased insulin sensitivity, and decreased NEFA, after the Cap treatment. Cap treatment impacted both insulin signaling and autophagy pathways at the mRNA levels in muscle and liver, indicating the potential role of ACE inhibition on insulin sensitivity and autophagy in T1D.

AVE 0991 Suppresses Astrocyte-Mediated Neuroinflammation of Alzheimer's Disease by Enhancing Autophagy

Purpose

Our previous study has shown that AVE 0991, a nonpeptide analogue of Ang-(1-7), ameliorates cognitive decline and inhibits NLRP3 inflammasome of astrocytes in Alzheimer's disease model mice. Additionally, several studies have suggested that activation of autophagy appears to effectively inhibit the progression of neuroinflammation. However, it is unclear whether AVE 0991 can modulate astrocyte autophagy to suppress neuroinflammation in Alzheimer's disease.

Materials and Methods

APP/PS1 mice and Aβ-treated primary astrocytes were used as the research objects in vivo and in vitro, respectively. Water maze test was used to evaluate cognitive function of mice, Nissl staining and immunofluorescence staining was used to assess neuronal damage. ELISA kits were used to detect the levels of Ang-(1-7) and Aβ in the cortex, and qRT-PCR was used to detect the expression of cortical inflammation-related mediators. The expression of autophagy-related proteins in cortex were detected by Western blot. The upstream molecular responses involved in inflammation inhibition by AVE 0991 were validated by means of using the Mas1 antagonist and autophagy inhibitor.

Results

We found that 30 days of intraperitoneal administration of AVE 0991 improved. Aβ deposition, neuronal death, and cognitive deficits in APP/PS1 Alzheimer's disease model mice. Moreover, AVE 0991 treatment greatly suppressed astrocyte-mediated inflammation and up-regulated the expression of autophagy. Furthermore, the inhibitory effect of AVE 0991 on the expression of inflammatory factors was reversed by 3-MA, an autophagy inhibitor.

Conclusion

These findings suggest that regulation of autophagy is critical for inhibiting astrocyte neuroinflammatory responses and demonstrate a potential neuroprotective mechanism by which AVE 0991 could suppress neuroinflammatory responses by enhancing autophagy.

Involvement of shedding induced by ADAM17 on the nitric oxide pathway in hypertension

A Disintegrin and Metalloprotease 17 (ADAM17), also called tumor necrosis factor-ɑ (TNF-ɑ) convertase (TACE), is a well-known protease involved in the sheddase of growth factors, chemokines and cytokines. ADAM17 is also enrolled in hypertension, especially by shedding of angiotensin converting enzyme type 2 (ACE2) leading to impairment of angiotensin 1–7 [Ang-(1–7)] production and injury in vasodilation, induction of renal damage and cardiac hypertrophy. Activation of Mas receptor (MasR) by binding of Ang-(1–7) induces an increase in the nitric oxide (NO) gaseous molecule, which is an essential factor of vascular homeostasis and blood pressure control. On the other hand, TNF-ɑ has demonstrated to stimulate a decrease in nitric oxide bioavailability, triggering a disrupt in endothelium-dependent vasorelaxation. In spite of the previous studies, little knowledge is available about the involvement of the metalloprotease 17 and the NO pathways. Here we will provide an overview of the role of ADAM17 and Its mechanisms implicated with the NO formation.

The effects of glutamine supplementation on markers of apoptosis and autophagy in sickle cell disease peripheral blood mononuclear cells

OBJECTIVES

L-Glutamine was FDA-approved for sickle cell disease (SCD) in 2017, yet the mechanism(s)-of-action are poorly understood. This study investigates the potential activation of autophagy as a previously unexplored mechanism-of-benefit.

DESIGN

Prospective, open-label, 8-week, phase-2 trial of oral L-glutamine (10 g TID) in patients with SCD at risk for pulmonary hypertension identified by Doppler-echocardiography by an elevated tricuspid-regurgitant-jet-velocity (TRV)≥ 2.5 m/s. Peripheral blood mononuclear cells (PBMCs) were isolated from blood samples taken from SCD patients at baseline, two, four, six and eight weeks of glutamine therapy, and from controls at baseline; BAX (pro-apoptotic marker) and LC3-II/LC3-I (autophagy marker) were measured via western blot analysis to assess apoptosis and autophagy respectively.

SETTING

Comprehensive SCD Center in Oakland, California.

RESULTS

Patients with SCD (n = 8) had a mean age of 44 ± 16, 50% were male; 63% Hb-SS, and mean TRV= 3.1 ± 0.7 m/s. Controls' mean age (n = 5) was 32 ± 12% and 57% were male; all were Hb-AA with a mean TRV= 1.8 ± 0.6. At baseline, SCD-PBMCs had 2-times higher levels of BAX and LC3-I versus controls (both p = 0.03). Levels of BAX expression increased by 300% after 8-weeks of glutamine supplementation (p = 0.005); LC3-I protein levels decreased while LC3-II levels increased by 70%, giving a significant increase in the LC3-II/LC3-I ratio (p = 0.02).

CONCLUSION

PBMCs from glutamine-supplemented SCD patients have upregulated apoptotic and autophagy proteins. The parallel increase in BAX and the LC3-II / LC3-I ratio with glutamine supplementation suggest a possible role of autophagic cell death. The increase in apoptotic markers provide insight into a possible mechanism used by peripheral PBMCs during glutamine supplementation in patients with SCD.

SARS-CoV-2 interacts with renin-angiotensin system: impact on the central nervous system in elderly patients

SARS-CoV-2 is a recently identified coronavirus that causes the current pandemic disease known as COVID-19. SARS-CoV-2 uses angiotensin-converting enzyme 2 (ACE2) as a receptor, suggesting that the initial steps of SARS-CoV-2 infection may have an impact on the renin-angiotensin system (RAS). Several processes are influenced by RAS in the brain. The neurological symptoms observed in COVID-19 patients, including reduced olfaction, meningitis, ischemic stroke, cerebral thrombosis, and delirium, could be associated with RAS imbalance. In this review, we focus on the potential role of disturbances in the RAS as a cause for central nervous system sequelae of SARS-CoV-2 infection in elderly patients.

Update on Angiotensin II Subtype 2 Receptor: Focus on Peptide and Nonpeptide Agonists

Angiotensin II (Ang II) is the most dominant effector component of the renin-angiotensin system (RAS) that generally acts through binding to two main classes of G protein-coupled receptors, namely Ang II subtype 1 receptor (AT1R) and angiotensin II subtype 2 receptor (AT2R). Despite some controversial reports, the activation of AT2R generally antagonizes the effects of Ang II binding on AT1R. Studying AT2R signaling, function, and its specific ligands in cell culture or animal studies has confirmed its beneficial effects throughout the body. These characteristics classify AT2R as part of the protective arm of the RAS that, along with functions of Ang (1-7) through Mas receptor signaling, modulates the harmful effects of Ang II on AT1R in the activated classic arm of the RAS. Although Ang II is the primary ligand for AT2R, we have summarized other natural or synthetic peptide and nonpeptide agonists with critical evaluation of their structure, mechanism of action, and biologic activity. SIGNIFICANCE STATEMENT: AT2R is one of the main components of the RAS and has a significant prospective for mediating the beneficial action of the RAS through its protective arm on the body's homeostasis. Targeting AT2R offers substantial clinical application possibilities for modulating various pathological conditions. This review provided concise information regarding the AT2R peptide and nonpeptide agonists and their potential clinical applications for various diseases.

ACE2/Ang-(1-7)/Mas1 axis and the vascular system: vasoprotection to COVID-19-associated vascular disease

The two axes of the renin-angiotensin system include the classical ACE/Ang II/AT1 axis and the counter-regulatory ACE2/Ang-(1-7)/Mas1 axis. ACE2 is a multifunctional monocarboxypeptidase responsible for generating Ang-(1-7) from Ang II. ACE2 is important in the vascular system where it is found in arterial and venous endothelial cells and arterial smooth muscle cells in many vascular beds. Among the best characterized functions of ACE2 is its role in regulating vascular tone. ACE2 through its effector peptide Ang-(1-7) and receptor Mas1 induces vasodilation and attenuates Ang II-induced vasoconstriction. In endothelial cells activation of the ACE2/Ang-(1-7)/Mas1 axis increases production of the vasodilator's nitric oxide and prostacyclin's and in vascular smooth muscle cells it inhibits pro-contractile and pro-inflammatory signaling. Endothelial ACE2 is cleaved by proteases, shed into the circulation and measured as soluble ACE2. Plasma ACE2 activity is increased in cardiovascular disease and may have prognostic significance in disease severity. In addition to its enzymatic function, ACE2 is the receptor for severe acute respiratory syndrome (SARS)-coronavirus (CoV) and SARS-Cov-2, which cause SARS and coronavirus disease-19 (COVID-19) respectively. ACE-2 is thus a double-edged sword: it promotes cardiovascular health while also facilitating the devastations caused by coronaviruses. COVID-19 is associated with cardiovascular disease as a risk factor and as a complication. Mechanisms linking COVID-19 and cardiovascular disease are unclear, but vascular ACE2 may be important. This review focuses on the vascular biology and (patho)physiology of ACE2 in cardiovascular health and disease and briefly discusses the role of vascular ACE2 as a potential mediator of vascular injury in COVID-19.

Angiotensin-(1-7) Prevents Lipopolysaccharide-Induced Autophagy via the Mas Receptor in Skeletal Muscle

Skeletal muscle atrophy, which occurs in lipopolysaccharide (LPS)-induced sepsis, causes a severe muscle function reduction. The increased autophagy contributes to sepsis-induced skeletal muscle atrophy in a model of LPS injection, increasing LC3II/LC3I ratio, autophagy flux, and autophagosomes. Angiotensin-(1-7) (Ang-(1-7)) has anti-atrophic effects via the Mas receptor in skeletal muscle. However, the impact of Ang-(1-7) on LPS-induced autophagy is unknown. In this study, we determined the effect of Ang-(1-7) on sepsis-induced muscle autophagy. C57BL6 wild-type (WT) mice and mice lacking the Mas receptor (KO Mas) were injected with LPS together with the systemic administration of Ang-(1-7) to determine autophagy in skeletal muscle. We also evaluated autophagy and p38 and c-Jun N-terminal kinase (JNK)activation. Our results show that Ang-(1-7) prevents LPS-induced autophagy in the diaphragm, tibialis anterior, and gastrocnemius of WT mice, which is demonstrated by a decrease in the LC3II/LC3I ratio and mRNA levels of lc3b and ctsl. This effect was lost in KO Mas mice, suggesting the role of the Mas receptor. The results in C2C12 cells show that Ang-(1-7) reduces several LPS-dependent effects, such as autophagy (LC3II/LC3I ratio, autophagic flux, and autophagosomes), activation of p38 and JNK, B-cell lymphoma-2 (BCL2) phosphorylation, and disassembly of the Beclin1/BCL2 complex. In conclusion, Ang-(1-7)/Mas receptor reduces LPS-induced autophagy in skeletal muscle. In vitro assays indicate that Ang-(1-7) prevents LPS-induced autophagy and modifies the MAPK signaling and the disassembly of a complex involved at the beginning of autophagy.

Autophagy in white matter disorders of the CNS: mechanisms and therapeutic opportunities

Autophagy is a constitutive process that degrades, recycles and clears damaged proteins or organelles, yet, despite activation of this pathway, abnormal proteins accumulate in neurons in neurodegenerative diseases and in oligodendrocytes in white matter disorders. Here, we discuss the role of autophagy in white matter disorders, including neurotropic infections, inflammatory diseases such as multiple sclerosis, and in hereditary metabolic disorders and acquired toxic‐metabolic disorders. Once triggered due to cell stress, autophagy can enhance cell survival or cell death that may contribute to oligodendrocyte damage and myelin loss in white matter diseases. For some disorders, the mechanisms leading to myelin loss are clear, whereas the aetiological agent and pathological mechanisms are unknown for other myelin disorders, although emerging studies indicate that a common mechanism underlying these disorders is dysregulation of autophagic pathways. In this review we discuss the alterations in the autophagic process in white matter disorders and the potential use of autophagy‐modulating agents as therapeutic approaches in these pathological conditions. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

How Does SARS-CoV-2 Affect the Central Nervous System? A Working Hypothesis

Interstitial pneumonia was the first manifestation to be recognized as caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); however, in just a few weeks, it became clear that the coronavirus disease-2019 (COVID-19) overrun tissues and more body organs than just the lungs, so much so that it could be considered a systemic pathology. Several studies reported the involvement of the conjunctiva, the gut, the heart and its pace, and vascular injuries such as thromboembolic complications and Kawasaki disease in children and toddlers were also described. More recently, it was reported that in a sample of 214 SARS-CoV-2 positive patients, 36.4% complained of neurological symptoms ranging from non-specific manifestations (dizziness, headache, and seizures), to more specific symptoms such hyposmia or hypogeusia, and stroke. Older individuals, especially males with comorbidities, appear to be at the highest risk of developing such severe complications related to the Central Nervous System (CNS) involvement. Neuropsychiatric manifestations in COVID-19 appear to develop in patients with and without pre-existing neurological disorders. Growing evidence suggests that SARS-CoV-2 binds to the human Angiotensin-Converting Enzyme 2 (ACE2) for the attachment and entrance inside host cells. By describing ACE2 and the whole Renin Angiotensin Aldosterone System (RAAS) we may better understand whether specific cell types may be affected by SARS-CoV-2 and whether their functioning can be disrupted in case of an infection. Since clear evidences of neurological interest have already been shown, by clarifying the topographical distribution and density of ACE2, we will be able to speculate how SARS-CoV-2 may affect the CNS and what is the pathogenetic mechanism by which it contributes to the specific clinical manifestations of the disease. Based on such evidences, we finally hypothesize the process of SARS-CoV-2 invasion of the CNS and provide a possible explanation for the onset or the exacerbation of some common neuropsychiatric disorders in the elderly including cognitive impairment and Alzheimer disease.

Autophagy in metabolic syndrome: breaking the wheel by targeting the renin-angiotensin system

Metabolic syndrome (MetS) is a complex, emerging epidemic which disrupts the metabolic homeostasis of several organs, including liver, heart, pancreas, and adipose tissue. While studies have been conducted in these research areas, the pathogenesis and mechanisms of MetS remain debatable. Lines of evidence show that physiological systems, such as the renin-angiotensin system (RAS) and autophagy play vital regulatory roles in MetS. RAS is a pivotal system known for controlling blood pressure and fluid balance, whereas autophagy is involved in the degradation and recycling of cellular components, including proteins. Although RAS is activated in MetS, the interrelationship between RAS and autophagy varies in glucose homeostatic organs and their cross talk is poorly understood. Interestingly, autophagy is attenuated in the liver during MetS, whereas autophagic activity is induced in adipose tissue during MetS, indicating tissue-specific discordant roles. We discuss in vivo and in vitro studies conducted in metabolic tissues and dissect their tissue-specific effects. Moreover, our review will focus on the molecular mechanisms by which autophagy orchestrates MetS and the ways future treatments could target RAS in order to achieve metabolic homeostasis.

Berberine mitigates cognitive decline in an Alzheimer's Disease Mouse Model by targeting both tau hyperphosphorylation and autophagic clearance

Berberine is a natural isoquinoline alkaloid isolated from the Rhizoma coptidis. Recent advances in research throw more lights of its beneficial role towards Alzheimer's disease (AD), including promoting β-amyloid (Aβ) clearance, as well as inhibiting Aβ production in the triple-transgenic mouse model of Alzheimer's disease (3×Tg AD). However, it remains unclarified if berberine has an effect on tau pathology. According to our study, berberine did not only significantly improve 3×Tg AD mice's spatial learning capacity and memory retentions, but also attenuated the hyperphosphorylation of tau. via modulating the activity of Akt/glycogen synthase kinase-3β and protein phosphatase 2A. Moreover, berberine reduced the level of tau through an autophagy-based route. It promoted autophagic clearance of tau by enhancing the activity of autophagy via the class III PI3K/beclin-1 pathway. Thus, our results suggest that berberine could mitigate cognitive decline by simultaneously targeting the hyperphosphorylation of tau and the autophagic clearance of tau in AD mice. These findings strongly support berberine as a potential drug candidate for AD.

AVE0991, a nonpeptide analogue of Ang-(1-7), attenuates aging-related neuroinflammation

During the aging process, chronic neuroinflammation induced by microglia is detrimental for the brain and contributes to the etiology of several aging-related neurodegenerative diseases such as Alzheimer’s disease and Parkinson’s disease. As a newly identified axis of renin-angiotensin system, ACE2/Ang-(1-7)/MAS1 axis plays a crucial role in modulating inflammatory responses under various pathological conditions. However, its relationship with aging-related neuroinflammation is less studied so far. In this study, by using SAMP8 mice, an animal model of accelerated aging, we revealed that the neuroinflammation in the aged brain might be attributed to a decreased level of Ang-(1-7). More importantly, we provided evidence that AVE0991, a nonpeptide analogue of Ang-(1-7), attenuated the aging-related neuroinflammation via suppression of microglial-mediated inflammatory response through a MAS1 receptor-dependent manner. Meanwhile, this protective effect might be ascribed to the M2 activation of microglia induced by AVE0991. Taken together, these findings reveal the association of Ang-(1-7) with the inflammatory response in the aged brain and uncover the potential of its nonpeptide analogue AVE0991 in attenuation of aging-related neuroinflammation.

Angiotensin-(1-7) exerts a protective action in a rat model of ventilator-induced diaphragmatic dysfunction

Background

Ventilator-induced diaphragmatic dysfunction (VIDD) is a common event during mechanical ventilation (MV) leading to rapid muscular atrophy and contractile dysfunction. Recent data show that renin-angiotensin system is involved in diaphragmatic skeletal muscle atrophy after MV. In particular, angiotensin-II can induce marked diaphragm muscle wasting, whereas angiotensin-(1–7) (Ang-(1–7)) could counteract this activity. This study was designed to evaluate the effects of the treatment with Ang-(1–7) in a rat model of VIDD with neuromuscular blocking agent infusion. Moreover, we studied whether the administration of A-779, an antagonist of Ang-(1–7) receptor (Mas), alone or in combination with PD123319, an antagonist of AT2 receptor, could antagonize the effects of Ang-(1–7).

Methods

Sprague-Dawley rats underwent prolonged MV (8 h), while receiving an iv infusion of sterile saline 0.9% (vehicle) or Ang-(1–7) or Ang-(1–7) + A-779 or Ang-(1–7) + A-779 + PD123319. Diaphragms were collected for ex vivo contractility measurement (with electric stimulation), histological analysis, quantitative real-time PCR, and Western blot analysis.

Results

MV resulted in a significant reduction of diaphragmatic contractility in all groups of treatment. Ang-(1–7)-treated rats showed higher muscular fibers cross-sectional area and lower atrogin-1 and myogenin mRNA levels, compared to vehicle treatment. Treatment with the antagonists of Mas and Ang-II receptor 2 (AT2R) caused a significant reduction of muscular contractility and an increase of atrogin-1 and MuRF-1 mRNA levels, not affecting the cross-sectional fiber area and myogenin mRNA levels.

Conclusions

Systemic Ang-(1–7) administration during MV exerts a protective role on the muscular fibers of the diaphragm preserving muscular fibers anatomy, and reducing atrophy. The involvement of Mas and AT2R in the mechanism of action of Ang-(1–7) still remains controversial.

Pre-treatment with angiotensin-(1-7) inhibits tumor growth via autophagy by downregulating PI3K/Akt/mTOR signaling in human nasopharyngeal carcinoma xenografts

Abstract

The highest incidence of nasopharyngeal carcinoma (NPC) is in southeast China, including Taiwan. Many side effects have been observed following radiation therapy with chemotherapy; hence, exploring new treatment modalities for NPC is an important future direction. Angiotensin-(1–7) [Ang-(1–7)] is an endogenous heptapeptide hormone and important component of the renin–angiotensin system that acts through both the Mas receptor and AT2 receptor, exhibiting anti-proliferative and anti-angiogenic properties in cancer cells. However, the anti-cancer activity of Ang-(1–7) related to autophagy in NPC remains largely debated. The effects and signaling pathway(s) involved in the Ang-(1–7)/Mas receptor axis in NPC were investigated both in vitro and in vivo. Ang-(1–7) inhibited cell proliferation, migration, and invasion in NPC-TW01 cells. Ang-(1–7) induced autophagy by increasing the levels of the autophagy marker LC3-II and by enhancing p62 degradation via activation of the Beclin-1/Bcl-2 signaling pathway with involvement of the PI3K/Akt/mTOR and p38 pathways in vitro study. In addition, pre-treatment with Ang-(1–7) inhibited tumor growth in NPC xenografts by inducing autophagy, suggesting a correlation between PI3K/Akt/mTOR pathway inhibition and the abovementioned anti-cancer activities. However, no autophagy was observed following Ang-(1–7) post-treatment. Taken together, these data indicate that Ang-(1–7) plays a novel role in autophagy downstream signaling pathways in NPC, supporting its potential as a therapeutic agent for alleviation the incidence of NPC and preventive treatment of recurrent NPC.

Key messages

Ang-(1–7) inhibits cell proliferation, migration, and invasion by activating autophagy

Ang-(1–7)pre-treatment inhibits tumor growth via autophagy by suppressing PI3K/Akt/mTOR pathway.

Ang-(1–7) may provide a novel preventative treatment for NPC and recurrent NPC

Electronic supplementary material

The online version of this article (10.1007/s00109-018-1704-z) contains supplementary material, which is available to authorized users.

Cognitive benefits of angiotensin IV and angiotensin-(1-7): A systematic review of experimental studies

OBJECTIVES

To explore effects of the brain renin-angiotensin system (RAS) on cognition.

DESIGN

Systematic review of experimental (non-human) studies assessing cognitive effects of RAS peptides angiotensin-(3-8) [Ang IV] and angiotensin-(1-7) [Ang-(1-7)] and their receptors, the Ang IV receptor (AT4R) and the Mas receptor.

RESULTS

Of 450 articles identified, 32 met inclusion criteria. Seven of 11 studies of normal animals found Ang IV had beneficial effects on tests of passive or conditioned avoidance and object recognition. In models of cognitive deficit, eight of nine studies found Ang IV and its analogs (Nle1-Ang IV, dihexa, LVV-hemorphin-7) improved performance on spatial working memory and passive avoidance tasks. Two of three studies examining Ang-(1-7) found it benefited memory. Mas receptor removal was associated with reduced fear memory in one study.

CONCLUSION

Studies of cognitive impairment show salutary effects of acute administration of Ang IV and its analogs, as well as AT4R activation. Brain RAS peptides appear most effective administered intracerebroventricularly, close to the time of learning acquisition or retention testing. Ang-(1-7) shows anti-dementia qualities.

Angiotensin II Type 2 Receptor and Receptor Mas Are Colocalized and Functionally Interdependent in Obese Zucker Rat Kidney

The actions of angiotensin II type 2 receptor (AT₂R) and the receptor Mas (MasR) are complex but show similar pronatriuretic function; particularly, AT₂R expression and natriuretic function are enhanced in obese/diabetic rat kidney. In light of some reports suggesting a potential positive interaction between these receptors, we tested hypothesis that renal AT₂R and MasR physically interact and are interdependent to stimulate cell signaling and promote natriuresis in obese rats. We found that infusion of AT₂R agonist C21 in obese Zucker rats (OZR) increased urine flow and urinary Na excretion which were attenuated by simultaneous infusion of the AT₂R antagonist PD123319 or the MasR antagonist A-779. Similarly, infusion of MasR agonist Ang-(1-7) in OZR increased urine flow and urinary Na excretion, which were attenuated by simultaneous infusion of A-779 or PD123319. Experiment in isolated renal proximal tubules of OZR revealed that both the agonists C21 and Ang-(1-7) stimulated NO which was blocked by either of the receptor antagonists. Dual labeling of AT₂R and MasR in OZR kidney sections and human proximal tubule epithelial cells showed that AT₂R and MasR are colocalized. The AT₂R also coimmunoprecipitated with MasR in cortical homogenate of OZR. Immunoblotting of cortical homogenate cross-linked with zero-length oxidative (sulfhydryl groups) cross-linker cupric-phenanthroline revealed a shift of AT₂R and MasR bands upward with overlapping migration for their complexes which were sensitive to the reducing β-mercaptoethanol, suggesting involvement of -SH groups in cross-linking. Collectively, the study reveals that AT₂R and MasR are colocalized and functionally interdependent in terms of stimulating NO and promoting diuretic/natriuretic response.

Angiotensin II type 2 receptor (AT2R) in renal and cardiovascular disease

Angiotensin II (Ang II) is well-considered to be the principal effector of the renin-angiotensin system (RAS), which binds with strong affinity to the angiotensin II type 1 (AT1R) and type 2 (AT2R) receptor subtype. However, activation of both receptors is likely to stimulate different signalling mechanisms/pathways and produce distinct biological responses. The haemodynamic and non-haemodynamic effects of Ang II, including its ability to regulate blood pressure, maintain water-electrolyte balance and promote vasoconstriction and cellular growth are well-documented to be mediated primarily by the AT1R. However, its biological and functional effects mediated through the AT2R subtype are still poorly understood. Recent studies have emphasized that activation of the AT2R regulates tissue and organ development and provides in certain context a potential counter-regulatory mechanism against AT1R-mediated actions. Thus, this review will focus on providing insights into the biological role of the AT2R, in particular its actions within the renal and cardiovascular system.

Berberine improves cognitive impairment by promoting autophagic clearance and inhibiting production of β-amyloid in APP/tau/PS1 mouse model of Alzheimer's disease

This study investigates the neuroprotective properties of berberine (a natural isoquinoline alkaloid isolated from the Rhizoma coptidis) and finds that berberine could promote β-amyloid (Aβ) clearance and inhibit Aβ production in the triple-transgenic mouse model of Alzheimer's disease (3×Tg-AD). During the study, berberine was first administrated to treat 3×Tg-AD mice and primary neurons. Morris water maze assay, western blotting, enzyme-linked immunosorbent assay (ELISA), immunofluorescence staining and histological analysis, transmission electron microscopic analysis were then used to evaluate the effects of the berberine administration. The result showed that berberine significantly improved 3×Tg-AD mice's spatial learning capacity and memory retention, promoted autophagy activity identified by the enhancement of brain LC3-II, beclin-1, hVps34, and Cathepsin-D levels as well as the reduction of brain P62 and Bcl-2 levels in AD mice, facilitated reduction of Aβ and APP levels, reduced Aβ plaque deposition in the hippocampus of AD mice, and inhibited b-site APP cleavage enzyme 1 (BACE1) expression. Similar results were also found in 3×Tg-AD primary hippocampal neurons: berbernine treatment decreased the levels of extracellular and intracellular Aβ1-42, increased the protein levels of LC3-II, beclin-1, hVps34, and Cathepsin-D, and decreased the levels of P62, Bcl-2, APP and BACE1 levels. In summary, berberine shows neuroprotective effects on 3×Tg-AD mice and may be a promising multitarget drug in the preventionand protection against AD.

Identification of Cofilin-1 Induces G0/G1 Arrest and Autophagy in Angiotensin-(1-7)-treated Human Aortic Endothelial Cells from iTRAQ Quantitative Proteomics

The angiotensin-converting enzyme 2/angiotensin-(1-7)/Mas axis is a pathway that acts against the detrimental effects of the renin-angiotensin system. However, the effects of angiotensin-(1-7) on endothelial protein expression and the related phenotypes are unclear. We performed a duplicate of iTRAQ quantitative proteomic analysis on human aortic endothelial cells (HAECs) treated with angiotensin-(1-7) for 6 hours. Cofilin-1 was identified as a highly abundant candidate with consistent >30% coverage and >1.2-fold overexpression in the angiotensin-(1-7)-treated group. Gene ontology analysis showed that the "regulation_of_mitosis" was significantly altered, and cell cycle analysis indicated that the 6-hour angiotensin-(1-7) treatment significantly induced G0/G1 arrest. Knockdown of the cofilin-1 (CFL1) gene suggested the G0/G1 phase arrest was mediated by the modulation of p27 and the p21/Cyclin/CDK complex by Cofilin-1. Interestingly, quiescent HAECs escaped G0/G1 arrest upon angiotensin-(1-7) treatment for 24 hours, and angiotensin-(1-7) induced autophagy by upregulating Beclin-1 and microtubule-associated protein 1 light chain 3b-II expression, which was also attenuated by A779 pre-treatment and CFL1 knockdown. After pre-treatment with 3-methyladenine (3MA), treatment with angiotensin-(1-7) for 24 h induced significant G0/G1 phase arrest and apoptosis, suggesting a pro-survival role of autophagy in this context. In conclusion, Cofilin-1 plays a dominant role in angiotensin-(1-7)-induced G0/G1 arrest and autophagy to maintain cellular homeostasis in HAECs.

Endogenous angiotensin-(1-7)/Mas receptor/NO pathway mediates the cardioprotective effects of pacing postconditioning

The aim of the present study was to investigate the role of the ANG-(1-7) receptor (Mas) and nitric oxide (NO) in pacing postconditiong (PPC)-mediated cardioprotection against ischemia-reperfusion injury. Cardiac contractility and hemodynamics were assessed using a modified Langendorff system, cardiac damage was assessed by measuring infarct size and creatinine kinase levels, and levels of phosphorylated and total endothelial NO synthase (eNOS) were determined by Western blot analysis. Isolated hearts were subjected to 30 min of regional ischemia, produced by fixed position ligation of the left anterior descending coronary artery, followed by 30 min of reperfusion (n = 6). Hearts were also subjected to PPC (three cycles of 30 s of left ventricular pacing alternated with 30 s of right atrial pacing) and/or treated during reperfusion with ANG-(1-7), N(G)-nitro-l-arginine methyl ester, or the Mas antagonist (d-Ala7)-ANG I/II (1-7). The PPC-mediated improvement in cardiac contractility and hemodyanamics, cardiac damage, and eNOS phosphorylation were significantly attenuated upon treatment with (d-Ala7)-ANG I/II (1-7) or N(G)-nitro-l-arginine methyl ester. Treatment with ANG-(1-7) improved cardiac function and reduced infarct size and creatinine kinase levels; however, the effects of ANG-(1-7) were not additive with PPC. In conclusion, these data provide novel insights into the cardioprotective mechanisms of PPC in that they involve the Mas receptor and eNOS and further suggest a potential therapeutic role for ANG-(1-7) in cardiac ischemic injury.

Angiotensin type 2 receptor (AT2R) and receptor Mas: a complex liaison

The angiotensin type 2 receptor (AT2R) and the receptor Mas are components of the protective arms of the renin-angiotensin system (RAS), i.e. they both mediate tissue protective and regenerative actions. The spectrum of actions of these two receptors and their signalling mechanisms display striking similarities. Moreover, in some instances, antagonists for one receptor are able to inhibit the action of agonists for the respective other receptor. These observations suggest that there may be a functional or even physical interaction of both receptors. This article discusses potential mechanisms underlying the phenomenon of blockade of angiotensin-(1-7) [Ang-(1-7)] actions by AT2R antagonists and vice versa. Such mechanisms may comprise dimerization of the receptors or dimerization-independent mechanisms such as lack of specificity of the receptor ligands used in the experiments or involvement of the Ang-(1-7) metabolite alamandine and its receptor MrgD in the observed effects. We conclude that evidence for a functional interaction of both receptors is strong, but that such an interaction may be species- and/or tissue-specific and that elucidation of the precise nature of the interaction is only at the very beginning.

Activation of Autophagy Contributes to the Angiotensin II-Triggered Apoptosis in a Dopaminergic Neuronal Cell Line

Our recent study indicated that angiotensin II (Ang II), the main component of renin-angiotensin system, participated in the pathogenesis of Parkinson's disease (PD) by triggering the apoptosis of dopaminergic neuronal cells. However, the underlying mechanisms are still not fully understood. In this study, by using CATH.a cells, a dopaminergic neuronal cell line stably expressing angiotensin II type 1 receptor (AT1R) and angiotensin II type 2 receptor (AT2R), we tested the hypothesis that activation of autophagy contributed to the apoptosis triggered by Ang II. We showed that Ang II activated autophagy and triggered apoptosis in CATH.a cells in a dose-dependent manner. More importantly, inhibition of autophagy by 3-methyladenine markedly attenuated the apoptosis caused by Ang II in CATH.a cells. In addition, the Ang II-induced autophagy and subsequent cell apoptosis could be fully abolished by an AT1R antagonist losartan rather than PD1223319, an antagonist for AT2R. Taken together, our study provides the first evidence that Ang II triggers apoptosis via activation of autophagy in a dopaminergic neuronal cell line through an AT1R-mediated manner. These findings have deepened our understanding on the role of Ang II in the pathogenesis of PD and support the use of AT1R antagonists for the treatment of this devastating neurodegenerative disease.

Acute metformin preconditioning confers neuroprotection against focal cerebral ischaemia by pre-activation of AMPK-dependent autophagy

BACKGROUND AND PURPOSE

Recent clinical trials report that metformin, an activator of AMP-activated protein kinase (AMPK) used to treat type 2 diabetes, significantly reduces the risk of stroke by actions that are independent of its glucose-lowering effects. However, the underlying molecular mechanisms are not known. Here, we tested the possibility that acute metformin preconditioning confers neuroprotection by pre-activation of AMPK-dependent autophagy in a rat model of permanent middle cerebral artery occlusion (pMCAO).

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were pretreated with either vehicle, an AMPK inhibitor, Compound C, or an autophagy inhibitor, 3-methyladenine, and were injected with a single dose of metformin (10 mg kg(-1), i.p.). Then, AMPK activity and autophagy biomarkers in the brain were assessed. At 24 h after metformin treatment, rats were subjected to pMCAO; infarct volume, neurological deficits and cell apoptosis were evaluated 24 and 96 h later.

KEY RESULTS

A single dose of metformin significantly activated AMPK and induced autophagy in the brain. The enhanced autophagic activity was inhibited by Compound C pretreatment. Furthermore, acute metformin preconditioning significantly reduced infarct volume, neurological deficits and cell apoptosis during a subsequent focal cerebral ischaemia. The neuroprotection mediated by metformin preconditioning was fully abolished by Compound C and partially inhibited by 3-methyladenine.

CONCLUSIONS AND IMPLICATIONS

These results provide the first evidence that acute metformin preconditioning induces autophagy by activation of brain AMPK, which confers neuroprotection against subsequent cerebral ischaemia. This suggests that metformin, a well-known hypoglycaemic drug, may have a practical clinical use for stroke prevention.

Angiotensin-(1-7) induces cerebral ischaemic tolerance by promoting brain angiogenesis in a Mas/eNOS-dependent pathway

BACKGROUND AND PURPOSE

As a newer component of the renin-angiotensin system, angiotensin-(1-7) [Ang-(1-7) ] has been shown to facilitate angiogenesis and protect against ischaemic damage in peripheral tissues. However, the role of Ang-(1-7) in brain angiogenesis remains unclear. The aim of this study was to investigate whether Ang-(1-7) could promote angiogenesis in brain, thus inducing tolerance against focal cerebral ischaemia.

EXPERIMENTAL APPROACH

Male Sprague-Dawley rats were i.c.v. infused with Ang-(1-7), A-779 (a Mas receptor antagonist), L-NIO, a specific endothelial NOS (eNOS) inhibitor, endostatin (an anti-angiogenic compound) or vehicle, alone or simultaneously, for 1-4 weeks. Capillary density, endothelial cell proliferation and key components of eNOS pathway in the brain were evaluated. Afterwards, rats were subjected to permanent middle cerebral artery occlusion (pMCAO), and regional cerebral blood flow (rCBF), infarct volume and neurological deficits were measured 24 h later.

KEY RESULTS

Infusion of Ang-(1-7) for 4 weeks significantly increased brain capillary density via promoting endothelial cell proliferation, which was accompanied by eNOS activation and up-regulation of NO and VEGF in brain. These effects were abolished by A-779 or L-NIO. More importantly, Ang-(1-7) improved rCBF and decreased infarct volume and neurological deficits after pMCAO, which could be reversed by A-779, L-NIO or endostatin.

CONCLUSIONS AND IMPLICATIONS

This is the first evidence that Ang-(1-7) promotes brain angiogenesis via a Mas/eNOS-dependent pathway, which enhances tolerance against subsequent cerebral ischaemia. These findings highlight brain Ang-(1-7)/Mas signalling as a potential target in stroke prevention.

Protective axis of the renin-angiotensin system in the brain

The RAS (renin-angiotensin system) is composed of two arms: the pressor arm containing AngII (angiotensin II)/ACE (angiotensin-converting enzyme)/AT1Rs (AngII type 1 receptors), and the depressor arm represented by Ang-(1-7) [angiotensin-(1-7)]/ACE2/Mas receptors. All of the components of the RAS are present in the brain. Within the brain, Ang-(1-7) contributes to the regulation of BP (blood pressure) by acting at regions that control cardiovascular function such that, when Ang-(1-7) is injected into the nucleus of the solitary tract, caudal ventrolateral medulla, paraventricular nucleus or anterior hypothalamic area, a reduction in BP occurs; however, when injected into the rostral ventrolateral medulla, Ang-(1-7) stimulates an increase in BP. In contrast with AngII, Ang-(1-7) improves baroreflex sensitivity and has an inhibitory neuromodulatory role in hypothalamic noradrenergic neurotransmission. Ang-(1-7) not only exerts effects related to BP regulation, but also acts as a cerebroprotective component of the RAS by reducing cerebral infarct size and neuronal apoptosis. In the present review, we provide an overview of effects elicited by Ang-(1-7) in the brain, which suggest a potential role for Ang-(1-7) in controlling the central development of hypertension.

Ischemic preconditioning provides neuroprotection by induction of AMP-activated protein kinase-dependent autophagy in a rat model of ischemic stroke

Accumulating evidence suggests that ischemic preconditioning (IPC) increases cerebral tolerance to the subsequent ischemic exposure. However, the underlying mechanisms are still not fully understood. In the present study, we tested the hypothesis that AMP-activated protein kinase (AMPK)-dependent autophagy contributed to the neuroprotection of IPC in rats with permanent cerebral ischemia. Male Sprague-Dawley rats were pretreated with vehicle, compound C (an AMPK inhibitor), or 3-methyladenine (3-MA, an autophagy inhibitor) and then were subjected to IPC induced by a 10-min middle cerebral artery occlusion. Afterward, the brain AMPK activity and autophagy biomarkers were measured. At 24 h after IPC, permanent cerebral ischemia was induced in these rats, and infarct volume, neurological deficits as well as cell apoptosis were evaluated 24 h later. We demonstrated that IPC activated AMPK and induced autophagy in the brain, which was accompanied by a reduction of infract volume, neurological deficits, and cell apoptosis after cerebral ischemia. Meanwhile, the IPC-induced autophagy was inhibited by compound C while the neuroprotection of IPC was abolished by compound C or 3-MA. These findings suggest that AMPK-mediated autophagy contributes to the neuroprotection of IPC, highlighting AMPK as a therapeutic target for stroke prevention and treatment.

Angiotensin 1-7 reduces mortality and rupture of intracranial aneurysms in mice

Angiotensin II (Ang II) stimulates vascular inflammation, oxidative stress, and formation and rupture of intracranial aneurysms in mice. Because Ang 1-7 acts on Mas receptors and generally counteracts deleterious effects of Ang II, we tested the hypothesis that Ang 1-7 attenuates formation and rupture of intracranial aneurysms. Intracranial aneurysms were induced in wild-type and Mas receptor-deficient mice using a combination of Ang II-induced hypertension and intracranial injection of elastase in the basal cistern. Mice received elastase+Ang II alone or a combination of elastase+Ang II+Ang 1-7. Aneurysm formation, prevalence of subarachnoid hemorrhage, mortality, and expression of molecules involved in vascular injury were assessed. Systolic blood pressure was similar in mice receiving elastase+Ang II (mean±SE, 148±5 mm Hg) or elastase+Ang II+Ang 1-7 (144±5 mm Hg). Aneurysm formation was also similar in mice receiving elastase+Ang II (89%) or elastase+Ang II+Ang 1-7 (84%). However, mice that received elastase+Ang II+Ang 1-7 had reduced mortality (from 64% to 36%; P<0.05) and prevalence of subarachnoid hemorrhage (from 75% to 48%; P<0.05). In cerebral arteries, expression of the inflammatory markers, Nox2 and catalase increased similarly in elastase+Ang II or elastase+Ang II+Ang 1-7 groups. Ang 1-7 increased the expression of cyclooxygenase-2 and decreased the expression of matrix metalloproteinase-9 induced by elastase+Ang II (P<0.05). In Mas receptor-deficient mice, systolic blood pressure, mortality, and prevalence of subarachnoid hemorrhage were similar (P>0.05) in groups treated with elastase+Ang II or elastase+Ang II+Ang 1-7. The expression of Mas receptor was detected by immunohistochemistry in samples of human intracranial arteries and aneurysms. In conclusion, without attenuating Ang II-induced hypertension, Ang 1-7 decreased mortality and rupture of intracranial aneurysms in mice through a Mas receptor-dependent pathway.

Temsirolimus promotes autophagic clearance of amyloid-β and provides protective effects in cellular and animal models of Alzheimer's disease

Accumulation of amyloid-β peptides (Aβ) within brain is a major pathogenic hallmark of Alzheimer's disease (AD). Emerging evidence suggests that autophagy, an important intracellular catabolic process, is involved in Aβ clearance. Here, we investigated whether temsirolimus, a newly developed compound approved by Food and Drug Administration and European Medicines Agency for renal cell carcinoma treatment, would promote autophagic clearance of Aβ and thus provide protective effects in cellular and animal models of AD. HEK293 cells expressing the Swedish mutant of APP695 (HEK293-APP695) were treated with vehicle or 100nM temsirolimus for 24h in the presence or absence of 3-methyladenine (5mM) or Atg5-siRNA, and intracellular Aβ levels as well as autophagy biomarkers were measured. Meanwhile, APP/PS1 mice received intraperitoneal injection of temsirolimus (20mg/kg) every 2 days for 60 days, and brain Aβ burden, autophagy biomarkers, cellular apoptosis in hippocampus, and spatial cognitive functions were assessed. Our results showed that temsirolimus enhanced Aβ clearance in HEK293-APP695 cells and in brain of APP/PS1 mice in an autophagy-dependent manner. Meanwhile, temsirolimus attenuated cellular apoptosis in hippocampus of APP/PS1 mice, which was accompanied by an improvement in spatial learning and memory abilities. In conclusion, our study provides the first evidence that temsirolimus promotes autophagic Aβ clearance and exerts protective effects in cellular and animal models of AD, suggesting that temsirolimus administration may represent a new therapeutic strategy for AD treatment. Meanwhile, these findings emphasize the notion that many therapeutic agents possess pleiotropic actions aside from their main applications.

Cerebroprotective action of angiotensin peptides in stroke

The goal of the present review is to examine the evidence for beneficial actions of manipulation of the RAS (renin-angiotensin system) in stroke, with particular focus on Ang-(1-7) [angiotensin-(1-7)] and its receptor Mas. The RAS appears to be highly involved in the multifactorial pathophysiology of stroke. Blocking the effects of AngII (angiotensin II) at AT1R (AngII type 1 receptor), through the use of commonly prescribed ACE (angiotensin-converting enzyme) inhibitors or AT1R blockers, has been shown to have therapeutic effects in both ischaemic and haemorrhagic stroke. In contrast with the deleterious actions of over activation of AT1R by AngII, stimulation of AT2Rs (AngII type 2 receptors) in the brain has been demonstrated to elicit beneficial effects in stroke. Likewise, the ACE2/Ang-(1-7)/Mas axis of the RAS has been shown to have therapeutic effects in stroke when activated, countering the effects of the ACE/AngII/AT1R axis. Studies have demonstrated that activating this axis in the brain elicits beneficial cerebral effects in rat models of ischaemic stroke, and we have also demonstrated the cerebroprotective potential of this axis in haemorrhagic stroke using stroke-prone spontaneously hypertensive rats and collagenase-induced striatal haemorrhage. The mechanism of cerebroprotection elicited by ACE2/Ang-(1-7)/Mas activation includes anti-inflammatory effects within the brain parenchyma. The major hurdle to overcome in translating these results to humans is devising strategies to activate the ACE2/Ang-(1-7)/Mas cerebroprotective axis using post-stroke treatments that can be administered non-invasively.