Angiotensin II-triggered kinase signaling cascade in the central nervous system

Impacts of SARS-CoV-2 on brain renin angiotensin system related signaling and its subsequent complications on brain: A theoretical perspective

Cellular ACE2 (cACE2), a vital component of the renin-angiotensin system (RAS), possesses catalytic activity to maintain AngII and Ang 1-7 balance, which is necessary to prevent harmful effects of AngII/AT2R and promote protective pathways of Ang (1-7)/MasR and Ang (1-7)/AT2R. Hemostasis of the brain-RAS is essential for maintaining normal central nervous system (CNS) function. Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a viral disease that causes multi-organ dysfunction. SARS-CoV-2 mainly uses cACE2 to enter the cells and cause its downregulation. This, in turn, prevents the conversion of Ang II to Ang (1-7) and disrupts the normal balance of brain-RAS. Brain-RAS disturbances give rise to one of the pathological pathways in which SARS-CoV-2 suppresses neuroprotective pathways and induces inflammatory cytokines and reactive oxygen species. Finally, these impairments lead to neuroinflammation, neuronal injury, and neurological complications. In conclusion, the influence of RAS on various processes within the brain has significant implications for the neurological manifestations associated with COVID-19. These effects include sensory disturbances, such as olfactory and gustatory dysfunctions, as well as cerebrovascular and brain stem-related disorders, all of which are intertwined with disruptions in the RAS homeostasis of the brain.

The Inhibitory Role of Hydrogen Sulfide in UII-Induced Cardiovascular Effects and the Underlying Signaling Pathways

Urotensin II (UII) could increase blood pressure and heart rate via increased central reactive oxygen species (ROS) levels. We reported previously that hydrogen sulfide (H2S) exerts an antihypertensive effect by suppressing ROS production. The aim of the current study is to further examine the effects of endogenous and exogenous H2S on UII-induced cardiovascular effects by using an integrated physiology approach. We also use cell culture and molecular biological techniques to explore the inhibitory role of H2S on UII-induced cardiovascular effects. In this study, we found that cystathionine-β-synthase (CBS), the main H2S synthesizing enzyme in CNS, was expressed in neuronal cells of the rostral ventrolateral medulla (RVLM) area. Cellular distribution of CBS and urotensin II receptor (UT) in SH-SY5Y cells that are confirmed as glutamatergic were identified by immunofluorescent and Western blots assay. In Sprague-Dawley rats, administration of UII into the RVLM resulted in an increase in mean arterial pressure (MAP), heart rate (HR), ROS production, nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity, and phosphorylation of p47phox, extracellular signal-regulated protein kinase (ERK)1/2 and p38MAPK, but not stress-activated protein kinase/Jun N-terminal kinase (SAPK/JNK). These effects of UII were attenuated by application into the RVLM of endogenous (L-cysteine, SAM) or exogenous (NaHS) H2S. These results were confirmed in SH-SY5Y cells. UII-induced cardiovascular effects were also significantly abolished by pretreatment with microinjection of Tempol, Apocynin, SB203580, or PD98059 into the RVLM. Preincubated SH-SY5Y cells with Apocynin before administration of UII followed by Western blots assay showed that ROS is in the upstream of p38MAPK/ERK1/2. Gao activation assay in SH-SY5Y cells suggested that H2S may exert an inhibitory role on UII-induced cardiovascular effects by inhibiting the activity of Gαo. These results suggest that both endogenous and exogenous H2S attenuate UII-induced cardiovascular effects via Gαo-ROS-p38MAPK/ERK1/2 pathway.

Ginsenoside Re attenuates memory impairments in aged Klotho deficient mice via interactive modulations of angiotensin II AT1 receptor, Nrf2 and GPx-1 gene

Ginseng is known to possess anti-aging potential. Klotho mutant mice exhibit phenotypes that resemble the phenotype of the human aging process. Similar to Klotho deficient mice, patients with chronic kidney disease (CKD) suffer vascular damage and cognitive impairment, which might upregulate the angiotensin II AT1 receptor. Since AT1 receptor expression was more pronounced than endothelin ET-1 expression in the hippocampus of aged Klotho deficient (±) mice, we focused on the AT1 receptor in this study. Ginsenoside Re (GRe), but not ginsenoside Rb1 (GRb1), significantly attenuated the increase in AT1 receptor expression in aged Klotho deficient mice. Both GRe and the AT1 receptor antagonist losartan failed to attenuate the decrease in phosphorylation of JAK2/STAT3 in aged Klotho deficient (±) mice but significantly activated nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated signaling. Both GRe and losartan attenuated the increased NADPH oxidase (NOX) activity and reactive oxygen species (ROS) in aged Klotho deficient mice. Furthermore, of all the antioxidant enzymes, GRe significantly increased glutathione peroxidase (GPx) activity. GRe significantly attenuated the reduced phosphorylation of ERK and CREB in GPx-1 knockout mice; however, genetic overexpression of GPx-1 did not significantly affect them in aged mice. Klotho-, Nrf2-, and GPx-1-immunoreactivities were co-localized in the same cells of the hippocampus in aged Klotho wild-type mice. Both the GPx inhibitor mercaptosuccinate and Nrf2 inhibitor brusatol counteracted the effects of GRe on all neurobehavioral impairments in aged Klotho deficient (±) mice. Our results suggest that GRe attenuates all alterations, such as AT1 receptor expression, NOX-, ROS-, and GPx-levels, and cognitive dysfunction in aged Klotho deficient (±) mice via upregulation of Nrf2/GPx-1/ERK/CREB signaling.

Demystifying the dual role of the angiotensin system in neuropathic pain

Neuropathic Pain is caused by damage to a nerve or disease of the somatosensory nervous system. Apart from the blood pressure regulating actions of angiotensin ligands, studies have shown that it also modulates neuropathic pain. In the animal models including surgical, chemotherapeutic, and retroviral-induced neuropathic pain, an increase in the levels of angiotensin II has been identified and it has been proposed that an increase in angiotensin II may participate in the induction of neuropathic pain. The pain-inducing actions of the angiotensin system are primarily due to the activation of AT₁ and AT₂ receptors, which trigger the diverse molecular mechanisms including the induction of neuroinflammation to initiate and maintain the state of neuropathic pain. On the other hand, the pain attenuating action of the angiotensin system has been attributed to decreasing in the levels of Ang_(1-7), and Ang IV and an increase in the levels of bradykinin. Ang_(1-7) may attenuate neuropathic pain via activation of the spinal Mas receptor. However, the detailed molecular mechanism involved in Ang_(1-7) and Ang IV-mediated pain attenuating actions needs to be explored. The present review discusses the dual role of angiotensin ligands in neuropathic pain along with the possible mechanisms involved in inducing or attenuating the state of neuropathic pain.

Angiotensin II inhibits the A-type K+ current of hypothalamic paraventricular nucleus neurons in rats with heart failure: role of MAPK-ERK1/2 signaling

Angiotensin II (ANG II)-mediated sympathohumoral activation constitutes a pathophysiological mechanism in heart failure (HF). Although the hypothalamic paraventricular nucleus (PVN) is a major site mediating ANG II effects in HF, the precise mechanisms by which ANG II influences sympathohumoral outflow from the PVN remain unknown. ANG II activates the ubiquitous intracellular MAPK signaling cascades, and recent studies revealed a key role for ERK1/2 MAPK signaling in ANG II-mediated sympathoexcitation in HF rats. Importantly, ERK1/2 was reported to inhibit the transient outward potassium current (IA) in hippocampal neurons. Given that IA is a critical determinant of the PVN neuronal excitability, and that downregulation of IA in the brain has been reported in cardiovascular disease states, including HF, we investigated here whether ANG II modulates IA in PVN neurons via the MAPK-ERK pathway, and, whether these effects are altered in HF rats. Patch-clamp recordings from identified magnocellular neurosecretory neurons (MNNs) and presympathetic (PS) PVN neurons revealed that ANG II inhibited IA in both PVN neuronal types, both in sham and HF rats. Importantly, ANG II effects were blocked by inhibiting MAPK-ERK signaling as well as by inhibiting epidermal growth factor receptor (EGFR), a gateway to MAPK-ERK signaling. Although no differences in basal IA magnitude were found between sham and HF rats under normal conditions, MAPK-ERK blockade resulted in significantly larger IA in both PVN neuronal types in HF rats. Taken together, our studies show that ANG II-induced ERK1/2 activity inhibits IA, an effect expected to increase the excitability of presympathetic and neuroendocrine PVN neurons, contributing in turn to the neurohumoral overactivity that promotes progression of the HF syndrome.

Into the Tissues: Extracellular Matrix and Its Artificial Substitutes: Cell Signalling Mechanisms

The existence of orderly structures, such as tissues and organs is made possible by cell adhesion, i.e., the process by which cells attach to neighbouring cells and a supporting substance in the form of the extracellular matrix. The extracellular matrix is a three-dimensional structure composed of collagens, elastin, and various proteoglycans and glycoproteins. It is a storehouse for multiple signalling factors. Cells are informed of their correct connection to the matrix via receptors. Tissue disruption often prevents the natural reconstitution of the matrix. The use of appropriate implants is then required. This review is a compilation of crucial information on the structural and functional features of the extracellular matrix and the complex mechanisms of cell-cell connectivity. The possibilities of regenerating damaged tissues using an artificial matrix substitute are described, detailing the host response to the implant. An important issue is the surface properties of such an implant and the possibilities of their modification.

Angiotensin I-converting enzyme inhibitory peptide: an emerging candidate for vascular dysfunction therapy

Abnormal vasoconstriction, inflammation, and vascular remodeling can be promoted by angiotensin II (Ang II) in the renin-angiotensin system (RAS), leading to vascular dysfunction diseases such as hypertension and atherosclerosis. Researchers have recently focused on angiotensin I-converting enzyme inhibitory peptides (ACEIPs), that have desirable efficacy in vascular dysfunction therapy due to Ang II reduction by inhibiting ACE activity. Promising methods for the large-scale preparation of ACEIPs include selective enzymatic hydrolysis and microbial fermentation. Thus far, ACEIPs have been widely reported to be hydrolyzed from protein-rich sources, including animals, plants, and marine organisms, while many emerging microorganism-derived ACEIPs are theoretically biosynthesized through the nonribosomal peptide synthase (NRPS) pathway. Notably, vasodilatation, anti-inflammation, and vascular reconstruction reversal of ACEIPs are strongly correlated. However, the related molecular mechanisms underlying signal transduction regulation in vivo remain unclear. We provide a comprehensive update of the ACE-Ang II-G protein-coupled type 1 angiotensin receptor (AT1R) axis signaling and its functional significance for potential translation into therapeutic strategies, particularly targeting AT1R by ACEIPs, as well as specific related signaling pathways. Future studies are expected to verify the biosynthetic regulatory mechanism of ACEIPs via the NRPS pathway, the effect of gut microbiota metabolism on vascular dysfunction and rigorous studies of ACE-Ang II-AT1R signaling pathways mediated by ACEIPs in large animals and humans.

Expression and Change of miRs 145, 221 and 222 in Hypertensive Subjects Treated with Enalapril, Losartan or Olmesartan

miR profile could be associated to CV risk, and also to prognosis/outcome in response to therapeutic approach. We aimed to evaluate if anti-hypertensive drugs enalapril, losartan or olmesartan have effects on monocyte miR profile in essential hypertensives without target organ involvement. For this purpose, 82 hypertensives and 49 controls were included; we evaluated SBP/DBP, lipid profile, glucose, CRP, fibrinogen, arterial stiffness indices (PWV; AIx), and cIMT at baseline (T0) and after 24 weeks of treatment (T1). Subjects with LDL-C ≥ 160 mg/dL, TG ≥ 200 mg/dL, BMI ≥ 30, and other additional CV risk factors were excluded. Patients who were prescribed to receive once-a-day enalapril 20 mg, losartan 100 mg or olmesartan 20 mg were eligible for the study. At T1, we found a significant improvement of SBP (-18.5%), DBP (-18%), HDL-C and LDL-C (+3% and -5.42%), glucose (-2.15%), BMI (-3.23%), fibrinogen (-11%), CRP (-17.5%,), AIx (-49.1%) PWV (-32.2%), and monocyte miR expression (miR-221: -28.4%; miR-222: -36%; miR-145: +41.7%) with respect to baseline. miR profile was compared to control subjects at baseline and at T1. We found some little difference in the behaviour of the three treatments on some variables: olmesartan was the most effective in reducing fibrinogen, DBP, CRP, and AIx (-13.1%, -19.3%, -21.4%, and -56.8%, respectively). Enalapril was the drug more significantly increasing the expression of miR-145. In conclusion, enalapril, losartan and olmesartan are effective in improving mechanical and humoral factors associated to AS and atherogenesis. These drugs appear to be able to modify miRs 221/222 and miR-145 expression in drug-naïve hypertensives, making it closer to that of control subjects; additionally, this provides a good blood pressure compensation, contributing to slow the progression of vascular damage.

Angiotensin II induces cognitive decline and anxiety-like behavior via disturbing pattern of theta-gamma oscillations

Hypertension is the most common chronic disease accompanied by cognitive decline and anxiety-like behavior. Angiotensin II (Ang II) induces hypertension by activating angiotensin II receptor subtype 1 (AT1R). The purpose of the study was to examine the potential underlying mechanism of alterations in cognition and anxiety-like behavior induced by Ang II. Adult C57 mice were intraperitoneal injected with either 1 mg/kg/d Ang II or saline individually for 14 consecutive days. Ang II resulted in cognitive decline and anxious like behavior in C57 mice. Moreover, Ang II disturbed bidirectional synaptic plasticity and neural oscillation coupling between high theta and gamma on PP (perforant pathway)-DG (dentate gyrus) pathway. In addition, Ang II decreased the expression of N-methyl-d-aspartate receptor (NR) 2A and NR 2B and increased the expression of GABA_AR α1. The data suggest that Ang II disturb neural oscillations via altering excitatory and inhibitory (E/I) balance and eventually damage cognition and anxiety-like behavior in mice.

Pathophysiological Roles of Stress-Activated Protein Kinases in Pulmonary Fibrosis

Idiopathic pulmonary fibrosis (IPF) is one of the most symptomatic progressive fibrotic lung diseases, in which patients have an extremely poor prognosis. Therefore, understanding the precise molecular mechanisms underlying pulmonary fibrosis is necessary for the development of new therapeutic options. Stress-activated protein kinases (SAPKs), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (p38) are ubiquitously expressed in various types of cells and activated in response to cellular environmental stresses, including inflammatory and apoptotic stimuli. Type II alveolar epithelial cells, fibroblasts, and macrophages are known to participate in the progression of pulmonary fibrosis. SAPKs can control fibrogenesis by regulating the cellular processes and molecular functions in various types of lung cells (including cells of the epithelium, interstitial connective tissue, blood vessels, and hematopoietic and lymphoid tissue), all aspects of which remain to be elucidated. We recently reported that the stepwise elevation of intrinsic p38 signaling in the lungs is correlated with a worsening severity of bleomycin-induced fibrosis, indicating an importance of this pathway in the progression of pulmonary fibrosis. In addition, a transcriptome analysis of RNA-sequencing data from this unique model demonstrated that several lines of mechanisms are involved in the pathogenesis of pulmonary fibrosis, which provides a basis for further studies. Here, we review the accumulating evidence for the spatial and temporal roles of SAPKs in pulmonary fibrosis.

A Bioinformatics Investigation into the Pharmacological Mechanisms of Sodium-Glucose Co-transporter 2 Inhibitors in Diabetes Mellitus and Heart Failure Based on Network Pharmacology

PURPOSE

Diabetes mellitus (DM) is a major risk factor for the development of heart failure (HF). Sodium-glucose co-transporter 2 (SGLT2) inhibitors have demonstrated consistent benefits in the reduction of hospitalization for HF in patients with DM. However, the pharmacological mechanism is not clear. To investigate the mechanisms of SGLT2 inhibitors in DM with HF, we performed target prediction and network analysis by a network pharmacology method.

METHODS

We selected targets of SGLT2 inhibitors and DM status with HF from databases and studies. The "Drug-Target" and "Drug-Target-Disease" networks were constructed using Cytoscape. Then the protein-protein interaction (PPI) was analyzed using the STRING database. Gene Ontology (GO) biological functions and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were performed to investigate using the Bioconductor tool for analysis.

RESULTS

There were 125 effective targets between SGLT2 inhibitors and DM status with HF. Through further screening, 33 core targets were obtained, including SRC, MAPK1, NARS, MAPK3 and EGFR. It was predicted that the Rap1 signaling pathway, MAPK signaling pathway, EGFR tyrosine kinase inhibitor resistance, AGE-RAGE signaling pathway in diabetic complications and other signaling pathways were involved in the treatment of DM with HF by SGLT2 inhibitors.

CONCLUSION

Our study elucidated the possible mechanisms of SGLT2 inhibitors from a systemic and holistic perspective based on pharmacological networks. The key targets and pathways will provide new insights for further research on the pharmacological mechanism of SGLT2 inhibitors in the treatment of DM with HF.

Endogenous β-endorphin plays a pivotal role in angiotensin II-mediated central neurochemical changes and pressor response

Endorphins are endogenous opioid neuropeptides that are mainly produced from pituitary gland in response to pain and different triggers including interleukin 1 beta (IL-1β) and corticotropin-releasing factor (CRF). Angiotensin II (Ang II) can stimulate β-endorphin production, but the exact molecular mechanisms involved in this effect, and the role of the released β-endorphin in Ang II-mediated pressor response remain elusive. Male rats were injected with IL-1β receptor antagonist (IL-1Ra, 100 μg/kg), the CRF receptor blocker, astressin (20 μg/rat) or a combination of both, prior to Ang II injection (200 μg/kg). Another group of rats was given naloxone (1.6 mg/kg) or telmisartan (5 mg/kg) before Ang II injection. Blood pressure and serum and Paraventricular nucleus (PVN) β-endorphin were detected. Moreover, IL-1β and CRF as well as markers of oxidative stress [malondialdehyde (MDA) and superoxide dismutase (SOD)], inflammation [C-reactive protein (CRP)] and neuronal activation (c-Fos, l-glutamate, and phosphorylated ERK) were measured in the PVN of different groups. Ang II induced a pressor response and increased serum and PVN β-endorphin levels that were attenuated in rats pre-treated with astressin or/and IL-1Ra. Moreover, Ang II increased PVN oxidative stress, inflammation and neuronal activation. Telmisartan abolished the previous effects, while naloxone, astressin and IL-1Ra aggravated Ang II-mediated pressor response and most of the biochemical changes. These findings suggest that, Ang II can induce β-endorphin release via increasing both IL-1β and CRF levels which in result mitigates Ang II-mediated central responses. This study highlights β-endorphin as a possible target for treating hypertension.

TNF-α-induced sympathetic excitation requires EGFR and ERK1/2 signaling in cardiovascular regulatory regions of the forebrain

Peripherally or centrally administered TNF-α elicits a prolonged sympathetically mediated pressor response, but the underlying molecular mechanisms are unknown. Activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2) in cardiovascular regions of the brain has recently been recognized as a key mediator of sympathetic excitation, and ERK1/2 signaling is induced by activation of epidermal growth factor receptor (EGFR) tyrosine kinase activity. The present study examined the role of EGFR and ERK1/2 signaling in the sympathetic response to TNF-α. In urethane-anesthetized rats, intracarotid artery injection of TNF-α increased phosphorylation of EGFR and ERK1/2 in the subfornical organ (SFO) and the hypothalamic paraventricular nucleus (PVN); upregulated the gene expression of excitatory mediators in SFO and PVN; and increased blood pressure (BP), heart rate (HR), and renal sympathetic nerve activity (RSNA). A continuous intracerebroventricular infusion of the selective EGFR tyrosine kinase inhibitor AG1478 or the ERK1/2 inhibitor PD98059 significantly attenuated these responses. Bilateral PVN microinjections of TNF-α also increased phosphorylated ERK1/2 and the gene expression of excitatory mediators in PVN, along with increases in BP, HR, and RSNA, and these responses were substantially reduced by prior bilateral PVN microinjections of AG1478. These results identify activation of EGFR in cardiovascular regulatory regions of the forebrain as an important molecular mediator of TNF-α-driven sympatho-excitatory responses and suggest that EGFR activation of the ERK1/2 signaling pathway plays an essential role. These mechanisms likely contribute to sympathetic excitation in pathophysiological states like heart failure and hypertension, in which circulating and brain TNF-α levels are increased.NEW & NOTEWORTHY Proinflammatory cytokines contribute to the augmented sympathetic nerve activity in hypertension and heart failure, but the central mechanisms involved are largely unknown. The present study reveals that TNF-α transactivates EGFR in the subfornical organ and the hypothalamic paraventricular nucleus to initiate ERK1/2 signaling, upregulate the gene expression of excitatory mediators, and increase sympathetic nerve activity. These findings identify EGFR as a gateway to sympathetic excitation and a potential target for intervention in cardiovascular disease states.

Use of dual-flow bioreactor to develop a simplified model of nervous-cardiovascular systems crosstalk: A preliminary assessment

Chronic conditions requiring long-term rehabilitation therapies, such as hypertension, stroke, or cancer, involve complex interactions between various systems/organs of the body and mutual influences, thus implicating a multiorgan approach. The dual-flow IVTech LiveBox2 bioreactor is a recently developed inter-connected dynamic cell culture model able to mimic organ crosstalk, since cells belonging to different organs can be connected and grown under flow conditions in a more physiological environment. This study aims to setup for the first time a 2-way connected culture of human neuroblastoma cells, SH-SY5Y, and Human Coronary Artery Smooth Muscle Cells, HCASMC through a dual-flow IVTech LiveBox2 bioreactor, in order to represent a simplified model of nervous-cardiovascular systems crosstalk, possibly relevant for the above-mentioned diseases. The system was tested by treating the cells with 10nM angiotensin II (AngII) inducing PKCβII/HuR/VEGF pathway activation, since AngII and PKCβII/HuR/VEGF pathway are relevant in cardiovascular and neuroscience research. Three different conditions were applied: 1- HCASMC and SH-SY5Y separately seeded in petri dishes (static condition); 2- the two cell lines separately seeded under flow (dynamic condition); 3- the two lines, seeded in dynamic conditions, connected, each maintaining its own medium, with a membrane as interface for biohumoral changes between the two mediums, and then treated. We detected that only in condition 3 there was a synergic AngII-dependent VEGF production in SH-SY5Y cells coupled to an AngII-dependent PKCβII/HuR/VEGF pathway activation in HCASMC, consistent with the observed physiological response in vivo. HCASMC response to AngII seems therefore to be generated by/derived from the reciprocal cell crosstalk under the dynamic inter-connection ensured by the dual flow LiveBox 2 bioreactor. This system can represent a useful tool for studying the crosstalk between organs, helpful for instance in rehabilitation research or when investigating chronic diseases; further, it offers the advantageous opportunity of cultivating each cell line in its own medium, thus mimicking, at least in part, distinct tissue milieu.

Roles of angiotensin II as vasopressor in vasodilatory shock

Shock is an acute condition of circulatory failure resulting in life-threatening organ dysfunction, high morbidity and high mortality. Current management includes fluid and catecholamine therapy to maintain adequate mean arterial pressure and organ perfusion. Norepinephrine is recommended as first-line vasopressor, but other agents are available. Angiotensin II is an alternative potent vasoconstrictor without chronotropic or inotropic properties. Several studies, including a large randomized controlled trial have demonstrated its ability to increase blood pressure with catecholamine-sparing effects. Angiotensin II was consequently approved by the US FDA in 2017 and the EU in 2019 as an add-on vasopressor in vasodilatory shock. This review aims to discuss its basic pharmacology, clinical efficacy, safety and future perspectives.

Angiotensin receptor expression revealed by reporter mice and beneficial effects of AT2R agonist in retinal cells

The renin-angiotensin system (RAS) plays a vital role in cardiovascular physiology and body homeostasis. In addition to circulating RAS, a local RAS exists in the retina. Dysfunction of local RAS, resulting in increased levels of Angiotensin II (Ang II) and activation of AT1R-mediated signaling pathways, contributes to tissue pathophysiology and end-organ damage. Activation of AT2R on other hand is known to counteract the effects of AT1R activation and produce anti-inflammatory and anti-oxidative effects. We examined the expression of angiotensin receptors in the retina by using transgenic dual reporter mice and by real-time RT-PCR. We further evaluated the effects of C21, a selective agonist of AT2R, in reducing Ang II, lipopolysaccharide (LPS) and hydrogen peroxide induced oxidative stress and inflammatory responses in cultured human ARPE-19 cells. We showed that both AT1Ra and AT2R positive cells are detected in different cell types of the eye, including the RPE/choroid complex, ciliary body/iris, and neural retina. AT1Ra is more abundantly expressed than AT2R in mouse retina, consistent with previous reports. In the neural retina, AT1Ra are also detected in photoreceptors whereas AT2R are mostly expressed in the inner retinal neurons and RGCs. In cultured human RPE cells, activation of AT2R with C21 significantly blocked Ang II, LPS and hydrogen peroxide -induced NF-κB activation and inflammatory cytokine expression; Ang II and hydrogen peroxide-induced reactive oxygen species (ROS) production and MG132-induced apoptosis, comparable to the effects of Angiotensin-(1-7) (Ang-(1-7)), another protective component of the RAS, although C21 is more potent in reducing some of the effects induced by Ang II, whereas Ang-(1-7) is more effective in reducing some of the LPS and hydrogen peroxide-induced effects. These results suggest that activation of AT2R may represent a new therapeutic approach for retinal diseases.

Endogenous AT1 receptor-protein kinase C activity in the hypothalamus augments glutamatergic input and sympathetic outflow in hypertension

KEY POINTS

The angiotensin AT1 receptor expression and protein kinase C (PKC)-mediated NMDA receptor phosphorylation levels in the hypothalamus are increased in a rat genetic model of hypertension. Blocking AT1 receptors or PKC activity normalizes the increased pre- and postsynaptic NMDA receptor activity of hypothalamic presympathetic neurons in hypertensive animals. Inhibition of AT1 receptor-PKC activity in the hypothalamus reduces arterial blood pressure and sympathetic nerve discharges in hypertensive animals. AT1 receptors in the hypothalamus are endogenously activated to sustain NMDA receptor hyperactivity and elevated sympathetic outflow via PKC in hypertension.

ABSTRACT

Increased synaptic N-methyl-d-aspartate receptor (NMDAR) activity in the hypothalamic paraventricular nucleus (PVN) plays a major role in elevated sympathetic output in hypertension. Although exogenous angiotensin II (AngII) can increase NMDAR activity in the PVN, whether endogenous AT1 receptor-protein kinase C (PKC) activity mediates the augmented NMDAR activity of PVN presympathetic neurons in hypertension is unclear. Here we show that blocking AT1 receptors with losartan or inhibiting PKC with chelerythrine significantly decreased the frequency of NMDAR-mediated miniature excitatory postsynaptic currents (mEPSCs) and the amplitude of puff NMDA currents of retrogradely labelled spinally projecting PVN neurons in spontaneously hypertensive rats (SHRs). Also, treatment with chelerythrine abrogated the potentiating effect of AngII on mEPSCs and puff NMDA currents of labelled PVN neurons in SHRs. In contrast, neither losartan nor chelerythrine had any effect on mEPSCs or puff NMDA currents in labelled PVN neurons in Wistar-Kyoto (WKY) rats. Furthermore, levels of AT1 receptor mRNA and PKC-mediated NMDAR phosphorylation in the PVN were significantly higher in SHRs than in WKY rats. In addition, microinjection of losartan or chelerythrine into the PVN substantially reduced blood pressure and renal sympathetic nerve discharges in SHRs but not in WKY rats. Chelerythrine blocked sympathoexcitatory responses to AngII microinjected into the PVN. Our findings suggest that endogenous AT1 receptor-PKC activity is essential for presynaptic and postsynaptic NMDAR hyperactivity of PVN presympathetic neurons and for the augmented sympathetic outflow in hypertension. This information advances our mechanistic understanding of the interplay between angiotensinergic and glutamatergic excitatory inputs in hypertension.

Downregulated microRNA‑133a induces HUVECs injury: Potential role of the (pro) renin receptor in angiotensin II‑dependent hypertension

The renin‑angiotensin system (RAS) serves an essential role in hypertension. MicroRNAs (miRs) have been reported to be important regulators in angiotensin (Ang) II‑dependent hypertension. We aimed to explore the roles of Ang II and miR‑133a in the mechanism underlying hypertension. Human umbilical vein endothelial cells (HUVECs) were identified by immunofluorescence staining. Cell viability and miR‑133a expression under the inhibition of Ang II of various concentrations were determined by an MTT assay and reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR), respectively. The effects of HUVECs transfected with miR‑133a mimic or inhibitor on Ang II‑induced apoptosis were measured using flow cytometry. The potential targeting of miR‑133a to the 3' untranslated region of (pro) renin receptor (PRR) was assessed using TargetScan and a dual‑luciferase assay. The effects of PRR interference using small interfering (si)RNA on PRR expression and the rate of apoptosis were determined by RT‑qPCR, western blotting and flow cytometry, respectively. Ang II at a concentration of 10‑5 M significantly inhibited the cell viability (P<0.05) and miR‑133a expression (P<0.01); Downregulation of miR‑133a suppressed cell viability. HUVECs transfected with miR‑133a mimic reduced the rate of Ang II‑induced apoptosis from 21.99 to 12.38%, but miR‑133a inhibitor promoted Ang II‑induced apoptosis (apoptosis rate, 28.9%). PRR was predicted to be a target gene of miR‑133a. Transfection with siPRR decreased the apoptotic rate in Ang II + negative control and Ang II + miR‑133a inhibitor group to 11.39 and 12.94%, respectively. Our findings also suggested that Ang II promoted PRR expression to enhance the apoptotic rate of HUVECs via the suppression of miR‑133a. Furthermore, siPRR efficiently decreased the Ang II‑induced apoptosis.

The Involvement of Renin-Angiotensin System in Lipopolysaccharide-Induced Behavioral Changes, Neuroinflammation, and Disturbed Insulin Signaling

Brain insulin signaling is accounted for the development of a variety of neuropsychiatric disorders, such as anxiety and depression, whereas both inflammation and the activated renin-angiotensin system (RAS) are two major contributors to insulin resistance. Intriguingly, inflammation and RAS can activate each other, forming a positive feedback loop that would result in exacerbated unwanted tissue damage. To further examine the interrelationship among insulin signaling, neuroinflammation and RAS in the brain, the effect of repeated lipopolysaccharide (LPS) exposure and co-treatment with the angiotensin II (Ang II) receptor type 1 (AT1) blocker, candesartan (Cand), on anxiety and depression-like behaviors, RAS, neuroinflammation and insulin signaling was explored. Our results demonstrated that prolonged LPS challenge successfully induced the rats into anxiety and depression-like state, accompanied with significant neural apoptosis and neuroinflammation. LPS also activated RAS as evidenced by the enhanced angiotensin converting enzyme (ACE) expression, Ang II generation and AT1 expression. However, blocking the activated RAS with Cand co-treatment conferred neurobehavioral protective properties. The AT1 blocker markedly ameliorated the microglial activation, the enhanced gene expression of the proinflammatory cytokines and the overactivated NF-κB signaling. In addition, Cand also mitigated the LPS-induced disturbance of insulin signaling with the normalized phosphorylation of serine 307 and tyrosine 896 of insulin receptor substrate-1 (IRS-1). Collectively, the present study, for the first time, provided the direct evidence indicating that the inflammatory condition may interact with RAS to impede brain insulin pathway, resulting in neurobehavioral damage, and inhibiting RAS seems to be a promising strategy to block the cross-talk and cut off the vicious cycle between RAS and immune system.

Angiotensin II in septic shock

Septic shock is a life threatening condition and a medical emergency. It is associated with organ dysfunction and hypotension despite optimal volume resuscitation. Refractory septic shock carries a very high rate of mortality and is associated with ischemic and arrhythmogenic complications from high dose vasopressors. Angiotensin II (AT-II) is a product of the renin-angiotensin-aldosterone system. It is a vasopressor agent that has been recently approved by FDA to be used in conjunction with other vasopressors (catecholamines) in refractory shock and to reduce catecholamine requirements. We have reviewed the physiology and current literature on AT-II in refractory septic/vasodilatory shock. Larger trials with longer duration of follow-up are warranted to address the questions which are unanswered by the ATHOS-3 trial, especially pertaining to its effects on lungs, brain, microcirculation, inflammation, and venous thromboembolism risk.

Importance of the commissural nucleus of the solitary tract in renovascular hypertension

The rodent renovascular hypertension model has been used to investigate the mechanisms promoting hypertension. The importance of the carotid body for renovascular hypertension has been demonstrated. As the commissural NTS (cNTS) is the first synaptic site in the central nervous system that receives information from carotid body chemoreceptors, we evaluated the contribution of cNTS to renovascular hypertension in the present study. Normotensive male Holtzman rats were implanted with a silver clip around the left renal artery to induce two-kidney, one-clip (2K1C) hypertension. Six weeks later, isoguvacine (a GABA_A agonist) or losartan (an AT1 antagonist) was injected into the cNTS, and the effects were compared with carotid body removal. Immunohistochemistry for Iba-1 and GFAP to label microglia and astrocytes, respectively, and RT-PCR for components of the renin-angiotensin system and cytokines in the NTS were also performed 6 weeks after renal surgery. The inhibition of cNTS with isoguvacine or the blockade of AT1 receptors with losartan in the cNTS decreased the blood pressure and heart rate of 2K1C rats even more than carotid body removal did. The mRNA expression of NOX2, TNF-α and IL-6, microglia, and astrocytes also increased in the cNTS of 2K1C rats compared to that of normotensive rats. These results indicate that tonically active neurons within the cNTS are essential for the maintenance of hypertension in 2K1C rats. In addition to signals from the carotid body, the present results suggest that angiotensin II directly activates the cNTS and may also induce microgliosis and astrogliosis within the NTS, which, in turn, cause oxidative stress and neuroinflammation.

Molecular Basis of the Brain Renin Angiotensin System in Cardiovascular and Neurologic Disorders: Uncovering a Key Role for the Astroglial Angiotensin Type 1 Receptor AT1R

The central renin angiotensin system (RAS) is one of the most widely investigated cardiovascular systems in the brain. It is implicated in a myriad of cardiovascular diseases. However, studies from the last decade have identified its involvement in several neurologic abnormalities. Understanding the molecular functionality of the various RAS components can thus provide considerable insight into the phenotypic differences and mechanistic drivers of not just cardiovascular but also neurologic disorders. Since activation of one of its primary receptors, the angiotensin type 1 receptor (AT1R), results in an augmentation of oxidative stress and inflammatory cytokines, it becomes essential to investigate not just neuronal RAS but glial RAS as well. Glial cells are key homeostatic regulators in the brain and are critical players in the resolution of overt oxidative stress and neuroinflammation. Designing better and effective therapeutic strategies that target the brain RAS could well hinge on understanding the molecular basis of both neuronal and glial RAS. This review provides a comprehensive overview of the major studies that have investigated the mechanisms and regulation of the brain RAS, and it also provides insight into the potential role of glial AT1Rs in the pathophysiology of cardiovascular and neurologic disorders.

Integrin CD11b mediates α-synuclein-induced activation of NADPH oxidase through a Rho-dependent pathway

The activation of microglial NADPH oxidase (NOX2) induced by α-synuclein has been implicated in Parkinson's disease (PD) and other synucleinopathies. However, how α-synuclein activates NOX2 remains unclear. Previous study revealed that both toll-like receptor 2 (TLR2) and integrin play important roles in α-synuclein-induced microglial activation. In this study, we found that blocking CD11b, the α chain of integrin α_Mβ₂, but not TLR2 attenuated α-synuclein-induced NOX2 activation in microglia. The involvement of CD11b in α-synuclein-induced activation of NOX2 was further confirmed in CD11b^-/- microglia by showing reduced membrane translocation of NOX2 cytosolic subunit p47^phox and superoxide production. Mechanistically, α-synuclein bound to CD11b and subsequently activated Rho signaling pathway. α-Synuclein induced activation of RhoA and downstream ROCK but not Rac1 in a CD11b-dependent manner. Moreover, siRNA-mediated knockdown of RhoA impeded NOX2 activation in response to α-synuclein. Furthermore, we found that inhibition of NOX2 failed to interfere with the activation of RhoA signaling and interactions between α-synuclein and CD11b, further confirming that NOX2 was the downstream target of CD11b. Finally, we found that genetic deletion of CD11b abrogated α-synuclein-induced NOX2 activatoin in vivo. Taken together, our results indicated that integrin CD11b mediates α-synuclein-induced NOX2 activation through a RhoA-dependent pathway, providing not only a novel mechanistic insight but also a new potential therapeutic target for synucleinopathies.

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Blocking CD11b, the α chain of integrin α_Mβ₂, but not TLR2 attenuates α-synuclein-induced NOX2 activation.

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α-Synuclein binds to CD11b.

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CD11b regulates NOX2 activation induced by α-synuclein through a RhoA-dependent pathway.