Brain Angiotensinogen Research Articles

Anxiolytic effect of alamandine in male transgenic rats with low brain angiotensinogen is dependent on activation of MrgD receptors

Alamandine is a peptide hormone belonging to the renin–angiotensin system (RAS). It acts through the Mas-related G-protein coupled receptor type D, MrgD, which is expressed in different tissues, including the brain. In the present study, we hypothesize that a lack of alamandine, through MrgD, could cause the anxiety-like behavior in transgenic rats with low brain angiotensinogen [TGR(ASrAOGEN)680]. Adult male transgenic rats exhibited a significant increase in the latency to feeding time in the novelty suppressed feeding test and a decrease in the percentage of time and entries in the open arms in the elevated plus maze. These effects were reversed by intracerebroventricular infusion of alamandine. Pretreatment with D-Pro7-Ang-(1–7), a Mas and MrgD receptor antagonist, prevented the anxiolytic effects induced by this peptide. However, its effects were not altered by the selective Mas receptor antagonist, A779. In conclusion, our data indicates that alamandine, through MrgD, attenuates anxiety-like behavior in male TGR(ASrAOGEN)680, which reinforces the importance of the counter-regulatory RAS axis as promising target for the treatment of neuropsychiatric disorders.

Evaluation of a Brain Angiotensinergic Circuit in Fear-Related Behavior

The renin-angiotensin system (RAS) has been implicated in post-traumatic stress disorder (PTSD). Here we examined components of the brain RAS, in particular the origin of brain angiotensinogen (AGT), angiotensin II type 1 receptor (AT1R) and their functional role in fear-related behavior.

DOCA-SALT DIMINISHES BRAIN RAS ACTIVITY IN PARALLEL WITH PLASMA AND RENAL RAS ACTIVITY – NO EVIDENCE FOR SELECTIVE BRAIN RAS ACTIVATION

Objective: Deoxycorticosterone acetate (DOCA)-salt is suggested to promote hypertension by selectively upregulating the brain renin-angiotensin system (RAS), while suppressing the circulating RAS. Yet, we previously observed parallel downregulation of plasma and brain renin in mice. Here, we quantified angiotensinogen (AGT) and angiotensin (Ang) in rat brainstems. Design and method: For 7 weeks, rats received DOCA (200 mg; 60-day release pellet) and saline as drinking water. The contribution of AGT (liver vs. kidney/brain), Ang II type 1 receptors (AT1R) and blood pressure to tissue Ang content was determined by treatment with vehicle, liver-targeted AGT siRNA (30 mg/kg fortnightly; s.c.), valsartan (31 mg/kg/day; s.c.) or spironolactone (80 mg/kg/day; s.c.) during the final 3 weeks (n = 7–8/group). Plasma renin and AGT were quantified by enzyme-kinetic assay, tissue AGT by western blotting, and Ang I and II by LC-MS/MS. Results: Plasma renin, AGT, Ang I and II in rats not exposed to DOCA-salt were 20 ± 4 ng Ang I/mL/h, 730 ± 37 nM, 140 ± 24 pM and 108 ± 24 pM. AGT was present in liver, kidney and brainstem. Kidney Ang I and II were 540 ± 135 and 510 ± 97 fmol/g, while brainstem Ang I and II were undetectable in all and 30% of the rats, respectively (LLOQ <6 fmol/g). DOCA-salt increased blood pressure by 19 ± 1 mmHg and lowered plasma and renal Ang I and II by ∼90%, while brainstem Ang II became undetectable in 70% of the rats. AGT siRNA lowered plasma AGT by 97 ± 0.3%, with similar reductions in the liver and kidney, while brain AGT was unaltered. Whereas spironolactone normalized blood pressure, it increased plasma renin, and plasma, renal and brain Ang I and II. siRNA and valsartan tended to further lower renal Ang, without affecting blood pressure, plasma renin or plasma and brain Ang I and II. Conclusions: DOCA-salt suppresses plasma, renal and brain Ang II in parallel. Renal Ang II depends on hepatic AGT and AT1R-mediated internalization. Brain AGT is liver-independent, but unaltered by DOCA-salt, thus not permitting selective brain RAS upregulation. The RAS upregulation during spironolactone, combined with its antihypertensive effect, argues against the (brain) RAS as a major blood pressure determinant in this model.

Alamandine through MrgD receptor induces antidepressant-like effect in transgenic rats with low brain angiotensinogen

Alamandine (Ala1-Arg2-Val3-Tyr4-Ile5-His6-Pro7), a heptapeptide hormone of the renin–angiotensin system (RAS), exerts its effects through the Mas-related G-protein coupled receptor of the type D, MrgD, which is expressed in different tissues, including the brain. In the present study, we tested the hypothesis that alamandine could attenuate the depression-like behavior observed in transgenic rats with low brain angiotensinogen, TGR (ASrAOGEN)680. Transgenic rats exhibited a significant increase in the immobility time in forced swim test, a phenotype reversed by intracerebroventricular infusion of alamandine. Pretreatment with D-Pro7-Ang-(1–7), a Mas/MrgD receptor antagonist, prevented the antidepressant-like effect induced by this peptide demonstrating, for the first time, that alamandine through MrgD receptor, can modulate depression-like behavior in TGR (ASrAOGEN)680. This result shows an action of alamandine which strengthens the importance of the counter-regulatory arms of the RAS in fight and treatment of neuropsychiatric diseases.

Evaluation of a brain angiotensinergic circuit in fear‐related behavior

BackgroundThe renin‐angiotensin system (RAS) has been implicated in post‐traumatic stress disorder (PTSD), however the mechanisms responsible for this connection and the therapeutic potential of targeting the RAS in PTSD remains unknown. Combining neuroanatomical, genetic knockdown and behavioral approaches, we examined components of the brain RAS, in particular the origin of brain angiotensinogen (AGT), angiotensin II type 1 receptor (AT1R) and their functional role in fear‐related behavior.MethodsRNA Scope combined with immunohistochemistry (IHC) were used to examine the expression pattern and cellular localization of brain AGT in C57BL/6J mice. Dual IHC was used to characterize AT1R‐eGFP+ cells in the amygdala of the AT1R‐eGFP‐BAC reporter mouse. Pavlovian fear conditioning and cre‐expressing lentivirus (LV) injection were used to demonstrate the effects of AT1R deletion on fear memory in male AT1R‐floxed mice.ResultsAGT mRNA was primarily expressed in the diencephalon, midbrain and hindbrain, including the parabrachial complex (PB) which sends strong neuropeptide projections to the amygdala. Some AGT positive cells in PB were determined to be of neuronal origin as they co‐localized with neuronal marker NeuN (FIG 1A). In the amygdala, AGT mRNA was highly expressed in the medial division of the central amygdala (CeM) and the medial amygdala (MeA), but not in the lateral division of the central amygdala (CeL) or basolateral amygdala (BLA) (FIG 1B). Different from AGT, the AT1R‐eGFP+ neurons in the amygdala were predominantly expressed in CeL, with little AT1R‐eGFP expression in BLA, MeA or CeM (FIG 1C). Characterization of AT1R‐eGFP+ neurons in the CeL demonstrated that the AT1R neurons are GABAergic (98.6%) and the majority were co‐located with fear off neuronal marker protein kinase C‐δ (65.7%) as opposed to the fear on neuronal marker somatostatin (9.4%). Next, using cre‐expressing lentivirus, AT1R was deleted from the central amygdala (CeA) of AT1R‐floxed mice. CeA AT1R deletion did not affect fear acquisition, but enhanced the extinction of fear as determined by a reduction in percent freezing during extinction training (57.04% ± 3.9 LV‐GFP v.s. 42.6% ± 4.1 LV‐Cre group, p<0.05, n=9) and retention tests (53.5% ± 5.3 LV‐GFP v.s. 34.4% ± 5.3 LV‐Cre group, p<0.05, n=9) (FIG 2).ConclusionsThese findings provide neuroanatomical and behavioral evidence for brain RAS pre‐cursor AGT and the AT1R in the extinction of fear memory. We speculate that AGT modulates the PB‐CeA circuit during threat responding in fear learning and memory. To further understand the neuroanatomy and function of this circuit, future studies are needed to apply retrograde tracing approaches combined with AGT RNA Scope and region specific deletion of the AGT positive neurons.Distribution of AGT and AT1R in PB and Amygdala Subdivisions(A) AGT mRNA was found in PB (left) and co‐localized with NeuN (right). (B) AGT mRNA was mainly expressed in CeM and MeA. (C) AT1R‐GFP+ neurons were predominately found in CeL.Figure 1Enhanced fear extinction following CeA AT1R deletion.(A) Auditory fear conditioning protocol. (B) AT1R deletion from the CeA did not affect fear acquisition (left) but enhanced the extinction of fear as shown by reduced percent freezing during extinction training (middle) and extinction retention test (right).Figure 2

Abstract P2030: DOCA-Salt Diminishes Brain RAS Activity In Parallel With Plasma And Renal RAS Activity - No Evidence For Selective Brain RAS Activation

Deoxycorticosterone acetate (DOCA)-salt is suggested to increase blood pressure via selective upregulation of the brain renin-angiotensin system (RAS), while suppressing the circulating RAS. Yet, we have observed parallel downregulation of plasma and brain renin in mice. Here, we quantified brainstem angiotensinogen (AGT) and angiotensin (Ang) levels in rats exposed to DOCA (200mg; 60-day release) and 0.9% NaCl as drinking water for 7 weeks. To determine the contribution of AGT (liver vs. kidney/brain), Ang II type 1 receptors (AT1R) and blood pressure to tissue Ang II content, rats received vehicle, liver-targeted AGT siRNA (10 mg/kg fortnightly; s.c.), valsartan (31 mg/kg/day; s.c.) or spironolactone (80 mg/kg/day; s.c.) during the final 3 weeks, the latter fully normalizing blood pressure (n=3-9 per group). Plasma renin and AGT were determined by enzyme-kinetic assay, tissue AGT by western blotting, and Ang I and II by LC-MS/MS. Plasma renin, AGT, Ang I and II in rats not exposed to DOCA-salt were 24±8ng Ang I/mL per h, 731±51nM, 123±38pM and 109±43pM. AGT was present in liver, kidney and brainstem. Kidney Ang I and II were 540±135and 510±97fmol/g, while brainstem Ang I and II were undetectable in all and 50% of the rats, respectively (<6 and <12±4 fmol/g). DOCA-salt lowered plasma and renal Ang I and II by ≈90%, while brainstem Ang II became undetectable in 70% of the rats. AGT siRNA reduced plasma AGT by 97±1%, with similar reductions in the liver and kidney, while brain AGT was unaltered. Neither valsartan nor spironolactone affected AGT at any site. Spironolactone increased plasma renin, and hence plasma, renal and brain Ang I and II also rose modestly. Both siRNA and valsartan tended to further lower renal Ang levels, while neither drug affected plasma renin or Ang I and II in plasma and brain. In conclusion, DOCA-salt suppresses plasma, renal and brain Ang II in parallel. Renal Ang II is determined by hepatic AGT and relies on AT1R-mediated internalization. Although brain AGT is liver-independent, it is unaltered by DOCA-salt and does not permit selective brain RAS upregulation. The RAS upregulation induced by spironolactone, combined with its blood pressure-normalizing effect, argues against the (brain) RAS as a major blood pressure determinant in this model.

Effect of Dehydration in Late Pregnancy on Fetal Rat Growth and Fetal Brain RAS Receptor Expression

To study the effect of maternal dehydration on fetal growth and fetal brain RAS development in late pregnancy. The dehydration model of the maternal mice during the late pregnancy was established. The experiment was divided into two groups: use blood-gas analyzer to detect the blood gas and electrolyte parameters of the mother and fetus, and use the osmometer to detect the plasma osmotic pressure; use LaserDoppler to detect the fetal brain surface blood flow; detect the levels of angiotensin II receptor protein and angiotensinogen in fetal brain. The dehydration of maternal mice during the late pregnancy can significantly reduce the dry and wet weights of fetus and fetal brain. The serum sodium, hematocrit (HCT) and plasma osmotic pressure of fetal rats increase, and there is a statistical difference compared with the control group; the fetal cerebral blood flow (CBF) of dehydration group is significantly lower than that of the control group. Dehydration in late pregnancy can significantly affect fetal rat growth and fetal brain RAS receptor expression.

Angiotensin generation in the brain: a re-evaluation.

The existence of a so-called brain renin-angiotensin system (RAS) is controversial. Given the presence of the blood-brain barrier, angiotensin generation in the brain, if occurring, should depend on local synthesis of renin and angiotensinogen. Yet, although initially brain-selective expression of intracellular renin was reported, data in intracellular renin knockout animals argue against a role for this renin in angiotensin generation. Moreover, renin levels in brain tissue at most represented renin in trapped blood. Additionally, in neurogenic hypertension brain prorenin up-regulation has been claimed, which would generate angiotensin following its binding to the (pro)renin receptor. However, recent studies reported no evidence for prorenin expression in the brain, nor for its selective up-regulation in neurogenic hypertension, and the (pro)renin receptor rather displays RAS-unrelated functions. Finally, although angiotensinogen mRNA is detectable in the brain, brain angiotensinogen protein levels are low, and even these low levels might be an overestimation due to assay artefacts. Taken together, independent angiotensin generation in the brain is unlikely. Indeed, brain angiotensin levels are extremely low, with angiotensin (Ang) I levels corresponding to the small amounts of Ang I in trapped blood plasma, and Ang II levels at most representing Ang II bound to (vascular) brain Ang II type 1 receptors. This review concludes with a unifying concept proposing the blood origin of angiotensin in the brain, possibly resulting in increased levels following blood-brain barrier disruption (e.g. due to hypertension), and suggesting that interfering with either intracellular renin or the (pro)renin receptor has consequences in an RAS-independent manner.

Development of obesity can be prevented in rats by chronic icv infusions of AngII but less by Ang(1-7).

Considering that obesity is one of the leading risks for death worldwide, it should be noted that a brain-related mechanism is involved in AngII-induced and AT1-receptor-dependent weight loss. It is moreover established that activation of the Ang(1-7)/ACE2/Mas axis reduces weight, but it remains unclear whether this Ang(1-7) effect is also mediated via a brain-related mechanism. Additionally to Sprague Dawley (SD) rats, we used TGR(ASrAOGEN) selectively lacking brain angiotensinogen, the precursor to AngII, as we speculated that effects are more pronounced in a model with low brain RAS activity. Rats were fed with high-calorie cafeteria diet. We investigated weight regulation, food behavior, and energy balance in response to chronic icv.-infusions of AngII (200ng•h-1), or Ang(1-7) (200/600ng•h-1) or artificial cerebrospinal fluid. High- but not low-dose Ang(1-7) slightly decreased weight gain and energy intake in SD rats. AngII showed an anti-obese efficacy in SD rats by decreasing energy intake and increasing energy expenditure and also improved glucose control. TGR(ASrAOGEN) were protected from developing obesity. However, Ang(1-7) did not reveal any effects in TGR(ASrAOGEN) and those of AngII were minor compared to SD rats. Our results emphasize that brain AngII is a key contributor for regulating energy homeostasis and weight in obesity by serving as a negative brain-related feedback signal to alleviate weight gain. Brain-related anti-obese potency of Ang(1-7) is lower than AngII but must be further investigated by using other transgenic models as TGR(ASrAOGEN) proved to be less valuable for answering this question.

Angiotensin-(1-7) attenuates the anxiety and depression-like behaviors in transgenic rats with low brain angiotensinogen

Transgenic rats with low brain angiotensinogen, TGR(ASrAOGEN)680, expressing an antisense RNA against angiotensinogen in glial cells, provide an interesting tool to evaluate the role of brain angiotensins in different behavior responses. The present study was conducted to test the hypothesis that angiotensin-(1-7) [Ang-(1-7)] and serotonin can modulate anxiety and depression-related behaviors in the TGR(ASrAOGEN)680 rats. Therefore, the effect of acute intracerebroventricular administration of Ang-(1-7) and intraperitoneal administration of the selective serotonin reuptake inhibitor fluoxetine was evaluated in TGR(ASrAOGEN) rats subjected to the elevated plus maze (EPM) and forced swimming (FST) tests. Transgenic rats spent a lower percentage of time in the open arms of EPM and showed a significant increase in the immobility time in FST, indicating that a low angiotensinogen level in the brain leads to anxiety-like behavior accompanied by a depression-like state. Administration of both, Ang-(1-7) and fluoxetine reversed the anxiety- and depressive-like behavior of transgenic rats with low brain angiotensinogen, suggesting that this may be, at least in part, related to a decreased level of Ang-(1-7) and serotonin in the brain of these animals.

Abstract 157: MAP Kinase Phosphatase-1 Inhibitor Injection into the Solitary Tract Nucleus Impairs Cardiovagal Baroreflex Function in Transgenic ASrAOGEN Rats

Hypotensive transgenic ASrAOGEN rats (AS) with low brain angiotensinogen resulting from glial overexpression of an antisense oligonucleotide to angiotensinogen, have enhanced baroreflex sensitivity (BRS) relative to hypertensive transgenic (mRen2)27 rats (mRen) that overexpress the murine Ren2 gene or normotensive Sprague Dawley rats (SD). The AS rats exhibit elevated protein expression and activity (less phosphorylated-ERK) of the MAP Kinase Phosphatase-1 [MKP-1], a negative regulator of MAP Kinase signaling in the brain dorsal medulla compared with either mRen or SD rats at 26 wks of age. To determine if MKP-1 plays a role in maintenance of BRS, we gave acute bilateral microinjections of an irreversible MKP-1 inhibitor {2,3-bis-[(2-Hydroxyethyl)thiol]-1,4-naphthoquinone, NSC 95397; 200 nM/120 nL} into the solitary tract nucleus (NTS), an important site in the dorsal medulla for modulation of BRS in urethane/chloralose anesthetized AS, mRen and SD rats at 21 wks of age. The MKP-1 inhibitor impaired the BRS for bradycardia in response to increases in pressure by 48 % at 10 min (1.01 ± 0.16 baseline vs. 0.49 ± 0.1 msec/mm Hg at 10 min), 56 % at 60 min and 64 % at 120 min in the AS rats (p = 0.02, n = 8), but not in the mRen or SD rats. In addition, NSC 95397 reduced resting pressure (91 ± 3 at baseline vs. 79 ± 3 at 60 min vs. 80 ± 3 mm Hg at 120 min) in the SD rats, with a similar trend in the other strains, without effects on resting heart rate in any strain. Thus, up-regulated expression of MKP-1 contributes to the higher resting BRS function in AS rats. AS animals are spared age-related declines in BRS and they maintain higher expression of MKP-1 protein in the dorsal medulla vs. either mRen or SD rats (AS: 1.6 ± 0.2, mRen: 0.8 ± 0.1, SD: 1 ± 0.1 arbitary units; p = 0.01, n = 6 per group) at 66 wks of age. Thus, higher MKP-1 may be involved the preservation of BRS in older AS rats, suggesting the phosphatase be a novel therapeutic target to improve BRS function in aging and hypertension.

Thermoregulatory adjustments induced by exercise in rats with low brain angiotensinogen

The effect of exercise on heat balance and performance were assessed in TGR(ASrAogen)‐680 rats (TG) with low glial angiotensinogen production. Sprague‐Dawley (SD) and TG rats (n=7/group) performed an incremental running test to determine their maximal performance. All animals run at 60% of maximal workload until fatigue while body (Tb) and tail (Ttail) temperatures were recorded. Workload (W), the rates of body heating (BHR) and heat storage (HSR) and Tb threshold for tail vasodilation (TTbV) were calculated. The speed that corresponded to 60% of maximal workload was lower in TG rats in comparison with SD animals (19.6 ± 0.5 m.min‐1, SD vs. 15.0 ± 0.3 m.min‐1, TG; p < 0.01). After 13 min of exercise, TG animals showed a greater rise in Tb (13 min: 38.2 ± 0.1 °C, SD vs. 38.5 ± 0.1 °C, TG; p < 0.01) due to the delay in tail skin vasodilation (7.7 ± 0.9 min, SD vs. 11.3 ± 0.7 min, TG; p < 0.01) as well as the higher TTbV (38.0 ± 0.1 °C, SD vs. 38.4 ± 0.1 °C, TG; p < 0.01). The BHR and the HSR of TG animals were, respectively, 39% and 41% higher (p<0.03), both of which closely related with their decreased time to fatigue (p<0.05). The data bring evidence that central angiotensin‐mediated pathways are involved in thermoregulatory heat loss during exercise since low brain angiotensinogen levels attenuate heat dissipation, leading to a faster exercise‐induced increase in Tb associated with decreased performance. Supported by CNPq, FAPEMIG and CAPES

The brain renin-angiotensin system and cardiovascular responses to stress: insights from transgenic rats with low brain angiotensinogen

The renin-angiotensin system (RAS) has been identified as an attractive target for the treatment of stress-induced cardiovascular disorders. The effects of angiotensin (ANG) peptides during stress responses likely result from an integration of actions by circulating peptides and brain peptides derived from neuronal and glial sources. The present review focuses on the contribution of endogenous brain ANG peptides to pathways involved in cardiovascular responses to stressors. During a variety of forms of stress, neuronal pathways in forebrain areas containing ANG II or ANG-(1-7) are activated to stimulate descending angiotensinergic pathways that increase sympathetic outflow to increase blood pressure. We provide evidence that glia-derived ANG peptides influence brain AT(1) receptors. This appears to result in modulation of the responsiveness of the neuronal pathways activated during stressors that elevate circulating ANG peptides to activate brain pathways involving descending hypothalamic projections. It is well established that increased cardiovascular reactivity to stress is a significant predictor of hypertension and other cardiovascular diseases. This review highlights the importance of understanding the impact of RAS components from the circulation, neurons, and glia on the integration of cardiovascular responses to stressors.

Astrocytes in NTS after exposure to chronic intermittent hypoxia

Chronic intermittent hypoxia (CIH) is a model of the arterial hypoxemia that accompanies sleep apnea and increases resting arterial pressure. Exposures to hypoxia activate astrocytes in the brain. Astrocytes are a primary source of brain angiotensinogen, the precursor to angiotensin II. We tested the hypothesis that chronic intermittent hypoxia increases astrocytes in the nucleus tractus solitarii (NTS). Sprague‐Dawley rats (13 ± 0.3 weeks old) were exposed to CIH (9% oxygen for 3min every 10 min, 8 h per day) for 7 days (n = 5) while control rats (n = 4) were maintained in normoxia. After the CIH protocol, brain stem tissue containing NTS was obtained. Protein levels of the astrocyte marker glial fibrillary acidic protein (GFAP) in the NTS were assessed by Western blot analysis. Relative protein levels of GFAP to actin in the caudal NTS did not differ between CIH and control groups (3.3 ± 1.7 vs. 4.0 ± 1.7, CIH vs. control, P=0.59). The GFAP levels tended to be lower in CIH than in the control group in intermediate and rostral NTS (intermediate: 2.3 ± 1.1 vs. 3.7 ± 0.6, P=0.11; rostral: 1.5 ± 0.9 vs. 2.7 ± 1.0, P=0.052). These results did not support the idea that hypertension induced by CIH is associated with an activation of astrocytes in the NTS. CIH might decrease astrocytes in the NTS as opposed to our hypothesis. Supported by HL‐088052

Cardiovascular responses evoked by activation or blockade of GABAA receptors in the hypothalamic PVN are attenuated in transgenic rats with low brain angiotensinogen

Previous evidence indicates that a balance between inhibitory gabaergic and excitatory angiotensinergic factors in the PVN is important for cardiovascular control. We investigated the cardiovascular response evoked from activation or blockade of GABAA receptors in the paraventricular nucleus (PVN), in transgenic rats with low brain angiotensinogen [TGR(ASrAOGEN)]. Brain Ang II and Ang-(1–7) levels were also determined. In functional experiments, TGR(ASrAOGEN) and Sprague–Dawley rats (SD, control) were anesthetized with urethane and blood pressure (BP), heart rate (HR) and renal sympathetic nerve activity (RSNA) were recorded. Brain Ang II and Ang-(1–7) levels were largely reduced in TGR(ASrAOGEN) compared with SD rats. Inhibition of PVN neurons with the GABAA agonist, muscimol (1nmol/100nL), resulted in an attenuated fall in all cardiovascular variables in TGR(ASrAOGEN) compared with SD rats. This difference was particularly pronounced in HR (TGR Mus −23±6bpm vs. −77±9bpm SD Mus; P<0.05) and RSNA (TGR −3±10% vs.−29±8% SD; P<0.05). Furthermore, the sympathetic response evoked by blockade of GABAA receptors in the PVN of TGR(ASrAOGEN) was also largely suppressed. The present data indicate that the sympathetic outflow mediated by PVN neurons under basal conditions is suppressed in TGR(ASrAOGEN) rats corroborating the functional significance of brain angiotensin production in the central regulation of sympathetic output to the cardiovascular system.

Autonomic Dysfunction in Heart Failure and Renal Disease

EDITORIAL article Front. Physiol., 26 June 2012Sec. Integrative Physiology Volume 3 - 2012 | https://doi.org/10.3389/fphys.2012.00219

Regulation of angiotensinogen by angiotensin II in mouse primary astrocyte cultures

Astrocytes are the major source of angiotensinogen in the brain and play an important role in the brain renin-angiotensin system. Regulating brain angiotensinogen production alters blood pressure and fluid and electrolyte homeostasis. In turn, several physiological and pathological manipulations alter expression of angiotensinogen in brain. Surprisingly, little is known about the factors that regulate astrocytic expression of angiotensinogen. There is evidence that angiotensinogen production in both hepatocytes and cardiac myocytes can be positively regulated via the angiotensin type 1 receptor, but this effect has not yet been studied in astrocytes. Therefore, the aim of this project was to establish whether angiotensin II modulates angiotensinogen production in brain astrocytes. Primary astrocyte cultures, prepared from neonatal C57Bl6 mice, expressed angiotensinogen measured by immunocytochemistry and real-time PCR. Using a variety of approaches we were unable to identify angiotensin receptors on cultured astrocytes. Exposure of cultured astrocytes to angiotensin II also did not affect angiotensinogen expression. When astrocyte cultures were transduced with the angiotensin type 1A receptor, using adenoviral vectors, angiotensin II induced a robust down-regulation (91.4% ± 1.8%, p < 0.01, n = 4) of angiotensinogen gene expression. We conclude that receptors for angiotensin II are present in extremely low levels in astrocytes, and that this concurs with available data in vivo. The signaling pathways activated by the angiotensin type 1A receptor are negatively coupled to angiotensinogen expression and represent a powerful pathway for decreasing expression of this protein, potentially via signaling pathways coupled to Gα(q/11) .

Prenatal water deprivation alters brain angiotensin system and dipsogenic changes in the offspring

Objective: Central renin–angiotensin system (RAS) plays an important role in regulating body fluid balance. The present study determined the effect of maternal dehydration on brain expression levels of angiotensinogen, angiotensin II receptor subtypes, and dipsogenic responses in offspring. Methods: Pregnant rats were deprived of water during late gestation. Expressions of brain angiotensinogen, angiotensin II receptors, and dipsogenic responses were determined. Results: Maternal water deprivation significantly decreased fetal body and brain weight, and body and tail length. Fetal plasma sodium, osmolality, and hematocrit were increased. Both AT1R and AT2R protein abundance was significantly increased in the fetal brain, associating with increased mRNA levels of AT1aR and AT2R. Additionally, angiotensinogen mRNA was increased. In adult offspring, prenatal dehydration resulted in significant increases in AT1R protein and AT1aR mRNA, as well as angiotensinogen mRNA in the forebrain in both males and females. In contrast, AT2R mRNA and protein were increased only in males. Prenatal dehydration resulted in a significant increase in intracerebroventricular angiotensin II-induced water intake in male, but not female, offspring. Conclusion: The results provided new information that antenatal water deprivation induces a reprogramming of brain RAS and Ang II receptor expression patterns and alters the central Ang II-mediated dipsogenic response in offspring in a sex-dependent manner.

Anxiety-related behaviour of low brain angiotensinogen transgenic rats in the canopy test

This study investigated risk assessment and anxiolytic/anxiogenic drug effects in “low brain angiotensinogen” transgenic rats (TGR) in comparison to wild-type Sprague–Dawley rats (SD) in the canopy test of anxiety-related behaviour. TGR showed a higher frequency of the risk assessment behaviour as indicated by performance of stretched attend posture (SAP) compared to SD. Diazepam (0.25 mg/kg) reduced SAP in both strains, whereas FG-7142 had no significant effect. The 5-HT 1B/2C agonist mCPP (0.5–2 mg/kg) reduced SAP in both strains. Diazepam (0.25–1 mg/kg) increased head dips and decreased the time spent under the canopy in SD rats. There were significant anxiogenic effects of both FG-7142 (3–6 mg/kg) and mCPP (0.5–2 mg/kg) on these parameters for SD but not TGR. Diazepam (1 mg/kg) increased the number of entries into the open zone in both strains. mCPP reduced this parameter in SD (2 mg/kg) and TGR (0.5–2 mg/kg). FG-7142 had a similar effect in SD (3–6 mg/kg) and TGR (6 mg/kg). This study showed a significant transgenic effect on SAP. The increased number of SAP seen in TGR could be reduced with diazepam. Although both FG-7142 and mCPP are generally anxiogenic, no significant effects of FG-7142 on SAP were observed and mCPP even reduced SAP.

Systemic candesartan reduces brain angiotensin II via downregulation of brain renin–angiotensin system

The renin-angiotensin system has an important function in the regulation of blood pressure as well as in pathophysiological processes in the central nervous system. We examined the effects of the angiotensin receptor blocker candesartan (10 mg kg(-1) per day, p.o.) on brain angiotensin II levels in angiotensin II-infused hypertensive rats. Angiotensin II or vehicle was infused subcutaneously for 14 days in Sprague-Dawley rats. Angiotensin II infusion resulted in increased blood pressure, an effect that was blocked by candesartan treatment. There was no effect of the angiotensin II infusion on Angiotensin II levels in the brain or on blood-brain barrier permeability. Brain tissue angiotensinogen and angiotensin converting enzyme mRNA levels were not changed by angiotensin II infusion but were decreased by candesartan treatment. At 2 weeks of treatment, CV11974, an active form of candesartan, was detectable in the plasma but was not detectable in brain tissue. These data suggest that treatment with candesartan decreases brain angiotensin II by decreasing brain angiotensinogen and angiotensin converting enzyme gene expression.