Chronic knockdown of the nucleus of the solitary tract AT1 receptors increases blood inflammatory-endothelial progenitor cell ratio and exacerbates hypertension in the spontaneously hypertensive rat

AT1 receptor subtype a (AT1Ra) expression is increased in the nucleus of the solitary tract (NTS) in spontaneously hypertensive rat (SHR) compared with Wistar Kyoto controls. However, the chronic role of AT1Ra in the NTS for cardiovascular control is not well understood. In this study, we investigated the hypothesis that the NTS AT1Ra is involved in the neural regulation of the peripheral inflammatory status and linked with hypertension. Transduction of brain neuronal cultures with recombinant adeno-associated virus type 2 (AAV2)-AT1R-small hairpin RNA (shRNA) resulted in a 72% decrease in AT1Ra mRNA and attenuated angiotensin II-induced increase in extracellular signal-regulated kinase 1/2 phosphorylation and neuronal firing. Specific NTS microinjection of AAV2-AT1R-shRNA vector in the SHR resulted in a ≈30 mm Hg increase in the mean arterial pressure compared with control vector-injected animals (Sc-shRNA: 154±4 mm Hg; AT1R-shRNA: 183±10 mm Hg) and induced a resetting of the baroreflex control of heart rate to higher mean arterial pressure. In addition, AAV2-AT1R-shRNA-treated SHRs exhibited a 74% decrease in circulating endothelial progenitor cells (CD90+, CD4- / CD5- / CD8-) and a 300% increase in the circulating inflammatory cells, including CD4+ + CD8+, CD45+ / 3+ T lymphocytes, and macrophages (CD68+). As a result, the endothelial progenitor cell/inflammatory cells ratio was decreased by 8- to 15-fold in the AT1R-shRNA-treated SHR. However, identical injection of AAV2-AT1R-shRNA into the NTS of Wistar Kyoto rats had no effect on mean arterial pressure and inflammatory cells. These observations suggest that increased expression of the AT1Ra in SHR NTS may present a counterhypertensive mechanism involving inflammatory/angiogenic cells.

Interleukin-10 inhibits angiotensin II-induced decrease in neuronal potassium current

Previously we demonstrated that viral-mediated increased expression of the anti-inflammatory cytokine interleukin-10 within the paraventricular nucleus of the hypothalamus significantly reduces blood pressure in normal rats made hypertensive by infusion of angiotensin II. However, the exact cellular locus of this interleukin-10 action within the paraventricular nucleus is unknown. In the present study we tested whether interleukin-10 exerts direct effects at its receptors located on hypothalamic neurons to offset the neuronal excitatory actions of angiotensin II via its type 1 receptors. The results indicated the presence of immunoreactive interleukin-10 receptors on neurons in normal rat paraventricular nucleus and that receptors for this cytokine were also expressed in neurons cultured from the hypothalamus. Patch-clamp electrophysiological recordings from these cultures revealed that extracellular application of interleukin-10 alone did not exert any alterations in neuronal membrane delayed rectifier or transient potassium currents. However, angiotensin II elicited a significant decrease in delayed rectifier potassium current, an effect that was abolished by interleukin-10 application. Since decreases in delayed rectifier potassium current contribute to increased neuronal excitability, this result is consistent with a direct inhibitory action of interleukin-10 on angiotensin-induced excitation of hypothalamic neurons. As such, these data are the first indication of a neuronal locus of action of interleukin-10 to temper the actions of angiotensin II in the hypothalamus.

Abstract TP111: Activation of the Brain Renin-Angiotensin System by Translational Approaches Following Stroke Onset Is Neuroprotective in a Rat Model of Ischemic Stroke

Background: Toward discovering novel stroke therapies, recent research has shown that activation of the newly-discovered angiotensin converting enzyme 2/angiotensin-(1-7)/mas (ACE2/Ang-(1-7)/Mas) pathway, a counter-regulatory axis of the brain renin-angiotensin system, is neuroprotective in ischemic stroke in rats. Specifically, intraventricular administration of the novel ACE2 activator diminazine aceturate (DIZE) before and during an ischemic stroke decreases cerebral infarct and neurologic deficits. Efficacy must now be demonstrated using minimally-invasive methods if this therapy is to be translated to the care of human patients. In this study, we assessed the hypothesis that systemic administration of DIZE post ischemic stroke would be neuroprotective.

Methods: Adult male Sprague-Dawley rats underwent ischemic stroke by endothelin-1 induced middle cerebral artery occlusion and were randomly divided into 2 groups (n=9-10/set): 1) intraperitoneal (IP) administrations of DIZE (7.5 mg/kg) at 4, 24, and 48 h after stroke; 2) IP administrations of 0.9% saline vehicle at the same time points. At 24 and 72 h after stroke, rats underwent blinded neurologic assessments. Immediately following the 72 h tests, animals were sacrificed, cerebral infarct volumes assessed by TTC staining, and IL-1β expression in the stroke region analyzed by rt-PCR. Data are expressed as mean ± SEM with significance inferred at p<0.05.

Results: Mean infarct volume was significantly decreased by IP injections of DIZE (9.4% ± 4.35) as compared to control (22.8%±3.6, p=0.039). At 24 h post stroke, neurologic deficits (Garcia Scale) were significantly improved in the DIZE treated group (16.7±0.40) versus the saline group (15.22±0.57, p=0.037). Although DIZE tended to improve neurologic deficits 72 h post stroke, this trend was not significant. Finally, DIZE treatment significantly reduced mRNA expression of IL-1β (0.43 ± 0.14) in the cerebral cortical stroke region as compared to saline treatment (1.47±0.08, p=0.001).

Conclusions: Our findings suggest that targeting the ACE2/Ang-(1-7)/Mas axis post stroke can improve function, decrease inflammation, and reduce infarct volume - a significant translational step in brain renin-angiotensin system research.

Nucleus of the solitary tract (pro)renin receptor-mediated antihypertensive effect involves nuclear factor-κB-cytokine signaling in the spontaneously hypertensive rat

The importance of the (pro)renin receptor (PRR) in the function of the central nervous system is increasingly evident because PRR seems to play a role in neuronal control of cardiovascular function. PRR expression is elevated in the nucleus of the solitary tract (NTS) of spontaneously hypertensive rats (SHR). In this study, we tested the hypothesis that altered activity of PRR in the NTS is linked to hypertension. Eight weeks of chronic knockdown of the NTS PRR, using recombinant adeno-associated virus type 2 (AAV2)-PRR-small hairpain RNA (shRNA)-mediated gene transduction, caused a significant increase in mean arterial pressure (MAP) in the SHR (shRNA, 173±5; Control, 151±6 mm Hg) but not in Wistar Kyoto rats (shRNA, 108±7; Control, 106±6 mm Hg). The MAP elevation in the SHR was associated with decreased inflammatory markers tumor necrosis factor-α, interleukin-6, C-C motif ligand 5, and their transcription factor, nuclear factor-κB. Consistent with the pressor effects of the PRR knockdown, acute bilateral NTS injection of human renin (2 pmol/side) decreased MAP and heart rate (HR) in SHR (ΔMAP, -38±4 mm Hg; Δheart rate, -40±10 bpm), with negligible responses in Wistar Kyoto rats (ΔMAP, -4±3 mm Hg; Δheart rate, -12±7 bpm). These effects in SHR were attenuated (80%) by prorenin handle region peptide but were not affected by angiotensin II type 1 or angiotensin II type 2 receptor blockers. Finally, PRR activation in SHR neuronal cultures by prorenin activated nuclear factor-κB and increased mRNA levels of interleukin-1β (250-fold), tumor necrosis factor-α (32-fold), interleukin-6 (35-fold), C-C motif ligand 5 (12-fold), and interleukin-10 (7-fold) in a nuclear factor-κB-dependent but angiotensin II type 1 receptor-independent manner. Therefore, NTS PRR mediates antihypertensive effects via an angiotensin II-independent mechanism in SHR, which involves stimulation of the nuclear factor-κB-cytokine signaling pathway.

Adenoviral and adeno-associated viral vectors-mediated neuronal gene transfer to cardiovascular control regions of the rat brain

Viral vectors have been utilized extensively to introduce genetic material into the central nervous system. In order to investigate gene functions in cardiovascular control regions of rat brain, we applied WPRE (woodchuck hepatitis virus post-transcriptional regulatory element) enhanced-adenoviral (Ad) and adeno-assoicated virus (AAV) type 2 vectors to mediate neuronal gene delivery to the paraventricular nucleus of the hypothalamus, the nucleus tractus solitarius and the rostral ventrolateral medulla, three important cardiovascular control regions known to express renin-angiotensin system (RAS) genes. Ad or AAV2 harboring an enhanced green fluorescent protein (EGFP) reporter gene or the angiotensin type 2 receptor gene were microinjected into these brain regions in adult rats. Our results demonstrated that both AAV2 and Ad vectors elicited long-term neuronal transduction in these regions. Interestingly, we found that the WPRE caused expression of GFP driven by the synapsin1 promoter in pure glial cultures or co-cultures of neurons and glia derived from rat hypothalamus and brainstem. However, in rat paraventricular nucleus WPRE did not cause expression of GFP in glia. This demonstrates the potential use of these vectors in studies of physiological functions of certain genes in the cardiovascular control regions of the brain.

Macrophage migration inhibitory factor in the nucleus of solitary tract decreases blood pressure in SHRs

AIMS

The macrophage migration inhibitory factor (MIF) is an intracellular inhibitor of the central nervous system actions of angiotensin II on blood pressure. Considering that angiotensin II actions at the nucleus of the solitary tract are important for the maintenance of hypertension in spontaneously hypertensive rats (SHRs), we tested if increased MIF expression in the nucleus of the solitary tract of SHR alters the baseline high blood pressure in these rats.

METHODS AND RESULTS

Eight-week-old SHRs or normotensive rats were microinjected with the vector AAV2-CBA-MIF into the nucleus of the solitary tract, resulting in MIF expression predominantly in neurons. Rats also underwent recordings of the mean arterial blood pressure (MAP) and heart rate (via telemetry devices implanted in the abdominal aorta), cardiac- and baroreflex function. Injections of AAV2-CBA-MIF into the nucleus of the solitary tract of SHRs produced significant decreases in the MAP, ranging from 10 to 20 mmHg, compared with age-matched SHRs that had received identical microinjections of the control vector AAV2-CBA-eGFP. This lowered MAP in SHRs was maintained through the end of the experiment at 31 days, and was associated with an improvement in baroreflex function to values observed in normotensive rats. In contrast to SHRs, similar increased MIF expression in the nucleus of the solitary tract of normotensive rats produced no changes in baseline MAP and baroreflex function.

CONCLUSION

These results indicate that an increased expression of MIF within the nucleus of the solitary tract neurons of SHRs lowers blood pressure and restores baroreflex function.

Abstract 394: Chronic Knockdown of the NTS AT1R Increases Circulating Inflammatory-Endothelial Progenitor Cells Ratio and Exacerbates Hypertension in the SHR

AT1R expression is increased in the nucleus of solitary tract (NTS) of many animal models of hypertension. However, the impact of its chronic regulation on cardiovascular control is not well understood. In this study, we investigated the hypothesis that NTS AT1R is involved in peripheral inflammatory status and hypertension-linked cardiovascular pathophysiology. AAV2- mediated expression of a shRNA targeted the AT1R in the NTS has been used to test the hypothesis. First,the efficacy of the AAV2-AR1R-shRNA was established with the use of neuronal cells in primary culture. Transduction of these cultures by AAV2-AT1R-shRNA resulted in a 72% decrease in AT1R mRNA compared with the AAV2- Sc-shRNA transduced control. This was accompanied by complete attenuation of AngII-induced increase in ERK1/2 phosphorylation and neuronal action potential frequency (control: 2.2±0.4 vs. AT1R-shRNA: 0.5±0.3 hz). We then microinjected AAV2-AT1R-shRNA or control vector, AAV2-Scrambled (Sc)-shRNA into the NTS of 8-week-old SHR and WKY rats. Nine weeks following microinjection, AAV2-AT1R-shRNA group of SHRs showed a 29 mmHg increase in mean arterial pressure (MAP) (control: 154.2±4.7; shRNA: 183.0±10.2 mmHg), insignificant effects on the MAP of WKY rats was observed. The increase in MAP in the SHR by AAV2-AT1R-shRNA was associated with a 42% decrease in baroreflex bradycardia (control: 0.57±0.02; shRNA: 0.33±0.06 ms/mmHg), profound cardiac hypertrophy, and significant increase in the plasma norepinephrine (control: 6.36±0.39, shRNA: 13.0±4.13 ng/mL). In addition, AAV2-AT1R-shRNA rats showed significant increases in water intake (control: 32.5±1.5; shRNA: 12.5±2.5 ml/16h) and urine output (control: 1.6 ±0.5; shRNA: 9.3±2.5 ml/16h). Furthermore, AAV2-AT1R-shRNA treated SHR exhibited 74% decrease in circulating endothelial progenitor cells (EPC, CD90+, CD4/5/8-), and ∼300% increases in inflammatory cells (IC) including CD4/8+, T lymphocytes (CD45/3+) and macrophages (CD68+) . As a result, EPC/IC ratio was decreased by 8∼15 fold in AT1R-shRNA treated SHR. These observations suggest that increased AT1R in the NTS of SHR may present a counter-hypertensive mechanism involving inflammatory/angiogenic cells.

Abstract 226: Elevated Brain MCP-1 Contributes to Neuroinflammation in Hypertension

Inflammation has been identified as a major contributor to hypertension, and increased inflammation is associated with activation of the renin-angiotensin system (RAS). In this study we hypothesized that the activated RAS increases monocyte attractant protein (MCP)-1, which recruits immune cells (both resident microglia and circulating monocytes) to the paraventricular nucleus (PVN),contributing to the elevated sympathetic tone in hypertension. Treatment of primary neurons cultured from the hypothalamus of newborn SD rats with Ang II or prorenin significantly increased the levels of MCP-1 in the medium (Con: 58±7; Ang II: 191±18; prorenin: 213±23 ng/ml). To determine the effects of MCP-1 on the recruitment of resident microglia, we examined primary microglial migration using a cell migration kit. MCP-1 caused a dose-dependent (10-100 ng/ml) increase in microglial migration (Con: 0±2.9; MCP-1 at 10 ng/ml: 3.7±1.3; 50 ng/ml: 10.7±1.7; 100 ng/ml: 35.2±2.6; unit is arbitrary). In comparison to normotensive WKY rats, SHR exhibited significant increases in blood pressure (148±5 mmHg vs. 98±7 mmHg, n=5 each group). The levels of MCP-1 were dramatically increased in blood serum (77±3.6 vs. 30±0.5ng/ml), cerebrospinal fluid (18±0.9 vs. 3±0.3 ng/ml), and PVN tissues (35±0.5 vs. 4±0.4 ng/ml) of the SHR vs. WKY rats. Bone marrow-derived monocytes dissociated from the same animals were found to express high levels of CCR2 mRNA (4 fold greater in SHR vs. WKY rats), the primary receptor for MCP-1. To examine whether there was an effect of MCP-1 on monocyte recruitment, the ability of monocytes to elicit migration was compared in SHR and WKY rats. The results showed that the migration of WKY monocytes reached a plateau by 50 ng/ml MCP-1. In contrast, SHR monocytes were recruited by MCP-1 in a dose-dependent manner (10-100 ng/ml). At 100 ng/ml, MCP-1 was significantly more effective in recruiting monocytes from SHR than WKY (94±5 vs. 38±6; unit is arbitrary). In summary, these data suggest that RAS components can increase MCP-1 expression, which in turn recruits immune cells such as resident microglia and circulating monocytes. The present study suggests a potential mechanism by which inflammation contributes to hypertension in the presence of RAS activation.

Abstract 278: Down-Regulation of Corticosterone Actions Within Nucleus of the Solitary Tract Catecholaminergic Neurons Attenuates Cardiovascular Responses to Stress

We previously reported that chronic increases in corticosterone within the dorsal hindbrain, including the Nuclues of the Solitary Tract (NTS), augment the arterial pressure response to restraint stress. This study tested the hypothesis that diminishing actions of corticosterone selectively within NTS catecholaminergic neurons would attenuate the cardiovascular responses to novel and repeated restraint stress. AAV2-based viral vectors were constructed to express either GFP or 11-beta-hydroxysteroid dehydrogenase 2 (HSD2) selectively in catecholaminergic neurons using the PRSx8 promoter. HSD2 degrades corticosterone to an inactive metabolite. Adult male Sprague-Dawley rats were instrumented with telemetry mitters to measure arterial pressure and heart rate. At least 3 weeks later AAV2-PRSx8-HSD2 (n=7) or AAV2-PRSx8-eGFP (n=8) was microinjected bilaterally into the NTS (125 nl/side). After another 3 weeks rats underwent daily restraint stress (60 min per day) for 15 days. Baseline mean arterial pressure was not significantly different in GFP- versus HSD2-transduced rats prior to stress 1 (98±2 and 99±3 mmHg respectively) or stress 15 (96±3 and 100±2 mmHg respectively). During the first restraint stress, the average increase in arterial pressure in response to restraint was significantly (P<0.05) greater in the GFP- compared with the HSD2-transduced rats during the final 10 min of stress (13±1 and 5±2 mmHg respectively). During the last restraint stress the average increase in arterial pressure in response to stress was significantly (P<0.05) greater in the GFP- compared with the HSD2- transduced rats throughout the stress (11±2 and 4±1 mmHg respectively). Baseline heart rate was significantly higher in GFP- versus HSD2- transduced rats prior to stress 1 (340±6 and 317±7 bpm respectively) but not prior to stress 15 (308±6 and 309±9 bpm respectively). HSD2 transduction had no significant effect on the heart rate response to the first stress, but significantly reduced the average heart rate response to the last restraint stress (63±13 and 30±7 bpm for GFP vs HSD2). We conclude that over-expression of HSD2 in NTS catecholaminergic neurons lowers baseline heart rate and attenuates the cardiovascular responses to restraint stress.

Abstract 230: AT2 Receptor Agonist, Compound 21, Attenuates Pulmonary Hypertension and Associated Cardiac Pathophysiology via the Vasoprotective ACE2/Ang-(1-7)/Mas axis

Pulmonary hypertension (PH) is a devastating disease affecting the lung vasculature. Recently, we determined that increased activation of the ACE2/Ang-(1-7)/Mas axis attenuates much of the associated pathophysiology. In other models of cardiovascular disease, the beneficial effects seen with ACE2/Ang-(1-7)/Mas activation are similar to those seen by AT2 receptor (AT2R) activation. We hypothesize that activation of the AT2R, via selective agonist Compound 21 (C21), will be an effective treatment against PH. SD rats were injected with 50mg/kg of monocrotaline (MCT) at 8 weeks of age, to induce PH. Control animals were given saline. Two weeks post MCT injection, when right ventricular systolic pressures (RVSP) were significantly elevated (MCT 48.3±8.8; Control 32.0 ±2.4 mmHg), animals received 0.03mg/kg/day C21 ip (MCT+C21) or vehicle for 2 weeks. Two weeks later, RV hemodynamic parameters were measured and tissues collected. Treatment with C21 significantly reduced PH and associated cardiac pathophysiologies. The mechanism by which C21 attenuates PH may be the restored balance between the RAS vasodeleterious and vasoprotective arms. Relative quantitation of lung mRNA expression showed C21 treatment normalized the ACE/ACE2 and AT1R/AT2R ratios, and increased Mas receptors. C21 also attenuated the increase in pro-inflammatory cytokines TGF-β, TNF-α, and Il-1b. The increased expression of the vasoprotective axis and resulting decrease in inflammatory cytokines may account for reduced PH and associated cardiopathophysiology. The increases in ACE2/Mas receptor expression may indicate an underlying connection between the AT2R and the vasoprotective axis of the RAS.

Angiotensin II type 2 receptor-stimulated activation of plasma prekallikrein and bradykinin release: role of SHP-1

ANG II type 2 receptors (AT(2)R) elicit cardioprotective effects in part by stimulating the release of kinins; however, the mechanism(s) responsible have not been fully explored. We demonstrated previously that overexpression of AT(2)R increased expression of prolylcarboxypeptidase (PRCP; a plasma prekallikrein activator) and release of bradykinin by mouse coronary artery endothelial cells (ECs). In the present study we hypothesized that the AT(2)R-stimulated increase in PRCP is mediated by the tyrosine phosphatase SHP-1, which in turn activates the PRCP-dependent prekallikrein-kallikrein pathway and releases bradykinin. We found that activation of AT(2)R using the specific agonist CGP42112A increased SHP-1 activity in ECs, which was blocked by the AT(2)R antagonist PD123319. Activation of AT(2)R also enhanced conversion of plasma prekallikrein to kallikrein, and this effect was blunted by a small interfering RNA (siRNA) to SHP-1 and abolished by the tyrosine phosphatase inhibitor sodium orthovanadate. Treating cells with a siRNA to PRCP also blunted AT(2)R-stimulated prekallikrein activation and bradykinin release. Furthermore, blocking plasma kallikrein with soybean trypsin inhibitor (SBTI) abolished AT(2)R-stimulated bradykinin release. These findings support our hypothesis that stimulation of AT(2)R activates a PRCP-dependent plasma prekallikrein pathway, releasing bradykinin. Activation of SHP-1 may also play an important role in AT(2)R-induced PRCP activation.