A decrease in angiotensin receptor binding in rat brain nuclei by antisense oligonucleotides to the angiotensin AT1 receptor

Tracking oxytocin functions in the rodent brain during the last 30 years: From push-pull perfusion to chemogenetic silencing

A short overview is provided of the last 30 years of oxytocin (and vasopressin) research performed in our laboratories, starting with attempts to monitor the release of this nonapeptide in the rodent brain during physiological conditions such as suckling in the lactating animal. Using push-pull perfusion and microdialysis approaches, release patterns in hypothalamic and limbic brain regions could be characterised to occur from intact neuronal structures, to be independent of peripheral secretion into blood, and to respond differentially to various stimuli, particularly those related to reproduction and stress. Parallel efforts focused on the functional impact of central oxytocin release, including neuroendocrine and behavioural effects mediated by nonapeptide receptor interactions and subsequent intraneuronal signalling cascades. The use of a variety of sophisticated behavioural paradigms to manipulate central oxytocin release, along with pharmacological, genetic and pharmacogenetic approaches, revealed multiple consequences on social behaviours, particularly social fear.

Renin Angiotensin System in Cognitive Function and Dementia

Angiotensin II represents a key molecule in hypertension and cerebrovascular pathology. By promoting inflammation and oxidative stress, enhanced Ang II levels accelerate the onset and progression of cell senescence. Sustained activation of RAS promotes end-stage organ injury associated with aging and results in cognitive impairment and dementia. The discovery of the angiotensin-converting enzyme ACE2-angiotensin (1–7)-Mas receptor axis that exerts vasodilator, antiproliferative, and antifibrotic actions opposed to those of the ACE-Ang II-AT1 receptor axis has led to the hypothesis that a decrease in the expression or activity of angiotensin (1–7) renders the systems more susceptible to the pathological actions of Ang II. Given the successful demonstration of beneficial effects of increased expression of ACE2/formation of Ang1–7/Mas receptor binding and modulation of Mas expression in animal models in containing cerebrovascular pathology in hypertensive conditions and aging, one could reasonably hope for analogous effects regarding the prevention of cognitive decline by protecting against hypertension and cerebral microvascular damage. Upregulation of ACE2 and increased balance of Ang 1–7/Ang II, along with positive modulation of Ang II signaling through AT2 receptors and Ang 1–7 signaling through Mas receptors, may be an appropriate strategy for improving cognitive function and treating dementia.

Not just angiotensinases: new roles for the angiotensin-converting enzymes

The renin-angiotensin system (RAS) is a critical regulator of blood pressure and fluid homeostasis. Angiotensin II, the primary bioactive peptide of the RAS, is generated from angiotensin I by angiotensin-converting enzyme (ACE). A homologue of ACE, ACE2, is able to convert angiotensin II to a peptide with opposing effects, angiotensin-(1-7). It is proposed that disturbance of the balance of ACE and ACE2 expression and/or function is important in pathologies in which angiotensin II plays a role. These include cardiovascular and renal disease, lung injury and liver fibrosis. The critical roles of ACE and ACE2 in regulating angiotensin II levels have traditionally focussed attention on their activities as angiotensinases. Recent discoveries, however, have illuminated the roles of these enzymes and of the ACE2 homologue, collectrin, in intracellular trafficking and signalling. This paper reviews the key literature regarding both the catalytic and non-catalytic roles of the angiotensin-converting enzyme gene family.

Angiotensin-converting enzyme 2 in the brain: properties and future directions

Angiotensin (Ang)-converting enzyme (ACE) 2 cleaves Ang-II into the vasodilator peptide Ang-(1-7), thus acting as a pivotal element in balancing the local effects of these peptides. ACE2 has been identified in various tissues and is supposed to be a modulator of cardiovascular function. Decreases in ACE2 expression and activity have been reported in models of hypertension, heart failure, atherosclerosis, diabetic nephropathy and others. In addition, the expression level and/or activity are affected by other renin-angiotensin system components (e.g., ACE and AT1 receptors). Local inhibition or global deletion of brain ACE2 induces a reduction in baroreflex sensitivity. Moreover, ACE2-null mice have been shown to exhibit either blood pressure or cardiac dysfunction phenotypes. On the other hand, over-expression of ACE2 exerts protective effects in local tissues, including the brain. In this review, we will first summarize the major findings linking ACE2 to cardiovascular function in the periphery then focus on recent discoveries related to ACE2 in the CNS. Finally, we will unveil new tools designed to address the importance of central ACE2 in various diseases, and discuss the potential for this carboxypeptidase as a new target in the treatment of hypertension and other cardiovascular diseases.

Brain renin angiotensin in disease

A brain renin angiotensin system (RAS) and its role in cardiovascular control and fluid homeostasis was at first controversial. This was because a circulating kidney-derived renin angiotensin system was so similar and well established. But, the pursuit of brain RAS has proven to be correct. In the course of accepting brain RAS, high standards of proof attracted state of the art techniques in all the new developments of biolo1gy. Consequently, brain RAS is a robust concept that has enlightened neuroscience as well as cardiovascular physiology and is a model neuropeptide system. Molecular biology confirmed the components of brain RAS and their location in the brain. Transgenic mice and rats bearing renin and extra copies of angiotensinogen genes revealed the importance of brain RAS. Cre-lox delivery in vectors has enabled pinpoint gene deletion of brain RAS in discrete brain nuclei. The new concept of brain RAS includes ACE-2, Ang1–7, and prorenin and Mas receptors. Angiotensin II (ANG II) generated in the brain by brain renin has many neural effects. It activates behavioral effects by selective activation of ANG II receptor subtypes in different locations. It regulates sympathetic activity and baroreflexes and contributes to neurogenic hypertension. New findings implicate brain RAS in a much wider range of neural effects. We review brain RAS involvement in Alzheimer’s disease, stroke memory, and learning alcoholism stress depression. There is growing evidence to consider developing treatment strategies for a variety of neurological disease states based on brain RAS.

[Mechanisms of hypertension in the central nervous system]

This article reviews studies by the author on central mechanisms of hypertension. Spontaneously hypertensive rats (SHR) have been developed as a rat model of genetic hypertension, and central acetylcholine has been implicated in hypertension in SHR. The rostral ventrolateral medulla (RVL), a major source of efferent sympathetic activity, has cholinergic pressor systems. The release of acetylcholine is enhanced in the RVL of SHR, leading to hypertension. The alteration of the RVL cholinergic system in SHR results from enhanced angiotensin systems in the anterior hypothalamic area (AHA). Angiotensin II-sensitive neurons are present in the AHA and they are tonically activated by endogenous angiotensins. The basal activity of AHA angiotensin II-sensitive neurons is enhanced in SHR, mainly due to enhanced sensitivity of AHA neurons to angiotensin II. The AHA angiotensin system is also responsible for hypertension induced by emotional stress and central Na(+) increases. These findings suggest that the AHA angiotensin system may play a critical role in the development of hypertension.

AT1 receptor mRNA antisense normalizes enhanced cardiac sympathetic afferent reflex in rats with chronic heart failure

Previous studies showed that the cardiac sympathetic afferent reflex (CSAR) is enhanced in dogs and rats with chronic heart failure (CHF) and that central ANG II type 1 receptors (AT(1)R) are involved in this augmented reflex. The aim of this study was to determine whether intracerebroventricular administration and microinjection of antisense oligodeoxynucleotides targeted to AT(1)R mRNA would attenuate the enhanced CSAR and decrease resting renal sympathetic nerve activity (RSNA) in rats with coronary ligation-induced CHF. The CSAR was elicited by application of bradykinin to the epicardial surface of the left ventricle. Reflex responses to epicardial administration of bradykinin were enhanced in rats with CHF. The response to bradykinin was determined every 50 min after intracerebroventricular administration (lateral ventricle) or microinjection (into paraventricular nucleus) of antisense or scrambled oligonucleotides to AT(1)R mRNA. AT(1)R mRNA and protein levels in the paraventricular nucleus were significantly reduced 5 h after administration of antisense. Antisense significantly decreased resting RSNA and normalized the enhanced CSAR responses to bradykinin in rats with CHF. Scrambled oligonucleotides did not alter resting RSNA or the enhanced responses to bradykinin in rats with CHF. No significant effects were found in sham-operated rats after administration of either antisense or scrambled oligonucleotides. These results strongly suggest that central AT(1)R mRNA antisense reduces expression of AT(1)R protein and normalizes the augmentation of this excitatory sympathetic reflex and that genetic manipulation of protein expression can be used to normalize the sympathetic enhancement in CHF.

Sp1 decoy oligodeoxynucleotide decreases angiotensin receptor expression and blood pressure in spontaneously hypertensive rats

The transcriptional factor Sp1 is associated with GC-rich promoters and involved in basal promoter activity. A GC-box-related sequence is located within the -58 to -34 base pair region of the angiotensin type 1 receptor gene promoter. We examined whether Sp1 in the hypothalamus was increased in spontaneously hypertensive rats (SHR) and whether inhibition of Sp1 binding sites suppressed angiotensin type 1 receptor expression and thus decreased blood pressure in SHR. Western blot analysis showed that Sp1 protein levels were increased in nuclear extracts of hypothalamus from SHR. Electrophoretic mobility shift assay (EMSA) using oligonucleotides containing Sp1 consensus sequence and -58 to -34 region sequence oligonucleotides showed that DNA-protein complexes were greater in nuclear extracts of hypothalamus from SHR than those of Wistar Kyoto rats (WKY). Sp1 decoy phosphorothioate oligodeoxynucleotides injected into the lateral ventricle produced a decrease in blood pressure in SHR, and decreased angiotensin type 1 receptor mRNA levels and number of angiotensin receptors in the hypothalamus of SHR. Pressor responses to angiotensin II but not to carbachol injected into the lateral ventricle were decreased in the Sp1 decoy-treated SHR. The results of the present study suggest that Sp1 levels in the hypothalamus of SHR are increased, and that inhibition of the binding of Sp1 to its binding sites decreases angiotensin type 1 receptor expression and blood pressure in SHR. The possibility cannot be ruled out that the Sp1 decoy oligodeoxynucleotides (ODN) also suppressed transcriptions of genes other than the angiotensin type 1 receptor gene.

Ten years of antisense inhibition of brain G-protein-coupled receptor function

Antisense oligonucleotides (AOs) are widely used as tools for inhibiting gene expression in the mammalian central nervous system. Successful gene suppression has been reported for different targets such as neurotransmitter receptors, neuropeptides, ion channels, trophic factors, cytokines, transporters, and others. This illustrates their potential for studying the expression and function of a wide range of proteins. AOs may even find therapeutic applications and provide an attractive strategy for intervention in diseases of the central nervous system (CNS). However, a lack of effectiveness and/or specificity could be a major drawback for research or clinical applications. Here we provide a critical overview of the literature from the past decade on AOs for the study of G-protein-coupled receptors (GPCRs). The following aspects will be considered: mechanisms by which AOs exert their effects, types of animal model system used, detection of antisense action, effects of AO design and delivery characteristics, non-antisense effects and toxicological properties, controls used in antisense studies to assess specificity, and our results (failures and successes). Although the start codon of the mRNA is the most popular region (46%) to target by AOs, targeting the coding region of GPCRs is almost as common (41%). Moreover, AOs directed to the coding region of the GPCR mRNA induce the highest reductions in receptor levels. To resist degradation by nucleases, the modified phosphorothioate AO (S-AO) is the most widely used and effective oligonucleotide. However, the end-capped phosphorothioate AOs (ECS-AOs) are increasingly used due to possible toxic and non-specific effects of the S-AO. Other parameters affecting the activity of a GPCR-targeting AO are the length (mostly an 18-, 20- or 21-mer) and the GC-content (mostly varying from 30 to 80%). Interestingly, one-third of the AOs successfully targeting GPCRs possess a GC/AT ratio of 61-70%. AO-induced reductions in GPCR expression levels and function range typically from 21 to 40% and 41 to 50%, respectively. In contrast to many antisense reviews, we therefore conclude that the functional activity of a GPCR after AO treatment correlates mostly with the density of the target receptors (maximum factor 2). However, AOs are no simple tools for experimental use in vivo. Despite successful results in GPCR research, no general guidelines exist for designing a GPCR-targeting AO or, in general, for setting up a GPCR antisense experiment. It seems that the correct choice of a GPCR targeting AO can only be ascertained empirically. This disadvantage of antisense approaches results mostly from incomplete knowledge about the internalisation and mechanism of action of AOs. Together with non-specific effects of AOs and the difficulties of assessing target specificity, this makes the use of AOs a complex approach from which conclusions must be drawn with caution. Further antisense research has to be carried out to ensure the adequate use of AOs for studying GPCR function and to develop antisense as a valuable therapeutic modality.

Intracisternal administration of Angiotensin II AT1 receptor antisense oligodeoxynucleotides protects against cerebral ischemia in spontaneously hypertensive rats

Pharmacological blockade of peripheral and brain Angiotensin II (Ang II) AT(1) receptors protects against brain ischemia. To clarify the protective role of brain AT(1) receptors, we examined the effects of specific antisense oligodeoxynucleotides (AS-ODN) targeted to AT(1) receptor mRNA administered intracisternally to spontaneously hypertensive rats (SHRs), 4 and 7 days before middle cerebral artery (MCA) occlusion, and we determined the infarct size and tissue swelling 24 h after surgery. A single intracisternal injection of AT(1) mRNA receptor antisense oligodeoxynucleotides reduced systemic blood pressure for 5 days and AT(1) receptor binding for at least 4 days in the area postrema and the nucleus of the solitary tract. A similar injection of scrambled oligodeoxynucleotides (SC-ODN) was without effect. Both blood pressure and AT(1) receptor binding returned to normal 7 days after antisense receptor mRNA administration. Both the infarction size and the tissue swelling after middle cerebral artery occlusion were reduced when the antisense oligodeoxynucleotide was administered 7 days, but not 4 days, before the operation. We conclude that 4 to 5 days of decrease in brain AT(1) receptor binding by a single administration of an AT(1) receptor mRNA oligodeoxynucleotide are sufficient to significantly protect the brain against ischemia resulting from total occlusion of a major cerebral vessel.

Expression of angiotensin type 1 and 2 receptors in brain after transient middle cerebral artery occlusion in rats

Angiotensin II (Ang II) type 2 receptors (AT2Rs) have been associated with apoptosis. We hypothesized that AT2Rs are increased in stroke and may contribute effects of stroke to the brain. To test this, we have examined the expression of Ang II type 1 receptor (AT1R), AT2R and Ang II levels in the brain 24 h after transient middle cerebral artery occlusion (MCAO). The densities of AT1R and AT2R were measured by quantitative autoradiography (n=6). The levels of Ang II were measured by radioimmunoassay (RIA) (n=6) and by immunohistochemistry (n=3). AT1R levels on autoradiography showed a significant decrease (0.87+/-0.06 to 1.39+/-0.07 fmol/mg, p<0.01) in the ventral cortex of the stroke side compared to the cortices of non-stroke (NS) rats (n=4). There was no significant difference on ATIR in the contralateral verbal cortex of the stroke rats compared to NS control. In contrast, levels of AT2R in the ventral cortex of both the stroke and the contralateral sides were significantly increased (0.77+/-0.06, p<0.05 and 0.91+/-0.05, p<0.01 compared to 0.60+/-0.03 fmol/mg tissue, respectively). RIA showed that Ang II in the ventral cortex of both the stroke and the contralateral sides were significantly increased (241.63+/-47.72, p<0.01 and 165.51+/-42.59, p<0.05 compared to 76.80+/-4.10 pg/g tissue, respectively). Also, Ang II in the hypothalamus was significantly increased (179.50+/-17.49 to 118.50+/-6.65 pg/g tissue, p<0.05). Immunohistochemistry confirmed the increase of Ang II. These results demonstrate that brain Ang II and AT2Rs are increased whereas AT1Rs are decreased after transient MCAO in rats. We conclude that in stroke, Ang II and AT2R are activated and may contribute neural effects to brain ischemia.

Angiotensin II AT(1A) receptor antisense lowers blood pressure in acute 2-kidney, 1-clip hypertension

To test the effectiveness of antisense oligonucleotides targeted to the angiotensin type 1A (AT(1A)) receptor mRNA on blood pressure reduction, the 2-kidney, 1-clip (2K1C) Goldblatt model of hypertension was studied in the acute phase of hypertension, when the peripheral renin-angiotensin system is overactive. A single injection of AT(1A) receptor antisense oligodeoxynucleotides significantly reduced systolic blood pressure for a period of 8 days in 2K1C rats after clipping, from 157.5+/-5 mm Hg on day 7 to 141.3+/-3.0 mm Hg on day 15 after clipping (P<0.01). The AT(1A) receptor antisense oligonucleotide labeled with fluorescein shows that the antisense oligonucleotide at 24 hours was taken up into aorta, mesenteric artery, liver, kidney glomeruli, and medulla, remaining up to 6 days. The AT(1A) receptor number in fmol/g tissue was significantly decreased after AT(1A) receptor antisense oligonucleotide treatment in the dorsal aorta, mesenteric artery, renal cortex, and renal medulla (P<0.05) compared with that of the AT(1A) receptor-scrambled antisense oligonucleotide control-treated group. The data clearly demonstrate a prolonged antihypertensive effect of AT(1A) receptor antisense oligonucleotide in the 2K1C renovascular model of hypertension when it is administered intravenously in a single low dose (0.33 mg/kg(-1)). It also shows that the AT(1A) receptor antisense oligonucleotide is actively taken up by AT(1A) target tissues and that there is a significant decrease in receptor density. We conclude that in the acute phase of 2K1C hypertension, antisense to AT(1A) receptor decreases AT(1A) receptor density, which attenuates the vascular vasoconstrictive effects of high plasma angiotensin II levels and in the kidney elicits natriuresis. The decrease in renal AT(1A) receptor density may also lead to sodium loss and reduction of extracellular volume.

Opposite regulation of brain angiotensin type 1 and type 2 receptors in cold-induced hypertension

Rats exposed chronically to mild cold (5 degrees C/41 degrees F) develop hypertension. This cold-induced hypertension (CIH) is an environmentally induced, non-surgical, non-pharmacological and non-genetic model for studying hypertension in rats. The blood renin angiotensin system (RAS) appears to play a role in both initiating and maintaining the high blood pressure in CIH. The goal of the present study was to evaluate the role of brain angiotensin type 1 and type 2 receptors (AT1R and AT2R) in CIH. Sprague-Dawley adult male rats were used. Thirty-six rats were kept in a cold room at 5 degrees C and the other 36 were kept at 24 degrees C as controls. Systolic blood pressure (SBP) was recorded by tail cuff. The SBP was elevated in rats exposed to cold within 1 week (n=12, P>0.05), significantly increased at 3 weeks (P<0.05) and reached a maximum (125%) at 5 weeks (P<0.01). Three subgroups of the cold-treated and the controls were sacrificed at 1, 3 and 5 weeks. Specific brain sections were removed, either for reverse transcription polymerase chain reaction (RT-PCR) to measure mRNA, or for autoradiography to measure receptor binding for AT1R and AT2R. The AT1R mRNA was increased significantly in hypothalamus and brainstem after the first week in cold-treated rats and was maintained throughout the time of exposure to cold (n=6, P<0.01). AT1R binding significantly increased initially in hypothalamus and thereafter in brainstem. The mRNA and the receptor binding for AT2R decreased significantly (P<0.01, n=6) in nucleus of inferior olive and locus coeruleus of brainstem in cold-treated rats after exposure to cold. The experiments show differential regulation of RAS components, AT1R and AT2R, in different brain areas in cold-exposed rats and provide evidence that up-regulated AT1R and down-regulated AT2R in different brain areas are involved in CIH. The opposing directions of expression of AT1R and AT2R suggest that they play counterbalancing roles in brain function.

Antisense inhibition of brain renin-angiotensin system decreased blood pressure in chronic 2-kidney, 1 clip hypertensive rats

The systemic renin-angiotensin system (RAS) plays an important role in blood pressure (BP) regulation during the development of 2-kidney, 1 clip (2K1C) hypertension. Its contributions decrease with time after constriction of the renal artery. During the chronic phase, the peripheral RAS returns to normal, but the hypertension is sustained for months. We hypothesized that in this phase the brain RAS contributes to the maintenance of high BP. To test the hypothesis, we studied the role of brain RAS by decreasing the synthesis of angiotensinogen (AGT) and the angiotensin II (Ang II) type 1a receptor (AT(1)R) with intracerebroventricular injections of antisense oligonucleotides (AS-ODNs). The response of systolic BP (SBP) to AS-ODNs to AGT mRNA was studied in 2K1C rats at 6 months after clipping, and the response to AS-ODNs to AT(1)R mRNA was studied at 10 months after clipping. Intracerebroventricular injection of AS-ODN-AGT (200 microgram/kg, n=5) significantly decreased SBP (-22+/-6 mm Hg, P<0.05) compared with the sense ODN (n=5) and saline (n=3) groups. Intracerebroventricular injection of AS-ODN-AGT reduced the elevated hypothalamic Ang II level. The hypothalamic Ang II content in sense ODN and saline groups was significantly (P<0.05) higher than in the nonclipped group. Compared with inverted ODN, intracerebroventricular injection of AS-ODN-AT(1)R (250 microgram/kg, n=6) significantly decreased SBP (-26+/-8 mm Hg, P<0.05) for 3 days after injection. This was a brain effect because intravenous AS-ODN-AT(1)R at a dose of 250 to 500 microgram/kg did not affect SBP. These results suggest that the brain RAS plays an important role in maintaining the elevated SBP in chronic 2K1C hypertension.

Expression of the purported sigma(1) (sigma(1)) receptor in the mammalian brain and its possible relevance in deficits induced by antagonism of the NMDA receptor complex as revealed using an antisense strategy

Sigma (sigma) receptors have generated a great deal of interest on the basis of their possible role in psychosis, neuroprotection and various other behaviors including learning processes. The existence of at least two classes of sigma receptor binding sites (sigma(1) and sigma(2)) is now well established. The recent cloning of the mouse, guinea pig and human sigma(1) receptors has allowed the study of the discrete distribution of the sigma(1) receptor mRNA in rodent and human brain tissues using in situ hybridization. Overall, the sites of expression of specific sigma(1) receptor mRNA signals were in accordance to the anatomical distribution of sigma(1) receptor protein first established by quantitative receptor autoradiography. Specific sigma(1) receptor hybridization signals were found to be widely, but discretely distributed, in mouse and guinea pig brain tissues. The highest levels of transcripts were seen in various cranial nerve nuclei. Lower, but still high hybridization signals were observed in mesencephalic structures such as the red nucleus, periaqueductal gray matter and substantia nigra, as well as in some diencephalic structures including such as the habenula and the arcuate, paraventricular and ventromedial hypothalamic nuclei. Superficial (I-II) and deeper (IV-VI) cortical laminae were moderately labeled in the mouse brain. Moderate levels of sigma(1) receptor mRNA were also found in the pyramidal cell layer and the dentate gyrus of the hippocampal formation. Other structures such as the thalamus and amygdaloid body also expressed the sigma(1) receptor mRNA although to a lesser extent. In murine peripheral tissues, strong hybridization signals were observed in the liver, white pulp of the spleen and the adrenal gland. In the postmortem human brain, moderate levels of sigma(1) receptor mRNA, distributed in a laminar fashion, were detected in the temporal cortex with the deeper laminae (IV-VI) being particularly enriched. In the hippocampal formation, the strongest hybridization signals were observed in the dentate gyrus while all other subfields of the human hippocampal formation expressed lower levels of the sigma(1) receptor mRNA. Antisense oligodeoxynucleotides against the purported sigma(1) receptor were used next to investigate the possible role of this receptor in dizocilpine (MK-801)/NMDA receptor blockade-induced amnesia. Following a continuous intracerebroventricular infusion of a specific sigma(1) receptor antisense into the third ventricle (0.4 nmol/h for 5 days), sigma(1)/[3H](+)pentazocine binding was significantly reduced in mouse brain membrane homogenates while a scrambled antisense control was without effect. Moreover, the sigma(1) receptor antisense treatments (5 nmol/injection, every 12 hx3 or 0.4 nmol/h for 5 days) attenuated (+)MK-801/NMDA receptor blockade-induced cognitive deficits in the treated mice while a scrambled antisense control had no effect. Taken together, these results demonstrate the widespread, but discrete, distribution of the sigma(1) receptor mRNA in the mammalian central nervous system. Moreover, antisense treatments against the purported sigma(1) receptor gene reduced specific sigma(1)/[3H](+)pentazocine binding and modulated cognitive behaviors associated with NMDA receptor blockade providing further evidence for the functional relevance of the cloned gene.

Antidepressant effects on GABA-stimulated 36Cl(-) influx in rat cerebral cortex are altered after treatment with GABA(A) receptor antisense oligodeoxynucleotides

Antidepressants act at the GABA(A) receptor to inhibit GABA-stimulated 36Cl(-) influx and GABA reduction of [35S]TBPS binding. This study examined how selective knock-down (via antisense oligodeoxynucleotides, aODNs) of GABA(A) receptor subunits modified antidepressant activity. The specific aODNs used were for the alpha1, beta1, beta2 or gamma2 subunits of the GABA(A) receptor. The aODN microinjections reduced corresponding GABA(A) receptor subunit mRNA levels by 30-40% as assessed by RT-PCR. The inhibitory effect of the antidepressants amitriptyline and mianserin on GABA-stimulated 36Cl(-) influx was decreased after microinjections of alpha1, beta1, or beta2 subunit aODNs but potentiated after microinjections of gamma2 subunit aODNs. This pattern of aODNs effect on amitriptyline and mianserin modulation of GABA-stimulated 36Cl(-) influx was the same for both antidepressants and similar to GABA but different than that of diazepam and bicuculline. We conclude that multiple subunits of the GABA(A) receptor regulate the effect of amitriptyline and mianserin on the GABA(A) receptor chloride ionophore complex. However, the exact identity of the subunit mediating the direct or allosteric modulation of the antidepressant effect on GABA-stimulated 36Cl(-) influx remains unclear.

Progesterone increases mRNA levels of pituitary adenylate cyclase-activating polypeptide (PACAP) and type I PACAP receptor (PAC(1)) in the rat hypothalamus

Pituitary adenylate cyclase-activating polypeptide (PACAP) regulates pituitary hormone biosynthesis and secretion through its cognate receptors. PACAP also plays an important role in the regulation of ovarian steroid biosynthesis. If so, there might be a feedback regulation of hypothalamic PACAP synthesis by the pituitary and by ovarian steroids. In the present study, we used RNase protection assays to determine changes in mRNA levels of PACAP and type I PACAP receptor (PAC(1)) under the conditions of ovariectomy and replacement with ovarian steroids. Progesterone (P) alone or in combination with estradiol (E) induced significant increases in PACAP mRNA level in the medial basal hypothalamus (MBH) and PAC(1) mRNA levels in MBH and the preoptic area (POA). This finding suggests that feedback regulation takes place between the ovary and hypothalamic PACAP neurons. P is known to be a major regulatory feedback factor for hypothalamic luteinizing hormone-releasing hormone (LHRH) neurons, but P receptor is not present in these neurons. Therefore, we examined a possible involvement of PACAP in the feedback regulatory pathway of P to LHRH neurons. After an antisense PAC(1) oligodeoxynucleotide (ODN) was i.c.v.-injected into the third ventricle of E and P-treated rats, LHRH mRNA levels were determined. The ODN markedly decreased the P-induced increase in the LHRH mRNA level. Taken together, the present data suggest that PACAP may play a role as a mediator in the regulation of LHRH synthetic machinery by stimulatory feedback of P.

Effects of treatment with GABA(A) receptor subunit antisense oligodeoxynucleotides on GABA-stimulated 36Cl- influx in the rat cerebral cortex

GABA(A) receptor function was studied in cerebral cortical vesicles prepared from rats after intracerebroventricular microinjections of antisense oligodeoxynucleotides (aODNs) for alpha1, gamma2, beta1, beta2 subunits. GABA(A) receptor alpha1 subunit aODNs decreased alpha1 subunit mRNA by 59+/-10%. Specific [3H]GABA binding was decreased by alpha1 or beta2 subunit aODNs (to 63+/-3% and 64+/-9%, respectively) but not changed by gamma2 subunit aODNs (94+/-5%). Specific [3H]flunitrazepam binding was increased by alpha1 or beta2 subunit aODNs (122+/-8% and 126+/-11%, respectively) and decreased by gamma2 subunit aODNs (50+/-13%). The "knockdown" of specific subunits of the GABA(A )receptor significantly influenced GABA-stimulated 36Cl- influx. Injection of alpha1 subunit aODNs decreased basal 36Cl- influx and the GABA Emax; enhanced GABA modulation by diazepam; and decreased antagonism of GABA activity by bicuculline. Injection of gamma2 subunit aODNs increased the GABA Emax; reversed the modulatory efficacy of diazepam from enhancement to inhibition of GABA-stimulation; and reduced the antagonist effect of bicuculline. Injection of beta2 subunit aODNs reduced the effect of diazepam whereas treatment with beta1 subunit aODNs had no effect on the drugs studied. Conclusions from our studies are: (1) alpha1 subunits promote, beta2 subunits maintain, and gamma2 subunits suppress GABA stimulation of 36Cl- influx; (2) alpha1 subunits suppress, whereas beta2, and gamma2 subunits promote allosteric modulation by benzodiazepines; (3) diazepam can act as an agonist or inverse agonist depending on the relative composition of the receptor subunits: and (4) the mixed competitive/non-competitive effects of bicuculline result from activity at alpha1 and gamma2 subunits and the lack of activity at beta1 and beta2 subunits.

Chronic central infusion of ANG II potentiates cardiac sympathetic afferent reflex in dogs

The aims of this study were to determine whether ANG II is involved in the central integration of the cardiac sympathetic afferent reflex (CSAR), and if this central effect of ANG II is mediated by the AT(1) receptor. Experiments were undertaken in dogs that were anesthetized with alpha-chloralose, sinoaortic denervated, and vagotomized. The renal sympathetic nerve activity (RSNA) responses to varying frequency and voltage stimulation of cardiac sympathetic afferent nerves were used to evaluate the central sensitivity of the CSAR. In two groups of dogs, two doses (50 and 100 ng/min icv) of ANG II were acutely infused. In a third group of dogs, ANG II was chronically infused for 3 days (100 ng/min, 1 microliter/h icv). We found that acute infusion into the cerebroventricle of two doses of ANG II did not affect the central sensitivity of the CSAR or the baseline hemodynamics, but the baseline RSNA increased significantly during the infusion of the higher dose of ANG II. However, chronic intracerebroventricular infusion of ANG II enhanced the central sensitivity of the CSAR significantly. In addition, chronic intracerebrovetricular infusion of ANG II elicited a significant increase in water intake and in arterial pressure from the first and second day of infusion, respectively. In the group that received chronic intracerebroventricular infusion of ANG II, the administration of an AT(1)-receptor antagonist losartan (0.125 mg/kg icv) abolished ANG II-induced augmentation of the CSAR. These results suggest that chronic elevation of central ANG II can sensitize the CSAR via central AT(1) receptors.

Antisense inhibition of angiotensinogen attenuates vasopressin release in the paraventricular hypothalamic nucleus of spontaneously hypertensive rats

It has been reported that intracerebroventricularly injected antisense oligonucleotide to angiotensinogen reduces arterial pressure in spontaneously hypertensive rats (SHR), but the mechanism and the sites of action remain unclear. In the present study, we examined whether injection of antisense oligonucleotide to angiotensinogen into the paraventricular hypothalamic nucleus (PVN) would influence arterial pressure and vasopressin release. For this purpose, 12-week-old male SHR were cannulated into the bilateral PVN. One week later, we injected antisense or sense oligonucleotide to angiotensinogen into the bilateral PVN (0.2 nmol/200 nl each side). After 24 h, we directly monitored arterial pressure, and then took blood samples to measure plasma vasopressin, catecholamines and renin activity. Mean arterial pressure did not change in either group (from 144+/-3 to 154+/-4 mmHg for the antisense oligonucleotide group, n=11; from 147+/-4 to 156+/-3 mmHg for the sense oligonucleotide group, n=11). Antisense oligonucleotide attenuated vasopressin release compared with sense oligonucleotide (1.30+/-0.28 vs. 3.29+/-0.60 pg/ml, respectively, P<0.01). Plasma catecholamines also decreased in the antisense oligonucleotide group compared with the sense oligonucleotide group. However, the plasma renin activity did not differ between the groups. In the additional experiment, we examined the neurohormonal and cardiovascular effects of intracerebroventricularly injected antisense oligonucleotide to angiotensinogen in SHR. Mean arterial pressure, plasma vasopressin and plasma norepinephrine were significantly lower in the antisense oligonucleotide group than in the sense oligonucleotide group. These results suggest that angiotensinogen in PVN plays important roles in vasopressin release and sympathetic nerve activity, but may not contribute to the maintenance of arterial pressure in SHR.

Antisense oligodeoxynucleotides against the muscarinic m2, but not m4, receptor supports its role as autoreceptors in the rat hippocampus

Antisense oligodeoxynucleotides against muscarinic m2 and m4 receptors were used to investigate the role of these receptor subtypes as negative autoreceptors in the regulation of acetylcholine (ACh) release in the rat hippocampus. Following the continuous infusion of antisenses into the third ventricle (1 microgram microliter-1 h-1, 3 days), 3H-AF-DX 384/muscarinic M2-like binding was significantly decreased in the medial septum by the antisense against the m2 receptor whereas M2-like binding in the dorsal striatum was decreased by the antisense against the m4 receptor. In contrast, 3H-pirenzepine/muscarinic M1-like binding was unaffected by either antisense treatment in any of the brain areas investigated. When perfused into the hippocampus via a dialysis probe, the purported muscarinic M2 receptor antagonist AF-DX 384 (100 nM) increased hippocampal ACh release in freely moving rats. This effect of AF-DX 384 was significantly attenuated by the m2, but not the m4, receptor antisense treatment. Hippocampal choline acetyltransferase activity was not affected by either antisense treatments. Taken together, these results suggest that the molecularly defined muscarinic m2 receptor regulates hippocampal ACh release by acting as a negative autoreceptor. In contrast, the molecularly defined m4 receptor is unlikely to be directly involved in the negative regulation of ACh release in the rat hippocampus. Therefore, inhibiting muscarinic m2 receptor function may be an alternative approach to regulate the release of ACh in neurodegenerative diseases associated with impaired cholinergic functions.

Modulation of arterial baroreflexes by antisense oligodeoxynucleotides to NMDAR1 receptors in the nucleus tractus solitarius

An antisense oligodeoxynucleotide which specifically blocked the production of the glutamate receptor subtype NMDAR1 was administered to the nucleus tractus solitarius (NTS) in order to examine the role of this receptor in baroreflex control of heart rate. Baseline blood pressure and heart rate were unchanged by NTS treatment with the antisense oligodeoxynucleotide to the NMDAR1 receptor subunit. However, the reflex bradycardia evoked in response to the hypertension induced by bolus administration of phenylephrine was significantly attenuated following bilateral NTS antisense oligodeoxynucleotide treatment. Administration of the corresponding mismatched antisense oligodeoxynucleotide did not significantly alter the reflex bradycardia. These data indicate that NMDAR1 receptors are involved in neurotransmission in the baroreflex arc at the level of the NTS. The specificity of antisense oligodeoxynucleotides may prove to be a useful technique to analyze the role of receptor subtypes mediating neurotransmission in central pathways.

Myocardial angiotensin II receptor expression and ischemia-reperfusion injury

The renin-angiotensin system plays an important role in myocardial ischemia-reperfusion injury. Angiotensin II (Ang II) contributes to the evolution of ischemic coronary events through its hemodynamic, hemostatic and mitogenic effects. Angiotensin-converting enzyme (ACE) inhibitors and Ang II receptor antagonists have been shown to be cardioprotective in experimental animal models, with ischemia-reperfusion injury and in patients with congestive heart failure. Ang II receptors include at least two different subtypes, AT1 and AT2. Both AT1 and AT2 are expressed in the rat heart. Myocardial AT1 receptor density increases in association with ACE expression, and AT1 receptor activation is related to collagen formation following myocardial infarction in rats. Studies from the authors' laboratory have shown significant myocardial dysfunction in association with a concurrent increase in AT1 receptor expression in the rat myocardium immediately following a brief period of ischemia and reperfusion. Application of antisense oligodeoxynucleotides (AS-ODN) directed at AT1 receptor messenger RNA and AT1 receptor antagonist, losartan, significantly attenuates myocardial dysfunction induced by ischemia-reperfusion in the isolated rat heart. These observations suggest that myocardial AT1 receptor expression is involved in myocardial dysfunction following ischemia-reperfusion. Unlike losartan, which upregulates the plasma Ang II level, administration of AS-ODN does not affect plasma Ang II level. Although the reason for this is not clear, the difference in plasma Ang II levels implies that AS-ODN may be, at least theoretically, more beneficial than losartan in limiting ischemia-reperfusion-induced cardiac dysfunction. Apoptosis, or programmed cell death, also contributes to the outcome of myocardial ischemia-reperfusion injury. Recent studies from the authors' laboratory have demonstrated that Ang II induces apoptosis in cultured human coronary artery endothelial cells via activation of AT1 receptors and this can be blocked by losartan. These observations collectively underscore the importance of myocardial AT1 receptor expression in ischemia-reperfusion injury.

Critical role of AT1 receptor expression after ischemia/reperfusion in isolated rat hearts: beneficial effect of antisense oligodeoxynucleotides directed at AT1 receptor mRNA

To examine the relevance of angiotensin II type 1 receptor (AT1R) expression in the determination of myocardial function after ischemia/reperfusion, Sprague-Dawley rats were treated intravenously with antisense oligodeoxynucleotides (AS-ODNs) directed at AT1R mRNA (100 microg/rat, n=9) or scrambled antisense oligodeoxynucleotides (Scr-ODNs, 100 microg/rat, n=6). Both AS-ODNs and Scr-ODNs were given along with 300 microg/rat of liposome DOTAP/DOPE, a positive electron carrier (wt:wt= 1:1). The hearts from AS-ODN- or Scr-ODN-treated rats were excised 24 hours later, perfused in vitro, and subjected to 25 minutes of global ischemia followed by 30 minutes of reperfusion. Parallel groups of rats were given the specific AT1R antagonist losartan (10 mg/kg IV, n=6) or saline (n=7) 4 to 6 hours before excising the hearts. Ischemia/reperfusion resulted in a significant increase in myocardial AT1R expression (autoradiography and binding assay) and myocardial dysfunction, indicated by increases in coronary perfusion pressure and left ventricular end-diastolic pressure and a decrease in developed left ventricular pressure (all P<0.01 versus baseline) in the saline-treated group. AT1R protein and mRNA levels also increased in ischemic/ reperfused myocardial tissues. Administration of AS-ODNs or losartan, but not Scr-ODNs, preserved myocardial function and blocked the increased AT1R binding after ischemia/reperfusion (both P<0.01). Myocardial AT1R mRNA levels were not affected by either AS-ODNs or losartan, and the AT1R protein levels were significantly reduced by AS-ODN, but not losartan, treatment. Plasma angiotensin II levels increased after administration of losartan but not after administration of AS-ODNs. These observations imply a critical role of AT1R upregulation in determining myocardial function immediately after ischemia/reperfusion. AS-ODNs to AT1R mRNA may be more beneficial than losartan, because losartan does not affect the plasma angiotensin II level. The sustained increase in AT1R mRNA, but diminished protein expression, in rat hearts treated with AS-ODNs suggests that AS-ODNs block AT1R at the translational level.

Reduction of cold-induced hypertension by antisense oligodeoxynucleotides to angiotensinogen mRNA and AT1-receptor mRNA in brain and blood

Rats exposed chronically to mild cold (5 degrees C/41 degrees F) develop hypertension and cardiac hypertrophy. This provides a unique model of hypertension that is environmentally induced. The blood renin-angiotensin system (RAS) has been shown to play a role in both initiating and maintaining the high blood pressure (BP) in cold-induced hypertension. The mechanism also appears to involve both the tissue and brain RAS because there is increased mRNA for angiotensinogen (AGT) and angiotensin type 1 (AT1) receptors in brain and peripheral tissues, an increased spontaneous drinking response, and an increased dipsogenic response to acute administration of angiotensin II (Ang II) in cold-treated rats. Antisense oligodeoxynucleotides (AS-ODN), targeted to the RAS, have been shown to reduce BP in spontaneously hypertensive rats. Therefore, we injected AS-ODN in rats with cold-induced hypertension to test whether antisense inhibition was effective in reducing this nongenetic nonsurgical hypertension. Sprague-Dawley rats were made hypertensive by cold exposure and injected intracerebroventricularly with AS-ODN to AGT mRNA (n=6) or AT1 receptor mRNA (n=6). Systolic BP was recorded by tail cuff 24 hours later for 2 or 7 days, respectively. Systolic BP decreased significantly in response to AGT-AS-ODN (40+/-6 mm Hg, P<0.01) within 1 day after injection and to AT1 receptor-AS-ODN (P<0.05) for 3 days after injection. The maximum decrease was 41+/-10 mm Hg. Systolic BP then gradually increased to the preinjection level. The spontaneous drinking response to cold treatment also decreased significantly (P<0.05) after AGT-AS-ODN or AT1 receptor-AS-ODN intracerebroventricular injection. Intracardiac injection of AT1-AS-ODN (n=6) reduced systolic BP by 36+/-8 mm Hg (P<0.05) and decreased AT1 receptor as measured by autoradiography in aorta, adrenal glands, and kidneys 24 hours after injection. These data show that AS-ODN reduces BP in cold-induced hypertension and that the hypertension involves both peripheral tissues and central RAS in addition to blood-borne RAS mechanisms.

G protein-coupled receptors: functional and mechanistic insights through altered gene expression

G protein-coupled receptors (GPCRs) comprise a large and diverse family of molecules that play essential roles in signal transduction. In addition to a constantly expanding pharmacological repertoire, recent advances in the ability to manipulate GPCR expression in vivo have provided another valuable approach in the study of GPCR function and mechanism of action. Current technologies now allow investigators to manipulate GPCR expression in a variety of ways. Graded reductions in GPCR expression can be achieved through antisense strategies or total gene ablation or replacement can be achieved through gene targeting strategies, and exogenous expression of wild-type or mutant GPCR isoforms can be accomplished with transgenic technologies. Both the techniques used to achieve these specific alterations and the consequences of altered expression patterns are reviewed here and discussed in the context of GPCR function and mechanism of action.

Expression of angiotensin type-1 (AT1) and type-2 (AT2) receptor mRNAs in the adult rat brain: a functional neuroanatomical review

The discovery that all components of the renin-angiotensin system (RAS) are present in the central nervous system led investigators to postulate the existence of a local brain RAS. Supporting this, angiotensin immunoreactive neurons have been visualized in the brain. Two major pathways were described: a forebrain pathway which connects circumventricular organs to the median preoptic nucleus, paraventricular nucleus, and supraoptic nucleus, and a second pathway connecting the hypothalamus to the medulla oblongata. Blood-brain barrier deficient circumventricular organs are rich in angiotensin II receptors. By activating these receptors, circulating angiotensin II may act on central cardiovascular centers via angiotensinergic neurons, providing a link between peripheral and central angiotensin II systems. Among the effector peptides of the brain RAS, angiotensin II and angiotensin III have the same affinity for the two pharmacologically well-defined receptors: type 1 (AT1) and type 2 (AT2). When injected in the brain, these peptides increase blood pressure, water intake, and anterior and posterior pituitary hormone release and may modify memory and learning. The cloning of AT1 and AT2 receptor cDNAs has revealed that these receptors belong to the seven transmembrane domain receptor family. In rodents, two AT1 receptor subtypes, AT1A and AT1B, have been isolated. Using specific riboprobes for in situ hybridization histochemistry, recent studies mapped the distribution of AT1A, AT1B, and AT2 receptor mRNAs in the adult rat and found a predominant expression of AT1A and AT2 mRNA in the brain and of AT1B in the pituitary. Very limited overlap was found between the brain expression of AT1A and AT2 mRNAs. In several functional entities of the brain, such as the preoptic region, the hypothalamus, the olivocerebellary system, and the brainstem baroreflex arc, the colocalization of receptor mRNA, binding sites, and angiotensin immunoreactive nerve terminals suggests local synthesis and expression of angiotensin II receptors. In other areas, such as the bed nucleus of the stria terminalis, the median eminence, or certain parts of the nucleus of the solitary tract, angiotensin II receptors are likely of extrinsic origin. The neuronal expression of AT1A and AT2 receptors was demonstrated in the subfornical organ, the hypothalamus, and the lateral septum. By using double label in situ hybridization, AT1A receptor expression was localized in corticotropin releasing hormone but not in vasopressin containing neurons in the hypothalamus. The information is discussed together with functional data concerning the role of brain angiotensins, in an attempt to provide a better understanding of the physiological and functional roles of each receptor subtype.

Antisense strategies in neurobiology

The use of antisense oligodeoxynucleotides, targeted to the transcripts encoding biologically active proteins in the nervous system, provides a novel and highly selective means to further our understanding of the function of these proteins. Recent studies of these agents also suggest the possibility of their being used therapeutically for a variety of diseases involving neuronal tissue. In this paper we review studies showing the in vitro and in vivo effects of antisense oligodeoxynucleotides as they relate to neurobiological functions. Particular attention is paid to the behavioral and biochemical effects of antisense oligodeoxynucleotides directed to the various subtypes of receptors for the neurotransmitter dopamine. An example is also provided showing the effects of a plasmid vector expressing an antisense RNA targeted to the calmodulin mRNAs in the PC12 pheochromocytoma cell line. The advantages of antisense oligodeoxynucleotides over traditional pharmacological treatments are assessed, and the advantages of using vectors encoding antisense RNA over the use of antisense oligodeoxynucleotides are also considered. We also describe the criteria that should be used in designing antisense oligodeoxynucleotides and several controls that should be employed to assure their specificity of action.

Antisense oligonucleotides in neuroendocrinology: enthusiasm and frustration

Antisense oligodeoxynucleotides (ODN) offer the potential advantage to manipulate neuropeptide or neuropeptide receptor expression within the brain transiently and site-specifically, thus providing a tool for neuroendocrinological research into the physiological function of a particular neuropeptide system. In this study, various approaches are introduced which reveal that antisense ODN may exert acute, short-term effects on neuronal responsiveness to afferent stimuli, as well as long-term effects on neuropeptide/receptor protein availability in a given system depending on the duration of treatment. Short-term effects were seen in that oxytocin (OXT) and vasopressin (AVP) antisense ODN affected electrophysiological and secretory parameters of oxytocinergic and vasopressinergic neurons, respectively, as well as their ability to express the Fos protein in response to afferent stimulation a few hours after a single infusion into the hypothalamic supraoptic nucleus. In this study, two methodological approaches to study long-term effects of the antisense ODN are exemplified, in which antisense ODN directed against the mRNA coding for the neuropeptide itself or its receptor were used. The repeated infusion of corticotropin releasing hormone (CRH) antisense ODN into the paraventricular nucleus resulted in reduced immunoreactive CRH, but not AVP, in the external zone of the median eminence. Furthermore, in order to evaluate the receptor-mediated effects of CRH and AVP released locally within the paraventricular nucleus on adrenocorticotropin (ACTH) release from the pituitary, CRH receptor (and also AVP receptor) antisense ODN were repeatedly infused into the hypothalamic nuclei; this treatment resulted in an elevation of stimulated, but not basal, ACTH release into the blood. However, in addition to these obvious antisense effects, results are discussed which demonstrate sequence-unspecific effects of phosphorothioated ODN, suggesting that some of their mechanisms of action are not yet understood.

Corticotropin-releasing factor CRF1, but not CRF2, receptors mediate anxiogenic-like behavior

The recent identification and differential localization in brain of three binding sites for corticotropin-releasing factor (CRF)-like peptides (CRF1 and CRF2 receptors as well as CRF-binding protein) suggest the existence of functionally distinct neurobiological systems which mediate CRF activation. For instance, evidence from receptor knockdown and pharmacological studies suggest involvement of the CRF1 receptor in anxiogenic-like behavior and the CRF-binding protein in learning and memory processes. The present studies examined the potential functional significance of the CRF2 receptor in relation to the CRF1 receptor using two animal models of anxiety and endocrine reactivity to a stressor. CRF1 and CRF2 receptor knockdown was achieved and confirmed autoradiographically within brain regions relevant to behavioral reactivity to stressors by chronic, central administration of antisense oligonucleotides. CRF1 but not CRF2, know down produced a significant anxiolytic-like effect in the Defensive Withdrawal relative to vehicle-treated and two missense oligonucleotide negative control groups. In contrast, neither antisense treatment altered endocrine or behavioral reactivity to a swim stressor. Thus, the present data support the reported role of CRF1 receptors in the mediation of anxiogenic-like behavior and suggest a functionally distinct for role for CRF2 receptors in brain.

Prolonged reduction of high blood pressure with an in vivo, nonpathogenic, adeno-associated viral vector delivery of AT1-R mRNA antisense

To produce a prolonged decrease in blood pressure, we have developed a nonpathogenic adeno-associated viral vector (AAV) with the antisense DNA for AT1-R. AAV has many advantages over other viral vectors. AAV does not stimulate inflammation or immune reaction. AAV enters nondividing cells and does not replicate. Therefore, it is an appropriate choice for gene therapy. Recombinant AAV was prepared with a cassette containing a cytomegalovirus promoter and the cDNA for the AT1 receptor inserted in the antisense direction. The cassette was packaged in the virion. Stable transfection of NG108-15 cells with the PAAV-AS (plasmid AAV) antisense to AT1-R produced a significant reduction in AT1 receptors. A single injection of the rAAV-AS (viral vector) was made in adult spontaneously hypertensive rats, either directly in the hypothalamus (1 microL) or in the lateral ventricles (5 microL). The result shows that there is a significant decrease of blood pressure (approximately 23 +/- 2 mm Hg) for up to 9 weeks after injection. Control injections of mock vector produced no change in blood pressure during the same time period in age-matched controls. In young spontaneously hypertensive rats (3 weeks), a single intracardiac injection of recombinant rAAV-AS reduced blood pressure and slowed the development of hypertension compared with controls (P < .01). The results suggest that a prolonged reduction in high blood pressure can be achieved with AAV vectors delivering antisense to inhibit AT1 receptors with a single administration.

Antisense inhibition and adeno-associated viral vector delivery for reducing hypertension

Antisense oligodeoxynucleotides have been designed to inhibit the production of specific proteins. In models of hypertension, we have targeted the renin-angiotensin system at the level of synthesis (angiotensinogen) and the receptor (AT1 receptor). The design of antisense oligonucleotides requires choosing a site to inhibit mRNA processig or translation. The strategy we use is to make three oligonucleotides of antisense sequences, upstream and downstream from the AUG site and over the AUG site. The oligonucleotides are tested in a screening test. Antisense oligonucleotides to AT1-receptor mRNA and to angiotensinogen mRNA reduce blood pressure in spontaneously hypertensive rats when injected into the brain. They significantly reduce the concentration of the appropriate protein. The oligonucleotides are also effective when administered systemically. The decrease in blood pressure with antisense oligonucleotides delivered in blood or brain lasts 3 to 7 days. To prolong the action, direct injection of naked DNA and injection of DNA in liposome carriers have been tested. Viral vectors have been developed to deliver antisense DNA. The viral vectors available include retroviruses and adenovirus, but the adeno-associated virus (AAV) vector is the vector of choice for ultimate use in gene therapy. It offers safety because it is nonpathogenic, has longevity because it integrates into the genome, and has sufficient carrying capacity to carry up to 4.5 kb antisense or gene in a recombinant AAV. Using rAAV-antisense to AT1 mRNA, there is efficient transfection into cells and an inhibition of AT1 receptor number. In in vivo tests, rAAV-AS AT1-receptor when injected into the brains of SHR reduces blood pressure for more than 2 months. In young rats (3 weeks old), rAAV-AS AT1-receptor decreases blood pressure and slows the development of hypertension. While further experiments need to be done on dose-response relationships and on the cellular mechanisms of these effects, the results show the feasibility of AAV as a vector for antisense inhibition, which may ultimately be used in gene therapy for hypertension.