Activation of the brain angiotensin system by in vivo human angiotensin-converting enzyme gene transfer in rats

Identification of genes involved in neuronal cell death and recovery over time in rat axotomy and neurorrhaphy models through RNA sequencing

Facial nerves are frequently injured during cosmetic or other types of facial surgery. However, information on the genes involved in the damage and recovery of the facial nerves is limited. Here, we aimed to identify the genes affected by facial nerve injury and repair using next-generation sequencing. We established a rat axotomy model and a parallel epineurial neurorrhaphy model, in which gene expression was analyzed from 3 days to 8 weeks after surgery. We discovered that ARRB1, SGK1, and GSK3B genes associated with neuronal cell death were upregulated in the axotomy model. In contrast, MFRP, MDK, and ACE genes involved in neural recovery and regeneration exhibited higher expression in the neurorrhaphy model. In the present study, the analysis of the big data obtained from the next-generation sequencing (RNA-seq) technology reveals that the expression of genes involved in neuronal cell death is induced during nerve damage, and those associated with neural recovery are more abundantly expressed during repair processes. These results are considered to be useful for the establishment of the treatment of related diseases and basic research in various neuroscience fields by utilizing damage and recovery mechanism of facial nerves.

Role of brain renin angiotensin system in neurodegeneration: An update

Renin angiotensin system (RAS) is an endocrine system widely known for its physiological roles in electrolyte homeostasis, body fluid volume regulation and cardiovascular control in peripheral circulation. However, brain RAS is an independent form of RAS expressed locally in the brain, which is known to be involved in brain functions and disorders. There is strong evidence for a major involvement of excessive brain angiotensin converting enzyme (ACE)/Angiotensin II (Ang II)/Angiotensin type-1 receptor (AT-1R) axis in increased activation of oxidative stress, apoptosis and neuroinflammation causing neurodegeneration in several brain disorders. Numerous studies have demonstrated strong neuroprotective effects by blocking AT1R in these brain disorders. Additionally, the angiotensin converting enzyme 2 (ACE2)/Angiotensin (1–7)/Mas receptor (MASR), is another axis of brain RAS which counteracts the damaging effects of ACE/Ang II/AT1R axis on neurons in the brain. Thus, angiotensin II receptor blockers (ARBs) and activation of ACE2/Angiotensin (1–7)/MASR axis may serve as an exciting and novel method for neuroprotection in several neurodegenerative diseases. Here in this review article, we discuss the expression of RAS in the brain and highlight how altered RAS level may cause neurodegeneration. Understanding the pathophysiology of RAS and their links to neurodegeneration has enormous potential to identify potentially effective pharmacological tools to treat neurodegenerative diseases in the brain.

Integrative Physiological Aspects of Brain RAS in Hypertension

PURPOSE OF REVIEW

The renin-angiotensin system (RAS) plays an important role in modulating cardiovascular function and fluid homeostasis. While the systemic actions of the RAS are widely accepted, the role of the RAS in the brain, its regulation of cardiovascular function, and sympathetic outflow remain controversial. In this report, we discuss the current understanding of central RAS on blood pressure (BP) regulation, in light of recent literature and new experimental techniques.

RECENT FINDINGS

Studies using neuronal or glial-specifc mouse models have allowed for greater understanding into the site-specific expression and role centrally expressed RAS proteins have on BP regulation. While all components of the RAS have been identified in cardiovascular regulatory regions of the brain, their actions may be site specific. In a number of animal models of hypertension, reduction in Ang II-mediated signaling, or upregulation of the central ACE2/Ang 1-7 pathway, has been shown to reduce BP, via a reduction in sympathetic signaling and increase parasympathetic tone, respectively. Emerging evidence also suggests that, in part, the female protective phenotype against hypertension may be due to inceased ACE2 activity within cardiovascular regulatory regions of the brain, potentially mediated by estrogen. Increasing evidence suggests the importance of a central renin-angiotensin pathway, although its localization and the mechanisms involved in its expression and regulation still need to be clarified and more precisely defined. All reported studies/experiments with human or animal subjects performed by the authors have been previously published and complied with all applicable ethical standards (including the Helsinki declaration and its amendments, institutional/national research committee standards, and international/national/institutional guidelines).

The Prorenin and (Pro)renin Receptor: New Players in the Brain Renin-Angiotensin System?

It is well known that the brain renin-angiotensin (RAS) system plays an essential role in the development of hypertension, mainly through the modulation of autonomic activities and vasopressin release. However, how the brain synthesizes angiotensin (Ang) II has been a debate for decades, largely due to the low renin activity. This paper first describes the expression of the vasoconstrictive arm of RAS components in the brain as well as their physiological and pathophysiological significance. It then focus on the (pro)renin receptor (PRR), a newly discovered component of the RAS which has a high level in the brain. We review the role of prorenin and PRR in peripheral organs and emphasize the involvement of brain PRR in the pathogenesis of hypertension. Some future perspectives in PRR research are heighted with respect to novel therapeutic target for the treatment of hypertension and other cardiovascular diseases.

A current view of brain renin-angiotensin system: Is the (pro)renin receptor the missing link?

The renin-angiotensin system (RAS) plays a central role in the brain to regulate blood pressure (BP). This role includes the modulation of sympathetic nerve activity (SNA) that regulates vascular tone; the regulation of secretion of neurohormones that have a critical role in electrolyte as well as fluid homeostasis; and by influencing behavioral processes to increase salt and water intake. Based on decades of research it is clear that angiotensin II (Ang II), the major bioactive product of the RAS, mediates these actions largely via its Ang II type 1 receptor (AT1R), located within hypothalamic and brainstem control centers. However, the mechanisms of brain RAS function have been questioned, due in large part to low expression levels of the rate limiting enzyme renin within the central nervous system. Tissue localized RAS has been observed in heart, kidney tubules and vascular cells. Studies have also given rise to the hypothesis for localized RAS function within the brain, so that Ang II can act in a paracrine manner to influence neuronal activity. The recently discovered (pro)renin receptor (PRR) may be key in this mechanism as it serves to sequester renin and prorenin for localized RAS activity. Thus, the PRR can potentially mitigate the low levels of renin expression in the brain to propagate Ang II action. In this review we examine the regulation, expression and functional properties of the various RAS components in the brain with particular focus on the different roles that PRR may have in BP regulation and hypertension.

Role of oxidant stress on AT1 receptor expression in neurons of rabbits with heart failure and in cultured neurons

We have previously reported that the expression of Angiotensin II (Ang II) type 1 receptors (AT1R) was increased in the rostral ventrolateral medulla (RVLM) of rabbits with chronic heart failure (CHF) and in the RVLM of normal rabbits infused with intracerebroventricular (ICV) Ang II. The present study investigated whether oxidant stress plays a role in Ang II-induced AT1R upregulation and its relationship to the transcription factor activator protein 1 (AP1) in CHF rabbits and in the CATHa neuronal cell line. In CATHa cells, Ang II significantly increased AT1R mRNA by 123+/-11%, P<0.01; c-Jun mRNA by 90+/-20%, P<0.01; c-fos mRNA by 148+/-49%, P<0.01; NADPH oxidase activity by 126+/-43%, P<0.01 versus untreated cells. Tempol and Apocynin reversed the increased expression of AT1R mRNA, c-Jun mRNA, c-fos mRNA, and superoxide production induced by Ang II. We also examined the effect of ICV Tempol on the RVLM of CHF rabbits. Compared to vehicle treated CHF rabbits, Tempol significantly decreased AT1R protein expression (1.6+/-0.29 versus 0.88+/-0.16, P<0.05), phosphorylated Jnk protein (0.4+/-0.05 versus 0.2+/-0.04, P<0.05), cytosolic phosphorylated c-Jun (0.56+/-0.1 versus 0.36+/-0.05, P<0.05), and nuclear phosphorylated c-Jun (0.67+/-0.1 versus 0.3+/-0.08, P<0.01). Tempol also significantly decreased the AP-1-DNA binding activity in the RVLM of CHF rabbits compared to the vehicle group (9.14 x 10(3) versus 41.95 x 10(3) gray level P<0.01). These data suggest that Ang II induces AT1R upregulation at the transcriptional level by induction of oxidant stress and activation of AP1 in both cultured neuronal cells and in intact brain of rabbits. Antioxidant agents may be beneficial in CHF and other states where brain Ang II is elevated by decreasing AT1R expression through the Jnk and AP1 pathway.

Functional genomics as an emerging strategy for the investigation of central mechanisms in experimental hypertension

Centrally mediated increases in sympathetic nerve activity and attenuated arterial baroreflexes contribute to the pathogenesis of hypertension. Despite the characterization of cellular and physiological mechanisms that regulate blood pressure and alterations that contribute to hypertension, the genetic and molecular basis of this pathophysiology remains poorly understood. Strategies to identify genes that contribute to central pathophysiologic mechanisms in hypertension include integrative biochemistry and physiology as well as functional genomics. This article summarizes recent progress in applying functional genomics to elucidate the genetic basis of altered central blood pressure regulatory mechanisms in hypertension. We describe approaches others and we have undertaken to investigate gene expression profiles in hypertensive models in order to identify genes that contribute to the pathogenesis of hypertension. Finally, we provide the readers a roadmap for negotiating the route from experimental findings of gene expression profiling to translating their therapeutic potential. The combination of gene expression profiling and the phenotypic characterization of in vitro and in vivo loss or gain of function experiments for candidate genes have the potential to identify genes involved in the pathogenesis of hypertension and may present novel targets for therapy.

Brain renin-angiotensin system dysfunction in hypertension: recent advances and perspectives

This review focuses on the dysfunction of the intrinsic brain renin-angiotensin system (RAS) in the pathogenesis of hypertension. Hyperactivity of the brain RAS plays a critical role in mediating hypertension in both humans and animal models of hypertension, including the spontaneously hypertensive rat (SHR). The specific mechanisms by which increased brain RAS activity results in hypertension are not well understood but include increases in sympathetic vasomotor tone and impaired arterial baroreflex function. We discuss the contribution of endogenous angiotensin (Ang) II actions on presympathetic vasomotor rostral ventrolateral medulla neurons to enhance sympathetic activity and maintain hypertension. In addition, we discuss Ang II-induced attenuation of afferent baroreceptor feedback within the nucleus tractus solitarius and its relevance to the development of hypertension. We also outline the cellular and molecular mechanisms of Ang II signal transduction that may be critical for the initiation and establishment of hypertension. In particular, we present evidence for a phosphoinositide-3-kinase-dependent signaling pathway that appears to contribute to hypertension in the SHR, possibly via augmented Ang II-induced increases in neuronal firing rate and enhanced transcriptional noradrenaline neuromodulation. Finally, we outline future directions in utilizing our understanding of the brain RAS dysfunction in hypertension for the development of improved therapeutic intervention in hypertension.

The renin-angiotensin system in the brain: possible therapeutic implications for AT(1)-receptor blockers

Biochemical, physiological and functional studies suggest that the brain renin-angiotensin system (RAS) is regulated independently of the peripheral RAS. The classical actions of angiotensin II in the brain include blood pressure control, drinking behaviour, natriuresis and the release of vasopressin into the circulation. At least two subtypes of G-protein coupled receptors, the AT(1) and the AT(2) receptor, have been identified. Most of the classic actions of angiotensin II in the brain are mediated by AT(1) receptors. The AT(2) receptor is involved in brain development and neuronal regeneration and protection. Additionally, AT(2) receptors can modulate some of the classic angiotensin II actions in the brain. Selective non-peptide AT(1) receptor blockers, applied systemically, have been shown to inhibit both peripheral and brain AT(1)receptors. In genetically hypertensive rats, inhibition of brain AT(1) receptors may contribute to the blood pressure lowering effects of AT(1) receptor blockers. Animal studies have shown that AT(1) receptor antagonists enable endogenous angiotensin II to stimulate neuronal regeneration via activation of AT(2) receptors. In animal models, inhibition of the brain RAS proved to be beneficial with respect to stroke incidence and outcome. Blockade of brain and cerebrovascular AT(1) receptors by AT(1) receptor blockers prevents the reduction in blood flow during brain ischaemia, reduces the volume of ischaemic injury and improves neurological outcome after brain ischaemia. This paper reviews the actions of angiotensin II and its receptors in the brain, and discusses the possible consequences of AT(1) receptor blockade in neuroprotection, neuroregeneration, cerebral haemodynamics and ischaemia.

The hypothalamus and hypertension

Most forms of hypertension are associated with a wide variety of functional changes in the hypothalamus. Alterations in the following substances are discussed: catecholamines, acetylcholine, angiotensin II, natriuretic peptides, vasopressin, nitric oxide, serotonin, GABA, ouabain, neuropeptide Y, opioids, bradykinin, thyrotropin-releasing factor, vasoactive intestinal polypeptide, tachykinins, histamine, and corticotropin-releasing factor. Functional changes in these substances occur throughout the hypothalamus but are particularly prominent rostrally; most lead to an increase in sympathetic nervous activity which is responsible for the rise in arterial pressure. A few appear to be depressor compensatory changes. The majority of the hypothalamic changes begin as the pressure rises and are particularly prominent in the young rat; subsequently they tend to fluctuate and overall to diminish with age. It is proposed that, with the possible exception of the Dahl salt-sensitive rat, the hypothalamic changes associated with hypertension are caused by renal and intrathoracic cardiopulmonary afferent stimulation. Renal afferent stimulation occurs as a result of renal ischemia and trauma as in the reduced renal mass rat. It is suggested that afferents from the chest arise, at least in part, from the observed increase in left auricular pressure which, it is submitted, is due to the associated documented impaired ability to excrete sodium. It is proposed, therefore, that the hypothalamic changes in hypertension are a link in an integrated compensatory natriuretic response to the kidney's impaired ability to excrete sodium.

Adenovirus-mediated gene transfer into the NTS in conscious rats. A new approach to examining the central control of cardiovascular regulation

The nucleus tractus solitarii (NTS) is an important site for the regulation of sympathetic nerve activity. It receives the signals through afferent fibers from arterial baroreceptors, chemoreceptors, cardiopulmonary receptors, and other visceral receptors. Many studies have examined the role of nitric oxide (NO) in the NTS in cardiovascular regulation. However, most of these studies were conducted in an acute state with anesthesia. We have developed a novel technique of endothelial nitric oxide synthase (eNOS) gene transfer into the NTS in vivo. Adenovirus vectors encoding either the beta-galactosidase gene (Ad beta gal) or the endothelial nitric oxide synthase gene (AdeNOS) gene were transfected into the NTS. In the Ad beta gal-treated rats, the local expression of beta-galactosidase was confirmed by X-Gal staining, and beta-galactosidase activity was quantified using a colorimetric assay. In the AdeNOS-treated rats, the local expression of eNOS protein was confirmed by immunohistochemistry, and eNOS production was measured by in vivo microdialysis. Blood pressure and heart rate were monitored by a radiotelemetry system in a conscious state. The expression of each gene was observed from day 5 to day 10 after the gene transfer. In the AdeNOS-treated rats, blood pressure and heart rate significantly decreased from day 5 to day 10, and then thereafter gradually recovered over time. Our method may be useful in examining the local effect of a particular substance produced by a specific gene in the brain on cardiovascular function.