The Prorenin and (Pro)renin Receptor: New Players in the Brain Renin-Angiotensin System? Int J Hypertens. 2012;2012:290635. [PMID: 23316344 PMCID: PMC3536329 DOI: 10.1155/2012/290635]

Upregulation of the Renin-Angiotensin System Is Associated with Patient Survival and the Tumour Microenvironment in Glioblastoma

Glioblastoma is a highly aggressive disease with poor survival outcomes. An emerging body of literature links the role of the renin-angiotensin system (RAS), well-known for its function in the cardiovascular system, to the progression of cancers. We studied the expression of RAS-related genes (ATP6AP2, AGTR1, AGTR2, ACE, AGT, and REN) in The Cancer Genome Atlas (TCGA) glioblastoma cohort, their relationship to patient survival, and association with tumour microenvironment pathways. The expression of RAS genes was then examined in 12 patient-derived glioblastoma cell lines treated with chemoradiation. In cases of glioblastoma within the TCGA, ATP6AP2, AGTR1, ACE, and AGT had consistent expressions across samples, while AGTR2 and REN were lowly expressed. High expression of AGTR1 was independently associated with lower progression-free survival (PFS) (p = 0.01) and had a non-significant trend for overall survival (OS) after multivariate analysis (p = 0.095). The combined expression of RAS receptors (ATP6AP2, AGTR1, and AGTR2) was positively associated with gene pathways involved in hypoxia, microvasculature, stem cell plasticity, and the molecular characterisation of glioblastoma subtypes. In patient-derived glioblastoma cell lines, ATP6AP2 and AGTR1 were upregulated after chemoradiotherapy and correlated with an increase in HIF1A expression. This data suggests the RAS is correlated with changes in the tumour microenvironment and associated with glioblastoma survival outcomes.

Autonomic Dysreflexia in Spinal Cord Injury: Mechanisms and Prospective Therapeutic Targets

High-level spinal cord injury (SCI) often results in cardiovascular dysfunction, especially the development of autonomic dysreflexia. This disorder, characterized as an episode of hypertension accompanied by bradycardia in response to visceral or somatic stimuli, causes substantial discomfort and potentially life-threatening symptoms. The neural mechanisms underlying this dysautonomia include a loss of supraspinal control to spinal sympathetic neurons, maladaptive plasticity of sensory inputs and propriospinal interneurons, and excessive discharge of sympathetic preganglionic neurons. While neural control of cardiovascular function is largely disrupted after SCI, the renin-angiotensin system (RAS), which mediates blood pressure through hormonal mechanisms, is up-regulated after injury. Whether the RAS engages in autonomic dysreflexia, however, is still controversial. Regarding therapeutics, transplantation of embryonic presympathetic neurons, collected from the brainstem or more specific raphe regions, into the injured spinal cord may reestablish supraspinal regulation of sympathetic activity for cardiovascular improvement. This treatment reduces the occurrence of spontaneous autonomic dysreflexia and the severity of artificially triggered dysreflexic responses in rodent SCI models. Though transplanting early-stage neurons improves neural regulation of blood pressure, hormonal regulation remains high and baroreflex dysfunction persists. Therefore, cell transplantation combined with selected RAS inhibition may enhance neuroendocrine homeostasis for cardiovascular recovery after SCI.

The Renin Angiotensin System as a Therapeutic Target in Traumatic Brain Injury

Traumatic brain injury (TBI) is a major public health problem, with limited pharmacological options available beyond symptomatic relief. The renin angiotensin system (RAS) is primarily known as a systemic endocrine regulatory system, with major roles controlling blood pressure and fluid homeostasis. Drugs that target the RAS are used to treat hypertension, heart failure and kidney disorders. They have now been used chronically by millions of people and have a favorable safety profile. In addition to the systemic RAS, it is now appreciated that many different organ systems, including the brain, have their own local RAS. The major ligand of the classic RAS, Angiotensin II (Ang II) acts predominantly through the Ang II Type 1 receptor (AT1R), leading to vasoconstriction, inflammation, and heightened oxidative stress. These processes can exacerbate brain injuries. Ang II receptor blockers (ARBs) are AT1R antagonists. They have been shown in several preclinical studies to enhance recovery from TBI in rodents through improvements in molecular, cellular and behavioral correlates of injury. ARBs are now under consideration for clinical trials in TBI. Several different RAS peptides that signal through receptors distinct from the AT1R, are also potential therapeutic targets for TBI. The counter regulatory RAS pathway has actions that oppose those stimulated by AT1R signaling. This alternative pathway has many beneficial effects on cells in the central nervous system, bringing about vasodilation, and having anti-inflammatory and anti-oxidative stress actions. Stimulation of this pathway also has potential therapeutic value for the treatment of TBI. This comprehensive review will provide an overview of the various components of the RAS, with a focus on their direct relevance to TBI pathology. It will explore different therapeutic agents that modulate this system and assess their potential efficacy in treating TBI patients.

The hypothalamus as a key regulator of glucose homeostasis: emerging roles of the brain renin-angiotensin system

The regulation of plasma glucose levels is a complex and multifactorial process involving a network of receptors and signaling pathways across numerous organs that act in concert to ensure homeostasis. However, much about the mechanisms and pathways by which the brain regulates glycemic homeostasis remains poorly understood. Understanding the precise mechanisms and circuits employed by the central nervous system to control glucose is critical to resolving the diabetes epidemic. The hypothalamus, a key integrative center within the central nervous system, has recently emerged as a critical site in the regulation of glucose homeostasis. Here, we review the current understanding of the role of the hypothalamus in regulating glucose homeostasis, with an emphasis on the paraventricular nucleus, the arcuate nucleus, the ventromedial hypothalamus, and lateral hypothalamus. In particular, we highlight the emerging role of the brain renin-angiotensin system in the hypothalamus in regulating energy expenditure and metabolic rate, as well as its potential importance in the regulation of glucose homeostasis.

Renin-Angiotensin System: Updated Understanding and Role in Physiological and Pathophysiological States

The classical view of the renin-angiotensin system (RAS) is that of the circulating hormone pathway involved in salt and water homeostasis and blood pressure regulation. It is also involved in the pathogenesis of cardiac and renal disorders. This led to the creation of drugs blocking the actions of this classical pathway, which improved cardiac and renal outcomes. Our understanding of the RAS has significantly expanded with the discovery of new peptides involved in this complex pathway. Over the last two decades, a counter-regulatory or protective pathway has been discovered that opposes the effects of the classical pathway. Components of RAS are also implicated in the pathogenesis of obesity and its metabolic diseases. The continued discovery of newer molecules also provides novel therapeutic targets to improve disease outcomes. This article aims to provide an overview of an updated understanding of the RAS, its role in physiological and pathological processes, and potential novel therapeutic options from RAS for managing cardiorenal disorders, obesity, and related metabolic disorders.

Angiotensin II increases respiratory rhythmic activity in the preBötzinger complex without inducing astroglial calcium signaling

Angiotensin II (Ang II) is the primary modulator of the renin-angiotensin system and has been widely studied for its effect on the cardiovascular system. While a few studies have also indicated an involvement of Ang II in the regulation of breathing, very little is known in this regard and its effect on brainstem respiratory regions such as the preBötzinger complex (preBötC), the kernel for inspiratory rhythm generation, has not been investigated yet. This study reports that Ang II temporarily increases phrenic nerve activity in the working heart-brainstem preparation, indicating higher central respiratory drive. Previous studies have shown that the carotid body is involved in mediating this effect and we revealed that the preBötC also plays a part, using acute slices of the brainstem. It appears that Ang II is increasing the respiratory drive in an AT1R-dependent manner by optimizing the interaction of inhibitory and excitatory neurons of the preBötC. Thus, Ang II-mediated effects on the preBötC are potentially involved in dysregulating breathing in patients with acute lung injury.

Renin-a in the Subfornical Organ Plays a Critical Role in the Maintenance of Salt-Sensitive Hypertension

The brain renin-angiotensin system plays important roles in blood pressure and cardiovascular regulation. There are two isoforms of prorenin in the brain: the classic secreted form (prorenin/sREN) encoded by renin-a, and an intracellular form (icREN) encoded by renin-b. Emerging evidence indicates the importance of renin-b in cardiovascular and metabolic regulation. However, the role of endogenous brain prorenin in the development of salt-sensitive hypertension remains undefined. In this study, we test the hypothesis that renin-a produced locally in the brain contributes to the pathogenesis of hypertension. Using RNAscope, we report for the first time that renin mRNA is expressed in several regions of the brain, including the subfornical organ (SFO), the paraventricular nucleus of the hypothalamus (PVN), and the brainstem, where it is found in glutamatergic, GABAergic, cholinergic, and tyrosine hydroxylase-positive neurons. Notably, we found that renin mRNA was significantly elevated in the SFO and PVN in a mouse model of DOCA-salt–induced hypertension. To examine the functional importance of renin-a in the SFO, we selectively ablated renin-a in the SFO in renin-a–floxed mice using a Cre-lox strategy. Importantly, renin-a ablation in the SFO attenuated the maintenance of DOCA-salt–induced hypertension and improved autonomic function without affecting fluid or sodium intake. Molecularly, ablation of renin-a prevented the DOCA-salt–induced elevation in NADPH oxidase 2 (NOX2) in the SFO without affecting NOX4 or angiotensin II type 1 and 2 receptors. Collectively, our findings demonstrate that endogenous renin-a within the SFO is important for the pathogenesis of salt-sensitive hypertension.

The Role of (Pro)Renin Receptor in the Metabolic Syndrome

The prorenin receptor (PRR) is a complex multi-functional single transmembrane protein receptor that is ubiquitously expressed in organs and tissues throughout the body. PRR is involved in different cellular mechanisms that comprise the generation of Angiotensin II, the activation of Wnt/β-catenin signaling, the stimulation of ERK 1/2 pathway, and the proper functioning of the vacuolar H+-ATPase. Evidence supports the role of PRR and its soluble form, sPRR, in the classical features of the metabolic syndrome, including obesity, hypertension, diabetes, and disruption of lipid homeostasis. This review summarizes our current knowledge and highlights new advances in the pathophysiological function of PRR and sPRR in adipogenesis, adipocyte differentiation, lipolysis, glucose and insulin resistance, lipid homeostasis, energy metabolism, and blood pressure regulation.

Functions of the (pro)renin receptor (Atp6ap2) at molecular and system levels: pathological implications in hypertension, renal and brain development, inflammation, and fibrosis

The (pro)renin receptor [(P)RR, Atp6ap2] was initially discovered as a membrane-bound binding partner of prorenin and renin. A soluble (P)RR has additional paracrine effects and is involved in metabolic syndrome and kidney damage. Meanwhile it is clear that most of the effects of the (P)RR are independent of prorenin. In the kidney, (P)RR plays an important role in renal dysfunction by activating proinflammatory and profibrotic molecules. In the brain, (P)RR is expressed in cardiovascular regulatory nuclei and is linked to hypertension. (P)RR is known to be an essential component of the v-ATPase as a key accessory protein and plays an important role in kidney, brain and heart via regulating the pH of the extracellular space and intracellular compartments. V-ATPase and (P)RR together act on WNT and mTOR signalling pathways, which are responsible for cellular homeostasis and autophagy. (P)RR through its role in v-ATPase assembly and function is also important for fast recycling endocytosis by megalin. In the kidney, megalin together with v-ATPase and (P)RR is crucial for endocytic uptake of components of the RAS and their intracellular processing. In the brain, (P)RR, v-ATPases and megalin are important regulators both during development and in the adult. All three proteins are associated with diseases such as XLMR, XMRE, X-linked parkinsonism and epilepsy, cognitive disorders with Parkinsonism, spasticity, intellectual disability, and Alzheimer's Disease which are characterized by impaired neuronal function and/or neuronal loss. The present review focusses on the relevant effects of Atp6ap2 without assigning them necessarily to the RAS. Mechanistically, many effects can be well explained by the role of Atp6ap2 for v-ATPase assembly and function. Furthermore, application of a soluble (P)RR analogue as new therapeutic option is discussed.

Effect of Angiotensin II on Chondrocyte Degeneration and Protection via Differential Usage of Angiotensin II Receptors

The renin–angiotensin system (RAS) controls not only systemic functions, such as blood pressure, but also local tissue-specific events. Previous studies have shown that angiotensin II receptor type 1 (AT₁R) and type 2 (AT₂R), two RAS components, are expressed in chondrocytes. However, the angiotensin II (ANG II) effects exerted through these receptors on chondrocyte metabolism are not fully understood. In this study, we investigated the effects of ANG II and AT₁R blockade on chondrocyte proliferation and differentiation. Firstly, we observed that ANG II significantly suppressed cell proliferation and glycosaminoglycan content in rat chondrocytic RCS cells. Additionally, ANG II decreased CCN2, which is an anabolic factor for chondrocytes, via increased MMP9. In Agtr1a-deficient RCS cells generated by the CRISPR-Cas9 system, Ccn2 and Aggrecan (Acan) expression increased. Losartan, an AT₁R antagonist, blocked the ANG II-induced decrease in CCN2 production and Acan expression in RCS cells. These findings suggest that AT₁R blockade reduces ANG II-induced chondrocyte degeneration. Interestingly, AT₁R-positive cells, which were localized on the surface of the articular cartilage of 7-month-old mice expanded throughout the articular cartilage with aging. These findings suggest that ANG II regulates age-related cartilage degeneration through the ANG II–AT₁R axis.

Expression of Cathepsins B, D, and G in Extracranial Arterio-Venous Malformation

Objectives: We have previously identified a population of cells that expressed stemness-associated markers in extracranial arterio-venous malformation (AVM) and demonstrated expression of cathepsins B, D, and G on embryonic stem cell (ESC)-like populations in other vascular anomalies. This study investigated the expression of cathepsins B, D, and G, and their localization in relation to this primitive population in extracranial AVM.

Methods: Immunohistochemical staining was performed on AVM tissue samples from 13 patients to demonstrate expression of cathepsins B, D, and G. Western blotting was performed on four AVM tissue samples and three AVM-derived primary cell lines to confirm protein expression of cathepsins B and D proteins. RT-qPCR was performed on three AVM-derived primary cell lines to demonstrate transcript expression of cathepsins B, D, and G. Enzymatic activity assays were performed on three AVM-derived primary cell lines to investigate if cathepsins B and D were active. Localization of the cathepsins was investigated using immunofluorescence dual-staining of the cathepsins with the ESC markers OCT4 and SOX2, and mast cells marker chymase on two of the 13 AVM tissue samples.

Results: Immunohistochemical staining demonstrated expression of cathepsins B, D, and G in all 13 AVM tissue samples. Western blotting showed expression of cathepsins B and D proteins in all four AVM tissue samples and all three AVM-derived primary cell lines. RT-qPCR demonstrated transcripts of cathepsins B, D, and G in all three AVM-derived primary cell lines. Enzymatic activity assays showed that cathepsins B and D were active. Immunofluorescence staining showed expression of cathepsins B and D on the OCT4+/SOX2+ endothelium and media of the lesional vessels and cells within the stroma in AVM nidus. Cathepsin G was expressed on the chymase+ phenotypic mast cells.

Conclusions: This study demonstrated the novel finding of the expression of cathepsins B, D, and G in AVM. Cathepsins B and D were expressed by the primitive population, and cathepsin G was localized to mast cells, within the AVM nidus.

Angiotensin-(1-7) and Mas receptor in the brain

The renin-angiotensin system (RAS) is a key regulator of blood pressure and electrolyte homeostasis. Besides its importance as regulator of the cardiovascular function, the RAS has also been associated to the modulation of higher brain functions, including cognition, memory, depression and anxiety. For many years, angiotensin II (Ang II) has been considered the major bioactive component of the RAS. However, the existence of many other biologically active RAS components has currently been recognized, with similar, opposite, or distinct effects to those exerted by Ang II. Today, it is considered that the RAS is primarily constituted by two opposite arms. The pressor arm is composed by Ang II and the Ang II type 1 (AT1) receptor (AT1R), which mediates the vasoconstrictor, proliferative, hypertensive, oxidative and pro-inflammatory effects of the RAS. The depressor arm is mainly composed by Ang-(1-7), its Mas receptor (MasR) which mediates the depressor, vasodilatory, antiproliferative, antioxidant and anti-inflammatory effects of Ang-(1-7) and the AT2 receptor (AT2R), which opposes to the effects mediated by AT1R activation. Central Ang-(1-7) is implicated in the control of the cardiovascular function, thus participating in the regulation of blood pressure. Ang-(1-7) also exerts neuroprotective actions through MasR activation by opposing to the harmful effects of the Ang II/AT1R axis. This review is focused on the expression and regulation of the Ang-(1-7)/MasR axis in the brain, its main neuroprotective effects and the evidence regarding its involvement in the pathophysiology of several diseases at cardiovascular and neurological level.

Brain Renin-Angiotensin System at the Intersect of Physical and Cognitive Frailty

The renin–angiotensin system (RAS) was initially considered to be part of the endocrine system regulating water and electrolyte balance, systemic vascular resistance, blood pressure, and cardiovascular homeostasis. It was later discovered that intracrine and local forms of RAS exist in the brain apart from the endocrine RAS. This brain-specific RAS plays essential roles in brain homeostasis by acting mainly through four angiotensin receptor subtypes; AT₁R, AT₂R, MasR, and AT₄R. These receptors have opposing effects; AT₁R promotes vasoconstriction, proliferation, inflammation, and oxidative stress while AT₂R and MasR counteract the effects of AT₁R. AT₄R is critical for dopamine and acetylcholine release and mediates learning and memory consolidation. Consequently, aging-associated dysregulation of the angiotensin receptor subtypes may lead to adverse clinical outcomes such as Alzheimer’s disease and frailty via excessive oxidative stress, neuroinflammation, endothelial dysfunction, microglial polarization, and alterations in neurotransmitter secretion. In this article, we review the brain RAS from this standpoint. After discussing the functions of individual brain RAS components and their intracellular and intracranial locations, we focus on the relationships among brain RAS, aging, frailty, and specific neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, and vascular cognitive impairment, through oxidative stress, neuroinflammation, and vascular dysfunction. Finally, we discuss the effects of RAS-modulating drugs on the brain RAS and their use in novel treatment approaches.

Mineralocorticoid Dysfunction during Critical Illness: A Review of the Evidence

The recent demonstration of the significant reduction in mortality in patients with septic shock treated with adjunctive glucocorticoids combined with fludrocortisone and the effectiveness of angiotensin II in treating vasodilatory shock have renewed interest in the role of the mineralocorticoid axis in critical illness. Glucocorticoids have variable interactions at the mineralocorticoid receptor. Similarly, mineralocorticoid receptor-aldosterone interactions differ from mineralocorticoid receptor-glucocorticoid interactions and predicate receptor-ligand interactions that differ with respect to cellular effects. Hyperreninemic hypoaldosteronism or selective hypoaldosteronism, an impaired adrenal response to increasing renin levels, occurs in a subgroup of hemodynamically unstable critically ill patients. The suggestion is that there is a defect at the level of the adrenal zona glomerulosa associated with a high mortality rate that may represent an adaptive response aimed at increasing cortisol levels. Furthermore, cross-talk exists between angiotensin II and aldosterone, which needs to be considered when employing therapeutic strategies.

The role of the brain renin-angiotensin system (RAS) in mild traumatic brain injury (TBI)

There is considerable interest in traumatic brain injury (TBI) induced by repeated concussions suffered by athletes in sports, military personnel from combat-and non-combat related activities, and civilian populations who suffer head injuries from accidents and domestic violence. Although the renin-angiotensin system (RAS) is primarily a systemic cardiovascular regulatory system that, when dysregulated, causes hypertension and cardiovascular pathology, the brain contains a local RAS that plays a critical role in the pathophysiology of several neurodegenerative diseases. This local RAS includes receptors for angiotensin (Ang) II within the brain parenchyma, as well as on circumventricular organs outside the blood-brain-barrier. The brain RAS acts primarily via the type 1 Ang II receptor (AT₁R), exacerbating insults and pathology. With TBI, the brain RAS may contribute to permanent brain damage, especially when a second TBI occurs before the brain recovers from an initial injury. Agents are needed that minimize the extent of injury from an acute TBI, reducing TBI-mediated permanent brain damage. This review discusses how activation of the brain RAS following TBI contributes to this damage, and how drugs that counteract activation of the AT₁R including AT₁R blockers (ARBs), renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, and agonists at type 2 Ang II receptors (AT₂) and at Ang (1-7) receptors (Mas) can potentially ameliorate TBI-induced brain damage.

The neuronal (pro)renin receptor and astrocyte inflammation in the central regulation of blood pressure and blood glucose in mice fed a high-fat diet

We report here that the neuronal (pro)renin receptor (PRR), a key component of the brain renin-angiotensin system (RAS), plays a critical role in the central regulation of high-fat-diet (HFD)-induced metabolic pathophysiology. The neuronal PRR is known to mediate formation of the majority of angiotensin (ANG) II, a key bioactive peptide of the RAS, in the central nervous system and to regulate blood pressure and cardiovascular function. However, little is known about neuronal PRR function in overnutrition-related metabolic physiology. Here, we show that PRR deletion in neurons reduces blood pressure, neurogenic pressor activity, and fasting blood glucose and improves glucose tolerance without affecting food intake or body weight following a 16-wk HFD. Mechanistically, we found that a HFD increases levels of the PRR ligand (pro)renin in the circulation and hypothalamus and of ANG II in the hypothalamus, indicating activation of the brain RAS. Importantly, PRR deletion in neurons reduced astrogliosis and activation of the astrocytic NF-κB p65 (RelA) in the arcuate nucleus and the ventromedial nucleus of the hypothalamus. Collectively, our findings indicate that the neuronal PRR plays essential roles in overnutrition-related metabolic pathophysiology.

Neuroinflammation in heart failure: new insights for an old disease

Heart failure (HF) is a complex clinical syndrome affecting roughly 26 million people worldwide. Increased sympathetic drive is a hallmark of HF and is associated with disease progression and higher mortality risk. Several mechanisms contribute to enhanced sympathetic activity in HF, but these pathways are still incompletely understood. Previous work suggests that inflammation and activation of the renin-angiotensin system (RAS) increases sympathetic drive. Importantly, chronic inflammation in several brain regions is commonly observed in aged populations, and a growing body of evidence suggests neuroinflammation plays a crucial role in HF. In animal models of HF, central inhibition of RAS and pro-inflammatory cytokines normalizes sympathetic drive and improves cardiac function. The precise molecular and cellular mechanisms that lead to neuroinflammation and its effect on HF progression remain undetermined. This review summarizes the most recent advances in the field of neuroinflammation and autonomic control in HF. In addition, it focuses on cellular and molecular mediators of neuroinflammation in HF and in particular on brain regions involved in sympathetic control. Finally, we will comment on what is known about neuroinflammation in the context of preserved vs. reduced ejection fraction HF.

Exacerbated effects of prorenin on hypothalamic magnocellular neuronal activity and vasopressin plasma levels during salt-sensitive hypertension

Accumulating evidence supports that the brain renin-angiotensin system (RAS), including prorenin (PR) and its receptor (PRR), two newly discovered RAS players, contribute to sympathoexcitation in salt-sensitive hypertension. Still, whether PR also contributed to elevated circulating levels of neurohormones such as vasopressin (VP) during salt-sensitive hypertension, and if so, what are the precise underlying mechanisms, remains to be determined. To address these questions, we obtained patch-clamp recordings from hypothalamic magnocellular neurosecretory neurons (MNNs) that synthesize the neurohormones oxytocin and VP in acute hypothalamic slices obtained from sham and deoxycorticosterone acetate (DOCA)-salt-treated hypertensive rats. We found that focal application of PR markedly increased membrane excitability and firing responses in MNNs of DOCA-salt, compared with sham rats. This effect included a shorter latency to spike initiation and increased numbers of spikes in response to depolarizing stimuli and was mediated by a more robust inhibition of A-type K⁺ channels in DOCA-salt compared with sham rats. On the other hand, the afterhyperpolarizing potential mediated by the activation of Ca²⁺-dependent K⁺ channel was not affected by PR. mRNA expression of PRR, VP, and the Kv4.3 K⁺ channel subunit in the supraoptic nucleus of DOCA-salt hypertensive rats was increased compared with sham rats. Finally, we report a significant decrease of plasma VP levels in neuron-selective PRR knockdown mice treated with DOCA-salt, compared with wild-type DOCA-salt-treated mice. Together, these results support that activation of PRR contributes to increased excitability and firing discharge of MNNs and increased plasma levels of VP in DOCA-salt hypertension.NEW & NOTEWORTHY Our studies support that prorenin (PR) and its receptor (PRR) within the hypothalamus contribute to elevated plasma vasopressin levels in deoxycorticosterone acetate-salt hypertension, in part because of an exacerbated effect of PR on magnocellular neurosecretory neuron excitability; Moreover, our study implicates A-type K+ channels as key underlying molecular targets mediating these effects. Thus, PR/PRR stands as a novel therapeutic target for the treatment of neurohumoral activation in salt-sensitive hypertension.

(Pro)Renin receptor mediates obesity-induced antinatriuresis and elevated blood pressure via upregulation of the renal epithelial sodium channel

Recent studies have demonstrated that the renal (pro)renin receptor (PRR) regulates expression of the alpha subunit of the epithelial sodium channel (α-ENaC). In this study we hypothesized that the renal PRR mediates high fat diet (HFD)-induced sodium retention and elevated systolic blood pressure (SBP) by enhancing expression of the epithelial sodium channel (α-ENaC). In our study we used a recently developed inducible nephron specific PRR knockout mouse. Mice (n = 6 each group) were allocated to receive regular diet (RD, 12 kcal% fat) or a high-fat diet (HFD, 45 kcal% fat) for 10 weeks. Body weight (BW), SBP, urine volume (UV) and urine sodium (U_NaV), as well as renal interstitial Angiotensin II (Ang II), and renal medullary expression of PRR, p-SGK-1, α-ENaC were monitored in RD and HFD mice with or without PRR knockout. At baseline, there were no significant differences in BW, BP, UV or U_NaV between different animal groups. At the end of the study, HFD mice had significant increases in SBP, BW, and significant reductions in UV and U_NaV. Compared to RD, HFD significantly increased mRNA and protein expression of PRR, α-ENaC, p-SGK-1, and Ang II. Compared to HFD alone, PRR knockout mice on HFD had reduced mRNA and protein expression of PRR, p-SGK-1, and α-ENaC, as well as increased UV, U_NaV and significantly reduced SBP. RIF Ang II was significantly increased by HFD and did not change in response to PRR knockout. We conclude that obesity induced sodium retention and elevated SBP are mediated by the PRR-SGK-1- α-ENaC pathway independent of Ang II.

The prorenin receptor in the cardiovascular system and beyond

Since the prorenin receptor (PRR) was first reported, its physiological role in many cellular processes has been under intense scrutiny. The PRR is currently recognized as a multifunctional receptor with major roles as an accessory protein of the vacuolar-type H+-ATPase and as an intermediary in the Wnt signaling pathway. As a member of the renin-angiotensin system (RAS), the PRR has demonstrated to be of relevance in cardiovascular diseases (CVD) because it can activate prorenin and enhance the enzymatic activity of renin, thus promoting angiotensin II formation. Indeed, there is an association between PRR gene polymorphisms and CVD. Independent of angiotensin II, the activation of the PRR further stimulates intracellular signals linked to fibrosis. Studies using tissues and cells from a variety of organs and systems have supported its roles in multiple functions, although some remain controversial. In the brain, the PRR appears to be involved in the central regulation of blood pressure via activation of RAS- and non-RAS-dependent mechanisms. In the heart, the PRR promotes atrial structural and electrical remodeling. Nonetheless, animals overexpressing the PRR do not exhibit cardiac injury. In the kidney, the PRR is involved in the development of ureteric bud branching, urine concentration, and regulation of blood pressure. There is great interest in the PRR contributions to T cell homeostasis and to the development of visceral and brown fat. In this mini-review, we discuss the evidence for the pathophysiological roles of the PRR with emphasis in CVD.

Increased (pro)renin receptor expression in the subfornical organ of hypertensive humans

The central nervous system plays an important role in essential hypertension in humans and in animal models of hypertension through modulation of sympathetic activity and Na⁺ and body fluid homeostasis. Data from animal models of hypertension suggest that the renin-angiotensin system in the subfornical organ (SFO) of the brain is critical for hypertension development. We recently reported that the brain (pro)renin receptor (PRR) is a novel component of the brain renin-angiotensin system and could be a key initiator of the pathogenesis of hypertension. Here, we examined the expression level and cellular distribution of PRR in the SFO of postmortem human brains to assess its association with the pathogenesis of human hypertension. Postmortem SFO tissues were collected from hypertensive and normotensive human subjects. Immunolabeling for the PRR and a retrospective analysis of clinical data were performed. We found that human PRR was prominently expressed in most neurons and microglia, but not in astrocytes, in the SFO. Importantly, PRR levels in the SFO were elevated in hypertensive subjects. Moreover, PRR immunoreactivity was significantly correlated with systolic blood pressure but not body weight, age, or diastolic blood pressure. Interestingly, this correlation was independent of antihypertensive drug therapy. Our data indicate that PRR in the SFO may be a key molecular player in the pathogenesis of human hypertension and, as such, could be an important focus of efforts to understand the neurogenic origin of hypertension. NEW & NOTEWORTHY This study provides evidence that, in the subfornical organ of the human brain, the (pro)renin receptor is expressed in neurons and microglia cells but not in astrocytes. More importantly, (pro)renin receptor immunoreactivity in the subfornical organ is increased in hypertensive humans and is significantly correlated with systolic blood pressure.

A-type K+ channels contribute to the prorenin increase of firing activity in hypothalamic vasopressin neurosecretory neurons

Recent studies have supported an important contribution of prorenin (PR) and its receptor (PRR) to the regulation of hypothalamic, sympathetic, and neurosecretory outflows to the cardiovascular system, including systemic release of vasopressin (VP), both under physiological and cardiovascular disease conditions. Still, the identification of precise cellular mechanisms and neuronal/molecular targets remain unknown. We have recently shown that PRR is expressed in VP neurons and that their activation increases neuronal activity. However, the underlying ionic channel mechanisms are undefined. Here, we performed patch-clamp electrophysiology from identified VP neurons in acute hypothalamic slices obtained from enhanced green fluorescent protein-VP transgenic rats. Voltage-clamp recordings showed that PR inhibited the magnitude of A-type K⁺ current (I_A; ~50% at -25 mV), a subthreshold voltage-dependent current that restrains VP firing activity. PR also increased the inactivation rate of I_A and shifted the steady-state voltage-dependent inactivation function toward more hyperpolarized membrane potential (~7 mV shift), thus resulting in less channel availability to be activated at any given membrane potential. PR also inhibited a sustained component of I_A ("window" current). PR-mediated changes in action potential waveform and increased firing activity were occluded when I_A was blocked by 4-aminopyridine. Finally, PR failed to increase superoxide production within the supraoptic nucleus/paraventricular nucleus, and PR excitatory effects persisted in slices treated with the SOD mimetic tempol. Taken together, these experiments indicated that PR excitatory effects on vasopressin neurons involve inhibition of I_A, due, in part, to increases in its voltage-dependent inactivation properties. Moreover, our results indicate that PR effects did not involve an increase in oxidative stress.NEW & NOTEWORTHY Here, we demonstrate that prorenin/the prorenin receptor is an important signaling unit for the regulation of vasopressin firing activity and, thus, systemic hormonal release. We identified A-type K⁺ channels as key molecular targets mediating prorenin stimulation of vasopressin neuronal activity, thus standing as a potential therapeutic target for neurohumoral activation in cardiovascular disease.

A novel role for miR-133a in centrally mediated activation of the renin-angiotensin system in congestive heart failure

An activated renin-angiotensin system (RAS) within the central nervous system has been implicated in sympathoexcitation during various disease conditions including congestive heart failure (CHF). In particular, activation of the RAS in the paraventricular nucleus (PVN) of the hypothalamus has been recognized to augment sympathoexcitation in CHF. We observed a 2.6-fold increase in angiotensinogen (AGT) in the PVN of CHF. To elucidate the molecular mechanism for increased expression of AGT, we performed in silico analysis of the 3'-untranslated region (3'-UTR) of AGT and found a potential binding site for microRNA (miR)-133a. We hypothesized that decreased miR-133a might contribute to increased AGT in the PVN of CHF rats. Overexpression of miR-133a in NG108 cells resulted in 1.4- and 1.5-fold decreases in AGT and angiotensin type II (ANG II) type 1 receptor (AT₁R) mRNA levels, respectively. A luciferase reporter assay performed on NG108 cells confirmed miR-133a binding to the 3'-UTR of AGT. Consistent with these in vitro data, we observed a 1.9-fold decrease in miR-133a expression with a concomitant increase in AGT and AT₁R expression within the PVN of CHF rats. Furthermore, restoring the levels of miR-133a within the PVN of CHF rats with viral transduction resulted in a significant reduction of AGT (1.4-fold) and AT₁R (1.5-fold) levels with a concomitant decrease in basal renal sympathetic nerve activity (RSNA). Restoration of miR-133a also abrogated the enhanced RSNA responses to microinjected ANG II within the PVN of CHF rats. These results reveal a novel and potentially unique role for miR-133a in the regulation of ANG II within the PVN of CHF rats, which may potentially contribute to the commonly observed sympathoexcitation in CHF.NEW & NOTEWORTHY Angiotensinogen (AGT) expression is upregulated in the paraventricular nucleus of the hypothalamus through posttranscriptional mechanism interceded by microRNA-133a in heart failure. Understanding the mechanism of increased expression of AGT in pathological conditions leading to increased sympathoexcitation may provide the basis for the possible development of new therapeutic agents with enhanced specificity.

(Pro)renin receptor contributes to regulation of renal epithelial sodium channel

BACKGROUND

Recent studies reported increased (Pro)renin receptor (PRR) expression during low-salt intake. We hypothesized that PRR plays a role in regulation of renal epithelial sodium channel (ENaC) through serum and glucocorticoid-inducible kinase isoform 1 (SGK-1)-neural precursor cell expressed, developmentally downregulated 4-2 (Nedd4-2) signaling pathway.

METHOD

Male Sprague-Dawley rats on normal-sodium diet and mouse renal inner medullary collecting duct cells treated with NaCl at 130  mmol/l (normal salt), or 63  mmol/l (low salt) were studied. PRR and α-ENaC expressions were evaluated 1 week after right uninephrectomy and left renal interstitial administration of 5% dextrose, scramble shRNA, or PRR shRNA (n = 6 each treatment).

RESULTS

In-vivo PRR shRNA significantly reduced expressions of PRR throughout the kidney and α-ENaC subunits in the renal medulla. In inner medullary collecting duct cells, low salt or angiotensin II (Ang II) augmented the mRNA and protein expressions of PRR (P < 0.05), SGK-1 (P < 0.05), and α-ENaC (P < 0.05). Low salt or Ang II increased the phosphorylation of Nedd4-2. In cells treated with low salt or Ang II, PRR siRNA significantly downregulated the mRNA and protein expressions of PRR (P < 0.05), SGK-1 (P < 0.05), and α-ENaC expression (P < 0.05).

CONCLUSION

We conclude that PRR contributes to the regulation of α-ENaC via SGK-1-Nedd4-2 signaling pathway.

Receptor Autoradiography Protocol for the Localized Visualization of Angiotensin II Receptors

This protocol describes receptor binding patterns for Angiotensin II (Ang II) in the rat brain using a radioligand specific for Ang II receptors to perform receptor autoradiographic mapping. Tissue specimens are harvested and stored at -80 °C. A cryostat is used to coronally section the tissue (brain) and thaw-mount the sections onto charged slides. The slide-mounted tissue sections are incubated in (125)I-SI-Ang II to radiolabel Ang II receptors. Adjacent slides are separated into two sets: 'non-specific binding' (NSP) in the presence of a receptor saturating concentration of non-radiolabeled Ang II, or an AT1 Ang II receptor subtype (AT1R) selective Ang II receptor antagonist, and 'total binding' with no AT1R antagonist. A saturating concentration of AT2 Ang II receptor subtype (AT2R) antagonist (PD123319, 10 µM) is also present in the incubation buffer to limit (125)I-SI-Ang II binding to the AT1R subtype. During a 30 min pre-incubation at ~22 °C, NSP slides are exposed to 10 µM PD123319 and losartan, while 'total binding' slides are exposed to 10 µM PD123319. Slides are then incubated with (125)I-SI-Ang II in the presence of PD123319 for 'total binding', and PD123319 and losartan for NSP in assay buffer, followed by several 'washes' in buffer, and water to remove salt and non-specifically bound radioligand. The slides are dried using blow-dryers, then exposed to autoradiography film using a specialized film and cassette. The film is developed and the images are scanned into a computer for visual and quantitative densitometry using a proprietary imaging system and a spreadsheet. An additional set of slides are thionin-stained for histological comparisons. The advantage of using receptor autoradiography is the ability to visualize Ang II receptors in situ, within a section of a tissue specimen, and anatomically identify the region of the tissue by comparing it to an adjacent histological reference section.

The critical role of the central nervous system (pro)renin receptor in regulating systemic blood pressure

The systemic renin-angiotensin system (RAS) has long been recognized as a critically important system in blood pressure (BP) regulation. However, extensive evidence has shown that a majority of RAS components are also present in many tissues and play indispensable roles in BP regulation. Here, we review evidence that RAS components, notably including the newly identified (pro)renin receptor (PRR), are present in the brain and are essential for the central regulation of BP. Binding of the PRR to its ligand, prorenin or renin, increases BP and promotes progression of cardiovascular diseases in an angiotensin II-dependent and -independent manner, establishing the PRR a promising antihypertensive drug target. We also review the existing PRR blockers, including handle region peptide and PRO20, and propose a rationale for blocking prorenin/PRR activation as a therapeutic approach that does not affect the actions of the PRR in vacuolar H(+)-ATPase and development. Finally, we summarize categories of currently available antihypertensive drugs and consider future perspectives.

Compromised blood-brain barrier permeability: novel mechanism by which circulating angiotensin II signals to sympathoexcitatory centres during hypertension

Angiotensin II (AngII) is a pivotal peptide implicated in the regulation of blood pressure. In addition to its systemic vascular and renal effects, AngII acts centrally to modulate the activities of neuroendocrine and sympathetic neuronal networks, influencing in turn sympatho-humoral outflows to the circulation. Moreover, a large body of evidence supports AngII signalling dysregulation as a key mechanism contributing to exacerbated sympathoexcitation during hypertension. Due to its hydrophilic actions, circulating AngII does not cross the blood-brain barrier (BBB), signalling to the brain via the circumventricular organs which lack a tight BBB. In this review, we present and discuss recent studies from our laboratory showing that elevated circulating levels of AngII during hypertension result in disruption of the BBB integrity, allowing access of circulating AngII to critical sympathoexcitatory brain centres such as the paraventricular nucleus of the hypothalamus and the rostral ventrolateral medulla. We propose the novel hypothesis that AngII-driven BBB breakdown constitutes a complementary mechanism by which circulating AngII, working in tandem with the central renin-angiotensin system, further exacerbates sympatho-humoral activation during hypertension. These results are discussed within the context of a growing body of evidence in the literature supporting AngII as a pro-inflammatory signal, and brain microglia as key cell targets mediating central AngII actions during hypertension.

Activation of the (pro)renin receptor in the paraventricular nucleus increases sympathetic outflow in anesthetized rats

Previous studies have indicated that hyperactivity of brain prorenin receptors (PRR) is implicated in neurogenic hypertension. However, the role of brain PRR in regulating arterial blood pressure (ABP) is not well understood. Here, we test the hypothesis that PRR activation in the hypothalamic paraventricular nucleus (PVN) contributes to increased sympathetic nerve activity (SNA). In anaesthetized adult Sprague-Dawley (SD) rats, bilateral PVN microinjection of human prorenin (2 pmol/side) significantly increased splanchnic SNA (SSNA; 71 ± 15%, n = 7). Preinjection of either prorenin handle region peptide, the PRR binding blocker (PRRB), or tiron (2 nmol/side), the scavenger of reactive oxygen species (ROS), significantly attenuated the increase in SSNA (PRRB: 32 ± 5% vs. control, n = 6; tiron: 8 ± 10% vs. control, n = 5; P < 0.05) evoked by prorenin injection. We further investigated the effects of PRR activation on ROS production as well as downstream gene expression using cultured hypothalamus neurons from newborn SD rats. Incubation of brain neurons with human prorenin (100 nM) dramatically enhanced ROS production and induced a time-dependent increase in mRNA levels of inducible nitric oxide synthase (iNOS), NAPDH oxidase 2 subunit cybb, and FOS-like antigen 1 (fosl1), a marker for neuronal activation and a component of transcription factor activator protein-1 (AP-1). The maximum mRNA increase in these genes occurred 6 h following incubation (iNOS: 201-fold; cybb: 2 -fold; Ffosl1: 11-fold). The increases in iNOS and cybb mRNA were not attenuated by the AT1 receptor antagonist losartan but abolished by the AP-1 blocker curcumin. Our results suggest that PVN PRR activation induces sympathoexcitation possibly through stimulation of an ANG II-independent, ROS-AP-1-iNOS signaling pathway.

Angiotensin II regulates brain (pro)renin receptor expression through activation of cAMP response element-binding protein

We reported that brain (pro)renin receptor (PRR) expression levels are elevated in DOCA-salt-induced hypertension; however, the underlying mechanism remained unknown. To address whether ANG II type 1 receptor (AT1R) signaling is involved in this regulation, we implanted a DOCA pellet and supplied 0.9% saline as the drinking solution to C57BL/6J mice. Sham pellet-implanted mice that were provided regular drinking water served as controls. Concurrently, mice were intracerebroventricularly infused with the AT1R blocker losartan, angiotensin-converting-enzyme inhibitor captopril, or artificial cerebrospinal fluid for 3 wk. Intracerebroventricular infusion of losartan or captopril attenuated DOCA-salt-induced PRR mRNA elevation in the paraventricular nucleus of the hypothalamus, suggesting a role for ANG II/AT1R signaling in regulating PRR expression during DOCA-salt hypertension. To test which ANG II/AT1R downstream transcription factors were involved in PRR regulation, we treated Neuro-2A cells with ANG II with or without CREB (cAMP response element-binding protein) or AP-1 (activator protein-1) inhibitors, or CREB siRNA. CREB and AP-1 inhibitors, as well as CREB knockdown abolished ANG II-induced increases in PRR levels. ANG II also induced PRR upregulation in primary cultured neurons. Chromatin immunoprecipitation assays revealed that ANG II treatment increased CREB binding to the endogenous PRR promoter in both cultured neurons and hypothalamic tissues of DOCA-salt hypertensive mice. This increase in CREB activity was reversed by AT1R blockade. Collectively, these findings indicate that ANG II acts via AT1R to upregulate PRR expression both in cultured cells and in DOCA-salt hypertensive mice by increasing CREB binding to the PRR promoter.

Intracerebroventricular infusion of the (Pro)renin receptor antagonist PRO20 attenuates deoxycorticosterone acetate-salt-induced hypertension

We previously reported that binding of prorenin to the (pro)renin receptor (PRR) plays a major role in brain angiotensin II formation and the development of deoxycorticosterone acetate (DOCA)-salt hypertension. Here, we designed and developed an antagonistic peptide, PRO20, to block prorenin binding to the PRR. Fluorescently labeled PRO20 bound to both mouse and human brain tissues with dissociation constants of 4.4 and 1.8 nmol/L, respectively. This binding was blocked by coincubation with prorenin and was diminished in brains of neuron-specific PRR-knockout mice, indicating specificity of PRO20 for PRR. In cultured human neuroblastoma cells, PRO20 blocked prorenin-induced calcium influx in a concentration- and AT(1) receptor-dependent manner. Intracerebroventricular infusion of PRO20 dose-dependently inhibited prorenin-induced hypertension in C57Bl6/J mice. Furthermore, acute intracerebroventricular infusion of PRO20 reduced blood pressure in both DOCA-salt and genetically hypertensive mice. Chronic intracerebroventricular infusion of PRO20 attenuated the development of hypertension and the increase in brain hypothalamic angiotensin II levels induced by DOCA-salt. In addition, chronic intracerebroventricular infusion of PRO20 improved autonomic function and spontaneous baroreflex sensitivity in mice treated with DOCA-salt. In summary, PRO20 binds to both mouse and human PRRs and decreases angiotensin II formation and hypertension induced by either prorenin or DOCA-salt. Our findings highlight the value of the novel PRR antagonist, PRO20, as a lead compound for a novel class of antihypertensive agents and as a research tool to establish the validity of brain PRR antagonism as a strategy for treating hypertension.

Direct pro-inflammatory effects of prorenin on microglia

Neuroinflammation has been implicated in hypertension, and microglia have been proposed to play an important role in the progression of this disease. Here, we have studied whether microglia are activated within cardiovascular regulatory area(s) of the brain during hypertension, especially in high blood pressure that is associated with chronic activation of the renin-angiotensin-system. In addition, we determined whether prorenin, an essential component of the renin-angiotensin-system, exerts direct pro-inflammatory effects on these microglia. Our data indicate that two rodent models which display neurogenic hypertension and over activation of the renin-angiotensin-system in the brain (sRA mice and spontaneously hypertensive rats) exhibit microglial activation, and increased levels of pro-inflammatory cytokines, in the paraventricular nucleus of the hypothalamus, an area crucial for regulation of sympathetic outflow. Further, the renin-angiotensin-system component prorenin elicits direct activation of hypothalamic microglia in culture and induction of pro-inflammatory mechanisms in these cells, effects that involve prorenin receptor-induced NFκB activation. In addition, the prorenin-elicited increases in cytokine expression were fully abolished by microglial inhibitor minocycline, and were potentiated by pre-treatment of cells with angiotensin II. Taken together with our previous data which indicate that pro-inflammatory processes in the paraventricular nucleus are involved in the hypertensive action of renin-angiotensin-system, the novel discovery that prorenin exerts direct stimulatory effects on microglial activation and pro-inflammatory cytokine production provides support for the idea that renin-angiotensin-system -induced neurogenic hypertension is not restricted to actions of angiotensin II alone.

What have we learned about the kallikrein-kinin and renin-angiotensin systems in neurological disorders?

The kallikrein-kinin system (KKS) is an intricate endogenous pathway involved in several physiological and pathological cascades in the brain. Due to the pathological effects of kinins in blood vessels and tissues, their formation and degradation are tightly controlled. Their components have been related to several central nervous system diseases such as stroke, Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, epilepsy and others. Bradykinin and its receptors (B1R and B2R) may have a role in the pathophysiology of certain central nervous system diseases. It has been suggested that kinin B1R is up-regulated in pathological conditions and has a neurodegenerative pattern, while kinin B2R is constitutive and can act as a neuroprotective factor in many neurological conditions. The renin angiotensin system (RAS) is an important blood pressure regulator and controls both sodium and water intake. AngII is a potent vasoconstrictor molecule and angiotensin converting enzyme is the major enzyme responsible for its release. AngII acts mainly on the AT1 receptor, with involvement in several systemic and neurological disorders. Brain RAS has been associated with physiological pathways, but is also associated with brain disorders. This review describes topics relating to the involvement of both systems in several forms of brain dysfunction and indicates components of the KKS and RAS that have been used as targets in several pharmacological approaches.

Animal models in obesity and hypertension

Although obesity is a well-known risk factor for hypertension, the mechanisms by which hypertension develops in obese patients are not entirely clear. Animal models of obesity and their different susceptibilities to develop hypertension have revealed some of the mechanisms linking obesity and hypertension. Adipose tissue is an endocrine organ secreting hormones that impact blood pressure, such as elements of the renin-angiotensin system whose role in hypertension have been established. In addition, the appetite-suppressing adipokine leptin activates the sympathetic nervous system via the melanocortin system, and this activation, especially in the kidney, increases blood pressure. Leptin secretion from adipocytes is increased in most models of obesity due to leptin resistance, although the resistance is often selective to the anorexigenic effect, while the susceptibility to the hypertensive effect remains intact. Understanding the pathways by which obesity contributes to increased blood pressure will hopefully pave the way to and better define the appropriate treatment for obesity-induced hypertension.

Neuron-specific (pro)renin receptor knockout prevents the development of salt-sensitive hypertension

The (pro)renin receptor (PRR), which binds both renin and prorenin, is a newly discovered component of the renin-angiotensin system that is highly expressed in the central nervous system. The significance of brain PRRs in mediating local angiotensin II formation and regulating blood pressure remains unclear. The current study was performed to test the hypothesis that PRR-mediated, nonproteolytic activation of prorenin is the main source of angiotensin II in the brain. Thus, PRR knockout in the brain is expected to prevent angiotensin II formation and development of deoxycorticosterone acetate-salt-induced hypertension. A neuron-specific PRR (ATP6AP2) knockout mouse model was generated using the Cre-LoxP system. Physiological parameters were recorded by telemetry. PRR expression, detected by immunostaining and reverse transcription-polymerase chain reaction, was significantly decreased in the brains of knockout mice compared with wild-type mice. Intracerebroventricular infusion of mouse prorenin increased blood pressure and angiotensin II formation in wild-type mice. This hypertensive response was abolished in PRR-knockout mice in association with a reduction in angiotensin II levels. Deoxycorticosterone acetate-salt increased PRR expression and angiotensin II formation in the brains of wild-type mice, an effect that was attenuated in PRR-knockout mice. PRR knockout in neurons prevented the development of deoxycorticosterone acetate-salt-induced hypertension as well as activation of cardiac and vasomotor sympathetic tone. In conclusion, nonproteolytic activation of prorenin through binding to the PRR mediates angiotensin II formation in the brain. Neuron-specific PRR knockout prevents the development of deoxycorticosterone acetate-salt-induced hypertension, possibly through diminished angiotensin II formation.

Antenatal betamethasone exposure is associated with lower ANG-(1-7) and increased ACE in the CSF of adult sheep

Antenatal betamethasone (BM) therapy accelerates lung development in preterm infants but may induce early programming events with long-term cardiovascular consequences. To elucidate these events, we developed a model of programming whereby pregnant ewes are administered BM (2 doses of 0.17 mg/kg) or vehicle at the 80th day of gestation and offspring are delivered at term. BM-exposed (BMX) offspring develop elevated blood pressure; decreased baroreflex sensitivity; and alterations in the circulating, renal, and brain renin-angiotensin systems (RAS) by 6 mo of age. We compared components of the choroid plexus fourth ventricle (ChP4) and cerebral spinal fluid (CSF) RAS between control and BMX male offspring at 6 mo of age. In the choroid plexus, high-molecular-weight renin protein and ANG I-intact angiotensinogen were unchanged between BMX and control animals. Angiotensin-converting enzyme 2 (ACE2) activity was threefold higher than either neprilysin (NEP) or angiotensin 1-converting enzyme (ACE) in control and BMX animals. Moreover, all three enzymes were equally enriched by approximately 2.5-fold in ChP4 brush-border membrane preparations. CSF ANG-(1-7) levels were significantly lower in BMX animals (351.8 ± 76.8 vs. 77.5 ± 29.7 fmol/mg; P < 0.05) and ACE activity was significantly higher (6.6 ± 0.5 vs. 8.9 ± 0.5 fmol·min(-1)·ml(-1); P < 0.05), whereas ACE2 and NEP activities were below measurable limits. A thiol-sensitive peptidase contributed to the majority of ANG-(1-7) metabolism in the CSF, with higher activity in BMX animals. We conclude that in utero BM exposure alters CSF but not ChP RAS components, resulting in lower ANG-(1-7) levels in exposed animals.

The (pro)renin receptor and body fluid homeostasis

The renin-angiotensin system (RAS) has long been established as one of the major mechanisms of hypertension through the increased levels of angiotensin (ANG) II and its resulting effect on the sympathetic nerve activity, arterial vasoconstriction, water reabsorption, and retention, etc. In the central nervous system, RAS activation affects body fluid homeostasis through increases in sympathetic nerve activity, water intake, food intake, and arginine vasopressin secretion. Previous studies, however, have shown that ANG II can be made in the brain, and it could possibly be through a new component called the (pro)renin receptor. This review intends to summarize the central and peripheral effects of the PRR on body fluid homeostasis.