Presence of cellular renin-angiotensin system in chromaffin cells of bovine adrenal medulla

Exploration of cardiometabolic and developmental significance of angiotensinogen expression by cells expressing the leptin receptor or agouti-related peptide

Angiotensin II (ANG II) Agtr1a receptor (AT_1A) is expressed in cells of the arcuate nucleus of the hypothalamus that express the leptin receptor (Lepr) and agouti-related peptide (Agrp). Agtr1a expression in these cells is required to stimulate resting energy expenditure in response to leptin and high-fat diets (HFDs), but the mechanism activating AT_1A signaling by leptin remains unclear. To probe the role of local paracrine/autocrine ANG II generation and signaling in this mechanism, we bred mice harboring a conditional allele for angiotensinogen (Agt, encoding AGT) with mice expressing Cre-recombinase via the Lepr or Agrp promoters to cause cell-specific deletions of Agt (Agt^Lepr-KO and Agt^Agrp-KO mice, respectively). Agt^Lepr-KO mice were phenotypically normal, arguing against a paracrine/autocrine AGT signaling mechanism for metabolic control. In contrast, Agt^Agrp-KO mice exhibited reduced preweaning survival, and surviving adults exhibited altered renal structure and steroid flux, paralleling previous reports of animals with whole body Agt deficiency or Agt disruption in albumin (Alb)-expressing cells (thought to cause liver-specific disruption). Surprisingly, adult Agt^Agrp-KO mice exhibited normal circulating AGT protein and hepatic Agt mRNA expression but reduced Agt mRNA expression in adrenal glands. Reanalysis of RNA-sequencing data sets describing transcriptomes of normal adrenal glands suggests that Agrp and Alb are both expressed in this tissue, and fluorescent reporter gene expression confirms Cre activity in adrenal gland of both Agrp-Cre and Alb-Cre mice. These findings lead to the iconoclastic conclusion that extrahepatic (i.e., adrenal) expression of Agt is critically required for normal renal development and survival.

TGF-β1 Induced by High Glucose is Controlled by Angiotensin-Converting Enzyme Inhibitor and Angiotensin II Receptor Blocker on Cultured Human Peritoneal Mesothelial Cells

Background

Loss of peritoneal function is a major complication associated with long-term peritoneal dialysis. Observed changes include loss and degeneration of the mesothelium, submesothelial thickening, alterations in the structure and number of blood vessels, and reduplication of the vascular basement membrane. Exposure to high glucose concentrations in peritoneal dialysis solutions is known to cause injury to cultured human peritoneal mesothelial cells (HPMC) as a result of overexpression of transforming growth factor beta 1 (TGF-β1). Previous studies have demonstrated that angiotensin II (AII) increases expression of TGF-β1 in a number of different cell types; although this has not been demonstrated in HPMC.

Objective

To clarify possible mechanisms involved in peritoneal fibrosis, we investigated whether HPMC expressed AII-forming pathway mRNA and whether increases in AII induced by high glucose contribute to the production of TGF-β1. We also examined the effects of the angiotensin-converting enzyme inhibitor (ACEI) perindoprilat and the AII receptor blocker (ARB) candesartan on expression of TGF-β1 and proliferation of HPMC.

Methods

Expression of mRNA for the AII-forming pathway and TGF-β1 in HPMC was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative RT-PCR. Levels of AII and TGF-β1 following 48 hours of incubation of the cells in a range of glucose concentrations were measured by enzyme immunoassay and enzyme linked immunosorbent assay respectively. The effect of glucose on cell proliferation was examined using the water-soluble tetrazolium salt WST-1 and [3H]-thymidine uptake. We also investigated the effect of ACEI and ARB on the expression of TGF-β1 and the proliferation of HPMC incubated at high glucose for 48 hours.

Results

AII-forming pathway mRNA was detected in HPMC, with expression of angiotensinogen, angiotensin-converting enzyme (ACE), AII type 1 receptor, and TGF-β1 mRNA increasing following exposure to glucose according to glucose concentration. High glucose was also shown to increase the production of AII and TGF-β1 and decrease the proliferation of HPMC. In contrast, we found that both the ACEI and the ARB attenuated the increase in TGF-β1 production and reduced cell proliferation caused by exposure to high glucose. These effects were greater with a combination of the two drugs.

Conclusion

The present study provides evidence that ( 1 ) HPMC express mRNA for the AII-forming pathway; ( 2 ) ACEI and ARB inhibit the TGF-β1 production induced by high glucose; ( 3 ) the AII-forming pathway is one mechanism by which high glucose causes production of TGF-β1. In addition to having antihypertensive and renal-protective effects, combination therapy with an ACEI and an ARB may also be effective in preventing loss of peritoneal function and decreasing peritoneal fibrosis.

Dysregulation of the Renin-Angiotensin System and the Vasopressinergic System Interactions in Cardiovascular Disorders

Purpose of Review

In many instances, the renin-angiotensin system (RAS) and the vasopressinergic system (VPS) are jointly activated by the same stimuli and engaged in the regulation of the same processes.

Recent Findings

Angiotensin II (Ang II) and arginine vasopressin (AVP), which are the main active compounds of the RAS and the VPS, interact at several levels. Firstly, Ang II, acting on AT1 receptors (AT1R), plays a significant role in the release of AVP from vasopressinergic neurons and AVP, stimulating V1a receptors (V1aR), regulates the release of renin in the kidney. Secondly, Ang II and AVP, acting on AT1R and V1aR, respectively, exert vasoconstriction, increase cardiac contractility, stimulate the sympathoadrenal system, and elevate blood pressure. At the same time, they act antagonistically in the regulation of blood pressure by baroreflex. Thirdly, the cooperative action of Ang II acting on AT1R and AVP stimulating both V1aR and V2 receptors in the kidney is necessary for the appropriate regulation of renal blood flow and the efficient resorption of sodium and water. Furthermore, both peptides enhance the release of aldosterone and potentiate its action in the renal tubules.

Summary

In this review, we (1) point attention to the role of the cooperative action of Ang II and AVP for the regulation of blood pressure and the water-electrolyte balance under physiological conditions, (2) present the subcellular mechanisms underlying interactions of these two peptides, and (3) provide evidence that dysregulation of the cooperative action of Ang II and AVP significantly contributes to the development of disturbances in the regulation of blood pressure and the water-electrolyte balance in cardiovascular diseases.

Angiotensin II AT2 Receptors Contribute to Regulate the Sympathoadrenal and Hormonal Reaction to Stress Stimuli

Angiotensin II, through AT1 receptor stimulation, mediates multiple cardiovascular, metabolic, and behavioral functions including the response to stressors. Conversely, the function of Angiotensin II AT2 receptors has not been totally clarified. In adult rodents, AT2 receptor distribution is very limited but it is particularly high in the adrenal medulla. Recent results strongly indicate that AT2 receptors contribute to the regulation of the response to stress stimuli. This occurs in association with AT1 receptors, both receptor types reciprocally influencing their expression and therefore their function. AT2 receptors appear to influence the response to many types of stressors and in all components of the hypothalamic-pituitary-adrenal axis. The molecular mechanisms involved in AT2 receptor activation, the complex interactions with AT1 receptors, and additional factors participating in the control of AT2 receptor regulation and activity in response to stressors are only partially understood. Further research is necessary to close this knowledge gap and to clarify whether AT2 receptor activation may carry the potential of a major translational advance.

The Renin-Angiotensin-aldosterone system in vascular inflammation and remodeling

The RAAS through its physiological effectors plays a key role in promoting and maintaining inflammation. Inflammation is an important mechanism in the development and progression of CVD such as hypertension and atherosclerosis. In addition to its main role in regulating blood pressure and its role in hypertension, RAAS has proinflammatory and profibrotic effects at cellular and molecular levels. Blocking RAAS provides beneficial effects for the treatment of cardiovascular and renal diseases. Evidence shows that inhibition of RAAS positively influences vascular remodeling thus improving CVD outcomes. The beneficial vascular effects of RAAS inhibition are likely due to decreasing vascular inflammation, oxidative stress, endothelial dysfunction, and positive effects on regeneration of endothelial progenitor cells. Inflammatory factors such as ICAM-1, VCAM-1, TNFα, IL-6, and CRP have key roles in mediating vascular inflammation and blocking RAAS negatively modulates the levels of these inflammatory molecules. Some of these inflammatory markers are clinically associated with CVD events. More studies are required to establish long-term effects of RAAS inhibition on vascular inflammation, vascular cells regeneration, and CVD clinical outcomes. This review presents important information on RAAS's role on vascular inflammation, vascular cells responses to RAAS, and inhibition of RAAS signaling in the context of vascular inflammation, vascular remodeling, and vascular inflammation-associated CVD. Nevertheless, the review also equates the need to rethink and rediscover new RAAS inhibitors.

Local renin-angiotensin systems in the adrenal gland

In the adrenal gland all components of the renin-angiotensin system (RAS) are expressed in both the adrenal cortex and the adrenal medulla. In this review evidence shall be presented that a local secretory RAS exists in the adrenal cortex that stimulates aldosterone production and serves as an amplification system for circulating angiotensin (ANG) II. The regulation of the secretory adrenal RAS clearly differs from the regulation of the circulatory RAS in terms of renin expression as well as of renin secretion. For example under potassium load the activity of the renal and circulatory RAS is suppressed whereas the activity of the adrenal RAS is stimulated. Thus the activity of the adrenal RAS but not of the circulating RAS correlates well with the regulation of aldosterone production by potassium. The present review also summarizes the knowledge about the expression and functions of an additional renin transcript that has recently been discovered. This transcript encodes for a non-secretory cytosolic renin isoform. The cytosolic renin may be a basis for the existence of an intracellular renin system in the adrenal gland that has long been proposed. The present state of knowledge shall be discussed indicating that such an intracellular system modulates cell survival and cell death such as apoptosis and necrosis or cell functions such as aldosterone production.

Transforming growth factor-beta and angiotensin in fibrosis and burn injuries

This review considers the roles of transforming growth factor-beta (TGF-beta), the signaling Smad proteins, and angiotensin II (AT II) in conditions leading to human fibrosis. The goal is to update the burn practitioner and researcher about this important pathway and to introduce AT II as a possible synergistic signal to TGF-beta in burn scarring. Literature searches of the MEDLINE database were performed for English manuscripts combinations of TGF-beta, Smad, angiotensin, fibrosis, burn, and scar. AT II and TGF-beta both activate the Smad protein system, which leads to the expression of genes related to fibrosis. In fibrotic conditions, such as tubulointerstitial nephritis, systemic sclerosis, and myocardial infarctions, AT II acts both independently and synergistically with TGF-beta. Both AT II and TGF-beta act through a messenger system, the Smad proteins that lead to excessive extracellular matrix formation. Treatment and research implications are reviewed. The interaction between AT II and TGF-beta leading to fibrosis is well described in some human diseases. This pathway may be of importance in human burn scarring as well.

Diversity of pathways for intracellular angiotensin II synthesis

PURPOSE OF REVIEW

The renin-angiotensin system (RAS) has undergone continuous advancement since the initial identification of renin as a pressor agent. Traditionally considered a circulatory system, the RAS is now known to exist as a tissue system as well. Recently, the tissue RAS has been further categorized as intracellular and extracellular. Owing to the unique location, the intracellular RAS encompasses new components, such as cathepsin D and chymase, which participate in intracellular angiotensin (Ang) II synthesis. In this review, evidence of the intracellular RAS and the mechanism of Ang II synthesis in various cell types will be discussed.

RECENT FINDINGS

A physiological role for intracellular Ang II in vascular and cardiac cells has recently been demonstrated. Evidence of intracellular Ang II generation has been shown in several cell types, particularly cardiac, renal, and vascular. Importantly, intracellular synthesis of Ang II is more prominent in hyperglycemic conditions and generally involves angiotensin-converting enzyme-dependent and angiotensin-converting enzyme-independent mechanisms.

SUMMARY

There is significant diversity in the mechanism of intracellular synthesis of Ang II in various cell types and pathological conditions. These observations suggest that a therapeutic intervention to block the RAS should take into consideration the nature of the disorder and the cell type involved.

Angiotensin II upregulates Toll-like receptor 4 and enhances lipopolysaccharide-induced CD40 expression in rat peritoneal mesothelial cells

OBJECTIVE

Activation of Toll-like receptor 4 (TLR4) in peritoneal mesothelial cells by endotoxin contributes to peritoneal inflammation and fibrosis. Here we investigated TLR4 expression induced by angiotensin II (Ang II) and functional consequences of nuclear factor-kappaB (NF-kappaB) activation and CD40 expression in rat peritoneal mesothelial cells (RPMCs).

METHODS

TLR4, CD40, tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) were determined by reverse transcription polymerase chain reaction (RT-PCR) and TLR4, IkappaBalpha, phospho-IkappaBalpha, NF-kappaB p65, and phospho-NF-kappaB p65 were analyzed by Western blot. The intracellular distribution of NF-kappaB p65 was detected by immunofluorescence.

RESULTS

Treatment of RPMCs with Ang II resulted in an increase in the expression of TLR4 mRNA and protein levels. Preincubation of RPMCs with Ang II significantly increased lipopolysaccharide (LPS)-induced phospho-IkappaBalpha and phospho-NF-kappaB p65 protein (P < 0.05 vs. LPS alone) and CD40, TNF-alpha, and IL-6 mRNA levels (P < 0.05 vs. LPS alone). A significantly increased nuclear staining of NF-kappaB p65 in cells treated with Ang II plus LPS was also observed.

CONCLUSIONS

Ang II upregulates the expression of TLR4 by RPMCs, resulting in enhanced NF-kappaB signaling and induction of CD40, TNF-alpha, and IL-6 expression. Locally produced Ang II in the peritoneum may have an amplified role in LPS-induced peritoneal inflammation.

Nuclear angiotensin II type 2 (AT2) receptors are functionally linked to nitric oxide production

Expression of nuclear angiotensin II type 1 (AT(1)) receptors in rat kidney provides further support for the concept of an intracellular renin-angiotensin system. Thus we examined the cellular distribution of renal ANG II receptors in sheep to determine the existence and functional roles of intracellular ANG receptors in higher order species. Receptor binding was performed using the nonselective ANG II antagonist (125)I-[Sar(1),Thr(8)]-ANG II ((125)I-sarthran) with the AT(1) antagonist losartan (LOS) or the AT(2) antagonist PD123319 (PD) in isolated nuclei (NUC) and plasma membrane (PM) fractions obtained by differential centrifugation or density gradient separation. In both fetal and adult sheep kidney, PD competed for the majority of cortical NUC (> or =70%) and PM (> or =80%) sites while LOS competition predominated in medullary NUC (> or =75%) and PM (> or =70%). Immunodetection with an AT(2) antibody revealed a single approximately 42-kDa band in both NUC and PM extracts, suggesting a mature molecular form of the NUC receptor. Autoradiography for receptor subtypes localized AT(2) in the tubulointerstitium, AT(1) in the medulla and vasa recta, and both AT(1) and AT(2) in glomeruli. Loading of NUC with the fluorescent nitric oxide (NO) detector DAF showed increased NO production with ANG II (1 nM), which was abolished by PD and N-nitro-l-arginine methyl ester, but not LOS. Our studies demonstrate ANG II receptor subtypes are differentially expressed in ovine kidney, while nuclear AT(2) receptors are functionally linked to NO production. These findings provide further evidence of a functional intracellular renin-angiotensin system within the kidney, which may represent a therapeutic target for the regulation of blood pressure.

The chromaffin vesicle: advances in understanding the composition of a versatile, multifunctional secretory organelle

Chromaffin vesicles (CV) are highly sophisticated secretory organelles synthesized in adrenal medullary chromaffin cells. They contain a complex mixture of structural proteins, catecholamine neurotransmitters, peptide hormones, and the relative processing enzymes, as well as protease inhibitors. In addition, CV store ATP, ascorbic acid, and calcium. During the last decades, extensive studies have contributed to increase our understanding of the molecular composition of CV. Yet, the recent development of biochemical and imaging procedures has greatly increased the list of CV-soluble constituents and opened new horizons as to the complexity of CV involvement in acute stress responses. Thus, a coherent picture of CV molecular composition is still to be drawn. This review article will provide a detailed account of the content of CV soluble molecules as it emerges from the most recent analytical studies. Moreover, this review article will attempt at focussing on the physiological and pathophysiological implications of the products released by CV.

The intracellular renin-angiotensin system: a new paradigm

More than a century after its discovery, the physiological implications of the renin-angiotensin system (RAS) continue to expand, with the identification of new components, functions and subsystems. These advancements have led to better management and understanding of a broad range of cardiovascular and metabolic disorders. The RAS has traditionally been viewed as a circulatory system, involved in the short-term regulation of volume and blood pressure homeostasis. Recently, local RASs have been described as regulators of chronic tissue effects. Most recently, studies have provided evidence of a complete, functional RAS within cells, described as an 'intracrine' or intracellular system. A more comprehensive understanding of the intracellular RAS provides for new strategies in system regulation and a more efficacious approach to the management of RAS-related diseases.

Tissue renin angiotensin systems

The RAAS is a powerful regulator of vascular tone and intravascular volume and of tissue architecture and a variety of other functions. The recent appreciation of the immunoregulatory role of angiotensin II and its possible involvement in the genesis of atherosclerosis and in plaque rupture all speak to the wide-ranging physiologic and pathophysiologic activities of the peptide. So do its actions in fat cell differentiation and in neuromodulation. The system exists in the circulation, and RAASs, whole or partial, exist in many tissues. These systems are regulated at many levels ranging from the synthesis of renin to the dimerization of angiotensin receptors. Regulation occurs in multiple tissues and, as a result, tissue concentrations of angiotensin II and the concentration of other RAS components and their active metabolites can vary independently of the circulating system in these tissues. An RAS seems also to function within certain cells. Therapeutic interventions involving ACEIs and ARBs seem likely to provide benefit at least in part through the interruption of local systems. It is to be expected that with enhanced understanding of the biology of the multiple RASs, new suggestions for therapeutic interventions will be forthcoming.

Angiotensin II causes calcium entry into bovine adrenal chromaffin cells via pathway(s) activated by depletion of intracellular calcium stores

The characteristics and properties of the increase in cytosolic [Ca2+] that occurs in bovine adrenal medullary chromaffin cells on exposure to angiotensin 11 have been investigated. In fura-2 loaded cells exposure to a maximally effective concentration of angiotensin II (100 nM) caused a rapid, but transient increase in cytosolic [Ca2+] followed by a lower plateau that was sustained as long as external Ca2+ was present. In the absence of external Ca2+ only the initial brief transient was observed. In cells previously treated with thapsigargin in Ca2+-free medium to deplete the internal Ca2+ stores, angiotensin II caused no increase in cytosolic [Ca2+] when external Ca2+ was absent. Reintroduction of external Ca2+ to thapsigargin-treated, store-depleted cells caused a sustained increase in cytosolic [Ca2+] that was not further increased upon exposure to angiotensin II. Analysis of the data suggests that in bovine chromaffin cells angiotensin II causes Ca2+ entry via a pathway(s) activated as a consequence of internal store mobilization, and entry through this pathway(s) forms the majority of the sustained Ca2+ influx evoked by angiotensin II.