The intrarenal renin-angiotensin and dopaminergic systems: control of renal sodium excretion and blood pressure

Multi-omics profiles refine L-dopa decarboxylase (DDC) as a reliable biomarker for prognosis and immune microenvironment of clear cell renal cell carcinoma

Background

Increasing evidence indicates that L-dopa decarboxylase (DDC), which mediates aberrant amino acid metabolism, is significantly associated with tumor progression. However, the impacts of DDC are not elucidated clearly in clear cell renal cell carcinoma (ccRCC). This study aimed to evaluate DDC prognostic value and potential mechanisms for ccRCC patients.

Methods

Transcriptomic and proteomic expressions of and clinical data including 532 patients with ccRCC (The Cancer Genome Atlas RNA-seq data), 226 ccRCC samples (Gene Expression Omnibus), 101 ccRCC patients from the E-MTAB-1980 cohort, and 232 patients with ccRCC with proteogenomic data (Fudan University Shanghai Cancer Center) were downloaded and analyzed to investigate the prognostic implications of DDC expression. Cox regression analyses were implemented to explore the effect of DDC expression on the prognosis of pan-cancer. The "limma" package identified the differentially expressed genes (DEGs) between high DDC subgroups and low DDC groups. Functional enrichments were performed based DEGs between DDC subgroups. The differences of immune cell infiltrations and immune checkpoint genes between DDC subgroups were analyzed to identify potential influence on immune microenvironment.

Results

We found significantly decreased DDC expression in ccRCC tissues compared with normal tissues from multiple independent cohorts based on multi-omics data. We also found that DDC expression was correlated with tumor grades and stages.The following findings revealed that lower DDC expression levels significantly correlated with shorter overall survival (P <0.001) of patients with ccRCC. Moreover, we found that DDC expression significantly correlated with an immunosuppressive tumor microenvironment, higher intra-tumoral heterogeneity, elevated expression of immune checkpoint CD274, and possibly mediated malignant behaviors of ccRCC cells via the PI3k/Akt signaling pathway.

Conclusion

The present study is the first to our knowledge to indicate that decreased DDC expression is significantly associated with poor survival and an immune-suppressive tumor microenvironment in ccRCC. These findings suggest that DDC could serve as a biomarker for guiding molecular diagnosis and facilitating the development of novel individual therapeutic strategies for patients with advanced ccRCC.

The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

Amelioration of Hypertension by Oryeongsan through Improvements of Body Fluid and Sodium Balance: Roles of the Renin-Angiotensin System and Atrial Natriuretic Peptide System

Oryeongsan (Wulingsan in China and Goreisan in Japan), a formula composed of five herbal medicines, has long been used for the treatment of imbalance of the body fluid homeostasis in Asian countries. However, the mechanism by which Oryeongsan (ORS) improves the impaired body fluid and salt metabolism is not clearly defined. The present study was performed to define the role of the cardiorenal humoral system in the ORS-induced changes in blood pressure and renal function in hypertension. Experiments were performed in normotensive and two-kidney, one-clip hypertensive rats. Changes in the fluid and salt balance were measured in rats individually housed in metabolic cages. Changes in the systemic and local renin-angiotensin system (RAS) and cardiac natriuretic peptide hormone system (NPS) were evaluated. ORS water extract was administered by oral gavage (100 mg/kg daily) for 3 weeks. ORS induced diuresis and natriuresis along with an increase in glomerular filtration rate and downregulation of the Na⁺/H⁺ exchanger 3 (NHE3) and aquaporin 2 expression in the renal cortex and medulla, respectively. Furthermore, treatment with ORS significantly decreased systolic blood pressure with contraction of body sodium and water accumulation in hypertensive rats. ORS-induced changes were accompanied by modulation of the RAS and NPS, downregulation of the systemic RAS and cardiorenal expression of angiotensin-converting enzyme (ACE) and angiotensin II subtype 1 (AT₁) receptor, and upregulation of the plasma ANP concentration and cardiorenal expression of ANP, ACE2, Mas receptor, and AT₂ receptor. These findings indicate that ORS induces beneficial effects on the high blood pressure through modulation of the RAS and NPS of the cardiorenal system, suppression of the prohypertensive ACE-AT₁ receptor pathway and NHE3, accentuation of the antihypertensive ACE2-Mas axis/AT₂ receptor pathway in the kidney, suppression of the systemic RAS, and elevation of the plasma ANP levels and its synthesis in the heart. The present study provides a biological basis for the use of ORS in the treatment of impaired volume and pressure homeostasis.

Saccharomyces boulardii exerts renoprotection by modulating oxidative stress, renin angiotensin system and uropathogenic microbiota in a murine model of diabetes

AIMS

We aimed to investigate whether Saccharomyces boulardii strain might exert renoprotective effects by modulating renal renin angiotensin system, oxidative stress and intestinal microbiota in streptozotocin-diabetic mice.

MAIN METHODS

Thirty-six C57BL/6 male mice were divided into four groups: control (C), control + probiotic (CP), diabetes (D), diabetes + probiotic (DP). Diabetes was induced by one intraperitoneal injection of streptozotocin and Saccharomyces boulardii was administered by oral gavage for 8 weeks. Blood glucose, albuminuria and urinary volume were measured. Renal levels of angiotensin peptides (angiotensin I, II and 1-7) and the activities of angiotensin-converting enzyme (ACE) and ACE2 were determined, besides that, renal morphology, serotonin and dopamine levels and also microbiota composition were analyzed.

KEY FINDINGS

Probiotics significantly increased C-peptide secretion and reduced blood glucose of diabetic animals. Saccharomyces boulardii also improved renal antioxidant defense, restored serotonin and dopamine concentration, and activated the renin-angiotensin system (RAS) vasodilator and antifibrotic axis. The modulation of these markers was associated with a beneficial impact on glomerular structure and renal function of diabetic treated animals. The phenotypic changes induced by Saccharomyces boulardii were also related to modulation of intestinal microbiota, evidenced by the decreased abundance of Proteus and Escherichia-Shigella, considered diabetic nephropathy biomarkers.

SIGNIFICANCE

Therefore, probiotic administration to streptozotocin-induced diabetic mice improves kidney structure and function in a murine model and might represent a reasonable strategy to counteract nephropathy-associated maladaptive responses in diabetes.

Angiotensin Type-2 Receptors: Transducers of Natriuresis in the Renal Proximal Tubule

Angiotensin II (Ang II) type-2 receptors (AT₂R) are expressed in the adult kidney, prominently in renal proximal tubule cells (RPTCs), and play an important role in opposing renal sodium (Na⁺) retention induced by Ang II stimulation of Ang II type-1 receptor (AT₁R). Natriuresis induced by AT₁R blockade is due at least in part to AT₂R activation and whole body deletion of AT₂Rs reduces the natriuretic response to increased blood pressure (BP). The major endogenous AT₂R agonist mediating the natriuretic response is Ang III, the Ang II heptapeptide metabolite generated by aminopeptidase A, and the principal nephron site mediating inhibition of Na⁺ reabsorption by the AT₂R is the renal proximal tubule (RPT). AT₂Rs induce natriuresis via a bradykinin, nitric oxide and cyclic GMP (cGMP) signaling cascade. Recent studies demonstrated a key role for protein phosphatase 2A (PP2A) in the AT₂R-mediated natriuretic response upstream of cGMP. By inducing natriuresis, AT₂Rs lower BP in the Ang II-infusion model of hypertension. PP2A activation and the natriuretic response to AT₂R stimulation are defective in spontaneously hypertensive rats, a model of primary hypertension in humans. AT₂R agonists are candidates for proximal tubule natriuretic agents in Na⁺ and fluid retention disorders.

Renal AT2 Receptors Mediate Natriuresis via Protein Phosphatase PP2A

BACKGROUND

How signals from activated angiotensin type-2 receptors (AT₂R) mediate inhibition of sodium ion (Na⁺) reabsorption in renal proximal tubule cells is currently unknown. Protein phosphatases including PP2A (protein phosphatase 2A) have been implicated in AT₂R signaling in tissues other than kidney. We investigated whether inhibition of protein phosphatase PP2A reduced AT₂R-mediated natriuresis and evaluated changes in PP2A activity and localization after renal AT₂R activation in normal 4- and 10-week-old control Wistar-Kyoto rats and 4-week-old prehypertensive and 10-week-old hypertensive spontaneously hypertensive rats.

METHODS AND RESULTS

In Wistar-Kyoto rats, direct renal interstitial administration of selective AT₂R nonpeptide agonist Compound-21 (C-21) increased renal interstitial cyclic GMP (cGMP) levels, urine Na⁺ excretion, and simultaneously increased PP2A activity ≈2-fold in homogenates of renal cortical tubules. The cyclic GMP and natriuretic responses were abolished by concurrent renal interstitial administration of protein phosphatase inhibitor calyculin A. In renal proximal tubule cells in response to C-21, PP2A subunits A, B55α and C, but not B56γ, were recruited to apical plasma membranes together with AT₂Rs. Calyculin A treatment abolished C-21-induced translocation of both AT₂R and PP2A regulatory subunit B55α to apical plasma membranes. Immunoprecipitation of AT₂R solubilized from renal cortical homogenates demonstrated physical association of AT₂R with PP2A A, B55α, and C but not B56γ subunits. In contrast, in spontaneously hypertensive rats, administration of C-21 did not alter urine Na⁺ excretion or PP2A activity and failed to translocate AT₂Rs and PP2A subunits to apical plasma membranes.

CONCLUSIONS

In renal proximal tubule cells of Wistar-Kyoto rats, PP2A is activated and PP2A subunits AB55αC are recruited to C-21-activated AT₂Rs during induction of natriuresis. This response is defective in prehypertensive and hypertensive spontaneously hypertensive rats, presenting a potential novel therapeutic target for treating renal Na⁺ retention and hypertension.

Reinvestigation of the tonic natriuretic action of intrarenal dopamine: comparison of two variants of salt-dependent hypertension and spontaneously hypertensive rats

The intrarenal dopamine system has been thoroughly investigated at all levels, especially its role in salt-dependent and other forms of hypertension. However, the evidence regarding dopamine's tonic influence on renal tubular transport of sodium remains equivocal. We reinvestigated its tonic influence on sodium excretion and systemic and renal haemodynamics. Early effects of dopamine D1 receptor blockade using 90-min Schering 23390 (SCH) infusion were examined in anaesthetized rats on 7 days' high salt diet (HS), early uninephrectomized rats on 14 days' HS diet, drinking 1% saline (HS/UNX), and in spontaneously hypertensive rats (SHR). In the HS group (baseline BP ~133 mm Hg) renal intracortical SCH promptly decreased sodium, water and total solute excretion (U_Na V, V, U_osm V), with significant difference from the solvent-infused group. BP and renal artery blood flow (RBF, Transonic probe) did not change. In HS/UNX model (baseline BP ~150 mm Hg), characterized by hypertrophy of the remaining kidney, the excretion parameters only tended to decrease whereas SCH induced an ~20% fall in RBF. In SHR (BP ~180 mm Hg), U_Na V and V tended to increase in solvent-infused rats; this increasing tendency was abolished by SCH infusion. During experiments the renal vascular resistance increased significantly in SCH- and solvent-infused SHR. Despite some contradictory findings regarding the genuine tonic control of renal excretion by intrarenal dopamine, our results clearly support such role in rats on HS diet and in SHR, the model resembling human essential hypertension. The observations strengthen the experimental basis and the rationale for targeting the intrarenal dopamine system in attempts to combat arterial hypertension.

The Role of the Renal Dopaminergic System and Oxidative Stress in the Pathogenesis of Hypertension

The kidney is critical in the long-term regulation of blood pressure. Oxidative stress is one of the many factors that is accountable for the development of hypertension. The five dopamine receptor subtypes (D₁R–D₅R) have important roles in the regulation of blood pressure through several mechanisms, such as inhibition of oxidative stress. Dopamine receptors, including those expressed in the kidney, reduce oxidative stress by inhibiting the expression or action of receptors that increase oxidative stress. In addition, dopamine receptors stimulate the expression or action of receptors that decrease oxidative stress. This article examines the importance and relationship between the renal dopaminergic system and oxidative stress in the regulation of renal sodium handling and blood pressure. It discusses the current information on renal dopamine receptor-mediated antioxidative network, which includes the production of reactive oxygen species and abnormalities of renal dopamine receptors. Recognizing the mechanisms by which renal dopamine receptors regulate oxidative stress and their degree of influence on the pathogenesis of hypertension would further advance the understanding of the pathophysiology of hypertension.

Involvement of dopaminergic signaling in the cross talk between the renin-angiotensin system and inflammation

The renin-angiotensin system (RAS) is a fundamental regulator of blood pressure and has emerged as an important player in the control of inflammatory processes. Accordingly, imbalance on RAS components either systemically or locally might trigger the development of inflammatory disorders by affecting immune cells. At the same time, alterations in the dopaminergic system have been consistently involved in the physiopathology of inflammatory disorders. Accordingly, the interaction between the RAS and the dopaminergic system has been studied in the context of inflammation of the central nervous system (CNS), kidney, and intestine, where they exert antagonistic actions in the regulation of the immune system. In this review, we summarized, integrated, and discussed the cross talk of the dopaminergic system and the RAS in the regulation of inflammatory pathologies, including neurodegenerative disorders, such as Parkinson’s disease. We analyzed the molecular mechanisms underlying the interaction between both systems in the CNS and in systemic pathologies. Moreover, we also analyzed the impact of the commensal microbiota in the regulation of RAS and dopaminergic system and how it is involved in inflammatory disorders. Furthermore, we summarized the therapeutic approaches that have yielded positive results in preclinical or clinical studies regarding the use of drugs targeting the RAS and dopaminergic system for the treatment of inflammatory conditions. Further understanding of the molecular and cellular regulation of the RAS-dopaminergic cross talk should allow the formulation of new therapies consisting of novel drugs and/or repurposing already existing drugs, alone or in combination, for the treatment of inflammatory disorders.

Angiotensin type 2 receptors: Role in aging and neuroinflammation in the substantia nigra

Overactivity of the angiotensin-type-1 receptor (AT1)/NADPH-oxidase axis enhances aging processes, neuroinflammation and neurodegeneration. The role of AT2 receptors in the above-mentioned AT1-related effects in the aged brain, particularly substantia nigra, was investigated in this study. In the nigra, we observed a progressive decrease in AT2 mRNA expression with aging, and AT2 deletion led to changes in spontaneous motor behavior, dopamine receptors, renin-angiotensin system, and pro-oxidative and pro-inflammatory markers similar to those observed in aged wild type (WT) mice. Both aged WT mice and young AT2 KO mice showed an increased AT1, decreased MAS receptor and increased angiotensinogen mRNA and/or protein expression, as well as upregulation of pro-oxidative and pro-inflammatory markers. In cultures of microglial cells, activation of AT2 receptors inhibited the LPS-induced increase in AT1 mRNA and protein expression and neuroinflammatory markers. Both in AT2 KO microglial cultures and microglia obtained from adult AT2 KO mice, an increase in AT1 mRNA expression was observed. In cultured dopaminergic neurons, AT2 activation down-regulated AT1 mRNA and protein, and dopaminergic neurons from adult AT2 KO mice showed upregulation of AT1 mRNA expression. Both in microglia and dopaminergic neurons the pathway AT2/nitric oxide/cyclic guanosine monophosphate mediates the regulation of the AT1 mRNA and protein expression through downregulation of the Sp1 transcription factor. MAS receptors are also involved in the regulation of AT1 mRNA and protein expression by AT2. The results suggest that an aging-related decrease in AT2 expression plays a major role in the aging-related AT1 overexpression and AT1-related pro-inflammatory pro-oxidative effects.

Identification of a Primary Renal AT2 Receptor Defect in Spontaneously Hypertensive Rats

RATIONALE

Previous studies identified a defect in Ang III (angiotensin III [des-aspartyl¹-angiotensin II])-elicited AT₂R (Ang type-2 receptor)-mediated natriuresis in renal proximal tubule cells of spontaneously hypertensive rats (SHR).

OBJECTIVE

This study aimed to delineate in prehypertensive SHR kidneys the receptor or postreceptor defect causing impaired AT₂R signaling and renal sodium (Na⁺) retention by utilizing the selective AT₂R agonist compound-21 (C-21).

METHODS AND RESULTS

Female 4-week-old Wistar Kyoto and SHR rats were studied after 24-hour systemic AT₁R (Ang II type-1 receptor) blockade. Left kidneys received 30-minute renal interstitial infusions of vehicle followed by C-21 (20, 40, and 60 ng/[kg·min], each dose 30 minutes). Right kidneys received vehicle infusions. In Wistar Kyoto, C-21 dose-dependently increased urine Na⁺ excretion from 0.023±0.01 to 0.064±0.02, 0.087±0.01, and 0.089±0.01 µmol/min (P=0.008, P<0.0001, and P<0.0001, respectively) and renal interstitial fluid levels of AT₂R downstream signaling molecule cGMP (cyclic guanosine 3',5' monophosphate) from 0.91±0.3 to 3.1±1.0, 5.9±1.2 and 5.3±0.5 fmol/mL (P=nonsignificant, P<0.0001, and P<0.0001, respectively). In contrast, C-21 did not increase urine Na⁺ excretion or renal interstitial cGMP in SHR. Mean arterial pressure was slightly higher in SHR but within the normotensive range and unaffected by C-21. In Wistar Kyoto, but not SHR, C-21 induced AT₂R translocation to apical plasma membranes of renal proximal tubule cells, internalization/inactivation of NHE-3 (sodium-hydrogen exchanger-3) and Na⁺/K⁺ATPase (sodium-potassium-atpase) and phosphorylation of AT₂R-cGMP downstream signaling molecules Src (Src family kinase), ERK (extracellular signal-related kinase), and VASP (vasodilator-stimulated phosphoprotein). To test whether cGMP could bypass the natriuretic defect in SHR, we infused 8-bromo-cGMP. This restored natriuresis, Na⁺ transporter internalization/inactivation, and Src and VASP phosphorylation, but not apical plasma membrane AT₂R recruitment. In contrast, 8-bromo-cAMP administration had no effect on natriuresis or AT₂R recruitment in SHR.

CONCLUSIONS

The results demonstrate a primary renal proximal tubule cell AT₂R natriuretic defect in SHR that may contribute to the development of hypertension. Since the defect is abrogated by exogenous intrarenal cGMP, the renal cGMP pathway may represent a viable target for the treatment of hypertension. Visual Overview: An online visual overview is available for this article.

Angiotensin-converting enzyme insertion/deletion gene polymorphisms and the risk of glioma in an Algerian population

Introduction

Just recently, it has been established that the angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism is linked to the pathogenesis and to the evolution of human cancers. Therefore, the present study was concerned with the investigation of an eventual association between glioma and I/D polymorphism of the ACE gene.

Methods

The expression of ACE gene was detected by polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) analysis in 36 Algerian patients with glioma and 195 healthy controls.

Results

In glioma cases, allelic frequencies and genotypes distribution of the ACE I/D polymorphism were different from controls cases. ACE DD genotype were highly presented in glioma cases (63.9%) than controls (33.8%) and conferred 3.64-fold risk for predisposition in glioma cases (vs ID genotype, p<0.001). Recessive model (ACE II + ID genotypes vs DD) was associated with a 72% reduced risk of glioma (OR = 0.28, 95% CI: 0.13-0.60, p <0.001). Per copy D allele frequency was found higher in glioma cases (79.2%) than in controls (63.3 %), OR = 2.20, 95% CI: 1.20 - 4.03, p = 0.009.

Conclusion

The obtained data showed that the presence of the D allele might be a risk factor for the development of glioma. Further studies considering different ethnic groups with large samples are required to confirm this finding.

Diabetes and Hypertension Differentially Affect Renal Catecholamines and Renal Reactive Oxygen Species

Patients with diabetic hypertensive nephropathy have accelerated disease progression. Diabetes and hypertension have both been associated with changes in renal catecholamines and reactive oxygen species. With a specific focus on renal catecholamines and oxidative stress we examined a combined model of hypertension and diabetes using normotensive BPN/3J and hypertensive BPH/2J Schlager mice. Induction of diabetes (5 × 55 mg/kg streptozotocin i.p.) did not change the hypertensive status of BPH/2J mice (telemetric 24 h avg. MAP, non-diabetic 131 ± 2 vs. diabetic 129 ± 1 mmHg, n.s at 9 weeks of study). Diabetes-associated albuminuria was higher in BPH/2J vs. diabetic BPN/3J (1205 + 196/-169 versus 496 + 67/-59 μg/24 h, p = 0.008). HPLC measurement of renal cortical norepinephrine and dopamine showed significantly greater levels in hypertensive mice whilst diabetes was associated with significantly lower catecholamine levels. Diabetic BPH/2J also had greater renal catecholamine levels than diabetic BPN/3J (diabetic: norepinephrine BPN/3J 40 ± 4, BPH/2J 91 ± 5, p = 0.010; dopamine: BPN/3J 2 ± 1; BPH/2J 3 ± 1 ng/mg total protein, p < 0.001 after 10 weeks of study). Diabetic BPH/2J showed greater cortical tubular immunostaining for monoamine oxidase A and cortical mitochondrial hydrogen peroxide formation was greater in both diabetic and non-diabetic BPH/2J. While cytosolic catalase activity was greater in non-diabetic BPH/2J it was significantly lower in diabetic BPH/2J (cytosolic: BPH/2J 127 ± 12 vs. 63 ± 6 nmol/min/ml, p < 0.001). We conclude that greater levels of renal norepinephrine and dopamine associated with hypertension, together with diabetes-associated compromised anti-oxidant systems, contribute to increased renal oxidative stress in diabetes and hypertension. Elevations in renal cortical catecholamines and reactive oxygen species have important therapeutic implications for hypertensive diabetic patients.

A new common functional coding variant at the DDC gene change renal enzyme activity and modify renal dopamine function

The intra-renal dopamine (DA) system is highly expressed in the proximal tubule and contributes to Na+ and blood pressure homeostasis, as well as to the development of nephropathy. In the kidney, the enzyme DOPA Decarboxylase (DDC) originating from the circulation. We used a twin/family study design, followed by polymorphism association analysis at DDC locus to elucidate heritable influences on renal DA production. Dense single nucleotide polymorphism (SNP) genotyping across the DDC locus on chromosome 7p12 was analyzed by re-sequencing guided by trait-associated genetic markers to discover the responsible genetic variation. We also characterized kinetics of the expressed DDC mutant enzyme. Systematic polymorphism screening across the 15-Exon DDC locus revealed a single coding variant in Exon-14 that was associated with DA excretion and multiple other renal traits indicating pleiotropy. When expressed and characterized in eukaryotic cells, the 462Gln variant displayed lower Vmax (maximal rate of product formation by an enzyme) (21.3 versus 44.9 nmol/min/mg) and lower Km (substrate concentration at which half-maximal product formation is achieved by an enzyme.)(36.2 versus 46.8 μM) than the wild-type (Arg462) allele. The highly heritable DA excretion trait is substantially influenced by a previously uncharacterized common coding variant (Arg462Gln) at the DDC gene that affects multiple renal tubular and glomerular traits, and predicts accelerated functional decline in chronic kidney disease.

The Relationship between the Intrarenal Dopamine System and Intrarenal Renin-angiotensin System Depending on the Renal Function

Objective The mechanisms underlying the intrarenal renin-angiotensin system (RAS) activation depend on the conditions of kidney diseases. In angiotensin II (AngII) infusion models, the circulating AngII is filtered into the renal tubular lumens, activating intrarenal RAS. However, in the chronic kidney disease (CKD) models, plasma angiotensinogen (AGT) is filtered into the tubular lumens because of glomerular injury, activating intrarenal RAS. The intrarenal dopamine system activation reduces intrarenal AGT expression and suppresses the intrarenal RAS activity in AngII infusion models. However, the relationship between the intrarenal dopamine system and intrarenal RAS has not been elucidated. Therefore, this study was conducted to determine that relationship in CKD patients. Methods We recruited 46 CKD patients (age: 51.1±20.0 years; 16 men; causes of CKD: chronic glomerulonephritis, 34; diabetic nephropathy, 2; nephrosclerosis, 4; and others, 6) not undergoing dialysis or taking RAS blockers. The urinary dopamine (U-DOPA) level, an indicator of intrarenal dopamine activity, and the urinary AGT (U-AGT) level, a surrogate marker of intrarenal RAS activity, were measured. Results As the CKD stages progressed, the U-DOPA levels decreased while the U-AGT levels increased. The U-DOPA levels were significantly and negatively correlated with the U-AGT levels but significantly and positively correlated with the estimated glomerular filtration rate (eGFR). A multiple regression analysis revealed that the U-DOPA levels were associated with the U-AGT levels after adjusting for age, sex, body mass index, and blood pressure (β=-0.38, p=0.045). However, no correlation was observed when eGFR was also adjusted (β=-0.17, p=0.29). Conclusion The negative correlation between the intrarenal dopamine system and intrarenal RAS in CKD patients may be affected by the renal function.

G-Protein-Coupled Receptor Signaling in Cilia

G-protein-coupled receptors (GPCRs) are the largest and most versatile family of signaling receptors in humans. They respond to diverse external signals, such as photons, proteins, peptides, chemicals, hormones, lipids, and sugars, and mediate a myriad of functions in the human body. Signaling through GPCRs can be optimized by enriching receptors and downstream effectors in discrete cellular domains. Many GPCRs have been found to be selectively targeted to cilia on numerous mammalian cell types. Moreover, investigations into the pathophysiology of human ciliopathies have implicated GPCR ciliary signaling in a number of developmental and cellular pathways. Thus, cilia are now appreciated as an increasingly important nexus for GPCR signaling. Yet, we are just beginning to understand the precise signaling pathways mediated by most ciliary GPCRs and how they impact cellular function and mammalian physiology.

Differential Response to Low-Dose Dopamine or Low-Dose Nesiritide in Acute Heart Failure With Reduced or Preserved Ejection Fraction: Results From the ROSE AHF Trial (Renal Optimization Strategies Evaluation in Acute Heart Failure)

BACKGROUND

The ROSE AHF trial (Renal Optimization Strategies Evaluation in Acute Heart Failure) found that when compared with placebo, neither low-dose dopamine (2 µg/kg per minute) nor low-dose nesiritide (0.005 μg/kg per minute without bolus) enhanced decongestion or preserved renal function in AHF patients with renal dysfunction. However, there may be differential responses to vasoactive agents in AHF patients with reduced versus preserved ejection fraction (EF). This post hoc analysis examined potential interaction between treatment effect and EF (EF ≤40% versus >40%) on the ROSE AHF end points.

METHODS AND RESULTS

ROSE AHF enrolled AHF patients (n=360; any EF) with renal dysfunction. The coprimary end points were cumulative urine volume and the change in serum cystatin-C in 72 hours. The effect of dopamine (interaction P=0.001) and nesiritide (interaction P=0.039) on urine volume varied by EF group. In heart failure with reduced EF, urine volume was higher with active treatment versus placebo, whereas in heart failure with preserved EF, urine volume was lower with active treatment. The effect of dopamine and nesiritide on weight change, sodium excretion, and incidence of AHF treatment failure also varied by EF group (interaction P<0.05 for all). There was no interaction between vasoactive treatment's effect and EF on change in cystatin-C. Compared with placebo, dopamine was associated with improved clinical outcomes in heart failure with reduced EF and worse clinical outcomes in heart failure with preserved EF. With nesiritide, there were no differences in clinical outcomes when compared with placebo in both heart failure with reduced EF and heart failure with preserved EF.

CONCLUSIONS

In this post hoc analysis of ROSE AHF, the response to vasoactive therapies differed in patients with heart failure with reduced EF and heart failure with preserved EF. Investigations of AHF therapies should assess the potential for differential responses in AHF with preserved versus reduced EF.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT01132846.

Angiotensin II type 2 receptor (AT2R) in renal and cardiovascular disease

Angiotensin II (Ang II) is well-considered to be the principal effector of the renin-angiotensin system (RAS), which binds with strong affinity to the angiotensin II type 1 (AT1R) and type 2 (AT2R) receptor subtype. However, activation of both receptors is likely to stimulate different signalling mechanisms/pathways and produce distinct biological responses. The haemodynamic and non-haemodynamic effects of Ang II, including its ability to regulate blood pressure, maintain water-electrolyte balance and promote vasoconstriction and cellular growth are well-documented to be mediated primarily by the AT1R. However, its biological and functional effects mediated through the AT2R subtype are still poorly understood. Recent studies have emphasized that activation of the AT2R regulates tissue and organ development and provides in certain context a potential counter-regulatory mechanism against AT1R-mediated actions. Thus, this review will focus on providing insights into the biological role of the AT2R, in particular its actions within the renal and cardiovascular system.

Circulating angiotensin type II receptor: Possible marker for antibody mediated rejection after renal transplantation?

BACKGROUND

Presence of antibody [Ab] against angiotensin receptor [AT1R] indicates heightened risk for antibody mediated rejection [AMR] after transplantation but is insufficient as a marker. We speculated AT1R might be released systemically because of AMR and might be a useful biomarker.

METHODS

AT1R was measured in blood from 73 Normals and 72 renal patients pre- and post-transplantation. Patients were stratified as AMR-free [Gp1], AMR<1yr [Gp2] and AMR>1yr [Gp3].

RESULTS

AT1R was higher [13±26vs.367±537, p<0.01)] and more prevalent [20% vs. 92%, p<0.01] among renal patients than Normals. Pretransplant levels were similar [p=ns] between groups. One-year posttransplant levels approached [p<0.01] normalcy for Gps1+3 but spiked during AMR and remained elevated [155±58, p<0.01] for 50% Gp2 patients. One-year AT1R levels were higher among subsequent graft failures than surviving grafts [171±267vs. 38±50, p<0.01].

CONCLUSIONS

Pretransplant AT1R was abnormally elevated: possibly indicating ongoing tissue injury. Pretransplant AT1R didn't predict risk for AMR. However, AT1R spiked during early AMR and sustained elevations were associated with poorer outcomes.

AT2 Receptors: Potential Therapeutic Targets for Hypertension

The renin-angiotensin system (RAS) is arguably the most important and best studied hormonal system in the control of blood pressure (BP) and the pathogenesis of hypertension. The RAS features its main effector angiotensin II (Ang II) acting via its 2 major receptors, angiotensin type-1(AT1R) and type-2 (AT2R). In general, AT2Rs oppose the detrimental actions of Ang II via AT1Rs. AT2R activation induces vasodilation and natriuresis, but its effects to lower BP in hypertension have not been as clear as anticipated. Recent studies, however, have demonstrated that acute and chronic AT2R stimulation can induce natriuresis and lower BP in the Ang II infusion model of experimental hypertension. AT2R activation induces receptor recruitment from intracellular sites to the apical plasma membranes of renal proximal tubule cells via a bradykinin, nitric oxide, and cyclic guanosine 3',5' monophosphate signaling pathway that results in internalization and inactivation of sodium (Na+) transporters Na+-H+ exchanger-3 and Na+/K+ATPase. These responses do not require the presence of concurrent AT1R blockade and are effective both in the prevention and reversal of hypertension. This review will address the role of AT2Rs in the control of BP and Na+ excretion and the case for these receptors as potential therapeutic targets for hypertension in humans.

Do renin-angiotensin system inhibitors influence the recurrence, metastasis, and survival in cancer patients?: Evidence from a meta-analysis including 55 studies

BACKGROUND

Renin-angiotensin system inhibitors (RAS inhibitors) are antihypertensive agents with potential antitumor effects. However, various studies have yielded conflicting results on the influence of RAS inhibitors on survival of cancer patients. The aim of this study was to evaluate the effect of RAS inhibitors on recurrence, metastasis, and survival in cancer patients through a meta-analysis.

METHODS

PubMed, Web of Science, EMBASE, and Cochrane Library were systematically searched from inception to December 2016. The pooled hazard ratio (HR) with its 95% confidence interval (95% CI) was calculated to evaluate the association between RAS inhibitors and recurrence, metastasis, and survival in cancer patients.

RESULTS

Fifty-five eligible studies were included in the present meta-analysis. Results showed that there were significant improvements in overall survival (OS) (HR = 0.82; 95% CI: 0.77-0.88; P < 0.001), progression-free survival (HR = 0.74; 95% CI: 0.66-0.84; P < 0.001), and disease-free survival (HR = 0.80; 95% CI: 0.67-0.95; P = 0.01) in RAS inhibitor users compared with nonusers. Subgroup analyses revealed that the effect of RAS inhibitors on OS depended on the cancer type or different RAS inhibitors.

CONCLUSION

This meta-analysis suggests that RAS inhibitors could improve the survival of cancer patients and depend on cancer type and types of RAS inhibitors.

Antenatal betamethasone attenuates the angiotensin-(1-7)-Mas receptor-nitric oxide axis in isolated proximal tubule cells

We previously reported a sex-specific effect of antenatal treatment with betamethasone (Beta) on sodium (Na⁺) excretion in adult sheep whereby treated males but not females had an attenuated natriuretic response to angiotensin-(1-7) [Ang-(1-7)]. The present study determined the Na⁺ uptake and nitric oxide (NO) response to low-dose Ang-(1-7) (1 pM) in renal proximal tubule cells (RPTC) from adult male and female sheep antenatally exposed to Beta or vehicle. Data were expressed as percentage of basal uptake or area under the curve for Na⁺ or percentage of control for NO. Male Beta RPTC exhibited greater Na⁺ uptake than male vehicle cells (433 ± 28 vs. 330 ± 26%; P < 0.05); however, Beta exposure had no effect on Na⁺ uptake in the female cells (255 ± 16 vs. 255 ± 14%; P > 0.05). Ang-(1-7) significantly inhibited Na⁺ uptake in RPTC from vehicle male (214 ± 11%) and from both vehicle (190 ± 14%) and Beta (209 ± 11%) females but failed to attenuate Na⁺ uptake in Beta male cells. Beta exposure also abolished stimulation of NO by Ang-(1-7) in male but not female RPTC. Both the Na⁺ and NO responses to Ang-(1-7) were blocked by Mas receptor antagonist d-Ala⁷-Ang-(1-7). We conclude that the tubular Ang-(1-7)-Mas-NO pathway is attenuated in males and not females by antenatal Beta exposure. Moreover, since primary cultures of RPTC retain both the sex and Beta-induced phenotype of the adult kidney in vivo they appear to be an appropriate cell model to examine the effects of fetal programming on Na⁺ handling by the renal tubules.

Resetting of renal tissular renin-angiotensin and bradykinin-kallikrein systems after unilateral kidney denervation in rats

The renal tissular renin-angiotensin and bradykinin-kallikrein systems control kidney function together with the renal sympathetic innervation but their interaction is still unclear. To further elucidate this relationship, we investigated these systems in rats 6 days after left kidney denervation (DNX, n = 8) compared to sham-operated controls (CTR, n = 8). Plasma renin concentration was unchanged in DNX vs. CTR (p = NS). Kidney bradykinin (BK) and angiotensin (Ang) I and II concentrations decreased bilaterally in DNX vs. CTR rats (~20 to 40%, p < 0.05) together with Ang IV and V concentrations that were extremely low (p = NS). Renin, Ang III and dopamine concentrations decreased by ~25 to 50% and norepinephrine concentrations by 99% in DNX kidneys (p < 0.05) but were unaltered in opposite kidneys. Ang II/I and KA were comparable in DNX, contralateral and CTR kidneys. Ang III/II increased in right vs. DNX or CTR kidneys (40-50%, p < 0.05). Ang II was mainly located in tubular epithelium by immunocytological staining and its cellular distribution was unaffected by DNX. Moreover, the angiotensinergic and catecholaminergic innervation of right kidneys was unchanged vs. CTR. We found an important dependency of tissular Ang and BK levels on the renal innervation that may contribute to the resetting of kidney function after DNX. The DNX-induced peptide changes were not readily explained by kidney KA, renin or plasma Ang I generation. However, tissular peptide metabolism and compartmentalization may have played a central role. The mechanisms behind the concentration changes remain unclear and deserve further clarification.

ISN Forefronts Symposium 2015: Maintaining Balance Under Pressure-Hypertension and the Proximal Tubule

Renal control of effective circulating volume (ECV) is key for circulatory performance. When renal sodium excretion is inadequate, blood pressure rises and serves as a homeostatic signal to drive natriuresis to re-establish ECV. Recognizing that hypertension involves both renal and vascular dysfunction, this report concerns proximal tubule sodium hydrogen exchanger 3 (NHE3) regulation during acute and chronic hypertension. NHE3 is distributed in tall microvilli (MV) in the proximal tubule, where it reabsorbs a significant fraction of the filtered sodium. NHE3 redistributes, in the plane of the MV membrane, between the MV body, where NHE3 is active, and the MV base, where NHE3 is less active. A high-salt diet and acute hypertension both retract NHE3 to the base and reduce proximal tubule sodium reabsorption independent of a change in abundance. The renin angiotensin system provokes NHE3 redistribution independent of blood pressure: The angiotensin-converting enzyme (ACE) inhibitor captopril redistributes NHE3 to the base and subsequent angiotensin II (AngII) infusion returns NHE3 to the body of the MV and restores reabsorption. Chronic AngII infusion presents simultaneous AngII stimulation and hypertension; that is, NHE3 remains in the body of the MV, due to the high local AngII level and inflammation, and exhibits a compensatory decrease in abundance driven by the hypertension. Genetically modified mice with blunted hypertensive responses to chronic AngII infusion (due to lack of the proximal tubule AngII receptors interleukin-17A or interferon-γ expression) exhibit reduced local AngII accumulation and inflammation and larger decreases in NHE3 abundance, which improves the pressure natriuresis response and reduces the need for elevated blood pressure to facilitate circulating volume balance.

Kidney tubules: intertubular, vascular, and glomerular cross-talk

PURPOSE OF REVIEW

The kidney mediates the excretion or conservation of water and electrolytes in the face of changing fluid and salt intake and losses. To ultrafilter and reabsorb the exact quantities of free water and salts to maintain euvolemia a range of endocrine, paracrine, and hormonal signaling systems have evolved linking the tubules, capillaries, glomeruli, arterioles, and other intrinsic cells of the kidney. Our understanding of these systems remains incomplete.

RECENT FINDINGS

Recent work has provided new insights into the workings of the communication pathways between tubular segments and the glomeruli and vasculature, with novel therapeutic agents in development. Particular progress has also been made in the visualization of tubuloglomerular feedback.

SUMMARY

The review summarizes our current understanding of pathway functions in health and disease, as well as future therapeutic options to protect the healthy and injured kidney.

Enhanced Natriuresis and Diuresis in Wistar Rats Caused by the Costimulation of Renal Dopamine D3 and Angiotensin II Type 2 Receptors

BACKGROUND

The kidney, via its regulation of sodium excretion, which is modulated by humoral factors, including the dopamine and renin-angiotensin systems, keeps the blood pressure in the normal range. We have reported a negative interaction between dopamine D3 and AT1 receptors (D3R and AT1R) in renal proximal tubule (RPT) cells. Here, we studied the interaction between D3R and AT2R in vitro and in vivo.

METHODS AND RESULTS

Stimulation of either the D3R or AT2R, by the intrarenal arterial infusion of PD128907, a D3R agonist, or CGP42112A, an AT2R agonist, induced natriuresis and diuresis that were enhanced by the simultaneous infusion of PD128907 and CGP42112A in Wistar rats. The D3/AT2 receptor interaction was confirmed in in vitro, i.e., stimulation of either the D3R or AT2R inhibited Na(+)-K(+)-ATPase activity that was enhanced by the costimulation of these receptors. D3R and AT2R colocalized and coimmunoprecipitated in kidney and RPT cells (RPTCs). Stimulation of one receptor increased the localization of the other receptor at the plasma cell membrane. ERK1/2-MAPK is involved in the signaling pathway of D3R and AT2R interaction because costimulation of D3R and AT2R significantly increased ERK1/2-MAPK expression in RPTCs; inhibition of ERK1/2-MAPK abolished the inhibition of Na(+)-K(+)-ATPase activity that was enhanced by D3R and AT2R costimulation.

CONCLUSIONS

Our current study indicates that D3R, in combination with AT2R, enhances natriuresis and diuresis, via ERK1/2-MAPK pathway, that may be involved in the regulation of blood pressure.

Peripheral and central effects of circulating catecholamines

Physical challenges, emotional arousal, increased physical activity, or changes in the environment can evoke stress, requiring altered activity of visceral organs, glands, and smooth muscles. These alterations are necessary for the organism to function appropriately under these abnormal conditions and to restore homeostasis. These changes in activity comprise the "fight-or-flight" response and must occur rapidly or the organism may not survive. The rapid responses are mediated primarily via the catecholamines, epinephrine, and norepinephrine, secreted from the adrenal medulla. The catecholamine neurohormones interact with adrenergic receptors present on cell membranes of all visceral organs and smooth muscles, leading to activation of signaling pathways and consequent alterations in organ function and smooth muscle tone. During the "fight-or-flight response," the rise in circulating epinephrine and norepinephrine from the adrenal medulla and norepinephrine secreted from sympathetic nerve terminals cause increased blood pressure and cardiac output, relaxation of bronchial, intestinal and many other smooth muscles, mydriasis, and metabolic changes that increase levels of blood glucose and free fatty acids. Circulating catecholamines can also alter memory via effects on afferent sensory nerves impacting central nervous system function. While these rapid responses may be necessary for survival, sustained elevation of circulating catecholamines for prolonged periods of time can also produce pathological conditions, such as cardiac hypertrophy and heart failure, hypertension, and posttraumatic stress disorder. In this review, we discuss the present knowledge of the effects of circulating catecholamines on peripheral organs and tissues, as well as on memory in the brain.

Renal dopaminergic system: Pathophysiological implications and clinical perspectives

Fluid homeostasis, blood pressure and redox balance in the kidney are regulated by an intricate interaction between local and systemic anti-natriuretic and natriuretic systems. Intrarenal dopamine plays a central role on this interactive network. By activating specific receptors, dopamine promotes sodium excretion and stimulates anti-oxidant and anti-inflammatory pathways. Different pathological scenarios where renal sodium excretion is dysregulated, as in nephrotic syndrome, hypertension and renal inflammation, can be associated with impaired action of renal dopamine including alteration in biosynthesis, dopamine receptor expression and signal transduction. Given its properties on the regulation of renal blood flow and sodium excretion, exogenous dopamine has been postulated as a potential therapeutic strategy to prevent renal failure in critically ill patients. The aim of this review is to update and discuss on the most recent findings about renal dopaminergic system and its role in several diseases involving the kidneys and the potential use of dopamine as a nephroprotective agent.

The intrarenal renin-angiotensin system in hypertension

The renin-angiotensin system (RAS) is a well-studied hormonal cascade controlling fluid and electrolyte balance and blood pressure through systemic actions. The classical RAS includes renin, an enzyme catalyzing the conversion of angiotensinogen to angiotensin (Ang) I, followed by angiotensin-converting enzyme (ACE) cleavage of Ang I to II, and activation of AT1 receptors, which are responsible for all RAS biologic actions. Recent discoveries have transformed the RAS into a far more complex system with several new pathways: the (des-aspartyl(1))-Ang II (Ang III)/AT2 receptor pathway, the ACE-2/Ang (1-7)/Mas receptor pathway, and the prorenin-renin/prorenin receptor/mitogen-activated protein kinase pathway, among others. Although the classical RAS pathway induces Na(+) reabsorption and increases blood pressure, several new pathways constitute a natriuretic/vasodilator arm of the system, opposing detrimental actions of Ang II through Ang II type 1 receptors. Instead of a simple circulating RAS, several independently functioning tissue RASs exist, the most important of which is the intrarenal RAS. Several physiological characteristics of the intrarenal RAS differ from those of the circulating RAS, autoamplifying the activity of the intrarenal RAS and leading to hypertension. This review will update current knowledge on the RAS with particular attention to the intrarenal RAS and its role in the pathophysiology of hypertension.

Antenatal glucocorticoid treatment alters Na+ uptake in renal proximal tubule cells from adult offspring in a sex-specific manner

We have shown a sex-specific effect of fetal programming on Na(+) excretion in adult sheep. The site of this effect in the kidney is unknown. Therefore, we tested the hypothesis that renal proximal tubule cells (RPTCs) from adult male sheep exposed to betamethasone (Beta) before birth have greater Na(+) uptake than do RPTCs from vehicle-exposed male sheep and that RPTCs from female sheep similarly exposed are not influenced by antenatal Beta. In isolated RPTCs from 1- to 1.5-yr-old male and female sheep, we measured Na(+) uptake under basal conditions and after stimulation with ANG II. To gain insight into the mechanisms involved, we also measured nitric oxide (NO) levels, ANG II receptor mRNA levels, and expression of Na(+)/H(+) exchanger 3. Basal Na(+) uptake increased more in cells from Beta-exposed male sheep than in cells from vehicle-exposed male sheep (400% vs. 300%, P < 0.00001). ANG II-stimulated Na(+) uptake was also greater in cells from Beta-exposed males. Beta exposure did not increase Na(+) uptake by RPTCs from female sheep. NO production was suppressed more by ANG II in RPTCs from Beta-exposed males than in RPTCs from either vehicle-exposed male or female sheep. Our data suggest that one site of the sex-specific effect of Beta-induced fetal programming in the kidney is the RPTC and that the enhanced Na(+) uptake induced by antenatal Beta in male RPTCs may be related to the suppression of NO in these cells.

The renal dopaminergic system: novel diagnostic and therapeutic approaches in hypertension and kidney disease

Salt sensitivity of blood pressure, whether in hypertensive or normotensive subjects, is associated with increased cardiovascular risk and overall mortality. Salt sensitivity can be treated by reducing NaCl consumption. However, decreasing salt intake in some may actually increase cardiovascular risk, including an increase in blood pressure, that is, inverse salt sensitivity. Several genes have been associated with salt sensitivity and inverse salt sensitivity. Some of these genes encode proteins expressed in the kidney that are needed to excrete a sodium load, for example, dopamine receptors and their regulators, G protein-coupled receptor kinase 4 (GRK4). We review here research in this field that has provided several translational opportunities, ranging from diagnostic tests to gene therapy, such as (1) a test in renal proximal tubule cells isolated from the urine of humans that may determine the salt-sensitive phenotype by analyzing the recruitment of dopamine D1 receptors to the plasma membrane; (2) the presence of common GRK4 gene variants that are not only associated with hypertension but may also be predictive of the response to antihypertensive therapy; (3) genetic testing for polymorphisms of the dopamine D2 receptor that may be associated with hypertension and inverse salt sensitivity and may increase the susceptibility to chronic kidney disease because of loss of the antioxidant and anti-inflammatory effects of the renal dopamine D2 receptor, and (4) in vivo renal selective amelioration of renal tubular genetic defects by a gene transfer approach, using adeno-associated viral vectors introduced to the kidney by retrograde ureteral infusion.

L-DOPA decarboxylase mRNA levels provide high diagnostic accuracy and discrimination between clear cell and non-clear cell subtypes in renal cell carcinoma

OBJECTIVES

Renal cell carcinoma (RCC) is the most frequent type of kidney cancer. RCC patients frequently present with arterial hypertension due to various causes, including intrarenal dopamine deficiency. L-DOPA decarboxylase (DDC) is the gene encoding the enzyme that catalyzes the biosynthesis of dopamine in humans. Several studies have shown that the expression levels of DDC are significantly deregulated in cancer. Thus, we herein sought to analyze the mRNA levels of DDC and evaluate their clinical significance in RCC.

DESIGN AND METHODS

DDC levels were analyzed in 58 surgically resected RCC tumors and 44 adjacent non-cancerous renal tissue specimens via real-time PCR. Relative levels of DDC were estimated by applying the 2(-ΔΔC)T method, while their diagnostic accuracy and correlation with the clinicopathological features of RCC tumors were assessed by comprehensive statistical analysis.

RESULTS

DDC mRNA levels were found to be dramatically downregulated (p<0.001) in RCC tumors, exhibiting remarkable diagnostic accuracy as assessed by ROC curve analysis (AUC: 0.910; p<0.001) and logistic regression (OR: 0.678; p=0.001). Likewise, DDC was found to be differentially expressed between clear cell RCC and the group of non-clear cell subtypes (p=0.001) consisted of papillary and chromophobe RCC specimens. Furthermore, a statistically significant inverse correlation was also observed when the mRNA levels of DDC were analyzed in relation to tumor grade (p=0.049).

CONCLUSIONS

Our data showed that DDC constitutes a highly promising molecular marker for RCC, exhibiting remarkable diagnostic accuracy and potential to discriminate between clear cell and non-clear cell histological subtypes of RCC.

Angiotensin type 2 receptors: blood pressure regulation and end organ damage

In most situations, the angiotensin AT2-receptor (AT2R) mediates physiological actions opposing those mediated by the AT1-receptor (AT1R), including a vasorelaxant effect. Nevertheless, experimental evidence vastly supports that systemic application of AT2R-agonists is blood pressure neutral. However, stimulation of AT2R locally within the brain or the kidney apparently elicits a systemic blood pressure lowering effect. A systemic effect of AT2R stimulation on blood pressure can also be achieved, when the prevailing effect of continuous background AT1R-stimulation is attenuated by low-dose AT1R blockade. Despite a lack of effect on blood pressure, AT2R stimulation still protects from hypertensive end-organ damage. Current data and evidence therefore suggest that AT2R agonists will not be suitable as future anti-hypertensive drugs, but that they may well be useful for end-organ protection in combination with established anti-hypertensives.

Expression of ocular albinism 1 (OA1), 3, 4- dihydroxy- L-phenylalanine (DOPA) receptor, in both neuronal and non-neuronal organs

Oa1 is the casual gene for ocular albinism-1 in humans. The gene product OA1, alternatively designated as GPR143, belongs to G-protein coupled receptors. It has been reported that OA1 is a specific receptor for 3, 4-dihydroxy- L-phenylalanine (DOPA) in retinal pigmental epithelium where DOPA facilitates the pigmentation via OA1 stimulation. We have recently shown that OA1 mediates DOPA-induced depressor response in rat nucleus tractus solitarii. However, the distribution and function of OA1 in other regions are largely unknown. We have generated oa1 knockout mice and examined OA1 expression in both neuronal and non-neuronal tissues by immunohistochemical analyses using anti-mouse OA1 monoclonal antibodies. In the telencephalon, OA1 was expressed in cerebral cortex and hippocampus. Predominant expression of OA1 was observed in the pyramidal neurons in these regions. OA1 was also expressed in habenular nucleus, hypothalamus, substantia nigra, and medulla oblongata. The expression of OA1 in the nucleus tractus solitarii of medulla oblongata may support the reduction of blood pressure by the microinjection of DOPA into this region. Outside of the nervous system, OA1 was expressed in heart, lung, liver, kidney and spleen. Abundant expression was observed in the renal tubules and the splenic capsules. These peripheral regions are innervated by numerous sympathetic nerve endings. In addition, substantia nigra contains a large population of dopaminergic neurons. Thus, the immunohistochemical analyses suggest that OA1 may modulate the monoaminergic functions in both peripheral and central nervous systems.

Contribution of the renin-angiotensin system in chronic foot-shock induced hypertension in rats

AIMS

Chronic foot shock has been demonstrated to induce hypertension. The present study was designed to explore whether the renin-angiotensin system (RAS) plays a role in this process and the possible mechanisms involved in chronic-foot-shock-induced hypertension.

MAIN METHODS

Male Sprague-Dawley rats were subjected to a two-week foot shock with or without an angiotensin II (Ang II) type 1 receptor blocker (ARB, candesartan) or an angiotensin I converting enzyme inhibitor (ACEI, captopril). The expression of RAS components in the central nervous and circulatory systems was examined. Antioxidant levels in the plasma were monitored.

KEY FINDINGS

Two-week foot shock significantly increased systolic blood pressure (SBP). Angiotensinogen, angiotensin I converting enzyme (ACE)-1, ACE-2, angiotensin type 1a and type 1b receptors, and vasopressin (VAP) mRNA expression in the cerebral cortex and hypothalamus were increased along with the concentration of renin and Ang II in the plasma; these changes were accompanied by decreased glutathione peroxidase activity and increased lipid peroxidation levels and plasma corticosterone concentrations. Both candesartan and captopril suppressed not only the increases in SBP but also the increases in VAP expression in the hypothalamus and RAS components in the central nervous system and the circulatory system. The decreases in antioxidant levels and the increases in lipid peroxidation and corticosterone levels were also partially reversed by candesartan or captopril treatment.

SIGNIFICANCE

Chronic foot shock increases expression of the main RAS components, which play an important role in the development of high blood pressure through increased VAP levels, oxidative stress levels and stress hormone levels.

Signaling pathways involved in renal oxidative injury: role of the vasoactive peptides and the renal dopaminergic system

The physiological hydroelectrolytic balance and the redox steady state in the kidney are accomplished by an intricate interaction between signals from extrarenal and intrarenal sources and between antinatriuretic and natriuretic factors. Angiotensin II, atrial natriuretic peptide and intrarenal dopamine play a pivotal role in this interactive network. The balance between endogenous antioxidant agents like the renal dopaminergic system and atrial natriuretic peptide, by one side, and the prooxidant effect of the renin angiotensin system, by the other side, contributes to ensuring the normal function of the kidney. Different pathological scenarios, as nephrotic syndrome and hypertension, where renal sodium excretion is altered, are associated with an impaired interaction between two natriuretic systems as the renal dopaminergic system and atrial natriuretic peptide that may be involved in the pathogenesis of renal diseases. The aim of this review is to update and comment the most recent evidences about the intracellular pathways involved in the relationship between endogenous antioxidant agents like the renal dopaminergic system and atrial natriuretic peptide and the prooxidant effect of the renin angiotensin system in the pathogenesis of renal inflammation.

Cardiovascular effects of the angiotensin type 2 receptor

The angiotensin type 2 receptor, AT2R, has been described as having opposite effects to the angiotensin type 1 receptor, AT1R. Although the quantities of the AT2R found in the adult are low, its expression rises in pathological situations. The AT2R has three major signaling pathways: activation of serine/threonine phosphatases (promoting apoptosis and antioxidant effects), activation of the bradykinin/NO/cGMP pathway (promoting vasodilation), and activation of phospholipase A2 (associated with regulation of potassium currents). The AT2R appears to have effects in vascular remodeling, atherosclerosis prevention and blood pressure lowering (when associated with an AT1R inhibitor). After myocardial infarction, the AT2R appears to decrease infarct size, cardiac hypertrophy and fibrosis, and to improve cardiac function. However, its role in the heart is controversial. In the kidney, the AT2R promotes natriuresis. Until now, treatment directed at the renin-angiotensin-aldosterone system has been based on angiotensin-converting enzyme inhibitors or angiotensin type 1 receptor blockers. The study of the AT2R has been revolutionized by the discovery of a direct agonist, C21, which promises to become part of the treatment of cardiovascular disease.

Atrial natriuretic peptide and renal dopaminergic system: a positive friendly relationship?

Sodium metabolism by the kidney is accomplished by an intricate interaction between signals from extrarenal and intrarenal sources and between antinatriuretic and natriuretic factors. Renal dopamine plays a central role in this interactive network. The natriuretic hormones, such as the atrial natriuretic peptide, mediate some of their effects by affecting the renal dopaminergic system. Renal dopaminergic tonus can be modulated at different steps of dopamine metabolism (synthesis, uptake, release, catabolism, and receptor sensitization) which can be regulated by the atrial natriuretic peptide. At tubular level, dopamine and atrial natriuretic peptide act together in a concerted manner to promote sodium excretion, especially through the overinhibition of Na+, K+-ATPase activity. In this way, different pathological scenarios where renal sodium excretion is dysregulated, as in nephrotic syndrome or hypertension, are associated with impaired action of renal dopamine and/or atrial natriuretic peptide, or as a result of impaired interaction between these two natriuretic systems. The aim of this review is to update and comment on the most recent evidences demonstrating how the renal dopaminergic system interacts with atrial natriuretic peptide to control renal physiology and blood pressure through different regulatory pathways.

Differential effects and potential adverse outcomes of ionic silver and silver nanoparticles in vivo and in vitro

Nanoparticles are of concern because of widespread use, but it is unclear if metal nanoparticles cause effects directly or indirectly. We explored whether polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs) cause effects through intact nanoparticles or dissolved silver. Females of the model species fathead minnow (Pimephales promelas) were exposed to either 4.8 μg/L of AgNO3 or 61.4 μg/L of PVP-AgNPs for 96h. Microarray analyses were used to identify impacted receptors and toxicity pathways in liver and brain tissues that were confirmed using in vitro mammalian assays. AgNO3 and PVP-AgNP exposed fish had common and distinct effects consistent with both intact nanoparticles and dissolved silver causing effects. PVP-AgNPs and AgNO3 both affected pathways involved in Na(+), K(+), and H(+) homeostasis and oxidative stress but different neurotoxicity pathways. In vivo effects were supported by PVP-AgNP activation of five in vitro nuclear receptor assays and inhibition of ligand binding to the dopamine receptor. AgNO3 inhibited ligand binding to adrenergic receptors α1 and α2 and cannabinoid receptor CB1, but had no effect in nuclear receptor assays. PVP-AgNPs have the potential to cause effects both through intact nanoparticles and metal ions, each interacting with different initiating events. Since the in vitro and in vivo assays examined here are commonly used in human and ecological hazard screening, this work suggests that environmental health assessments should consider effects of intact nanoparticles in addition to dissolved metals.

Roles of dopamine receptor on chemosensory and mechanosensory primary cilia in renal epithelial cells

Dopamine plays a number of important physiological roles. However, activation of dopamine receptor type-5 (DR5) and its effect in renal epithelial cells have not been studied. Here, we show for the first time that DR5 is localized to primary cilia of LLCPK kidney cells. Renal epithelial cilia are mechanosensory organelles that sense and respond to tubular fluid-flow in the kidney. To determine the roles of DR5 and sensory cilia, we used dopamine to non-selectively and fenoldopam to selectively activate ciliary DR5. Compared to mock treatment, dopamine treated cells significantly increases the length of cilia. Fenoldopam further increases the length of cilia compared to dopamine treated cells. The increase in cilia length also increases the sensitivity of the cells in response to fluid-shear stress. The graded responses to dopamine- and fenoldopam-induced increase in cilia length further show that sensitivity to fluid-shear stress correlates to the length of cilia. Together, our studies suggest for the first time that dopamine or fenoldopam is an exciting agent that enhances structure and function of primary cilia. We further propose that dopaminergic agents can be used in “cilio-therapy” to treat diseases associated with abnormal cilia structure and/or function.

Local Renin-Angiotensin system in the reproductive system

The renin-angiotensin system (RAS) is well known as regulator of electrolytes and blood pressure. Besides this function, there are numerous studies supporting the idea of a local tissue RAS. This system controls the local activity of the different RAS family members, especially of the functional proteins Angiotensin II and Angiotensin (1-7). Those antagonistically acting proteins have been described to be expressed in different organ systems including the human reproductive tract. Therefore, this local RAS has been suspected to be involved in the control and regulation of physiological and pathological conditions in the female reproduction tract. This review of the available literature summarizes the physiological influence of the RAS on the follicular development, ovarian angiogenesis, and placental- and uterine function. In addition, in the second part the role of the RAS concerning ovarian- and endometrial cancer becomes elucidated. This section includes possible novel therapeutic strategies via inhibition of RAS-mediated tumor growth and angiogenesis. Looking at a very complex system of agonistic and antagonistic tissue factors, it may be supposed that the RAS in the female reproduction tract will be of rising scientific interest in the upcoming years.