Altered functioning of both renal dopamine D1 and angiotensin II type 1 receptors causes hypertension in old rats

Fasting recovers age-related hypertension in the rats: reset of renal renin-angiotensin system components and klotho

BACKGROUND

The renal renin-angiotensin system (RAS) plays a vital part in the control of blood pressure and is known to be affected by aging. This study aimed to investigate the effects of intermittent fasting on age-related hypertension and the expression of local renal RAS components.

METHODS

The Wistar rats were categorized into three main age groups (young, middle aged, and elderly) and three dietary treatment models, including ad libitum feeding (AL), every other day fasting (EOD), and one day per week of fasting (FW). After three months, blood pressure (BP) was assessed. Some genes and proteins of the renal RAS system were measured by using Real time PCR and Western blot. α-klotho and Ang II proteins were assessed by ELISA method.

RESULTS

Old rats exhibited significantly increase in BP and Ang II (P < 0.001 vs. young rats) and a significant reduction in circulating levels of α-klotho and kidney AT2R protein (P < 0.001, P < 0.01, vs. young rats, respectively). Additionally, they respond to aging by increasing the AT1aR/AT2R proteins ratio (P < 0.05). Two model of feeding reduced BP in old rats and circulating Ang II in middle-aged and older rats. Moreover, by fasting, ACE2 protein expression was elevated in old rats. EOD fasting also significantly elevated the AT2 receptor protein and reduced the AT1aR/AT2R proteins ratio in the older rats (P < 0.001, P < 0.01, respectively).

CONCLUSION

Our findings suggest that fasting, particularly EOD, can attenuate age-related hypertension, partly through reset of the local renal RAS and increase of klotho protein expression.

G protein-coupled receptor kinases in hypertension: physiology, pathogenesis, and therapeutic targets

G protein-coupled receptors (GPCRs) mediate cellular responses to a myriad of hormones and neurotransmitters that play vital roles in the regulation of physiological processes such as blood pressure. In organs such as the artery and kidney, hormones or neurotransmitters, such as angiotensin II (Ang II), dopamine, epinephrine, and norepinephrine exert their functions via their receptors, with the ultimate effect of keeping normal vascular reactivity, normal body sodium, and normal blood pressure. GPCR kinases (GRKs) exert their biological functions, by mediating the regulation of agonist-occupied GPCRs, non-GPCRs, or non-receptor substrates. In particular, increasing number of studies show that aberrant expression and activity of GRKs in the cardiovascular system and kidney inhibit or stimulate GPCRs (e.g., dopamine receptors, Ang II receptors, and α- and β-adrenergic receptors), resulting in hypertension. Current studies focus on the effect of selective GRK inhibitors in cardiovascular diseases, including hypertension. Moreover, genetic studies show that GRK gene variants are associated with essential hypertension, blood pressure response to antihypertensive medicines, and adverse cardiovascular outcomes of antihypertensive treatment. In this review, we present a comprehensive overview of GRK-mediated regulation of blood pressure, role of GRKs in the pathogenesis of hypertension, and highlight potential strategies for the treatment of hypertension. Schematic representation of GPCR desensitization process. Activation of GPCRs begins with the binding of an agonist to its corresponding receptor. Then G proteins activate downstream effectors that are mediated by various signaling pathways. GPCR signaling is halted by GRK-mediated receptor phosphorylation, which causes receptor internalization through β-arrestin.

The role of the brain renin-angiotensin system in Parkinson´s disease

The renin-angiotensin system (RAS) was classically considered a circulating hormonal system that regulates blood pressure. However, different tissues and organs, including the brain, have a local paracrine RAS. Mutual regulation between the dopaminergic system and RAS has been observed in several tissues. Dysregulation of these interactions leads to renal and cardiovascular diseases, as well as progression of dopaminergic neuron degeneration in a major brain center of dopamine/angiotensin interaction such as the nigrostriatal system. A decrease in the dopaminergic function induces upregulation of the angiotensin type-1 (AT1) receptor activity, leading to recovery of dopamine levels. However, AT1 receptor overactivity in dopaminergic neurons and microglial cells upregulates the cellular NADPH-oxidase-superoxide axis and Ca2+ release, which mediate several key events in oxidative stress, neuroinflammation, and α-synuclein aggregation, involved in Parkinson's disease (PD) pathogenesis. An intraneuronal antioxidative/anti-inflammatory RAS counteracts the effects of the pro-oxidative AT1 receptor overactivity. Consistent with this, an imbalance in RAS activity towards the pro-oxidative/pro-inflammatory AT1 receptor axis has been observed in the substantia nigra and striatum of several animal models of high vulnerability to dopaminergic degeneration. Interestingly, autoantibodies against angiotensin-converting enzyme 2 and AT1 receptors are increased in PD models and PD patients and contribute to blood-brain barrier (BBB) dysregulation and nigrostriatal pro-inflammatory RAS upregulation. Therapeutic strategies addressed to the modulation of brain RAS, by AT1 receptor blockers (ARBs) and/or activation of the antioxidative axis (AT2, Mas receptors), may be neuroprotective for individuals with a high risk of developing PD or in prodromal stages of PD to reduce progression of the disease.

Angiotensin II-stimulated proximal nephron superoxide production and fructose-induced salt-sensitive hypertension

Angiotensin II (ANG II) increases proximal tubule superoxide (O2-) production more in rats fed a 20% fructose normal-salt diet compared with rats fed a 20% glucose normal-salt diet. A 20% fructose high-salt diet (FHS) increases systolic blood pressure (SBP), whereas a 20% glucose high-salt diet (GHS) does not. However, it is unclear whether FHS enhances ANG II-induced oxidative stress in proximal tubules and whether this contributes to increases in blood pressure in this model. We hypothesized that FHS augments the ability of ANG II to stimulate O2- production by proximal tubules, and this contributes to fructose-induced salt-sensitive hypertension. We measured SBP in male Sprague-Dawley rats fed FHS and GHS and determined the effects of 3 mM tempol and 50 mg/kg losartan for 7 days. We then measured basal and ANG II-stimulated (3.7 × 10-8 M) O2- production by proximal tubule suspensions and the role of protein kinase C. FHS increased SBP by 27 ± 5 mmHg (n = 6, P < 0.006) but GHS did not. Rats fed FHS + tempol and GHS + tempol showed no significant increases in SBP. ANG II increased O2- production by 11 ± 1 relative light units/µg protein/s in proximal tubules from FHS-fed rats (n = 6, P < 0.05) but not in tubules from rats fed GHS. ANG II did not significantly stimulate O2- production by proximal tubules from rats fed FHS + tempol or FHS + losartan. The protein kinase C inhibitor Gö6976 blunted ANG II-stimulated O2- production. In conclusion, FHS enhances the sensitivity of proximal tubule O2- production to ANG II, and this contributes to fructose-induced salt-sensitive hypertension.NEW & NOTEWORTHY A diet containing amounts of fructose consumed by 17 million Americans causes salt-sensitive hypertension. Oxidative stress is an initiating cause of this model of fructose-induced salt-sensitive hypertension increasing blood pressure. This salt-sensitive hypertension is prevented by losartan and thus is angiotensin II (ANG II) dependent. Fructose-induced salt-sensitive hypertension depends on ANG II stimulating oxidative stress in the proximal tubule. A fructose/high-salt diet augments the ability of ANG II to stimulate proximal tubule O2- via protein kinase C.

Paeonol improves renal and vascular angiotensin II type 1 receptor function via inhibiting oxidative stress in spontaneously hypertensive rats

BACKGROUND

Oxidative stress has been shown to play a critical role in the pathogenesis of hypertension. Paeonol, a major phenolic component extracted from Moutan Cortex, exerts a beneficial effect in preventing cardiovascular disease via reducing oxidative stress. The present study investigated the protective mechanism of paeonol against high blood pressure in spontaneous hypertension rats (SHRs).

METHODS

Wistar-Kyoto (WKY) rats and SHRs received vehicle or peaonol in the drinking water for 5 weeks. Blood pressure was measured by tail-cuff plethysmography and oxidative stress in kidney and vascular tissue was examined by enzyme-linked immunosorbed assay. The functions of angiotensin II type 1 receptors (AT₁R) in the kidney and mesenteric artery were measured by natriuresis and vasoconstrictor response, respectively.

RESULTS

Compared with vehicle-treated WKY rats, vehicle-treated SHRs exhibited higher blood pressure, increased oxidative stress, accompanied by exaggerated diuretic and natriuretic responses to candesartan (AT₁ receptor antagonist) and vasoconstrictor responses to angiotensin II (Ang II). Moreover, SHRs had higher ACE and AT₁R in the kidney and mesenteric artery, and higher Ang II and lower renin levels. Interestingly, paeonol treatment reduced the candesartan-induced increase in diuresis and natriuresis and vasoconstrictor responses to Ang II, and lowered blood pressure in SHRs, accompanied by reducing AT₁R protein expression in the kidney and mesenteric artery of SHR, and Ang II levels in plasma and increasing renin levels in renal cortex. In addition, these changes were associated with reducing oxidative stress.

CONCLUSIONS

The present study suggests that paeonol improves renal and vascular AT₁R functions by inhibition of oxidative stress, thus lowering blood pressure in SHRs.

The low dopamine hypothesis: A plausible mechanism underpinning residual urine, overactive bladder and nocturia (RON) syndrome in older patients

INTRODUCTION

Aging is associated with a combination of several lower urinary tract (LUT) signs and symptoms, including residual urine, overactive bladder and nocturia. One of the mechanisms of this LUT dysfunction that has not been discussed in dept so far is the role of dopamine (DA).

METHODS

In this narrative review, we explore the dopaminergic hypothesis in the development of this combination of LUT signs and symptoms in older adults.

RESULTS

DA is one of the neurotransmitters whose regulation and production is disrupted in aging. In synucleinopathies, altered DAergic activity is associated with the occurrence of LUTS and sleep disorders. Projections of DAergic neurons are involved in the regulation of sleep, diuresis, and bladder activity. The low dopamine hypothesis could explain the genesis of a set of LUT signs and symptoms commonly seen in this population, including elevated residual urine, Overactive bladder syndrome and Nocturia (discussed as the RON syndrome). This presentation is however also common in older patients without synucleinopathies or neurological disorders and therefore we hypothesise that altered DAergic activity because of pathological aging, and selective destruction of DAergic neurons, could underpin the presentation of this triad of LUT dysfunction in the older population.

CONCLUSION

The concept of RON syndrome helps to better understand this common phenotypic presentation in clinical practice, and therefore serves as a useful platform to diagnose and treat LUTS in older adults. Besides recognizing the synucleinopathy "red flag" symptoms, this set of multi-causal LUT signs and symptoms highlights the inevitable need for combination therapy, a challenge in older people with their comorbidities and concomitant medications.

Comprehensive insights in GRK4 and hypertension: From mechanisms to potential therapeutics

G protein-coupled receptors (GPCRs) mediate cellular responses to diverse extracellular stimuli that play vital roles in the regulation of biology, including behavior. Abnormal G protein-coupled receptor kinase (GRK)-mediated regulation of GPCR function is involved in the pathogenesis of hypertension. Among the seven GRK subtypes, GRK4 has attracted attention because of its constitutive activity and tissue-specific expression. Increasing number of studies show that GRK4 affects blood pressure by GPCR-mediated regulation of renal and arterial function. The target receptor of GRK4 is confined not only to GPCRs, but also to other blood pressure-regulating receptors, such as the adiponectin receptor. Genetic studies in humans show that in several ethnic groups, GRK4 gene variants (R65L, A142V, and A486V) are associated with salt-sensitive or salt-resistant essential hypertension and blood pressure responses to antihypertensive medicines. In this article, we present a comprehensive overview of GRK-mediated regulation of blood pressure, focusing on the latest research progress on GRK4 and hypertension and highlighting potential and novel strategies for the prevention and treatment of hypertension.

Renal Dopamine Receptors and Oxidative Stress: Role in Hypertension

Significance: The kidney plays an important role in the long-term control of blood pressure. Oxidative stress is one of the fundamental mechanisms responsible for the development of hypertension. Dopamine, via five subtypes of receptors, plays an important role in the control of blood pressure by various mechanisms, including the inhibition of oxidative stress. Recent Advances: Dopamine receptors exert their regulatory function to decrease the oxidative stress in the kidney and ultimately maintain normal sodium balance and blood pressure homeostasis. An aberration of this regulation may be involved in the pathogenesis of hypertension. Critical Issues: Our present article reviews the important role of oxidative stress and intrarenal dopaminergic system in the regulation of blood pressure, summarizes the current knowledge on renal dopamine receptor-mediated antioxidation, including decreasing reactive oxygen species production, inhibiting pro-oxidant enzyme nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase, and stimulating antioxidative enzymes, and also discusses its underlying mechanisms, including the increased activity of G protein-coupled receptor kinase 4 (GRK4) and abnormal trafficking of renal dopamine receptors in hypertensive status. Future Directions: Identifying the mechanisms of renal dopamine receptors in the regulation of oxidative stress and their contribution to the pathogenesis of hypertension remains an important research focus. Increased understanding of the role of reciprocal regulation between renal dopamine receptors and oxidative stress in the regulation of blood pressure may give us novel insights into the pathogenesis of hypertension and provide a new treatment strategy for hypertension.

The intracellular renin-angiotensin system: Friend or foe. Some light from the dopaminergic neurons

The renin-angiotensin system (RAS) is one of the oldest hormone systems in vertebrate phylogeny. RAS was initially related to regulation of blood pressure and sodium and water homeostasis. However, local or paracrine RAS were later identified in many tissues, including brain, and play a major role in their physiology and pathophysiology. In addition, a major component, ACE2, is the entry receptor for SARS-CoV-2. Overactivation of tissue RAS leads several oxidative stress and inflammatory processes involved in aging-related degenerative changes. In addition, a third level of RAS, the intracellular or intracrine RAS (iRAS), with still unclear functions, has been observed. The possible interaction between the intracellular and extracellular RAS, and particularly the possible deleterious or beneficial effects of the iRAS activation are controversial. The dopaminergic system is particularly interesting to investigate the RAS as important functional interactions between dopamine and RAS have been observed in the brain and several peripheral tissues. Our recent observations in mitochondria and nucleus of dopaminergic neurons may clarify the role of the iRAS. This may be important for the developing of new therapeutic strategies, since the effects on both extracellular and intracellular RAS must be taken into account, and perhaps better understanding of COVID-19 cell mechanisms.

Vascular Aging and Central Aortic Blood Pressure: From Pathophysiology to Treatment

Large conductive arteries undergo to structural modifications by aging, eventually leading to increased vascular stiffness. As consequence, cardiovascular hemodynamic changes by increasing central blood pressure which may be also associated to the remodelling of peripheral resistance arteries that contribute to increase further the central vascular stiffness and blood pressure. These modifications resemble the ones that has been shown in essential hypertension, thus a condition of "early vascular aging" has been described in hypertensive patients. Since hypertension related target organs, particularly the heart, face aortic blood pressure rather than brachial blood pressure, it has been recently suggested that central blood pressure and other parameters of large arteries' stiffness, including pulse wave velocity (PWV), may better correlate with subclinical organ damage and might be useful to assess the cardiovascular risk of patients beyond the traditional risk factors. Different devices have been validated to measure central blood pressure and PWV, and are currently available for clinical use. The increasing application of these tools in clinical practice could improve the management of hypertensive patients by better defining the cardiovascular risk and address the antihypertensive therapy.

Sodium-hydrogen exchanger regulatory factor-1 (NHERF1) confers salt sensitivity in both male and female models of hypertension in aging

Hypertension is a risk factor for premature death and roughly 50% of hypertensive patients are salt-sensitive. The incidence of salt-sensitive hypertension increases with age. However, the mechanisms of salt-sensitive hypertension are not well understood. We had demonstrated decreased renal sodium‑hydrogen exchanger regulatory factor 1 (NHERF1) expression in old salt-resistant F344 rats. Based on those studies we hypothesized that NHERF1 expression is required for the development of some forms of salt-sensitive hypertension. To address this hypothesis, we measured blood pressure in NHERF1 expressing salt-sensitive 4-mo and 24-mo-old male and female Fischer Brown Norway (FBN) rats male and female 18-mo-old NHERF1 knock-out (NHERF1-/-) mice and wild-type (WT) littermates on C57BL/6J background after feeding high salt (8% NaCl) diet for 7 days. Our data demonstrate that 8% salt diet increased blood pressure in both male and female 24-mo-old FBN rats but not in 4-mo-old FBN rats and in 18-mo-old male and female WT mice but not in NHERF1-/- mice. Renal dopamine 1 receptor (D1R) expression was decreased in 24-mo-old rats, compared with 4-mo-old FBN rats. However, sodium chloride cotransporter (NCC) expression increased in 24-mo-old FBN rats. In FBN rats, age had no effect on NaK ATPase α1 and NKCC2 expression. By contrast, high salt diet increased the renal expressions of NKCC2, and NCC in 24-mo-old FBN rats. High salt diet also increased NKCC2 and NCC expression in WT mice but not NHERF1-/- mice. Our data suggest that renal NHERF1 expression confers salt sensitivity with aging, associated with increased expression of sodium transporters.

Exposure to graphene nanoparticles induces changes in measures of vascular/renal function in a load and form-dependent manner in mice

Graphenes isolated from crystalline graphite are used in several industries. Employees working in the production of graphenes may be at risk of developing respiratory problems attributed to inhalation or contact with particulate matter (PM). However, graphene nanoparticles might also enter the circulation and accumulate in other organs. The aim of this study was to examine how different forms of graphene affect peripheral vascular functions, generation of reactive oxygen species (ROS) and changes in gene expression that may be indicative of cardiovascular and/or renal dysfunction. In the first investigation, different doses of graphene nanoplatelets were administered to mice via oropharyngeal aspiration. These effects were compared to those of dispersion medium (DM) and carbon black (CB). Gene expression alterations were observed in the heart for CB and graphene; however, only CB produced changes in peripheral vascular function. In the second study, oxidized forms of graphene were administered. Both oxidized forms increased the sensitivity of peripheral blood vessels to adrenoreceptor-mediated vasoconstriction and induced changes in ROS levels in the heart. Based upon the results of these investigations, exposure to graphene nanoparticles produced physiological and alterations in ROS and gene expression that may lead to cardiovascular dysfunction. Evidence indicates that the effects of these particles may be dependent upon dose and graphene form to which an individual may be exposed to.

Genetic polymorphisms associated with reactive oxygen species and blood pressure regulation

Hypertension is the most prevalent cause of cardiovascular disease and kidney failure, but only about 50% of patients achieve adequate blood pressure control, in part, due to inter-individual genetic variations in the response to antihypertensive medication. Significant strides have been made toward the understanding of the role of reactive oxygen species (ROS) in the regulation of the cardiovascular system. However, the role of ROS in human hypertension is still unclear. Polymorphisms of some genes involved in the regulation of ROS production are associated with hypertension, suggesting their potential influence on blood pressure control and response to antihypertensive medication. This review provides an update on the genes associated with the regulation of ROS production in hypertension and discusses the controversies on the use of antioxidants in the treatment of hypertension, including the antioxidant effects of antihypertensive drugs.

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.

Exposure to Maternal Diabetes Mellitus Causes Renal Dopamine D1 Receptor Dysfunction and Hypertension in Adult Rat Offspring

Epidemiological and experimental studies suggest that maternal diabetes mellitus programs hypertension that is associated with impaired sodium excretion in the adult offspring. However, the underlying mechanisms are not clear. Because dopamine receptor function is involved in the pathogenesis of hypertension, we hypothesized that impaired renal dopamine D1 receptor function is also involved in the hypertension in offspring of maternal diabetes mellitus. Maternal diabetes mellitus was induced by a single intraperitoneal injection of streptozotocin (35 mg/kg) to pregnant Sprague-Dawley rats at day 0 of gestation. Compared with the offspring of mothers injected with citrate buffer (control mother offspring), the diabetic mother offspring (DMO) had increased systolic blood pressure and impaired D1 receptor-mediated diuresis and natriuresis, accompanied by increased renal PKC (protein kinase C) expression and activity, GRK-2 (G protein-coupled receptor kinase-2) expression, D1 receptor phosphorylation, D1 receptor/Gαs uncoupling, and loss of D1 receptor-mediated inhibition of Na+-K+-ATPase activity in renal proximal tubule cells from DMO. Inhibition of PKC reduced the increased GRK-2 expression and normalized D1 receptor function in primary cultures of renal proximal tubule cells from DMO. In addition, DMO, relative to control mother offspring, in vivo, had increased oxidative stress, indicated by decreased renal glutathione and increased renal malondialdehyde and urine 8-isoprostane. Normalization of oxidative stress with tempol also normalized the renal D1 receptor phosphorylation, D1 receptor-mediated diuresis and natriuresis, and blood pressure in DMO. Our present study indicates that maternal diabetes mellitus-programed hypertension in the offspring is caused by impaired renal D1 receptor function because of oxidative stress that is mediated by increased PKC-GRK-2 activity.

Superoxide via Sp3 mechanism increases renal renin activity, renal AT1 receptor function, and blood pressure in rats

We tested a hypothesis that superoxide, by inducing Sp3, increases renal renin activity, renal angiotensin II type 1 receptor (AT1R) function, and blood pressure (BP) in rats. Group 1 rats were treated with vehicle, saline. Group 2 rats were treated with superoxide dismutase (SOD) inhibitor diethylthiocarbamate (DETC). Group 3 rats were treated with DETC and an SOD mimetic, tempol. Group 4 rats were treated with tempol only. All four groups of rats were treated for 2 wk then anesthetized, and BP was recorded. Thereafter, diuresis and natriuresis in response to AT1R blocker candesartan were determined. When compared with vehicle rats, BP increased in DETC rats. The increased BP in DETC rats decreased with tempol. Diuresis and natriuresis in response to candesartan increased in controls, and this further increased in DETC rats and decreased with tempol. A second set of four groups of rats underwent the same treatment as above and were anesthetized, and their kidneys were obtained for biochemical studies. The levels of superoxide but not hydrogen peroxide increased, whereas SOD activities decreased further in the renal cortical tissues of DETC rats than vehicle rats. These effects were attenuated with tempol in DETC rats. Moreover, tissue renin activity and abundance of membranous AT1R proteins increased more in DETC rats than vehicle rats, and decreased with tempol in DETC rats. Furthermore, the levels of lysine-acetylated, but not serine-phosphorylated, Sp3 increased more in the nuclei of DETC rats than vehicle rats. The increased levels of Sp3 lysine acetylation decreased in DETC rats with tempol. Taken together, our results suggest that superoxide activates renal Sp3 via lysine acetylation increasing renin activity, AT1R function, and BP in rats.

In Utero Exposure to Fine Particulate Matter Causes Hypertension Due to Impaired Renal Dopamine D1 Receptor in Offspring

BACKGROUND/AIMS

Adverse environment in utero can modulate adult phenotypes including blood pressure. Fine particulate matter (PM2.5) exposure in utero causes hypertension in the offspring, but the exact mechanisms are not clear. Renal dopamine D1 receptor (D1R), regulated by G protein-coupled receptor kinase type 4 (GRK4), plays an important role in the regulation of renal sodium transport and blood pressure. In this present study, we determined if renal D1R dysfunction is involved in PM2.5-induced hypertension in the offspring.

METHODS

Pregnant Sprague-Dawley rats were given an oropharyngeal drip of PM2.5 (1.0 mg/kg) at gestation day 8, 10, and 12. The blood pressure, 24-hour sodium excretion, and urine volume were measured in the offspring. The expression levels of GRK4 and D1R were determined by immunoblotting. The phosphorylation of D1R was investigated using immunoprecipitation. Plasma malondialdehyde and superoxide dismutase levels were also measured in the offspring.

RESULTS

As compared with saline-treated dams, offspring of PM2.5-treated dams had increased blood pressure, impaired sodium excretion, and reduced D1R-mediated natriuresis and diuresis, accompanied by decreased renal D1R expression and GRK4 expression. The impaired renal D1R function and increased GRK4 expression could be caused by increased reactive oxidative stress (ROS) induced by PM2.5 exposure. Administration of tempol, a redox-cycling nitroxide, for 4 weeks in the offspring of PM2.5-treated dam normalized the decreased renal D1R expression and increased renal D1R phosphorylation and GRK4 expression. Furthermore, tempol normalized the increased renal expression of c-Myc, a transcription factor that regulates GRK4 expression.

CONCLUSIONS

In utero exposure to PM2.5 increases ROS and GRK4 expression, impairs D1R-mediated sodium excretion, and increases blood pressure in the offspring. These studies suggest that normalization of D1R function may be a target for the prevention and treatment of the hypertension in offspring of mothers exposed to PM2.5 during pregnancy.

Mechanisms of altered renal sodium handling in age-related hypertension

The prevalence of hypertension rises with age to approximately two out of three adults over the age of 60 in the United States. Although the mechanisms underlying age-related hypertension are incompletely understood, sodium homeostasis is critical to the long-term regulation of blood pressure and there is strong evidence that aging is associated with alterations in renal sodium handling. This minireview focuses on recent advancements in our understanding of the vascular, neurohumoral, and renal mechanisms that influence sodium homeostasis and promote age-related hypertension.

Aging-related dysregulation in enteric dopamine and angiotensin system interactions: implications for gastrointestinal dysfunction in the elderly

Gastrointestinal dysfunction is a common problem in the elderly. Aging-related changes in interactions between local dopaminergic and renin-angiotensin systems (RAS) have been observed in the brain, renal and vascular tissues. However, it is not known if these interactions also occur in the gut, and are dysregulated with aging. We showed a mutual regulation between the colonic dopaminergic system and RAS using young and aged mice deficient for major angiotensin and dopamine receptors. Aged rats showed a marked decrease in colonic dopamine D2 receptor expression, together with an increase in angiotensin type 1 (AT1) receptor expression, a decrease in angiotensin type 2 (AT2) receptor expression (i.e. an increase in the RAS pro-inflammatory arm activity), and increased levels of inflammatory and oxidative markers. Aged rats also showed increased levels of colonic dopamine and noradrenalin, and a marked decrease in acetylcholine and serotonin levels. The present observations contribute to explain an aging-related pro-inflammatory state and dysregulation in gastrointestinal function, which may be counteracted by treatment of aged animals with the AT1 receptor blocker candesartan.

Long-Term Exposure of Fine Particulate Matter Causes Hypertension by Impaired Renal D1 Receptor-Mediated Sodium Excretion via Upregulation of G-Protein-Coupled Receptor Kinase Type 4 Expression in Sprague-Dawley Rats

BACKGROUND

Epidemiological evidence supports an important association between air pollution exposure and hypertension. However, the mechanisms are not clear.

METHODS AND RESULTS

Our present study found that long-term exposure to fine particulate matter (PM2.5) causes hypertension and impairs renal sodium excretion, which might be ascribed to lower D1 receptor expression and higher D1 receptor phosphorylation, accompanied with a higher G-protein-coupled receptor kinase type 4 (GRK4) expression. The in vivo results were confirmed in in vitro studies (ie, PM2.5 increased basal and decreased D1 receptor mediated inhibitory effect on Na+-K+ ATPase activity, decreased D1 receptor expression, and increased D1 receptor phosphorylation in renal proximal tubule cells). The downregulation of D1 receptor expression and function might be attributable to a higher GRK4 expression after the exposure of renal proximal tubule cells to PM2.5, because downregulation of GRK4 by small-interfering RNA reversed the D1 receptor expression and function. Because of the role of reactive oxygen species on D1 receptor dysfunction and its relationship with air pollution exposure, we determined plasma reactive oxygen species and found the levels higher in PM2.5-treated Sprague-Dawley rats. Inhibition of reactive oxygen species by tempol (4-hydroxy-2,2,6,6-tetramethylpiperidin-1-oxyl) reduced blood pressure and increased sodium excretion in PM2.5-treated Sprague-Dawley rats, accompanied by an increase in the low D1 receptor expression, and decreased the hyperphosphorylated D1 receptor and GRK4 expression.

CONCLUSIONS

Our present study indicated that long-term exposure of PM2.5 increases blood pressure by decreasing D1 receptor expression and function; reactive oxygen species, via regulation of GRK4 expression, plays an important role in the pathogenesis of PM2.5-induced hypertension.

Dopamine reduces cell surface Na+/H+ exchanger-3 protein by decreasing NHE3 exocytosis and cell membrane recycling

The intrarenal autocrine-paracrine dopamine (DA) system mediates a significant fraction of the natriuresis in response to a salt load. DA inhibits a number of Na⁺ transporters to effect sodium excretion, including the proximal tubule Na⁺/H⁺ exchanger-3 (NHE3). DA represent a single hormone that regulates NHE3 at multiple levels, including translation, degradation, endocytosis, and protein phosphorylation. Because cell surface NHE3 protein is determined by the balance between exocytotic insertion and endocytotic retrieval, we examined whether DA acutely affects the rate of NHE3 exocytosis in a cell culture model. DA inhibited NHE3 exocytosis at a dose-dependent manner with a half maximal around 10^-6 M. The DA effect on NHE3 exocytosis was blocked by inhibition of protein kinase A and by brefeldin A, which inhibits endoplasmic reticulum-to-Golgi transport. NHE3 directly interacts with the ε-subunit of coatomer protein based on yeast-two-hybrid and coimmunoprecipitation. Because NHE3 has been shown to be recycled back to the cell membrane after endocytosis, we measured NHE3 recycling using a biochemical reinsertion assay and showed that reinsertion of NHE3 back to the membrane is also inhibited by DA. In conclusion, among the many mechanisms by which DA reduces apical membrane NHE3 and induces proximal tubule natriuresis, one additional mechanism is inhibition of exocytotic insertion and reinsertion of NHE3 in the apical cell surface.

Protein disulfide isomerase regulates renal AT1 receptor function and blood pressure in rats

The role and mechanism of renal protein disulfide isomerase (PDI) in blood pressure regulation has not been tested before. Here, we test this possibility in Sprague-Dawley rats. Rats were treated with PDI inhibitor bacitracin (100 mg·kg^-1 ip·day^-1 for 14 days), and then blood pressure and renal angiotensin II type 1 (AT₁) receptor function were determined in anesthetized rats. Renal AT₁ receptor function was determined as the ability of candesartan (an AT₁ receptor blocker) to increase diuresis and natriuresis. A second set of vehicle- and bacitracin-treated rats was used to determine biochemical parameters. Systolic blood pressure as well as diastolic blood pressure increased in bacitracin-treated compared with vehicle-treated rats. Compared with vehicle, bacitracin-treated rats showed increased diuresis and natriuresis in response to candesartan (10-µg iv bolus dose) suggesting higher AT₁ receptor function in these rats. These were associated with higher renin activities in the plasma and renal tissues. Furthermore, urinary 8-isoprostane and kidney injury molecule-1 levels were higher and urinary antioxidant capacity was lower in bacitracin-treated rats. Renal protein carbonyl and nitrotyrosine levels also were higher in bacitracin- compared with vehicle-treated rats, suggesting oxidative stress burden in bacitracin-treated rats. Moreover, PDI activity decreased and its protein levels increased in renal tissues of bacitracin-treated rats. Also, nuclear levels of Nrf2 transcription factor, which regulates redox homeostasis, were decreased in bacitracin-treated rats. Furthermore, tissue levels of Keap1, an Nrf2 inhibitory molecule, and tyrosine 216-phosphorylated GSK3β protein, an Nrf2 nuclear export protein, were increased in bacitracin-treated rats. These results suggest that renal PDI by regulating Keap1-Nrf2 pathway acts as an antioxidant, maintaining redox balance, renal AT₁ receptor function, and blood pressure in rats.

QGQS Granule in SHR Serum Metabonomics Study Based on Tools of UPLC-Q-TOF and Renin-Angiotensin-Aldosterone System Form Protein Profilin-1

QGQS granule is effective for the therapeutic of hypertension in clinic. The aim of this research is to observe the antihypertension effect of QGQS granule on SHR and explain the mechanism of its lowering blood pressure. 30 SHR were selected as model group, captopril group, and QGQS group, 10 WKYr were used as control group, and RBP were measured on tail artery consciously. And all the serum sample analysis was carried out on UPLC-TOF-MS system to determine endogenous metabolites and to find the metabonomics pathways. Meanwhile, ELISA kits for the determination pharmacological indexes of PRA, AngI, AngII, and ALD were used for pathway confirmatory; WB for determination of profilin-1 protein expression was conducted for Ang II pathway analysis as well. It is demonstrated that QGQS granule has an excellent therapeutic effect on antihypertension, which exerts effect mainly on metabonomics pathway by regulating glycerophospholipid, sphingolipid, and arachidonic acid metabolism, and it could inhibit the overexpression of the profilin-1 protein. We can come to a conclusion that RAAS should be responsible mainly for the metabonomics pathway of QGQS granule on antihypertension, and it plays a very important role in protein of profilin-1 inhibition.

Superoxide increases angiotensin II AT1 receptor function in human kidney-2 cells

The redox-sensitive Sp family transcription factor has been linked to the regulation of angiotensin II type 1 receptor (AT1R). However, the exact mechanism of AT1R regulation in renal cells is poorly understood. We tested the specificity of reactive oxygen species (ROS), superoxide vs. hydrogen peroxide (H₂O₂), and the specific role of Sp3 transcription factor, if any, in the regulation of AT1R in human kidney cells (HK2 cells). Superoxide dismutase (SOD) inhibitor diethyldithiocarbamate (DETC), but not H₂O₂ treatment, increased fluorescence levels of superoxide probe dihydroethidium (DHE). H₂O_2, but not DETC, treatment increased the fluorescence of the H₂O₂-sensitive probe dichloro-dihydro-fluorescein (DCFH). These data suggest that SOD inhibition by DETC increases the superoxide but not H₂O₂ and exogenously added H₂O₂ is not converted to superoxide in renal cells. Furthermore, DETC, but not H₂O₂, treatment increased nuclear accumulation of Sp3, which was attenuated with the superoxide dismutase (SOD)-mimetic tempol. DETC treatment also increased AT1R mRNA and protein levels that were attenuated with tempol, whereas H₂O₂ did not have any effects on AT1R mRNA. Moreover, Sp3 overexpression increased, while Sp3 depletion by siRNA decreased, protein levels of AT1R. In addition, Sp3 siRNA in the presence of DETC decreased AT1R protein expression. Furthermore, DETC treatment increased the levels of cell surface AT1R as measured by biotinylation and immunofluorescence studies. Angiotensin II increased PKC activity in vehicle-treated cells that further increased in DETC-treated cells, which was attenuated by AT1R blocker candesartan and SOD-mimetic tempol. Taken together, our results suggest that superoxide, but not H₂O₂, via Sp3 up-regulates AT1R expression and function in the renal cells.

Noncoding RNA Regulation of Dopamine Signaling in Diseases of the Central Nervous System

Dopaminergic neurotransmission mediates a majority of the vital central nervous system functions. Disruption of these synaptic events provokes a multitude of neurological pathologies, including Parkinson's, schizophrenia, depression, and addiction. Growing evidence supports a key role for noncoding RNA (ncRNA) regulation in the synapse. This review will discuss the role of both short and long ncRNAs in dopamine signaling, including bioinformatic examination of the pathways they target. Specifically, we focus on the contribution of ncRNAs to dopaminergic dysfunction in neurodegenerative as well as psychiatric disease.

Grape Powder Improves Age-Related Decline in Mitochondrial and Kidney Functions in Fischer 344 Rats

We examined the effects and mechanism of grape powder- (GP-) mediated improvement, if any, on aging kidney function. Adult (3-month) and aged (21-month) Fischer 344 rats were treated without (controls) and with GP (1.5% in drinking water) and kidney parameters were measured. Control aged rats showed higher levels of proteinuria and urinary kidney injury molecule-1 (KIM-1), which decreased with GP treatment in these rats. Renal protein carbonyls (protein oxidation) and gp^91phox-NADPH oxidase levels were high in control aged rats, suggesting oxidative stress burden in these rats. GP treatment in aged rats restored these parameters to the levels of adult rats. Moreover, glomerular filtration rate and sodium excretion were low in control aged rats suggesting compromised kidney function, which improved with GP treatment in aged rats. Interestingly, low renal mitochondrial respiration and ATP levels in control aged rats were associated with reduced levels of mitochondrial biogenesis marker MtTFA. Also, Nrf2 proteins levels were reduced in control aged rats. GP treatment increased levels of MtTFA and Nrf2 in aged rats. These results suggest that GP by potentially regulating Nrf2 improves aging mitochondrial and kidney functions.

Gut microbiota in hypertension

PURPOSE OF REVIEW

Hypertension, which is present in about one quarter of the world's population, is responsible for about 41% of the number one cause of death - cardiovascular disease. Not included in these statistics is the effect of sodium intake on blood pressure, even though an increase or a marked decrease in sodium intake can increase blood pressure. This review deals with the interaction of gut microbiota and the kidney with genetics and epigenetics in the regulation of blood pressure and salt sensitivity.

RECENT FINDINGS

The abundance of the gut microbes, Firmicutes and Bacteroidetes, is associated with increased blood pressure in several models of hypertension, including the spontaneously hypertensive and Dahl salt-sensitive rats. Decreasing gut microbiota by antibiotics can increase or decrease blood pressure that is influenced by genotype. The biological function of probiotics may also be a consequence of epigenetic modification, related, in part, to microRNA. Products of the fermentation of nutrients by gut microbiota can influence blood pressure by regulating expenditure of energy, intestinal metabolism of catecholamines, and gastrointestinal and renal ion transport, and thus, salt sensitivity.

SUMMARY

The beneficial or deleterious effect of gut microbiota on blood pressure is a consequence of several variables, including genetics, epigenetics, lifestyle, and intake of antibiotics. These variables may influence the ultimate level of blood pressure and control of hypertension.

Structural equation modeling identifies markers of damage and function in the aging male Fischer 344 rat

The male Fischer 344 rat is an established model to study progressive renal dysfunction that is similar, but not identical, to chronic kidney disease (CKD) in humans. These studies were designed to assess age-dependent alterations in renal structure and function at late-life timepoints, 16-24 months. Elevations in BUN and plasma creatinine were not significant until 24 months, however, elevations in the more sensitive markers of function, plasma cystatin C and proteinuria, were detectable at 16 and 18 months, respectively. Interestingly, cystatin C levels were not corrected by caloric restriction. Urinary Kim-1, a marker of CKD, was elevated as early as 16 months. Klotho gene expression was significantly decreased at 24 months, but not at earlier timepoints. Alterations in renal structure, glomerulosclerosis and tubulointerstitial fibrosis, were noted at 16 months, with little change from 18 to 24 months. Tubulointerstitial inflammation was increased at 16 months, and remained similar from 18 to 24 months. A SEM (structural equation modeling) model of age-related renal dysfunction suggests that proteinuria is a marker of renal damage, while urinary Kim-1 is a marker of both damage and function. Taken together, these results demonstrate that age-dependent nephropathy begins as early as 16 months and progresses rapidly over the next 8 months.

Human GRK4γ142V Variant Promotes Angiotensin II Type I Receptor-Mediated Hypertension via Renal Histone Deacetylase Type 1 Inhibition

The influence of a single gene on the pathogenesis of essential hypertension may be difficult to ascertain, unless the gene interacts with other genes that are germane to blood pressure regulation. G-protein-coupled receptor kinase type 4 (GRK4) is one such gene. We have reported that the expression of its variant hGRK4γ(142V) in mice results in hypertension because of impaired dopamine D1 receptor. Signaling through dopamine D1 receptor and angiotensin II type I receptor (AT1R) reciprocally modulates renal sodium excretion and blood pressure. Here, we demonstrate the ability of the hGRK4γ(142V) to increase the expression and activity of the AT1R. We show that hGRK4γ(142V) phosphorylates histone deacetylase type 1 and promotes its nuclear export to the cytoplasm, resulting in increased AT1R expression and greater pressor response to angiotensin II. AT1R blockade and the deletion of the Agtr1a gene normalize the hypertension in hGRK4γ(142V) mice. These findings illustrate the unique role of GRK4 by targeting receptors with opposite physiological activity for the same goal of maintaining blood pressure homeostasis, and thus making the GRK4 a relevant therapeutic target to control blood pressure.

Antihypertensive mechanisms of intra-renal dopamine

PURPOSE OF REVIEW

This review will highlight recent findings concerning the regulation and signalling of the intrarenal dopaminergic system and the emerging evidence for its importance in blood pressure regulation.

RECENT FINDINGS

There is an increasing evidence that the intrarenal dopaminergic system plays an important role in the regulation of blood pressure, and defects in dopamine signalling appear to be involved in the development of hypertension. Recent experimental models have definitively demonstrated that abnormalities in intrarenal dopamine production or receptor signalling can predispose to salt-sensitive hypertension and a dysregulated renin-angiotensin system. There are also new results indicating the importance of dopamine receptor mediated regulation of salt and water homeostasis along the nephron, and new studies indicating the role that the intrarenal dopaminergic system plays to mitigate the production of reactive oxygen species and progression of chronic renal disease.

SUMMARY

New studies underscore the importance of the intrarenal dopaminergic system in the regulation of renal function and indicate how alterations in dopamine production or signalling may underlie the development of hypertension and kidney injury.

Regulation of blood pressure, oxidative stress and AT1R by high salt diet in mutant human dopamine D5 receptor transgenic mice

Humans have dopamine D5 receptors (hD5R) with single-nucleotide polymorphisms and a diminished function. We generated hD5(F173L) cDNA that has a decreased response to D5R agonist-mediated increase in cAMP production and increased production of reactive oxygen species, relative to wild-type hD5R (hD5(WT)) cDNA expressed in Chinese hamster ovary cells. To investigate the role of hD5(F173L) in the pathogenesis of salt-sensitive hypertension, we generated transgenic mice overexpressing hD5(F173L) or hD5(WT) and fed them normal (0.8% NaCl) or high (4% NaCl) salt diet. On normal salt diet, the blood pressure, and renal NADPH oxidase activity and angiotensin type 1 receptor (AT1R) expression were higher in hD5(F173L) than hD5(WT) transgenic mice. After 2 weeks on high salt diet, the blood pressure and renal NADPH oxidase activity, but not AT1R expression, were increased in hD5(F173L) but not in hD5(WT) transgenic mice. Candesartan, an AT1R antagonist, decreased the blood pressure and NADPH oxidase activity in hD5(F173L) but not in hD5(WT) transgenic mice. We suggest that the ability of the hD5R to negatively regulate the renal NADPH oxidase activity and AT1R function may have important implications in the pathogenesis of salt-sensitive blood pressure. However, the mechanisms involved in regulating the balance of renal D5R and AT1R function in the oxidative stress-mediated salt-sensitive blood pressure remain to be determined.

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.

Vascular biology of ageing-Implications in hypertension

Ageing is associated with functional, structural and mechanical changes in arteries that closely resemble the vascular alterations in hypertension. Characteristic features of large and small arteries that occur with ageing and during the development of hypertension include endothelial dysfunction, vascular remodelling, inflammation, calcification and increased stiffness. Arterial changes in young hypertensive patients mimic those in old normotensive individuals. Hypertension accelerates and augments age-related vascular remodelling and dysfunction, and ageing may impact on the severity of vascular damage in hypertension, indicating close interactions between biological ageing and blood pressure elevation. Molecular and cellular mechanisms underlying vascular alterations in ageing and hypertension are common and include aberrant signal transduction, oxidative stress and activation of pro-inflammatory and pro-fibrotic transcription factors. Strategies to suppress age-associated vascular changes could ameliorate vascular damage associated with hypertension. An overview on the vascular biology of ageing and hypertension is presented and novel molecular mechanisms contributing to these processes are discussed. The complex interaction between biological ageing and blood pressure elevation on the vasculature is highlighted. This article is part of a Special Issue entitled: CV Ageing.

Age-related hypertension and salt sensitivity are associated with unique cortico-medullary distribution of D1R, AT1R, and NADPH-oxidase in FBN rats

We examined effects of normal (NS) and high salt (HS) on blood pressure (BP) and cortico-medullary distribution of dopamine D1 receptor (D1R), angiotensin AT1 receptor (AT1R), NADPH oxidase-gp(91phox), and sodium transporters (NHE-3, Na, K ATPase) in adult and aged rats. Aged rats fed with NS diet had higher BP, which further increased with HS. HS increased D1R mRNA and protein levels in cortex and medulla of adult rats. NS or HS fed-aged rats had higher AT1R and gp(91phox) mRNA levels in cortex and medulla. Aged rats fed with NS diet had higher gp(91phox) protein levels in cortex. HS diet increased AT1R and gp(91phox) protein levels in medulla of aged rats. Aged rats fed with NS or HS diet had higher NHE-3 protein levels in medulla. HS increased Na, K ATPase protein levels in medulla of aged rats. HS increased urinary kidney injury molecule-1 (KIM-1) but not protein or albumin levels in aged rats. These results suggest that cortical gp(91phox) and medullary NHE-3 contribute to age-related hypertension. Whereas D1R (cortical and medullary) together with medullary AT1R, gp(91phox) and Na, K-ATPase contribute to salt sensitivity in aged rats. And, KIM-1 may be a better marker for kidney damage.

Prenatal lipopolysaccharide exposure results in dysfunction of the renal dopamine D1 receptor in offspring

Adverse environment in early life can modulate the adult phenotype, including blood pressure. Lipopolysaccharide (LPS) exposure in utero results in increased blood pressure in the offspring, but the exact mechanisms are not clear. Studies have shown that the renal dopamine D1 receptor (D1R) plays an important role in maintaining sodium homeostasis and normal blood pressure; dysfunction of D1R is associated with oxidative stress and hypertension. In this study, we determined if dysfunction of the renal D1R is involved in fetal-programmed hypertension, and if oxidative stress contributes to this process. Pregnant Sprague-Dawley (SD) rats were intraperitoneally injected with LPS (0.79 mg/kg) or saline at gestation days 8, 10, and 12. As compared with saline-injected (control) dams, offspring of LPS-treated dams had increased blood pressure, decreased renal sodium excretion, and increased markers of oxidative stress. In addition, offspring of LPS-treated dams had decreased renal D1R expression, increased D1R phosphorylation, and G protein-coupled receptor kinase type 2 (GRK2) and type 4 (GRK4) protein expression, and impaired D1R-mediated natriuresis and diuresis. All of the findings in the offspring of LPS-treated dams were normalized after treatment with TEMPOL, an oxygen free radical scavenger. In conclusion, prenatal LPS exposure, via an increase in oxidative stress, impairs renal D1R function and leads to hypertension in the offspring. Normalization of renal D1R function by amelioration of oxidative stress may be a therapeutic target of fetal programming of hypertension.

Altered signaling pathways linked to angiotensin II underpin the upregulation of renal Na(+)-ATPase in chronically undernourished rats

This study has investigated the participation of altered signaling linked to angiotensin II (Ang II) that could be associated with increased Na(+) reabsorption in renal proximal tubules during chronic undernutrition. A multideficient chow for rats (basic regional diet, BRD) was used, which mimics several human diets widely taken in developing countries. The Vmax of the ouabain-resistant Na(+)-ATPase resident in the basolateral membranes increased >3-fold (P<0.001) accompanied by an increase in Na(+) affinity from 4.0 to 0.2mM (P<0.001). BRD rats had a >3-fold acceleration of the formation of phosphorylated intermediates in the early stage of the catalytic cycle (in the E1 conformation) (P<0.001). Immunostaining showed a huge increase in Ang II-positive cells in the cortical tubulointerstitium neighboring the basolateral membranes (>6-fold, P<0.001). PKC isoforms (α, ε, λ, ζ), Ang II type 1 receptors and PP2A were upregulated in BRD rats (in %): 55 (P<0.001); 35 (P<0.01); 125, 55, 11 and 30 (P<0.001). PKA was downregulated by 55% (P<0.001). With NetPhosK 1.0 and NetPhos 2.0, we detected 4 high-score (>0.70) regulatory phosphorylation sites for PKC and 1 for PKA in the primary sequence of the Na(+)-ATPase α-subunit, which are located in domains that are key for Na(+) binding and catalysis. Therefore, chronic undernutrition stimulates tubulointerstitial activity of Ang II and impairs PKC- and PKA-mediated regulatory phosphorylation, which culminates in an exaggerated Na(+) reabsorption across the proximal tubular epithelium.

Renal molecular mechanisms underlying altered Na+ handling and genesis of hypertension during adulthood in prenatally undernourished rats

In the present study, we investigated the development of hypertension in prenatally undernourished adult rats, including the mechanisms that culminate in dysfunctions of molecular signalling in the kidney. Dams were fed a low-protein multideficient diet throughout gestation with or without α-tocopherol during lactation. The time course of hypertension development followed in male offspring was correlated with alterations in proximal tubule Na+-ATPase activity, expression of angiotensin II (Ang II) receptors, and activity of protein kinases C and A. After the establishment of hypertension, Ang II levels, cyclo-oxygenase 2 (COX-2) and NADPH oxidase subunit expression, lipid peroxidation and macrophage infiltration were examined in renal tissue. Lipid peroxidation in undernourished rats, which was very intense at 60 d, decreased at 90 d and returned to control values by 150 d. During the prehypertensive phase, prenatally undernourished rats exhibited elevated renal Na+-ATPase activity, type 2 Ang II receptor down-regulation and altered protein kinase A:protein kinase C ratio. Stable late hypertension coexisted with highly elevated levels of Ang II-positive cells in the cortical tubulointerstitium, enhanced increase in the expression of p47phox (NADPH oxidase regulatory subunit), marked down-regulation of COX-2 expression, expanded plasma volume and decreased creatinine clearance. These alterations were reduced when the dams were given α-tocopherol during lactation. The offspring of well-nourished dams treated with α-tocopherol exhibited most of the alterations encountered in the offspring of undernourished dams not treated with α-tocopherol. Thus, alterations in proximal tubule Na+ transport, subcellular signalling pathways and reactive oxygen species handling in renal tissue underpin the development of hypertension.

Aging-related dysregulation of dopamine and angiotensin receptor interaction

It is not known whether the aging-related decrease in dopaminergic function leads to the aging-related higher vulnerability of dopaminergic neurons and risk for Parkinson's disease. The renin-angiotensin system (RAS) plays a major role in the inflammatory response, neuronal oxidative stress, and dopaminergic vulnerability via type 1 (AT1) receptors. In the present study, we observed a counterregulatory interaction between dopamine and angiotensin receptors. We observed overexpression of AT1 receptors in the striatum and substantia nigra of young adult dopamine D1 and D2 receptor-deficient mice and young dopamine-depleted rats, together with compensatory overexpression of AT2 receptors or compensatory downregulation of angiotensinogen and/or angiotensin. In aged rats, we observed downregulation of dopamine and dopamine receptors and overexpression of AT1 receptors in aged rats, without compensatory changes observed in young animals. L-Dopa therapy inhibited RAS overactivity in young dopamine-depleted rats, but was ineffective in aged rats. The results suggest that dopamine may play an important role in modulating oxidative stress and inflammation in the substantia nigra and striatum via the RAS, which is impaired by aging.

Depression, anxiety-like behavior and memory impairment are associated with increased oxidative stress and inflammation in a rat model of social stress

In the present study, we have examined the behavioral and biochemical effect of induction of psychological stress using a modified version of the resident-intruder model for social stress (social defeat). At the end of the social defeat protocol, body weights, food and water intake were recorded, depression and anxiety-like behaviors as well as memory function was examined. Biochemical analysis including oxidative stress measurement, inflammatory markers and other molecular parameters, critical to behavioral effects were examined. We observed a significant decrease in the body weight in the socially defeated rats as compared to the controls. Furthermore, social defeat increased anxiety-like behavior and caused memory impairment in rats (P<0.05). Socially defeated rats made significantly more errors in long term memory tests (P<0.05) as compared to control rats. Furthermore, brain extracellular signal-regulated kinase-1/2 (ERK1/2), and an inflammatory marker, interleukin (IL)-6 were activated (P<0.05), while the protein levels of glyoxalase (GLO)-1, glutathione reductase (GSR)-1, calcium/calmodulin-dependent protein kinase type (CAMK)-IV, cAMP-response-element-binding protein (CREB) and brain-derived neurotrophic factor (BDNF) were significantly less (P<0.05) in the hippocampus, but not in the prefrontal cortex and amygdala of socially defeated rats, when compared to control rats. We suggest that social defeat stress alters ERK1/2, IL-6, GLO1, GSR1, CAMKIV, CREB, and BDNF levels in specific brain areas, leading to oxidative stress-induced anxiety-depression-like behaviors and as well as memory impairment in rats.

A high-salt diet further impairs age-associated declines in cognitive, behavioral, and cardiovascular functions in male Fischer brown Norway rats

Aging-associated declines in cognitive, emotional, and cardiovascular function are well known. Environmental stress triggers critical changes in the brain, further compromising cardiovascular and behavioral health during aging. Excessive dietary salt intake is one such stressor. Here, we tested the effect of high salt (HS) on anxiety, learning-memory function, and blood pressure (BP) in male Fischer brown Norway (FBN) rats. Adult (A; 2 mo) and old (O; 20 mo) male rats were fed normal-salt (NS; 0.4% NaCl) or HS (8% NaCl) diets for 4 wk after being implanted with telemeter probes for conscious BP measurement. Thereafter, tests to assess anxiety-like behavior and learning-memory were conducted. The rats were then killed, and samples of plasma, urine, and brain tissue were collected. We found that systolic BP was higher in O-NS (117 ± 1.2 mm Hg) than in A-NS (105 ± 0.8 mm Hg) rats (P < 0.05). Furthermore, BP was higher in O-HS (124 ± 1.4 mm Hg) than in O-NS (117 ± 1.2 mm Hg) rats (P < 0.05). Moreover, anxiety-like behavior (light-dark and open-field tests) was not different between A-NS and O-NS rats but was greater in O-HS rats than in A-NS, O-NS, or A-HS rats (P < 0.05). Short-term memory (radial arm water maze test) was similar in A-NS and O-NS rats but was significantly impaired in O-HS rats compared with A-NS, O-NS, or A-HS rats (P < 0.05). Furthermore, oxidative stress variables (in plasma, urine, and brain) as well as corticosterone (plasma) were greater in O-HS rats when compared with A-NS, O-NS, or A-HS rats (P < 0.05). The antioxidant enzyme glyoxalase-1 expression was selectively reduced in the hippocampus and amygdala of O-HS rats compared with A-NS, O-NS, or A-HS rats (P < 0.05), whereas other antioxidant enzymes, glutathione reductase 1, manganese superoxide dismutase (SOD), and Cu/Zn SOD remained unchanged. We suggest that salt-sensitive hypertension and behavioral derangement are associated with a redox imbalance in the brain of aged FBN rats.

Transcription factor Nrf2 protects renal dopamine D1 receptor function during oxidative stress

The renal dopaminergic system plays a significant role in controlling sodium excretion and blood pressure (BP). Overwhelming evidence shows that oxidative stress downregulates renal dopamine receptors (D1R), and antioxidant supplementation protects D1R function. However, the mechanisms for benefits of antioxidants in protecting D1R function are unknown. We investigated the role of nuclear factor E2-related factor 2 (Nrf2), a redox-sensitive transcription factor, in reducing oxidative stress, protecting renal D1R function and lowering BP in rats. Male Sprague-Dawley rats were treated with L-buthionine-sulfoximine (BSO) and sulforaphane for 4 weeks. Rats treated with BSO exhibited significant increase in oxidative stress and BP. BSO treatment reduced renal D1R expression and abolished SKF38393 (a D1R agonist)-induced Na/K-ATPase and Na/H-exchanger (NHE3) inhibition. Also, in these rats, SKF38393 failed to promote sodium excretion. BSO caused an increase in nuclear factor-κB expression, a modest nuclear translocation of Nrf2 and a moderate activation of phase II antioxidant enzymes. Treatment of rats with sulforaphane alone induced modest activation of Nrf2 and phase II antioxidant enzymes, although having no effect on BP, redox status, or D1R function. However, sulforaphane prevented oxidative stress, protected D1R function, and abrogated hypertension in BSO-treated rats. In these animals, sulforaphane, whereas attenuating nuclear factor-κB activation, caused a robust stimulation of Nrf2 and phase II antioxidant enzyme pathway. In conclusion, oxidative stress via nuclear factor-κB activation downregulated D1R function causing a decrease in sodium excretion, which contributed to an increase in BP. Sulforaphane via activation of Nrf2-phase II antioxidant enzyme pathway mitigated oxidative stress and nuclear factor-κB activation, preserved D1R function, and prevented hypertension.

Human kidney-2 cells harbor functional dopamine D1 receptors that require Giα for Gq/11α signaling

A recent study demonstrated that the dopamine D1 receptor (D1R) is nonfunctional in human kidney cells, HK2 cells, in terms of their inability to couple to Gs protein in response to the D1R agonist fenoldopam. Since D1R also couples to Gq protein, we tested whether D1R is functional in HK2 cells in terms of their ability to couple to Gq and produce downstream signaling. For comparison, we also studied another receptor, angiotensin II type 1 receptor (AT1R) known to couple to Gq. Protein kinase C (PKC) and (86)rubidium transport activities were determined as surrogate downstream signaling markers. Fenoldopam and angiotensin II increased PKC activity, which decreased in the presence of respective receptor antagonists (SCH23390 for D1R; candesartan for AT1R), PKC (chelerythrine chloride) and Gi protein (pertussis toxin) inhibitors and Gq/11α siRNA. Furthermore, fenoldopam and angiotensin II increased (35)S-GTPγS binding, an index of receptor-G protein coupling, which decreased with pertussis toxin and in Gq/11α-depleted cells. Also, fenoldopam-mediated inhibition of (86)rubidium transport (an index of Na-K-ATPase activity) was attenuated with SCH23390, chelerythrine chloride, pertussis toxin, and Gq/11α siRNA. Moreover, fenoldopam caused a decrease in cytosolic and increase in membranous abundance of Gq/11α. The immunoprecipitated levels of Gq/11α in the membranes were greater in fenoldopam-treated cells, and Giα coimmunoprecipitated with Gq/11α. Our results suggest that both D1R and AT1R are functional in HK2 cells, enabling Gq-mediated downstream signaling in a Gi dependent manner.

Smooth muscle cell mineralocorticoid receptors: role in vascular function and contribution to cardiovascular disease

The mineralocorticoid receptor (MR), a member of the steroid receptor family, regulates blood pressure by mediating the effects of the hormone aldosterone on renal sodium handling. In recent years, it has become clear that MR is expressed in vascular smooth muscle cells (SMCs), and interest has grown in understanding the direct role of SMC MR in regulating vascular function. This interest stems from multiple clinical studies where MR inhibitor treatment reduced the incidence of cardiovascular events and mortality. This review summarizes the most recent advances in our understanding of SMC MR in regulating normal vascular function and in promoting vascular disease. Many new studies suggest a role for SMC MR activation in stimulating vascular contraction and contributing to vessel inflammation, fibrosis, and remodeling. These detrimental vascular effects of MR activation appear to be independent of changes in blood pressure and are synergistic with the presence of endothelial dysfunction or damage. Thus, in humans with underlying cardiovascular disease or cardiovascular risk factors, SMC MR activation may promote hypertension, atherosclerosis, and vascular aging. Further exploration of the molecular mechanisms for the effects of SMC MR activation has the potential to identify novel therapeutic targets to prevent or treat common cardiovascular disorders.

Renal dopamine and angiotensin II receptor signaling in age-related hypertension

Kidneys play a vital role in long-term regulation of blood pressure. This is achieved by actions of many renal and nonrenal factors acting on the kidney that help maintain the body's water and electrolyte balance and thus control blood pressure. Several endogenously formed or circulating hormones/peptides, by acting within the kidney, regulate fluid and water homeostasis and blood pressure. Dopamine and angiotensin II are the two key renal factors that, via acting on their receptors and counterregulating each other's function, maintain water and sodium balance. In this review, we provide recent advances in the signaling cascades of these renal receptors, especially at the level of their cross talk, and discuss their roles in blood pressure regulation in the aging process.