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

Interactions between the intrarenal dopaminergic and the renin-angiotensin systems in the control of systemic arterial pressure

Systemic arterial hypertension is one of the leading causes of morbidity and mortality in the general population, being a risk factor for many cardiovascular diseases. Although its pathogenesis is complex and still poorly understood, some systems appear to play major roles in its development. This review aims to update the current knowledge on the interaction of the intrarenal renin-angiotensin system (RAS) and dopaminergic system in the development of hypertension, focusing on recent scientific hallmarks in the field. The intrarenal RAS, composed of several peptides and receptors, has a critical role in the regulation of blood pressure (BP) and, consequently, the development of hypertension. The RAS is divided into two main intercommunicating axes: the classical axis, composed of angiotensin-converting enzyme, angiotensin II, and angiotensin type 1 receptor, and the ACE2/angiotensin-(1-7)/Mas axis, which appears to modulate the effects of the classical axis. Dopamine and its receptors are also increasingly showing an important role in the pathogenesis of hypertension, as abnormalities in the intrarenal dopaminergic system impair the regulation of renal sodium transport, regardless of the affected dopamine receptor subtype. There are five dopamine receptors, which are divided into two major subtypes: the D1-like (D1R and D5R) and D2-like (D2R, D3R, and D4R) receptors. Mice deficient in any of the five dopamine receptor subtypes have increased BP. Intrarenal RAS and the dopaminergic system have complex interactions. The balance between both systems is essential to regulate the BP homeostasis, as alterations in the control of both can lead to 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.

Dopamine Receptors and the Kidney: An Overview of Health- and Pharmacological-Targeted Implications

The dopaminergic system can adapt to the different physiological or pathological situations to which the kidneys are subjected throughout life, maintaining homeostasis of natriuresis, extracellular volume, and blood pressure levels. The role of renal dopamine receptor dysfunction is clearly established in the pathogenesis of essential hypertension. Its associations with other pathological states such as insulin resistance and redox balance have also been associated with dysfunction of the dopaminergic system. The different dopamine receptors (D1-D5) show a protective effect against hypertension and kidney disorders. It is essential to take into account the various interactions of the dopaminergic system with other elements, such as adrenergic receptors. The approach to therapeutic strategies for essential hypertension must go through the blocking of those elements that lead to renal vasoconstriction or the restoration of the normal functioning of dopamine receptors. D1-like receptors are fundamental in this role, and new therapeutic efforts should be directed to the restoration of their functioning in many patients. More studies will be needed to allow the development of drugs that can be targeted to renal dopamine receptors in the treatment of 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.

Kidney dopamine D1-like receptors and angiotensin 1-7 interaction inhibits renal Na+ transporters

The role of dopamine D₁-like receptors (DR) in the regulation of renal Na⁺ transporters, natriuresis, and blood pressure is well established. However, the involvement of the angiotensin 1-7 (ANG 1-7)-Mas receptor in the regulation of Na⁺ balance and blood pressure is not clear. The present study aimed to investigate the hypothesis that ANG 1-7 can regulate Na⁺ homeostasis by modulating the renal dopamine system. Sprague-Dawley rats were infused with saline alone (vehicle) or saline with ANG 1-7, ANG 1-7 antagonist A-779, DR agonist SKF38393, and antagonist SCH23390. Infusion of ANG 1-7 caused significant natriuresis and diuresis compared with saline alone. Both natriuresis and diuresis were blocked by A-779 and SCH23390. SKF38393 caused a significant, SCH23390-sensitive natriuresis and diuresis, and A-779 had no effect on the SKF38393 response. Concomitant infusion of ANG 1-7 and SKF38393 did not show a cumulative effect compared with either agonist alone. Treatment of renal proximal tubules with ANG 1-7 or SKF38393 caused a significant decrease in Na⁺-K⁺-ATPase and Na⁺/H⁺ exchanger isoform 3 activity. While SCH23390 blocked both ANG 1-7- and SKF38393-induced inhibition, the DR response was not sensitive to A-779. Additionally, ANG 1-7 activated PKG, enhanced tyrosine hydroxylase activity via Ser⁴⁰ phosphorylation, and increased renal dopamine production. These data suggest that ANG 1-7, via PKG, enhances tyrosine hydroxylase activity, which increases renal dopamine production and activation of DR and subsequent natriuresis. This study provides evidence for a unidirectional functional interaction between two G protein-coupled receptors to regulate renal Na⁺ transporters and induce natriuresis.

Role of Thioredoxin 1 in Impaired Renal Sodium Excretion of hD 5 R F173L Transgenic Mice

Background Dopamine D5 receptor (D5R) plays an important role in the maintenance of blood pressure by regulating renal sodium transport. Our previous study found that human D5R mutant F173L transgenic ( hD 5 R F173L-TG) mice are hypertensive. In the present study, we aimed to investigate the mechanisms causing this renal D5R dysfunction in hD 5 R F173L-TG mice. Methods and Results Compared with wild-type D5R-TG ( hD 5 R WT-TG) mice, hD 5 R F173L-TG mice have higher blood pressure, lower basal urine flow and sodium excretion, and impaired agonist-mediated natriuresis and diuresis. Enhanced reactive oxygen species production in hD 5 R F173L-TG mice is caused, in part, by decreased expression of antioxidant enzymes, including thioredoxin 1 (Trx1). Na+-K+-ATPase activity is increased in mouse renal proximal tubule cells transfected with hD 5 R F173L, but is normalized by treatment with exogenous recombinant human Trx1 protein. Regulation of Trx1 by D5R occurs by the phospholipase C/ protein kinase C (PKC) pathway because upregulation of Trx1 expression by D5R does not occur in renal proximal tubule cells from D1R knockout mice in the presence of a phospholipase C or PKC inhibitor. Fenoldopam, a D1R and D5R agonist, stimulates PKC activity in primary renal proximal tubule cells of hD5R WT -TG mice, but not in those of hD 5 R F173L-TG mice. Hyperphosphorylation of hD5RF173L and its dissociation from Gαs and Gαq are associated with impairment of D5R-mediated inhibition of Na+-K+-ATPase activity in hD 5 R F173L-TG mice. Conclusions These suggest that hD 5 R F173L increases blood pressure, in part, by decreasing renal Trx1 expression and increasing reactive oxygen species production. Hyperphosphorylation of hD5RF173L, with its dissociation from Gαs and Gαq, is the key factor in impaired D5R function of hD 5 R F173L-TG mice.

Dopamine promotes colonic mucus secretion through dopamine D5 receptor in rats

Dopamine regulates gastrointestinal mucosal barrier. Mucus plays important roles in the protection of intestinal mucosa. Here, the regulatory effect of dopamine on rat colonic mucus secretion was investigated. RT-PCR, immunofluorescence, Periodic Acid-Schiff reagent assay, Alcian blue-Periodic Acid-Schiff staining, and enzyme-linked immunosorbent assay were used to observe the expression of dopamine receptor and the direct effect of dopamine on the colonic mucus. Mice injected intraperitoneally with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) destroying enteric dopamine (DA) neurons, rats microinjected with 6-hydroxydopamine (6-OHDA) into the bilateral substantia nigra damaging central dopaminergic neurons, and dopamine D₅ receptor-downregulated transgenic mice were used to detect the effect of endogenous enteric dopamine or dopamine receptors on distal colonic mucus. Our results indicated that D₅ immunoreactivity was widely distributed on the colonic goblet cells. Dopamine dose-dependently increased rat distal colonic mucus secretion in vitro. D₁-like receptor antagonist SCH23390 inhibited dopamine (1 μΜ)-induced distal colonic mucus secretion. D1-like receptor agonist SKF38393 promoted mucin 2 (MUC2) secretion and increased the intracellular cAMP level of colonic mucosa. D₅ receptor-downregulated transgenic mice showed a decreased colonic MUC2 content. MPTP-treated mice exhibited lower colonic dopamine content and decreased colonic mucus content. 6-OHDA rats had an increase in the dopamine content in colonic mucosa but decreases in the protein levels of D₁ and D₅ receptors and MUC2 content in the colonic mucosa. These findings reveal that dopamine is able to promote distal colonic mucus secretion through the D₅ receptor, which provides important evidence to better understand the possible role of dopamine in the colonic mucosal barrier.

Over-expression of a cardiac-specific human dopamine D5 receptor mutation in mice causes a dilated cardiomyopathy through ROS over-generation by NADPH oxidase activation and Nrf2 degradation

Dilated cardiomyopathy (DCM) is a severe disorder caused by medications or genetic mutations. D₅ dopamine receptor (D5R) gene knockout (D5^-/-) mice have cardiac hypertrophy and high blood pressure. To investigate the role and mechanism by which the D5R regulates cardiac function, we generated cardiac-specific human D5R F173L(hD5^F173L-TG) and cardiac-specific human D5R wild-type (hD5^WT-TG) transgenic mice, and H9c2 cells stably expressing hD5^F173L and hD5^WT. We found that cardiac-specific hD5^F173L-TG mice, relative to hD5^WT-TG mice, presented with DCM and increased cardiac expression of cardiac injury markers, NADPH oxidase activity, Nrf2 degradation, and activated ERK1/2/JNK pathway. H9c2-hD5^F173L cells also had an increase in NADPH oxidase activity, Nrf2 degradation, and phospho-JNK (p-JNK) expression. A Nrf2 inhibitor also increased p-JNK expression in H9c2-hD5^F173L cells but not in H9c2-hD5^WT cells. We suggest that the D5R may play an important role in the preservation of normal heart function by inhibiting the production of reactive oxygen species, via inhibition of NADPH oxidase, Nrf2 degradation, and ERK1/2/JNK pathways.

Dopamine enhances duodenal epithelial permeability via the dopamine D5 receptor in rodent

AIM

The intestinal barrier is made up of epithelial cells and intercellular junctional complexes to regulate epithelial ion transport and permeability. Dopamine (DA) is able to promote duodenal epithelial ion transport through D1-like receptors, which includes subtypes of D₁ (D₁ R) and D₅ (D₅ R), but whether D1-like receptors influence the duodenal permeability is unclear.

METHODS

FITC-dextran permeability, short-circuit current (I_SC ), Western blot, immunohistochemistry and ELISA were used in human D₅ R transgenic mice and hyperendogenous enteric DA (HEnD) rats in this study.

RESULTS

Dopamine induced a downward deflection in I_SC and an increase in FITC-dextran permeability of control rat duodenum, which were inhibited by the D1-like receptor antagonist, SCH-23390. However, DA decreased duodenal transepithelial resistance (TER), an effect also reversed by SCH-23390. A strong immunofluorescence signal for D₅ R, but not D₁ R, was observed in the duodenum of control rat. In human D₅ R knock-in transgenic mice, duodenal mucosa displayed an increased basal I_SC with high FITC-dextran permeability and decreased TER with a lowered expression of tight junction proteins, suggesting attenuated duodenal barrier function in these transgenic mice. D₅ R knock-down transgenic mice manifested a decreased basal I_SC with lowered FITC-dextran permeability. Moreover, an increased FITC-dextran permeability combined with decreased TER and tight junction protein expression in duodenal mucosa were also observed in HEnD rats.

CONCLUSION

This study demonstrates, for the first time, that DA enhances duodenal permeability of control rat via D₅ R, which provides new experimental and theoretical evidence for the influence of DA on duodenal epithelial barrier function.

Genetic susceptibility to salt-sensitive hypertension in a Han Chinese population: a validation study of candidate genes

Salt-sensitive hypertension is a complex disease associated with genetic factors. This study aimed to identify the association between 29 candidate single-nucleotide polymorphisms and salt-sensitive hypertension in a Han Chinese population. Sixty-three participants with salt-sensitive hypertension and 279 controls with salt-resistant hypertension were recruited. A modified Sullivan's acute oral saline load and diuresis shrinkage test was used to detect blood pressure salt sensitivity. Lifestyle risk factors were obtained via a questionnaire. We used the Sequenom Mass ARRAY Platform to genotype the 29 candidate single-nucleotide polymorphisms, and the cumulative genetic risk score was used to evaluate the joint genetic effect. The frequencies of eight genotypes and five alleles in CYP11B2, PRKG1, ADRB2, FGF5, SLC8A1 and BCAT1 genes differed significantly between the salt-sensitive and salt-resistant hypertension groups. Multiple logistic regression adjusted for age and sex showed that subjects carrying rs7897633-A (PRKG1), rs434082-A (SLC8A1) and rs1042714-G (ADRB2) risk alleles had 1.83-, 2.84- and 2.40-fold increased risk for salt-sensitive hypertension, respectively. Combined risk allele analysis using the cumulative genetic risk score showed that subjects carrying one risk had 2.30-fold increased risk, and those carrying 2-4 risks had 3.32-fold increased risk for salt-sensitive hypertension. Among 29 candidate single-nucleotide polymorphisms, rs7897633-A in PRKG1, rs434082-A in SLC8A1 and rs1042714-G in ADRB2 were significantly associated with salt-sensitive hypertension. A joint effect of single-nucleotide polymorphisms from different pathways contributed to a high risk of salt-sensitive hypertension.

Na/K-ATPase Signaling and Salt Sensitivity: The Role of Oxidative Stress

Other than genetic regulation of salt sensitivity of blood pressure, many factors have been shown to regulate renal sodium handling which contributes to long-term blood pressure regulation and have been extensively reviewed. Here we present our progress on the Na/K-ATPase signaling mediated sodium reabsorption in renal proximal tubules, from cardiotonic steroids-mediated to reactive oxygen species (ROS)-mediated Na/K-ATPase signaling that contributes to experimental salt sensitivity.

Activation of angiotensin II type 1 receptors increases D4 dopamine receptor expression in rat renal proximal tubule cells

Both the dopaminergic and renin-angiotensin systems play important roles in the regulation of blood pressure. Our previous study showed that the stimulation of dopaminergic D₄ receptors reduced angiotensin II type 1 (AT₁) receptor expression in renal proximal tubule (RPT) cells. In this study, we tested whether AT₁ receptors, in return, would regulate D₄ receptor expression and function in RPT cells. Expression of the D₄ receptor from Wistar-Kyoto (WKY) or spontaneously hypertensive rats (SHRs) RPT cells and renal cortex tissues were determined by western blot, and Na⁺-K⁺ ATPase activity was determined using an enzyme assay. Urine volume and urine sodium of WKY rats and SHRs treated with or without D₄ receptor stimulation were measured. Thus, activation of AT₁ receptors with angiotensin II (Ang II) increased D₄ receptor protein expression in RPT cells, and this increase was blocked by nicardipine, a calcium influx blocker. The D₄ receptor agonist PD168077 inhibited Na⁺-K⁺ ATPase activity in WKY RPT cells but not in SHR RPT cells. Ang II pre-treatment promoted D₄ receptor-mediated inhibition of Na⁺-K⁺ ATPase in RPT cells in WKY rats but not in SHRs. Meanwhile, Ang II pre-treatment augmented the natriuretic effect of PD168077 in WKY rats but not in SHRs. In conclusion, AT₁ stimulation can regulate the expression and natriuretic function of dopaminergic D₄ receptors in RPT cells and might be involved in the pathogenesis of essential hypertension.

Aliskiren and l-arginine treatments restore depressed baroreflex sensitivity and decrease oxidative stress in renovascular hypertension rats

Renovascular hypertension is characterized by increased angiotensin II and oxidative stress, and by endothelial dysfunction. The purpose of this study was to test whether the administration of aliskiren (ALSK) and l-arginine (l-ARG) would restore impaired baroreflex sensitivity and reduce oxidative stress in a rat renovascular hypertension model. Hypertension was induced by clipping the left renal artery, and the following five groups were created: SHAM; two-kidney, 1-clip (2K1C); 2K1C plus ALSK (ALSK); 2K1C plus l-ARG (l-ARG); and 2K1C plus ALSK+l-ARG (ALSK+l-ARG). After 21 days of treatment, only the ALSK+l-ARG group was effective in normalizing the arterial pressure (108.8±2.8 mm Hg). The l-ARG and ALSK+l-ARG groups did not show hypertrophy of the left ventricle. All the treatments restored the depressed baroreflex sensitivity to values found in the SHAM group. Acute administration of TEMPOL restored the depressed baroreflex sensitivity in the 2K1C group to values that resembled those presented by the other groups. All treatments were effective for an increase in the antioxidant pathway and reduction in the oxidative pathway. In conclusion, the treatment with ALSK or l-ARG reduced oxidative stress and restored reduced baroreflex sensitivity in renovascular hypertension. In addition, the treatments were able to normalize blood pressure and reverse left ventricular hypertrophy when used in combination.