Role of Gα(12)- and Gα(13)-protein subunit linkage of D(3) dopamine receptors in the natriuretic effect of D(3) dopamine receptor in kidney

Synergistic Effect of Uroguanylin and D1 Dopamine Receptors on Sodium Excretion in Hypertension

Background

Oral NaCl produces a greater natriuresis and diuresis than the intravenous infusion of the same amount of NaCl, indicating the existence of a gastro‐renal axis. As one of the major natriuretic hormones secreted by both the intestines and the kidney, we hypothesized that renal uroguanylin interacts with dopamine receptors to increase sodium excretion synergistically, an impaired interaction of which may be involved in the pathogenesis of hypertension.

Methods and Results

In Wistar‐Kyoto rats, the infusion of uroguanylin or fenoldopam (a D₁‐like receptor agonist) induced natriuresis and diuresis. Although subthreshold dosages of uroguanylin or fenoldopam had no effect, the coinfusion of subthreshold dosages of those reagents significantly increased sodium excretion. The coinfusion of an antagonist against D₁‐like receptors, SCH23390, or an antagonist against uroguanylin, 2‐methylthioadenosine triphosphate, prevented the fenoldopam‐ or uroguanylin‐mediated natriuresis and diuresis in Wistar‐Kyoto rats. However, the natriuretic effects of uroguanylin and fenoldopam were not observed in spontaneously hypertensive rats. The uroguanylin/D₁‐like receptor interaction was also confirmed in renal proximal tubule cells. In renal proximal tubule cells from Wistar‐Kyoto rats but not spontaneously hypertensive rats, stimulation of either D₁‐like receptors or uroguanylin inhibited Na⁺‐K⁺‐ATPase activity, an effect that was blocked in the presence of SCH23390 or 2‐methylthioadenosine triphosphate. In renal proximal tubule cells from Wistar‐Kyoto rats, guanylyl cyclase C receptor (uroguanylin receptor) and D₁ receptor coimmunoprecipitated, which was increased after stimulation by either uroguanylin or fenoldopam; stimulation of one receptor increased renal proximal tubule cell membrane expression of the other.

Conclusions

These data suggest that there is synergism between uroguanylin and D₁‐like receptors to increase sodium excretion. An aberrant interaction between the renal uroguanylin and D₁‐like receptors may play a role in the pathogenesis of 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.

Lipid Rafts and Dopamine Receptor Signaling

The renal dopaminergic system has been identified as a modulator of sodium balance and blood pressure. According to the Centers for Disease Control and Prevention, in 2018 in the United States, almost half a million deaths included hypertension as a primary or contributing cause. Renal dopamine receptors, members of the G protein-coupled receptor family, are divided in two groups: D1-like receptors that act to keep the blood pressure in the normal range, and D2-like receptors with a variable effect on blood pressure, depending on volume status. The renal dopamine receptor function is regulated, in part, by its expression in microdomains in the plasma membrane. Lipid rafts form platforms within the plasma membrane for the organization and dynamic contact of molecules involved in numerous cellular processes such as ligand binding, membrane sorting, effector specificity, and signal transduction. Understanding all the components of lipid rafts, their interaction with renal dopamine receptors, and their signaling process offers an opportunity to unravel potential treatment targets that could halt the progression of hypertension, chronic kidney disease (CKD), and their complications.

Heterotrimeric Gα12/13 proteins in kidney injury and disease

Gα₁₂ and Gα₁₃ are ubiquitous members of the heterotrimeric guanine nucleotide-binding protein (G protein) family that play central and integrative roles in the regulation of signal transduction cascades within various cell types in the kidney. Gα₁₂/Gα₁₃ proteins enable the kidney to adapt to an ever-changing environment by transducing stimuli from cell surface receptors and accessory proteins to effector systems. Therefore, perturbations in Gα₁₂/Gα₁₃ levels or their activity can contribute to the pathogenesis of various renal diseases, including renal cancer. This review will highlight and discuss the complex and expanding roles of Gα₁₂/Gα₁₃ proteins on distinct renal pathologies, with emphasis on more recently reported findings. Deciphering how the different Gα₁₂/Gα₁₃ interaction networks participate in the onset and development of renal diseases may lead to the discovery of new therapeutic strategies.

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.

Stimulation of Dopamine D3 Receptor Attenuates Renal Ischemia-Reperfusion Injury via Increased Linkage With Gα12

BACKGROUND

Renal ischemia-reperfusion (I/R) injury causes renal tubular necrosis, apoptosis, and inflammation leading to acute renal dysfunction. Recent studies have revealed that deletion of Gα12 mitigates the renal damage due to I/R injury. Our previous study showed that activation of dopamine D3 receptor (D3R) increased its linkage with Gα12, and hampered Gα12-mediated stimulation of renal sodium transport. In the present study, we used an in-vivo rat model and an in vitro study of the renal epithelial cell line (NRK52E) to investigate whether or not an increased linkage between D3R and Gα12 contributes to the protective effect of D3R on renal I/R injury.

METHODS

For in vivo studies, I/R injury was induced in a rat renal unilateral clamping model. For in vitro studies, hypoxia/reoxygenation and cold storage/rewarming injuries were performed in NRK52E cells. PD128907, a D3R agonist, or vehicle, was administered 15 minutes before clamping (or hypoxia) in both the in vivo or in vitro studies.

RESULTS

In the rat renal unilateral clamping model, pretreatment with PD128907 (0.2 mg/kg, intravenous) protected against renal I/R injury and increased survival rate during a long-term follow-up after 7 days. A decrease in the generation of reactive oxygen species, apoptosis, and inflammation may be involved in the D3R-mediated protection because pretreatment with PD128907 increased renal glutathione and superoxide dismutase levels and decreased malondialdehyde levels in the I/R group. The increase in cytokines (TNF-α, IL-1β, and IL-10) and myeloperoxidase in I/R injured kidney was also prevented with a simultaneous decrease in the apoptosis of the epithelial cells and expression of apoptosis biomarkers in kidney harvested 1 day after I/R injury. The increase in the coimmunoprecipitation between D3R and Gα12 with D3R stimulation paralleled the observed renal protection from I/R injury. Moreover, in vitro studies showed that transient overexpression of Gα12 in the NRK52E cells attenuated the protective effect of PD128907 on hypoxia/reoxygenation injury. The protective effect of PD128907 might be of significance to renal transplantation because cold storage/rewarming induced injury increased lactate dehydrogenase release and decreased cell viability in NRK52E cells. Conversely, in the presence of PD128907, the increased lactate dehydrogenase release and decreased cell viability were reversed.

CONCLUSIONS

These results suggest that activation of D3R, by decreasing Gα12-induced renal damage, may exert a protective effect from I/R injury.

Transcriptional gene silencing of dopamine D3 receptor caused by let-7d mimics in immortalized renal proximal tubule cells of rats

Transcriptional gene silencing (TGS) induced by synthetic exogenous short interfering RNAs (siRNAs) that are fully complementary to gene promoters has been demonstrated in mammalian cells. However, it remains unclear whether microRNAs (miRNAs), which are endogenous small regulatory RNAs, can also silence gene transcription. We investigated the regulation mechanism of let-7d on dopamine D3 receptor (DRD3) in immortalized renal proximal tubule (RPT) cells of rats, where let-7d has a predicted homologous target site within DRD3 promoter. We found that let-7d mimics repressed DRD3 expression at the transcription level in RPT cells. Let-7d induced DRD3 inhibition via DNA-methyltransferase 1 (DNMT1) and DNA-methyltransferase 3b (DNMT3b) dependent DNA methylation and the inhibition could be abolished by 5'-aza-2'-deoxycytidine (5-aza-dc), a DNA methylation inhibitor. Let-7d induced DRD3 repression was associated with the recruitment of Argonaute 2 (AGO2) protein. Histone 3 lysine 9 dimethylation (H3K9me2) was involved in the let-7d induced DRD3 TGS, indicating the chromatin-level silencing. In conclusion, our results demonstrated that let-7d may induce DRD3 repression in a transcriptional manner by means of DNMTs dependent DNA methylation and histone modification. It is suggested that miRNAs may act as a transcriptional gene regulator via the recognition of the homologous target site within the gene promoter.

Dopamine D3 receptor agonists as pharmacological tools

Dysregulation of the dopaminergic innervation in the central nervous system plays a key role in different neurological disorders like Parkinson´s disease, restless legs syndrome, schizophrenia etc. Although dopamine D3 receptors have been recognized as an important target in these diseases, their full pharmacological properties need further investigations. With focus on dopamine D3 receptor full agonists, this review has divided the ergoline and non-ergoline ligands in dissimilar chemical subclasses describing their pharmacodynamic properties on different related receptors, on species differences and their functional properties on different signaling mechanism. This is combined with a short description of structure-activity relationships for each class. Therefore, this overview should support the rational choice for the optimal compound selection based on affinity, selectivity and efficacy data in biochemical and pharmacological studies.

Opposing effects on the phrenic motor pathway attributed to dopamine-D1 and -D3/D2 receptor activation

Previous in vivo studies revealed that dopamine-D1-agonists elevate excitability of ventral respiratory column (VRC) neurons and increase discharge activity in the phrenic motor output through actions in the brainstem. In this in vivo study performed on pentobarbital-anesthetized cats, we show that D1-agonists (SKF-38393, dihydrexidine) given intravenously enhanced discharge activity in VRC inspiratory neurons and the phrenic nerve in two stages; discharge intensity first increased to a peak and then discharge duration increased. Cross-correlation analysis of VRC inspiratory neuron and phrenic nerve discharges showed that both stages increased strength of coupling between medullary inspiratory neurons and the phrenic motoneuron output. Intracellular recording and microiontophoresis experiments indicated that D1-agonists produced their stimulatory effects indirectly through actions on synaptic inputs to VRC inspiratory neurons. Because other laboratories have provided evidence that dopamine acting on other types of receptors depresses respiratory neuron excitability we tested the effects of piribedil, an agonist that activates receptors of the generally depressant D3/D2-dopamine receptor family, on phrenic nerve activity. Piribedil depressed phrenic nerve inspiratory discharge intensity, prolonged discharge duration, slowed burst frequency and slowed rate of action potential augmentation. The effects of piribedil were partially counteracted by intravenous injection of dihydrexidine. We propose that under normal, steady state conditions, D1-receptor-mediated excitatory modulation of phrenic motor output overrides D3/D2-receptor mediated inhibition.