D5 dopamine receptor knockout mice and hypertension

Advances in Dopamine D1 Receptor Ligands for Neurotherapeutics

The dopamine D1 receptor (D1R) is essential for neurotransmission in various brain pathways where it modulates key functions including voluntary movement, memory, attention and reward. Not surprisingly, the D1R has been validated as a promising drug target for over 40 years and selective activation of this receptor may provide novel neurotherapeutics for neurodegenerative and neuropsychiatric disorders. Several pharmacokinetic challenges with previously identified small molecule D1R agonists have been recently overcome with the discovery and advancement of new ligands, including drug-like non-catechol D1R agonists and positive allosteric modulators. From this, several novel molecules and mechanisms have recently entered clinical studies. Here we review the major classes of D1R selective ligands including antagonists, orthosteric agonists, non-catechol biased agonists and positive allosteric modulators, highlighting their structure-activity relationships and medicinal chemistry. Recent chemistry breakthroughs and innovative approaches to selectively target and activate the D1R also hold promise for creating pharmacotherapy for several neurological diseases.

Discovery of D1 Dopamine Receptor Positive Allosteric Modulators: Characterization of Pharmacology and Identification of Residues that Regulate Species Selectivity

The present studies represent the first published report of a dopamine D1 positive allosteric modulator (PAM). D1 receptors have been proposed as a therapeutic target for the treatment of cognitive deficits associated with schizophrenia. However, the clinical utility of orthosteric agonist compounds is limited by cardiovascular side effects, poor pharmacokinetics, lack of D1 selectivity, and an inverted dose response. A number of these challenges may be overcome by utilization of a selective D1 PAM. The current studies describe two chemically distinct D1 PAMs: Compound A [1-((rel-1S,3R,6R)-6-(benzo[d][1,3]dioxol-5-yl)bicyclo[4.1.0]heptan-3-yl)-4-(2-bromo-5-chlorobenzyl)piperazine] and Compound B [rel-(9R,10R,12S)-N-(2,6-dichloro-3-methylphenyl)-12-methyl-9,10-dihydro-9,10-ethanoanthracene-12-carboxamide]. Compound A shows pure PAM activity, with an EC50 of 230 nM and agonist activity at the D2 receptor in D2-expressing human embryonic kidney cells. Compound B shows superior potency (EC50 of 43 nM) and selectivity for D1 versus D2 dopamine receptors. Unlike Compound A, Compound B is selective for human and nonhuman primate D1 receptors, but lacks activity at the rodent (rat and mouse) D1 receptors. Using molecular biology techniques, a single amino acid was identified at position 130, which mediates the species selectivity of Compound B. These data represent the first described D1-selective PAMs and define critical amino acids that regulate species selectivity.

The cooperative roles of the dopamine receptors, D1R and D5R, on the regulation of renal sodium transport

Determining the individual roles of the two dopamine D₁-like receptors (D₁R and D₅R) on sodium transport in the human renal proximal tubule has been complicated by their structural and functional similarity. Here we used a novel D₅R-selective antagonist (LE-PM436) and D₁R or D₅R-specific gene silencing to determine second messenger coupling pathways and heterologous receptor interaction between the two receptors. D₁R and D₅R co-localized in renal proximal tubule cells and physically interact, as determined by co-immunoprecipitation and FRET microscopy. Stimulation of renal proximal tubule cells with fenoldopam (D₁R/D₅R agonist) led to both adenylyl cyclase and phospholipase C (PLC) activation using real-time FRET biosensors ICUE3 and CYPHR, respectively. Fenoldopam increased cAMP accumulation and PLC activity and inhibited both NHE3 and NaKATPase activities. LE-PM436 and D₅R siRNA blocked the fenoldopam-stimulated PLC pathway but not cAMP accumulation, while D₁R siRNA blocked both fenoldopam-stimulated cAMP accumulation and PLC signaling. Either D₁R or D₅R siRNA, or LE-PM436 blocked the fenoldopam dependent inhibition of sodium transport. Further studies using the cAMP-selective D₁R/D₅R agonist SKF83822 and PLC-selective D₁R/D₅R agonist SKF83959 confirmed the cooperative influence of the two pathways on sodium transport. Thus, D₁R and D₅R interact in the inhibition of NHE3 and NaKATPase activity, the D₁R primarily by cAMP, while the D₁R/D₅R heteromer modulates the D₁R effect through a PLC pathway.

Regulation of renalase expression by D5 dopamine receptors in rat renal proximal tubule cells

The dopaminergic and sympathetic systems interact to regulate blood pressure. Our previous studies showed regulation of α1-adrenergic receptor function by D1-like dopamine receptors in vascular smooth muscle cells. Because renalase could regulate circulating epinephrine levels and dopamine production in renal proximal tubules (RPTs), we tested the hypothesis that D1-like receptors regulate renalase expression in kidney. The effect of D1-like receptor stimulation on renalase expression and function was measured in immortalized RPT cells from Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHRs). We found that the D1-like receptor agonist fenoldopam (10(-7)-10(-5) mol/l) increased renalase protein expression and function in WKY RPT cells but decreased them in SHR cells. Fenoldopam also increased renalase mRNA levels in WKY but not in SHR cells. In contrast, fenoldopam increased the degradation of renalase protein in SHR cells but not in WKY cells. The regulation of renalase by the D1-like receptor was mainly via the D5 receptor because silencing of the D5 but not D1 receptor by antisense oligonucleotides blocked the stimulatory effect of the D1-like receptor on renalase expression in WKY cells. Moreover, inhibition of PKC, by the PKC inhibitor 19-31, blocked the stimulatory effect of fenoldopam on renalase expression while stimulation of PKC, by a PKC agonist (PMA), increased renalase expression, indicating that PKC is involved in the process. Our studies suggest that the D5 receptor positively regulates renalase expression in WKY but not SHR RPT cells; aberrant regulation of renalase by the D5 receptor may be involved in the pathogenesis of hypertension.

Gene expression profiling on the molecular action of danshen-gegen formula in a randomized placebo-controlled trial of postmenopausal women with hypercholesterolemia

The Danshen-Gegen formula (DG) is a traditional Chinese herbal formula which has long been used to treat cardiovascular disease. DG was found to be a cardiovascular tonic in our recent research. However, a comprehensive investigation of the molecular mechanism of DG in cardiovascular disease has not been performed. The aim of this study was to clarify the transcriptional profiling of genes modulated by DG on postmenopausal women by using DNAmicroarray technology. We obtained 29 whole blood samples both from DG-treated and placebo-treated subjects. Blood lipid profile and intima-media thickness (IMT) were measured. Affymetrix GeneChip was used to identify differentially expressed genes (DEGs), followed by validation by the real-time PCR method. The results showed that DG-treated group has a significant improvement in IMT and lipid profile as compared to placebo-treated group. For the genomic study, the DG-treated group has a higher number of DEGs identified as compared to the placebo-treated group. Two important biological processes of “regulation of systemic arterial blood pressure by hormone” and “regulation of smooth muscle proliferation” have been identified by GePS in the DG-treated group. No significant biological process and cellular components were identified in the placebo-treated group. This genomic study on the molecular action of DG in postmenopausal women gathered sufficient molecular targets and pathways to reveal that DG could improve neointima thickening and hypertension.

Sorting nexin 1 loss results in D5 dopamine receptor dysfunction in human renal proximal tubule cells and hypertension in mice

The peripheral dopaminergic system plays a crucial role in blood pressure regulation through its actions on renal hemodynamics and epithelial ion transport. The dopamine D5 receptor (D(5)R) interacts with sorting nexin 1 (SNX1), a protein involved in receptor retrieval from the trans-Golgi network. In this report, we elucidated the spatial, temporal, and functional significance of this interaction in human renal proximal tubule cells and HEK293 cells stably expressing human D(5)R and in mice. Silencing of SNX1 expression via RNAi resulted in the failure of D(5)R to internalize and bind GTP, blunting of the agonist-induced increase in cAMP production and decrease in sodium transport, and up-regulation of angiotensin II receptor expression, of which expression was previously shown to be negatively regulated by D(5)R. Moreover, siRNA-mediated depletion of renal SNX1 in C57BL/6J and BALB/cJ mice resulted in increased blood pressure and blunted natriuretic response to agonist in salt-loaded BALB/cJ mice. These data demonstrate a crucial role for SNX1 in D(5)R trafficking and that SNX1 depletion results in D(5)R dysfunction and thus may represent a novel mechanism for the pathogenesis of essential hypertension.

Insulin increases D5 dopamine receptor expression and function in renal proximal tubule cells from Wistar-Kyoto rats

BACKGROUND

Ion transport in the renal proximal tubule (RPT) is regulated by numerous hormones and humoral factors, including insulin and dopamine. Previous studies show an interaction between insulin and the D(1) receptor. Because both D(1) and D(5) receptors belong to the D(1)-like receptor subfamily, it is possible that an interaction between insulin and the D(5) dopamine receptor exists in RPT cells from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHRs).

METHODS

D(5) receptor expression in immortalized RPT cells from WKY and SHRs was quantified by immunoblotting and D(5) receptor function by measuring Na(+)-K(+) ATPase activity.

RESULTS

Insulin increased the expression of the D(5) receptor. Stimulation with insulin (10(-7) mol/l) for 24 h increased D(5) receptor expression in RPT cells from WKY rats. This effect of insulin on D(5) receptor expression was aberrant in RPT cells from SHRs. The stimulatory effect of insulin on D(5) receptor expression in RPT cells from WKY rats was inhibited by a protein kinase C (PKC) inhibitor (PKC inhibitor peptide 19-31, 10(-6) mol/l) or a phosphatidylinositol 3 (PI3) kinase inhibitor (wortmannin, 10(-6) mol/l), indicating that both PKC and PI3 kinase were involved in the signaling pathway. Stimulation of the D(5) receptor heterologously expressed in HEK293 cells with fenoldopam (10(-7) mol/l/15 min) inhibited Na(+)-K(+) ATPase activity, whereas pretreatment with insulin (10(-7) mol/l/24 h) increased the D(5) receptor-mediated inhibition.

CONCLUSIONS

Insulin and D(5) receptors interact to regulate renal sodium transport; an aberrant interaction between insulin and D(5) receptor may participate in the pathogenesis of hypertension.

The dopaminergic system in hypertension

Dopamine plays an important role in the pathogenesis of hypertension by regulating epithelial sodium transport, vascular smooth muscle contractility and production of reactive oxygen species and by interacting with the renin–angiotensin and sympathetic nervous systems. Dopamine receptors are classified into D1-like (D1 and D5) and D2-like (D2, D3 and D4) subtypes based on their structure and pharmacology. Each of the dopamine receptor subtypes participates in the regulation of blood pressure by mechanisms specific for the subtype. Some receptors regulate blood pressure by influencing the central and/or peripheral nervous system; others influence epithelial transport and regulate the secretion and receptors of several humoral agents. This review summarizes the physiology of the different dopamine receptors in the regulation of blood pressure, and the relationship between dopamine receptor subtypes and hypertension.

Identification of human dopamine receptors agonists from Chinese herbs

AIM

To find human dopamine receptors, especially D1-like receptor specific agonists from Chinese herbs as potential antihypertension drug leads.

METHODS

Two D1-like receptor cell lines carrying a beta-lactamase reporter gene, and a D2 receptor cell line coexpressing a promiscuous G protein G15 were constructed using HEK293 cells. A natural compound library made from fractionated samples of herbal extracts was used for high-throughput screening (HTS) against one of the cell lines, HEK/D5R/CRE-blax. The interested hits were evaluated for their activities against various dopamine receptors.

RESULTS

Fourteen hits were identified from primary screening, of which 2 of the better hit samples, HD0522 and HD0059, were selected for further material and activity analysis, and to obtain 2 compounds that appeared as 2 single peaks in HPLC, HD0522H01 and HD0059H01. HD0059H01 could activate D1, D2, and D5 receptors, with EC(50 ) values of 2.28 microg/mL, 0.85 microg/mL, and 1.41 microg/mL, respectively. HD0522H01 could only activate D1R and D5R with EC(50 ) values of 2.95 microg/mL and 8.38 microg/mL.

CONCLUSION

We established cellbased assays for 3 different human dopamine receptors and identified specific agonists HD0522H01 and HD0059H01 through HTS. The specific agonist to D1-like receptors, HD0522H01, may become a new natural product-based drug lead for antihypertension treatment.

Murine models of inherited monoaminergic and GABAergic neurotransmitter disorders

Monoamine and amino acid neurotransmitters perform diverse biological functions in mammals, including the regulation of inhibitory/excitatory neurotransmission in the brain and spinal cord, movement and sleep, autonomic function, mood and reward, and numerous other processes. The primary transmitters involved include dopamine, serotonin, epinephrine, norepinephrine and γ-aminobutyric acid (GABA). With the exception of the amino acid transmitter GABA, the cofactor integrating these systems is tetrahydrobiopterin, an oxidizable intermediate found in high concentrations in dopaminergic neurons. With growing awareness of the clinical phenotypes, expanding numbers of patients with monoaminergic and GABAergic neurotransmitter disorders are being identified. For some people, therapeutic intervention demonstrates remarkably positive benefits; conversely, for most other disorders therapy offers limited efficacy. Decoding of the complete mouse genome, coupled with methodology capable of ablating specific genes, has revolutionized how geneticists understand and treat human genetic disease. This is well-exemplified in the disorders covered in this review, which focuses predominantly on monoaminergic (tetrahydrobiopterin-dependent) and GABAergic signaling neurotransmitter disorders.

D3 dopamine receptor directly interacts with D1 dopamine receptor in immortalized renal proximal tubule cells

D3 receptors act synergistically with D1 receptors to inhibit sodium transport in renal proximal tubules; however, the mechanism by which this occurs is not known. Because dopamine receptor subtypes can regulate and interact with each other, we studied the interaction of D3 and D1 receptors in rat renal proximal tubule (RPT) cells. The D3 agonist PD128907 increased the immunoreactive expression of D1 receptors in a concentration- and time-dependent manner; these effects were blocked by the D3 antagonist U99194A. PD128907 also transiently (15 minutes) increased the amount of cell surface membrane D1 receptors. Laser confocal immunofluorescence microscopy showed that D3 receptor and D1 receptor colocalized in RPT cells more distinctly in Wistar-Kyoto rats than in spontaneously hypertensive rats (SHRs). In addition, D3 and D1 receptors could be coimmunoprecipitated, and this interaction was increased after D3 receptor agonist stimulation for 24 hours in Wistar-Kyoto rats but not in SHRs. We propose that the synergistic effects of D3 and D1 receptors may be caused by a D3 receptor-mediated increase in total, as well as cell surface membrane D1 receptor expression, and direct D3 and D1 receptor interaction, both of which are impaired in SHRs.

CNS-induced natriuresis, neurohypophyseal peptides and renal dopamine and noradrenaline excretion in prehypertensive salt-sensitive Dahl rats

To identify defects in the salt-sensitive Dahl rat (Dahl-S), the natriuretic, catecholaminergic and pressor responses to 60-min elevation of the cerebroventricular sodium concentration (CNS-induced natriuresis) were compared between prehypertensive salt-sensitive Dahl-S and salt-resistant Dahl rats (Dahl-R). The plasma concentrations of the rat natriuretic hormone oxytocin, which has implications for the development of hypertension, and vasopressin (AVP) were also measured. Basal sodium and catecholamine excretion and mean arterial blood pressure (MAP) were similar in both strains. Sodium excretion during CNS stimulation increased more than 15-fold in Dahl-R but only 10-fold in Dahl-S. Dopamine excretion increased only transiently and similarly in both strains. Noradrenaline excretion and response to CNS stimulation were similar, suggesting a comparable sympathetic nervous activity between the strains. MAP increased comparably in Dahl-R and Dahl-S. Plasma AVP concentration was similar in both strains while plasma oxytocin concentration after CNS stimulation was more than 2-fold higher in Dahl-S than in Dahl-R. In conclusion, the prehypertensive Dahl-S has an attenuated natriuretic response to elevations of the cerebroventricular fluid sodium concentration and a higher plasma level of the natriuretic hormone oxytocin. Dopamine is not a mediator of CNS-induced natriuresis in neither strain. The attenuated natriuretic response may partly explain the salt-sensitivity in Dahl-S, and the higher plasma oxytocin value may either represent an effort to compensate for the deficient natriuretic response or reflect a primary defect in this system. Due to the known involvement of oxytocin in central MAP regulation in some hypertensive animal models, the findings warrant further investigation.