G protein-coupled receptor kinase 4 gene variants in human essential hypertension

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.

Clinical Pharmacogenetics Implementation Consortium Guideline (CPIC) for CYP2D6, ADRB1, ADRB2, ADRA2C, GRK4, and GRK5 Genotypes and Beta-Blocker Therapy

Beta-blockers are widely used medications for a variety of indications, including heart failure, myocardial infarction, cardiac arrhythmias, and hypertension. Genetic variability in pharmacokinetic (e.g., CYP2D6) and pharmacodynamic (e.g., ADRB1, ADRB2, ADRA2C, GRK4, GRK5) genes have been studied in relation to beta-blocker exposure and response. We searched and summarized the strength of the evidence linking beta-blocker exposure and response with the six genes listed above. The level of evidence was high for associations between CYP2D6 genetic variation and both metoprolol exposure and heart rate response. Evidence indicates that CYP2D6 poor metabolizers experience clinically significant greater exposure and lower heart rate in response to metoprolol compared with those who are not poor metabolizers. Therefore, we provide therapeutic recommendations regarding genetically predicted CYP2D6 metabolizer status and metoprolol therapy. However, there was insufficient evidence to make therapeutic recommendations for CYP2D6 and other beta-blockers or for any beta-blocker and the other five genes evaluated (updates at www.cpicpgx.org).

Quantitative proteomics assay reveals G protein-coupled receptor kinase 4-induced HepG2 cell growth inhibition

Background and aim

To investigate the biological effects and putative biological mechanism of G protein-coupled receptor kinase 4 (GRK4) on HepG2 cells.

Materials and methods

Cell proliferation, cycle, and apoptosis were evaluated by Cell Counting Kit-8 and flow cytometry (FCM) in HepG2 cells infected with either the GRK4-overexpressing lentivirus vector (OE) or the negative control lentivirus vector (NC). The protein profiles and differentially expressed proteins (DEPs) of the OE and NC cells were analyzed and compared using the quantitative proteomics technique, and their function, expression, and probable mechanism were investigated using bioinformatic assays and parallel reaction monitoring (PRM).

Results

HepG2 cells that received the OE grew more slowly than those that received the NC. FCM revealed that, when compared to the NC cells, the OE cells had undergone S-phase cycle arrest, and neither the OE nor NC cells underwent apoptosis. Among the 7006 proteins that were identified by quantitative proteomics, 403 DEPs were examined based on the filtering parameters, with the expressions of 135 being downregulated and 268 being upregulated. In addition to being involved in the peroxisome proliferator-activated receptor (PPAR) signaling pathway, the DEPs were implicated in the biological processes of cell proliferation, cycle, and metabolism. PRM verified the expressions of DEPs that were connected to the PPAR pathway.

Conclusions

This study shows that GRK4 prevents HepG2 cells from proliferating and causes cell cycle arrest in the S-phase, while the PPAR pathway is involved in the regulation of HepG2 cells via GRK4.

Exercise ameliorates skeletal muscle insulin resistance by modulating GRK4-mediated D1R expression

Exercise has been recommended as a nonpharmaceutical therapy to treat insulin resistance (IR). Previous studies showed that dopamine D1-like receptor agonists, such as fenoldopam, could improve peripheral insulin sensitivity, while antipsychotics, which are dopamine receptor antagonists, increased susceptibility to Type 2 diabetes mellitus (T2DM). Meanwhile, exercise has been proved to stimulate dopamine receptors. However, whether the dopamine D1 receptor (D1R) is involved in exercise-mediated amelioration of IR remains unclear. We found that the D1-like receptor antagonist, SCH23390, reduced the effect of exercise on lowering blood glucose and insulin in insulin-resistant mice and inhibited the contraction-induced glucose uptake in C2C12 myotubes. Similarly, the opposite was true for the D1-like receptor agonist, fenoldopam. Furthermore, the expression of D1R was decreased in skeletal muscles from streptozotocin (STZ)- and high-fat intake-induced T2DM mice, accompanied by increased D1R phosphorylation, which was reversed by exercise. A screening study showed that G protein-coupled receptor kinase 4 (GRK4) may be the candidate kinase for the regulation of D1R function, because, in addition to the increased GRK4 expression in skeletal muscles of T2DM mice, GRK4 transgenic T2DM mice exhibited lower insulin sensitivity, accompanied by higher D1R phosphorylation than control mice, whereas the AAV9-shGRK4 mice were much more sensitive to insulin than AAV9-null mice. Mechanistically, the up-regulation of GRK4 expression caused by increased reactive oxygen species (ROS) in IR was ascribed to the enhanced expression of c-Myc, a transcriptional factor of GRK4. Taken together, the present study shows that exercise, via regulation of ROS/c-Myc/GRK4 pathway, ameliorates D1R dysfunction and improves insulin sensitivity.

Kinase Activity Is Not Required for G Protein-Coupled Receptor Kinase 4 Restraining mTOR Signaling during Cilia and Kidney Development

SIGNIFICANCE STATEMENT

G protein-coupled receptor kinase 4 (GRK4) regulates renal sodium and water reabsorption. Although GRK4 variants with elevated kinase activity have been associated with salt-sensitive or essential hypertension, this association has been inconsistent among different study populations. In addition, studies elucidating how GRK4 may modulate cellular signaling are sparse. In an analysis of how GRK4 affects the developing kidney, the authors found that GRK4 modulates mammalian target of rapamycin (mTOR) signaling. Loss of GRK4 in embryonic zebrafish causes kidney dysfunction and glomerular cysts. Moreover, GRK4 depletion in zebrafish and cellular mammalian models results in elongated cilia. Rescue experiments suggest that hypertension in carriers of GRK4 variants may not be explained solely by kinase hyperactivity; instead, elevated mTOR signaling may be the underlying cause.

BACKGROUND

G protein-coupled receptor kinase 4 (GRK4) is considered a central regulator of blood pressure through phosphorylation of renal dopaminergic receptors and subsequent modulation of sodium excretion. Several nonsynonymous genetic variants of GRK4 have been only partially linked to hypertension, although these variants demonstrate elevated kinase activity. However, some evidence suggests that function of GRK4 variants may involve more than regulation of dopaminergic receptors alone. Little is known about the effects of GRK4 on cellular signaling, and it is also unclear whether or how altered GRK4 function might affect kidney development.

METHODS

To better understand the effect of GRK4 variants on the functionality of GRK4 and GRK4's actions in cellular signaling during kidney development, we studied zebrafish, human cells, and a murine kidney spheroid model.

RESULTS

Zebrafish depleted of Grk4 develop impaired glomerular filtration, generalized edema, glomerular cysts, pronephric dilatation, and expansion of kidney cilia. In human fibroblasts and in a kidney spheroid model, GRK4 knockdown produced elongated primary cilia. Reconstitution with human wild-type GRK4 partially rescues these phenotypes. We found that kinase activity is dispensable because kinase-dead GRK4 (altered GRK4 that cannot result in phosphorylation of the targeted protein) prevented cyst formation and restored normal ciliogenesis in all tested models. Hypertension-associated genetic variants of GRK4 fail to rescue any of the observed phenotypes, suggesting a receptor-independent mechanism. Instead, we discovered unrestrained mammalian target of rapamycin signaling as an underlying cause.

CONCLUSIONS

These findings identify GRK4 as novel regulator of cilia and of kidney development independent of GRK4's kinase function and provide evidence that the GRK4 variants believed to act as hyperactive kinases are dysfunctional for normal ciliogenesis.

Influence of AGTR1 and ABCB1 Gene Polymorphism on the Curative Effect of Irbesartan

The interindividual heterogeneity in response to the antihypertensive effect of irbesartan has received considerable attention because of gene polymorphism. In this study, we investigated the new combinational influences of AGTR1 and ABCB1 gene polymorphism on the therapeutic effect of irbesartan among Chinese hypertensive patients. A total of 353 samples including 168 normal people and 185 hypertensive patients were adopted, and genotypes comprise ABCB1 (CC, CT, and TT) and AGTR1 (AA and AC) in this study. The results of multiple linear regression models showed that no statistically significant differences were observed in blood pressure change following irbesartan administration in each genotype from either ABCB1 (CC, CT, and TT) or AGTR1 (AA and AC). However, spline smoothing analysis demonstrated that the blood pressure therapeutic responses of irbesartan presented a noticeable difference among different ABCB1 genotypes when irbesartan doses reached over 300 ng/mL. Eventually, we assumed that the different drug responses of irbesartan among various AGTR1 genotypes were due to the diversity of the irbesartan-conjugated protein, which is responsible for crossing-coupled intracellular G-protein-coupled receptors (GPCRs).

A Single Nucleotide Polymorphism in SH2B3/LNK Promotes Hypertension Development and Renal Damage

BACKGROUND

SH2B3 (SH2B adaptor protein 3) is an adaptor protein that negatively regulates cytokine signaling and cell proliferation. A common missense single nucleotide polymorphism in SH2B3 (rs3184504) results in substitution of tryptophan (Trp) for arginine (Arg) at amino acid 262 and is a top association signal for hypertension in human genome-wide association studies. Whether this variant is causal for hypertension, and if so, the mechanism by which it impacts pathogenesis is unknown.

METHODS

We used CRISPR-Cas9 technology to create mice homozygous for the major (Arg/Arg) and minor (Trp/Trp) alleles of this SH2B3 polymorphism. Mice underwent angiotensin II (Ang II) infusion to evaluate differences in blood pressure (BP) elevation and end-organ damage including albuminuria and renal fibrosis. Cytokine production and Stat4 phosphorylation was also assessed in Arg/Arg and Trp/Trp T cells.

RESULTS

Trp/Trp mice exhibit 10 mmHg higher systolic BP during chronic Ang II infusion compared to Arg/Arg controls. Renal injury and perivascular fibrosis are exacerbated in Trp/Trp mice compared to Arg/Arg controls following Ang II infusion. Renal and ex vivo stimulated splenic CD8+ T cells from Ang II-infused Trp/Trp mice produce significantly more interferon gamma (IFNg) compared to Arg/Arg controls. Interleukin-12 (IL-12)-induced IFNg production is greater in Trp/Trp compared to Arg/Arg CD8+ T cells. In addition, IL-12 enhances Stat4 phosphorylation to a greater degree in Trp/Trp compared to Arg/Arg CD8+ T cells, suggesting that Trp-encoding SH2B3 exhibits less negative regulation of IL-12 signaling to promote IFNg production. Finally, we demonstrated that a multi-SNP model genetically predicting increased SH2B3 expression in lymphocytes is inversely associated with hypertension and hypertensive chronic kidney disease in humans..

CONCLUSIONS

Taken together, these results suggest that the Trp encoding allele of rs3184504 is causal for BP elevation and renal dysfunction, in part through loss of SH2B3-mediated repression of T cell IL-12 signaling leading to enhanced IFNg production.

G-protein-coupled receptor kinase 4 causes renal angiotensin II type 2 receptor dysfunction by increasing its phosphorylation

Activation of the angiotensin II type 2 receptor (AT2R) induces diuresis and natriuresis. Increased expression or/and activity of G-protein-coupled receptor kinase 4 (GRK4) or genetic variants (e.g., GRK4γ142V) cause sodium retention and hypertension. Whether GRK4 plays a role in the regulation of AT2R in the kidney remains unknown. In the present study, we found that spontaneously hypertensive rats (SHRs) had increased AT2R phosphorylation and impaired AT2R-mediated diuretic and natriuretic effects, as compared with normotensive Wistar-Kyoto (WKY) rats. The regulation by GRK4 of renal AT2R phosphorylation and function was studied in human (h) GRK4γ transgenic mice. hGRK4γ142V transgenic mice had increased renal AT2R phosphorylation and impaired AT2R-mediated natriuresis, relative to hGRK4γ wild-type (WT) littermates. These were confirmed in vitro; AT2R phosphorylation was increased and AT2R-mediated inhibition of Na+-K+-ATPase activity was decreased in hGRK4γ142V, relative to hGRK4γ WT-transfected renal proximal tubule (RPT) cells. There was a direct physical interaction between renal GRK4 and AT2R that was increased in SHRs, relative to WKY rats. Ultrasound-targeted microbubble destruction of renal GRK4 decreased the renal AT2R phosphorylation and restored the impaired AT2R-mediated diuresis and natriuresis in SHRs. In vitro studies showed that GRK4 siRNA reduced AT2R phosphorylation and reversed the impaired AT2R-mediated inhibition of Na+-K+-ATPase activity in SHR RPT cells. Our present study shows that GRK4, at least in part, impairs renal AT2R-mediated diuresis and natriuresis by increasing its phosphorylation; inhibition of GRK4 expression and/or activity may be a potential strategy to improve the renal function of AT2R.

G Protein-Coupled Receptor Kinase 4 Is a Novel Prognostic Factor in Hepatocellular Carcinoma

Purpose

We previously reported that G protein-coupled receptor kinase (GRK) 4 halts cell cycle progression and induces cellular senescence in HEK293 cells. The present study was aimed at assessing the prognostic value of GRK4 in hepatocellular carcinoma (HCC).

Methods

GRK4 expression was detected by immunohistochemistry in paired tumoral and peritumoral tissues of 325 HCC patients. One hundred and twenty-six patients from Western China were utilized as a training cohort to develop a nomogram, while 86 patients from Eastern China were used as a validation cohort. The proliferation and migration of lentiviral-GRK4 expressing HepG2 cells were determined by MTT and wound healing assays.

Results

GRK4 was differentially expressed in HCC tissues. Tumoral GRK4 intensity, tumor type, and T stage were independent prognostic factors and used to form a nomogram for predicting overall survival (OS), which obtained a good concordance index of 0.82 and 0.77 in training and validation cohort, respectively. The positive and negative prediction values with nomogram were, respectively, 83% and 75% in training cohort and 100% and 52% in validation cohort. Patients with nomogram scores > 32 and 78 showed high risk for OS. Proliferation and motility capabilities were significantly restrained in GRK4-overexpressing HCC cells. Discussion. Low GRK4 expression in HCC tumor tissues indicates poor clinical outcomes. A prognostic nomogram including tumoral GRK4 expression would improve the predictive accuracy of OS in HCC patients. We also demonstrated that GRK4 overexpression inhibits proliferation and migration of HCC cells. The molecular mechanism underlying is worth further study.

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.

GRK4, A Potential Link between Hypertension and Breast Cancer

Hypertension and breast cancer are two common diseases occurring in women. Clinical studies have shown increased breast cancer incidence in hypertensive women. Several lines of evidence demonstrate that G protein-coupled Receptor Kinase 4 (GRK4) could be a common risk factor for hypertension and breast cancer. This article reviews our current understanding of molecular mechanisms of GRK4 in hypertension and breast cancer.

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

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

Current concepts and molecular mechanisms in pharmacogenetics of essential hypertension

Hypertension is a leading age-related disease in our society and if left untreated, leads to fatal cardiovascular complications. The prevalence of hypertension has increased and becomes a significant global health economic burden, particularly in lower-income societies. Many loci associated with blood pressure and hypertension have been reported by genome-wide association studies that provided potential targets for pharmacotherapy. Pharmacogenetic research had shown interindividual variations in drug efficacy, safety, and tolerability. This could be due to genetic polymorphisms in the pharmacokinetics (genes involved in a transporter, plasma protein binding, and metabolism) or pharmacodynamic pathway (receptors, ion channels, enzymes). Pharmacogenetics promises great hope toward targeted therapy, but challenges remain in implementing pharmacogenetic aided antihypertensive therapy in clinical practice. Using various databases, we analyzed the underlying mechanisms between the candidate gene polymorphisms and antihypertensive drug interactions and the challenges of implementing precision medicine. We review the emergence of pharmacogenetics and its relevance to clinical pharmacological practice.

Targeted capture sequencing identifies genetic variations of GRK4 and RDH8 in Han Chinese with essential hypertension in Xinjiang

Essential hypertension is a common cardiovascular disease with complex etiology, closely related to genetic and environmental factors. The pathogenesis of hypertension involves alteration in vascular resistance caused by sympathetic nervous system (SNS) and renin angiotensin system (RAS). Susceptibility factors of hypertension vary with regions and ethnicities. In this study, we conducted target capture sequencing on 54 genes related to SNS and RAS derived from a collection of Han nationality, consisting of 151 hypertension patients and 65 normal subjects in Xinjiang, China. Six non-synonymous mutations related to hypertension were identified, including GRK4 rs1644731 and RDH8 rs1801058, Mutations are predicted to affect 3D conformation, force field, transmembrane domain and RNA secondary structure of corresponding genes. Based on protein interaction network and pathway enrichment, GRK4 is predicted to participate in hypertension by acting on dopaminergic synapse, together with interacting components. RDH8 is involved in vitamin A (retinol) metabolism and consequent biological processes related to hypertension. Thus, GRK4 and RDH8 may serve as susceptibility genes for hypertension. This finding provides new genetic evidence for elucidating risk factors of hypertension in Han nationality in Xinjiang, which in turn, enriches genetic resource bank of hypertension susceptibility genes.

The Hypertension Related Gene G-Protein Coupled Receptor Kinase 4 Contributes to Breast Cancer Proliferation

PURPOSE

Clinical studies have shown that breast cancer risk is increased in hypertensive women. The underlying molecular mechanism remains undetermined. The current study tests our hypothesis that G protein coupled receptor kinase 4 (GRK4) is a molecule that links hypertension and breast cancer. GRK4 plays an important role in regulation of renal sodium excretion. Sustained activation of GRK4 as in the circumstances of single nucleotide polymorphism (SNPs) causes hypertension. Expression of GRK4 in the kidney is regulated by cMyc, an oncogene that is amplified in breast cancer.

METHODS

Western analysis was used to evaluate GRK4 protein expression in seven breast cancer cell lines. GRK4 gene single nucleotide polymorphism in breast cancer cell lines and in breast cancer cDNA arrays were determined using TaqMan Genotyping qPRC. The function of GRK4 was evaluated in MCF-7 cells with cMyc knock-down and GRK4 re-expression and in MDA-MB-468 cells expressing inducible GRK4 shRNA lentivirus constructs. Nuclei counting and 5-Bromo-2'-deoxy-uridine (BrdU) labeling were used to evaluate cell growth and proliferation.

RESULTS

Genotyping of GRK4 SNPs in breast cancer cDNA arrays (n = 94) revealed that the frequency of carrying two hypertension related SNPs A142 V or R65 L is threefold higher in breast cancer patients than in healthy people (P = 7.53E-11). GRK4 protein is expressed in seven breast cancer cell lines but not the benign mammary epithelial cell line, MCF-10A. Three hypertension related SNPs in the GRK4 gene were identified in the breast cancer cell lines. Except for BT20, all other breast cancer lines have 1-3 GRK4 SNPs of which A142 V occurs in all 6 lines. MDA-MB-468 cells contain homozygous A142 V and R65 L SNPs. Knocking down cMyc in MCF-7 cells significantly reduced the growth rate, which was rescued by re-expression of GRK4. We then generated three stable GRK4 knock-down MDA-MB-468 lines using inducible lentiviral shRNA vectors. Doxycycline (Dox) induced GRK4 silencing significantly reduced GRK4 mRNA and protein levels, growth rates, and proliferation. As a marker of cell proliferation, the percentage of BrdU-labeled cells decreased from 45 ± 3% in the cells without Dox to 32 ± 5% in the cells treated with 0.1 µg/mL Dox.

CONCLUSIONS

GRK4 acts as an independent proliferation promotor in breast cancer. Our results suggest that targeted inhibition of GRK4 could be a new therapy for both hypertension and breast cancer.

NFAT5 Is Involved in GRP-Enhanced Secretion of GLP-1 by Sodium

Gastrin, secreted by G-cells, and glucagon-like peptide-1 (GLP-1), secreted by L-cells, may participate in the regulation of sodium balance. We studied the effect of sodium in mice in vivo and mouse ileum and human L-cells, on GLP-1 secretion, and the role of NFAT5 and gastrin-releasing peptide receptor (GRPR) in this process. A high-sodium diet increases serum GLP-1 levels in mice. Increasing sodium concentration stimulates GLP-1 secretion from mouse ileum and L-cells. GRP enhances the high sodium-induced increase in GLP-1 secretion. High sodium increases cellular GLP-1 expression, while low and high sodium concentrations increase NFAT5 and GRPR expression. Silencing NFAT5 in L-cells abrogates the stimulatory effect of GRP on the high sodium-induced GLP-1 secretion and protein expression, and the sodium-induced increase in GRPR expression. GLP-1 and gastrin decrease the expression of Na⁺-K⁺/ATPase and increase the phosphorylation of sodium/hydrogen exchanger type 3 (NHE3) in human renal proximal tubule cells (hRPTCs). This study gives a new perspective on the mechanisms of GLP-1 secretion, especially that engendered by ingested sodium, and the ability of GLP-1, with gastrin, to decrease Na⁺-K⁺/ATPase expression and NHE3 function in hRPTCs. These results may contribute to the better utilization of current and future GLP-1-based drugs in the treatment of hypertension.

The role of G protein-coupled receptor kinase 4 in cardiomyocyte injury after myocardial infarction

AIMS

G protein-coupled receptor kinase 4 (GRK4) has been reported to play an important role in hypertension, but little is known about its role in cardiomyocytes and myocardial infarction (MI). The goal of present study is to explore the role of GRK4 in the pathogenesis and progression of MI.

METHODS AND RESULTS

We studied the expression and distribution pattern of GRK4 in mouse heart after MI. GRK4 A486V transgenic mice, inducible cardiomyocyte-specific GRK4 knockout mice, were generated and subjected to MI with their control mice. Cardiac infarction, cardiac function, cardiomyocyte apoptosis, autophagic activity, and HDAC4 phosphorylation were assessed. The mRNA and protein levels of GRK4 in the heart were increased after MI. Transgenic mice with the overexpression of human GRK4 wild type (WT) or human GRK4 A486V variant had increased cardiac infarction, exaggerated cardiac dysfunction and remodelling. In contrast, the MI-induced cardiac dysfunction and remodelling were ameliorated in cardiomyocyte-specific GRK4 knockout mice. GRK4 overexpression in cardiomyocytes aggravated apoptosis, repressed autophagy, and decreased beclin-1 expression, which were partially rescued by the autophagy agonist rapamycin. MI also induced the nuclear translocation of GRK4, which inhibited autophagy by increasing HDAC4 phosphorylation and decreasing its binding to the beclin-1 promoter. HDAC4 S632A mutation partially restored the GRK4-induced inhibition of autophagy. MI caused greater impairment of cardiac function in patients carrying the GRK4 A486V variant than in WT carriers.

CONCLUSION

GRK4 increases cardiomyocyte injury during MI by inhibiting autophagy and promoting cardiomyocyte apoptosis. These effects are mediated by the phosphorylation of HDAC4 and a decrease in beclin-1 expression.

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.

SNX-PXA-RGS-PXC Subfamily of SNXs in the Regulation of Receptor-Mediated Signaling and Membrane Trafficking

The SNX-PXA-RGS-PXC subfamily of sorting nexins (SNXs) belongs to the superfamily of SNX proteins. SNXs are characterized by the presence of a common phox-homology (PX) domain, along with other functional domains that play versatile roles in cellular signaling and membrane trafficking. In addition to the PX domain, the SNX-PXA-RGS-PXC subfamily, except for SNX19, contains a unique RGS (regulators of G protein signaling) domain that serves as GTPase activating proteins (GAPs), which accelerates GTP hydrolysis on the G protein α subunit, resulting in termination of G protein-coupled receptor (GPCR) signaling. Moreover, the PX domain selectively interacts with phosphatidylinositol-3-phosphate and other phosphoinositides found in endosomal membranes, while also associating with various intracellular proteins. Although SNX19 lacks an RGS domain, all members of the SNX-PXA-RGS-PXC subfamily serve as dual regulators of receptor cargo signaling and endosomal trafficking. This review discusses the known and proposed functions of the SNX-PXA-RGS-PXC subfamily and how it participates in receptor signaling (both GPCR and non-GPCR) and endosomal-based membrane trafficking. Furthermore, we discuss the difference of this subfamily of SNXs from other subfamilies, such as SNX-BAR nexins (Bin-Amphiphysin-Rvs) that are associated with retromer or other retrieval complexes for the regulation of receptor signaling and membrane trafficking. Emerging evidence has shown that the dysregulation and malfunction of this subfamily of sorting nexins lead to various pathophysiological processes and disorders, including hypertension.

Targeting GRK5 for Treating Chronic Degenerative Diseases

G protein-coupled receptors (GPCRs) are the largest family of cell-surface receptors and they are responsible for the transduction of extracellular signals, regulating almost all aspects of mammalian physiology. These receptors are specifically regulated by a family of serine/threonine kinases, called GPCR kinases (GRKs). Given the biological role of GPCRs, it is not surprising that GRKs are also involved in several pathophysiological processes. Particular importance is emerging for GRK5, which is a multifunctional protein, expressed in different cell types, and it has been found located in single or multiple subcellular compartments. For instance, when anchored to the plasma membrane, GRK5 exerts its canonical function, regulating GPCRs. However, under certain conditions (e.g., pro-hypertrophic stimuli), GRK5 translocates to the nucleus of cells where it can interact with non-GPCR-related proteins as well as DNA itself to promote “non-canonical” signaling, including gene transcription. Importantly, due to these actions, several studies have demonstrated that GRK5 has a pivotal role in the pathogenesis of chronic-degenerative disorders. This is true in the cardiac cells, tumor cells, and neurons. For this reason, in this review article, we will inform the readers of the most recent evidence that supports the importance of targeting GRK5 to prevent the development or progression of cancer, cardiovascular, and neurological diseases.

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.

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.

GRK4-mediated adiponectin receptor-1 phosphorylative desensitization as a novel mechanism of reduced renal sodium excretion in hypertension

Hypertensive patients have impaired sodium excretion. However, the mechanisms are incompletely understood. Despite the established association between obesity/excess adiposity and hypertension, whether and how adiponectin, one of the adipokines, contributes to impaired sodium excretion in hypertension has not been previously investigated. The current study tested the hypothesis that adiponectin promotes natriuresis and diuresis in the normotensive state. However, impaired adiponectin-mediated natriuresis and diuresis are involved in pathogenesis of hypertension. We found that sodium excretion was reduced in adiponectin knockout (Adipo-/-) mice; intrarenal arterial infusion of adiponectin-induced natriuresis and diuresis in Wistar-Kyoto (WKY) rats. However, the natriuretic and diuretic effects of adiponectin were impaired in spontaneously hypertensive rats (SHRs), which were ascribed to the hyperphosphorylation of adiponectin receptor and subsequent uncoupling from Gαi. Inhibition of adiponectin receptor phosphorylation by a specific point mutation restored its coupling with Gαi and the adiponectin-mediated inhibition of Na+-K+-ATPase activity in renal proximal tubule (RPT) cells from SHRs. Finally, we identified G protein-coupled receptor kinase 4 (GRK4) as a mediator of adiponectin receptor hyperphosphorylation; mice transgenic for a hyperphosphorylating variant of GRK4 replicated the abnormal adiponectin function observed in SHRs, whereas down-regulation of GRK4 by renal ultrasound-directed small interfering RNA (siRNA) restored the adiponectin-mediated sodium excretion and reduced the blood pressure in SHRs. We conclude that the stimulatory effect of adiponectin on sodium excretion is impaired in hypertension, which is ascribed to the increased renal GRK4 expression and activity. Targeting GRK4 restores impaired adiponectin-mediated sodium excretion in hypertension, thus representing a novel strategy against hypertension.

Angiotensin Receptors Heterodimerization and Trafficking: How Much Do They Influence Their Biological Function?

G-protein–coupled receptors (GPCRs) are targets for around one third of currently approved and clinical prescribed drugs and represent the largest and most structurally diverse family of transmembrane signaling proteins, with almost 1000 members identified in the human genome. Upon agonist stimulation, GPCRs are internalized and trafficked inside the cell: they may be targeted to different organelles, recycled back to the plasma membrane or be degraded. Once inside the cell, the receptors may initiate other signaling pathways leading to different biological responses. GPCRs’ biological function may also be influenced by interaction with other receptors. Thus, the ultimate cellular response may depend not only on the activation of the receptor from the cell membrane, but also from receptor trafficking and/or the interaction with other receptors. This review is focused on angiotensin receptors and how their biological function is influenced by trafficking and interaction with others receptors.

Role of GRK4 in the regulation of the renal ETB receptor in hypertension

The endothelin receptor type B (ETBR) regulates water and electrolyte balance and blood pressure, in part, by inhibiting renal sodium transport. Our preliminary study found that the ETBR-mediated diuresis and natriuresis are impaired in hypertension with unknown mechanism. Persistently increased activity of G protein-coupled receptor kinase 4 (GRK4), caused by increased expression or genetic variants (eg, GRKγ142V), impairs the ability of the kidney to excrete a sodium load, in part, by impairing renal dopamine D₁ receptor function through persistent phosphorylation. Our present study found that although renal ETBR expression was not different between Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHRs), renal ETBR phosphorylation was higher in SHRs. The role of hyper-phosphorylation in impaired ETBR-function was supported by results in human (h) GRK4γ transgenic mice. Stimulation of ETBR by BQ3020-induced natriuresis in human (h) GRK4γ wild-type (WT) mice. However, in hGRK4γ 142V transgenic mice, the renal ETBR was hyperphosphorylated and ETBR-mediated natriuresis and diuresis were not evident. There were co-localization and co-immunoprecipitation of ETBR and GRK4 in renal proximal tubule (RPT) cells from both WKY and SHRs but was greater in the latter than the former group. SiRNA-mediated downregulation of GRK4 expression, recovered the impaired inhibitory effect of ETBR on Na⁺ -K⁺ -ATPase activity in RPT cells from SHR. In vivo downregulation of renal GRK4 expression, via ultrasound-targeted microbubble destruction, decreased ETBR phosphorylation and restored ETBR-mediated natriuresis and diuresis in SHRs. This study provides a mechanism by which GRK4, via regulation of renal ETBR function, participates in the pathogenesis of hypertension.

Sorting nexin 1 loss results in increased oxidative stress and hypertension

Acute renal depletion of sorting nexin 1 (SNX1) in mice results in blunted natriuretic response and hypertension due to impaired dopamine D₅ receptor (D₅ R) activity. We elucidated the molecular mechanisms for these phenotypes in Snx1^-/- mice. These mice had increased renal expressions of angiotensin II type 1 receptor (AT₁ R), NADPH oxidase (NOX) subunits, D₅ R, and NaCl cotransporter. Basal reactive oxygen species (ROS), NOX activity, and blood pressure (BP) were also higher in Snx1^-/- mice, which were normalized by apocynin, a drug that prevents NOX assembly. Renal proximal tubule (RPT) cells from hypertensive (HT) Euro-American males had deficient SNX1 activity, impaired D₅ R endocytosis, and increased ROS compared with cells from normotensive (NT) Euro-American males. siRNA-mediated depletion of SNX1 in RPT cells from NT subjects led to a blunting of D₅ R agonist-induced increase in cAMP production and decrease in Na⁺ transport, effects that were normalized by over-expression of SNX1. Among HT African-Americans, three of the 12 single nucleotide polymorphisms interrogated for the SNX1 gene were associated with a decrease in systolic BP in response to hydrochlorothiazide (HCTZ). The results illustrate a new paradigm for the development of hypertension and imply that the trafficking protein SNX1 may be a crucial determinant for hypertension and response to antihypertensive therapy.

Lipid rafts are required for effective renal D1 dopamine receptor function

Effective receptor signaling is anchored on the preferential localization of the receptor in lipid rafts, which are plasma membrane platforms replete with cholesterol and sphingolipids. We hypothesized that the dopamine D₁ receptor (D₁ R) contains structural features that allow it to reside in lipid rafts for its activity. Mutation of C347 palmitoylation site and Y218 of a newly identified Cholesterol Recognition Amino Acid Consensus motif resulted in the exclusion of D₁ R from lipid rafts, blunted cAMP response, impaired sodium transport, and increased oxidative stress in renal proximal tubule cells (RPTCs). Kidney-restricted silencing of Drd1 in C57BL/6J mice increased blood pressure (BP) that was normalized by renal tubule-restricted rescue with D₁ R-wild-type but not the mutant D₁ R 347A that lacks a palmitoylation site. Kidney-restricted disruption of lipid rafts by β-MCD jettisoned the D₁ R from the brush border, decreased sodium excretion, and increased oxidative stress and BP in C57BL/6J mice. Deletion of the PX domain of the novel D₁ R-binding partner sorting nexin 19 (SNX19) resulted in D₁ R partitioning solely to non-raft domains, while silencing of SNX19 impaired D₁ R function in RPTCs. Kidney-restricted silencing of Snx19 resulted in hypertension in C57BL/6J mice. Our results highlight the essential role of lipid rafts for effective D₁ R signaling.

Transcriptional analysis of renal dopamine-mediated Na+ homeostasis response to environmental salinity stress in Scatophagus argus

Background

To control the osmotic pressure in the body, physiological adjustments to salinity fluctuations require the fish to regulate body fluid homeostasis in relation to environmental change via osmoregulation. Previous studies related to osmoregulation were focused primarily on the gill; however, little is known about another organ involved in osmoregulation, the kidney. The salinity adaptation of marine fish involves complex physiological traits, metabolic pathways and molecular and gene networks in osmoregulatory organs. To further explore of the salinity adaptation of marine fish with regard to the role of the kidney, the euryhaline fish Scatophagus argus was employed in the present study. Renal expression profiles of S. argus at different salinity levels were characterized using RNA-sequencing, and an integrated approach of combining molecular tools with physiological and biochemical techniques was utilized to reveal renal osmoregulatory mechanisms in vivo and in vitro.

Results

S. argus renal transcriptomes from the hyposaline stress (0‰, freshwater [FW]), hypersaline stress (50‰, hypersaline water [HW]) and control groups (25‰) were compared to elucidate potential osmoregulatory mechanisms. In total, 19,012 and 36,253 differentially expressed genes (DEGs) were obtained from the FW and HW groups, respectively. Based on the functional classification of DEGs, the renal dopamine system-induced Na⁺ transport was demonstrated to play a fundamental role in osmoregulation. In addition, for the first time in fish, many candidate genes associated with the dopamine system were identified. Furthermore, changes in environmental salinity affected renal dopamine release/reuptake by regulating the expression of genes related to dopamine reuptake (dat and nkaα1), vesicular traffic-mediated dopamine release (pink1, lrrk2, ace and apn), DAT phosphorylation (CaMKIIα and pkcβ) and internalization (akt1). The associated transcriptional regulation ensured appropriate extracellular dopamine abundance in the S. argus kidney, and fluctuations in extracellular dopamine produced a direct influence on Na⁺/K⁺-ATPase (NKA) expression and activity, which is associated with Na⁺ homeostasis.

Conclusions

These transcriptomic data provided insight into the molecular basis of renal osmoregulation in S. argus. Significantly, the results of this study revealed the mechanism of renal dopamine system-induced Na⁺ transport is essential in fish osmoregulation.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5795-x) contains supplementary material, which is available to authorized users.

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.

Genetics of Hypertension in African Americans and Others of African Descent

Hypertension is the leading cause of cardiovascular disease in the United States, affecting up to one-third of adults. When compared to other ethnic or racial groups in the United States, African Americans and other people of African descent show a higher incidence of hypertension and its related comorbidities; however, the genetics of hypertension in these populations has not been studied adequately. Several genes have been identified to play a role in the genetics of hypertension. They include genes regulating the renin-aldosterone-angiotensin system (RAAS), such as Sodium Channel Epithelial 1 Beta Subunit (SCNN1B), Armadillo Repeat Containing 5 (ARMC5), G Protein-Coupled Receptor Kinase 4 (GRK4), and Calcium Voltage-Gated Channel Subunit Alpha1 D (CACNA1D). In this review, we focus on recent genetic findings available in the public domain for potential differences between African Americans and other populations. We also cover some recent and relevant discoveries in the field of low-renin hypertension from our laboratory at the National Institutes of Health. Understanding the different genetics of hypertension among various groups is essential for effective precision-guided medical therapy of high blood pressure.

Non-additive effects of ACVR2A in preeclampsia in a Philippine population

BACKGROUND

Multiple interrelated pathways contribute to the pathogenesis of preeclampsia, and variants in susceptibility genes may play a role among Filipinos, an ethnically distinct group with high prevalence of the disease. The objective of this study was to examine the association between variants in maternal candidate genes and the development of preeclampsia in a Philippine population.

METHODS

A case-control study involving 29 single nucleotide polymorphisms (SNPs) in 21 candidate genes was conducted in 150 patients with preeclampsia (cases) and 175 women with uncomplicated normal pregnancies (controls). Genotyping for the GRK4 and DRD1 gene variants was carried out using the TaqMan Assay, and all other variants were assayed using the Sequenom MassARRAY Iplex Platform. PLINK was used for SNP association testing. Multilocus association analysis was performed using multifactor dimensionality reduction (MDR) analysis.

RESULTS

Among the clinical factors, older age (P <  1 × 10-4), higher BMI (P <  1 × 10-4), having a new partner (P = 0.006), and increased time interval from previous pregnancy (P = 0.018) associated with preeclampsia. The MDR algorithm identified the genetic variant ACVR2A rs1014064 as interacting with age and BMI in association with preeclampsia among Filipino women.

CONCLUSIONS

The MDR algorithm identified an interaction between age, BMI and ACVR2A rs1014064, indicating that context among genetic variants and demographic/clinical factors may be crucial to understanding the pathogenesis of preeclampsia among Filipino women.

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.

G protein-coupled receptor kinase 4-induced cellular senescence and its senescence-associated gene expression profiling

Senescent cells have lost their capacity for proliferation and manifest as irreversibly in cell cycle arrest. Many membrane receptors, including G protein-coupled receptors (GPCRs), initiate a variety of intracellular signaling cascades modulating cell division and potentially play roles in triggering cellular senescence response. GPCR kinases (GRKs) belong to a family of serine/threonine kinases. Although their role in homologous desensitization of activated GPCRs is well established, the involvement of the kinases in cell proliferation is still largely unknown. In this study, we isolated GRK4-GFP expressing HEK293 cells by fluorescence-activated cell sorting (FACS) and found that the ectopic expression of GRK4 halted cell proliferation. Cells expressing GRK4 (GRK4(+)) demonstrated cell cycle G1/G0 phase arrest, accompanied with significant increase of senescence-associated-β-galactosidase (SA-β-Gal) activity. Expression profiling analysis of 78 senescence-related genes by qRT-PCR showed a total of 17 genes significantly changed in GRK4(+) cells (≥ 2 fold, p < 0.05). Among these, 9 genes - AKT1, p16^INK4, p27^KIP1, p19^INK4, IGFBP3, MAPK14, PLAU, THBS1, TP73 - were up-regulated, while 8 genes, Cyclin A2, Cyclin D1, CDK2, CDK6, ETS1, NBN, RB1, SIRT1, were down-regulated. The increase in cyclin-dependent kinase inhibitors (p16, p27) and p38 MAPK proteins (MAPK14) was validated by immunoblotting. Neither p53 nor p21^Waf1/Cip1 protein was detectable, suggesting no p53 activation in the HEK293 cells. These results unveil a novel function of GRK4 on triggering a p53-independent cellular senescence, which involves an intricate signaling network.

Primary Pediatric Hypertension: Current Understanding and Emerging Concepts

The rising prevalence of primary pediatric hypertension and its tracking into adult hypertension point to the importance of determining its pathogenesis to gain insights into its current and emerging management. Considering that the intricate control of BP is governed by a myriad of anatomical, molecular biological, biochemical, and physiological systems, multiple genes are likely to influence an individual's BP and susceptibility to develop hypertension. The long-term regulation of BP rests on renal and non-renal mechanisms. One renal mechanism relates to sodium transport. The impaired renal sodium handling in primary hypertension and salt sensitivity may be caused by aberrant counter-regulatory natriuretic and anti-natriuretic pathways. The sympathetic nervous and renin-angiotensin-aldosterone systems are examples of antinatriuretic pathways. An important counter-regulatory natriuretic pathway is afforded by the renal autocrine/paracrine dopamine system, aberrations of which are involved in the pathogenesis of hypertension, including that associated with obesity. We present updates on the complex interactions of these two systems with dietary salt intake in relation to obesity, insulin resistance, inflammation, and oxidative stress. We review how insults during pregnancy such as maternal and paternal malnutrition, glucocorticoid exposure, infection, placental insufficiency, and treatments during the neonatal period have long-lasting effects in the regulation of renal function and BP. Moreover, these effects have sex differences. There is a need for early diagnosis, frequent monitoring, and timely management due to increasing evidence of premature target organ damage. Large controlled studies are needed to evaluate the long-term consequences of the treatment of elevated BP during childhood, especially to establish the validity of the current definition and treatment of pediatric hypertension.

Pathophysiological consequences of receptor mistraffic: Tales from the platelet P2Y12 receptor

Genetic variations in G protein-coupled receptor (GPCR) genes can disrupt receptor function in a wide variety of human genetic diseases, including platelet bleeding disorders. Platelets are critical for haemostasis with inappropriate platelet activation leading to the development of arterial thrombosis, which can result in heart attack and stroke whilst decreased platelet activity is associated with an increased risk of bleeding. GPCRs expressed on the surface of platelets play key roles in regulating platelet activity and therefore function. Receptors include purinergic receptors (P2Y₁ and P2Y₁₂), proteinase-activated receptor (PAR1 and PAR4) and thromboxane receptors (TPα), among others. Pharmacological blockade of these receptors forms a powerful therapeutic tool in the treatment and prevention of arterial thrombosis. With the advance of genomic technologies, there has been a substantial increase in the identification of naturally occurring rare and common GPCR variants. These variants include single-nucleotide polymorphisms (SNPs) and insertion or deletions that have the potential to alter GPCR expression or function. A number of defects in platelet GPCRs that disrupt receptor function have now been characterized in patients with mild bleeding disorders. This review will focus on rare, function-disrupting variants of platelet GPCRs with particular emphasis upon mutations in the P2Y₁₂ receptor gene that affect receptor traffic to modulate platelet function. Further this review will outline how the identification and characterization of function-disrupting GPCR mutations provides an essential link in translating our detailed understanding of receptor traffic and function in cell line studies into relevant human biological systems.

G Protein-Coupled Receptor Kinases in the Inflammatory Response and Signaling

G protein-coupled receptor kinases (GRKs) are serine/threonine kinases that regulate a large and diverse class of G protein-coupled receptors (GPCRs). Through GRK phosphorylation and β-arrestin recruitment, GPCRs are desensitized and their signal terminated. Recent work on these kinases has expanded their role from canonical GPCR regulation to include noncanonical regulation of non-GPCR and nonreceptor substrates through phosphorylation as well as via scaffolding functions. Owing to these and other regulatory roles, GRKs have been shown to play a critical role in the outcome of a variety of physiological and pathophysiological processes including chemotaxis, signaling, migration, inflammatory gene expression, etc. This diverse set of functions for these proteins makes them popular targets for therapeutics. Role for these kinases in inflammation and inflammatory disease is an evolving area of research currently pursued in many laboratories. In this review, we describe the current state of knowledge on various GRKs pertaining to their role in inflammation and inflammatory diseases.

Increased renal oxidative stress in salt-sensitive human GRK4γ486V transgenic mice

We tested the hypothesis that salt-sensitive hypertension is caused by renal oxidative stress by measuring the blood pressure and reactive oxygen species-related proteins in the kidneys of human G protein-coupled receptor kinase 4γ (hGRK4γ) 486V transgenic mice and non-transgenic (Non-T) littermates on normal and high salt diets. High salt diet increased the blood pressure, associated with impaired sodium excretion, in hGRK4γ486V mice. Renal expressions of NOX isoforms were similar in both strains on normal salt diet but NOX2 was decreased by high salt diet to a greater extent in Non-T than hGRK4γ486V mice. Renal HO-2, but not HO-1, protein was greater in hGRK4γ486V than Non-T mice on normal salt diet and normalized by high salt diet. On normal salt diet, renal CuZnSOD and ECSOD proteins were similar but renal MnSOD was lower in hGRK4γ486V than Non-T mice and remained low on high salt diet. High salt diet decreased renal CuZnSOD in hGRK4γ486V but not Non-T mice and decreased renal ECSOD to a greater extent in hGRK4γ486V than Non-T mice. Renal SOD activity, superoxide production, and NOS3 protein were similar in two strains on normal salt diet. However, high salt diet decreased SOD activity and NOS3 protein and increased superoxide production in hGRK4γ486V mice but not in Non-T mice. High salt diet also increased urinary 8-isoprostane and 8-hydroxydeoxyguanosine to a greater extent in hGRK4γ486V than Non-T mice. hGRK4γwild-type mice were normotensive and hGRK4γ142V mice were hypertensive but both were salt-resistant and in normal redox balance. Chronic tempol treatment partially prevented the salt-sensitivity of hGRK4γ486V mice. Thus, hGRK4γ486V causes salt-sensitive hypertension due, in part, to defective renal antioxidant mechanisms.

Downregulation of Renal G Protein-Coupled Receptor Kinase Type 4 Expression via Ultrasound-Targeted Microbubble Destruction Lowers Blood Pressure in Spontaneously Hypertensive Rats

BACKGROUND

G protein-coupled receptor kinase type 4 (GRK4) plays a vital role in the long-term control of blood pressure (BP) and sodium excretion by regulating renal G protein-coupled receptor phosphorylation, including dopamine type 1 receptor (D1R). Ultrasound-targeted microbubble destruction (UTMD) is a promising method for gene delivery. Whether this method can deliver GRK4 small interfering RNA (siRNA) and lower BP is not known.

METHODS AND RESULTS

BP, 24-hour sodium excretion, and urine volume were measured after UTMD-targeted GRK4 siRNA delivery to the kidney in spontaneously hypertensive rats. The expression levels of GRK4 and D1R were determined by immunoblotting. The phosphorylation of D1R was investigated using immunoprecipitation. The present study revealed that UTMD-mediated renal GRK4 siRNA delivery efficiently reduced GRK4 expression and lowered BP in spontaneously hypertensive rats, accompanied by increased sodium excretion. The increased sodium excretion might be accounted for by the UTMD regulation of D1R phosphorylation and function in spontaneously hypertensive rats. Further analysis showed that, although UTMD had no effect on D1R expression, it reduced D1R phosphorylation in spontaneously hypertensive rats kidneys and consequently increased D1R-mediated natriuresis and diuresis.

CONCLUSIONS

Taken together, these study results indicate that UTMD-targeted GRK4 siRNA delivery to the kidney effectively reduces D1R phosphorylation by inhibiting renal GRK4 expression, improving D1R-mediated natriuresis and diuresis, and lowering BP, which may provide a promising novel strategy for gene therapy for hypertension.

G-Protein-Coupled Receptor Kinase 2 (GRK2) Inhibitors: Current Trends and Future Perspectives

G-protein-coupled receptor kinase 2 (GRK2) is a G-protein-coupled receptor kinase that is ubiquitously expressed in many tissues and regulates various intracellular mechanisms. The up- or down-regulation of GRK2 correlates with several pathological disorders. GRK2 plays an important role in the maintenance of heart structure and function; thus, this kinase is involved in many cardiovascular diseases. GRK2 up-regulation can worsen cardiac ischemia; furthermore, increased kinase levels occur during the early stages of heart failure and in hypertensive subjects. GRK2 up-regulation can lead to changes in the insulin signaling cascade, which can translate to insulin resistance. Increased GRK2 levels also correlate with the degree of cognitive impairment that is typically observed in Alzheimer's disease. This article reviews the most potent and selective GRK2 inhibitors that have been developed. We focus on their mechanism of action, inhibition profile, and structure-activity relationships to provide insight into the further development of GRK2 inhibitors as drug candidates.

G Protein-Coupled Receptor-G-Protein βγ-Subunit Signaling Mediates Renal Dysfunction and Fibrosis in Heart Failure

Development of CKD secondary to chronic heart failure (CHF), known as cardiorenal syndrome type 2 (CRS2), clinically associates with organ failure and reduced survival. Heart and kidney damage in CRS2 results predominantly from chronic stimulation of G protein-coupled receptors (GPCRs), including adrenergic and endothelin (ET) receptors, after elevated neurohormonal signaling of the sympathetic nervous system and the downstream ET system, respectively. Although we and others have shown that chronic GPCR stimulation and the consequent upregulated interaction between the G-protein βγ-subunit (Gβγ), GPCR-kinase 2, and β-arrestin are central to various cardiovascular diseases, the role of such alterations in kidney diseases remains largely unknown. We investigated the possible salutary effect of renal GPCR-Gβγ inhibition in CKD developed in a clinically relevant murine model of nonischemic hypertrophic CHF, transverse aortic constriction (TAC). By 12 weeks after TAC, mice developed CKD secondary to CHF associated with elevated renal GPCR-Gβγ signaling and ET system expression. Notably, systemic pharmacologic Gβγ inhibition by gallein, which we previously showed alleviates CHF in this model, attenuated these pathologic renal changes. To investigate a direct effect of gallein on the kidney, we used a bilateral ischemia-reperfusion AKI mouse model, in which gallein attenuated renal dysfunction, tissue damage, fibrosis, inflammation, and ET system activation. Furthermore, in vitro studies showed a key role for ET receptor-Gβγ signaling in pathologic fibroblast activation. Overall, our data support a direct role for GPCR-Gβγ in AKI and suggest GPCR-Gβγ inhibition as a novel therapeutic approach for treating CRS2 and AKI.

Novel round cells in urine sediment and their clinical implications

BACKGROUND

Voided urine contains a variety of cells from the kidney and urinary tract and urinalysis provides us various information by investigating cellular components. We investigated urine sediment from renal impaired patients.

RESULTS

We found 'round cell' to be distinct from known cells in sediment and is close to proximal convoluted tubule-derived cells based on morphology and molecular marker expression (GGT1 but not podocalyxin). Also it was positive for undifferentiated cell markers, including PAX2, WT1, OSR1, and SIX2. They were observed in end-stage renal failure patients and the number of cells was correlated with the severity of chronic kidney disease. A prospective analysis revealed that patients who had more round cells were more likely to require hemodialysis within a year.

CONCLUSION

Round cells are a novel marker that can be used to predict the need for hemodialysis.

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.

Mycophenolate mofetil and curcumin provide comparable therapeutic benefit in experimental chronic kidney disease: role of Nrf2-Keap1 and renal dopamine pathways

Increased oxidative stress and inflammation have an important role in the pathophysiology of chronic kidney disease (CKD). On the other hand, more affordable therapeutic alternatives for treating this disease are urgently needed. Therefore, we compared the therapeutic efficacy of curcumin and mycophenolate mofetil (MMF) in 5/6 nephrectomy (5/6 Nx) model of CKD. Also, we evaluated whether both compounds provide benefit through the preservation of similar antioxidant mechanisms. Four groups of male Wistar were studied over a period of 4 wk. Control sham group (n= 12), 5/6 Nx (n = 12), 5/6 Nx + MMF (30 mg/k BW/day, n = 11) and 5/6 Nx + Curcumin (120 mg/k BW/day, n = 12). Renal function and markers of oxidative stress and inflammation were evaluated. Also Nrf2-Keap1 and renal dopamine, antioxidant pathways were assessed. 5/6 Nx induced an altered renal autoregulation response, proteinuria, and hypertension; these effects were in association with increased oxidative stress, endothelial dysfunction and renal inflammation. The mechanisms associated with these alterations included a reduced nuclear translocation of Nrf2 and hyperphosphorylation of dopamine D1 receptor with a concurrent overactivation of renal NADPH oxidase. Treatments with MMF and curcumin provided equivalent therapeutic efficacy as both prevented functional renal alterations as well as preserved antioxidant capacity and avoided renal inflammatory infiltration. Moreover, both treatments preserved Nrf2-Keap1 and renal dopamine antioxidant pathways. In summary, therapeutic strategies aimed to preserve renal antioxidant pathways can help to retard the progression of CKD.