Recent Updates on the Proximal Tubule Renin-Angiotensin System in Angiotensin II-Dependent Hypertension

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Leonotis ocymifolia (Burm.f.) Iwarsson aerial parts aqueous extract mitigates cisplatin-induced nephrotoxicity via attenuation of inflammation, and DNA damage

Herein, we explored the protective effect of Leonotis ocymifolia (Burm.f.) Iwarsson aerial parts extract (LO) against cisplatin (CP)-induced nephrotoxicity in rats and profiled their phytocontents. A total of 31 compounds belonging to organic and phenolic acids and their glycosides as well as flavonoids and their O- and C-glycosides were identified through LC-MS/MS. The DPPH and FRAP assays revealed that the extract had powerful antioxidant properties. The in vivo results demonstrated that administering LO extract for 30 days (40 and 80 mg/kg b. w.) significantly improved the altered renal injury markers via reducing creatinine (high dose only) and uric acid levels compared to the Cp-group. The deleterious action of cisplatin on renal oxidative stress markers (GSH, MDA, SOD, and CAT) were also mitigated by LO-pretreatment. The reduction of the inflammatory marker (IL-6), and inhibition of DNA fragmentation, highlighted the prophylactic action of LO in kidney tissue. Molecular docking followed by a 100 ns molecular dynamic simulation analyses revealed that, amongst the 31 identified compounds in LO, chlorogenic and caffeoylmalic acids had the most stable binding to IL-6. The nephroprotective effects were further confirmed by histopathological observations, which showed improvement in ultrastructural changes induced by cisplatin. The observed findings reinforce the conclusion that L. ocymifolia extract exerts nephroprotective properties, which could be related to its antioxidant and anti-inflammatory activities. Further studies are required to determine the therapeutic doses and the proper administration time.

Urinary Angiotensinogen in Patients With Type 1 Diabetes With Microalbuminuria: Gender Differences and Effect of Intensive Insulin Therapy

Introduction

Angiotensinogen (AOG) is the precursor of peptides of the renin angiotensin system (RAS). Because insulin up-regulates transcriptional factors that normally repress kidney AOG synthesis, we evaluated urinary AOG (uAOG) in patients with type 1 diabetes (T1D) and microalbuminuria who are receiving either intensive or conventional insulin therapy.

Methods

Urine samples from participants of the Diabetes Control and Complications Trial (DCCT) were used for the following: (i) uAOG/creatinine measurements in 103 patients with microalbuminuria and 103 patients with normoalbuminuria, matched for age, gender, disease duration, and allocation to insulin therapy; and (ii) uAOG/creatinine measurements from patients with microalbuminuria allocated to intensive insulin therapy (n = 58) or conventional insulin therapy (n = 41) after 3 years on each modality.

Results

uAOG was higher in patients who started with microalbuminuria than in those with normoalbuminuria (6.65 vs. 4.0 ng/mg creatinine, P < 0.01). uAOG was higher in females than in males with microalbuminuria (11.7 vs. 5.4 ng/mg creatinine, P = 0.015). uAOG was lower in patients with microalbuminuria allocated to intensive insulin therapy than in conventional insulin therapy (3.98 vs. 7.42 ng/mg creatinine, P < 0.01). These differences in uAOG were observed though albumin excretion rate (AER) was not significantly different.

Conclusion

In patients with T1D and microalbuminuria, uAOG is increased and varies with gender and the type of insulin therapy independently of AER. This suggests that AOG production is increased in females and it is decreased by intensive insulin therapy. The reduction in uAOG with intensive insulin therapy, by kidney RAS downregulation, may contribute to the known renoprotective action associated with intensive insulin and improved glycemic control.

Immune system changes in those with hypertension when infected with SARS-CoV-2

The coronavirus disease 2019 (COVID-19) outbreak has become an evolving global health crisis. With an increasing incidence of primary hypertension, there is greater awareness of the relationship between primary hypertension and the immune system [including CD4+, CD8+ T cells, interleukin-17 (IL-17)/T regulatory cells (Treg) balance, macrophages, natural killer (NK) cells, neutrophils, B cells, and cytokines]. Hypertension is associated with an increased risk of various infections, post-infection complications, and increased mortality from severe infections. Despite ongoing reports on the epidemiological and clinical features of COVID-19, no articles have systematically addressed the role of primary hypertension in COVID-19 or how COVID-19 affects hypertension or specific treatment in these high-risk groups. Here, we synthesize recent advances in understanding the relationship between primary hypertension and COVID-19 and its underlying mechanisms and provide specific treatment guidelines for these high-risk groups.

Angiotensin II and AT1a Receptors in the Proximal Tubules of the Kidney: New Roles in Blood Pressure Control and Hypertension

Contrary to public perception, hypertension remains one of the most important public health problems in the United States, affecting 46% of adults with increased risk for heart attack, stroke, and kidney diseases. The mechanisms underlying poorly controlled hypertension remain incompletely understood. Recent development in the Cre/LoxP approach to study gain or loss of function of a particular gene has significantly helped advance our new insights into the role of proximal tubule angiotensin II (Ang II) and its AT₁ (AT_1a) receptors in basal blood pressure control and the development of Ang II-induced hypertension. This novel approach has provided us and others with an important tool to generate novel mouse models with proximal tubule-specific loss (deletion) or gain of the function (overexpression). The objective of this invited review article is to review and discuss recent findings using novel genetically modifying proximal tubule-specific mouse models. These new studies have consistently demonstrated that deletion of AT₁ (AT_1a) receptors or its direct downstream target Na⁺/H⁺ exchanger 3 (NHE3) selectively in the proximal tubules of the kidney lowers basal blood pressure, increases the pressure-natriuresis response, and induces natriuretic responses, whereas overexpression of an intracellular Ang II fusion protein or AT₁ (AT_1a) receptors selectively in the proximal tubules increases proximal tubule Na⁺ reabsorption, impairs the pressure-natriuresis response, and elevates blood pressure. Furthermore, the development of Ang II-induced hypertension by systemic Ang II infusion or by proximal tubule-specific overexpression of an intracellular Ang II fusion protein was attenuated in mutant mice with proximal tubule-specific deletion of AT₁ (AT_1a) receptors or NHE3. Thus, these recent studies provide evidence for and new insights into the important roles of intratubular Ang II via AT₁ (AT_1a) receptors and NHE3 in the proximal tubules in maintaining basal blood pressure homeostasis and the development of Ang II-induced hypertension.

Oxidized alkyl phospholipids stimulate sodium transport in proximal tubules via a non-genomic PPARγ-dependent pathway

Oxidized phospholipids have been shown to exhibit pleiotropic effects in numerous biological contexts. For example, 1-O-hexadecyl-2-azelaoyl-sn-glycero-3-phosphocholine (azPC), an oxidized phospholipid formed from alkyl phosphatidylcholines, is a peroxisome proliferator–activated receptor gamma (PPARγ) nuclear receptor agonist. Although it has been reported that PPARγ agonists including thiazolidinediones can induce plasma volume expansion by enhancing renal sodium and water retention, the role of azPC in renal transport functions is unknown. In the present study, we investigated the effect of azPC on renal proximal tubule (PT) transport using isolated PTs and kidney cortex tissues and also investigated the effect of azPC on renal sodium handling in vivo. We showed using a microperfusion technique that azPC rapidly stimulated Na⁺/HCO₃⁻ cotransporter 1 (NBCe1) and luminal Na⁺/H⁺ exchanger (NHE) activities in a dose-dependent manner at submicromolar concentrations in isolated PTs from rats and humans. The rapid effects (within a few minutes) suggest that azPC activates NBCe1 and NHE via nongenomic signaling. The stimulatory effects were completely blocked by specific PPARγ antagonist GW9662, ERK kinase inhibitor PD98059, and CD36 inhibitor sulfosuccinimidyl oleate. Treatment with an siRNA against PPAR gamma completely blocked the stimulation of both NBCe1 and NHE by azPC. Moreover, azPC induced ERK phosphorylation in rat and human kidney cortex tissues, which were completely suppressed by GW9662 and PD98059 treatments. These results suggest that azPC stimulates renal PT sodium-coupled bicarbonate transport via a CD36/PPARγ/mitogen-activated protein/ERK kinase/ERK pathway. We conclude that the stimulatory effects of azPC on PT transport may be partially involved in volume expansion.

Patterns of differentiation of renin lineage cells during nephrogenesis

Developmentally heterogeneous renin expressing cells serve as progenitors for mural, glomerular and tubular cells during nephrogenesis and are collectively termed renin lineage cells (RLCs). In this study, we quantified different renal vascular and tubular cell types based on specific markers, assessed proliferation, and de-novo differentiation in the RLC population. We used kidney sections of mRenCre-mT/mG mice throughout nephrogenesis. Marker positivity was evaluated in whole digitalized sections. At embryonic day 16, RLCs appeared in the developing kidney, and expression of all stained markers in RLCs was observed. The proliferation rate of RLCs did not differ from the proliferation rate of non-RLCs. The RLCs expanded mainly by de-novo differentiation (neogenesis). The fractions of RLCs originating from the stromal progenitors of the metanephric mesenchyme (renin producing cells, vascular smooth muscle cells, mesangial cells) decreased during nephrogenesis. In contrast, aquaporin 2 positive RLCs in the collecting duct system that embryonically emerges almost exclusively from the ureteric bud, expanded postpartum. The cubilin positive RLC fraction in the proximal tubule, deriving from the cap mesenchyme, remained constant. During nephrogenesis, RLCs were continuously detectable in the vascular and tubular compartments of the kidney. Therein, various patterns of RLC differentiation that depend on the embryonic origin of the cells were identified.

Modulation of the rat angiotensin type 1a receptor by an upstream short open reading frame

The rat angiotensin type 1a receptor (AT_1aR) is a peptide hormone G protein-coupled receptor (GPCR) that plays a key role in electrolyte homeostasis and blood pressure control. There is a highly conserved short open reading frame (sORF) in exon 2 (E2) that is downstream from exon 1 (E1) and upstream of the AT_1aR coding region located in exon 3 (E3). To determine the role of this E2 sORF in AT_1aR signaling, human embryonic kidney-293 (HEK293) cells were transfected with plasmids containing AT_1aR cDNA with either an intact or disrupted E2 sORF. The intact sORF attenuated the efficacy of angiotensin (Ang) II (p < 0.001) and sarcosine¹,Ile⁴,Ile⁸-Ang II (SII), (p < 0.01) to activate AT_1aR signaling through extracellular signal-related kinases 1/2 (ERK1/2). A time-course showed agonist-induced AT_1aR-mediated ERK1/2 activation was slower in the presence of the intact compared to the disrupted sORF [Ang II: p < 0.01 and SII: p < 0.05]. Ang II-induced ERK1/2 activation was completely inhibited by the protein kinase C (PKC) inhibitor Ro 31-8220 regardless of whether the sORF was intact or disrupted. Flow cytometric analyses suggested the intact sORF improved cell survival; the percentage of live cells increased (p < 0.05) while the percentage of early apoptotic cells decreased (p < 0.01) in cells transfected with the AT_1aR plasmid containing the intact sORF. These findings have implications for the regulation of AT₁Rs in physiological and pathological conditions and warrant investigation of sORFs in the 5' leader sequence (5'LS) of other GPCRs.

The Prevalence of Inorganic Mercury in Human Kidneys Suggests a Role for Toxic Metals in Essential Hypertension

The kidney plays a dominant role in the pathogenesis of essential hypertension, but the initial pathogenic events in the kidney leading to hypertension are not known. Exposure to mercury has been linked to many diseases including hypertension in epidemiological and experimental studies, so we studied the distribution and prevalence of mercury in the human kidney. Paraffin sections of kidneys were available from 129 people ranging in age from 1 to 104 years who had forensic/coronial autopsies. One individual had injected himself with metallic mercury, the other 128 were from varied clinicopathological backgrounds without known exposure to mercury. Sections were stained for inorganic mercury using autometallography. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used on six samples to confirm the presence of autometallography-detected mercury and to look for other toxic metals. In the 128 people without known mercury exposure, mercury was found in: (1) proximal tubules of the cortex and Henle thin loops of the medulla, in 25% of kidneys (and also in the man who injected himself with mercury), (2) proximal tubules only in 16% of kidneys, and (3) Henle thin loops only in 23% of kidneys. The age-related proportion of people who had any mercury in their kidney was 0% at 1-20 years, 66% at 21-40 years, 77% at 41-60 years, 84% at 61-80 years, and 64% at 81-104 years. LA-ICP-MS confirmed the presence of mercury in samples staining with autometallography and showed cadmium, lead, iron, nickel, and silver in some kidneys. In conclusion, mercury is found commonly in the adult human kidney, where it appears to accumulate in proximal tubules and Henle thin loops until an advanced age. Dysfunctions of both these cortical and medullary regions have been implicated in the pathogenesis of essential hypertension, so these findings suggest that further studies of the effects of mercury on blood pressure are warranted.

Renal ischemia-reperfusion leads to hypertension and changes in proximal tubule Na+ transport and renin-angiotensin-aldosterone system: Role of NADPH oxidase

Acute renal injury (AKI) is a risk factor for the development of hypertension, which involves oxidative stress, changes in Na⁺ handling, and the intrarenal renin-angiotensin-aldosterone system (RAAS) as underlying mechanisms. We investigated in rats whether renal ischemia-reperfusion (IR) leads to changes in the proximal tubule ATP-dependent Na⁺ transport and the intrarenal content of RAAS components, as well as the role of NADPH oxidase. Rats weighing 300-350 g were submitted to AKI by bilateral IR (n = 25). After IR injury, the animals were followed up for 4 weeks. One part (n = 7) received daily treatment with the NADPH oxidase inhibitor apocynin (100 mg/kg, drinking water), while another part (n = 9) received apocynin 24 h before and after IR. One group was submitted to sham surgery (n = 8). Four weeks after IR, the rats presented elevated systolic blood pressure, as well as increased lipid peroxidation, NADPH oxidase activity, (Na⁺+K⁺)ATPase activity, and upregulation of type 1 angiotensin II receptor in the renal cortex. On the other hand, there was a decrease in Na⁺-ATPase activity and downregulation of the isoforms 1 and 2 of the angiotensin-converting enzyme, type 2 angiotensin II receptor, and of the α and ε isoforms of protein kinase C. Most of these alterations was prevented by both apocynin treatment protocols. Thus, we conclude that AKI-induced by IR may induce changes in proximal tubule ATPases and RAAS components compatible with renal Na⁺ retention and hypertension. These data also indicate that the NADPH oxidase represents a key factor in the origin of these alterations.

The emerging role of angiotensinogen in cardiovascular diseases

Angiotensinogen (AGT) is the unique precursor of all angiotensin peptides. Many of the basic understandings of AGT in cardiovascular diseases have come from research efforts to define its effects on blood pressure regulation. The development of novel techniques targeting AGT manipulation such as genetic animal models, adeno-associated viral approaches, and antisense oligonucleotides made it possible to deeply investigate the relationship between AGT and cardiovascular diseases. In this brief review, we provide contemporary insights into the emerging role of AGT in cardiovascular diseases. In light of the recent progress, we emphasize some newly recognized features and mechanisms of AGT in heart failure, hypertension, atherosclerosis, and cardiovascular risk factors.

Beneficial Effects of Isoflavones in the Kidney of Obese Rats Are Mediated by PPAR-Gamma Expression

Several studies have demonstrated an important association between altered lipid metabolism and the development of kidney injury because of a high-fat diet. Fructose is also closely associated with renal injury. We opted for a combination of fructose and saturated fats in a diet (DH) that is a model known to induce renal damage in order to evaluate whether soy isoflavones could have promising use in the treatment of renal alterations. After two months of ingestion, there was an expansion of visceral fat, which was associated with long-term metabolic disorders, such as sustained hyperglycemia, insulin resistance, polyuria, dyslipidemia, and hypertension. Additionally, we found a decrease in renal blood flow and an increase in renal vascular resistance. Biochemical markers of chronic kidney disease were detected; there was an infiltration of inflammatory cells with an elevated expression of proinflammatory cytokines (tumor necrosis factor-α, interleukin (IL)-6, and IL-1β), the activation of the renin–angiotensin system, and oxidative/nitrosative stress. Notably, in rats exposed to the DH diet for 120 days, the concomitant treatment with isoflavones after 60 days was able to revert metabolic parameters, renal alterations, and oxidative/nitrosative stress. The beneficial effects of isoflavones in the kidney of the obese rats were found to be mediated by expression of peroxisome proliferator-activated receptor gamma (PPAR-γ).

Potential role of estradiol in ovariectomy-induced derangement of renal endocrine functions

Menopause is an important physiological event associated with structural and functional changes in the kidneys. An animal model of bilateral ovariectomy was used to study the effects of estrogen depletion, replacement and antiestrogen on renal structure and endocrine function. Sixty female rats were divided into six groups; group I was the control group, the remaining five groups underwent ovariectomy: group II received no treatment. The other groups received estradiol in group III, tamoxifen in group IV, estradiol followed by tamoxifen in group V and tamoxifen followed by estradiol in group VI. Serum creatinine, blood urea nitrogen, and endocrine functions of kidney were measured. Tissue samples were examined both microscopically for beta estrogen receptors and ultrastructurally for cell changes. Groups II, IV & VI showed a significant increase in creatinine, blood urea nitrogen, renal malondialdehyde, renal erythropoietin, plasma renin and plasma prostaglandin E2 and a significant decrease in renal antioxidants and serum vitamin D3. Groups III &V had a significant decrease in creatinine, blood urea nitrogen, renal malondialdehyde and renal erythropoietin with an increase in renal antioxidants, plasma prostaglandin E2 and serum vitamin D3. Histopathological and ultrastructural examinations revealed atrophic tubular changes in group II. The changes were less marked in groups III &V and more extensive in groups IV & VI. Estrogen receptor beta staining showed progressively increased expression in the absence of estrogen. Structural and most endocrine functions of the kidney were significantly affected by estradiol deficiency. Estradiol replacement exhibited a protective effect on renal tissue and endocrine functions.

Angiotensin II type 1 receptor-associated protein deficiency attenuates sirtuin1 expression in an immortalised human renal proximal tubule cell line

The proximal tubule is a particularly important site for ageing-related kidney damage. Sirtuin 1 (SIRT1), an NAD⁺ (nicotinamide adenine dinucleotide)-dependent deacetylase in the proximal tubule, may be involved in renal injury associated with ageing. However, the mechanisms of SIRT1 regulation remain to be elucidated. We recently reported that angiotensin II type 1 receptor (AT1R)-associated protein (ATRAP)-deficient mice displayed age-associated renal function decline and tubulointerstitial fibrosis. Our data showed that SIRT1 protein expression was reduced in ATRAP-deficient mice, although the relationship between ATRAP deficiency and age-associated renal fibrosis is still not fully understood. It is, therefore, necessary to investigate how ATRAP affects SIRT1 protein expression to resolve ageing-associated kidney dysfunction. Here, since ageing studies are inherently lengthy, we used an ex vivo model of the proximal tubule to determine the role of ATRAP in SIRT1 protein expression. We first generated a clonal immortalised human renal proximal tubule epithelial cell line (ciRPTEC) expressing AT1R and ATRAP. Using this cell line, we demonstrated that ATRAP knockdown reduced SIRT1 protein expression in the ciRPTEC but did not alter SIRT1 mRNA expression. Thus, ATRAP likely mediates SIRT1 protein abundance in ciRPTEC.

Downregulated microRNA‑133a induces HUVECs injury: Potential role of the (pro) renin receptor in angiotensin II‑dependent hypertension

The renin‑angiotensin system (RAS) serves an essential role in hypertension. MicroRNAs (miRs) have been reported to be important regulators in angiotensin (Ang) II‑dependent hypertension. We aimed to explore the roles of Ang II and miR‑133a in the mechanism underlying hypertension. Human umbilical vein endothelial cells (HUVECs) were identified by immunofluorescence staining. Cell viability and miR‑133a expression under the inhibition of Ang II of various concentrations were determined by an MTT assay and reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR), respectively. The effects of HUVECs transfected with miR‑133a mimic or inhibitor on Ang II‑induced apoptosis were measured using flow cytometry. The potential targeting of miR‑133a to the 3' untranslated region of (pro) renin receptor (PRR) was assessed using TargetScan and a dual‑luciferase assay. The effects of PRR interference using small interfering (si)RNA on PRR expression and the rate of apoptosis were determined by RT‑qPCR, western blotting and flow cytometry, respectively. Ang II at a concentration of 10‑5 M significantly inhibited the cell viability (P<0.05) and miR‑133a expression (P<0.01); Downregulation of miR‑133a suppressed cell viability. HUVECs transfected with miR‑133a mimic reduced the rate of Ang II‑induced apoptosis from 21.99 to 12.38%, but miR‑133a inhibitor promoted Ang II‑induced apoptosis (apoptosis rate, 28.9%). PRR was predicted to be a target gene of miR‑133a. Transfection with siPRR decreased the apoptotic rate in Ang II + negative control and Ang II + miR‑133a inhibitor group to 11.39 and 12.94%, respectively. Our findings also suggested that Ang II promoted PRR expression to enhance the apoptotic rate of HUVECs via the suppression of miR‑133a. Furthermore, siPRR efficiently decreased the Ang II‑induced apoptosis.

Evidence of Augmented Intrarenal Angiotensinogen Associated With Glomerular Swelling in Gestational Hypertension and Preeclampsia: Clinical Implications

Background AGT (angiotensinogen) synthesis occurs in renal proximal tubular epithelial cells, independent from systemic AGT , as a component of the intrarenal renin-angiotensin system. We investigated urinary AGT , as a biomarker for renin-angiotensin system activation, and electrolyte concentrations, in relation to glomerular volume, as a proxy for glomerular endotheliosis in renal biopsy tissue from pregnant normotensive control and hypertensive women. Methods and Results Urine samples were collected from normotensive control (n=10), gestational hypertensive (n=6), and pre-eclamptic (n=16) women at the time a renal biopsy was obtained. Samples were collected from Lund University Hospital between November 1999 and June 2001. Urinary AGT , potassium, and sodium were measured, normalized to urinary creatinine. Mean glomerular volume was estimated from biopsy sections. AGT protein expression and localization were assessed in renal biopsies by immunohistochemistry. Urinary AGT concentrations were higher in hypertensive pregnancies (median, gestational hypertension: 11.3 ng/mmol [interquartile range: 2.8-13.6]; preeclampsia: 8.4 ng/mmol [interquartile range: 4.2-29.1]; normotensive control: 0.6 ng/mmol [interquartile range: 0.4-0.8]; P<0.0001) and showed a positive relationship with estimated mean glomerular volume. Urinary potassium strongly correlated with urinary AGT ( P<0.0001). Although numbers were small, AGT protein was found in both glomeruli and proximal tubules in normotensive control but was present only in proximal tubules in women with hypertensive pregnancy. Conclusions This study shows that pregnant women with gestational hypertension or preeclampsia have increased urinary AGT and potassium excretion associated with signs of glomerular swelling. Our data suggest that the kidneys of women with hypertensive pregnancies and endotheliosis have inappropriate intrarenal renin-angiotensin system activation, which may contribute toward the pathogenesis of hypertension and renal injury.

EXPRESSION OF THE RENIN-ANGIOTENSIN SYSTEM COMPONENTS IN ONCOLOGIC DISEASES

The literature devoted to changes in the expression of the renin-angiotensin system (RAS) proteins of cancer cells was analyzed. The dynamics of RAS protein expression in malignant tumors and the possible role of epigenetic mechanisms in these processes are briefly reviewed. Through research of the epigenetic mechanisms in cancer, principally new techniques for their correction based on the use of selective regulatory systems of covalent modification of histone proteins (for example, deacetylase inhibitor) and microRNA synthesis technologies have been developed. Literature data show promising pharmacological correction of epigenetic modification of chromatin in the treatment of cancer.

Identification of the Transcriptional Networks and the Involvement in Angiotensin II-Induced Injury after CRISPR/Cas9-Mediated Knockdown of Cyr61 in HEK293T Cells

BACKGROUND

The transcriptional networks of Cyr61 and its function in cell injury are poorly understood. The present study depicted the lncRNA and mRNA profiles and the involvement in angiotensin II-induced injury after Cyr61 knockdown mediated by CRISPR/Cas9 in HEK293T cells.

METHODS

HEK293T cells were cultured, and Cyr61 knockdown was achieved by transfection of the CRISPR/Cas9 KO plasmid. lncRNA and mRNA microarrays were used to identify differentially expressed genes (DEGs). Gene ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses were performed to determine biofunctions and signaling pathways. RT-PCR was used to validate the microarray results. Cells were divided into four groups: control, Cyr61 knockdown, angiotensin II (Ang II) without Cyr61 knockdown, and Ang II with Cyr61 knockdown. CCK8, western blotting, and flow cytometry analysis were carried out to dissect cellular function.

RESULTS

A total of 23184 lncRNAs and 28264 mRNAs were normalized. 26 lncRNAs and 212 mRNAs were upregulated, and 74 lncRNAs and 233 mRNAs were downregulated after Cyr61 knockdown. Analysis of cellular components, molecular functions, biological processes, and regulatory pathways associated with the differentially expressed mRNAs revealed downstream mechanisms of the Cyr61 gene. The differentially expressed genes were affected for small cell lung cancer, axon guidance, Fc gamma R-mediated phagocytosis, MAPK signaling pathway, focal adhesion, insulin resistance, and metabolic pathways. In addition, Cyr61 expression was increased in accordance with induction of cell cycle arrest and apoptosis and inhibition of cell proliferation induced by Ang II. Knockdown of Cyr61 in HEK293T cells promoted cell cycle procession, decreased apoptosis, and promoted cell proliferation.

CONCLUSIONS

The Cyr61 gene is involved in Ang II-induced injury in HEK293T cells. Functional mechanisms of the differentially expressed lncRNAs and mRNAs as well as identification of metabolic pathways will provide new therapeutic targets for Cyr61-realated diseases.

Therapeutic value of stimulating the nitrate-nitrite-nitric oxide pathway to attenuate oxidative stress and restore nitric oxide bioavailability in cardiorenal disease

Cardiovascular disorders including hypertension and associated renal disease are major health problems affecting more than 1.5 billion people worldwide. Apart from nonmodifiable factors such as ageing, family history and gender, both sedentary lifestyle and unhealthy dietary habits are considered as major risk factors. The disorders are interrelated suggesting common pathological pathways. Mechanistically, oxidative stress and compromised function of the nitric oxide synthase (NOS) system leading to endothelial dysfunction and reduction in nitric oxide (NO) bioavailability have been widely implicated and associated with development and progression of disease. New strategies that correct this redox imbalance and increase NO bioactivity may have major clinical implications. The inorganic anions, nitrate and nitrite, are endogenously formed by oxidization of NOS-derived NO, but there are also high amounts of nitrate in our daily diet. In this regard, accumulated evidence over the past two decades demonstrates that these anions can be recycled back to NO and other bioactive nitrogen oxides, thus offering an attractive alternative strategy for therapeutic exploitation. In this review, we describe how dietary stimulation of the nitrate-nitrite-NO pathway affects cardiovascular and renal functions in health and disease via modulation of oxidative stress and NO bioavailability. Clinical studies addressing potential effects on the renal system are still limited, but blood pressure-lowering effects of nitrate supplementation have been demonstrated in healthy and hypertensive subjects as well as in patients with chronic kidney disease. However, larger clinical studies are warranted to reveal whether chronic nitrate treatment can slow-down the progression of cardiorenal disease and associated complications.

Mechanisms underlying blood pressure reduction by dietary inorganic nitrate

Nitric oxide (NO) importantly contributes to cardiovascular homeostasis by regulating blood flow and maintaining endothelial integrity. Conversely, reduced NO bioavailability is a central feature during natural ageing and in many cardiovascular disorders, including hypertension. The inorganic anions nitrate and nitrite are endogenously formed after oxidation of NO synthase (NOS)-derived NO and are also present in our daily diet. Knowledge accumulated over the past two decades has demonstrated that these anions can be recycled back to NO and other bioactive nitrogen oxides via serial reductions that involve oral commensal bacteria and various enzymatic systems. Intake of inorganic nitrate, which is predominantly found in green leafy vegetables and beets, has a variety of favourable cardiovascular effects. As hypertension is a major risk factor of morbidity and mortality worldwide, much attention has been paid to the blood pressure reducing effect of inorganic nitrate. Here, we describe how dietary nitrate, via stimulation of the nitrate-nitrite-NO pathway, affects various organ systems and discuss underlying mechanisms that may contribute to the observed blood pressure-lowering effect.

Human Missense Mutations in Regulator of G Protein Signaling 2 Affect the Protein Function Through Multiple Mechanisms

Regulator of G protein signaling 2 (RGS2) plays a significant role in alleviating vascular contraction and promoting vascular relaxation due to its GTPase accelerating protein activity toward Gαq. Mice lacking RGS2 display a hypertensive phenotype, and several RGS2 missense mutations have been found predominantly in hypertensive human subjects. However, the mechanisms whereby these mutations could impact blood pressure is unknown. Here, we selected 16 rare, missense mutations in RGS2 identified in various human exome sequencing projects and evaluated their ability to inhibit intracellular calcium release mediated by angiotensin II receptor type 1 (AT1R). Four of them had reduced function and were further investigated to elucidate underlying mechanisms. Low protein expression, protein mislocalization, and reduced G protein binding were identified as likely mechanisms of the malfunctioning mutants. The Q2L mutant had 50% lower RGS2 than wild-type (WT) protein detected by Western blot. Confocal microscopy demonstrated that R44H and D40Y had impaired plasma membrane targeting; only 46% and 35% of those proteins translocated to the plasma membrane when coexpressed with Gα_q Q209L compared with 67% for WT RGS2. The R188H mutant had a significant reduction in Gα_q binding affinity (10-fold increase in K_i compared with WT RGS2 in a flow cytometry competition binding assay). This study provides functional data for 16 human RGS2 missense variants on their effects on AT1R-mediated calcium mobilization and provides molecular understanding of those variants with functional loss in vitro. These molecular behaviors can provide insight to inform antihypertensive therapeutics in individuals with variants having reduced function.

Mammalian Glutamyl Aminopeptidase Genes (ENPEP) and Proteins: Comparative Studies of a Major Contributor to Arterial Hypertension

Glutamyl aminopeptidase (ENPEP) is a member of the M1 family of endopeptidases which are mammalian type II integral membrane zinc-containing endopeptidases. ENPEP is involved in the catabolic pathway of the renin-angiotensin system forming angiotensin III, which participates in blood pressure regulation and blood vessel formation. Comparative ENPEP amino acid sequences and structures and ENPEP gene locations were examined using data from several mammalian genome projects. Mammalian ENPEP sequences shared 71-98% identities. Five N-glycosylation sites were conserved for all mammalian ENPEP proteins examined although 9-18 sites were observed, in each case. Sequence alignments, key amino acid residues and predicted secondary and tertiary structures were also studied, including transmembrane and cytoplasmic sequences and active site residues. Highest levels of human ENPEP expression were observed in the terminal ileum of the small intestine and in the kidney cortex. Mammalian ENPEP genes contained 20 coding exons. The human ENPEP gene promoter and first coding exon contained a CpG island (CpG27) and at least 6 transcription factor binding sites, whereas the 3'-UTR region contained 7 miRNA target sites, which may contribute to the regulation of ENPEP gene expression in tissues of the body. Phylogenetic analyses examined the relationships of mammalian ENPEP genes and proteins, including primate, other eutherian, marsupial and monotreme sources, using chicken ENPEP as a primordial sequence for comparative purposes.

Intracellular renin increases the inward calcium current in smooth muscle cells of mesenteric artery of SHR. Implications for hypertension and vascular remodeling

The influence of intracellular renin on the inward calcium current in isolated smooth muscle cells from SHR mesenteric arteries was investigated. Measurements of calcium current were performed using the whole cell configuration of pCLAMP. The results indicated that: 1) renin (100nM) dialyzed into smooth muscle cells, increased the inward calcium current; 2) verapamil (10-9M) administered to the bath inhibited the effect of renin on the inward calcium current; 3) concurrently with the increase of calcium current a depolarization of 6.8+/-2.1mV (n=16)(P<0.05) was found in cells dialyzed with renin; 4) intracellular dialysis of renin (100nM) into smooth muscle cells isolated from mesenteric arteries of normal Wystar Kyoto rats showed no significant change on calcium current; 5) aliskiren (10-9M) dialyzed into the cell together with renin (100nM) abolished the effect of the enzyme on the calcium current in SHR; 6) Ang II (100nM) dialyzed into the smooth muscle cell from mesenteric artery of SHR in absence of renin, decreased the calcium current-an effect greatly reduced by valsartan (10-9M) added to the cytosol; 7) administration of renin (100nM) plus angiotensinogen (100nM) into the cytosol of muscles cells from SHR rats reduced the inward calcium current; 8) extracellular administration of Ang II (100nM) increased the inward calcium current in mesenteric arteries of SHR.

CONCLUSIONS

intracellular renin in vascular resistance vessels from SHR due to internalization or expression, contributes to the regulation of vascular tone and control of peripheral resistance-an effect independently of Ang II. Implications for hypertension and vascular remodeling are discussed.