Molecular and genetic aspects of guanylyl cyclase natriuretic peptide receptor-A in regulation of blood pressure and renal function

Present and future of drug therapy in hypertension: an overview

Purpose: High blood pressure (HBP) is the leading cause of mortality and years of disability, and its prevalence is increasing. Therefore, diagnosis and effective treatment of HBP is one of the main goals to prevent and reduce its complications, and pharmacological treatment is the cornerstone of hypertension management.Materials and Methods: The gradual introduction of different drug families has led to the development of new molecules that have improved efficacy and reduced adverse effects. Results: Current drugs include a large number that target key mechanisms of blood pressure regulation as well as those that contribute to hypertension-induced organ damage. Recently, new antihypertensive drugs have been introduced that not only aim to lower blood pressure but also provide additional protection against organ damage and metabolic disorders. Some of them were introduced for specific indications other than hypertension and other are based in a pharmacogenomic approach. Other routes of administration, such subcutaneous injection, are also being explored to improve protection and compliance.Conclusions: The main characteristics of each class of antihypertensive drug are summarised.

Epigenetic mechanisms differentially regulate blood pressure and renal dysfunction in male and female Npr1 haplotype mice

We determined the epigenetic mechanisms regulating mean arterial pressure (MAP) and renal dysfunction in guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) gene-targeted mice. The Npr1 (encoding NPRA) gene-targeted mice were treated with class 1 specific histone deacetylase inhibitor (HDACi) mocetinostat (MGCD) to determine the epigenetic changes in a sex-specific manner. Adult male and female Npr1 haplotype (1-copy; Npr1+/-), wild-type (2-copy; Npr1+/+), and gene-duplicated heterozygous (3-copy; Npr1++/+) mice were intraperitoneally injected with MGCD (2 mg/kg) for 14 days. BP, renal function, histopathology, and epigenetic changes were measured. One-copy male mice showed significantly increased MAP, renal dysfunction, and fibrosis than 2-copy and 3-copy mice. Furthermore, HDAC1/2, collagen1alpha-2 (Col1α-2), and alpha smooth muscle actin (α-SMA) were significantly increased in 1-copy mice compared with 2-copy controls. The expression of antifibrotic microRNA-133a was attenuated in 1-copy mice but to a greater extent in males than females. NF-κB was localized at significantly lower levels in cytoplasm than in the nucleus with stronger DNA binding activity in 1-copy mice. MGCD significantly lowered BP, improved creatinine clearance, and repaired renal histopathology. The inhibition of class I HDACs led to a sex-dependent distinctive stimulation of acetylated positive histone marks and inhibition of methylated repressive histone marks in Npr1 1-copy mice; however, it epigenetically lowered MAP, repaired renal fibrosis, and proteinuria and suppressed NF-kB differentially in males versus females. Our results suggest a role for epigenetic targets affecting hypertension and renal dysfunction in a sex-specific manner.

Genetic and Epigenetic Mechanisms Regulating Blood Pressure and Kidney Dysfunction

The pioneering work of Dr Lewis K. Dahl established a relationship between kidney, salt, and high blood pressure (BP), which led to the major genetic-based experimental model of hypertension. BP, a heritable quantitative trait affected by numerous biological and environmental stimuli, is a major cause of morbidity and mortality worldwide and is considered to be a primary modifiable factor in renal, cardiovascular, and cerebrovascular diseases. Genome-wide association studies have identified monogenic and polygenic variants affecting BP in humans. Single nucleotide polymorphisms identified in genome-wide association studies have quantified the heritability of BP and the effect of genetics on hypertensive phenotype. Changes in the transcriptional program of genes may represent consequential determinants of BP, so understanding the mechanisms of the disease process has become a priority in the field. At the molecular level, the onset of hypertension is associated with reprogramming of gene expression influenced by epigenomics. This review highlights the specific genetic variants, mutations, and epigenetic factors associated with high BP and how these mechanisms affect the regulation of hypertension and kidney dysfunction.

Effect of sacubitril/valsartan on brain natriuretic peptide level and prognosis of acute cerebral infarction

BACKGROUND AND PURPOSE

Previous studies demonstrated that elevated brain natriuretic peptide (BNP) level is associated with adverse clinical outcomes of acute cerebral infarction (ACI). Researchers hypothesized that BNP might be a potential neuroprotective factor against cerebral ischemia because of the antagonistic effect of the natriuretic peptide system on the renin-angiotensin system and regulation of cardiovascular homeostasis. However, whether decreasing the BNP level can improve the prognosis of ACI has not been studied yet. The main effect of sacubitril/valsartan is to enhance the natriuretic peptide system. We investigated whether the intervention of plasma BNP levels with sacubitril/valsartan could improve the prognosis of patients with ACI.

METHODS

In a randomized, controlled, parallel-group trial of patients with ACI within 48 hours of symptom onset and need for antihypertensive therapy, patients have randomized within 24 hours to sacubitril/valsartan 200mg once daily (the intervention group) or to conventional medical medication (the control group). The primary outcome was a change in plasma BNP levels before and after sacubitril/valsartan administration. The secondary outcomes included plasma levels of brain-derived neurotrophic factor (BDNF), Corin and neprilysin (NEP) before and after medication, the modified Rankin scale, and the National Institutes of Health Stroke Scale (at onset, at discharge, 30 days, and 90 days after discharge).

RESULTS

We evaluated 80 eligible patients admitted to the Stroke Center of Lianyungang Second People's Hospital between 1st May, 2021 and 31st June, 2022. Except for 28 patients excluded before randomization and 14 patients who did not meet the criteria or dropped out or lost to follow-up during the trial, the remaining 38 patients (intervention group: 17, control group: 21) had well-balanced baseline features. In this trial, we found that plasma BNP levels (P = 0.003) decreased and NEP levels (P = 0.006) increased in enrolled patients after treatment with sacubitril/valsartan. There were no differences in plasma BDNF and Corin levels between the two groups. Furthermore, no difference in functional prognosis was observed between the two groups (all P values>0.05).

CONCLUSIONS

Sacubitril/valsartan reduced endogenous plasma BNP levels in patients with ACI and did not affect their short-term prognosis.

Evidence for Angiotensin II as a Naturally Existing Suppressor for the Guanylyl Cyclase A Receptor and Cyclic GMP Generation

The natriuretic peptide system (NPS) and renin-angiotensin-aldosterone system (RAAS) function oppositely at multiple levels. While it has long been suspected that angiotensin II (ANGII) may directly suppress NPS activity, no clear evidence to date supports this notion. This study was designed to systematically investigate ANGII-NPS interaction in humans, in vivo, and in vitro. Circulating atrial, b-type, and c-type natriuretic peptides (ANP, BNP, CNP), cyclic guanosine monophosphate (cGMP), and ANGII were simultaneously investigated in 128 human subjects. Prompted hypothesis was validated in vivo to determine the influence of ANGII on ANP actions. The underlying mechanisms were further explored via in vitro approaches. In humans, ANGII demonstrated an inverse relationship with ANP, BNP, and cGMP. In regression models predicting cGMP, adding ANGII levels and the interaction term between ANGII and natriuretic peptides increased the predictive accuracy of the base models constructed with either ANP or BNP, but not CNP. Importantly, stratified correlation analysis further revealed a positive association between cGMP and ANP or BNP only in subjects with low, but not high, ANGII levels. In rats, co-infusion of ANGII even at a physiological dose attenuated cGMP generation mediated by ANP infusion. In vitro, we found the suppressive effect of ANGII on ANP-stimulated cGMP requires the presence of ANGII type-1 (AT1) receptor and mechanistically involves protein kinase C (PKC), as this suppression can be substantially rescued by either valsartan (AT1 blocker) or Go6983 (PKC inhibitor). Using surface plasmon resonance (SPR), we showed ANGII has low binding affinity to the guanylyl cyclase A (GC-A) receptor compared to ANP or BNP. Our study reveals ANGII is a natural suppressor for the cGMP-generating action of GC-A via AT1/PKC dependent manner and highlights the importance of dual-targeting RAAS and NPS in maximizing beneficial properties of natriuretic peptides in cardiovascular protection.

Longitudinal association between N-terminal B-type natriuretic peptide, anxiety and social support in patients with HFpEF: results from the multicentre randomized controlled Aldo-DHF trial

BACKGROUND

Higher plasma levels of natriuretic peptides (NPs) have been associated with reduced anxiety in experimental research and a number of patient samples. As NP levels are elevated in heart failure patients, we investigate whether this elevation is related to anxiety in patients with heart failure with preserved ejection fraction (HFpEF).

METHODS

Post-hoc regression and mediation analyses were conducted, using data of 422 patients with HFpEF from the randomized, placebo-controlled, double-blinded, two-armed, multicentre aldosterone in diastolic heart failure trial, testing associations and their mediators between the N-terminal B-type natriuretic peptide (NT-proBNP) and anxiety at baseline and over 12-month follow-up. Anxiety was measured by the Hospital Anxiety and Depression Scale (HADS), social support by the ENRICHD Social Support Inventory and physical functioning by the Short Form 36 Health Survey.

RESULTS

The mean age of the study population was 66.8 ± 7.6 years, 47.6% were male and 86.0% had NYHA class II. NT-proBNP showed a weak negative correlation with HADS anxiety scores at baseline (r = - 0.087; p = 0.092), which was significant (r = - 0.165; p = 0.028) in men but not in women. NT-proBNP also tended to predict lower anxiety at 12-months in men. On the other hand, higher anxiety at baseline was associated with lower NT-proBNP scores 12 months later (r = - 0.116; p = 0.026). All associations lost significance in multivariate regression for age, perceived social support (ESSI), physical function (SF-36) and study arm. Mediation analyses revealed that social support acts as a full mediator for the link between NT-proBNP levels and anxiety.

CONCLUSION

The mechanisms linking NT-proBNP to anxiety may be more complex than originally assumed. While effects of NT-proBNP on anxiety may be mediated by perceived social support, there may be an additional negative effect of anxiety on NT-proBNP. Future research should consider this possible bi-directionality of the association and assess the potential influence of gender, social support, oxytocin and vagal tone on the interaction of anxiety and natriuretic peptide levels. Trial Registration http://www.controlled-trials.com  (ISRCTN94726526) on 07/11/2006. Eudra-CT-number: 2006-002,605-31.

Post-myocardial infarction fibrosis: Pathophysiology, examination, and intervention

Cardiac fibrosis plays an indispensable role in cardiac tissue homeostasis and repair after myocardial infarction (MI). The cardiac fibroblast-to-myofibroblast differentiation and extracellular matrix collagen deposition are the hallmarks of cardiac fibrosis, which are modulated by multiple signaling pathways and various types of cells in time-dependent manners. Our understanding of the development of cardiac fibrosis after MI has evolved in basic and clinical researches, and the regulation of fibrotic remodeling may facilitate novel diagnostic and therapeutic strategies, and finally improve outcomes. Here, we aim to elaborate pathophysiology, examination and intervention of cardiac fibrosis after MI.

EVIDENCE FOR ANGIOTENSIN II AS A NATURALLY EXISTING SUPPRESSOR FOR THE NATRIURETIC PEPTIDE SYSTEM

Background

Natriuretic peptide system (NPS) and renin angiotensin aldosterone system (RAAS) function oppositely at multiple levels. While it has long been suspected that angiotensin II (ANGII) may directly suppress NPS activity, no clear evidence to date support this notion.

Objectives

This study was designed to systematically investigate ANGII-NPS interaction in humans, in vivo, and in vitro for translational insights.

Methods

Circulating atrial, b-type, and c-type natriuretic peptides (ANP, BNP, CNP), cyclic guanosine monophosphate (cGMP), and ANGII were simultaneously investigated in 128 human subjects. Prompted hypothesis was validated in rat model to determine influence of ANGII on ANP actions. Multiple engineered HEK293 cells and surface plasmon resonance (SPR) technology were leveraged for mechanistic exploration.

Results

In humans, ANGII showed inverse relationship with ANP, BNP, and cGMP. In regression models predicting cGMP, adding ANGII levels and interaction term between ANGII and natriuretic peptide increased predicting accuracy of base models constructed with either ANP or BNP, but not CNP. Importantly, stratified correlation analysis further revealed positive association between cGMP with ANP or BNP only in subjects with low, but not high, ANGII levels. In rats, co-infusion of ANGII even at physiological dose attenuated blood pressure reduction and cGMP generation triggered by ANP infusion. In vitro, we showed that the suppression effect of ANGII on ANP-stimulated cGMP requires the presence of ANGII type-1 (AT1) receptor and mechanistically involves protein kinase C (PKC), which can be substantially rescued by either valsartan (AT1 blocker) or Go6983 (PKC inhibitor). Using SPR, we showed ANGII has low affinity for particulate guanylyl cyclase A (GC-A) receptor binding compared to ANP or BNP.

Conclusions

Our study reveals ANGII as a natural suppressor for cGMP-generating action of GC-A via AT1/PKC dependent manner and highlights importance of dual-targeting RAAS and NPS in maximizing beneficial properties of natriuretic peptides in cardiovascular disease.

Guanylyl cyclase/natriuretic peptide receptor-A: Identification, molecular characterization, and physiological genomics

The natriuretic peptides (NPs) hormone family, which consists mainly of atrial, brain, and C-type NPs (ANP, BNP, and CNP), play diverse roles in mammalian species, ranging from renal, cardiac, endocrine, neural, and vascular hemodynamics to metabolic regulations, immune responsiveness, and energy distributions. Over the last four decades, new data has transpired regarding the biochemical and molecular compositions, signaling mechanisms, and physiological and pathophysiological functions of NPs and their receptors. NPs are incremented mainly in eliciting natriuretic, diuretic, endocrine, vasodilatory, and neurological activities, along with antiproliferative, antimitogenic, antiinflammatory, and antifibrotic responses. The main locus responsible in the biological and physiological regulatory actions of NPs (ANP and BNP) is the plasma membrane guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), a member of the growing multi-limbed GC family of receptors. Advances in this field have provided tremendous insights into the critical role of Npr1 (encoding GC-A/NPRA) in the reduction of fluid volume and blood pressure homeostasis, protection against renal and cardiac remodeling, and moderation and mediation of neurological disorders. The generation and use of genetically engineered animals, including gene-targeted (gene-knockout and gene-duplication) and transgenic mutant mouse models has revealed and clarified the varied roles and pleiotropic functions of GC-A/NPRA in vivo in intact animals. This review provides a chronological development of the biochemical, molecular, physiological, and pathophysiological functions of GC-A/NPRA, including signaling pathways, genomics, and gene regulation in both normal and disease states.

Ligand-Dependent Downregulation of Guanylyl Cyclase/Natriuretic Peptide Receptor-A: Role of miR-128 and miR-195

Cardiac hormones act on the regulation of blood pressure (BP) and cardiovascular homeostasis. These hormones include atrial and brain natriuretic peptides (ANP, BNP) and activate natriuretic peptide receptor-A (NPRA), which enhance natriuresis, diuresis, and vasorelaxation. In this study, we established the ANP-dependent homologous downregulation of NPRA using human embryonic kidney-293 (HEK-293) cells expressing recombinant receptor and MA-10 cells harboring native endogenous NPRA. The prolonged pretreatment of cells with ANP caused a time- and dose-dependent decrease in ¹²⁵I-ANP binding, Guanylyl cyclase (GC) activity of receptor, and intracellular accumulation of cGMP leading to downregulation of NPRA. Treatment with ANP (100 nM) for 12 h led to an 80% decrease in ¹²⁵I-ANP binding to its receptor, and BNP decreased it by 62%. Neither 100 nM c-ANF (truncated ANF) nor C-type natriuretic peptide (CNP) had any effect. ANP (100 nM) treatment also decreased GC activity by 68% and intracellular accumulation cGMP levels by 45%, while the NPRA antagonist A71915 (1 µM) almost completely blocked ANP-dependent downregulation of NPRA. Treatment with the protein kinase G (PKG) stimulator 8-(4-chlorophenylthio)-cGMP (CPT-cGMP) (1 µM) caused a significant increase in ¹²⁵I-ANP binding, whereas the PKG inhibitor KT 5823 (1 µM) potentiated the effect of ANP on the downregulation of NPRA. The transfection of miR-128 significantly reduced NPRA protein levels by threefold compared to control cells. These results suggest that ligand-dependent mechanisms play important roles in the downregulation of NPRA in target cells.

Lack of NPR1 Increases Vascular Endothelial Adhesion through Induction of Integrin Beta 4

Natriuretic peptide receptor 1 (NPR1) serves as a modulator of vascular endothelial homeostasis. Interactions between monocytes and endothelial cells may initiate endothelium dysfunction, which is known as an early hallmark of atherosclerosis. In this study, we performed RNA-sequencing analysis for the aorta of Npr1 knockout (Npr1^+/−) mice and found that differentially expressed genes were significantly related to cell adhesion. This result was supported by an increased expression of intercellular adhesion molecule 1 (ICAM-1) in the aortic endothelium of Npr1^+/− mice. Moreover, we observed that the knockdown of NPR1 increased ICAM-1 expression and promoted THP-1 monocyte adhesion to human umbilical vein endothelial cells (HUVECs). NPR1 overexpression decreased ICAM-1 expression and inhibited the adhesion of monocytes to HUVECs treated by TNF-α (a cell adhesion inducer). Further analysis showed that adhesion-related genes were enriched in the focal adhesion signaling pathway, in which integrin beta 4 (Itgb4) was determined as a key gene. Notably, ITGB4 expression increased in vascular endothelium of Npr1^+/− mice and in NPR1-knockdown HUVECs. The deficiency of ITGB4 decreased ICAM-1 expression and attenuated monocyte adhesion to NPR1-knockdown endothelial cells. Additionally, a reduced NPR1 and an increased ITGB4 expression level were found in an atherosclerosis mouse model. In conclusion, our findings demonstrate that NPR1 deficiency increases vascular endothelial cell adhesion by stimulating ITGB4 expression, which may contribute to the development of atherosclerosis.

Genetic Disruption of Guanylyl Cyclase/Natriuretic Peptide Receptor-A Triggers Differential Cardiac Fibrosis and Disorders in Male and Female Mutant Mice: Role of TGF-β1/SMAD Signaling Pathway

The global targeted disruption of the natriuretic peptide receptor-A (NPRA) gene (Npr1) in mice provokes hypertension and cardiovascular dysfunction. The objective of this study was to determine the mechanisms regulating the development of cardiac fibrosis and dysfunction in Npr1 mutant mice. Npr1 knockout (Npr1^-/-, 0-copy), heterozygous (Npr1^+/-, 1-copy), and wild-type (Npr1^+/+, 2-copy) mice were treated with the transforming growth factor (TGF)-β1 receptor (TGF-β1R) antagonist GW788388 (2 µg/g body weight/day; ip) for 28 days. Hearts were isolated and used for real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR), Western blot, and immunohistochemical analyses. The Npr1^-/- (0-copy) mice showed a 6-fold induction of cardiac fibrosis and dysfunction with markedly induced expressions of collagen-1α (3.8-fold), monocyte chemoattractant protein (3.7-fold), connective tissue growth factor (CTGF, 5.3-fold), α-smooth muscle actin (α-SMA, 6.1-fold), TGF-βRI (4.3-fold), TGF-βRII (4.7-fold), and phosphorylated small mothers against decapentaplegic (pSMAD) proteins, including pSMAD-2 (3.2-fold) and pSMAD-3 (3.7-fold), compared with wild-type mice. The expressions of phosphorylated extracellular-regulated kinase ERK1/2 (pERK1/2), matrix metalloproteinases-2, -9, (MMP-2, -9), and proliferating cell nuclear antigen (PCNA) were also significantly upregulated in Npr1 0-copy mice. The treatment of mutant mice with GW788388 significantly blocked the expression of fibrotic markers, SMAD proteins, MMPs, and PCNA compared with the vehicle-treated control mice. The treatment with GW788388 significantly prevented cardiac dysfunctions in a sex-dependent manner in Npr1 0-copy and 1-copy mutant mice. The results suggest that the development of cardiac fibrosis and dysfunction in mutant mice is predominantly regulated through the TGF-β1-mediated SMAD-dependent pathway.

Molecular Mechanism of Blood Pressure Regulation through the Atrial Natriuretic Peptide

Simple Summary

Atrial natriuretic peptide (ANP) is a cardiac peptide hormone that was identified by Kangawa and Matsuo in 1984. In Japan, ANP has been used as an intravenous drug for the treatment of acute heart failure since 1995. Because ANP has a hypotensive effect, it is important to avoid excessive lowering of blood pressure when ANP is used. Recently, a compound that inhibits neutral endopeptidase, the enzyme that degrades ANP, has been developed (angiotensin receptor-neprilysin inhibitor (ARNI)). ARNI has been approved worldwide for the treatment of chronic heart failure and has been authorized in Japan as an antihypertensive drug. However, it is not understood exactly how ANP exerts its hypotensive effect. In this review, we discuss the molecular mechanism of the blood pressure-regulating effects of ANP, focusing on our recent findings.

Abstract

Natriuretic peptides, including atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and C-type natriuretic peptide (CNP), have cardioprotective effects and regulate blood pressure in mammals. ANP and BNP are hormones secreted from the heart into the bloodstream in response to increased preload and afterload. Both hormones act through natriuretic peptide receptor 1 (NPR1). In contrast, CNP acts through natriuretic peptide receptor 2 (NPR2) and was found to be produced by the vascular endothelium, chondrocytes, and cardiac fibroblasts. Based on its relatively low plasma concentration compared with ANP and BNP, CNP is thought to function as both an autocrine and a paracrine factor in the vasculature, bone, and heart. The cytoplasmic domains of both NPR1 and NPR2 display a guanylate cyclase activity that catalyzes the formation of cyclic GMP. NPR3 lacks this guanylate cyclase activity and is reportedly coupled to G_i-dependent signaling. Recently, we reported that the continuous infusion of the peptide osteocrin, an endogenous ligand of NPR3 secreted by bone and muscle cells, lowered blood pressure in wild-type mice, suggesting that endogenous natriuretic peptides play major roles in the regulation of blood pressure. Neprilysin is a neutral endopeptidase that degrades several vasoactive peptides, including natriuretic peptides. The increased worldwide clinical use of the angiotensin receptor-neprilysin inhibitor for the treatment of chronic heart failure has brought renewed attention to the physiological effects of natriuretic peptides. In this review, we provide an overview of the discovery of ANP and its translational research. We also highlight our recent findings on the blood pressure regulatory effects of ANP, focusing on its molecular mechanisms.

Chronological attenuation of NPRA/PKG/AMPK signaling promotes vascular aging and elevates blood pressure

Hypertension is common in elderly population. We designed to search comprehensively for genes that are chronologically shifted in their expressions and to define their contributions to vascular aging and hypertension. RNA sequencing was conducted to search for senescence-shifted transcripts in human umbilical vein endothelial cells (HUVECs). Small interfering RNA (siRNA), small-molecule drugs, CRISPR/Cas9 techniques, and imaging were used to determine genes' function and contributions to age-related phenotypes of the endothelial cell and blood vessel. Of 25 genes enriched in the term of "regulation of blood pressure," NPRA was changed most significantly. The decreased NPRA expression was replicated in aortas of aged mice. The knockdown of NPRA promoted HUVEC senescence and it decreased expressions of protein kinase cGMP-dependent 1 (PKG), sirtuin 1 (SIRT1), and endothelial nitric oxide synthase (eNOS). Suppression of NPRA also decreased the phosphorylation of AMP-activated protein kinase (AMPK) as well as the ratio of oxidized nicotinamide adenine dinucleotide (NAD⁺ )/reduced nicotinamide adenine dinucleotide (NADH) but increased the production of reactive oxygen species (ROS). 8-Br-cGMP (analog of cGMP), or AICAR (AMPK activator), counteracted the observed changes in HUVECs. The Npr1^+/- mice presented an elevated systolic blood pressure and their vessels became insensitive to endothelial-dependent vasodilators. Further, vessels from Npr1^+/- mice increased Cdkn1a but decreased eNos expressions. These phenotypes were rescued by intravenously administrated 8-Br-cGMP and viral overexpression of human PKG, respectively. In conclusion, we demonstrate NPRA/PKG/AMPK as a novel and critical signaling axis in the modulation of endothelial cell senescence, vascular aging, and hypertension.

Inhibition of Mammalian Target of Rapamycin Attenuates Recurrent Seizures Associated Cardiac Damage in a Zebrafish Kindling Model of Chronic Epilepsy

Sudden Unexpected Death in Epilepsy (SUDEP) is primarily linked with the cardiac irregularities that occur due to recurrent seizures. Our previous studies found a role of mTOR pathway activation in seizures-linked cardiac damage in a rat model. In continuation to the earlier work, the present study was devised to explore the role of rapamycin (mTOR inhibitor and clinically used immunosuppressive agent) in a zebrafish kindling model and associated cardiac damage. Adult zebrafish were incubated with increasing concentrations of rapamycin (1, 2 and, 4 μM), followed by pentylenetetrazole (PTZ) exposure to record seizure latency and severity. In another experiment, zebrafish were subjected to a standardized PTZ kindling protocol. The kindled fish were treated daily with rapamycin for up to 25 days, along with PTZ to record seizure severity. At the end, zebrafish heart was excised for carbonylation assay, gene expression, and protein quantification studies. In the acute PTZ convulsion test, treatment with rapamycin showed a significant increase in seizure latency and decreased seizure severity without any change in seizure incidence. Treatment with rapamycin also reduced the severity of seizures in kindled fish. The cardiac expressions of gpx, nppb, kcnh2, scn5a, mapk8, stat3, rps6 and ddit were decreased, whereas the levels of trxr2 and beclin 1 were increased following rapamycin treatment in kindled fish. Furthermore, rapamycin treatment also decreased p-mTOR expression and protein carbonyls level in the fish cardiac tissue. The present study concluded that rapamycin reduces seizures and associated cardiac damage by inhibiting mTOR activation in the zebrafish kindling model.

Hypertension: Potential Player in Cardiovascular Disease Incidence in Preeclampsia

Preeclampsia (PE) is one of the complications, that threatens pregnant mothers during pregnancy. According to studies, it accounts for 3-7% of all pregnancies, and also is effective in preterm delivery. PE is the third leading cause of death in pregnant women. High blood pressure in PE can increase the risk of developing cardiovascular disease (CVD) in cited individuals, and is one of the leading causes of death in PE individuals. Atrial natriuretic peptide (ANP), Renin-Angiotensin system and nitric oxide (NO) are some of involved factors in regulating blood pressure. Therefore, by identifying the signaling pathways, that are used by these molecules to regulate and modulate blood pressure, appropriate treatment strategies can be provided to reduce blood pressure through target therapy in PE individuals; consequently, it can reduce CVD risk and mortality.

IGFBP7-AS1 is a p53-responsive long noncoding RNA downregulated by Epstein-Barr virus that contributes to viral tumorigenesis

Epstein-Barr virus (EBV) is closely related to the development of several malignancies, such as B-cell lymphoma (B-CL), by the mechanism through which these malignancies develop remains largely unknown. We previously observed downregulation of the long noncoding RNA (lncRNA) IGFBP7-AS1 in response to EBV infection. However, the role of IGFBP7-AS1 in EBV-associated cancers has not been clarified. Here, we found that expression of IGFBP7-AS1, as well as its sense gene IGFBP7, is decreased in EBV-positive B-CL cells and clinical tissues. IGFBP7-AS1 stabilizes IGFBP7 mRNA by forming a duplex based on their overlapping regions. The tumour suppressor p53 transcriptionally activates IGFBP7-AS1 expression by binding to the promoter region of the lncRNA gene. The IGFBP7-AS1 expression is able to be rescued in EBV-positive cells in wild-type (wt) p53-dependent manner. IGFBP7-AS1 inhibits the proliferation and promotes the apoptosis of B-CL cells. Moreover, tumorigenic properties due to the depletion of IGFBP7-AS1 were restored by exogenous expression of IGFBP7 or wt-p53. Furthermore, the functional p53/IGFBP7-AS1/IGFBP7 axis facilitates apoptosis by suppressing the production and secretion of the NPPB signal peptide and further regulating the cGMP-PKG signalling pathway. This study demonstrates that EBV promotes tumorigenesis, particularly in B-CL progression, by downregulating the novel p53-responsive lncRNA IGFBP7-AS1.

Discovery of small molecule guanylyl cyclase A receptor positive allosteric modulators

The particulate guanylyl cyclase A receptor (GC-A), via activation by its endogenous ligands atrial natriuretic peptide (ANP) and b-type natriuretic peptide (BNP), possesses beneficial biological properties such as blood pressure regulation, natriuresis, suppression of adverse remodeling, inhibition of the renin-angiotensin-aldosterone system, and favorable metabolic actions through the generation of its second messenger cyclic guanosine monophosphate (cGMP). Thus, the GC-A represents an important molecular therapeutic target for cardiovascular disease and its associated risk factors. However, a small molecule that is orally bioavailable and directly targets the GC-A to potentiate cGMP has yet to be discovered. Here, we performed a cell-based high-throughput screening campaign of the NIH Molecular Libraries Small Molecule Repository, and we successfully identified small molecule GC-A positive allosteric modulator (PAM) scaffolds. Further medicinal chemistry structure-activity relationship efforts of the lead scaffold resulted in the development of a GC-A PAM, MCUF-651, which enhanced ANP-mediated cGMP generation in human cardiac, renal, and fat cells and inhibited cardiomyocyte hypertrophy in vitro. Further, binding analysis confirmed MCUF-651 binds to GC-A and selectively enhances the binding of ANP to GC-A. Moreover, MCUF-651 is orally bioavailable in mice and enhances the ability of endogenous ANP and BNP, found in the plasma of normal subjects and patients with hypertension or heart failure, to generate GC-A-mediated cGMP ex vivo. In this work, we report the discovery and development of an oral, small molecule GC-A PAM that holds great potential as a therapeutic for cardiovascular, renal, and metabolic diseases.

The Natriuretic Peptides for Hypertension Treatment

Hypertension is a common pathological condition predisposing to a higher occurrence of cardiovascular diseases and events. Unfortunately, treatment of hypertension is still suboptimal worldwide. More efforts are needed to implement the availability of anti-hypertensive drugs. The family of natriuretic peptides, including atrial and brain natriuretic peptides (ANP and BNP), play a key role on blood pressure regulation through the natriuretic, diuretic and vasorelaxant effects. A large number of experimental and human studies, ranging from pathophysiological to genetic investigations, supported ANP as the most relevant component of the family able to modulate blood pressure and to contribute to hypertension development. On this background, it is expected that ANP-based therapeutic approaches may give a significant contribution to the development of efficacious therapies against hypertension. Since native ANP cannot be administered due to its short half-life, several approaches were attempted over the years to overcome the difficulties inherent to the ANP instability. These approaches included ANP recombinant and fusion peptides, gene therapy, inhibition of ANP degradation by neprilysin inhibition, and designer peptides. The most relevant achievements in the field are discussed in this article. Based on the available evidence, therapies targeting ANP represent efficacious and clinically applicable anti-hypertensive agents.

Molecular Signaling Mechanisms and Function of Natriuretic Peptide Receptor-A in the Pathophysiology of Cardiovascular Homeostasis

The discovery of atrial, brain, and C-type natriuretic peptides (ANP, BNP, and CNP) and their cognate receptors has greatly increased our knowledge of the control of hypertension and cardiovascular homeostasis. ANP and BNP are potent endogenous hypotensive hormones that elicit natriuretic, diuretic, vasorelaxant, antihypertrophic, antiproliferative, and antiinflammatory effects, largely directed toward the reduction of blood pressure (BP) and cardiovascular diseases (CVDs). The principal receptor involved in the regulatory actions of ANP and BNP is guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA), which produces the intracellular second messenger cGMP. Cellular, biochemical, molecular, genetic, and clinical studies have facilitated understanding of the functional roles of natriuretic peptides (NPs), as well as the functions of their receptors, and signaling mechanisms in CVDs. Transgenic and gene-targeting (gene-knockout and gene-duplication) strategies have produced genetically altered novel mouse models and have advanced our knowledge of the importance of NPs and their receptors at physiological and pathophysiological levels in both normal and disease states. The current review describes the past and recent research on the cellular, molecular, genetic mechanisms and functional roles of the ANP-BNP/NPRA system in the physiology and pathophysiology of cardiovascular homeostasis as well as clinical and diagnostic markers of cardiac disorders and heart failure. However, the therapeutic potentials of NPs and their receptors for the diagnosis and treatment of cardiovascular diseases, including hypertension, heart failure, and stroke have just begun to be expanded. More in-depth investigations are needed in this field to extend the therapeutic use of NPs and their receptors to treat and prevent CVDs.

Role of natriuretic peptides in the cardiovascular-adipose communication: a tale of two organs

Natriuretic peptides have long been known for their cardiovascular function. However, a growing body of evidence emphasizes the role of natriuretic peptides in the energy metabolism of several substrates in humans and animals, thus interrelating the heart, as an endocrine organ, with various insulin-sensitive tissues and organs such as adipose tissue, muscle skeletal, and liver. Adipose tissue dysfunction is associated with altered regulation of the natriuretic peptide system, also indicated as a natriuretic disability. Evidence points to a contribution of this natriuretic disability to the development of obesity, type 2 diabetes mellitus, and cardiometabolic complications; although the causal relationship is not fully understood at present. However, targeting the natriuretic peptide pathway may improve metabolic health in obesity and type 2 diabetes mellitus. This review will focus on the current literature on the metabolic functions of natriuretic peptides with emphasis on lipid metabolism and insulin sensitivity. Natriuretic peptide system alterations could be proposed as one of the linking mechanisms between adipose tissue dysfunction and cardiovascular disease.

Berberine ameliorates vascular dysfunction by a global modulation of lncRNA and mRNA expression profiles in hypertensive mouse aortae

Objective

The current study investigated the mechanism underlying the therapeutic effects of berberine in the vasculature in hypertension.

Methods

Angiotensin II (Ang II)-loaded osmotic pumps were implanted in C57BL/6J mice with or without berberine administration. Mouse aortae were suspended in myograph for force measurement. Microarray technology were performed to analyze expression profiles of lncRNAs and mRNAs in the aortae. These dysregulated expressions were then validated by qRT-PCR. LncRNA-mRNA co-expression network was constructed to reveal the specific relationships.

Results

Ang Ⅱ resulted in a significant increase in the blood pressure of mice, which was suppressed by berberine. The impaired endothelium-dependent aortic relaxation was restored in hypertensive mice. Microarray data revealed that 578 lncRNAs and 554 mRNAs were up-regulated, while 320 lncRNAs and 377 mRNAs were down-regulated in the aortae by Ang Ⅱ; both were reversed by berberine treatment. qRT-PCR validation results of differentially expressed genes (14 lncRNAs and 6 mRNAs) were completely consistent with the microarray data. GO analysis showed that these verified differentially expressed genes were significantly enriched in terms of “cellular process”, “biological regulation” and “regulation of biological process”, whilst KEGG analysis identified vascular function-related pathways including cAMP signaling pathway, cGMP-PKG signaling pathway, and calcium signaling pathway etc. Importantly, we observed that lncRNA ENSMUST00000144849, ENSMUST00000155383, and AK041185 were majorly expressed in endothelial cells.

Conclusion

The present results suggest that the five lncRNAs ENSMUST00000144849, NR_028422, ENSMUST00000155383, AK041185, and uc.335+ might serve critical regulatory roles in hypertensive vasculature by targeting pivotal mRNAs and subsequently affecting vascular function-related pathways. Moreover, these lncRNAs were modulated by berberine, therefore providing the novel potential therapeutic targets of berberine in hypertension. Furthermore, lncRNA ENSMUST00000144849, ENSMUST00000155383, and AK041185 might be involved in the preservation of vascular endothelial cell function.

Novel doses of sacubitril/valsartan in patients unable to tolerate traditional therapy: Effects on N-terminal pro B-type natriuretic peptide levels

BACKGROUND

Widespread use of angiotensin receptor blocker and neprilysin inhibitor (ARNI) remains low, and many patients are unable to tolerate the medication due to hypotension at the currently recommended starting dose.

HYPOTHESIS

The aim of this study is to assess if lower than standard doses of ARNI, sacubitril/valsartan (S/V), significantly reduces NT-proBNP and leads to any change in diuretic dose, serum potassium, or creatinine.

METHODS

In a retrospective study of 278 patients who were started on a low dose S/V at a single medical center, 45 patients were selected for the study cohort. Patients were subcategorized to Group 1 (n = 10): very low dose S/V (half a tab of 24/26 mg BID), Group 2 (n = 10): very low dose titrated to low dose S/V, and Group 3 (n = 25): low dose S/V (24/26 mg BID). NT-proBNP, diuretic dose, serum potassium, and creatinine were compared before and after initiation of S/V.

RESULTS

Among all groups, there was a significant reduction in NT-proBNP level (Group 1: p < .01, Group 2: p < .01, and Group 3: p < .001). In addition, there was a significant reduction in diuretic dose across all groups combined (furosemide 53 mg/day vs. 73 mg/day; p = .03), with 17.8% (8/45) patients being able to discontinue their diuretic completely. There was no significant change in potassium or creatinine.

CONCLUSIONS

Lower than standard dose of S/V significantly reduces NT-proBNP and diuretic requirement without change in potassium or creatinine, which provides hope that patients who cannot tolerate standard doses of S/V due to hypotension may be able to receive the benefits of S/V therapy.

Spatial Transcriptomics Reveals Genes Associated with Dysregulated Mitochondrial Functions and Stress Signaling in Alzheimer Disease

Alzheimer disease (AD) is a devastating neurological disease associated with progressive loss of mental skills and cognitive and physical functions whose etiology is not completely understood. Here, our goal was to simultaneously uncover novel and known molecular targets in the structured layers of the hippocampus and olfactory bulbs that may contribute to early hippocampal synaptic deficits and olfactory dysfunction in AD mice. Spatially resolved transcriptomics was used to identify high-confidence genes that were differentially regulated in AD mice relative to controls. A diverse set of genes that modulate stress responses and transcription were predominant in both hippocampi and olfactory bulbs. Notably, we identify Bok, implicated in mitochondrial physiology and cell death, as a spatially downregulated gene in the hippocampus of mouse and human AD brains. In summary, we provide a rich resource of spatially differentially expressed genes, which may contribute to understanding AD pathology.

•

Spatial transcriptomics identifies differentially expressed genes with spatial patterns

•

Early application of spatial transcriptomics to olfactory bulbs from AD models

•

Bok gene is spatially differentially expressed in AD mouse and patient brains

•

Paip1 and Homer1 genes are regulated in a PolB-dependent manner

The Role of Natriuretic Peptides in the Regulation of Cardiac Tolerance to Ischemia/Reperfusion and Postinfarction Heart Remodeling

In the past 10 years, mortality from acute myocardial infarction has not decreased despite the widespread introduction of percutaneous coronary intervention. The reason for this situation is the absence in clinical practice of drugs capable of preventing reperfusion injury of the heart with high efficiency. In this regard, noteworthy natriuretic peptides (NPs) which have the infarct-limiting effect, prevent reperfusion cardiac injury, prevent adverse post-infarction remodeling of the heart. Atrial natriuretic peptide does not have the infarct-reducing effect in rats with alloxan-induced diabetes mellitus. NPs have the anti-apoptotic and anti-inflammatory effects. There is indirect evidence that NPs inhibit pyroptosis and autophagy. Published data indicate that NPs inhibit reactive oxygen species production in cardiomyocytes, aorta, heart, kidney and the endothelial cells. NPs can suppress aldosterone, angiotensin II, endothelin-1 synthesize and secretion. NPs inhibit the effects aldosterone, angiotensin II on the post-receptor level through intracellular signaling events. NPs activate guanylyl cyclase, protein kinase G and protein kinase A, and reduce phosphodiesterase 3 activity. NO-synthase and soluble guanylyl cyclase are involved in the cardioprotective effect of NPs. The cardioprotective effect of natriuretic peptides is mediated via activation of kinases (AMPK, PKC, PI3 K, ERK1/2, p70s6 k, Akt) and inhibition of glycogen synthase kinase 3β. The cardioprotective effect of NPs is mediated via sarcolemmal K_ATP channel and mitochondrial K_ATP channel opening. The cardioprotective effect of brain natriuretic peptide is mediated via MPT pore closing. The anti-fibrotic effect of NPs may be mediated through inhibition TGF-β1 expression. Natriuretic peptides can inhibit NF-κB activity and activate GATA. Hemeoxygenase-1 and peroxisome proliferator-activated receptor γ may be involved in the infarct-reducing effect of NPs. NPs exhibit the infarct-limiting effect in patients with acute myocardial infarction. NPs prevent post-infarction remodeling of the heart. To finally resolve the question of the feasibility of using NPs in AMI, a multicenter, randomized, blind, placebo-controlled study is needed to assess the effect of NPs on the mortality of patients after AMI.

Cardiac natriuretic peptides

Investigations into the mixed muscle-secretory phenotype of cardiomyocytes from the atrial appendages of the heart led to the discovery that these cells produce, in a regulated manner, two polypeptide hormones - the natriuretic peptides - referred to as atrial natriuretic factor or atrial natriuretic peptide (ANP) and brain or B-type natriuretic peptide (BNP), thereby demonstrating an endocrine function for the heart. Studies on the gene encoding ANP (NPPA) initiated the field of modern research into gene regulation in the cardiovascular system. Additionally, ANP and BNP were found to be the natural ligands for cell membrane-bound guanylyl cyclase receptors that mediate the effects of natriuretic peptides through the generation of intracellular cGMP, which interacts with specific enzymes and ion channels. Natriuretic peptides have many physiological actions and participate in numerous pathophysiological processes. Important clinical entities associated with natriuretic peptide research include heart failure, obesity and systemic hypertension. Plasma levels of natriuretic peptides have proven to be powerful diagnostic and prognostic biomarkers of heart disease. Development of pharmacological agents that are based on natriuretic peptides is an area of active research, with vast potential benefits for the treatment of cardiovascular disease.

Angiotensin II represses Npr1 expression and receptor function by recruitment of transcription factors CREB and HSF-4a and activation of HDACs

The two vasoactive hormones, angiotensin II (ANG II; vasoconstrictive) and atrial natriuretic peptide (ANP; vasodilatory) antagonize the biological actions of each other. ANP acting through natriuretic peptide receptor-A (NPRA) lowers blood pressure and blood volume. We tested hypothesis that ANG II plays critical roles in the transcriptional repression of Npr1 (encoding NPRA) and receptor function. ANG II significantly decreased NPRA mRNA and protein levels and cGMP accumulation in cultured mesangial cells and attenuated ANP-mediated relaxation of aortic rings ex vivo. The transcription factors, cAMP-response element-binding protein (CREB) and heat-shock factor-4a (HSF-4a) facilitated the ANG II-mediated repressive effects on Npr1 transcription. Tyrosine kinase (TK) inhibitor, genistein and phosphatidylinositol 3-kinase (PI-3K) inhibitor, wortmannin reversed the ANG II-dependent repression of Npr1 transcription and receptor function. ANG II enhanced the activities of Class I histone deacetylases (HDACs 1/2), thereby decreased histone acetylation of H3K9/14ac and H4K8ac. The repressive effect of ANG II on Npr1 transcription and receptor signaling seems to be transduced by TK and PI-3K pathways and modulated by CREB, HSF-4a, HDACs, and modified histones. The current findings suggest that ANG II-mediated repressive mechanisms of Npr1 transcription and receptor function may provide new molecular targets for treatment and prevention of hypertension and cardiovascular diseases.

Identifying roles for peptidergic signaling in mice

Despite accumulating evidence demonstrating the essential roles played by neuropeptides, it has proven challenging to use this information to develop therapeutic strategies. Peptidergic signaling can involve juxtacrine, paracrine, endocrine, and neuronal signaling, making it difficult to define physiologically important pathways. One of the final steps in the biosynthesis of many neuropeptides requires a single enzyme, peptidylglycine α-amidating monooxygenase (PAM), and lack of amidation renders most of these peptides biologically inert. PAM, an ancient integral membrane enzyme that traverses the biosynthetic and endocytic pathways, also affects cytoskeletal organization and gene expression. While mice, zebrafish, and flies lacking Pam (Pam^KO/KO ) are not viable, we reasoned that cell type-specific elimination of Pam expression would generate mice that could be screened for physiologically important and tissue-specific deficits. Conditional Pam^cKO/cKO mice, with loxP sites flanking the 2 exons deleted in the global Pam^KO/KO mouse, were indistinguishable from wild-type mice. Eliminating Pam expression in excitatory forebrain neurons reduced anxiety-like behavior, increased locomotor responsiveness to cocaine, and improved thermoregulation in the cold. A number of amidated peptides play essential roles in each of these behaviors. Although atrial natriuretic peptide (ANP) is not amidated, Pam expression in the atrium exceeds levels in any other tissue. Eliminating Pam expression in cardiomyocytes increased anxiety-like behavior and improved thermoregulation. Atrial and serum levels of ANP fell sharply in PAM myosin heavy chain 6 conditional knockout mice, and RNA sequencing analysis identified changes in gene expression in pathways related to cardiac function. Use of this screening platform should facilitate the development of therapeutic approaches targeted to peptidergic pathways.

Genetic Ablation and Guanylyl Cyclase/Natriuretic Peptide Receptor-A: Impact on the Pathophysiology of Cardiovascular Dysfunction

Mice bearing targeted gene mutations that affect the functions of natriuretic peptides (NPs) and natriuretic peptide receptors (NPRs) have contributed important information on the pathogenesis of hypertension, kidney disease, and cardiovascular dysfunction. Studies of mice having both complete gene disruption and tissue-specific gene ablation have contributed to our understanding of hypertension and cardiovascular disorders. These phenomena are consistent with an oligogenic inheritance in which interactions among a few alleles may account for genetic susceptibility to hypertension, renal insufficiency, and congestive heart failure. In addition to gene knockouts conferring increased risks of hypertension, kidney disorders, and cardiovascular dysfunction, studies of gene duplications have identified mutations that protect against high blood pressure and cardiovascular events, thus generating the notion that certain alleles can confer resistance to hypertension and heart disease. This review focuses on the intriguing phenotypes of Npr1 gene disruption and gene duplication in mice, with emphasis on hypertension and cardiovascular events using mouse models carrying Npr1 gene knockout and/or gene duplication. It also describes how Npr1 gene targeting in mice has contributed to our knowledge of the roles of NPs and NPRs in dose-dependently regulating hypertension and cardiovascular events.

Pulmonary Arterial Hypertension Due to NPR-C Mutation: A Novel Paradigm for Normal and Pathologic Remodeling?

Idiopathic Pulmonary Arterial Hypertension (IPAH) is a deadly and disabling disease characterized by severe vascular remodeling of small pulmonary vessels by fibroblasts, myofibroblasts and vascular smooth muscle cell proliferation. Recent studies suggest that the Natriuretic Peptide Clearance Receptor (NPR-C) signaling pathways may play a crucial role in the development of IPAH. Reduced expression or function of NPR-C signaling in pulmonary artery smooth muscle cells may contribute to the pulmonary vascular remodeling, which is characteristic of this disease. The likely mechanisms may involve an impaired interaction between NPR-C, specific growth factors and other signal transduction pathways including but not limited to Gqα/mitogen-activated protein kinase (MAPK)/PI3K and AKT signaling. The resulting failure of growth suppression in pulmonary artery smooth muscle cells provides critical clues to the cellular pathobiology of IPAH. The reciprocal regulation of NPR-C signaling in models of tissue remodeling may thus provide new insights to our understanding of IPAH.

Genetic disruption of Npr1 depletes regulatory T cells and provokes high levels of proinflammatory cytokines and fibrosis in the kidneys of female mutant mice

The present study was designed to determine the effects of gene knockout of guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) on immunogenic responses affecting kidney function and blood pressure (BP) in Npr1 (coding for GC-A/NPRA)-null mutant mice. We used female Npr1 gene-disrupted (Npr1^-/-, 0 copy), heterozygous (Npr1^+/-, 1 copy), wild-type (Npr1^+/+, 2 copy), and gene-duplicated (Npr1^++/++, 4 copy) mice. Expression levels of Toll-like receptor (TLR)2/TLR4 mRNA were increased 4- to 5-fold in 1-copy mice and 6- to 10-fold in 0-copy mice; protein levels were increased 2.5- to 3-fold in 1-copy mice and 4- to 5-fold in 0-copy mice. Expression of proinflammatory cytokines and BP was significantly elevated in 1-copy and 0-copy mice compared with 2-copy and 4-copy mice. In addition, 0-copy and 1-copy mice exhibited drastic reductions in regulatory T cells (Tregs). After rapamycin treatment, Tregs were increased by 17% (P < 0.001) in 0-copy mice and 8% (P < 0.001) in 1-copy mice. Renal mRNA and protein levels of TLR2 and TLR4 were decreased by 70% in 0-copy mice and 50% in 1-copy mice. There were significantly higher levels of Tregs and very low levels of TLR2/TLR4 expression in 4-copy mice (P < 0.001). These findings indicate that the disruption of Npr1 in female mice triggers renal immunogenic pathways, which transactivate the expression of proinflammatory cytokines and renal fibrosis with elevated BP in mutant animals. The data suggest that rapamycin treatment attenuates proinflammatory cytokine expression, dramatically increases anti-inflammatory cytokines, and substantially reduces BP and renal fibrosis in mutant animals.

Emerging concepts of receptor endocytosis and concurrent intracellular signaling: Mechanisms of guanylyl cyclase/natriuretic peptide receptor-A activation and trafficking

Endocytosis is a prominent clathrin-mediated mechanism for concentrated uptake and internalization of ligand-receptor complexes, also known as cargo. Internalization of cargo is the fundamental mechanism for receptor-dependent regulation of cell membrane function, intracellular signal transduction, and neurotransmission, as well as other biological and physiological activities. However, the intrinsic mechanisms of receptor endocytosis and contemporaneous intracellular signaling are not well understood. We review emerging concepts of receptor endocytosis with concurrent intracellular signaling, using a typical example of guanylyl cyclase/natriuretic peptide receptor-A (NPRA) internalization, subcellular trafficking, and simultaneous generation of second-messenger cGMP and signaling in intact cells. We highlight the role of short-signal motifs located in the carboxyl-terminal regions of membrane receptors during their internalization and subsequent receptor trafficking in organelles that are not traditionally studied in this context, including nuclei and mitochondria. This review sheds light on the importance of future investigations of receptor endocytosis and trafficking in live cells and intact animals in vivo in physiological context.

Genetic disruption of guanylyl cyclase/natriuretic peptide receptor-A upregulates renal (pro) renin receptor expression in Npr1 null mutant mice

The objective of the present study was to determine whether targeted-disruption of Npr1 gene (encoding for guanylyl cyclase/natriuretic peptide receptor-A; GC-A/NPRA) upregulates pro(renin) receptor (P)RR expression and leads to the activation of MAPKs in Npr1 gene-knockout mice. The Npr1 homozygous (Npr1^-/-; 0-copy), heterozygous (Npr1^+/-; 1-copy), wild-type (Npr1^+/+; 2-copy), and gene-duplicated (Npr1^++/++; 4-copy) mice were utilized. To identify the canonical pathway of (P)RR, we administered ACE-1 inhibitor (captopril), AT1R blocker (losartan), and MAPKs inhibitors (U0126 and SB203580) to all Npr1 mice genotypes. The renal expression of (P)RR mRNA was increased by 3-fold in 0-copy mice and 2-fold in 1-copy mice compared with 2-copy mice, which was also associated with significantly increased expression of ACE-1 and AT1R mRNA levels. Similarly, the phosphorylation of MAPKs (Erk1/2 and p-p38) was enhanced by 3.5-fold and 3.2-fold, respectively, in 0-copy mice with significant increases in 1-copy mice compared with 2-copy mice. The kidney and plasma levels of proinflammatory cytokines were significantly elevated in 0-copy and 1-copy mice. Treatment with captopril and losartan did not alter the expression of (P)RR in any of the Npr1 mice genotypes. Interestingly, losartan significantly reduced the phosphorylation of Erk1/2 and p38 in Npr1 mice. The present results suggest that the ablation of Npr1 upregulates (P)RR, MAPKs (Erk1/2 and p38), and proinflammatory cytokines in 0-copy and 1-copy mice. In contrast, the duplication of Npr1 exhibits the anti-inflammatory and antihypertensive effects by reducing the activation of MAPKs and inhibiting the expression levels of RAAS components and proinflammatory cytokines.