The publication data currently available has been vetted by Vanderbilt faculty, staff, administrators and trainees. The data itself is retrieved directly from NCBI's PubMed and is automatically updated on a weekly basis to ensure accuracy and completeness.
If you have any questions or comments, please contact us.
A frameshift (fs) mutation in the natriuretic peptide precursor A (NPPA) gene, encoding a mutant atrial natriuretic peptide (Mut-ANP), has been linked with familial atrial fibrillation (AF) but the underlying mechanisms by which the mutation causes AF remain unclear. We engineered 2 transgenic (TG) mouse lines expressing the wild-type (WT)-NPPA gene (H-WT-NPPA) and the human fs-Mut-NPPA gene (H-fsMut-NPPA) to test the hypothesis that mice overexpressing the human NPPA mutation are more susceptible to AF and elucidate the underlying electrophysiologic and molecular mechanisms. Transthoracic echocardiography and surface electrocardiography (ECG) were performed in H-fsMut-NPPA, H-WT-NPPA, and Non-TG mice. Invasive electrophysiology, immunohistochemistry, Western blotting and patch clamping of membrane potentials were performed. To examine the role of the Mut-ANP in ion channel remodeling, we measured plasma cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP) levels and protein kinase A (PKA) activity in the 3 groups of mice. In H-fsMut-NPPA mice mean arterial pressure (MAP) was reduced when compared to H-WT-NPPA and Non-TG mice. Furthermore, injection of synthetic fs-Mut-ANP lowered the MAP in H-WT-NPPA and Non-TG mice while synthetic WT-ANP had no effect on MAP in the 3 groups of mice. ECG characterization revealed significantly prolonged QRS duration in H-fsMut-NPPA mice when compared to the other two groups. Trans-Esophageal (TE) atrial pacing of H-fsMut-NPPA mice showed increased AF burden and AF episodes when compared with H-WT-NPPA or Non-TG mice. The cardiac Na (NaV1.5) and Ca (CaV1.2/CaV1.3) channel expression and currents (I, I) and action potential durations (APD/APD/APD) were significantly reduced in H-fsMut-NPPA mice while the rectifier K channel current (I) was markedly increased when compared to the other 2 groups of mice. In addition, plasma cGMP levels were only increased in H-fsMut-NPPA mice with a corresponding reduction in plasma cAMP levels and PKA activity. In summary, we showed that mice overexpressing an AF-linked NPPA mutation are more prone to develop AF and this risk is mediated in part by remodeling of the cardiac Na, Ca and K channels creating an electrophysiologic substrate for reentrant AF.
Copyright © 2019 Elsevier Ltd. All rights reserved.
Nppa is a cardiac hormone which plays critical roles in regulating salt-water balance. Its expression is restricted to the atria of the healthy post-natal heart. During heart development, spatio-temporal expression of Nppa is dynamically changed within the heart and becomes restricted to the atria upon birth. In contrast to its atrial specific expression after birth, Nppa is re-expressed in the adult ventricles in response to cardiac hypertrophy. To study cardiac chamber specification during development and pathological cardiac remodeling during heart disease, we generated a novel Nppa reporter mouse line by knocking-in a tagBFP reporter cassette into 3'-UTR of the Nppa gene without disrupting the endogenous gene. Our results demonstrated dynamic tagBFP expression in the developing heart, recapitulating the spatiotemporal expression pattern of endogenous Nppa. We also found that Nppa-tagBFP is induced in the ventricle during pathological remodeling. Taken together, Nppa-tagBFP reporter knock-in mouse model described in this article will serve as a valuable tool to study cardiac chamber specification during development as well as pathological cardiac remodeling.
© 2019 Wiley Periodicals, Inc.
BACKGROUND - The natriuretic peptide hormones play an important role in salt and blood pressure regulation. In observational studies, obesity and insulin resistance have been consistently associated with lower concentrations of natriuretic peptides. It has been proposed that insulin influences natriuretic peptide production.
OBJECTIVE - We sought to determine the acute effects of insulin administration on natriuretic peptide concentrations.
METHODS - 31 men and women (11 lean, 10 overweight, and 10 obese), ages 30-70 years, without cardiovascular disease or overt diabetes underwent a hyperinsulinemic-euglycemic insulin clamp. Plasma concentrations of N-terminal pro atrial natriuretic peptide (NT-proANP) and N-terminal pro B-type natriuretic peptide (NT-proBNP) were measured at baseline and steady-state (the final 30 minutes of the clamp protocol).
RESULTS - From baseline to steady-state, insulin levels increased from a mean level of 9.5 to 176.7 μU/ml (p<0.001). Over this period, circulating NT-proANP concentrations decreased by 9% (-1933 ng/L, p = 0.01). The changes in NT-proANP did not differ between lean, overweight, and obese individuals. Steady-state NT-proANP levels, adjusted for baseline, were lower in individuals with greater insulin resistance, independent of BMI. In contrast to NT-proANP, NT-proBNP levels did not change significantly during the clamp (p = 0.41).
CONCLUSION - Insulin administration was associated with a moderate decrease in circulating NT-proANP, but not NT-proBNP. The lowest NT-proANP concentrations were found in insulin-resistant individuals. Further investigations are warranted to elucidate potential mechanisms underlying the effects of insulin on the cardiac hormonal axis.
OBJECTIVE - Activation of thermogenesis in brown adipose tissue (BAT) and the ability to increase uncoupling protein 1 (UCP1) levels and mitochondrial biogenesis in white fat (termed 'browning'), has great therapeutic potential to treat obesity and its comorbidities because of the net increase in energy expenditure. β-adrenergic-cAMP-PKA signaling has long been known to regulate these processes. Recently PKA-dependent activation of mammalian target of rapamycin complex 1 (mTORC1) was shown to be necessary for adipose 'browning' as well as proper development of the interscapular BAT. In addition to cAMP-PKA signaling pathways, cGMP-PKG signaling also promotes this browning process; however, it is unclear whether or not mTORC1 is also necessary for cGMP-PKG induced browning.
METHOD - Activation of mTORC1 by natriuretic peptides (NP), which bind to and activate the membrane-bound guanylyl cyclase, NP receptor A (NPRA), was assessed in mouse and human adipocytes in vitro and mouse adipose tissue in vivo.
RESULTS - Activation of mTORC1 by NP-cGMP signaling was observed in both mouse and human adipocytes. We show that NP-NPRA-PKG signaling activate mTORC1 by direct PKG phosphorylation of Raptor at Serine 791. Administration of B-type natriuretic peptide (BNP) to mice induced Ucp1 expression in inguinal adipose tissue in vivo, which was completely blocked by the mTORC1 inhibitor rapamycin.
CONCLUSION - Our results demonstrate that NP-cGMP signaling activates mTORC1 via PKG, which is a component in the mechanism of adipose browning.
Copyright © 2018 The Authors. Published by Elsevier GmbH.. All rights reserved.
In addition to controlling blood pressure, cardiac natriuretic peptides (NPs) can stimulate lipolysis in adipocytes and promote the "browning" of white adipose tissue. NPs may also increase the oxidative capacity of skeletal muscle. To unravel the contribution of NP-stimulated metabolism in adipose tissue compared to that in muscle in vivo, we generated mice with tissue-specific deletion of the NP clearance receptor, NPRC, in adipose tissue ( ) or in skeletal muscle ( ). We showed that, similar to null mice, mice, but not mice, were resistant to obesity induced by a high-fat diet. mice exhibited increased energy expenditure, improved insulin sensitivity, and increased glucose uptake into brown fat. These mice were also protected from diet-induced hepatic steatosis and visceral fat inflammation. These findings support the conclusion that NPRC in adipose tissue is a critical regulator of energy metabolism and suggest that inhibiting this receptor may be an important avenue to explore for combating metabolic disease.
Copyright © 2017 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
OBJECTIVE - Cardiac natriuretic peptides (NPs) bind to two receptors (NPRA-mediator of signaling; NPRC-clearance receptor) whose ratio, NPRR (NPRA/NPRC), determines the NP bioactivity. This study investigated the relationship of NP receptor gene expression in adipose tissue and muscle with obesity and glucose intolerance. Prospectively, the study also assessed whether changes in NP receptor expression and thermogenic gene markers accompanied improvements of insulin sensitivity.
METHODS - A cross-sectional study of subjects with a wide range of BMI and glucose tolerance (n = 50) was conducted, as well as a randomized 12-week trial of subjects with type 2 diabetes mellitus (T2DM) treated with pioglitazone (n = 9) or placebo (n = 10).
RESULTS - NPRR mRNA was significantly lower in adipose tissue of subjects with obesity when compared with lean subjects (P ≤ 0.001). NPRR decreased with progression from normal glucose tolerance to T2DM (P < 0.01) independently of obesity. Treatment of subjects with T2DM with pioglitazone increased NPRR in adipose tissue (P ≤ 0.01) in conjunction with improvements in insulin sensitivity and increases of the thermogenic markers PPARγ coactivator-1α and uncoupling protein 1 (P ≤ 0.01).
CONCLUSIONS - Decreased adipose tissue NPRR was associated with obesity, glucose intolerance, and insulin resistance. This relationship was not observed for skeletal muscle NPRR. Pharmacological improvement of insulin sensitivity in subjects with T2DM was tied to improvement in NPRR and increased expression of genes involved in thermogenic processes.
© 2016 The Authors Obesity published by Wiley Periodicals, Inc. on behalf of The Obesity Society (TOS).
BACKGROUND - Increasing evidence indicates that proteotoxicity plays a pathophysiologic role in experimental and human cardiomyopathy. In organ-specific amyloidoses, soluble protein oligomers are the primary cytotoxic species in the process of protein aggregation. While isolated atrial amyloidosis can develop with aging, the presence of preamyloid oligomers (PAOs) in atrial tissue has not been previously investigated.
METHODS AND RESULTS - Atrial samples were collected during elective cardiac surgery in patients without a history of atrial arrhythmias, congestive heart failure, cardiomyopathy, or amyloidosis. Immunohistochemistry was performed for PAOs using a conformation-specific antibody, as well as for candidate proteins identified previously in isolated atrial amyloidosis. Using a myocardium-specific marker, the fraction of myocardium colocalizing with PAOs (PAO burden) was quantified (green/red ratio). Atrial samples were obtained from 92 patients, with a mean age of 61.7±13.8 years. Most patients (62%) were male, 23% had diabetes, 72% had hypertension, and 42% had coronary artery disease. A majority (n=62) underwent aortic valve replacement, with fewer undergoing coronary artery bypass grafting (n=34) or mitral valve replacement/repair (n=24). Immunostaining detected intracellular PAOs in a majority of atrial samples, with a heterogeneous distribution throughout the myocardium. Mean green/red ratio value for the samples was 0.11±0.1 (range 0.03 to 0.77), with a value ≥0.05 in 74 patients. Atrial natriuretic peptide colocalized with PAOs in myocardium, whereas transthyretin was located in the interstitium. Adjusting for multiple covariates, PAO burden was independently associated with the presence of hypertension.
CONCLUSION - PAOs are frequently detected in human atrium, where their presence is associated with clinical hypertension.
© 2014 The Authors. Published on behalf of the American Heart Association, Inc., by Wiley Blackwell.
Rapid activation causes remodeling of atrial myocytes resembling that which occurs in experimental and human atrial fibrillation (AF). Using this cellular model, we previously observed transcriptional upregulation of proteins implicated in protein misfolding and amyloidosis. For organ-specific amyloidoses such as Alzheimer's disease, preamyloid oligomers (PAOs) are now recognized to be the primary cytotoxic species. In the setting of oxidative stress, highly-reactive lipid-derived mediators known as γ-ketoaldehydes (γ-KAs) have been identified that rapidly adduct proteins and cause PAO formation for amyloid β1-42 implicated in Alzheimer's. We hypothesized that rapid activation of atrial cells triggers oxidative stress with lipid peroxidation and formation of γ-KAs, which then rapidly crosslink proteins to generate PAOs. To investigate this hypothesis, rapidly-paced and control, spontaneously-beating atrial HL-1 cells were probed with a conformation-specific antibody recognizing PAOs. Rapid stimulation of atrial cells caused the generation of cytosolic PAOs along with a myocyte stress response (e.g., transcriptional upregulation of Nppa and Hspa1a), both of which were absent in control, unpaced cells. Rapid activation also caused the formation of superoxide and γ-KA adducts in atriomyocytes, while direct exposure of cells to γ-KAs resulted in PAO production. Increased cytosolic atrial natriuretic peptide (ANP), and the generation of ANP oligomers with exposure to γ-KAs and rapid atrial HL-1 cell stimulation, strongly suggest a role for ANP in PAO formation. Salicylamine (SA) is a small molecule scavenger of γ-KAs that can protect proteins from modification by these reactive compounds. PAO formation and transcriptional remodeling were inhibited when cells were stimulated in the presence of SA, but not with the antioxidant curcumin, which is incapable of scavenging γ-KAs. These results demonstrate that γ-KAs promote protein misfolding and PAO formation as a component of the atrial cell stress response to rapid activation, and they provide a potential mechanistic link between oxidative stress and atrial cell injury.
Copyright © 2014 Elsevier Ltd. All rights reserved.
Organ development is a highly regulated process involving the coordinated proliferation and differentiation of diverse cellular populations. The pathways regulating cell proliferation and their effects on organ growth are complex and for many organs incompletely understood. In all vertebrate species, the cardiac natriuretic peptides (ANP and BNP) are produced by cardiomyocytes in the developing heart. However, their role during cardiogenesis is not defined. Using the embryonic zebrafish and neonatal mammalian cardiomyocytes we explored the natriuretic peptide signaling network during myocardial development. We observed that the cardiac natriuretic peptides ANP and BNP and the guanylate cyclase-linked natriuretic peptide receptors Npr1 and Npr2 are functionally redundant during early cardiovascular development. In addition, we demonstrate that low levels of the natriuretic peptides preferentially activate Npr3, a receptor with Gi activator sequences, and increase cardiomyocyte proliferation through inhibition of adenylate cyclase. Conversely, high concentrations of natriuretic peptides reduce cardiomyocyte proliferation through activation of the particulate guanylate cyclase-linked natriuretic peptide receptors Npr1 and Npr2, and activation of protein kinase G. These data link the cardiac natriuretic peptides in a complex hierarchy modulating cardiomyocyte numbers during development through opposing effects on cardiomyocyte proliferation mediated through distinct cyclic nucleotide signaling pathways.
Numerous common genetic variants have been linked to blood pressure, but no underlying mechanism has been elucidated. Population studies have revealed that the variant rs5068 (A/G) in the 3' untranslated region of NPPA, the gene encoding atrial natriuretic peptide (ANP), is associated with blood pressure. We selected individuals on the basis of rs5068 genotype (AG vs. AA) and fed them a low- or high-salt diet for 1 week, after which they were challenged with an intravenous saline infusion. On both diets, before and after saline administration, ANP levels were up to 50% higher in AG individuals than in AA individuals, a difference comparable to the changes induced by high-salt diet or saline infusion. In contrast, B-type natriuretic peptide levels did not differ by rs5068 genotype. We identified a microRNA, miR-425, that is expressed in human atria and ventricles and is predicted to bind the sequence spanning rs5068 for the A, but not the G, allele. miR-425 silenced NPPA mRNA in an allele-specific manner, with the G allele conferring resistance to miR-425. This study identifies miR-425 as a regulator of ANP production, raising the possibility that miR-425 antagonists could be used to treat disorders of salt overload, including hypertension and heart failure.