Clearance Receptor Research Articles

Keep it positive: loss of positive charge induced by R1205H von Willebrand factor change accelerates von Willebrand factor clearance through enhanced binding to macrophage clearance receptors LRP1 and SR-A1

Keep it positive: loss of positive charge induced by R1205H von Willebrand factor change accelerates von Willebrand factor clearance through enhanced binding to macrophage clearance receptors LRP1 and SR-A1

Right Ventricular Hypertrophy in Spontaneously Hypertensive Rats (SHR/NHsd) Is Associated with Inter-Individual Variations of the Pulmonary Endothelin System.

Spontaneously hypertensive rats (SHRs) develop severe hypertension and subsequently left ventricular hypertrophy. Whether they also develop right ventricular hypertrophy is not clear. We analyzed 76 female SHRs (strain SHR/NHsd) and observed severe right ventricular hypertrophy in 7% of these rats (SHR-RVH). Right ventricular hypertrophy did not correlate with the age of the rats and was already seen in one rat at the pre-hypertensive state. The current study investigated the molecular fingerprint of the lung and right ventricle from SHR-RVH and compared this first to SHRs that did develop left but not right ventricular hypertrophy, and second to normotensive rats without hypertrophy. Rats with right ventricular hypertrophy had a decreased expression of the endothelin-B receptor (EDNRB) in the lung, together with an increased protein content of endothelin-1 and an increased expression of ACTA2A. Furthermore, in the right ventricle, a down-regulation of the endothelin-A receptor (EDNRA) was found, consistent with a mild phenotype. The data suggest that in a sub-group of SHR/NHsd rats, low expression of the endothelin clearance receptor (endothelin-B receptor) in the lung triggers an increase in vascular resistance to the right ventricle that then triggers hypertrophy. Our study is the first description of a genetic variant in a defined SHR strain.

Myelin debris phagocytosis in demyelinating disease.

Demyelinating diseases are often caused by a variety of triggers, including immune responses, viral infections, malnutrition, hypoxia, or genetic factors, all of which result in the loss of myelin in the nervous system. The accumulation of myelin debris at the lesion site leads to neuroinflammation and inhibits remyelination; therefore, it is crucial to promptly remove the myelin debris. Initially, Fc and complement receptors on cellular surfaces were the primary clearance receptors responsible for removing myelin debris. However, subsequent studies have unveiled the involvement of additional receptors, including Mac-2, TAM receptors, and the low-density lipoprotein receptor-related protein 1, in facilitating the removal process. In addition to microglia and macrophages, which serve as the primary effector cells in the disease phase, a variety of other cell types such as astrocytes, Schwann cells, and vascular endothelial cells have been demonstrated to engage in the phagocytosis of myelin debris. Furthermore, we have concluded that oligodendrocyte precursor cells, as myelination precursor cells, also exhibit this phagocytic capability. Moreover, our research group has innovatively identified the low-density lipoprotein receptor as a potential phagocytic receptor for myelin debris. In this article, we discuss the functional processes of various phagocytes in demyelinating diseases. We also highlight the alterations in signaling pathways triggered by phagocytosis, and provide a comprehensive overview of the various phagocytic receptors involved. Such insights are invaluable for pinpointing potential therapeutic strategies for the treatment of demyelinating diseases by targeting phagocytosis.

R1205H (Vicenza) causes conformational changes in the von Willebrand factor D′D3 domains and enhances von Willebrand factor binding to clearance receptors LRP1 and SR-AI

Backgroundvon Willebrand factor (VWF)-R1205H variant (Vicenza) results in markedly enhanced VWF clearance in humans that has been shown to be largely macrophage-mediated. However, the biological mechanisms underlying this enhanced clearance remain poorly understood. ObjectivesThis study aimed to investigate the roles of (i) specific VWF domains and (ii) different macrophage receptors in regulating enhanced VWF-R1205H clearance. MethodsIn vivo clearance of full-length and truncated wild-type (WT)-VWF and VWF with R1205 substitutions was investigated in VWF−/− mice. Plate-binding assays were employed to characterize VWF binding to purified scavenger receptor class A member 1 (SR-AI), low-density lipoprotein receptor–related protein-1 (LRP1) cluster II or cluster IV receptors, and macrophage galactose-type lectin. ResultsIn full-length VWF missing the A1 domain, introduction of R1205H led to significantly enhanced clearance in VWF−/− mice compared with WT-VWF missing the A1 domain. Importantly, R1205H in a truncated VWF-D′D3 fragment also triggered increased clearance compared with WT-VWF-D′D3. Additional in vivo studies demonstrated that VWF-R1205K (which preserves the positive charge at 1205) exhibited normal clearance, whereas VWF-R1205E (which results in loss of the positive charge) caused significantly enhanced clearance, pinpointing the importance of the positive charge at VWF-R1205. In vitro plate-binding studies confirmed increased VWF-R1205H interaction with SR-AI compared with WT-VWF. Furthermore, significantly enhanced VWF-R1205H binding to LRP1 cluster IV (P < .001) and less marked enhanced binding to LRP1 cluster II (P = .034) was observed. In contrast, VWF-R1205H and WT-VWF demonstrated no difference in binding affinity to macrophage galactose-type lectin. ConclusionDisruption of the positive charge at amino acid R1205 causes conformational changes in the VWF-D′D3 domains and triggers enhanced LRP1-mediated and SR-AI–mediated clearance.

Dynamic Response of Musclin, a Myokine, to Aerobic Exercise and Its Interplay with Natriuretic Peptides and Receptor C.

Musclin, recently identified as a myokine, has been recognized for its physiological significance in potentiating the functional properties of natrieutic peptides (NPs) through competitive inhibition of their clearance receptor, natrieutic peptide receptor C (NPR-C). This study, for the first time in the literature, investigated the dynamic response of musclin during and after aerobic exercise in humans, exploring its potential as a myokine and its interaction with NPs and NPR-C in the context of exercise-induced metabolic responses. Twenty-one inactive young males participated, and we assessed changes in serum levels of musclin, atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), epinephrine (Epi), and glycerol as an indicative of lipid mobilization, during and after moderate-intensity aerobic exercise. Furthermore, we evaluated the gene expression of NPR-C in subcutaneous fat biopsies. Serum musclin levels increased significantly during aerobic exercise, followed by a decline during recovery, remaining elevated compared to baseline. Significant correlations were found between musclin responses and lean body mass (LBM), indicating its regulation by skeletal muscle mass and exercise. Exercise-induced changes in musclin positively correlated with those of ANP, potentially preventing ANP degradation. Additionally, a potential interplay between NPR-C expression and musclin dynamics on ANP was suggested. However, musclin's influence on lipid mobilization was not predominant when considering other lipolytic factors during exercise. Musclin's classification as a myokine is supported by its response to aerobic exercise and its association with LBM. Additionally, its interactions with NPR-C and NPs suggest its physiological relevance and potential clinical implications.

Unraveling the role of natriuretic peptide clearance receptor (NPR3) in glomerular diseases

Natriuretic peptides (NPs) are cardio-derived hormones that have a crucial role in maintaining cardiovascular homeostasis. Physiological effects of NPs are mediated by binding to natriuretic peptide receptors 1 and 2 (NPR1/2), whereas natriuretic peptide receptor 3 (NPR3) acts as a clearance receptor that removes NPs from the circulation. Mouse studies have shown that local NP-signaling in the kidney glomerulus is important for the maintenance of renal homeostasis. In this study we examined the expression of NPR3 in kidney tissue and explored its involvement in renal physiology and disease by generating podocyte-specific knockout mice (NPR3podKO) as well as by using an NPR3 inhibitor (NPR3i) in rodent models of kidney disease. NPR3 was highly expressed by podocytes. NPR3podKO animals showed no renal abnormalities under healthy conditions and responded similarly to nephrotoxic serum (NTS) induced glomerular injury. However, NPR3i showed reno-protective effects in the NTS-induced model evidenced by decreased glomerulosclerosis and reduced podocyte loss. In a ZSF1 rat model of diabetic kidney injury, therapy alone with NPR3i did not have beneficial effects on renal function/histology, but when combined with losartan (angiotensin receptor blocker), NPR3i potentiated its ameliorative effects on albuminuria. In conclusion, these results suggest that NPR3 may contribute to kidney disease progression.

Aging impairs cold-induced beige adipogenesis and adipocyte metabolic reprogramming.

The energy-burning capability of beige adipose tissue is a potential therapeutic tool for reducing obesity and metabolic disease, but this capacity is decreased by aging. Here, we evaluate the impact of aging on the profile and activity of adipocyte stem and progenitor cells (ASPCs) and adipocytes during the beiging process in mice. We found that aging increases the expression of Cd9 and other fibro-inflammatory genes in fibroblastic ASPCs and blocks their differentiation into beige adipocytes. Fibroblastic ASPC populations from young and aged mice were equally competent for beige differentiation in vitro, suggesting that environmental factors suppress adipogenesis in vivo. Examination of adipocytes by single nucleus RNA-sequencing identified compositional and transcriptional differences in adipocyte populations with aging and cold exposure. Notably, cold exposure induced an adipocyte population expressing high levels of de novo lipogenesis (DNL) genes, and this response was severely blunted in aged animals. We further identified Npr3, which encodes the natriuretic peptide clearance receptor, as a marker gene for a subset of white adipocytes and an aging-upregulated gene in adipocytes. In summary, this study indicates that aging blocks beige adipogenesis and dysregulates adipocyte responses to cold exposure and provides a resource for identifying cold and aging-regulated pathways in adipose tissue.

Suppressing the Hypoxia‐Adenosinergic Axis by a Tailored Nanoreactor for Enhanced Photothermal Immunotherapy

Cell metabolite adenosine can induce extensive and persistent immunosuppression by binding to adenosine receptors on immune cells. Seriously, the hypoxia‐driven adenosinergic axis aggravates adenosine accumulation via dephosphorizing immune‐activating adenosine triphosphate (ATP) released during immunogenic cell death (ICD). Different from direct adenosine clearance or adenosine receptor blockade or directly using ecto‐enzyme (CD39/CD73) antagonist, it is hoped to use an innovative small science engineering to regulate the upstream hypoxia/HIF‐1α signal of the hypoxia‐adenosinergic axis, thereby reducing the immunosuppressive extracellular adenosine and enhancing ICD‐triggered antitumor immunity. PM@Mn is constructed by gradually integrating metformin and MnO2 on polydopamine (PDA) nanoparticles. PM@Mn can effectively suppress hypoxia‐adenosinergic axis via combining catalytic oxygen production with reduced endogenous oxygen consumption. Such motif of hypoxia relief suppresses the metabolism of ATP to adenosine via down‐regulating the expression of HIF‐1α, CD39, and CD73. Meanwhile, PDA in PM@Mn can induce local tumor ablation and trigger the “vaccine effect” of ICD under near‐infrared radiation. In a mouse breast cancer model with low immunogenicity, our strategy can effectively reduce adenosine accumulation, PM@Mn group exhibits 4.51‐fold cytotoxic T lymphocyte infiltration and tumor inhibition rate of 75.4%. This study provides a new strategy to advance ICD‐triggered antitumor immunity through supressing hypoxia‐adenosinergic axis.

Matrix viscoelasticity promotes liver cancer progression in the pre-cirrhotic liver.

Type 2 diabetes mellitus is a major risk factor for hepatocellular carcinoma (HCC). Changes in extracellular matrix (ECM) mechanics contribute to cancer development1,2, and increased stiffness is known to promote HCC progression in cirrhotic conditions3,4. Type 2 diabetes mellitus is characterized by an accumulation of advanced glycation end-products (AGEs) in the ECM; however, how this affects HCC in non-cirrhotic conditions is unclear. Here we find that, in patients and animal models, AGEs promote changes in collagen architecture and enhance ECM viscoelasticity, with greater viscous dissipation and faster stress relaxation, but not changes in stiffness. High AGEs and viscoelasticity combined with oncogenic β-catenin signalling promote HCC induction, whereas inhibiting AGE production, reconstituting the AGE clearance receptor AGER1 or breaking AGE-mediated collagen cross-links reduces viscoelasticity and HCC growth. Matrix analysis and computational modelling demonstrate that lower interconnectivity of AGE-bundled collagen matrix, marked by shorter fibre length and greater heterogeneity, enhances viscoelasticity. Mechanistically, animal studies and 3D cell cultures show that enhanced viscoelasticity promotes HCC cell proliferation and invasion through an integrin-β1-tensin-1-YAP mechanotransductive pathway. These results reveal that AGE-mediated structural changes enhance ECM viscoelasticity, and that viscoelasticity can promote cancer progression in vivo, independent of stiffness.

Exercise performance is not improved in mice with skeletal muscle deletion of natriuretic peptide clearance receptor.

Natriuretic peptides (NP), including atrial, brain, and C-type natriuretic peptides (ANP, BNP, and CNP), play essential roles in regulating blood pressure, cardiovascular homeostasis, and systemic metabolism. One of the major metabolic effects of NP is manifested by their capacity to stimulate lipolysis and the thermogenesis gene program in adipocytes, however, in skeletal muscle their effects on metabolism and muscle function are not as well understood. There are three NP receptors (NPR): NPRA, NPRB, and NPRC, and all three NPR genes are expressed in skeletal muscle and C2C12 myocytes. In C2C12 myocytes treatment with either ANP, BNP, or CNP evokes the cGMP signaling pathway. Since NPRC functions as a clearance receptor and the amount of NPRC in a cell type determines the signaling strength of NPs, we generated a genetic model with Nprc gene deletion in skeletal muscle and tested whether enhancing NP signaling by preventing its clearance in skeletal muscle would improve exercise performance in mice. Under sedentary conditions, Nprc skeletal muscle knockout (MKO) mice showed comparable exercise performance to their floxed littermates in terms of maximal running velocity and total endurance running time. Eight weeks of voluntary running-wheel training in a young cohort significantly increased exercise performance, but no significant differences were observed in MKO compared with floxed control mice. Furthermore, 6-weeks of treadmill training in a relatively aged cohort also increased exercise performance compared with their baseline values, but again there were no differences between genotypes. In summary, our study suggests that NP signaling is potentially important in skeletal myocytes but its function in skeletal muscle in vivo needs to be further studied in additional physiological conditions or with new genetic mouse models.

Impact of Asialoglycoprotein Receptor and Mannose Receptor Deficiency on Murine Plasma N-glycome Profiles

The asialoglycoprotein receptor (ASGPR) and the mannose receptor C-type 1 (MRC1) are well known for their selective recognition and clearance of circulating glycoproteins. Terminal galactose and N-Acetylgalactosamine are recognized by ASGPR, while terminal mannose, fucose, and N-Acetylglucosamine are recognized by MRC1. The effects of ASGPR and MRC1 deficiency on the N-glycosylation of individual circulating proteins have been studied. However, the impact on the homeostasis of the major plasma glycoproteins is debated and their glycosylation has not been mapped with high molecular resolution in this context. Therefore, we evaluated the total plasma N-glycome and plasma proteome of ASGR1 and MRC1 deficient mice. ASGPR deficiency resulted in an increase in O-acetylation of sialic acids accompanied by higher levels of apolipoprotein D, haptoglobin, and vitronectin. MRC1 deficiency decreased fucosylation without affecting the abundance of the major circulating glycoproteins. Our findings confirm that concentrations and N-glycosylation of the major plasma proteins are tightly controlled and further suggest that glycan-binding receptors have redundancy, allowing compensation for the loss of one major clearance receptor.

Discovery of another mechanism for the inhibition of particulate guanylyl cyclases by the natriuretic peptide clearance receptor

The cardiac natriuretic peptides (NPs) control pivotal physiological actions such as fluid and electrolyte balance, cardiovascular homeostasis, and adipose tissue metabolism by activating their receptor enzymes [natriuretic peptide receptor-A (NPRA) and natriuretic peptide receptor-B (NPRB)]. These receptors are homodimers that generate intracellular cyclic guanosine monophosphate (cGMP). The natriuretic peptide receptor-C (NPRC), nicknamed the clearance receptor, lacks a guanylyl cyclase domain; instead, it can bind the NPs to internalize and degrade them. The conventional paradigm is that by competing for and internalizing NPs, NPRC blunts the ability of NPs to signal through NPRA and NPRB. Here we show another previously unknown mechanism by which NPRC can interfere with the cGMP signaling function of the NP receptors. By forming a heterodimer with monomeric NPRA or NPRB, NPRC can prevent the formation of a functional guanylyl cyclase domain and thereby suppress cGMP production in a cell-autonomous manner.

Deletion of the Npr3 gene increases severity of acute lung injury in obese mice.

Previous studies have shown that atrial natriuretic peptide (ANP) attenuates agonist-induced pulmonary edema and that this effect may be mediated in part by the ANP clearance receptor, natriuretic peptide receptor-C (NPR-C). Obesity has been associated with lower plasma ANP levels due to increased expression of NPR-C, and with decreased severity of acute lung injury (ALI). Therefore, we hypothesized that increased expression of NPR-C may attenuate ALI severity in obese populations. To test this, we examined ALI in Npr3 wild-type (WT) and knockout (KO) mice fed normal chow (NC) or high-fat diets (HFD). After 12 weeks, ALI was induced with intra-tracheal administration of Pseudomonas aeruginosa strain 103 (PA103) or saline. ALI severity was determined by lung wet-to-dry ratio (W/D) along with measurement of cell count, protein levels from bronchoalveolar lavage fluid (BALF), and quantitative polymerase chain reaction was performed on whole lung to measure cytokine/chemokine and Npr3 mRNA expression. ANP levels were measured from plasma. PA103 caused ALI as determined by significant increases in W/D, BALF protein concentration, and whole lung cytokine/chemokine expression. PA103 increased Npr3 expression in the lungs of wild-type (WT) mice regardless of diet. There was a nonsignificant trend toward increased Npr3 expression in the lungs of WT mice fed HFD versus NC. No differences in ALI were seen between Npr3 knockout (KO) mice and WT-fed NC, but Npr3 KO mice fed HFD had a significantly greater W/D and BALF protein concentration than WT mice fed HFD. These findings support the hypothesis that Npr3 may help protect against ALI in obesity.

Npr3 regulates neural crest and cranial placode progenitors formation through its dual function as clearance and signaling receptor.

Natriuretic peptide signaling has been implicated in a broad range of physiological processes, regulating blood volume and pressure, ventricular hypertrophy, fat metabolism, and long bone growth. Here we describe a completely novel role for natriuretic peptide signaling in the control of neural crest (NC) and cranial placode (CP) progenitors formation. Among the components of this signaling pathway, we show that natriuretic peptide receptor 3 (Npr3) plays a pivotal role by differentially regulating two developmental programs through its dual function as clearance and signaling receptor. Using a combination of MO-based knockdowns, pharmacological inhibitors and rescue assays we demonstrate that Npr3 cooperate with guanylate cyclase natriuretic peptide receptor 1 (Npr1) and natriuretic peptides (Nppa/Nppc) to regulate NC and CP formation, pointing at a broad requirement of this signaling pathway in early embryogenesis. We propose that Npr3 acts as a clearance receptor to regulate local concentrations of natriuretic peptides for optimal cGMP production through Npr1 activation, and as a signaling receptor to control cAMP levels through inhibition of adenylyl cyclase. The intracellular modulation of these second messengers therefore participates in the segregation of NC and CP cell populations.

RAGE is a critical factor of sex-based differences in age-induced kidney damage.

Introduction: Advanced glycation end products (AGEs) are a heterogeneous group of molecules with potential pathophysiological effects on the kidneys. Fibrosis together with the accumulation of AGEs has been investigated for its contribution to age-related decline in renal function. AGEs mediate their effects in large parts through their interactions with the receptor for AGEs (RAGE). RAGE is a transmembrane protein that belongs to the immunoglobulin superfamily and has the ability to interact with multiple pro-inflammatory/pro-oxidative ligands. The role of RAGE in aging kidneys has not been fully characterized, especially for sex-based differences. Methods: Therefore, we analyzed constitutive RAGE knockout (KO) mice in an age- and sex-dependent manner. Paraffin-embedded kidney sections were used for histological analysis and protein expression of fibrosis and damage markers. RNA expression analysis from the kidney cortex was done by qPCR for AGE receptors, kidney damage, and early inflammation/fibrosis factors. FACS analysis was used for immune cell profiling of the kidneys. Results: Histological analysis revealed enhanced infiltration of immune cells (positive for B220) in aged (>70weeks old) KO mice in both sexes. FACS analysis revealed a similar pattern of enhanced B-1a cells in aged KO mice. There was an age-based increase in pro-fibrotic and pro-inflammatory markers (IL-6, TNF, TGF-β1, and SNAIL1) in KO male mice that presumably contributed to renal fibrosis and renal damage (glomerular and tubular). In fact, in KO mice, there was an age-dependent increase in renal damage (assessed by NGAL and KIM1) that was accompanied by increased fibrosis (assessed by CTGF). This effect was more pronounced in male KO mice than in the female KO mice. In contrast to the KO animals, no significant increase in damage markers was detectable in wild-type animals at the age examined (>70weeks old). Moreover, there is an age-based increase in AGEs and scavenger receptor MSR-A2 in the kidneys. Discussion: Our data suggest that the loss of the clearance receptor RAGE in male animals further accelerates age-dependent renal damage; this could be in part due to an increase in AGEs load during aging and the absence of protective female hormones. By contrast, in females, RAGE expression seems to play only a minor role when compared to tissue pathology.

Pharmacologic blockade of the natriuretic peptide clearance receptor promotes weight loss and enhances insulin sensitivity in type 2 diabetes

While natriuretic peptides (NPs) are primarily known for their renal and cardiovascular actions, NPs stimulate lipolysis in adipocytes and induce a thermogenic program in white adipose tissue (WAT) that resembles brown fat. The biologic effects of NPs are negatively regulated by the NP clearance receptor (NPRC), which binds and degrades NPs. Knockout (KO) of NPRC protects against diet induced obesity and improves insulin sensitivity in obese mice. To determine if pharmacologic blockade of NPRC enhanced the beneficial metabolic actions of NPs in type 2 diabetes, we blocked NP clearance in a mouse model of type 2 diabetes using the specific NPRC ligand ANP(4-23). We found that treatment with ANP(4-23) caused a significant decrease in body weight by increasing energy expenditure and reducing fat mass without a change in lean body mass. The decrease in fat mass was associated with a significant improvement in insulin sensitivity and reduced serum insulin levels. These beneficial effects were accompanied by a decrease in infiltrating macrophages in adipose tissue, and reduced expression of inflammatory markers in both serum and WAT. These data suggest that inhibiting NP clearance may be an effective pharmacologic approach to promote weight loss and enhance insulin sensitivity in type 2 diabetes. Optimizing the therapeutic approach may lead to useful therapies for obesity and type 2 diabetes.

Localization of natriuretic peptide receptors A, B, and C in healthy and diseased mouse kidneys

The natriuretic peptides (NPs) ANP (atrial natriuretic peptide) and BNP (B-type natriuretic peptide) mediate their widespread effects by activating the natriuretic peptide receptor-A (NPR-A), while C-type natriuretic peptide (CNP) acts via natriuretic peptide receptor-B (NPR-B). NPs are removed from the circulation by internalization via the natriuretic peptide clearance receptor natriuretic peptide receptor-C (NPR-C). In addition to their well-known functions, for instance on blood pressure, all three NPs confer significant cardioprotection and renoprotection. Since neither the NP-mediated renal functions nor the renal target cells of renoprotection are completely understood, we performed systematic localization studies of NP receptors using in situ hybridization (RNAscope) in mouse kidneys. NPR-A mRNA is highly expressed in glomeruli (mainly podocytes), renal arterioles, endothelial cells of peritubular capillaries, and PDGFR-receptor β positive (PDGFR-β) interstitial cells. No NPR-A mRNA was detected by RNAscope in the tubular system. In contrast, NPR-B expression is highest in proximal tubules. NPR-C is located in glomeruli (mainly podocytes), in endothelial cells and PDGFR-β positive cells. To test for a possible regulation of NPRs in kidney diseases, their distribution was studied in adenine nephropathy. Signal intensity of NPR-A and NPR-B mRNA was reduced while their spatial distribution was unaltered compared with healthy kidneys. In contrast, NPR-C mRNA signal was markedly enhanced in cell clusters of myofibroblasts in fibrotic areas of adenine kidneys. In conclusion, the primary renal targets of ANP and BNP are glomerular, vascular, and interstitial cells but not the tubular compartment, while the CNP receptor NPR-B is highly expressed in proximal tubules. Further studies are needed to clarify the function and interplay of this specific receptor expression pattern.

Role of Cardiac Natriuretic Peptides in Heart Structure and Function.

Cardiac natriuretic peptides (NPs), atrial NP (ANP) and B-type NP (BNP) are true hormones produced and released by cardiomyocytes, exerting several systemic effects. Together with C-type NP (CNP), mainly expressed by endothelial cells, they also exert several paracrine and autocrine activities on the heart itself, contributing to cardiovascular (CV) health. In addition to their natriuretic, vasorelaxant, metabolic and antiproliferative systemic properties, NPs prevent cardiac hypertrophy, fibrosis, arrhythmias and cardiomyopathies, counteracting the development and progression of heart failure (HF). Moreover, recent studies revealed that a protein structurally similar to NPs mainly produced by skeletal muscles and osteoblasts called musclin/osteocrin is able to interact with the NPs clearance receptor, attenuating cardiac dysfunction and myocardial fibrosis and promoting heart protection during pathological overload. This narrative review is focused on the direct activities of this molecule family on the heart, reporting both experimental and human studies that are clinically relevant for physicians.

SORLA mediates endocytic uptake of proIAPP and protects against islet amyloid deposition

ObjectiveSorting-related receptor with type A repeats (SORLA) is a neuronal sorting receptor that prevents accumulation of amyloid-beta peptides, the main constituent of senile plaques in Alzheimer disease. Recent transcriptomic studies show that SORLA transcripts are also found in beta cells of pancreatic islets, yet the role of SORLA in islets is unknown. Based on its protective role in reducing the amyloid burden in the brain, we hypothesized that SORLA has a similar function in the pancreas via regulation of amyloid formation from islet amyloid polypeptide (IAPP). MethodsWe generated human IAPP transgenic mice lacking SORLA (hIAPP:SORLA KO) to assess the consequences of receptor deficiency for islet histopathology and function in vivo. Using both primary islet cells and cell lines, we further investigated the molecular mechanisms whereby SORLA controls the cellular metabolism and accumulation of IAPP. ResultsLoss of SORLA activity in hIAPP:SORLA KO resulted in a significant increase in islet amyloid deposits and associated islet cell death compared to hIAPP:SORLA WT animals. Aggravated islet amyloid deposition was observed in mice fed a normal chow diet, not requiring high-fat diet feeding typically needed to induce islet amyloidosis in mouse models. In vitro studies showed that SORLA binds to and mediates the endocytic uptake of proIAPP, but not mature IAPP, delivering the propeptide to an endolysosomal fate. ConclusionsSORLA functions as a proIAPP-specific clearance receptor, protecting against islet amyloid deposition and associated cell death caused by IAPP.

MANP Activation Of The cGMP Inhibits Aldosterone Via PDE2 And CYP11B2 In H295R Cells And In Mice.

Aldosterone is a critical pathological driver for cardiac and renal diseases. We recently discovered that mutant atrial natriuretic peptide (MANP), a novel atrial natriuretic peptide (ANP) analog, possessed more potent aldosterone inhibitory action than ANP in vivo. MANP and natriuretic peptide (NP)-augmenting therapy sacubitril/valsartan are under investigations for human hypertension treatment. Understanding the elusive mechanism of aldosterone inhibition by NPs remains to be a priority. Conflicting results were reported on the roles of the pGC-A (particulate guanylyl cyclase A receptor) and NP clearance receptor in aldosterone inhibition. Furthermore, the function of PKG (protein kinase G) and PDEs (phosphodiesterases) on aldosterone regulation are not clear. In the present study, we investigated the molecular mechanism of aldosterone regulation in a human adrenocortical cell line H295R and in mice. We first provided evidence to show that pGC-A, not NP clearance receptor, mediates aldosterone inhibition. Next, we confirmed that MANP inhibits aldosterone via PDE2 (phosphodiesterase 2) not PKG, with specific agonists, antagonists, siRNA silencing, and fluorescence resonance energy transfer experiments. Further, the inhibitory effect is mediated by a reduction of intracellular Ca2+ levels. We then illustrated that MANP directly reduces aldosterone synthase CYP11B2 (cytochrome p450 family 11 subfamily b member 2) expression via PDE2. Last, in PDE2 knockout mice, consistent with in vitro findings, embryonic adrenal CYP11B2 is markedly increased. Our results innovatively explore and expand the NP/pGC-A/3',5', cyclic guanosine monophosphate (cGMP)/PDE2 pathway for aldosterone inhibition by MANP in vitro and in vivo. In addition, our data also support the development of MANP as a novel ANP analog drug for aldosterone excess treatment.