Peptide Clearance Research Articles

Response to Comments on “ApoE-Directed Therapeutics Rapidly Clear β-Amyloid and Reverse Deficits in AD Mouse Models”

The data reported in the Technical Comments by Fitz et al., Price et al., Tesseur et al., and Veeraraghavalu et al. replicate and validate our central conclusion that bexarotene stimulates the clearance of soluble β-amyloid peptides and results in the reversal of behavioral deficits in mouse models of Alzheimer's disease (AD). The basis of the inability to reproduce the drug-stimulated microglial-mediated reduction in plaque burden is unexplained. However, we concluded that plaque burden is functionally unrelated to improved cognition and memory elicited by bexarotene.

Conjugated equine estrogens and estradiol benzoate differentially modulate the natriuretic peptide system in spontaneously hypertensive rats

The purpose of this study was to compare the effects of conjugated equine estrogens (CEE) and estradiol benzoate on the blood pressure and body weight of spontaneously hypertensive rats (SHRs) and the associated changes in several components of the natriuretic peptide system. The blood pressure of randomly distributed female SHRs and Wistar rats was determined by tail plethysmography. The rats were ovariectomized and, after 3 weeks, injected daily for 4 days with estradiol benzoate (5 μg/100 g/d), CEE (50 μg/100 g/d), or vehicle (corn oil 0.1 mL/100 g/d). One day after the last injection, the rats were decapitated, and their blood was collected to measure atrial natriuretic peptide (ANP) and estradiol. The atria were removed to measure ANP levels using radioimmunoassay and to quantify ANP messenger RNA expression using real-time polymerase chain reaction. The kidneys and adipose tissue were removed to analyze the expression of natriuretic peptide clearance receptor messenger RNA. A reduction in blood pressure was observed in estradiol-treated SHRs, but CEE treatment had no effect. Estradiol decreased the body weight and parametrial adipose tissue mass of SHRs. Estradiol-induced alterations in SHRs were accompanied by increased synthesis and release of ANP. CEE had no effect on body weight but increased the mesenteric adipose tissue mass of SHRs. These results indicate that estradiol and CEE have different effects on the reduction in body weight and blood pressure. These results are correlated with changes in plasma ANP levels.

Binding of Apolipoprotein E Inhibits the Oligomer Growth of Amyloid-β Peptide in Solution as Determined by Fluorescence Cross-correlation Spectroscopy

One of the primary neuropathological hallmarks of Alzheimer disease is the presence of extracellular amyloid plaques resulting from the aggregation of amyloid-β (Aβ) peptides. The intrinsic disorder of the Aβ peptide drives self-association and progressive reordering of the conformation in solution, and this dynamic distribution of Aβ complicates biophysical studies. This property poses a challenge for understanding the interaction of Aβ with apolipoprotein E (apoE). ApoE plays a pivotal role in the aggregation and clearance of Aβ peptides in the brain, and the ε4 allele of APOE is the most significant known genetic modulator of Alzheimer risk. Understanding the interaction between apoE and Aβ will provide insight into the mechanism by which different apoE isoforms determine Alzheimer disease risk. Here we applied alternating laser excitation fluorescence cross-correlation spectroscopy to observe the single molecule interaction of Aβ with apoE in the hydrated state. The diffusion time of freely diffusing Aβ in the absence of apoE shows significant self-aggregation, whereas in the presence of apoE, binding of the protein results in a more stable complex. These results show that apoE slows down the oligomerization of Aβ in solution and provide direct insight into the process by which apoE influences the deposition and clearance of Aβ peptides in the brain. Furthermore, by developing an approach to remove signals arising from very large Aβ aggregates, we show that real-time single particle observations provide access to information regarding the fraction of apoE bound and the stoichiometry of apoE and Aβ in the complex.

Effect of microsphere encapsulation on peptide clearance from the respiratory tract

Microspheres harbor great potential as an effective means of targeted delivery to specific tissues for use in cancer treatment and vaccinations. Both encapsulation volume and size were examined in this research. Microspheres were created by the encapsulation of EP67‐FITC in Poly Lactic‐co‐Glycolic Acid (PLGA). Different sizes (360–370 nm and 8.8 ìm) and volumes (15 ìl and 50 ìl of the same 50ìg dose) of microspheres were investigated to determine their effect on localization and clearance in the respiratory tract of female BALB‐c mice. Results indicate that the PLGA encapsulated EP67‐FITC was more rapidly cleared than unencapsulated EP67‐FITC. Also, the 50 ìl volume of unencapsulated EP67‐FITC localized to the stomach of the mice while encapsulated EP67‐FITC did not. This research shows a clear advantage to PLGA encapsulation and additionally to smaller particles (360–370 nm). This publication was made possible by grants from the National Center for Research Resources (5P20RR016469) and the National Institute for General Medical Science (NIGMS) (8P20GM103427), a component of the National Institutes of Health (NIH) and its contents are the sole responsibility of the authors and do not necessarily represent the official views of NIGMS or NIH.

Natriuretic Peptide Receptor-3 Gene ( NPR3 )

Background— The primary role of natriuretic peptide receptor-3 (NPR3) or NPR-C is in the clearance of natriuretic peptides that play an important role in modulating intravascular volume and vascular tone. Genetic variation in NPR3 has been associated with variation in blood pressure and obesity. Despite the importance of NPR3, sequence variation in the gene has not been addressed using DNA from different ethnic populations. We set out to identify and functionally characterize genetic variation in NPR3 in 3 ethnic groups. Methods and Results— DNA samples from 96 European American, 96 African American, and 96 Han Chinese American healthy subjects were used to resequence NPR3 exons, splice junctions, and flanking regions. We identified 105 polymorphisms, 50 of which were novel, including 8 nonsynonymous single-nucleotide polymorphisms, 7 were novel. Expression constructs were created for the nonsynonymous single-nucleotide polymorphisms. HEK293 cells were transfected with constructs for wild type and variant allozymes; and recombinant proteins were measured by quantitative Western blot analysis. The most significant change in NPR3 protein was observed for the Arg146 variant allozyme, with 20% of wild-type protein, primarily because of autophagy-dependent degradation. NPR3 structural modeling confirmed that the Arg146 variant protein was not compatible with wild-type conformation and could result in protein misfolding or instability. Conclusions— Multiple novel NPR3 genetic polymorphisms were identified in 3 ethnic groups. The Arg146 allozyme displayed a significant decrease in protein quantity because of degradation mediated predominantly by autophagy. This genetic variation could have a significant effect on the metabolism of natriuretic peptides with potential clinical implications.

Clearance of Genetic Variants of Amyloid β Peptide by Neuronal and Non-neuronal Cells

The presence of senile plaques in the brain is one of the pathological hallmarks of Alzheimer's disease (AD). The biogenesis and clearance of the amyloid β peptide (A β ), the main component of the lesions, lie at the center of the pathogenesis of AD. In sporadic AD, the increase of A β levels seems to be indicative of failure of clearance mechanisms. We previously showed that the clearance of the wild type A β40 peptide by various neuronal and non-neuronal cells occurs through a same proteolytic process and that A β degradation was primarily dictated by its conformational state (Panchal et al., 2007). To gain further insights on the role of the peptide conformation in the clearance mechanism of A β , two A β40 peptides, known to be associated with amyloid angiopathy (Dutch and Flemish mutations), and the rodent A β40 peptide were catabolized by several cells by using the same experimental approach. The peptide fragments, generated by proteolytic cleavage of substrates in cell supernatants, were identified by LC-MS and the cleavage sites of proteases were deduced. In parallel, conformational states of wild type A β 40 peptide and of the three A β 40 variants were characterized by circular dichroism spectroscopy. We provide data suggesting that discrete conformational changes of A β 40 peptide regulate its clearance rate by neuronal and non-neuronal cells.

Nanoparticle PET/CT imaging of natriuretic peptide clearance receptor in prostate cancer.

Atrial natriuretic peptide has been recently discovered to have anticancer effects via interaction with cell surface natriuretic peptide receptor A (NPRA) and natriuretic peptide clearance receptor (NPRC). In a preclinical model, NPRA expression has been identified during tumor angiogenesis and may serve as a potential prognostic marker and target for prostate cancer (PCa) therapy. However, the presence of NPRC receptor in the PCa model has not yet been assessed. Furthermore, there is still no report using nanoparticle for PCa positron emission tomography (PET) imaging. Herein, an amphiphilic comb-like nanoparticle was synthesized with controlled properties through modular construction containing C-atrial natriuretic factor (CANF) for NPRC receptor targeting and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelator for high specific activity Cu-64 radiolabeling. The pharmacokinetics of (64)Cu-CANF-Comb exhibited tuned biodistribution and optimized in vivo profile in contrast to the nontargeted (64)Cu-Comb nanoparticle. PET imaging with (64)Cu-CANF-Comb in CWR22 PCa tumor model showed high blood pool retention, low renal clearance, enhanced tumor uptake, and decreased hepatic burden relative to the nontargeted (64)Cu-Comb. Immunohistochemistry staining confirmed the presence of NPRC receptor in tumor tissue. Competitive PET receptor blocking study demonstrated the targeting specificity of (64)Cu-CANF-Comb to NPRC receptor in vivo. These results establish a new nanoagent for prostate cancer PET imaging.

Elevated amyloid-β plaque deposition in dietary selenium-deficient Tg2576 transgenic mice

Selenium-containing proteins (e.g., glutathione peroxidases) are important antioxidants in neuronal defense against oxidative stress. In this study, the production of amyloid-β (Aβ) plaques in the brain of the Tg2576 transgenic mice was investigated under dietary selenium-deficient conditions. The 16-week-old mice were fed a selenium-deficient diet (0.004 μg-selenium g(-1)-diet) or a selenium-adequate diet (0.386 μg-selenium g(-1) diet) for 76 weeks. The selenium concentrations of the organs/tissues in the selenium-deficient diet-fed mice were significantly decreased in comparison to those in the selenium-adequate diet-fed mice; 1.7% of that in the selenium-adequate diet-fed mice in the liver and 43% of that in the selenium-adequate diet-fed mice in the brain. The Aβ plaques formed in the brain were fluorescently stained with thioflavin T, and then the obtained images of the brain slices were qualitatively analyzed. The feeding of the selenium-deficient diet to the Tg2576 transgenic mice resulted in more than a two-fold increase in the total area of the Aβ plaques in comparison to that of the selenium-adequate diet. The elevated Aβ plaque deposition in the selenium-deficient mice can be explained as a consequence of decrease in the selenium concentration, which suggests that the selenium status is associated with the production and/or the clearance of the Aβ peptide. The selenium-deficiency could possibly promote the onset and/or progression of Alzheimer's disease (AD) dementia, if the Aβ peptides initiate a sequence of events that lead to AD dementia. Consequently, the results shown here suggest that AD has an important relation with the selenium status in vivo.

Alzheimer's disease (AD) as a disorder of the plasma membrane

GENERAL COMMENTARY article Front. Physiol., 15 February 2013Sec. Membrane Physiology and Membrane Biophysics https://doi.org/10.3389/fphys.2013.00024

Is Amyloid Binding Alcohol Dehydrogenase a Drug Target for Treating Alzheimer's Disease?

Current strategies for the treatment of Alzheimer's disease (AD) involve tackling the formation or clearance of the amyloid-beta peptide (Aβ) and/or hyper-phosphorylated tau, or the support and stabilization of the remaining neuronal networks. However, as we gain a clearer idea of the large number of molecular mechanisms at work in this disease, it is becoming clearer that the treatment of AD should take a combined approach of dealing with several aspects of the pathology. The concept that we also need to protect specific sensitive targets within the cell should also be considered. In particular the role of protecting the function of a specific mitochondrial protein, amyloid binding alcohol dehydrogenase (ABAD), will be the focus of this review. Mitochondrial dysfunction is a well-recognized fact in the progression of AD, though until recently the mechanisms involved could only be loosely labeled as changes in 'metabolism'. The discovery that Aβ can be present within the mitochondria and specifically bind to ABAD, has opened up a new area of AD research. Here we review the evidence that the prevention of Aβ binding to ABAD is a drug target for the treatment of AD.

Is Amyloid Binding Alcohol Dehydrogenase a Drug Target for Treating Alzheimer’s Disease?

Current strategies for the treatment of Alzheimer’s disease (AD) involve tackling the formation or clearance of the amyloid-beta peptide (Aβ) and/or hyper-phosphorylated tau, or the support and stabilization of the remaining neuronal networks. However, as we gain a clearer idea of the large number of molecular mechanisms at work in this disease, it is becoming clearer that the treatment of AD should take a combined approach of dealing with several aspects of the pathology. The concept that we also need to protect specific sensitive targets within the cell should also be considered. In particular the role of protecting the function of a specific mitochondrial protein, amyloid binding alcohol dehydrogenase (ABAD), will be the focus of this review. Mitochondrial dysfunction is a well-recognized fact in the progression of AD, though until recently the mechanisms involved could only be loosely labeled as changes in ‘metabolism’. The discovery that Aβ can be present within the mitochondria and specifically bind to ABAD, has opened up a new area of AD research. Here we review the evidence that the prevention of Aβ binding to ABAD is a drug target for the treatment of AD.

Circular RNA (circRNA) in Alzheimer's disease (AD)

Circular RNAs (circRNAs) are a naturally occurring family of noncoding RNAs (ncRNAs) highly represented in the eukaryotic transcriptome. Recently characterized, traditional methods of RNA detection and analysis requiring a free 5′ or 3′ ribonucleotide terminus may have significantly underestimated circRNA abundance and significance in eukaryotic cells (Salzman et al., 2012; Wilusz and Sharp, 2013; unpublished observations). Intrinsically resistant to exonucleolytic RNA decay, circRNAs appear to be enriched in mammalian brain tissues (Hansen et al., 2013; Memczak et al., 2013). Interestingly, specific ncRNAs such as the evolutionary ancient microRNA-7 (miRNA-7; chr 9q21.32; an important post-transcriptional regulator of human brain gene expression), are not only highly abundant in human brain, but are also associated with a circRNA for miRNA-7 (ciRS-7), in the same tissues; ciRS-7 contains multiple, tandem anti-miRNA-7 sequences (Burmistrova et al., 2007; Hansen et al., 2013; Lukiw et al., 2013). ciRS-7 thereby acts as a kind of endogenous, competing, anti-complementary miRNA “sponge” to adsorb, and hence quench, normal miRNA-7 functions. Using Northern blot hybridization techniques and the circularity-sensitive circRNA probe RNaseR we here provide initial evidence of a mis-regulated miRNA-7-circRNA system in the sporadic Alzheimer's disease (AD) hippocampal CA1 region (Figure ​(Figure1).1). Deficits in ciRS-7, and ciRS-7 “sponging activities” might be expected to increase ambient miRNA-7 levels in AD-affected brain cells, as is observed, to ultimately contribute to the down-regulation of selective miRNA-7-sensitive messenger RNA (mRNA) targets (Cogswell et al., 2008; unpublished observations). The presence of up-regulated miRNA-7, due to a deficiency in ciRS-7 “sponging” effects, has high probability to down-regulate AD-relevant targets, such as, for example, the ubiquitin protein ligase A (UBE2A; miRNA-7-UBE2A mRNA energy of association, EA = −22.86 kcal/mol). UBE2A, an autophagic, phagocytic protein essential in the clearance of amyloid peptides in AD and other progressive inflammatory degenerations of the human CNS, is depleted in AD brain (Bingol and Sheng, 2011; Lonskaya et al., 2013). Such miRNA-mRNA regulatory systems mediated by a family of cell- and/or tissue-enriched circRNAs may represent another important layer of epigenetic control over gene expression in health and disease. Indeed, technological advancement and recent discoveries in the field of ncRNAs continue to challenge our basic doctrines of nucleic acid biochemistry and evolutionary biology. Deficits in other circRNA-mediated “miRNA sponging systems” and ambient up-regulation of specific inducible miRNAs may help explain the widely observed, generalized and progressive down-regulation of gene expression that is characteristic of the sporadic AD brain (Loring et al., 2001; Colangelo et al., 2002; Ginsberg et al., 2012; Lukiw, 2013). Figure 1 (A) Detection of circRNA for miRNA-7 (ciRS-7) in sporadic Alzheimer's disease (AD) and age-matched control hippocampal CA1 [control (C) N = 4; AD (A) N = 6]; the single upper ciRS-7 (~1400 nt) band contains ~70 selectively conserved miRNA-7 binding sites ...

Positron Emission Tomography Imaging of Atherosclerosis

Atherosclerosis-related cardiovascular events are the leading causes of death in the industrialized world. Atherosclerosis develops insidiously and the initial manifestation is usually sudden cardiac death, stroke, or myocardial infarction. Molecular imaging is a valuable tool to identify the disease at an early stage before fatal manifestations occur. Among the various molecular imaging techniques, this review mainly focuses on positron emission tomography (PET) imaging of atherosclerosis. The targets and pathways that have been investigated to date for PET imaging of atherosclerosis include: glycolysis, cell membrane metabolism (phosphatidylcholine synthesis), integrin αvβ3, low density lipoprotein (LDL) receptors (LDLr), natriuretic peptide clearance receptors (NPCRs), fatty acid synthesis, vascular cell adhesion molecule-1 (VCAM-1), macrophages, platelets, etc. Many PET tracers have been investigated clinically for imaging of atherosclerosis. Early diagnosis of atherosclerotic lesions by PET imaging can help to prevent the premature death caused by atherosclerosis, and smooth translation of promising PET tracers into the clinic is critical to the benefit of patients.

Abstract 9027: A Novel Polymorphism Arg146 of the Natriuretic Peptide Receptor-3 Gene Results in a Significant Reduction in Protein Expression Due to Accelerated Degradation

Background: The primary role of natriuretic peptide receptor 3 (NPR3) is clearance of natriuretic peptides. Genetic variation in NPR3 has been associated with blood pressure regulation and obesity. Despite its importance, variation in NPR3 characterizing coding single nucleotide polymorphisms (SNPs) has not been addressed by resequencing the gene. Objective: We set out to identify and functionally characterize common variation in NPR3 in 3 ethnic groups. DNA samples from such subjects are studied because common genetic variation needs to be defined initially in “normal” individuals prior to studying drug effect and response. Also, rare variants identified by sequencing are enriched in complex disease traits. Methods and Results: DNA samples from 96 European-American, 96 African-American, and 96 Han Chinese-American healthy subjects were used to resequence NPR3. There were 105 polymorphisms identified of which 50 were novel, including 8 nonsynonymous (ns) SNPs of which 7 were novel. Expression constructs for the nsSNPs were created and HEK-293 cells were transfected with constructs for wild type (WT) and the variants. Recombinant proteins were analyzed by quantitative Western blot analysis. A significant reduction in NPR3 immunoreactive protein (60% or less of WT) was observed for the following variants Cys3, Arg146, Val499, and Ser477+Asp521. The Arg146 novel polymorphism resulted in the least protein expression (20% of WT). After treatment of WT and Arg146 cells with proteasome (MG132) and autophagy (3MA) inhibtors, it was determined that autophagy and not proteasomes plays an important role in the degradation of the Arg 146 variant protein. Modeling based on the NPR3 x-ray crystallography structure confirmed that the Arg146 variant were not compatible with WT conformation and could result in protein misfolding or instability. Conclusions: Multiple novel polymorphisms of NPR3 were identified in 3 ethnic groups. There were 4 variant receptors that displayed a significant decrease in NPR3 protein quantity, Arg146 being the variant with the least expression. Degradation of the variant Arg146 was mediated predominantly by autophagy. This SNP could have a significant effect on the metabolism of natriuretic peptides with clinical implications.

Amyloid-β-dependent compromise of microvascular structure and function in a model of Alzheimer’s disease

The majority of patients with Alzheimer's disease have cerebral amyloid angiopathy, thus showing deposition of amyloid-β peptides in the walls of leptomeningeal and cortical arterioles. These deposits are believed to result from impaired clearance of parenchymal amyloid-β peptides. In the current work, we examined the changes in cortical microvascular structure and function in situ in TgCRND8, a transgenic mouse model of Alzheimer's disease. In contrast to venules, cortical arterioles were shown to increase in tortuosity and decrease in calibre with amyloid-β peptide accumulation. These structural changes were accompanied by progressive functional compromise, reflected in higher dispersion of microvascular network transit times, elongation of the transit times, and impaired microvascular reactivity to hypercapnia in the transgenic mice. Moreover, inhibition of amyloid-β peptide oligomerization and fibrillization via post-weaning administration of scyllo-inositol, a naturally occurring stereoisomer of myo-inositol, rescued both structural and functional impairment of the cortical microvasculature in this Alzheimer's disease model. These results demonstrate that microvascular impairment is directly correlated with amyloid-β accumulation and highlight the importance of targeting cerebrovascular amyloid angiopathy clearance for effective diagnosis, monitoring of disease progression and treatment of Alzheimer's disease.

RbAp48 and 46 Disassociate GATA4 from p300 and Inhibit Hypertrophy-responsive Gene Transcription in Cardiomyocytes

cardiovasculature of rats with chronic heart failure (CHF). Methods and Results: Male Sprague-Dawley rats underwent left coronary artery ligation (LCAL) to induce CHF, and were randomly assigned to sedentary or treadmill exercise groups at 4 weeks after the LCAL. Exercise training for 4weeks improved cardiac and renal function in CHF rats, as indicated by echocardiographic data, plasma brain natriuretic peptide (BNP) and creatinine clearance. The NOS activity and expression of eNOS, nNOS protein were significantly decreased in the left ventricle, renal cortex, outer medulla and inner medulla of CHF rats, and exercise training markedly increased the NOS activity and expressions in those tissues of CHF rats. Conclusion: Exercise training improves cardiac and renal function in CHF rats through upregulating the NOS activity and eNOS, nNOS expressions in the kidney in addition to in the cardiovasculature. The beneficial effects of exercise training in CHF may be mediated in part by upregulation of the NOS in the kidney.

Association of a single nucleotide polymorphism of the NPR3 gene promoter with early onset ischemic stroke in an Italian cohort

BackgroundNPR3, located on human chromosome 5 (5p14–p13), encodes the natriuretic peptide receptor type C (NPR-C) that is mainly known as the natriuretic peptide clearance receptor. Involvement of NPR3 in susceptibility to cardiovascular diseases, i.e. hypertension, has been previously shown. With regard to stroke predisposition, evidence for a potential role of genetic variation within or nearby NPR3 has been suggested by a previous genome wide association study. MethodsWe investigated the contribution to early-onset ischemic stroke susceptibility of the NPR3 −55 C>A transition by genotyping this variant in an Italian cohort of 368 cases and 335 controls. ResultsIn a multivariable logistic regression analysis adjusting for age, gender, hypertension, hypercholesterolemia, smoking habit and diabetes, a significant association of the −55 AA genotype with stroke was observed (OR=3.2, 95% CI 1.2–8.3, p=0.016). Remarkably, the polymorphism remained associated with stroke after adjusting for hypertensive status. ConclusionOur observation obtained in an Italian cohort of early onset ischemic strokes suggests that a NPR3 promoter gene variant could have a role on cerebrovascular disease susceptibility.

P2‐151: PICALM regulates Aβ42 production by modulation of gamma‐secretase trafficking

Alzheimer disease (AD) is the most common type of dementia worldwide. Several lines of evidence suggest that aberrant production, clearance and aggregation of amyloid-beta peptide (Aβ) in human brain are linked to the etiology of AD. Recently, genome-wide association studies in late-onset AD patients have reported evidence that variation in phosphatidylinositol binding clathrin assembly protein (PICALM) gene confer genetic risk for AD. To investigate the role of PICALM in Aβ generation, we analyzed the effects of knockdown or overexpression of PICALM in cultured cells on the processing of amyloid precursor protein (APP). We also monitored the trafficking of the gamma-secretase by monoclonal antibody A5226A, which recognizes the extracellular domain of mature Nicastrin on the cell surface (Hayashi et al., Oncogene 2011). Depletion of PICALM caused a decrease in the production ratio of Aβ42, the most aggregable Aβ species. Moreover, PICALM RNAi altered the endocytic rate of gamma-secretase, while the endocytosis of transferrin, one of the typical cargo proteins for clathrin-mediated endocytosis, was not affected. In contrast, total Aβ levels as well as Aβ42 ratio were increased by the overexpression of PICALM. These results suggest PICALM modulates gamma-secretase activity by regulating its clathrin-mediated endocytosis. Alteration in endocytic rate of gamma-secretase by PICALM RNAi/overexpression may change its steady-state subcellular localization, leading to alteration in both the total Aβ generation and the Aβ42 ratio.

Mechanisms of Amyloid-β Peptide Clearance: Potential Therapeutic Targets for Alzheimer's Disease

Amyloid-β peptide (Aβ) is still best known as a molecule to cause Alzheimer’s disease (AD) through accumulation and deposition within the frontal cortex and hippocampus in the brain. Thus, strategies on developing AD drugs have been focused on the reduc-tion of Aβ in the brain. Since accumulation of Aβ depends on the rate of its synthesis and clearance, the metabolic pathway of Aβ in the brain and the whole body should be carefully explored for AD research. Although the synthetic pathway of Aβ is equally important, we summarize primarily the clearance pathway in this paper because the former has been extensively reviewed in previous studies. The clearance of Aβ from the brain is accomplished by several mechanisms which include non-enzymatic and enzymatic pathways. Nonenzymatic pathway includes interstitial fluid drainage, uptake by microglial phagocytosis, and transport across the blood vessel walls into the circulation. Multiple Aβ-degrading enzymes (ADE) implicated in the clearance process have been identified, which include neprilysin, insulin-degrading enzyme, matrix metalloproteinase-9, glutamate carboxypeptidase II and others. A series of studies on Aβ clearance mechanism provide new insight into the pathogenesis of AD at the molecular level and suggest a new target for the development of novel therapeutics.

Insulin up-regulates natriuretic peptide clearance receptor expression in the subcutaneous fat depot in obese subjects: a missing link between CVD risk and central obesity?

Aims: Natriuretic peptides (NPs) regulate cardiovascular homeostasis and have multiple metabolic properties. Decreased levels of NP or “natriuretic handicap” are signs of insulin resistance such as central obesity. Increased expression of natriuretic peptide clearance receptor (NPRC) in subcutaneous adipose tissue (SAT) was observed in insulin resistant subjects. We hypothesized that insulin acutely regulates NPR receptors expression in adipose tissue.