Neuropeptide Y fragments derived from neprilysin processing are neuroprotective in a transgenic model of Alzheimer's disease

ABCA7-dependent induction of neuropeptide Y is required for synaptic resilience in Alzheimer's disease through BDNF/NGFR signaling

Genetic variants in ABCA7, an Alzheimer's disease (AD)-associated gene, elevate AD risk, yet its functional relevance to the etiology is unclear. We generated a CRISPR-Cas9-mediated abca7 knockout zebrafish to explore ABCA7's role in AD. Single-cell transcriptomics in heterozygous abca7+/- knockout combined with Aβ42 toxicity revealed that ABCA7 is crucial for neuropeptide Y (NPY), brain-derived neurotrophic factor (BDNF), and nerve growth factor receptor (NGFR) expressions, which are crucial for synaptic integrity, astroglial proliferation, and microglial prevalence. Impaired NPY induction decreased BDNF and synaptic density, which are rescuable with ectopic NPY. In induced pluripotent stem cell-derived human neurons exposed to Aβ42, ABCA7-/- suppresses NPY. Clinical data showed reduced NPY in AD correlated with elevated Braak stages, genetic variants in NPY associated with AD, and epigenetic changes in NPY, NGFR, and BDNF promoters linked to ABCA7 variants. Therefore, ABCA7-dependent NPY signaling via BDNF-NGFR maintains synaptic integrity, implicating its impairment in increased AD risk through reduced brain resilience.

Proteomic changes in the hippocampus of large mammals after total-body low dose radiation

There is a growing interest in low dose radiation (LDR) to counteract neurodegeneration. However, LDR effects on normal brain have not been completely explored yet. Recent analyses showed that LDR exposure to normal brain tissue causes expression level changes of different proteins including neurodegeneration-associated proteins. We assessed the proteomic changes occurring in radiated vs. sham normal swine brains. Due to its involvement in various neurodegenerative processes, including those associated with cognitive changes after high dose radiation exposure, we focused on the hippocampus first. We observed significant proteomic changes in the hippocampus of radiated vs. sham swine after LDR (1.79Gy). Mass spectrometry results showed 190 up-regulated and 120 down-regulated proteins after LDR. Western blotting analyses confirmed increased levels of TPM1, TPM4, PCP4 and NPY (all proteins decreased in various neurodegenerative processes, with NPY and PCP4 known to be neuroprotective) in radiated vs. sham swine. These data support the use of LDR as a potential beneficial tool to interfere with neurodegenerative processes and perhaps other brain-related disorders, including behavioral disorders.

ABCA7-dependent Neuropeptide-Y signalling is a resilience mechanism required for synaptic integrity in Alzheimer's disease

Alzheimer's disease (AD) remains a complex challenge characterized by cognitive decline and memory loss. Genetic variations have emerged as crucial players in the etiology of AD, enabling hope for a better understanding of the disease mechanisms; yet the specific mechanism of action for those genetic variants remain uncertain. Animal models with reminiscent disease pathology could uncover previously uncharacterized roles of these genes. Using CRISPR/Cas9 gene editing, we generated a knockout model for abca7, orthologous to human ABCA7 - an established AD-risk gene. The abca7 +/- zebrafish showed reduced astroglial proliferation, synaptic density, and microglial abundance in response to amyloid beta 42 (Aβ42). Single-cell transcriptomics revealed abca7 -dependent neuronal and glial cellular crosstalk through neuropeptide Y (NPY) signaling. The abca7 knockout reduced the expression of npy, bdnf and ngfra , which are required for synaptic integrity and astroglial proliferation. With clinical data in humans, we showed reduced NPY in AD correlates with elevated Braak stage, predicted regulatory interaction between NPY and BDNF , identified genetic variants in NPY associated with AD, found segregation of variants in ABCA7, BDNF and NGFR in AD families, and discovered epigenetic changes in the promoter regions of NPY, NGFR and BDNF in humans with specific single nucleotide polymorphisms in ABCA7 . These results suggest that ABCA7-dependent NPY signaling is required for synaptic integrity, the impairment of which generates a risk factor for AD through compromised brain resilience.

Abstract Figure

Cross talk about the role of Neuropeptide Y in CNS disorders and diseases

A peptide composed of a 36 amino acid called Neuropeptide Y (NPY) is employed in a variety of physiological processes to manage and treat conditions affecting the endocrine, circulatory, respiratory, digestive, and neurological systems. NPY naturally binds to G-protein coupled receptors, activating the Y-receptors (Y1-Y5 and y6). The findings on numerous therapeutic applications of NPY for CNS disease are presented in this review by the authors. New targets for treating diseases will be revealed by medication combinations that target NPY and its receptors. This review is mainly focused on disorders such as anxiety, Alzheimer's disease, Parkinson's disease, Huntington's disease, Machado Joseph disease, multiple sclerosis, schizophrenia, depression, migraine, alcohol use disorder, and substance use disorder. The findings from the preclinical studies and clinical studies covered in this article may help create efficient therapeutic plans to treat neurological conditions on the one hand and psychiatric disorders on the other. They may also open the door to the creation of novel NPY receptor ligands as medications to treat these conditions.

Dose-dependent toxic effects of di-(2-ethylhexyl) phthalate in male rats: Focus on behavioral alterations and inducing TLR4/NF-κB signaling pathway

Di -(2-ethylhexyl) phthalate (DEHP) is a widely used phthalate that possesses a public health concern. Different concentrations of DEHP, including 50, 300, and 750 mg/kg, were administrated orally for 28 days in male rats. Body weight and vital organs weight were measured as well as anxiety-like behavior, short and long-term memory were investigated. Brain inflammatory cytokines, including IL-1β, TLR4, NF-κB, TNF-α, and IL1-6, were assessed. Brain caspase-3, neuropeptide-Y (NPY), and brain histopathology were also evaluated. DEHP triggers the release of pro-inflammatory cytokines via inducing the nuclear translocation of the signaling pathway; TLR 4/ NF-κB leads to cognitive impairment and neurodegeneration, which is confirmed by the impaired brain architecture. Also, DEHP upgrades the expression levels of brain caspase-3 and NPY. In conclusion, exposure to high doses of DEHP persuades great toxicity visualized by behavioral, biochemical, and histological impairments when compared to the low dose.

Neprilysin-dependent neuropeptide Y cleavage in the liver promotes fibrosis by blocking NPY-receptor 1

Development of liver fibrosis is paralleled by contraction of hepatic stellate cells (HSCs), the main profibrotic hepatic cells. Yet, little is known about the interplay of neprilysin (NEP) and its substrate neuropeptide Y (NPY), a potent enhancer of contraction, in liver fibrosis. We demonstrate that HSCs are the source of NEP. Importantly, NPY originates majorly from the splanchnic region and is cleaved by NEP in order to terminate contraction. Interestingly, NEP deficiency (Nep-/-) showed less fibrosis but portal hypertension upon liver injury in two different fibrosis models in mice. We demonstrate the incremental benefit of Nep-/- in addition to AT1R blocker (ARB) or ACE inhibitors for fibrosis and portal hypertension. Finally, oral administration of Entresto, a combination of ARB and NEP inhibitor, decreased hepatic fibrosis and portal pressure in mice. These results provide a mechanistic rationale for translation of NEP-AT1R-blockade in human liver fibrosis and portal hypertension.

Neprilysin Inhibitors in Heart Failure: The Science, Mechanism of Action, Clinical Studies, and Unanswered Questions

This article provides a contemporary review and a new perspective on the role of neprilysin inhibition in heart failure (HF) in the context of recent clinical trials and addresses potential mechanisms and unanswered questions in certain HF patient populations. Neprilysin is an endopeptidase that cleaves a variety of peptides such as natriuretic peptides, bradykinin, adrenomedullin, substance P, angiotensin I and II, and endothelin. It has a broad role in cardiovascular, renal, pulmonary, gastrointestinal, endocrine, and neurologic functions. The combined angiotensin receptor and neprilysin inhibitor (ARNi) has been developed with an intent to increase vasodilatory natriuretic peptides and prevent counterregulatory activation of the angiotensin system. ARNi therapy is very effective in reducing the risks of death and hospitalization for HF in patients with HF and New York Heart Association functional class II to III symptoms, but studies failed to show any benefits with ARNi when compared with angiotensin-converting enzyme inhibitors or angiotensin receptor blocker in patients with advanced HF with reduced ejection fraction or in patients following myocardial infarction with left ventricular dysfunction but without HF. These raise the questions about whether the enzymatic breakdown of natriuretic peptides may not be a very effective solution in advanced HF patients when there is downstream blunting of the response to natriuretic peptides or among post-myocardial infarction patients in the absence of HF when there may not be a need for increased natriuretic peptide availability. Furthermore, there is a need for additional studies to determine the long-term effects of ARNi on albuminuria, obesity, glycemic control and lipid profile, blood pressure, and cognitive function in patients with HF.

Neuroprotective Effects of Neuropeptide Y against Neurodegenerative Disease

Neuropeptide Y (NPY), a 36 amino acid peptide, is widely expressed in the mammalian brain. Changes in NPY levels in different brain regions and plasma have been described in several neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, Huntington's disease, Amyotrophic Lateral Sclerosis, and Machado-Joseph disease. The changes in NPY levels may reflect the attempt to set up an endogenous neuroprotective mechanism to counteract the degenerative process. Accumulating evidence indicates that NPY can function as an anti-apoptotic, anti-inflammatory, and pro-phagocytic agent, which may be used effectively to halt or to slow down the progression of the disease. In this review, we will focus on the neuroprotective roles of NPY in several neuropathological conditions, with a particular focus on the anti-inflammatory properties of NPY.

A nonsense mutation in MME gene associates with autosomal recessive late-onset Charcot-Marie-Tooth disease

Background

The genetic cause for the majority of patients with late‐onset axonal form of neuropathies have remained unknown. In this study we aimed to identify the causal mutation in a family with multiple affected individuals manifesting a range of phenotypic features consistent with late‐onset sensorimotor axonal polyneuropathy.

Methods

Whole exome sequencing (WES) followed by targeted variant screening and prioritization was performed to identify the candidate mutation. The co‐segregation of the mutation with the phenotype was confirmed by Sanger sequencing.

Results

We identified a nonsense mutation (c.1564C>T; p.Q522*) in membrane metalloendopeptidase (MME) gene as the cause of the disease condition. The mutation has a combined annotation‐ dependent depletion (CADD) score 45 and predicted to be deleterious based on various algorithms. The mutation was inherited in an autosomal recessive mode and further confirmed to co‐segregate with the disease phenotype in the family and showed to has the required criteria including rarity and deleteriousness to be considered as pathogenic.

Conclusion

The MME gene encodes for the membrane bound endopeptidase neprilysin (NEP) which is involved in processing of various peptide substrates. The identified mutation causes a complete loss of carboxy‐terminal region of the NEP protein which contains the zinc binding site and the catalytic domain and thus considered to be a loss‐of‐function mutation. The loss of NEP activity is likely associated with impaired myelination and axonal injury which is hallmark of CMT diseases.

Contribution of proteases to the hallmarks of aging and to age-related neurodegeneration

Protein quality control ensures the degradation of damaged and misfolded proteins. Derangement of proteostasis is a primary cause of aging and age-associated diseases. The ubiquitin-proteasome and autophagy-lysosome play key roles in proteostasis but, in addition to these systems, the human genome encodes for ~600 proteases, also known as peptidases. Here, we examine the role of proteases in aging and age-related neurodegeneration. Proteases are present across cell compartments, including the extracellular space, and their substrates encompass cellular constituents, proteins with signaling functions, and misfolded proteins. Proteolytic processing by proteases can lead to changes in the activity and localization of substrates or to their degradation. Proteases cooperate with the autophagy-lysosome and ubiquitin-proteasome systems but also have independent proteolytic roles that impact all hallmarks of cellular aging. Specifically, proteases regulate mitochondrial function, DNA damage repair, cellular senescence, nutrient sensing, stem cell properties and regeneration, protein quality control and stress responses, and intercellular signaling. The capacity of proteases to regulate cellular functions translates into important roles in preserving tissue homeostasis during aging. Consequently, proteases influence the onset and progression of age-related pathologies and are important determinants of health span. Specifically, we examine how certain proteases promote the progression of Alzheimer's, Huntington's, and/or Parkinson's disease whereas other proteases protect from neurodegeneration. Mechanistically, cleavage by proteases can lead to the degradation of a pathogenic protein and hence impede disease pathogenesis. Alternatively, proteases can generate substrate byproducts with increased toxicity, which promote disease progression. Altogether, these studies indicate the importance of proteases in aging and age-related neurodegeneration.

Sleep Disturbance and Alzheimer's Disease: The Glial Connection

Poor quality and quantity of sleep are very common in elderly people throughout the world. Growing evidence has suggested that sleep disturbances could accelerate the process of neurodegeneration. Recent reports have shown a positive correlation between sleep deprivation and amyloid-β (Aβ)/tau aggregation in the brain of Alzheimer's patients. Glial cells have long been implicated in the progression of Alzheimer's disease (AD) and recent findings have also suggested their role in regulating sleep homeostasis. However, how glial cells control the sleep-wake balance and exactly how disturbed sleep may act as a trigger for Alzheimer's or other neurological disorders have recently gotten attention. In an attempt to connect the dots, the present review has highlighted the role of glia-derived sleep regulatory molecules in AD pathogenesis. Role of glia in sleep disturbance and Alzheimer's progression.

Design and Experimental Evaluation of a Peptide Antagonist against Amyloid β(1-42) Interactions with Calmodulin and Calbindin-D28k

Amyloid β_1–42 (Aβ(1–42)) oligomers have been linked to the pathogenesis of Alzheimer’s disease (AD). Intracellular calcium (Ca²⁺) homeostasis dysregulation with subsequent alterations of neuronal excitability has been proposed to mediate Aβ neurotoxicity in AD. The Ca²⁺ binding proteins calmodulin (CaM) and calbindin-D28k, whose expression levels are lowered in human AD brains, have relevant roles in neuronal survival and activity. In previous works, we have shown that CaM has a high affinity for Aβ(1–42) oligomers and extensively binds internalized Aβ(1–42) in neurons. In this work, we have designed a hydrophobic peptide of 10 amino acid residues: VFAFAMAFML (amidated-C-terminus amino acid) mimicking the interacting domain of CaM with Aβ (1–42), using a combined strategy based on the experimental results obtained for Aβ(1–42) binding to CaM and in silico docking analysis. The increase in the fluorescence intensity of Aβ(1–42) HiLyte^TM-Fluor555 has been used to monitor the kinetics of complex formation with CaM and with calbindin-D28k. The complexation between nanomolar concentrations of Aβ(1–42) and calbindin-D28k is also a novel finding reported in this work. We found that the synthetic peptide VFAFAMAFML (amidated-C-terminus amino acid) is a potent inhibitor of the formation of Aβ(1–42):CaM and of Aβ(1–42):calbindin-D28k complexes.

Neuropeptide Y Y2 and Y5 receptors as potential targets for neuroprotective and antidepressant therapies: Evidence from preclinical studies

There is currently no effective treatment either for neurological illnesses (ischemia and neurodegenerative diseases) or psychiatric disorders (depression), in which the Glu/GABA balance is disturbed and accompanied by significant excitotoxicity. Therefore, the search for new and effective therapeutic strategies is imperative for these disorders. Studies conducted over the last several years indicate that the neuropeptide Y (NPY)-ergic system may be a potential therapeutic target for neuroprotective or antidepressant compounds. This review focuses on the neuroprotective roles of Y2 and Y5 receptors (YRs) in neurological disorders such as ischemia, Alzheimer's disease, Parkinson's disease, Huntington's disease, and in psychiatric disorders such as depression. It summarizes current knowledge on the possible mechanisms underlying the neuroprotective or antidepressant-like actions of Y2R and Y5R ligands. The review also discusses ligands acting at Y2R and Y5R and their limitations as in vivo pharmacological tools. The results from the preclinical studies discussed here may be useful in developing effective therapeutic strategies to treat neurological diseases on the one hand and psychiatric disorders on the other, and may pave the way for the development of novel Y2R and Y5R ligands as candidate drugs for the treatment of these diseases.

Regulation of neuropeptide Y in body microenvironments and its potential application in therapies: a review

Neuropeptide Y (NPY), one of the most abundant neuropeptides in the body, is widely expressed in the central and peripheral nervous systems and acts on the cardiovascular, digestive, endocrine, and nervous systems. NPY affects the nutritional and inflammatory microenvironments through its interaction with immune cells, brain-derived trophic factor (BDNF), and angiogenesis promotion to maintain body homeostasis. Additionally, NPY has great potential for therapeutic applications against various diseases, especially as an adjuvant therapy for stem cells. In this review, we discuss the research progress regarding NPY, as well as the current evidence for the regulation of NPY in each microenvironment, and provide prospects for further research on related diseases.

Redox-Active Metal Ions and Amyloid-Degrading Enzymes in Alzheimer's Disease

Redox-active metal ions, Cu(I/II) and Fe(II/III), are essential biological molecules for the normal functioning of the brain, including oxidative metabolism, synaptic plasticity, myelination, and generation of neurotransmitters. Dyshomeostasis of these redox-active metal ions in the brain could cause Alzheimer’s disease (AD). Thus, regulating the levels of Cu(I/II) and Fe(II/III) is necessary for normal brain function. To control the amounts of metal ions in the brain and understand the involvement of Cu(I/II) and Fe(II/III) in the pathogenesis of AD, many chemical agents have been developed. In addition, since toxic aggregates of amyloid-β (Aβ) have been proposed as one of the major causes of the disease, the mechanism of clearing Aβ is also required to be investigated to reveal the etiology of AD clearly. Multiple metalloenzymes (e.g., neprilysin, insulin-degrading enzyme, and ADAM10) have been reported to have an important role in the degradation of Aβ in the brain. These amyloid degrading enzymes (ADE) could interact with redox-active metal ions and affect the pathogenesis of AD. In this review, we introduce and summarize the roles, distributions, and transportations of Cu(I/II) and Fe(II/III), along with previously invented chelators, and the structures and functions of ADE in the brain, as well as their interrelationships.

Neuropathology of the Brainstem to Mechanistically Understand and to Treat Alzheimer's Disease

Alzheimer’s disease (AD) is a devastating neurodegenerative disorder as yet without effective therapy. Symptoms of this disorder typically reflect cortical malfunction with local neurohistopathology, which biased investigators to search for focal triggers and molecular mechanisms. Cortex, however, receives massive afferents from caudal brain structures, which do not only convey specific information but powerfully tune ensemble activity. Moreover, there is evidence that the start of AD is subcortical. The brainstem harbors monoamine systems, which establish a dense innervation in both allo- and neocortex. Monoaminergic synapses can co-release neuropeptides either by precisely terminating on cortical neurons or, when being “en passant”, can instigate local volume transmission. Especially due to its early damage, malfunction of the ascending monoaminergic system emerges as an early sign and possible trigger of AD. This review summarizes the involvement and cascaded impairment of brainstem monoaminergic neurons in AD and discusses cellular mechanisms that lead to their dysfunction. We highlight the significance and therapeutic challenges of transmitter co-release in ascending activating system, describe the role and changes of local connections and distant afferents of brainstem nuclei in AD, and summon the rapidly increasing diagnostic window during the last few years.

Peptide Profile of Zebrafish Brain in a 6-OHDA-Induced Parkinson Model

Parkinson's disease (PD) is a chronic neurodegenerative disorder mainly attributed to the progressive loss of dopaminergic neurons in the substantia nigra, which leads to uncontrolled voluntary movements causing tremors, postural instability, joint stiffness, and speech and locomotion difficulties, among other symptoms. Previous studies have shown the participation of specific peptides in neurodegenerative diseases. In this context, the present work analyzed changes in the peptide profile in zebrafish brain induced to parkinsonian conditions with 6-hydroxydopamine, using isotopic labeling techniques plus mass spectrometry. These analyses allowed the relative quantitation and identification of 118 peptides. Of these, nine peptides showed significant changes, one peptide was increased and eight decreased. The most altered sequences were fragment of cytosolic and extracellular proteins related to lipid metabolism and dynamic cytoskeleton. These results open new perspectives of study about the function of peptides in PD.

Assessment of the Effects of Altered Amyloid-Beta Clearance on Behavior following Repeat Closed-Head Brain Injury in Amyloid-Beta Precursor Protein Humanized Mice

Traumatic brain injury (TBI) increases the risk for dementias including Alzheimer's disease (AD) and chronic traumatic encephalopathy. Further, both human and animal model data indicate that amyloid-beta (Aβ) peptide accumulation and its production machinery are upregulated by TBI. Considering the clear link between chronic Aβ elevation and AD as well as tau pathology, the role(s) of Aβ in TBI is of high importance. Endopeptidases, including the neprilysin (NEP)-like enzymes, are key mediators of Aβ clearance and may affect susceptibility to pathology post-TBI. Here, we use a "humanized" mouse model of Aβ production, which expresses normal human amyloid-beta precursor protein (APP) under its natural transcriptional regulation and exposed them to a more clinically relevant repeated closed-head TBI paradigm. These transgenic mice also were crossed with mice deficient for the Aβ degrading enzymes NEP or NEP2 to assess models of reduced cerebral Aβ clearance in our TBI model. Our results show that the presence of the human form of Aβ did not exacerbate motor (Rotarod) and spatial learning/memory deficits (Morris water maze) post-injuries, while potentially reduced anxiety (Open Field) was observed. NEP and NEP2 deficiency also did not exacerbate these deficits post-injuries and was associated with protection from motor (NEP and NEP2) and spatial learning/memory deficits (NEP only). These data suggest that normally regulated expression of wild-type human APP/Aβ does not contribute to deficits acutely after TBI and may be protective at this stage of injury.

Molecular Mechanisms and Aspects on the Role of Neuropeptide Y as a Zn2+ and Cu2+ Chelator

The concept of metal chelation is based on simple coordination chemistry. The development of an ideal metal chelator that completely and selectively removes toxic metals from a specific metal binding site in proteins is required to prevent and or inhibit a variety of diseases, among them neurodegenerative diseases. This work examines neuropeptide Y (NPY) as a Zn²⁺ and Cu²⁺ chelator agent. NPY is a natural peptide that is produced in the human body; therefore, it is not a toxic agent and the complex that it forms is not toxic as well. Our simulations reveal that NPY has an efficient Zn²⁺ chelation activity but is less effective in chelating Cu²⁺. Moreover, while NPY demonstrates several conformations, the metal chelation occurs more efficiently in its native structure. Beyond the exploration of the activity of NPY as a Zn²⁺ and Cu²⁺ chelator agent, this work provides an insight into the molecular mechanisms of the chelation of these metals at the molecular level. The outcomes from this work may guide future experimental studies to examine NPY in metal chelation therapy for neurodegenerative diseases.

Target Enzymes Considered for the Treatment of Alzheimer's Disease and Parkinson's Disease

Various amyloidogenic proteins have been suggested to be involved in the onset and progression of neurodegenerative diseases (ND) such as Alzheimer's disease (AD) and Parkinson's disease (PD). Particularly, the aggregation of misfolded amyloid-β and hyperphosphorylated tau and α-synuclein are linked to the pathogenesis of AD and PD, respectively. In order to care the diseases, multiple small molecules have been developed to regulate the aggregation pathways of these amyloid proteins. In addition to controlling the aggregation of amyloidogenic proteins, maintaining the levels of the proteins in the brain by amyloid degrading enzymes (ADE; neprilysin (NEP), insulin-degrading enzyme (IDE), asparagine endopeptidase (AEP), and ADAM10) is also essential to cure AD and PD. Therefore, numerous biological molecules and chemical agents have been investigated as either inducer or inhibitor against the levels and activities of ADE. Although the side effect of enhancing the activity of ADE could occur, the removal of amyloidogenic proteins could result in a relatively good strategy to treat AD and PD. Furthermore, since the causes of ND are diverse, various multifunctional (multitarget) chemical agents have been designed to control the actions of multiple risk factors of ND, including amyloidogenic proteins, metal ions, and reactive oxygen species. Many of them, however, were invented without considerations of regulating ADE levels and actions. Incorporation of previously created molecules with the chemical agents handling ADE could be a promising way to treat AD and PD. This review introduces the ADE and molecules capable of modulating the activity and expression of ADE.

The neuroprotective effect of ethanolic extract Ocimum sanctum Linn. in the regulation of neuronal density in hippocampus areas as a central autobiography memory on the rat model of Alzheimer's disease

The aim of this study was to identify the effects of Ocimum sanctum Linn. ethanolic extract (OSE) on the neurons of the CA1, CA3, and DG hippocampal areas with the use of in vivo and in vitro models of Alzheimer's diseases (AD). Twenty-one two-month-old male rats were divided into three groups: untreated (Group A, n = 3), AD rats model pretreated with OSE followed by induction for Trimethyltin (TMT) on day 7 (group B, n = 9), and AD rats model treated with OSE both as pre-TMT introduction for 7 days and post-TMT induction for 21 days (group C, n = 9). AD rats were sacrificed on days 7, 14, and 21, and brain samples were collected and analyzed for neuronal density and neuropeptide Y (NPY) immunoreactivity. To corroborate the in vivo observations, HEK-293 cells were treated with TMT and used as an in vitro model of AD. The results were then analyzed using FITC Annexin V and flow cytometry. Nuclear fragmentation was observed in cells stained with Hoechst 33342 by confocal microscopy. The results showed a significant increase in the number of neurons and NPY expression in the AD rats that were pre- and post-treated with OSE (p < 0.05). Indeed, OSE was able to retain and promote neuronal density in the rat model of AD. Further studies of an in vitro model of neurodegeneration with Ocimum sanctum Linn. ethanolic extract inhibited apoptosis in TMT-induced HEK-293 cells. Moreover, OSE prevented nuclear fragmentation, which was confirmed by staining the nuclei of HEK-293 cells. Taken together, there findings suggest that OSE has the potential as a neuroprotective agent (retaining the autobiographical memory),and the neuroproliferation of neurons in the CA1, CA3, and DG hippocampal areas in the rats¡ model of neurodegeneration was mediated by activation of NPY expression.

Neuropeptide Y Expression Defines a Novel Class of GABAergic Projection Neuron in the Inferior Colliculus

Located in the midbrain, the inferior colliculus (IC) integrates information from numerous auditory nuclei and is an important hub for sound processing. Despite its importance, little is known about the molecular identity and functional roles of defined neuron types in the IC. Using a multifaceted approach in mice of both sexes, we found that neuropeptide Y (NPY) expression identifies a major class of inhibitory neurons, accounting for approximately one-third of GABAergic neurons in the IC. Retrograde tracing showed that NPY neurons are principal neurons that can project to the medial geniculate nucleus. In brain slice recordings, many NPY neurons fired spontaneously, suggesting that NPY neurons may drive tonic inhibition onto postsynaptic targets. Morphologic reconstructions showed that NPY neurons are stellate cells, and the dendrites of NPY neurons in the tonotopically organized central nucleus of the IC cross isofrequency laminae. Immunostaining confirmed that NPY neurons express NPY, and we therefore hypothesized that NPY signaling regulates activity in the IC. In crosses between Npy1r^cre and Ai14 Cre-reporter mice, we found that NPY Y₁ receptor (Y₁R)-expressing neurons are glutamatergic and were broadly distributed throughout the rostrocaudal extent of the IC. In whole-cell recordings, application of a high-affinity Y₁R agonist led to hyperpolarization in most Y₁R-expressing IC neurons. Thus, NPY neurons represent a novel class of inhibitory principal neurons that are well poised to use GABAergic and NPY signaling to regulate the excitability of circuits in the IC and auditory thalamus.SIGNIFICANCE STATEMENT The identification of neuron types is a fundamental question in neuroscience. In the inferior colliculus (IC), the hub of the central auditory pathway, molecular markers for distinct classes of inhibitory neurons have remained unknown. We found that neuropeptide Y (NPY) expression identifies a class of GABAergic principal neurons that constitute one-third of the inhibitory neurons in the IC. NPY neurons fire spontaneously, have a stellate morphology, and project to the auditory thalamus. Additionally, we found that NPY signaling hyperpolarized the membrane potential of a subset of excitatory IC neurons that express the NPY Y₁ receptor. Thus, NPY neurons are a novel class of inhibitory neurons that use GABA and NPY signaling to regulate activity in the IC and auditory thalamus.

An evaluation of the fixed-dose combination sacubitril/valsartan for the treatment of arterial hypertension

INTRODUCTION

Essential hypertension is a significant risk factor for cardiovascular disease, renal disease, and mortality with increasing prevalence. Despite the availability of various antihypertensive agents, hypertension is still poorly controlled. Therefore, new chemical compounds with antihypertensive efficacy need to be developed. The dual angiotensin II receptor-neprilysin inhibitor LCZ696 is a single molecule synthesized by co-crystallization of valsartan and the neprilysin inhibitor prodrug sacubitril (1:1 molar ratio).

AREAS COVERED

This review includes an overview of hypertension and the current pharmacotherapy. The authors summarize the LCZ696 drug chemistry, pharmacodynamics, pharmacokinetics, metabolism, randomized control trials (RCTs), and safety concerns. Databases searched included PubMed, Google Scholar, Embase, and ClinicalTrials.gov.

EXPERT OPINION

LCZ696 is effective in hypertension treatment. Short-term RCTs have shown that the highest doses of LCZ696 (200 and 400 mg [q.d.]) were more effective at lowering office and ambulatory blood pressure than angiotensin II receptor blockers (ARB) alone while having a similar tolerability profile. The effects of LCZ696 on hypertensive organ damage are only sparsely investigated and so far no studies have established the impact of LCZ696 on cardiovascular event rates. Future studies should focus on the comparison of LCZ696 and combination therapies already in use such as ARB and calcium channel blockers.

The catalytic kinetics of chicken transthyretin towards human Aβ1-42

The novel property of transthyretin (TTR) as a protease has been proposed to be significant. However, the study of TTR proteolysis properties has not been completely elucidated. Herein, we first report the catalytic activity of chicken TTR from plasma determined by using fluorescently labeled amyloid beta 1-42 peptide (Aβ_1-42), and compared it with human TTR (human TTR) from plasma and recombinant Crocodylus porosus TTR. The enzyme kinetic study revealed that the affinity for Aβ_1-42 of chicken TTR and C. porosus TTR (K_M values were 12.72 ± 0.27 μM and 16.21 ± 0.02 μM, respectively) were significantly lower than human TTR (K_M was 43.05 ± 0.39 μM). In addition, the catalytic efficiency of chicken TTR (K_cat/K_M was 310,386.87 ± 13,627.12 M^-1 s^-1) was 4.3 and 5.5 folds higher than those of C. porosus TTR and human TTR (K_cat/K_M were 72,893.80 ± 355.74 M^-1 s^-1 and 56,519.12 ± 5009.50 M^-1 s^-1, respectively), respectively. These results does not only indicated the relationship between structure and the proteolytic activity of TTR, but also suggested a potential development of TTR as a therapeutic anti-Aβ agent.

Roles of Neuropeptide Y in Neurodegenerative and Neuroimmune Diseases

Neuropeptide Y (NPY) is a neurotransmitter or neuromodulator that mainly exists in the nervous system. It plays a neuroprotective role in organisms and widely participates in the regulation of various physiological processes in vivo. Studies in both humans and animal models have been revealed that NPY levels are altered in some neurodegenerative and neuroimmune disorders. NPY plays various roles in these diseases, such as exerting a neuroprotective effect, increasing trophic support, decreasing excitotoxicity, regulating calcium homeostasis, and attenuating neuroinflammation. In this review, we will focus on the roles of NPY in the pathological mechanisms of neurodegenerative and neuroimmune diseases, highlighting NPY as a potential therapeutic target in these diseases.

The hydrophobic C-terminal sequence of transthyretin affects its catalytic kinetics towards amidated neuropeptide Y

Transthyretin (TTR) is a transporter for thyroid hormone and retinol binding protein that has recently been reported to have proteolytic activity against certain substrates, including amidated neuropeptide Y (NPY). However, the proteolytic activity of TTR towards NPY is not fully understood. Here, we used fluorescence-based assays to determine the catalytic kinetics of human TTR towards human amidated NPY. The Michaelis constant (KM) and catalytic efficiency (kcat/KM) of TTR proteolysis were 15.88 ± 0.44 μm and 687 081 ± 35 692 m -1·s-1, respectively. In addition, we demonstrated an effect of the C-terminal sequence of TTR. When the C-terminal sequence of TTR was made more hydrophobic, the KM and kcat/KM changed to 12.87 ± 0.22 μm and 983 755 ± 18 704 m -1·s-1, respectively. Our results may be useful for the development of TTR as a therapeutic agent with low risk of the undesirable symptoms that develop from amidated NPY, and for further improvement of the kcat/KM of TTR.

Neuropeptides Exert Neuroprotective Effects in Alzheimer's Disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder characterized by cognitive deficits and neuronal loss. Deposition of beta-amyloid peptide (Aβ) causes neurotoxicity through the formation of plaques in brains of Alzheimer's disease. Numerous studies have indicated that the neuropeptides including ghrelin, neurotensin, pituitary adenylate cyclase-activating polypeptide (PACAP), neuropeptide Y, substance P and orexin are closely related to the pathophysiology of Alzheimer's disease. The levels of neuropeptides and their receptors change in Alzheimer's disease. These neuropeptides exert neuroprotective roles mainly through preventing Aβ accumulation, increasing neuronal glucose transport, increasing the production of neurotrophins, inhibiting endoplasmic reticulum stress and autophagy, modulating potassium channel activity and hippocampal long-term potentiation. Therefore, the neuropeptides may function as potential drug targets in the prevention and cure of Alzheimer's disease.

Copper Binding Induces Nitration of NPY under Nitrative Stress: Complicating the Role of NPY in Alzheimer's Disease

Neuropeptide Y (NPY) is a 36 amino acid peptide that regulates a multitude of physiological functions in the central nervous system and has been shown to be involved in Alzheimer's disease (AD). A change in copper homeostasis is a remarkable feature of AD, and the dysregulation may contribute to toxicity in neural cells. Moreover, it has been shown that copper could interact with many neuropeptides and result in catalyzing the production of reactive oxygen species, which may lead to peptide oxidation. Besides, copper could also catalyze protein tyrosine nitration under oxidative stress, and there are two tyrosine residues playing an important role in NPY. Therefore, it is also likely that copper has an action on NPY and potentially influences its functions through tyrosine nitration. In this paper, the studies of the interaction of copper with NPY and the copper-catalyzed NPY nitration were performed. The electrochemical techniques, UV-vis spectroscopy, mass spectrometry, and fluorescence titration, have been applied to show that copper can interact with NPY to form a Cu-NPY complex with a conditional dissociation constant of 0.021 μmol/L, and the binding promotes the generation of •OH. Dot blotting results reveal that NPY can be nitrated upon binding with copper under nitrative stress. Furthermore, liquid chromatography-mass spectrometry (LC-MS) identify that the tyrosine residues in NPY are all nitrated during the nitration process, which will cause the inactivation of NPY shown by our previous study. This study supports the hypothesis that copper has a close correlation with NPY and implicates the peptide in AD. These data may provide a new insight into understanding the pathology and pathogenesis of AD.

Secretory vesicle trafficking in awake and anaesthetized mice: differential speeds in axons versus synapses

KEY POINTS

Despite their immense physiological and pathophysiological importance, we know very little about the biology of dense core vesicle (DCV) trafficking in the intact mammalian brain. DCVs are transported at similar average speeds in the anaesthetized and awake mouse brain compared to neurons in culture, yet maximal speed and pausing fraction of transport were higher. Microtubule plus (+)-end extension imaging visualized microtubular growth at 0.12 μm/s and revealed that DCVs were transported faster in the anterograde direction. DCV transport slowed down upon presynaptic bouton approach, possibly promoting synaptic localization and cargo release. Our work provides a basis to extrapolate DCV transport properties determined in cultured neurons to the intact mouse brain and reveals novel features such as slowing upon bouton approach and brain state-dependent trafficking directionality.

ABSTRACT

Neuronal dense core vesicles (DCVs) transport many cargo molecules like neuropeptides and neurotrophins to their release sites in dendrites or axons. The transport properties of DCVs in axons of the intact mammalian brain are unknown. We used viral expression of a DCV cargo reporter (NPY-Venus/Cherry) in the thalamus and two-photon in vivo imaging to visualize axonal DCV trafficking in thalamocortical projections of anaesthetized and awake mice. We found an average speed of 1 μm/s, maximal speeds of up to 5 μm/s and a pausing fraction of ∼11%. Directionality of transport differed between anaesthetized and awake mice. In vivo microtubule +-end extension imaging using MACF18-GFP revealed microtubular growth at 0.12 μm/s and provided positive identification of antero- and retrograde axonal transport. Consistent with previous reports, anterograde transport was faster (∼2.1 μm/s) than retrograde transport (∼1.4 μm/s). In summary, DCVs are transported with faster maximal speeds and lower pausing fraction in vivo compared to previous results obtained in vitro. Finally, we found that DCVs slowed down upon presynaptic bouton approach. We propose that this mechanism promotes synaptic localization and cargo release.

Targeting Alzheimer's disease with gene and cell therapies

Alzheimer's disease (AD) causes dementia in both young and old people affecting more than 40 million people worldwide. The two neuropathological hallmarks of the disease, amyloid beta (Aβ) plaques and neurofibrillary tangles consisting of protein tau are considered the major contributors to the disease. However, a more complete picture reveals significant neurodegeneration and decreased cell survival, neuroinflammation, changes in protein and energy homeostasis and alterations in lipid and cholesterol metabolism. In addition, gene and cell therapies for severe neurodegenerative disorders have recently improved technically in terms of safety and efficiency and have translated to the clinic showing encouraging results. Here, we review broadly current data within the field for potential targets that could modify AD through gene and cell therapy strategies. We envision that not only Aβ will be targeted in a disease-modifying treatment strategy but rather that a combination of treatments, possibly at different intervention times may prove beneficial in curing this devastating disease. These include decreased tau pathology, neuronal growth factors to support neurons and modulation of neuroinflammation for an appropriate immune response. Furthermore, cell based therapies may represent potential strategies in the future.

Chronic intermittent hypoxia induces changes on the expression and activity of neprilysin (EC 3.4.24.11) in the brain of rats

Obstructive sleep apnea (OSA) is a frequent sleeping breathing disorder associated with cognitive impairments. Neprilysin (NEP) is responsible for degrading several substrates related to cognition; however, the effect of chronic intermittent hypoxia (CIH) on NEP is still unknown. This study aimed to evaluate the expression and activity of NEP in cognitive-related brain structures of rats submitted to CIH. Western blot, qRT-PCR and enzyme activity assay, demonstrated that a six-week intermittent hypoxia increased NEP expression and activity, selectively in temporal cortex, but not in the hippocampus and frontal cortex. The increase in NEP activity and expression was reverted followed by two weeks recovery in normoxia. These data show that CIH protocol increases the expression and activity of NEP selectively in the temporal cortex. Additional mechanisms must be investigated to elucidate the effects of CIH in cognition.

Caloric restriction stimulates autophagy in rat cortical neurons through neuropeptide Y and ghrelin receptors activation

Caloric restriction is an anti-aging intervention known to extend lifespan in several experimental models, at least in part, by stimulating autophagy. Caloric restriction increases neuropeptide Y (NPY) in the hypothalamus and plasma ghrelin, a peripheral gut hormone that acts in hypothalamus to modulate energy homeostasis. NPY and ghrelin have been shown to be neuroprotective in different brain areas and to induce several physiological modifications similar to those induced by caloric restriction. However, the effect of NPY and ghrelin in autophagy in cortical neurons is currently not known. Using a cell culture of rat cortical neurons we investigate the involvement of NPY and ghrelin in caloric restriction-induced autophagy. We observed that a caloric restriction mimetic cell culture medium stimulates autophagy in rat cortical neurons and NPY or ghrelin receptor antagonists blocked this effect. On the other hand, exogenous NPY or ghrelin stimulate autophagy in rat cortical neurons. Moreover, NPY mediates the stimulatory effect of ghrelin on autophagy in rat cortical neurons. Since autophagy impairment occurs in aging and age-related neurodegenerative diseases, NPY and ghrelin synergistic effect on autophagy stimulation may suggest a new strategy to delay aging process.

Drosophila Neprilysins Are Involved in Middle-Term and Long-Term Memory

Neprilysins are type II metalloproteinases known to degrade and inactivate a number of small peptides. Neprilysins in particular are the major amyloid-β peptide-degrading enzymes. In mouse models of Alzheimer's disease, neprilysin overexpression improves learning and memory deficits, whereas neprilysin deficiency aggravates the behavioral phenotypes. However, whether these enzymes are involved in memory in nonpathological conditions is an open question. Drosophila melanogaster is a well suited model system with which to address this issue. Several memory phases have been characterized in this organism and the neuronal circuits involved are well described. The fly genome contains five neprilysin-encoding genes, four of which are expressed in the adult. Using conditional RNA interference, we show here that all four neprilysins are involved in middle-term and long-term memory. Strikingly, all four are required in a single pair of neurons, the dorsal paired medial (DPM) neurons that broadly innervate the mushroom bodies (MBs), the center of olfactory memory. Neprilysins are also required in the MB, reflecting the functional relationship between the DPM neurons and the MB, a circuit believed to stabilize memories. Together, our data establish a role for neprilysins in two specific memory phases and further show that DPM neurons play a critical role in the proper targeting of neuropeptides involved in these processes.

SIGNIFICANCE STATEMENT

Neprilysins are endopeptidases known to degrade a number of small peptides. Neprilysin research has essentially focused on their role in Alzheimer's disease and heart failure. Here, we use Drosophila melanogaster to study whether neprilysins are involved in memory. Drosophila can form several types of olfactory memory and the neuronal structures involved are well described. Four neprilysin genes are expressed in adult Drosophila Using conditional RNA interference, we show that all four are specifically involved in middle-term memory (MTM) and long-term memory (LTM) and that their expression is required in the mushroom bodies and also in a single pair of closely connected neurons. The data show that these two neurons play a critical role in targeting neuropeptides essential for MTM and LTM.

Neuropeptide Y-based recombinant peptides ameliorate bone loss in mice by regulating hematopoietic stem/progenitor cell mobilization

Ovariectomy-induced bone loss is related to an increased deposition of osteoclasts on bone surfaces. We reported that the 36-amino-acid-long neuropeptide Y (NPY) could mobilize hematopoietic stem/progenitor cells (HSPCs) from the bone marrow to the peripheral blood by regulating HSPC maintenance factors and that mobilization of HSPCs ameliorated low bone density in an ovariectomy-induced osteoporosis mouse model by reducing the number of osteoclasts. Here, we demonstrated that new NPY peptides, recombined from the cleavage of the full-length NPY, showed better functionality for HSPC mobilization than the full-length peptide. These recombinant peptides mediated HSPC mobilization with greater efficiency by decreasing HSPC maintenance factors. Furthermore, treatment with these peptides reduced the number of osteoclasts and relieved ovariectomy-induced bone loss in mice more effectively than treatment with full-length NPY. Therefore, these results suggest that peptides recombined from full-length NPY can be used to treat osteoporosis.

NPY binds with heme to form a NPY–heme complex: enhancing peroxidase activity in free heme and promoting NPY nitration and inactivation

NPY binding with heme enhances the peroxidase activity of free heme, resulting in the important tyrosine nitration, which will attenuate its bioactivity.

Long-term neprilysin inhibition - implications for ARNIs

Neprilysin has a major role in both the generation and degradation of bioactive peptides. LCZ696 (valsartan/sacubitril, Entresto), the first of the new ARNI (dual-acting angiotensin-receptor-neprilysin inhibitor) drug class, contains equimolar amounts of valsartan, an angiotensin-receptor blocker, and sacubitril, a prodrug for the neprilysin inhibitor LBQ657. LCZ696 reduced blood pressure more than valsartan alone in patients with hypertension. In the PARADIGM-HF study, LCZ696 was superior to the angiotensin-converting enzyme inhibitor enalapril for the treatment of heart failure with reduced ejection fraction, and LCZ696 was approved by the FDA for this purpose in 2015. This approval was the first for chronic neprilysin inhibition. The many peptides metabolized by neprilysin suggest many potential consequences of chronic neprilysin inhibitor therapy, both beneficial and adverse. Moreover, LBQ657 might inhibit enzymes other than neprilysin. Chronic neprilysin inhibition might have an effect on angio-oedema, bronchial reactivity, inflammation, and cancer, and might predispose to polyneuropathy. Additionally, inhibition of neprilysin metabolism of amyloid-β peptides might have an effect on Alzheimer disease, age-related macular degeneration, and cerebral amyloid angiopathy. Much of the evidence for possible adverse consequences of chronic neprilysin inhibition comes from studies in animal models, and the relevance of this evidence to humans is unknown. This Review summarizes current knowledge of neprilysin function and possible consequences of chronic neprilysin inhibition that indicate a need for vigilance in the use of neprilysin inhibitor therapy.

Neuregulin 1 improves cognitive deficits and neuropathology in an Alzheimer's disease model

Several lines of evidence suggest that neuregulin 1 (NRG1) signaling may influence cognitive function and neuropathology in Alzheimer’s disease (AD). To test this possibility, full-length type I or type III NRG1 was overexpressed via lentiviral vectors in the hippocampus of line 41 AD mouse. Both type I and type III NRG1 improves deficits in the Morris water-maze behavioral task. Neuropathology was also significantly ameliorated. Decreased expression of the neuronal marker MAP2 and synaptic markers PSD95 and synaptophysin in AD mice was significantly reversed. Levels of Aβ peptides and plaques were markedly reduced. Furthermore, we showed that soluble ectodomains of both type I and type III NRG1 significantly increased expression of Aβ-degrading enzyme neprilysin (NEP) in primary neuronal cultures. Consistent with this finding, immunoreactivity of NEP was increased in the hippocampus of AD mice. These results suggest that NRG1 provides beneficial effects in candidate neuropathologic substrates of AD and, therefore, is a potential target for the treatment of AD.

Major amyloid-β-degrading enzymes, endothelin-converting enzyme-2 and neprilysin, are expressed by distinct populations of GABAergic interneurons in hippocampus and neocortex

Impaired clearance of amyloid-β peptide (Aβ) has been postulated to significantly contribute to the amyloid accumulation typical of Alzheimer's disease. Among the enzymes known to degrade Aβ in vivo are endothelin-converting enzyme (ECE)-1, ECE-2, and neprilysin (NEP), and evidence suggests that they regulate independent pools of Aβ that may be functionally significant. To better understand the differential regulation of Aβ concentration by its physiological degrading enzymes, we characterized the cell and region-specific expression pattern of ECE-1, ECE-2, and NEP by in situ hybridization and immunohistochemistry in brain areas relevant to Alzheimer's disease. In contrast to the broader distribution of ECE-1, ECE-2 and NEP were found enriched in GABAergic neurons. ECE-2 was majorly expressed by somatostatin-expressing interneurons and was active in isolated synaptosomes. NEP messenger RNA was found mainly in parvalbumin-expressing interneurons, with NEP protein localized to perisomatic parvalbuminergic synapses. The identification of somatostatinergic and parvalbuminergic synapses as hubs for Aβ degradation is consistent with the possibility that Aβ may have a physiological function related to the regulation of inhibitory signaling.

Neural stem/progenitor cells in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease and a worldwide health challenge. Different therapeutic approaches are being developed to reverse or slow the loss of affected neurons. Another plausible therapeutic way that may complement the studies is to increase the survival of existing neurons by mobilizing the existing neural stem/progenitor cells (NSPCs) - i.e. "induce their plasticity" - to regenerate lost neurons despite the existing pathology and unfavorable environment. However, there is controversy about how NSPCs are affected by the unfavorable toxic environment during AD. In this review, we will discuss the use of stem cells in neurodegenerative diseases and in particular how NSPCs affect the AD pathology and how neurodegeneration affects NSPCs. In the end of this review, we will discuss how zebrafish as a useful model organism with extensive regenerative ability in the brain might help to address the molecular programs needed for NSPCs to respond to neurodegeneration by enhanced neurogenesis.

Neuropeptide Y: A stressful review

Stress is defined as an adverse condition that disturbs the homeostasis of the body and activates adaptation responses. Among the many pathways and mediators involved, neuropeptide Y (NPY) stands out due to its unique stress-relieving, anxiolytic and neuroprotective properties. Stress exposure alters the biosynthesis of NPY in distinct brain regions, the magnitude and direction of this effect varying with the duration and type of stress. NPY is expressed in particular neurons of the brainstem, hypothalamus and limbic system, which explains why NPY has an impact on stress-related changes in emotional-affective behaviour and feeding as well as on stress coping. The biological actions of NPY in mammals are mediated by the Y1, Y2, Y4 and Y5 receptors, Y1 receptor stimulation being anxiolytic whereas Y2 receptor activation is anxiogenic. Emerging evidence attributes NPY a role in stress resilience, the ability to cope with stress. Thus there is a negative correlation between stress-induced behavioural disruption and cerebral NPY expression in animal models of post-traumatic stress disorder. Exogenous NPY prevents the negative consequences of stress, and polymorphisms of the NPY gene are predictive of impaired stress processing and increased risk of neuropsychiatric diseases. Stress is also a factor contributing to, and resulting from, neurodegenerative diseases such as Alzheimer's, Parkinson's and Huntington's disease, in which NPY appears to play an important neuroprotective role. This review summarizes the evidence for an implication of NPY in stress-related and neurodegenerative pathologies and addresses the cerebral NPY system as a therapeutic target.

Meta-analysis of synaptic pathology in Alzheimer's disease reveals selective molecular vesicular machinery vulnerability

INTRODUCTION

Loss of synapses best correlates to cognitive deficits in Alzheimer's disease (AD) in which oligomeric neurotoxic species of amyloid-β appears to contribute synaptic pathology. Although a number of clinical pathologic studies have been performed with limited sample size, there are no systematic studies encompassing large samples. Therefore, we performed a meta-analysis study.

METHODS

We identified 417 publications reporting postmortem synapse and synaptic marker loss from AD patients. Two meta-analyses were performed using a single database of subselected publications and calculating the standard mean differences.

RESULTS

Meta-analysis confirmed synaptic loss in selected brain regions is an early event in AD pathogenesis. The second meta-analysis of 57 synaptic markers revealed that presynaptic makers were affected more than postsynaptic markers.

DISCUSSION

The present meta-analysis study showed a consistent synaptic loss across brain regions and that molecular machinery including endosomal pathways, vesicular assembly mechanisms, glutamate receptors, and axonal transport are often affected.

Systemic Central Nervous System (CNS)-targeted Delivery of Neuropeptide Y (NPY) Reduces Neurodegeneration and Increases Neural Precursor Cell Proliferation in a Mouse Model of Alzheimer Disease

Neuropeptide Y (NPY) is one of the most abundant protein transmitters in the central nervous system with roles in a variety of biological functions including: food intake, cardiovascular regulation, cognition, seizure activity, circadian rhythms, and neurogenesis. Reduced NPY and NPY receptor expression is associated with numerous neurodegenerative disorders including Alzheimer disease (AD). To determine whether replacement of NPY could ameliorate some of the neurodegenerative and behavioral pathology associated with AD, we generated a lentiviral vector expressing NPY fused to a brain transport peptide (apoB) for widespread CNS delivery in an APP-transgenic (tg) mouse model of AD. The recombinant NPY-apoB effectively reversed neurodegenerative pathology and behavioral deficits although it had no effect on accumulation of Aβ. The subgranular zone of the hippocampus showed a significant increase in proliferation of neural precursor cells without further differentiation into neurons. The neuroprotective and neurogenic effects of NPY-apoB appeared to involve signaling via ERK and Akt through the NPY R1 and NPY R2 receptors. Thus, widespread CNS-targeted delivery of NPY appears to be effective at reversing the neuronal and glial pathology associated with Aβ accumulation while also increasing NPC proliferation. Overall, increased delivery of NPY to the CNS for AD might be an effective therapy especially if combined with an anti-Aβ therapeutic.

Amyloid cascade hypothesis: Pathogenesis and therapeutic strategies in Alzheimer's disease

Alzheimer's disease is an irreversible, progressive neurodegenerative disorder. Various therapeutic approaches are being used to improve the cholinergic neurotransmission, but their role in AD pathogenesis is still unknown. Although, an increase in tau protein concentration in CSF has been described in AD, but several issues remains unclear. Extensive and accurate analysis of CSF could be helpful to define presence of tau proteins in physiological conditions, or released during the progression of neurodegenerative disease. The amyloid cascade hypothesis postulates that the neurodegeneration in AD caused by abnormal accumulation of amyloid beta (Aβ) plaques in various areas of the brain. The amyloid hypothesis has continued to gain support over the last two decades, particularly from genetic studies. Therefore, current research progress in several areas of therapies shall provide an effective treatment to cure this devastating disease. This review critically evaluates general biochemical and physiological functions of Aβ directed therapeutics and their relevance.

Adipokine pathways are altered in hippocampus of an experimental mouse model of Alzheimer's disease

A growing body of evidence suggests that β-amyloid peptides (Aβ) are unlikely to be the only factor involved in Alzheimer's disease (AD) aetiology. In fact, a strong correlation has been established between AD patients and patients with type 2 diabetes and/or cholesterol metabolism alterations. In addition, a link between adipose tissue metabolism, leptin signalling in particular, and AD has also been demonstrated. In the present study we analyzed the expression of molecules related to metabolism, with the main focus on leptin and prolactin signalling pathways in an APPswe/PS1dE9 (APP/PS1) transgenic mice model, at 3 and 6 months of age, compared to wild-type controls. We have chosen to study 3 months-old APP/PS1 animals at an age when neither the cognitive deficits nor significant Aβ plaques in the brain are present, and to compare them to the 6 months-old mice, which exhibit elevated levels of Aβ in the hippocampus and memory loss. A significant reduction in both mRNA and protein levels of the prolactin receptor (PRL-R) was detected in the hippocampi of 3 months old APP/PS1 mice, with a decrease in the levels of the leptin receptor (OB-R) first becoming evident at 6 months of age. We proceeded to study the expression of the intracellular signalling molecules downstream of these receptors, including stat (1-5), sos1, kras and socs (1-3). Our data suggest a downregulation in some of these molecules such as stat-5b and socs (1-3), in 3 months-old APP/PS1 brains. Likewise, at the same age, we detected a significant reduction in mRNA levels of lrp1 and cyp46a1, both of which are involved in cholesterol homeostasis. Taken together, these results demonstrate a significative impairment in adipokine receptors signalling and cholesterol regulation pathways in the hippocampus of APP/PS1 mice at an early age, prior to the Aβ plaque formation.

Neuropeptide Y stimulates autophagy in hypothalamic neurons

Aging is characterized by autophagy impairment that contributes to age-related disease aggravation. Moreover, it was described that the hypothalamus is a critical brain area for whole-body aging development and has impact on lifespan. Neuropeptide Y (NPY) is one of the major neuropeptides present in the hypothalamus, and it has been shown that, in aged animals, the hypothalamic NPY levels decrease. Because caloric restriction (CR) delays aging, at least in part, by stimulating autophagy, and also increases hypothalamic NPY levels, we hypothesized that NPY could have a relevant role on autophagy modulation in the hypothalamus. Therefore, the aim of this study was to investigate the role of NPY on autophagy in the hypothalamus. Using both hypothalamic neuronal in vitro models and mice overexpressing NPY in the hypothalamus, we observed that NPY stimulates autophagy in the hypothalamus. Mechanistically, in rodent hypothalamic neurons, NPY increases autophagy through the activation of NPY Y1 and Y5 receptors, and this effect is tightly associated with the concerted activation of PI3K, MEK/ERK, and PKA signaling pathways. Modulation of hypothalamic NPY levels may be considered a potential strategy to produce protective effects against hypothalamic impairments associated with age and to delay aging.

Transgenic mice overexpressing amyloid precursor protein exhibit early metabolic deficits and a pathologically low leptin state associated with hypothalamic dysfunction in arcuate neuropeptide Y neurons

Weight loss is a prominent early feature of Alzheimer's disease (AD) that often precedes the cognitive decline and clinical diagnosis. While the exact pathogenesis of AD remains unclear, accumulation of amyloid-β (Aβ) derived from the amyloid precursor protein (APP) in the brain is thought to lead to the neuronal dysfunction and death underlying the dementia. In this study, we examined whether transgenic mice overexpressing the Swedish mutation of APP (Tg2576), recapitulating selected features of AD, have hypothalamic leptin signaling dysfunction leading to early body weight deficits. We found that 3-month-old Tg2576 mice, before amyloid plaque formation, exhibit decreased weight with markedly decreased adiposity, low plasma leptin levels, and increased energy expenditure without alterations in feeding behavior. The expression of the orexigenic neuropeptide Y (NPY) in the hypothalamus to the low leptin state was abnormal at basal and fasting conditions. In addition, arcuate NPY neurons exhibited abnormal electrophysiological responses to leptin in Tg2576 hypothalamic slices or wild-type slices treated with Aβ. Finally, the metabolic deficits worsened as Tg2576 mice aged and amyloid burden increased in the brain. These results indicate that excess Aβ can potentially disrupt hypothalamic arcuate NPY neurons leading to weight loss and a pathologically low leptin state early in the disease process that progressively worsens as the amyloid burden increases. Collectively, these findings suggest that weight loss is an intrinsic pathological feature of Aβ accumulation and identify hypothalamic leptin signaling as a previously unrecognized pathogenic site of action for Aβ.

The effect of neuropeptide Y on cell survival and neurotrophin expression in in-vitro models of Alzheimer's disease

Alzheimer's disease (AD) is a disorder characterized by the accumulation of abnormally folded protein fragments in neurons, i.e., β-amyloid (Aβ) and tau protein, leading to cell death. Several neuropeptides present in the central nervous system (CNS) are believed to be involved in the pathophysiology of AD. Among them, neuropeptide Y (NPY), a small peptide widely distributed throughout the brain, has generated interest because of its role in neuroprotection against excitotoxicity in animal models of AD. In addition, it has been shown that NPY modulates neurogenesis. Interestingly, these latter effects are similar to those elicited by neurotrophins, which are critical molecules for the function and survival of neurons that degenerate during the course of AD. In this review we summarize the evidence for the involvement of NPY and neurotrophins in AD pathogenesis, and the similarity between them in CNS neurons. Finally, we recapitulate our recent in-vitro evidence for the involvement of neurotrophin nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) in the neuroprotective effect elicited by NPY in AD neuron-like models (neuroblastoma cells or primary cultures exposed to toxic concentrations of Aβ's pathogenic fragment 25-35), and propose a putative mechanism based on NPY-induced inhibition of voltage-dependent Ca(2+) influx in pre- and post-synaptic neurons.

A neuroprotective brain-penetrating endopeptidase fusion protein ameliorates Alzheimer disease pathology and restores neurogenesis

Alzheimer disease (AD) is characterized by widespread neurodegeneration throughout the association cortex and limbic system, deposition of amyloid-β peptide (Aβ) in the neuropil and around the blood vessels, and formation of neurofibrillary tangles. The endopeptidase neprilysin has been successfully used to reduce the accumulation of Aβ following intracranial viral vector delivery or ex vivo manipulated intracranial delivery. These therapies have relied on direct injections into the brain, whereas a clinically desirable therapy would involve i.v. infusion of a recombinant enzyme. We previously characterized a recombinant neprilysin that contained a 38-amino acid brain-targeting domain. Recombinant cell lines have been generated expressing this brain-targeted enzyme (ASN12). In this report, we characterize the ASN12 recombinant protein for pharmacology in a mouse as well as efficacy in two APPtg mouse models of AD. The recombinant ASN12 transited to the brain with a t½ of 24 h and accumulated to 1.7% of injected dose at 24 h following i.v. delivery. We examined pharmacodynamics in the tg2576 APPtg mouse with the prion promoter APP695 SWE mutation and in the Line41 mThy1 APP751 mutation mouse. Treatment of either APPtg mouse resulted in reduced Aβ, increased neuronal synapses, and improved learning and memory. In addition, the Line41 APPtg mice showed increased levels of C-terminal neuropeptide Y fragments and increased neurogenesis. These results suggest that the recombinant brain-targeted neprilysin, ASN12, may be an effective treatment for AD and warrant further investigation in clinical trials.

Continuation of exercise is necessary to inhibit high fat diet-induced β-amyloid deposition and memory deficit in amyloid precursor protein transgenic mice

High fat diet (HFD) is prevalent in many modern societies and HFD-induced metabolic condition is a growing concern worldwide. It has been previously reported that HFD clearly worsens cognitive function in amyloid precursor protein (APP) transgenic mice. On the other hand, we have demonstrated that voluntary exercise in an enriched environment is an effective intervention to rescue HFD-induced β-amyloid (Aβ) deposition and memory deficit. However, it had been unclear whether consumption of HFD after exercising abolished the beneficial effect of exercise on the inhibition of Alzheimer's disease (AD) pathology. To examine this question, we exposed wild type (WT) and APP mice fed with HFD to exercise conditions at different time periods. In our previous experiment, we gave HFD to mice for 20 weeks and subjected them to exercise during weeks 10–20. In the present study, mice were subjected to exercise conditions during weeks 0–10 or weeks 5–15 while being on HFD. Interestingly, we found that the effect of exercise during weeks 0–10 or weeks 5–15 on memory function was not abolished in WT mice even if they kept having HFD after finishing exercise. However, in APP transgenic mice, HFD clearly disrupted the effect of exercise during weeks 0–10 or weeks 5–15 on memory function. Importantly, we observed that the level of Aβ oligomer was significantly elevated in the APP mice that exercised during weeks 0–10: this might have been caused by the up-regulation of Aβ production. These results provide solid evidence that continuation of exercise is necessary to rescue HFD-induced aggravation of cognitive decline in the pathological setting of AD.

Commentary to the recently published review "Drug pipeline in neurodegeneration based on transgenic mice models of Alzheimer's disease" by Li, Evrahimi and Schluesener. Ageing Res. Rev. 2013 Jan;12(1):116-40

Li and colleagues summarized the most frequently used Alzheimer's disease (AD) mouse models available for drug testing and the mediating effects of the different compounds. With almost 300 cited publications, authors present the research community's effort of the last 10 years in finding a new drug for the treatment of AD. Some of the transgenic mouse lines mentioned by Li and colleagues are discussed only very briefly. Since we are convinced that a couple of these models indeed have a great value for AD research and the development of new AD drugs we will subsequently describe a few of them in more detail. A suitable mouse model of AD does not only have to mimic major hallmarks of AD that are modifiable by different test substances as mentioned by the authors; they also have to be translational to clinical trials in humans. For the following discussion, we will therefore also include information on clinical trials of drugs previously tested in the different transgenic mice.