Prodromal Alzheimer’s disease: Constitutive upregulation of neuroglobin prevents the initiation of Alzheimer’s pathology

In humans, a considerable number of the autopsy samples of cognitively normal individuals aged between 57 and 102 years have revealed the presence of amyloid plaques, one of the typical signs of AD, indicating that many of us use mechanisms that defend ourselves from the toxic consequences of Aß. The human APP NL/F (hAPP NL/F) knockin mouse appears as the ideal mouse model to identify these mechanisms, since they have high Aß42 levels at an early age and moderate signs of disease when old. Here we show that in these mice, the brain levels of the hemoprotein Neuroglobin (Ngb) increase with age, in parallel with the increase in Aß42. In vitro, in wild type neurons, exogenous Aß increases the expression of Ngb and Ngb over-expression prevents Aß toxicity. In vivo, in old hAPP NL/F mice, Ngb knockdown leads to dendritic tree simplification, an early sign of Alzheimer’s disease. These results could indicate that Alzheimer’s symptoms may start developing at the time when defense mechanisms start wearing out. In agreement, analysis of plasma Ngb levels in aged individuals revealed decreased levels in those whose cognitive abilities worsened during a 5-year longitudinal follow-up period.This work was partially supported by the Stichting Alzheimer Onderzoek (SAO; S16013) and the FWO (research project G0B2519N) to LC-G, SAF2016-76722 (AEI/FEDER, UE) to CD, Marie Skłodowska-Curie Actions – Individual Fellowships (T2DMand AD, EU 708152) to FG and EU JPND “EpiAD” Grant to AF-G and CD, SAF2016-78603-R to MM and M

Increased exosome secretion in neurons aging in vitro by NPC1-mediated endosomal cholesterol buildup

As neurons age, they show a decrease in their ability to degrade proteins and membranes. Because undegraded material is a source of toxic products, defects in degradation are associated with reduced cell function and survival. However, there are very few dead neurons in the aging brain, suggesting the action of compensatory mechanisms. We show in this work that ageing neurons in culture show large multivesicular bodies (MVBs) filled with intralumenal vesicles (ILVs) and secrete more small extracellular vesicles than younger neurons. We also show that the high number of ILVs is the consequence of the accumulation of cholesterol in MVBs, which in turn is due to decreased levels of the cholesterol extruding protein NPC1. NPC1 down-regulation is the consequence of a combination of upregulation of the NPC1 repressor microRNA 33, and increased degradation, due to AktmTOR targeting of NPC1 to the phagosome. Although releasing more exosomes can be beneficial to old neurons, other cells, neighbouring and distant, can be negatively affected by the waste material they contain.Fil: Guix, Francesc X.. Universidad Autónoma de Madrid; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Marrero Capitán, Ana. Consejo Superior de Investigaciones Científicas; España. Universidad Autónoma de Madrid; EspañaFil: Casadomé Perales, Álvaro. Consejo Superior de Investigaciones Científicas; España. Universidad Autónoma de Madrid; EspañaFil: Palomares Pérez, Irene. Consejo Superior de Investigaciones Científicas; España. Universidad Autónoma de Madrid; EspañaFil: Lopez del Castillo, Irene. Consejo Superior de Investigaciones Científicas; España. Universidad Autónoma de Madrid; EspañaFil: Miguel, Verónica. Consejo Superior de Investigaciones Científicas; España. Universidad Autónoma de Madrid; EspañaFil: Goedeke, Leigh. University of Yale; Estados UnidosFil: Martín, Mauricio Gerardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra. Universidad Nacional de Córdoba. Instituto de Investigación Médica Mercedes y Martín Ferreyra; ArgentinaFil: Lamas, Santiago. Consejo Superior de Investigaciones Científicas; España. Universidad Autónoma de Madrid; EspañaFil: Peinado, Héctor. Centro Nacional de Investigaciones Oncológicas; EspañaFil: Fernández Hernando, Carlos. University of Yale; Estados UnidosFil: Dotti, Carlos. Universidad Autónoma de Madrid; España. Consejo Superior de Investigaciones Científicas; Españ

Detection of Aggregation-Competent Tau in Neuron-Derived Extracellular Vesicles

Progressive cerebral accumulation of tau aggregates is a defining feature of Alzheimer’s disease (AD). A popular theory that seeks to explain the apparent spread of neurofibrillary tangle pathology proposes that aggregated tau is passed from neuron to neuron. Such a templated seeding process requires that the transferred tau contains the microtubule binding repeat domains that are necessary for aggregation. While it is not clear how a protein such as tau can move from cell to cell, previous reports have suggested that this may involve extracellular vesicles (EVs). Thus, measurement of tau in EVs may both provide insights on the molecular pathology of AD and facilitate biomarker development. Here, we report the use of sensitive immunoassays specific for full-length (FL) tau and mid-region tau, which we applied to analyze EVs from human induced pluripotent stem cell (iPSC)-derived neuron (iN) conditioned media, cerebrospinal fluid (CSF), and plasma. In each case, most tau was free-floating with a small component inside EVs. The majority of free-floating tau detected by the mid-region assay was not detected by our FL assays, indicating that most free-floating tau is truncated. Inside EVs, the mid-region assay also detected more tau than the FL assay, but the ratio of FL-positive to mid-region-positive tau was higher inside exosomes than in free solution. These studies demonstrate the presence of minute amounts of free-floating and exosome-contained FL tau in human biofluids. Given the potential for FL tau to aggregate, we conclude that further investigation of these pools of extracellular tau and how they change during disease is merited

Activation of PKR Causes Amyloid ß-Peptide Accumulation via De-Repression of BACE1 Expression

BACE1 is a key enzyme involved in the production of amyloid ß-peptide (Aß) in Alzheimer's disease (AD) brains. Normally, its expression is constitutively inhibited due to the presence of the 5′untranslated region (5′UTR) in the BACE1 promoter. BACE1 expression is activated by phosphorylation of the eukaryotic initiation factor (eIF)2-alpha, which reverses the inhibitory effect exerted by BACE1 5′UTR. There are four kinases associated with different types of stress that could phosphorylate eIF2-alpha. Here we focus on the double-stranded (ds) RNA-activated protein kinase (PKR). PKR is activated during viral infection, including that of herpes simplex virus type 1 (HSV1), a virus suggested to be implicated in the development of AD, acting when present in brains of carriers of the type 4 allele of the apolipoprotein E gene. HSV1 is a dsDNA virus but it has genes on both strands of the genome, and from these genes complementary RNA molecules are transcribed. These could activate BACE1 expression by the PKR pathway. Here we demonstrate in HSV1-infected neuroblastoma cells, and in peripheral nervous tissue from HSV1-infected mice, that HSV1 activates PKR. Cloning BACE1 5′UTR upstream of a luciferase (luc) gene confirmed its inhibitory effect, which can be prevented by salubrinal, an inhibitor of the eIF2-alpha phosphatase PP1c. Treatment with the dsRNA analog poly (I∶C) mimicked the stimulatory effect exerted by salubrinal over BACE1 translation in the 5′UTR-luc construct and increased Aß production in HEK-APPsw cells. Summarizing, our data suggest that PKR activated in brain by HSV1 could play an important role in the development of AD

Extracellular Vesicles Derived from Young Neural Cultures Attenuate Astrocytic Reactivity In Vitro

Extracellular vesicles (EVs) play an important role in intercellular communication and are involved in both physiological and pathological processes. In the central nervous system (CNS), EVs secreted from different brain cell types exert a sundry of functions, from modulation of astrocytic proliferation and microglial activation to neuronal protection and regeneration. However, the effect of aging on the biological functions of neural EVs is poorly understood. In this work, we studied the biological effects of small EVs (sEVs) isolated from neural cells maintained for 14 or 21 days in vitro (DIV). We found that EVs isolated from 14 DIV cultures reduced the extracellular levels of lactate dehydrogenase (LDH), the expression levels of the astrocytic protein GFAP, and the complexity of astrocyte architecture suggesting a role in lowering the reactivity of astrocytes, while EVs produced by 21 DIV cells did not show any of the above effects. These results in an in vitro model pave the way to evaluate whether similar results occur in vivo and through what mechanisms

The pathophysiology of triose phosphate isomerase dysfunction in Alzheimer’s disease

Alzheimer’s disease (AD), the most prevalent neurodegenerative disease worldwide, has two main hallmarks: extracellular deposits of amyloid ß- peptide (Aß) and intracellular neurofibrillary tangles composed by tau protein. Most AD cases are sporadic and are not dependent on known genetic causes; aging is the major risk factor for AD. Therefore, the oxidative stress has been proposed to initiate the uncontrolled increase in Aß production and also to mediate the Aß’s deleterious effects on brain cells, especially on neurons from the cortex and hippocampus. The production of free radicals in the presence of nitric oxide (NO) yields to the peroxynitrite generation, a very reactive agent that nitrotyrosinates the proteins irreversibly. The nitrotyrosination produces a loss of protein physiological functions, contributing to accelerate AD progression. One of the most nitrotyrosinated proteins in AD is the enzyme triosephosphate isomerase (TPI) that isomerises trioses, regulating glucose consumption by both phosphate pentose and glycolytic pathways and thereby pyruvate production. Hence, any disturbance in the glucose supply could affect the proper brain function, considering that the brain has a high rate of glucose consumption. Besides this directly affecting to the energetic metabolism of the neurons, TPI modifications, such as mutation or nitrotyrosination, increase methylglyoxal production, a toxic precursor of advanced glycated end-products (AGEs) and responsible for protein glycation. Moreover, nitro-TPI aggregates interact with tau protein inducing the intraneuronal aggregation of tau. Here we review the relationship between modified TPI and AD, highlighting the relevance of this protein in AD pathology and the consequences of protein nitro-oxidative modifications

Tspan6 does not affect synapse formation and maturation <i>in vitro</i> and <i>in vivo</i>.

<p><b>(A)</b>Representative images from WT and <i>Tspan6</i> KO hippocampal primary neurons transfected with EGFP and fixed after 14 days <i>in vitro</i> (scale bar = 20 μm). Right panels show box sections in higher magnification (scale bar = 10μm). 15 neurons and more than 90 dendritic sections were examined from 3 independent cultures. Only spines more than 80μm from the soma were analyzed. Histograms compare mean (±S.E.M) filopodia and spine density (number/10μm of dendrite). <b>(B)</b> Golgi staining of 100 μm coronal sections from 10 month-old <i>Tspan6</i> KO and WT mice. Scale bar = 100 μm. <b>(C)</b> Representative images of dendritic spines from basal secondary dendrites from CA1 hippocampal neurons and the IMARIS reconstruction to analyze spine morphology. Scale bar = 5μm. Histograms compare mean (±S.E.M) spine density (number/10μm of dendrite) <b>(D)</b>, length <b>(E)</b> and head width <b>(F)</b> between Tspan6 KO and WT mice. <i>n</i> = 19 to 22 neurons from 3 different mice.</p