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Progressive accumulation of Amyloid-β (Aβ) deposits in the brain is a characteristic neuropathological hallmark of Alzheimer's disease (AD). During disease progression, extracellular Aβ plaques undergo specific changes in their composition by the sequential deposition of different modified Aβ species. Microglia are implicated in the restriction of amyloid deposits and play a major role in internalization and degradation of Aβ. Recent studies showed that rare variants of the Triggering Receptor Expressed on Myeloid cells 2 (TREM2) are associated with an increased risk for AD. Post-translational modifications of Aβ could modulate the interaction with TREM2, and the uptake by microglia. Here, we demonstrate that genetic deletion of TREM2 or expression of a disease associated TREM2 variant in mice lead to differential accumulation of modified and non-modified Aβ species in extracellular plaques and intraneuronal deposits. Human brains with rare TREM2 AD risk variants also showed altered deposition of modified Aβ species in the different brain lesions as compared to cases with the common variant of TREM2. These findings indicate that TREM2 plays a critical role in the development and the composition of Aβ deposits, not only in extracellular plaques, but also intraneuronally, that both could contribute to the pathogenesis of AD., (© 2021. The Author(s).)

Alzheimer disease (AD) is characterized by the accumulation of amyloid plaques, which are predominantly composed of amyloid-β peptide. Two principal physiological pathways either prevent or promote amyloid-β generation from its precursor, β-amyloid precursor protein (APP), in a competitive manner. Although APP processing has been studied in great detail, unknown proteolytic events seem to hinder stoichiometric analyses of APP metabolism in vivo. Here we describe a new physiological APP processing pathway, which generates proteolytic fragments capable of inhibiting neuronal activity within the hippocampus. We identify higher molecular mass carboxy-terminal fragments (CTFs) of APP, termed CTF-η, in addition to the long-known CTF-α and CTF-β fragments generated by the α- and β-secretases ADAM10 (a disintegrin and metalloproteinase 10) and BACE1 (β-site APP cleaving enzyme 1), respectively. CTF-η generation is mediated in part by membrane-bound matrix metalloproteinases such as MT5-MMP, referred to as η-secretase activity. η-Secretase cleavage occurs primarily at amino acids 504-505 of APP695, releasing a truncated ectodomain. After shedding of this ectodomain, CTF-η is further processed by ADAM10 and BACE1 to release long and short Aη peptides (termed Aη-α and Aη-β). CTFs produced by η-secretase are enriched in dystrophic neurites in an AD mouse model and in human AD brains. Genetic and pharmacological inhibition of BACE1 activity results in robust accumulation of CTF-η and Aη-α. In mice treated with a potent BACE1 inhibitor, hippocampal long-term potentiation was reduced. Notably, when recombinant or synthetic Aη-α was applied on hippocampal slices ex vivo, long-term potentiation was lowered. Furthermore, in vivo single-cell two-photon calcium imaging showed that hippocampal neuronal activity was attenuated by Aη-α. These findings not only demonstrate a major functionally relevant APP processing pathway, but may also indicate potential translational relevance for therapeutic strategies targeting APP processing.

Alzheimer's disease (AD) is thought to be caused by accumulation of amyloid-β protein (Aβ), which is a cleavage product of amyloid precursor protein (APP). Transgenic mice overexpressing APP have been used to recapitulate amyloid-β pathology. Among them, APP23 and APPswe/PS1deltaE9 (deltaE9) mice are extensively studied. APP23 mice express APP with Swedish mutation and develop amyloid plaques late in their life, while cognitive deficits are observed in young age. In contrast, deltaE9 mice with mutant APP and mutant presenilin-1 develop amyloid plaques early but show typical cognitive deficits in old age. To unveil the reasons for different progressions of cognitive decline in these commonly used mouse models, we analyzed the number and turnover of dendritic spines as important structural correlates for learning and memory. Chronic in vivo two-photon imaging in apical tufts of layer V pyramidal neurons revealed a decreased spine density in 4-5-month-old APP23 mice. In age-matched deltaE9 mice, in contrast, spine loss was only observed on cortical dendrites that were in close proximity to amyloid plaques. In both cases, the reduced spine density was caused by decreased spine formation. Interestingly, the patterns of alterations in spine morphology differed between these two transgenic mouse models. Moreover, in APP23 mice, APP was found to accumulate intracellularly and its content was inversely correlated with the absolute spine density and the relative number of mushroom spines. Collectively, our results suggest that different pathological mechanisms, namely an intracellular accumulation of APP or extracellular amyloid plaques, may lead to spine abnormalities in young adult APP23 and deltaE9 mice, respectively. These distinct features, which may represent very different mechanisms of synaptic failure in AD, have to be taken into consideration when translating results from animal studies to the human disease.

Microtubule dynamics in neurons play critical roles in physiology, injury and disease and determine microtubule orientation, the cell biological correlate of neurite polarization. Several microtubule binding proteins, including end-binding protein 3 (EB3), specifically bind to the growing plus tip of microtubules. In the past, fluorescently tagged end-binding proteins have revealed microtubule dynamics in vitro and in non-mammalian model organisms. Here, we devise an imaging assay based on transgenic mice expressing yellow fluorescent protein-tagged EB3 to study microtubules in intact mammalian neurites. Our approach allows measurement of microtubule dynamics in vivo and ex vivo in peripheral nervous system and central nervous system neurites under physiological conditions and after exposure to microtubule-modifying drugs. We find an increase in dynamic microtubules after injury and in neurodegenerative disease states, before axons show morphological indications of degeneration or regrowth. Thus increased microtubule dynamics might serve as a general indicator of neurite remodelling in health and disease.

Sensory experience alters neuronal circuits, which is believed to form the basis for learning and memory. On a microscopic level, structural changes of the neuronal network are prominently observable as experience-dependent addition and removal of cortical dendritic spines. By environmental enrichment, we here applied broad sensory stimulation to mice and followed the consequences to dendritic spines in the somatosensory cortex utilizing in vivo microscopy. Additionally to apical dendrites of layer V neurons, which are typically analyzed in in vivo imaging experiments, we investigated basal dendrites of layer II/III neurons and describe for the first time experience-dependent alterations on this population of dendrites. On both classes of cortical dendrites, enriched environment-induced substantial changes determined by increases in density and turnover of dendritic spines. Previously established spines were lost after enriched stimulation. A fraction of experience-induced gained spines survived for weeks, which might therefore be functionally integrated into the neuronal network. Furthermore, we observed an increased density of spines that appeared only transiently. Together, we speculate that the cognitive benefits seen in environmental-enriched animals might be a consequence of both, a higher connectivity of the neuronal network due to more established synapses and an enhanced flexibility due to more transient spines.

β1-class integrins play essential roles both in developmental biology as well as in cancer. Particularly, a Nestin-driven deletion of β1-integrin receptors results in severe abnormalities of brain development including a laminar disorganization of cerebellar granule neurons. However, since Nestin is expressed in all kinds of neural precursors, these data do not allow conclusions to be drawn about the role of β1-integrins in distinct neuronal and glial cell types. By generating conditional knockout mice using granule cell-specific Math1-promoter sequences, we show here that the expression of β1-integrins in granule neurons is dispensable for the development of the cerebellum. Also, deletion of β1-integrin from tumors that arise in a mouse model of granule cell precursor-derived medulloblastoma did not result in a significant survival benefit. Last, expression levels of β1-integrin in human medulloblastoma samples did not predict patient's outcome. However, a β1-integrin knockout using hGFAP-promoter sequences led to cerebellar hypoplasia, inappropriate positioning of Bergmann glia cells in the molecular layer, undirected outgrowth of radial glia fibers, and granule cell ectopia. We therefore conclude that β1-integrin expression in cerebellar granule neurons is not essential during normal development or medulloblastoma formation. In fact, it is the expression of β1-integrin in glia that is crucial for the proper development of the cerebellar cortex., (Copyright © 2012 Wiley Periodicals, Inc.)

Numerous loss-of-function mutations in the progranulin (GRN) gene cause frontotemporal lobar degeneration with ubiquitin and TAR-DNA binding protein 43-positive inclusions by reduced production and secretion of GRN. Consistent with the observation that GRN has neurotrophic properties, pharmacological stimulation of GRN production is a promising approach to rescue GRN haploinsufficiency and prevent disease progression. We therefore searched for compounds capable of selectively increasing GRN levels. Here, we demonstrate that four independent and highly selective inhibitors of vacuolar ATPase (bafilomycin A1, concanamycin A, archazolid B, and apicularen A) significantly elevate intracellular and secreted GRN. Furthermore, clinically used alkalizing drugs, including chloroquine, bepridil, and amiodarone, similarly stimulate GRN production. Elevation of GRN levels occurs via a translational mechanism independent of lysosomal degradation, autophagy, or endocytosis. Importantly, alkalizing reagents rescue GRN deficiency in organotypic cortical slice cultures from a mouse model for GRN deficiency and in primary cells derived from human patients with GRN loss-of-function mutations. Thus, alkalizing reagents, specifically those already used in humans for other applications, and vacuolar ATPase inhibitors may be therapeutically used to prevent GRN-dependent neurodegeneration.

Microglia, the immune cells of the brain, can have a beneficial effect in Alzheimer's disease by phagocytosing amyloid-beta. Two-photon in vivo imaging of neuron loss in the intact brain of living Alzheimer's disease mice revealed an involvement of microglia in neuron elimination, indicated by locally increased number and migration velocity of microglia around lost neurons. Knockout of the microglial chemokine receptor Cx3cr1, which is critical in neuron-microglia communication, prevented neuron loss.

One of the strongest anatomical correlates of the degree of clinical impairment in Alzheimer's disease is a decrease in synaptic density. A detailed understanding of the pathophysiological mechanism operating at a synaptic level remains incomplete, in particular whether the pre- or the post-synaptic compartment is initially involved. Here, we studied synaptic transmission in autaptic hippocampal cultures from a double-transgenic mouse model (APPPS1, APP(swe) and PS1(L166P)) and a single-mutant APP transgenic model (APP23, APPswe). APPPS1 neurons revealed significantly reduced amplitudes of evoked AMPA- and NMDA-receptor-mediated excitatory post-synaptic currents, whereas the amplitudes of spontaneous miniature synaptic responses were not altered. The size of the readily releasable synaptic vesicle pool was also decreased, whereas the release probability was not affected. Morphometric immunohistochemical analysis showed a reduction in synaptophysin-positive puncta. In contrast, we did not identify any alterations in synaptic transmission in neurons derived from single APP(swe) transgenic mice. Taken together, our findings suggest that cultured neurons of APPPS1 double-transgenic mice have a significantly reduced number of functional excitatory synapses.

Mutations in presenilins are the major cause of familial Alzheimer disease, but the precise pathogenic mechanism by which presenilin (PS) mutations cause synaptic dysfunction leading to memory loss and neurodegeneration remains unclear. Using autaptic hippocampal cultures from transgenic mice expressing human PS1 with the A246E mutation, we demonstrate that mutant PS1 significantly depressed the amplitude of evoked alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid and N-methyl-D-aspartate receptor-mediated synaptic currents. Analysis of the spontaneous miniature synaptic activity revealed a lower frequency of miniature currents but normal miniature amplitude. Both alterations could be rescued by the application of a gamma-secretase blocker. On the other hand, the application of synthetic soluble Abeta42 in wild-type neurons induced the PS1 mutant phenotype on synaptic strength. Together, these findings strongly suggest that the expression of mutant PS1 in cultured neurons depresses synaptic transmission by causing a physical reduction in the number of synapses. This hypothesis is consistent with morphometic and semiquantitative immunohistochemical analysis, revealing a decrease in synaptophysin-positive puncta in PS1 mutant hippocampal neurons.

The physiological function of the cellular prion protein (PrP(C)) is still under intense investigation. It has been suggested that PrP(C) has a protective role in neuronal cells, particularly against environmental stress caused by reactive oxygen species (ROS). Here we analysed the acute effect of a major ROS, hydrogen peroxide (H(2)O(2)), on intracellular calcium homeostasis in cultured cerebellar granule cells and immortalized hippocampal neuronal cells. Both neuronal cell culture models showed that the rise in intracellular calcium following application of H(2)O(2) was strongly dependent on the presence of PrP(C). Moreover, the N-terminal octapeptide repeats of PrP(C) were required for this effect, because neuronal cells expressing a PrP(C) lacking the N-terminus resembled the PrP(C)-deficient phenotype. Neurones deficient of fyn kinase, or pharmacological inhibition of fyn, also abrogated the calcium response to H(2)O(2) treatment, indicating that fyn activation is a critical step within the PrP(C) signalling cascade. Finally, we identified a possible role of this PrP(C) signalling pathway in the neuroprotective response of PrP(C) to oxidative stress. In conclusion, we put forward the hypothesis that PrP(C) functions as a sensor for H(2)O(2), thereby activating a protective signalling cascade involving fyn kinase that leads to calcium release from intracellular stores.

Previous neurophysiological studies on prion protein deficient (Prnp(-/-)) mice have revealed a significant reduction of slow afterhyperpolarization currents (sI(AHP)) in hippocampal CA1 pyramidal cells. Here we aim to determine whether loss of PrP(C.) directly affects the potassium channels underlying sI(AHP) or if sI(AHP) is indirectly disturbed by altered intracellular Ca(2+) fluxes. Patch-clamp measurements and confocal Ca(2+) imaging in acute hippocampal slice preparations of Prnp(-/-) mice compared to littermate control mice revealed a reduced Ca(2+) rise in CA1 neurons lacking PrP(C) following a depolarization protocol known to induce sI(AHP). Moreover, we observed a reduced Ca(2+) influx via l-type voltage gated calcium channels (VGCCs). No differences were observed in the protein expression of the pore forming alpha1 subunit of VGCCs Prnp(-/-) mice. Surprisingly, the beta2 subunit, critically involved in the transport of the alpha1 subunit to the plasma membrane, was found to be up-regulated in knock out hippocampal tissue. On mRNA level however, no differences could be detected for the alpha1C, D and beta2-4 subunits. In conclusion our data support the notion that lack of PrP(C.) does not directly affect the potassium channels underlying sI(AHP), but modulates these channels due to its effect on the intracellular free Ca(2+) concentration via a reduced Ca(2+) influx through l-type VGCCs.

The cellular prion protein (PrP(C)) is thought to be involved in protection against cell death, however the exact cellular mechanisms involved are still controversial. Herein we present data that strongly indicate a functional link between PrP(C) expression and phosphatidylinositol 3-kinase (PI 3-kinase) activation, a protein kinase that plays a pivotal role in cell survival. Both mouse neuroblastoma N2a cells and immortalized murine hippocampal neuronal cell lines expressing wild-type PrP(C) had significantly higher PI 3-kinase activity levels than their respective controls. Moreover, PI 3-kinase activity was found to be elevated in brain lysates from wild-type mice, as compared to prion protein-knockout mice. Recruitment of PI 3-kinase by PrP(C) was shown to contribute to cellular survival toward oxidative stress by using 3-morpholinosydnonimine (SIN-1) and serum deprivation. Moreover, both PI 3-kinase activation and cytoprotection by PrP(C) appeared to rely on copper binding to the N-terminal octapeptide of PrP(C). Thus, we propose a model in which the interaction of copper(II) with the N-terminal domain of PrP(C) enables transduction of a signal to PI 3-kinase; the latter, in turn, mediates downstream regulation of cell survival.

The prion protein (PrPC) has a primary role in the pathogenesis of transmissible spongiform encephalopathies. Here we analysed in detail the effect of recombinant PrPC and N- and C-terminal fragments of PrPC on the whole-cell current amplitude through voltage-gated calcium channels (VGCCs) of cultured wild-type cerebellar granule cells. With the application of full-length recombinant PrPC (50-500 nm), a highly significant reduction of the whole-cell current amplitude was observed in a dose-dependent manner. Amplitude reduction was abolished when cells were pre-incubated with nifedipine, a specific blocker of voltage-gated L-type calcium channels. N-terminal PrP fragments also led to a dose-dependent reduction of the maximal current amplitude, whereas a C-terminal fragment did not affect the current amplitude. These data demonstrate that nanomolar concentrations of PrPC modulate L-type VGCCs in mouse cerebellar granule cells, an effect that is dependent upon the copper-binding amino-terminal domain of PrPC.

The pathogenesis underlying the typical findings in Creutzfeldt-Jakob disease (CJD) such as periodic EEG changes or myoclonus is not fully understood. The thalamus possesses a high density of inhibitory neurones and serves as a crucial pacemaker of rhythmic EEG activity. As inhibitory neurones expressing parvalbumin (PV) are reduced in the cerebral cortex and hippocampus in sporadic CJD (sCJD), we studied the distribution and number of PV-immunoreactive neurones in sCJD thalami in order to determine whether damage to them could account for certain clinical findings. Immuno histochemical analysis was performed on the thalami from 21 sCJD patients and five controls. The number of PV+ neurones was counted in the thalamic nuclei and compared with clinical and molecular findings. In sCJD patients, PV+ neurones were significantly reduced in the ventrolateral posterior (VLp), ventrolateral anterior (VLa), anteroventral (AV), lateral dorsal (LD), mediodorsal (MD) and reticular (Re) thalamic nuclei (P < 0.05). The VLp was especially damaged in sCJD patients with homozygosity for methionine at codon 129 and scrapie prion protein (PrP(Sc)) type 1. Patients with typical EEG changes [periodic sharp wave complexes (PSWCs)] and myoclonus had a predominant loss of PV+ cells in the reticular thalamic nucleus. In conclusion, our data support the hypothesis that the damage to PV-immunoreactive neurones determines the generation of certain typical clinical features of CJD, i.e. PSWCs associated with myoclonus.

Objectives: To identify the clinical characteristics of the subgroup of benign progressive supranuclear palsy with particularly long disease duration; to define neuropathological determinants underlying variability in disease duration in progressive supranuclear palsy.Methods: Clinical and pathological features were compared among 186 autopsy-confirmed cases with progressive supranuclear palsy with ≥10 years and shorter survival times.Results: The 45 cases (24.2%) had a disease duration of ≥10 years. The absence of ocular motor abnormalities within the first 3 years from disease onset was the only significant independent clinical predictor of longer survival. Histopathologically, the neurodegeneration parameters in each survival group were paralleled anatomically by the distribution of neuronal cytoplasmic inclusions, whereas the tufted astrocytes displayed anatomically an opposite severity pattern. Most interestingly, we found significantly less coiled bodies in those who survive longer, in contrast to patients with less favorable course.Interpretation: A considerable proportion of patients had a more "benign" disease course with ≥10 years survival. They had a distinct pattern and evolution of core symptoms compared to patients with short survival. The inverted anatomical patterns of astrocytic tau distribution suggest distinct implications of these cell types in trans-cellular propagation. The tempo of disease progression appeared to be determined mostly by oligodendroglial tau, where the high degree of oligodendroglial tau pathology might affect neuronal integrity and function on top of neuronal tau pathology. The relative contribution of glial tau should be further explored in cellular and animal models. ANN NEUROL 2022;92:637-649. [ABSTRACT FROM AUTHOR]

Pathological alterations of tau protein play a significant role in the emergence and progression of neurodegenerative disorders. Tauopathies are characterized by detachment of the tau protein from neuronal microtubules, and its subsequent aberrant hyperphosphorylation, aggregation and cellular distribution. The exact nature of tau protein species causing neuronal malfunction and degeneration is still unknown. In the present study, we used mice transgenic for human tau with the frontotemporal dementia with parkinsonism-associated P301S mutation. These mice are prone to develop fibrillar tau inclusions, especially in the spinal cord and brainstem. At the same time, cortical neurons are not as strongly affected by fibrillar tau forms, but rather by soluble tau forms. We took advantage of the possibility to induce formation of neurofibrillary tangles in a subset of these cortical neurons by local injection of preformed synthetic tau fibrils. By using chronic in vivo two-photon calcium imaging in awake mice, we were able for the first time to follow the activity of individual tangle-bearing neurons and compare it to the activity of tangle-free neurons over the disease course. Our results revealed strong reduction of calcium transient frequency in layer 2/3 cortical neurons of P301S mice, independent of neurofibrillary tangle presence. These results clearly point to the impairing role of soluble, mutated tau protein species present in the majority of the neurons investigated in this study. [ABSTRACT FROM AUTHOR]

Tcf4 is a transcription factor which regulates neurogenesis and neuronal migration in the brain. In humans, loss of function of Tcf4 leads to the rare neurodevelopmental disorder Pitt-Hopkins syndrome, which is characterized by intellectual disability, developmental delay and autistic behavior. We analyzed the consequences of functional loss of Tcf4 on dendritic spines in mature principal neurons. To this end, we crossed mice in which the DNA-binding domain of the Tcf4 gene is flanked by LoxP sites to mice expressing tamoxifen-inducible cre recombinase in a sparse subset of fluorescently labelled neurons (SlickV line). This resulted in a mouse model with an inducible functional knockout of Tcf4 in a subset of cortical and hippocampal neurons, in which we analyzed dendritic spines, which are the morphological correlate of excitatory postsynapses. Heterozygous as well as homozygous loss of Tcf4 led to a reduction in the number of dendritic spines in the cortex as well as in the hippocampus. This was accompanied by morphological changes of dendritic spines. These results suggest that Tcf4 is involved in synaptic plasticity in mature neurons, and functional loss of Tcf4 may contribute to the neurological symptoms in Pitt-Hopkins syndrome. [ABSTRACT FROM AUTHOR]

The pathology of Alzheimer's disease (AD) is characterized by the accumulation of amyloid-β (Aβ) peptide, hyperphosphorylated tau protein, neuronal death, and synaptic loss. By means of long-term two-photon in vivo imaging and confocal imaging, we characterized the spatio-temporal pattern of dendritic spine loss for the first time in 3xTg-AD mice. These mice exhibit an early loss of layer III neurons at 4 months of age, at a time when only soluble Aβ is abundant. Later on, dendritic spines are lost around amyloid plaques once they appear at 13 months of age. At the same age, we observed spine loss also in areas apart from amyloid plaques. This plaque independent spine loss manifests exclusively at dystrophic dendrites that accumulate both soluble Aβ and hyperphosphorylated tau intracellularly. Collectively, our data shows that three spatiotemporally independent events contribute to a net loss of dendritic spines. These events coincided either with the occurrence of intracellular soluble or extracellular fibrillar Aβ alone, or the combination of intracellular soluble Aβ and hyperphosphorylated tau. [ABSTRACT FROM AUTHOR]

Discusses the measurement of the intracellular free Ca[sup 2+] concentration in hippocampal neurons from six different combinations of transgenic and geneablated mice to demonstrate that mutant presenilin-1 attenuated capacitive calcium entry (CCE) directly, independent of the expression of the amyloid precursor protein (APP). Direct attenuation of CCE; Indirect increase of endoplasmic reticulum (ER)-calcium stores.

Abstract: Previous studies have indicated that recombinant cellular prion protein (PrPC), as well as a synthetic peptide of PrPC, affects intracellular calcium homeostasis. To analyze whether calcium homeostasis in neurons is also affected by a loss of PrPC, we performed microfluorometric calcium measurements on cultured cerebellar granule cells derived from prion protein-deficient (Prnp0/0) mice. The resting concentration of intracellular free calcium ([Ca2+]i) was found to be slightly, but significantly, reduced in Prnp0/0 mouse granule cell neurites. Moreover, we observed a highly significant reduction in the [Ca2+]i increase after high potassium depolarization. Pharmacological studies further revealed that the L-type specific blocker nifedipine, which reduces the depolarization-induced [Ca2+]i increase by 66% in wild-type granule cell somas, has no effect on [Ca2+]i in Prnp0/0 mouse granule cells. Patch-clamp measurements, however, did not reveal a reduced calcium influx through voltage-gated calcium channels in Prnp0/0 mice. These data clearly indicate that loss of PrPC alters the intracellular calcium homeostasis of cultured cerebellar granule cells. There is no evidence, though, that this change is due to a direct alteration of voltage-gated calcium channels. [ABSTRACT FROM AUTHOR]

The amyloid precursor protein (APP) is critical in the pathogenesis of Alzheimer's disease. The question of its normal biological function in neurons, in which it is predominantly located at synapses, is still unclear. Using autaptic cultures of hippocampal neurons, we demonstrate that hippocampal neurons lacking APP show significantly enhanced amplitudes of evoked AMPA- and NMDA-receptor-mediated EPSCs. The size of the readily releasable synaptic vesicle pool was also increased in neurons lacking APP, whereas the release probability was not affected. In addition, the analysis of spontaneous miniature synaptic currents revealed an augmented frequency in neurons lacking APP, whereas the amplitude of miniature synaptic currents was not found to be altered. Together, these findings strongly indicate that lack of APP increases the number of functional synapses. This hypothesis is further supported by morphometric immunohistochemical analysis revealing an increase of synaptophysin-positive puncta per cultured APP knock-out neuron. In conclusion, lack of APP affects synapse formation and transmission in cultured hippocampal neurons. [ABSTRACT FROM AUTHOR]

Background BACE1 (beta site amyloid precursor protein cleaving enzyme 1) is the rate limiting protease in amyloid β production, hence a promising drug target for the treatment of Alzheimer’s disease. Inhibition of BACE1, as the major β-secretase in vivo with multiple substrates, however is likely to have mechanism-based adverse effects. We explored the impact of long-term pharmacological inhibition of BACE1 on dendritic spine dynamics, synaptic functions, and cognitive performance of adult mice. Methods Sandwich enzyme-linked immunosorbent assay was used to assess Aβ40 levels in brain and plasma after oral administration of BACE1 inhibitors SCH1682496 or LY2811376. In vivo two-photon microscopy of the somatosensory cortex was performed to monitor structural dynamics of dendritic spines while synaptic functions and plasticity were measured via electrophysiological recordings of excitatory postsynaptic currents and hippocampal long-term potentiation in brain slices. Finally, behavioral tests were performed to analyze the impact of pharmacological inhibition of BACE1 on cognitive performance. Results Dose-dependent decrease of Aβ40 levels in vivo confirmed suppression of BACE1 activity by both inhibitors. Prolonged treatment caused a reduction in spine formation of layer V pyramidal neurons, which recovered after withdrawal of inhibitors. Congruently, the rate of spontaneous and miniature excitatory postsynaptic currents in pyramidal neurons and hippocampal long-term potentiation were reduced in animals treated with BACE1 inhibitors. These effects were not detected in Bace1 −/− mice treated with SCH1682496, confirming BACE1 as the pharmacological target. Described structural and functional changes were associated with cognitive deficits as revealed in behavioral tests. Conclusions Our findings indicate important functions to BACE1 in structural and functional synaptic plasticity in the mature brain, with implications for cognition. [ABSTRACT FROM AUTHOR]