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Objective: Metabolic syndrome, obesity, and steatosis are characterized by a range of dysregulations including defects in ubiquitin ligase tagging proteins for degradation. The identification of novel hepatic genes associated with fatty liver disease and metabolic dysregulation may be relevant to unravelling new mechanisms involved in liver disease progression Methods: Through integrative analysis of liver transcriptomic and metabolomic obtained from obese subjects with steatosis, we identified itchy E ubiquitin protein ligase (ITCH) as a gene downregulated in human hepatic tissue in relation to steatosis grade. Wild-type or ITCH knockout mouse models of non-alcoholic fatty liver disease (NAFLD) and obesity-related hepatocellular carcinoma were analyzed to dissect the causal role of ITCH in steatosis Results: We show that ITCH regulation of branched-chain amino acids (BCAAs) degradation enzymes is impaired in obese women with grade 3 compared with grade 0 steatosis, and that ITCH acts as a gatekeeper whose loss results in elevation of circulating BCAAs associated with hepatic steatosis. When ITCH expression was specifically restored in the liver of ITCH knockout mice, ACADSB mRNA and protein are restored, and BCAA levels are normalized both in liver and plasma Conclusions: Our data support a novel functional role for ITCH in the hepatic regulation of BCAA metabolism and suggest that targeting ITCH in a liver-specific manner might help delay the progression of metabolic hepatic diseases and insulin resistance.

BACE1 (beta-site amyloid precursor protein cleaving enzyme 1) was initially cloned and characterized in 1999. It is required for the generation of all monomeric forms of amyloid-β (Aβ), including Aβ42, which aggregates into bioactive conformational species and likely initiates toxicity in Alzheimer's disease (AD). BACE1 concentrations and rates of activity are increased in AD brains and body fluids, thereby supporting the hypothesis that BACE1 plays a critical role in AD pathophysiology. Therefore, BACE1 is a prime drug target for slowing down Aβ production in early AD. Besides the amyloidogenic pathway, BACE1 has other substrates that may be important for synaptic plasticity and synaptic homeostasis. Indeed, germline and adult conditional BACE1 knockout mice display complex neurological phenotypes. Despite BACE1 inhibitor clinical trials conducted so far being discontinued for futility or safety reasons, BACE1 remains a well-validated therapeutic target for AD. A safe and efficacious compound with high substrate selectivity as well as a more accurate dose regimen, patient population, and disease stage may yet be found. Further research should focus on the role of Aβ and BACE1 in physiological processes and key pathophysiological mechanisms of AD. The functions of BACE1 and the homologue BACE2, as well as the biology of Aβ in neurons and glia, deserve further investigation. Cellular and molecular studies of BACE1 and BACE2 knockout mice coupled with biomarker-based human research will help elucidate the biological functions of these important enzymes and identify their substrates and downstream effects. Such studies will have critical implications for BACE1 inhibition as a therapeutic approach for AD. ispartof: BIOLOGICAL PSYCHIATRY vol:89 issue:8 pages:745-756 ispartof: location:United States status: published

Neuroinflammation commences decades before Alzheimer's disease (AD) clinical onset and represents one of the earliest pathomechanistic alterations throughout the AD continuum. Large-scale genome-wide association studies point out several genetic variants—TREM2, CD33, PILRA, CR1, MS4A, CLU, ABCA7, EPHA1, and HLA-DRB5-HLA-DRB1—potentially linked to neuroinflammation. Most of these genes are involved in proinflammatory intracellular signaling, cytokines/interleukins/cell turnover, synaptic activity, lipid metabolism, and vesicle trafficking. Proteomic studies indicate that a plethora of interconnected aberrant molecular pathways, set off and perpetuated by TNF-α, TGF-β, IL-1β, and the receptor protein TREM2, are involved in neuroinflammation. Microglia and astrocytes are key cellular drivers and regulators of neuroinflammation. Under physiological conditions, they are important for neurotransmission and synaptic homeostasis. In AD, there is a turning point throughout its pathophysiological evolution where glial cells sustain an overexpressed inflammatory response that synergizes with amyloid-β and tau accumulation, and drives synaptotoxicity and neurodegeneration in a self-reinforcing manner. Despite a strong therapeutic rationale, previous clinical trials investigating compounds with anti-inflammatory properties, including non-steroidal anti-inflammatory drugs (NSAIDs), did not achieve primary efficacy endpoints. It is conceivable that study design issues, including the lack of diagnostic accuracy and biomarkers for target population identification and proof of mechanism, may partially explain the negative outcomes. However, a recent meta-analysis indicates a potential biological effect of NSAIDs. In this regard, candidate fluid biomarkers of neuroinflammation are under analytical/clinical validation, i.e., TREM2, IL-1β, MCP-1, IL-6, TNF-α receptor complexes, TGF-β, and YKL-40. PET radio-ligands are investigated to accomplish in vivo and longitudinal regional exploration of neuroinflammation. Biomarkers tracking different molecular pathways (body fluid matrixes) along with brain neuroinflammatory endophenotypes (neuroimaging markers), can untangle temporal–spatial dynamics between neuroinflammation and other AD pathophysiological mechanisms. Robust biomarker–drug codevelopment pipelines are expected to enrich large-scale clinical trials testing new-generation compounds active, directly or indirectly, on neuroinflammatory targets and displaying putative disease-modifying effects: novel NSAIDs, AL002 (anti-TREM2 antibody), anti-Aβ protofibrils (BAN2401), and AL003 (anti-CD33 antibody). As a next step, taking advantage of breakthrough and multimodal techniques coupled with a systems biology approach is the path to pursue for developing individualized therapeutic strategies targeting neuroinflammation under the framework of precision medicine., Sorbonne University Foundation and sponsored by la Fondation pour la Recherche sur Alzheimer. HH is an employee of Eisai Inc. During his previous work (until April 2019), he was supported by the AXA Research Fund, the Fondation partenariale Sorbonne Université and the Fondation pour la Recherche sur Alzheimer, Paris, France

International audience; AbstractMounting evidence suggests that the nervous and immune systems are intricately linked. Many proteins first identified in the immune system have since been detected at synapses, playing different roles in normal and pathological situations. In addition, novel immunological functions are emerging for proteins typically expressed at synapses. Under normal conditions, release of inflammatory mediators generally represents an adaptive and regulated response of the brain to immune signals. On the other hand, when immune challenge becomes prolonged and/or uncontrolled, the consequent inflammatory response leads to maladaptive synaptic plasticity and brain disorders. In this review, we will first provide a summary of the cell signaling pathways in neurons and immune cells. We will then examine how immunological mechanisms might influence synaptic function, and in particular synaptic plasticity, in the healthy and pathological CNS. A better understanding of neuro-immune system interactions in brain circuitries relevant to neuropsychiatric and neurological disorders should provide specific biomarkers to measure the status of the neuroimmunological response and help design novel neuroimmune-targeted therapeutics.

Parvalbumin (PV)-positive interneurons modulate cortical activity through highly specialized connectivity patterns onto excitatory pyramidal neurons (PNs) and other inhibitory cells. PV cells are autoconnected through powerful autapses, but the contribution of this form of fast disinhibition to cortical function is unknown. We found that autaptic transmission represents the most powerful inhibitory input of PV cells in neocortical layer V. Autaptic strength was greater than synaptic strength onto PNs as a result of a larger quantal size, whereas autaptic and heterosynaptic PV-PV synapses differed in the number of release sites. Overall, single-axon autaptic transmission contributed to approximately 40% of the global inhibition (mostly perisomatic) that PV interneurons received. The strength of autaptic transmission modulated the coupling of PV-cell firing with optogenetically induced γ-oscillations, preventing high-frequency bursts of spikes. Autaptic self-inhibition represents an exceptionally large and fast disinhibitory mechanism, favoring synchronization of PV-cell firing during cognitive-relevant cortical network activity., Parvalbumin-positive interneurons modulate cortical activity via highly specialized connections to excitatory pyramidal neurons and other inhibitory cells. However, this study shows that fast autaptic self-inhibition is the major output of parvalbumin-positive basket cells in the neocortex and serves to modulate phase-locking of these interneurons during gamma-oscillations.

Introduction The longitudinal trajectories of functional brain dynamics and the impact of genetic risk factors in individuals at risk for Alzheimer's disease are poorly understood. Methods In a large-scale monocentric cohort of 224 amyloid stratified individuals at risk for Alzheimer's disease, default mode network (DMN) resting state functional connectivity (FC) was investigated between two serial time points across 2 years. Results Widespread DMN FC changes were shown in frontal and posterior areas, as well as in the right hippocampus. There were no cross-sectional differences, however, apolipoprotein E e4 (APOE e4) carriers demonstrated slower increase in FC in frontal lobes. There was no impact of individual brain amyloid load status. Discussion For the first time, we demonstrated that the pleiotropic biological effect of the APOE e4 allele impacts the dynamic trajectory of the DMN during aging. Dynamic functional biomarkers may become useful surrogate outcomes for the development of preclinical targeted therapeutic interventions.

Numerous therapeutic approaches for Duchenne and Becker Muscular Dystrophy (DMD and BMD), the most common X-linked muscle degenerative disease, have been proposed. So far, the only one showing a clear beneficial effect is the use of corticosteroids. Recent evidence indicates an improvement of dystrophic cardiac and skeletal muscles in the presence of sustained cGMP levels secondary to a blocking of their degradation by phosphodiesterase five (PDE5). Due to these data, we performed a study to investigate the effect of the specific PDE5 inhibitor, tadalafil, on dystrophic skeletal muscle function. Chronic pharmacological treatment with tadalafil has been carried out in mdx mice. Behavioral and physiological tests, as well as histological and biochemical analyses, confirmed the efficacy of the therapy. We then performed a microarray-based genomic analysis to assess the pattern of gene expression in muscle samples obtained from the different cohorts of animals treated with tadalafil. This scrutiny allowed us to identify several classes of modulated genes. Our results show that PDE5 inhibition can ameliorate dystrophy by acting at different levels. Tadalafil can lead to (1) increased lipid metabolism; (2) a switch towards slow oxidative fibers driven by the up-regulation of PGC-1; (3) an increased protein synthesis efficiency; (4) a better actin network organization at Z-disk. J. Cell. Physiol. 230: 224-232, 2016. (c) 2015 Wiley Periodicals, Inc.

The hippocampus, in the temporal lobe, is phylogenetically one of the oldest parts of the brain and forms part of the limbic system. The hippocampus proper is defined by the dentate gyrus and Cornu Ammonis (CA). While the dentate gyrus contains the fascia dentata and the hilus, the CA is anatomically and functionally differentiated into distinct subfields named CA1, CA2, CA3, and CA4. The CA3 region has attracted major attention in recent years for its specific role in memory processes, susceptibility to seizures and neuro-degeneration. Internal connectivity in the CA3 subfield is more rich than in other hippocampal regions. Recurrent axon collaterals of CA3 pyramidal cells ramify extensively making excitatory contacts with neighboring excitatory and inhibitory neurons (Lorente de No, 1934). This circuit is implicated in encoding spatial representations (O'Keefe and Nadel, 1978) and episodic memories (Scoville and Milner, 1957). It generates coherent population synchronies, including gamma, theta and sharp-waves, presumed to associate firing in selected assemblies of cells in different behavioral conditions (Buzsaki et al., 1983). The CA3 region receives inputs from the entorhinal cortex either directly via the perforant path or indirectly from the dentate gyrus via the mossy fibers (Amaral and Witter, 1983). Mossy fiber connections made with principal or mossy cells terminate with large boutons (5–8 μm) while those with interneurons are targeted by smaller filopodial extensions. The mossy fiber pathway acts as a high-pass filter that translates densely coded cortical signals to a sparse, specific hippocampal code, essential for memory formation. This e-book aims to highlight recent advances by bringing together experts on the cellular and molecular mechanisms regulating the wiring properties of the CA3 hippocampal microcircuit in both physiological and pathological conditions. The seven reviews and four research articles are organized to follow neuronal information flowing from the dentate gyrus to the CA3 associative network. Firstly, Munster-Wandowski et al. (2013) (Inst. Integrative Neuroanatomy, La Charite, Berlin and Instituto Politecnico Nacional, Mexico City) review recent data showing that MF terminals can transiently release GABA as well as glutamate, both in early post-natal life and after periods of intense activity in adulthood. GABA and glutamate co-release from single identified MF boutons has been recently demonstrated. Mossy fibers apparently form electrical synapses, as well as chemical synapses, with CA3 pyramidal cells potentially permitting a fast excitation to overcome a strong, but delayed, feed-forward inhibition. Since MF axons of dentate granule cells may be generated post-natally, Pedroni et al. (2014) (Dept. Neurosci, SISSA, Trieste and European Brain Research Inst, Rome) studied immature granule cells at P0–P3. At this age, with a clear GABAergic phenotype, granule cells have small somata, few dendritic branches and axons often terminate as growth cones in the CA3 region. Depolarization induces either rudimentary or overshooting sodium spikes and low threshold calcium spikes. Post-synaptic CA3 pyramidal cells participate in spontaneous GDPs driven by synergistic actions of GABA and glutamate. The excitatory actions of GABA released from mossy fiber terminals may be crucial for network synchrony, suggested to refine microcircuits of the CA3 region. Radial glial cells guide migrating CA3 neurons during development. After characterizing signaling molecules and the temporal sequence of hippocampal development, Belvindrah et al. (2014) (INSERM U839, Inst. Fer a Moulin, Paris) review abnormalities of migration linked to human brain malformations: agenesia, lissencephaly, holoprosencephaly, polymicrogyria, heterotopia, and focal cortical dysplasia. Mutations in genes associated with neuronal migration in mouse models result in lamination defects of the CA3 area, a region especially vulnerable to stress and seizure-induced damage. This review links genetic, migration and cellular defects and multiple inherited neurological and psychiatric disorders. An overview of how CA3 neurons process afferent activity from dentate granule cells is provided by Evstratova and Toth (2014) (Dept. Psychiatry and Neuroscience, Universite Laval, Quebec City). They describe how the shape of mossy fiber terminals affects transmission to both CA3 pyramidal cells and interneurons. Transmission exhibits short-term plasticities over different frequencies which vary according to post-synaptic cell type. Granule cells usually fire at 0.01–0.1 Hz, but frequency can increase to 15–50 Hz or even higher when spatial information is coded. At these higher frequencies, glutamate also activates presynaptic autoreceptors, which modulate calcium signaling and release from mossy fiber terminals. These processes, including synaptic plasticity, differ at MF. Lorente de No (1934) suggested that recurrent cortical connections might underly reverberating neuronal discharges as a short-term electrical memory. Le Duigou et al. (2014) (INSERM U112, Inst. du Cerveau et de la Moelle, Paris) review recurrent circuits in the CA3 region. CA3 pyramidal cell axons form an associative network associated with sharp waves and other EEG oscillations as well as epileptiform synchrony. Paired records from CA3 pyramidal cells and interneurons have provided data on synaptic contacts and efficacy within recurrent circuits. Connectivity in the associative recurrent CA3 network seems to be spatially more extensive and sparse than in other sensory cortices possibly facilitating representation coding. Kesner (2013) (Dept. Psychology, Univ. Utah, Salt Lake City) reviews contributions from the CA3 region subfields CA3a, b and c in acquiring and encoding spatial information. Mnemonic functions depend on synaptic interactions of CA3 associative networks, operating as an attractor, with inputs from the dentate gyrus and entorhinal cortex (Kesner and Hunsaker, 2010). Fields CA3a and b encode spatial information in short-term memory and also support retrieval by spatial pattern completion. In contrast, the CA3c field may support pattern separation via interactions with the DG. The output subfields, CA3a and b process information sequentially communicating with the CA1 region via the Schaffer collaterals. Rolls (2013) (Centre for Computational Neuroscience, Univ Oxford and Dept. Computer Science, Univ. Warwick) describes quantitatively how the CA3 region operates and how it contributes to episodic memory. The CA3 system, through its recurrent collateral connections, is presented as a single attractor enabling fast, one trial, associations between any spatial location and an object or reward. A recurrent structure permits memory completion during recall from any subset of acquired links. This theory permits associations between time, objects and rewards to provide the temporal order needed for episodic memory. Neurophysiological tests and supports of the theory are described with novel hypotheses on the advantages of a low recurrent connectivity in CA3. Cerasti and Treves (2013) (Cognitive Neuroscience, SISSA, Trieste, College de France, Paris and Kavli Inst., Trondheim) next discuss how self-organizing recurrent connections enable spatial representations to be acquired in the CA3 area. A simplified network model shows that self-organization can lead to the emergence of multiple loosely organized discrete point-like attractors which differ from structures associated with a single, continuous attractor. The pivotal role of the CA3 region in humans is discussed by Deuker et al. (2014) (Dept. Epileptology and Center for Neurodegenerative Diseases Univ. Bonn and Donders Inst., Univ. Nijmegen). They describe how the human CA3 region forms associations during encoding and how during retrieval it reconstructs memory representations with pattern separation and completion based on partial cues (Deuker et al., 2013). Functional properties of different hippocampal subfields can be identified with high resolution fMRI and related to behavioral, and structural alterations associated with mild cognitive impairment in early Alzheimer's disease. Spatial information is encoded by the phase of principal cell firing during theta oscillations. The hyperpolarization activated cation current Ih is a critical regulator of this phase dependent firing. The research article of Borel et al. (2013) (Dept. Physiology, Development and Neuroscience, Univ. Cambridge and Dept. Brain and Cognitive Engineering, Korea Univ. Seoul) asks how Ih controls firing of CA1 and CA3 pyramidal cells. CA1 neurons are suggested to express Ih at higher levels than CA3 pyramidal cells ensuring larger responses to hyperpolarization and thus more prominent resonance peaks. With a strong Ih, excitatory inputs during theta can delay firing, an effect counteracted by phasic inhibitory currents during theta oscillations. Interactions between synaptic inputs and active Ih currents may then account for distinct phase responses of CA1 and CA3 neurons in temporal outputs during theta oscillations. The final article from Nava-Mesa et al. (2013) (Lab. Neurofisiologia y Comportamiento, Univ. Castilla-La Mancha, Ciudad Real and Dept. Fisiologia y Farmacologia, Univ. Salamanca) shows how the Aβ peptide affects synapses made by fimbrial afferents with CA3 pyramidal cells. Stimulation of the lateral fimbria evokes AMPA-mediated EPSPs followed by early and late IPSPs mediated by distinct GABA receptors. Aβ depolarizes CA3 pyramidal cells, increases their input resistance and decreases the late GABAB-mediated IPSP current. This post-synaptic effect, is mediated via the G protein-gated inwardly rectifying potassium channel GirK. Dysfunction of septo-hippocampal oscillations involving GirK at fimbria-CA3 synapses may account for memory deficits during early stages of Alzheimer's disease.

International audience; The striatum is the input structure of the basal ganglia network that contains heterogeneous neuronal populations, including two populations of projecting neurons called the medium spiny neurons (MSNs), and different types of interneurons. We developed a transgenic mouse model enabling inducible ablation of the striatonigral MSNs constituting the direct pathway by expressing the human diphtheria toxin (DT) receptor under the control of the Slc35d3 gene promoter, a gene enriched in striatonigral MSNs. DT injection into the striatum triggered selective elimination of the majority of striatonigral MSNs. DT-mediated ablation of striatonigral MSNs caused selective loss of cholinergic interneurons in the dorsal striatum but not in the ventral striatum (nucleus accumbens), suggesting a region-specific critical role of the direct pathway in striatal cholinergic neuron homeostasis. Mice with DT injection into the dorsal striatum showed altered basal and cocaine-induced locomotion and dramatic reduction of L-DOPA-induced dyskinesia in the parkinsonian condition. In addition, these mice exhibited reduced anxiety, revealing a role of the dorsal striatum in the modulation of behaviors involving an emotional component, behaviors generally associated with limbic structures. Altogether, these results highlight the implication of the direct striatonigral pathway in the regulation of heterogeneous functions from cell survival to regulation of motor and emotion-associated behaviors.

Long-term potentiation of inhibitory GABAergic transmission controls synaptic integration and action potential generation of specific neocortical neurons., In the neocortex, the coexistence of temporally locked excitation and inhibition governs complex network activity underlying cognitive functions, and is believed to be altered in several brain diseases. Here we show that this equilibrium can be unlocked by increased activity of layer 5 pyramidal neurons of the mouse neocortex. Somatic depolarization or short bursts of action potentials of layer 5 pyramidal neurons induced a selective long-term potentiation of GABAergic synapses (LTPi) without affecting glutamatergic inputs. Remarkably, LTPi was selective for perisomatic inhibition from parvalbumin basket cells, leaving dendritic inhibition intact. It relied on retrograde signaling of nitric oxide, which persistently altered presynaptic GABA release and diffused to inhibitory synapses impinging on adjacent pyramidal neurons. LTPi reduced the time window of synaptic summation and increased the temporal precision of spike generation. Thus, increases in single cortical pyramidal neuron activity can induce an interneuron-selective GABAergic plasticity effectively altering the computation of temporally coded information., Author Summary The proper activity of cortical neurons (the brain cells responsible for memory and consciousness) relies on the precise integration of excitatory and inhibitory inputs. The excitation and inhibition (E/I) ratio has to remain constant both in time and strength to prevent neurological and psychiatric diseases. Fast inhibitory synaptic inputs to cortical pyramidal neurons originate from a rich diversity of GABAergic interneurons that operate a strict division of labor by differentially targeting precise regions of the pyramidal neurons. Here, we show that large pyramidal neurons of neocortical layer 5 can unlock the E/I ratio in response to their own activity. Excitatory activity of pyramidal neurons, in the form of membrane depolarization or trains of action potentials, induces a Ca2+-dependent mobilization of nitric oxide, which diffuses to inhibitory synapses and triggers a persistent enhancement of GABA release. Notably, this potentiation of inhibition is specific for synapses originating from parvalbumin (PV)-expressing interneurons that target mainly the perisomatic region of pyramidal neurons. Long-term potentiation of perisomatic inhibition, in turn, changes the ability of pyramidal neurons to integrate excitatory inputs as well as the temporal properties of their own action potential output. Selective plasticity of perisomatic inhibition can thus play a crucial role in cortical activity, such as sensory processing and integration.

International audience; The role of amyloid beta (Aβ) in brain function and in the pathogenesis of Alzheimer's disease (AD) remains elusive. Recent publications reported that an increase in Aβ concentration perturbs pre-synaptic release in hippocampal neurons. In particular, it was shown in vitro that Aβ is an endogenous regulator of synaptic transmission at the CA3-CA1 synapse, enhancing its release probability. How this synaptic modulator influences neuronal output during physiological stimulation patterns, such as those elicited in vivo, is still unknown. Using a realistic model of hippocampal CA1 pyramidal neurons, we first implemented this Aβ-induced enhancement of release probability and validated the model by reproducing the experimental findings. We then demonstrated that this synaptic modification can significantly alter synaptic integration properties in a wide range of physiologically relevant input frequencies (from 5 to 200 Hz). Finally, we used natural input patterns, obtained from CA3 pyramidal neurons in vivo during free exploration of rats in an open field, to investigate the effects of enhanced Aβ on synaptic release under physiological conditions. The model shows that the CA1 neuronal response to these natural patterns is altered in the increased-Aβ condition, especially for frequencies in the theta and gamma ranges. These results suggest that the perturbation of release probability induced by increased Aβ can significantly alter the spike probability of CA1 pyramidal neurons and thus contribute to abnormal hippocampal function during AD.

The 7WD4 and 7PA2 cell lines, widely used as cellular models for Alzheimer's disease (AD), have been used to investigate the effects of amyloid-beta protein precursor overexpression and amyloid-beta (A beta) oligomer accumulation on mitochondrial function. Under standard culture conditions, both cell lines, compared to Chinese hamster ovary (CHO) control cells, displayed an similar to 5% decrease of O-2 respiration as sustained by endogenous substrates. Functional impairment of the respiratory chain was found distributed among the protein complexes, though more evident at the level of complex I and complex IV. Measurements of ATP showed that its synthesis by oxidative phosphorylation is decreased in 7WD4 and 7PA2 cells by similar to 25%, this loss being partly compensated by glycolysis (Warburg effect). Compensation proved to be more efficient in 7WD4 than in 7PA2 cells, the latter cell line displaying the highest reactive oxygen species production. The strongest deficit was observed in mitochondrial membrane potential that is almost 40% and 60% lower in 7WD4 and 7PA2 cells, respectively, in comparison to CHO controls. All functional parameters point to a severe bioenergetic impairment of the AD cells, with the extent of mitochondrial dysfunction being correlated to the accumulation of A beta peptides and oligomers.

International audience; Under sustained input current of increasing strength neurons eventually stop firing, entering a depolarization block. This is a robust effect that is not usually explored in experiments or explicitly implemented or tested in models. However, the range of current strength needed for a depolarization block could be easily reached with a random background activity of only a few hundred excitatory synapses. Depolarization block may thus be an important property of neurons that should be better characterized in experiments and explicitly taken into account in models at all implementation scales. Here we analyze the spiking dynamics of CA1 pyramidal neuron models using the same set of ionic currents on both an accurate morphological reconstruction and on its reduction to a single-compartment. The results show the specific ion channel properties and kinetics that are needed to reproduce the experimental findings, and how their interplay can drastically modulate the neuronal dynamics and the input current range leading to a depolarization block. We suggest that this can be one of the rate-limiting mechanisms protecting a CA1 neuron from excessive spiking activity.

International audience; The transcription factor cAMP response element binding protein (CREB) is a key player in synaptic plasticity and learning. Phosphorylation of CREB induced by neuronal activity leads to gene transcription, a process thought to contribute to memory formation. We have previously reported that increasing CREB activity in glutamatergic CA1 pyramidal neurons or in dentate gyrus (DG) granule cells is sufficient to enhance hippocampal-dependent memory formation. This enhancement correlates with an increase in CA1 glutamatergic synaptic plasticity. However, the effects of increasing CREB activity on DG glutamatergic plasticity have not been investigated. To address this issue, we boosted CREB-dependent transcription in DG granule cells in vivo via viral mediated expression of a constitutively active form of CREB (CREBCA). Using in vitro extracellular field recordings of infected slices, we observed an increase in long-term potentiation (LTP) while short-term plasticity and basic synaptic transmission remained unaffected. These data demonstrate that boosting CREB activity in DG granule cells is sufficient to enhance LTP and suggest that this enhancement participates in the formation of better memories.

Transgenic (Tg) mouse models of Alzheimer’s disease (AD) are used to investigate mechanisms underlying disease pathology and identify therapeutic strategies. Most Tg AD models, which at least partly recapitulate the AD phenotype, are based on insertion of one or more human mutations (identified in Familial AD) into the mouse genome, with the notable exception of the anti-NGF mouse, which is based on the cholinergic unbalance hypothesis. It has recently emerged that impaired hippocampal synaptic function is an early detectable pathological alteration, well before the advanced stage of amyloid plaque accumulation and general cell death. Nevertheless, electrophysiological studies performed on different Tg models or on the same model by different research groups have yielded contrasting results. We therefore summarized data from original research papers studying hippocampal synaptic function using electrophysiology, to review what we have learned so far. We analyzed results obtained using the following Tg models: (1) single/multiple APP mutations; (2) single presenilin (PS) mutations; (3) APPxPS1 mutations; (4) APPxPS1xtau mutations (3xTg); and (5) anti-NGF expressing (AD11) mice. We observed that the majority of papers focus on excitatory basic transmission and long-term potentiation, while few studies evaluate inhibitory transmission and long-term depression. We searched for common synaptic alterations in the various models that might underlie the memory deficits observed in these mice. We also considered experimental variables that could explain differences in the reported results and briefly discuss successful rescue strategies. These analyses should prove useful for future design of electrophysiology experiments to assess hippocampal function in AD mouse models.

International audience; Nerve Growth Factor is an essential protein that supports neuronal survival during development and influences neuronal function throughout adulthood, both in the central and peripheral nervous system. The unprocessed precursor of NGF, proNGF, seems to be endowed with biological functions distinct from those of the mature protein, such as chaperone-like activities and apoptotic and/or neurotrophic properties. We have previously suggested, based on Small Angle X-ray Scattering data, that recombinant murine proNGF has features typical of an intrinsically unfolded protein. Using complementary biophysical techniques, we show here new evidence that clarifies and widens this hypothesis through a detailed comparison of the structural properties of NGF and proNGF. Our data provide direct information about the dynamic properties of the pro-peptide and indicate that proNGF assumes in solution a compact globular conformation. The N-terminal pro-peptide extension influences the chemical environment of the mature protein and protects the protein from proteolytic digestion. Accordingly, we observe that unfolding of proNGF involves a two-steps mechanism. The distinct structural properties of proNGF as compared to NGF agree with and rationalise a different functional role of the precursor.

Introduction: the current practice of quantifying cerebrospinal fluid (CSF) biomarkers as an aid in the diagnosis of Alzheimer's disease (AD) varies from center to center. For a same biochemical profile, interpretation and reporting of results may differ, which can lead to misunderstandings and raises questions about the commutability of tests. Methods: We obtained a description of (pre-)analytical protocols and sample reports from 40 centers worldwide. A consensus approach allowed us to propose harmonized comments corresponding to the different CSF biomarker profiles observed in patients. Results: the (pre-)analytical procedures were similar between centers. There was considerable heterogeneity in cutoff definitions and report comments. We therefore identified and selected by consensus the most accurate and informative comments regarding the interpretation of CSF biomarkers in the context of AD diagnosis. Discussion: this is the first time that harmonized reports are proposed across worldwide specialized laboratories involved in the biochemical diagnosis of AD. This manuscript was facilitated by the Alzheimer's Association International Society to Advance Alzheimer's Research and Treatment (ISTAART), through the Biofluid Based Biomarkers Professional Interest Area (BBB-PIA). The views and opinions expressed in this publication represent those of the authors and do not necessarily reflect those of the BBB-PIA membership, ISTAART, or the Alzheimer's Association. The authors thank the French Society of Clinical Biology, the ISTAART BBB-PIA, and the Society for Neurochemistry and Clinical CSF analysis for their help in initiating this work. Constance Delaby received no support for the present manuscript. Charlotte Teunissen received the following grants during the last 36 months: Research of CET is supported by the European Commission (Marie Curie International Training Network, grant agreement No 860197 [MIRIADE], and JPND), Health Holland, the Dutch Research Council (ZonMw), Alzheimer Drug Discovery Foundation, The Selfridges Group Foundation, Alzheimer Netherlands, Alzheimer Association. CT and WF are recipients of ABOARD, which is a public-private partnership receiving funding from ZonMw (#73305095007) and Health∼Holland, Topsector Life Sciences & Health (PPP-allowance; #LSHM20106). More than 30 partners participate in ABOARD. ABOARD also receives funding from Edwin Bouw Fonds and Gieskes-Strijbisfonds. IV is appointed on a research grant by Alzheimer Nederland (NL-17004). She received no support for the present manuscript. Kaj Blennow is supported by the Swedish Alzheimer Foundation (#AF-742881) and Hjärnfonden, Sweden (#FO2017-0243). He received no support for the present manuscript. Daniel Alcolea received funding from Institute of Health Carlos III (ISCIII), Spain PI18/00435 and INT19/00016, and by the Department of Health Generalitat de Catalunya PERIS program SLT006/17/125. He received no support for the present manuscript. Ivan Arisi was partly supported by: Fondo Ordinario Enti (FOE D.M 865/2019) funds in the framework of a collaboration agreement between the Italian National Research Council and EBRI (2019-2021); POR (Operative Program Lazio Region, Italy) FESR (European Program Regional Development) 2014-2020, Public Notice “LIFE 2020” MODIAG Project. Elodie Bouaziz-Amar received no support for the present manuscript. Anne Beaume received no support for the present manuscript. Aurélie Bedel received no support for the present manuscript. Giovanni Bellomo is supported by University of Perugia, CIRMMP, IRST Istituto Romagnolo per lo Studio e la Cura dei Tumori, Innuvatech srl. He received no support for the present manuscript. Edith Bigot-Corbel received no support for the present manuscript. Maria Bjerke received no support for the present manuscript. Marie-Céline Blanc-Quintin received no support for the present manuscript. Mercè Boada received support from LA CAIXA, IMI, ISCIII H2020 the European Union/EFPIA Innovative Medicines Initiative Joint Undertaking MOPEAD project (Grants No. 115985) and is also supported by national grant, PI17/01474 from Acción Estratégica en Salud, integrated into the Spanish National Plan of R+D+I and founded by ISCIII (Instituto de Salud Carlos III)-Subdirección General de Evaluación and the Fondo Europeo de Desarrollo Regional (FEDER- “Una manera de Hacer Europa”). She received no support for the present manuscript. Olivier Bousigues is supported by A2MCL Alsace Alzheimer. He received no support for the present manuscript. Miles D. Chapman received no support for the present manuscript. Mari L. DeMarco is supported by the Michael Smith Foundation for Health Research, Brain Canada (Canada Brain Research Fund), Health Canada, Women's Brain Health Initiative, Alzheimer Society of Canada, St. Paul's Foundation, Djavad Mowafaghian Centre for Brain Health at the University of British Columbia and the Canadian Consortium for Neurodegeneration and Aging; with all funds provided to the University of British Columbia. Mara D'Onofrio was partly supported by Fondo Ordinario Enti (FOE D.M 865/2019) funds in the framework of a collaboration agreement between the Italian National Research Council POR (Operative Program Lazio Region, Italy) FESR (European Program Regional Development) 2014-2020, Public Notice “LIFE 2020″, MODIAG Project. She received no support for the present manuscript. Julien Dumurgier received no support for the present manuscript. Diane Dufour received no support for the present manuscript. Sebastiaan Engelborghs is supported for various projects: Research Project GSKE/FMRE, Research Project FWO Vlaanderen, PhD fellowship FWO Vlaanderen (n = 3), VLAIO PhD fellowship. He received no support for the present manuscript. Hermann Esselmann received no support for the present manuscript. Anne Fogli received no support for the present manuscript. Audrey Gabelle received no support for the present manuscript. Elisabetta Galloni received no support for the present manuscript. Clémentine Gondolf received no support for the present manuscript. Frédérique Grandhomme received no support for the present manuscript. Oriol Grau-Rivera receives grants from the Spanish Ministry of Science, Innovation and Universities (FJCI-2017-33437), and from the Alzheimer's Association Research Fellowship Program (2019-AARF-644568). He received no support for the present manuscript. Melanie Hart receives UCLH Biomedical Research Centre support from NIHR (Neurosciences). She received no support for the present manuscript. Takeshi Ikeuchi received the following grants to his institution AMED: 21dk0207049, 21dk0207045, 21ek0109545, 20ek0109350, 20ek0109392. He received no support for the present manuscript. Andreas Jeromin received no support for the present manuscript. Kensaku Kasuga received no support for the present manuscript. Ashvini Keshavan is supported by the Weston Brain Institute/Selfridges Foundation grant UB170045. She received no support for the present manuscript. Michael Khalil received unrestricted research grants from Biogen and Novartis. He received no support for the present manuscript. Peter Körtvelyessy received no support for the present manuscript. Agnieszka Kulczynska-Przybik received no support for the present manuscript. Jean-Louis Laplanche received no support for the present manuscript. Qiao-Xin Li received no support for the present manuscript. Alberto Lleó is supported by grants from Generalitat de Catalunya (PERIS SLT002/16/00408), Instituto de Salud Carlos III (PI17/01896), Instituto de Salud Carlos III CIBERNED. He received no support for the present manuscript. Catherine Malaplate received no support for the present manuscript. Marta Marquié is supported by the Instituto de Salud Carlos III (ISCIII) Acción Estratégica en Salud, integrated in the Spanish National RCDCI Plan and financed by ISCIII-Subdirección General de Evaluación and the Fondo Europeo de Desarrollo Regional (FEDER-Una manera de hacer Europa) grant PI19/00335. She received no support for the present manuscript. Colin M. Masters received no support for the present manuscript. Barbara Mroczko received a grant from The Binding Site Group and Biokom Diagnostyka. She received no support for the present manuscript. Léonor Nogueira received no support for the present manuscript. Adelina Orellana received no support for the present manuscript. Markus Otto is supported by BMBF, Thierry Latran foundation, EU, DFG. He received no support for the present manuscript. Jean-Baptiste Oudart is supported by Astrazeneca grant for a research program on EGFR targeted therapy resistance in NSCLC. He received no support for the present manuscript. Claire Paquet received no support for the present manuscript. Federico Paolini received no support for the present manuscript. Lucilla Parnetti received no support for the present manuscript. Armand Perret-Liaudet received no support for the present manuscript. Katell Peoc'h is supported by contract with Siemens Healthineers. She received no support for the present manuscript. Koen Poesen received no support for the present manuscript. Albert Puig-Pijoan received no support for the present manuscript. Isabelle Quadrio received no support for the present manuscript. Murielle Quillard-Muraine received no support for the present manuscript. Benoît Rucheton received no support for the present manuscript. Susanne Schraen received no support for the present manuscript. Jonathan M. Schott is supported by the Medical Research Council, Alzheimer's Research UK, Weston Brain Institute, British Heart Foundation, Alzheimer's Association. He received no support for the present manuscript. Leslie M. Shaw is supported by NIA for ADNI Biomarker Core, UPENN ADRC Biomarker Corr, MJ Fox PPMI for CSF Biomarker measurements, Roche for IIS study of AD biomarkers. He received no support for the present manuscript. Marc Suárez-Calvet receives funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation program (Grant agreement No. 948677). He also receives funding from the Instituto de Salud Carlos III (PI19/00155) and from the Spanish Ministry of Science, Innovation and Universities (Juan de la Cierva Programme grant IJC2018-037478-I). He received no support for the present manuscript. Magda Tsolaki received no support for the present manuscript. Hayrettin Tumani is supported by Alexion, Bayer, Biogen, Celgene, Genzyme-Sanofi, Merck, Novartis, Roche, Teva. He received no support for the present manuscript. Chinedu T Udeh-Momoh is supported by Alzheimer research UK (Project Grant). He received no support for the present manuscript. Lucie Vaudran received no support for the present manuscript. Marcel M. Verbeek is supported by the BIONIC project (no. 733050822, which has been made possible by ZonMw within the framework of “Memorabel,” the research and innovation program for dementia, as part of the Dutch national “Deltaplan for Dementia”: zonmw.nl/dementiaresearch), and the CAFÉ project (the National Institutes of Health, USA, grant number 5R01NS104147-02). The BIONIC project is a consortium of Radboudumc, LUMC, ADX Neurosciences, and University of Rhode Island University. MM Verbeek is also supported by a grant from the Selfridges Group Foundation. He received no support for the present manuscript. Federico Verde received no support for the present manuscript. Lisa Vermunt is supported by Alzheimer Nederland. She received no support for the present manuscript. Jonathan Volgesgang is supported by Clinician Scientist Research Fellowship, German Research Foundation (Deutsche Forschungsgesellschaft, project number: 413501650; 09/01/2019-02/28/2021); Eric Dorris Memorial Fellowship (McLean Hospital; 07/01/2020-06/30/2021). He received no support for the present manuscript. Jens Wiltfang is supported by Federal Ministry of Education and Research (BMBF) State of Lower Saxony; He received no support for the present manuscript. Henrik Zetterberg is a Wallenberg Scholar supported by grants from the Swedish Research Council (#2018-02532), the European Research Council (#681712), Swedish State Support for Clinical Research (#ALFGBG-720931), the Alzheimer Drug Discovery Foundation (ADDF), USA (#201809-2016862), the AD Strategic Fund and the Alzheimer's Association (#ADSF-21-831376-C, #ADSF-21-831381-C and #ADSF-21-831377-C), the Olav Thon Foundation, the Erling-Persson Family Foundation, Stiftelsen för Gamla Tjänarinnor, Hjärnfonden, Sweden (#FO2019-0228), the European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 860197 (MIRIADE), and the UK Dementia Research Institute at UCL. He received no support for the present manuscript. Sylvain Lehmann received no support for the present manuscript.