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In this high-throughput proteomic study of autosomal dominant Alzheimer's disease (ADAD), we sought to identify early biomarkers in cerebrospinal fluid (CSF) for disease monitoring and treatment strategies. We examined CSF proteins in 286 mutation carriers (MCs) and 177 non-carriers (NCs). The developed multi-layer regression model distinguished proteins with different pseudo-trajectories between these groups. We validated our findings with independent ADAD as well as sporadic AD datasets and employed machine learning to develop and validate predictive models. Our study identified 137 proteins with distinct trajectories between MCs and NCs, including eight that changed before traditional AD biomarkers. These proteins are grouped into three stages: early stage (stress response, glutamate metabolism, neuron mitochondrial damage), middle stage (neuronal death, apoptosis), and late presymptomatic stage (microglial changes, cell communication). The predictive model revealed a six-protein subset that more effectively differentiated MCs from NCs, compared with conventional biomarkers., Competing Interests: Declaration of interests C.C. has received research support from GSK and EISAI. C.C. is a member of the advisory board of Circular Genomics and owns stocks in these companies. C.C. is on the advisory board of ADmit. J.L. reports speaker fees from Bayer Vital, Biogen, EISAI, TEVA, Zambon, Merck, and Roche; consulting fees from Axon Neuroscience, EISAI, and Biogen; author fees from Thieme medical publishers and W. Kohlhammer GmbH medical publishers; and is inventor in a patent “Oral Phenylbutyrate for Treatment of Human 4-Repeat Tauopathies” (EP 23 156 122.6). He receives compensation for serving as chief medical officer for MODAG GmbH and is a beneficiary of the phantom share program of MODAG GmbH. E.M. reports research support received from NIA (U01AG059798), Anonymous Foundation, GHR, Alzheimer Association, Eli Lilly Eisai, and Hoffmann-La Roche and paid consulting for Eli Lilly, Alector, Alzamend, Sanofi, AstraZeneca, Hoffmann-La Roche, Grifols, and Merck., (Copyright © 2024 The Author(s). Published by Elsevier Inc. All rights reserved.)

Neurotransmission is an energetically expensive process that underlies cognition. During intense electrical activity or dietary restrictions, the glucose level in the brain plummets, forcing neurons to utilize alternative fuels. However, the molecular mechanisms of neuronal metabolic plasticity remain poorly understood. Here, we demonstrate that glucose-deprived neurons activate the CREB and PGC1α transcriptional program, which induces expression of the mitochondrial deacetylase Sirtuin 3 (Sirt3) both in vitro and in vivo. We show that Sirt3 localizes to axonal mitochondria and stimulates mitochondrial oxidative capacity in hippocampal nerve terminals. Sirt3 plays an essential role in sustaining synaptic transmission in the absence of glucose by providing metabolic support for the retrieval of synaptic vesicles after release. These results demonstrate that the transcriptional induction of Sirt3 facilitates the metabolic plasticity of synaptic transmission., (© 2023 Tiwari et al.)

Proteins from the NANOS family are conserved translational repressors with a well-known role in gonad development in both vertebrates and invertebrates. In addition, Drosophila Nanos controls neuron maturation and function, and rodent Nanos1 affects cortical neuron differentiation. Here we show that rat Nanos1 is expressed in hippocampal neurons and that the siRNA-mediated knockdown of Nanos1 impairs synaptogenesis. We found that both dendritic spine size and number were affected by Nanos1 KD. Dendritic spines were smaller and more numerous. Moreover, whereas in control neurons most dendritic PSD95 clusters contact pre-synaptic structures, a larger proportion of PSD95 clusters lacked a synapsin counterpart upon Nanos1 loss-of-function. Finally, Nanos1 KD impaired the induction of ARC typically triggered by neuron depolarization. These results expand our knowledge on the role of NANOS1 in CNS development and suggest that RNA regulation by NANOS1 governs hippocampal synaptogenesis., Competing Interests: No authors have competing interest., (Copyright: © 2023 Maschi et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Among most prevalent deficits in individuals with Fragile X syndrome (FXS) is hypersensitivity to sensory stimuli and somatosensory alterations. Whether dysfunction in peripheral sensory system contributes to these deficits remains poorly understood. Satellite glial cells (SGCs), which envelop sensory neuron soma, play critical roles in regulating neuronal function and excitability. The potential contributions of SGCs to sensory deficits in FXS remain unexplored. Here we found major structural defects in sensory neuron-SGC association in the dorsal root ganglia (DRG), manifested by aberrant covering of the neuron and gaps between SGCs and the neuron along their contact surface. Single-cell RNAseq analyses demonstrated transcriptional changes in both neurons and SGCs, indicative of defects in neuronal maturation and altered SGC vesicular secretion. We validated these changes using fluorescence microscopy, qPCR, and high-resolution transmission electron microscopy (TEM) in combination with computational analyses using deep learning networks. These results revealed a disrupted neuron-glia association at the structural and functional levels. Given the well-established role for SGCs in regulating sensory neuron function, altered neuron-glia association may contribute to sensory deficits in FXS., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Avraham, Deng, Maschi, Klyachko and Cavalli.)

Synaptic active zone (AZ) contains multiple specialized release sites for vesicle fusion. The utilization of release sites is regulated to determine spatiotemporal organization of the two main forms of synchronous release, uni-vesicular (UVR) and multi-vesicular (MVR). We previously found that the vesicle-associated molecular motor myosin V regulates temporal utilization of release sites by controlling vesicle anchoring at release sites in an activity-dependent manner. Here we show that acute inhibition of myosin V shifts preferential location of vesicle docking away from AZ center toward periphery, and results in a corresponding spatial shift in utilization of release sites during UVR. Similarly, inhibition of myosin V also reduces preferential utilization of central release sites during MVR, leading to more spatially distributed and temporally uniform MVR that occurs farther away from the AZ center. Using a modeling approach, we provide a conceptual framework that unites spatial and temporal functions of myosin V in vesicle release by controlling the gradient of release site release probability across the AZ, which in turn determines the spatiotemporal organization of both UVR and MVR. Thus myosin V regulates both temporal and spatial utilization of release sites during two main forms of synchronous release., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Maschi, Gramlich and Klyachko.)

A synaptic active zone (AZ) can release multiple vesicles in response to an action potential. This multi-vesicular release (MVR) occurs at most synapses, but its spatiotemporal properties are unknown. Nanoscale-resolution detection of individual release events in hippocampal synapses revealed unprecedented heterogeneity among vesicle release sites within a single AZ, with a gradient of release probability decreasing from AZ center to periphery. Parallel to this organization, MVR events preferentially overlap with uni-vesicular release (UVR) events at sites closer to an AZ center. Pairs of fusion events comprising MVR are also not perfectly synchronized, and the earlier event tends to occur closer to AZ center. The spatial features of release sites and MVR events are similarly tightened by buffering intracellular calcium. These observations revealed a marked heterogeneity of release site properties within individual AZs, which determines the spatiotemporal features of MVR events and is controlled, in part, by non-uniform calcium elevation across the AZ., Competing Interests: DM, VK No competing interests declared, (© 2020, Maschi and Klyachko.)

Synaptic vesicle fusion occurs at specialized release sites at the active zone. How refilling of release sites with new vesicles is regulated in central synapses remains poorly understood. Using nanoscale-resolution detection of individual release events in rat hippocampal synapses we found that inhibition of myosin V, the predominant vesicle-associated motor, strongly reduced refilling of the release sites during repetitive stimulation. Single-vesicle tracking revealed that recycling vesicles continuously shuttle between a plasma membrane pool and an inner pool. Vesicle retention at the membrane pool was regulated by neural activity in a myosin V dependent manner. Ultrastructural measurements of vesicle occupancy at the plasma membrane together with analyses of single-vesicle trajectories during vesicle shuttling between the pools suggest that myosin V acts as a vesicle tether at the plasma membrane, rather than a motor transporting vesicles to the release sites, or directly regulating vesicle exocytosis., Competing Interests: DM, MG, VK No competing interests declared, (© 2018, Maschi et al.)

The number and availability of vesicle release sites at the synaptic active zone (AZ) are critical factors governing neurotransmitter release; yet, these fundamental synaptic parameters have remained undetermined. Moreover, how neural activity regulates the spatiotemporal properties of the release sites within individual central synapses is unknown. Here, we combined a nanoscale imaging approach with advanced image analysis to detect individual vesicle fusion events with ∼27 nm localization precision at single hippocampal synapses under physiological conditions. Our results revealed the presence of multiple distinct release sites within individual hippocampal synapses. Release sites were distributed throughout the AZ and underwent repeated reuse. Furthermore, the spatiotemporal properties of the release sites were activity dependent with a reduction in reuse frequency and a shift in location toward the AZ periphery during high-frequency stimulation. These findings have revealed fundamental spatiotemporal properties of individual release sites in small central synapses and their activity-dependent modulation., (Copyright © 2017 Elsevier Inc. All rights reserved.)

The ability of synapses to sustain neurotransmitter release during continuous activity critically relies on an efficient vesicle recycling program. Despite extensive research on synaptic function, the basic mechanisms of vesicle recycling remain poorly understood due to the relative inaccessibility of central synapses to conventional recording techniques. The extremely small size of synaptic vesicles, nearly five times below the diffraction-limited resolution of conventional light microscopy, has hampered efforts to define the mechanisms controlling their cycling. The complex sequence of dynamic processes that occur within the nerve terminals and link vesicle endocytosis and the subsequent round of release has been particularly difficult to study. The recent development of nanoscale-resolution imaging techniques has provided an opportunity to overcome these limitations and begin to reveal the mechanisms controlling vesicle recycling within individual nerve terminals. Here we summarize the recent advances in the implementation of super-resolution imaging and single-particle tracking approaches to study the dynamic steps of the vesicle recycling process within presynaptic terminals., (© 2014 Wiley Periodicals, Inc.)

The production of proteins from mRNAs localized at the synapse ultimately controls the strength of synaptic transmission, thereby affecting behavior and cognitive functions. The regulated transcription, processing, and transport of mRNAs provide dynamic control of the dendritic transcriptome, which includes thousands of messengers encoding multiple cellular functions. Translation is locally modulated by synaptic activity through a complex network of RNA-binding proteins (RBPs) and various types of non-coding RNAs (ncRNAs) including BC-RNAs, microRNAs, piwi-interacting RNAs, and small interference RNAs. The RBPs FMRP and CPEB play a well-established role in synaptic translation, and additional regulatory factors are emerging. The mRNA repressors Smaug, Nanos, and Pumilio define a novel pathway for local translational control that affects dendritic branching and spines in both flies and mammals. Recent findings support a role for processing bodies and related synaptic mRNA-silencing foci (SyAS-foci) in the modulation of synaptic plasticity and memory formation. The SyAS-foci respond to different stimuli with changes in their integrity thus enabling regulated mRNA release followed by translation. CPEB, Pumilio, TDP-43, and FUS/TLS form multimers through low-complexity regions related to prion domains or polyQ expansions. The oligomerization of these repressor RBPs is mechanistically linked to the aggregation of abnormal proteins commonly associated with neurodegeneration. Here, we summarize the current knowledge on how specificity in mRNA translation is achieved through the concerted action of multiple pathways that involve regulatory ncRNAs and RBPs, the modification of translation factors, and mRNA-silencing foci dynamics.

Mammalian Smaug1/Samd4A is a translational repressor. Here we show that Smaug1 forms mRNA-silencing foci located at postsynapses of hippocampal neurons. These structures, which we have named S-foci, are distinct from P-bodies, stress granules, or other neuronal RNA granules hitherto described, and are the first described mRNA-silencing foci specific to neurons. RNA binding was not required for aggregation, which indicates that S-foci formation is not a consequence of mRNA silencing. N-methyl-D-aspartic acid (NMDA) receptor stimulation provoked a rapid and reversible disassembly of S-foci, transiently releasing transcripts (the CaMKIIα mRNA among others) to allow their translation. Simultaneously, NMDA triggered global translational silencing, which suggests the specific activation of Smaug1-repressed transcripts. Smaug1 is expressed during synaptogenesis, and Smaug1 knockdown affected the number and size of synapses, and also provoked an impaired response to repetitive depolarizing stimuli, as indicated by a reduced induction of Arc/Arg3.1. Our results suggest that S-foci control local translation, specifically responding to NMDA receptor stimulation and affecting synaptic plasticity.

FKBP51 and FKBP52 (FK506-binding protein 51 and 52) are tetratricopeptide repeat-domain immunophilins belonging to the tetratricopeptide-protein•hsp90•hsp70•p23 heterocomplex bound to steroid receptors. Immunophilins are related to receptor folding, subcellular localization, and hormone-dependent transcription. Also, they bind the immunosuppressant macrolide FK506, which shows neuroregenerative and neuroprotective actions by a still unknown mechanism. In this study, we demonstrate that in both, undifferentiated neuroblastoma cells and embryonic hippocampal neurons, the FKBP52•hsp90•p23 heterocomplex concentrates in a perinuclear structure. Upon cell stimulation with FK506, this structure disassembles and this perinuclear area becomes transcriptionally active. The acquisition of a neuronal phenotype is accompanied by increased expression of βIII-tubulin, Map-2, Tau-1, but also hsp90, hsp70, p23, and FKBP52. During the early differentiation steps, the perinuclear heterocomplex redistributes along the cytoplasm and nascent neurites, p23 binds to intermediate filaments and microtubules acquired higher filamentary organization. While FKBP52 moves towards neurites and concentrates in arborization bodies and terminal axons, FKBP51, whose expression remains constant, replaces FKBP52 in the perinuclear structure. Importantly, neurite outgrowth is favored by FKBP52 over-expression or FKBP51 knock-down, and is impaired by FKBP52 knock-down or FKBP51 over-expression, indicating that the balance between these FK506-binding proteins plays a key role during the early mechanism of neuronal differentiation., (© 2010 The Authors. Journal of Neurochemistry © 2010 International Society for Neurochemistry.)

During the preimplantation phase of pregnancy the endometrial stroma differentiates into decidua, a process that implies numerous morphological changes and is an example of physiological transdifferentiation. Here we show that UIII rat endometrial stromal cells cultured in the presence of calf serum acquired morphological features of decidual cells and expressed decidual markers. To identify genes involved in decidualization we compared gene expression patterns of control and decidualized UIII cells using cDNA microarray. We found 322 annotated genes exhibiting significant differences in expression (>3-fold, fold discovery rate (FDR) >0.005), of which 312 have not been previously related to decidualization. Analysis of overrepresented functions revealed that protein synthesis, gene expression, and chromatin architecture and remodeling are the most relevant modified functions during decidualization. Relevant genes are also found in the functional terms differentiation, cell proliferation, signal transduction, and matrix/structural proteins. Several of these new genes involved in decidualization (Csdc2, Trim27, Eef1a1, Bmp1, Wt1, Aes, Gna12, and Men1) are shown to be also regulated in uterine decidua during normal pregnancy. Thus, the UIII cell culture model will allow future mechanistic studies to define the transcriptional network regulating reprogramming of stromal cells into decidual cells.