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Science (New York, N.Y.) Oct 2020Dementia is a rapidly rising global health crisis that silently disables families and ends lives and livelihoods around the world. To date, however, no early biomarkers... (Review)
Review
Dementia is a rapidly rising global health crisis that silently disables families and ends lives and livelihoods around the world. To date, however, no early biomarkers or effective therapies exist. It is now clear that brain microglia are more than mere bystanders or amyloid phagocytes; they can act as governors of neuronal function and homeostasis in the adult brain. Here, we highlight the fundamental role of microglia as tissue-resident macrophages in neuronal health. Then, we suggest how chronic impairment in microglia-neuron cross-talk may secure the permanence of the failure of synaptic and neuronal function and health in Alzheimer's and Parkinson's diseases. Understanding how to assess and modulate microglia-neuron interactions critical for brain health will be key to developing effective therapies for dementia.
Topics: Alzheimer Disease; Amyloid; Animals; Cell Communication; Humans; Macrophages; Mice; Microglia; Neurons; Parkinson Disease; Synapses; Synaptosomes; alpha-Synuclein
PubMed: 33004513
DOI: 10.1126/science.abb8587 -
Cell Nov 2023Neurons build synaptic contacts using different protein combinations that define the specificity, function, and plasticity potential of synapses; however, the diversity...
Neurons build synaptic contacts using different protein combinations that define the specificity, function, and plasticity potential of synapses; however, the diversity of synaptic proteomes remains largely unexplored. We prepared synaptosomes from 7 different transgenic mouse lines with fluorescently labeled presynaptic terminals. Combining microdissection of 5 different brain regions with fluorescent-activated synaptosome sorting (FASS), we isolated and analyzed the proteomes of 18 different synapse types. We discovered ∼1,800 unique synapse-type-enriched proteins and allocated thousands of proteins to different types of synapses (https://syndive.org/). We identify shared synaptic protein modules and highlight the proteomic hotspots for synapse specialization. We reveal unique and common features of the striatal dopaminergic proteome and discover the proteome signatures that relate to the functional properties of different interneuron classes. This study provides a molecular systems-biology analysis of synapses and a framework to integrate proteomic information for synapse subtypes of interest with cellular or circuit-level experiments.
Topics: Animals; Mice; Brain; Mice, Transgenic; Proteome; Proteomics; Synapses; Synaptosomes
PubMed: 37918396
DOI: 10.1016/j.cell.2023.09.028 -
Nature Biotechnology Sep 2023Synapses are crucial structures that mediate signal transmission between neurons in complex neural circuits and display considerable morphological and...
Synapses are crucial structures that mediate signal transmission between neurons in complex neural circuits and display considerable morphological and electrophysiological heterogeneity. So far we still lack a high-throughput method to profile the molecular heterogeneity among individual synapses. In the present study, we develop a droplet-based single-cell (sc) total-RNA-sequencing platform, called Multiple-Annealing-and-Tailing-based Quantitative scRNA-seq in Droplets, for transcriptome profiling of individual neurites, primarily composed of synaptosomes. In the synaptosome transcriptome, or 'synaptome', profiling of both mouse and human brain samples, we detect subclusters among synaptosomes that are associated with neuronal subtypes and characterize the landscape of transcript splicing that occurs within synapses. We extend synaptome profiling to synaptopathy in an Alzheimer's disease (AD) mouse model and discover AD-associated synaptic gene expression changes that cannot be detected by single-nucleus transcriptome profiling. Overall, our results show that this platform provides a high-throughput, single-synaptosome transcriptome profiling tool that will facilitate future discoveries in neuroscience.
Topics: Humans; Mice; Animals; Synapses; Gene Expression Profiling; Synaptosomes; Transcriptome; Alzheimer Disease; Single-Cell Analysis; Sequence Analysis, RNA
PubMed: 36646931
DOI: 10.1038/s41587-022-01635-1 -
Glia Apr 2023Triggering receptor on myeloid cells 2 (TREM2) is an innate immune receptor, upregulated on the surface of microglia associated with amyloid plaques in Alzheimer's...
Triggering receptor on myeloid cells 2 (TREM2) is an innate immune receptor, upregulated on the surface of microglia associated with amyloid plaques in Alzheimer's disease (AD). Individuals heterozygous for the R47H variant of TREM2 have greatly increased risk of developing AD. We examined the effects of wild-type (WT), R47H and knock-out (KO) of human TREM2 expression in three microglial cell systems. Addition of mouse BV-2 microglia expressing R47H TREM2 to primary mouse neuronal cultures caused neuronal loss, not observed with WT TREM2. Neuronal loss was prevented by using annexin V to block exposed phosphatidylserine, an eat-me signal and ligand of TREM2, suggesting loss was mediated by microglial phagocytosis of neurons exposing phosphatidylserine. Addition of human CHME-3 microglia expressing R47H TREM2 to LUHMES neuronal-like cells also caused loss compared to WT TREM2. Expression of R47H TREM2 in BV-2 and CHME-3 microglia increased their uptake of phosphatidylserine-beads and synaptosomes versus WT TREM2. Human iPSC-derived microglia with heterozygous R47H TREM2 had increased phagocytosis of synaptosomes vs common-variant TREM2. Additionally, phosphatidylserine liposomes increased activation of human iPSC-derived microglia expressing homozygous R47H TREM2 versus common-variant TREM2. Finally, overexpression of TREM2 in CHME-3 microglia caused increased expression of cystatin F, a cysteine protease inhibitor, and knock-down of cystatin F increased CHME-3 uptake of phosphatidylserine-beads. Together, these data suggest that R47H TREM2 may increase AD risk by increasing phagocytosis of synapses and neurons via greater activation by phosphatidylserine and that WT TREM2 may decrease microglial phagocytosis of synapses and neurons via cystatin F.
Topics: Animals; Humans; Mice; Alzheimer Disease; Cystatins; Membrane Glycoproteins; Microglia; Neurons; Phagocytosis; Phosphatidylserines; Receptors, Immunologic; Synaptosomes
PubMed: 36480007
DOI: 10.1002/glia.24318 -
Methods in Molecular Biology (Clifton,... 2022Synaptosomes are re-sealed pinched off nerve terminals that maintain all the main structural and functional features of the original structures and that are appropriate...
Synaptosomes are re-sealed pinched off nerve terminals that maintain all the main structural and functional features of the original structures and that are appropriate to study presynaptic events. Because of the discovery of new structural and molecular events that dictate the efficiency of transmitter release and of its receptor-mediated control in the central nervous system, the interest in this tissue preparation is continuously renewing. Most of these events have been already discussed in previous reviews, but few of them were not and deserve some comments since they could suggest new functional and possibly therapeutic considerations. Among them, the "metamodulation" of receptors represents an emerging aspect that dramatically increased the complexity of the presynaptic compartment, adding new insights to the role of presynaptic receptors as modulators of chemical synapses. Deciphering the mechanism of presynaptic metamodulation would permit indirect approaches to control the activity of presynaptic release-regulating receptors that are currently orphans of direct ligands/modulators, paving the road for the proposal of new therapeutic approaches for central neurological diseases.
Topics: Central Nervous System; Presynaptic Terminals; Receptors, N-Methyl-D-Aspartate; Receptors, Presynaptic; Synapses; Synaptosomes
PubMed: 35099794
DOI: 10.1007/978-1-0716-1916-2_8 -
Current Neuropharmacology 2020Metabotropic glutamate (mGlu) receptors represent the largest family of glutamate receptors in mammals and act as fine tuners of the chemical transmission in central... (Review)
Review
Metabotropic glutamate (mGlu) receptors represent the largest family of glutamate receptors in mammals and act as fine tuners of the chemical transmission in central nervous system (CNS). In the last decade, results concerning the expression and the subcellular localization of mGlu receptors further clarified their role in physio-pathological conditions. Concomitantly, their pharmacological characterization largely improved thanks to the identification of new compounds (chemical ligands and antibodies recognizing epitopic sequences of the receptor proteins) that allowed to decipher the protein compositions of the naive receptors. mGlu receptors are expressed at the presynaptic site of chemical synapses. Here, they modulate intraterminal enzymatic pathways controlling the migration and the fusion of vesicles to synaptic membranes as well as the phosphorylation of colocalized receptors. Both the control of transmitter exocytosis and the phosphorylation of colocalized receptors elicited by mGlu receptors are relevant events that dictate the plasticity of nerve terminals, and account for the main role of presynaptic mGlu receptors as modulators of neuronal signalling. The role of the presynaptic mGlu receptors in the CNS has been the matter of several studies and this review aims at briefly summarizing the recent observations obtained with isolated nerve endings (we refer to as synaptosomes). We focus on the pharmacological characterization of these receptors and on their receptor-receptor interaction / oligo-dimerization in nerve endings that could be relevant to the development of new therapeutic approaches for the cure of central pathologies.
Topics: Animals; Central Nervous System; Humans; Receptors, Metabotropic Glutamate; Receptors, Presynaptic; Synapses; Synaptic Transmission; Synaptosomes
PubMed: 31775600
DOI: 10.2174/1570159X17666191127112339 -
International Journal of Molecular... Dec 2021The assembly of synaptic protein-DNA complexes by specialized proteins is critical for bringing together two distant sites within a DNA molecule or bridging two DNA...
The assembly of synaptic protein-DNA complexes by specialized proteins is critical for bringing together two distant sites within a DNA molecule or bridging two DNA molecules. The assembly of such synaptosomes is needed in numerous genetic processes requiring the interactions of two or more sites. The molecular mechanisms by which the protein brings the sites together, enabling the assembly of synaptosomes, remain unknown. Such proteins can utilize sliding, jumping, and segmental transfer pathways proposed for the single-site search process, but none of these pathways explains how the synaptosome assembles. Here we used restriction enzyme SfiI, that requires the assembly of synaptosome for DNA cleavage, as our experimental system and applied time-lapse, high-speed AFM to directly visualize the site search process accomplished by the SfiI enzyme. For the single-site SfiI-DNA complexes, we were able to directly visualize such pathways as sliding, jumping, and segmental site transfer. However, within the synaptic looped complexes, we visualized the threading and site-bound segment transfer as the synaptosome-specific search pathways for SfiI. In addition, we visualized sliding and jumping pathways for the loop dissociated complexes. Based on our data, we propose the site-search model for synaptic protein-DNA systems.
Topics: Binding Sites; Chromosome Pairing; DNA; DNA Restriction Enzymes; Plasmids; Protein Binding; Proteins; Synaptosomes
PubMed: 35008637
DOI: 10.3390/ijms23010212 -
Brain Research Nov 2020Synapse dysfunction is an integral feature of Alzheimer's disease (AD) pathophysiology. In fact, prodromal manifestation of structural and functional deficits in... (Review)
Review
Synapse dysfunction is an integral feature of Alzheimer's disease (AD) pathophysiology. In fact, prodromal manifestation of structural and functional deficits in synapses much prior to appearance of overt pathological hallmarks of the disease indicates that AD might be considered as a degenerative disorder of the synapses. Several research instruments and techniques have allowed us to study synaptic function and plasticity and their alterations in pathological conditions, such as AD. One such tool is the biochemically isolated preparations of detached and resealed synaptic terminals, the "synaptosomes". Because of the preservation of many of the physiological processes such as metabolic and enzymatic activities, synaptosomes have proved to be an indispensable ex vivo model system to study synapse physiology both when isolated from fresh or cryopreserved tissues, and from animal or human post-mortem tissues. This model system has been tremendously successful in the case of post-mortem tissues because of their accessibility relative to acute brain slices or cultures. The current review details the use of synaptosomes in AD research and its potential as a valuable tool in furthering our understanding of the pathogenesis and in devising and testing of therapeutic strategies for the disease.
Topics: Alzheimer Disease; Animals; Biomedical Research; Humans; Synaptosomes
PubMed: 32659233
DOI: 10.1016/j.brainres.2020.147009 -
Current Protein & Peptide Science 2021The current meta-analysis of the cohort review was designed to elucidate the progress made in neuroproteomics of the synaptosome. The association of the comprehensive... (Meta-Analysis)
Meta-Analysis Review
The current meta-analysis of the cohort review was designed to elucidate the progress made in neuroproteomics of the synaptosome. The association of the comprehensive synaptic proteome and its link to physiological or pathological setting is rapidly mounting. Chemical synapses in the brain are focal hot spots for interneuronal signalling, signal transduction, and its plasticity. Structurally, synapses comprise axon termini or the presynapse (vesicles filled with neurotransmitters that function as molecular signals), synaptic clefts (extracellular matrix and adhesion molecules), and Postsynaptic Density or PSD (with receptors for neurotransmitters that rely upon the chemical signalling). The pre- and post-synaptic clefts are responsible for mediating and regulating neurotransmitter release, their receptor binding, and perception rely on chemical signals. Moreover, short- and long-term structural and functional alterations that are necessary for the optimal higherorder brain functions are also mainly dependent on the protein dynamics at the synapses. Not surprisingly, disruptions in synaptic physiology are considered as the major pathogenic mechanisms underlying the progression of several neurodegenerative disorders, including Alzheimer's disease. This review briefly discusses the subcellular fractionation protocols and the related biochemical approaches for the isolation of synaptic compartments. Besides, it discusses the progress made in understanding the pathological alterations in the synaptic proteome in neurodegenerative disorders, particularly focussing on Alzheimer's disease dementia.
Topics: Alzheimer Disease; Humans; Proteome; Proteomics; Synapses; Synaptosomes
PubMed: 34148536
DOI: 10.2174/1389203722666210618110233 -
Neurochemical Research Jan 2022Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system (CNS). A family of five Na-dependent transporters maintain low levels of... (Review)
Review
Glutamate is the predominant excitatory neurotransmitter in the mammalian central nervous system (CNS). A family of five Na-dependent transporters maintain low levels of extracellular glutamate and shape excitatory signaling. Shortly after the research group of the person being honored in this special issue (Dr. Baruch Kanner) cloned one of these transporters, his group and several others showed that their activity can be acutely (within minutes to hours) regulated. Since this time, several different signals and post-translational modifications have been implicated in the regulation of these transporters. In this review, we will provide a brief introduction to the distribution and function of this family of glutamate transporters. This will be followed by a discussion of the signals that rapidly control the activity and/or localization of these transporters, including protein kinase C, ubiquitination, glutamate transporter substrates, nitrosylation, and palmitoylation. We also include the results of our attempts to define the role of palmitoylation in the regulation of GLT-1 in crude synaptosomes. In some cases, the mechanisms have been fairly well-defined, but in others, the mechanisms are not understood. In several cases, contradictory phenomena have been observed by more than one group; we describe these studies with the goal of identifying the opportunities for advancing the field. Abnormal glutamatergic signaling has been implicated in a wide variety of psychiatric and neurologic disorders. Although recent studies have begun to link regulation of glutamate transporters to the pathogenesis of these disorders, it will be difficult to determine how regulation influences signaling or pathophysiology of glutamate without a better understanding of the mechanisms involved.
Topics: Amino Acid Transport System X-AG; Animals; Central Nervous System; Excitatory Amino Acid Transporter 1; Excitatory Amino Acid Transporter 2; Glutamic Acid; Humans; Mammals; Sodium; Synaptosomes
PubMed: 33893911
DOI: 10.1007/s11064-021-03329-7