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Background: Synapse loss is an early event that precedes neuronal death and symptom onset and is considered the best neuropathological correlate of cognitive decline in Alzheimer's disease (AD). Vesicle-associated membrane protein 2 (VAMP-2) has emerged as a promising biomarker of AD-related synapse degeneration in cerebrospinal fluid (CSF). The aim of this study was to explore the CSF profile of VAMP-2 across the AD continuum in relation to core AD biomarkers, other synaptic proteins, neurogranin (Ng) and synaptosomal-associated Protein-25 kDa (SNAP-25) and cognitive performance., Methods: We developed a digital immunoassay on the Single Molecule Array platform to quantify VAMP-2 in CSF and used existing immunoassays to quantify Ng, SNAP-25 and core CSF AD biomarkers. The clinical study included 62 cognitively unimpaired AD biomarker-negative subjects and 152 participants across the AD continuum from the SPIN cohort (Sant Pau Initiative on Neurodegeneration). Cognitive measures of episodic, semantic, executive and visuospatial domains and global cognition were included. Statistical methods included χ 2 tests, spearman correlation, and ANCOVA analyses., Results: The VAMP-2 assay had a good analytical performance (repeatability 8.9%, intermediate precision 10.3%). Assay antibodies detected native VAMP-2 protein in human brain homogenates. CSF concentrations of VAMP-2, neurogranin and SNAP-25 were lower in preclinical AD stage 1 compared to controls and higher at later AD stages compared to AD stage 1 and were associated with core AD biomarkers, particularly total tau (adj. r 2  = 0.62 to 0.78, p < 0.001). All three synaptic proteins were associated with all cognitive domains in individuals on the AD continuum (adj. r 2  = 0.04 to 0.19, p < 0.05)., Conclusions: Our novel digital immunoassay accurately measures VAMP-2 changes in CSF, which reflect AD biomarkers and cognitive performance across multiple domains., (© 2023. The Author(s).)

Synaptic vesicle glycoprotein 2A (SV2A) is a 12-pass transmembrane glycoprotein ubiquitously expressed in presynaptic vesicles. In vivo imaging of SV2A using PET has potential applications in the diagnosis and prognosis of a variety of neuropsychiatric diseases, e.g., Alzheimer's disease, Parkinson's disease, schizophrenia, multiple sclerosis, autism, epilepsy, stroke, traumatic brain injury, post-traumatic stress disorder, depression, etc. Herein, we report the synthesis and evaluation of a new 18 F-labeled SV2A PET imaging probe, [ 18 F]SynVesT-2, which possesses fast in vivo binding kinetics and high specific binding signals in non-human primate brain.

Background: Identifying effective strategies to prevent memory loss in AD has eluded researchers to date, and likely reflects insufficient understanding of early pathogenic mechanisms directly affecting memory encoding. As synaptic loss best correlates with memory loss in AD, refocusing efforts to identify factors driving synaptic impairments may provide the critical insight needed to advance the field. In this study, we reveal a previously undescribed cascade of events underlying pre and postsynaptic hippocampal signaling deficits linked to cognitive decline in AD. These profound alterations in synaptic plasticity, intracellular Ca 2+ signaling, and network propagation are observed in 3-4 month old 3xTg-AD mice, an age which does not yet show overt histopathology or major behavioral deficits., Methods: In this study, we examined hippocampal synaptic structure and function from the ultrastructural level to the network level using a range of techniques including electron microscopy (EM), patch clamp and field potential electrophysiology, synaptic immunolabeling, spine morphology analyses, 2-photon Ca 2+ imaging, and voltage-sensitive dye-based imaging of hippocampal network function in 3-4 month old 3xTg-AD and age/background strain control mice., Results: In 3xTg-AD mice, short-term plasticity at the CA1-CA3 Schaffer collateral synapse is profoundly impaired; this has broader implications for setting long-term plasticity thresholds. Alterations in spontaneous vesicle release and paired-pulse facilitation implicated presynaptic signaling abnormalities, and EM analysis revealed a reduction in the ready-releasable and reserve pools of presynaptic vesicles in CA3 terminals; this is an entirely new finding in the field. Concurrently, increased synaptically-evoked Ca 2+ in CA1 spines triggered by LTP-inducing tetani is further enhanced during PTP and E-LTP epochs, and is accompanied by impaired synaptic structure and spine morphology. Notably, vesicle stores, synaptic structure and short-term plasticity are restored by normalizing intracellular Ca 2+ signaling in the AD mice., Conclusions: These findings suggest the Ca 2+ dyshomeostasis within synaptic compartments has an early and fundamental role in driving synaptic pathophysiology in early stages of AD, and may thus reflect a foundational disease feature driving later cognitive impairment. The overall significance is the identification of previously unidentified defects in pre and postsynaptic compartments affecting synaptic vesicle stores, synaptic plasticity, and network propagation, which directly impact memory encoding.

The function of synaptic transmission and presynaptic vesicular cycle in the neuromuscular synapses of the diaphragm was studied in transgenic APP/PS1 mice (Alzheimer's disease model). The decrease in the quantal content of end-plate potential, intense depression of the amplitude of terminal plate potentials under conditions of lasting high frequency stimulation (50 Hz), a drastic prolongation of the synaptic vesicle recycling time in APP/PS1 mice in comparison with wild type mice were detected. Manifest dysfunction of the neuromuscular synapses, caused by disordered neurosecretion and recycling of the synaptic vesicles in the presynaptic nerve endings, was detected in the Alzheimer's disease model on transgenic APP/PS1 mice. The study supplemented the notions on the pathogenesis of Alzheimer's disease as a systemic disease, while the detected phenomena could just partially explain the development of motor disorders in this disease.

Proton magnetic resonance spectroscopy ((1)H-MRS) is sensitive to early neurodegenerative processes associated with Alzheimer's disease (AD). Although (1)H-MRS metabolite ratios of N-acetyl aspartate (NAA)/creatine (Cr), NAA/myoinositol (mI), and mI/Cr measured in the posterior cingulate gyrus reveal evidence of disease progression in AD, pathologic underpinnings of the (1)H-MRS metabolite changes in AD are unknown. Pathologically diagnosed human cases ranging from no likelihood to high likelihood AD (n = 41, 16 females and 25 males) who underwent antemortem (1)H-MRS of the posterior cingulate gyrus at 3 tesla were included in this study. Immunohistochemical evaluation was performed on the posterior cingulate gyrus using antibodies to synaptic vesicles, hyperphosphorylated tau (pTau), neurofibrillary tangle conformational-epitope (cNFT), amyloid-β, astrocytes, and microglia. The slides were digitally analyzed using Aperio software, which allows neuropathologic quantification in the posterior cingulate gray matter. MRS and pathology associations were adjusted for time from scan to death. Significant associations across AD and control subjects were found between reduced synaptic immunoreactivity and both NAA/Cr and NAA/mI in the posterior cingulate gyrus. Higher pTau burden was associated with lower NAA/Cr and NAA/mI. Higher amyloid-β burden was associated with elevated mI/Cr and lower NAA/mI ratios, but not with NAA/Cr. (1)H-MRS metabolite levels reveal early neurodegenerative changes associated with AD pathology. Our findings support the hypothesis that a decrease in NAA/Cr is associated with loss of synapses and early pTau pathology, but not with amyloid-β or later accumulation of cNFT pathology in the posterior cingulate gyrus. In addition, elevation of mI/Cr is associated with the occurrence of amyloid-β plaques in AD., (Copyright © 2014 the authors 0270-6474/14/3416247-09$15.00/0.)

Synapses are essential for transmitting, processing, and storing information, all of which decline in aging and Alzheimer's disease (AD). Because synapse loss only partially accounts for the cognitive declines seen in aging and AD, we hypothesized that existing synapses might undergo molecular changes that reduce their functional capacity. Microarrays were used to evaluate expression profiles of 340 synaptic genes in aging (20-99 years) and AD across 4 brain regions from 81 cases. The analysis revealed an unexpectedly large number of significant expression changes in synapse-related genes in aging, with many undergoing progressive downregulation across aging and AD. Functional classification of the genes showing altered expression revealed that multiple aspects of synaptic function are affected, notably synaptic vesicle trafficking and release, neurotransmitter receptors and receptor trafficking, postsynaptic density scaffolding, cell adhesion regulating synaptic stability, and neuromodulatory systems. The widespread declines in synaptic gene expression in normal aging suggests that function of existing synapses might be impaired, and that a common set of synaptic genes are vulnerable to change in aging and AD., (Published by Elsevier Inc.)

The accumulation of Tau into aggregates is associated with key pathological events in frontotemporal lobe degeneration (FTD-Tau) and Alzheimer disease (AD). Recent data have shown that misfolded Tau can be internalized by cells in vitro (Frost, B., Jacks, R. L., and Diamond, M. I. (2009) J. Biol. Chem. 284, 12845-12852) and propagate pathology in vivo (Clavaguera, F., Bolmont, T., Crowther, R. A., Abramowski, D., Frank, S., Probst, A., Fraser, G., Stalder, A. K., Beibel, M., Staufenbiel, M., Jucker, M., Goedert, M., and Tolnay, M. (2009) Nat. Cell Biol. 11, 909-913; Lasagna-Reeves, C. A., Castillo-Carranza, D. L., Sengupta, U., Guerrero-Munoz, M. J., Kiritoshi, T., Neugebauer, V., Jackson, G. R., and Kayed, R. (2012) Sci. Rep. 2, 700). Here we show that recombinant Tau misfolds into low molecular weight (LMW) aggregates prior to assembly into fibrils, and both extracellular LMW Tau aggregates and short fibrils, but not monomers, long fibrils, nor long filaments purified from brain extract are taken up by neurons. Remarkably, misfolded Tau can be internalized at the somatodendritic compartment, or the axon terminals and it can be transported anterogradely, retrogradely, and can enhance tauopathy in vivo. The internalized Tau aggregates co-localize with dextran, a bulk-endocytosis marker, and with the endolysosomal compartments. Our findings demonstrate that exogenous Tau can be taken up by cells, uptake depends on both the conformation and size of the Tau aggregates and once inside cells, Tau can be transported. These data provide support for observations that tauopathy can spread trans-synaptically in vivo, via cell-to-cell transfer.

The quantification and measurement of synapses is a major goal in the study of brain organization in both health and disease. Serial section electron microscopy (EM) is the ideal method since it permits the direct quantification of crucial features such as the number of synapses per unit volume or the distribution and size of synapses. However, a major limitation is that obtaining long series of ultrathin sections is extremely time-consuming and difficult. Consequently, quantitative EM studies are scarce and the most common method employed to estimate synaptic density in the human brain is indirect, by counting at the light microscopic level immunoreactive puncta using synaptic markers. The recent development of automatic EM methods in experimental animals, such as the combination of focused ion beam milling and scanning electron microscopy (FIB/SEM), are opening new avenues. Here we explored the utility of FIB/SEM to examine the cerebral cortex of Alzheimer's disease patients. We found that FIB/SEM is an excellent tool to study in detail the ultrastructure and alterations of the synaptic organization of the human brain. Using this technology, it is possible to reconstruct different types of plaques and the surrounding neuropil to find new aspects of the pathological process associated with the disease, namely; to count the exact number and types of synapses in different regions of the plaques, to study the spatial distribution of synapses, and to analyze the morphology and nature of the various types of dystrophic neurites and amyloid deposits.

Synaptic loss is currently established as the best neurobiological correlate of the cognitive deficits of Alzheimer's disease (AD) [Ann. Neurol. 27 (1990) 457; Ann. Neurol. 30 (1991) 572]. We provide evidence that still living neurons lose synapses in AD, in addition to the synapse loss due to death of neurons. We also provide evidence indicating that in addition to loss of synapses, synaptic function is also affected in AD by decrements in transcript species related to synaptic vesicle trafficking.

Neuritic plaques are one of the stereotypical hallmarks of Alzheimer's disease (AD) pathology. These structures are composed of extracellular accumulations of fibrillar forms of the amyloid-beta peptide (Abeta), a variety of other plaque-associated proteins, activated glial cells, and degenerating nerve processes. To study the neuritic toxicity of different structural forms of Abeta in the context of regional connectivity and the entire cell, we crossed PDAPP transgenic (Tg) mice, a model with AD-like pathology, to Tg mice that stably express yellow fluorescent protein (YFP) in a subset of neurons in the brain. In PDAPP; YFP double Tg mice, markedly enlarged YFP-labeled axonal and dendritic varicosities were associated with fibrillar Abeta deposits. These varicosities were absent in areas where there were nonfibrillar Abeta deposits. Interestingly, YFP-labeled varicosities revealed changes that corresponded with changes seen with electron microscopy and the de Olmos silver staining technique. Other silver staining methods and immunohistochemical localization of phosphorylated neurofilaments or phosphorylated tau were unable to detect the majority of these dystrophic neurites. Some but not all synaptic vesicle markers accumulated abnormally in YFP-labeled varicosities associated with neuritic plaques. In addition to the characterization of the effects of Abeta on axonal and dendritic structure, YFP-labeled neurons in Tg mice should prove to be a valuable tool to interpret the localization patterns of other markers and for future studies examining the dynamics of axons and dendrites in a variety of disease conditions in living tissue both in vitro and in vivo., (Copyright 2003 Wiley-Liss, Inc.)

Using a novel approach, including affinity chromatography, reversed-phase chromatography, and chemiluminescence immunoblotting, we have for the first time been able to demonstrate one of the small synaptic vesicle proteins, synaptotagmin I, in cerebrospinal fluid (CSF). Two other small synaptic vesicle proteins, rab3a and synaptophysin, were not detectable. The approximate molecular weight of CSF-synaptotagmin was 65 kDa, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Further characterization of CSF synaptotagmin by high-performance capillary electrophoresis (HPCE) showed a single peak. These findings support that the whole synaptotagmin molecule is present in CSF, without significant proteolytic degradation. After high-speed centrifugation of CSF, synaptotagmin was exclusively found in the supernatant, suggesting that synaptotagmin is present in CSF as a free protein, and not as a constituent of synaptic vesicles. In a preliminary study, we found a marked reduction of CSF synaptotagmin in patients with early onset Alzheimer disease (EAD) as compared with age-matched healthy individuals. To elucidate the biological relevance of this finding, we also quantified synaptotagmin in brain tissue. A marked reduction in synaptotagmin was found both in the hippocampus and frontal cortex of EAD, suggesting that a decrease in synaptotagmin in the brain is followed by a concomitant decrease in the CSF. Analysis of CSF synaptotagmin might provide a tool to study synaptic function and pathology in the human brain.

Alzheimer's disease (AD) is characterised by an increased number of senile plaques (SP) and neurofibrillary tangles (NFT) as compared with that found in non-demented individuals of the same age, and a marked degeneration and loss of synapses. One of the main risk-factors for the disorder is inheritance of the apolipoprotein E4 (ApoE4) allele. To further study the relation between these pathogenetic substrates for AD, we quantified the synaptic vesicle membrane protein rab3a in brain tissue from 19 patients with AD and 9 age-matched control subjects. Rab3a levels were reduced in AD, both in the hippocampus (60% of control level, p < 0.0001), and in the frontal cortex (68% of control level, p < 0.01), but not in the cerebellum (92% of control level). Within the AD group, lower rab3a levels were found both with increasing duration and severity of dementia. These findings further support that synaptic pathology is closely correlated to the clinical dementia in AD. In contrast, no significant correlations were found between SP counts and duration or severity of dementia, while higher NFT counts in the frontal cortex were found with increasing severity of dementia (r = 0.54, p < 0.05). There were no significant correlations between the rab3a level and SP or NFT counts, and by immunohistochemistry, reduced rab3a immunostaining was found throughout the neuropil in AD brain, without relation to SP or NFT. These findings suggest that the synaptic pathology in AD is not closely related to the presence of SP and NFT. No significant differences in rab3a levels were found in any brain region between AD patients possessing different numbers of the ApoE4 allele, suggesting that, although ApoE4 is A risk factor for earlier development of AD, the degree of synaptic pathology does not differ between patients with or without the ApoE4 allele.