Synaptic Markers Research Articles

Mir324 knockout regulates the structure of dendritic spines and impairs hippocampal long-term potentiation

MicroRNAs are an emerging class of synaptic regulators. These small noncoding RNAs post-transcriptionally regulate gene expression, thereby altering neuronal pathways and shaping cell-to-cell communication. Their ability to rapidly alter gene expression and target multiple pathways makes them interesting candidates in the study of synaptic plasticity. Here, we demonstrate that the proconvulsive microRNA miR-324-5p regulates excitatory synapse structure and function in the hippocampus of mice. Both Mir324 knockout (KO) and miR-324-5p antagomir treatment significantly reduce dendritic spine density in the hippocampal CA1 subregion, and Mir324 KO, but not miR-324-5p antagomir treatment, shift dendritic spine morphology, reducing the proportion of thin, “unstable” spines. Western blot and quantitative Real-Time PCR revealed changes in protein and mRNA levels for potassium channels, cytoskeletal components, and synaptic markers, including MAP2 and Kv4.2, which are important for long-term potentiation (LTP). In line with these findings, slice electrophysiology revealed that LTP is severely impaired in Mir324 KO mice, while neurotransmitter release probability remains unchanged. Overall, this study demonstrates that miR-324-5p regulates dendritic spine density, morphology, and plasticity in the hippocampus, potentially via multiple cytoskeletal and synaptic modulators.

Early Age- and Sex-Dependent Regulation of Astrocyte-Mediated Glutamatergic Synapse Elimination in the Rat Prefrontal Cortex: Establishing an Organotypic Brain Slice Culture Investigating Tool.

Clinical and pre-clinical studies of neuropsychiatric (NP) disorders show altered astrocyte properties and synaptic networks. These are refined during early postnatal developmental (PND) stages. Thus, investigating early brain maturational trajectories is essential to understand NP disorders. However, animal experiments are highly time-/resource-consuming, thereby calling for alternative methodological approaches. The function of MEGF10 in astrocyte-mediated synapse elimination (pruning) is crucial to refine neuronal networks during development and adulthood. To investigate the impact of MEGF10 during PND in the rat prefrontal cortex (PFC) and its putative role in brain disorders, we established and validated an organotypic brain slice culture (OBSC) system. Using Western blot, we characterized the expression of MEGF10 and the synaptic markers synaptophysin and PSD95 in the cortex of developing pups. We then combined immunofluorescent-immunohistochemistry with Imaris-supported 3D analysis to compare age- and sex-dependent astrocyte-mediated pruning within the PFC in pups and OBSCs. We thereby validated this system to investigate age-dependent astrocyte-mediated changes in pruning during PND. However, further optimizations are required to use OBSCs for revealing sex-dependent differences. In conclusion, OBSCs offer a valid alternative to study physiological astrocyte-mediated synaptic remodeling during PND and might be exploited to investigate the pathomechanisms of brain disorders with aberrant synaptic development.

Synaptic dysfunction, Tau pathology and Neurodegeneration

AbstractBackgroundTau plays a prominent role in the synapse and has been shown to be closely related to neurodegeneration. Recent evidence show that cerebrospinal fluid (CSF) synaptic markers are related to CSF tau and degeneration. However, it is not clear whether synaptic dysfunction in combination with tau tangles is associated with neurodegeneration in the same brain regions. Our study aims to map in the brain the association of synaptic markers with tau and degeneration.MethodWe evaluated 147 individuals from the TRIAD cohort with CSF GAP43, SYT1, SNAP25, neurogranin (Ng), ptau217, neurofilament light protein (NfL) quantification, as well as tau positron emission tomography (PET), magnetic resonance imaging, and clinical assessments. One‐way ANOVA tested group differences on synaptic levels. Spearman correlation tested the association among synaptic proteins. Linear regressions tested the association between biomarkers. Voxel‐based morphometry (VBM) was considered as an index of neurodegeneration.ResultWe observed an increase in synaptic markers across age and the AD spectrum, reaching a plateau when cognition is affected (Figure 1A). Among the synaptic markers, SNAP25 showed the greatest magnitude of change, on average, between young, aged cognitively unimpaired, mild cognitive impaired, and AD individuals (mean 62.44%). (Figure 1B‐C). In addition, we found that all synaptic markers are significantly intercorrelated (Figure 1D). Moreover, CSF ptau217 correlated with all synaptic biomarkers, GAP43 (β = ‐044), SYT1 (β = ‐0.41), SNAP25 (β = ‐0.59) and Ng (β = ‐0.25). Conversely, CSF NfL was strongly but only correlated with GAP43 (β = 0.62) (Figure 2). Voxel‐wise correlation revealed that tau tangles measured by [18F]‐MK6240 PET, was positively associated with SNAP25 in AD‐related regions, and VBM was associated with all synaptic markers, but more closely with GAP43. Furthermore, the interaction between synaptic markers and temporal meta‐ROI [18F]‐MK6240 on VBM was significant for Ng and GAP43 (Figure 3).ConclusionOur results support a heterogenous role of synaptic markers in the AD continuum and suggest that synaptic dysfunction in the presence of tau pathology may not be driving atrophy.

Synaptic dysfunction in the presence of tau tangles is not a strong predictor of atrophy

AbstractBackgroundTau plays a prominent role in the synapse and has been shown to be closely related to neurodegeneration. Recent evidence show that cerebrospinal fluid (CSF) synaptic markers are related to CSF tau and degeneration. However, it is not clear whether synaptic dysfunction in combination with tau tangles is associated with neurodegeneration in the same brain regions. Our study aims to map in the brain the association of synaptic markers with tau and degeneration.MethodWe evaluated 147 individuals from the TRIAD cohort with CSF GAP43, SYT1, SNAP25, neurogranin (Ng), ptau217, neurofilament light protein (NfL) quantification, as well as tau positron emission tomography (PET), magnetic resonance imaging, and clinical assessments. One‐way ANOVA tested group differences on synaptic levels. Spearman correlation tested the association among synaptic proteins. Linear regressions tested the association between biomarkers. Voxel‐based morphometry (VBM) was considered as an index of neurodegeneration.ResultWe observed an increase in synaptic markers across age and the AD spectrum, reaching a plateau when cognition is affected (Figure 1A). Among the synaptic markers, SNAP25 showed the greatest magnitude of change, on average, between young, aged cognitively unimpaired, mild cognitive impaired, and AD individuals (mean 62.44%). (Figure 1B‐C). In addition, we found that all synaptic markers are significantly intercorrelated (Figure 1D). Moreover, CSF ptau217 correlated with all synaptic biomarkers, GAP43 (ß = ‐044), SYT1 (ß = ‐0.41), SNAP25 (ß = ‐0.59) and Ng (ß = ‐0.25). Conversely, CSF NfL was strongly but only correlated with GAP43 (ß = 0.62) (Figure 2). Voxel‐wise correlation revealed that tau tangles measured by [18F]‐MK6240 PET, was positively associated with SNAP25 in AD‐related regions, and VBM was associated with all synaptic markers, but more closely with GAP43. Furthermore, the interaction between synaptic markers and temporal meta‐ROI [18F]‐MK6240 on VBM was significant for Ng and GAP43 (Figure 3).ConclusionOur results support a heterogenous role of synaptic markers in the AD continuum and suggest that synaptic dysfunction in the presence of tau pathology may not be driving atrophy.

Hippocampal subregion‐specific proteomic differences between Alzheimer disease (AD) and primary age‐related tauopathy (PART)

AbstractBackgroundAlthough Alzheimer disease (AD) and primary age‐related tauopathy (PART) both harbor 3R/4R‐tau immunopositive Alzheimer‐type neurofibrillary degeneration, they differ in the spatial development of neurofibrillary tangles (NFTs) in the hippocampus. PART displays an early predilection for neurofibrillary degeneration in the CA2 subregion of the hippocampus, whereas AD typically develops NFTs in the entorhinal cortex and CA1 subregion initially (Figures 1‐2).MethodUsing Nanostring’s GeoMx™ Digital Spatial Profiling (DSP), we compared hippocampal subregion protein expression differences between AD and PART. The DSP panel allows for spatial analysis of the level of expression of 73 different proteins in multiple regions of interest (ROIs) on formalin‐fixed paraffin embedded sections. Our ROIs were NFT‐bearing neurons and non‐NFT‐bearing neurons in the entorhinal cortex, CA1 and CA2 hippocampal subregions, as well as the neuronal microenvironments in these regions.ResultAnalyses identified several proteins displaying differential expression in tangle‐bearing neurons when comparing AD to PART. These included higher levels of synaptic and neuronal markers in PART, such as Synaptophysin, MAP2, Calbindin and NRGN, as well as higher levels of proteins involved in degradation pathways, such as CTSD, GPNMB, Park7 and FUS. PART also displayed higher levels of Neprilysin in CA2, and higher IDE in CA1, which are proteins that help degrade β‐amyloid (Figure 3). Many of these proteins were also differentially expressed in the non‐tangle bearing neurons. In addition, AD demonstrated higher levels of p‐tau T231, S214, S199, and S396 in non‐tangle bearing neurons of CA1, as well as higher expression of Aβ1‐40. In the microenvironment, NEFL, NRGN, CLEC7a, GPNMB, and CTSD were higher in PART, while p‐tau S396 and BACE1 were higher in AD.ConclusionIn conclusion, PART cases displayed higher levels of neuronal and synaptic markers, suggesting better maintenance of neuronal and synaptic integrity than AD, as well as higher levels of proteins important for degradation of detrimental proteins. AD cases expressed higher levels of certain p‐tau epitopes, especially in and around CA1 non‐tangle bearing neurons. In addition, AD displayed higher levels of BACE1, whereas PART displayed higher levels of CTSD, Neprilysin and IDE, which could explain the differences in β‐amyloid deposition in these cases.

Astrocyte reactivity is associated with synaptic dysfunction across the aging and Alzheimer’s disease spectrum, whereas microglial reactivity is specifically associated with synaptic dysfunction related to cognitive impairment

AbstractBackgroundHealthy synapses are the key to proper brain function, ensuring communication between neurons. Recent studies have associated synaptic dysfunction with Alzheimer’s disease (AD) proteins, however, little is known about the role of glial reactivity, another pathology closely linked to AD, in brain synaptic dysfunction (Figure 1).MethodWe evaluated 123 individuals (67 cognitively unimpaired (CU) and 56 cognitively impaired (CI)) who had available Aβ‐ and Tau‐PET as well as cerebrospinal fluid measures of glial fibrillary acidic protein (GFAP), chitinase‐3‐like protein 1 (YKL‐40), soluble triggering receptor expressed on myeloid cells 2 (sTREM2), synaptic markers (growth‐associated protein 43 (GAP‐43), neurogranin (Ng), synaptotagmin 1 (SYT1), and presynaptic protein synaptosomal‐associated protein 25 (SNAP‐25)). ANCOVA adjusted for clinical diagnosis, age, and sex was used to compare levels of CSF biomarkers; whereas linear regressions adjusted for age, sex, clinical diagnosis, and Aβ/tau‐PET were used to test the associations between glial reactivity and synaptic markers.ResultDemographic information is shown in Table 1. Increased levels of GAP‐43, SNAP‐25, and Ng were observed in CI compared to CU individuals. CSF GFAP was highly associated with both presynaptic and postsynaptic biomarkers in CU and CI groups. CSF YKL‐40 was associated only with presynaptic biomarkers in both clinical groups. On the other hand, CSF sTREM2 showed an association with all synaptic markers but only in the CI group (Figure 2).ConclusionWe found a heterogeneous association between synaptic markers and glial activation. The presence of GFAP+ astrocytes was associated with dysfunction of presynaptic/postsynaptic markers, whereas YKL‐40+ astrocytes specifically reflected presynaptic dysfunction across aging and AD spectrums. On the other hand, microglial activation reflected synaptic dysfunction associated with dementia symptoms. Our results support recent experimental observations suggesting that clarifying the heterogeneity of different glial cell phenotypes is crucial to advancing our understanding of the role of immune cells in cognitive decline.

Astrocyte reactivity is associated with synaptic dysfunction across the aging and Alzheimer’s disease spectrum, whereas microglial reactivity is specifically associated with synaptic dysfunction related to cognitive impairment

AbstractBackgroundHealthy synapses are the key to proper brain function, ensuring communication between neurons. Recent studies have associated synaptic dysfunction with Alzheimer’s disease (AD) proteins, however, little is known about the role of glial reactivity, another pathology closely linked to AD, in brain synaptic dysfunction (Figure 1).MethodWe evaluated 123 individuals (67 cognitively unimpaired (CU) and 56 cognitively impaired (CI)) who had available Aß‐ and Tau‐PET as well as cerebrospinal fluid measures of glial fibrillary acidic protein (GFAP), chitinase‐3‐like protein 1 (YKL‐40), soluble triggering receptor expressed on myeloid cells 2 (sTREM2), synaptic markers (growth‐associated protein 43 (GAP‐43), neurogranin (Ng), synaptotagmin 1 (SYT1), and presynaptic protein synaptosomal‐associated protein 25 (SNAP‐25)). ANCOVA adjusted for clinical diagnosis, age, and sex was used to compare levels of CSF biomarkers; whereas linear regressions adjusted for age, sex, clinical diagnosis, and Aß/tau‐PET were used to test the associations between glial reactivity and synaptic markers.ResultDemographic information is shown in Table 1. Increased levels of GAP‐43, SNAP‐25, and Ng were observed in CI compared to CU individuals. CSF GFAP was highly associated with both presynaptic and postsynaptic biomarkers in CU and CI groups. CSF YKL‐40 was associated only with presynaptic biomarkers in both clinical groups. On the other hand, CSF sTREM2 showed an association with all synaptic markers but only in the CI group (Figure 2).ConclusionWe found a heterogeneous association between synaptic markers and glial activation. The presence of GFAP+ astrocytes was associated with dysfunction of presynaptic/postsynaptic markers, whereas YKL‐40+ astrocytes specifically reflected presynaptic dysfunction across aging and AD spectrums. On the other hand, microglial activation reflected synaptic dysfunction associated with dementia symptoms. Our results support recent experimental observations suggesting that clarifying the heterogeneity of different glial cell phenotypes is crucial to advancing our understanding of the role of immune cells in cognitive decline.

GFAP Upregulation by Astrocytes May Attenuate Phospho‐Tau Levels in a Tauopathy Mouse Model

AbstractBackgroundAstrocytes react to amyloid‐β plaques and phospho‐tau (pTau) neurofibrillary tangles in the Alzheimer’s disease brain but their net effect on these Alzheimer’s neuropathological hallmarks remains controversial. A well‐known feature of these so‐called “reactive astrocytes” is the upregulation of the intermediate filament glial fibrillary acidic protein (GFAP), which is thought to be necessary for astrocyte process motility and glial scar formation. Here we asked whether this cytoskeletal remodeling helps reactive astrocytes control the burden of pTau species and/or protect synapses and neurons.MethodWe overexpressed human GFAP isoform 1 specifically in astrocytes of 4‐month‐old, sex‐balanced, THY‐Tau22 mice (Thy1.2‐MAPT G272V/P301S 1N4R, GFAP mice, n = 11)—when neurofibrillary tangles start to appear in the hippocampal CA1 subfield—using a viral transfer strategy with single retro‐orbital intravenous injection of AAV‐PHP.B (2.5×1011 vg) and the gfaABC1D promoter. We euthanized the mice at 11 months of age (i.e., prior to the tauopathy plateau) and performed immunohistochemical and/or biochemical analysis of astrocyte, tau, and synaptic markers. Negative control groups consisted of THY‐Tau22 littermates injected with either phosphate‐buffered saline (PBS mice, n = 9) or an AAV‐PHP.B vector encoding the enhanced green fluorescent protein (EGFP mice, n = 10).ResultsImmunohistochemistry confirmed the astrocyte‐specific expression of human GFAP with an apparent integration in their intermediate filament network. We observed statistically significant reductions or marginally significant trends toward decrease in hippocampal SDS‐soluble levels AT8/pTauSer202/Thr205 and AT8‐immunoreactive area fraction, and a shift of AT180/pTauThr231 from SDS‐soluble (decreased) to TBS‐soluble (increased) hippocampal protein fractions, in GFAP vs. EGFP and/or PBS mice, but no changes in soluble or insoluble total tau or AT270/pTauThr181 across groups. In the cortex, we detected no changes in soluble or insoluble total tau, AT8/pTauSer202/Thr205, or AT270/pTauThr181 levels, nor in AT8‐immunoreactive area. Lastly, we found no significant differences across groups in brain weight, cortical or hippocampal areas, nor in the cortical levels of synaptophysin, Psd95, or the glutamate transporters Eaat1/Glast‐1 and Eaat2/Glt‐1.ConclusionOur findings indicate that GFAP upregulation by astrocytes—a classic feature of reactive astrogliosis—may attenuate neuronal pTau burden in a tauopathy mouse model. Ongoing work will further elucidate whether this aspect of reactive astrocytes impacts pTau‐induced neurodegeneration.

Cross‐sectional investigation of synaptic markers Neurogranin and BACE1 in CSF from the AIBL study

AbstractBackgroundSynaptic disfunction is a feature of Alzheimer’s disease. Recent studies show both pre‐ and post‐synaptic termini proteins change in concentration in the CSF across the A/T/N framework. Here we investigate BACE1, neurogranin (Ng) and alpha‐synuclein, along with total‐tau (t‐tau) and amyloid‐β 1‐42 (Aβ42), in relation to PET‐amyloid status.MethodParticipants (n = 105) with CSF and matching PET‐amyloid scans from the Australian Imaging, Biomarkers and Lifestyle (AIBL) study were analysed for CSF synaptic markers BACE1, Ng and alpha‐synuclein using commercially available antibody assays (EUROIMMUN). BACE1 used ADx401 (5G7) and ADx402 (10B8) antibodies, Neurogranin trunc p75 used monoclonal ADx403 (ADxNGCI2) and ADx451 (ADxNGCT1) antibodies, and alpha‐synuclein used ADx301 and ADx302 antibodies. Total‐tau and Aβ42 were measured using the Roche Elecsys®. PET‐amyloid status was defined using a Centiloid of <25 as negative, and 25 or greater positive.ResultCross‐sectional changes in biomarker values between the PET‐amyloid negative and positive groups were seen for Ng (p<0.05), but not for BACE1 or alpha‐syn. The ratio of Ng/BACE1 improved separation between groups (p<0.001). Total‐tau displayed the greatest differentiation of a single biomarker (p = 2.7×10−10) and this separation was improved using a ratio of t‐tau/BACE1 (p = 3.2×10−12). For predicting PET‐amyloid status (adjusting for age, APOE e4 and gender), t‐tau (AUC: 0.87 [95%CI: 0.80‐0.95]) was slightly improved using the ratio of t‐tau/BACE1 (AUC: 0.90 [95%CI: 0.82‐0.97]) to the same degree as using t‐tau/Aβ42 (AUC: 0.90 [95%CI: 0.82‐0.97]), although this was not significant (p>0.05).ConclusionThis study saw within a PET‐amyloid positive subpopulation of AIBL an increase in neurogranin, a post‐synaptic marker. The presynaptic marker BACE1 alone was not changed in concentration, but when BACE1 was used in a ratio with t‐tau, a marker of neuronal degradation, the differentiation between amyloid negative and positive groups increased. The predictive ability between t‐tau/BACE1 and t‐tau/Aβ42 to estimate PET‐amyloid load is comparable and measurements incorporating BACE1 may provide an alternative to Aβ42‐based assays and the inherent variability associated with Aβ42 measurement between testing sites.

Osteopontin exhibits a bidirectional relationship with Alzheimer’s disease pathology in asymptomatic individuals with a parental history of sporadic Alzheimer’s disease

AbstractBackgroundOsteopontin (OPN) is a secreted protein that plays pivotal roles in the recruitment and activation of immune cells, cell survival, and tissue repair following injury. OPN has been demonstrated to be increased in the cerebrospinal fluid (CSF) and brains of individuals with Alzheimer’s disease (AD). However, in order to elucidate the role of OPN in the asymptomatic stage of sporadic AD, we analyzed data from the PREVENT‐AD cohort, which consists of asymptomatic individuals with a parental or multi‐sibling history of AD.MethodThe Olink Proximity Extension Assay was used to measure CSF levels of OPN. CSF levels of amyloid beta (Aβ1‐42), and total Tau (t‐Tau) were measured by enzyme‐linked immunosorbent assay (Fujirebio). Participants were staged as CSF Aβ1‐42 or t‐Tau positive according to specified thresholds of 989 pg/mL and 336 pg/mL, respectively. CSF levels of synaptic proteins, including GAP43, SYT1, SNAP25 and NRGN were measured by immunoprecipitation followed by mass spectrometry. Tau and Aβ positron emission tomography (PET) burdens were measured using 18F‐AV1451 and 18F‐NAV4694.ResultAβ(+)/Tau(‐) individuals displayed a reduction in CSF OPN levels, relative to Aβ(‐)/Tau(‐) individuals (p = 0.001). Furthermore, Aβ(+)/Tau(+) individuals exhibited a significant increase in CSF OPN levels relative to Aβ(+)/Tau(‐) individuals (p < 0.001), and at a trend level, to Aβ(‐)/Tau(‐) individuals (p = 0.069). In addition, CSF OPN levels were positively correlated with synaptic markers in the CSF, including GAP43 (p < 0.001), SYT1 (p = 0.001), SNAP25 (p < 0.001) and NRGN (p = 0.004). Finally, in PET imaging analyses, CSF OPN levels were positively correlated with pTau burden in the entorhinal cortex (p = 0.009), fusiform gyrus (p = 0.030) and lingual gyrus (p = 0.003). However, CSF OPN levels were not correlated with global cortical Aβ burden (p = 0.374).ConclusionOur results suggest that early Aβ pathology dampens OPN levels in asymptomatic individuals with a family history of AD. Furthermore, our data provide compelling evidence that OPN plays a critical role in the compensatory response to neurofibrillary tangle formation, neuronal loss and synaptic dysfunction. Finally, our findings reveal that OPN may be a valuable therapeutic target.

Synapse dysfunction and astrocyte reactivity are associated independently of amyloid‐β and tau pathologies

AbstractBackgroundBiomarkers of astrocyte reactivity have the potential to improve diagnostic precision, disease monitoring, and treatment efficacy. Glial fibrillary acidic protein (GFAP) protein is expressed in astrocytes, which is important to synaptic plasticity, cell communication, and reactive gliosis.MethodCerebrospinal fluid (CSF) biomarkers were measured in participants of the McGill TRIAD cohort. 75 individuals (>50 years old, 44 cognitively unimpaired (CU), and 31 with cognitive impairment (CI)), had available Aβ and tau‐PET. We measured CSF GFAP and synaptic markers (growth‐associated protein 43 (GAP‐43), neurogranin (Ng), synaptotagmin 1 (SYT1), presynaptic protein synaptosomal‐associated protein 25 (SNAP‐25)). Linear regressions adjusted for age, sex, clinical diagnosis, and Aβ/tau‐PET were used to test the associations between astrocyte reactivity and synaptic function.ResultDemographic information is shown in Table 1. We found an association between CSF GFAP and presynaptic markers (GAP‐43: p<0.0001, β = 0.1076; SYT1: p<0.0001, β = 0.0024; SNAP‐25 long: p<0.0001, β = 0.0008) as well as postsynaptic markers (Ng: p<0.05, β = 0.0066) independently of Aβ and tau burden (Figure 1).ConclusionOur biomarker results support experimental literature suggesting that astrocyte reactivity plays a role in downstream synaptic dysfunction independent of the brain levels of Aβ and tau tangles pathologies. This supports in vitro literature suggesting that therapeutic interventions targeting astrocyte reactivity can contribute to halting AD progression.

Synapse dysfunction and astrocyte reactivity are associated independently of amyloid‐β and tau pathologies

AbstractBackgroundBiomarkers of astrocyte reactivity have the potential to improve diagnostic precision, disease monitoring, and treatment efficacy. Glial fibrillary acidic protein (GFAP) protein is expressed in astrocytes, which is important to synaptic plasticity, cell communication, and reactive gliosis.MethodCerebrospinal fluid (CSF) biomarkers were measured in participants of the McGill TRIAD cohort. 75 individuals (>50 years old, 44 cognitively unimpaired (CU), and 31 with cognitive impairment (CI)), had available Aß and tau‐PET. We measured CSF GFAP and synaptic markers (growth‐associated protein 43 (GAP‐43), neurogranin (Ng), synaptotagmin 1 (SYT1), presynaptic protein synaptosomal‐associated protein 25 (SNAP‐25)). Linear regressions adjusted for age, sex, clinical diagnosis, and Aß/tau‐PET were used to test the associations between astrocyte reactivity and synaptic function.ResultDemographic information is shown in Table 1. We found an association between CSF GFAP and presynaptic markers (GAP‐43: p<0.0001, ß = 0.1076; SYT1: p<0.0001, ß = 0.0024; SNAP‐25 long: p<0.0001, ß = 0.0008) as well as postsynaptic markers (Ng: p<0.05, ß = 0.0066) independently of Aß and tau burden (Figure 1).ConclusionOur biomarker results support experimental literature suggesting that astrocyte reactivity plays a role in downstream synaptic dysfunction independent of the brain levels of Aß and tau tangles pathologies. This supports in vitro literature suggesting that therapeutic interventions targeting astrocyte reactivity can contribute to halting AD progression.

Accelerated Ovarian Failure (AOF) is an Effective Transitional Menopausal Model for the Study of Alzheimer’s Disease

AbstractBackgroundBiological females account for 70% of Alzheimer’s disease (AD) cases. It’s hypothesized that the estrogen depletion females experience during menopause is a factor in the pathogenesis of AD1. The gold standard rodent model of ovariectomy doesn’t allow for the examination of the gradual loss of estrogen that occurs in humans through perimenopause to menopause2. Administration of 4‐vinylcyclohexene diepoxide (VCD) has emerged as a rodent model of transitional menopause. The goal of this study was to determine how AD and neuronal markers were impacted by the gradual depletion of estrogen in a VCD model of transitional menopause.MethodMature CD1 female mice were injected with VCD (160 mg/kg/d IP for 15 days) to cause gradual ovarian failure over 120 days. A control group was also injected with a vehicle. Sample was collected at four timepoints, two representative of early and late perimenopause (60 and 120 days post injection) while the other two represented early and late menopause (137 and 176 days post injection). At each timepoint, novel object recognition testing (NORT) was performed to assess changes in behavior and memory2. At euthanasia, the prefrontal cortex and hippocampus were collected for protein analysis.ResultThe NORT demonstrated that the VCD groups at all timepoints had lowered activate memory recall. The prefrontal cortex western blotting results demonstrated that the VCD mice had lower NeuN content across all timepoints. NeuN is a marker of mature neurons which when lowered can have detrimental consequences on memory. SNAP25, a pre‐synaptic protein involved in neuronal synaptic communication, was also lower in the prefrontal cortex of VCD mice across all timepoints.ConclusionThe VCD model had impacts on active memory recall which was accompanied by reductions in neuronal and synaptic markers. This indicates that the loss of estrogen through transitional menopause results in early changes in neuronal markers and memory.1. Iqbal, J. & Zaidi, M. Understanding Estrogen Action during Menopause. Endocrinology 150, 3443‐3445 (2009).2. Mohammad, A., Finch, M. S., Sweezey‐Munroe, J. & MacPherson, R. E. K. Voluntary wheel running alters markers of amyloid‐beta precursor protein processing in an ovarian hormone depleted model. Front. Endocrinol. 13, 1069404 (2022).

Understanding synaptic loss in PSP brains with UCB‐J

AbstractBackgroundProgressive supranuclear palsy (PSP) is a 4R‐tauopathy causing problems with balance, movement, vision, speech, and swallowing. There is a lack of biomarkers for PSP, which often leads to misdiagnosis, prescription of incorrect pharmacological treatments and likely underdiagnosis. Synaptic vesicle protein 2A (SV2A) PET‐tracer UCB‐J has shown great promise in imaging synaptic loss in many neurodegenerative diseases in vivo including PSP. UCB‐J‐PET imaging holds great potential for the early and accurate diagnosis of PSP, however, there is a substantial gap in knowledge around the extent of synaptic loss in PSP. Hence, it is of utmost importance to investigate synaptic changes in PSP brains with UCB‐J and to establish its correlation with other synaptic and neuropathological markers to gain a deeper understanding of underlying mechanisms for future biomarker validation.MethodWe performed specialized postmortem brain imaging (small and large frozen brain autoradiography) and radioligand binding assays (saturation, competition, and regional distribution), alongside immunohistochemistry and biochemical analyses in PSP and control (CN) brains.ResultSaturation studies in brain homogenates (BH) from the frontal cortex (FC) showed lower specific binding of 3H‐UCB‐J in PSP (Bmax: 348‐409 fmol/mg, Kd∼2.7nM) as compared to CN brains (Bmax:0.4‐0.5 pmol/mg, Kd∼3.5nM), indicating a loss in SV2A. Importantly, PSP brains showed much higher 3H‐UCB‐J specific binding in nuclear membrane P1‐fractions (Bmax 18.7‐22.1 pmol/mg, Kd ∼3.0nM) and synaptosomal‐membrane P2‐fractions (Bmax: 10.3‐12.3 pmol/mg, Kd∼2.4nM) as compared to BH (see above). Small section autoradiography showed lower 3H‐UCB‐J specific binding in PSP FC, but unexpectedly higher average specific binding in globus pallidus as compared to CN, suggesting regional differences and potential interaction with other brain tissue components/proteins.ConclusionOur findings clearly demonstrate that there are region‐specific changes in UCB‐J binding in PSP brains compared to CN and further reflect the need for its in‐depth validation in postmortem brains and correlation with other synaptic and neuropathological markers. Moreover, P2 fraction is most optimal for reflecting synaptic loss with UCB‐J. The ongoing regional distribution, biochemical and immunostaining studies will help elucidate changes in synaptic integrity in PSP.

Regulation of tau‐phosphorylation and other Alzheimer’s disease‐associated phenotypes in REST conditional knockout mice

AbstractBackgroundThe RE1‐silencing transcription factor (REST) has been strongly implicated in Alzheimer’s disease (AD), healthy ageing and longevity, and there is a clear need to understand better the exact mechanisms that mediate that role. Here we study the role of REST in a series of AD‐related phenotypes in the mouse brain.MethodWe have previously generated a conditional knockout (cKO) mouse model, lacking Rest in the postnatal forebrain. Immunohistochemistry and Western blot were used to evaluate the effect of REST on neuronal, synaptic and astrocytic markers and key proteins involved in tau phosphorylation. Furthermore, RNA‐Seq (including gene ontology, gene set enrichment and protein‐protein interaction analyses) was used to study the effect of REST inactivation at the transcriptome.ResultQuantification of labelled neuronal nuclei on brain sections revealed no major neurodegeneration in Rest cKO mice. However, mild phenotypes of dendritic degeneration and as astrocytic activation were suggested. The levels of an important postsynaptic protein, PSD‐95, appeared reduced in the brain of Rest cKO mice. Interestingly, levels of proteins involved in the phosphorylation of tau, such as glycogen synthase kinase‐3beta (GSK‐3β) and p35/p25 (activators of CDK5), as well as the levels of phosphorylated tau, were found increased in the brain of Rest cKO mice. RNA‐seq results suggest that postnatal inactivation of REST down‐regulates synaptic activity and neuronal pathways, while triggering an immune response.ConclusionOur results suggest dysregulation of one of the biochemical hallmarks of Alzheimer’s disease, tau phosphorylation, and of synaptic and neuronal pathways, as well as an immune response, when REST is inactivated in the adult mouse brain.

Brain‐age prediction and its associations with glial and synaptic CSF markers

AbstractBackgroundMRI‐derived brain‐age prediction is a promising biomarker of biological brain aging. Accelerated brain aging has been found in Alzheimer’s disease (AD) and other neurodegenerative diseases. However, no previous studies have investigated the relationship between specific pathophysiological pathways in AD and biological brain aging. Here, we studied whether glial activation and synaptic dysfunction are associated with biological brain aging in the earliest stages of the Alzheimer’s continuum.MethodWe included 418 cognitively unimpaired individuals (CU) from the ALFA+ study with available structural MRI, and CSF biomarkers of amyloid‐ß (Aß42/40) and tau pathology (p‐tau181), synaptic dysfunction (neurogranin, GAP43, SYT1, SNAP25), glial activation (sTREM2, YKL40, GFAP, interleukin‐6 and S100b) and a‐synuclein (Table 1). Aß42/40, neurogranin and the glial activation biomarkers were measured using the Roche NeuroToolKit. We computed brain‐age delta as the difference between chronological and predicted brain‐age. The latter was estimated using a previously pretrained machine learning algorithm on cerebral morphological measurements on individuals from the UKBioBank cohort (N = 22.000). General linear modeling was used to test the associations between CSF biomarkers and brain‐age delta, adjusting by p‐tau, age, APOE status and sex. For the biomarkers whose associations were significant, we evaluated the interaction term “biomarker” × AT status while adjusting by age, APOE status and sex. AT staging was performed using pre‐established cut‐off values. We then used hippocampal volume as a marker of AD‐related neurodegeneration and repeated the same association studies with CSF biomarkers, adjusting by p‐tau, age, APOE status, sex and TIV.ResultBrain‐age delta was negatively associated with CSF sTREM2 (Padjusted<0.001), meaning that younger‐appearing brains showed higher levels of this biomarker (Table 1). None of the other biomarkers survived multiple comparisons. Hippocampal volume was not significantly associated with any of the CSF biomarkers (Table 2). There was no significant interaction between AT status and CSF sTREM2 for brain‐age delta, nor for hippocampal volume.ConclusionThese results showed that higher levels of CSF sTREM2 were associated with younger‐appearing brains in CU individuals independently of AT status, which might indicate a protective effect of this microglial phenotype in brain aging. This effect might not be AD‐related.

Neuron‐derived extracellular vesicles blood‐based diagnosis of synuclein TDP43 autophagy and synaptic dysfunction pathologies

AbstractBackgroundStratifying dementia into different subgroups based on specific pathologies can facilitate the development of more effective treatments for subgroups of individuals with dementia. Effective stratification relies on reliable biomarkers. Neuron‐derived extracellular vesicles (NDEs) are lipid structures released by neurons into the extracellular space, and some get into the bloodstream. NDEs carry proteins and RNA that reflect their cell of origin and thus provide a promising biomarker platform.MethodNeuroDex developed two methods. ExoSORT is an optimized NDE isolation platform by immunoaffinity, where NDEs are captured with antibodies against the neuronal‐specific markers GAP43 and NLGN3. LuminEV is an intact extracellular vesicle (EV) immunoassay based on the Luminex platform. Antibodies against a potential biomarker, general EV marker, and IgG (negative control) are multiplexed to generate a robust assay.ResultThe vesicular nature and size of NDEs were confirmed by electron microscopy and nanoparticle tracking. EV markers were ascertained by western blot and proteomic analyses, and capture specificity was demonstrated by significantly elevated neuron‐specific proteins and mRNA levels compared to procedural control (IgG). Capture efficiency (∼80%) and precision (CV < 20%) demonstrated recovery of spiked NDEs. Measurements of αSYN following ExoSORT with an MSD assay and on EVs with the LuminEV generated a separation with 83% sensitivity and 86% specificity (45 Parkinson and 30 healthy controls plasma samples). LC3, an autophagy marker, was also measured following ExoSORT and was significantly (P<0.03) elevated in PD and Alzheimer’s disease (AD) (P<0.02, N = 30) plasma samples. TDP43 was also significantly (P<0.004) higher in AD plasma samples following ExoSORT. The synaptic marker GLUR2 was measured by the LuminEV assays and was significantly (P<0.001) reduced in AD and PD plasma samples. Its level was also significantly (P<0.03) correlated with the patient’s cognitive score.ConclusionImmunoaffinity isolation of EVs from plasma samples according to their cell of origin is a promising biomarker platform. We demonstrate the NDEs isolation selectivity, specificity, and precision. We also show the platform’s potential to identify pathologies like αSYN, TDP43, autophagy, and synaptic dysfunction; this reflects the potential for patient stratification.

Investigating the synaptic mechanisms of the spread of wild type and P301S 1N4R human tau in in vitro and in vivo models

AbstractBackgroundTau aggregates propagate across functionally connected neuronal networks in tauopathies as Alzheimer’s disease. However, the mechanisms underlying this process are poorly understood. Different studies showed that tau release is dependent on neuronal activity and that pathological tau can be found in the extracellular space confined in extracellular vesicles or in a free form. We recently showed that metabotropic glutamate receptors and SNAP25 modulate the release of pathologic tau from human and mouse synaptosomes. Here, with the use of blocking agents such as botulinum neurotoxins (BoNTs), we plan to test the effect on the synaptic release of tau in vitro and in vivo. BoNTs enter synapses and cleave specific synaptic SNARE proteins, impairing synaptic vesicle fusion and release. We aim at demonstrating the potential of BoNTs as tools to study neurodegenerative diseases.MethodsPrimary mouse hippocampal neurons were cultured in microfluidic chambers, transduced with lentiviruses expressing human tau (hTau) isoforms, and treated with BoNTs and stimulators. ELISA was used to quantify hTau in the culture media. AAVs expressing hTau were injected in the vitreous of wild‐type mice, and BoNT type A (BoNT/A) was injected in the superior colliculus (SC). Retina, SC and lateral geniculate nucleus (LGN) were analysed through immunohistochemistry.ResultsOverexpression of hTau in primary neurons increases the expression of synaptic markers as compared to non‐transduced cells, while any difference is detected between wild‐type and P301S hTau. Neuronal stimulation significantly increases the release of P301S hTau, whereas BoNT/A blocks it. Preliminary in vivo data show no difference in the expression and transfer of wild type and P301S hTau in the SC and LGN. The ongoing analysis of BoNT/A injected mice will reveal any effect on tau spread in the brain.ConclusionsThe release of hTau is modulated by specific SNARE proteins and differs depending on the isoform in vitro. The use of BoNT/A in vivo will help us to clarify the mechanisms modulating tau release in a complex system. Moreover, with the use of other BoNTs, we will provide novel insights into the mechanisms of synaptic tau release and identify novel molecular targets for the development of therapeutic interventions to treat tauopathies.

CSF levels of the synaptic marker Cyclase‐associated protein CAP2 in Alzheimer disease across clinical stages

AbstractBackgroundSynaptic dysfunction represent a key event in cognitive decline in Alzheimer disease. There is evidence that Cyclase‐associated protein 2 (CAP2) is involved in synaptic plasticity in AD models but its role in clinical setting has never extensively assessed. Aim of this study was to evaluate CAP2 levels in cerebrospinal fluids of AD and other neurodegenerative diseases and their relationship with amyloid and tau related biomarkers.Methodone‐hundred ten AD patients (prodromal AD n = 70; mild to moderate AD n = 40), 20 Lewy Body Dementia (LBD), 20 frontotemporal dementia (FTD) and 40 healthy controls (HC) were investigated and clinically assessed following a standardized neurological and cognitive behavioral assessment. All subjects underwent CSF analyses for h‐tau, p‐tau and Aß42 (Lumipulse) while CAP2 levels were assessed by using standard ELISA. Between‐groups differences and correlations between CSF biomarkers were evaluated using non‐parametric comparisons and partial correlation analyses adjusted for the effect of age, sex and disease duration.ResultAD patients across severity stages showed higher CAP2 levels compared to controls and non‐AD patients (p = 0.001). CAP2 levels did not correlate with disease severity and were independent of APOE genotype. In AD patients, CAP2 levels showed a positive correlation with t‐tau and p‐tau (p<0.001).ConclusionCSF levels of CAP2 were significantly increased in AD patients and correlated with t‐tau and p‐tau independently of amyloid pathology. Altogether, these findings support the hypothesis that AD is specifically associated with synaptic dysfunction since early stages and that amyloid‐related synaptic changes parallels tau‐related axonal degeneration.

Novel mechanisms to enhance omega‐3 brain metabolism with APOE4

AbstractBackgroundNeuroprotective nutritional interventions involving greater consumption of polyunsaturated fats (Mediterranean diet, fish consumption or DHA supplements) are less effective in APOE4 carriers with dementia compared to non‐carriers. We recently demonstrated greater activation of calcium dependent phospholipase A2 (cPLA2) in APOE4 compared with non‐APOE4 using both postmortem human brains and in brain tissues from APOE4 animal models. Activation of cPLA2 is associated with lower omega‐3 brain levels and lower measures of blood‐brain barrier (BBB) integrity as assessed using 7T DCE MRI to derive contrast transfer values (K trans).MethodHere, we present new data on aging (18 months) old APOE mouse models on a low DHA diet, APOE4‐TR mice treated with LPS and APOE knock out mice as a model of lower BBB integrity. All models were treated with the brain penetrant cPLA2 inhibitor ASB14780 at 10 mg/kg IP daily over 8 weeks in the aging model and acutely (7 days) in the younger LPS and APOE KO models.ResultcPLA2 inhibition was associated with increased brain omega‐3 levels in both the aging APOE4 model and in the younger APOE4 mice treated acutely with LPS. In the aging APOE4 mouse model, cPLA2 inhibition associated with better performance on novel object recognition, improved synaptic markers, and lower microglial activation. In the APOE KO model, treatment was associated with improved measures of BBB with lower K trans following treatment (Figure).ConclusionThe results here demonstrate how neuroinflammation associated with APOE4 depletes brain omega‐3s via activation of cPLA2 and how reducing cPLA2 activity can rescue this phenotype. The development of specific and potent brain penetrant cPLA2 inhibitors promises to enhance the brain effects of omega‐3 enriched diets by limiting the effects of neuroinflammation on the aging APOE4 brain.