Changes in the Synaptic Proteome in Tauopathy and Rescue of Tau-Induced Synapse Loss by C1q Antibodies

In the paper

“infiltration of pathological Tau can disrupt synaptic functions and lead to synapse loss (Hoover et al., 2010; Zhao et al., 2016”

What the sources say

• Partly supported

  The Discussion reports that pathological tau mislocalization into dendritic spines suppresses synaptic function. It places this impairment before synapse loss and describes later spine loss as a hypothesis, rather than demonstrating that tau infiltration leads to synapse loss. (LLM, conf=0.86)

  cites Hoover et al., 2010 sourceExperimental — accuracy not yet measured
• ?Not checked — no full text of the sourcecites Zhao et al., 2016 source

In the paper

“where variants in the underlying genes are associated with epilepsy, autism, schizophrenia, or intellectual disability (De Rubeis et al., 2014; Russell et al., 2014; Sadybekov et al., 2017; Shoubridge et al., 2010; Yang et al., 2014”

What the sources say

• Partly supported

  The Transmission and De novo Association section identifies TRIO among genes previously found mutated in people with autism, and Extended Data Table 1 lists an IQGAP2 deletion in an ASD subject. The passages do not establish the claimed associations for IQGAP1, IQSEC2, or Kalirin, or link the named genes individually to epilepsy, schizophrenia, or intellectual disability. Page numbers are not available in our copy. (LLM, conf=0.86)

  cites De Rubeis et al., 2014 sourceExperimental — accuracy not yet measured
• Supported

  The Introduction states that KALRN has been associated with schizophrenia risk through resequencing and association analyses. This supports the Kalirin–schizophrenia part of the multi-citation claim; the paper does not establish that its own rare variant increases schizophrenia risk. (LLM, conf=0.88)

  cites Russell et al., 2014 source
• Supported

  The Results section (‘ASD-related mutations in Trio’) reports de novo TRIO variants in individuals with ASD or related disorders, including intellectual disability. In this multi-citation sentence, the paper supports the association for TRIO; the other genes are not attributed specifically to this source. (LLM, conf=0.91)

  cites Sadybekov et al., 2017 source

In the paper

“it is Tau pathology and synapse loss that temporally correlate with cognitive impairment and precede overt neurodegeneration (Jack et al., 2010; Scheff et al., 2006; Spires-Jones and Hyman, 2014”

What the sources say

• Partly supported

  The 'AD clinical features and pathological changes' section links NFTs and especially synapse loss to clinical symptoms and cognitive impairment. The 'Neurodegenerative biomarkers are temporally ordered' section says CSF tau and FDG-PET abnormalities precede MRI-detected atrophy, not neurodegeneration generally; it describes synapse loss itself as a form of neurodegeneration. The claim therefore overstates what precedes what. (LLM, conf=0.88)

  cites Jack et al., 2010 sourceExperimental — accuracy not yet measured
• ?Not checked — no full text of the sourcecites Scheff et al., 2006 source
• Partly supported

  The paper states that tau tangles correlate with cognitive decline (Abstract; “Alzheimer’s disease pathology – tau”) and that synapse loss is the strongest pathological correlate of dementia (“Synaptic dysfunction, synapse loss and relationships to pathology”; page unavailable). It does not establish that both tau pathology and synapse loss precede overt neurodegeneration; the Abstract instead describes synapse degeneration as part of the neurodegenerative process. (LLM, conf=0.86)

  cites Spires-Jones and Hyman, 2014 sourceExperimental — accuracy not yet measured

In the paper

“In particular, C1q, the initiator of the classical complement pathway, which is produced by microglia in the brain, colocalizes with synaptic markers and may contribute to synapse loss in several neurodegenerative models (Hong et al., 2016a; Lui et al., 2016; Vasek et al., 2016”

What the sources say

• ?Not matched

  Couldn’t be matched to a paper in Crossref, so it can’t be checked.

  cites Hong et al., 2016a
• Supported

  The Results section on age-dependent complement activation reports C1qa next to synaptophysin-positive synapses in Grn−/− mice. The Results section on synaptic pruning says C1qa is made by microglia and that its loss reduces microglial pruning. This paper supports the Grn−/− model as one example within the several-model statement, which cites multiple papers. (LLM, conf=0.88)

  cites Lui et al., 2016 source
• Partly supported

  The paper’s Abstract identifies C1QA as an initiator of the classical complement cascade, detects its expression alongside the microglial marker IBA1, and reports increased colocalization with VGlut1-positive presynaptic terminals. It links complement and microglia to synapse loss in West Nile virus-infected mice, but does not establish that C1q contributes to synapse loss in several neurodegenerative models. (LLM, conf=0.87)

  cites Vasek et al., 2016 sourceExperimental — accuracy not yet measured

In the paper

“During progression of AD and other tauopathies, abnormally phosphorylated forms of Tau aggregate and accumulate in the somatodendritic compartment in neurons and can localize to synapses (Ittner and Götz, 2011; Tai et al., 2012”

What the sources say

• ?Not checked — no full text of the sourcecites Ittner and Götz, 2011 source
• Partly supported

  The sections “p-tau is Localized to Both Presynaptic and Postsynaptic Sites” and “Synaptic tau in the Context of Other AD Lesions” (pages unavailable) report that hyperphosphorylated tau oligomers accumulate at AD synapses, including postsynaptic sites. The cited paper does not establish the broader claim of somatodendritic accumulation in neurons across AD and other tauopathies. (LLM, conf=0.86)

  cites Tai et al., 2012 sourceExperimental — accuracy not yet measured

In the paper

“Synapse loss is a hallmark of Alzheimer’s disease (AD) and other tauopathies and is central to the neurodegenerative process (Spires-Jones and Hyman, 2014”

What the sources say

• Partly supported

  The Abstract describes synaptic changes as central to the AD disease process, and “Synaptic dysfunction, synapse loss and relationships to pathology” calls synapse loss the strongest pathological correlate of dementia in AD. That section also reports fewer synapses on tangle-bearing neurons in mouse models of tauopathy, but does not establish synapse loss as a hallmark of other human tauopathies. (LLM, conf=0.86)

  cites Spires-Jones and Hyman, 2014 sourceExperimental — accuracy not yet measured

In the paper

“The postsynaptic density (PSD) of excitatory synapses is usually located on dendritic spines, whose growth and stability depend on the actin cytoskeleton and whose dynamic modulation is essential for synaptic integrity and plasticity (Fukazawa et al., 2003; Okamoto et al., 2004”

What the sources say

• Partly supported

  The Introduction describes dynamic actin in dendritic spines, and the Abstract and Discussion link spine actin reorganization to spine morphology and maintenance of hippocampal LTP. Our copy does not establish that the PSD of excitatory synapses is usually on spines, or that spine growth, stability, and synaptic integrity generally depend on actin. (LLM, conf=0.82)

  cites Fukazawa et al., 2003 sourceExperimental — accuracy not yet measured
• ?Not checked — no full text of the sourcecites Okamoto et al., 2004 source

In the paper

“During development, complement-dependent synaptic pruning by microglia is modulated by synaptic activity such that active synapses are preserved and less active synapses are removed (Schafer et al., 2012”

What the sources say

• Supported

  The Results section, “Microglia-mediated engulfment of RGC inputs is regulated by neural activity,” reports preferential engulfment of inputs from the less active eye rather than the more active eye. The Discussion identifies CR3/C3-dependent signaling as a mechanism of microglial pruning and proposes that activity and complement work cooperatively. Preservation here is relative, not a claim that every active synapse survives. (LLM, conf=0.88)

  cites Schafer et al., 2012 source

In the paper

“Iqgap1, Iqgap2, Iqsec2, Kalirin, and Trio are localized in dendritic spines of hippocampal neurons (Figure S3A) and enriched in PSD fractions of the mouse hippocampus (Figure S3B)”

What the sources say

• Partly supported

  The Results section reports that IQGAP1 is present in hippocampal neuronal processes and that its loss reduces dendritic spine density. The Discussion identifies IQGAP1 in complexes with PSD-95, but neither passage establishes localization within spines or enrichment in mouse hippocampal PSD fractions. The paper does not establish those claims for IQGAP2, IQSEC2, Kalirin, or Trio either. Page numbers were not available in our copy. (LLM, conf=0.87)

  cites Gao et al., 2011 sourceExperimental — accuracy not yet measured
• Partly supported

  The Results section, “BRAG1 localization to the postsynaptic density” (page unavailable), identifies BRAG1 as IQSec2 and reports its colocalization with PSD-95 in rat hippocampal neurons. It does not establish the localization of Iqgap1, Iqgap2, Kalirin, or Trio, or enrichment of the five proteins in PSD fractions from mouse hippocampus. (LLM, conf=0.88)

  cites Myers et al., 2012 sourceExperimental — accuracy not yet measured
• Partly supported

  The Results say kalirin-7 is enriched in dendritic spines, and the Discussion describes it as anchored to the PSD in spines. Our copy does not establish the claimed localization or PSD-fraction enrichment for Iqgap1, Iqgap2, Iqsec2, or Trio, nor does it establish enrichment of all five proteins in mouse hippocampal PSD fractions. (LLM, conf=0.88)

  cites Xie et al., 2007 sourceExperimental — accuracy not yet measured

In the paper

“Recently, using light sheet fluorescence microscopy and CLEM, microglia have been shown to “nibble” and phagocytose presynaptic, but not postsynaptic, terminals during development (Weinhard et al., 2018”

What the sources say

• Partly supported

  The Discussion reports nibbling (trogocytosis) of presynaptic boutons and axons, with no evidence of postsynaptic material being eliminated. But it distinguishes this partial uptake from phagocytosis of entire synapses, so the claim overstates the finding if “phagocytose presynaptic terminals” means engulfing whole terminals. (LLM, conf=0.87)

  cites Weinhard et al., 2018 sourceExperimental — accuracy not yet measured

In the paper

“complement activation and synapse loss seems to be a feature of multiple neurological diseases, including progranulin-deficient frontotemporal dementia (Lui et al., 2016”

What the sources say

• Supported

  The citation is attached to progranulin-deficient frontotemporal dementia, not the other listed diseases. The Discussion section on FTLD reports complement activation in patients with GRN mutations, while the section on PGRN deficiency reports complement-dependent synapse loss in a mouse model of FTLD. (LLM, conf=0.90)

  cites Lui et al., 2016 source
• Supported

  The cited paper supports the virus-induced memory impairment example in the list. Its Abstract reports complement-mediated loss of hippocampal presynaptic terminals after West Nile virus infection and impaired spatial learning in recovered mice. The other diseases listed are not attributed to this citation. (LLM, conf=0.93)

  cites Vasek et al., 2016 source
• Partly supported

  The Discussion reports C1q at retinal synapses early in a mouse model of glaucoma, before or alongside synapse loss, and suggests complement-mediated elimination may occur there. Our copy does not address progranulin-deficient frontotemporal dementia, virus-induced memory impairment, or CNS lupus, so it supports only the glaucoma example in the supplied claim. (LLM, conf=0.86)

  cites Stevens et al., 2007 sourceExperimental — accuracy not yet measured

In the paper

“C1q-blocking antibody prevents microglial synapse removal and rescues synapse density”

In the paper

“A total of 1,257 unique proteins were identified in the PSD, of which 76 were significantly decreased and 45 significantly increased in Tau-P301S PSD fractions, relative to nonTg”

In the paper

“Electrophysiological analysis of hippocampal brain slices from 9-month-old Tau-P301S mice showed exaggerated short-term synaptic facilitation (increased paired-pulse ratio; PPR), and significantly reduced long-term potentiation (LTP) of excitatory postsynaptic potentials (EPSPs) and population spikes”

In the paper

“Notably, AT8, AT100, and AT180 antibodies (which recognize phosphoepitopes that are abundant in pathological aggregated and filamentous Tau of human AD) showed an elevated signal in Tau-P301S mice that was markedly enriched in PSD fractions and only weak or undetectable in nonTg mice”

In the paper

“At 12 months, Tau-P301S mice showed obvious neurodegeneration and clear hippocampal atrophy”

In the paper

“Tau-P301S mice behaved similarly to nonTg mice at 6 and 9 months of age but showed elevated total motor activity at 12 months of age”

In the paper

“A C1q-blocking antibody inhibited microglial synapse removal in cultured neurons and in Tau-P301S mice, rescuing synapse density”

In the paper

“When AT8 phospho-Tau antibody was used in immunoEM, the AT8 immunogold particles were often found on dense aggregates (Figures S2F and S2G), which were also detected in presynaptic termini and in dendritic spines”

In the paper

“Tau immunoblots of Tau-P301S brain, however, showed a complex banding pattern with marked differences between the PSD and total lysate, suggesting that specific Tau species were enriched in synapses”

In the paper

“In the Morris water maze test, which measures spatial learning and memory, 9-month-old Tau-P301S-mice learned more slowly than nonTg controls, traveling a greater distance to the target platform and spending less time in the target quadrant”

In the paper

“While total Tau was increased in Tau-P301S mice, there was no significant difference in Tau levels in lysates versus PSD fractions within either nonTg or Tau-P301S mice when the total immunoreactivity of all Tau-bands was quantified”

In the paper

“hTau was readily detectable in presynaptic termini, often associated with synaptic vesicles, and in the majority (>80%) of postsynaptic compartments close to the PSD”

In the paper

“PSDs of tauopathy-affected neurons are depleted of a specific set of intracellular signaling proteins with known postsynaptic functions (small GTPase regulators) while accumulating an extracellular protein involved in innate immunity (complement C1q).”

In the paper

“we confirmed that C1q was greatly increased (with high inter-animal variability) in PSDs of 9-month-old Tau-P301S hippocampi and barely detectable in the nonTg PSD (Figure 4A).”

In the paper

“C1q was elevated in total lysate and highly enriched in the PSD fractions from EAD as well as AD patients (Figure 5D).”

In the paper

“In nonTg mice, hippocampal C1q immunostaining stayed roughly constant from 6–12 months of age, whereas in Tau-P301S mice it increased in intensity at 9 and 12 months (Figure S4B).”

In the paper

“Despite amelioration of synapse density, a single injection of anti-C1q did not improve LTP.”

In the paper

“The average level of C1q in the PSD of Tau-P301S mice was elevated ∼9-fold above nonTg controls, whereas it was increased only 2- to 3-fold in the PSD of PS2/APP mice (Figure 4G).”

In the paper

“AT8 immunoreactivity was enriched in PSD fractions compared to total lysates from AD brains, similar to Tau-P301S mice.”

In the paper

“Control IgG showed diffuse staining in hippocampus and cortex (ipsilateral > contralateral) with no specific colocalization with C1q (Figures 8A and 8B).”

In the paper

“We also found elevated C1q in AD patient brains, not only in bulk tissue, but also in purified PSD fractions, consistent with synaptic tagging by C1q in AD.”

In the paper

“Phallacidin had no effect on spines in control cultures but restored spine density in neurons treated with siRNAs targeting Iqsec2, Kalirin, Trio, or Iqgap1 and Iqgap2, or even led to spine density greater than control neurons (Figure 3C).”

In the paper

“Although conspicuously localized at synapses in tauopathy mice, C1q is also deposited at non-synaptic sites on neurons and possibly other cells”

In the paper

“The injected anti-C1q antibodies were present throughout the ipsilateral hippocampus and, to a lesser extent, the contralateral side (Figures 8A and 8B).”

In the paper

“antibodies against PSD-95 (but not Gephyrin, the scaffold of GABAergic synapses) co-immunoprecipitated C1q and hTau from hippocampal lysates, confirming that C1q and Tau are specifically in the PSD-95 complex associated with excitatory synapses (Figure 4F).”

In the paper

“synapse density, as measured by PSD-95 clusters, was reduced by ∼30% on “microglia-proximal” dendrites (overlapping or in contact with Iba1+ cells) but was unchanged on “microglia-distant” dendrites (>30 μm separated from Iba1+ cells) (Figure S7C)”

In the paper

“The amount of C1q co-immunoprecipitated with PSD-95 was greater from Tau-P301S than from nonTg hippocampus and mirrored the amount of co-immunoprecipitated phospho-Tau”

In the paper

“the increase in synaptic C1q labeling in Tau-P301S mice was mainly driven by augmented postsynaptic C1q, as the percentage of presynaptic labeling by C1q was only slightly increased between Tau-P301S and nonTg mice (Figure 4D).”

In the paper

“The density of Gephyrin clusters was not affected by microglia or by addition of C1q antibodies”

In the paper

“In brains injected with anti-C1q, the intensity of C1q staining was reduced in the ipsilateral hippocampus, while control IgG injection had no effect (Figures 8A and 8B).”

In the paper

“mean levels of C1q in superior frontal gyrus (SFG) lysates were increased ∼1.5-fold in patients with a diagnosis of early-stage AD (EAD) and ∼2-fold elevated in patients with autopsy-confirmed AD (Figure 5A; Table S3).”

In the paper

“We also analyzed the downstream complement factor C3, which was unchanged in SFG lysates of EAD patients but increased ∼2-fold in AD patients (Figure 5A)”

In the paper

“C1q tags Tau-affected synapses, leading to microglial engulfment and synapse loss”

In the paper

“Normally, Tau is enriched in axons, where it interacts with microtubules (MTs) and may regulate MT polymerization and dynamics, axonal outgrowth, and transport (Wang and Mandelkow, 2016”

What the sources say

• ?Not checked — no full text of the sourcecites Wang and Mandelkow, 2016 source

In the paper

“suggesting that these proteins are specifically depleted from (Prrt1, SynGAP1) or augmented (Ezrin), in the PSD”

In the paper

“the biochemical and imaging data show that there is increased microglial engulfment of synapses (both pre- and postsynaptic compartments) in Tau-P301S mice at 9 months of age, temporally correlating with accumulation of C1q and a drop in synapse density.”

In the paper

“which can lead to dysregulation of the actin cytoskeleton and potentially contribute to the spine loss seen in AD and other tauopathies.”

In the paper

“Sample size was chosen according to that used for similar experiments in previously published literature.”

In the paper

“our results demonstrate that C1q antibodies can reduce synapse removal by microglia and lead to a recovery of synapse density in cultures and in vivo.”

In the paper

“All behavioral scorings, electrophysiological, microscopic and histological analyses were carried out by experimenters blind to genotype and treatment groups.”

In the paper

“Results were further filtered to a confidence score of 83 or greater.”

In the paper

“This rescue of synapse number suggests an ongoing dynamic turnover of synapses in the Tau-P301S brain that can be rebalanced in a favorable direction by neutralization of C1q.”

In the paper

“consistent with the idea that Tau pathology causes C1q accumulation and that C1q associates with synapses that have been affected by phospho-Tau.”

In the paper

“Animals were always processed in pairs (1 nonTg and 1 Tau-Tg) and sorted simultaneously in two BD FACS ARIA sorters.”

In the paper

“suggesting that other structures could be targets of microglial engulfment or complement-mediated damage.”

In the paper

“while tauopathy seems to be sufficient to induce the C1q tagging of synapses, it may not be absolutely necessary for this outcome, as synaptic C1q buildup is also stimulated by amyloidosis and can occur in early AD brain tissue prior to the detection of AT8-immunoreactive phospho-Tau (see Figure 5D).”

In the paper

“The biochemical analysis of the PSD provides only a view of the “average” synapse and so may hide the heterogeneity of changes in individual PSDs that occur in response to tauopathy.”

In the paper

“Peak areas were normalized on a sample-by-sample basis to ensure equal median peak intensities across all samples.”

In the paper

“Filtered peptides were subsequently filtered to a 2% protein FDR.”

In the paper

“All animal studies were authorized and approved by the Genentech Institutional Animal Care and Use Committee.”

In the paper

“further suggesting that microglia selectively remove excitatory synapses without damaging the dendrite (Figures 7A and 7B).”

In the paper

“suggesting that microglia engulf synapses and perhaps not neuronal soma and arguing against a non-specific contamination of the microglial prep by neuronal cells.”

In the paper

“All images, segmentation overlays, and data were reviewed by a pathologist.”

In the paper

“These data indicate that C1q is enriched in human AD brains and appears to be associated with synapses in EAD and AD.”

In the paper

“Peptide-spectral matches were first filtered to a false discovery rate (FDR) of 5% at the peptide level using a linear discriminant approach.”

In the paper

“Human samples were procured with Ethics Committee approval and written informed consent.”

In the paper

“Further stringent filters were applied to the results, requiring p-values < 0.01, and at least 4 differentially abundant genes overlapping a given ontology category.”

In the paper

“No outlier analysis was performed or data points excluded.”

In the paper

“The experimenter was blinded to the treatment of analyzed neurons.”

In the paper

“Experimenters were blinded whenever possible to experimental condition during data acquisition or quantification.”

In the paper

“In all experiments, animals were randomly assigned to experimental or treatment groups and matched for age and littermate controls.”