MAP2 caps tau fibrils and inhibits aggregation

Small quantities of MAP2 have been identified in neurofibrillary tangles.

“Nevertheless, small quantities of MAP2 have been identified in neurofibrillary tangles (34, 35), and interactome studies in human AD brain have captured MAP2 together with oligomeric tau (35, 36).”

• cites [34] Rudrabhatla, 2011, Direct evidence of phosphorylated neuronal intermediate filament proteins in neurofibrillary tangles (NFTs): phosphoproteomics of Alzheimer's NFTs, FASEB J. sourcePartly supported

  Table 3 (Results; page not provided) identifies MAP2 phosphopeptides in purified neurofibrillary tangles, supporting the identification of MAP2. The paper does not quantify MAP2 as present in “small quantities”; the Discussion instead describes an abundance of phosphorylated MAP peptides. (LLM, conf=0.84)

  Experimental — accuracy not yet measured
• cites [35] Drummond, 2020, Phosphorylated tau interactome in the human Alzheimer's disease brain, Brain sourceCould not verify

  The ‘Proteome of neurofibrillary tangles in sporadic Alzheimer’s disease’ section reports proteins identified in tangle-containing samples, but the passages retrieved do not identify MAP2 or describe its quantity. Searches for ‘MAP2’ and ‘microtubule-associated protein 2’ did not locate a passage establishing the claim in our copy. (LLM, conf=0.70)

  Experimental — accuracy not yet measured
• cites [36] Hsieh, 2019, Tau-mediated disruption of the spliceosome triggers cryptic rna splicing and neurodegeneration in Alzheimer's Disease, Cell Rep. sourceCould not verify

  The Introduction says tau forms neurofibrillary tangles, and the Results discuss spliceosome components associated with tangles, but neither identifies MAP2 in them. Searches for MAP2 and microtubule-associated protein 2 found no passage in our copy addressing MAP2’s presence or quantity in tangles; page numbers were unavailable. (LLM, conf=0.75)

  Experimental — accuracy not yet measured

Tau and MAP2 share significant sequence similarity in the microtubule binding repeats.

“Tau and MAP2 share significant sequence similarity in the microtubule binding repeats (Fig. 1A), the same region that forms part of the core region of pathological tau filaments (15).”

• cites [15] Taniguchi-Watanabe, 2016, Biochemical classification of tauopathies by immunoblot, protein sequence and mass spectrometric analyses of sarkosyl-insoluble and trypsin-resistant tau, Acta Neuropathol. sourceSupported

In vitro experiments have demonstrated that MAP2 forms either fibrillar or granular, non-amyloidogenic aggregates.

“In vitro experiments have demonstrated that MAP2 forms either fibrillar (30, 31) or granular, non-amyloidogenic aggregates (32, 33).”

• cites [30] DeTure, 1996, In vitro polymerization of embryonic MAP-2c and fragments of the MAP-2 microtubule binding region into structures resembling paired helical filaments, J. Biol. Chem. sourceSupported
• cites [31] DeTure, 2002, In vitro assembly of Alzheimer-like filaments. How a small cluster of charged residues in Tau and MAP2 controls filament morphology, J. Biol. Chem. sourceNot checked — no full text of the source
• cites [32] Xie, 2014, The homologous carboxyl-terminal domains of microtubule-associated protein 2 and TAU induce neuronal dysfunction and have differential fates in the evolution of neurofibrillary tangles, PLoS One sourcePartly supported

  The Results section (‘Tau but not MAP2c forms ThT-positive, insoluble aggregates in the presence of heparin’; page unavailable) reports an in vitro aggregation assay in which MAP2c showed a small, early increase in ThT fluorescence but formed fewer stable aggregates than Tau. It does not identify MAP2c aggregates as granular or establish that they are non-amyloidogenic—the portion of the sentence attributed to this source. (LLM, conf=0.83)

  Experimental — accuracy not yet measured
• cites [33] Xie, 2015, Identification of key amino acids responsible for the distinct aggregation properties of microtubule-associated protein 2 and tau, J. Neurochem. sourceSupported

All three acceptor-labeled monomers (K18, 3R MAP2, 4R MAP2) had added to the fibril end.

“Since the Förster radius for this pair is ∼6 nm (46) and energy transfer efficiency at longer distances drops precipitously, the data suggest that all three acceptor-labeled monomers (K18, 3R MAP2, and 4R MAP2) had added to the fibril end as schematically shown for K18 in the inset of Figure 5A.”

• cites [46] Margittai, 2003, Single-molecule fluorescence resonance energy transfer reveals a dynamic equilibrium between closed and open conformations of syntaxin 1, Proc. Natl. Acad. Sci. U. S. A. sourceSupported

The fibrils employed in the current study are known to have different folds.

“The fibrils that were employed in the current study are known to have different folds.”

• cites [51] Weismiller, 2018, Structural disorder in four-repeat Tau fibrils reveals a new mechanism for barriers to cross-seeding of Tau isoforms, J. Biol. Chem. sourcePartly supported

  The section “Pro-301 mutants and htau40 form distinct clouds of fibril conformers” reports that htau40 fibrils differ structurally from P301S- and P301L-seeded fibrils. It also says that all three types form clouds of conformers and that insight into their particular structures is limited, so it does not establish distinct, defined folds for the fibrils described in the citing sentence. (LLM, conf=0.81)

  Experimental — accuracy not yet measured
• cites [52] Siddiqua, 2012, Conformational basis for asymmetric seeding barrier in filaments of three- and four-repeat tau, J. Am. Chem. Soc. sourceSupported
• cites [54] Fichou, 2018, Heparin-induced tau filaments are structurally heterogeneous and differ from Alzheimer's disease filaments, Chem. Commun. (Camb) sourceNot checked — no full text of the source

4R MAP2 is slightly more potent than 3R MAP2 at inhibiting tau aggregation.

“We find that both proteins block the spontaneous and seeded aggregation of 4R tau, with 4R MAP2 being slightly more potent.”

4R MAP2 and 3R MAP2 monomers have higher affinity for K18 seeds than K18 monomers.

“The apparent dissociation constants suggest that 4R MAP2 (KD = 1.3 μM) and 3R MAP2 (KD = 1.6 μM) monomers have a higher affinity for K18 seeds than K18 (KD = 5.4 μM) monomers have.”

Biotinylated K18, 3R MAP2, and 4R MAP2 were able to capture K18 seeds.

“Analysis by SDS-PAGE and Coomassie staining revealed that biotinylated K18, 3R MAP2, and 4R MAP2 were able to capture K18 seeds since in these cases a pronounced K18 monomer band is visible in the gel (Fig. 4B).”

K18 has an apparent KD of 5.4 μM for K18 seeds.

“The apparent dissociation constants suggest that 4R MAP2 (KD = 1.3 μM) and 3R MAP2 (KD = 1.6 μM) monomers have a higher affinity for K18 seeds than K18 (KD = 5.4 μM) monomers have.”

MAP2 inhibits amplification of AD tau filaments.

“Densitometric analysis revealed that tau amplification in AD samples was reduced by over 80% when either one of the MAP2 variants (3R or 4R) was present (Fig. 8B).”

In the absence of MAP2, K18 was effectively recruited onto fibrils.

“In the absence of MAP2, K18 was effectively recruited onto the fibril as judged by the steady increase in ThT fluorescence (Fig. 2A, red trace).”

Biotinylated K19 was unable to capture fibrils.

“Notably, biotinylated K19 was unable to capture fibrils (Fig. 4B), consistent with the observation that K19 does not grow onto K18 seeds (42).”

• cites [42] Dinkel, 2011, Variations in filament conformation dictate seeding barrier between three- and four-repeat Tau, Biochemistry sourceNot checked — no full text of the source

Addition of 3.2 μM 3R MAP2 or 4R MAP2 at the beginning of K18 aggregation increased t1/2 by almost twofold.

“Notably, the addition of substoichiometric quantities of 3R MAP2 or 4R MAP2 (3.2 μM) at the beginning of the reaction increased t1/2 by almost twofold (Fig. 1C).”

3R MAP2 has an apparent KD of 1.6 μM for K18 seeds.

“The apparent dissociation constants suggest that 4R MAP2 (KD = 1.3 μM) and 3R MAP2 (KD = 1.6 μM) monomers have a higher affinity for K18 seeds than K18 (KD = 5.4 μM) monomers have.”

MAP2 inhibits elongation of full-length tau fibrils.

“Based on band intensities, tau fibril growth in the presence of 3R MAP2 and 4R MAP2 was reduced to 56% and 25%, respectively (Fig. 7B).”

• Also stated in: § MAP2 inhibits the elongation of full-length tau fibrils · plain

  “The data reveal that MAP2 inhibits the elongation of full-length tau fibrils.”

Gold nanoparticles were specifically localized to fibril ends.

“Gold nanoparticles were specifically localized to the fibril ends (Fig. 5, E and F).”

Half-maximal aggregation of K18 was reached after 3.0 h.

“Half-maximal aggregation, which is reflected in t1/2, was reached after 3.0 h.”

4R MAP2 has an apparent KD of 1.3 μM for K18 seeds.

“The apparent dissociation constants suggest that 4R MAP2 (KD = 1.3 μM) and 3R MAP2 (KD = 1.6 μM) monomers have a higher affinity for K18 seeds than K18 (KD = 5.4 μM) monomers have.”

Tau fibril growth in the presence of 3R MAP2 was reduced to 56%.

“Based on band intensities, tau fibril growth in the presence of 3R MAP2 and 4R MAP2 was reduced to 56% and 25%, respectively (Fig. 7B).”

Our binding data (Fig. 3) were best fit with a one-site binding model.

“Our binding data (Fig. 3) were best fit with a one-site binding model”

In the absence of MAP2, all three AD samples resulted in tau amplification.

“In the absence of MAP2, all three AD samples resulted in tau amplification as revealed by the enhanced htau40 bands (Fig. 8A).”

MAP2 inhibited the seeding of all tau fibrils studied.

“MAP2 inhibited the seeding of all tau fibrils studied”

Tau amplification in AD samples was reduced by over 80% when either 3R or 4R MAP2 was present.

“Densitometric analysis revealed that tau amplification in AD samples was reduced by over 80% when either one of the MAP2 variants (3R or 4R) was present (Fig. 8B).”

Tau fibril growth in the presence of 4R MAP2 was reduced to 25%.

“Based on band intensities, tau fibril growth in the presence of 3R MAP2 and 4R MAP2 was reduced to 56% and 25%, respectively (Fig. 7B).”

In the presence of K18 seeds, about 25% of HEK293 cells contained inclusions.

“In the presence of K18 seeds, about 25% of the cells contained inclusions, visible in the shape of puncta (Fig. 6B).”

MAP2 could play a significant role in modulating tau propagation in disease.

“The findings uncover a new function for MAP2 as a tau fibril cap that could play a significant role in modulating tau propagation in disease”

MAP2 was found sequestered in a sedimentable fraction from AD brain homogenate containing small tau aggregates/oligomers referred to as AD P-tau.

“Furthermore, MAP2 was found sequestered in a sedimentable fraction from AD brain homogenate containing small tau aggregates/oligomers referred to as AD P-tau (37).”

• cites [37] Alonso, 1997, Abnormal phosphorylation of tau and the mechanism of Alzheimer neurofibrillary degeneration: sequestration of microtubule-associated proteins 1 and 2 and the disassembly of microtubules by the abnormal tau, Proc. Natl. Acad. Sci. U. S. A. sourceNot checked — no full text of the source

There is no evidence that MAP2 forms fibrillar deposits in the human AD brain.

“Despite its similarities with tau, there is no evidence, however, that MAP2 forms fibrillar deposits in the human AD brain.”

MAP2 is a tau fibril cap.

“The findings uncover a new function for MAP2 as a tau fibril cap that could play a significant role in modulating tau propagation in disease”

In this sequestered form, MAP2 lost its ability to facilitate microtubule assembly.

“Markedly, in this sequestered form, MAP2 lost its ability to facilitate microtubule assembly (37).”

• cites [37] Alonso, 1997, Abnormal phosphorylation of tau and the mechanism of Alzheimer neurofibrillary degeneration: sequestration of microtubule-associated proteins 1 and 2 and the disassembly of microtubules by the abnormal tau, Proc. Natl. Acad. Sci. U. S. A. sourceNot checked — no full text of the source

MAP2 monomers bind to the end of tau fibrils.

“The combined data suggest that MAP2 caps tau fibrils.”

Pull-down experiments corroborate that MAP2 monomers associate with tau fibrils.

“In summary, the pull-down experiments corroborate that MAP2 monomers associate with tau fibrils.”

MAP2 acts as an inhibitor of spontaneous tau aggregation.

“These results suggest that MAP2 acts as an inhibitor of spontaneous tau aggregation.”

These studies suggest there must be some interaction between aggregated tau and MAP2.

“Combined, these studies suggest that there must be some interaction between aggregated tau and MAP2.”

Inhibition of K18 aggregation is due to binding.

“The values are in good agreement with the IC50 values (Fig. 2, D and E) corroborating that the inhibition of K18 aggregation is due to binding.”

3R and 4R MAP2 monomers are the main species inhibiting tau elongation.

“These results suggest that 3R and 4R MAP2 monomers are the main species inhibiting tau elongation.”

The two ends of the fibril are asymmetric.

“Another important aspect of capping is that the two ends of the fibril are asymmetric.”

• cites [73] Heldt, 2011, Asymmetric amyloid fibril elongation: a new perspective on a symmetric world, Proteins sourceNot checked — no full text of the source

Combined data suggest MAP2 caps tau fibrils.

“The combined data suggest that MAP2 caps tau fibrils.”

MAP2 may preferentially interact with one end of the fibril.

“suggesting that MAP2 may preferentially interact with one end of the fibril”

MAP2 inhibits tau amplification in AD samples.

“Combined, the data suggest that tau amplification is specific for AD samples and that MAP2 inhibits this amplification.”

MAP2 engages with a broad spectrum of conformers.

“suggesting that it engages with a broad spectrum of conformers”

The structures of heparin-formed fibrils vary from those in AD.

“with structures varying from those in AD (54, 55)”

• cites [54] Fichou, 2018, Heparin-induced tau filaments are structurally heterogeneous and differ from Alzheimer's disease filaments, Chem. Commun. (Camb) sourceNot checked — no full text of the source
• cites [55] Zhang, 2019, Heparin-induced tau filaments are polymorphic and differ from those in Alzheimer's and Pick's diseases, ElifeNot checked yet

  Not checked in the free run.

The exposed contact surfaces at the fibril tips can vary widely.

“Hence, the exposed contact surfaces at the fibril tips can vary widely.”

It is likely that multiple mechanisms are at play in MAP2 capping of tau fibrils.

“Although it is currently unknown which residues in MAP2 are responsible for the capping of tau fibrils, it is likely that multiple mechanisms are at play.”

In this model system, both variants of MAP2 inhibit recruitment of tau monomers into fibrils.

“Together, the findings suggest that in this model system, both variants of MAP2 inhibit the recruitment of tau monomers into fibrils.”

Tau amplification is specific for AD samples.

“Combined, the data suggest that tau amplification is specific for AD samples and that MAP2 inhibits this amplification.”

MAP2 generates a surface incompatible with binding of further tau or MAP2 monomers.

“MAP2 thus generates a surface incompatible with the binding of further tau or MAP2 monomers (Fig. 9).”