Combinatorial model of amyloid β and tau reveals synergy between amyloid deposits and tangle formation

Most, if not all, studies have examined the synergy between Aβ and tau using the tauopathy-associated P301L mutant tau.

“Most, if not all, of these studies have examined the synergy between Aβ and tau using the tauopathy-associated P301L mutant tau (9).”

• cites [9] Busche MA, Hyman BT. Synergy between amyloid-beta and tau in Alzheimer’s disease. Nat Neurosci. 2020; 23(10): 1183– 93. 32778792 PMC11831977 sourcePartly supported

  The “Mechanistic lessons from AD models” section describes several Aβ–tau studies using P301L-mutant tau mice. It also describes a study using wild-type tau, and the section on neural-system consequences reports further wild-type-tau studies. The review therefore supports P301L as one model used, but not the claim that most, if not all, studies used it; page numbers are unavailable in our copy. (LLM, conf=0.88)

  Experimental — accuracy not yet measured

WT tau is not generally amenable to form NFT.

“As shown by other groups (37, 38), WT tau is not generally amenable to form NFT.”

• cites [37] Andorfer C, Kress Y, Espinoza M, de Silva R, Tucker KL, Barde YA, Hyperphosphorylation and aggregation of tau in mice expressing normal human tau isoforms. Journal of neurochemistry. 2003; 86(3): 582– 90. 12859672 sourceNot checked — no full text of the source
• cites [38] Saito T, Mihira N, Matsuba Y, Sasaguri H, Hashimoto S, Narasimhan S, Humanization of the entire murine Mapt gene provides a murine model of pathological human tau propagation. The Journal of biological chemistry. 2019; 294(34): 12754– 65. 31273083 PMC6709628 sourcePartly supported

  The Abstract (page unavailable) reports that NFTs did not appear during the lifespan of the authors’ mouse models. The propagation section (page unavailable) also reports no NFT formation after inoculation with AD-derived pathological tau. These findings support difficulty inducing NFTs in the studied mice, but not the broader claim that wild-type tau generally cannot form them. (LLM, conf=0.84)

  Experimental — accuracy not yet measured

AAV-P301L tau formed misfolded NFTs only when expressed in adult mice with pre-existing Aβ plaques.

“We found that AAV-P301L tau formed misfolded NFTs only when expressed in adult mice with pre-existing Aβ plaques but not when expressed in neonatal mice that lack cerebral Aβ plaques.”

In the pre-deposit cohort, neonatal delivery of AAV-tau resulted in tau being uniformly distributed throughout the hippocampus and cortex at 3 months of age.

“In the pre-deposit cohort, neonatal delivery of AAV-tau resulted in tau being uniformly distributed throughout the hippocampus (Fig. 1F–G; WT tau: p<0.05; P301L tau: p<0.05; S320F tau: p<0.05 relative to EGFP) as well as the cortex (Fig. 1F,H; WT tau: p<0.05; P301L tau: p<0.01 relative to EGFP) at 3 months of age.”

In the pre-deposit cohort, S320F tau induced neuroinflammation.

“In the pre-deposit cohort, S320F tau induced Aβ plaque deposition, neuroinflammation and synaptic abnormalities, suggesting that early tau tangles affect the amyloid cascade.”

P301L tau did not produce NFT-type inclusions in the pre-deposit cohort.

“P301L tau produced NFT-type inclusions in the post-deposit cohort, but not in the pre-deposit cohort, indicating pathological synergy with pre-existing Aβ deposits.”

• Also stated in: § Expression of recombinant AAV-tau leads to differential induction of NFT pathology in TgCRND8 mice · plain

  “we observed pretangle pathology exclusively in the AAV-S320F tau expressing mice but not in the AAV-WT tau or AAV-P301L tau mice (Fig. 2I–J; S320F: p<0.001 relative to EGFP).”

S320F tau induced NFT pathology in both the pre-deposit and post-deposit cohorts.

“As expected, S320F tau induced NFT pathology in both cohorts but accelerated amyloid deposition in the pre-deposit group but not in the post-deposit group.”

In the post-deposit cohort, CP13 immunoreactivity burden in the cortex and hippocampus of S320F tau expressing mice was limited relative to WT tau and P301L tau expressing mice.

“The CP13 immunoreactivity burden in the cortex and hippocampus of S320F tau expressing mice was limited relative to WT tau and P301L tau expressing mice (Fig. 2A–C).”

In the post-deposit cohort, MC1 positive somatodendritic pretangle inclusions were observed in P301L tau and S320F tau expressing mice, but not in WT tau expressing mice.

“We observed MC1 positive somatodendritic pretangle inclusions in the P301L tau expressing mice and S320F tau expressing mice, but not in WT tau expressing mice (Fig. 2D–E; P301L tau: p<0.01 relative to EGFP; S320F tau: p<0.01 relative to EGFP).”

In the pre-deposit cohort, pretangle pathology was exclusively in AAV-S320F tau expressing mice, not in AAV-WT tau or AAV-P301L tau mice.

“When we quantified MC1-immunopositive inclusion pathology, we observed pretangle pathology exclusively in the AAV-S320F tau expressing mice but not in the AAV-WT tau or AAV-P301L tau mice (Fig. 2I–J; S320F: p<0.001 relative to EGFP).”

Expression of WT tau did not alter Aβ in either the pre-deposit or post-deposit TgCRND8 cohort.

“Expression of WT tau did not produce NFT or altered Aβ in either cohort.”

In the pre-deposit cohort, ptau levels were considerably lower in AAV-S320F tau expressing mice.

“The levels of ptau were considerably lower in the AAV-S320F tau expressing mice (Fig. 2F–H), as expected from our previous data in nonTG mice (10).”

• cites [10] Koller EJ, Gonzalez De La Cruz E, Machula T, Ibanez KR, Lin W-L, Williams T, Riffe CJ, Ryu D, Strang KH, Liu X, Janus C, Golde TE, Dickson DW, Giasson BI, Chakrabarty P. Combining P301L and S320F tau variants produces a novel accelerated model of tauopathy. Human molecular genetics. 2019; 28(19): 3255– 3269. 31261380 PMC6859436 sourceNot checked — no full text of the source

In the pre-deposit cohort, normalizing MC1 inclusion numbers to ptau burden confirmed that only S320F tau showed self-aggregation properties.

“Normalizing the MC1 inclusion numbers to the ptau burden confirmed that only S320F tau showed self-aggregation properties in the pre-deposit cohort (Fig. S3C), also consistent with our previous data in nonTG mice (10).”

• cites [10] Koller EJ, Gonzalez De La Cruz E, Machula T, Ibanez KR, Lin W-L, Williams T, Riffe CJ, Ryu D, Strang KH, Liu X, Janus C, Golde TE, Dickson DW, Giasson BI, Chakrabarty P. Combining P301L and S320F tau variants produces a novel accelerated model of tauopathy. Human molecular genetics. 2019; 28(19): 3255– 3269. 31261380 PMC6859436 sourceNot checked — no full text of the source

In the pre-deposit cohort, S320F tau induced Aβ plaque deposition.

“In the pre-deposit cohort, S320F tau induced Aβ plaque deposition, neuroinflammation and synaptic abnormalities, suggesting that early tau tangles affect the amyloid cascade.”

• Also stated in: § The relationship of tau expression to Aβ levels in TgCRND8 mice · plain

  “AAV-S320F tau mice had significantly higher Aβ plaque burden relative to the other AAV-tau mice and control mice (Fig. 4G–H; p<0.05 compared to AAV-P301L tau mice).”

In the 6-month post-deposit cohort, CP13 immunostaining burden was robustly upregulated in the hippocampus and cortex in both P301L tau and WT tau.

“In the 6 month old post-deposit cohort (Fig. 2A–E), we observed that CP13 immunostaining burden (indicative of pSer202 tau) was robustly upregulated in the hippocampus and cortex in both P301L tau and WT tau (Fig. 2A–C; P301L tau: p<0.05 relative to EGFP in hippocampus; WT tau: p<0.05 relative to EGFP in hippocampus).”

Expression of WT tau did not produce neurofibrillary tangles in either the pre-deposit or post-deposit TgCRND8 cohort.

“Expression of WT tau did not produce NFT or altered Aβ in either cohort.”

• Also stated in: § Introduction · plain

  “WT tau did not form NFTs in either of the two cohorts tested.”

In nonTG mice injected neonatally with AAV-WT tau, no discernible NFTs developed even at 9 months of age.

“Using Alz50 antibody indicative of NFT pathology, we found that AAV-P301L tau mice developed cortical NFT tau at this age while the WT tau expressing animals still had no discernible NFTs even at this age (Fig. S1).”

In the pre-deposit cohort, S320F tau induced synaptic abnormalities.

“In the pre-deposit cohort, S320F tau induced Aβ plaque deposition, neuroinflammation and synaptic abnormalities, suggesting that early tau tangles affect the amyloid cascade.”

In the post-deposit cohort, contemporaneous expression of S320F tau did not exacerbate amyloid pathology.

“In the post-deposit cohort, contemporaneous expression of S320F tau did not exacerbate amyloid pathology, showing a dichotomy in Aβ-tau synergy based on the nature of Aβ.”

In nonTG mice injected neonatally with AAV-P301L tau, cortical NFT tau developed by 9 months of age.

“Using Alz50 antibody indicative of NFT pathology, we found that AAV-P301L tau mice developed cortical NFT tau at this age while the WT tau expressing animals still had no discernible NFTs even at this age (Fig. S1).”

S320F tau accelerated amyloid deposition in the pre-deposit group.

“As expected, S320F tau induced NFT pathology in both cohorts but accelerated amyloid deposition in the pre-deposit group but not in the post-deposit group.”

A small proportion of MC1 immunopositive pretangle inclusions observed in AAV-P301L tau expressing post-deposit mice stained with Gallyas silver, indicating the presence of NFT.

“We also confirmed that a small proportion of these MC1 immunopositive pretangle inclusions observed in the AAV-P301L tau expressing mice stained with Gallyas silver, indicating the presence of NFT (Fig. S3A).”

In the 3-month pre-deposit cohort, CP13 staining was upregulated in the hippocampus and cortex of AAV-P301L tau mice and AAV-WT tau mice.

“In the 3 month old pre-deposit cohort, we found that CP13 staining was upregulated in the hippocampus and cortex of AAV-P301L tau mice and AAV-WT tau mice (Fig. 2F–H; hippocampus - WT tau: p<0.01, P301L tau: p<0.01 relative to EGFP; cortex - WT tau: p<0.05, P301L tau: p<0.01 relative to EGFP).”

AAV-P301L tau did not form misfolded NFTs when expressed in neonatal mice that lack cerebral Aβ plaques.

“We found that AAV-P301L tau formed misfolded NFTs only when expressed in adult mice with pre-existing Aβ plaques but not when expressed in neonatal mice that lack cerebral Aβ plaques.”

S320F tau did not accelerate amyloid deposition in the post-deposit group.

“As expected, S320F tau induced NFT pathology in both cohorts but accelerated amyloid deposition in the pre-deposit group but not in the post-deposit group.”

P301L tau produced NFT-type inclusions in the post-deposit cohort.

“P301L tau produced NFT-type inclusions in the post-deposit cohort, but not in the pre-deposit cohort, indicating pathological synergy with pre-existing Aβ deposits.”

• Also stated in: § Expression of recombinant AAV-tau leads to differential induction of NFT pathology in TgCRND8 mice · plain

  “We observed MC1 positive somatodendritic pretangle inclusions in the P301L tau expressing mice and S320F tau expressing mice, but not in WT tau expressing mice (Fig. 2D–E; P301L tau: p<0.01 relative to EGFP; S320F tau: p<0.01 relative to EGFP).”

In the pre-deposit cohort, none of AAV-EGFP, AAV-WT tau, or AAV-P301L tau mice displayed TauC3 immunoreactivity.

“None of the other mice in this pre-deposit cohort - AAV-EGFP, AAV-WT tau or AAV-P301L tau mice - displayed TauC3 immunoreactivity (Fig. 3C–D).”

In 6-month-old post-deposit TgCRND8 mice, AAV-tau expression (all variants) did not alter GFAP, Iba-1, or Tmem119 immunoreactivity relative to AAV-EGFP controls.

“In the 6 month old post-deposit cohort, none of the AAV-tau mice were associated with altered GFAP, Iba-1 or Tmem119 immunoreactivity relative to AAV-EGFP control mice (Fig. 6A–I).”

• AssumptionRests on an assumption: The antibodies used (GFAP, Iba-1, Tmem119) reliably measure astrogliosis and microgliosis.

P301L tau, but not self-aggregating S320F tau or WT tau, induced significant changes in DAM score.

“Interestingly, in our study, we observed that the P301L tau, but not self-aggregating S320F tau or WT tau, induced significant changes in DAM score, showing that Aβ-triggered misfolded P301L tau triggers changes in brain immunity associated with this particular phenotype.”

Only one gene, Itgax, was identified to be commonly altered in a comparison of the DEG in P301L tau and S320F tau mice.

“Only one gene – Itgax – was identified to be commonly altered in a comparison of the DEG in P301L tau and S320F tau mice (Table S6).”

In the post-deposit cohort, AAV-S320F tau mice showed reduced detergent-soluble Aβ40 compared to EGFP mice.

“Detergent-soluble Aβ42 and Aβ40 (SDS extracted fraction) were reduced in some of the AAV-tau expressing mice – WT tau expression reduced detergent soluble Aβ42 (p<0.01 compared to EGFP mice) while AAV-S320F tau mice showed reduced Aβ40 (p<0.01 compared to EGFP mice) (Fig. 4E–F).”

In the post-deposit cohort, the distribution of plaque sizes in AAV-EGFP, AAV-WT tau, AAV-P301L tau, and AAV-S320F tau groups was uniformly similar across treatment groups.

“Upon counting Aβ plaques based on diameter, we found that the distribution of plaque sizes in AAV-EGFP, AAV-WT tau, AAV-P301L tau and AAV-S320F tau groups were uniformly similar across the treatment groups (Fig. S6A).”

In the 3-month pre-deposit cohort, AAV-P301L tau mice showed significantly upregulated Iba-1 staining in the cortex (p<0.05) compared to control CRND8 mice.

“AAV-P301L tau mice showed significantly upregulated Iba-1 staining in the cortex (p<0.05 compared to control CRND8 mice) respectively (Fig. 7D–F).”

In the 3-month pre-deposit cohort, Tmem119-reactive microglial population showed a subtle lowering trend in the cortex and hippocampus of AAV-P301L tau and AAV-S320F tau expressing mice relative to control transgenic mice.

“Tmem119-reactive microglial population showed subtle lowering trend in the cortex and hippocampus of AAV-P301L tau and AAV-S320F tau expressing mice relative to control transgenic mice (Fig. 7G–I).”

In the 6-month post-deposit cohort, the post-synaptic marker spinophilin is upregulated in AAV WT tau mice relative to control (p<0.05), AAV-P301L tau (p<0.01), and AAV-S320F tau (p<0.01) mice.

“In the 6 month old post-deposit cohort, we found that the post-synaptic marker, spinophilin, is upregulated in the AAV WT tau mice relative to control (p<0.05), AAV-P301L tau (p<0.01) and AAV-S320F tau (p<0.01) mice (Fig. 8A).”

None of the AAV-tau led to extensive changes in Aβ burden or plaque morphology when expressed in the presence of pre-existing Aβ deposits.

“None of the AAV-tau led to extensive changes in Aβ burden or plaque morphology when expressed in the presence of pre-existing Aβ deposits.”

In the 3-month pre-deposit cohort, S320F tau mice showed high levels of Iba-1 immunoreactivity in hippocampus (p<0.001) and cortex (p<0.01) relative to control CRND8 mice.

“In both hippocampus and cortex, the S320F tau mice showed high levels of Iba-1 immunoreactivity (p<0.001 in hippocampus, p<0.01 in cortex relative to control CRND8 mice) (Fig. 7D–F).”

In the post-deposit cohort, neither AAV-EGFP nor AAV-WT tau expressing mice showed any TauC3 staining.

“Neither AAV-EGFP nor AAV-WT tau expressing mice showed any TauC3 staining (Fig. 3A–B).”

In S320F tau cohorts, the ratio of NFT tau (MC1) to ptau (CP13) is higher in the pre-deposit cohort than the post-deposit cohort.

“Indeed, the ratio of NFT tau (MC1) to ptau (CP13) in the S320F tau cohorts is higher in the pre-deposit cohort than the post-deposit cohort,”

In the pre-deposit cohort, there were no significant differences in Aβ plaque burden between AAV-EGFP, AAV-WT tau, and AAV-P301L tau mice.

“There were no significant differences between AAV-EGFP, AAV-WT tau and AAV-P301L tau mice (Fig. 4G–H).”

In the post-deposit cohort, WT tau expression reduced detergent-soluble Aβ42 compared to EGFP mice.

“Detergent-soluble Aβ42 and Aβ40 (SDS extracted fraction) were reduced in some of the AAV-tau expressing mice – WT tau expression reduced detergent soluble Aβ42 (p<0.01 compared to EGFP mice) while AAV-S320F tau mice showed reduced Aβ40 (p<0.01 compared to EGFP mice) (Fig. 4E–F).”

In the pre-deposit cohort, S320F tau mice showed higher detergent-soluble Aβ42 relative to AAV-EGFP and AAV-P301L tau.

“In the detergent soluble fraction, the S320F tau mice also showed higher biochemical levels of Aβ42 (Fig. 4K–L; p<0.01 relative to AAV-EGFP and p<0.05 relative to AAV-P301L tau).”

In the pre-deposit cohort, neither P301L tau nor WT tau expressing mice showed significant changes in biochemical Aβ levels relative to control mice.

“Neither the P301L tau mice nor the WT tau (Fig. 4I–L) expressing mice showed any significant changes in biochemical Aβ levels relative to control mice.”

The pattern of upregulated genes in S320F tau mice was consistent primarily with enrichment in pathways related to immune response, actin polymerization, and response to cAMP.

“The pattern of upregulated genes was consistent primarily with enrichment in pathways related to immune response (p=0.001), actin polymerization (p=0.001) and response to cAMP (p=0.0005), which was reflected in the protein-protein expression network analysis (Fig. 5J–K).”

In the post-deposit cohort, no significant alterations in activated microglial (Iba-1) or mature microglial (Tmem119) burden were observed in P301L tau expressing TgCRND8 mice.

“In spite of changes in DAM phenotype in the post-deposit cohort, we did not observe significant alterations in activated microglial (Iba-1) or mature microglial (Tmem119) burden in the P301L tau expressing TgCRND8 mice.”

In the pre-deposit cohort, S320F tau expressing mice showed increased insoluble Aβ42 and Aβ40 relative to AAV-P301L tau mice.

“In terms of biochemical levels of insoluble plaque associated Aβ, the S320F tau expressing mice showed increased Aβ42 and Aβ40 (Fig. 4I–J; p<0.01 for insoluble Aβ42 and p<0.05 for insoluble Aβ40 relative to AAV-P301L tau mice).”

In the 6-month post-deposit cohort, PSD95 was upregulated specifically in AAV-P301L tau mice relative to control mice (p<0.01).

“Another post-synaptic marker, PSD95, was upregulated specifically in AAV-P301L tau mice relative to control mice (p<0.01) (Fig. 8D).”

In the 6-month post-deposit group, robust levels of TauC3 immunopositivity were found in the cortex and hippocampus of S320F tau expressing TgCRND8 mice.

“In the 6 month post-deposit group, we found robust levels of TauC3-immunopositivity in the cortex and hippocampus of S320F tau expressing TgCRND8 mice (Fig. 3A–B; p<0.01 relative to EGFP, WT tau and P301L tau).”

In the pre-deposit cohort, TauC3 was observed only in S320F tau expressing mice.

“In the pre-deposit cohort, we observed Tau C3 only in the S320F tau expressing mice (Fig. 3C–D; p<0.001 relative to EGFP, WT tau and P301L tau).”

WT tau expressing mice showed the largest changes in differential expression of genes compared to EGFP controls.

“The WT tau expressing mice showed the largest changes in differential expression of genes (DEG) when compared to EGFP controls, with the top affected genes being Slc6a3 (Log2FC=4.38; p=0.0174), Ddc (Log2FC=1.54; p=0.007) and Mutyh (Log2FC=0.59; p=0.0458) (Fig. 5B–C; Table S2).”

In the post-deposit cohort, a very small proportion of large diameter plaques (>150 μm) appeared only in AAV-S320F tau mice.

“However, we noticed the appearance of a very small proportion of large diameter plaques (>150 μm) only in the AAV-S320F tau mice (Fig. S6A).”

In the 3-month pre-deposit cohort, AAV-WT tau mice showed increased Iba-1 staining in the hippocampus (p<0.05) compared to control CRND8 mice.

“AAV-WT tau mice showed increased Iba-1 staining in the hippocampus (p<0.05 compared to control CRND8 mice) (Fig. 7D–F).”

Mice did not show any alterations in Stage 1 DAM score.

“While the mice did not show any alterations in Stage 1 DAM score (Fig 5T), the AAV-P301L tau expressing mice displayed significantly reduced Stage 2 DAM score compared to control mice (Fig. 5U; p<0.05).”

S320F tau expression initiated at birth, before the onset of Aβ deposition, accelerates amyloid plaque deposition.

“Surprisingly, S320F tau expression initiated at birth, before the onset of Aβ deposition, accelerates amyloid plaque deposition.”

Enrichment analysis of downregulated genes revealed that WT tau expression is associated with negative regulation of lipid catabolism, regulation of amine transport, and inflammatory response.

“Enrichment analysis of downregulated genes revealed that WT tau expression is associated with negative regulation of lipid catabolism (p=0.0003), regulation of amine transport (p=0.0008) and inflammatory response (p=0.0002) (Fig. 5F).”

Gene enrichment analysis and protein-protein co-expression analysis showed robust changes in immunity in AAV-P301L tau mice, especially in pathways related to antigen presentation and leukocyte activation.

“Overall, gene enrichment analysis and protein-protein co-expression analysis showed robust changes in immunity in the AAV-P301L tau mice, especially in pathways related to antigen presentation and leukocyte activation.”

S320F tau expressing mice showed a uniquely distinctive DEG, with the top upregulated genes being Slc6a3, Ret, and Ddc.

“The S320F tau expressing mice showed a uniquely distinctive DEG, with the top upregulated genes being Slc6a3 (Log2FC=3.82; p=0.031), Ret (Log2FC=1.44; p=0.044), Ddc (Log2FC=1.28; p=0.0188) (Fig. 5H–I; Table S3).”

Downregulated genes in S320F tau expressing mice include Itgax, Npas4, and Ntf3.

“Among the downregulated genes include Itgax (Log2FC= −1.39; p=0.0186), Npas4 (Log2FC= −1.15; p=0.005) and Ntf3 (Log2FC= −1; p=0.0475) (Fig. 5H–I; Table S3).”

In the post-deposit cohort, biochemical levels of insoluble Aβ42 and Aβ40 were unchanged across all tau expressing groups.

“The biochemical levels of insoluble Aβ42 and Aβ40 (formic acid extracted, detergent insoluble fraction) were unchanged across all the tau expressing groups (Fig. 4C–D), consistent with the plaque burden analysis.”

GO analysis of upregulated genes showed that AAV-WT tau expression resulted in genes enriched for regulating endothelial permeability across tricellular tight junctions, lipoprotein transport, and dopamine biosynthesis.

“GO analysis of upregulated genes showed that AAV-WT tau expression resulted in genes enriched for regulating endothelial permeability across tricellular tight junctions, including blood brain barrier (p=0.008), lipoprotein transport (p=0.012) and dopamine biosynthesis (p=0.002) (Fig. 5D).”

In AAV-S320F tau mice, downregulated DEGs were associated with pathways related to actin cytoskeleton reorganization, immune response, and regulation of protein phosphorylation.

“In the AAV-S320F tau mice, the downregulated DEGs were associated with pathways related to actin cytoskeleton reorganization (p=0.003), immune response (p=0.0031) and regulation of protein phosphorylation (p=0.002) (Fig. 5L–M).”

Analysis of downregulated genes in P301L tau mice revealed co-expression networks related to induction of antigen presentation, dendritic cell apoptosis, and chemokine signalling.

“Analysis of downregulated genes revealed co-expression networks related to induction of antigen presentation (p=0.0135), dendritic cell apoptosis (p=0.009) and chemokine signalling (p=0.001) (Fig. 5R–S).”

When tau expression was initiated prior to onset of Aβ deposition, S320F tau expression increased the abundance of activated microglia.

“Interestingly, when tau expression was initiated prior to onset of Aβ deposition, S320F tau expression increased the abundance of activated microglia.”

In the post-deposit cohort, no gross changes in total levels of neuronal-specific proteins NeuN and CaMKII were observed.

“Despite increased TauC3 levels, we did not observe any gross changes in total levels of neuronal-specific proteins, NeuN and CaMKII in the post-deposit cohort (Fig. S5A–D).”

Relative to AAV-EGFP, the three AAV-tau constructs showed distinctive gene expression patterns in the post-deposit cohort, especially in pathways related to neuroinflammation, cell structure integrity, neurotransmission, and neuroplasticity.

“We observed that relative to AAV-EGFP, the three AAV-tau constructs showed distinctive gene expression patterns (Fig. 5A), especially in pathways related to neuroinflammation, cell structure integrity, neurotransmission and neuroplasticity.”

In the 3-month pre-deposit cohort, changes in synaptic protein levels correlated generally with the increase in misfolded tau levels and neuroinflammation found in AAV-S320F tau mice.

“In the 3 month old pre-deposit cohort, the changes in synaptic proteins levels correlated generally with the increase in misfolded tau levels and neuroinflammation found in AAV-S320F tau mice (Fig. 8E–H).”

Comparison of gene expression patterns in mice expressing AAV-P301L tau relative to AAV-EGFP revealed that maximally induced genes include Slc6a3, Fas, and Lsr.

“Comparison of gene expression patterns in mice expressing AAV-P301L tau relative to AAV-EGFP revealed that genes that are maximally induced include Slc6a3 (Log2FC=3.5; p=0.044), Fas (Log2FC=0.80; p=0.0404) and Lsr (Log2FC=0.51; p=0.001) (Fig. 5N–O; Table S4).”

Co-expression analysis shows that genes related to catecholamine synthesis and blood brain barrier integrity were upregulated in WT tau expressing mice.

“Co-expression analysis shows that genes related to catecholamine synthesis and blood brain barrier integrity were upregulated (Fig. 5E).”

In the 3-month pre-deposit cohort, S320F tau mice had reduced levels of synaptophysin and synaptogyrin 3 (p<0.05 relative to control mice).

“The S320F tau mice had reduced levels of synaptophysin and synaptogyrin 3 (p<0.05 relative to control mice) at this age (Fig. 8F,G).”

In nonTG littermates injected with AAV-P301L tau, no silver positive tangles were observed.

“We observed robust tau expression (Fig. S4, CP27 immunostaining) and induction of hyperphoshorylated tau (Fig. S4, CP13 immunostaining), but we did not observe any silver positive tangles in these mice.”

In the 3-month pre-deposit cohort, AAV-S320F tau mice had significantly higher Aβ plaque burden relative to the other AAV-tau mice and control mice.

“In the 3 month old pre-deposit cohort, we found that AAV-S320F tau mice had significantly higher Aβ plaque burden relative to the other AAV-tau mice and control mice (Fig. 4G–H; p<0.05 compared to AAV-P301L tau mice).”

Only two genes, Ryr1 and Taf10, were identified in the DEG comparison of P301L tau mice and WT tau mice.

“Further only two genes – Ryr1 and Taf10 – were identified in the DEG comparison of P301L tau mice and WT tau mice (Table S6).”

In the 6-month post-deposit cohort, AAV-tau expression slightly lowered total Aβ plaque burden relative to AAV-EGFP mice.

“In the 6 month old post-deposit cohort, we observed that AAV-tau expression slightly lowered total Aβ plaque burden relative to AAV-EGFP mice (Fig. 4A–B).”

Genes exclusively altered in AAV-P301L mice were Cxcl12, Des, Slc18a3, Tie1, Fas, Mapt, and Notch 3.

“Genes that were exclusively altered in AAV-P301L mice were Cxcl12, Des, Slc18a3, Tie1, Fas, Mapt and Notch 3 (Table S5).”

A larger number of genes were identified to be commonly altered between WT tau and S320F tau: Cdc27, Cx3cr1, Npas4, Ntf3, Ptprr, Ddc, and Gad2.

“Surprisingly, a larger number of genes were identified to be commonly altered between WT tau and S320F tau – Cdc27, Cx3cr1, Npas4, Ntf3, Ptprr, Ddc and Gad2 (Table S6).”

AAV-P301L tau expressing mice displayed significantly reduced Stage 2 DAM score compared to control mice.

“While the mice did not show any alterations in Stage 1 DAM score (Fig 5T), the AAV-P301L tau expressing mice displayed significantly reduced Stage 2 DAM score compared to control mice (Fig. 5U; p<0.05).”

The top affected genes in WT tau expressing mice were Slc6a3, Ddc, and Mutyh.

“The WT tau expressing mice showed the largest changes in differential expression of genes (DEG) when compared to EGFP controls, with the top affected genes being Slc6a3 (Log2FC=4.38; p=0.0174), Ddc (Log2FC=1.54; p=0.007) and Mutyh (Log2FC=0.59; p=0.0458) (Fig. 5B–C; Table S2).”

Robustly downregulated genes in WT tau expressing mice include Atp6v0e2, Ntf3, and Gdnf.

“The robustly downregulated genes include Atp6v0e2 (Log2FC= −3.52; p=0.0001), Ntf3 (Log2FC= −1.09; p=0.0357) and Gdnf (Log2FC= −0.929; p=0.0401) (Fig. 5B–C; Table S2).”

Downregulated genes in AAV-P301L tau mice include Slc18a3, Itgax, and Des.

“Among the genes that were downregulated were Slc18a3, also known as Vesicular acetylcholine transporter (Log2FC= −1.3; p=0.015), Itgax, an integrin involved in immunity (Log2FC= −1.22; p=0.0282) and Des, an intermediate filament (Log2FC= −0.903; p=0.0488) (Fig. 5O; Table S4).”

In the 6-month post-deposit cohort, none of the pre-synaptic proteins (synaptophysin and synaptogyrin 3) showed significant changes.

“None of the pre-synaptic proteins (synaptophysin and synaptogyrin 3) showed significant changes (Fig. 8B,C).”

In the 3-month-old pre-deposit cohort, the astrogliosis pattern in AAV-tau mice correlated with the increased Aβ burden found in S320F tau expressing mice.

“In the 3 month old pre-deposit cohort, the astrogliosis pattern in AAV-tau mice correlated with the increased Aβ burden found in S320F tau expressing mice.”

In the post-deposit cohort, sparse TauC3 immunopositive cells were found in the hippocampus and cortex of AAV-P301L tau expressing TgCRND8 mice.

“We also found sparse TauC3 immunopositive cells in the hippocampus and cortex of AAV-P301L tau expressing TgCRND8 mice (Fig. 3A–B).”

In the pre-deposit cohort, all groups had similar levels of neuritic plaques.

“We also examined NP pathology using ptau specific CP13 antibody colocalizing with Thioflavin S reactive plaques and observed that all the groups had similar levels of NPs (Fig. S7).”

Synaptic proteins were increased in the post-deposit cohort.

“We observed that synaptic proteins were increased in the post-deposit cohort, which is somewhat inconsistent with the observations of synapse loss in AD patients (reviewed in (29)).”

Gene enrichment analysis of upregulated genes in P301L tau mice revealed affected pathways including tricellular tight junction assembly, Fas signalling pathway, and lipoprotein transport.

“Gene enrichment analysis of upregulated genes revealed several affected pathways in the P301L tau mice, such as tricellular tight junction assembly which is associated with blood brain barrier (p=0.008), Fas signalling pathway (p=0.008) and lipoprotein transport (p= 0.008) (Fig. 5P–Q).”

In the 3-month pre-deposit cohort, S320F tau mice had higher levels of spinophilin (p<0.05 relative to P301L tau).

“The S320F tau mice had higher levels of spinophilin (p<0.05 relative to P301L tau) (Fig. 8E).”

Trem2 was downregulated in AAV-P301L tau mice.

“Based on such consistent changes in immune gene co-expression networks and because we observed that Trem2 was downregulated in AAV-P301L tau mice (Log2= −0.659; p=0.0143), we next generated a damage associated microglia (DAM) score based on a subset of immune genes characteristic of microglia shifting from homeostatic to DAM phenotype (20).”

In the post-deposit cohort, no frank neurodegenerative features (reduced neuronal markers and synaptic markers) were observed at this time point.

“In our post-deposit cohort, we did not observe frank neurodegenerative features (reduced neuronal markers and synaptic markers) at this time point, and it remains a testable hypothesis that aging would exacerbate neurodegeneration in the P301L tau expressing TgCRND8 mice.”

S320F tau shows self-aggregating properties in cell culture.

“whereas the S320F tau showed self-aggregating properties in cell culture (11) and in nonTG mice (10).”

• cites [11] Strang KH, Croft CL, Sorrentino ZA, Chakrabarty P, Golde TE, Giasson BI. Distinct differences in prion-like seeding and aggregation between Tau protein variants provide mechanistic insights into tauopathies. The Journal of biological chemistry. 2018; 293(12): 4579. 29572329 PMC5868274Not matched

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

Different tau mutations representing specific folding variants of tau synergize with Aβ to different extents, depending on the presence of cerebral deposits.

“Our data shows that different tau mutations representing specific folding variants of tau synergize with Aβ to different extents, depending on the presence of cerebral deposits.”

There is a dichotomy in Aβ-tau synergy based on the nature of Aβ.

“In the post-deposit cohort, contemporaneous expression of S320F tau did not exacerbate amyloid pathology, showing a dichotomy in Aβ-tau synergy based on the nature of Aβ.”

There is a unique neuropathological synergy between Aβ plaques and P301L tau recapitulating AD-type neuropathology.

“In summary, using a combinatorial approach of AAV transgenesis and transgenic mice, we demonstrate a unique neuropathological synergy between Aβ plaques and P301L tau recapitulating AD-type neuropathology.”

Early tau tangles affect the amyloid cascade.

“In the pre-deposit cohort, S320F tau induced Aβ plaque deposition, neuroinflammation and synaptic abnormalities, suggesting that early tau tangles affect the amyloid cascade.”

Human WT tau and P301L tau do not form NFT tau following 6 months of sustained expression in mice.

“Human WT tau and P301L tau does not form NFT tau following 6 months of sustained expression in mice, whereas the S320F tau showed self-aggregating properties in cell culture (11) and in nonTG mice (10).”

• cites [10] Koller EJ, Gonzalez De La Cruz E, Machula T, Ibanez KR, Lin W-L, Williams T, Riffe CJ, Ryu D, Strang KH, Liu X, Janus C, Golde TE, Dickson DW, Giasson BI, Chakrabarty P. Combining P301L and S320F tau variants produces a novel accelerated model of tauopathy. Human molecular genetics. 2019; 28(19): 3255– 3269. 31261380 PMC6859436 sourceNot checked — no full text of the source

P301L tau pathology synergizes with pre-existing Aβ deposits.

“P301L tau produced NFT-type inclusions in the post-deposit cohort, but not in the pre-deposit cohort, indicating pathological synergy with pre-existing Aβ deposits.”

Human Aβ and tau show pathological cooperativity in transgenic models.

“Taken together these studies demonstrate that human Aβ and tau show pathological cooperativity in transgenic models, but questions remain as to which species of Aβ and tau synergize with each other.”

S320F tau shows self-aggregating properties in nonTG mice.

“whereas the S320F tau showed self-aggregating properties in cell culture (11) and in nonTG mice (10).”

• cites [10] Koller EJ, Gonzalez De La Cruz E, Machula T, Ibanez KR, Lin W-L, Williams T, Riffe CJ, Ryu D, Strang KH, Liu X, Janus C, Golde TE, Dickson DW, Giasson BI, Chakrabarty P. Combining P301L and S320F tau variants produces a novel accelerated model of tauopathy. Human molecular genetics. 2019; 28(19): 3255– 3269. 31261380 PMC6859436 sourceNot checked — no full text of the source

Aβ leads to exacerbated tau pathologies in mouse models expressing a tauopathy-related mutant tau gene.

“Several mouse modelling studies have shown that Aβ leads to exacerbated tau pathologies in mouse models expressing a tauopathy-related mutant tau gene (3, 4).”

• cites [3] Lewis J, Dickson DW, Lin WL, Chisholm L, Corral A, Jones G, Enhanced neurofibrillary degeneration in transgenic mice expressing mutant tau and APP. Science. 2001; 293(5534): 1487– 91. 11520987 sourceNot checked — no full text of the source
• cites [4] Gotz J, Chen F, van Dorpe J, Nitsch RM. Formation of neurofibrillary tangles in P301l tau transgenic mice induced by Abeta 42 fibrils. Science. 2001; 293(5534): 1491– 5. 11520988 sourceNot checked — no full text of the source

There is a synergistic relationship between P301L tau and Aβ plaques.

“Together, our data shows a synergistic relationship between P301L tau and Aβ plaques, reinforcing the idea that co-occurrence of specific types of misfolded tau and Aβ pathologies can synergize and aggravate the pathologic trajectory.”

Overall, WT tau expression predominantly affected pathways related to cellular metabolism and transport.

“Overall, WT tau expression predominantly affected pathways related to cellular metabolism and transport.”

P301L tau represents a uniquely folded variant that is vulnerable to misfolding into NFT readily in the presence of Aβ deposits.

“Our results indicate that P301L tau represents a uniquely folded variant that is vulnerable to misfolding into NFT readily in the presence of Aβ deposits.”

• AssumptionRests on an assumption: The AAV-tau expression in TgCRND8 mice is a valid model for studying the Aβ-tau interaction in AD.

Aβ-triggered misfolded P301L tau triggers changes in brain immunity associated with the DAM phenotype.

“showing that Aβ-triggered misfolded P301L tau triggers changes in brain immunity associated with this particular phenotype.”

The study used mutant tau to explore the relationship between Aβ and tau to model the AD scenario.

“One of the caveats is that we are using mutant tau to explore the relationship between Aβ and tau to model the AD scenario.”

On the whole, AAV-S320F tau expression induced changes related to altered actin dynamics and immune response.

“On the whole, AAV-S320F tau expression induced changes related to altered actin dynamics and immune response.”

The tau mutations have confirmed prion properties.

“Thus, these mutations, that have confirmed prion properties (11), were selected by us as exemplars of different tau conformers that could form tau tangles in an accelerated manner.”

• cites [11] Strang KH, Croft CL, Sorrentino ZA, Chakrabarty P, Golde TE, Giasson BI. Distinct differences in prion-like seeding and aggregation between Tau protein variants provide mechanistic insights into tauopathies. The Journal of biological chemistry. 2018; 293(12): 4579. 29572329 PMC5868274Not matched

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

In the pre-deposit cohort, the effect of tau dominates the synaptic landscape, reflected in reduced levels of synaptogyrin 3, synaptophysin, and PSD95.

“When Aβ is relatively low as in the pre-deposit cohort, we would expect that the effect of tau would dominate the synaptic landscape, which is probably reflected in reduced levels of synaptogyrin 3, synaptophysin and PSD95.”

Aβ could be the primary driver of neuroinflammation, at least in the early disease phases.

“Since the S320F tau cohort showed higher amyloid burden than the other tau-expressing mice, this is suggestive that Aβ could be the primary driver of neuroinflammation, at least in the early disease phases.”

Presence of Aβ deposits does not amplify the inherent self-aggregation properties of S320F tau.

“indicating that presence of Aβ deposits does not amplify the inherent self-aggregation properties of S320F tau.”

Other factors, such as aging-related factors, are required for the DAM-related gene expression signature to cause morphological changes.

“This suggests that other factors, such as aging-related factors, are required for this DAM-related gene expression signature to cause morphological changes.”

Presence of Aβ deposits is necessary to induce P301L tau to form tangles.

“More importantly, since expression of P301L tau in the hippocampus of adult nonTG mice did not produce NFT, our data confirms that the presence of Aβ deposits is necessary to induce P301L tau to form tangles.”

Increased synaptic proteins in the post-deposit cohort are in agreement with Aβ-induced hyperactivity effects.

“The synaptic levels in the post-deposit cohort data, where Aβ is abundant, would be in agreement with Aβ-induced hyperactivity effects, as we generally observed increased levels of synaptic proteins.”

Presence of Aβ induces tau misfolding and tangle-type features in P301L tau expressing mice.

“Together, this data suggests that presence of Aβ induces tau misfolding and tangle-type features in the P301L tau expressing mice.”

In the presence of Aβ, tau might be suppressing immune function, as evident from reduced Trem2 expression and downregulation of immune pathways.

“While Aβ induces immune activation and Trem2 expression in CRND8 mice (33), we show here that in the presence of Aβ, tau might be suppressing immune function as evident from reduced Trem2 expression and downregulation of immune pathways.”

In an accompanying manuscript using trigenic mice, presence of Aβ plaques was shown to worsen concurrent as well as emerging tauopathy in rTg4510 mice.

“Indeed, our data is supported by an accompanying manuscript in which using trigenic mice, the presence of Aβ plaques was shown to worsen concurrent as well as emerging tauopathy in rTg4510 mice (Xu et al. TAPPing into the potential of inducible tau/APP transgenic mice).”

• cites Xu et al. TAPPing into the potential of inducible tau/APP transgenic miceNot matched

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

All three tau variants had equivalent expression levels.

“all of which had equivalent expression levels.”