Small, soluble aggregates of the Aβ1-42 peptide are now believed to be the toxic factor that is responsible for synaptic dysfunction and eventual neuronal degeneration in Alzheimer's disease. This work adds to this consensus by showing that soluble extracts of brains from five cases of AD react with an antiserum specific for the Aβ1-42 peptide. Samples of both naturally derived Aβ1-42 peptides and synthetic versions were also found to bind in a punctate fashion to the external surfaces of culture hippocampal neurons. The authors suggest that Aβ oligomers might be binding to sites of signaling specializations, possibly related to synaptic terminals. To rule out non-specific binding, the Aβ oligomers were incubated with specific antibodies before adding them to the cultured cells. This blocked the binding of the added Aβ peptides to the cells, but this step in effect removed the oligomers from contact with the neurons and did not address whether oligomers that were available to the cells could bind non-specifically. It was also found, using the SDS gel overlay technique, that...  Read more

Small, soluble aggregates of the Aβ1-42 peptide are now believed to be the toxic factor that is responsible for synaptic dysfunction and eventual neuronal degeneration in Alzheimer's disease. This work adds to this consensus by showing that soluble extracts of brains from five cases of AD react with an antiserum specific for the Aβ1-42 peptide. Samples of both naturally derived Aβ1-42 peptides and synthetic versions were also found to bind in a punctate fashion to the external surfaces of culture hippocampal neurons. The authors suggest that Aβ oligomers might be binding to sites of signaling specializations, possibly related to synaptic terminals. To rule out non-specific binding, the Aβ oligomers were incubated with specific antibodies before adding them to the cultured cells. This blocked the binding of the added Aβ peptides to the cells, but this step in effect removed the oligomers from contact with the neurons and did not address whether oligomers that were available to the cells could bind non-specifically. It was also found, using the SDS gel overlay technique, that synthetic Aβ peptides bind to a number if unidentified proteins of hippocampal membrane fractions. While these preliminary observations are provocative, more direct evidence is needed to support the claim that oligomeric Aβ ligands bind in a biologically meaningful way to specific neuronal proteins that mediate signal transduction and that they are directly involved in reversible memory loss.

View all comments by Vincent Marchesi

Response to comment by Vincent Marchesi

Dr. Marchesi provides a thoughtful summary of our study and calls attention to an issue that's of central concern to us—specificity. AD is so memory-specific, especially early on, that one would hope to identify molecular pathogens capable of explaining this key feature of the disease. It's turning out that the property of specificity is a most intriguing aspect of ADDL nerve cell biology.

As Dr. Pascale Lacor will show in her poster at SFN-New Orleans, those hot spots of ADDL binding are neither random nor nonspecific. They actually are just what the doctor ordered—synapses. And when ADDLs get lodged in those synapses, they disrupt particular molecular mechanisms essential for memory. (Since Dr. Lacor's study is out for review, I won't comment further on its details.) The bottom line is that the specific manner in which ADDLs attack neurons can provide a synaptically localized mechanism to account for memory loss in AD.

However, even with these further interesting findings, we would, of course, agree that as always, more...  Read more

Response to comment by Vincent Marchesi

Dr. Marchesi provides a thoughtful summary of our study and calls attention to an issue that's of central concern to us—specificity. AD is so memory-specific, especially early on, that one would hope to identify molecular pathogens capable of explaining this key feature of the disease. It's turning out that the property of specificity is a most intriguing aspect of ADDL nerve cell biology.

As Dr. Pascale Lacor will show in her poster at SFN-New Orleans, those hot spots of ADDL binding are neither random nor nonspecific. They actually are just what the doctor ordered—synapses. And when ADDLs get lodged in those synapses, they disrupt particular molecular mechanisms essential for memory. (Since Dr. Lacor's study is out for review, I won't comment further on its details.) The bottom line is that the specific manner in which ADDLs attack neurons can provide a synaptically localized mechanism to account for memory loss in AD.

However, even with these further interesting findings, we would, of course, agree that as always, more evidence is desirable.

View all comments by William Klein

This is an impressive and important contribution. It links the appearance of a particular multimeric species of the amyloid-β peptide—Aβ*56—to a specific behavioral perturbation, and induces the same perturbation in naïve rats by reintroducing the Aβ*56 species purified from Tg2576 brains. It begins to address the conundrum that Aβ levels, soluble or insoluble, do not correlate with the onset and severity of behavioral changes in these animals.

Expectedly, this report stimulates a raft of questions, not with the work itself, but in teasing out more of the details and in stimulating new approaches. It will also energize corroboration of their findings in other Tg mouse models, as well as a search for correlates in Alzheimer disease brain. The findings from those studies will either further validate the animal model or set limits on its interpretation, both of which will be valuable. To begin to understand this complex paper, you must also study the supplementary information...  Read more

This is an impressive and important contribution. It links the appearance of a particular multimeric species of the amyloid-β peptide—Aβ*56—to a specific behavioral perturbation, and induces the same perturbation in naïve rats by reintroducing the Aβ*56 species purified from Tg2576 brains. It begins to address the conundrum that Aβ levels, soluble or insoluble, do not correlate with the onset and severity of behavioral changes in these animals.

Expectedly, this report stimulates a raft of questions, not with the work itself, but in teasing out more of the details and in stimulating new approaches. It will also energize corroboration of their findings in other Tg mouse models, as well as a search for correlates in Alzheimer disease brain. The findings from those studies will either further validate the animal model or set limits on its interpretation, both of which will be valuable. To begin to understand this complex paper, you must also study the supplementary information provided online.

Hypothesizing that a particular species of Aβ was responsible for deficits in memory retention that progress in a specific pattern with age in Tg 2576 mice, the authors developed a sequential extraction method to distinguish pools of Aβ peptide in the brains of these mice. They were able to empirically quasi-separate “extracellular-enriched” and “intracellular-enriched” fractions, although it is not clear how detergent-containing extractions can avoid solubilizing membranes. Perhaps a specific detergent/protein ratio limits the effect of the detergent.

Combined with primary neuronal and astrocyte culture work, this fractionation allowed them to conclude that oligomers of Aβ larger than trimers assemble extracellularly. Interestingly, cultured cells contained only trimers, while the extracellular species were trimers and tetramers, but not hexamers, nonamers, or Aβ*56 (dodecamers), which are observed in the whole aged animals. This could be due to the fact that the cultured cells are embryonic, not mature neurons, and they are not in a tissue environment. What is apparent is that oligomer formation in cells yields a different size spectrum of products from those reported in the literature for synthetic peptides and from those observed in aged (>6 months) animals (this article). This may be due to clearance mechanisms and/or modulating intra- and extracellular processes.

The importance of these observations is that they direct attention to extracellular events as being important in the maturation of trimers and tetramers into Aβ*56. This has not previously been appreciated. It also suggests that the change occurring at 6 months of age in Tg 2576 mice may be in the cellular environment. This will undoubtedly launch new lines of research focusing on that aspect. An extracellular target is also an easier one to reach with therapeutics.

In the studies reported here, Aβ*56 is purified by immunoprecipitation. Along with the specificity of that method for Aβ peptides comes the risk of missing cryptic epitopes. As an example, in Lesne et al., hexamers do not seem to IP well, yet they can be readily seen in non-IPed material. Antigen recovery by boiling of the blots before immunodetection affects the relative intensity of the species observed, as noted by the authors.

The authors are careful not to claim that Aβ*56 is the only species capable of inducing behavioral effects; indeed, they do not report testing the other SEC-separated species they isolate.

The story, of course, is far from complete with the identification of an Aβ*56 species that reproduces particular behavioral deficits in rats that are seen in the transgenic APP mice. Transgenic mice are at best a partial model of the uniquely human Alzheimer disease. There is minimal neuronal cell death in mice and in most cases (including Tg 2576), only moderate synapse loss is apparent. While more detailed study may reveal subtle changes in synaptic architecture/function, the devastation in the Alzheimer brain is not recapitulated. Thus, mice may represent a model of the earliest stages of a process that becomes Alzheimer disease in humans. That is a particularly important issue, because it is precisely at that stage at which intervention is likely to be most effective and detection of pathology first possible.

View all comments by Harry LeVine III

Amyloid-β protein dodecamer in the brain impairs memory in the Tg2576 mouse
The experience from genetic findings in the early 1990s strongly point to Aβ as the culprit in Alzheimer disease. However, we still do not understand how Aβ confers cognitive dysfunction and neuronal atrophy. Recent years have witnessed an increased interest in soluble Aβ oligomers as being the important pathogenic form of Aβ. This article is a significant contribution to the field. Most impressive is perhaps the author’s ability to isolate a soluble Aβ species from the brain and prove that it affects cognition. The research team, headed by Karen Ashe, has for a long time sought the elusive Aβ species responsible for cognitive decline in their transgenic mouse model Tg2576, which harbors the Swedish APP mutation.

Tg2576 lack neuropathology and are cognitively unimpaired until 6 months of age, when spatial memory declines but then remains stable for another 7-8 months. Animals aged more than 14 months develop neuropathology including neuritic plaques containing amyloid-β peptides and...  Read more

Amyloid-β protein dodecamer in the brain impairs memory in the Tg2576 mouse
The experience from genetic findings in the early 1990s strongly point to Aβ as the culprit in Alzheimer disease. However, we still do not understand how Aβ confers cognitive dysfunction and neuronal atrophy. Recent years have witnessed an increased interest in soluble Aβ oligomers as being the important pathogenic form of Aβ. This article is a significant contribution to the field. Most impressive is perhaps the author’s ability to isolate a soluble Aβ species from the brain and prove that it affects cognition. The research team, headed by Karen Ashe, has for a long time sought the elusive Aβ species responsible for cognitive decline in their transgenic mouse model Tg2576, which harbors the Swedish APP mutation.

Tg2576 lack neuropathology and are cognitively unimpaired until 6 months of age, when spatial memory declines but then remains stable for another 7-8 months. Animals aged more than 14 months develop neuropathology including neuritic plaques containing amyloid-β peptides and further cognitive deficits. The authors posited the existence of an Aβ oligomeric form, designated Aβ*, responsible for early cognitive decline in Tg2576. Two criteria were used: Aβ* should appear at 6 months of age and remain stable between 6-14 months of age. The best correlation was found between Aβ 12-mers and spatial memory.

Curiously, non-transgenic mice also show a trend toward impaired spatial memory at 6 months of age (Figure 1a). It would be interesting to investigate whether increase in Aβ* is coincident with cognitive deficits also in other APP mouse models, since cognitive dysfunction is known to be highly dependent upon strain background.

Most surprisingly, levels of Aβ*56 in brain do not increase upon onset of senile plaque deposition when total Aβ levels increase 100-fold (Kawarabayashi et al. 2001). This would tend to suggest a dichotomous model of Aβ amyloidosis in the brain, where Aβ* formation is unrelated to senile plaque formation. It would be interesting to determine turnover of endogenous Aβ* in the brain, especially since Aβ* confers a transient effect on memory retention. What would happen with levels of Aβ* in Tg2576 following acute or chronic treatment with a potent γ-secretase inhibitor or in a TET-off APP transgenic model?

Most important would be, of course, to investigate if Aβ* exists in the brain or CSF of Alzheimer disease patients, and if Aβ* levels are linked to mild cognitive impairment (MCI) and further cognitive decline in the human disease.

View all comments by Lars Lannfelt
View all comments by Lars Nilsson

Star-struck by Amyloid
Lesne and colleagues show that Aβ*56 is found in cognitively impaired Tg2576 animals without Aβ plaques, but not in unimpaired animals, and that it correlates to early declines in memory but not later ones. Notably, when isolated and injected into rats, Aβ*56 leads to reversible cognitive deficits. This is an interesting study and will definitely appeal to supporters of the amyloid hypothesis. However, before we get ahead of ourselves, a few salient aspects bear remembrance.

First, different groups have reported that knockout of PS1 (i.e., no Aβ and probably no Aβ*56, either), while attenuating Aβ pathology in APP mutant transgenic mice, does not cure cognitive deficits (Dewachter et al., 2002; Saura et al., 2005). Therefore, cognitive deficits do not relate to Aβ (in any guise, even *). Second, mitochondrial, apoptotic, and oxidative events all precede frank Aβ deposition and are linked to cognitive decline in APP transgenic mice (Pratico et al., 2001; Reddy et al., 2004). Since oxidative stress leads to increases in Aβ (Yan et al., 1995;...  Read more

Star-struck by Amyloid
Lesne and colleagues show that Aβ*56 is found in cognitively impaired Tg2576 animals without Aβ plaques, but not in unimpaired animals, and that it correlates to early declines in memory but not later ones. Notably, when isolated and injected into rats, Aβ*56 leads to reversible cognitive deficits. This is an interesting study and will definitely appeal to supporters of the amyloid hypothesis. However, before we get ahead of ourselves, a few salient aspects bear remembrance.

First, different groups have reported that knockout of PS1 (i.e., no Aβ and probably no Aβ*56, either), while attenuating Aβ pathology in APP mutant transgenic mice, does not cure cognitive deficits (Dewachter et al., 2002; Saura et al., 2005). Therefore, cognitive deficits do not relate to Aβ (in any guise, even *). Second, mitochondrial, apoptotic, and oxidative events all precede frank Aβ deposition and are linked to cognitive decline in APP transgenic mice (Pratico et al., 2001; Reddy et al., 2004). Since oxidative stress leads to increases in Aβ (Yan et al., 1995; Li et al., 2004), we suspect this is the true star. Third, related to these issues, mutations in APP cause increases in oxidative stress (Yamatsuji et al., 1996; Hashimoto et al., 2000).

In sum, Aβ*56 may be the brightest star, but, as any amateur astronomer can attest, “stars that burn brightest burn fastest and thus have the shortest lifetimes.”

References:
Dewachter I, Reverse D, Caluwaerts N, Ris L, Kuiperi C, Van den Haute C, Spittaels K, Umans L, Serneels L, Thiry E, Moechars D, Mercken M, Godaux E, Van Leuven F. Neuronal deficiency of presenilin 1 inhibits amyloid plaque formation and corrects hippocampal long-term potentiation but not a cognitive defect of amyloid precursor protein [V717I] transgenic mice. J Neurosci. 2002 May 1;22(9):3445-53. Abstract

Hashimoto Y, Niikura T, Ito Y, Nishimoto I. Multiple mechanisms underlie neurotoxicity by different types of Alzheimer's disease mutations of amyloid precursor protein. J Biol Chem. 2000 Nov 3;275(44):34541-51. Abstract

Li F, Calingasan NY, Yu F, Mauck WM, Toidze M, Almeida CG, Takahashi RH, Carlson GA, Flint Beal M, Lin MT, Gouras GK. Increased plaque burden in brains of APP mutant MnSOD heterozygous knockout mice. J Neurochem. 2004 Jun;89(5):1308-12. Abstract

Pratico D, Uryu K, Leight S, Trojanoswki JQ, Lee VM. Increased lipid peroxidation precedes amyloid plaque formation in an animal model of Alzheimer amyloidosis. J Neurosci. 2001 Jun 15;21(12):4183-7. Abstract

Reddy PH, McWeeney S, Park BS, Manczak M, Gutala RV, Partovi D, Jung Y, Yau V, Searles R, Mori M, Quinn J. Gene expression profiles of transcripts in amyloid precursor protein transgenic mice: up-regulation of mitochondrial metabolism and apoptotic genes is an early cellular change in Alzheimer's disease. Hum Mol Genet. 2004 Jun 15;13(12):1225-40. Epub 2004 Apr 28. Abstract

Saura CA, Chen G, Malkani S, Choi SY, Takahashi RH, Zhang D, Gouras GK, Kirkwood A, Morris RG, Shen J. Conditional inactivation of presenilin 1 prevents amyloid accumulation and temporarily rescues contextual and spatial working memory impairments in amyloid precursor protein transgenic mice. J Neurosci. 2005 Jul 20;25(29):6755-64. Abstract

Yamatsuji T, Matsui T, Okamoto T, Komatsuzaki K, Takeda S, Fukumoto H, Iwatsubo T, Suzuki N, Asami-Odaka A, Ireland S, Kinane TB, Giambarella U, Nishimoto I. G protein-mediated neuronal DNA fragmentation induced by familial Alzheimer's disease-associated mutants of APP. Science. 1996 May 31;272(5266):1349-52. Abstract

Yan SD, Yan SF, Chen X, Fu J, Chen M, Kuppusamy P, Smith MA, Perry G, Godman GC, Nawroth P, et al. Non-enzymatically glycated tau in Alzheimer's disease induces neuronal oxidant stress resulting in cytokine gene expression and release of amyloid beta-peptide. Nat Med. 1995 Jul;1(7):693-9. Abstract

View all comments by Hyoung-gon Lee
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View all comments by George Perry
View all comments by Mark A. Smith
View all comments by Xiongwei Zhu

This exciting paper set outs to define the site and conformation of Aβ in the brain that may be critical for cognitive dysfunction in Tg2576 mice. The co-occurrence of Aβ*56 with behavioral alterations is quite interesting, yet aspects of the study are surprising. Aβ* does not progressively increase, while Alzheimer disease and Tg2576 mice are characterized by progressive synaptic pathology. Aβ* appears at the onset of what seems to be a progressive decline in behavior in Tg2576 mice, were it not for transient improvement at 13 months, which surprisingly also occurs in wild-type mice.

The data used to support that Aβ* accumulates extracellularly in Tg2576 mice are challenging. As suggested in previous comments (LeVine; Marchesi), it would seem difficult to be certain that one is mainly looking at extracellular peptides after detergent treatment (0.01 percent NP-40; 0.1 percent SDS) and homogenization of the intricate mass of neurons and processes of brain by 10 passages through a 20-gauge needle. The authors did provide some data on other intracellular proteins not leaking...  Read more

This exciting paper set outs to define the site and conformation of Aβ in the brain that may be critical for cognitive dysfunction in Tg2576 mice. The co-occurrence of Aβ*56 with behavioral alterations is quite interesting, yet aspects of the study are surprising. Aβ* does not progressively increase, while Alzheimer disease and Tg2576 mice are characterized by progressive synaptic pathology. Aβ* appears at the onset of what seems to be a progressive decline in behavior in Tg2576 mice, were it not for transient improvement at 13 months, which surprisingly also occurs in wild-type mice.

The data used to support that Aβ* accumulates extracellularly in Tg2576 mice are challenging. As suggested in previous comments (LeVine; Marchesi), it would seem difficult to be certain that one is mainly looking at extracellular peptides after detergent treatment (0.01 percent NP-40; 0.1 percent SDS) and homogenization of the intricate mass of neurons and processes of brain by 10 passages through a 20-gauge needle. The authors did provide some data on other intracellular proteins not leaking out in the process, although one might expect cytoskeleton proteins, such as tau and MAP2, to be more readily retained in cells in the presence of detergent compared to a hydrophobic/lipid-associated peptide such as Aβ. A readily releasable marker such as LDH could have been helpful.

In the supplement, the authors compare previous work addressing Aβ increases in Tg2576 mice, including work from our lab on intraneuronal Aβ42 increases. Their interpretation appears inconsistent with our immunoelectron microscopy studies demonstrating pathological intraneuronal Aβ42 increases and oligomerization in Tg2576 mouse brains (Takahashi et al., 2002; 2004). Remarkably, a fascinating report relating Pin1 and amyloid by Lu and colleagues (Pastorino et al., 2006) in the following issue of Nature provided further confirmation of intraneuronal Aβ accumulation in MVBs of Tg2576 mice.

Can the findings of Lesne et al. be reconciled with evidence for intraneuronal Aβ? It is possible that Aβ* is the specific oligomer responsible for the invariable association of intracellular pathology with Aβ oligomers (Takahashi et al., 2004), which could then be released from neurites following destruction of the plasma membrane from within. This is not inconsistent with a subsequent important role for extracellular Aβ* as well. A potentially similar scenario of intracellular amyloid formation is described in a recent article on diabetes, another common amyloid associated age-related disease (Paulsson et al., 2006).

View all comments by Gunnar K. Gouras

The work of Shankar and colleagues provides new evidence supporting the concept that soluble Aβ oligomers disrupt synaptic function in Alzheimer disease. The recent publication from Rowan, Wang, and their colleagues (Rowan et al., 2007) suggesting that synaptic dysfunction caused by Aβ oligomers is mediated by TNF-α is highly relevant. This new publication extends Rowan and Wang’s previous work, which suggested that β amyloid inhibition of LTP is mediated via TNF (Wang et al., 2005). In Rowan and Wang’s most recent paper, experimental evidence is presented that pretreatment with a biologic inhibitor of TNF-α to neutralize TNF-α prevented Aβ inhibition of LTP induction at medial perforant pathway synapses.

These are observations of great importance, because they help bridge the gap between the amyloid hypothesis and the neuroinflammatory hypothesis of AD. These interrelated mechanisms may help explain the positive clinical effects my colleagues and I have observed using anatomically targeted anti-TNF treatment in AD (Tobinick et al., 2006) and underscores the need to further...  Read more

The work of Shankar and colleagues provides new evidence supporting the concept that soluble Aβ oligomers disrupt synaptic function in Alzheimer disease. The recent publication from Rowan, Wang, and their colleagues (Rowan et al., 2007) suggesting that synaptic dysfunction caused by Aβ oligomers is mediated by TNF-α is highly relevant. This new publication extends Rowan and Wang’s previous work, which suggested that β amyloid inhibition of LTP is mediated via TNF (Wang et al., 2005). In Rowan and Wang’s most recent paper, experimental evidence is presented that pretreatment with a biologic inhibitor of TNF-α to neutralize TNF-α prevented Aβ inhibition of LTP induction at medial perforant pathway synapses.

These are observations of great importance, because they help bridge the gap between the amyloid hypothesis and the neuroinflammatory hypothesis of AD. These interrelated mechanisms may help explain the positive clinical effects my colleagues and I have observed using anatomically targeted anti-TNF treatment in AD (Tobinick et al., 2006) and underscores the need to further investigate this treatment approach (see also Tweedie et al., 2007).

References:
Rowan MJ, Klyubin I, Wang Q, Hu NW, Anwyl R. Synaptic memory mechanisms: Alzheimer's disease amyloid beta-peptide-induced dysfunction. Biochem Soc Trans 2007 Oct; 35(Pt 5):1219-23. Abstract

Wang Q, Wu J, Rowan MJ, Anwyl R. Beta-amyloid inhibition of long-term potentiation is mediated via tumor necrosis factor. Eur J Neurosci 2005 Dec; 22(11):2827-32. Abstract

Tobinick E, Gross H, Weinberger A, Cohen H. TNF-alpha Modulation for Treatment of Alzheimer's Disease: A 6-Month Pilot Study. MedGenMed 2006; 8(2):25. Abstract

Tweedie D, Sambamurti K, Greig NH. TNF-alpha Inhibition as a Treatment Strategy for Neurodegenerative Disorders: New Drug Candidates and Targets. Curr Alzheimer Res 2007 Sep; 4(4):375-8. Abstract

View all comments by E T

Regarding the data presented by Dennis Selkoe's group: when they isolate the oligomeric material from AD brain, they separate it by a Sephadex75 column. The material goes with the void in that column (“fraction 4”), which means that it is larger than 65 kDa. Our synthetic protofibrils behave in the same way on the same column. Selkoe’s group then immunoprecipitate the material and run it on Western blot, where it appears as a dimer.

There are at least two explanations for the difference observed:

1. The dimer is broken down from a larger oligomeric species through immunoprecipitation and Western blot.

2. The dimer is bound to a larger protein which gives a molecular weight of more than 65 kDa.

[Editor's note: see Oligo report Part 2]

View all comments by Lars Lannfelt

I would like to further detail some of the statements present in Dr. Pimplikar's comments regarding our studies using human brain tissues (20 Non-Cognitively Impaired, 10 Mild Cognitively Impaired and 10 AD selected from the Religious Order Study by Dr. David Bennett, director of the program).

It is true that during my Minisymposium talk, I reported a greater than 3-fold increase in Aβ*56 levels in brains of individuals clinically diagnosed with MCI or AD. Aβ*56 levels in both MCI and AD groups were not different compared to each other, suggesting that Aβ*56 may be a molecule initiating Aβ-induced cognitive decline. I also mentioned that we did not observe changes in levels of soluble monomeric Aβ, nor in levels of Aβ trimers. Finally, we reported that cerebral levels of Aβ*56 are inversely correlated with MMSE score, while soluble Aβ monomers, Aβ trimers, or amyloid burden were not associated with neurological status.

As for our poster presentation, we demonstrated that Aβ*56 was not associated with changes in levels of synaptophysin or drebrin (among other pre- and...  Read more

I would like to further detail some of the statements present in Dr. Pimplikar's comments regarding our studies using human brain tissues (20 Non-Cognitively Impaired, 10 Mild Cognitively Impaired and 10 AD selected from the Religious Order Study by Dr. David Bennett, director of the program).

It is true that during my Minisymposium talk, I reported a greater than 3-fold increase in Aβ*56 levels in brains of individuals clinically diagnosed with MCI or AD. Aβ*56 levels in both MCI and AD groups were not different compared to each other, suggesting that Aβ*56 may be a molecule initiating Aβ-induced cognitive decline. I also mentioned that we did not observe changes in levels of soluble monomeric Aβ, nor in levels of Aβ trimers. Finally, we reported that cerebral levels of Aβ*56 are inversely correlated with MMSE score, while soluble Aβ monomers, Aβ trimers, or amyloid burden were not associated with neurological status.

As for our poster presentation, we demonstrated that Aβ*56 was not associated with changes in levels of synaptophysin or drebrin (among other pre- and postsynaptic markers), suggesting that Aβ*56 is not triggering synaptic loss (contrary to 7PA2 CM-derived Aβ dimers/trimers). In addition, we reported that in human tissues, trimeric Aβ levels were dependent on monomeric Aβ levels. Finally, Aβ dimers were not detected in soluble fractions of protein extracts from human or transgenic mouse brains.

View all comments by Sylvain Lesne

At this moment, perhaps the greatest contribution to the field of AD would be focusing on efforts to further define and compare the various preparations of amyloid-β (Aβ) aggregates, continuing research in the vein of recent SfN presentations from the Ashe/Cleary and Selkoe groups. The nomenclature for oligomers is inconsistent at best. The Aβ assemblies/aggregates preparations studied by particular investigators are defined by numerous methods, including neurotoxic activities, isolation technique (primarily size exclusion chromatography), size estimation by SDS or native PAGE, and several imaging techniques. In addition, reactivity with various Aβ conformation-specific antibodies is now also being used to identify specific species of Aβ. Thus, comparison of results across different preparations of Aβ oligomers is virtually impossible. Establishing a common series of definitions and encouraging future publications to work within these established parameters would greatly advance the study of the relationship between Aβ structure and function.

View all comments by Mary Jo LaDu

Alzheimer Disease, Aβ Oligomers, and Shrek
Gabrielle Strobel and Alzforum should be congratulated on bringing to our attention the excitement the “amyloid oligomer hypothesis” has generated in the AD field. Her three-part presentation (Oligomers Live Up to Bad Reputation) summarizes the enormous amount of data presented at the meeting and leaves little doubt that “oligomer” is the buzzword of today.

That the three oligomeric forms of Aβ (7PA2 derived small oligomers; high “n”-oligomers termed ADDLs; and “star”-oligomers) exhibit deleterious effects at various concentrations, in various experimental paradigms, is not surprising, and perhaps, not significant. After all, the literature of the 1990s is littered with reports of Aβ monomers or fibrils being toxic to cells. What is important (to come out of the San Diego meeting) is that two studies found the presence of Aβ oligomers in the AD brains but not in the control tissues. Surely, this should silence the critics, right?

In oral and poster presentations, Lesne et al. reported increased levels of Aβ*56...  Read more

Alzheimer Disease, Aβ Oligomers, and Shrek
Gabrielle Strobel and Alzforum should be congratulated on bringing to our attention the excitement the “amyloid oligomer hypothesis” has generated in the AD field. Her three-part presentation (Oligomers Live Up to Bad Reputation) summarizes the enormous amount of data presented at the meeting and leaves little doubt that “oligomer” is the buzzword of today.

That the three oligomeric forms of Aβ (7PA2 derived small oligomers; high “n”-oligomers termed ADDLs; and “star”-oligomers) exhibit deleterious effects at various concentrations, in various experimental paradigms, is not surprising, and perhaps, not significant. After all, the literature of the 1990s is littered with reports of Aβ monomers or fibrils being toxic to cells. What is important (to come out of the San Diego meeting) is that two studies found the presence of Aβ oligomers in the AD brains but not in the control tissues. Surely, this should silence the critics, right?

In oral and poster presentations, Lesne et al. reported increased levels of Aβ*56 oligomers in brains from AD patients but apparently did not find a similar increase in the small oligomers. Conversely, Shankar et al. found increased levels of Aβ dimers/trimers in AD patients but detected no star oligomers. If Aβ oligomers are the causative factors of the disease and exist in AD brains, one wonders whether this is too much of a coincidence that these two groups observed only “their” type of oligomers from AD brains.

An important assumption underlying both these studies is that the oligomeric forms of Aβ, detected at the end of a Western blot protocol, already exist in the diseased tissue prior to homogenization/isolation/purification/detection. However, Aβ is an amphipathic peptide (hydrophobic at one end and hydrophilic at the other), and work by Teplow, Bitan, and colleagues has conclusively shown how easily Aβ can create different higher-order multimers depending on experimental conditions. Some may consider this to be hypercritical, but the observation that two productive and respected groups in the field find only their favorite oligomers in AD brains should raise alarm bells: do oligomers exist in vivo or are they created by the very experimental manipulations that are used to detect their presence? Surely, two different protocols are likely to yield two different higher-order forms.

It is a common observation that naysayers are often irritating and sometimes wrong, but objective, dispassionate criticism is essential for the relevance of the amyloid hypothesis (which has been instrumental in promoting AD research) to AD pathogenesis. Shrek, the large, green, intimidating giant also caught our attention and we have come to like it. However, unless ogres exist in real life, Shrek adds little value to our lives other than entertainment.

References:
Bitan G, Fradinger EA, Spring SM, Teplow DB. Neurotoxic protein oligomers--what you see is not always what you get. Amyloid. 2005 Jun 1;12(2):88-95. Abstract

View all comments by Sanjay W. Pimplikar

Our lab has begun looking at Aβ oligomers in our mouse model and in vitro. To add to this series, our findings presented at the SfN meeting can be summarized as follows:

1. We observe entry into the cell cycle (as evidenced by expression of cell cycle proteins and DNA replication by FISH) of selected neuronal populations in our APP YAC transgenic mouse model of AD at 6 months of age. This cell cycle entry is dependent upon amyloidogenic processing of APP and occurs about 6 months prior to Aβ deposition.

2. We can identify the presence of Aβ oligomers at this age (bands on SDS-PAGE) recognized by both 6E10 and the oligomer-specific antibodies NU1 and A11, including the presence of dimers and trimers as well as higher-MW Aβ species.

3. In-vitro preparations of oligomeric Aβ (prepared in Hams F12 media or purified via SEC) and, to a much lesser extent, monomeric Aβ, induced concentration-dependent aberrant neuronal cell cycle entry as measured by BrdU incorporation and expression of cell cycle proteins, in primary cortical neurons. Oligomeric Aβ also induced loss of...  Read more

Our lab has begun looking at Aβ oligomers in our mouse model and in vitro. To add to this series, our findings presented at the SfN meeting can be summarized as follows:

1. We observe entry into the cell cycle (as evidenced by expression of cell cycle proteins and DNA replication by FISH) of selected neuronal populations in our APP YAC transgenic mouse model of AD at 6 months of age. This cell cycle entry is dependent upon amyloidogenic processing of APP and occurs about 6 months prior to Aβ deposition.

2. We can identify the presence of Aβ oligomers at this age (bands on SDS-PAGE) recognized by both 6E10 and the oligomer-specific antibodies NU1 and A11, including the presence of dimers and trimers as well as higher-MW Aβ species.

3. In-vitro preparations of oligomeric Aβ (prepared in Hams F12 media or purified via SEC) and, to a much lesser extent, monomeric Aβ, induced concentration-dependent aberrant neuronal cell cycle entry as measured by BrdU incorporation and expression of cell cycle proteins, in primary cortical neurons. Oligomeric Aβ also induced loss of neurites.

4. Exposure to increasing concentrations of in-vitro preparations of oligomeric Aβ induced altered morphology of primary microglia, consistent with activation and similar to that observed with lipopolysaccharide (LPS). Conditioned media from oligomer-exposed or LPS-stimulated microglia also induced neuronal cell cycle entry, suggesting that Aβ oligomers may act both directly on neurons and perhaps indirectly through activation of microglia.

[Editor's note: See also ARF conference story on cell cycle symposium.]

View all comments by Kiran Bhaskar
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Editor’s note: The Alzforum editors invited Bill Klein of Northwestern University’s Cognitive Neurology and Alzheimer’s Disease Center in Evanston, Illinois, to round off this series of SfN conference news and commentary. Readers who came late to the story can kick back and use Klein’s perspective on the biology and structure of Aβ oligomers as their frame of reference for this current coverage. Below, Klein offers an informal overview of some milestones, along with his take on today’s central questions. If these remarks whet your appetite, you’ll find an in-depth discussion of the broader topic in Klein’s chapter in Synaptic Plasticity and the Mechanism of Alzheimer’s Disease, Selkoe, Dennis J.; Triller, Antoine; Christen, Yves (Eds.), due out January 2008 from Springer.

Oligomers as Alzheimer’s toxins.
Thanks to the work of many labs, we now know that soluble Aβ oligomers are long-lived, neurologically active molecules, not simply...  Read more

Editor’s note: The Alzforum editors invited Bill Klein of Northwestern University’s Cognitive Neurology and Alzheimer’s Disease Center in Evanston, Illinois, to round off this series of SfN conference news and commentary. Readers who came late to the story can kick back and use Klein’s perspective on the biology and structure of Aβ oligomers as their frame of reference for this current coverage. Below, Klein offers an informal overview of some milestones, along with his take on today’s central questions. If these remarks whet your appetite, you’ll find an in-depth discussion of the broader topic in Klein’s chapter in Synaptic Plasticity and the Mechanism of Alzheimer’s Disease, Selkoe, Dennis J.; Triller, Antoine; Christen, Yves (Eds.), due out January 2008 from Springer.

Oligomers as Alzheimer’s toxins.
Thanks to the work of many labs, we now know that soluble Aβ oligomers are long-lived, neurologically active molecules, not simply intermediates in fibrillogenesis. Oligomers accumulate in brains and CSF of individuals afflicted by AD, where they are believed responsible for dementia-producing neuron damage (see, e.g., the “Pathway to Harm,” in the Progress Report on Alzheimer’s Disease published by the Department of Health and Human Services). Neurologically active oligomers have been given many names—we initially called them ADDLs, for Aβ-derived diffusible ligands. (The pronunciation, by the way, is “addles,” as in “Not paying attention to the Alzheimer Research Forum addles the brain.”) Their oligomeric structure endows ADDLs with the capacity to attack particular synapses, mainly at spines and near NMDA receptors. In essence, extracellular ADDLs act as gain-of-function pathogenic ligands. This capacity for highly specific synaptic targeting provides a putative mechanism to explain why AD is a disease of memory. Binding disrupts synaptic plasticity, causes overexpression of the memory-linked immediate early gene Arc, and triggers pathological changes in synapse shape and composition. Because ADDL binding also instigates synapse loss, oxidative damage, AD-type tau hyperphosphorylation, and selective nerve cell death, the attack on synapses provides a plausible mechanism unifying memory dysfunction with major features of AD neuropathology. Most recently, ADDLs were shown to trigger downregulation of synaptic insulin receptors, providing a mechanism to explain insulin resistance in AD brain (“type 3 diabetes”; Zhao et al., 2007). Acting as novel neurotoxins that putatively account for memory loss and neuropathology, ADDLs present significant targets for disease-modifying therapeutics in AD, with proof-of-concept already evident from animal models.

Structurally speaking, Aβ is the peptide from hell.
I’ve lost track of who wrote this first, but the truth still holds. Aβ is one-third hydrophobic, two-thirds hydrophilic, and almost 100 percent erratic in its biochemistry, which is why the problem of how Aβ produces Alzheimer’s dementia is still unsolved after almost 25 years. Darwin may have been thinking of something like Aβ when he said, “Nature will tell you a direct lie when she can.”

The challenges in working with Aβ are exemplified by the remarkable contentiousness of the early 1990s regarding whether Aβ was or was not toxic—some evidence said yes, other evidence said no. Fortunately, despite Aβ’s recalcitrance, insightful research can outsmart it. Seminal work by Christian Pike and Carl Cotman, Alfredo Lorenzo and Bruce Yankner, and their colleagues, resolved the controversy by showing that Aβ preparations are indeed toxic but only if monomers undergo a process of self-assembly. Since their toxic solutions showed amyloid fibrils, it was concluded that toxicity required these emergent fibrils. The apparent requirement for fibrils, certainly consistent with Occam’s razor, provided major support for the original amyloid cascade hypothesis. It made good sense at the time that Alzheimer’s was a pathology of nerve cell death instigated by large insoluble amyloid fibrils.

In keeping with this concept, the first reports of SDS-stable oligomers in AD brain regarded oligomers simply as subunits responsible for ongoing formation of fibrils. Colin Masters, Konrad Beyreuther, and colleagues found that formic acid extracts of isolated amyloid plaques contained dimers and tetramers, as well as a pH-sensitive presence of larger oligomers (Masters et al., 1985). Janusz Frackowiak et al. in 1994 showed SDS-stable dimers and tetramers in extracts of meningeal blood vessels; they concluded that during amyloid formation in AD vessel walls, non-fibrillar oligomers accumulate (Frackowiak et al., 1994). However, 1994 also brought a glimmer of an extremely different concept for structure and toxicity. Tomiichiro Oda and colleagues, working in Tuck Finch’s lab, mixed Aβ with clusterin (ApoJ) and found large fibrils were blocked from forming (Oda et al., 1994). They anticipated a protective effect. To their surprise, their non-pelleting material robustly impaired the ability of PC12 cells to metabolize MTT. They wrote, “Inhibition of Aβ aggregation and enhancement of Aβ toxicity by clusterin suggest new mechanisms in AD.” Supporting this possibility, Alex Roher and colleagues reported that dimers chemically extracted from amyloid deposits were capable of killing neurons via a mechanism requiring microglia (Roher et al., 1996).

Stimulated by the clue provided by Oda et al., our group collaborated closely with Tuck Finch and Grant Krafft in studies that lead to the first ADDL paper (Lambert et al., 1998). Together, we identified small Aβ oligomers as a new type of neurotoxin structurally distinct from amyloid fibrils and protofibrils. We coined the name ADDLs to broadly cover this new class of soluble Aβ-derived molecules showing potent CNS neurotoxicity. We described three different preparative methods, and all yielded solutions of neurotoxic Aβ assemblies that were totally free of fibrils and protofibrils. By atomic force microscopy, ADDLs comprised globular structures roughly comparable in size to soluble proteins smaller than 50 kDa. SDS-PAGE with Tris-glycine gels indicated the assemblies were made of SDS-resistant tetramers and pentamers. Currently, Western blots using Tris-tricine gels with BioRad markers routinely show trimers, tetramers, and 12mers. Native, non-denaturing gels also showed fibril-free oligomers, so oligomers were neither SDS-induced nor products of protofibril breakdown. A later study confirmed that fresh Aβ42, never put in aqueous solution, migrates as monomer in SDS-PAGE (Chromy et al., 2003). In terms of structure-function, the bottom line was that certain conditions promote assembly of Aβ into potent CNS neurotoxins that comprise long-lived soluble oligomers.

The Lambert paper revealed an aspect of ADDL activity that, because of its clear relevance to memory mechanisms, made this new toxin particularly exciting. Within minutes, and greatly in advance of cellular degeneration, ADDLs inhibited long-term potentiation (LTP). We hypothesized that memory dysfunction in early Alzheimer’s was the result of impaired synaptic plasticity caused by ADDLs.

At the end of our Discussion we wrote, “ADDLs thus have profound neurological effects well in advance of tissue damage. If Aβ derivatives such as ADDLs prove to be part of Alzheimer’s pathogenesis, these results suggest that it would be theoretically feasible to halt or reverse the disease during its early stages.” Our prediction that memory loss could be reversed was confirmed 4 years later in mouse model passive immunization experiments by Steve Paul’s group at Eli Lilly (Dodart et al., 2002) and Karen Ashe’s group at Minnesota (Kotilinek et al., 2002). Most recently, the use of conformation-sensitive antibodies targeting non-monomeric Aβ in memory recovery experiments by Trojanowski and Lee specifically supported the pathogenic role of oligomers (Lee et al., 2006).

A PubMed search of amyloid-β oligomer(s) now yields over 500 hits. Knowing what is implied structurally by “toxic oligomer” has become a central issue. There clearly is a wide variety of preparations, resultant structures, and even nomenclature. With respect to ADDLs, the name is generic and broadly encompasses oligomers associated with dementing activity. It was chosen to sharply distinguish AD-relevant globular assemblies from fibrillar toxins.

A neurologically active ADDL preparation typically comprises two classes of oligomers by HPLC-SEC in aqueous buffer. Some migrate in a peak near putative 12mers and some migrate in a peak near putative 3- and 4mers. The relative abundance of the peaks varies from preparation to preparation. The two peaks also can be separated by ultrafiltration. Both peaks are SDS-resistant but not completely SDS-stable, as indicated originally in the Lambert paper. Silver stains from each peak show prominent 4mers, 3mers, and monomers; this is the case even for the larger peak, which contains oligomers that do not pass a 50 kDa cutoff filter in aqueous solution. Ultrafiltration actually indicates that ADDL preparations in physiological buffer contain almost undetectable amounts of monomer (compared, e.g., with positive controls using Aβ40 monomers). The fraction comprising larger oligomers, when analyzed by Western blots with our conformation-sensitive antibodies, shows 12mers. In overexposed Western blots of ADDLs, it is possible to detect a full spectrum of oligomers up to 24mers, although particular species (3- and 4mers, and 12mers) are favored in a temperature-dependent manner (Klein, 2002). We note that some non-toxic Aβ preparations also show oligomers (Chromy et al., 2003), so quality control monitoring both structure and function is essential. Greatly increased SDS-resistance in the 12mer fraction is promoted by incubation with certain prostaglandins or levuglandins (Boutaud et al., 2002; Boutaud et al., 2006) or by copper and H202 (Atwood et al., 2004).

The fraction with 12mers is particularly interesting to us, because it contains the most striking ligand activity, detected as binding to particular synapses in cell biology experiments (Lacor et al., 2004; 2007). The 12mer fraction also gives the most robust induction of drebrin loss and synaptic spine degeneration (Lacor et al., 2007). Regarding our fraction of 3- and 4mers, current data suggest much less binding and pathogenicity, although absence of evidence is not necessarily evidence of absence. We are investigating possible neuronal responses to the small ADDLs. The findings of Walsh, Selkoe, and colleagues are extremely significant and certainly substantiate a robust pathogenicity for trimers produced by cellular metabolism.

Oligomers in AD brain.
The salient issue is the nature of toxins in human brain—what are the neurologically significant oligomers in AD-afflicted brain tissue? Can these molecules explain why early Alzheimer’s is a disease of memory, and can they account for AD’s other major pathologies?

Our studies of human brain samples using physiological buffer for gentle extraction showed that human brain-derived ADDLs and synthetic ADDLs are biologically and structurally equivalent (Gong et al., 2003). Whether obtained from Alzheimer-affected brain or prepared in vitro, ADDLs act in cell biology experiments as specific ligands that bind to particular synapses (Lacor et al., 2004), a specificity that strongly suggests equivalent conformation in solution. After binding, both ADDLs stimulate AD-type hyperphosphorylation of tau (De Felice et al., 2007). With respect to direct structural comparisons (Gong et al., 2003), human ADDLs are readily detected by conformation-sensitive antibodies that we previously generated against synthetic ADDLs (Lambert et al., 2001). The antibodies, which recognize assembled Aβ but not monomers, bind human and mouse brain-derived and synthetic ADDLs in blots, in solution, and when attached as ligands to synapses, consistent with conformational equivalence. The antibodies also prevent both types of ADDLs from binding to synapses and triggering tau hyperphosphorylation. With respect to precedents for conformational-sensitive antibodies, several years earlier Austin Yang, Charlie Glabe, and colleagues found that antibodies they produced could discriminate in Western blots between monomers and larger structures they called insoluble amyloidogenic fragments—which we now would recognize as Aβ oligomers. They noted their blots were consistent with conformational epitopes being uniquely present in the larger structures (Yang et al.,1995).

When we used 2D gel analysis to look further at structure, we found that both brain-derived and synthetic ADDLs show pIs of 5.6. Of greatest interest, given current attention to oligomer size, both brain-derived and synthetic ADDLs were found to comprise prominent 12mers (54 kDa).

The fact that AD brain manifests 12mers that act as pathogenic synaptic ligands is particularly significant given the subsequent detection of neurologically active 12mers in transgenic mouse models (Lesne et al., 2006). The mouse 12mers become detectable roughly coincident with the onset of memory dysfunction. The 12mers in the mouse model have been referred to as Aβ*56 by Sylvain Lesne, Karen Ashe, and colleagues. The extent to which the mouse 12mer differs from the pathogenic human 12mer has not yet been determined.

Isolation of neurologically active dimers from Alzheimer’s brain tissue reported at the SfN meeting by Ganesh Shankar, Dennis Selkoe, and colleagues, and summarized by Gabrielle for ARF in this news series, is the latest important addition to our understanding of the involvement of oligomers in dementia.

For all the oligomers—whether dimers, 12mers, or other pathogenic species still to be characterized—we’ll need to learn how they form, why they accumulate, how they target particular neurons, and the extent to which they give a unifying mechanism that explains AD memory loss and brain pathology. These are still big questions for small toxins….

As if that were not enough, one final point makes these questions even more important. We should remember that Aβ oligomers represent a whole new type of toxic structure derived from a fibrillogenic protein. Now a number of other fibrillogenic, disease-causing proteins have been found to generate sub-fibrillar, oligomeric toxins (see Gabrielle’s latest SfN story about α-synuclein and also Klein WL. [2006] Cytotoxic intermediates in the fibrillation pathway: Aβ oligomers in Alzheimer’s disease as a case study. In Protein Misfolding, Aggregation, and Conformational Diseases. Vol. 1. V. Uversky, ed. Kluwer Academic/Plenum Publishers, New York, NY). Even innocuous proteins can turn toxic when forced to form oligomers (Vieira et al., 2007). Toxic Aβ oligomers were just the first of many.

View all comments by William Klein

We have read with great interest all the recent reports and comments on the toxicity of Aβ oligomers. We would like to start our own comment with a citation from Dr. Klein’s recent comment on this topic:

“For all the oligomers—whether dimers, 12mers, or other pathogenic species still to be characterized—we’ll need to learn how they form, why they accumulate, how they target particular neurons,...”

Our lab has been interested in characterizing axonal transport in neurodegenerative diseases, in particular in Alzheimer disease (AD). We wanted to ask whether the Aβ deposition in AD might result from a deficient axonal transport, a question that Dr. Larry Goldstein’s lab—and other labs as well—are also trying to answer. Experimentally, this question is difficult to address in animal models of AD, due to the difficulty of identifying early modifications in individual neurons. To circumvent this problem, we have employed a cell culture system, where CAD cells (a mouse neuronal cell line derived from the locus coeruleus) [1] produce and accumulate within their processes large...  Read more

We have read with great interest all the recent reports and comments on the toxicity of Aβ oligomers. We would like to start our own comment with a citation from Dr. Klein’s recent comment on this topic:

“For all the oligomers—whether dimers, 12mers, or other pathogenic species still to be characterized—we’ll need to learn how they form, why they accumulate, how they target particular neurons,...”

Our lab has been interested in characterizing axonal transport in neurodegenerative diseases, in particular in Alzheimer disease (AD). We wanted to ask whether the Aβ deposition in AD might result from a deficient axonal transport, a question that Dr. Larry Goldstein’s lab—and other labs as well—are also trying to answer. Experimentally, this question is difficult to address in animal models of AD, due to the difficulty of identifying early modifications in individual neurons. To circumvent this problem, we have employed a cell culture system, where CAD cells (a mouse neuronal cell line derived from the locus coeruleus) [1] produce and accumulate within their processes large amounts of Aβ, similar to what may occur in brain neurons, in the initial phases of AD [2]. Using this system, we showed that accumulation of Aβ likely begins within neurites, prior to any detectable signs of neurodegeneration or abnormal vesicular transport, and long before Aβ deposits are detected extracellularly. We found that neuritic accumulation of Aβ is restricted to a small population of neighboring cells that express normal levels of APP, but show redistribution of BACE1 to the neurites, where it colocalizes with Aβ and markers of late endosomes and autophagic vacuoles. Importantly, cells that accumulate Aβ appeared in isolated islets, indicating that Aβ accumulation is initiated in a small number of neurons, probably by intracellular determinants that alter APP metabolism and lead to Aβ aggregation.

We found the fact that CAD cells occasionally produce and accumulate large amounts of Aβ remarkable, since these are cells that express normal levels of APP (they are not transfected, and only express endogenous APP). Previously, such neuritic accumulations have been mostly found in neuronal cultures derived from mice that largely overexpress mutated human APP (e.g., Tg2576 mice). We found it also very interesting that CAD cells that show neuritic Aβ accumulations may contain such high levels of Aβ that it is detectable by Western blots in whole cell lysates, without immunoprecipitation. Most importantly, this Aβ is oligomeric (we found dimers, trimers, as well as higher-number oligomers detectable with Dr. Charles Glabe’s anti-oligomer antibody, A11).

We are now using the CAD cell system to investigate what leads to the formation of these accumulations of Aβ at the neurite terminals, and—most importantly—why these accumulations appear in clusters of cells. Do these cells originate from a few progenitors present in the culture? Are there intrinsic or extrinsic factors that determine this phenotype? Certainly, CAD cells appear to recapitulate some of the biochemical processes leading to Aβ aggregation, and may thus provide an experimental in vitro system for studying the molecular pathobiology of AD.

References:
1. Qi Y, Wang JK, McMillian M, Chikaraishi DM. Characterization of a CNS cell line, CAD, in which morphological differentiation is initiated by serum deprivation. J Neurosci. 1997 Feb 15;17(4):1217-25. Abstract

2. Muresan Z, Muresan V. Neuritic deposits of amyloid-beta peptide in a subpopulation of central nervous system-derived neuronal cells. Mol Cell Biol. 2006 Jul;26(13):4982-97. Abstract

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