Participants: Nikolaos Robakis, Rachael Neve, Dennis Selkoe, Peter Nelson, Marc Paradis, Chris Weihl, James Vickers, Dave Small, Wilma Wasco, Ben Wolozin, June Kinoshita

Robakis says, "Hi Dennis this is Nick, how're you doing"

Peter Nelson says, "Hi Dr. Robakis, Dr. Selkoe. I'm Pete Nelson. I guess I'll be moderator. June suggested that I request messages in 'private' from the guests, and then put them to you in an orderly way. If that sounds reasonable to you, that's how I'll proceed, but if you have other thoughts or suggestions, that's fine too. Is there anything that you want covered, or not covered, that I should know about now? June suggested also that we wait until about 5 after the hour to begin, and then I'll give a shpiel about the format."

Robakis says, "OK"

Robakis says, "Hi Rachael how are you (Tasos,Nick)"

Selkoe says, "Hi Rachael and Nick. Hope all is well."

{PRIVATE} Peter Nelson tells Selkoe "Hi Dr. Selkoe! Not sure if you remember me; I used to be in Dr. Saper's lab, and visited you a few times while I was in Boston."

Robakis says, "Everything is OK thanks"

Selkoe says, "Peter, I remember us sitting together at the scope, looking at tangles in sheep brains. I must commend you on the responses you made in your overview. I concur with virtually all of them!"

Peter Nelson says, "Thanks, Dr. Selkoe, nice of you to remember."

{PRIVATE} Marc Paradis tells Selkoe "Hi Dennis - Good to "see" you again so soon."

Selkoe says, "Rachael, I'm looking forward to seeing you at McLean next Friday."

Peter Nelson says, "I guess that maybe Dr. Neve is having technical difficulties..."

Selkoe says, "Hi Marc. I enjoyed our discussion last night."

Peter Nelson says, "It would be nice if the text of the ongoing "conversation" was put up for all who come in. However, I think that only the conversation that occurs while you're "logged in" is visible to you. And, if anyone does not put input for fifteen minutes (NOTE THAT), that person gets automatically logged off. I'll repeat that maybe, in a half-hour or so."

Peter Nelson says, "Hi June! Give the word, and I'll get this thing going."

June_kinoshita says, "Hello everybody. Sorry to be late. Let's roll!"

Robakis says, "OK"

Peter Nelson says, "Hello, welcome one and all to the discussion. Todays regards the role of beta-AP in Alzheimer's disease. Three distinguished panelists (Drs. Robakis, Neve, and Selkoe) will be discussing the issue, (one hopes) contentiously. My name is Pete Nelson, and I'll be moderator. Perhaps we should first have everyone introduce themselves..."

Selkoe says, "I'm Dennis Selkoe in Boston. I favor amyloid's central role in AD."

June_kinoshita says, "I'm with the Alzheimer Research Forum, which hosts these journal clubs. Welcome!"

Marc Paradis says, "Hello All, I'm Marc Paradis, a graduate student at MIT"

Robakis says, "I'm Nick Robakis at Mt.Sinai School of Medicine in NY"

James_vickers says, "Hello, James Vickers from Tasmania (Australia not Africa)"

Cweihl says, "I'm Chris Weihl a graduate student at the University of Chicago"

Peter Nelson says, "People should send questions to the panelists through me, in private. The private message icon is the dark little man in the upper left of the mini-screen. Remember, give input within fifteen minutes, or you're automatically logged off!"

{PRIVATE} Peter Nelson tells Cweihl "Hey Chris! Wassup?"

Peter Nelson says, "My first point is to ask Dr. Robakis if he feels that there is a specific toxin that "poisons" cells in Alzheimer's disease...and, if it is not, B-AP, then what else might it be?"

Marc Paradis waves at everyone.

{PRIVATE} Marc Paradis tells Wasco "Hi wilma"

Robakis says, "I don't think that there's a toxin with the classical meaning of the word. I think that we have a dysfunction of the protein transport and cytoskeletal system of the cell. In fact changes in AB production in APP and PS FAD mutations may be an indicator of a disturbance in cellular protein transport."

Peter Nelson says, "Again, to Dr. Robakis: So, there's not a substance within neuritic plaques, for example, that causes the neurites to become dystrophic; and the observation that cells that project to the cerebral cortex die only implies that something specific to those cells is "sick"?"

Robakis says, "There are more than 1/3 of normal aged people have enough neuritic amyloid depositions to satisfy the AD criteria, yet they are normal"

Selkoe says, "Nick's last statement is incorrect. Certainly people with many diffuse plaques may be normal but normal aged people have small numbers of neuritic plaques generally confined to medial temporal structures."

Robakis says, "Dennis hi. That's not my impression from many neuropathologists. In any event you will agree with me that there is no correlation between amyloid deposition and synapse or neuronal loss"

Peter Nelson says, "This comment by Dr. Robakis prompted further questions. However, I shall turn to Dr. Selkoe now. Dr. Selkoe, your work suggests that presenilin mutations work through increasing beta-AP. Some people disbelieve this relationship. Could you describe some of your newer thoughts of the interrelationship of A-beta and presenilins?"

Rneve says, "I'm sorry I'm late. Had to reload Ichat"

Selkoe says, "The fact that PS mutations increase A-beta42 in cells mice, human brain and human plasma in all published studies (but not A-beta40) strongly suggests that mutant PS acts by increasing gamma secretase cleavage at A-beta 42."

Rneve says, "Do you make a distinction between intracellular and extracellular A-beta42? Which is the culprit?"

Peter Nelson says, "Wait! Let's stay for a moment on the Presenilin-b-AP connection!"

Rneve says, "The reason I ask: there is some unpublished work showing that PS1 mutations do not increase extracellular A-beta42 in neurons. How would you respond to that?"

Peter Nelson says, "My most important class in high school was typing!"

Selkoe says, "Who is the source of the unpublished data? Clearly, Cindy Lemere's published data showing significant increases in A-beta42 plaques in PS1 mutant brains provides direct "in vivo" relevance to the many reports of increased A-beta42."

Rneve says, "Nick presented it at the Soc for Neuroscience meeting, in a session that you were in. He and I have generated those data."

Selkoe says, "Do you see any increase in A-beta40 or 42 and how were the neurons made to express mutant PS1?"

Rneve says, "We used HSV vectors. I don't think we saw any overall increase in A-beta, either 40 or 42 -- isn't that correct, Nick?"

Robakis says, "Yes it's correct"

Peter Nelson says, "Dr. Neve pointed in passing to a central point, I think, and that is, the central point of difference between you three panelists (pro b-APPtists all, if I'm not mistaken) is now which PART of the b-APP matters, and where it matters (internal or external to the cell). Internal cell processing of b-APP is certainly a hot topic these days. I'd like the three of you to maybe give some thoughts on how your opinions differ in this regard."

Rneve says, "I would like to hear how you stand on this point at the present, Dennis."

Rneve says, "The data that we have generated with Nick suggests strongly that expression of PS1 mutants in neurons does not cause increased release of Abeta. However, we have not measured intracellular levels. Isn't there a trend these days among the amyloidophiles that the important increase in Abeta42 is _in_ the cell?"

Selkoe says, "I think internal APP processing is critical of course, and that A-beta first appears intracellularly and then is quantitatively secreted. It could be that increased intracellular A-beta42 in for example, PS and APP mutant patients, causes some toxicity. This is not yet known. But we do know that there is increased A-beta42 accumulation extracellularly. And in PS APP double transgenic mice, this increased extracellular accumulation is associated with surrounding glial and neuritic change. Probably both are important."

Robakis says, "What I'm saying is that at this point there's not clear data that amyloid beta depositions is the main cause of AD. We need further research to clearly say whether amyloid is or is not the primary cause"

Robakis says, "I think that changes in A beta production in FAD may actually be an indicator of a general protein transport disturbance in the cell."

Selkoe says, "I agree there is no direct proof but the combination of the four AD-linked genes, all APP transgenic mouse models, and the clear association of fibrillar but not diffuse A-beta plaques in AD and DS brains with surrounding microglial and neuritic changes provides very strong circumstantial evidence that A-beta is necessary although by itself not sufficient for AD to occur."

Peter Nelson says, "There is clearly decent evidence that plaques matter, and harm nervous tissue. What is the reaction of Dr. Neve to the intuitive observation that amyloid plaques are surrounded by degenerating (PHF-filled) neurites? It seems like something in there is poisonous. Dr. Vickers points out that this could be a mechanical influence, putting stress on the axons..."

Wolozin says, "I don't quite buy that intracellular Abeta is the key, I think that it is much more likely that rat brains are resistant to extracellular Abeta."

Rneve says, "Those are good points, Dennis. The reason I bring up the data that we obtained with Nick is that, as you know, we showed that expression of FAD APP mutants in neurons causes increased intracellular C100 (and increased extracellular Abeta). Now, we don't see increased intracellular C100 when we express PS1 mutants in neurons, nor do we see increased extracellular Abeta. So I see a precursor-product relationship between C100 and A-beta (as does everyone else). Whether C100 is simply a source of toxic A-beta or is the culprit itself is still an unanswered question that needs to be answered."

Rneve says, "I acknowledge that amyloid plaques might be unhealthy for the neurons around them, but I don't think they are the primary cause of the disease."

Robakis says, "How do we know that in PS-/- cells C-terminal fragments which are substrates for g-secretase fail to be transported to the appropriate subcellular compartment for g-secretase cleavage. Please consider that PS1 is present in transport vesicles and may"

Wolozin says, "If C100 were the problem, would you see mutations that produced just C100 and wouldn't you see a major league accumulation of C100 in AD brains?"

Selkoe says, "If C100 were the toxin, then the more A-beta that is produced (and thus the less C100) the better the patient would be. An increase in C100 in humans with AD should be associated with less A-beta and vice versa. And yet I think that mutant PS patients have significantly more A-beta in their brains than sporadic AD cases and certainly than aged normals. So, I think C100, while able to cause toxicity in vitro and in vivo, is not the key toxic species in humans with AD."

Peter Nelson says, "A response, Dr. Neve?"

{PRIVATE} Peter Nelson tells Selkoe "As a side-bar question, it'd be nice if you would tell your opinion of which of the many different toxicity explanations (some of which are described in the review paper) you put most stock in as the key determinant of b-AP toxicity?"

Robakis says, "Hi Ben how're you doing?"

Rneve says, "Dennis, a flaw in that argument is that increases in C100 should not be associated with less A-beta. They will be associated with more A-beta, because it is a byproduct of C100. I just don't think that the increase in A-beta that you get with increased C100 is the problem."

Wolozin says, "Nick - Doing fine! Adjusting to the extramural world."

{PRIVATE} Selkoe tells Peter Nelson "I agree with your point in your overview that there are far too many possible mechanisms for A-beta toxicity and I think we cannot choose one at present. As you pointed out, this in no way detracts from the potential central role for A-beta. It's like saying that smoking does not cause cancer just because we don't know how it causes cancer."

Rneve says, "The experiments that need to be done -- and Donna is working on them -- are to produce C100 that cannot be broken down to A-beta and show that C100 still has its toxic effects. Ikuo did that with the FAD APP mutants, showing that they still caused apoptosis even when A-beta42 was not produced from them."

Peter Nelson says, "And yet, La Ferla et al. showed that just A-beta in a transgenic mouse causes apoptosis like crazy..."

{PRIVATE} Dsmall tells June_kinoshita "Just come in from San Diego, so I am jet lagged and have no idea where we are in the conversation."

Rneve says, "Yes, but that phenotype was very strange. It caused apoptosis but the pathology was nothing like AD pathology."

{PRIVATE} Wolozin tells Peter Nelson "How much does background have to do with the apoptotic phenotype?"

Marc_paradis says, "I think that you have to be careful with overexpression and transgenic experiments. Apoptosis is a general response to many kinds of insults, including such blunt genetic alterations"

Rneve says, "That's an excellent point."

Peter Nelson says, "Dr. Wolozin wonders how much that matters; apoptosis is apoptosis, I guess."

Robakis says, "If soluble A-beta were toxic, how do you explain the fact that it is present in almost equal amounts in the CSF of normal and AD people"

Rneve says, "Another excellent point :-)"

Peter Nelson says, "I don't think apoptosis should be such a "general" thing. Dr. Selkoe, do you think A-beta's mechanism works through apoptosis?"

Marc_paradis says, "In answer to robakis: its really a matter of concentration, levels in CSF may not be high enough to be toxic"

Selkoe says, "Rachael, the fact that humans with PS and APP mutations have excess A-beta levels in brain, plasma and fibroblast media indicates that A-beta buildup from C100 is definitely happening excessively in the AD state, therefore a C100 model that does not produce A-beta might still produce toxicity from C100 itself but could not be considered a model of the AD state."

Cweihl says, "Sensitization could occur through environmental insults in sporadic AD"

Robakis says, "This conference is not about apoptosis. So we should focus on amyloid and C100"

Rneve says, "I'd like to get back to Nick's questions. And add to that the fact that inter individual variation in soluble A-beta in CSF is far greater than the statistical difference between control and AD patients in soluble Abeta."

Wolozin says, "Actually - the issue of apoptosis is overblown. Depending on the cell's cytoprotective phenotype the same response can give an apoptotic or a necrotic response. So that is probably why genetic background is important."

Robakis says, "I want to ask how Dennis responds to the Braak & Braak data showing that AD pathology starts in the absence of amyloid depositions"

Peter Nelson says, "CSF A-beta! We need not stay there too long. Nobody puts too much stock in that, I think. Clearly, AD patients have tons of A-beta in their brains!"

Selkoe says, "Nick, Braak did not use sensitive A-beta ICC or biochemical assays to ensure that there is no A-beta accumulation in those brains. We don't know that all of their cases were definitely destined to develop AD."

Rneve says, "Dennis, how would you go about determining whether C100 or its catabolic products are the key players?"

Selkoe says, "Rachael, even with the great individual variation, there are statistically significant increases in A-beta42 in PS and APP, plasmas, and fibroblast media that exceed the mean levels in controls. This is the same as many other biological parameters in humans."

Dsmall says, "I think we have to be very careful in clearly separating amyloid deposition from plaques. There may be deposition where you cannot see plaques."

Peter Nelson says, "So you are saying, Dr. Selkoe, that you believe that there was non-noticed A-beta in those brains?"

Selkoe says, "Peter, that is correct."

Peter Nelson says, "Dr. Selkoe has addressed that point before, but perhaps he ought to again: How come NFTs happen in the absence of plaques?"

Selkoe says, "NFTs occur in numerous diseases of diverse cause and likely represent a response to many causes . In AD, I believe NFTs are caused indirectly or directly by A-beta accumulation."

Rneve says, "What are the data supporting that hypothesis, Dennis?"

Peter Nelson says, "Drs Neve and Robakis have not responded to the point that neuritic plaques appear to be a physical nexus of EXTRAcellular amyloid and INTRAcellular neurofibrillary pathology. It's hard not to think something in the plaques is poisoning those neuronal processes."

Robakis says, "Dennis, how do you explain the fact that the amount of A-beta produced by FAD PS and APP mutations does not correlate with the years of onset of the disease"

Rneve says, "Well, I said this earlier -- I think that something in the plaques _is_ poisoning those neuronal processes, but I am guessing that that is a relatively minor side effect of amyloid deposition in AD and is not a primary cause of the disease."

{PRIVATE} Wolozin tells June_kinoshita "Yup-you've done a great job setting this up (as usual)."

{PRIVATE} June_kinoshita tells Wolozin "N 0 Thanks! :)"

Selkoe says, "Bruce Yankner has very nice data showing that A-beta micro injections (200 pg) induce tau immunoreactive neuronal cell bodies in aged but not young rhesus monkeys. There are many other correlations between A-beta accumulation in mouse or human brain and the appearance of NFT or at least tau alterations."

Peter Nelson says, "I'll say, to look at a mature AD brain, with all its neuritic plaques, it's hard to think that's minor. Not saying it couldn't be..."

Robakis says, "Rachael how can you explain that there are dystrophic neurites where there's no amyloid deposition and neuronal loss were there's no amyloid deposition?"

Rneve says, "Tau alterations can be produced by many, many insults, if one looks at the literature, so it is hard to know what to make of Bruce's data."

{PRIVATE} Marc_paradis tells Peter Nelson "I would assume that Bruce did sham injection controls"

Rneve says, "I can't explain it; perhaps Dennis can?"

Peter Nelson says, "Marc Paradis points out, Bruce Yankner did controls."

Selkoe says, "Rachael, just as many things can intoxicate neurons including C100 and A-beta. So this doesn't convince us as much as the genetics which clearly point to a role for increased A-beta prior to tangle formation."

Rneve says, "Can you outline those genetic data, please?"

Peter Nelson says, "Dr. Wolozin asks whether Dennis thinks the ability of human tau to form PHFs (in contrast to mouse tau) has anything to do with the toxicity and the different response of human vs. mouse brains to Abeta."

Selkoe says, "Peter which question should we address next?"

{PRIVATE} Wolozin tells Peter Nelson "No Peter - I am specifically addressing the question of whether the ability of HUMAN Tau to form PHF's is important. Mouse tau doesn't do this."

Peter Nelson says, "Dr. Selkoe, I'd suggest you address the genetic data and segue into why humans appear able to develop neurofibrillary pathology, but mice, only in the presence of amyloid plaques, do not."

Marc_paradis says, "Sorry, but I must go. Thank you all for a very interesting discussion."

Marc_paradis bows gracefully.

Peter Nelson tells Wolozin "Sorry about that...it's a little afield of the issue of the moment, though. My theory is that it pertains to the native amino acid sequence of the tau protein."

Marc_paradis tells June_kinoshita "Nice turnout today! See you next week -Marc"

Peter Nelson tells Marc_paradis "Thanks a lot, Marc!"

Wolozin tells Peter Nelson "Ug - the issue is whether A-beta kills human cells because it can stimulate PHF formation but it doesn't kill mouse neurons in vivo because no PHF."

Selkoe says, "All 4 AD linked genes have been shown in vitro and in humans to increase brain A-beta levels. Because APP mutations are a direct, primary cause of AD (even though very rare) we can say that increased A-beta can be an initiating event in AD. I think that all 4 AD genes increase A-beta by different mechanisms and various neuronal and glial changes occur secondarily. Also, DS argues strongly that excess APP and excess A-beta precede tangles and other neuronal changes."

Peter Nelson says, "Why doesn't A-beta appear to kill mouse neurons in transgenic animals?"

Robakis says, "But the data is not there"

Rneve says, "I think that we can only say that increased A-beta is an event that _correlates_ with AD, not that _initiates_ it."

Robakis says, "by definition"

Selkoe says, "Bruce [Yankner] shows that rat brain is far more resistant to micro injected A-beta than monkey, both at old age. I think mouse neurons are probably more resistant to A-beta, and the high levels of APPs in tg brains may also protect neurons."

Peter Nelson says, "What do you say about the FAD families with b-APP mutations, Dr. Robakis?"

Robakis says, "in what respect?"

Peter Nelson says, "As perhaps the most solid support for b-AP proponents, how would you argue that it does NOT support their argument? ...I mean, the linkage of b-APP mutations to the AD phenotype."

Rneve says, "I would go back to Nishimoto's data, which show clearly that FAD mutants of APP can cause apoptosis even in the absence of the generation of A-beta from these mutants. I know that begs the questions of whether the FAD APP mutants kill in AD by causing apoptosis, but it's quite compelling data."

Robakis says, "As I have indicated earlier I think these mutations interfere with the intracellular transport. There are other examples of diseases caused by point mutations in transmembrane proteins that interfere with cellular transport. This is a topic that we sh"

Selkoe says, "Of course many transport defects could cause cellular disease but we have to come back to the phenotype in humans with AD and they invariably have large amounts of A-beta extracellularly."

Peter Nelson says, "After this answer, perhaps we'll wrap up. People should give additional questions to June, who'll pass them along to the panelists and they will be answered later."

Peter Nelson says, "A quickie: do the FAD mutations increase C-100 too?"

Rneve says, "Yes, they do. All of the FAD APP mutations do."

Robakis says, "which may indicate problems with protein transport"

Rneve says, "Touche :-)"

Peter Nelson says, "How about a last word from each of the panelists."

Robakis says, "These are very useful discussions because I feel that they advance and improve our views of the disease."

Rneve says, "I don't think that the correlation of the FAD mutations with increased release of A-beta is any more compelling than, say, the correlation of the FAD mutations with increased C100 or with apoptosis. We need to consider all of these hypotheses."

Selkoe says, "I think that Brian Cummings data showing correlation coefficients of greater than 0.9 between total A-beta burden and degree of cognitive impairment is very impressive. It can no longer be said that A-beta amount and also plaque amount does not correlate with presence and degree of dementia."

June_kinoshita says, "I want to thank everyone for being here and doing a marvelous job!"

Peter Nelson says, "Thank you all very much. I hope most of the questions were answered to people's satisfactions."

June_kinoshita applauds fervently.

Peter Nelson smiles.

Rneve says, "Peter, you did a superb job on the commentary that you prepared for this!"

Selkoe says, "I agree."

June_kinoshita says, "I want especially to thank Pete too for his deft moderating!"

Peter Nelson says, "Thank you very much, Dr. Neve. I've long been a big fan of your work."

Rneve says, "I applaud Peter as well -- it was a tough job, done very well."

Robakis says, "I would like to thank everybody including Dennis, Rachael, June and Peter"

James_vickers tells Peter Nelson "Thanks Peter! Excellent prepared discussion by the way. See you next time."

Peter Nelson tells James_vickers "Thanks a lot, Dr. Vickers, I look forward to "chatting" with you next time."

June_kinoshita says, "Thank you Nick for braving the cybernet!"

June_kinoshita applauds Robakis fervently.

Rneve says, "Yes, Nick, you never cease to surprise me."

June_kinoshita says, "Thank you Dennis and Rachael for your time and energy!"

Peter Nelson says, "Okey-doke. Best to all, this has been very fun."

Rneve says, "Are there typing courses on the internet? :-)"

June_kinoshita says, "Farewell until next time."

Peter Nelson tells Robakis "A pleasure "chatting" with you, Dr. Robakis. I've followed your work w/interest for a while."

Robakis leaves.

Peter Nelson tells Selkoe "Nice "chatting" w/you again, Dr. Selkoe."

Selkoe says, "Peter: Great job. Let's keep in touch."

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