Posted 29 August 2006

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Participants: Benjamin Wolozin, Michael Schlossmacher, Ted Dawson, June Kinoshita, Shai Shoham.

Note: The transcript has been edited for clarity and accuracy.

June: Hello and welcome everyone on this snowy morning! Let's get started.

Benjamin Wolozin: Hello Michael - can you comment on what you see as the role of parkin in ubiquitinating synuclein?

Michael Schlossmacher: Regarding the interaction of parkin and α-synuclein: α-synuclein is probably just one of parkin's many substrates. It is the one most interesting to us because of the link to autosomal dominant aS-linked PD and sporadic PD.

Benjamin Wolozin: I guess one of the questions that must be frequently posed to you, Michael, is whether the glycosylated form of α-synuclein plays a role in PD. For instance by initiating aggregation.

Michael Schlossmacher: We don't yet know whether it mediates aggregation. We wish to study this, but don't have sufficient amounts of it yet.

Ted Dawson: {enters}

Benjamin Wolozin: Hi Ted!!

Michael Schlossmacher: Hideki Shimura just joined me; we are a 2-man team now.

June: Hello Ted and Hideki!

Ted Dawson: Hello everyone.

Benjamin Wolozin: Michael and Hideki - do you think the absence of glycosylated α-synuclein in Lewy bodies is significant or just a sensitivity issue?

Michael Schlossmacher: We are working on raising an antibody that is specific for the glycosylated form of α-synuclein and does not cross-react with regular α-synuclein p16. Only then can we judge whether it is present or not.

guest4 {enters}

June: Hello Guest 4, who are you?

guest4: Yuan Bin, I am a rotatation PhD student from Wolozin's lab.

Shai Shoham: Hello, this is Shai Shoham

June: Welcome Shai. Where are you logging in from today?

Shai Shoham: Jerusalem, Israel

June: Just before this discussion, Michael Schlossmacher sent a comment to Ben's background text for this discussion. It is posted below Ben's text. Let's pick up his thoughts.

Benjamin Wolozin: In responding to Michael's comment-I agree entirely. We are seeing this with multiple neurodegenerative diseases, where inherited forms of the illness suggest common mechanisms of pathogenesis for the disease in general.

Michael - Very good points in your comment.

June: Do you agree that the nomenclature should be changed to reflect this view?

Benjamin Wolozin: I agree with the nomenclature change somewhat. However, one issue is that late-onset PD has Lewy body pathology or other inclusions that are generally not present in ARJP. I have addressed this in the second paragraph of my comment.

Ted Dawson: I would not support a change in the nomenclature at this early juncture of characterizing genetic PD. It is still instructive to discuss AR-PD and AR-JP. As we learn more about the genetics we may define PD based upon an individual's mutation.

Benjamin Wolozin: Michael, I like the idea of heritable forms of PD. I just think that there might be a difference between cases where parkin is active vs. cases where parkin is inactive. Ted's point relates to this.

Michael Schlossmacher: In reference to your previous thought, Ben, if glycosylated α-synuclein p22 is involved in Lewy body formation, we would expect little to be present in non-ubiquitinated form. This is in press at the American Journal of Pathology.

Benjamin Wolozin: Yup, glycosylated a-SP22 makes sense for LB if it is there.

Benjamin Wolozin: Ted - what would you say about the role of synphilin and CDCrel1 in PD?

Ted Dawson: Regarding synphilin and the synaptice vesicle-associated protein CDCrel-1 (Zang et al. 2000), I think that synphilin plays a potentially important role as it links non-glycosylated synuclein and parkin in a common pathogenic pathway in PD. Obviously more work needs to be done to clarify its role in PD (see ARF news story).

Michael Schlossmacher: I predict that there will be several adaptor proteins for the parkin-E3 complex in human brain, as is the case with other ubiquitin-ligase complexes. The binding partners Ted identified may represent such adaptors.

Benjamin Wolozin: There are an increasing number of proteins that bind α-synuclein. So you think that perhaps synphilin is one of several proteins present in the Lewy bodies that might bind non-ubiquitinated synuclein?

Ted Dawson: The Arg275Trp mutation described in the Farrer paper (Farrer et al., 2001) is a partially active mutant as described in our Nature Medicine paper (see ARF news story). Thus it is the exception that proves the rule that parkin is required for Lewy body formation

Benjamin Wolozin: Ted - I agree that parkin is probably required for Lewy body formation. Hence the abundance of ubiquitin in Lewy bodies. Do people think that ubiquitination might help to sequester proteins that cannot be degraded by the proteasome?

Ted Dawson: It is possible, but how the system works to send proteins to Lewy bodies versus the proteasome is a puzzle.

Shai Shoham {leaves}

Benjamin Wolozin: Does anyone know whether it has been definitively shown whether or not α-synuclein in Lewy bodies is ubiquitinated?

Ted Dawson: I have not seen any convincing data. In fact, there seems to be a dissociation between ubiquitin immunreactivity and synuclein immunoreactivity when using confocal dissection.

Benjamin Wolozin: Interesting. Is one more peripheral than the other, or something else?

Michael Schlossmacher: Our immunohistochemical data suggest that parkin and UbcH7 localize to the core, whereas most of the immunoreactivity for α-synuclein is in the periphery, at least by conventional Immunohistochemistry.

Ted Dawson: They seem to be in different microcompartments. It could be a problem with antibody penetration or epitope recognition. Synphilin is in the core.

Benjamin Wolozin: What about ubiquitin?

Michael Schlossmacher Ubiquitin also is predominantly, but not exclusively, in the core as per Gai et al., 2000. Ben, why do you doubt the presence of ubiquitinated aS in Lewy body extracts (See Trojanowski et al, 1998.)

Benjamin Wolozin: I don't doubt the question, I'm just trying to bring out people's opinions for the discussion.

June: This is perhaps slightly off topic, but are the Lewy bodies seen in PD identical at the molecular level to those seen in AD? For that matter, are Lewy bodies in the various subtypes of PD all created equal?

Benjamin Wolozin: Cortical Lewy bodies have a different structure than Lewy bodies in the substantia nigra, but I don't know whether cortical Lewy bodies in diseases like dementia with Lewy body disease (DLBD) differ from those in AD.

Michael Schlossmacher: Based on my impression, I'd say that the formation of Lewy bodies in AD, PD, and DLBD rests on the interaction of some key players, but that they vary to some extent between diseases and within neuroanatomic regions.

Ted Dawson Is Pael-r in Lewy bodies? (See ARF news story.)

Michael Schlossmacher Rumor has it that Pael-R is in Lewy bodies, yes.

Benjamin Wolozin: Pael-R is an interesting question because it is an ER protein. Parkin is known to affect the ER stress response, which raises the issue of the role of ER in PD. We have looked at ER stress markers in PD, but don't see evidence of elevation more than in controls.

Ted Dawson: So is parkin dysfunction involved in sporadic PD?

Benjamin Wolozin: This is different than asking if Pael-r is in Lewy bodies. But the involvement of Pael-r inherently raises the question of whether ER stress plays a role in PD.

Michael Schlossmacher: Ted, two papers on polymorphisms in parkin in sporadic PD out of Japan would suggest that (Satoh & Kuroda, 1999; Wang et al., 1999).

Benjamin Wolozin: Ted, I think Michael's comment about Farrer's work is apt. It certainly suggests a role, right? Although Farrer's case is by no means sporadic PD, but it is a late-onset case - hence the comment.

Ted Dawson: So parkin dysfunction might involve different mechanisms of cellular toxicity depending on the mutation?

Terry Bowers {enters}

Ted Dawson Yes, but this will take some time to prove.

Michael Schlossmacher I'd predict that there is a common denominator for parkin dysfunction-related cellular toxicity based on other E3 ligase work.

Ted Dawson: What is your favorite common denominator?

Michael Schlossmacher: I don't have one yet.

Benjamin Wolozin: Here is something somewhat far afield, but perhaps worth bringing up for discussion. What I find particularly interesting, recently, is the comparison of mechanisms of death in Huntington's vs. other diseases. It seems that recent results in Huntington's point to a mechanism relating to gene transcription, whereas many of us in AD and PD have focused on free radicals and/or proteasomal dysfunction. (See for example, ARF news story, ARF news story.) Any thoughts?

Michael Schlossmacher: Excellent point. I think dysregulation of transcriptional control is subject of ongoing PD research work now, too.

Ted Dawson: I have to go to a meeting so I must sign off. Best regards to everyone.

Benjamin Wolozin: Ciao!

Benjamin Wolozin: The Huntington's stuff is fascinating, and there are two issues raised by it. One is the question of whether the inclusion is good or bad. My sense is that many have postulated that inclusions in both HD and PD are protective because they sequester small toxic aggregates, but here is a mechanism whereby sequestration is bad. The second point is the connection between transcription and neuroprotection/growth factor signaling. (See ARF news story.) Any thoughts from people?

Benjamin Wolozin: Mike, when you say parkin dysfunction, do you discriminate between gain or loss of function, with respect to a hypothetical common denominator?

Yuan Bin: Unlike in ARJD, sporadic PD shows a normal parkin, so parkin might not be the key. Maybe the key point is other proteins.

Michael Schlossmacher: Brown and Goldstein and many other examples have taught us that the relentless pursuit of altered genotypes in human disorders is at the root of better understanding of complex biochemical pathways.

Benjamin Wolozin: Yuan, this is always a question, but I agree with Mike because historically investigating inherited forms of disease has been very productive.

June: I just want to note that our hour is up. Thank you all very much! We will be circulating a transcript, so you will all have a chance to carry forward the discussion via e-mail.

Michael Schlossmacher: Yes, thanks for your thoughts, and bye all.

Benjamin Wolozin: June, bye. Mike and Ted - thanks so much for participating. You guys are doing great work. Thanks to everyone else for adding comments or listening in.

Nico And thanks Mike, Ted and everyone else!

guest4: Bye and thanks, everyone.

Nico: Bye, number 4, bye everyone!

Terry Bowers: Since the science is over we can chat on other subjects, yes?

Terry Bowers: Can't believe I've missed this website…