All posts by Angela Tam

Reconciling conflicting results in Alzheimer’s disease research

VerghesevCarloAmyloid beta (Aß) deposition is a hallmark pathology in Alzheimer’s disease (AD). The apolipoprotein E (ApoE) gene, which encodes for the ApoE protein, has been established as a strong influence for the development of late-onset AD(1). The link between ApoE and Aß is unclear. One theory postulates that ApoE directly binds with Aß to mediate Aß clearance(2-4), while a second theory suggests the effects of ApoE on Aß clearance are indirect(5-7). Recent papers by Carlo et al(8) and Verghese et al(9) support these two respective contradicting theories.

In line with the first theory of a direct interaction between ApoE and Aß, Carlo et al found that sortilin, and not low-density lipoprotein receptor-related protein 1 (LRP1), mediates the cellular uptake of Aß/ApoE complexes, suggesting that sortilin is a major ApoE receptor that is essential for Aß clearance(8). In contrast, Verghese et al demonstrated that ApoE and Aß rarely bind together and that ApoE competes with Aß to bind with LRP1(9), which plays a role in neuronal Aß uptake(10). Thus, Verghese et al’s results suggest that ApoE inhibits Aß clearance via binding to LRP1(9). Verghese et al’s findings therefore are in accordance with the second theory that ApoE indirectly affects Aß clearance.

It would appear as though the experiments done by Carlo et al and Verghese et al are in contradiction with each other. However, there are important differences between these studies that may contribute to their contrasting results. First, Carlo et al examined the effects of sortilin and LRP1 on Aß/ApoE complexes, while Verghese et al did not use Aß/ApoE complexes in their experiments with LRP1. This might indicate that LRP1 is capable of binding to Aß only when it is not bound to ApoE. While there is an overwhelming amount of evidence that shows a direct interaction between ApoE and Aß(11-16), which supports Carlo et al, Verghese et al pointed out that the majority of studies demonstrating Aß/ApoE binding used synthetically prepared Aß at above physiological concentrations and did not assess the mechanisms behind the effects of Aß/ApoE complexes on Aß metabolism9. Verghese et al challenges previous literature as they show that Aß and ApoE rarely bind together under physiological conditions yet ApoE continues to affect Aß clearance, suggesting that the primary role of ApoE in Aß clearance is unlikely due to ApoE sequestering Aß. This implies that the two groups examined different pathways of ApoE-related Aß clearance: one pathway that depends on Aß/ApoE complexes and one that does not. Thus, the results from the two groups do not necessarily oppose each other as they targeted different pathways that may both contribute to Aß clearance, but the question remains as to which pathway contributes the most to Aß clearance.

In order to reconcile the results from Carlo et al and Verghese et al, several experiments could be done. Aß uptake should be measured in sortilin-expressing, sortilin-deficient, LRP1-expressing, and LRP1- deficient cells incubated with soluble Aß only, soluble Aß with ApoE (with molar ratios in the physiological range, as previously described(9)), and Aß complexed with ApoE (as previously described(8)). This would enable us to determine how free ApoE and Aß-bound ApoE influence Aß clearance with and without sortilin and LRP1. This would also enable us to see whether sortilin is capable of clearing Aß when it is not complexed with ApoE and conversely, whether LRP1 is capable of clearing Aß when complexed with ApoE. These experiments may clarify which pathway has the largest influence on Aß clearance. ApoE expression can be controlled by LXRs(17). Therefore, upregulating and downregulating the expression of ApoE with LXR agonists and antagonists in amyloid mouse models to examine the effects on Aß clearance may also be useful. If Aß clearance is increased by ApoE upregulation, then that would support Carlo et al’s finding that ApoE binding to Aß is essential for the latter’s clearance. If Aß clearance is increased by ApoE downregulation, then that would support Verghese et al’s finding that ApoE inhibits Aß clearance. In fact, there have been conflicting results regarding the effects of increasing or decreasing ApoE expression, as upregulating ApoE has been shown to facilitate Aß clearance(18), yet reduced ApoE expression may reduce Aß levels(19). Therefore, modifying ApoE expression in sortilin-expressing, sortilin knock-outs, LRP1- expressing, and LRP1-knock-outs crossed with amyloid mice could also be done to see how these receptors impact Aß clearance depending on the level of ApoE expression.


1 Poirier, J. et al. Apolipoprotein E polymorphism and Alzheimer’s disease. Lancet 342, 697-699, doi:0140-6736(93)91705-Q [pii] (1993).

2 Koistinaho, M. et al. Apolipoprotein E promotes astrocyte colocalization and degradation of deposited amyloid-beta peptides. Nat Med 10, 719-726, doi:10.1038/nm1058nm1058 [pii] (2004).

3 Morikawa, M. et al. Production and characterization of astrocyte-derived human apolipoprotein E isoforms from immortalized astrocytes and their interactions with amyloid-beta. Neurobiol Dis 19, 66-76, doi:S0969-9961(04)00279-7 [pii]10.1016/j.nbd.2004.11.005 (2005).

4 Jiang, Q. et al. ApoE promotes the proteolytic degradation of Abeta. Neuron 58, 681- 693, doi:10.1016/j.neuron.2008.04.010S0896-6273(08)00328-0 [pii] (2008). 5 Kim, J. et al. Overexpression of low-density lipoprotein receptor in the brain

markedly inhibits amyloid deposition and increases extracellular A beta clearance. Neuron 64, 632-644, doi:10.1016/j.neuron.2009.11.013S0896-6273(09)00896-4 [pii] (2009).

6 Basak, J. M., Verghese, P. B., Yoon, H., Kim, J. & Holtzman, D. M. Low-density lipoprotein receptor represents an apolipoprotein E-independent pathway of Abeta uptake and degradation by astrocytes. J Biol Chem 287, 13959-13971, doi:10.1074/jbc.M111.288746M111.288746 [pii] (2012).

7 Katsouri, L. & Georgopoulos, S. Lack of LDL receptor enhances amyloid deposition and decreases glial response in an Alzheimer’s disease mouse model. PLoS One 6, e21880, doi:10.1371/journal.pone.0021880PONE-D-11-05741 [pii] (2011).

8 Carlo, A. S. et al. The pro-neurotrophin receptor sortilin is a major neuronal apolipoprotein E receptor for catabolism of amyloid-beta peptide in the brain. J Neurosci 33, 358-370, doi:10.1523/JNEUROSCI.2425-12.201333/1/358 [pii] (2013).

9 V erghese, P . B. et al. ApoE influences amyloid-beta (Abeta) clearance despite minimal apoE/Abeta association in physiological conditions. Proc Natl Acad Sci U S A 110, E1807-1816, doi:10.1073/pnas.12204841101220484110 [pii] (2013).

10 Kanekiyo, T. et al. Heparan sulphate proteoglycan and the low-density lipoprotein receptor-related protein 1 constitute major pathways for neuronal amyloid-beta uptake. J Neurosci 31, 1644-1651, doi:10.1523/JNEUROSCI.5491-10.201131/5/1644 [pii] (2011).

11 Namba, Y., Tomonaga, M., Kawasaki, H., Otomo, E. & Ikeda, K. Apolipoprotein E immunoreactivity in cerebral amyloid deposits and neurofibrillary tangles in Alzheimer’s disease and kuru plaque amyloid in Creutzfeldt-Jakob disease. Brain Res 541, 163-166, doi:0006-8993(91)91092-F [pii] (1991).

12 Strittmatter, W. J. et al. Apolipoprotein E: high-avidity binding to beta-amyloid and increased frequency of type 4 allele in late-onset familial Alzheimer disease. Proc Natl Acad Sci U S A 90, 1977-1981 (1993).

13 Bales, K. R. et al. Apolipoprotein E is essential for amyloid deposition in the APP(V717F) transgenic mouse model of Alzheimer’s disease. Proc Natl Acad Sci U S A 96, 15233-15238 (1999).

14 LaDu, M. J. et al. Isoform-specific binding of apolipoprotein E to beta-amyloid. J Biol Chem 269, 23403-23406 (1994).

NEUR 602: Carlo et al vs Verghese et al Angela Tam

15 Yang, D. S., Smith, J. D., Zhou, Z., Gandy, S. E. & Martins, R. N. Characterization of the binding of amyloid-beta peptide to cell culture-derived native apolipoprotein E2, E3, and E4 isoforms and to isoforms from human plasma. J Neurochem 68, 721- 725 (1997).

16 Kim, J., Basak, J. M. & Holtzman, D. M. The role of apolipoprotein E in Alzheimer’s disease. Neuron 63, 287-303, doi:10.1016/j.neuron.2009.06.026S0896- 6273(09)00549-2 [pii] (2009).

17 Laffitte, B. A. et al. LXRs control lipid-inducible expression of the apolipoprotein E gene in macrophages and adipocytes. Proc Natl Acad Sci U S A 98, 507-512, doi:10.1073/pnas.021488798021488798 [pii] (2001).

18 Riddell, D. R. et al. The LXR agonist TO901317 selectively lowers hippocampal Abeta42 and improves memory in the Tg2576 mouse model of Alzheimer’s disease. Mol Cell Neurosci 34, 621-628, doi:S1044-7431(07)00021-8 [pii]10.1016/j.mcn.2007.01.011 (2007).

19 Bien-Ly, N., Gillespie, A. K., Walker, D., Yoon, S. Y. & Huang, Y. Reducing human apolipoprotein E levels attenuates age-dependent Abeta accumulation in mutant human amyloid precursor protein transgenic mice. J Neurosci 32, 4803-4811, doi:10.1523/JNEUROSCI.0033-12.201232/14/4803 [pii] (2012).

Q&A: How should I prepare for a conference?

Conferences can be great opportunities to learn, to present, and to network.  For grad students who are attending or presenting at a conference for the first time, here are some tips.

For those attending:

Read the program!  You’re there to learn.  Find the events that interest you most or are most pertinent to your own research.  Plan which posters or talks you’d like to see or hear.  Large conferences can be very overwhelming, so planning is key.

Read the abstracts carefully.  Try to prepare any questions ahead of seeing the poster.  Go to that poster and ask the presenter to go through it with you.  Don’t be shy about asking questions or bringing up critique; just be courteous.  Don’t let one person hog all of the presenter’s time – some people are extremely aggressive at conferences, so if you insert yourself into the conversation, the presenter will probably love you for it.

Take notes.  You never know what you can learn that you could later use in your own analyses.  If you can, take copies of posters you liked.

For those presenting:

Prepare your poster.  People enjoy diagrams and no one likes reading.  Be prepared with a speech detailing your rationale, methods, and results for when people ask you to explain your poster.

Think about any critiques or questions other people may bring up about your poster.  Come up with potential answers.

Know your literature.  This will help with tackling any hard questions.

Be prepared to defend your work.  Some people can be really mean at conferences.  Relax.  As long as you know what you’re talking about, you’ll be okay.

Look friendly and engaging.  No one wants to stop by a poster when the presenter looks angry.

Lastly, practice, practice, practice!


Canadian Grad Schools: FAQ

So you’re thinking of doing grad school in Canada?  Here’s a run-down on how to do it.

Research your desired program

After figuring out what kind of research interests you, do some research into universities and programs you might enjoy.  Find out their eligibility requirements (e.g. GPA minimums, prerequisite courses, GRE…) and see if you meet them.  Then look into their admission process (e.g. transcripts, letters of reference, statement of interests…).  Always find out when their deadlines are and make sure you (and your referees!) can make them.  Some programs have very early deadlines, while others are much later.  Don’t slack on your applications for later deadlines though.  A lot of schools do rolling admissions, where they’ll look at applications as they come along rather than after a certain date, and some schools even offer recruitment awards to early applicants, so it actually is to your advantage to submit sooner rather than later.

Find a supervisor

Now you need to find a supervisor.  In Canada, your supervisor will be the one to supply your stipend (unless you have external funding from a grant agency), so if your grades, letters of reference, and GRE scores are good, your admission into a program will mainly depend on whether someone is willing to pay you.  In other words, if you can’t find a supervisor to take you, don’t bother applying to the program.  This step is really important because your potential supervisor can make or break your career so don’t underestimate it.

If you don’t already have your heart set on a specific PI, try looking through the faculty listed at each program at the schools you like.  Many profs will have research lab pages.  Read some of their recent articles to see if you like their current research.  Contact the ones whose research interests match your own.  Tell them you’re interested in doing grad studies with them because you like their research.  Attach your CV and maybe consider a copy of your transcripts.

If they get back to you with a positive response, suggest meeting them in person or at least speaking with them over the phone.  Remember, you might be spending the next 6 years of your life working with this person.  You need to know if you’ll feel comfortable.  Be prepared to talk about your research experiences and what skills you can bring to their lab.  However, you should also be aware that this interview is a two-way street.  You’re interviewing them as much as they’re interviewing you.  Don’t be shy about asking them about their current and future research projects (a.k.a. what will probably be your project).  The more details they give, the better!  Ask them how many students they’ve had and what those students have done after graduation (i.e. were they successful?).  Ask them what they expect from you as their student and try to figure out if they’ll be what you expect as a supervisor.  If it’s possible, talk to their current students and ask them how they like working with their PI.

The interview part will not only help you make an informed decision about joining the lab but it can also prevent any surprises (or future regrets) once you get there.

Now make your application(s)!