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Hefendehl JK, Wegenast-Braun BM, Liebig C, Eicke D, Milford D, Calhoun ME, Kohsaka S, Eichner M, Jucker M. Long-term in vivo imaging of β-amyloid plaque appearance and growth in a mouse model of cerebral β-amyloidosis. J Neurosci. 2011 Jan 12;31(2):624-9. PubMed.
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As a graduate student who reviewed this subject in great detail for a journal club (see Meyer-Luehmann et al., 2008 and Yan et al., 2009), I am surprised at some of the opinions presented here after these most recent papers on plaque dynamics (Hefendehl et al., 2011; Burgold et al., 2010), which I think are interesting and thorough examinations of plaque growth in vivo. In contrast, when reviewing the initial paper on this topic from the Hyman Lab (Meyer-Luehmann et al., 2008), it became apparent to me and the people with whom I discussed it that the reason why they saw very rapid plaque appearance and no further plaque growth within 14 days was because of an artifact of incomplete dye labeling. If one inspects in detail Figure 1 in their paper, one can see that the plaque that “appeared” after 24 hours of dye injection was really present even before (just poorly labeled). Consistent with this, the adjacent large plaque seen in the same image underwent a very marked increase in dye labeling within this same interval. This is almost certain to be explained by ongoing dye labeling.
Interestingly, in this same figure, they present their data of all new plaques observed, and coincidentally they all appeared within one day of the first dye injection. This again is consistent with an artifact in which dye labeling is incomplete after 24 hours of initial dye injection. The appearance of a plaque at around 24 hours just reflects the ongoing dye labeling. Incomplete labeling also explains why they did not see any new plaques appearing at any time other than after the first day of dye injection. In my opinion, their paper remains at odds with these more recent papers in the Journal of Neuroscience and Acta Neuropathologica, which show no rapid plaque appearance and report continuous plaque growth over much longer intervals. The lack of growth seen in the Hyman paper is likely to be related to neuroinflammation induced by their imaging procedure as previously demonstrated (Yan et al., 2009).
References:
Meyer-Luehmann M, Spires-Jones TL, Prada C, Garcia-Alloza M, de Calignon A, Rozkalne A, Koenigsknecht-Talboo J, Holtzman DM, Bacskai BJ, Hyman BT. Rapid appearance and local toxicity of amyloid-beta plaques in a mouse model of Alzheimer's disease. Nature. 2008 Feb 7;451(7179):720-4. PubMed.
Hefendehl JK, Wegenast-Braun BM, Liebig C, Eicke D, Milford D, Calhoun ME, Kohsaka S, Eichner M, Jucker M. Long-term in vivo imaging of β-amyloid plaque appearance and growth in a mouse model of cerebral β-amyloidosis. J Neurosci. 2011 Jan 12;31(2):624-9. PubMed.
Burgold S, Bittner T, Dorostkar MM, Kieser D, Fuhrmann M, Mitteregger G, Kretzschmar H, Schmidt B, Herms J. In vivo multiphoton imaging reveals gradual growth of newborn amyloid plaques over weeks. Acta Neuropathol. 2011 Mar;121(3):327-35. PubMed.
Christie RH, Bacskai BJ, Zipfel WR, Williams RM, Kajdasz ST, Webb WW, Hyman BT. Growth arrest of individual senile plaques in a model of Alzheimer's disease observed by in vivo multiphoton microscopy. J Neurosci. 2001 Feb 1;21(3):858-64. PubMed.
Yan P, Bero AW, Cirrito JR, Xiao Q, Hu X, Wang Y, Gonzales E, Holtzman DM, Lee JM. Characterizing the appearance and growth of amyloid plaques in APP/PS1 mice. J Neurosci. 2009 Aug 26;29(34):10706-14. PubMed.
View all comments by Jason FrommerSeveral papers now have used multiphoton imaging to monitor plaques over time in AD transgenic models (Hefendehl et al., 2011; Burgold et al., 2010; Yan et al., 2009), following on the initial work we published in 2001 (Christie et al., 2001). Over the years we have imaged thousands of plaques using either “thin skull” or “coverslip” approaches in three different APP or APP/PS1 overexpressing models. The new papers, emerging from analogous work at Washington University and in Germany, show similar approaches to dissect the natural history of plaques in living animals.
Overall, there is general concurrence in our observations. It is obvious that animals initially have no plaques, then many months later have many plaques. What happens in between? We found that plaques form surprisingly quickly, then reach a near maximal size within days. The other groups, using slightly different models and methods, found that plaques form and then may well continue to grow initially for some time, then reach a plateau where growth ceases. That growth ultimately ceases is obvious—otherwise there would be one large plaque in the brains of elderly mice, and, of course, that is not the case. In fact, postmortem analysis of plaque size distribution reveals no change in the average size of plaques or in the distribution of sizes regardless of age.
Why are there any differences in the observations regarding the slope of the growth of plaques in animal models? Any number of technical issues—ranging from mouse variability to differences in imaging techniques—might help explain the discrepancies. We have measured cross-sectional areas because of the increased resolution of images in the X-Y plane, while other groups use a full Z stack and estimate volume, essentially trading the increased information in the Z stack for the increased uncertainties of the measurements at the top and bottom (given relatively poor Z resolution compared to X-Y resolution in multiphoton optics). Different surgical procedures, different ways of administering dyes, different software packages, or even different optics might impact the subtle analysis of these high-resolution images.
However, the important point is whether any of these observations accurately model what happens in Alzheimer’s disease itself. From this point of view, we have recently completed an analysis of the temporal neocortex of 92 individuals with Alzheimer's disease, and 16 controls, ranging in duration of dementia from six months to almost 20 years. Of course, this is a postmortem histological analysis, so that longitudinal imaging of individual plaques is not possible. Nonetheless, if plaques dramatically grew with increasing duration of illness, we would expect to see evidence of that in the size distribution of either the thioflavin S core or the anti-Aβ immunostained deposits. We found only the most subtle changes over time, with an increase in plaque size over 20 years of ~2 percent per year. We conclude that dramatic continued plaque growth is unlikely to be a central feature of Alzheimer's disease progression, although the conundrum still remains as to why plaques form in the first place, grow to their rather large size, and then presumably ultimately reach a plateau where further growth is inhibited. It may be that careful analysis of what impacts the rate of growth, or of the phenomena that occur after plaques stabilize, will help provide insight. We hope that in vivo multiphoton longitudinal imaging of animal models will continue to help point towards answers to these sorts of questions.
References:
Hefendehl JK, Wegenast-Braun BM, Liebig C, Eicke D, Milford D, Calhoun ME, Kohsaka S, Eichner M, Jucker M. Long-term in vivo imaging of β-amyloid plaque appearance and growth in a mouse model of cerebral β-amyloidosis. J Neurosci. 2011 Jan 12;31(2):624-9. PubMed.
Burgold S, Bittner T, Dorostkar MM, Kieser D, Fuhrmann M, Mitteregger G, Kretzschmar H, Schmidt B, Herms J. In vivo multiphoton imaging reveals gradual growth of newborn amyloid plaques over weeks. Acta Neuropathol. 2011 Mar;121(3):327-35. PubMed.
Yan P, Bero AW, Cirrito JR, Xiao Q, Hu X, Wang Y, Gonzales E, Holtzman DM, Lee JM. Characterizing the appearance and growth of amyloid plaques in APP/PS1 mice. J Neurosci. 2009 Aug 26;29(34):10706-14. PubMed.
Christie RH, Bacskai BJ, Zipfel WR, Williams RM, Kajdasz ST, Webb WW, Hyman BT. Growth arrest of individual senile plaques in a model of Alzheimer's disease observed by in vivo multiphoton microscopy. J Neurosci. 2001 Feb 1;21(3):858-64. PubMed.
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