Wirkungsweise und Auswirkungen einer Aβ-Impfung bei APP-transgenen Mäusen

Projektdetails:

Thematik:	Prävention und Therapie
Förderstatus:	abgeschlossen
Art der Förderung:	Research
Institution:	Goethe-Universität Frankfurt, Dr. Senckenbergische Anatomie, Institut für klinische Neuroanatomie
Projektleitung:	Prof. Dr. Thomas Deller
Laufzeit:	01. November 2001 - 31. Oktober 2003
Fördersumme:	51.129,00 Euro

Projektbeschreibung

Ein Charakteristikum der Alzheimer-Krankheit ist der Aufbau des Proteins β-Amyloid in vielen Bereichen des Gehirns. Dieses Protein bildet Klümpchen, die so genannten Plaques. Obwohl diese Plaques als diagnostische Kennzeichen für Alzheimer angesehen werden, ist noch ungeklärt, wie bzw. ob sie die Gedächtnisstörungen und Persönlichkeits­veränderungen bei Alzheimer bewirken. Zum besseren Verständnis der Rolle von Plaques bei der Alzheimer-Krankheit wurden transgene Mäuse produziert, bei denen sich mit fortschreitendem Alter β-Amyloid-Plaques entwickeln. Diese Mäuse tragen ein mutiertes Gen und erzeugen daher ein mutiertes Protein, das in den seltenen Fällen von erblicher Alzheimer beobachtet wurde. Durch diese Mäuse eröffneten sich viele neue Forschungswege.

Die Mäuse werden zur Überprüfung neuer therapeutischer Strategien eingesetzt. Eine besonders viel versprechende Strategie beruht auf der Beobachtung, dass diese Mäuse mit β-Amyloid immunisiert werden können. Auffallend ist, dass bei den so immunisierten Mäuse keine Amyloidablagerungen im Gehirn mehr auftreten. Wird in einem Alter mit der Immunisierung begonnen, in dem sich bei den Mäusen bereits Amyloidplaques gebildet haben, wurde sogar von einer erheblichen Reduzierung des bereits vorhandenen Amyloids berichtet. Wenngleich diese Ergebnisse viel versprechend sind und Wege zu einer „therapeutischen Impfung“ gegen Alzheimer aufzeigen, sind viele Fragen noch ungeklärt.

In seinem Forschungsprojekt will Prof. Deller in Zusammenarbeit mit Priv.-Doz. Dr. Mathias Jucker, Universität Basel, Schweiz, transgene Mäuse passiv immunisieren und die Wirkung der Immunisierung auf die Amyloidablagerungen und die krankhaften Veränderungen von Nervenzellen eingehend untersuchen. Wenn das Amyloid durch die Impfung tatsächlich entfernt wird, was geschieht dann mit der Veränderungen von Nervenzellen und Nervenfasern rund um die Amyloidplaques? Findet nach der Beseitigung des Amyloids eine Selbstheilung statt oder bleibt die Schädigung be­stehen? Eine weitere Forschungsidee der Forscher ist es, transgene Mäuse ohne funk­tionsfähigen Fc-Rezeptor zu immunisieren, um dadurch herauszufinden, ob der Abbau des Amyloids durch diesen Rezeptor vermittelt wird.

Innovative Strategien, wie die Verwendung transgener Mäuse und die Impfung, führen zu einem besseren Verständnis der Bedeutung und der Auswirkungen von Amyloidplaques auf das Gehirn und beschleunigen die Entwicklung neuer therapeutischer Vorgehensweisen.

Abschlussbericht

Alzheimer's disease (AD) is a growing problem in our progressively aging society. Although many scientific laboratories are working to better understand what causes this memory robbing disorder, much remains unknown. What is well known, and has been known since Alois Alzheimer first characterized the disease, is that the brains of affected individuals have a build-up of a protein, now called ß-amyloid, in many regions of their brain. This protein forms small clusters called plaques. Although the presence of plaques is considered to be one of the diagnostic hallmark of AD, it remains unclear how these plaques lead to the memory defects and personality abnormalities seen in AD patients.

To help better understand the role plaques play in AD, transgenic mice have been created which develop ß-amyloid plaques as they age. Such mice have been genetically altered to carry a mutated gene, and thus make a mutated protein, which has been found in rare cases of inherited AD. These mice have opened many new avenues of investigation. Scientists can now study the progressive development of these plaques in many experimental situations rather then simply seeing the end product of the disease in human patients.

These mice are now being used to examine new therapeutic strategies. One such enthusiastically followed strategy is based on the observation that such mice can be immunized with ß-amyloid. Strikingly, such immunized mice do no longer exhibit amyloid deposition in their brains. When immunization is started at an age when the mice have already developed amyloid plaques, significant removal of existing amyloid has even been reported. Although these results are very exiting and may open the way to “therapeutic vaccination” towards A D, many open questions remain.

In our present research proposal, we have immunized transgenic mice and have studied the effect of immunization on amyloid deposition. We could show that passive immunization with antibodies against ß-amyloid can reduce the amount of amyloid in the brains of our transgenic mice. Although this reduction in amyloid was highly significant in the grey and white matter brain areas, amyloid-deposition around blood vessels in the brain was not reduced. Because we have previously observed that amyloid-laden blood vessels bleed more frequently than unaffected control blood vessels, we also studied whether the immunization treatment affects bleeding frequency. Can bleeding frequency be reduced with immunotherapy? Unfortunately, our data indicate that immunization treatment increases the frequency of bleeding from amyloid-laden blood vessels. This suggests that "therapeutic vaccination" may have severe side-effects, such as stroke. It may, therefore, be of importance to identify those patients, which are at risk prior to Aß immunotherapy. This shows that a detailed analysis of immunized transgenic mice can improve our understanding of the impact of immunization strategies on the brain.

In addition, we wanted to know more about the biological effects amyloid-plaques have on the brain. Although they are one of the hallmarks of AD, their effects on the brain and their contribution to the cognitive decline is poorly understood. Several years ago, we could show in transgenic mice that amyloid plaque deposition induces aberrant growth of axons that are, unfortunately, in their vicinity. These axons, which are required for the communication between nerve cells, form large boutons in the vicinity of plaques, which disrupts their function. It was assumed that these axonal changes are caused by local inflammatory reactions around plaques. We could now show that, in fact, inflammatory cells surrounding the plaques produce a molecule, brain-derived neurotrophic factor that regulates axonal growth. This growth factor could induce axonal growth of axons surrounding the plaques. However, in the inflamed and toxic environment produced by the plaques, this growth is abnormal and, ultimately, prevents the normal functioning of the axons. Thus, amyloid plaques can disrupt the normal connections between the neurons and this, in turn, could contribute to the cognitive decline seen in AD patients. We will now study the inflammatory response surrounding amyloid plaques in detail.

Wissenschaftliche Publikationen auf Basis des geförderten Projekts

Burbach, G.J., Dehn, D., Del Turco, D., Deller, T. (2004). Laser microdissection reveals regional and cellular differences in GFAP mRNA upregulation following brain injury, axonal denervation, and amyloid plaque disposition. Glia, 48(1):76-84.

Burbach, G.J., Dehn, D., Nagel, B., Del Turco, D., and Deller, T. (2004). Laser microdissection of immunolabeled astrocytes allows quantification of astrocytic gene expression. Journal of Neuroscience Methods, 138(1-2):141-148.

Burbach, G.J., Hellweg, R., Haas, C.A., Del Turco, D., Deike, U., Abramowski, D. Jucker, M., Staufenbiel, M., Deller, T. (2004). Induction of brain-derived neurotrophic factor (BDNF) in plaque-associated glial cells of aged APP23 transgenic mice. J. Neurosci., 24:2421-2430.

Burbach, G. J., Dehn, D., Del Turco, D., and Deller, T. (2003). Quantification of layer-specific gene expression in the hippocampus: effective use of laser microdissection in combination with quantitative RT-PCR. Journal of Neuroscience Methods, 131(1-2):83-91.

Deller,T., Haas, C.A., Freiman, T.M., Phinney, A., Jucker, M., Frotscher, M. (2003). Lesion-incuced axonal sprouting in the central nervous system. In: Brain Repair (M.Bähr, ed.). Landes Bioscience, Georgetown.

Pfeifer, M., Bomcristiano, S., Bondolfi, L., Stalder, A., Deller, T., Staufenbiel, M., Methewa, P., Jucker, M.(2003). Cerebral hemorrrhage and amyloid-β. Science, 299, 1014.

Pfeifer, M., Boncristiano, S., Bondolfi, L., Stalder, A., Deller, T., Staufenbiel, M., Mathews, P. & Jucker, M. (2002). Cerebral hemorrhage following anti-Aß Immunotherapy. Science, 298:1379.