Tom Van Dooren

Occurrence and co-localization of amyloid β-protein and apolipoprotein E in perivascular drainage channels of wild-type and APP-transgenic mice

The deposition of the amyloid beta-protein (Abeta) is a hallmark of Alzheimers disease (AD). One reason for Abeta-accumulation and deposition in the brain may be an altered drainage along perivascular channels. Extracellular fluid is drained from the brain towards the cervical lymph nodes via perivascular channels. The perivascular space around cerebral arteries is the morphological correlative of these drainage channels. Here, we show that Abeta is immunohistochemically detectable within the perivascular space of 25 months old wild-type and amyloid precursor protein (APP)-transgenic mice harboring the Swedish double mutation driven by a neuron specific promoter. Only small amounts of Abeta can be detected immunohistochemically in the perivascular space of wild-type mice. Cerebrovascular and parenchymal Abeta-deposits were absent. In APP-transgenic mice, large amounts of Abeta were found in the perivascular drainage channels accompanied with cerebrovascular and parenchymal Abeta-deposition. The apolipoprotein E (apoE) immunostaining within the perivascular channels did not vary between wild-type and APP-transgenic mice. Almost 100% of the area that represents the perivascular space was stained with an antibody directed against apoE. Here, Abeta co-localized with apoE indicating an involvement of apoE in the perivascular clearance of Abeta. Fibrillar congophilic amyloid was not seen in wild-type mice. In APP-transgenic animals, congophilic fibrillar amyloid material was seen in the wall of cerebral blood vessels but not in the perivascular space. In conclusion, our results suggest that non-fibrillar forms of Abeta are drained along perivascular channels and that apoE is presumably involved in this clearance mechanism. Overloading such a clearance mechanism in APP-transgenic mice appears to result in insufficient Abeta-clearance, increased Abeta-levels in the brain and the perivascular drainage channels, and finally in Abeta-deposition. In so doing, our results strengthen the hypothesis that an alteration of perivascular drainage supports Abeta-deposition and the development of AD.

Transgenic Mouse Models for APP Processing and Alzheimer’s Disease: Early and Late Defects

Transgenic mice with neuronal expression of human AD-mutant APP[V7171] in their brain recapitulate robustly the amyloid pathology as seen in Alzheimers disease (AD) patients. The AD related pathological phenotype consisting of amyloid plaques and vascular amyloid pathology, develop progressively and relative late in ageing APP transgenic mice, between 10 and 15 months of age. In contrast to the late - and clinically irrelevant - amyloid plaque-pathology, the early cognitive defects and behavioural features are clinically more interesting. This review discusses the generation and in depth phenotypic characterization of both aspects of the APP[V7171] transgenic mice. Attention is focussed on the relation of biochemical data of the different APP fragments and amyloid peptides to the formation of the typical early defects and the late parenchymal and vascular amyloid depositions. The APP[V7171] transgenic mice are a perfect model to characterize and investigate early biochemical and cognitive aspects and a potential resource to define pathological interactions of different factors known to be involved in AD. Finally, any therapeutic intervention can be directly tested and explored in these transgenic mice as excellent pre-clinical models.

Pathological Hallmarks, Clinical Parallels, and Value for Drug Testing in Alzheimer's Disease of the APP[V717I] London Transgenic Mouse Model

The APP[V717I] London (APP-Ld) mouse model recapitulates important pathological and clinical hallmarks of Alzheimers disease (AD) and is therefore a valuable paradigm for evaluating therapeutic candidates. Historically, both the parenchymal and vascular amyloid deposits, and more recently, truncated and pyroglutamate-modified Abeta3(pE)-42 species, are perceived as important hallmarks of AD-pathology. Late stage symptoms are preceded by robust deficits in orientation and memory that correlate in time with Abeta oligomerization and GSK3β-mediated phosphorylation of endogenous murine Tau, all markers that have gained considerable interest during the last decade. Clinical parallels with AD patients and the value of the APP-Ld transgenic mouse model for preclinical in vivo testing of candidate drugs are discussed.

Derailed Intraneuronal Signalling Drives Pathogenesis in Sporadic and Familial Alzheimer’s Disease

Although a wide variety of genetic and nongenetic Alzheimers disease (AD) risk factors have been identified, their role in onset and/or progression of neuronal degeneration remains elusive. Systematic analysis of AD risk factors revealed that perturbations of intraneuronal signalling pathways comprise a common mechanistic denominator in both familial and sporadic AD and that such alterations lead to increases in Aβ oligomers (Aβo) formation and phosphorylation of TAU. Conversely, Aβo and TAU impact intracellular signalling directly. This feature entails binding of Aβo to membrane receptors, whereas TAU functionally interacts with downstream transducers. Accordingly, we postulate a positive feedback mechanism in which AD risk factors or genes trigger perturbations of intraneuronal signalling leading to enhanced Aβo formation and TAU phosphorylation which in turn further derange signalling. Ultimately intraneuronal signalling becomes deregulated to the extent that neuronal function and survival cannot be sustained, whereas the resulting elevated levels of amyloidogenic Aβo and phosphorylated TAU species self-polymerizes into the AD plaques and tangles, respectively.

P4-245: Nanobodies™ targeting amyloid beta as potential therapeutics for Alzheimer’s disease

discovery of a GSI possessing minimal inhibition of Notch processing and maximal inhibition of APP processing to reduce 40/42 levels. Utilizing HTS screening of the Wyeth and ArQule compound collections, we have identified the lead, 4-chloro-N-[(1S,2S)-1-(hydroxymethyl)-2-methylbutyl]-benzenesulfonamide, which not only inhibited -secretase cleavage of APP (EC50 40 and 42 2078 nM and 1938 nM, respectively) but also was sparing of Notch cleavage (EC50 20,000 nM). Structure-activity relationships in this new series and the discovery of more potent GSIs will be discussed.

Modifying Rap1-signalling by targeting Pde6δ is neuroprotective in models of Alzheimer’s disease

BackgroundNeuronal Ca2+ dyshomeostasis and hyperactivity play a central role in Alzheimer’s disease pathology and progression. Amyloid-beta together with non-genetic risk-factors of Alzheimer’s disease contributes to increased Ca2+ influx and aberrant neuronal activity, which accelerates neurodegeneration in a feed-forward fashion. As such, identifying new targets and drugs to modulate excessive Ca2+ signalling and neuronal hyperactivity, without overly suppressing them, has promising therapeutic potential.MethodsHere we show, using biochemical, electrophysiological, imaging, and behavioural tools, that pharmacological modulation of Rap1 signalling by inhibiting its interaction with Pde6δ normalises disease associated Ca2+ aberrations and neuronal activity, conferring neuroprotection in models of Alzheimer’s disease.ResultsThe newly identified inhibitors of the Rap1-Pde6δ interaction counteract AD phenotypes, by reconfiguring Rap1 signalling underlying synaptic efficacy, Ca2+ influx, and neuronal repolarisation, without adverse effects in-cellulo or in-vivo. Thus, modulation of Rap1 by Pde6δ accommodates key mechanisms underlying neuronal activity, and therefore represents a promising new drug target for early or late intervention in neurodegenerative disorders.ConclusionTargeting the Pde6δ-Rap1 interaction has promising therapeutic potential for disorders characterised by neuronal hyperactivity, such as Alzheimer’s disease.

Phenotypic and genetic subclassification of Alzheimer's disease

Background: Two different types of Alzheimers disease (AD)-related cerebral amyloid angiopathy (CAA) can be distinguished by the presence or absence of capillary amyloid β-protein (Aβ)-deposition. Genetically, CAA-type 1 with capillary CAA is strongly associated with the apolipoprotein E (APOE) e4-allele, while CAA-type 2 lacking capillary Aβ did not show this association. The objective of this study was to test whether there exist further phenotypic and genotypic differences between CAA-type 1 and CAA-type 2 cases that may allow the distinction of different types of AD. Methods: Autopsy brains from 58 AD cases and 254 non-demented elderly controls were studied neuropathologically for vascular and parenchymal Aβ-deposition and for the expansion of neurofibrillary tangles as represented by the Braak-stage. In selected cases the astroglial expression of the glutamate transporters EAAT-1 and EAAT-2 was studied immunohistochemically. Double label immunohistochemistry was used to demonstrate the relationship between capillary CAA and EAAT-2 expression in astrocytes.Genotyping of the following polymorphisms was performed: APOE4-allele, CYP46A1 rs7157609 and CH25H rs13500 and rs1131706. Logistic regression analysis was used to study the association of these polymorphisms with CAA-type 1 and CAA-type 2. Results: The CAA-type 1-related form of AD was also associated with the CH25H rs1131706 TT genotype and with a loss of perivascular, excitatory amino acid transporter (EAAT-2) expressing astrocytes in the cortex. In contrast, AD cases lacking capillary Aβ-deposition showed an association with the G-allele of the CYP46A1 rs7157609 polymorphism and exhibited more widespread neurofibrillary tangle (NFT) pathology in relation to the expansion of Aβ-deposition than AD cases with CAA-type 1. Conclusions: One form of sporadic AD is characterized by capillary CAA, astroglial alterations and is genetically associated with the APOE e4-allele and the CH25H∗2 TT genotype, whereas the second form of sporadic AD lacks capillary CAA, exhibits a NFT predominant pattern of AD-related lesions and is associated with the CYP46A1 rs7157609 G-allele. AD cases with an additional pathology (e.g. vascular lesions and/ or other tauopathies) segregated clinicopathologically as an additional “mixed dementia” type of AD. This subclassification points to distinct pathogenetic features in subtypes of sporadic AD which may have therapeutic relevance in the future.