Jesus Benavides

Massive CA1/2 Neuronal Loss with Intraneuronal and N-Terminal Truncated Aβ42 Accumulation in a Novel Alzheimer Transgenic Model

Alzheimers disease (AD) is characterized by a substantial degeneration of pyramidal neurons and the appearance of neuritic plaques and neurofibrillary tangles. Here we present a novel transgenic mouse model, APP(SL)PS1KI that closely mimics the development of AD-related neuropathological features including a significant hippocampal neuronal loss. This transgenic mouse model carries M233T/L235P knocked-in mutations in presenilin-1 and overexpresses mutated human beta-amyloid (Abeta) precursor protein. Abeta(x-42) is the major form of Abeta species present in this model with progressive development of a complex pattern of N-truncated variants and dimers, similar to those observed in AD brain. At 10 months of age, an extensive neuronal loss (>50%) is present in the CA1/2 hippocampal pyramidal cell layer that correlates with strong accumulation of intraneuronal Abeta and thioflavine-S-positive intracellular material but not with extracellular Abeta deposits. A strong reactive astrogliosis develops together with the neuronal loss. This loss is already detectable at 6 months of age and is PS1KI gene dosage-dependent. Thus, APP(SL)PS1KI mice further confirm the critical role of intraneuronal Abeta(42) in neuronal loss and provide an excellent tool to investigate therapeutic strategies designed to prevent AD neurodegeneration.

ABCA2 is a strong genetic risk factor for early-onset Alzheimer's disease

Recent epidemiological, biological and genetic data indicate a relationship between cholesterol and Alzheimers disease (AD) including the association of polymorphisms of ABCA1 (a gene that is known to participate in cholesterol and phospholipid transport) with AD prevalence. Based on these data, we postulated that genetic variation in the related and brain-specific ABCA2 gene leads to increase risk of AD. A large case-control study was conducted where the sample was randomly divided into a hypothesis-testing sample (230 cases/286 controls) and a validation sample (210 cases/233 controls). Among the 45 SNPs we tested, one synonymous SNP (rs908832) was found significantly associated with AD in both samples. Additional analyses performed on the whole sample showed a very strong association between this marker and early-onset AD (OR = 3.82, 95% C.I. = [2.00 - 7.30], P = 5 x 10(-5)). Further research is needed to understand the functional role of this polymorphism. However, together with the reported associations of AD with APOE, CYP46A1 and ABCA1, the present result adds a very significant support for the role of cholesterol and phospholipid homeostasis in AD and a rationale for testing novel cholesterol homeostasis-related therapeutic strategies in AD.

An in vitro and in vivo study of early deficits in associative learning in transgenic mice that over‐express a mutant form of human APP associated with Alzheimer's disease

Transgenic mice over‐expressing a mutated form of the human amyloid precursor protein (APP, 695 isoform) bearing a mutation associated with Alzheimers disease (V642I, so‐called London mutation, hereafter APPLd2) and wild‐type controls were studied at age periods (3 and 10u2003months) prior to the overt development of neuritic amyloid plaques. Both 3‐ and 10‐month‐old APPLd2 mice had reflex eyelid responses like those of controls, but only younger mice were able to acquire a classical conditioning of eyelid responses in a trace paradigm. In vitro studies on hippocampal slices showed that 10‐month‐old APPLd2 mice also presented deficits in paired‐pulse facilitation and long‐term potentiation, but presented a normal synaptic activation of CA1 pyramidal cells by the stimulation of Schaffer collaterals. It is proposed that definite functional changes may appear well in advance of noticeable structural alterations in this animal model of Alzheimers disease, and that specific learning tasks could have a relevant diagnostic value.

Increased regional cerebral glucose uptake in an APP/PS1 model of Alzheimer's disease.

Alzheimers disease (AD), the most common age-related neurodegenerative disorder, is characterized by the invariant cerebral accumulation of β-amyloid peptide. This event occurs early in the disease process. In humans, [18F]-fluoro-2-deoxy-D-glucose ([18F]-FDG) positron emission tomography (PET) is largely used to follow-up in vivo cerebral glucose utilization (CGU) and brain metabolism modifications associated with the Alzheimers disease pathology. Here, [18F]-FDG positron emission tomography was used to study age-related changes of cerebral glucose utilization under resting conditions in 3-, 6-, and 12-month-old APP(SweLon)/PS1(M146L), a mouse model of amyloidosis. We showed an age-dependent increase of glucose uptake in several brain regions of APP/PS1 mice but not in control animals and a higher [18F]-FDG uptake in the cortex and the hippocampus of 12-month-old APP/PS1 mice as compared with age-matched control mice. We then developed a method of 3-D microscopic autoradiography to evaluate glucose uptake at the level of amyloid plaques and showed an increased glucose uptake close to the plaques rather than in amyloid-free cerebral tissues. These data suggest a macroscopic and microscopic reorganization of glucose uptake in relation to cerebral amyloidosis.

In vivo imaging of neuroinflammation in the rodent brain with [11C]SSR180575, a novel indoleacetamide radioligand of the translocator protein (18 kDa).

PurposeNeuroinflammation is involved in neurological disorders through the activation of microglial cells. Imaging of neuroinflammation with radioligands for the translocator protein (18 kDa) (TSPO) could prove to be an attractive biomarker for disease diagnosis and therapeutic evaluation. The indoleacetamide-derived 7-chloro-N,N,5-trimethyl-4-oxo-3-phenyl-3,5-dihydro-4H-pyridazino[4,5-b]indole-1-acetamide, SSR180575, is a selective high-affinity TSPO ligand in human and rodents with neuroprotective effects.MethodsHere we report the radiolabelling of SSR180575 with 11C and in vitro and in vivo imaging in an acute model of neuroinflammation in rats.ResultsThe image contrast and the binding of [11C]SSR180575 are higher than that obtained with the isoquinoline-based TSPO radioligand, [11C]PK11195. Competition studies demonstrate that [11C]SSR180575 has high specific binding for the TSPO.Conclusion[11C]SSR180575 is the first PET radioligand for the TSPO based on an indoleacetamide scaffold designed for imaging neuroinflammation in animal models and in the clinic.

Gadolinium-staining reveals amyloid plaques in the brain of Alzheimer's transgenic mice

Detection of amyloid plaques in the brain by in vivo neuroimaging is a very promising biomarker approach for early diagnosis of Alzheimers disease (AD) and evaluation of therapeutic efficacy. Here we describe a new method to detect amyloid plaques by in vivo magnetic resonance imaging (MRI) based on the intracerebroventricular injection of a nontargeted gadolinium (Gd)-based contrast agent, which rapidly diffuses throughout the brain and increases the signal and contrast of magnetic resonance (MR) images by shortening the T1 relaxation time. This gain in image sensitivity after in vitro and in vivo Gd staining significantly improves the detection and resolution of individual amyloid plaques in the cortex and hippocampus of AD transgenic mice. The improved image resolution is sensitive enough to demonstrate an age-dependent increase of amyloid plaque load and a good correlation between the amyloid load measured by μMRI and histology. These results provide the first demonstration that nontargeted Gd staining can enhance the detection of amyloid plaques to follow the progression of AD and to evaluate the activity of amyloid-lowering therapeutic strategies in longitudinal studies.

A risk for early-onset Alzheimer's disease associated with the APBB1 gene (FE65) intron 13 polymorphism.

Alzheimers disease (AD) is a genetically complex neurodegenerative disorder and the leading cause of dementia of the elderly. Recently, Hu et al. suggested that a trinucleotide deletion in intron 13 of the APBB1 gene was a factor protecting against late-onset AD. We report here the results of a case/control study aimed at replicating this association. Our study included 461 AD patients and 397 matched controls. We compared the allele and genotype frequencies of the polymorphism between the two groups but did not find any statistically significant difference (P=0.08 and P=0.09, respectively). By contrast, adjusting for age and sex, we found a slight risk associated with the deletion (odds ratio=1.47, 95% confidence interval=1.05-2.04). Stratification by age showed that the risk effect associated with the deletion concerned subjects aged less than 65 years.