Wanda Leon

A Novel Transgenic Rat Model with a Full Alzheimer's-Like Amyloid Pathology Displays Pre-Plaque Intracellular Amyloid-β-Associated Cognitive Impairment

Alzheimers disease (AD) is a neurodegenerative pathology in which amyloid-beta (Abeta) peptide accumulates in different brain areas leading to deposition of plaques and a progressive decline of cognitive functions. After a decade in which a number of transgenic (Tg) mouse models mimicking AD-like amyloid-deposition pathology have been successfully generated, few rat models have been reported that develop intracellular and extracellular Abeta accumulation, together with impairment of cognition. The generation of a Tg rat reproducing the full AD-like amyloid pathology has been elusive. Here we describe the generation and characterization of a new transgenic rat line, coded McGill-R-Thy1-APP, developed to express the human amyloid-beta precursor protein (AbetaPP) carrying both the Swedish and Indiana mutations under the control of the murine Thy1.2 promoter. The selected mono-transgenic line displays an extended phase of intraneuronal Abeta accumulation, already apparent at 1 week after birth, which is widespread throughout different cortical areas and the hippocampus (CA1, CA2, CA3, and dentate gyrus). Homozygous Tg animals eventually produce extracellular Abeta deposits and, by 6 months of age, dense, thioflavine S-positive, amyloid plaques are detected, associated with glial activation and surrounding dystrophic neurites. The cognitive functions in transgenic McGill-R-Thy1-APP rats, as assessed using the Morris water maze task, were found already altered as early as at 3 months of age, when no CNS plaques are yet present. The spatial cognitive impairment becomes more prominent in older animals (13 months), where the behavioral performance of Tg rats positively correlates with the levels of soluble Abeta (trimers) measured in the cortex.

Amyloid β-Induced Nerve Growth Factor Dysmetabolism in Alzheimer Disease

We previously reported that the precursor form of nerve growth factor (pro-NGF) and not mature NGF is liberated in the CNS in an activity-dependent manner, and that its maturation and degradation occur in the extracellular space by the coordinated action of proteases.Here, we present evidence of diminished conversion of pro-NGF to its mature form and of greater NGF degradation in Alzheimer disease (AD) brain samples compared with controls. These alterations of the NGF metabolic pathway likely resulted in the increased pro-NGF levels. The pro-NGF was largely in a peroxynitrited form in the AD samples. Intrahippocampal injection of amyloid-&bgr; oligomers provoked similar upregulation of pro-NGF in naive rats that wasaccompanied by evidence of microglial activation (CD40), increased levels of inducible nitric oxide synthase, and increased activity of the NGF-degrading enzyme matrix metalloproteinase 9. The elevated inducible nitric oxide synthase provoked the generation of biologically inactive, peroxynitrite-modified pro-NGF in amyloid-&bgr; oligomer-injected rats. These parameters were corrected by minocycline treatment. Minocycline also diminished altered matrix metalloproteinase 9, inducible nitric oxide synthase, and microglial activation (CD40); improved cognitive behavior; and normalized pro-NGF levels in a transgenic mouse AD model. The effects of amyloid-&bgr; amyloid CNS burden on NGF metabolism may explain the paradoxical upregulation of pro-NGF in AD accompanied by atrophy of forebrain cholinergic neurons.

Cholinergic Involvement in Alzheimer’s Disease. A Link with NGF Maturation and Degradation

Basal forebrain cholinergic neurons are highly dependent on nerve growth factor (NGF) supply for the maintenance of their cholinergic phenotype as well as their cholinergic synaptic integrity. The precursor form of NGF, proNGF, abounds in the CNS and is highly elevated in Alzheimer’s disease. In order to obtain a deeper understanding of the NGF biology in the CNS, we have performed a series of ex vivo and in vivo investigations to elucidate the mechanisms of release, maturation and degradation of this neurotrophin. In this short review, we describe this NGF metabolic pathway, its significance for the maintenance of basal cholinergic neurons, and its dysregulation in Alzheimer’s disease. We are proposing that the conversion of proNGF to mature NGF occurs in the extracellular space by the coordinated action of zymogens, convertases, and endogenous regulators, which are released in the extracellular space in an activity-dependent fashion. We further discuss our findings of a diminished conversion of the NGF precursor molecule to its mature form in Alzheimer’s disease as well as an augmented degradation of mature NGF. These combined effects on NGF metabolism would explain the well-known cholinergic atrophy found in Alzheimer’s disease and would offer new therapeutic opportunities aimed at correcting the NGF dysmetabolism along with Aβ-induced inflammatory responses.

Engagement of the PFC in consolidation and recall of recent spatial memory

The standard model of system consolidation proposes that memories are initially hippocampus dependent and become hippocampus independent over time. Previous studies have demonstrated the involvement of the medial prefrontal cortex (mPFC) in the retrieval of remote memories. The transformations required to make a memory undergo systems consolidation are thought to require synaptic plasticity. In this study, we investigated the participation of the mitogen-activated protein kinase (MAPK)/ERK pathway in acquisition, memory consolidation, and recent memory recall of the Morris water maze (MWM) task using a 1-d training protocol. To this end, bilateral injections of the MEK inhibitor U0126 into the rat mPFC were performed. The injection of the MEK inhibitor in the mPFC did not affect the acquisition of the MWM. However, MEK inhibitor resulted in impairments on recent memory retrieval either when applied at the end of the learning phase (memory consolidation) or prior to the retention test. The results strongly support the concept that recently acquired and consolidated spatial memories require the mPFC, and that local activation of the MAPK/ERK pathway in the mPFC is necessary for the consolidation and recall of recent memories.

Early-Stage Inflammation and Experimental Therapy in Transgenic Models of the Alzheimer-Like Amyloid Pathology

Background: Intracellular accumulation of β-amyloid (Aβ) is one of the early features in the neuropathology of Alzheimer’s disease (AD) and Down’s syndrome. This can be reproduced in cell and transgenic animal models of the AD-like amyloid pathology. In a transgenic rat model, our lab has previously shown that the intracellular accumulation of Aβ is sufficient to provoke cognitive impairments and biochemical alterations in the cerebral cortex and hippocampus in the absence of amyloid plaques. Objective: To investigate an early, pre-plaque inflammatory process in AD-like transgenic models and establish whether the neurotoxic effects of Aβ oligomers and proinflammatory responses can be arrested with minocycline. Methods: For these studies, we used naïve mice and transgenic animal models of the AD-like amyloid pathology and applied neurochemical, immunohistochemical and behavioral experimental approaches. Results: In the early stages of the AD-like amyloid pathology, intracellular Aβ oligomers accumulate within neurons of the cerebral cortex and hippocampus. Coincidental with this, behavioral impairments occur prior to the appearance of amyloid plaques, together with an upregulation of MHC-II, i-NOS and COX-2, well-known proinflammatory markers. Treatment with minocycline corrected behavioral impairments, lowered inflammatory markers and levels of Aβ trimers. Conclusion: A pharmacological approach targeting the early neuroinflammatory effects of Aβ might be a promising strategy to prevent or delay the onset of AD.

P3-380: Aβ-induced nerve growth factor trophic disconnection in Alzheimer's disease

Background: The causative mechanisms for the atrophy of forebrain cholinergic neurons in Alzheimer’s disease (AD) remain undefined. Methods: Western blot analysis of members of the NGF maturation/degradation cascade in the CNS and of key inflamatory markers in human brain samples of Alzheimer’s patients and controls as well as in rodents after the application of oligomeric A beta 42 and treatment with minocycline. Results: We found evidence for a diminished conversion of the NGF precursor molecule to its mature form and for increased NGF-degradation in Alzheimer’s brain samples, resulting in an up-regulation of proNGF levels. We further observed that soluble A -oligomers injections provoked a similar up-regulation of proNGF levels in the rat hippocampus. These experiments revealed an A -induced inflammatory microglia activation, increased inducible nitric oxide synthase (iNOS) which activated the NGFdegrading enzyme MMP-9 and facilitated the CNS accumulation of peroxynitrite-modified proNGF. These combined effects markedly reduced the level and biological activity of mature NGF and provoked the accumulation of proNGF. These changes were prevented with the application of minocycline. Accordingly, the administration of minocycline in a transgenic AD mouse model also corrected the altered levels of MMP-9, iNOS and microglial activation, preserving cognitive behavior and normalizing proNGF levels. Conclusions: These effects of A amyloid CNS burden on NGF metabolism would explain the well-known cholinergic atrophy found in AD and it offers a novel therapeutic target.

Naive and pyroglutamated amyloid beta accumulation in the McGill-R-THY1-APP rat model of Alzheimer's disease

P4-280 NAIVE AND PYROGLUTAMATEDAMYLOID BETA ACCUMULATION IN THE MCGILL-R-THY1-APP RAT MODEL OFALZHEIMER’S DISEASE Fabio Canneva, Tiziana Melis, Wanda Leon, Florencia Iulita, Julia Dobner, Adriana Ducatenzeiler, Stephan Schilling, Stephan vonHoersten, Claudio Cuello, University of Erlangen-N€urnberg, Erlangen, Germany; University of Cagliari, Cagliari, Italy; McGill University, Montreal, Quebec, Canada; Probiodrug AG, Halle, Germany.