ABSTRACT
The development of novel therapeutic strategies for Alzheimer's disease (AD) represents one of the biggest unmet medical needs today. Application of neurotrophic factors able to modulate neuronal survival and synaptic connectivity is a promising therapeutic approach for AD. We aimed to determine whether the loco-regional delivery of ciliary neurotrophic factor (CNTF) could prevent amyloid-beta (Abeta) oligomer-induced synaptic damages and associated cognitive impairments that typify AD. To ensure long-term administration of CNTF in the brain, we used recombinant cells secreting CNTF encapsulated in alginate polymers. The implantation of these bioreactors in the brain of Abeta oligomer-infused mice led to a continuous secretion of recombinant CNTF and was associated with the robust improvement of cognitive performances. Most importantly, CNTF led to full recovery of cognitive functions associated with the stabilization of synaptic protein levels in the Tg2576 AD mouse model. In vitro as well as in vivo, CNTF activated a Janus kinase/signal transducer and activator of transcription-mediated survival pathway that prevented synaptic and neuronal degeneration. These preclinical studies suggest that CNTF and/or CNTF receptor-associated pathways may have AD-modifying activity through protection against progressive Abeta-related memory deficits. Our data also encourage additional exploration of ex vivo gene transfer for the prevention and/or treatment of AD.
Subject(s)
Alzheimer Disease/complications , Ciliary Neurotrophic Factor/biosynthesis , Ciliary Neurotrophic Factor/therapeutic use , Memory Disorders/etiology , Memory Disorders/therapy , Synapses/drug effects , Alzheimer Disease/genetics , Amyloid beta-Peptides/administration & dosage , Amyloid beta-Peptides/metabolism , Amyloid beta-Peptides/pharmacology , Amyloid beta-Protein Precursor/genetics , Animals , Apoptosis/genetics , Brain/pathology , Cell Count/methods , Cell- and Tissue-Based Therapy/methods , Cells, Cultured , Ciliary Neurotrophic Factor/administration & dosage , Disease Models, Animal , Enzyme Inhibitors/pharmacology , Enzyme-Linked Immunosorbent Assay/methods , Gene Expression Regulation/drug effects , Gene Expression Regulation/genetics , Green Fluorescent Proteins/genetics , Humans , Male , Maze Learning/physiology , Mice , Mice, Inbred C57BL , Mice, Transgenic , Mutation/genetics , Neurons/drug effects , Neurons/metabolism , Peptide Fragments/administration & dosage , Peptide Fragments/pharmacology , Signal Transduction/drug effects , Synapses/metabolism , Synaptosomes/metabolism , Synaptosomes/pathology , Synaptosomes/ultrastructure , Time Factors , Transfection/methodsABSTRACT
In the absence of efficient diagnostic and therapeutic tools, Alzheimer's disease (AD) is a major public health concern due to longer life expectancy in the Western countries. Although the precise cause of AD is still unknown, soluble beta-amyloid (Abeta) oligomers are considered the proximate effectors of the synaptic injury and neuronal death occurring in the early stages of AD. Abeta oligomers may directly interact with the synaptic membrane, leading to impairment of synaptic functions and subsequent signalling pathways triggering neurodegeneration. Therefore, membrane structure and lipid status should be considered determinant factors in Abeta-oligomer-induced synaptic and cell injuries, and therefore AD progression. Numerous epidemiological studies have highlighted close relationships between AD incidence and dietary patterns. Among the nutritional factors involved, lipids significantly influence AD pathogenesis. It is likely that maintenance of adequate membrane lipid content could prevent the production of Abeta peptide as well as its deleterious effects upon its interaction with synaptic membrane, thereby protecting neurons from Abeta-induced neurodegeneration. As major constituents of neuronal lipids, n-3 polyunsaturated fatty acids are of particular interest in the prevention of AD valuable diet ingredients whose neuroprotective properties could be essential for designing preventive nutrition-based strategies. In this review, we discuss the functional relevance of neuronal membrane features with respect to susceptibility to Abeta oligomers and AD pathogenesis, as well as the prospective capacities of lipids to prevent or to delay the disease.
Subject(s)
Alzheimer Disease/metabolism , Amyloid beta-Peptides/metabolism , Lipid Metabolism/physiology , Alzheimer Disease/pathology , Alzheimer Disease/physiopathology , Animals , Apoptosis/physiology , Fatty Acids, Omega-3/metabolism , Humans , Membrane Microdomains/metabolism , Models, Biological , Signal Transduction/physiologyABSTRACT
N-terminal-truncated forms of amyloid-beta (A beta) peptide have been recently suggested to play a pivotal role early in Alzheimer's disease (AD). Among them, A beta 3(pE)-42 peptide, starting with pyroglutamyl at residue Glu-3, is considered as the predominant A beta species in AD plaques and pre-amyloid lesions. Its abundance is reported to be directly proportional to the severity of the clinical phenotype. The present study investigates the effects of soluble oligomeric A beta 3(pE)-42 after intracerebroventricular injection on mice learning ability and the molecular mechanisms of its in vitro neurotoxicity. Mice injected with soluble A beta 3(pE)-42 or A beta(l-42) displayed impaired spatial working memory and delayed memory acquisition in Y-maze and Morris water maze tests, while those injected with soluble A beta(42-1) showed no effect. These cognitive alterations were associated with free radical overproduction in the hippocampus and olfactory bulbs, but not in the cerebral cortex or cerebellum. In vitro, A beta 3(pE)-42 oligomers induced a redox-sensitive neuronal apoptosis involving caspase activation and an arachidonic acid-dependent pro-inflammatory pathway. These data suggest that A beta 3(pE)-42 could mediate the neurodegenerative process and subsequent cognitive alteration occurring in preclinical AD stages.
Subject(s)
Amyloid beta-Peptides/administration & dosage , Maze Learning/drug effects , Neurons/drug effects , Neurons/pathology , Peptide Fragments/administration & dosage , Animals , Apoptosis/drug effects , Cells, Cultured , Dose-Response Relationship, Drug , Male , Mice , Mice, Inbred C57BLABSTRACT
Alzheimer's disease (AD) is a major public health concern in all countries. Although the precise cause of AD is still unknown, a growing body of evidence supports the notion that soluble amyloid beta-peptide (Abeta) may be the proximate cause of synaptic injuries and neuronal death early in the disease. AD patients display lower levels of docosahexaenoic acid (DHA, C22:6 ; n-3) in plasma and brain tissues as compared to age-matched controls. Furthermore, epidemiological studies suggest that high DHA intake might have protective properties against neurodegenerative diseases. These observations are supported by in vivo studies showing that DHA-rich diets limits the synaptic loss and cognitive defects induced by Abeta peptide. Although the molecular basis of these neuroprotective effects remains unknown, several mechanisms have been proposed such as (i) regulation of the expression of potentially protective genes, (ii) activation of anti-inflammatory pathways, (iii) modulation of functional properties of the synaptic membranes along with changes in their physicochemical and structural features.
Subject(s)
Alzheimer Disease/diet therapy , Alzheimer Disease/prevention & control , Amyloid beta-Peptides/antagonists & inhibitors , Brain/drug effects , Brain/metabolism , Docosahexaenoic Acids/therapeutic use , Encephalitis/diet therapy , Neuroprotective Agents/therapeutic use , Alzheimer Disease/metabolism , Amyloid beta-Peptides/metabolism , Animals , Brain/physiopathology , Docosahexaenoic Acids/metabolism , Encephalitis/metabolism , Encephalitis/physiopathology , Food, Formulated/standards , Humans , Lipid Metabolism/drug effects , Lipid Metabolism/physiology , Neuroprotective Agents/metabolism , Synapses/drug effects , Synapses/metabolismABSTRACT
Recent data have revealed that soluble oligomeric amyloid-beta peptide (Abeta) may be the proximate effectors of neuronal injuries and death in Alzheimer's disease (AD) by unknown mechanisms. Consistently, we recently demonstrated the critical role of a redox-sensitive cytosolic calcium-dependent phospholipase A2 (cPLA2)-arachidonic acid (AA) pathway in Abeta oligomer-induced cell death. According to the involvement of oxidative stress and polyunsaturated fatty acids like AA in the regulation of sphingomyelinase (SMase) activity, the present study underlines the role of SMases in soluble Abeta-induced apoptosis. Soluble Abeta oligomers induced the activation of both neutral and acidic SMases, as demonstrated by the direct measurement of their enzymatic activities, by the inhibitory effects of both specific neutral and acidic SMase inhibitors, and by gene knockdown using antisense oligonucleotides. Furthermore, soluble Abeta-mediated activation of SMases and subsequent cell death were found to be inhibited by antioxidant molecules and a cPLA2-specific inhibitor or antisense oligonucleotide. We also demonstrate that sphingosine-1-phosphate is a potent neuroprotective factor against soluble Abeta oligomer-induced cell death and apoptosis by inhibiting soluble Abeta-induced activation of acidic sphingomyelinase. These results suggest that Abeta oligomers induce neuronal death by activating neutral and acidic SMases in a redox-sensitive cPLA2-AA pathway.
