β-amyloid induces a dying-back process and remote trans-synaptic alterations in a microfluidic-based reconstructed neuronal network

IntroductionRecent histopathological studies have shown that neurodegenerative processes in Alzheimer's and Parkinson's Disease develop along neuronal networks and that hallmarks could propagate trans-synaptically through neuronal pathways. The underlying molecular mechanisms are still unknown, and investigations have been impeded by the complexity of brain connectivity and the need for experimental models allowing a fine manipulation of the local microenvironment at the subcellular level.ResultsIn this study, we have grown primary cortical mouse neurons in microfluidic (μFD) devices to separate soma from axonal projections in fluidically isolated microenvironments, and applied β-amyloid (Aβ) peptides locally to the different cellular compartments. We observed that Aβ application to the somato-dendritic compartment triggers a “dying-back” process, involving caspase and NAD+ signalling pathways, whereas exposure of the axonal/distal compartment to Aβ deposits did not induce axonal degeneration. In contrast, co-treatment with somatic sub-toxic glutamate and axonal Aβ peptide triggered axonal degeneration. To study the consequences of such subcellular/local Aβ stress at the network level we developed new μFD multi-chamber devices containing funnel-shaped micro-channels which force unidirectional axon growth and used them to recreate in vitro an oriented cortico-hippocampal pathway. Aβ application to the cortical somato-dendritic chamber leads to a rapid cortical pre-synaptic loss. This happens concomitantly with a post-synaptic hippocampal tau-phosphorylation which could be prevented by the NMDA-receptor antagonist, MK-801, before any sign of axonal and somato-dendritic cortical alteration.ConclusionThanks to μFD-based reconstructed neuronal networks we evaluated the distant effects of local Aβ stress on neuronal subcompartments and networks. Our data indicates that distant neurotransmission modifications actively take part in the early steps of the abnormal mechanisms leading to pathology progression independently of local Aβ production. This offers new tools to decipher mechanisms underlying Braak's staging. Our data suggests that local Aβ can play a role in remote tauopathy by distant disturbance of neurotransmission, providing a putative mechanism underlying the spatiotemporal appearance of pretangles.

[1]  Noo Li Jeon,et al.  β‐Amyloid is transmitted via neuronal connections along axonal membranes , 2014, Annals of neurology.

[2]  Jean-Louis Viovy,et al.  Synapto-Protective Drugs Evaluation in Reconstructed Neuronal Network , 2013, PloS one.

[3]  Jean-Louis Viovy,et al.  Axon diodes for the reconstruction of oriented neuronal networks in microfluidic chambers. , 2011, Lab on a chip.

[4]  F. Schmitt,et al.  Synaptic alterations in CA1 in mild Alzheimer disease and mild cognitive impairment , 2007, Neurology.

[5]  Nick C Fox,et al.  Molecular nexopathies: a new paradigm of neurodegenerative disease , 2013, Trends in Neurosciences.

[6]  L. Mucke,et al.  Epilepsy and cognitive impairments in Alzheimer disease. , 2009, Archives of neurology.

[7]  Jean-Louis Viovy,et al.  Wallerian-Like Degeneration of Central Neurons After Synchronized and Geometrically Registered Mass Axotomy in a Three-Compartmental Microfluidic Chip , 2010, Neurotoxicity Research.

[8]  J. Viovy,et al.  NAD+ acts on mitochondrial SirT3 to prevent axonal caspase activation and axonal degeneration , 2013, FASEB journal : official publication of the Federation of American Societies for Experimental Biology.

[9]  F. García-Sierra,et al.  Earliest stages of tau conformational changes are related to the appearance of a sequence of specific phospho-dependent tau epitopes in Alzheimer's disease. , 2007, Journal of Alzheimer's disease : JAD.

[10]  H. Braak,et al.  Phases of Aβ-deposition in the human brain and its relevance for the development of AD , 2002, Neurology.

[11]  R. Terry Cell death or synaptic loss in Alzheimer disease. , 2000, Journal of neuropathology and experimental neurology.

[12]  L. Mucke,et al.  Amyloid-β–induced neuronal dysfunction in Alzheimer's disease: from synapses toward neural networks , 2010, Nature Neuroscience.

[13]  C. Cotman,et al.  A microfluidic culture platform for CNS axonal injury, regeneration and transport , 2005, Nature Methods.

[14]  Mathias Jucker,et al.  Self-propagation of pathogenic protein aggregates in neurodegenerative diseases , 2013, Nature.

[15]  R. Adalbert,et al.  Review: Axon pathology in age‐related neurodegenerative disorders , 2013, Neuropathology and applied neurobiology.

[16]  I. Grundke‐Iqbal,et al.  Dysregulation of tau phosphorylation in mouse brain during excitotoxic damage. , 2009, Journal of Alzheimer's disease : JAD.

[17]  M. Gillette,et al.  New perspectives on neuronal development via microfluidic environments , 2012, Trends in Neurosciences.

[18]  G. Krafft,et al.  In Vitro Characterization of Conditions for Amyloid-β Peptide Oligomerization and Fibrillogenesis* , 2003, The Journal of Biological Chemistry.

[19]  Anatol C. Kreitzer,et al.  Aberrant Excitatory Neuronal Activity and Compensatory Remodeling of Inhibitory Hippocampal Circuits in Mouse Models of Alzheimer's Disease , 2007, Neuron.

[20]  H. Braak,et al.  Staging of Alzheimer disease-associated neurofibrillary pathology using paraffin sections and immunocytochemistry , 2006, Acta Neuropathologica.

[21]  S. Kar,et al.  β-Amyloid-related peptides potentiate K+-evoked glutamate release from adult rat hippocampal slices , 2010, Neurobiology of Aging.

[22]  F. Polleux,et al.  The CAMKK2-AMPK Kinase Pathway Mediates the Synaptotoxic Effects of Aβ Oligomers through Tau Phosphorylation , 2013, Neuron.