Emergence of Neurodegeneration in Alzheimer’s disease – EarlyAD

The overarching goal of this research proposal is the discovery of the seminal structural and functional neural defects that initiate neurodegeneration in Alzheimer’s disease (AD). By applying the most sensitive imaging methodologies currently available for in vivo studies in mouse models of ß-amyloidosis, such as high-speed LOTOS two-photon imaging and super-resolution STED-SUSHI, we will perform a mechanistic structure-function analysis of impaired neurons and their synaptic contacts over the course of the early stages of Aß plaque formation. The central hypothesis of the project is that the initial neuronal damage at glutamatergic synapses occurs already at early stages of Aß plaque formation and involves structural changes at the level of dendritic spines and the associated peri-synaptic astrocytic processes. This hypothesis is based on the observation of early synaptic dysfunction both in AD models in vivo and in vitro. The relationship between the early synaptic dysfunction and concomitant morphological changes has remained obscure because of technical limitations. In the proposed project, we will largely overcome these bottlenecks by capitalizing on recent technical developments our groups have pioneered, including in vivo glutamate imaging with single-spine resolution and in vitro STED microscopy of astroglial processes. Associating these advances for the first time, we will study the morphology of in vivo assessed dysfunctional individual glutamatergic synapses at nanometer resolution. Thus, a main focus of the study will be the precise mapping of pathological glutamate spillover at the level of individual dendritic spines and the determination of the impact on synaptic function, including the elucidation of the role of astrocytes, a critical target for Aß in the brain, for the degeneration of dendrites and spines and their functional impairment.
The specific objectives of the proposed research are as follows:
1. Establishment, test and validation of a recording pipeline for the combined study in vivo (two-photon in Munich) and in vitro (STED in Bordeaux) of individual dysfunctional neurons and astrocytes in AD models.
2. In vivo mapping of glutamate spillover at the level of individual spines in dysfunctional neurons in mouse models of AD using LOTOS-based two-photon glutamate imaging.
3. STED imaging-based in vitro function-structure analysis of single spines and associated peri-synaptic astrocytic processes and extracellular space of dysfunctional neurons identified in AD models in vivo.
4. Assessing the acute actions of synthetic and human patient-derived Aß dimers on peri-synaptic astrocytic processes and the extracellular space at the level of individual glutamatergic synapses.
The planned study is highly innovative as it employs a new combination of state-of-the-art methodologies, namely in vivo high-speed LOTOS two-photon microscopy and recent variants of STED microscopy in vitro. The Munich lab has pioneered in vivo calcium imaging of dendritic spines and advanced in vivo glutamate imaging at the level of individual spines. The Bordeaux lab has developed super-resolution fluorescence microscopy approaches to study the structure-function relationship of synapses and glial processes and the extracellular space at the nanoscale in living brain tissue.