Direct in vivo assessment of glutamate dysfunction in APPPS1 mice using iGluSnFR 2- Photon imaging

• Applicant: Professorin Dr. Jasmin Kim Hefendehl
• Subject Area: Molecular and Cellular Neurology and Neuropathology
• Term: from 2012 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 232671375

The aggregation and deposition of beta-amyloid in the brain parenchyma is a major characteristic of Alzheimers Disease (AD). Several gene mutations have been identified to be causative for AD and these mutations all promote the deposition of Abeta in the brain. The deposition of beta-amyloid has been proposed to be the starting point of negative downstream events eventually leading to the loss of neurons and clinical symptoms. The toxic effect of plaques is much debated, as the deposition does not correlate well with the loss of neurons. However, recent studies showed that in early stages of AD dysfunction of cells in the close vicinity of Abeta plaques are detectable. This impairment of large populations of cells takes place without the direct induction of cell death but reveals neuritic dystrophies, loss of dendritic spines, increases in activity and resting calcium concentration in glial cells, an increase in resting calcium levels in subsets of dendrites and an increase in the fraction of hyperactive neurons. Moreover, it is now known that Abeta plaques are already present several years prior to the onset of clinical symptoms. Thus, it is essential to investigate the toxic effects on different cell types in the early non-clinical stages of AD in order to better understand the pathological mechanism of AD and thus create new therapeutic strategies. Glutamate is the mayor excitatory neurotransmitter in the central nervous system. If it is present in high concentrations due to pathological changes it leads to severe cell dysfunction and neuronal death known as excitotoxicity. Glutamate has long been suspected to be a mediator of hyperactivity that has been reported in cells surrounding abeta deposits and thus to contribute to pathological changes in AD at an early stage. Until now however there was no way to test this hypothesis in vivo. In our current project we are able to investigate the toxicity of the plaques microenvironment on glutamate signalling using the novel glutamate sensor iGluSnFR. This technique provides us with the opportunity to observe pathological changes over long-term periods in order to create a timeline of pathological events concerning neuronal glutamate signalling dysfunction and changes in Glutamate reuptake by astrocytes. We furthermore will try to prevent the excitotoxic effects by up regulating receptors that are responsible for glutamate reuptake. In another set of experiments we will test a novel antibody and a small molecule peptide, both with the goal to inhibit the oligomerisation of monomeric Abeta into toxic higher forms soluble and insoluble Abeta. The on going studies can shed light on the connection between Abeta deposition and dysfunction of different cell types in the early stages of AD and support time-dependent therapies aiming at an early phase intervention as well as amyloid reduction and inhibition halting negative downstream effects that will lead to neuronal cell death and cognitive decline.

• DFG Programme: Research Fellowships
• International Connection: Canada
• Host: Professor Brian MacVicar, Ph.D.