Spreading of Alzheimer pathology in organotypic brain slices

Alzheimers disease (AD) is a severe neurodegenerative disorder of the brain characterized by memory loss. The causes for AD are not known yet, but age (>60 years) is the most important risk factor for AD and thus the number of AD patients will dramatically increase within the next 50 years. Pathologically one finds in the AD brain extracellular depositions (beta- amyloid plaques), intraneuronal inclusions (tau), dying neurons (neurotransmitter acetylcholine), as well as vascular impairments and inflammation. So far it is fully unclear how the AD pathology is induced in the brain. The "spreading hypothesis" suggests that the pathology can spread from one brain region to another and "altered" proteins can induce and potentiate this effect. We aim to study this "spreading" in an organotypic brain slice ex vivo model. In my lab we are working with 3-dimensional organotypic brain slices for nearly 20 years and Prof. Humpel has been awarded the "Governmental Award for alternatives to animal research" in 2000. This model is very useful to explore the spreading, because we can connect two brain areas and we can selectively stimulate them. The aim of this FWF application is to study the spreading of both AD pathologies, the beta-amyloid as well as tau pathology in organotypic brain slices. We hypothesize that a cascade of events such as e.g. inflammation or oxidative stress may play a role in induction of the spreading process. Further, we aim to study if phagocytic microglial cells are involved in the spreading process. Finally, we also aim to explore if spreading occurs in nerve fiber tracts. Taken together we aim to simulate and study spreading of AD-like pathologies between brain areas in an ex vivo organotypic brain slice model, which may give us better insights into molecular processes and offer therapeutic strategies. Such a model could also be useful in the pharmaceutical industry to screen for novel therapeutic drugs, which will result in reducing severe animal experiments (3Rs).

Alzheimers Disease is a severe neurodegenerative disorder of the brain and characterized by massive depositions of the small peptide beta-amyloid in the brain, as well as depositions in neurons caused by the protein Tau. This all results in neurodegeneration and inflammation in the brain. Up do date, it is fully unclear how and why these depositions are produced, but it takes several years for this process. The "spreading hypothesis" says that proteins or peptides mutate and spread over from one brain area into another. The aim of this FWF project was to study the spreading in a 3-dimensional organotypic brain slice model. We could show that the small peptide beta-amyloid spreads over the brain slice and is modulated by the immune cells, the microglia. Similarly, also the larger protein Tau spreads from one brain area to another in the slice. In addition, we could also show that another protein, the alpha-synuclein, spreads in the brain slice, which may play a role in the progression of Parkinsons disease. In this project, we could develop for the first time a novel innovative method, the microcontact printing, to study spreading. Using this method, we can print small micrometer lanes and load with a peptide (e.g. beta-amyloid) and we investigate the spreading via nerve fibers or the migration of microglia or the formation of new vessel. In this FWF project we could show that specific peptides or proteins can spread in the brain and can contribute to a brain disorder. In future studies, we aim to transfer these findings to the human brain and to prevent the spreading process.