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The project

ToPAG (Toxic Protein AGgregation in Neurodegeneration) is a six-year interdisciplinary research project that started in June 2013. The involved research departments create a unique synergy by combining the scientific excellence of four leading research groups from two Max Planck Institutes (MPIs): the MPI of Biochemistry and the MPI of Neurobiology. ToPAG was awarded an ERC Synergy grant of 13.9 million EUR, the highest EU funding for a single project so far. The consortium relies on the complementary expertise of its research groups to take on this remarkable challenge of investigating neurodegenerative diseases.

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From left to right: Prof. Hartl, Prof. Baumeister, Prof. Klein, Prof. Mann

Contributions from the 4 research departments

Prof. Dr. Wolfgang Baumeister has been director at the Max Planck Institute of Biochemistry since 1988. His department studies large protein complexes that cannot be visualized with conventional methods. For this challenging task he developed the method of cryo-electron tomography, which is now used for investigating large protein aggregates in neurodegenerative diseases. This method allows 3D imaging of quickly frozen cells at molecular resolution.

Prof. Dr. F.-Ulrich Hartl has been director at the Max Planck Institute of Biochemistry since 1997. His department studies how proteins acquire their three-dimensional structure. In neurodegenerative diseases such as Alzheimer’s, misfolded and defective proteins play a crucial role. Professor Hartl is the coordinator of the ERC Synergy Grant and contributes his insights about protein folding to the analysis of biochemical and biophysical characteristics of protein aggregates.

Prof. Dr. Rüdiger Klein has been director at the Max Planck Institute of Neurobiology since 2001, where his department studies the role of receptors on the cell surface and their binding partners in the network of nerve cells throughout their entire life span. His particular expertise lies in the development and analysis of cell culture and mouse models of human diseases. Using these models the scientists can explore how the protein aggregates arise and what effects they have.

Prof. Dr. Matthias Mann has been director at the Max Planck Institute of Biochemistry since 2005. His department is the world leader in the analysis of the proteome, the entirety of all proteins in an organism. Using mass spectrometry, they aim to identify proteins in the above-mentioned cell culture and mouse models which cause toxicity in neurodegenerative diseases.

Project Goals

We combine biochemical, cell biological, systems biology and structural approaches to obtain a comprehensive understanding of the basic cellular mechanisms by which protein aggregation causes cellular toxicity and disease. Our main goals are:

Goal 1: Characterization of toxic aggregation pathways

Since not all protein aggregations are necessarily toxic, we aim to distinguish toxic aggregates from protein aggregates that have no deleterious effects. We will use live cell imaging to observe how the aggregates evolve in size and how they move around the cell. These results will then be linked with different markers of cell toxicity. We will further investigate how protein aggregates are modified depending on their location in the cells. In addition, we aim to find out whether aggregating proteins are able to spread to other cells in cell cultures or specific regions of the mouse brain.

Goal 2: Identification of the mechanisms of protein aggregation toxicity

We currently do not know what causes protein aggregate toxicity and how cells, tissues and organs respond to the formation and accumulation of these aggregates. Therefore, we will investigate the interactions of specific protein aggregates with other molecules and compartments of the cell whilst they evolve in both cell culture and the mouse brain. In addition, we will isolate aggregate fractions in order to analyze their composition and potential modifications using mass spectrometry. We will use high resolution light microscopy and cryo-electron tomography to reveal possible effects of protein aggregates on other cell structures (e.g. synapses) that may be affected in neurodegenerative diseases.

Goal 3: Understanding the cellular defense against toxic protein aggregation

Chaperones are proteins that help other proteins to acquire their three-dimensional structure. Therefore, chaperones play an important role in cells by maintaining the protein homeostasis or “proteostasis”. If proteins are misfolded, chaperones either refold these proteins or guide them to the cellular recycling machines. Misfolded proteins may also form “inclusion bodies”, insoluble and potentially protective deposits of protein clumps. At some point, however, all these cellular defense mechanisms fail and neurodegeneration progresses. To find out why this is the case, we will monitor changes in the proteostasis network using cultured cells and transgenic mice. We aim to reveal which specific aggregates are linked with proteostasis activation and survival of the cell or proteostasis impairment and cytotoxicity.

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In addition, by inhibiting or activating stress response pathways, we aim to reveal how the cellular chaperone network influences the formation of the protein aggregates. We will use cryo-electron tomography to construct three-dimensional models of inclusion bodies and investigate how they may be associated with macromolecules such as chaperones or proteasomes.

The images a), b) and c) show primary mouse neurons expressing a sensor protein (in green) that shows how well the defense mechanisms of the cell are functioning. Diffuse distribution of the sensor (image a) indicates that the cell is healthy and its protective mechanisms are working well. Appearance of sensor accumulations (green dots, image b) indicates that the cell is under stress. Cell nuclei are labeled in blue. The presence of an aggregating protein, mutant Huntingtin that is found in Huntington¹s disease (red dot, image c) also causes stress and compromises the cellular defence mechanisms, as shown by the sensor (green dot, image c).