Development of a new method for the characterization and quantification of protein accumulation in ALS

ALS Research Results by Christopher Secker, Press Release April 2018

Summary of the research results on ALS

“In approximately 95% of ALS patients, the protein TDP-43 is deposited in the brain and spinal cord regions affected by neurodegeneration. This protein is suspected to be significantly involved in the progress of ALS. In a research project, Christopher Secker has developed a new test method that can be used, among other things, to study the accumulation of the TDP-43 protein.”

In approximately 95% of ALS patients, the RNA-binding protein TDP-43 is deposited in the brain and spinal cord regions affected by neurodegeneration, especially where the motor neurons are located (motor cortex, anterior spinal horn). It forms an insoluble accumulation in the cell body of neurons, which is not or only rarely found in healthy individuals.

 

It is now known that these insoluble protein species, like prion proteins of prion diseases and also protein deposits found in other neurodegenerative diseases such as Parkinson’s, Alzheimer’s, Huntington’s, are able to induce the accumulation of soluble, yet functional TDP-43 proteins. On the one hand, this means that the TDP-43 can no longer sufficiently perform its natural function and, on the other hand, heavy deposition of misfolded proteins burdens and damages other vital processes in the affected cells.

 

The insoluble TDP-43 protein species in the neurons affected by protein deposition are also delivered to their immediate environment, as well as along their nerve fiber connections. When other cells pick up these misfolded proteins, they induce the accumulation of soluble TDP-43. A common hypothesis is that this spread of insoluble TDP-43 protein species across the central
nervous system plays an important role in the progression of ALS.

 

On September 1, 2016, a research project to fundamental research started at ALS in cooperation with the Max DelbrĂĽck Center for Molecular Medicine (MDC, Erich Wanker working group) in Berlin and the German Center for Neurodegenerative Diseases (DZNE, Harald PrĂĽĂź working group). The project is designed for five years and investigates the harmful protein deposits (protein aggregations) in nerve cells in the ALS. Part of this research project is done by Christopher Secker, an experimental physician who has already worked on protein deposits in Alzheimer’s disease at the MDC in Berlin. He brings his research and methodological knowledge of experimental medicine acquired in Alzheimer’s research into fundamental ALS research and develops it further in relation to ALS.

 

Together with the research group, he has developed a novel test method that can be used to study the accumulation of the TDP-43 protein and the induction of already misfolded proteins on the soluble protein. For this purpose, TDP-43 proteins or their aggregating, C-terminal fragments are coupled to two different fluorescent proteins. Thus, the aggregation of the initially soluble proteins can be tracked over time by energy transfer from one TDP-43 protein to another (Förster Resonance Energy Transfer – FRET). The stronger the accumulation and the less soluble the TDP-43, the stronger the signal becomes. In addition, the group investigates the influence of already misfolded ALS proteins on the accumulation of soluble TDP-43 proteins in order to better understand the process of induced misfolding.

 

The aim of this approach is to characterize the dynamics of protein malformations in ALS and to evaluate whether this method can be used to measure the burden of already misfolded TDP-43 proteins in affected patients. This could act as a biomarker to biologically monitor the course of the ALS disease and, in particular, help test new drugs in studies to assess the effect of the tested substances on the deposition of these proteins.

 

As this innovative test method is also high-throughput-compatible and it can also be (partially) automated on a larger scale, the research team also tests entire compound libraries to identify potential drugs that can prevent the misfolding and accumulation of the TDP-43 protein.

 

Figure 1: Tracking of TDP Accumulation using atomic force microscopy (left). The developed test method can reliably measure the misfolding and accumulation over time.

 

Figure 2: A cell affected by TDP protein deposition under the microscope. Using this cell-based test system, we investigate the molecular causes of protein misfolding and identify possible starting points for a causal therapy of ALS.