Molecular Mechanisms of RNA-binding Protein Dysfunction in Neurodegenerative Diseases

Our research focuses on the molecular mechanisms of neurodegenerative diseases, most notably ALS (amyotrophic lateral sclerosis), FTD (frontotemporal dementia) and Alzheimer’s disease (AD). These progressive, age-related diseases are an enormous burden for patients and family members. Existing therapies are designed to treat only the symptoms of disease and no therapies are available to slow down or stop disease progression. The main objective of our research is to obtain a molecular understanding of the mechanisms that drive these devastating disorders, to inspire new therapeutic approaches.

 

A common pathological hallmark of all neurodegenerative diseases is the accumulation of insoluble protein aggregates in degenerating brain areas. These protein deposits are found in neurons and glia cells and are intimately linked to the process of neurodegeneration. In ALS and FTD, which are clinically and genetically related diseases, the main aggregating proteins are the ubiquitously expressed RNA-binding proteins (RBPs) TDP-43 and FUS. TDP-43 aggregates occur in the majority of ALS and FTD patients, as well as in up to 60% of AD patients. In contrast, FUS aggregates are less common in ALS and FTD patients.

 

TDP-43 and FUS are usually found in the cell nucleus, where they regulate essential steps in RNA processing and DNA damage repair. However, in the affected brain region of patients, they instead aggregate in the cytoplasm of neurons and glial cells (Figure 1). This is thought to cause neuronal dysfunction and eventually neurodegeneration through a combination of loss-of-function and gain-of-function mechanisms, e.g. disturbed RNA processing and elevated DNA damage. Hence, key questions are: what drives the mislocalisation and aggregation of these RBPs in disease, and how one could potentially prevent or revert these pathological changes?






 

 

 

 

 

 

 

 

 

 

 

 

 

​
​

Previous research in our lab demonstrated that RBP mislocalisation and aggregation in disease are intimately linked to molecular defects in 1) nucleocytoplasmic transport, 2) control of phase separation and stress granules, and 3) post-translational modifications (PTMs) (Figure 2). This is based on our finding that mutations in the nuclear localisation signal or impaired nuclear import receptor function can disrupt the import of RBPs into the nucleus in ALS and FTD patients (Dormann et al., EMBO J 2010; Hutten et al., Cell Reports 2020). The RBPs are then mislocalised to the cytosol and accumulate in stress granules, which may give rise to pathological RBP aggregates through aberrant phase separation (Hofweber et al., Cell 2018; Alberti & Dormann, Annu Rev Genetics 2019). Moreover, we found that post-translational modifications (PTMs), e.g. FUS arginine methylation and TDP-43 phosphorylation, are misregulated in disease and can affect nuclear import, phase separation and aggregation of these RBPs (Dormann et al., EMBO J 2012; Hofweber et al., Cell 2018; Gruijs da Silva et al., EMBO J 2022). Interestingly, aberrant phase separation and disruption of nuclear transport and PTMs also appear to play a role in other neurodegenerative diseases, e.g. Huntington’s disease and Tauopathies associated with pathological aggregation of the microtubule-binding protein Tau. An important goal of our research is to understand these defects at the molecular level. By understanding the molecular basis underlying RBP mislocalization and aggregation, we hope to inspire new therapeutic approaches to treat neurodegenerative diseases.





 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

​​​​​​​​​​​​​​​​


​​

​

Research Aims and Questions

The primary aim of our research is to decipher the molecular mechanisms that underlie RBP mislocalisation and aggregation in the context of neurodegenerative diseases. We would also like to understand the physiological functions of neurodegeneration-linked RBPs, how they are regulated and how dysfunctional RBPs cause neurodegeneration. Our long-term goal is to understand the control mechanisms that maintain cellular stress resilience and protect against protein aggregation and neurodegeneration, thereby allowing healthy ageing.

 

We are interested in the following research questions:

​

(1) Role of the nuclear transport machinery in neurodegeneration and ageing:

Which cellular proteins require chaperoning by nuclear transport receptors in the cytoplasm and aggregate when transport receptors become limiting? How are the levels of nuclear transport receptors regulated in different cell types/during ageing? Can FUS and TDP-43 utilise alternative transport receptors, in addition to those that we know? How do different protein aggregates affect nucleocytoplasmic transport rates? Do they interact with and alter the nuclear pore complex?

 

(2) Phase separation of disease-linked proteins - functional relevance and control mechanisms:

How does phase separation affect the normal physiological functions of TDP-43 and FUS, e.g. RNA binding, RNA processing and DNA damage repair? Which binding partners and PTMs control phase separation of TDP-43 and FUS? How does the cellular protein degradation machinery (proteasome, autophagy) cope with aberrant RBP phase separation? Do proteins that co-aggregate in neurodegenerative diseases, e.g. TDP-43 and Tau in AD, influence each others phase separation and aggregation behavior? And finally, how exactly are phase separation and protein aggregation linked to each other?

 

(3) Post-translational modifications of neurodegeneration-linked proteins:

Which PTMs are found on TDP-43 and FUS under normal physiological conditions, versus during cellular stress and disease? How do altered PTMs, e.g. reduced FUS arginine methylation and TDP-43 hyperphosphorylation, arise in disease? How do disease-linked PTMs on TDP-43 and FUS affect their physiological localisation, function, macromolecular interactions and phase separation/aggregation behaviour? Can we modulate disease-linked PTMs to counteract RBP pathology?

 

 

 

​

Experimental approach

​

We study the complex, multifaceted pathomechanisms of RBP-related neurodegenerative diseases in a reductionist approach, based on in vitro reconstitution combined with cellular experiments. We use recombinant proteins, protein/RNA biochemistry and biophysics to dissect molecular events in vitro. We employ cell lines and neuronal cell culture models to study intracellular RBP behaviour using different imaging techniques (e.g. confocal microscopy, live cell imaging) combined with biochemical and cell biological methods and proteomics. Through collaborations, we also include animal models and human post-mortem brains in our research.

 

 

​

Recruitment

​

We are always looking for motivated students and postdocs to join us! We are an international, diverse and enthusiastic research group that loves science, teamwork and a good lab spirit.

Postdoc applicants are encouraged to contact Dorothee Dormann by email, including a CV, statement of research interests and the names of two referees.

PhD applicants please apply through the International PhD Program (IPP) of IMB Mainz International PhD Programme (IPP) or the International Max Planck Research School on Cellular Biophysics (IMPRS-CBP) https://imprs-cbp.mpg.de/.