The Project

Overall goal

The overall goal of the EMINA-2 consortium is to dissect the molecular pathophysiology of Chorea-acanthocytosis (ChAc) caused by mutations in the VPS13A gene as a model neuroacanthocytosis (NA) syndromes to provide novel drug targets for causative therapies.

 

Experimental approach

Human patient-specific induced pluripotent stem cells (hiPS) are believed to be an ideal human cell model of neurodegenerative diseases. These disease-specific iPS cells allow us to directly study all types of neuronal cells affected in ChAc. We will use ChAc-specific iPS-derived neurons, VPS13A/Chorein mouse-derived neurons, VPS13A/Chorein brain tissue as well as human brain specimens.

Recent findings in EMINA-1 have generated new insight into the mechanism(s) underlying erythrocyte deformation in ChAc, e.g. alterations in the band 3-mediated linkages between the cytoskeleton and the cell membrane. Many aspects of erythroid differentiation from hematopoietic stem cells can be recapitulated in in-vitro cultivation systems with generation of high numbers of erythroid progenitor cells under defined conditions. We have established these methods and also protocols for terminal differentiation into enucleated erythrocytes/reticulocytes.

Thus we will use in-vitro cultivated human erythroid cells and neurons as well as patient erythrocytes to gain more insights into the pathophysiology of the VPS13A/Chorein in morphological/cytoskeletal dysfunction. Additionally, we will further elucidate the signaling events involved in neuronal and erythrocyte dysfunction in ChAc to identify possible drug targets.

 

Epileptic seizures are an early symptom of ChAc. It is well accepted that seizure result from an unbalance between excitation and inhibition in different neuronal networks. It is therefore crucial to understand the changes in intrinsic properties as well as network activity in ChAc neurons. Reports of patients diagnosed with ChAc showed also an abnormal hypoperfusion. Although this might be the result of atrophy, one might consider vascular deficiencies as a cause and not an effect on this and other neurodegenerative deceases. These changes, both in structure and function of brain vasculature, have the potential to detrimentally alter the parenchymal homeostatic environment, leading to neuronal death and the accompanying unbalanced network activity. In the case of ChAc, there is an additional argument for considering this alternative as — in some cases — close to 50% of the erythrocytes are affected, likely imposing a serious concern on their ability to efficiently transport oxygen to the brain.

The goal is to characterize the networks properties of human-derived ChAc neurons and to understand the contribution of chronic hypoperfusion to neuronal network activity in a mouse model of ChAc.

 

An established Drosophila model for PKAN is available. The Drosophila VPS13 orthologue (dVPS13) has been identified. Different approaches will be used to mimic ChAc in Drosophila We will study the role of VPS13 in Drosophila models and the consequences of impaired VPS13 function at molecular, cellular, organismal and behavioral levels. Furthermore, candidate regulators found in above mentioned projects will be proven in this model organism by above mentioned techniques. All findings can be subsequently investigated in available mammalian models for ChAc or in patient material.