The fifth session of the ENCALS meeting focussed on the role of TDP-43 in ALS.
The first talk during this session was given by myself (Jakub Scaber, MRC/MND Association Lady Edith Wolfson Fellow, University of Oxford). I was given the opportunity to present neuropathological data from the Oxford Brain Bank.
Our study reaffirmed previous findings of the central role of TDP-43 pathology in C9orf72 cases as a common pathway between FTD and ALS cases. We were able to show that TDP-43 pathology at post-mortem correlated very well with the disease phenotype during life, more so than GA dipeptides and sense foci, which are direct pathological consequences of the hexanucleotide repeat. There was some increased GA dipeptide burden in disease-relevant areas of patient brains who had FTD during their lifetime, and sense foci were ubiquitously present in all cells. How the C9orf72 pathology and the later TDP-43 pathology are linked remains a key question in the investigation of this mutation.
The second talk was given by Dr Mario Sabatelli from the Istituto di Neurologia, Università Cattolica del Sacro Cuore from Rome. He showed published data as well as additional unpublished data from fibroblasts from familial and sporadic ALS patients. Different patterns of TDP-43 dysregulation were seen in fibroblasts from patient groups. Patients with TDP-43 and C9orf72 mutations showed increased overall TDP-43 but only TDP-43 mutant fibroblasts showed a reduction of TDP-43 in the nucleus. Interestingly, fibroblasts from SOD1 patients had markedly reduced overall TDP-43 levels. Even patients from sporadic ALS patients showed a redistribution of TDP-43 into the cytoplasm but no changes in overall protein levels. Moreover all mutant patient lines showed a staining for a phospho-TDP antibody, but there was only one band on western blot at 25kDa. While these striking results need to be replicated, they do show the potential of fibroblasts culture in modelling some aspects of ALS at a relatively low cost.
The third talk was by Eva-Maria Hock from the University of Zurich. In an exciting presentation, Eva-Maria showed the potential of mouse organotypic slice cultures in disease modelling on examples of hippocampal and cortical slices. These were currently taken from nontransgenic mice. The experiment had two key stages: firstly the slice cultures were spiked with synthetically produced urea-insoluble TDP-43/FUS oligomers followed by induction of stress states, (e.g. sorbitol). Slices spiked with FUS oligomers showed typical colocalisation between FUS and stress granule markers after 4 hours of sorbitol treatment but returned to normal at 8 hours. Slices spiked with TDP showed aggregation that was reminiscent of human aggregation and that resulted in the generation of detergent resistant-TDP after 3 weeks in culture. An interesting discussion included the significance of aggregation in TDP-43 models and future plans to look at mutant mouse models.
The fourth talk in this session by Marisa Feiler, from the University of Ulm. Marisa studied the question of cell to cell transmission using a very promising TDP-43-luciferase construct which luminesces upon aggregation. Using this construct together with primary mouse neurons growing in a microfluidic chamber she showed the results from multiple axonal studies showing both anterorgrade and retrograde transport and was able to show that fragments triggered oligomerisation.
The final talk was given by Professor Francisco Baralle, who was the biologist who first discovered the role of TDP-43 in splicing the cystic fibrosis transmembrane regulator gene and has since made major contributions to the field studying the TDP-43 transcription and regulation. After giving a wonderful overview of the field, he showed current unpublished data on the study of TDP-43 orthologue (TBPH) aggregation in a fly model overexpressing the most important protein interaction region of the gene. The flies had a disease phenotype as well as aggregates. Interestingly, in the mouse TBPH expression decreased with age, providing a potential “unmasking” explanation of the pathology in flies, as the pathology is present earlier. He showed how a fly model could be used for drug screening in the latter part of his presentations showing how drugs like Chlorpromazine and Nortryptilline could stimulate TDP-43 clearance in this model, at least at a biochemical level, as functional studies are still outstanding.
The presentations and the continuing interest in TDP-43 show how promising and exciting the research into this area of ALS continues to be and promises interesting findings and developments for the future.