The role of the endoplasmic reticulum and protein disulphide isomerase in Amyotrophic lateral sclerosis

Submission note: A thesis submitted in total fulfilment of the requirements for the degree of Doctor of Philosophy to the School of Psychology and Public Health, Faculty of Science, Technology and Engineering, La Trobe University, Bundoora, Victoria, 3086, Australia.

Thesis with publications.

Amyotrophic lateral sclerosis (ALS) early pathogenesis is associated with endoplasmic reticulum (ER) stress that is linked to the accumulation of misfolded proteins in the ER. Thus the primary aim of this thesis was to investigate cellular trafficking mechanisms associated with ER stress. The secondary aim of this thesis was to examine protein disulphide isomerase (PDI), an ER chaperone that is upregulated as a protective response to ER stress, by exploring potential binding partners of PDI as well as the therapeutic value of a PDI mimic. The first study examined ER-Golgi transport inhibition in ALS-linked mutations in superoxide dismutase 1 (SOD1), fused in sarcoma (FUS) and transactive response (TAR) DNA-binding protein 43 (TDP-43). Transport from the ER to the ER-Golgi intermediate compartment (ERGIC) was not affected in mutant SOD1 expressing cells, while mutant TDP-43 and FUS were found to inhibit ERERGIC transport and to be associated with ERGIC disorganisation. This suggests that mutant TDP-43 and FUS inhibit an earlier stage of ER-Golgi transport than mutant SOD1. Rab1, a molecular switch that regulates ER-Golgi trafficking, was found to form aggregate-like structures that colocalised with TDP-43 in a proportion of spinal cord motor neurons from ALS patients. The second study found that ALS-linked UBQLN2 mutations inhibited ER-Golgi transport and were associated with ER stress, ERGIC disorganisation, Golgi fragmentation and autophagy dysfunction. In the third study, apolipoprotein AII (apoA-II) was found to be a potential binding partner of PDI in the spinal cords of ALS patients and to SOD1 in cells expressing mutant SOD1, suggesting lipid transport dysfunction in ALS. In the final chapter the therapeutic efficacy of PDI mimic compound 35 was examined in the SOD1G93A mouse, but was found to be ineffective potentially due to the poor solubility of the drug. In conclusion, the main finding of this thesis is that disruption of trafficking in the early secretory pathway is associated with the pathogenesis of ALS.