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Studies of VAPB and TDP-43 in neurodegeneration

Student thesis: Doctoral ThesisDoctor of Philosophy

The aggregation of TDP-43 in the cytoplasm of motor neurons is a hallmark pathology in many sporadic and familial cases of amyotrophic lateral sclerosis (ALS). A mutation in the protein VAPB at proline 56 (VAPB P56S) was identified as the causative mutation for ALS type 8 and transgenic mice expressing VAPB P56S develop TDP-43 pathology. VAPB has been proposed to be involved in ER stress and the unfolded protein response (UPR) suggesting that disruption of these pathways may play a role in the pathogenesis of ALS.
Previous work has not clearly identified the function of VAPB in the UPR. Additionally, the mechanism underlying the development of TDP-43 pathology in mice expressing mutated VAPB has not been identified. In this thesis, the role of VAPB and the effects of the pathogenic VAPB mutation in the UPR and the mechanisms behind TDP-43 pathology in relation to ER stress and VAPB P56S expression were investigated in detail. Additionally, the dynamic relationship between ER and mitochondria, for which VAPB is crucial, was studied.
The studies presented here reveal that both VAPB and VAPB P56S can induce the UPR. Conversely, siRNA mediated knockdown of VAPB decreased the UPR. Moreover, UPR induction triggered by increased ER stress promotes processing of TDP-43 into C-terminal fragments. Interestingly, overexpression of VAPB P56S induces the mislocalisation of TDP-43 from the nucleus to the cytoplasm but does not directly mediate the processing of TDP-43 into C-terminal fragments.
Finally, studies presented here provide evidence for the involvement of VAPB in the formation of dynamic connections between the ER and mitochondria, which is regulated by direct interaction of VAPB with the mitochondrial protein PTPIP51. These experiments show that the VAPB-PTPIP51 interaction can be regulated by the kinases GSK3β and ERK 1/2. This thesis provides novel insights into the function of VAPB and into possible mechanisms by which mutations in VAPB may be causative for ALS type 8.
Original languageEnglish
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Award date2015

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