Linking mitochondrial dynamics with neurotoxicity in yeast cell death models

Mitochondria are key organelles in programmed cell death. They constantly fuse and divide, and are subject to degradation and biogenesis. These processes influence neuronal dysfunction and cell death in neurodegenerative disorders. This project aims at a better understanding of the poorly investigated causal links between these processes. For this purpose an easy-to-handle and genetically tractable yeast cell system will be used, in which molecular mechanisms of programmed cell death, as well as of mitochondrial dynamics and turnover can be precisely analyzed. Our previous work revealed that expression of neurotoxic proteins in yeast result in programmed cell death with critical mitochondrial contribution. In this project, we will express different neurotoxic proteins associated with various neurodegenerative disorders: We will describe mitochondrial damage and the induction of mitochondrion-dependent cell death pathways. We will define the consequences on mitochondrial morphology and dynamics, and their role in executing cell death. We will investigate pathways of mitochondrial turnover, and dissect their role in providing cytotoxicity. We trust to elucidate novel cellular mechanisms of neurotoxic cell death in yeast, enabling the targeted validation of these concepts in other model systems for cell death in the human disorders.

Neurodegenerative disorders, such as Alzheimers or Parkinsons disease, are proteinopathies in which disease-specific neurotoxic proteins, such as the ß-amyloid peptide Aß42, the mutant ubiquitin UBB+1, or a-synuclein (aSyn) accumulate or aggregate, leading to neuronal dysfunction. Beside the formation of toxic protein oligomers/aggregates, common disease hallmarks encompass impairment of cellular protein quality control mechanisms and mitochondrial damage, whereas the different toxic proteins evoke these phenotypes to a different degree and by distinct means. In this project we aimed at a better understanding of the poorly investigated causal links between this processes during neurodegeneration. For this purpose, we employed various yeast and fly models for neurodegenerative diseases and combined them with both, genetic disruptions and genetic or pharmacological modulation of the aforementioned processes to identify causal molecular determinants. These experiments helped to narrow down the putative molecular effectors for each model, namely the ubiquitin- proteasome system and Cdc48/Vms1p-guided mitochondrial proteostasis for UBB+1, chaperone-mediated protein aggregate formation and their mitochondrial translocation for Aß42 and cellular Ca2+ homeostasis by the Golgi-resident ion pump Pmr1 as well as cell death execution by the mitochondrial protein endonuclease G for aSyn. In addition, we could show that administration of the naturally occurring polyamine spermidine, which declines continuously during aging in various species, alleviates a series of PD-related degenerative processes in the fruit fly Drosophila melanogaster and the nematode Caenorhabditis elegans. Given the fact that key results of our studies in model organisms could be corroborated by testing disease patient samples, our findings translated into potentially applicable, novel diagnostic tools.