Date of Award
Doctor of Philosophy (PhD)
The specific and timely degradation of proteins is achieved by the Ubiquitin-Proteasome System (UPS), which governs a variety of cellular processes such as apoptosis, cell cycle progression, protein quality control, and metabolism. Using this system, cells maintain homeostasis by quickly and irreversibly altering signaling pathways in response to changing environmental stimuli. Protein degradation by UPS requires two consecutive steps, 1) the covalent attachment of the substrate by ubiquitin and 2) the delivery of the substrate to the 26S proteasome for breakdown and recycling of reusable ubiquitin. The 26S proteasome is a 2.5- MDa multicatalytic protease consisting of two subcomplexes: a 20S core particle (CP) and a 19S regulatory particle (RP) that caps one or both ends of the 20S proteasome. Most investigations on proteasome regulation have focused on substrate recognition, binding, deubiquitination, unfolding, and translocation. However, evidence shows that the 26S complex itself can be regulated by the abundance of available subunits, rates of assembly and disassembly, posttranslational modification, localization, and a variety of interacting proteins. Yet, this data is limited and an extensive amount of knowledge remains to be uncovered regarding 26S proteasome regulation since it differs depending on the tissue and cellular context. Aging, for example, leads to reduced proteasome activity but it is unknown how proteasomes are affected throughout the aging process. In this thesis, the aim is to reveal how proteasomes are regulated by changes in nicotinamide adenine dinucleotide (NAD+) metabolism and how this impacts neurodegeneration. Using Drosophila melanogaster, I describe the necessity for the proteasome regulator, DmPI31, in neuronal maintenance and show that dietary restriction and NAD+ repletion, can regulate both DmPI31 and proteasome activity. Generation of dmPI31 mutant clones in the Drosophila eye show rapid degeneration of photoreceptor cells and RNAi knockdown of DmPI31 leads to eclosion defects and shortened lifespan. I demonstrate the ability of NAD+ repletion to increase proteasome activity and DmPI31 protein levels and show NAD+ acts via DmPI31 to increase 26S proteasome activity. The importance of this pathway is illustrated by the finding that elevated levels of DmPI31 can extend lifespan and partially rescue neuronal degeneration in a Drosophila model of spinocerebellar ataxia type 1(SCA1). These results demonstrate a link between NAD+ and proteasomes that may ultimately prove useful for developing interventions that counter the effects of neurodegeneration and allow for an understanding why this system begins to fail in aging and age-associated diseases.
Jones, Sandra, "A Role for PI31-Mediated Proteasome Regulation in Proteostasis and Neuronal Health" (2018). Student Theses and Dissertations. 470.