All ETDs from UAB

Advisory Committee Chair

James H Meador-Woodruff

Advisory Committee Members

Scott Wilson

Vlad Parpura

Lori L McMahon

Yogesh Dwivedi

Document Type

Dissertation

Date of Award

2019

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Protein homeostasis is an emerging component of schizophrenia (SZ) pathophysiology. Proteomic alterations in SZ are well-documented; however the underlying mechanism driving these changes remains unknown. The ubiquitin proteasome system (UPS) is fundamental to protein homeostasis regulation, and UPS transcript abnormalities in both blood and brain have been observed in SZ. Supporting a role for UPS dysfunction in SZ, we have reported decreased protein expression of ubiquitin-associated proteins in SZ brain. However, previous work on the proteasome has been limited to transcript expression. In the following studies we sought to address this gap in knowledge by characterizing proteasome dysfunction in the STG of SZ subjects. We first measured protein expression of various proteasome subunits associated with different complexes in 14 pairs of comparison and SZ subjects, followed by assaying enzymatic activity associated with the proteasome (chymotrypsin-, trypsin-, and caspase-like) in 25 SZ and 25 comparison subjects using flourogenic substrates. As localization regulates which cellular processes the proteasome contributes to, I measured proteasome activity and subunit expression in fractions enriched for nucleus, cytosolic, and membrane compartments. I observed decreased expression of 19S RP subunits and trypsin-like activity in cortical homogenates of SZ subjects. Trypsin-like activity was also decreased in the nucleus-enriched fraction and was not associated with changes in proteasome subunit expression. Interestingly, both chymotrypsin-like activity and protein expression of 19S RP subunits, which facilitate ubiquitin-dependent degradation, were decreased in the cytosol-enriched fraction of SZ subjects. While this implicated reduced expression of 26S proteasome complexes, I did not observe differences in either complex expression or complex-specific chymotrypsin-like activity in the same cohort of SZ subjects. Our findings of intracellular compartment-specific proteasome dysfunction implicate dysregulation of protein expression both through altered ubiquitin-dependent degradation of cytosolic proteins and regulation of protein synthesis due to degradation of transcription factors and transcription machinery in the nucleus. Together, these findings implicate proteasome dysfunction in SZ, which likely has a broad impact on the proteomic landscape and cellular function in the pathophysiology of this illness.

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