Dissertation
The Golgi under distress: unraveling cytokine-mediated Golgi remodeling and its role in early β-cell dysfunction in type 1 diabetes
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2025
DOI: 10.25820/etd.008162
Abstract
Type 1 Diabetes (T1D) results from autoimmune-mediated destruction of pancreatic β-cells. Currently, no long-term treatments have been successful in preventing disease. Emerging evidence highlights the β-cell as an active participant in T1D development, yet how the β-cell contributes to its own demise remains a critical knowledge gap in the field. Our recent work demonstrates that proinflammatory cytokines, interleukin-1β (IL-1β), tumor necrosis factor-α (TNF-α), and interferon-γ (IFN-γ), substantially disrupt β-cell Golgi structure and function in mouse, rat, and human β-cells, which may explain early defects in β-cell secretory function that occur prior to clinical onset of T1D. The structural modifications include Golgi compaction and, in some instances, loss of the inter-connecting ribbon leading to Golgi fragmentation. Using publicly available TEM datasets, we further show that Golgi alteration is a progressive and persistent feature of human T1D disease. We demonstrate that cytokine-mediated Golgi alterations are inducible nitric oxide synthase (iNOS) dependent and are the result of iNOS driven mitochondrial dysfunction, and the inability of β-cells to switch their energy production from TCA metabolism to anaerobic glycolysis. This metabolic inflexibility provides an important clue to the specificity of iNOS-mediated β-cell damage compared to other islet cell types. Importantly, Golgi structural changes coincide with decreased cell-surface glycosylation and improper secretion of cathepsin D, which has been documented in human diseases with altered Golgi structure but is yet to be reported in T1D. Our data also demonstrates knockdown (KD) of GRASP55, a key Golgi structural protein, can substantially block Golgi fragmentation during cytokine stress. Interestingly, we also show that multiple cytokines are necessary to elicit Golgi remodeling, indicating a cytokine signaling network is driving the observed changes. Collectively, our data demonstrate that β-cell Golgi structure is uniquely susceptible to proinflammatory cytokine mediated Golgi structural alteration and dysfunction, which could provide insight into the β-cell specific destruction observed during T1D pathogenesis. This data further suggests that Golgi disruption could provide a source for neo-antigenic generation with altered cell-surface protein-glycans and altered protein secretion. Further studies are necessary to determine the mechanisms of how NO and GRASP55 mediate Golgi remodeling and how these relate to the pathways driving altered protein glycosylation and secretion. Ultimately, this work advances understanding of proinflammatory cytokine mediated β-cell damage and provides critical insight into β-cell contributions early in T1D etiology.
Details
- Title: Subtitle
- The Golgi under distress: unraveling cytokine-mediated Golgi remodeling and its role in early β-cell dysfunction in type 1 diabetes
- Creators
- Sandra E. Blom
- Contributors
- Samuel B Stephens (Advisor)Ling Yang (Committee Member)D. Thomas Rutkowski (Committee Member)Vitor A Lira (Committee Member)Yumi Imai (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Biomedical Science (Molecular Medicine)
- Date degree season
- Summer 2025
- DOI
- 10.25820/etd.008162
- Publisher
- University of Iowa
- Number of pages
- xviii, 151 pages
- Copyright
- Copyright 2025 Sandra E. Blom
- Language
- English
- Date submitted
- 07/25/2025
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (pages 132-151).
- Public Abstract (ETD)
Blood sugar is tightly regulated by the hormone insulin, which is produced by cells in the pancreas called ?-cells. Type 1 diabetes (T1D) is a disease that results from autoimmune destruction of these cells. As these cells are the only source of insulin in the body, this results in life-long insulin dependence, demonstrating the critical need to understand why these cells are mistakenly targeted in T1D. Currently, there are no treatments preventing T1D. While it was originally thought that the ?-cell is an innocent bystander in this destruction, recent research suggests ?-cells may actually play a role in their own destruction. However, how they may contribute to T1D development is not known. Part of the initial damage to the ?-cells during T1D development is the production of immune proteins called cytokines which are linked to inflammation and direct immune cell activity. Cytokines have been shown to cause ?-cell damage and loss of function. The goal of my thesis work is to understand how cytokines affect the ?-cell Golgi, which is the part of the cell responsible for packaging and shipping proteins such as insulin.
I have identified that cytokines cause the structure of the Golgi to change. Golgi structure is very specific for its function, and changes to Golgi structure have been shown to disrupt function. Importantly, cytokines cause ?-cell damage through production of a chemical called nitric oxide (NO), and I found that Golgi structural changes were dependent on NO production. NO damages the energy generation center of the cell called the mitochondria. ?-cells can only use mitochondria for energy while other cells have back-up energy generating methods. This could explain why ?-cells are the only cells destroyed during T1D. Many of the early problems in ?-cell function can be linked to Golgi activities. To this end, I also found that cytokines cause changes in protein processing and sorting, which are functions associated with the Golgi. This results in the possibility that different versions of proteins may be visible to the immune system than normal and could influence immune activity.
Golgi structure is maintained by many proteins; one protein specifically is GRASP55. I found that GRASP55 controls, in partnership with NO, cytokine induced changes in Golgi structure. In short, my work shows that cytokines cause damage to ?-cell Golgi structure that results in disrupted Golgi function, and that the changes in structure are controlled by NO and GRASP55. How GRASP55 and NO work together to regulate changes in Golgi structure is not known, but understanding these changes in structure and function could help to create better treatments to prevent and stop T1D development.
- Academic Unit
- Biomedical Science Program
- Record Identifier
- 9984948238302771
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