Host cellular defense against metabolic alterations induced by Helicobacter pylori vacuolating cytotoxin A

Persistent Helicobacter pylori (Hp) infection is the main risk factor for gastric adenocarcinoma in humans, which is a leading cause of cancer-related death world-wide. Hp infection poses a serious global biomedical problem as a human specific gastric pathogen that impacts half of the world’s population. How chronic Hp infection results in cancer development is not yet well-understood, largely due to the multi-factorial and complex nature of gastric cancer. Vacuolation cytotoxin A (VacA) is one of the major virulence factors of Hp that is secreted into the gastric environment. VacA fundamentally alters the function of the stomach and remodels the gastric environment through modifying host cellular metabolism. Upon internalization into gastric epithelial cells, VacA targets host mitochondria, where its pore-forming function dissipates the inner mitochondrial membrane potential and cripples the cellular ability to generate energy. This dissertation addressed the following major gap in knowledge: the mechanisms by which gastric cells escape cell death despite the long-term VacA-mediated mitochondrial dysfunction during Hp infection. Studies were performed to address the mechanism by which host cells detect and respond to intracellular VacA through the adenosine monophosphate (AMP)-activated protein kinase (AMPK) as a sensor of toxin-dependent alterations in cellular energy status. Activation of AMPK in response to VacA was demonstrated to orchestrate alterations in mitochondrial dynamics, which resulted in restoration of mitochondrial function. Specifically, upregulation of dynamin-related protein 1 (Drp-1)-dependent mitochondrial fission resulted in fragmentation of filamentous mitochondria and time-dependent reduction in mitochondrial-associated VacA, suggesting that mitochondrial fragmentation is important for removal of VacA from mitochondria. Cells with reduced levels of Drp-1 were more susceptible to VacA-dependent cell death, suggesting that mitochondrial dynamics is important for maintaining cell viability through the reduction in mitochondrial-associated toxin. Moreover, the studies here revealed the mechanism by which mitochondrial-associated VacA is trafficked to the degradative lysosomal compartment. In particular, the time-dependent loss of mitochondrial-associated and total intracellular VacA levels were dependent on an early endosomal marker, Rab5. The involvement of a component from the endocytic pathway in transporting pathogenic protein factors from mitochondria to lysosomes as a cellular defense tactic is a novel intracellular trafficking mechanism. Collectively, these studies supported a model that host cell modulation of mitochondrial dynamics is a direct response to VacA-dependent mitochondrial dysfunction, which enables for the reestablishment of cellular homeostasis that is required to prevent undergoing cell death. These studies provided insights into the cellular recognition of and responses to intracellular-acting toxin modulation of host cell function, which may be relevant for a growing list of pathogenic microbes that have been identified to target mitochondria as part of their virulence strategies.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Microbiology

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2023

Author dc:creator

• Seeger, Ami Y.

Contributors dc:contributor

• Blanke, Steven R
• Wilson, Brenda A
• Chen, Jie
• Kehl-Fie, Thomas E

• Helicobacter Pylori
• Vaca
• Mitochondrial Dysfunction
• Mitochondrial Dynamics
• Proton Motive Force
• Transmembrane Potential
• Mitochondrial Depolarization

Statement dc:rights

• Copyright 2023 Ami Seeger

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/122227

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F122227