Dissertation
Francisella Tularensis infection uncovers a link between neutrophil metabolism and apoptosis
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Summer 2022
DOI: 10.25820/etd.006524
Abstract
Francisella tularensis is the etiological agent of tularemia, one of the most infectious pathogens known and one of few pathogens capable of infecting host neutrophils (polymorphonuclear leukocytes; PMNs). PMNs are vital innate immune cells that undergo constitutive apoptosis 24 hours after entering circulation, and disruption of this tightly regulated process leads to an impaired immune response that is incapable of resolving infection. Our laboratory discovered that Francisella tularensis delays human PMN apoptosis by inhibiting the intrinsic, extrinsic, and phagocytosis-induced cell death pathways, but the mechanisms by which this is achieved are not fully understood.
We demonstrate here that metabolic reprogramming of neutrophils, including induction of glycolysis, is an important and previously unappreciated aspect of neutrophil longevity. Specifically, our data indicate that Francisella-infected PMNs released significantly more lactate and upregulated expression of genes encoding glucose transporters and 10 of 11 glycolytic enzymes. Direct measurements made using a Seahorse XF analyzer demonstrate that glycolysis (measured as the extracellular acidification rate) nearly quadrupled, and glycolytic capacity doubled by 12 hours after Francisella infection. Inhibition of glycolysis or glucose uptake using 2-deoxy-D-glucose or WZB-117 blocked the ability of Francisella tularensis to delay PMN apoptosis, thus confirming that these processes are mechanistically linked. Intriguingly, Francisella-infected PMNs also contained significantly more glycogen than their uninfected counterparts. Furthermore, inhibition of glycogen breakdown with the glycogen phosphorylase inhibitor CP-91149 was sufficient to delay uninfected PMN apoptosis and significantly enhanced the apoptosis delay in Francisella-infected PMNs. Finally, we show that treating PMNs with the pan-caspase inhibitor Q-VD-OPH not only caused delayed apoptosis, but also significantly upregulated glycolysis and glycogen content, further supporting the hypothesis that PMN metabolism and lifespan are fundamentally linked.
p38 mitogen-associated protein kinase (MAPK) and class IA phosphoinositide-3 kinase (PI3K) influence PMN lifespan in a stimulus-specific manner, and also have established roles as glycolytic regulators. Our laboratory demonstrated that inhibition of p38 MAPK or PI3K signaling blocks Francisella-mediated apoptosis delay, and we hypothesize that Francisella-mediated glycolytic upregulation is mechanistically linked to extension of PMN lifespan by host p38 MAPK and PI3K signaling.
Details
- Title: Subtitle
- Francisella Tularensis infection uncovers a link between neutrophil metabolism and apoptosis
- Creators
- Samantha Jo Krysa
- Contributors
- Lee-Ann H. Allen (Advisor)Anil K Chauhan (Committee Member)Jason H Barker (Committee Member)Hasem Habelhah (Committee Member)Matthew Potthoff (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Biomedical Science (Molecular Medicine)
- Date degree season
- Summer 2022
- Publisher
- University of Iowa
- DOI
- 10.25820/etd.006524
- Number of pages
- xxvi, 132 pages
- Copyright
- Copyright 2022 Samantha Jo Krysa
- Language
- English
- Description illustrations
- illustrations (some color)
- Description bibliographic
- Includes bibliographical references (pages 120-132).
- Public Abstract (ETD)
Many kinds of bacteria invade the human body every day and the immune system protects the body against infection or illness from these bacteria. The immune system is composed of various types of cells, and one important cell type for preventing infections is the neutrophil. Neutrophils are on the front lines defending the body, meaning they are one of the first cells to recognize invading bacteria. Neutrophils eat and kill the bacteria with toxic compounds, and once they have fulfilled this function, neutrophils die and are subsequently eaten by another type of immune cell, the macrophage. Macrophages consume neutrophils after they die to prevent the toxic compounds contained inside neutrophils from leaking out and damaging the body’s tissues.
However, some bacteria that are eaten by neutrophils are able to avoid being killed, which prevents neutrophils from fulfilling their function, ultimately preventing the neutrophils from dying and hindering resolution of the infection. Francisella tularensis is one of few bacteria capable of blocking neutrophil function, preventing neutrophils from dying, surviving and hiding inside neutrophils to avoid detection from other immune cells.
We believe that infection with Francisella tularensis may be changing how certain components inside the neutrophil are interacting with each other, a process referred to as “signaling”. We also believe that infection changes neutrophil metabolism, and the combined changes in signaling and metabolism are extending neutrophil lifespan. The goal of this research is to understand how Francisella tularensis prevents neutrophils from dying by examining how the signaling and metabolism inside the neutrophil changes following infection. This work establishes that signaling and metabolism are both altered in neutrophils infected with Francisella tularensis, and these changes are required for the neutrophils to be able to live longer. These data provide insight into the mechanism by which Francisella-infected neutrophils evade death, and are among some of the first to establish that neutrophil metabolism and lifespan are intimately linked.
- Academic Unit
- Biomedical Science Program
- Record Identifier
- 9984285248602771
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