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2021.04.26_Thesis_RemshaAfzal_HardBound.pdf (7 MB)

Investigating the Metabolic Role of Interleukin-10 in Inflammatory Macrophages

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posted on 2022-07-25, 09:12 authored by Remsha Afzal
Interleukin-10 (IL-10) is a pleotropic cytokine implicated in infection-associated immunopathology, autoimmunity, and allergy. It was tested as a potential therapeutic agent against several inflammatory and autoimmune disorders. However, systemic IL-10 administration proved to be of limited value, which indicated that its production needed to be carefully targeted in order to be efficacious therapeutically. Hence, research focus shifted on understanding the regulation of IL-10’s downstream targets, so they could be utilised instead in a more cell-specific approach to therapy.
Macrophages are regulated by the modulation of metabolic events, and can shift their functional status in response to their changing microenvironmental stimuli. The focus of this project was to investigate how IL-10 impacted on inflammatory macrophage metabolism and whether manipulating targets of IL-10 could result in a reduced inflammatory burden overall. Here, I uncover two targets of IL-10, both part of the arginine-polyamine pathway, as being attractive candidates for modulating macrophage polarisation. The first target, Spermine oxidase (Smox), is a catabolic enzyme of the polyamine pathway, which was upregulated in lipolysaccharide (LPS)-stimulated inflammatory macrophages, but was significantly inhibited in the presence of IL-10. Chemical inhibition of Smox in LPS-treated cells significantly reduced cytotoxicity, pro-inflammatory cytokine secretion, and reactive oxygen species (ROS) production.
The second target that is more extensively characterised in this thesis is the mitochondrial isoform of arginase, Arginase-2 (Arg2), which was significantly enhanced by the presence of IL-10 in LPS-stimulated murine and human macrophages. I demonstrated that Arg2 was essential for enhancing mitochondrial respiration in both quiescent and inflammatory macrophage cells. I further delineated that Arg2 enhanced macrophage mitochondrial respiration by enhancing the activity and assembly of a particular node of the electron transport chain at Complex II/Succinate dehydrogenase (Sdh). The product of Sdh, the metabolite fumarate, was found to be downregulated in Arg2–/– macrophages, while the substrate of Sdh, succinate was upregulated. This finding correlated with a significant increase in the expression of the transcription factor Hypoxia Inducible Factor-1α (HIF-1α) and the pro-inflammatory cytokine Interleukin-1β (IL-1β) in the Arg2–/– cells. Collectively, this is the first report of the Arg2 isoform affecting mitochondrial oxidative output in an immune cell type, which in turn modulates the overall inflammatory output of the cell.

Funding

Science Foundation Ireland ((SFI16/FRL/3855)

History

First Supervisor

Dr. Claire E McCoy

Second Supervisor

Dr. Jennifer K Dowling

Comments

Submitted for the Award of Doctor of Philosophy to the Royal College of Surgeons in Ireland, 2022

Published Citation

Afzal R,. Investigating the Metabolic Role of Interleukin-10 in Inflammatory Macrophages [PhD Thesis] Dublin: Royal College of Surgeons in Ireland; 2022

Degree Name

  • Doctor of Philosophy (PhD)

Date of award

2022-06-01

Programme

  • Doctor of Philosophy (PhD)

Research Area

  • Immunity, Infection and Inflammation