Modulation of prostaglandin production by indole-3-pyruvate and 4-octyl itaconate in proinflammatory
Citation:
Diskin, Ciana, Modulation of prostaglandin production by indole-3-pyruvate and 4-octyl itaconate in proinflammatory, Trinity College Dublin.School of Biochemistry & Immunology, 2022Download Item:
Abstract:
The recent surge in immunometabolism research has revealed how specific changes in the level of metabolites can affect the immune response. One important feature of the immune response is the production of a class of lipid mediators termed prostaglandins (PGs). PGs exhibit a wide range of effector functions, many of which are proinflammatory. This is highlighted by the widespread and efficacious use of nonsteroidal anti-inflammatory drugs (NSAIDs), which inhibit PG production, to treat inflammation. In order to block PG synthesis, NSAIDs target the cyclooxygenase enzymes, of which there are two isoforms. COX1 is ubiquitously and constitutively expressed whereas COX2 is inducible by proinflammatory stimuli. Here I have investigated the impact of two metabolites with known immunomodulatory properties, indole-3-pyruvate (I3P) and 4-octyl itaconate (4-OI), on COX2 expression and PG production in macrophages.
I3P is one of several aromatic keto acids, which are derived from metabolism of amino acids and secreted by the bloodstream form of the protozoan parasite Trypanosoma brucei. T. brucei is the causative agent of the neglected tropical disease human African trypanosomiasis, also known as sleeping sickness. Trypanosomes have evolved many immune-evasion mechanisms and here I describe a novel immunomodulatory role for trypanosome-derived I3P. I have found that I3P inhibits the production of PGs from LPS-stimulated macrophages, while counterintuitively augmenting COX2 expression. I demonstrate that the I3P-mediated boost in COX2 levels is dependent on two distinct mechanisms. This increase is in part due to I3P relieving a negative feedback loop on COX2 by PGE2. Additionally, I3P activates the aryl hydrocarbon receptor, which can subsequently upregulate COX2 expression. However, the enhancement of COX2 expression is of little functionality as I also demonstrate that I3P directly inhibits COX2 activity to limit PG production. I3P thereby facilitates an evasion strategy by which T. brucei may modulate host PGs during infection, which is likely to be advantageous to the parasite.
I have also evaluated the impact that the itaconate derivative 4-OI has on COX2 and PG secretion. Itaconate synthesis occurs via conversion of the Krebs cycle intermediate cis-aconitate. This reaction is catalysed by the enzyme IRG1, which is potently upregulated in macrophages in response to TLR ligands. Both itaconate, and its derivative 4-OI, are known to exhibit a wide range of anti-inflammatory effects, many of which are dependent on its capacity to modify cysteine residues on protein targets. Here I demonstrate that 4-OI decreases PG production in proinflammatory macrophages. This reduction is due to a robust suppression of COX2 expression, with both mRNA and protein levels affected. As there was no difference in COX2 expression and PG production between Irg1+/+ and Irg1-/- macrophages, I have concluded that endogenous itaconate has no bearing on this pathway. Another Krebs cycle metabolite derivative, dimethyl fumarate (DMF), which shares a number of the immunomodulatory properties associated with 4-OI, also decreases COX2 expression and limits PG production. As both 4-OI and DMF are known to potently activate the master antioxidant transcription factor NRF2, I also demonstrate that the modulation of COX2 expression and PG synthesis by 4-OI and DMF is NRF2-independent. Furthermore, I have shown that both of these Krebs cycle derivatives induce the secretion of annexin A1 from macrophages, a protein that is known to elicit a plethora of anti-inflammatory functions.
Overall, I have identified novel metabolic modulators of PG production in macrophages. These findings have identified a potential immune evasion strategy by trypanosomes during infection, as well as providing novel insight into the potential of 4-OI as an anti-inflammatory agent.
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Author: Diskin, Ciana
Advisor:
Oneill, LukePublisher:
Trinity College Dublin. School of Biochemistry & Immunology. Discipline of BiochemistryType of material:
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