Itaconate modulates immune responses via inhibition of peroxiredoxin 5, 2025, Tomas Paulenda et al

Hear hear.

His comment about the strong evolutionary conservation of IRG1 and its activity/products also struck me as interesting.

 

IRG1 encodes the protein that catalyzes itaconate production--they did an IRG1 knockdown to see if interferon beta production is dependent on itaconate, I believe.

The theory about itaconate regulating ROS is that most cells have fine tuned mechanisms that kick in when ROS ramp up [e.g. PRDX5] precisely because ROS are generally bad for cell function. However, macrophages kill pathogens via ROS, so they don't want these inhibitory mechanisms ramped up. If TLR4 is stimulated, IRG1 activity facilitates upregulation of itaconate, which has the ability to essentially block the ROS block. Meaning it lets ROS increase beyond what would normally be allowed in other cells so that the macrophages can use it for pathogen clearance

[Edit: the connection with interferon beta is that blocking-the-ROS-block seems to be the thing that enables interferon beta production. Other non-natural itaconate derivatives don't have this block-the-block action, therefore if you administer them to cells, you'll end up with an "anti-inflammatory" anti-ROS effect that is not seen with endogenous itaconate]

 

I guess one question I have from having looked at public cell expression databases, IRG1/ACOD1 is also highly expressed in Monocyctes. We know from Hanson et al in ME/CFS and Long Covid studies that a subset of monocytes have different genetic expression in patients vs controls. How does IRG1/Itaconate play a role in those cells before they mature into macrophages?

 

macrophages come from monocytes! (if they're not self-proliferating tissue-resident macrophages)

 

Please allow me to adjust some of the points.

1. You are absolutely correct. The problem arises especially when people use derivatives of itaconate and simply call it itaconate.

2. 2-Methyl succinct acid is not Irg1 inhibitor. Just like itaconate, it inhibits PRDX5, boosts IFNb production and inhibits inflammasome activation.

4. Natural itaconate by nature is not at all or poorly membrane permeable. But there are transporters that allow it to enter cells without the need of membrane-permeable derivatives.

 

This all is ongoing and experiments are running. I have reason to believe (I have experimental proof that is not yet perfect) Prdx3 is not affected. This opens huge avenue of novel research on multiple fronts. It remains to be seen, whether it is also in ME/CFS. I hope it does. But we need a hard proof. Otherwise it's just talking .

 

You don't want to use SDH inhibitors as therapeutics. They can be helpful in some cases. But one of the side effects is Alzheimers.

 

We did Irg1 knock-out. This is different from knock-down. In case of knock-down, you are decreasing protein expression by targeting mRNA. Usually efficiency around 50-90% decrease.

In the case of knock-out, you delete the gene encoding your protein in the animal. Resulting in a complete loss of protein expression in the animal or primary ccells.This is step above knock-down.

For the edit, derivatives of itaconate like DI or 4-OI induce NRF2. On one hand NRF2 is a pathway that induces antioxidant response. It gets triggered in presence of large quantities of ROS. It literally evolved after emergence of oxygen in the atmosphere and oceans. It is also known to inhibit IFNb. This is why there is inhibition in DI treated macrophages. And it is not only IFNb but also IL1b and IL6, that are inhibited by DI/NRF2.

 

Ah thank you, I misspoke.

Yes I'm familiar with the pathway from a rotation professor that was interested in CRISPR screens of homeostatic pathways. I've been looking into NRF2 since proteasome findings seem to come up repeatedly in ME/CFS. Initially I did not hold much confidence in those findings since, as a GO pathway, it tends to come up very often in the absence of other strong signals (at least in my work). However, since NRF2 is regulated by constant ubiquination, I'm now thinking that pre-existing differences in proteasome degradation may be related in some way as a triggering event. I am still trying to work out a testable hypothesis though, I'm just noting the possible connection

[Edit: glutathione was also found to be predictive pre-ME/CFS in a longitudinal study done by Leonard Jason's group when I was interning there, possibly pointing to something about ROS regulation as a common thread]

 

Yes, Irg1 is expressed in monocytes, macrophages, neutrophils and to some extent in dendritic cells.

My assumption is that the effect of itaconate we observe in macrophages will also work in monocytes. I don't doubt that Prdx5 and SDH will be inhibited by itaconate. If it will translate into immunoregulation as observed in macrophages has to be investigated.

 

Was not suggesting using it as a therapeutic! Just wondering aloud about potentially using co-IP or another method to determine if there is something differentially bound to SDH in ME/CFS vs control

 

I apologize, I misunderstood. How do you envision a role of adaptive immune system in the disease? Do you expect autoimmunity targeting neurons (cytotoxic T cells or autoantibodies)? If I'm not wrong that doesn't seem to be the case. Or something more like dysfunctional Treg cells leading to inappropriate reaction to a pathogen?

 

At the moment I only have speculation with a lot of unknowns. My suspicion does not rely on autoimmunity. Rather, I'm tossing around the idea of a feedback loop of metabolic reprogramming between adaptive and innate immune cells, in which interferon gamma release (or maybe another signal) would "prime" macrophages to some stimulus released during activity similar to your itaconic acid pretreatment, and some metabolite released by activated macrophages perpetuates metabolic reprogramming in lymphocytes to produce higher than normal levels of interferon gamma.

What I see in the literature is potential indirect evidence of malate-aspartate shuttle impairment, so I am thinking that the same metabolite released by macrophages would affect most neighboring cells, and potentially be present in low levels in the circulation to also affect lymphocytes.

Since a shift towards aerobic glycolysis seems to be required for interferon gamma production, I am wondering if a signal which continuously alters the TCA cycle (such as SDH impairment) in lymphocytes might be sufficient on its own to cause continued interferon gamma production in the absence of a de novo stimulus (or perhaps hyperreaction to normal stimuli). Obviously that would be a feedback loop that also exists in healthy people, so if such a loop exists, the question is whether there is something that normally blocks it after infection resolves so that healthy people aren't developing ME/CFS.

I do not currently have the resources to test this out myself and am just starting to formulate the idea, so I'd be happy to hear your insight if you have any.

 

Could inhibition of PRDX be the cause of red blood deformability problems observed in ME/CFS? Per Grok, PRDX2 seems to be important for maintaining RBC deformability.

 

I’m a bit late to this discussion and can’t access the full paper but from the “how did we get here” overview and ideas about crossovers with other theories people like @jnmaciuch have it sounds really interesting.

Look forward to the talk being available somewhere. Happy to help extracting and sharing the audio from the video it if that helps.