Two-stage metabolic remodelling in macrophages in response to lipopolysaccharide and interferon-γ stimulation, 2020, Seim et al.

Two-stage metabolic remodelling in macrophages in response to lipopolysaccharide and interferon-γ stimulation

Gretchen L Seim, Emily C Britt, Steven V John, Franklin J Yeo, Aaron R Johnson, Richard S Eisenstein, David J Pagliarini, Jing Fan

Abstract

In response to signals associated with infection or tissue damage, macrophages undergo a series of dynamic phenotypic changes. Here we show that during the response to LPS and interferon-γ stimulation, metabolic reprogramming in macrophages is also highly dynamic.

Specifically, the TCA cycle undergoes a two-stage remodeling: the early stage is characterized by a transient accumulation of intermediates including succinate and itaconate, while the late stage is marked by the subsidence of these metabolites.

The metabolic transition into the late stage is largely driven by the inhibition of pyruvate dehydrogenase complex (PDHC) and oxoglutarate dehydrogenase complex (OGDC), which is controlled by the dynamic changes in lipoylation state of both PDHC and OGDC E2 subunits and phosphorylation of PDHC E1 subunit.

This dynamic metabolic reprogramming results in a transient metabolic state that strongly favors HIF-1α stabilization during the early stage, which subsides by the late stage; consistently, HIF-1α levels follow this trend.

This study elucidates a dynamic and mechanistic picture of metabolic reprogramming in LPS and interferon-γ stimulated macrophages, and provides insights into how changing metabolism can regulate the functional transitions in macrophages over a course of immune response.

Link | PDF

[Emphasis added]

 

The reason I'm interested in this is a possible time course that could potentially line up with PEM, [edit: and the idea that short term experiments looking at interferon gamma may not show its full long-term effect]

 

That might explain why some of us suffer only some hours of PEM, while others crash for days or longer. It might also explain why some people's thresholds for PEM lower after initial triggering.

I get the impression that many "experts" use overly simplistic models for biological processes. Cells aren't the equivalent of a engine with a simple fuel pump; that "fuel pump" is better modeled as a complex fuel delivery subsystem with a large number of computers involved it its function, fed by a large number of sensors, possibly interacting with each other, with various delays and memories. Yes, these individual subsystems might get reprogrammed at various times by various factors, so it's just not simple.

I wouldn't be surprised if after exploring this mechanism further, they find that chemicals from the gut microbiome play an important role too, and maybe memory of previous viral infections.

 

That’s exactly the thread I’m trying to pull. It seems like the cytokines that are most likely to be involved in things like muscle pain and (histological) inflammation (TNF-a and IL-6) are released early, and other cytokines seem to be released late.

My thought is that if something in pwME prevents that initial TNF-a and IL-6 in the early period, you may only be left with the signaling that occurs later. Stimulant usage shifted by PEM experience so that it started within a few hours of activity, and suddenly presented with muscle pain/stiffness/weakness when that never occurred before. Moreover, I no longer experienced the same delayed PEM symptoms unless I really kept pushing through initial PEM.

I am wondering if something about the stimulant allows that initial TNF-a and IL-6 response to go through whereas it normally would be blocked in ME. I’m also wondering if something about that early stage actually helps counteract that later response provided that I don’t keep stimulating it through activity, so that I don’t end up with general malaise delayed PEM anymore.

This theory could possibly explain the extreme inconsistency in cytokine profiles in pwME—if you’re selecting participants for delayed PEM, you might be selecting against TNF-a and IL-6. If your selection criteria allow more heterogeneity, you might get more of a mix.

This is why I’m very interested in a deep subtyping analysis that takes into account molecular profiles and all those little details about PEM.

 

Yes unfortunately that’s always the issue with in-vitro models. There are many things you can do in-vitro that you simply can’t do in animal models, but that comes at the expense of missing other effects at the systemic level.

It’s a great hypothesis. I’m wondering how much priming it takes before the immune system starts being constantly activated by LPS from gut bacteria. My thought is that for milder pwME, exertion itself is the primarily “stimulation” for innate immune cell activation.

But the more severe you get, the lower the threshold of activation, so gut bacteria may suddenly become a trigger when they would normally be ignored. Then you’re riling everything up both by minimal amounts of exertion and by just having microbes in your gut—things rarely get a chance to calm down and you’re stuck in near-constant “PEM”.

 

n=1, but I never get delayed (~24h+) PEM without pain and weakness.

 

That would be a good thing to poll about, possibly. Though my fear is that we’re all talking about subtly different things with the same words.

As it happens, I’m currently recovering from a bad delayed PEM episode caused by accidentally taking too little malic acid and letting it wear off in the middle of a long walk after cleaning my whole apartment. First time I’ve experienced that since pre-stimulant.

I definitely had muscle symptoms along with the general feeling of having the worst flu of my life, but it was qualitatively different than the “immediate PEM” muscle pain and stiffness I normally get with just a stimulant. I struggle to even put it into words—I only was able to notice a difference because I experienced both.

I feel like the only way we could accurately discern is by actually detecting the specific immune signals.

 

Follow up question @Utsikt are you getting muscle stiffness as well? That seems to be a predominant feature alongside pain and weakness in immediate PEM.

delayed PEM felt like everything hurt and I would collapse trying to get to the kitchen.

Immediate PEM feels like everything hurt and also is locked up. Like every movement comes with crackling as if I’m made of sytrofoam. I think I probably had some low level of that during delayed PEM but it wasn’t predominant.

 

No stiffness, but I struggle to move because it feels like the signals don’t do much. It’s like having to overcome a lot of inertia and wind resistance when I get it going.

I have some soreness, but that’s more like a flu ache and not like what you get from playing sports.

 

Do we need to posit an early TNF and IL-6 response? Why not have an interaction that just produces interferons? As far as I know there isn't any TNF or IL-6 much in muscle when you feel dreadful with flu.

 

Interesting, thank you. That might be a very relevant clue. I’ll look into the literature though this might end up being a question that can only be solved by injecting individual cytokines and my institutional review board will probably have some things to say about doing that to myself

[edit: joking! for anyone concerned I’m not planning to start injecting random things into myself]

 

I’m only interested in them because of my experiences with “immediate” PEM primarily characterized by muscle pain and stiffness without the flu-like malaise of delayed PEM.

[edit: also the fact that, if I’m remembering correctly, those two have been associated with exercise-induced inflammatory responses with healthy people. So something can clearly get triggered by exertion alone, but something else may cause it to look very different in pwME and to be triggered by much less activity than high intensity cardio]

 

And here I was hoping that you’d take one for the team and do a Marshall!

I remember discussing the inertia thing with Yann somewhere recently, I’ll see if I can find it again.

 

Unfortunately if you suggest drawing your own blood on the spot one too many times in a research setting, people tend to ask a lot of extra questions about why you need those syringes

I’m certainly not against trying it myself—I believe someone else linked a study somewhere about this exact thing being tested out to explain viral myalgia—but it would have to be in the context of an actual study where I and other participants are monitored and there’s a lot of input from medical professionals in the study design.

 

Found it:
https://www.s4me.info/threads/a-thought-experiment-on-muscles.43407/page-13#post-602922

 

Thanks for linking that. Between this and the description of the poisoned feeling that many have shared, part of me has been suspecting transient lactic acidosis or hyperammonemia for a while. I don’t think it would be nearly to the extent of a renal or liver crisis, for example, but I have seen reports elsewhere from pwME that it tended to be accompanied by increased urination and thirst and relieved by IV saline.

It would be exactly in line with all the other metabolic theorizing I’ve been doing. Only problem is that to confirm it, I’d need to be able to run to someone’s home exactly when they’re experiencing it to do a blood draw. I suppose if it’s happening in some milder people as well, it could be triggered in a lab setting and then you’d have them wait around until they confirm the feeling.

 

We really need those dedicated beds for ME/CFS patients..