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

[jnmaciuch]

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]

 

[jnmaciuch]

Using metabolomics and isotopic labeling approaches, we elucidated the metabolic reprogramming in murine bone marrow-derived macrophages (BMDM) and RAW 264.7 cells throughout a time-course of LPS and IFN-γ stimulation, and determined the underlying mechanisms driving the metabolic transitions. We found that after an extended period (48–72h), macrophages transit into a unique metabolic and functional state that is distinct from what observed during the initial response to stimulation (6–24h) or in unstimulated (0h) macrophages.

In contrast to these persisting changes, many other metabolites showed drastic differences in early and late phases post stimulation. It is particularly intriguing that several important metabolites in, or immediately derived from, the TCA cycle, including citrate, succinate, succinyl-CoA, and itaconate, showed dynamic patterns similar to the production of the cytokines TNF-α and IL-6 - a profound increase after 6–24h of stimulation followed by a reduction, to levels similar to, or below, that in unstimulated macrophages (Figure 1c)

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]

 

[Creekside]

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.

 

[jnmaciuch]

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.

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.

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.

[Edited to remove a tangential point]

 

[jnmaciuch]

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.

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.

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.

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”.

 

[Utsikt]

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.

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

 

[jnmaciuch]

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.

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

[Edited to remove a tangential point]

 

[jnmaciuch]

Follow up question @Utsikt are you getting muscle stiffness as well?

[Edited to remove a tangential point]

 

[Utsikt]

Follow up question @Utsikt are you getting muscle stiffness as well?

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.

 

[Jonathan Edwards]

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.

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.

 

[jnmaciuch]

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.

[Edit: 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

 

[Utsikt]

Responding to a deleted post

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

 

[Utsikt]

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.

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

 

[jnmaciuch]

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.

 

[Utsikt]

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..

 

[Creekside]

How risky is testing cytokines at levels typically encountered due to exertion or viral infections? Imagine if someone did do those experiments and found that IL-14 (or whatever) reliably triggered PEM.

 

[Creekside]

My thought is that for milder pwME, exertion itself is the primarily “stimulation” for innate immune cell activation.

Yesterday I read an article on SciDaily about memory engrams affecting metabolism. That was about memories of cold response triggering metabolic stimulation. It made me wonder whether engrams could play a role in ME. Maybe a past response to a viral infection formed an engram that triggered the sickness behavior response, which thereafter responds to some similar immune system signal. I'm not pushing that as a theory, but it's an example of how interactions between subsystems in the body might be important. ME might involve a specific molecular interaction in some cells, but the conditions for that interaction to occur might involve brain circuits not using those cells and gut microbiome metabolites and how much chewing you did that day. I think it's more likely that ME will turn out to have that sort of complexity than a simple "this one gene is responsible" answer.

 

[jnmaciuch]

How risky is testing cytokines at levels typically encountered due to exertion or viral infections? Imagine if someone did do those experiments and found that IL-14 (or whatever) reliably triggered PEM.

We already know the effect of the interferon used for treating hepatitis, and it sounds very close to PEM (at least the experience of it, not the fact that it’s triggered by exertion afaik), but signaling molecules trigger other signaling molecules so you can’t really zero it down. Perhaps it’s not really important to narrow it down in the first place if it is likely a cumulative effect anyways

 

[Murph]

I'm always interested to see theories where LPS can trigger PEM-like symptoms. I have poor digestion and often digestive disturbances can leave me exhausted and very brainfogged.

I've come to think of that as leaky gut pushing LPS into the blood.

Duration is usually not as bad as PEM from exericse. The two can stack though.

 

[Creekside]

Perhaps it’s not really important to narrow it down

It might not identify the mechanism, but a reliable response from the majority of PWME would be valuable, if for nothing more than verifying that ME is biological rather than psychological. It needn't be a cytokine; I just think it's likely that a cytokine would affect ME symptoms. That's just my experience with immune activation of various types worsening my ME symptoms.