Inactivation of ATG13 stimulates chronic demyelinating pathologies in muscle‑serving nerves and spinal cord, 2025, Drosen et al.

[InitialConditions]

Abstract
Chronic muscle fatigue is a condition characterized by debilitating muscle weakness and pain. Based on our recent finding to study the potential effect of mTOR on ATG13 inactivation in chronic muscle fatigue, we report that biweekly oral administration with MHY1485, a potent inducer of mTOR, develops chronic illness in mice resulting in severe muscle weakness. As a mechanism, we observed that MHY1485 feeding impaired ATG13-dependent autophagy, caused the infiltration of inflammatory M1 macrophages (Mφ), upregulated IL6 and RANTES by STAT3 activation, and augmented demyelination in muscle-serving nerve fibers. Interestingly, these mice displayed worsened muscle fatigue during 2-day post-treadmill exercise, suggesting the critical role of chronic mTOR activation in potential PEM pathogenesis. Interestingly,
ATG13-repressor mice exhibited enhanced infiltration of M1Mφ cells, STAT3 activation, demyelination of nerve fibers, and PEM-like symptoms, suggesting the potential role of ATG13 impairment in post-exertional fatigue.

Link: https://link.springer.com/article/10.1007/s12026-024-09557-7
PDF: https://link.springer.com/content/pdf/10.1007/s12026-024-09557-7.pdf

 

[Mij]

Congrats to the entire team
@RedefiningMECFS
and
@AvikRoy74969264
on this breakthrough paper describing a disease-relevant model of PEM Here, we show that chronic mTOR activation disrupts autophagy function, leading to PEM and the production of IL-6 and RANTES via STAT3 phosphorylation!

https://twitter.com/user/status/1876635872633778616


re metformin

Yes. Perhaps even in combination with low dose rapamycin.
https://twitter.com/user/status/1876661323188126101

 

[Ash]

If we have something demyelinating wouldn’t this have been found before, or would it be hard to find/see?

 

[Turtle]

I already use metformin for diabetes II and it does nothing special for me in PEM.
My PEM is sore muscles, more fatigue and more brainfog, no flu like symptoms.
Metformin did shorten the muscle pain after excertion (groceries) from 4 days to 2 days.
But that does not seem to work for everyone.

 

[Murph]

I find this very interesting because of an effect I've noticed when i'm on a diet: high risk but slow-building benefit.

if i reduce my food intake, I risk acute energy shortage if I push too hard, and that can cause PEM. However, if I succesfully avoid that acute problem, the calorie restriction periods seem to correlate with better health and a bigger PEM threshold.

I've wondered if maybe I usually eat a lot to avoid blood sugar variations that can spark PEM, but if I avoid eating a lot, perhaps I can stop activating mTor and slowly be better off overall. I'd like to go on metformin to see what happens.

 

[Hutan]

I think this is going to be a really interesting paper and I'm look forward to reading it.

The first paragraph is not quite right though:

ME/CFS is a chronic inflammatory disease characterized by severe muscle fatigue, pain, and cognitive impairment [1]. The most reliable pathological symptom of ME/CFS is post-exertional malaise (PEM) [2], which is persistent muscle fatigue and pain after treadmill exercise [3, 4]. Sometimes, the post-exertional fatigue becomes so severe that the patient remains bedridden for a long time [6]. However, until now, the molecular mechanism of PEM is poorly understood, primarily due to the unavailability of a reliable disease model that successfully displays PEM pathology after treadmill exercise.

ME/CFS is a chronic inflammatory disease

We don't know that ME/CFS is an inflammatory disease.

The most reliable pathological symptom of ME/CFS is post-exertional malaise (PEM) [2], which is persistent muscle fatigue and pain after treadmill exercise [3, 4].

I would not characterise PEM as "persistent muscle fatigue and pain after treadmill exercise". For a start lots of people have PEM but have never been on a treadmill in their life. 'Treadmill exercise' is not a requirement for PEM. Also that definition makes it sound as though the fatigue starts immediately after exercise, when a defining feature of PEM is that there is a delay.

Upon treadmill exercise, patients are often reported to have a “crash” or “collapse” with severe and prolonged mental and physical tiredness [5, 6].

That sentence also makes it sounds as though PEM happens during or immediately after treadmill exercise. I don't know why the authors would say that patients are often reported to have a crash. Could they not have just said that patients have a crash? 'Often reported to' suggests that there is there some doubt as to whether the patients do or not. Also, PEM is not 'prolonged mental and physical tiredness'.

Sometimes, the post-exertional fatigue becomes so severe that the patient remains bedridden for a long time [6].

PEM is not just post-exertional fatigue; fatigue is not the only thing keeping people bedridden. A person in bed with ME/CFS doing nothing might not even have fatigue, or certainly not severe fatigue; it's just that if they do something other than lie in bed they may get a whole range of horrible symptoms.

However, until now, the molecular mechanism of PEM is poorly understood, primarily due to the unavailability of a reliable disease model that successfully displays PEM pathology after treadmill exercise.

I think it's a stretch to say that the molecular mechanism of PEM is poorly understood primarily because of the lack of a reliable disease model.

I'm grateful for the work of this team. But, why don't they have an expert patient or three on board to help them avoid mis-statements like these? If they want someone, I'm sure we could find someone to help.

 

[Hutan]

Graphical abstract

Recently, our research [7] identified that ATG13, an early autophagy protein, was phosphorylated and elevated in the serum of a small cohort (n=10) of ME/CFS patients, sug- gesting a potential role of ATG13 inactivation and subsequent autophagy impairment in ME/CFS.

 

[Hutan]

So, on the left hand side of the figure above, mTOR is inactivated, which allows for autophagy (the clean up of damaged or redundant molecules in the cell, essentially intracellular recycling), which makes for healthy muscle function.

Therefore, in our cur- rent paper, we attempted to make a drug-induced mouse model with a chemical induction of mTORC1 by the compound MHY- 1485. MHY-1485 is a potent cell-permeable mTOR activator [12, 13] that targets the ATP domain of mTOR.

They fed a compound - MHY-1485 - to mice in order to activate mTOR. The activation of MTOR has some flow on effects that the authors propose leads to ME/CFS-like muscle problems, including the inactivation of ATG13. So, that relates to the top and centre right hand side of the figure.

A dose-dependent feeding study followed by a bilateral EMG recording analysis demonstrated that oral administration of 5 mg/kg bwt MHY-1485, a selective agonist of mTOR, once an alternative day for 2 weeks induced S355 phosphorylation of ATG13, autophagy impairment, and severe muscle fatigue in 3- to 4-week-old female B6 mice. Immunohistochemical studies in muscle biopsies revealed that the mTOR-mediated autophagy impairment induced an elevated infiltration of M1 macrophages (M1Mφ), demyelinating response in nerve bundles and nerve fibers serving skeletal muscle, and apoptosis in muscle cells. While investigating the molecular mechanism, our research highlighted that the chronic activation of mTOR triggered the activation of STAT3 following upregulations of inflammatory cytokines such as IL6 and RANTES.

On the bottom right, they are talking about their transgenic mice with ATG13 inactivated.

The direct role of ATG13 inactivation in muscle fatigue was further corroborated by a post-treadmill fatigue assessment study in our in-house trans- genic ATG13 suppressor mouse model (Tg-ATG13), in which a single-session treadmill exercise at a speed of 14 rpm for 7 min exacerbated muscle fatigue even after 2 days. Taken together, our present study highlighted a molecular mechanism of chronic mTOR activation in ATG13 inactivation to trigger a demyelinat- ing response resulting in chronic muscle fatigue in mice.

They noted that these mice had prolonged fatigue (2 days) after a session of treadmill exercise.

They seem to be proposing that chronic activation of mTOR results in 'a demyelinating response' causing chronic muscle fatigue. I'm intrigued to read more about the 'demyelinating response' - it isn't clear if that is permanent.

 

[SNT Gatchaman]

I was excited to read this paper too, but I don't think they're describing ME/CFS: eg "we did not see any changes in neurocognitive behavior in these animals as tested by Barnes maze analyses."

I haven't seen evidence of demyelination in ME/CFS, and would the described histological changes recover in two weeks? (There are LC neuroimaging studies suggesting micro-integrity changes in myelin though.)

The severe fatigue pathology persisted until 2 weeks after the last dose. […] However, this fatigue is transient, and after 2 weeks of the last dose, mice recovered from movement deficit and started to recover body weight.

We performed Bielschowsky’s silver staining to determine myelin integrity as described elsewhere.

MHY1485 significantly compromised the integrity of myelin layers on muscle fibers, as indicated with lightly colored, disintegrated, and vacuolated myelin layers on muscle parenchyma.

The presence of myelin layers as indicated with strong MBP staining was expected to mask axons as indicated with less TUJ1 signal. Accordingly, the dual immunostaining of MBP and TUJ1 in transversely sectioned muscle tissue indicated that the integrity of myelin layers in the muscle-serving nerve terminal of the MHY-fed group was severely compromised, and as a result, the TUJ1-ir axons were exposed, whereas MBP-ir myelin layers remained tightly wrapped around axonal fibers of vehicle-fed mice.

MHY, but not the vehicle, significantly damaged the myelin integrity.

LFB staining in the dorsoventrally sectioned spinal cord tissue indicated a strong reduction of myelin staining, particularly in the ventral spinal tissue of MHY-fed mice.

There's also the problem with the male mice not being anywhere near as affected.

MHY1485 feeding caused fatigue only in female mice.

Interestingly, male mice across all different groups gained body weight and size over time. That observation intrigued us to study muscle fatigue in these female mice.

 

[SNT Gatchaman]

In their drawbacks section —

There is a huge role of cardiovascular abnormalities in chronic fatigue, which was not explored in this paper. Therefore, it will be far-fetched and premature to conclude that our model satisfies the clinical hallmarks of PEM. Second, we observed a diverse range of chronic symptoms in male Tg-ATG13 mice, such as hair loss or baldness, obesity, and infertility, which are not yet established in chronic fatigue syndrome. Third, in our model, the post-exertional fatigue is transient and sustains no longer than a week. However, in patients, the PEM persists for weeks and even longer. Nevertheless, our model highlights a specific component of muscle fatigue, which is the chronic demyelination in muscle-serving nerve fiber, and also highlights how that deficiency causes severe muscle fatigue after treadmill exercise.

(The mice heart rates reduced.)

 

[Hutan]

Third, in our model, the post-exertional fatigue is transient and sustains no longer than a week. However, in patients, the PEM persists for weeks and even longer. Nevertheless, our model highlights a specific component of muscle fatigue, which is the chronic demyelination in muscle-serving nerve fiber, and also highlights how that deficiency causes severe muscle fatigue after treadmill exercise.

Again, I think they could have used the input of people with ME/CFS. PEM does not necessarily persist 'for weeks and even longer'. It depends on the person and the exertion event (and probably accumulated consequences from previous exertion events). It's perfectly possible to have the crash of PEM for a few hours. So, the fact that their mice appeared to be fatigued for no longer than a week isn't necessarily a problem.

I want to see if they identified any delay in the onset of identified fatigue in the mice. There was no sign in the introduction that the authors understood that PEM is typically delayed.

 

[Jonathan Edwards]

If we have something demyelinating wouldn’t this have been found before, or would it be hard to find/see?

It would be plain as a pikestaff. this model appears to have nothing to do with ME/CFS.

 

[Jonathan Edwards]

I'm grateful for the work of this team. But, why don't they have an expert patient or three on board to help them avoid mis-statements like these? If they want someone, I'm sure we could find someone to help.

Why don't they have someone with a basic understanding of the ME/CFS in biological terms? One of the authors is Daniel Peterson, who is supposed to have that. Yet there is all this stuff about PEM being muscle pain after a treadmill.

What do they mean by 'Persistent muscle fatigue'? Do they mean weakness? Pain? It does not sound like ME/CFS to me. There is no inflammation in ME/CFS. And so on.

 

[InitialConditions]

The first few sentences of this paper put me right off, as does the tweet about 'groundbreaking work' from one of the authors. These are supposed to be ME/CFS experts.

Do they really think you only get PEM after being on a treadmill, or is it the case that the authors write poorly....? Who knows!

 

[Peter T]

If we have something demyelinating wouldn’t this have been found before, or would it be hard to find/see?

Sorry I never remember details unfortunately, but did some autopsy studies from some years back find loss of both grey and white matter in the brains of people with severe ME?

 

[Yann04]

The first paragraph is not quite right though

Yes it’s full of falsehoods. It’s as if they made up a definition of ME/CFS to match their theory, but that definition reads nothing like how ME/CFS is usually described, in fact to me it reads a little closer to fibro.

 

[Ash]

Sorry I never remember details unfortunately, but did some autopsy studies from some years back find loss of both grey and white matter in the brains of people with severe ME?

I think so.

 

[alex3619]

In discussing mTOR activation, I would like to see how this compares to mTOR activation in type 2 diabetes. If the model is to even try to explain PEM, it must explain how mTOR activation is different in ME compared to type 2 diabetes. It might be, or there might be something wrong with these claims.

I am unsure if there are detailed studies on mTOR in diabetes, I have yet to investigate, but elevated insulin will drive mTOR.

It is unlikely this new model completely explains PEM, but that does not rule out its a partial mechanism. There are indications that inhibiting mTOR might help with ME, but its very far from conclusive at this point. It might however help some individuals, but that might be for other reasons than ME.

 

[alex3619]

Sorry I never remember details unfortunately, but did some autopsy studies from some years back find loss of both grey and white matter in the brains of people with severe ME?

I think not just the brain but some ganglions.

 

[Dolphin]

Solve-Funded Research at Simmaron Finds New Animal Models to Study ME/CFS–Related Muscle Fatigue and PEM

https://solvecfs.org/solve-funded-research-finds-new-animal-models-to-study-me-cfs-related-muscle-fatigue-and-pem/