The Mitochondrial Permeability Transition Pore (mPTP)

rg2000

New Member
Greetings. This is my first post here, and my reason for joining. I'd just like to draw some attention to the mPTP (mitochondrial permeability transition pore), as I feel it rarely comes up in any of the research I've read in any greater capacity than an aside - I've not seen it posed as a core mechanism.

As a disclaimer, I myself am not credentialed - the following hypothesis is more of "a sick guy's best attempt at connecting the dots". That being said, I certainly find this idea interesting and, perhaps plausible enough to pose as a probable mechanism, and feel it would be amiss to not at least bring this to the attention of a group capable of either shooting it down logically, or exploring the notion further, if indeed it leads somewhere.

To clarify, the mPTP is a channel that can be induced in the inner-membrane of the mitochondria. It can be induced transiently, or for an extended period - the latter of these is where the most damage occurs. When the mPTP is induced, two key things happen as a direct consequence:

* Ions begin to move in to the mitochondria through the open channel. When this happens consistently, or for an extended period, the mitochondria loses the electrochemical gradient required to build ATP, and, at worst (can) die completely.​

* mtDNA can be released as a downstream consequence, provoking an immune response.​

In regulatory T-cell mitochondria, this can cause the cell to become dysfunctional, which, in addition to the release of mtDNA, further compounds the potential for autoimmunity. Among other things, the mPTP can be induced by:

* Numerous different viruses (including SARS-CoV-2) in the event of an infection.​
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* Certain chemicals (including some antidepressants, like Sertraline).​
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* Chronic physical and mental stress (β-adrenergic stimulation, at least demonstrated in-vivo)​
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* The downstream effects of high glucose.​

Each of the above stressors induces the mPTP to a different degree - most of these alone, at regular day-to-day levels, are insufficient to induce the mPTP to a problematic degree in a healthy individual. My idea is that when multiple of them co-occur - especially alongside a virus which specifically targets mPTP induction - you get an escalation of this incremental energy baseline deterioration that we see in ME/CFS. And each time it happens, there's less remaining mitochondrial capacity to buffer the damage, so it takes less 'stress' to surpass your ATP availability.

If one's energy baseline corresponds to their remaining mitochondrial production capacity, then a reduction of said baseline by further calcium overloading makes sense; at a certain point, you may have too little available energy to continue mitogenesis, causing you to get stuck at these distinct baselines - we cannot replenish mitochondria as fast as we are rendering them non-functional / depleting them. The less your remaining mitochondrial function, the more severe your condition.

Of course, recoveries do happen - but they aren't too common. And those in remission seem to have a tendency to fall ill again, which seems to suggest in many cases, a permanent state of variable global mitochondrial sufficiency. This is basically my hypothesis, distilled. I've kept it concise, on account of brain fog, but I hope that even this rough picture demonstrates the idea well enough. If any of this reads as "you have no idea what you're talking about", then, apologies.

The following are footnotes, but still worth mentioning:

Magnesium and NADH, both quite common in ME/CFS supplement stacks, help to prevent mPTP induction.
(https://pmc.ncbi.nlm.nih.gov/articles/PMC5393273/)

Additionally, while I'm not able to find the actual source, an article from the ME Association states that cyclosporine has shown "good results".
(https://meassociation.org.uk/2021/0...ging-treatment-options-for-autoimmune-me-cfs/)
This seems notable, not because cyclosporine is an immunosuppressant, but specifically because cyclosporine A inhibits mPTP opening by binding cyclophilin D, a regulator of the pore’s gating.
(https://www.nature.com/articles/cddis201480)
 
A further thought, @rg2000. We have previous experience of people joining the forum to share their hypothesis and presenting it as you have done with multiple links to research. Thus can be off-putting as most of us have limited capacity to tackle so much input at once. It also leads to confusion as so many different research papers are commented on on the same thread.

I suggest you pick a few of your references that you think introduce the topic most helpfully, and make a new thread for each, and link those threads from this thread. Then each piece of your evidence can be examined separately.
 
I just happened to open the wikipedia on the MPTP, i fell into reading about it after following a long thread.


I was doing some reading on the unfolded protein response (UPR) (I'm trying to work on understanding more about that and whether it could fit into PEM) and the MPTP came up as something that could cause mitochondrial problems in a situation where the UPR was unable to resolve endoplasmic reticulum stress.

Now, here's what's interesting: Viruses have an ability to inhibit the cell's response to endoplasmic reticulum stress. They can block the UPR. One theory I am weighing up is whether that blockage could be long-lasting.

The UPR tries to fix endoplasmic reticulum (ER) stress in a few ways, one important one is that it shuts down protein making. But viruses rely on protein making to survive, so they like to interrupt the UPR nad keep that protein machinery running.

The UPR is also meant to be triggered by exercise. If you don't get the UPR you can't recover from exercise properly. If a virus (or its after-effects) is blocking your UPR you might find you can't handle exericse. This could all fit together!!

Another cool aspect of the theory is different viruses use different ways of hijacking the UPR, so maybe some of those methods (e.g. those used by HHV6, SARS-Cov-2, enteroviruses, ross river fever) might tend to be long lasting under certain conditions while the methods used by others (flu, other?) might not. I need to do more reading on all the different ways viruses inhibit the UPR.

I feel the MPTP could be part of the whole catastrophe that ensues when the cell is overloaded by stress and can't resolve it. Might well be part of the big matrix of things that make us feel so bad during PEM.

edit: to be clear this theory is not of my own invention, I just can't get over this one bit from Hwang's wasf3 paper and keep drlling down on it:
ER stress normally induces the chaperone protein BiP and suppresses protein translational factor eIF2α via PERK to mitigate the unfolded protein response. However, the muscle samples of ME/CFS patients showed an opposite relationship and the cells of patient S1 also revealed loss of concordance in the levels of these ER stress proteins, implying that abnormal ER stress response may underlie the disruption in mitochondrial metabolism. Although the reason for the increased ER stress is unclear, its specific reduction in the patient’s cells by salubrinal implicates the activation of eIF2α by dysregulated phosphatase PP1 as has been reported, for example, by viral infection (44).
 
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A further thought, @rg2000. We have previous experience of people joining the forum to share their hypothesis and presenting it as you have done with multiple links to research. Thus can be off-putting as most of us have limited capacity to tackle so much input at once. It also leads to confusion as so many different research papers are commented on on the same thread.

I suggest you pick a few of your references that you think introduce the topic most helpfully, and make a new thread for each, and link those threads from this thread. Then each piece of your evidence can be examined separately.

Apologies for the enormously delayed response to this. I had lost my password, and was quite busy dealing with my health.

I understand that overloaded hypothesis posts can be off-putting for people already struggling with brain fog. My initial intent was not that everyone read all of the supplied materials necessarily; I provided them more as optional further reading, context for otherwise well-established biology.

Respectfully, I think that making new threads for each of these would ultimately be cluttering the forum, as most of these papers are only really relevant to the mPTP itself. I can still make those threads if you consider it worthwhile though.

I was doing some reading on the unfolded protein response (UPR) (I'm trying to work on understanding more about that and whether it could fit into PEM) and the MPTP came up as something that could cause mitochondrial problems in a situation where the UPR was unable to resolve endoplasmic reticulum stress.

Intriguing. I'm not as familiar with the UPR as with other mechanisms, but after having read about it as far as I currently can, it seems potentially rather interesting. Especially given, as you say, that the UPR is ordinarily triggered by exertion.

I feel the MPTP could be part of the whole catastrophe that ensues when the cell is overloaded by stress and can't resolve it.

I very-much agree, as it's implicated in many different mechanisms that seem awfully relevant to the condition...

The mPTP can be induced by matrix calcium overload, and lowers the membrane potential. Insufficient membrane potential can cause dysfunction of various mitochondrial components, (including NCLX-mediated calcium extrusion), as well as ROS production. A loss of membrane potential also means the charge gradient which powers ATP production via ATP synthase is reduced.

In a cell whose mitochondria are dysfunctional like so, this dysfunction might be among the things responsible for the failure to resolve ER stress in the first place. Then, this unresolved stress could lead to further calcium accumulation, ergo, further mPTP opening. Unfortunately, I don't quite have the brain power at this stage to read this whole paper, but from what I can gather, it seems to point in the direction of the behaviour I just outlined, although it doesn't specifically mention UPR, only ER stress. It still might be of worth though.

But if the cell is unable to resolve the ER stress, the UPR may continue for a prolonged period. Supposedly, a prolonged UPR can itself cause calcium overload.... There looks to be feedback loop potential in that, as it's spelled out.

With regard to the other ER stress-specific details you mentioned, I'm not confident enough to comment on them at this time, but they're definitely going in to my research pile.



While I've demoted the mPTP from the "core mechanism" rank I'd naively assigned it back when I made this thread, I still can't help but find it important in some way. I have a more expansive hypothesis which incorporates it, but it's understandably perhaps not the kind of thing that fits here, as it pieces together many different independently verified mechanisms that haven't been formally tested together.

I think it would be nice if more (or any) research groups were doing mPTP assays to measure susceptibility to permeability transition, and perhaps paid more mind to membrane potential too, as these variables are rather meaningfully connected to calcium handling in general, which we know to be dysfunctional... And if there were any abnormalities there, I'd be even more interested to see them stratified by severity.
 
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