A Muscle Biopsy Study to Understand the Molecular Mechanisms of PEM

• Post-exertional malaise (PEM) is a debilitating symptom of ME/CFS with an unknown cause.
• Systrom, the Director of The Ronald G. Tompkins Harvard ME/CFS Collaboration, has designed a study to help better understand the relationship between poor oxygen extraction, vascular abnormalities, and mitochondrial dysfunction and how they might relate to PEM.
• The study team will explore molecular changes that occur with PEM through proteomics, metabolomics, and transcriptomics conducted on blood samples and analysis of mitochondrial function completed on muscle biopsies.
• This study is ongoing, placing it in the “Recruitment, Data Collection” stage of the research process.

Video Transcript

Dr. Meadows: Hi everyone, and welcome to a series of interviews with Open Medicine Foundation’s directors that we’ll be sharing with you throughout our Triple Giving November. I’m Dr. Danielle Meadows, OMF’s Vice President of Research and Operations, and this week, to kick things off, I am really thrilled to be joined by the director of our Ronald G. Tompkins Harvard ME/CFS Collaboration, Dr. David Systrom.

As a brief introduction, Dr. Systrom center focuses on understanding the mechanisms underlying ME/CFS, Long COVID and other chronic complex diseases, with a special emphasis on post-exertional malaise and then finding new and better treatments to improve patient care. So welcome Dr. Systrom.

Dr. Systrom: Thank you, Danielle, for inviting me.

Dr. Meadows: So today I want to chat with you about one of your studies that’s trying to understand post-exertional malaise, the muscle biopsy study. To start us out, can you give us a high-level overview of the rationale and background for this project?

Dr. Systrom: Sure. I think as many in the audience know, post-exertional malaise is one of the characteristic features of ME/CFS. It’s a distinct feature and it serves to differentiate clinically from other forms of fatigue and exertional intolerance, for instance.

So, post-exertional malaise is a characteristic feature, in fact, required for the diagnosis of ME/CFS. What patients tell us in the clinic is that if they overdo on one occasion, and generally speaking that’s physical activity, but it can also be overdoing cognitively or even emotionally, that they will, quote, pay the price later, and that later is usually 12, 24, 48 hours later.

Severe PEM is often described as a crash and it can persist for days, weeks and even months at a time. So it is again a characteristic feature of the disease and studying it, we think, will serve several purposes. One is to gain insight into the pathophysiology of the disease, what actually is triggering all of the symptoms, including exertional intolerance, in such patients.

But it’s also a really debilitating symptom, so better understanding the symptom and what drives it physiologically is incredibly important for the patients, and hopefully ultimately, we can direct therapy at PEM, post-exertional malaise, and make patients better.

This particular study is designed to determine, in a pathophysiologic sense, what is driving post-exertional malaise. We have several angles, several different approaches, with biomarkers, blood-borne biomarkers and muscle biopsies in an attempt to better understand post-exertional malaise.

One of the things that has piqued our interest in all of this has been our invasive cardiopulmonary exercise test at the Brigham, which we’ve been doing for over six or seven years in ME/CFS, and of course, more recently in Long COVID. What we’ve discovered is that there are some vascular abnormalities, apparent vascular abnormalities, in patients both with ME/CFS and Long COVID.

They seem to be shared disproportionately in women, where we have some evidence of preload failure or preload insufficiency, which is low pressures feeding the right heart during upright cycling exercise. But additionally, in a subset of patients, especially women, impaired oxygen extraction by the muscle at peak exercise.

There are two schools of thought about what might be driving that ladder phenomenon. One is a vascular abnormality, very similar to the preload failure, where we have a very high prevalence of something called small fiber neuropathy that we diagnose with a skin biopsy.

The small fiber nerves mediate things like pain, but we’ve also more recently discovered that they play a major role in autonomic function, including blood vessel tone and therefore blood flow during exercise. So one hypothesis is that what ails patients during exercise, and with post-exertional malaise, is this impaired vascular function, neurovascular function, where blood flow is not appropriately directed to the exercising muscle, and even more particularly to the exercising muscle mitochondria.

So that’s one theory that impaired oxygen extraction and things like fatigue, brain fog, lightheadedness, and even PEM, is a blood flow abnormality related to the autonomic nervous system. But the second possibility and this has gained some traction, really, over the past eight to nine months with our work and with the work of some collaborators in Amsterdam, is that the muscle mitochondrion may play a role in this impaired oxygen extraction.

So with the invasive CPET, which involves a mouthpiece and a metabolic card, and a pulmonary artery catheter and a radial artery catheter. This impaired oxygen extraction by the muscle we can demonstrate, but we can’t really differentiate between blood flow abnormalities and mitochondrial dysfunction, intrinsic mitochondrial dysfunction.

So this study is meant to address that very question. When we see, most often, a woman with ME/CFS and or Long Covid, who has post-exertional malaise, is this a mitochondrial problem in the muscle? Is this a blood flow abnormality or is it both? And this muscle biopsy study is meant to address that.

So the protocol is pretty simple. On day one, they have some baseline blood drawn, we’re sending plasma for proteomics to SomaLogic, we are sending plasma to a collaborator in Montreal, Alain Moreau, who is doing transcriptomics, and we are doing metabolomics at Metabolon.

So there will be a variety of blood-borne biomarkers that will be obtained both on day one and as I’ll tell you about day eight, which is the last day of the study. The other thing we do on day one is a muscle biopsy. It’s frozen so that we can interrogate live mitochondria later.

So all that’s done on day one, is a muscle biopsy done by one of our interventionalists and the blood, which is plasma for the omics that I just mentioned. Additionally, we’re sending whole blood to Dr. Maureen Hanson at Cornell for interrogation of peripheral blood mononuclear cells, which may give us some further insight into mitochondrial function, for instance.

So on day seven, they return and they do semi-exhaustive exercise. It’s not meant to be too onerous, but what we’re attempting to do is precipitate a little bit of PEM the next day. Of course, our patients are aware of that. It’s a non-invasive cardiopulmonary exercise test.

We purposely create a shallow workload, meaning they go about twice as long as they did for a previously clinically indicated invasive CPET. And again, that’s meant to increase the exercise burden a bit and precipitate PEM the next day. And the next day they return for the very same things they get on the baseline day. So another needle muscle biopsy, frozen, sent to our collaborators and all the bloodborne omics.

So what we’re doing is based on the initial invasive CPET, is determining all the patients, by definition, and it’s an inclusion criterion, have the clinical phenomenon of PEM. Half of the patients have poor oxygen extraction at peak exercise and half of them do not.

So we’re asking the question, does the invasive CPET identification of poor oxygen extraction enrich the possibility of having mitochondrial dysfunction?

Dr. Meadows: Yeah. Excellent. That’s great. You’ve covered some of your hypotheses around this work and connected vascular dysfunction to mitochondrial dysfunction. Having that comparator group is also going to be really interesting to not have the post-exertional malaise and see what that difference is. So that’s going to be really great work. Can you talk a little bit about how might results be translated to the clinic in the future?

Dr. Systrom: Yeah. So at least with current thinking, the treatment of neurovascular dysfunction is very different from the treatment of intrinsic mitochondrial dysfunction. There is a national organization called The Mitochondrial Medicine Society that has recommendations about treatment mostly directed at genetic forms of mitochondrial myopathy.

But the treatment of the neurovascular dysregulation is a different animal, at least with current knowledge. It’s directed largely at this small fiber autonomic neuropathy that we have treated actively with another off-label comment, drugs such as pyridostigmine or Mestinon, which is FDA-approved medication for myasthenia gravis.

So anyway, the original question was, how would we potentially create some precision medicine in treating individual neurovascular dysregulation versus mitochondrial dysfunction? And right now, they are very different animals, as it were.

Dr. Meadows: Yeah. So it almost sounds like if you find the connections that you’re potentially expecting to find from this study between vascular dysregulation and mitochondrial dysfunction, you might be able to guide treatments in the future just using the invasive CPET that you use in the clinic as it is. Does that sound right?

Dr. Systrom: That’s exactly right.

Dr. Meadows: Great. So oftentimes when we talk about ME/CFS and especially PEM, it triggers an automatic thought of doing a two-day CPET. So in this particular study, why are you using just one day of CPET, and how does that differ from a two-day CPET?

Dr. Systrom: Right. The two-day CPET, pioneered by Betsy Keller and Ithaca is a useful modality. It’s noninvasive and it appears to identify reasonably reliably this, at least some physiologic manifestations of PEM. So the idea is you do the first exercise test and get a VO2 max and a noninvasive anaerobic threshold, and then you repeat it the next day when the patient is suffering from PEM and you can quantify a decrease in the VO2 peak and decrease in the anaerobic threshold.

This is really taking a deeper dive, we think, into the pathophysiology of what might drive those two things. So the V02 peak decreasing and the anaerobic threshold decreasing on day two can be driven by neurovascular dysregulation, or it can be driven by newly acquired or worsened mitochondrial dysfunction, perhaps on the setting of inflammation that is precipitated by the first exercise bout.

So really our exercise intervention and then studying the patient the next day is a deeper dive into the pathophysiology of what Doctor Keller has observed.

Dr. Meadows: Yeah. So in some ways, the two-day CPET is a way of diagnosing PEM, but in this case, you’re using the CPET to induce PEM and then look more at the molecular mechanism behind it using the proteomics and metabolomics and all the muscle analysis. Is that accurate?

Dr. Systrom: That is fiercely accurate.

Dr. Meadows: Okay, great. So maybe just kind of the last little bit I’ll ask is what stage is the study in now? And are there any observations that you can share at this point?

Dr. Systrom: Sure. So with the help of the team, who include Johanna, Shreya, and others, we’ve accomplished eight muscle biopsies with a projected total number of 50 patients. So we’re on our way. We have an additional two coming up in the next week or two, and this is all over the past month or so. So we’ve launched this with our collaborators, receiving the samples that I mentioned. That took a little bit to organize, but is now a well-greased path and we are well on our way.

Dr. Meadows: Well, that’s very exciting. Good to hear. With that, I will just wrap things up for a little short interview today. And thank you so much for joining me, Dr. Systrom.

Dr. Systrom: Thank you, Dr. Meadows. It was my pleasure.