The best biomarker of mitochondrial disease is GDF15. Most organs, except one, seem to make GDF15. Only the brain has the GFRAL receptor for GDF15. Upon detecting GDF15 the brain both conserves energy & mobilizes energetic substrates to feed those cells that are in trouble
Martin Picard, PhD: "[There are some] small proteins that convey information called cytokines. Those proteins are made and then they're secreted outside the cell. There are different cytokines that mean different things. The cytokine that seems to be the most specific and sensitive to reductive stress, and therefore to energy resistance, is this protein called GDF15, growth differentiation factor 15. […] GDF15 across the board, across multiple studies, was the number one protein that increased exponentially with age. So old people have much higher levels of GDF15 in their blood than younger people."
Nick Jikomes, PhD: "So higher GDF15 indicates that there's energy resistance problems, correct?"
Nirosha Murugan, PhD: "Correct."
Martin Picard, PhD: "So that was for aging. Now we look at aging from an energy resistance lens. I think it makes a lot of things make sense. […] In the world of pregnancy also the protein that spikes the highest during pregnancy is GDF15, and we've seen in some women over 10,000-fold increase in GDF15."
Nick Jikomes, PhD: "Before we get to some of that stuff, if everything's working properly, what happens at the end of this? So I'm a cell, I've got electron flow issues, I'm increasing my NADH / NAD ratio. I'm eventually communicating that to the nucleus of my cell, and I'm making more cytokines, like GDF15. I'm secreting those to tell other cells, I've got an issue. How is the issue resolved?"
Martin Picard, PhD: "Ah, that's a great question."
Nirosha Murugan, PhD: "Those are the mechanisms that we kind of talked about about alleviating or"
Martin Picard, PhD: "relieving"
Nirosha Murugan, PhD: "relieving that energy"
Martin Picard, PhD: "resistance."
Nirosha Murugan, PhD: "Yeah. Increasing flux or reducing the energy potential. So there's different knobs within the energy resistance worlds that you can modulate. And I think why this is so pervasive on a system scale is that local cell-level changes in energy resistance can manifest at a systems level, and then you can see changes on a systems, like breathing, like you can change your respiratory rate which will affect at a cellular level. . ."
Nick Jikomes, PhD: "OK, so maybe the cells are saying I have an electron flow issue. I need more oxygen."
Martin Picard, PhD: "Yes."
Nirosha Murugan, PhD: "Correct. And so like the whole system, typically with cytokines you're kind of looking at a singular landscape of information exchange, you're looking at cell to cell,"
Martin Picard, PhD: "cell to brain"
Nirosha Murugan, PhD: "Cell to brain. But with energy resistance it's a whole systems physiology of communication that comes on."
Martin Picard, PhD: "Yeah. So as far as we know the increase in breathing, the increase in heart rate that you experience when you start running, right, with exercise, or with the cell, like a mitochondrial disease, it's very clear there's an electron resistance, energy resistance issue in the mitochondria, right, which again is a really special opportunity to ask, 'How does this manifest at different levels of biology and physiology and psychology?' And what we see in these patients the best biomarker of mitochondrial disease is GDF15. So if you want to know if someone has mitochondrial disease or not, you take a blood sample. What do you measure? GDF15 is what offers the highest sensitivity and specificity. It's quite remarkable.
"And then Nirosha kind of highlighted the broad principle, right? A cell experiences high energy resistance. It wants to relieve that, right? How does this work? So there's a number of things that happens: increase heart rate, increase breathing to relieve, to diffuse energy resistance. Probably that happens, not driven by GDF15, as far as we know. What we think GDF15 does, and there's nice animal studies that have shown this, and then some human correlational evidence, it suggests that GDF15 goes from your cell as a little cytokine, enters the blood, then goes everywhere in the body. There's a concentration of the receptor for GDF15 in one very specific part of the body.
"Interestingly, every cell in the body seems to be able to make GDF15, and we've done an analysis of gene expression by RNA sequencing across 50 different pieces of the human body, 50 different organs, and those are postmortem samples that were analyzed for gene expression signatures. What you find is most tissues in the body can make some amount of GDF15 except the one organ that doesn't seem to make GDF15 under normal conditions. Can you guess which one?
"The brain. And then you ask, 'OK, every organ in the body seems to be able to make the signal, GDF15, that cytokine, where's the receptor?' Right? Which organ in the body expresses the GDF15 receptor? It's called GFRAL. And there's only one organ in the body that expresses a receptor. Can you guess which one?"
Nick Jikomes, PhD: "The brain."
Martin Picard, PhD: "The BRAIN!"
Nick Jikomes, PhD: "OK, so it's a brain-body communication."
Martin Picard, PhD: "Exactly. It's like the prototypical brain-body communication access. The signal is made in the periphery, and the receptor is centrally located in the brain stem, specifically the area postrema. There are really nice mouse studies that have been done to ask what happens if I inject GDF15 in the brain stem, or peripherally then it goes to the brain and then there's nice optogenetic studies where people you know encoded this optogenetic light sensitive channel of rhodopsin, typically in the neurons in the brain stem that have this receptor. And what you find and then you ask, 'What happens to the mouse?' I activate this GFRAL signaling axis, I stimulate the neurons that are sensitive to GDF15 in the brain stem. What happens to the mouse? There are two things that seem to happen in parallel that then brings us to relieving the energy resistance in those cells that were crying out for help, spitting out GDF15. One thing is energy conservation. So if you stimulate those receptors in the brain stem, the animal is going into a state called torpor. So their body temperature drops. Maybe that says something about what this means for relieving energy resistance. The sympathetic nervous system gets activated, right, so they secrete norepinephrine, like adrenaline and noradrenaline, which goes to the liver to stimulate glucose production release from the the liver. So that feeds those cells that are energetically starved, right? Maybe they're out of energy substrates.
"So GDF15 stimulation on the brain stem drives energy conservation. The mice stop moving and they look like they're really sick. And then the second thing is the activation of those energy mobilization systems, like you increase blood glucose through the hepatic stimulation and you increase lipolysis, you break down fat in the fat stores, and the adipose tissue. Then the blood lipids increase, the blood glucose increase, which are really like the food substrates that the cells need to relieve their energy resistance, perhaps. So by conserving energy, right, by acting like you're sick and that might be why the the whole purpose of sickness behavior. If your immune system kicks in, increasing energy resistance in your body, what you do?"
Nirosha Murugan, PhD: "You stop."
Martin Picard, PhD: "You stop moving."
Nirosha Murugan, PhD: "You stop producing more heat."
Martin Picard, PhD: "You go lie down, and you and you chill out. So that would be adaptive and a way of reducing energy resistance."
"So GDF15 then, to come back to the original point, a cell is experiencing higher energy resistance, NADH / NAD ratio signals to the nucleus, nucleus says let's tell the rest of the body. You secrete GDF15, goes to the brain, the brain says, 'Shit. Something in the body is running really high resistance. Let's address this in two ways: conserving energy, and mobilizing energetic substrates to feed those cells that might be in trouble.' So there's a dual action it seems like GDF15 serves or mobilizes this energy conservation and energy mobilization which is like the perfect recipe for relieving cells of of excessive resistance."
Martin Picard, PhD & Nirosha Murugan, PhD with Nick Jikomes, PhD @ 01:23:42–01:32:03 (posted 2025-10-29)
https://youtu.be/GiwDfsIgziA&t=5022