Inside nearly every cell in the body, mitochondria do far more than produce energy. They also release tiny signaling proteins called mitochondrial-derived microproteins, or MDPs. These molecules are so small they were overlooked for decades, but researchers now think they carry messages between tissues, helping the body adapt to stress, exercise, and aging.
A recent paper published in Experimental Physiology set out to understand whether people with cerebral palsy, a condition that affects motor control and is often accompanied by reduced muscle mass and lower cardiorespiratory fitness, show different circulating levels of these microproteins compared with people without the condition. The study also asked how a single session of endurance exercise changes those levels.
The results were unexpected. Despite clear physical differences between groups, the mitochondrial signaling measured through these microproteins looked remarkably similar across everyone studied.
Background on mitochondrial microproteins
MDPs are encoded by short stretches of DNA inside the mitochondria themselves, which is unusual because most proteins are coded by nuclear DNA. Three of the most studied MDPs are humanin, MOTS-c, and SHMOOSE. Each circulates in the bloodstream and appears to influence processes such as energy regulation, cellular stress responses, and metabolic signaling.
MOTS-c in particular has attracted attention in exercise research because its circulating levels tend to rise with physical activity in some populations. Whether that same response occurs in people with neuromuscular conditions like cerebral palsy had not been studied before this paper.
Understanding how these signals behave in different populations matters because MDPs may help explain why exercise produces health benefits at the cellular level. If the molecular machinery that generates these signals is disrupted, it could partly explain why some individuals adapt differently to training.
Study design and participants
The research team recruited three groups. One group was adults with cerebral palsy, averaging around 25 years of age, classified at Gross Motor Function Classification System levels II through IV, meaning they ranged from people who walk with some difficulty to those who require assistive devices for mobility. All had at least three months of experience using a running frame, a wheeled support structure that allows people with limited motor function to move at a running pace.
The comparison groups were typically developing adults averaging around 31 years old and typically developing adolescents averaging around 16 years old. Including an adolescent group allowed the researchers to check whether the cerebral palsy group, which tends to have younger physiological profiles in some measures, was more comparable to younger healthy individuals.
Before exercise, researchers measured habitual physical activity using standard tools, muscle thickness via ultrasound, and peak oxygen uptake through exercise testing. The exercise session itself was 45 minutes of frame running for the cerebral palsy group and 45 minutes of conventional running for the typically developing participants. Blood was drawn before exercise and again one hour after the session finished. Plasma concentrations of humanin, MOTS-c, and SHMOOSE were measured using enzyme-linked immunosorbent assay, a standard laboratory technique for detecting proteins in blood.
Baseline differences in fitness and muscle
As expected given the nature of cerebral palsy, adults with the condition had lower muscle thickness and lower peak oxygen uptake than both groups of typically developing individuals. These differences confirm that the cerebral palsy group entered the study with measurably different physical characteristics, making the microprotein findings that followed all the more striking.
The researchers also checked whether the severity of motor impairment, or the specific subtype of cerebral palsy, was related to MDP levels at rest. No such associations were found, suggesting that within the cerebral palsy group, the variety in motor function did not translate into proportional variation in these circulating signals.
Resting microprotein levels across groups
At rest, circulating levels of humanin, MOTS-c, and SHMOOSE in adults with cerebral palsy were comparable to those measured in both typically developing adults and adolescents. The literature suggests that when muscle mass is substantially lower, the mitochondrial output that produces these signals might also be expected to be lower. The fact that levels were preserved is therefore a notable finding.
The researchers frame this as evidence of what they call preserved mitochondrial-derived signaling in cerebral palsy. In other words, even though the muscles themselves are smaller and peak aerobic capacity is reduced, the mitochondria within those tissues appear to maintain their capacity to produce and release these microproteins at levels similar to those seen in people without the condition.
This finding raises interesting questions about the relationship between muscle size and mitochondrial signaling quality. It is possible that mitochondrial function, at least as reflected by MDP output, is maintained even when muscle quantity is reduced.
Exercise response and post-exercise changes
After the 45-minute exercise session, the changes in circulating MDP levels were modest across all three groups, and no meaningful differences emerged between the cerebral palsy group and the typically developing groups. Some microproteins showed slight shifts, but the overall pattern was one of stability rather than large exercise-induced surges.
This outcome differs from what some earlier research has suggested about MOTS-c responding robustly to exercise in healthy populations. The authors note that the acute exercise stimulus used here, a single 45-minute session, may not be sufficient to drive large changes in circulating MDPs, or that the timing of the blood draw at one hour post-exercise may have missed a transient peak.
Importantly, people with cerebral palsy showed no blunted response compared with their peers. The exercise-related microprotein dynamics, modest as they were, looked essentially the same regardless of whether participants had cerebral palsy or not.
What this means for research
This study is among the first to examine MDPs in a population with a neuromuscular condition, and it opens a number of directions for follow-up work. Researchers may now ask whether longer or more intense exercise programs change these signals over time, whether the timing of blood collection matters for capturing transient peaks, and whether other MDPs beyond the three measured here behave differently in cerebral palsy.
The finding of preserved MDP signaling is relevant to any framework trying to explain why frame running and similar exercise interventions can improve cardiorespiratory fitness in people with cerebral palsy even when the muscular starting point is different from that of typically developing individuals. If mitochondrial signaling is intact, that pathway remains available as a driver of adaptation.
For the broader field of MDP research, this study adds an important data point: circulating levels of humanin, MOTS-c, and SHMOOSE are not simply a direct readout of muscle volume. The relationship between muscle mass and MDP output appears more complex than a straightforward linear link, and future studies will need to account for that complexity.
