For most of medical history, aging has been treated as a kind of slow damage accumulation, the body accruing wear the way a car does. A small army of researchers is now making a different argument, and the evidence behind it is starting to accumulate faster than anyone expected.
“The aging cell is a cell that’s lost metabolic fidelity,” said Eric Verdin, MD, president and CEO of the Buck Institute for Research on Aging, “and that loss is measurable, mechanistically grounded, and in principle correctable.”
That last phrase is doing a lot of heavy lifting. If cellular aging is correctable in principle, it may eventually be correctable in practice, which is why the field is attracting both serious science and serious money. Life Biosciences recently closed an $80 million funding round to advance its epigenetic restoration program into human trials — and a human received the first treatment this week. Meanwhile, Texas A&M researchers have created a nasal spray that calmed neuroinflammaging and restored more youthful mitochondria function in the brain.
All that to say the field is moving very, very fast.
The question physicians will increasingly face is how to separate the signal from the noise.
Cellular Age
Think of it as the difference between a corrupted file and a corrupted reader. David Sinclair, PhD, professor of genetics at Harvard Medical School, Boston, has argued since 2008 that what we call aging is largely the second problem.
His Information Theory of Aging holds that the DNA itself stays largely intact, while the epigenetic machinery responsible for reading and regulating it accumulates errors. Methylation patterns drift. Chromatin organization shifts. The instructions are still there; the cell just can’t read them the way it used to.
That framing changes how to approach an aging cell. A cell with structural damage needs to be replaced, but a cell that’s lost the ability to read its own instructions might just need to be reminded how.
“Aged tissues and organs can recover youthful patterns of gene expression, DNA methylation, and function without becoming stem cells,” said Sinclair. He co-founded Life Biosciences and chairs its board, so his enthusiasm for epigenetic restoration isn’t without a financial dimension. But other researchers with less skin in the game have arrived at similar conclusions.
That consensus rests on a second observation, one that turns out to be just as important: The metabolic and epigenetic systems aren’t separate. Consider NAD+ (nicotinamide adenine dinucleotide) and sirtuin in cellular function. When NAD+ levels fall, as they do with aging, sirtuin activity declines. Mitochondrial function deteriorates. DNA repair becomes less efficient. The epigenome drifts further.
“Sirtuins are NAD-dependent deacylases,” Verdin explained, “which means their activity is directly coupled to the metabolic state of the cell.”
Understanding cellular aging means understanding that these processes reinforce each other.
The Metabolic Entry Point
Before the field arrives at gene therapy, it passes through metabolism, and Charles Brenner, PhD, Alfred E. Mann Family Foundation Chair in Diabetes and Cancer Metabolism at City of Hope, wants physicians to understand what that territory looks like from a clinical evidence standpoint.
“NAD coenzymes are the central catalysts of metabolism,” Brenner said, “required to generate energy, repair macromolecules, and convert everything we eat into everything we are and everything we do.”
The problem is that NAD doesn’t hold steady. Metabolic stress depletes it, and once it drops, tissues start losing the capacity for the basic functions it enables. Nicotinamide riboside, a form of vitamin B3 that the body converts into NAD, is designed to replenish those levels before the damage compounds.
Brenner declines to frame this as antiaging medicine. “I don’t like the term,” he said. What he said is that at least eight randomized clinical trials have shown nicotinamide riboside to be anti-inflammatory in humans, and that a well-powered trial demonstrated that one g/d improved walking speed in patients with peripheral artery disease.
Verdin is thinking bigger. NAD biology, he argues, is one thread in a much larger metabolic tapestry that already has serious functional evidence behind it. The oldest and most reproducible example is caloric restriction, which works across species and does so largely by elevating NAD and activating sirtuins. The supplements are trying to get there chemically, but caloric restriction gets there by making you hungry.
His lab has also shown that beta-hydroxybutyrate, the ketone body your liver produces when you fast or restrict carbohydrates, moonlights as a signaling molecule, tamping down the inflammatory gene expression that accumulates with age. Rapamycin extends lifespan in mice even when given late, which remains one of the more startling findings in the field. GLP-1 receptor agonists are proving to be tissue-protective in ways that have little to do with the reason most patients are taking them.
“These are not biomarker stories,” Verdin said. “They are functional stories, with downstream effects on tissue health and disease incidence.”
That distinction between a therapy that moves a number and one that improves what a tissue does is one Verdin considers the central methodological problem in the field.
“A therapy that lowers your GrimAge score by 2 years is interesting,” he said, “but it tells you nothing about whether your hippocampus is working better, whether your vasculature is more resilient, or whether you are less likely to develop Alzheimer’s.”
Problem Inside the Cell or Around It?
Irina Conboy, PhD, professor of bioengineering at UC Berkeley and co-founder and chief science officer of Generation Lab, approaches cellular aging from a different angle. Her research asks whether the problem is primarily inside the cell or in what the blood is telling it, and her answer has shifted how the field thinks about systemic aging.
Her lab’s work, beginning with a 2005 paper in Nature and continuing through a series of subsequent publications, demonstrated that the circulatory environment plays a determining role in tissue age. When old and young blood are mixed in equal proportions, Conboy said, “the old factors dominate, rapidly inducing aging and senescence of young cells.”
That finding punctures one of the more appealing theories in the field. Young blood transfusions sound elegant in principle, but if old factors dominate when the two are mixed, the problem isn’t a deficit of youthful signals. It’s an excess of aging ones.
Her lab’s therapeutic plasma exchange work showed that diluting plasma in older adults, without adding any young blood, produced measurable changes in human leukocytes, including reduced DNA damage, reduced senescence markers, and restored lymphoid-to-myeloid proportions. A 2022 publication reported months-long stability in those changes and documented reversal of biological age as measured by systemic markers.
Her group’s most recent work, published in March 2026 in Nature Biomedical Engineering, made the point even more viscerally. When researchers exposed human fat and liver tissue grown on microfluidic chips to blood serum from older donors, the cells aged. Not over decades, the way aging normally works, but in 4 days.
This is where the field gets interesting. Sinclair and others are working from the inside out, trying to restore the cell’s internal programming to a more youthful state. Conboy’s work keeps pulling the camera back, suggesting that as long as the cellular environment stays old, internal corrections may only go so far.
The two positions aren’t incompatible. They just don’t agree on where to start.
Reprogramming: Resetting the Clock
Of all the strategies moving toward human trials, one stands out for sheer ambition. The idea is to briefly switch on the molecular factors that can restore youthful epigenetic patterns inside a cell, then cut them off before the cell forgets what it is.
This brings us to the human trials now underway by Life Biosciences.
Sinclair’s lab settled on three reprogramming factors, Oct4, Sox2, and Klf4, delivered to retinal ganglion cells via adeno-associated virus. The standard approach uses four, but the fourth, c-Myc, is an oncogene, and including it would’ve made the path to the clinic considerably harder.
In mice, the trimmed-down combination did what the theory predicted. Youthful DNA methylation patterns returned. Damaged optic nerves regenerated. Vision improved. The results held up in nonhuman primates, and we’ll soon see what the human trials reveal.
The eye is about as cooperative a target as medicine gets. It’s accessible, so “therapies can be delivered locally,” Sinclair said, “and outcomes such as visual acuity, retinal structure, axon regeneration, and retinal ganglion cell survival can be measured with high precision.” Starting there is a way to generate clean human data before attempting systemic applications.
Vittorio Sebastiano, PhD, associate professor at Stanford and co-founder and head of research at Turn Biotechnologies, works from the same conceptual foundation but uses a different delivery approach.
Sebastiano favors mRNA rather than viral vectors, a choice that sidesteps one of the field’s bigger concerns. mRNA doesn’t integrate into the genome, which means the reprogramming signal is temporary by design. You can dial it up, let it run, and then watch it disappear.
“Transient exposure to reprogramming factors can restore youthful, molecular, and functional characteristics in aged human cells while maintaining their differentiated identity,” he said, citing work published in Nature Communications. The mRNA approach trades some delivery efficiency for a safety profile that doesn’t require long-term factor expression.
Both researchers agree on the core principle: Duration of reprogramming determines biological outcome, and the goal is to stop before cell identity is erased.
Sebastiano is direct about what true rejuvenation needs to show. “A temporary shift in gene expression alone is not sufficient evidence,” he said. “Cells routinely alter transcriptional programs in response to stress, injury, or metabolic perturbation.”
Changes have to show up across multiple independent biomarkers, not just one. They have to last after the intervention stops. And the cell has to remain recognizably itself, with no signs of dedifferentiation or the kind of runaway growth that precedes cancer.
The Measurement Problem
Verdin has little patience for the way biological age clocks are currently being used to evaluate these interventions. Most epigenetic clocks were trained to predict chronological age or mortality risk in large population cohorts. A worthy goal, but not the same as being able to detect what a targeted intervention actually does inside a cell.
Apply two different clocks to the same person after the same treatment and you’ll often get two different answers. The field has no reliable way to decide which one to believe. And that’s before you get to the tissue problem: A clock trained on blood can tell you something about immune aging and relatively little about what’s happening in the brain or the heart.
Conboy is more direct in her skepticism. She describes the methodology behind some widely used clocks as transforming biomedical data “without a biological justification” to correlate results with known ages or health scores, producing outputs that “look pristine but do not seem to be biologically relevant.”
Conboy’s own approach at Generation Lab tries to sidestep the prediction problem altogether, quantifying biological age directly through epigenetic noise across hundreds of biomarkers rather than inferring it from population statistics. Whether that methodology ultimately holds up is still being established. But the measurement problem, taken seriously, doesn’t undermine the science. It just demands honesty about how much the current tools can tell us.
The Intervention Hiding in Plain Sight
While researchers work on scaling reprogramming therapies and therapeutic plasma exchange, one intervention has been quietly improving mitochondrial function, upregulating NAD-dependent pathways, and slowing cellular aging for as long as humans have been moving their bodies: exercise.
Endurance and interval training reliably increase skeletal muscle mitochondrial content across age groups, fitness levels, and disease states according to a 2024 systematic review in Sports Medicine that drew on 353 studies and data from nearly 6000 participants. For physicians, the practical implication is difficult to ignore. The cellular pathway that expensive experimental interventions are working to activate is already responsive to a prescription that costs nothing. Research also continues to examine diet’s effect on cellular age.
None of that is an argument for sitting on the experimental work. The patients who need these interventions most are often those for whom exercise at therapeutic doses isn’t realistic, and that gap is real. But physicians already have something proven, accessible, and free. Most of their patients just aren’t using it consistently enough.
What Physicians Should Hold Onto
The science behind cellular age manipulation is real, mechanistically grounded, and advancing faster than most clinical training has prepared physicians to evaluate.
Partial epigenetic reprogramming has moved from mouse retinas to human trials. Plasma-based interventions have early human data. NAD biology has randomized trial support for specific conditions. None of that means the field has arrived.
“The longevity field will not earn clinical credibility by moving fast,” Verdin said. “It will earn it by being right.”
Physicians are already living with the consequences of this field’s momentum. Patients arrive having bought biological age tests, read about plasma therapies, and decided they should probably be taking NAD supplements. The questions are only going to get more sophisticated.
The evidentiary standard for answering them isn’t complicated: peer-reviewed data, effects that replicate across independent labs, functional benefit rather than an encouraging biomarker, long-term safety data, and trials built around endpoints that reflect real patient outcomes.
The biology here is serious. The researchers are serious. The gap between a cell that’s been rejuvenated in a laboratory and a patient who’s been helped in a clinic is also serious, and it hasn’t closed yet. That gap is not a reason for cynicism. It’s a reason for rigor. And for now, that’s where clinical judgment has to live.
Brenner reported having no conflicts. Verdin reported being the president and CEO of the Buck Institute for Research on Aging. Conboy reported being co-founder and chief science officer of Generation Lab. Sebastiano reported being co-founder and head of research at Turn Biotechnologies. Sinclair reported being co-founder and chairman of Life Biosciences.Disclosure information for study authors is available in the original study publications.
https://www.medscape.com/viewarticle/inside-quest-make-old-cells-young-again-2026a1000jrf
