Researchers at Sanford Burnham Prebys and UC San Diego measured both autophagy gene expression and actual autophagic activity (flux) in three cell types from the same healthy volunteers: cultured skin fibroblasts, neurons converted from those fibroblasts, and freshly isolated blood immune cells (PBMCs). Autophagy genes were switched up with age, but real activity did not follow. Instead it moved in different directions depending on cell type and sex. In adults over 70, higher immune-cell autophagy flux went along with poorer physical fitness. In a five-person, uncontrolled pilot, a 12-week mild exercise program was accompanied by lower flux and better physical performance scores. The authors propose that high autophagy in old age reflects cells coping with stress rather than a healthier recycling system.
For two decades, the story of autophagy and aging has sounded simple. Autophagy, the process cells use to package and digest their own worn-out proteins and organelles, is supposed to fade as we get older, and anything that revs it back up, from fasting to rapamycin to spermidine, should help. A new study of healthy adults in San Diego suggests the real picture is messier, and that in the oldest people, more autophagy may be a sign of strain rather than vigor.
The team took skin cells and blood from volunteers aged 23 to 80. They grew the skin cells in the lab, converted some into neuron-like cells, and isolated immune cells straight from fresh blood. Then they did something most human studies skip. Instead of counting autophagy markers or reading autophagy genes, they measured flux, the actual rate at which the recycling system processes cargo. They did this by briefly blocking the final digestion step with the drug chloroquine and measuring how much undigested material piled up.
The gene readouts and the activity readouts told different stories. In older donors’ skin cells, autophagy genes were turned up, yet recycling activity fell in cells from men and held steady in cells from women. In lab-made neurons, activity rose with age in cells from women but not men. In blood immune cells, age alone predicted nothing, but the spread between people widened sharply after about 70, with some older people showing unusually high activity. Activity in one cell type did not predict activity in another cell type from the same person.
The most provocative finding concerns what that activity means. Across the whole group, higher autophagy in blood cells went along with some signs of better cardiovascular fitness, such as a lower resting heart rate. In people over 70, the relationship reversed. Higher blood-cell autophagy went along with lower aerobic capacity, slower walking and a slower chair-stand test. The authors argue that in older bodies, a busier recycling system may reflect cells working overtime to handle damage.
To probe this, the team measured blood-cell autophagy in five people aged 77 to 88 before and after a 12-week, once-weekly balance and strength class. Four of the five started with high activity. After the program, activity fell in four of them, and their scores on a standard 12-point physical performance test rose by about 1.2 points on average.
It is an intriguing result, but a fragile one. Five people, no comparison group, and a change in autophagy that the authors did not report as statistically significant cannot show that exercise normalizes autophagy. Many of the age-specific correlations rest on six to ten people, and the lab assay tracks a single marker of a complex pathway.
Still, the study lands a useful blow on a popular assumption. If raised autophagy in older people signals stress rather than health, then drugs and diets designed simply to push it higher may not deliver what their marketing implies. The question the field now needs to answer is not how to boost autophagy, but when boosting it helps.
Actionable Insights
- Higher autophagy is not automatically better in later life. In adults over 70, those with the highest immune-cell autophagy walked more slowly and had lower aerobic capacity. The correlations were strong (around r = -0.75, meaning roughly half the person-to-person differences lined up), but each rested on only about 8 to 10 people, so the true relationship could be anywhere from modest to very strong. [Confidence: Low]
- Low-dose exercise remains a sensible bet for older adults. One hour a week of balance and strength training for 12 weeks raised physical performance scores from 8.6 to 9.8 out of 12, a 1.2-point (14%) gain. Geriatric research places the smallest change that matters at roughly half a point on this test and a substantial change at about 1 point. The standardized effect was large (about 1.4), but with five people and no control group the real effect is likely smaller; the plausible range of improvement runs from about 0.2 to 2.2 points. [Confidence: Low to Medium] ResearchGate
- The study tested no drug, supplement or fasting protocol. Its only lesson for rapamycin, spermidine or fasting users is that “more autophagy” is not a proven target in itself.
Context and Source
- Open access paper: Autophagy Flux Is Remodeled Sex- and Cell Type-Specifically During Human Aging, and Is Linked to Reduced Physical Function in Older Adults
- Institutions: Sanford Burnham Prebys Medical Discovery Institute and University of California San Diego (Division of Geriatrics; Exercise and Physical Activity Resource Center; Herbert Wertheim School of Public Health; Sanford Consortium for Regenerative Medicine), La Jolla, California
- Country: USA
- Journal: Aging Cell (Wiley, on behalf of the Anatomical Society)
- Impact evaluation: The impact score of this journal is 7.7, evaluated against a typical high-end range of 0-60+ for top general science and medicine journals, therefore this is a Medium impact journal.