The Long RunA protein that fades with age kept blood-vessel cells young in the lab, in mice and in worms
The protein MTR4 dwindles as the cells lining blood vessels age. Adding it back made aged human cells in a dish look younger, boosting it in the vessel lining of old mice eased signs of aging in their vessels and organs, and extra MTR4 made worms live much longer. This is early lab and animal work with small groups of mice; nothing here has been tested in people.
The inside of every blood vessel is lined with a single thin layer of cells, the endothelium. These cells do far more than form a smooth tube: they help set how wide vessels are, control what leaks out of the blood and keep inflammation and clotting in check. Because they face the constant push of blood flow and whatever is dissolved in it, they are among the first cells to show wear with age. Aged lining cells can turn into senescent cells, cells that have stopped dividing and send out inflammatory signals that harm the tissue around them.
A new study in Aging Cell points to one protein, called MTR4, as a guard against this. In human cells, mice and worms, the team found that MTR4 declines with age, that removing it speeds up signs of aging, and that adding it back slows them. The work is entirely in cells and animals.
What MTR4 normally does
MTR4 is an old protein in evolution, shared by many animals. Its known job is in the cell's nucleus, where it helps process and break down RNA molecules that are no longer needed. Hints that it might also matter for cell aging came from other work: cells lacking parts of the same machinery tend to stop dividing.
What they did
The researchers worked with lining cells taken from human umbilical-cord veins, a standard model for blood-vessel cells. They made these cells old either by letting them divide until they stopped, or with stress such as hydrogen peroxide. They then lowered or raised MTR4 levels and measured classic markers of cell aging. They also looked for the proteins MTR4 binds to, and for the reason it disappears.
In mice, they used harmless viruses to deliver genetic tools: one that lowered Mtr4 in young mice, and one that raised it only in the vessel lining of aged mice. They measured the mice's movement in an open arena, blood flow in the main artery, the appearance of their organs under the microscope, and markers of aging cells. Each group had only four to six mice. Finally, they lowered or raised the matching gene in the roundworm C. elegans, a tiny animal often used to study lifespan.
What they found
- MTR4 fades with age. Its protein levels dropped in aged human lining cells, and in the aorta (the body's main artery), heart, liver, spleen and lung of 20-month-old mice compared with young ones. Cells that had simply paused dividing did not lose it, so the drop is linked to aging rather than to resting.
- Too little MTR4 ages cells; more of it rejuvenates them. Lowering MTR4 in young cells pushed them into a senescent state with more inflammatory signals. Adding MTR4 to aged cells reduced these markers.
- How it works. MTR4 binds and protects another protein, BUB3, which helps cells divide their chromosomes correctly and limits DNA damage. In aging cells, an enzyme called SYVN1 rises and tags MTR4 for destruction. A version of MTR4 that could not be tagged still made aged cells look younger.
- Mice. Young mice with less Mtr4 moved around less, showed signs of poorer vessel function (faster blood flow in the arch of the aorta and a narrower aorta lower down), aging-like changes in several organs, more senescent cells and more inflammatory signals in the blood. Aged mice given extra Mtr4 in their vessel lining showed the opposite: more exploring, better vessel measurements, fewer senescent cells and organ tissue that looked closer to that of young mice.
- Worms. Lowering the worm version of MTR4 shortened lifespan. Raising it made worms live much longer, about twice as long in the authors' words, similar to well-known long-lived worm strains, and they stayed more active and coped better with heat and chemical stress.
What to keep in mind
- No people. The authors themselves say that samples from older people are still needed to find out whether MTR4 is also reduced in their blood vessels.
- Small mouse groups, no lifespan. Each mouse test used four to six animals, and the mice were not followed to see whether they lived longer. Whether MTR4 can extend life in mammals is, as the authors write, a question for future studies.
- Genetic tools, not a drug. The effects came from changing genes with viruses. There is no medicine that raises MTR4, and such gene tools are far from use in people.
- Open questions. Exactly how MTR4 keeps BUB3 stable, and whether MTR4 matters in diseases such as hardened arteries or diabetes, has not yet been studied.
- Worms are not people. Genes that double a worm's lifespan often have much smaller effects in mammals, if any.
Why it matters
Most efforts against aging cells so far try to kill them (senolytics) or to quiet their signals. Both have downsides: removing aged vessel-lining cells for long periods can weaken the vessel wall's barrier, and blocking the signals may hamper the immune system and slow repair. This study points to a third route, helping the cells stay young in the first place, and names a concrete protein and the enzyme that destroys it. It is an early, mechanistic result, but one that links an everyday RNA-handling protein to the aging of blood vessels and, in worms, to lifespan itself.