Four proteins that can transform adult cells into embryonic-like ones can also turn back the aging clock, a new study in mice suggests.
Partial reprogramming of cells within prematurely aging mice’s bodies extended the rodents’ average life span from 18 weeks to 24 weeks, researchers report December 15 in Cell. Normal mice saw benefits, too: Muscles and pancreas cells healed better in middle-aged mice that got rejuvenation treatments than in mice that did not. The experiment could be evidence that epigenetic marks — chemical tags on DNA and proteins that change with age, experience, disease and environmental exposures — are a driving factor of aging. Some marks accumulate with age while others are lost.
“It’s an inspiring paper,” says Jan van Deursen, a biologist at the Mayo Clinic in Rochester, Minn., who studies diseases of aging. He gives the paper an “A” for sparking imagination, but lower marks for practical applications to human aging because it would involve gene therapy and could be risky. “It’s all cool, but I don’t see that it could ever be applied in medicine,” he says. “We could be terribly wrong. Hopefully we are.”
Researchers reset the mice’s aging clock by genetically engineering the animals to make four proteins when the rodents were treated with the antibiotic doxycycline. Those four proteins — Oct4, Sox2, Klf4 and c-Myc — are known as “Yamanaka factors” after Shinya Yamanaka. The Nobel Prize‒winning scientist demonstrated in 2006 that the proteins could turn an adult cell into an embryonic-like cell known as an induced pluripotent stem cell, or iPS cell (SN: 11/3/12, p. 13; SN: 7/14/07, p. 29).
The factors help strip away epigenetic marks that enable cells to know whether they are heart, brain, muscle or kidney cells, for example. As a result, stripped cells revert to the ultraflexible pluripotent state and are capable of becoming nearly any type of cell. Other researchers have used the Yamanaka factors to reprogram cells within living mice before, but those attempts resulted in the growth of tumors. (Cancer cells resemble stem cells in that they don’t have a specific identity and are “undifferentiated.”)
Those tumors indicated to Alejandro Ocampo and colleagues that the proteins were rewriting epigenetic programming to take cells back to an undifferentiated state. But “you don’t need to go all the way back to pluripotency” to erase the marks associated with aging, says Ocampo, a stem cell biologist at the Salk Institute for Biological Studies in La Jolla, Calif. A milder reprogramming treatment might reverse aging without stripping away cells’ identity, leading to cancer, Ocampo and colleagues thought.
The researchers put genetically engineered mice with a premature aging disease called progeria on a regimen in which the animals were treated with doxycycline two days per week to turn on the Yamanaka factors. Mice that made the reprogramming proteins lived six weeks longer on average than mice that didn’t get the treatment. The mice didn’t get cancer, but still died prematurely (lab mice usually live two to three years on average). “We are far away from perfection,” Ocampo says.
Normally aging mice also got benefits from the treatment. When the animals were 1 year old (roughly middle-aged), the researchers treated them with doxycycline two days per week for three weeks. Treated mice were better able to repair muscles and replace insulin-producing cells in the pancreas than untreated mice. Not all organs fared as well, Ocampo says, citing preliminary evidence. Ongoing experiments will determine whether the epigenetic reprogramming can make the mice live any longer or healthier.
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People probably won’t be genetically engineered the way mice are. But chemicals and small molecules might also be able to wipe away epigenetic residue that builds up with aging and restore marks that were lost over time, returning to a pattern seen in youth, Ocampo suggests.
Researchers still don’t know whether all cells are rejuvenated by the treatment. Yamanaka factors may breathe new life into aging stem cells, allowing them to replenish damaged tissues. Or the factors may wake up senescent cells — cells that have shut down normal functions and cease to divide, but may send signals to neighboring cells that cause them to age (SN: 3/5/16, p. 8). Reviving senescent cells could be dangerous, says van Deursen; the body shuts cells down to prevent them from becoming cancerous.
Plenty of evidence indicates that resetting epigenetic programming can extend life, says Ocampo. He points to a recent report that Dolly the Sheep’s cloned sisters are aging normally (SN: 8/20/16, p. 6) as a hopeful sign that reprogramming probably isn’t dangerous, and might one day safely prevent many of the diseases associated with aging in people, if not lengthening life spans.