Scientists at the Babraham Institute have developed a method to “time jump” human skin cells by 30 years, turning back the cellular aging clock without losing specialized cellular function. Researchers from the Institute’s epigenetics program showed that by using the “maturation phase transient reprogramming” approach they could partly restore the function of older cells, as well as rejuvenate molecular measures of biological age. The work is still at an early stage, but the researchers suggest future developments could one day revolutionize regenerative medicine.

Wolf Reik, PhD, a group leader in the epigenetics research program, who recently moved to lead the Altos Labs Cambridge Institute, said, “This work has very exciting implications. Eventually, we may be able to identify genes that rejuvenate without reprogramming, and specifically target those to reduce the effects of aging. This approach holds promise for valuable discoveries that could open up an amazing therapeutic horizon.”

Reik, together with first author postdoc Diljeet Gill, PhD, and colleagues, reported on their discoveries in eLife, in a paper titled, “Multi-omic rejuvenation of human cells by maturation phase transient reprogramming,” in which they concluded, “Overall, we demonstrate that it is possible to separate rejuvenation from complete pluripotency reprogramming, which should facilitate the discovery of novel anti-aging genes and therapies.”

As we age, our cells’ ability to function declines and the genome accumulates marks of aging. “Aging is the gradual decline in cell and tissue function over time that occurs in almost all organisms, and is associated with a variety of molecular hallmarks such as telomere attrition, genetic instability, epigenetic and transcriptional alterations, and an accumulation of misfolded proteins,” the authors wrote. Some aging-related changes, such as transcriptomic and epigenetic alterations, can be accurately measured, and so they can be used to generate “aging clocks” that can predict chronological age with high precision, both in humans and in other mammals, the team continued. And given that, in principle at least, transcriptomic and epigenetic changes are reversible, “this raises the intriguing question of whether molecular attributes of aging can be reversed and cells phenotypically rejuvenated.”

Regenerative biology aims to repair or replace cells including old ones. One of the most important tools in regenerative biology is our ability to create “induced” stem cells. In 2007, Shinya Yamanaka, MD, PhD, was the first scientist to turn normal cells, which have a specific function, into stem cells that have the special ability to develop into any cell type. The maturation phase transient reprogramming method reported by Reik and colleagues is based on the Nobel Prize winning technique that was used to make stem cells, but overcomes the problem of entirely erasing cell identity, by halting reprogramming part of the way through the process. And it is this ability that allowed the researchers to find the precise balance between reprogramming cells, making them biologically younger, while still being able to regain specialized cell function.

So, while the full process of stem cell reprogramming takes around 50 days using four key molecules—called Yamanaka factors—maturation phase transient reprogramming exposes cells to Yamanaka factors for just 13 days. At this point, age-related changes are removed and the cells have temporarily lost their identity.

The scientists then gave the partly reprogrammed cells time to grow under normal conditions, to observe whether their specific skin cell function returned. Genome analysis showed that the cells had regained markers characteristic of skin cells (fibroblasts), and this was confirmed by observing collagen production in the reprogrammed cells.

“To our knowledge, this is the first method for maturation phase transient reprogramming, where Yamanaka factors are transiently expressed up to the maturation phase of reprogramming before expression of the factors is abolished,” the authors stated.

To show that the cells had been rejuvenated, the researchers looked for changes in the hallmarks of aging. Gill explained, “Our understanding of aging on a molecular level has progressed over the last decade, giving rise to techniques that allow researchers to measure age-related biological changes in human cells. We were able to apply this to our experiment to determine the extent of reprogramming our new method achieved.”

The researchers looked at the cells’ epigenetic clock—the presence of chemical tags in the genome—and transcriptomic measures of cellular aging. They found that the reprogrammed cells matched the profile of cells that were 30 years younger compared to reference data sets. “As expected, we observed an overall reversal of the aging trends, with genes upregulated during aging being downregulated following transient reprogramming and genes downregulated during aging being upregulated following transient reprogramming,” they wrote. “Overall, our data demonstrate that transient reprogramming for 13 days (but apparently not for longer or shorter periods) represents a ‘sweet spot’ that facilitates partial rejuvenation of both the methylome and transcriptome, reducing epigenetic and transcriptional age by approximately 30 years.”

The potential applications of the newly reported technique will be dependent upon the cells not only appearing younger, but also functioning as young cells. Fibroblasts produce collagen, a molecule found in bones, skin tendons, and ligaments, helping provide structure to tissues and heal wounds. The team confirmed that the fibroblasts regenerated using the new method produced more collagen proteins compared with control cells that did not undergo the reprogramming process. Fibroblasts also move into areas that need repairing, and when the scientists tested the partially rejuvenated cells by creating an artificial cut in a layer of cells in a dish, they found that the treated fibroblasts moved into the gap faster than older cells.

This represents a promising indication that the team’s cell rejuvenation approach could eventually be used to create cells that are better at healing wounds. “Our data show that transient reprogramming followed by reversion can rejuvenate fibroblasts both transcriptionally and at the protein level, at least based on collagen production, and functionally at least in part,” the team stated. “This indicates that our rejuvenation protocol can, in principle, restore youthful functionality in human cells.”

The research may also open up other therapeutic possibilities. The investigators observed that maturation phase transient reprogramming also had an effect on other genes linked to age-related diseases and symptoms. The APBA2 gene, associated with Alzheimer’s disease, and the MAF gene, which plays a role in the development of cataracts, both showed changes towards youthful levels of transcription.

The authors concluded, “Overall, our results demonstrate that substantial rejuvenation is possible without acquiring stable pluripotency and suggest the exciting concept that the rejuvenation program may be separable from the pluripotency program. Future studies are warranted to determine the extent to which these two programs can be separated and could lead to discovery of novel targets that promote rejuvenation without the need for iPSC reprogramming.”

The mechanism behind the successful transient reprogramming is not yet fully understood, and this will be the focus of ongoing research. The researchers speculate that key areas of the genome involved in shaping cell identity might escape the reprogramming process.

Gill further concluded: “Our results represent a big step forward in our understanding of cell reprogramming. We have proved that cells can be rejuvenated without losing their function and that rejuvenation looks to restore some function to old cells. The fact that we also saw a reverse of aging indicators in genes associated with diseases is particularly promising for the future of this work.”

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