We're all familiar with the inescapable effects that the march of time has on our bodies, but the processes that drive aging are still offering up surprises. Scientists have long known that DNA segments called telomeres play a crucial part in our aging process, but new research has discovered a protein that acts as a kind of cellular timekeeper, regulating the length of telomeres to maintain healthy cell division and prevent the development of cancer.

Each time a cell divides, a tiny section of DNA is lost, and while this could be devastating to the cell, our bodies have a natural defense against the loss of any important genetic information. Telomeres are little caps made of repetitive sections of DNA at the end of each chromosome, and whenever a cell divides they take the hit. The problem is, telomeres have a set length, and as they degrade over time that buffer zone eventually stops protecting the important bits of information, leading to the well-known bodily wear-and-tear we associate with aging.

"Telomeres represent the clock of a cell," says Eros Lazzerini Denchi, corresponding author of the study. "You are born with telomeres of a certain length, and every time a cell divides, it loses a little bit of the telomere. Once the telomere is too short, the cell cannot divide anymore."

Logically then, longer telomeres should lead to longer lives, right? Technically yes, and that's an area that scientists have been experimenting with for years. Back in 2010, a Harvard study was able to slow and even reverse the aging process in mice by manipulating telomerase, an enzyme that helps replenish telomeres. Breakthroughs on the road to applying the process to human cells followed, with the discovery that telomerase can function like an "off" switch, and a new procedure to extend the life of lab-grown cells.

But it's not as simple as just lengthening telomeres and enjoying a similarly-lengthened life. If cells are allowed to divide unchecked, that same freedom also applies to cancerous cells, increasing the risk of tumors developing.

"This cellular clock needs to be finely tuned to allow sufficient cell divisions to develop differentiated tissues and maintain renewable tissues in our body and, at the same time, to limit the proliferation of cancerous cells," says Lazzerini Denchi.

Associate Professor Eros Lazzerini Denchi (left) and Gracrditduate Student Julia Su Zhou Li led the study at The Scripps Research Institute (Credit: Madeline McCurry-Schmidt)

Until recently, scientists thought they knew of all proteins that bind to telomeres: namely telomerase and Shelterin, a protein complex that helps protect telomeres and regulate telomerase. But now scientists from the Scripps Research Institute have discovered a new protein, called TZAP.

TZAP's role is to control a process called telomere trimming, which keeps the telomeres within that sweet spot of proliferation: long enough to be healthy, but below the risky upper limit. While the discovery may not have a direct application to increasing overall human lifespan yet, improving our understanding of these crucial processes can help pave the way for these kinds of advances in future.

"This study opens up a lot of new and exciting questions," says Lazzerini Denchi.

The research was published in the journal, Science.

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