When Jeanne Calment died at the age of 122, her longevity had researchers scratching their heads. Although physically active for most of her life, she was also a regular smoker and enjoyed wine—lifestyle choices that are generally thought to decrease healthy lifespan.
Teasing apart the intricacies of human longevity is complicated. Diet, exercise, and other habits can change the trajectory of a person’s health as they grow older. Genetics also plays a role—especially during the twilight years. But experiments to test these ideas are difficult, in part because of our relatively long lifespan. Following a large population of people as they age is prohibitively expensive, and results could take decades. So, most studies have turned to animal aging models—including flies, rodents, and dogs—with far shorter lives.
But what if we could model human “aging in a dish” using cells derived from people with exceptionally long lives?
A new study, published in Aging Cell, did just that. Leveraging blood draws from the New England Centenarian Study—the largest and most comprehensive database of centenarians—they transformed blood cells into induced-pluripotent stem cells (iPSCs).
These cells contain their donor’s genetic blueprint. In essence, the team created a biobank of cells that could aid researchers in their search for longevity-related genes.
“Models of human aging, longevity, and resistance to and/or resilience against disease that allow for the functional testing of potential interventions are virtually non-existent,” wrote the team.
They’ve already shared these “super-aging” stem cells with the rest of the longevity community to advance understanding of the genes and other factors contributing to a healthier, longer life.
“This bank is really exciting,” Chiara Herzog, a longevity researcher at Kings College London, who was not involved in the study, told Nature.
Precious Resource
Centenarians are rare. According to the Pew Research Center, based on data from the US Census Bureau, they make up only 0.03 percent of the country’s population. Across the globe, roughly 722,000 people have celebrated their 100th birthday—a tiny fraction of the over eight billion people currently on Earth.
Centenarians don’t just live longer. They’re also healthier, even in extreme old age, and less likely to suffer age-related diseases, such as dementia, Type 2 diabetes, cancer, or stroke. Some evade these dangerous health problems altogether until the very end.
What makes them special? In the last decade, several studies have begun digging into their genes to see which are active (or not) and how this relates to healthy aging. Others have developed aging clocks, which use myriad biomarkers to determine a person’s biological age—that is, how well their bodies are working. Centenarians frequently stood out, with a genetic landscape and bodily functions resembling people far younger than expected for their chronological age.
Realizing the potential for studying human aging, the New England Centenarian Study launched in 1995. Now based at Boston University and led by Tom Perls and Stacy Andersen, both authors of the new study, the project has recruited centenarians through a variety of methods—voter registries, news articles, or mail to elderly care facilities.
Because longevity may have a genetic basis, their children were also invited to join, with spouses serving as controls. All participants reported on their socioeconomic status and medical history. Researchers assessed their cognition on video calls and screened for potential mental health problems. Finally, some participants had blood samples taken. Despite their age, many centenarians remained sharp and could take care of themselves.
Super-Ager Stem Cells
The team first tested participants with a variety of aging clocks. These measured methylation, which shuts genes down without changing their DNA sequences. Matching previous results, centenarians were, on average, six and a half years younger than their chronological age.
The anti-aging boost wasn’t as prominent in their children. Some had higher biological ages and others lower. This could be because of variation in who inherited a genetic “signature” associated with longevity, wrote the team.
They then transformed blood cells from 45 centenarians into iPSCs. The people they chose were “at the extremes of health and functionality,” the team wrote. Because of their age, they initially expected that turning back the clock might not work on old blood cells.
Luckily, they were wrong. Several proteins showed the iPSCs were healthy and capable of making other cells. They also mostly maintained their genomic integrity—although surprisingly, cells from three male centenarians showed a slight loss of the Y chromosome.
Previous studies have found a similar deletion pattern in blood cells from males over 70 years of age. It could be a marker for aging and a potential risk factor for age-related conditions such as cancer and heart disease. Women, on average, live longer than men. The findings “allow for interesting research opportunities” to better understand why Y chromosome loss happens.
Unraveling Aging
Turning blood cells into stem cells erases signs of aging, especially those related to the cells’ epigenetic state. This controls whether genes are turned on or off, and it changes with age. But the underlying genetic code remains the same.
If the secrets to longevity are, even only partially, hidden in the genes, these super-aging stem cells could help researchers figure out what’s protective or damaging, in turn prompting new ideas that slow the ticking of the clock.
In one example, the team nudged the stem cells to become cortical neurons. These neurons form the outermost part of the brain responsible for sensing and reasoning. They’re also the first to decay in dementia or Alzheimer’s disease. Those derived from centenarians better fought off damage, such as rapidly limiting the spread of toxic proteins that accumulate with age.
Researchers are also using the cells to test for resilience against Alzheimer’s. Another experiment observed cell cultures made of healthy neurons, immune cells, and astrocytes. The latter, supporting cells that help keep brains healthy, were created using centenarian stem cells. Astrocytes have increasingly been implicated in Alzheimer’s, but their role has been hard to study in humans. Those derived from centenarian stem cells offer a way forward.
Each line of centenarian stem cells is linked to its donor—their demographics, cognitive, and physical state. This additional information could guide researchers in choosing the best centenarian cell line for their investigations into different aspects of aging. And because the cells can be transformed into a wide variety of tissues that decline with age—muscles, heart, or immune cells—they offer a new way to explore how aging affects different organs, and at what pace.
“The result of this work is a one-of-a-kind resource for studies of human longevity and resilience that can fuel the discovery and validation of novel therapeutics for aging-related disease,” wrote the authors.
Image Credit: Danie Franco on Unsplash
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