The biological age of humans and mice undergoes a rapid increase in response to diverse forms of stress, which is reversed following recovery from stress, according to a study publishing on April 21 in the journal Cell Metabolism. These changes occur over relatively short time periods of days or months, according to multiple independent epigenetic aging clocks.
“This finding of fluid, fluctuating, malleable age challenges the longstanding conception of a unidirectional upward trajectory of biological age over the life course,” says co-senior study author James White of Duke University School of Medicine. “Previous reports have hinted at the possibility of short-term fluctuations in biological age, but the question of whether such changes are reversible has, until now, remained unexplored. Critically, the triggers of such changes were also unknown.”
The biological age of organisms is thought to steadily increase over the life course, but it is now clear that biological age is not indelibly linked to chronological age. Individuals can be biologically older or younger than their chronological age implies. Moreover, increasing evidence in animal models and humans indicates that biological age can be influenced by disease, drug treatment, lifestyle changes, and environmental exposures, among other factors.
The liver has a unique ability to regenerate after damage. However, it was unknown whether this ability decreases as we age. International scientists led by Dr. Olaf Bergmann at the Center for Regenerative Therapies Dresden (CRTD) at TU Dresden used a technique known as retrospective radiocarbon birth dating to determine the age of the human liver. They showed that no matter the person’s age, the liver is always on average less than three years old. The results demonstrate that aging does not influence liver renewal, making the liver an organ that replaces its cells equally well in young and old people.
The liver is an essential organ that takes care of clearing toxins in our bodies. Because it constantly deals with toxic substances, it is likely to be regularly injured. To overcome this, the liver has a unique capacity among organs to regenerate itself after damage. Because a lot of the body’s ability to heal itself and regenerate decreases as we age, scientists were wondering if the liver’s capacity to renew also diminishes with age.
The nature of liver renewal in humans also remained a mystery. The animal models provided contradictory answers. “Some studies pointed to the possibility that liver cells are long-lived while others showed a constant turnover. It was clear to us that if we want to know what happens in humans, we need to find a way to directly assess the age of human liver cells,” says Dr. Olaf Bergmann, research group leader at the Center for Regenerative Therapies Dresden (CRTD) at TU Dresden.
I have always been fascinated by the dichotomy between chronological age and biological age.
There are two types of age: chronological age, or the number of years a person or animal has lived, and biological age, which accounts for various lifestyle factors that can shorten or extend lifespan, including diet, exercise, and environmental exposures. Overall, biological age has been shown to be a better predictor of all-cause mortality and disease onset than chronological age.
A newly discovered ribosomal DNA (rDNA) clock can be used to accurately determine an individual’s chronological and biological age, according to research led by Harvard T.H. Chan School of Public Health. The ribosomal clock is a novel biomarker of aging based on the rDNA, a segment of the genome that has previously been mechanistically linked to aging. The ribosomal clock has potentially wide applications, including measuring how exposures to certain pollutants or dietary interventions accelerate or slow aging in a diversity of species, including mice and humans.
“We have hopes that the ribosomal clock will provide new insights into the impact of the environment and personal choices on long-term health,” said senior author Bernardo Lemos, associate professor of environmental epigenetics. “Determining biological age is a central step to understanding fundamental aspects of aging as well as developing tools to inform personal and public health choices.”
The study was published online in Genome Research on February 14, 2019. Continue reading →