Charvet Seeks to Understand Comparative Aging
To Christine Charvet, age is only a number.
But it is a number she absolutely, positively wants to pin down as precisely as possible. It’s a number that will elucidate how human development and aging compare with other species.
Charvet, an Assistant Professor in the Auburn University College of Veterinary Medicine’s Department of Anatomy, Physiology and Pharmacology, has a passion for determining ages — but not just of people, but of creatures ranging from mice to monkeys to cats and more.
A graduate of the University of California-Los Angeles and Cal-Irvine, she did her postdoctoral training in neuroimaging at Harvard Medical School and statistical genetics at Cornell University prior to joining the Auburn CVM faculty.
While at Cornell, she worked with the developers of a website called Translating Time (www.translatingtime.org) — a statistical model that equates the timing of brain developmental events across different mammalian species. The site uses behavioral, neurological and transcriptional markers to estimate equivalent stages of development between species as diverse as mice and humans. At Auburn, Charvet has been dedicated to expanding both the number of species and range of ages included in the model.
The empirical data generating the model for each species currently comprises 1600 biological time points, including measures of initial neurogenesis, axon extension and establishment, and refinement of brain connections. Later events, such as myelin formation, brain growth and early behavioral milestones, are also included.
Charvet and her collaborators, including Dr. Alexandra de Sousa, researcher at Auburn, focus on utilizing a multi-omics approach, which integrates transcription, epigenetic and structural variation to expand the model’s data to determine equivalency across varying species’ lifetimes. That effort is particularly challenging because none of the other species studied so far — even chimpanzees, which she and the team added to the site’s species list and have focused on of late — experience life spans as lengthy as humans.
That’s not a problem when determining timepoints, or markers of comparative development over time, for great apes and humans using prenatal and early development comparisons. In fact, Charvet said the research has highlighted both interesting similarities and differences.
“Both humans and great apes are born ready to take on the world,” she noted. “They are born with eyes open and the ability to process sensory information. But even so, they are still largely helpless to react to it in a meaningful way. As for differences, locomotion takes longer in humans. Young apes are able to grasp things and knuckle walk sooner.”
But early development aside, the difference in life spans is a problem when trying to make comparisons between apes and humans as they age. “We quickly realized one thing unique to humans compared to other apes is old age,” Charvet explained. “It is very rare for chimpanzees to live past 45 years, which roughly equates to the fifties in humans.
“That means the biological processes that occur in humans beyond their 60s are difficult to observe in great apes because many of them do not live sufficiently long life spans for these biological processes to become manifest,” she continued. “That is problematic, because there are many health developments in human old age such as Alzheimer’s disease, and great apes do not live sufficiently long enough to recapitulate geriatric stages.”
But Charvet and her team are not focused solely on apes. They have expanded their studies to 66 species so far, including big cats such as lions and — appropriately enough for Auburn research — tigers. In 2023, they also launched a program featuring research on the domestic cat.
“We are now looking at cats because they may have a counterpart to human old age. We are focusing on capturing multi-omic metrics we can collect in their old age,” she added. “But their biological processes obviously differ more from humans.”
The “Catage Project,” which is also led by Dr. Ryan Gibson, a veterinary neurologist and lecturer in the Department of Anatomy, Physiology and Pharmacology, has utilized data gathered from cats coming in at the CVM’s Bailey Small Animal Hospital as well as from more than 3,000 cats whose humans allowed their information to be used.
These volunteers from across the nation have submitted exact or approximate birth dates for their pets. By comparing the developmental timepoints for cats with a known date of birth to those whose birth date is only approximate, an estimate of the latter groups’ ages can be made.
This information will eventually be added into the Translating Time database. But even better, the results will help veterinarians administer the best possible care for cats through providing age-appropriate treatment when the pet’s age is not known.
The research conducted by Charvet and her team is gaining increasing attention. Recent articles in the scientific journals Trends in Cognitive Sciences, Communications Biology, and PNAS Nexus, in addition to the children’s educational publication Frontiers for Young Minds, have helped demonstrate the importance of and uses for the studies of comparative aging.
As for Charvet, she says she and her team are just getting started. There’s no stopping at 66 species. There are enough species still to be studied to keep a researcher busy into old age herself. “I’d eventually like to study all mammals,” she said, then reluctantly reduced that target slightly. “Well maybe not all. But we are just recently starting to look at the big cats. Elephants are interesting, because their life spans are similar to humans. And eventually, maybe, there are reptiles and birds.”