For some years now, scientists have been debating whether humans are the only animal capable of developing Alzheimer’s disease. However, now it's looking more likely we share this trait with our closest evolutionary relative, the chimpanzee.
Researchers from the Raghanti laboratory at Kent State University, Ohio were given the opportunity to study 20 brains of chimpanzees that died of old age. In chimp years, that’s between 37 and 62 years. The study, part of the dissertation research of Melissa Edler, will be published in an upcoming edition of the journal Neurobiology of Aging.
Within the researchers' samples, there were the same physical signs you expect to see in a human brain with Alzheimer’s disease, like the presence of beta-amyloid plaques and tangles. Among these chimps, 13 had amyloid plaques and 4 had tangles. The numbers of plaques were also significantly higher as the chimps got older.
In humans, these plaques and tangles are the prime suspects for cell death and tissue loss in the brains of people with Alzheimer’s disease. It starts with the buildup of “sticky” bits of protein, called amyloid beta peptides, between the brain cells. Eventually, this prompts tau proteins in the brain to collapse into twisted strands, called tangles, which causes the neurons to die.
A previous study, in 2008, discovered “the first conclusive evidence” of Alzheimer's-associated signs (plaques and tangles) in a chimpanzee. However, this study was based on the brain of a single chimp who died of a stroke, which could perhaps explain the presence of these tangles.
While all the signs are there, the research did not show whether they are associated with other symptoms we see in humans, such as cognitive decline, memory problems, disorientation, mood swings, etc.
"The aged chimpanzee brains had been collected over the last couple decades and had been from individuals housed at various zoos and research institutions. Therefore, we did not have cognitive data for these individuals," researcher Mary Ann Raghanti of Kent State University told IFLScience.
"Previous work did find at least mild cognitive deficits in aged chimpanzees, but more work is needed."
Raghanti said the next step was collect cognitive data from chimpanzees currently in captivity, as they age. "This data can then be compared with brain pathology scores after their deaths. Importantly, these cognitive data can be collected as part of enrichment for chimpanzees that benefit their health and well-being."
At least 46.8 million people are living with dementia and, with the world facing an ever-aging population, that number is forecasted to double every 20 years. Worse still, a cure is still a fair way off. However, even research on non-human species such as this could help dig deeper into the root cause and underlying mechanisms of Alzheimer's disease among humans and other primates alike.
[H/T: New Scientist]