New insights into brain aging and Alzheimer's from non-human primates

A new review was published in Aging (listed by MEDLINE/PubMed as "Aging (Albany NY)" and "Aging-US" by Web of Science), on October 29, 2024, Volume 16, Issue 20, titled, "Brain aging and Alzheimer's disease, a perspective from non-human primates."

In the review, Ferrer Isidro from the University of Barcelona and Reial Acadèmia de Medicina de Catalunya, explores the differences in brain aging and Alzheimer's disease between humans and their closest evolutionary relatives, such as chimpanzees, baboons, and macaques. The study highlights that while humans are uniquely susceptible to severe cognitive decline and memory loss caused by Alzheimer's disease, non-human primates typically experience only mild changes as they age.

Alzheimer's affects over 50 million people worldwide, making it crucial to understand how aging impacts the brain. This review sheds light on the differences between humans and non-human primates and reveals that while brain aging in primates involves some structural and protein changes, it does not result in the toxic protein deposits that drive Alzheimer's in humans.

In humans, harmful tau protein deposits, known as tau tangles, appear early in life and spread widely through the brain, which damages cells and contributes to memory loss. In non-human primates, tau tangles are rare and typically confined to small regions. While primates may develop beta-amyloid deposits-;fragments derived from amyloid precursor protein-;these deposits are less toxic and do not interact with tau tangles to trigger Alzheimer's-like symptoms. Aging primates experience only mild memory or behavioral changes, avoiding the severe cognitive decline and dementia often seen in humans.

Humans' unique vulnerability to Alzheimer's may be linked to traits that emerged through evolution, including larger brains, longer lifespans, and higher cognitive abilities. These adaptations may have come at a cost, making human brains more susceptible to aging-related damage.

This review also suggests that tau tangles play a more critical role in Alzheimer's progression than previously thought. While traditional treatments focus on targeting beta-amyloid deposits, this research highlights the need to shift attention to tau pathology. The work challenges the widely accepted amyloid cascade hypothesis, which suggests that beta-amyloid is the main driver of Alzheimer's. Instead, it points to tau tangles as the initial and most damaging change in human brains. This insight could encourage new treatments that focus on preventing or reducing tau deposits.

The findings also emphasize the value of studying non-human primates to understand why their brains are more resistant to severe aging-related damage. By identifying protective mechanisms in primates, researchers may discover new strategies to delay or prevent Alzheimer's in humans. 

"These observations show that human brain aging differs from brain aging in non-human primates, and humans constitute the exception among primates in terms of severity and extent of brain aging damage."

In conclusion, this review not only improves our understanding of why humans are uniquely vulnerable to Alzheimer's disease but also opens new avenues for exploring innovative strategies to combat aging-related brain damage in humans.