The study, published in Science, focused on how aging disrupts "proteostasis," or protein homeostasis. This system helps cells correctly build, maintain, and dispose of proteins. When proteostasis fails, damaged proteins can accumulate into harmful clumps that interfere with normal brain function.

Researchers say the findings provide one of the clearest explanations yet for why aging brains become increasingly vulnerable to disease and mental decline.

"We know that many processes become more dysfunctional with aging, but we really don't understand the fundamental molecular principles of why we age," said study author Judith Frydman, the Donald Kennedy Chair in the School of Humanities and Sciences at Stanford. "Our new study begins to provide a mechanistic explanation for a phenomenon widely seen during aging, which is increased aggregation and dysfunction in the processes that make proteins."

A Tiny Fish With Big Clues About Aging

To investigate what happens in aging brains, the researchers turned to the turquoise killifish, Nothobranchius furzeri. Native to temporary freshwater pools in the African savanna, these brightly colored fish have extremely short lifespans and develop many age-related problems rapidly, making them ideal for aging research.

Because mice and other mammals age much more slowly, studying the biological causes of aging can take years. Killifish allow scientists to observe those same processes on a much faster timeline.

The team compared young, adult, and old fish, examining many aspects of protein production inside brain cells. They measured amino acid levels, transfer RNA, messenger RNA (mRNA), proteins, and other components involved in cellular protein manufacturing.

How Protein Production Starts Breaking Down

Proteostasis relies on a careful balance between creating proteins and removing damaged ones. It also helps prevent proteins from folding incorrectly and sticking together in toxic aggregates. These protein clumps are strongly associated with neurodegenerative diseases, including Alzheimer's.

Frydman's lab has spent years studying how cells maintain proteostasis in simpler organisms such as yeast and roundworms. The new findings show that similar aging mechanisms also occur in more complex vertebrates like killifish and humans.

"With aging, problems mysteriously emerge at many levels -- at the mechanistic, cellular, and organ level -- but one commonality is that all those processes are mediated by proteins," Frydman said. "This study confirms that during aging, the central machinery that makes proteins starts to have quality problems."

The researchers traced the issue to a specific phase of protein synthesis known as translation elongation. During this process, ribosomes move along mRNA strands and assemble proteins by adding amino acids one at a time.

In older fish brains, the ribosomes frequently stalled or collided with one another. These molecular "traffic jams" reduced the production of healthy proteins and increased protein aggregation.

"Our results show that changes in the speed of ribosome movement along the mRNA can have a profound impact on protein homeostasis -- and highlight the essential nature of 'regulated' translation elongation speed of different mRNAs in the context of aging," said Jae Ho Lee, co-lead author of the paper who worked on this as a postdoctoral scholar in the Frydman lab. He is now an assistant professor at Stony Brook University.

Solving Another Aging Mystery

The discovery may also help explain another puzzling hallmark of aging called "protein-transcript decoupling." In aging organisms, changes in mRNA levels often stop matching changes in protein levels, even though mRNA carries the instructions needed to build proteins.

The Stanford team found that aging-related disruptions in protein synthesis, particularly involving ribosomes, can explain why this disconnect occurs.

Many of the proteins affected by these failures are involved in maintaining genome stability and cellular integrity. As those systems weaken, broader aging-related dysfunction can follow.

"Showing that the process of protein production loses fidelity with aging provides a kind of underlying rationale for why all these other processes start to malfunction with age," said Frydman. "And, of course, the key to solving a problem is to understand why it's gone wrong. Otherwise, you're just fumbling in the dark."

Potential New Targets for Alzheimer's and Cognitive Decline

The researchers now plan to investigate whether ribosome dysfunction directly contributes to human neurodegenerative diseases and whether therapies aimed at improving protein production could help protect the aging brain.

They are especially interested in exploring whether boosting translation efficiency or improving ribosome quality control could restore healthier protein balance in brain cells and potentially slow cognitive decline.

"This work provides new insights on protein biogenesis, function, and homeostasis in general, as well as a new potential target for intervention for aging-associated diseases," said Lee.

The team is also studying how these molecular processes influence longevity and cognitive aging across multiple species.

Frydman, a professor of biology in the School of Humanities and Sciences and of genetics in the School of Medicine, is also a member of Stanford Bio-X, the Stanford Cancer Institute, and the Wu Tsai Neurosciences Institute, and a faculty fellow of Sarafan ChEM-H. Frydman is also co-director of the Paul F. Glenn Center for Biology of Aging Research at Stanford. Additional work on the mechanisms of human neuronal aging and its link to Alzheimer's Disease in the Frydman lab is funded by the Knight Initiative for Brain Resilience.