New Insights into Alzheimer’s Disease Origins

The debate around the origins of Alzheimer’s disease continues, but recent research indicates that competition between two key proteins might play a crucial role within brain cells.

Alzheimer’s, known to be the most prevalent form of dementia, has typically been linked to the accumulation of amyloid-beta and tau proteins in the brain. This study combines both proteins under a “unifying theory,” which the researchers believe helps clarify some of the uncertainties surrounding Alzheimer’s.

Amyloid-beta peptides are fragments that stick together and form plaques in the brains of those affected by Alzheimer’s. Interestingly, these plaques might start developing as long as 20 years prior to any symptoms. Yet, some studies show that tau tangles—these knots formed by misfolded tau proteins—might serve as a more accurate marker of cognitive decline than amyloid-beta plaques.

In a healthy state, tau stabilizes microtubules, which are essential for cellular structure. However, during Alzheimer’s, tau detaches, causing disruption within cells.

Over the years, the relevance of these two factors has been challenged, yet they remain key areas of research. Experts are trying to untangle which protein appears first, their individual impacts, and whether they are the primary cause of the disease or simply byproducts.

“For an Alzheimer’s diagnosis, both [amyloid-beta] and tau need to accumulate in the brain,” notes Ryan Julian, a chemistry professor at the University of California, Riverside, and the senior author of the study.

“Yet, many laboratories often focus on just one of these proteins, overlooking the other.”

Julian and his team conducted protein binding experiments to see how amyloid-beta and tau interact around microtubules. They found similarities in the sequences that suggest amyloid-beta peptides might compete with tau for attachment points on microtubules. When they mixed the proteins together, along with tubulin, the basic component of microtubules, they made an interesting observation.

According to Julian, “Our findings show that amyloid-beta and tau compete for the same spots on microtubules, and that amyloid-beta might be obstructing tau from functioning properly.” By using fluorescent markers, they could witness the instances where amyloid-beta “stole” tau’s binding sites.

They even tested amyloid-beta’s affinity for another protein, myoglobin, and still found that amyloid-beta had a stronger inclination to bind to microtubules, implying it’s not just sticking to any available protein.

The researchers propose this may help address the “chicken or egg” dilemma regarding the relationship between amyloid-beta and tau, while also acknowledging the limitations of studying purified proteins, as understanding their behavior within actual cells is much more intricate.

If the amyloid-beta peptides are indeed displacing tau from its usual binding sites, as these studies suggest, it might shed light on how tau forms tangles and destabilizes microtubules, ultimately leading to neuron death.

“The crucial point here is recognizing that tau doesn’t cause problems on its own but rather becomes detrimental after it’s displaced by [amyloid-beta],” the researchers explain in their paper.

They also hypothesize that this tau displacement may represent a primary source of toxicity for brain cells, rather than the mere accumulation of amyloid-beta or tau itself, even though both contribute to the overall issue.

“This new hypothesis helps frame many past observations in the literature and clarifies contradictions between traditional hypotheses regarding Alzheimer’s disease causes,” Julian and his team convey.

This study also brings a fresh perspective to previous clinical trials regarding Alzheimer’s therapies that didn’t yield promising results, especially those aiming to clear amyloid-beta, which often failed to restore critical brain functions.

If further research validates these insights, it might shift the direction for developing effective Alzheimer’s treatments, a condition that represents about 70 percent of dementia cases and currently lacks a cure.

Interestingly, recent studies involving animals have suggested that lithium could provide protective effects, potentially helping to stabilize microtubules.

As a result, pursuing therapies that safeguard these microtubules might be a promising alternative instead of merely attempting to eliminate protein accumulations, which has generally been the focus of current Alzheimer’s treatments.

Overall, Julian expresses, “This study brings clarity to many previously disparate results, offering a more coherent view of what might be happening inside neurons and where new treatment avenues could begin.”

This research is available in PNAS Nexus.