A new study whereby a team of scientists analysed over 3500 brains that were donated suggests that rogue protein known as tau, as opposed to another protein, amyloid, is the trigger for the cognitive decline in the development of Alzheimer’s disease. Tau has previously been suspected to be the main drive of the decline.
Alzheimer’s disease is a chronic neurodegenerative disease, characterised by the gradual loss of brain tissues. As the disease progresses, two proteins have been observed to accumulate: amyloid-β and tau. The proteins are known for their important roles in brain cell function, but, if they fold abnormally, they clump in and out of cells, thereby obstructing normal cellular processes that might even lead to cell death. Amyloid has received more attention from researchers than tau has. But, the findings of a new research has provided insight into tau’s role in the disease from another angle.
The results of the new study have shifted the focus from amyloid to tau. The research has not, however, established which of the two proteins contributes to the disease to the greatest extent. Rather, it points out that scientists might explore the role of tau instead of just following the trend of analysing amyloid.
The journey of abnormal tau pertaining to Alzheimer’s is said to start in the neurones of the hippocampus (the region of the brain associated with learning and memory). The distorted protein then spreads to the cortex which is linked with higher brain functions like thinking, awareness and language. This is in contrast to the propagation of amyloid – the latter starts in the outer areas of the cortex and then reaches the hippocampus.
The scientists who authored the new study had as objective to clarify whether the proteins were a cause of the disease or a consequence. They made use of the Mayo brain bank (a collection of thousands of donated postmortem brains).
The brains of patients with and without Alzheimer’s were examined; different stages of the disease were compared, with the aim to shedding light on the roles of the two proteins.
The findings showed that though a decline in cognition had a strong link with the accumulation of amyloid, the relationship disappeared when tau accumulation was taken into consideration. Moreover, the level of tau aggregation forecasted age at onset of the cognitive decline, disease duration, and final score on a test of mental function – tau and not amyloid. The researchers thus concluded that tau should be the main driver of the disease.
“Our findings highlight the need to focus on tau for therapeutics,” says lead author Dr. Murray.