Alzheimer's tipping point tied to brain immune cells in study

A possible Alzheimer's tipping point may lie in how the brain’s immune cells respond as amyloid plaques give way to tau-related damage, according to researchers from VIB, KU Leuven, the UK Dementia Research Institute and Muna Therapeutics. The finding matters because it may help explain why some people show Alzheimer’s-related brain changes but do not develop dementia.

The study, published in Nature Medicine, used donated human brain tissue from older adults with and without cognitive decline, along with samples from cognitively healthy people over age 100. VIB said the work points to microglia, the brain’s resident immune cells, as a potential target for treatments meant to extend cognitive resilience.

Alzheimer’s disease is commonly linked to amyloid-beta plaques and tau tangles in the brain. VIB said more than 55 million people worldwide are affected by the disease, but the amount of plaque and tau in a person’s brain does not always match that person’s cognitive condition.

What is the Alzheimer's tipping point?

The researchers describe the tipping point as a biological shift between brain regions dominated by amyloid-beta plaques and regions marked by tau pathology and neurodegeneration. At that transition, microglia appeared to change from an early inflammatory state linked to amyloid into a later antigen-presenting state seen alongside tau pathology.

Antigen presentation is an immune process in which cells display molecular material to help organize an immune response. In this study, that shift may mark the point where Alzheimer’s pathology becomes more closely tied to brain cell damage and dementia, according to the research team.

How the researchers mapped the shift

The team used spatial transcriptomics and single-cell sequencing, methods that examine tissue and gene activity at fine cellular resolution. Those tools allowed the researchers to identify six tissue domains that appeared to reflect stages of Alzheimer’s progression.

Prof. Bart De Strooper of the VIB-KU Leuven Center for Neuroscience and KU Leuven, a co-senior author, said the study was based entirely on human donor material and gave insight into one type of resilience mechanism in the progression from Alzheimer’s disease to dementia. Prof. Mark Fiers of VIB-KU Leuven, also a co-senior author, said understanding how the brain resists disease could open paths toward therapies aimed at preventing neurodegeneration and dementia.

Resilience did not follow one pattern

The study found different routes to cognitive resilience. In octogenarians who had amyloid plaques but no dementia, microglia showed the earlier response linked to amyloid, but did not shift into the later immune state associated with progression.

Cognitively healthy centenarians showed a different pattern, according to VIB. Their brains activated the later microglial program, but the response was largely not tied to tau accumulation.

That finding suggests resilience may depend not only on avoiding Alzheimer’s pathology, but also on how the brain controls or separates immune responses from damaging effects. The researchers said the same cellular program can appear in different biological contexts, with different links to neurodegeneration.

What it could mean for treatment

The findings could broaden Alzheimer’s drug strategies beyond plaque removal, VIB said. Future approaches may try to preserve protective early microglial activity, alter the shift between microglial states, or target molecules involved in those transitions.

Niels Plath, chief scientific officer of Muna Therapeutics, said the work opens opportunities to target microglial states, including pathways such as TREM2, and to study how those transitions may contribute to disease progression. The researchers said timing may be important, with interventions potentially most useful before inflammatory activity becomes linked to tau pathology, neurodegeneration and cognitive decline.

This story draws on original reporting from ScienceDaily.