A study conducted with the participation of several scientific organizations has identified key biological changes that may help determine whether brain alterations associated with Alzheimer's disease lead to the development of dementia.

Study Features

The research utilized brain tissue samples from elderly individuals both with and without cognitive impairments, as well as samples from centenarians who maintained cognitive function. The analysis revealed that the brain’s immune cells—microglia—exhibit different cellular programs and states, some linked to disease progression and others to resistance. These findings highlight the important role of microglia in the development of Alzheimer's disease and open new directions for therapeutic research.

Alzheimer’s Disease and Microglia

Alzheimer’s disease affects more than 55 million people worldwide and is typically associated with the accumulation of amyloid-β plaques and tau protein tangles in the brain. However, the presence of these biological markers does not always correspond to a person’s cognitive state: some individuals with pronounced pathological changes retain cognitive health. This observation has led to a more detailed study of how brain cells respond to abnormal proteins, rather than just assessing the extent of pathology.

Microglia serve protective functions in the brain, but their behavior can change as the disease progresses. Understanding these changes may explain why some people remain resilient to cognitive decline and could help in developing new preventive strategies for dementia.

Different Paths to Resilience

The study showed that resilience to damage associated with Alzheimer’s disease can be achieved through various biological pathways. Comparing brain tissue from people with dementia, without dementia, and centenarians with preserved cognitive abilities revealed distinct microglial responses related to protection against disease consequences.

To investigate the mechanisms of resilience, researchers combined advanced spatial transcriptomics and single-cell sequencing methods. This allowed them to identify six tissue domains reflecting different stages of disease progression. Of particular importance was the transition from regions dominated by amyloid-β plaques to areas associated with tau pathology and neurodegeneration, which was accompanied by significant changes in microglial behavior.

Stages and Mechanisms of Change

In the early stages of the disease, microglia shifted to an inflammatory state associated with amyloid plaques. At later stages, the cells transitioned to a state linked to antigen presentation, coinciding with the development of tau pathology. This transition may represent a biological tipping point that determines whether Alzheimer’s pathology leads to brain cell damage and dementia.

Resilience manifested differently among individuals. In elderly people with amyloid plaques but without dementia, an early microglial response was observed without a shift to the later immune state. In centenarians, a later microglial program was activated, but this response generally occurred without a connection to tau protein accumulation.

Thus, resilience is not merely the absence of pathology, but also the brain’s ability to control, redirect, or adapt its response to pathological changes.

Therapeutic Perspectives

The data obtained may contribute to the development of more precise treatments for Alzheimer’s disease. Instead of focusing solely on removing amyloid plaques, future therapies could aim to support beneficial early microglial activity or influence the transitions between different cellular states. Molecules involved in these transitions may become promising therapeutic targets.

The timing of treatment initiation may also play a crucial role: the greatest effectiveness might be achieved before inflammatory activity becomes linked to tau pathology, neurodegeneration, and cognitive decline.

These discoveries open new possibilities for influencing microglial states, including through pathways such as TREM2, and for prolonging resilience rather than just removing plaques. Understanding the causal role of microglial transitions could lead to new therapeutic approaches to slow or prevent the progression of Alzheimer’s disease.