This is an interesting study on Alzheimer’s disease. Unlike the multitude of low-quality academic studies, here the authors explore the complexity of the central nervous system, which is not limited to neurons, and show that this population of neuronal and non-neuronal cells interact and change over time.
Currently, the diagnosis of Alzheimer’s disease includes cognitive decline leading to dementia, associated with the observation of two major proteinopathies in the brain tissue. These two proteinopathies are plaques, formed by the aggregation of beta-amyloid proteins, and tangles, which are composed of hyperphosphorylated tau proteins.
However, the interaction between amyloid, tau, and cognitive decline is complex.
These proteinopathies follow a stereotypical propagation throughout the brain during the disease. This has led to staging paradigms such as CERAD, Thal, and Braak.
In this new study, scientists reconstructed the changing dynamics of the brain’s cellular environment and identified a pathway to Alzheimer’s disease that is distinct from other aging-related effects.
The authors suggest that two different types of non-neuronal cells initiate the process of amyloid and tau accumulation that defines Alzheimer’s disease.
Once pathology has accumulated, different cells called astrocytes play a key role in altering the brain’s electrical connectivity leading to cognitive impairment. The cells communicate with each other and bring in additional cell types that lead to a profound disruption in human brain function.
To achieve this, the authors constructed a comprehensive cellular atlas of the aged prefrontal cortex from 1.65 million single-nuclear RNA sequencing profiles sampled from 437 older adults and identified specific glial and neuronal subpopulations associated with Alzheimer’s disease-related traits.
Modeling identified two distinct lipid-associated microglial subpopulations: - one drives amyloid-β proteinopathy - the other mediates the effect of amyloid-β on tau proteinopathy In addition, a subpopulation of astrocytes mediates the effect of tau on cognitive decline.
They designed the BEYOND methodology to model the temporal change in cellular environments. It identified two distinct trajectories of brain aging, each defined by coordinated progressive changes in certain cellular communities that lead to either Alzheimer's dementia or classical brain aging.