The Two Phases of Alzheimer's Disease
Alzheimer's disease is characterized by a long, slow buildup of amyloid-β aggregates in the brain, and in this period symptoms are minor to non-existent. The amyloid cascade hypothesis of Alzheimer's disease suggests that this aggregation sets the stage for a later feedback loop between tau protein aggregation and chronic inflammation in the brain, which produces a more rapid, sizable increase in pathology and loss of function. Researchers here use omics technologies to produce a map of postmortem diseased brains that supports this two phase view of the development of Alzheimer's disease, adding more detail to the existing picture.
Alzheimer's disease (AD) is the leading cause of dementia in older adults. Although AD progression is characterized by stereotyped accumulation of proteinopathies, the affected cellular populations remain understudied. Here we use multiomics, spatial genomics, and reference atlases from the BRAIN Initiative to study middle temporal gyrus cell types in 84 donors with varying AD pathologies. This cohort includes 33 male donors and 51 female donors, with an average age at time of death of 88 years.
We used quantitative neuropathology to place donors along a disease pseudoprogression score. Pseudoprogression analysis revealed two disease phases: an early phase with a slow increase in pathology, presence of inflammatory microglia, reactive astrocytes, loss of somatostatin+ inhibitory neurons, and a remyelination response by oligodendrocyte precursor cells; and a later phase with exponential increase in pathology, loss of excitatory neurons and Pvalb+ and Vip+ inhibitory neuron subtypes. These findings were replicated in other major AD studies.