Astrocytes, cells that are involved in the brain’s support system, might play an important role in the progression of Alzheimer disease, according to results from 1016 participants with and without amyloid-β pathology who were all cognitively unimpaired. Participants were aged 70 years on average.

Amyloid-β accumulation was linked with an increase in tau tangles only in the participants who tested positive for astrocyte reactivity, a cellular response to brain pathology. Because amyloid-β tends to increase in people’s brains before tau tangles—a signal of Alzheimer disease development—accumulate, abnormal levels of astrocyte reactivity might function as an upstream warning sign of Alzheimer disease development before symptoms appear, the researchers wrote in Nature Medicine.