Northwestern Medicine researchers have identified a largely overlooked space between brain cells that may explain why nearly two-thirds of Americans with Alzheimer's disease are women—a discovery that could reshape how doctors think about memory loss tied to menopause.
The breakthrough centers on the extracellular matrix, or ECM, a network of molecules that fills the spaces between brain cells like mortar between bricks. Though it makes up nearly 20% of the brain's volume and is abundant in the hippocampus, the region crucial for memory, scientists have historically overlooked it in favor of studying brain cells themselves. For the first time, researchers led by Dr. Hong Zhao at Northwestern University Feinberg School of Medicine examined what happens to this matrix when estrogen declines in women's brains.
Using young and old male and female mice, both with and without loss of brain estrogen, the team pinpointed effects specifically relevant to aging women. The findings, published in the journal Aging Cell, reveal something striking: females—but not males—appear uniquely sensitive to brain estrogen loss at older ages, potentially driving their increased Alzheimer's risk.
The mechanism is becoming clearer. Before menopause, a woman's ovaries produce most of her body's estrogen. After menopause, estrogen levels drop sharply, though small amounts continue to be produced in the brain, fat tissue, bone, muscle, and blood vessels. The brain is especially important here: in males, estrogen is synthesized locally in both the brain and gonadal fat, but in females it is produced predominantly in the brain alone. When that production declines, the ECM appears to suffer, compromising its job as a supportive scaffold that helps brain cells communicate and function properly.
The significance is hard to overstate. "Once memory is gone, it's gone," said Dr. Serdar Bulun, chair of obstetrics and gynecology at Feinberg and senior author of the study, emphasizing that the window for prevention may be narrow and precious. Research has already shown that women with Alzheimer's disease have even lower estrogen levels in the brain than women without it, and this work strengthens that connection.
Current Alzheimer's treatments, such as lecanemab and donanemab, focus on removing abnormal amyloid protein buildup—one main hallmark of the disease. Yet their clinical benefits remain modest and inconsistent, with some studies showing small improvements in memory loss while others report little meaningful change in daily functioning. The Northwestern findings suggest a different path forward: rather than targeting amyloid alone, researchers could explore therapies that restore the brain's supportive environment by strengthening the extracellular matrix.
Dr. Zhao hopes the study will motivate clinicians to recognize estrogen's essential role in women's brain health—and spur future research into how the matrix changes in postmenopausal women and how those changes might trigger Alzheimer's susceptibility. The implications extend beyond Alzheimer's disease; estrogen's effects on memory and mood function in the female brain appear far more fundamental than previously appreciated.
This discovery opens a new lens on a disease that has long puzzled researchers: why women bear such a disproportionate burden. The answer may lie not in the cells themselves, but in the spaces between them.