Brain Estrogen Loss May Drive Alzheimer’s Risk in Women
Brain-specific estrogen loss triggered memory decline and brain matrix changes in aging female mice.
Why are women more disproportionately affected by Alzheimer's disease (AD)?
A new multi-institutional study, led by Northwestern University found that localized estrogen loss in the brain alters the structural matrix, leading to severe memory impairment in older females.
The link between menopause, estrogen, and Alzheimer's
AD affects women more than men, with women making up nearly two-thirds of American AD patients. Despite the clear sex difference, the biological reasons behind it remain poorly understood.
Historically, scientists focused on menopause. After menopause, a woman's circulating estrogen drops, and this reduction is thought to contribute to a loss of neuroprotective effects.
While hormone replacement therapy (HRT) has been explored to prevent cognitive decline, clinical trials have yielded mixed results, and the National Institute for Health and Care Excellence (NICE) Menopause Guidelines advise that HRT should not be prescribed for the specific purpose of preventing cognitive decline or dementia.
Prior research has found that whole-body estrogen deficiency harms memory. However, traditional research models depleted estrogen across all tissues, which obscured the specific role of estrogen synthesized locally within the brain. Researchers also still do not fully understand how localized estrogen loss drives female-specific vulnerability to AD.
Previous studies predominantly focused on brain cells, including neurons and glial cells, while neglecting the extracellular matrix (ECM), which is highly abundant in the hippocampus.
The extracellular matrix (ECM)
The ECM is a non-cellular network of proteins and molecules that surrounds cells. It acts like a scaffold and makes up nearly 20% of the brain's volume, providing structural support and helping cells communicate with one another within the brain.
In the new study, the team set out to measure the effects of brain-derived estrogen deficiency while assessing its mechanistic link to sex-specific AD vulnerability. Specifically, they looked at how losing localized estrogen impacts memory, affective behavior, and gene expression profiles in the aging brain.
How brain estrogen loss changes the brain
The researchers developed two specialized mouse models with targeted deletion of aromatase, the essential enzyme required for estrogen synthesis. In the brain-specific knockout mice (bArKO) aromatase was deleted only in the brain, whereas in the total-body knockout mice(tArKO), aromatase was deleted throughout the body. Aromatase deletion reduced brain estrogen levels in bArKO mice, and circulating and brain estrogen levels in tArKO mice.
Male and female mice underwent a series of behavioral tests. The mice were categorized as either young (6–8 months) or old (older than 19 months). They completed assessments for spatial working memory as well as tests for social interaction and anxiety or depression-like behaviors.
Old female mice missing estrogen only in the brain displayed significant impairments in spatial working memory and social interactions. These deficits were not observed in the male counterparts.
A total systemic lack of estrogen also triggered depression-like behaviors exclusively in the female mice.
To understand the molecular cause, the team examined the hippocampus.
They discovered that old female mice lacking brain estrogen exhibited an upregulation of genes linked to the ECM, including Col1a1, Ccn2, Dcn, and Ogn.
Four key ECM genes
Col1a1 (Collagen Type I Alpha 1): Directs the production of collagen, a core structural protein that acts as the "glue" holding the brain's cellular environment together.
Ccn2 (Cellular Communication Network Factor 2): Coordinates communication between cells and manages the remodeling and repair of the surrounding matrix.
Dcn (Decorin): Acts as a structural organizer by binding to collagen, ensuring the matrix fibers wrap together neatly instead of tangling.
Ogn (Osteoglycin): Helps assemble and stabilize the matrix network to keep the brain's physical support system strong.
What estrogen research means for postmenopausal treatments
“This study tells us that females—but not males—may be uniquely sensitive to loss of brain estrogen at old age, potentially contributing to an increased risk of AD,” said corresponding author Dr. Hong Zhao, a research professor at Northwestern University Feinberg School of Medicine.
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Clinically, this suggests that therapeutically restoring the brain's ECM environment could be a viable new strategy for preventing cognitive decline.
The authors note that the study does have limitations, relying on small sample sizes for some analyses and only identifying a correlation rather than a proven direct causation.
“More research is needed to understand how estrogen affects the female brain and why estrogen loss increases AD risk in women,” Zhao said. “Understanding these mechanisms could help researchers develop safer and more effective HRT strategies to prevent or slow the progression of AD in women.”
The researchers plan to determine exactly which brain cell types drive these ECM changes. Future experiments will attempt to manipulate these components directly to determine whether this rescues memory deficits.
“We have provided some of the most compelling evidence that estrogen is so important for memory function and other mood functions in the female brain,” said senior author Dr. Serdar Bulun, chair of the department of obstetrics and gynecology at Feinberg School of Medicine, and a Northwestern Medicine physician. “This should motivate clinicians to be more aware of the essential role of estrogen for women’s brains, because once memory is gone, it’s gone.”
“Our findings will hopefully motivate future studies to better understand how this matrix is altered in postmenopausal women, and how it could potentially induce susceptibility to AD,” Zhao said.
Reference: Piehl NC, Halle AW, Rodriguez G, et al. Loss of brain-derived estrogen is associated with sex- and age-dependent alterations in memory, affective behavior, and hippocampal extracellular matrix gene expression. Aging Cell. 2026;25(6):e70551. doi: 10.1111/acel.70551
This article is a rework of a press release issued by Northwestern University. Material has been edited for length and content.
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