A surprise revealed by tau PET imaging was that women tend to accumulate more tangles than men at the same clinical stage of Alzheimer’s disease. What might explain this? Some previous studies hinted at a hormonal cause, and new data strengthen this theory. In the May JAMA Neurology, researchers led by Rachel Buckley at Massachusetts General Hospital, Boston, report that women with early AD whose menopause began before the age of 46—or who had started hormone replacement therapy late—tended to have more tangles than their comparison groups. The data echo previous findings of greater dementia risk in women who started taking hormones many years after menopause.
- Early menopause came with more tangles in women who had brain amyloid.
- Ditto for hormone replacement therapy, when started late.
- In male mice only, a protein arrests the hormonal stress response, slowing AD pathology.
- Hormones influence the known sex difference in AD risk in multiple ways.
“To our knowledge, this is the first study to show that tau deposition may underlie the pre-established association between late HT intervention and AD dementia,” the authors wrote.
Even so, female sex hormones are not the whole story (for review, see Cui et al., 2023). Other studies have tied tangles to X-linked genes, as either risk or protective factors (Aug 2020 news; Oct 2022 news). Furthermore, sex-specific stress responses via the body's hypothalamic-pituitary-adrenal axis may influence AD pathology, as well. In the May 2 Brain, researchers led by John Cirrito and Carla Yuede at Washington University in St. Louis reported that stress boosted release of Aβ from neurons only in female mice. Males had a protector, called β-arrestin. This type of stress has been linked to tau hyperphosphorylation and aggregation, as well.
Michelle Mielke at Wake Forest University in Winston-Salem, North Carolina, noted that women’s higher risk is likely to have multiple causes. “Hormones are a contributor, but there are a lot of other factors that differ for men and women, such as cardiovascular and metabolic risk, and responses to stress and depression,” she told Alzforum. The relative contribution of each remains unclear.
Hormones and Tangles. In multiple brain regions, women who had premature (orange), or early (blue), menopause had more tangles than those whose menopause started after age 45 (black). The association only held in the presence of amyloid plaque (dotted blue line). [Courtesy of Coughlan et al., JAMA Neurology, ©2023 American Medical Association, all rights reserved.]
Prior imaging studies from Buckley and others have reported more advanced tangle pathology in women than men at a given stage of AD (Aug 2018 conference news; Feb 2019 news; Nov 2019 news). To find out if hormones played a role, Buckley and colleagues mined data from the Wisconsin Registry for Alzheimer Prevention, an observational study of cognitively healthy older adults. First author Gillian Coughlan compared MK6240 tau PET scan data among 193 women and 99 men. Their average age was 67, and 52 of them were amyloid-positive on PiB PET.
In WRAP, as in prior studies, women had a higher average tau PET signal than age-matched men across several brain regions. This association between sex and tangles was only seen in the presence of amyloid plaques. The authors calculated the threshold needed to see this link as being between 19 to 38 centiloids; 24 is considered the threshold for brain-wide amyloid positivity.
The sample was tiny, though. Thirty-one women in the study were amyloid-positive. Among them, the six women whose menopause started before age 46 had worse tangles across multiple brain regions than did the others; the findings were statistically significant.
About half the women in WRAP had used hormone replacement therapy. Here, too, amyloid-positive women with a history of HRT had more tangles than those without. This effect was mostly in women who had started HRT more than five years after menopause.
This matches earlier data. The large Women’s Health Initiative first reported the link between HT and dementia (Jul 2002 news; Nov 2002 news; May 2003 news), causing a massive drop in the clinical use of HRT. Later studies refined this, showing that when given early, hormones do no harm (Jun 2013 news; Aug 2018 news).
In the present paper, Buckley and colleagues report that, besides the tangle effect, they see that the same two factors—early menopause and late HRT—correlated with subtle deficits on cognitive tests. They believe that future, larger studies should follow up on these data.
Mielke agreed. “The results need to be taken with caution, given that the sample size was so small,” she told Alzforum. Even so, she believes the findings add to the evidence that hormonal factors influence dementia risk in women. “What is it about the menopause transition that may be contributing to that risk?” she asked.
Roberta Brinton at the University of Arizon, Tucson, noted that Buckley’s data jibe with her own findings that women have more amyloid plaque than age-matched men, and that this accumulation often begins around menopause. “Women are at greater risk of AD not because they live longer than men, but because the disease can start earlier in women—during the menopausal transition,” she wrote to Alzforum (full comment below).
For their part, Cirrito and colleagues examined a different sex effect, and in mice instead of people. Because stress-related health conditions are more common in women than men of this generation, and hormones can alter stress responses, the researchers wondered if this might affect AD risk (Nolen-Hoeksema et al., 1999; Henein et al., 2022; Klusmann et al., 2023).
First author Hannah Edwards measured, every hour for 18 hours, levels of Aβ40 in the interstitial fluid of APP/PS1 mice that were confined inside a tight plastic cone for three hours. This type of restraint spikes physiological signs of stress, and indeed, levels of plasma corticosterone rose in both male and female mice during this experience.
A sex difference appeared in the brain. In female mice, the stress hormone corticotropin releasing factor (CRF) signaled neurons in the hippocampus to dial up synaptic transmission, firing 10- to 30-fold more than before the stress. In male mice, the adaptor protein β-arrestin plucked CRF receptors off the surface of neurons, keeping their activity low. As a result, ISF Aβ40 shot up 50 percent in female mice within two hours after stress, and stayed high for the entire measurement period. In male mice, Aβ40 stayed unchanged.
Blocking the CRF receptor in females prevented a rise of Aβ in their interstitial fluid, while knocking out β-arrestin in male mice caused them to respond like females. As in females, blocking CRF-R in male β-arrestin knockouts prevented the spike in Aβ. “[Our study is] the first to determine at the cell signalling level why stress differentially affects disease-related proteins in males and females,” the authors wrote.
Cirrito and colleagues did not investigate what happened to tau after stress. However, a previous study from the late John Trojanowski and colleagues at the University of Pennsylvania, Philadelphia, found that restraint stress elevated tau hyperphosphorylation and aggregation in PS19 tauopathy mice. It also caused neurodegeneration and memory deficits. Blocking the CRF receptor stopped this, demonstrating that the underlying mechanism was the same as in Cirrito’s study. Trojanowski’s study did not break down effects by sex (Carroll et al., 2011).—Madolyn Bowman Rogers
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- Coughlan GT, Betthauser TJ, Boyle R, Koscik RL, Klinger HM, Chibnik LB, Jonaitis EM, Yau WW, Wenzel A, Christian BT, Gleason CE, Saelzler UG, Properzi MJ, Schultz AP, Hanseeuw BJ, Manson JE, Rentz DM, Johnson KA, Sperling R, Johnson SC, Buckley RF. Association of Age at Menopause and Hormone Therapy Use With Tau and β-Amyloid Positron Emission Tomography. JAMA Neurol. 2023 May 1;80(5):462-473. PubMed.
- Edwards HM, Wallace CE, Gardiner WD, Doherty BM, Harrigan RT, Yuede KM, Yuede CM, Cirrito JR. Sex-dependent effects of acute stress on amyloid-β in male and female mice. Brain. 2023 Jun 1;146(6):2268-2274. PubMed.