Science Progress: Women are more likely to suffer from Alzheimer's disease, which is originally related to estrogen depletion!

Alzheimer's disease (AD) is a chronic neurodegenerative disease with insidious onset and progressive development, which seriously affects the physical and mental health and quality of life of the elderly, and brings a heavy medical and economic burden to society [1].

According to the International AD Association, the number of AD patients worldwide reached 55 million as of 2021, and by 2050, this number will increase about 130 million to more than 130 million as countries age[2].

According to the "China Alzheimer's Disease Report 2021", in 2019, the number of AD patients in China was 13143950, accounting for about 25.
5%
of the global number.
Among them, the prevalence rate of men was 669.
3/100,000, and the prevalence of women was 1188.
9/100,000, and the prevalence of women was significantly higher than that of men, about 1.
8 times that of men [3].

In fact, not only in China, epidemiological statistics show that the number of AD women worldwide is significantly higher than that of men, the number ratio is 3:1, and the trend of AD younger is more common in female patients [4], but the reasons why women are more likely to suffer from AD have always been diverse
.

Recently, Steve R.
Tannenbaum of the Massachusetts Institute of Technology and Stuart A.
Lipton of the Scripps Institute of the United States published the latest research results
online in the top international journal Science Advances.

In this study, they found that in postmenopausal women, the depletion of estrogen leads to excessive elevation of nitric oxide (NO) in the brain, resulting in the production of s-nitrosolate complement factor C3 (SNO-C3), which triggers the activation of innate immune cells in the brain microglia phagocytosis synapses, ultimately leading to cognitive decline in female patients [5].

Screenshot of the first page of the article

Protein thionitrosylation (SNO) is a typical redox-dependent protein post-translational modification, SNO can affect protein activity, localization, conformation, or interaction with other proteins, abnormal protein SNO may play a key role
in the pathogenesis of various neurodegenerative diseases.

Therefore, Steve R.
Tannenbaum et al.
first used the modified SNOTRAP technique to perform semi-quantitative proteomic analysis (n=40) on age-appropriate male and female AD patients and control healthy subjects from the frontal cortex cortex flash samples (n=40) to identify key SNO proteins
that may contribute to the pathogenesis of AD.

The experimental results showed that there was no significant difference
in the number of SNO proteins or SNO sites between the AD group and the non-AD group.
On average, there are 464 SNO proteins and 729 SSO sites in each AD brain and 447 SNO proteins and 708 SSO sites in each non-AD brain
.

However, in addition to the number of SNO proteins and SNO sites, changes in the expression level of SNO proteins may also lead to the occurrence of
diseases.

Therefore, the researchers further performed label-free quantitative analysis and found that compared with the non-AD group, some SNO proteins such as p62, C3, NRXN3 and PLD3 were significantly upregulated in AD patients
.
Among them, the upregulation of SNO-C3 showed obvious sex differences, and the enrichment factor was as high as 34.
2 in the female AD group and only 5.
6
in the male AD group.

SNO proteomics identifies SNO protein differences in the brains of male and female AD patients and non-AD patients

By enriching the differential SNO proteins in AD patients and non-AD patients, the researchers further compared the differences
in the brain SNO proteome of male and female AD patients.

A total of 285 SSO proteins were upregulated in male AD patients and 245 SNO proteins in female AD patients, of which 77 SNO proteins were upregulated
in both male and female AD patients.
Pathway enrichment analysis showed that the upregulated SNO proteins of male and female AD patients were concentrated in the "immune response, complement" and "complement activation and substitution" pathways
.

Pathway analysis of upregulated SNO protein in both male and female AD patients

To verify the reliability of the aforementioned proteome results, the researchers manually searched the mass spectrometry database and found that p62, PLD3, C3, and NRXN3 could indeed be SNO-modified, with SNO sites identified as Cys44, Cys487, Cys720, and Cys1018
.

In addition, Steve R.
Tannenbaum et al.
also used western blotting analysis to detect the levels of the SNO-modified proteins SNO-p62, SNO-C3, SNO-NRXN3, and SNO-PLD3 up-regulated in AD patients to verify the reliability
of the aforementioned proteomic results.
It can be seen that the levels of SNO-p62, SNO-C3, SNO-NRXN3 and SNO-PLD3 in the AD group are significantly increased
compared with the non-AD group.

Complement factor C3 plays a key role in the innate immune system and is one of the most abundant sSNO proteins in the AD brain, and C3 was previously found to be associated with
AD pathology.
Cys720 is the main site of C3 SNO modification in the brain of AD patients, 5 out of 10 female AD patients have a large increase in SNO-Cys720 levels, while only 3 out of 10 male AD patients detected a mild increase in SNO-Cys720 levels, why is SNO-C3 more common in the brains of women with Alzheimer's disease?

Differences in SNO-C3 levels between male and female AD patients relative to non-AD patients

Consider that previous studies have shown that estrogen in women can protect the brain in certain situations
.
Therefore, Steve R.
Tannenbaum et al.
hypothesized that estrogen specifically protects women's brains from SNO-C3, and that this protection is lost
when estrogen levels drop dramatically with menopause.

To test the above hypothesis, the researchers conducted experiments with artificially cultured human brain cells in which nanomolar β-estradiol inhibited SNO modification of C3 in induced pluripotent stem cell-derived microglia, and the results showed that β-estradiol may protect premenopausal women from SNO-C3 abnormalities
.

So what role does elevated SNO-C3 levels play in the development of AD? Steve R.
Tannenbaum et al.
used pHrodo™ Red avidin-fluorescent pH-sensitive probes to find that SNO-C3 increases the phagocytosis of microglia to synapses, resulting in synaptic loss in the patient's brain, ultimately leading to cognitive decline
.

SNO-C3 increases the phagocytosis of synapses by microglia

Overall, this study identified that estrogen can reduce C3 SSO levels and protect premenopausal women from abnormal SNOs
of C3.
After menopause, as estrogen levels decrease, C3 will undergo excessive sulfhydryl nitrosylation, and excessive SNOylation of C3 leads to enhanced phagocytosis of synapses by microglia, resulting in synaptic loss and cognitive function decline
.
The finding provides a whole new scientific basis
for the fact that women are more likely to get AD.

References:

[1] YANG Xiaomin,BAO Tianhao,RUAN Ye.
Risk factors for Alzheimer's disease[J].
Sichuan Mental Health,2020,33(06):560-565.
)

[2] of the WHO Global Status Report on the Public Health Response to Dementia

[3] REN Rujing, YIN Peng, WANG Zhihui, QI Jinlei, TANG Ran, WANG Jintao, HUANG Qiang, LI Jianping, XIE Xinyi, HU Yongbo, CUI Shishuang, YU Xiaoping, ZHU Yuan, LIU Xinya, ZHU Yikang, LIN Shaohui, WANG Yiran, HUANG Yanyan, HU Yisong, WANG Xuefeng, WANG Hongli, CHU Jingshen, WANG Ying, LI Chunbo, ZHOU Meigeng, WANG Gang.
Chinese Alzheimer's Disease Report 2021[J].
Diagnostics-Theory & Practice,2021,20(04):317-337.
)

[4] Altmann A, et al.
Alzheimer's Disease Neuroimaging Initiative Investigators.
Sex modifies the APOE-related risk of developing Alzheimer disease.
Ann Neurol.
2014 Apr; 75(4):563-73.

[5] Yang Hongmei,Oh ChangKi,Amal Haitham,Wishnok John S,Lewis Sarah,Schahrer Emily,Trudler Dorit,Nakamura Tomohiro,Tannenbaum Steven R,Lipton Stuart A.
Mechanistic insight into female predominance in Alzheimer's disease based on aberrant protein S-nitrosylation of C3.
[J].
Science advances,2022,8(50).