Could overexpression of certain genes put women at a higher risk of Alzheimer’s disease? This seems to be the case for USP11, which partially evades silencing on one of the X chromosomes. This gene encodes a peptidase that removes ubiquitin chains from tau, which opens it up to acetylation instead, claim scientists led by David Kang and Jung-A Woo at Case Western Reserve University, Cleveland. This acetylation makes the protein more likely to aggregate, the authors concluded. In the September 22 Cell, the researchers reported that knocking out USP11 protected female mice from tauopathy. They found that USP11 levels tracked with neurofibrillary tangle burden in women, but not in men.
“This exciting finding links female-specific biology to tau,” wrote Dena Dubal, University of California, San Francisco. She noted that studies are increasingly uncovering a critical role for the X chromosome in brain aging and in Alzheimer’s disease. Li Gan of Weill Cornell Medicine, New York, who co-authored this paper, agreed. “The study highlights the need to consider sex differences in mechanisms underlying neurodegenerative diseases,” she wrote (comments below).
Because women have two X chromosomes, one must be silenced to avoid duplicate expression. However, some genes can evade this X-inactivation. “Up to a third of X chromosome genes are typically expressed on both the activated and inactivated X chromosome, and the degree of genetic expression varies across individuals,” noted Andrew Pieper of Case Western. Pieper is a co-author on the Cell paper. For example, Dubal previously pegged overexpression of another slippery X-gene, Kdm6a, as protective against AD (Aug 2020 news).
First author Yan Yan and colleagues came upon USP11 when they screened the 22 known de-ubiquitinases in the central nervous system for modulators of tau. Yan found two hits—USP11 and USP13. Because the USP11 gene sits on the X chromosome, the scientists wondered if it might help explain why women are more susceptible to tau pathology. To find out, they began by knocking down USP11 in HEK cells expressing P301L mutant tau. This halved tau concentration without changing its mRNA level, and reduced acetylation of lysine 281 in tau’s microtubule-binding domain. In contrast, overexpressing the enzyme increased the amount of insoluble, but not soluble, tau. What was going on?
The researchers found that USP11 chopped ubiquitin from 20 lysine residues, exposing them to acetylation. Tau acetylated at lysine 281 (K281Ac) was three times as insoluble as wild-type tau, they found, and acetylated tau is prone to aggregation, explaining how USP11 could keep that pathology in check (Mar 2011 news; Sep 2015 news; Trzeciakiewicz et al., 2017).
No USP11, Less P-tau. Hippocampal (left two columns) and cortical (right two columns) tissue from female USP11 knockout/P301S mice (bottom) had less ptau-202 (green) and less ptau262 (red) than did P301S mice (top). [Courtesy of Yan et al., Cell, 2022.]
These shenanigans held true in vivo, also, but there was a sex difference. Female mice carrying P301S tau had two to three times as much cortical USP11 and K281Ac tau as did males, in keeping with the idea that the gene evades X inactivation. Compared to wild-type female mice, 7-month-old P301S females had more soluble and insoluble tau, poorer long-term potentiation, and less synaptophysin, a synaptic vessel protein. They also had trouble finding a hidden platform in a water maze. Knocking out USP11 in the P301S females reduced soluble and insoluble total tau by 25 and 60 percent, respectively, soluble and insoluble K281Ac tau by 35 and 80 percent, and phospho-tau species by half (see image above). Synaptic signaling and memory were normalized. In contrast, knocking out USP11 had little effect in male P301S mice. These results suggest that loss of USP11 reduces tau pathology and restores synaptic plasticity and memory only in female mice.
This sex dichotomy was also apparent in people. The researchers analyzed frontal gyrus samples from 17 donors who had had AD, seven who had had frontotemporal dementia with tau pathology (FTD-tau), and 10 controls from the Emory University AD Research Center. Donors were 40 to 94 years old when they died, and half were female. Healthy women had three times more USP11 than did healthy men.
As a group, the people who had had AD or FTD had 9.5- and 6.5-fold more of the enzyme in the brain samples, respectively, than did controls. While USP11 co-localized with AT8-positive tangles in both men and women, this was much stronger in women (see image above). “The correlation of USP11 with tau pathology in female (not male) AD brains is striking,” Gan wrote. “It suggests that the moderate elevation of USP11, and the resulting increased tau acetylation, plays a critical role in tipping the balance of ubiquitination and acetylation that results in tau accumulation.”
All told, the researchers believe that inhibiting USP11, and therefore tau deubiquitination, might be a therapeutic strategy to help women stave off AD and other tauopathies.—Chelsea Weidman Burke
- Does Second X Chromosome Boost Women’s Resilience Against Alzheimer’s?
- Tau Modification—Move Over Phosphate, Make Room for Acetylation
- New Type of Toxic Tau? Acetylated Form Correlates With Memory Defects
Research Models Citations
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