Summary: Researchers have identified a protein that appears to undermine the brain’s natural defense against oxidative damage, a process that contributes to Alzheimer’s disease (AD). The protein Slingshot Homolog-1 (SSH1) interferes with the activity of Nuclear factor erythroid 2-related factor 2 (Nrf2). In laboratory and animal models, removing SSH1 enhances Nrf2 activity, reduces oxidative injury and the accumulation of toxic amyloid and tau, and preserves neuronal connections. These findings point to SSH1 as a promising target for new neuroprotective therapies.
Oxidative stress—chemical damage caused by reactive oxygen species—is an early and central driver of pathological change in AD and related dementias. Normally, Nrf2 is activated in response to oxidative stress and orchestrates cellular defenses that protect neurons. The new study shows that SSH1 suppresses Nrf2’s protective signaling, tipping the balance toward neurodegeneration. By blocking SSH1’s harmful interaction with Nrf2, researchers slowed disease-related damage in experimental models, suggesting a potential therapeutic strategy to slow or prevent progression when applied early.
Key facts:
- SSH1 was identified as a molecular inhibitor of Nrf2, the transcription factor that mounts antioxidant defenses in the brain.
- Genetic removal of SSH1 increases Nrf2 activation in experimental models, resulting in reduced oxidative damage and decreased accumulation of amyloid-β and tau—two hallmark features of Alzheimer’s disease.
- Case Western Reserve University researchers are pursuing SSH1 inhibitor compounds as a possible new class of neuroprotective medications aimed at preserving neuronal function and slowing AD progression.
David E. Kang, Howard T. Karsner Professor in Pathology at Case Western Reserve School of Medicine and the study’s lead author, explains that the team has uncovered a previously unknown mechanism responsible for the loss of antioxidant defense in AD. While Nrf2 ordinarily responds to oxidative stress by activating genes that defend cells, in Alzheimer’s-affected brains that protective response is diminished. The new work identifies SSH1 as a factor that sequesters and inactivates Nrf2, thereby undermining the brain’s capacity to respond to oxidative injury.
Published in the peer-reviewed journal PNAS, the study used a combination of cell-based experiments, animal models, and analyses of human AD brain tissue. The researchers show that oxidative stress activates SSH1, which then binds Nrf2 complexes to the actin cytoskeleton and strengthens the interaction between Nrf2 and its regulator Keap1. This sequestration prevents Nrf2 from entering the nucleus and turning on protective genes. Importantly, the inhibitory effect on Nrf2 occurs independently of SSH1’s enzymatic phosphatase activity, revealing a distinct mode of pathogenic action.
When SSH1 was genetically eliminated in AD models, Nrf2 signaling recovered, leading to lower levels of amyloid-β and tau accumulation, less oxidative injury and inflammation, and protection against neurodegeneration. Synaptic connections and normal gene-expression patterns were preserved in models lacking SSH1, indicating that inhibiting this protein can maintain neuronal function and resilience.
The implications for therapy are significant because many prior clinical trials have targeted patients with advanced dementia and focused on symptomatic relief. The team emphasizes that treatments aimed at early-stage disease—before extensive neuronal loss—are more likely to succeed. As Kang notes, early intervention increases the chance to slow disease progression, and he expects incremental improvements in AD treatments over the next several years.
Case Western Reserve researchers are actively developing SSH1 inhibitor compounds that could serve as neuroprotective drugs. While further preclinical and clinical testing will be required, blocking SSH1-mediated suppression of Nrf2 represents a novel strategy to bolster the brain’s innate antioxidant defenses and potentially slow the course of Alzheimer’s disease. The research also complements ongoing efforts to evaluate therapies that target amyloid and tau, such as recently approved treatments for early AD that aim to slow progression.
About this Alzheimer’s disease research news
Author: William Lubinger
Source: Case Western Reserve University
Contact: William Lubinger – Case Western Reserve
Image: The image is credited to Neuroscience News
Original Research: Closed access.
Slingshot homolog-1–mediated Nrf2 sequestration tips the balance from neuroprotection to neurodegeneration in Alzheimer’s disease by David E. Kang et al., PNAS.
Abstract
Slingshot homolog-1–mediated Nrf2 sequestration tips the balance from neuroprotection to neurodegeneration in Alzheimer’s disease
Oxidative damage within the brain is an early driver of pathology in Alzheimer’s disease and related dementias, often appearing before and then worsening clinical symptoms. Under normal conditions, nuclear factor erythroid 2-related factor 2 (Nrf2) is activated in response to oxidative stress and protects brain cells from damage.
However, Nrf2-mediated defense declines in Alzheimer’s disease, leaving neural tissue more vulnerable. Until now, the mechanistic basis for this decline was unclear. This study demonstrates, using in vitro and in vivo models as well as human AD brain tissue, that Slingshot homolog-1 (SSH1) counteracts Nrf2’s neuroprotective function during oxidative stress and disease progression.
Specifically, SSH1 activated by oxidative stress suppresses nuclear Nrf2 signaling by binding Nrf2 complexes to actin filaments and by enhancing Keap1–Nrf2 interactions, independently of SSH1’s phosphatase activity. Eliminating Ssh1 in AD models restores Nrf2 activation, reduces tau and amyloid-β accumulation, and protects against oxidative injury, neuroinflammation, and neurodegeneration. Loss of Ssh1 also preserves synaptic function and normal gene-expression patterns in tauP301S mice. Human AD brain samples show elevated interactions of Nrf2 with both SSH1 and Keap1, supporting the relevance of this mechanism in patients.
These results reveal a distinct pathway by which SSH1 blocks Nrf2 and drives oxidative damage in Alzheimer’s disease. Therapeutic strategies that prevent SSH1-mediated suppression of Nrf2—while preserving other SSH1 functions—may provide new neuroprotective approaches for AD and related dementias.