Research has unveiled a crucial molecular switch that accelerates chronic inflammation and synapse degradation in Alzheimer’s disease. This breakthrough centers on a chemical modification called S-nitrosylation (SNO), which excessively activates an essential immune protein known as STING.
By inhibiting this modification at a specific site on the protein—cysteine 148—scientists successfully mitigated the brain’s inflammatory response in mouse models, preserving the critical connections between nerve cells that are typically compromised by the disease.
Understanding Brain Immunity
The brain possesses its own immune system, tasked with identifying threats and initiating a defense response. Evidence has increasingly indicated that in Alzheimer’s disease, these immune cells become persistently overactive, leading to inflammation that damages the connections between neurons.
In a preclinical study utilizing human Alzheimer’s brain cells, researchers from Scripps Research have pinpointed a molecular switch and potential therapeutic target that drives this chronic inflammation.
The Role of STING
The study, published in Cell Chemical Biology, focuses on the STING protein, which usually acts as part of the immune system’s early detection mechanism. The researchers discovered that in Alzheimer’s-affected brains, STING undergoes S-nitrosylation, leading to its overactivation. Inhibiting this alteration in a mouse model resulted in reduced neuroinflammation.
Senior author Stuart Lipton, a clinical neurologist and endowed chair at Scripps Research, emphasizes the significance of this finding as a new therapeutic avenue for Alzheimer’s. The results are promising, as blocking this molecular switch in mice decreased inflammation and safeguarded the neural connections typically lost in the disease.
Historical Context of S-nitrosylation
Stuart Lipton has a long history with S-nitrosylation, having discovered the process over thirty years ago. This modification occurs when a nitric oxide-related molecule binds to cysteine amino acids in proteins, resulting in S-nitrosylation that influences protein functionality. His research has linked this process to various conditions, including cancer, Parkinson’s disease, and Alzheimer’s.
In this latest study, the focus was on STING, previously associated with inflammation in Alzheimer’s. Led by postdoctoral researcher Lauren Carnevale, the team collaborated with mass spectrometry expert John Yates III to identify where S-nitrosylation occurs on STING.
Unraveling the Mechanism
The researchers determined that S-nitrosylation occurs specifically at cysteine 148, causing STING to form larger complexes and inciting inflammation. They observed elevated levels of SNO-STING in postmortem brain tissue from Alzheimer’s patients, in lab-grown human brain immune cells exposed to Alzheimer’s-related proteins, and in a mouse model of the disease.
Laboratory experiments indicated that the protein aggregates commonly found in Alzheimer’s, such as amyloid-beta and alpha-synuclein, can initiate the S-nitrosylation of STING. This suggests a cyclical process: initial protein accumulation, intensified by environmental factors and aging, leads to inflammation that generates nitric oxide, further driving STING’s overactivation.
Protective Measures in Alzheimer’s Research
The team engineered a version of STING that lacked cysteine 148, preventing its S-nitrosylation. When this modified protein was introduced into a mouse model of Alzheimer’s, there was a notable reduction in immune cell inflammation, and importantly, the synaptic connections were preserved. This preservation is crucial, as maintaining synapses is associated with protection against cognitive decline.
Lipton highlights the potential of targeting this modification as it allows for the reduction of pathological STING activation without impairing the essential immune response. “You still need STING to protect yourself from infections,” he notes, indicating that this strategy offers a targeted approach to managing Alzheimer’s without compromising overall immune function.
Future Directions
The research team is now focused on developing small molecules designed to inhibit cysteine 148 for further testing in preclinical models. This innovative approach could pave the way for new treatments aimed at mitigating neuroinflammation and potentially slowing disease progression.
Key Takeaways
- Researchers discovered a molecular switch, S-nitrosylation of STING, that drives inflammation in Alzheimer’s disease.
- Blocking S-nitrosylation at cysteine 148 in mouse models reduced neuroinflammation and protected synaptic connections.
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The findings suggest a cyclical relationship between protein aggregation, inflammation, and STING activation that exacerbates Alzheimer’s pathology.
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Targeting specific modifications in immune proteins could offer a promising therapeutic strategy without compromising the immune system’s overall functionality.
In conclusion, this research marks a significant advancement in understanding the molecular mechanisms underlying Alzheimer’s disease. By identifying a specific target for intervention, scientists are one step closer to developing effective therapies that could change the course of this devastating illness.
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