The brain has its own guard cells that watch for danger and protect nerve cells. In Alzheimer’s disease these guards stay turned on all the time, causing constant inflammation that harms the links between brain cells.
Researchers at Scripps Research found a tiny chemical change that makes this problem worse. By looking at human brain cells taken from Alzheimer patients and using lab models, they saw that a small modification to a protein pushes the brain’s immune system into overdrive. This new clue could help create future medicines for Alzheimer’s.
A Protein That Sparks Brain Inflammation
The team studied a protein named STING, which normally sounds an alarm when the body faces a threat. In Alzheimer’s brains, STING receives a chemical tag called S‑nitrosylation (or SNO). This tag makes STING act too strongly, leading to harmful inflammation.
When the scientists stopped this tagging in mice that model Alzheimer’s, the level of brain inflammation dropped sharply.
How the Chemical Tag Works
More than three decades ago, scientist Michael Lipton described S‑nitrosylation. In this reaction, a small piece of nitric oxide sticks to a building block (cysteine) inside a protein, forming an “SNO” group that changes how the protein behaves.
Things like getting older, chronic inflammation, or breathing polluted air can trigger S‑nitrosylation. When many proteins are altered at once, a “SNO‑storm” can upset normal cell functions. Researchers have linked this storm to cancers, Parkinson’s disease, and Alzheimer’s disease.
Finding the Exact Switch in STING
Lipton’s lab focused on STING because earlier work already tied it to Alzheimer‑related inflammation. Postdoctoral researcher Lauren Carnevale worked with mass‑spectrometry expert John Yates III to locate the exact spot where S‑nitrosylation occurs.
They discovered that the tag lands on a tiny part of STING called cysteine 148. Once this spot is modified, many STING molecules stick together, forming clusters that turn on inflammatory pathways.
High amounts of this altered STING (called SNO‑STING) were found in brain tissue taken from people who had Alzheimer’s, in lab‑grown human brain immune cells exposed to Alzheimer proteins, and in mouse models of the disease.
A Loop That Keeps Inflammation Going
Protein clumps that appear in Alzheimer’s, such as amyloid‑beta and alpha‑synuclein, can start the S‑nitrosylation of STING. This suggests a vicious cycle: protein aggregates, aging, and pollutants raise nitric‑oxide levels, which then add the SNO tag to STING, driving more inflammation and creating even more protein clumps.
To break the cycle, the scientists made a version of STING that lacks cysteine 148, so it cannot be S‑nitrosylated. Mice with this modified protein showed far less brain inflammation, and the connections (synapses) between nerve cells stayed healthy. Protecting these connections is linked to better memory and slower cognitive decline.
What This Means for Future Treatments
Targeting the cysteine 148 spot could calm the harmful over‑activity of STING without turning off its normal protective role against infections. The research team is now designing small molecules that block this spot and plans to test them in future animal studies.