A protein blamed for brain inflammation may also protect it, mouse study

For several years, a protein called cGAS has been cast as a troublemaker in the aging brain. Studies in mice tied it to the slow, low-level inflammation that comes with old age and to the loss of nerve cells and memory. A new mouse study suggests the picture is more mixed: mice born without cGAS ended up with weaker brain immune cells, nerve damage and memory problems that grew worse with time.¹

The work, led by Paola Murgas with Gonzalo I. Cancino as senior author, was published as an open-access paper in the journal Biological Research on 28 August 2026.¹ It was covered on 29 October 2026.¹

What the researchers set out to test

cGAS works as an alarm for DNA. When DNA shows up somewhere it should not be inside a cell, cGAS and a partner protein called STING switch on an immune response.² That response helps defend against viruses and bacteria.² It can also cause harm if it keeps running unchecked.³

In the brain, cGAS is found mostly in microglia, the brain’s own resident immune cells.¹ Microglia patrol the brain, clear debris and respond to injury. The team asked a question that the focus on inflammation had largely pushed aside: does cGAS do anything useful in microglia under normal, healthy conditions?¹ Their idea was that lacking cGAS from birth might weaken microglia and the links between the brain and the immune system across life, even without any disease.¹

The evidence so far

First, the researchers looked at ordinary mice. They measured cGAS in three kinds of immune cells in the brain: microglia, macrophages (immune cells that come in from the blood) and lymphocytes (another family of immune cells).¹ The biggest change happened between 3 and 6 months of age, which the authors read as a sign that high levels of cGAS may be limited to a window in early adulthood.¹ In older mice, the brain held markedly less cGAS and STING protein.¹ In other words, the pathway seems to fade naturally with age.¹

Then they studied “knockout” mice, bred so that the cGAS gene is missing from the start. These mice showed:

• Changes in how they explored their surroundings at every age examined.¹
• Problems with recognition and spatial memory (remembering objects and places) that began in adulthood and worsened over time.¹
• From 3 months of age, a larger area of nerve damage in the somatosensory cortex, a region that handles touch and body sensation, and in the hippocampus, a key memory center.¹
• Fewer microglia in both regions, with altered shapes and a weaker signal from Iba1, a standard marker for these cells.¹

The microglia that remained also looked less able to respond. Several surface proteins that immune cells use to signal and react (named MHCII, CD86 and CD206) stayed lower than normal, which the authors interpret as the cells being “hyporesponsive,” or blunted.¹ Coverage of the study described the cells as not just fewer and misshapen but less able to carry out their usual watchdog work.¹

Traffic of immune cells into the brain was also off. Macrophage entry was normal in the cortex but lower in the hippocampus.¹ Young knockout mice had more lymphocytes in the brain than normal mice, but they did not keep up the rise in lymphocytes that normal mice show with age.¹

The authors conclude that cGAS may play an essential housekeeping role in keeping microglia competent throughout life, and they suggest mice lacking it could serve as a model of faster microglial aging.¹

How it fits with earlier work

The new findings sit alongside a well-known 2023 study in the journal Nature led by Andrea Ablasser at EPFL in Switzerland.² That work reported that the cGAS-STING pathway is a critical driver of chronic inflammation and decline during aging.² In old mice, DNA leaking from mitochondria, the cell’s power plants, built up inside microglia and set off cGAS.² Blocking STING in aged mice lowered markers of inflammation in the body and the brain and improved spatial and associative memory, as well as muscle strength and endurance.² A summary of the same paper described it as the first to establish cGAS-STING as a significant driver of aging-related inflammation and nerve cell loss in the brain.⁴

Other groups have pursued the pathway as a possible target for Alzheimer’s disease. The Cure Alzheimer’s Fund notes that work it supported earlier found that drugs blocking cGAS improved learning and memory in a mouse model of tau, one of the proteins that build up in Alzheimer’s.³ Researchers it funds have also reported cGAS-STING switched on in microglia near amyloid plaques in a mouse model.³ That same description stresses that the pathway’s activation is generally protective and becomes a problem mainly when it is left unchecked.³

The new study does not contradict the idea that too much cGAS activity can harm the aging brain. It adds a second side: having none at all, from birth, also appears harmful in mice. Coverage framed it as reframing a pathway best known for inflammation as one whose early-life presence may quietly protect the brain.¹

What it does not show yet

This is a mouse study. Coverage of the paper stressed that the findings are associative and preclinical, and that whether the same protective role exists in the human brain remains an open question.¹

Several other limits follow from the design:

• The mice lacked cGAS from the start of life. That is very different from a drug that partly blocks the pathway in an older animal or person, which is what the earlier STING studies tested.²¹
• The study did not test any treatment, so it says nothing directly about the safety of drugs aimed at cGAS or STING.
• The coverage available to Biohack does not give the number of mice studied, so the size of the effects cannot be judged here.
• The study shows that missing cGAS goes along with microglial changes and nerve damage, but the coverage describes the link as associative rather than a fully traced chain of cause and effect.¹

Who is behind it

The paper lists five authors: Paola Murgas, S. Mesa, M. Escandón, M. S. Matus and Gonzalo I. Cancino.¹ It appeared in Biological Research as an open-access article, meaning anyone can read it.¹ The coverage Biohack reviewed does not name the funders or report any company ties or conflicts of interest. The illustration that ran with that coverage was labeled as AI-generated, not a picture from the study.¹

What to watch next

The open question is timing and dose. Earlier mouse work suggests that in old age, cGAS-STING activity can fuel inflammation and memory loss, and that blocking STING helped.² The new study suggests the pathway is strongest in early adulthood and may help keep microglia healthy, with its natural fading perhaps playing a part in how the brain copes with aging.¹ Things that would clarify the picture include:

• Studies that remove or block cGAS only later in life, to see whether the harm depends on losing it early.
• Measurements of cGAS in human brain immune cells across age.
• Results from groups testing cGAS or STING blockers in Alzheimer’s models, including the TBK1 work funded by the Cure Alzheimer’s Fund, which looks at how the same pathway balances cell cleanup and inflammation.³

Biohack will follow this thread as new results appear.