Youth-Linked Protein TIMP2 Restored Some Immune Cell Function in Aged Mouse Brains

The evidence comes from a mouse study published in Nature Communications in 2026 by Brittany Hemmer and colleagues, led by Joseph Castellano at the Icahn School of Medicine at Mount Sinai. It also used cells grown from mouse brains. It is not a human study, and the paper's text available to us does not give a full count of animals per experiment.

The protein is called TIMP2. According to the paper, its levels are high in very young human and mouse blood and fall quickly into adulthood and old age. The same team had earlier shown that giving TIMP2 to aged mice made their hippocampus, a memory region, behave more like that of younger animals.

This time the team looked at microglia, the brain's resident immune cells. With age, the paper notes, microglia can become more inflammatory, worse at clearing debris, and more likely to enter a state called senescence. Senescent cells stop dividing and can stress their surroundings. What drives these changes is not well understood.

The researchers first asked what happens without TIMP2. In mice genetically engineered to lack it, microglia showed gene activity pointing to more immune activation and more inflammatory signalling. Genes linked to microglial senescence were also enriched. In young mice, microglia from the knockout animals had gene activity tied to less synapse organization, the connections between neurons.

In the hippocampus of adult mice, about 21 percent of microglia made TIMP2 protein. At 3–4 months of age, knockout mice already had more microglia carrying CD68, a marker tied to the cell's waste-processing compartments. By 6–7 months, a larger share of the dentate gyrus area was covered by microglia staining. The number of microglia did not change.

Using a technique called in vivo microdialysis, which samples the fluid around brain cells in living animals, the team also found higher levels of stress and inflammatory proteins in mice without TIMP2. Removing TIMP2 from specific cell types, microglia or neurons, raised microglial CD68 and altered how microglia engulfed myelin, the insulation around nerve fibres.

The second step was treatment. Aged mice given TIMP2 showed less microglial activation and a smaller proportion of proinflammatory microglia. Their microglia also took up more of the physiological substrates tested. The authors say this reversed several of the features seen in the knockout mice. They describe TIMP2 as a modulator of age-associated microglial dysfunction.

There are limits. The work is in mice. A protein that is missing from birth is not the same as a protein that declines over a lifetime. The paper describes changes in cell states and markers, not whether the treated mice were healthier or lived longer. ScienceDaily's coverage, which described microglia as better at removing cellular debris, put it more broadly than the paper's more specific wording. ScienceDaily also reports that the National Institute on Aging supported the work and that the researchers caution it is unknown whether TIMP2 acts the same way in humans.

"TIMP2 facilitates healthy function for the brain's immune cells," Castellano said, according to ScienceDaily. He added that more studies are needed.

The study sits alongside The Arising's October 20 report on a separate mouse study, in which removing brain immune cells restored sleep in Alzheimer's mice. That was a different experiment with a different question, but both suggest microglia are a key part of how the aging brain changes.

What to watch next

Whether other labs reproduce these findings, whether TIMP2 has similar effects in human brain tissue, and whether any treatment aimed at it is ever tested in people.