A patient in his early sixties, a man who still runs the company he founded, asked me last month whether there was anything to the stories about "young blood" reversing brain aging. He had read about the parabiosis experiments, where an old mouse shares a circulation with a young one and gets sharper, and he wanted to know if there was a version of that for him. While we do not perform whole blood transfusions for our patients, the notion is worth exploring from the perspective that one day, brain aging may be much easier to treat, if not reverse. Recent discoveries have shed light on why sharing blood products may be a first step in that direction.
What Castellano's team found in umbilical cord plasma
In 2017, Joseph Castellano and colleagues at Stanford published a study in Nature that took the young-blood idea a step further than parabiosis. Instead of asking whether young plasma helps an old brain, they asked which molecules in it were responsible. They compared plasma from human umbilical cord, from young adults, and from elderly donors, and they found that a protein called TIMP2, tissue inhibitor of metalloproteinases 2, was abundant in cord plasma and declined with age in both humans and mice, with a larger drop in mice than in people.
They then gave recombinant TIMP2 by itself to aged mice, and the results were the reason the protein has since carried the label "youth-associated." Treated animals showed more activity in the dentate gyrus of the hippocampus, better synaptic plasticity, and better performance on memory tasks. When the team removed TIMP2 from cord plasma before infusing it, the cognitive benefit disappeared, and when they neutralized TIMP2 in young mice, spatial memory got worse. Radiolabeled TIMP2 crossed from blood into brain. Taken together, those experiments established that TIMP2 was both necessary and sufficient for the effect of cord plasma on the aged mouse hippocampus.
What TIMP2 actually does inside the brain
TIMP2 belongs to a four-member family of proteins that regulate the enzymes remodeling the extracellular matrix, the scaffolding around neurons and synapses. That scaffold accumulates with age, and a synapse that wants to strengthen or a new neuron that wants to migrate has to work against it. As the next section notes, the enzyme-regulating role is TIMP2's best-known job but may not be how it helps the aging brain.
A 2023 paper in Molecular Psychiatry from the same group, now at Mount Sinai and led by Ana Catarina Ferreira, showed that in the brain TIMP2 is made mainly by neurons and is enriched in the hippocampus. Deleting it in mice reduced dendritic spines in the dentate gyrus, impaired adult neurogenesis, caused matrix to pile up around synapses in a pattern that resembled the aged brain, and impaired hippocampus-dependent memory while leaving motor function alone.
The most recent piece, published this year in Nature Communications by Brittany Hemmer and colleagues, moved the story from neurons to microglia, the brain's resident immune cells. Mice lacking TIMP2 developed the microglial profile of an old brain earlier, with more inflammatory activation and altered handling of debris. Giving TIMP2 systemically to aged mice reversed several of those changes, reducing the proinflammatory microglial populations and improving the cells' ability to clear physiological substrates. The protein appears to keep both the hippocampal matrix and the microglial state in a younger configuration.
Emerging Evidence in Humans
Everything above is mouse work. The one human signal so far comes from a 2026 Neurobiology of Aging study by Federica Anastasi and colleagues, who built a genetic score predicting higher plasma TIMP2 levels and found that people carrying it had better global cognition and episodic memory among cognitively unimpaired adults at risk for Alzheimer's disease. It is worth noting that measured plasma TIMP2 itself was not significantly related to cognition in that cohort, so this is a genetic association, not a demonstration that raising the protein improves anything.
No clinical trial of TIMP2 for cognitive aging or neurodegeneration has been conducted. The closest thing is the PLASMA trial, a small Stanford study led by Sharon Sha and published in JAMA Neurology in 2019, which infused young plasma into patients with mild to moderate Alzheimer's disease. It showed the approach was safe and feasible, but it could not determine efficacy. A 2022 systematic review of blood-derivative therapies in Alzheimer's disease, most of them using intravenous immunoglobulin rather than young plasma, found no cognitive benefit on the pooled scales.
There are also biological reasons for caution. TIMP2 is elevated, not reduced, in the central nervous system in multiple sclerosis, Alzheimer's disease, and Huntington's disease, and its cognitive benefit does not appear to depend on its enzyme-blocking activity at all, since a mutant that binds those enzymes without inhibiting them works just as well, which means "more inhibition" is not the mechanism to reason from. In oncology, TIMP2 behaves mostly as a tumor suppressor, but its role is context-dependent, and high levels track with worse outcomes in some gastric cancers. Any strategy to raise it systemically would have to reckon with that.
Where TIMP2 meets mesenchymal stem cell exosomes
TIMP2 is holding my attention rather than in a file of interesting mouse papers because it is a natural cargo of the extracellular vesicles that mesenchymal stem cells release. Mass spectrometry of exosomes from human umbilical cord mesenchymal stem cells has shown high endogenous TIMP2 content, and TIMP2 is part of the immunomodulatory protein signature of exosomes from other mesenchymal sources as well. In a 2021 rat spinal cord injury model published in Molecular Neurobiology, exosomes from bone marrow mesenchymal stem cells preserved the blood-spinal cord barrier, and knocking TIMP2 down inside the exosomes largely removed that protection, which implicated exosomal TIMP2 as the working molecule in that experiment.
That experiment establishes less than a promotional reading would suggest. No study has tested TIMP2-carrying mesenchymal stem cell exosomes for cognitive aging. Human trials of mesenchymal stem cell exosomes for neurological conditions have begun, but the ones with results so far were small and uncontrolled, and placebo-controlled trials are only now being registered. The cardiac work with TIMP2-overexpressing cord exosomes was done in rats. What the literature supports is a mechanistic link: these exosomes carry this youth-associated protein among their many signaling molecules, and in one central nervous system model that specific cargo did the work.
That framing matters for how we practice. In our Cellular Rejuvenation Therapy program at the St. Marys office, we use neural exosomes derived from mesenchymal stem cells as part of brain-directed regenerative protocols. These are not FDA-approved drugs. The FDA has stated that exosomes offered to treat disease are regulated as drugs and biological products that require premarket approval, and no such approval exists for a neurological indication, so nothing here should be read as an approved therapy. We do not claim that mesenchymal stem cells or their exosomes treat, cure, or prevent Alzheimer's disease, traumatic brain injury, or any other specific disease. What we can say is that the signaling biology is described in animal models, that TIMP2 is one identified component of it, and that every patient who considers this option hears the distinction between what has been shown in animals and what has been shown in people before any decision is made. Whether it belongs in a given protocol is a clinical judgment made after the diagnostic workup.
What this means for you
If you are a high performer in your fifties or sixties who wants to protect cognition, the TIMP2 story is a reason for measured optimism about the direction of the field. However, I would not personally be asking my children for their blood to transfuse. The actionable part today is the biology surrounding TIMP2. Neuroinflammation, microglial state, and the metabolic conditions new neurons need in order to integrate can all be assessed and modified now, with imaging, blood biomarkers, and a protocol built from your own data. That is what a workup in the Intensive Brain Health Program is designed to do, and it is the foundation any regenerative intervention has to sit on.
Cognition is the asset that produces nearly everything else a person builds, which is the premise of the Neuroeconomy. Castellano's mice tell us that part of what makes an old brain old is a signal it stopped receiving, and that the signal can be identified. Turning that into human medicine will take trials that have not been run. Protecting the brain you have while those trials happen is something you can start now.
Illustration created with AI image tools.
This article was drafted with the assistance of AI writing tools, then reviewed, edited, and approved by Dr. Sean C. Orr, M.D., who holds full editorial responsibility for its content.
References
- Castellano, J. M., Mosher, K. I., Abbey, R. J., et al. (2017). Human umbilical cord plasma proteins revitalize hippocampal function in aged mice. Nature, 544(7651), 488-492. https://doi.org/10.1038/nature22067
- Ferreira, A. C., Hemmer, B. M., Philippi, S. M., et al. (2023). Neuronal TIMP2 regulates hippocampus-dependent plasticity and extracellular matrix complexity. Molecular Psychiatry, 28(9), 3943-3954. https://doi.org/10.1038/s41380-023-02296-5
- Hemmer, B. M., Philippi, S. M., Ferreira, A. C., et al. (2026). Youth-associated protein TIMP2 regulates microglial state and function in healthy and aged mice. Nature Communications, 17, 8173. https://doi.org/10.1038/s41467-026-74906-z
- Tang, J., Kang, Y., Zhou, Y., et al. (2024). TIMP2 ameliorates blood-brain barrier disruption in traumatic brain injury by inhibiting Src-dependent VE-cadherin internalization. The Journal of Clinical Investigation, 134(3), e164199. https://doi.org/10.1172/JCI164199
- Anastasi, F., Genius, P., Rodriguez-Fernandez, B., et al. (2026). Proteomic polygenic risk scores of age-related plasma protein levels reveal a role for TIMP2 in cognitive performance. Neurobiology of Aging, 157, 68-78. https://doi.org/10.1016/j.neurobiolaging.2025.10.003
- Sha, S. J., Deutsch, G. K., Tian, L., et al. (2019). Safety, tolerability, and feasibility of young plasma infusion in the Plasma for Alzheimer Symptom Amelioration (PLASMA) study. JAMA Neurology, 76(1), 35-40. https://doi.org/10.1001/jamaneurol.2018.3288
- Fei, Z., Pan, B., Pei, R., et al. (2022). Efficacy and safety of blood derivatives therapy in Alzheimer's disease: A systematic review and meta-analysis. Systematic Reviews, 11, 256. https://doi.org/10.1186/s13643-022-02115-y
- Ni, J., Liu, X., Yin, Y., et al. (2019). Exosomes derived from TIMP2-modified human umbilical cord mesenchymal stem cells enhance the repair effect in a rat model of myocardial infarction. Oxidative Medicine and Cellular Longevity, 2019, 1958941. https://doi.org/10.1155/2019/1958941
- Xin, W., Qiang, S., Jianing, D., et al. (2021). Human bone marrow mesenchymal stem cell-derived exosomes attenuate blood-spinal cord barrier disruption via the TIMP2/MMP pathway after acute spinal cord injury. Molecular Neurobiology, 58(12), 6490-6504. https://doi.org/10.1007/s12035-021-02565-w
- Wang, W., Zhang, Y., Liu, M., et al. (2018). TIMP2 is a poor prognostic factor and predicts metastatic biological behavior in gastric cancer. Scientific Reports, 8, 9629. https://doi.org/10.1038/s41598-018-27897-x
- U.S. Food and Drug Administration. (n.d.). Public safety notification on exosome products. https://www.fda.gov/vaccines-blood-biologics/safety-availability-biologics/public-safety-notification-exosome-products