L-Serine

Scientists discovered that declining levels of a protein called Menin may help drive aging, and restoring it in older mice reversed several age-related changes in just 30 days. Even more surprisingly, supplementing with a simple amino acid called D-serine improved memory and learning, offering a potential new approach to age-related cognitive decline.What if some of the changes we associate with aging begin with the loss of a single protein deep inside the brain? Scientists investigating that possibility found that restoring a protein called Menin in older mice improved memory, balance, bone mass, and skin thickness in just 30 days. Even more surprisingly, supplementing the animals with a naturally occurring amino acid improved their learning and memory in only three weeks. The findings, originally published in March 2023 in PLOS Biology, came from researchers led by Lige Leng of Xiamen University in China. Their experiments identified a previously overlooked connection between inflammation, brain chemistry, and aging throughout the body. Although the results were obtained in mice, they raised an intriguing possibility: Some effects of aging may be influenced by biological processes in the brain that scientists could eventually learn to modify. Research published since then has added evidence that the brain plays an important role in regulating aging. It has also revealed why the seemingly simple supplement findings deserve careful interpretation. How a Hidden Brain Protein May Influence Aging At the center of the discovery is the hypothalamus, a small but powerful region near the base of the brain. It helps regulate essential functions such as body temperature, hunger, metabolism, sleep, and hormone production. Because these systems affect nearly every organ, changes in the hypothalamus can have consequences throughout the body. Scientists have increasingly recognized the hypothalamus as an important player in aging. One possible reason involves neuroinflammation, the brain's inflammatory response. Although inflammation helps protect against infections and injuries, persistent inflammation can interfere with normal cellular function and contribute to age-related deterioration. Earlier work by Leng and colleagues had identified Menin as a protein that helps restrain inflammation in the hypothalamus. Menin also participates in regulating gene activity, allowing it to influence multiple biological pathways. The researchers wanted to understand what happens when this protective protein begins to disappear with age. They discovered that Menin levels gradually declined in certain hypothalamic neurons as mice grew older. Interestingly, the same decrease was not observed in astrocytes or microglia, two other important types of brain cells involved in supporting neurons and managing immune responses. To investigate whether this decline actually contributed to aging, the team developed genetically modified mice in which Menin could be selectively disabled. The results were striking. Mice with reduced Menin activity developed greater inflammation in the hypothalamus, thinner skin, reduced bone mass, and worsening cognitive performance. Their lifespans were also modestly shortened. Rather than simply accompanying aging, the loss of Menin appeared capable of helping drive several of its characteristic changes. Restoring Menin Reversed Several Signs of Aging in 30 Days The researchers then asked an even more interesting question: If declining Menin contributes to aging, could restoring the protein reverse some of the damage? To find out, they used a gene delivery technique to increase Menin production in a specific part of the hypothalamus in older (20-month-old) mice. This region, called the ventromedial hypothalamus, helps coordinate metabolism, energy balance, and other bodily functions. Just 30 days after treatment, the animals showed measurable improvements. Their skin became thicker, bone mass increased, and performance improved on tests measuring learning, memory, and balance. Researchers also observed reductions in inflammation and improvements in certain metabolic changes associated with aging. In a separate survival analysis, mice receiving the Menin treatment also lived longer than untreated controls. These findings suggested that some biological changes associated with old age could be at least partially reversed by restoring Menin activity in a specific group of brain cells. But the researchers also uncovered an important clue about how Menin produced these effects. A Simple Amino Acid Offers a Surprising Clue When Menin levels declined, the researchers noticed that concentrations of D-serine, an amino acid involved in brain signaling, also fell. Amino acids are best known as the building blocks of proteins, but some perform other important functions. D-serine helps regulate NMDA receptors, specialized proteins on nerve cells that are essential for communication between neurons, learning, and the formation of memories. D-serine is closely related to L-serine, an amino acid commonly found in foods such as soybeans, eggs, fish, and nuts. The two forms have different biological roles. Although D-serine is also available as a dietary supplement, consuming ordinary serine-rich foods is not equivalent to taking the form used in the experiments. Further investigation revealed that Menin helps control the production of PHGDH, an enzyme involved in the biochemical pathway that generates serine (which was in turn regulated by Menin). When Menin activity decreased, this pathway became less active, reducing the amount of D-serine available to the brain. Restoring Menin increased D-serine levels in the hippocampus, a region especially important for learning and memory. This connection suggested that the cognitive effects of declining Menin might be partly explained by disruptions in D-serine signaling. To test the idea directly, the scientists gave older mice D-serine in their drinking water for three weeks. The supplementation improved their performance on learning and memory tests, even without directly restoring Menin. However, there was an important distinction. While increasing Menin improved both cognitive function and physical signs of aging, D-serine supplementation primarily improved cognition. It did not restore the age-related losses in bone mass and skin thickness. That difference suggests Menin influences aging through several biological mechanisms, with D-serine accounting for only part of its effects. Later Research Strengthens the Link Between the Brain and Aging Since the original 2023 discovery, additional studies have provided evidence that the hypothalamus helps coordinate aging across the body. In a 2024 study published in Cell Metabolism, researchers at Washington University School of Medicine identified a different group of hypothalamic neurons that communicates with fat tissue. By maintaining or stimulating this communication pathway, they increased physical activity, improved age-related metabolic function, and extended lifespan in mice. That work involved a different protein and neural circuit from Menin, but supported the broader idea that signals originating in the hypothalamus can influence how the rest of the body ages. Another 2024 study in the Journal of Physiology and Biochemistry provided additional insight into Menin itself. Researchers found that increasing Menin helped protect cultured hippocampal cells against inflammation and a form of programmed cell death triggered by exposure to the stress hormone corticosterone. Although these laboratory experiments did not establish an anti-aging effect, they supported the idea that Menin has important protective functions in brain cells. An even larger picture emerged in January 2025, when scientists published a detailed analysis of approximately 1.2 million mouse brain cells in Nature. The researchers discovered that some of the brain cells most sensitive to aging were concentrated around the third ventricle, a fluid-filled cavity in the hypothalamus. Many aging cells showed reduced activity in genes involved in normal neuronal function and increased activity in genes associated with inflammation and immune responses. These findings highlighted the hypothalamus as a potential center of vulnerability during brain aging, although they did not directly test the Menin pathway. New Findings in 2026 Reveal More Aging Pathways Research published in 2026 has further strengthened the connection between hypothalamic activity and longevity. In a study published in Cell, scientists found that strengthening daily biological rhythms in a specific hypothalamic region improved several aging-related measurements and extended lifespan in male mice. The intervention also reduced estimates of biological age based on DNA methylation, chemical modifications to DNA that change with age. Another 2026 study in Cell Metabolism identified a protein called Mimecan that helps skeletal muscles communicate with the hypothalamus and brown fat, a specialized tissue involved in generating body heat. Restoring circulating Mimecan levels in older mice improved this communication and extended lifespan. Together, these discoveries suggest that aging involves complex communication between the brain and the rest of the body. Rather than depending on one master switch, multiple neural circuits, hormones, and metabolic signals appear to help determine how age-related changes unfold. Could D-Serine Supplements Protect the Human Brain? The possibility of improving memory with a relatively simple amino acid is especially appealing. However, evidence that D-serine can reverse age-related cognitive decline in humans remains limited. A small randomized clinical trial published in 2016 tested D-serine in 50 healthy older adults. Participants performed better on one assessment of spatial learning and problem-solving after receiving the amino acid, but researchers did not find significant improvements across the other cognitive tests or mood measurements. More importantly, later research suggests that the effects of D-serine depend on the biological circumstances. In an April 2025 study published in Cellular and Molecular Life Sciences, scientists investigated D-serine in mice genetically engineered to develop features of Alzheimer's disease. Unlike the Menin experiments, which associated reduced D-serine with age-related memory impairment, this study found that an early increase in D-serine accompanied disruptions in brain signaling. Removing the enzyme responsible for producing D-serine prevented or reduced several later cognitive impairments in those mice. These findings do not invalidate the earlier results. Instead, they suggest that D-serine signaling is more complicated than simply having too little or too much. Its effects may depend on the condition being studied, the timing of treatment, and how the brain's signaling systems are functioning. There are also unanswered questions about the long-term safety of D-serine supplementation. High doses have raised kidney safety concerns in animal experiments, and research has not established whether prolonged supplementation is a safe or effective way to prevent age-related memory loss in otherwise healthy people. For now, D-serine should be considered an experimental approach rather than a proven treatment for brain aging. Can Scientists Eventually Slow Aging by Targeting the Brain? Despite the encouraging mouse experiments, researchers still need to answer several fundamental questions. Why does Menin decline in the hypothalamus as animals age? How many of its effects could be reversed by treatment, and how long would those improvements last? Could restoring Menin influence other biological systems in unexpected ways? It is also unclear whether treatments targeting Menin or D-serine could reproduce similar results in humans. Nevertheless, the original researchers believe the pathway deserves further investigation. "We speculate that the decline of Menin expression in the hypothalamus with age may be one of the driving factors of aging, and Menin may be the key protein connecting the genetic, inflammatory, and metabolic factors of aging. D-serine is a potentially promising therapeutic for cognitive decline," said Leng. Leng adds, "Ventromedial hypothalamus (VMH) Menin signaling diminished in aged mice, which contributes to systemic aging phenotypes and cognitive deficits. The effects of Menin on aging are mediated by neuroinflammatory changes and metabolic pathway signaling, accompanied by serine deficiency in VMH, while restoration of Menin in VMH reversed aging-related phenotypes." The growing body of evidence points toward a potentially important shift in how scientists understand aging. Instead of viewing it only as the gradual deterioration of individual organs, researchers are investigating how specific brain pathways may actively shape the process. The possibility that restoring those pathways could improve memory, physical function, or longevity remains experimental. But the Menin discovery, together with subsequent findings, offers a compelling reason to explore whether some of the biological changes associated with aging are more reversible than previously thought.