Exercise & Liver Enzyme Restore Memory by Repairing Aging Brain Vessels

A newly discovered link between exercise, liver function, and the health of the brain’s blood vessels is offering fresh insight into how physical activity protects against cognitive decline and potentially Alzheimer’s disease. Researchers at the University of California, San Francisco (UCSF) have identified a specific liver enzyme, GPLD1, released during exercise, that appears to repair damage to the blood-brain barrier, restoring memory function in aging mice.

The blood-brain barrier (BBB) is a highly selective membrane that protects the brain from harmful substances circulating in the bloodstream. As we age, this barrier can become “leaky,” allowing damaging compounds to enter brain tissue and trigger inflammation – a process strongly linked to cognitive decline and Alzheimer’s disease. Previous research had established a connection between exercise and improved brain health, but the mechanism remained elusive. The UCSF team’s work, published in the journal Cell, sheds light on this long-standing question.

Leaky Vessels and Aging

The research builds on a 2020 discovery by the same team, which identified GPLD1 as a brain-rejuvenating enzyme produced by the liver in response to exercise. However, the enzyme itself couldn’t directly enter the brain, leaving scientists puzzled about how it exerted its beneficial effects. The current study reveals that GPLD1 doesn’t need to cross into the brain to work. Instead, it targets another protein, TNAP, which accumulates on the cells forming the blood-brain barrier as mice age. This buildup of TNAP contributes to the barrier’s leakiness.

“This discovery shows just how relevant the body is for understanding how the brain declines with age,” said Saul Villeda, PhD, associate director of the UCSF Bakar Aging Research Institute. “It reframes how we think about exercise and brain health, suggesting that the benefits aren’t solely about what happens *inside* the brain, but also about restoring the protective infrastructure surrounding it.”

How GPLD1 Repairs the Barrier

The researchers found that when mice exercise, their livers produce GPLD1, which then travels through the bloodstream to the vessels surrounding the brain. There, GPLD1 effectively “trims away” the accumulated TNAP from the cells of the blood-brain barrier, tightening the seal and reducing leakiness. In older mice treated with GPLD1, the blood-brain barrier showed significant improvement, with less dye leaking into the brain during testing. This repair process was also accompanied by a shift in gene expression within the vessel cells, indicating a return to a more youthful state.

Memory Restoration in Aging Mice

The restoration of the blood-brain barrier’s integrity had a direct impact on cognitive function. In mice equivalent to 70-year-old humans, reducing the TNAP buildup on vessel cells led to decreased brain inflammation and improved performance on memory tasks. Even reversing the buildup after it had occurred demonstrated a significant benefit, suggesting a potential therapeutic window for intervention.

Interestingly, the experiments also showed that vessel repair accounted for much, but not all, of exercise’s positive effects on memory. This suggests that other mechanisms are also at play, and further research is needed to fully understand the complex interplay between exercise and brain health.

A New Therapeutic Target

The UCSF team also tested a compound that lowered TNAP buildup on vessel surfaces without directly administering GPLD1. This compound, delivered in the mice’s food, also resulted in tighter vessel walls and improved memory performance, reinforcing the idea that targeting the blood-brain barrier itself could be a viable therapeutic strategy.

However, researchers caution that any future treatment would need to be carefully evaluated for safety, as the enzyme involved plays roles in other tissues throughout the body. Long-term blocking of this enzyme could potentially have unintended consequences.

Implications for Alzheimer’s Disease

The findings also have implications for Alzheimer’s disease. In mice bred to develop Alzheimer’s-like plaques, boosting GPLD1 levels reduced the accumulation of these plaques in the hippocampus, a brain region crucial for memory. Blocking the TNAP buildup produced similar results, lowering the overall plaque load. Human brain samples from older adults with Alzheimer’s disease showed higher levels of TNAP on the vessels, suggesting a similar process may be occurring in humans.

While these findings are promising, it’s important to note that they are preliminary and require further investigation. Clinical trials are needed to determine whether targeting the blood-brain barrier can effectively prevent or treat Alzheimer’s disease in humans.

Beyond Exercise: A Potential Treatment Pathway

The research opens the possibility of developing therapies that mimic the benefits of exercise for individuals who are unable to engage in regular physical activity. Large-scale studies have consistently linked higher levels of physical activity to a reduced risk of dementia, but establishing a direct causal link has been challenging. This new research provides a biological mechanism that helps explain this association.

“It may open new therapeutic possibilities beyond the traditional strategies that focus almost exclusively on the brain,” Villeda stated. “Before any drug reaches clinics, UCSF scientists must test safety, timing, and whether other GPLD1 targets also matter in humans.”

For now, the message remains clear: regular exercise remains the safest and most proven strategy for protecting brain health and reducing the risk of cognitive decline. This new research provides a deeper understanding of *how* exercise achieves these benefits, paving the way for potential new therapies in the future.