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How physical activity protects the brain from aging

Physical exercise has many benefits, including keeping muscles and bones strong, improving heart health, lowering blood pressure and promoting mental health. There are countless studies that confirm the important benefits associated with exercise and demonstrate that we should continue being physically active, particularly as we age. 

In a new study, scientists from UC San Francisco report that when elderly people stay physically active, their brains produce more of the proteins needed to enhance the connections between neurons (brain cells) and thereby maintain healthy cognitive function. 

“Our work is the first that uses human data to show that synaptic protein regulation is related to physical activity and may drive the beneficial cognitive outcomes we see,” said Kaitlin Casaletto, PhD, an assistant professor of neurology and lead author of the study. In the past, the beneficial effects of physical activity on cognition have been shown in mice but have been much harder to demonstrate in people. 

Casaletto, a neuropsychologist and member of the Weill Institute for Neurosciences, worked with William Honer, MD, a professor of psychiatry at the University of British Columbia and senior author of the study. They used data from the Memory and Aging Project at Rush University in Chicago that followed the late-life physical activity of elderly participants who, before they died, also donated their brains for scientific study after death.

Honer and Casaletto found that elderly people who remained active had higher levels of proteins that facilitate the exchange of information between neurons. Neurons are separated from each other by tiny gaps, known as synapses, and nerve impulses that travel along the nerve cells have to cross the gaps in order for the information to reach its destination (either the brain or peripheral muscles and glands). Proteins present in neurons just before and just after each synapse provide the chemical mechanism whereby information is transmitted and also link the neurons into cognitive networks. 

The results support previous research of Honer’s showing that people who had higher levels of these particular proteins in their brains when they died had been better able to maintain their cognition late in life. 

The presence of higher levels of these proteins was not only restricted to the area of the brain known as the hippocampus, which is the seat of memory. Other regions of the brain associated with cognitive function also showed higher levels of synaptic proteins present in elderly people who had remained physically active. 

“It may be that physical activity exerts a global sustaining effect, supporting and stimulating healthy function of proteins that facilitate synaptic transmission throughout the brain,” Honer said.

Most older adults accumulate amyloid and tau in their brains. These toxic proteins that are the hallmarks of Alzheimer’s disease form tangled masses within neurons and eventually block the synapses and prevent them from functioning effectively. This leads to the degeneration and death of the affected nerve cells. 

Casaletto previously found that the levels of synaptic proteins present in the spinal fluid of living adults, or in the brain tissue of autopsied adults, were indicative of synaptic functioning. Furthermore, when levels were low and synapses had degenerated, this was associated with the presence of the destructive amyloid and tau protein tangles. Thus, synaptic integrity appears to influence the relationship between amyloid and tau proteins, and between tau proteins and the further degeneration of neurons. 

“In older adults with higher levels of the proteins associated with synaptic integrity, this cascade of neurotoxicity that leads to Alzheimer’s disease appears to be attenuated,” Casaletto said. “Taken together, these two studies show the potential importance of maintaining synaptic health to support the brain against Alzheimer’s disease.” 

“Maintaining the integrity of these connections between neurons may be vital to fending off dementia, since the synapse is really the site where cognition happens,” she said. “Physical activity – a readily available tool – may help boost this synaptic functioning.”

The study is published today in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association.

By Alison Bosman, Staff Writer

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