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Study reveals a link between eye health and lifespan

For the first time, experts at the Buck Institute have identified a link between diet, circadian rhythms, eye health and lifespan. In addition, the researchers found that processes in the eye of a fruit fly are driving the aging process.

In humans, previous studies have shown an association between eye disorders and poor health. “Our study argues that it is more than correlation: dysfunction of the eye can actually drive problems in other tissues,” said study senior author Dr. Pankaj Kapahi. “We are now showing that not only does fasting improve eyesight, but the eye actually plays a role in influencing lifespan.”

“The finding that the eye itself, at least in the fruit fly, can directly regulate lifespan was a surprise to us,” said study lead author Dr. Brian Hodge.

The explanation for this connection lies in circadian “clocks,” the machinery within every cell of every organism. These cells have evolved to adapt to changes in light and temperature caused by the rising and setting of the sun. These 24-hour oscillations, or circadian rhythms, affect complex animal behaviors, such as predator-prey interactions and sleep/wake cycles. 

In 2016, Dr. Kapahi’s lab published a study which demonstrated that fruit flies on a restricted diet had significant changes in their circadian rhythms and a longer lifespan. For the current study, the researchers set out to investigate how circadian functions were altered by dietary change, and whether circadian processes were required for the longer lifespan associated with dietary restriction.

“The fruit fly has such a short lifespan, making it a really beautiful model that allows us to screen a lot of things at once,” said Dr. Hodge. 

The study began with a broad survey to see what genes oscillate in a circadian fashion when flies on an unrestricted diet were compared with those fed reduced proteins.

The experts found that numerous genes were diet-responsive and also exhibited ups and downs at different time points, or “rhythm.” Under a restricted diet, the rhythmic genes activated were coming from the eye, specifically from photoreceptors, the specialized neurons in the retina of the eye that respond to light.

This led to a series of experiments to understand how eye function fits into the connection between dietary restriction and extended lifespan. The researchers used bioinformatics to ask: Do the genes in the eye that are also rhythmic and responsive to dietary restriction influence lifespan? The answer was yes.

Since the eyes are exposed to the outside world, immune defenses are active, which can lead to inflammation. When present for long periods of time, inflammation can cause or worsen chronic diseases. Light in itself can cause photoreceptor degeneration and lead to inflammation.

“Staring at computer and phone screens, and being exposed to light pollution well into the night are conditions very disturbing for circadian clocks,” said Dr. Kapahi. This could have consequences beyond vision, such as damaging the body and brain. 

How eyes regulate the lifespans of other organisms, such as humans, is yet to be understood. Photoreceptors in mammals may not affect longevity as much as fruit flies, as the majority of energy in a fruit fly is devoted to the eye. 

Dr. Hodge explained that since photoreceptors are just specialized neurons, the stronger link is likely the role that circadian function plays in neurons, and how these can be harnessed to maintain neuronal function throughout aging.

Dr. Hodge said that once the researchers understand how these processes work, they can target the molecular clock to slow aging, “It might be through diet, drugs, lifestyle changes… A lot of really interesting research lies ahead.”

The study is published in the journal Nature Communications.

By Katherine Bucko, Staff Writer

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