Scientists have demonstrated for the first time the link between diet, circadian rhythm, eye health and longevity in fruit flies. Researchers from Barker Institute published an article in nature communication on June 7, 2022. They accidentally found that the aging process of fruit flies is related to the eyes.
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Previous studies have shown a link between eye disease and poor health in humans. "Our study believes that this is not just a correlation: eye dysfunction can actually drive the problems of other organizations," said Dr. Pankaj kapahi, senior author of the study and professor of Barker Institute. "We now find that fasting can not only improve vision, but also the eyes actually play a role in affecting life span." His laboratory has proved over the years that fasting and calorie restriction can improve many functions of the body.
Dr. Brian Hodge, the first author of the paper, said: "the discovery that the eye itself, at least in fruit flies, can directly regulate longevity is a surprise to us."
Hodge pointed out that the explanation for this connection lies in the circadian "clock", that is, the molecular mechanism in each cell of each organism, which has evolved to adapt to daily stresses, such as changes in light and temperature caused by the rising and setting of the sun. These 24-hour oscillations -- circadian rhythms -- affect complex animal behaviors, such as predator-prey interaction and sleep / wake cycles, until fine-tuning the time regulation of molecular functions of gene transcription and protein translation.
In 2016, kapahi's laboratory published a study in cell metabolism, which showed that in addition to prolonging the life span, the circadian rhythm of fruit flies with restricted diet also changed significantly. When Hodge joined the lab later that year, he wanted to dig deeper to find out which processes enhance circadian rhythm function change due to dietary changes and whether circadian rhythm processes are needed to prolong life as seen by diet restriction.
"The short life span of the fruit fly makes it a very beautiful model that allows us to screen out a lot of things at once," Hodge said. At present, he is a scientist of the South San Francisco based fountain therapeutics company. The study began with an extensive survey to understand which genes oscillate in a circadian rhythm when flies fed an unrestricted diet were compared with flies fed only 10% of the protein in an unrestricted diet.
Hodge immediately noticed that many genes respond to diet and show fluctuations or "rhythmic" at different time points. He later found that the most activated rhythmic genes in the case of diet restriction seemed to come from the eyes, especially from photoreceptors, the specialized neurons in the retina of the eyes that respond to light.
This finding has led to a series of experiments aimed at understanding how eye function fits into the story of how dietary restrictions can prolong life. As their experiments have shown, keeping flies in constant darkness can prolong their lifespan. "This seems very strange to us," Hodge said. "We used to think that flies needed lighting cues that were rhythmic, or circadian."
Then they used bioinformatics to answer. Genes in the eyes are also rhythmic and respond to dietary restrictions. Will these genes affect longevity-- The answer is yes, they do.
"We always think that the eye is something that serves us and provides vision. We don't think it is something that must be protected to protect the whole body," kapahi said.
He pointed out that because the eyes are exposed to the outside world, the immune defense system there is very active, which may lead to inflammation. If inflammation persists for a long time, it will lead to or aggravate various common chronic diseases. In addition, light itself can cause photoreceptor degeneration, which can cause inflammation.
"Staring at the computer and mobile phone screens and being exposed to light pollution at night are very disturbing to the circadian clock," kapahi said. "It disturbs the protection of the eyes, which may have consequences not only for eyesight, but also for other parts of the body."
There are still many things to understand about the role of the eye in the overall health and longevity of organisms, including how the eye regulates longevity, whether the same effect applies to other organisms, and so on.
The biggest question raised by this work, which may be applicable to humans, is simply whether mammalian photoreceptors affect longevity? Hodge pointed out that although it may not be as much as fruit flies, most of their energy is spent on the eyes. Since photoreceptors are only specialized neurons, "I think the stronger connection is the role of circadian rhythm function in general neurons, especially in terms of dietary restriction, and how to use these to maintain neuronal function throughout the aging process," Hodge said.
In addition, Hodge said that once researchers understand how these processes work, they can start targeting the molecular clock to slow down aging. In addition, he added, it is possible that humans can help maintain vision by activating the clock in our eyes. "This may be through diet, drugs, lifestyle changes... A lot of really interesting research is in front of us."