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circadian rhythms

Early Riser or Night Owl? New Study May Help to Explain the Difference

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Circadian Clock
Caption: Casein kinase 1 (CK1) regulates PERIOD, a core protein in the biological clock of people.
Credit: Clarisse Ricci, University of California, San Diego

Some people are early risers, wide awake at the crack of dawn. Others are night owls who can’t seem to get to bed until well after midnight and prefer to sleep in. Why is this? An NIH-funded team has some new clues based on evidence showing how a molecular “switch” wired into the biological clocks of extreme early risers leads them to operate on a daily cycle of about 20 hours instead of a full 24-hour, or circadian (Latin for “about a day”), cycle [1].

These new atomic-level details, shared from fruit flies to humans, may help to explain how more subtle clock variations predispose people to follow different sleep patterns. They also may lead to new treatments designed to reset the clock in people struggling with sleep disorders, jet lag, or night-shift work.

This work, published recently in the journal eLIFE, comes from Carrie Partch, University of California, Santa Cruz, and her colleagues at Duke-NUS Medical School in Singapore and the University of California, San Diego. It builds on decades of research into biological clocks, which help to control sleeping and waking, rest and activity, fluid balance, body temperature, cardiac rate, oxygen consumption, and even the secretions of endocrine glands.

These clocks, found in cells and tissues throughout the body, are composed of specialized sets of proteins. They interact in specific ways to regulate transcription of about 15 percent of the genome over a 24-hour period. All this interaction helps to align waking hours and other aspects of our physiology to the 24-hour passage of day and night.

In the latest paper, Partch and her colleagues focused on two core clock components: an enzyme known as casein kinase 1 (CK1) and a protein called PERIOD. Clock-altering mutations in CK1 and PERIOD have been known for many years. In fact, CK1 was discovered in studies of golden hamsters more than 20 years ago after researchers noticed one hamster that routinely woke up much earlier than the others [2,3].

It turns out that the timing of biological clocks is strongly influenced by the rise and fall of the PERIOD protein. This daily oscillation normally takes place over 24 hours, but that’s where CK1 enters the picture. The enzyme adjusts PERIOD levels by chemically modifying the protein at one of two sites, thereby adjusting its stability. When one site is modified, it keeps the protein protected and stable. At the other site, it leaves it unprotected and degradable.

Many of these details had been worked out over the years. But, Partch wanted to drill even deeper to answer an essential question: Why does this process normally take 24 hours, which is remarkably slow biochemically? And, what changes in those whose daily cycle gets cut far short?

To find out, her team performed a series of protein structure and biochemical analyses of the CK1 mutation originally found in hamsters, along with several other clock-altering versions of the enzyme found in organisms ranging from flies to humans. What they’ve discovered is a portion of CK1 acts as a switch. When this switch functions normally, it generates a near-perfect 24-hour cycle by keeping PERIOD’s stability just right. In this case, people easily and correctly align their internal clocks to the daily coming and going of daylight.

If the switch favors a faster breakdown of the protein, the daily cycle grows shorter and less tightly bound to daylight. For these early risers, it’s a constant struggle to adjust to life in a 24-hour world. Though they try to get in sync, these early risers are never able to catch up. Conversely, a switch that favors a slower breakdown will lengthen the clock, predisposing some to be night owls.

Such shifts in clock timing can arise from alterations either to the CK1 enzyme or the PERIOD protein. In fact, people with an inherited sleep disorder called Familial Advanced Sleep Phase Syndrome carry a mutation in the PERIOD protein at one of the places that CK1 modifies. The new work shows that this change makes PERIOD more stable by interfering with the enzyme’s ability to mark the protein for degradation.

One thing that makes the CK1 enzyme so fascinating is that it’s extremely ancient. A nearly identical version of the enzyme to the one in humans and hamsters can be found in single-celled green algae! It’s clear that this enzyme and its function in biological clocks is, evolutionarily speaking, rather special. And at one level, that makes total sense—our planet has operated on a 24-hour clock for the entire span of evolutionary time.

The versions of CK1 that Partch’s team studied here are rare in people. She now plans to study other variations that turn up in humans much more often.

Her discoveries are sure to offer a fascinating view on these internal clocks and, pardon the pun, how they make us all tick. She hopes they’ll lead to new ways to adjust the clock in those with sleep disorders and even the means to reset the clock in people who regularly travel overseas or work the night shift.

Ultimately, Partch would like to tap into the crosstalk between biological clocks and the ability of cells to repair their DNA. She wants to see if clock disruptions have any implications for cancer susceptibility. And yes, now’s a good time to find out the answer.


[1] Casein kinase 1 dynamics underlie substrate selectivity and the PER2 circadian phosphoswitch. Philpott JM, Narasimamurthy R, Ricci CG, Freeberg AM, Hunt SR, Yee LE, Pelofsky RS, Tripathi S, Virshup DM, Partch CL. eLIFE. 2020 Feb 11;9.

[2] A mutation of the circadian system in golden hamsters. Ralph MR, Menaker M. Science. 1988 Sep 2;241(4870):1225-7.

[3] Positional syntenic cloning and functional characterization of the mammalian circadian mutation tau. Lowrey PL, Shimomura K, Antoch MP, Yamazaki S, Zemenides PD, Ralph MR, Menaker M, Takahashi JS. Science. 2000 Apr 21;288(5465):483-92.


Circadian Rhythms (National Institute of General Medical Sciences/NIH)

Advanced Sleep Phase Syndrome, Familial (Genetic and Rare Disease Center/NIH)

Partch Lab (University of California, Santa Cruz)

NIH Support: National Institute of General Medical Sciences; Office of the Director

Why When You Eat Might Be as Important as What You Eat

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Fasting and eating schedule
Adapted from Wilkinson MJ, Cell Metab, 2019

About 1 in 3 American adults have metabolic syndrome, a group of early warning signs for increased risk of type 2 diabetes, heart disease, and stroke. To help avoid such health problems, these folks are often advised to pay close attention to the amount and type of foods they eat. And now it seems there may be something else to watch: how food intake is spaced over a 24-hour period.

In a three-month pilot study, NIH-funded researchers found that when individuals with metabolic syndrome consumed all of their usual daily diet within 10 hours—rather than a more customary span of about 14 hours—their early warning signs improved. Not only was a longer stretch of daily fasting associated with moderate weight loss, in some cases, it was also tied to lower blood pressure, lower blood glucose levels, and other improvements in metabolic syndrome.

The study, published in Cell Metabolism, is the result of a joint effort by Satchidananda Panda, Salk Institute for Biological Sciences, La Jolla, CA, and Pam R. Taub, University of California, San Diego [1]. It was inspired by Panda’s earlier mouse studies involving an emerging dietary intervention, called time-restricted eating (TRE), which attempts to establish a consistent daily cycle of feeding and fasting to create more stable rhythms for the body’s own biological clock [2, 3].

But would observations in mice hold true for humans? To find out, Panda joined forces with Taub, a cardiologist and physician-scientist. The researchers enlisted 19 men and women with metabolic syndrome, defined as having three or more of five specific risk factors: high fasting blood glucose, high blood pressure, high triglyceride levels, low “good” cholesterol, and/or extra abdominal fat. Most participants were obese and taking at least one medication to help manage their metabolic risk factors.

In the study, participants followed one rule: eat anything that you want, just do so over a 10-hour period of your own choosing. So, for the next three months, these folks logged their eating times and tracked their sleep using a special phone app created by the research team. They also wore activity and glucose monitors.

By the pilot study’s end, participants following the 10-hour limitation had lost on average 3 percent of their weight and about 3 percent of their abdominal fat. They also lowered their cholesterol and blood pressure. Although this study did not find 10-hour TRE significantly reduced blood glucose levels in all participants, those with elevated fasting blood glucose did have improvement. In addition, participants reported other lifestyle improvements, including better sleep.

The participants generally saw their metabolic health improve without skipping meals. Most chose to delay breakfast, waiting about two hours after they got up in the morning. They also ate dinner earlier, about three hours before going to bed—and then did no late night snacking.

After the study, more than two-thirds reported that they stuck with the 10-hour eating plan at least part-time for up to a year. Some participants were able to cut back or stop taking cholesterol and/or blood-pressure-lowering medications.

Following up on the findings of this small study, Taub will launch a larger NIH-supported clinical trial involving 100 people with metabolic syndrome. Panda is now exploring in greater detail the underlying biology of the metabolic benefits observed in the mice following TRE.

For people looking to improve their metabolic health, it’s a good idea to consult with a doctor before making significant changes to one’s eating habits. But the initial data from this study indicate that, in addition to exercising and limiting portion size, it might also pay to watch the clock.


[1] Ten-hour time-restricted eating reduces weight, blood pressure, and atherogenic lipids in patients with metabolic syndrome. Wilkinson MJ, Manoogian ENC, Zadourian A, Lo H, Fakhouri S, Shoghi A, Wang X, Fleisher JG, Panda S, Taub PR. Cell Metab. 2019 Jan 7; 31: 1-13. Epub 2019 Dec 5.

[2] Time-restricted feeding without reducing caloric intake prevents metabolic diseases in mice fed a high-fat diet. Hatori M, Vollmers C, Zarrinpar A, DiTacchio L, Bushong EA, Gill S, Leblanc M, Chaix A, Joens M, Fitzpatrick JA, Ellisman MH, Panda S. Cell Metab. 2012 Jun 6;15(6):848-60.

[3] Time-restricted feeding is a preventative and therapeutic intervention against diverse nutritional challenges. Chaix A, Zarrinpar A, Miu P, Panda S. Cell Metab. 2014 Dec 2;20(6):991-1005.


Metabolic Syndrome (National Heart, Lung, and Blood Institute/NIH)

Obesity (National Institute of Diabetes and Digestive and Kidney Diseases/NIH)

Body Weight Planner (NIDDK/NIH)

Satchidananda Panda (Salk Institute for Biological Sciences, La Jolla, CA)

Taub Research Group (University of California, San Diego)

NIH Support: National Institute of Diabetes and Digestive and Kidney Diseases

Creative Minds: Does Human Immunity Change with the Seasons?

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Micaela Martinez

Micaela Martinez

It’s an inescapable conclusion from the book of Ecclesiastes that’s become part of popular culture thanks to folk legends Pete Seeger and The Byrds: “To everything (turn, turn, turn), there is a season.” That’s certainly true of viral outbreaks, from the flu-causing influenza virus peaking each year in the winter to polio outbreaks often rising in the summer. What fascinates Micaela Martinez is, while those seasonal patterns of infection have been recognized for decades, nobody really knows why they occur.

Martinez, an infectious disease ecologist at Princeton University, Princeton, NJ, thinks colder weather conditions and the tendency for humans to stay together indoors in winter surely play a role. But she also thinks an important part of the answer might be found in a place most hadn’t thought to look: seasonal changes in the human immune system. Martinez recently received an NIH Director’s 2016 Early Independence Award to explore fluctuations in the body’s biological rhythms over the course of the year and their potential influence on our health.

LabTV: Curious About Sleep Disorders

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Ketema Paul
Ketema Paul remembers being wowed at an early age by his cousin’s chemistry set and always feeling drawn to science. This interest followed him to Howard University, Washington, D.C., where he earned an undergraduate degree in biology, and on to Georgia State University, Atlanta for his Ph.D. Now, an associate professor at Atlanta’s Morehouse School of Medicine and the subject of our latest LabTV video, Paul runs his own neuroscience lab studying sleep disorders, which affect at least 60 million Americans as chronic or occasional problems and account for an estimated $16 billion in medical costs each year [1].

Paul’s path to the research bench is an interesting one. The product of a tough neighborhood in Washington, D. C., Paul lost a lot of friends to violence and faced many uncertainties. After college, he moved to Atlanta to try his hand at being a music producer and eventually took a side gig as a disc jockey for the campus radio station at Georgia State. Then one day after his radio show, Paul wandered over to have a look inside a nearby neuroscience lab just for kicks and opened the door on a discussion that would change his life.