Structural biologists have made important progress towards better understanding the functioning of the circadian clock. The circadian or inner clock coordinates the sleep-wake rhythm and many other body processes that regulate, for example, metabolism, blood pressure, and the immune system. A research team led by Professor Eva Wolf, recently appointed Professor of Structural Biology at the Institute of General Botany of Johannes Gutenberg University Mainz (JGU) and Adjunct Director at the Institute of Molecular Biology (IMB), has for the first time identified the molecular structure of a protein complex that plays an important role in regulating the circadian rhythm.
At the same time, they also made a surprising discovery: The protein complex contains a zinc ion, which apparently stabilizes it. These results could form the basis for new strategies for treating illnesses that are the result of circadian clock dysfunction.
"Our circadian clock controls many important physiological functions," explained Professor Eva Wolf, according to the May 30, 2014 news release, "Atomic structure of essential circadian clock protein complex determined." If the natural rhythm is disrupted, as for example in the case of people on shift work, the likelihood of developing metabolic disorders, diabetes, or cancer is significantly increased.
The fundamental research conducted in the Wolf group is focused on obtaining insight into the molecular mechanisms of the circadian clock. Among the currently investigated topics are the cryptochromes, a class of proteins associated with the circadian clock in mammals.
In addition to regulating circadian rhythm, these also control glucose homeostasis and blood sugar levels. Together with another clock protein called period they form a complex, the structure of which has just been determined by Wolf's team.
By x-ray analysis of the cryptochrome-period complex structure, the researchers were able to observe atomic details of the interaction between the cryptochrome and period proteins and also discovered that the zinc ion mediates this interaction. "The metal ion stabilizes the complex and also appears to influence an adjacent disulfide bond," clarified Wolf.
Cell biological studies conducted in the collaborating group of Professor Achim Kramer at the Charité Berlin showed that this also is the case in human cells. The researchers had not expected to detect a disulfide bond in the presence of the redox state that prevails in the cytoplasm and the cell nucleus. Its existence is probably regulated by the zinc ion and the disulfide bond itself is perhaps a sensor that indicates the metabolic status of the cell.
"We assume that the formation of this cryptochrome-period protein complex provides a mechanism by which the circadian clock interacts with the metabolism, while the zinc ion and the disulfide bond play an important role in regulating the stability of the complex," summarized Wolf, according to the news release. The now Mainz-based biologist hopes that further findings about the basic functioning of the cryptochrome-period complex and her aim of determining the interaction patterns of further clock proteins may help in the development of future medical treatments.
How an internal body clock interference could contribute to obesity
If there's a disruption of your internal body clock, it could contribute to obesity. Here's how it works. Your eating patterns are subject to circadian rhythms. That's your internal body clock. Interrupt your internal body clock, and up pops certain metabolic disorders known as body clock dysregulation, which in turn may lead to inflammation and insulin resistance.
In another recent study by different researchers, a team of Texas A&M University System scientists have investigated how "body clock dysregulation" might affect obesity-related metabolic disorders, says a new study. The team was led by Dr. Chaodong Wu, associate professor in the department of nutrition and food sciences of Texas A&M's College of Agriculture and Life Sciences, and Dr. David Earnest, professor in the department of neuroscience and experimental therapeutics, Texas A&M Health Science Center. You can check out the abstract of the study, "Myeloid cell-specific Disruption of Period1 and Period2 Exacerbates Diet-induced Inflammation and Insulin Resistance," published online April 25, 2014 in the Journal of Biological Chemistry.
"Animal sleeping and eating patterns, including those of humans, are subject to a circadian rhythmicity," Earnest said, according to the May 14, 2014 news release, Texas A&M-led study shows how 'body clock' dysregulation underlies obesity, more. "And previous studies have shown an association between the dysregulation of circadian or body clock rhythms and some metabolic disorders."
Obesity-associated metabolic disorders and diet-induced inflammation may interfere with your internal body clock
Macrophage circadian dysregulation contributes to diet-induced inflammation and metabolic phenotypes in adipose and liver tissues. Why this is significant is that interactions between circadian clocks and pathways mediating adipose tissue inflammation are critical in the development and possibly treatment of obesity-associated metabolic disorders.
Wu said circadian clocks in peripheral tissues and cells drive daily rhythms and coordinate many physiological processes, including inflammation and metabolism. "And recent scientific observations suggest that disruption of circadian clock regulation plays a key role in the development of metabolic diseases, including obesity and diabetes," he noted.
He said this study affirms that eating unhealthy foods causes health problems and that it's much worse to eat unhealthy foods at the wrong time. It also indicates that "time-based treatment may provide better management of metabolic diseases.
"To promote human health, we need not only to eat healthy foods, but also more importantly to keep a healthy lifestyle, which includes avoiding sleeping late and eating at night," he said, according to the news release
Wu and Earnest said while previous studies using mice with genetic mutation of the removal of core clock genes has indicated that specific disruption of circadian clock function alters metabolism or produces obesity, the mechanism remained unknown. As key components of inflammation in obesity, macrophages, which are immune cells, contain cell-autonomous circadian clocks that have been shown to gate inflammatory responses.
"Our hypothesis was that overnutrition causes circadian clock dysregulation, which induces pro-inflammatory activity in adipose tissue. This then worsens inflammation and fat deposition, leading to systematic insulin resistance," Wu said, according to the news release.
To test the hypothesis, the team conducted experiments with "reporter mice" in which the circadian rhythmicity of various types of cells could be monitored by looking at their reporter activity. Accordingly, the reporter mice were put on a 12-hour light-dark cycle and were fed a high-fat diet. Additional reporter mice were fed a low-fat diet and served as controls. In this set of experiments, the team was able to characterize the effects of a high-fat diet on circadian clock rhythmicity and inflammatory responses in immune cells, or macrophages.
To further define a unique role for circadian clock dysregulation in metabolic disorders, the team conducted "bone marrow transplantation" experiments, through which the rhythmicity of circadian clocks was disrupted only in a specific type of immune cells. After high-fat diet feeding, the transplanted mice were used for collection of blood and tissue samples. A number of physiological and immunological assays also were performed on the mice.
Earnest said, according to the news release, that results showed that during obesity, that is when mice were fed a high-fat diet, the rhythmicity of circadian clocks in immune cells of fat tissue is dysregulated by a prolonged rhythmic period. This is, in turn, is linked to increased accumulation of immune cells in fat tissue and decreased whole-body insulin sensitivity.
"Animals on a high-fat diet display metabolic problems associated with obesity," Earnest said in the news release. "The problems are worsened in animals whose circadian clocks in immune cells are disrupted." Earnest and Wu explained, according to the news release, that the study will help those involved in human health and nutrition better understand the underlying mechanisms related to obesity and diabetes. For more information, you may wish to check out the Texas A&M AgriLife Communications website.