Cells lining the intestinal tract form a critical barrier, protecting our bodies from the billions of bacteria living in the gut. Breaches in this barrier are driven largely by a single signaling molecule called tumor necrosis factor (TNF), elevated amounts of which are associated with inflammatory bowel diseases like Crohn's disease and ulcerative colitis.
Drugs targeting TNF have become an effective treatment against these illnesses, but despite its clinical importance, it is still not clear what triggers an uptick in TNF levels in the gut, or how that event leads to the onset of disease.
Image of a zebrafish in which the entire intestine is highlighted in red and the expression of the TNF molecule is highlighted in green. Duke researchers have discovered that a gene called uhrf1 acts like a kind of molecular handbrake on TNF, keeping it from setting off the series of pro-inflammatory and immune signals that drive inflammatory bowel diseases.
Credit: Lindsay Marjoram, Duke University
Duke researchers now have discovered that a gene called uhrf1 acts like a kind of molecular handbrake on TNF. In the absence of uhrf1, TNF rolls out a series of pro-inflammatory and immune signals that inflame and damage the digestive tract.
"Our findings provide a new take on how inflammatory bowel diseases can emerge and develop," said Michel Bagnat, Ph.D., an assistant professor of cell biology at Duke University School of Medicine. "We already knew that genetic susceptibility could play a part, but we've found that it is not just the immune genes themselves, but also the regulation of those genes (through epigenetics), that can cause problems."
The findings appear the week of February 16 in the Proceedings of the National Academy of Sciences.
Inflammatory bowel diseases (IBD) are a group of chronic disorders of the gastrointestinal tract that affect over 1.6 million Americans. Though the origins of these diseases are unclear, recent research has implicated a number of factors, including genetic variation, intestinal microbes, overactive immunity, and environmental exposures.
Bagnat decided to use an experimental approach called forward genetics to uncover new causes of IBD. First, his postdoctoral fellow Lindsay Marjoram used chemicals to induce mutations in their model organism of choice, the zebrafish. Because these small aquarium fish are transparent as embryos, she could easily visualize any defects in the gut as they developed.
After screening hundreds of mutants, Marjoram found several strains that displayed marked gut defects, including a thinner protective barrier and chunks of floating cellular debris.
Next, the researchers decided to narrow down their results to only the mutants involved in inflammation. Because TNF activity is a hallmark of inflammation, they created a "reporter" zebrafish that lit up green wherever the TNF gene was "turned on" in the organism. The researchers then bred the TNF reporter fish to the mutants from their initial screen to see if any of the mutated genes affected the expression of this important pro-inflammatory molecule.
The experiment yielded two big surprises. First, they found that TNF, originally thought to be produced mostly by immune cells, was also being made by the epithelial cells that line the gut. Second, they discovered that one of the mutants actually pumped up the levels of TNF being produced in the digestive tract.
After a bit more genetic investigation, the researchers found that the gene responsible was uhrf1, which is involved in an epigenetic process known as DNA methylation. Whether a particular gene is turned "off" or "on" in a given cell is determined by the presence or absence of specific chemical tags or methyl groups -- methylation -- attached to the DNA.
Uhrf1 normally acts to turn off genes that produce TNF, but when that repression is lost, those genes get turned on and TNF is manufactured and released. "You can think about it in terms of a car parked in a driveway. If you get rid of the handbrake, the car is going to start rolling," Bagnat said.
In collaboration with Mary Goll of Memorial Sloan-Kettering Cancer Center, the researchers demonstrated that loss of uhrf1 did indeed remove methylation from the TNF gene.
Next, Bagnat turned to his Duke colleague John Rawls to explore whether the guts of the zebrafish had to be exposed to bacteria that set off TNF's pro-inflammatory activities. When they raised the zebrafish mutants in a germ-free environment, TNF was still activated, though to a lesser extent. The results suggested that losing uhrf1's brakes was enough to head TNF on a course for destruction, even without that extra push from intestinal microbes.
Now the researchers are trying to translate their findings to higher organisms like humans by looking for similar methylation defects in patients with IBD. Ultimately, the defects they find could provide targets for new diagnostics or therapeutics for the disease.
The research was supported by a National Institutes of Health New Innovator Award (DP2 3034656), a Bill & Melinda Gates Foundation Grand Challenges Exploration grant (OPP1108132), a Duke Multidisciplinary Fellowship in Pediatric Lung Disease (5T32HL098099-02), an F32 NRSA (DK098885-01A1), and a grant from the March of Dimes Foundation (5-FY12-93).
CITATION: "Epigenetic control of intestinal barrier function and inflammation in zebrafish," Lindsay Marjoram, Ashley Alvers, M. Elizabeth Deerhake, Jennifer Bagwell, Jamie Mankiewicz, Jordan Cocchiaro, Rebecca W. Beerman, Jason Willer, Kaelyn Sumigray, Nicholas Katsanis, David M. Tobin, John F. Rawls, Mary Goll, Michel Bagnat. PNAS, Feb. 16, 2015. DOI: 10.1073/pnas.1424089112
Karl Bates | EurekAlert!
A promising target for kidney fibrosis
21.04.2017 | Brigham and Women's Hospital
Stem cell transplants: activating signal paths may protect from graft-versus-host disease
20.04.2017 | Technische Universität München
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
20.04.2017 | Event News
18.04.2017 | Event News
03.04.2017 | Event News
25.04.2017 | Physics and Astronomy
25.04.2017 | Materials Sciences
25.04.2017 | Life Sciences