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!
Satellites, airport visibility readings shed light on troops' exposure to air pollution
09.12.2016 | Veterans Affairs Research Communications
Oxygen can wake up dormant bacteria for antibiotic attacks
08.12.2016 | Penn State
Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.
Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...
In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.
Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...
Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...
A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.
Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...
In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.
“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...
16.11.2016 | Event News
01.11.2016 | Event News
14.10.2016 | Event News
09.12.2016 | Life Sciences
09.12.2016 | Ecology, The Environment and Conservation
09.12.2016 | Health and Medicine