Affects a second gene linked to a hair-like appendage on brain cells
Researchers have discovered how a gene commonly linked to obesity—FTO—contributes to weight gain. The study shows that variations in FTO indirectly affect the function of the primary cilium, a little-understood hair-like appendage on brain and other cells. Specific abnormalities of cilium molecules, in turn, increase body weight, in some instances, by affecting the function of receptors for leptin, a hormone that suppresses appetite. The findings, made in mice, suggest that it might be possible to modify obesity through interventions that alter the function of the cilium, according to scientists at Columbia University Medical Center (CUMC).
"If our findings are confirmed, they could explain how common genetic variants in the gene FTO affect human body weight and lead to obesity," said study leader Rudolph L. Leibel, MD, the Christopher J. Murphy Memorial Professor of Diabetes Research, professor of pediatrics and medicine, and co-director of the Naomi Berrie Diabetes Center at CUMC. "The better we can understand the molecular machinery of obesity, the better we will be able to manipulate these mechanisms and help people lose weight."
The study was published on May 6 in the online edition of Cell Metabolism.
Since 2007, researchers have known that common variants in the fat mass and obesity-associated protein gene, also known as FTO, are strongly associated with increased body weight in adults. But it was not understood how alterations in FTO might contribute to obesity. "Studies have shown that knocking out FTO in mice doesn't necessarily lead to obesity, and not all humans with FTO variants are obese," said Dr. Leibel. "Something else is going on at this location that we were missing."
In experiments with mice, the CUMC team observed that as FTO expression increased or decreased, so did the expression of a nearby gene, RPGRIP1L. RPGRIP1L is known to play a role in regulating the primary cilium. "Aberrations in the cilium have been implicated in rare forms of obesity," said Dr. Leibel. "But it wasn't clear how this structure might be involved in garden-variety obesity."
Dr. Leibel and his colleague, George Stratigopoulos, PhD, associate research scientist, hypothesized that common FTO variations in noncoding regions of the gene do not change its primary function, which is to produce an enzyme that modifies DNA and RNA. Instead, they suspected that FTO variations indirectly affect the expression of RPGRIP1L. "When Dr. Stratigopoulos analyzed the sequence of FTO's intron—its noncoding, or nonprotein-producing, portion—we found that it serves as a binding site for a protein called CUX1," said Dr. Leibel. "CUX1 is a transcription factor that modifies the expression of RPGRIP1L."
Next, Dr. Stratigopoulos set out to determine whether RPGRIP1L plays a role in obesity. He created mice lacking one of their two RPGRIP1L genes, in effect, reducing but not eliminating the gene's function. (Mice that lack both copies of the gene have several serious defects that would obscure the effects on food intake.) Mice with one copy of RPGRIP1L had a higher food intake, gained significantly more weight, and had a higher percentage of body fat than controls.
In a subsequent experiment, the CUMC team found that RPGRIP1L-deficient mice had impaired leptin signaling. "The receptors didn't convene properly on the cell surface around the base of cilium," said Dr. Leibel. "RPGRIP1L appears to play a role in getting leptin receptors to form clusters, where they are more efficient in signaling."
"Overall," said Dr. Leibel, "our findings open a window onto the possible role of the primary cilium in common forms of obesity."
The CUMC team is now conducting studies to learn more about the various components of the FTO- RPGRIP1L pathway, which ciliary proteins are affected by changes in this pathway, and how these proteins mediate actions of leptin receptors.
The paper is titled, "Hypomorphism for RPGRIP1L, a Ciliary Gene Vicinal to the FTO Locus, Causes Increased Adiposity in Mice." The other contributors are Jayne F. Martin Carli (CUMC), Diana R. O'Day (University of Washington, Seattle, WA), Liheng Wang (CUMC), Charles A. LeDuc (CUMC), Patricia Lanzano (CUMC), Wendy K. Chung (CUMC), Michael Rosenbaum (CUMC), Dieter Egli (CUMC), and Daniel A. Doherty (University of Washington).
The authors declare no financial or other conflicts of interests.
The study was supported by grants from the National Institutes of Health (DK52431-15, DK26687-30, NS064077, and DK097399-01).
The Naomi Berrie Diabetes Center at CUMC opened in 1998 to serve the 1.6 million people with diabetes in the New York area, by combining world-class diabetes research and education programs with family-oriented patient care. Founded with support from the Russell Berrie Foundation and other friends, the center is named in honor of the mother of the late Russell Berrie, founder of RUSS™ Toys. The center's more than 100 faculty and students conduct basic and clinical research related to the pathogenesis and treatment of all forms of diabetes and its complications. For more information, visit http://www.nbdiabetes.org.
Columbia University Medical Center provides international leadership in basic, preclinical, and clinical research; medical and health sciences education; and patient care. The medical center trains future leaders and includes the dedicated work of many physicians, scientists, public health professionals, dentists, and nurses at the College of Physicians and Surgeons, the Mailman School of Public Health, the College of Dental Medicine, the School of Nursing, the biomedical departments of the Graduate School of Arts and Sciences, and allied research centers and institutions. Columbia University Medical Center is home to the largest medical research enterprise in New York City and State and one of the largest faculty medical practices in the Northeast. For more information, visit cumc.columbia.edu or columbiadoctors.org.
Karin Eskenazi | Eurek Alert!
Researchers simplify tiny structures' construction drip by drip
12.11.2018 | Princeton University, Engineering School
Mandibular movement monitoring may help improve oral sleep apnea devices
06.11.2018 | Elsevier
Researchers at the University of New Hampshire have captured a difficult-to-view singular event involving "magnetic reconnection"--the process by which sparse particles and energy around Earth collide producing a quick but mighty explosion--in the Earth's magnetotail, the magnetic environment that trails behind the planet.
Magnetic reconnection has remained a bit of a mystery to scientists. They know it exists and have documented the effects that the energy explosions can...
Biochips have been developed at TU Wien (Vienna), on which tissue can be produced and examined. This allows supplying the tissue with different substances in a very controlled way.
Cultivating human cells in the Petri dish is not a big challenge today. Producing artificial tissue, however, permeated by fine blood vessels, is a much more...
Faster and secure data communication: This is the goal of a new joint project involving physicists from the University of Würzburg. The German Federal Ministry of Education and Research funds the project with 14.8 million euro.
In our digital world data security and secure communication are becoming more and more important. Quantum communication is a promising approach to achieve...
On Saturday, 10 November 2018, the research icebreaker Polarstern will leave its homeport of Bremerhaven, bound for Cape Town, South Africa.
When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure
Now, a team of Penn Engineers has demonstrated a new material they call "nanocardboard," an ultrathin equivalent of corrugated paper cardboard. A square...
09.11.2018 | Event News
06.11.2018 | Event News
23.10.2018 | Event News
16.11.2018 | Health and Medicine
16.11.2018 | Life Sciences
16.11.2018 | Life Sciences