RICHMOND, Va. (Dec. 5, 2012) - Approximately 68 percent of U.S. adults are overweight or obese, according to the National Cancer Institute, which puts them at greater risk for developing cancer, cardiovascular disease, diabetes and a host of other chronic illnesses. But an international team of scientists led by Virginia Commonwealth University Massey Cancer Center researcher Andrew Larner, M.D., Ph.D., has successfully reversed obesity in mice by manipulating the production of an enzyme known as tyrosine-protein kinase-2 (Tyk2). In their experiments, the scientists discovered that Tyk2 helps regulate obesity in mice and humans through the differentiation of a type of fat tissue known as brown adipose tissue (BAT).
Published today in the online edition of the journal Cell Metabolism, the study is the first to provide evidence of the relationship between Tyk2 and BAT. Previous studies by Larner and his team discovered that Tyk2 helps suppress the growth and metastasis of breast cancer, and now the current study suggests this same enzyme could help protect against and even reverse obesity.
The scientists were able to reverse obesity in mice that do not express Tyk2 by expressing a protein known as signal transducer and activator of transcription-3 (Stat3). Stat3 mediates the expression of a variety of genes that regulate a host of cellular processes. The researchers found that Stat3 formed a complex with a protein known as PR domain containing 16 (PRDM16) to restore the development of BAT and decrease obesity.
"We discovered that Tyk2 levels in mice are regulated by diet. We then tested tissue samples from humans and found that levels of Tyk2 were more than 50 percent lower in obese humans," said Larner, Martha Anne Hatcher Distinguished Professor in Oncology and co-leader of the Cancer Cell Signaling program at VCU Massey Cancer Center. "Our findings open new potential avenues for research and development of new pharmacological and nutritional treatments for obesity."
There are two different types of fat - white adipose tissue (WAT) and BAT. WAT is the primary site of energy storage. BAT is responsible for energy expenditure in order to maintain body temperature. BAT deposits are present in all mammals, but until recently, scientists thought BAT was only active in infants and not in adult humans. Only in the last four years have scientists realized that BAT is present in adults and helps to regulate energy expenditure. Additionally, research has shown that diminished BAT activity is associated with metabolic syndrome, a combination of medical disorders that increase the risk of developing cardiovascular disease and diabetes. Researchers estimate metabolic syndrome could affect as much as 25 percent of the U.S. population.
"We have made some very interesting observations in this study, but there are many questions left unanswered," said Larner. "We plan to further investigate the actions of Tyk2 and Stat3 in order to better understand the mechanisms involved in the development of brown adipose tissue. We're hopeful this research will help lead to new targets to treat a variety of obesity-related diseases such as cancer, cardiovascular disease and diabetes."
Larner collaborated on this study with Marta Derecka, Magdalena Morgan, Vidisha Raje, Jennifer Sisler and Quifang Zhang, all from the Department of Biochemistry and Molecular Biology at VCU School of Medicine; Tomasz Kordula, Ph.D., Cancer Cell Signaling program member at VCU Massey; Agnieszka Gornicka, from the Cleveland Clinic Foundation; Sergei B. Koralov, Ph.D., from New York University Medical School; Dennis Otero, Ph.D., from the University of California; Joanna Cichy, Ph.D., from Jagiellonian University in Krakow, Poland; Klaus Rajewsky, Ph.D., from Harvard Medical School; Kazuya Shimoda, M.D., Ph.D., from Miyazaki University in Japan; Valeria Poli, Ph.D., from the University of Turin in Torino, Italy; Brigit Strobl, Ph.D., from the University of Veterinary Medicine in Vienna, Austria; Sandra Pellegrini, Ph.D., from Institut Pasteur in Paris, France; Thurl E. Harris, Ph.D., and Susanna R. Keller, M.D., from University of Virginia School of Medicine; Patrick Seale, Ph.D., from the University of Pennsylvania School of Medicine; Aaron P. Russell, Ph.D., from Deakin University in Burwood, Australia; Andrew J. McAinch, Ph.D., from Victoria University in St. Albans, Australia; Paul E. O'Brien, M.D., from Monash University in Melbourne, Australia; and Colleen M. Croniger, Ph.D., from Case Western University School of Medicine.
This study was supported by National Institutes of Health grants R01 AI059710-01 and R21 AI088487, the Austrian Science Fund and, in part, by funding from VCU Massey Cancer Center's NIH-NCI Cancer Center Support Grant P30 CA016059.
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About VCU Massey Cancer Center
VCU Massey Cancer Center is one of only 67 National Cancer Institute-designated institutions in the country that leads and shapes America's cancer research efforts. Working with all kinds of cancers, the Center conducts basic, translational and clinical cancer research, provides state-of-the-art treatments and clinical trials, and promotes cancer prevention and education. Since 1974, Massey has served as an internationally recognized center of excellence. It has one of the largest offerings of clinical trials in Virginia and serves patients in Richmond and in four satellite locations. Its 1,000 researchers, clinicians and staff members are dedicated to improving the quality of human life by developing and delivering effective means to prevent, control and ultimately to cure cancer. Visit Massey online at www.massey.vcu.edu or call 877-4-MASSEY for more information.
About VCU and the VCU Medical Center
Virginia Commonwealth University is a major, urban public research university with national and international rankings in sponsored research. Located in downtown Richmond, VCU enrolls more than 31,000 students in 222 degree and certificate programs in the arts, sciences and humanities. Sixty-six of the programs are unique in Virginia, many of them crossing the disciplines of VCU's 13 schools and one college. MCV Hospitals and the health sciences schools of Virginia Commonwealth University compose the VCU Medical Center, one of the nation's leading academic medical centers. For more, see www.vcu.edu.