HEALTH NEWS

Study Title:

Free Radicals Suppress Appetite

Study Abstract

Previous studies have proposed roles for hypothalamic reactive oxygen species (ROS) in the modulation of circuit activity of the melanocortin system1, 2. Here we show that suppression of ROS diminishes pro-opiomelanocortin (POMC) cell activation and promotes the activity of neuropeptide Y (NPY)- and agouti-related peptide (AgRP)-co-producing (NPY/AgRP) neurons and feeding, whereas ROS-activates POMC neurons and reduces feeding. The levels of ROS in POMC neurons were positively correlated with those of leptin in lean and ob/ob mice, a relationship that was diminished in diet-induced obese (DIO) mice. High-fat feeding resulted in proliferation of peroxisomes and elevated peroxisome proliferator–activated receptor γ (PPAR-γ) mRNA levels within the hypothalamus. The proliferation of peroxisomes in POMC neurons induced by the PPAR-γ agonist rosiglitazone decreased ROS levels and increased food intake in lean mice on high-fat diet. Conversely, the suppression of peroxisome proliferation by the PPAR antagonist GW9662 increased ROS concentrations and c-fos expression in POMC neurons. Also, it reversed high-fat feeding–triggered elevated NPY/AgRP and low POMC neuronal firing, and resulted in decreased feeding of DIO mice. Finally, central administration of ROS alone increased c-fos and phosphorylated signal transducer and activator of transcription 3 (pStat3) expression in POMC neurons and reduced feeding of DIO mice. These observations unmask a previously unknown hypothalamic cellular process associated with peroxisomes and ROS in the central regulation of energy metabolism in states of leptin resistance.

From press release:

Obesity is growing at alarming rates worldwide, and the biggest culprit is overeating. In a study of brain circuits that control hunger and satiety, Yale School of Medicine researchers have found that molecular mechanisms controlling free radicals -- molecules tied to aging and tissue damage -- are at the heart of increased appetite in diet-induced obesity.

Published Aug. 28 in the advanced online issue of Nature Medicine, the study found that elevating free radical levels in the hypothalamus directly or indirectly suppresses appetite in obese mice by activating satiety-promoting melanocortin neurons. Free radicals, however, are also thought to drive the aging process.

"It's a catch-22," said senior author Tamas Horvath, the Jean and David W. Wallace Professor of Biomedical Research, chair of comparative medicine and director of the Yale Program on Integrative Cell Signaling and Neurobiology of Metabolism. "On one hand, you must have these critical signaling molecules to stop eating. On the other hand, if exposed to them chronically, free radicals damage cells and promote aging."

"That's why, in response to continuous overeating, a cellular mechanism kicks in to suppress the generation of these free radicals," added lead author Sabrina Diano, associate professor of Ob/Gyn, neurobiology and comparative medicine. "While this free radical-suppressing mechanism -- promoted by growth of intracellular organelles, called peroxisomes -- protects the cells from damage, this same process will decrease the ability to feel full after eating."

After the mice ate, the team saw that the neurons responsible for stopping overeating had high levels of free radicals. This process is driven by the hormone leptin and glucose, which signal the brain to modulate food intake. When mice eat, leptin and glucose levels go up, as does free radical levels. However, in mice with diet-induced obesity, these same neurons display impaired firing and activity (leptin resistance), in these mice, levels of free radicals were buffered by peroxisomes, preventing the activation of these neurons and thus the ability to feel sated after eating.

According to Horvath and Diano, the crucial role of free radicals in promoting satiety as well as degenerative processes associated with aging may explain why it has been difficult to develop successful therapeutic strategies for obesity without major side effects. Current studies address the question of whether, under any circumstance, satiety could be promoted without sustained elevation of free radicals in the brain and periphery.

The study was supported by grants form the National Institutes of Health and the American Diabetes Association.

Study Information

1.Sabrina Diano, Zhong-Wu Liu, Jin Kwon Jeong, Marcelo O Dietrich, Hai-Bin Ruan, Esther Kim, Shigetomo Suyama, Kaitlin Kelly, Erika Gyengesi, Jack L Arbiser, Denise D Belsham, David A Sarruf, Michael W Schwartz, Anton M Bennett, Marya Shanabrough, Charles
Peroxisome proliferation–associated control of reactive oxygen species sets melanocortin tone and feeding in diet-induced obesity.
Nature Medicine
2011 August
Yale School of Medicine