PROVIDENCE, R.I. [Brown University] With obesity reaching epidemic levels in some parts of the world, scientists have only begun to understand why it is such a persistent condition. A study in the Journal of Biological Chemistry adds substantially to the story by reporting the discovery of a molecular chain of events in the brains of obese rats that undermined their ability to suppress appetite and to increase calorie burning.
It's a vicious cycle, involving a breakdown in how brain cells process key proteins, that allows obesity to beget further obesity. But in a finding that might prove encouraging in the long term, the researchers at Brown University and Lifespan also found that they could intervene to break that cycle by fixing the core protein-processing problem.
Before the study, scientists knew that one mechanism in which obesity perpetuates itself was by causing resistance to leptin, a hormone that signals the brain about the status of fat in the body. But years ago senior author Eduardo A. Nillni, professor of medicine at Brown University and a researcher at Rhode Island Hospital, observed that after meals obese rats had a dearth of another key hormone alpha-MSH compared to rats of normal weight.
Alpha-MSH has two jobs in parts of the hypothalamus region of the brain. One is to suppress the activity of food-seeking brain cells. The second is to signal other brain cells to produce the hormone TRH, which prompts the thyroid gland to spur calorie burning activity in the body.
In the obese rats alpha-MSH was low, despite an abundance of leptin and despite normal levels of gene expression both for its biochemical precursor protein called pro-opiomelanocortin (POMC) and for a key enzyme called PC2 that processes POMC in brain cells. There had to be more to the story than just leptin, and it wasn't a problem with expressing the needed genes.
Nillni and his co-authors, including lead authors Isin Cakir and
|Contact: David Orenstein|