Study: Mice develop 'healthy' obesity

DALLAS, Jan. 30 (UPI) -- Mice whose fat cells were allowed to grow larger than fat cells in normal mice developed "healthy" obesity, when fed a high-fat diet, U.S. researchers said.

Researchers at the University of Texas Southwestern Medical Center in Dallas said the fat but healthy mice lacked a protein called collagen VI, which normally surrounds fat cells and limits how large they can grow -- like a cage around a water balloon.

"The mice lacking collagen VI fared much better metabolically than their counterparts that retained this particular collagen," senior author Dr. Philipp Scherer, director of the Touchstone Center for Diabetes Research at UT Southwestern said in a statement.

"The mice without collagen VI don't develop inflammation or insulin resistance. They still get obese, but it's a 'healthy' obesity."

When people take in more calories than needed, excess calories are stored in fatty tissue. The fat cells are embedded in and secrete substances into an extracellular matrix, a type of connective tissue that provides support to fat tissue, like scaffolding. Collagen VI is one component of this extracellular matrix. Too much of this connective tissue prevents individual cells from expanding and can lead to inflammation, Scherer said.

"In this particular case, however, the large fat cells are not as inflamed as they would normally be," Scherer said. "Fat cells that lack collagen VI can grow to a huge size without becoming inflamed, suggesting that collagen VI directly affects the ability of fat cells to expand."

The findings appear online ahead of print in Molecular and Cellular Biology.