Long live the fat cells

Cells with higher fat content outlive lean cells, according to a new study.

The research, conducted by scientists from Michigan State University, supports the phenomenon known as the ‘obesity paradox’: that overweight people have the lowest all-cause mortality rates, while fit people have mortality rates comparable to those categorised as slightly obese.

“The obesity paradox baffles scientists across numerous disciplines,” said Min-Hao Kuo, MSU biochemist and molecular biologist who published the study in the current issue of PLoS Genetics. “But when it comes to yeast, which is an excellent model for the studies of human ageing, increasing the cellular content of triacylglycerol, or fat, extends the lifespan.”

Kuo’s team was the first to show a positive correlation between triacylglycerol, or TAG, content and lifespan. TAG is a fat found in all eukaryotes that include animals, plants and fungi. The lipid’s ability to store excessive energy, provide insulation and accumulate in response to many stressors is well known. What’s perplexing, though, is how TAG influences lifespan.

“Our team used genetic approaches to manipulate the cellular capacity of triacylglycerol reproduction and degradation,” Kuo said. “Via sophisticated analyses, we demonstrated that it preserves life through a mechanism that is largely independent of other lifespan regulation pathways common in yeast as well as humans.”

The scientists observed that the fat and long-living yeast cells did not seem to suffer from obvious growth defects. They mate and produce progeny well, and have normal resistance to different environmental stresses. However, being subjected to common methods of extending lifespan — such as caloric restriction and deletion of genes key to nutrient sensing — frequently caused the cells to grow slowly or be less tolerant of environmental stresses.

While the team suspects that the pro-longevity function exists in humans, they’ve yet to prove that triacylglycerol is the driver.

“Our paper likely will stimulate a new wave of research that has broad and deep impacts, including potential advances in human medicine,” Kuo said.