'Molecule linking weight gain to gut bacteria found'

Researchers have found a key molecule that helps bacteria living in the guts of mammals to influence the body's process behind the absorption of dietary fat.

The findings, published in the journal Science, may help understand the root causes of obesity in affluent countries, and malnutrition in impoverished countries.

The researchers, including those from the University of Texas Southwestern Medical Center in the US, found a key molecule involved in synchronising the absorption of nutrients in the gut with our body's natural clock that lets one's cells perceive the day-night cycle.

They found that the beneficial microbes in the gut wind up the body's biological clock, or circadian rhythm, by activating a protein called histone deacetylase 3 (HDAC3) which is made by cells lining the gut.

These cells, the researchers said, act as intermediaries between bacteria that aid in the digestion of food, and proteins that play a role in absorption of nutrients.

The experiments, performed in mice, revealed that HDAC3 activates genes that are involved in the absorption of fat.

They found that HDAC3 interacts with the biological clock related processes in the gut to refine the rhythmic flow of proteins involved in fat absorption.

According to the researchers, this regulation happens in the daytime in humans -- who eat during the day -- and at night in mice, which eat at night.

"The microbiome actually communicates with our metabolic machinery to make fat absorption more efficient," said lead author Zheng Kuang of UT Southwestern.

Kuang added that when fat is overabundant, the communication could result in obesity.

"Whether the same thing is going on in other mammals, including humans, is the subject of future studies," he said.

The researchers said that histone modifications - a chemical change made by enzymes like HDAC3 - control the expression of genes, which regulates the protein making machinery within cells.

Researchers at Lora Hooper's lab in UT Southwestern decided to perform a study in mice on histone modifications that seemed to rise and fall along with the circadian rhythms.

They compared normal, bacteria-laden mice with ones free of the microbes, and discovered that some histone modifications - including those made by HDAC3 - were rhythmic depending on the time of the day in normal mice, but held steady at a flat level in germ-free mice.

The researchers developed a mouse lacking HDAC3 only in the gut lining -- which they said was "unremarkable while eating a normal chow diet."