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Obesity 'caused by infectious virus which turns cells into fatty tissue'

August 27, 2007
Telegraph UK

Obesity can be caught like a cold, according to a laboratory study showing that a common infectious virus can turn human cells into fatty tissue, scientists said.

It is well established that the human adenovirus-36 causes respiratory and eye infections but now scientists found it can also transform adult stem cells found under the skin into the fat cells of adipose tissue.

The scientists also found there is a specific gene in the virus that appears to control this fatty transformation, which they observed when human stem cells grown in the laboratory became infected.

The findings, presented yesterday to the annual meeting of the American Chemical Society, suggest that the growing global epidemic of obesity may involve more than a lack of exercise and a love of high-calorie food.

"We're not saying a virus is the only cause of obesity, but this study provides stronger evidence that some obesity cases may involve viral infections," said Magdalena Pasarica of Louis-iana State University in Baton Rouge.

"Not all infected people will develop obesity," she said. "We would like to identify the underlying factors that predispose some obese people to develop this virus and eventually to find a way to treat it."

Previous research on animals suggested that adenovirus-36, and two related viruses known as Ad-37 and Ad-5, can trigger obesity. Another study found a high prevalence of adenovirus in overweight people; some 30 per cent of obese people had Ad-36 compared with 11 per cent of lean people.

This led to suggestions that respiratory viruses may play an important role in triggering the tendency towards obesity in susceptible people with the sort of sedentary lifestyle that favours putting on weight.

The latest study appears to support these claims at the cellular level by looking at how the virus interacts with human stem cells growing outside the body in laboratory cultures.

Dr Pasarica obtained the fatty tissue stem cells from a broad cross-section of patients who had undergone liposuction. She exposed only half of the stem cells to Ad-36.

After a week of growth in the laboratory, most of the virus-infected adult stem cells developed into fat cells but the non-infected stem cells did not, Dr Pasarica told the American Chemical Society. "A common virus appears to target stem cells in humans to generate more and bigger fat cells.

"The results are clear. Ad-36 prompts adult, fat-derived stem cells to convert to pre-fat cells, rather than other cell types," she said. "Furthermore, these fat cells accumulate lipids - fats - at an increased rate."

"We conclude that human adenovirus Ad-36 increases the number of fat cells and increases their fat content in humans, which might contribute to the development of obesity," she told the meeting.

The spread of obesity around the developed world is one of the fastest-growing epidemics. But the idea of it being even partly the result of viral infections is contentious; most experts put it down to a change in diet and lifestyle.

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