Different fat cell types may be key to obesity

Scientists have long believed fat is fat. There is white fat, which stores energy, and brown fat, which helps maintain body temperature, but it basically develops in the same way.

We also know being overweight or obese – as experienced by about 70 per cent of Australians – is linked with a higher risk of metabolic conditions like diabetes, cardiovascular disease and fatty liver disease.

But, in a world-first, University of Melbourne researchers have led an international study, which found differences in white fat cells. Some white fat cells actually help burn energy, while others are the culprits that release fat into the bloodstream at high rates.

The study, published in Cell Reports, is a major move towards not only helping people lose weight, but preventing them from developing obesity-related health issues.

That is because the discovery holds out the tantalising prospect that scientists are edging closer to working out how to ‘switch off’ the fat releasing cells and ‘switch on’ the fat burning cells.

Novel fat findings

Understanding how fat metabolism is regulated, and whether it can be made more efficient, is a question senior author Professor Matthew Watt is closing in on.

Head of Physiology at the University of Melbourne’s School of Biomedical Sciences, Professor Watt says the results of the six-year study indicate there are actually three types of white fat cell and how the different makeup of these fat cell subtypes in a person’s body could help to determine their health.

“Knowing how fat develops, and our own data showing there are different types of fat, extends our understanding of possible treatments for obesity-like conditions in the future,” says Professor Watt.

The study – a collaboration between the University of Melbourne, Monash University, Yale University and Alfred Health – took samples from 50 human volunteers.

Researchers, particularly co-author and former University of Melbourne post-doctoral researcher Arthe Raajendiran, worked on separating the different cell types, investigating their genes, and assessing proteins and metabolism.

They discovered three specific subtypes of the stem cells that go on to become white fat cells:

• Subtype 1 releases lots of fat into the bloodstream – at a rate 100 times faster than other fat cells
  
• Subtype 2 burns energy at a high rate and could possibly prevent weight gain
  
• Subtype 3 was a rather benign but slow operating, normal fat cell
  

While all three cell subtypes were present in fat tissue throughout the body, some people had more of some cell subtypes and less of others.

Most notably, the researchers found people with type 2 diabetes tended to have more of the fat-releasing subtype, and less of the fat-burning subtype.

This means, it is possible the make-up of a person’s fat may be promoting type 2 diabetes, rather than other factors such as their weight. In other words, the first fat cell subtype is thought to increase the risk of fatty deposits around the body and on organs, regardless of whether someone is overweight or not.

“The way you get fatty liver and cardiovascular disease is associated with having high blood fatty acids – so, if you have a lot of these cells that are spitting out a lot of fat into your bloodstream, these fats get taken up by the liver, muscles and other tissues, and that’s linked to disease development,” explains Professor Watt.

Combating obesity – what’s next?

With the burden of obesity increasing, particularly the rates of associated chronic illnesses and disability, now is a critical time to further investigate how these different fat cell subtypes could be used to prevent obesity.

Diabetes, for example, is the fastest growing chronic condition in Australia. It is increasing at a faster rate than heart disease and cancer, meaning a better understanding of fat cell distribution and linked metabolic complications is paramount.

Professor Watt says more work is needed to determine ways to possibly ‘switch off’ the fat releasing cells and ‘switch on’ the fat burning cells. This would involve developing drug therapies and could take at least 10 years.

“We first need to determine whether the number of fat cell subtypes affects disease development. Then we can work out ways to decrease or increase a certain type of fat cell to improve health,” says Professor Watt.

Eventually treatments could be developed to help prevent some illnesses, and would be much less invasive than surgery designed to constrict the stomach so people eat less, like gastric banding.

However, lifestyle changes – including having a good diet – will always be necessary in the fight against Australia’s bodyweight concerns.

“Whilst we advocate for new discoveries to inform the development of anti-obesity therapies, a healthy lifestyle, including daily activity and reduced food intake, is important,” says Professor Watt.

Banner: Immunofluorescence staining inside an adipocyte (fat cell) showing proteins in green and lipids in red/Supplied