How to fight fat with fat

Scientists have discovered a trigger that turns muscle stem cells into brown fat, a form of good fat that could play a critical role in the fight against obesity.

This discovery significantly advances our ability to harness this good fat in the battle against bad fat and all the associated health risks that come with being overweight and obese, said Dr. Michael Rudnicki, a senior scientist and director for the Regenerative Medicine Program and Sprott Centre for Stem Cell Research at the Ottawa Hospital Research Institute.

In 2007, Dr. Rudnicki led a team that was the first to prove the existence of adult skeletal muscle stem cells.

In the new study, Dr. Rudnicki shows (again for the first time) that these adult muscle stem cells not only have the ability to produce muscle fibres, but also to become brown fat. Brown fat is an energy-burning tissue that is important to the body's ability to keep warm and regulate temperature. In addition, more brown fat is associated with less obesity.

Perhaps more importantly, he identifies how adult muscle stem cells become brown fat. The key is a small gene regulator called microRNA-133, or miR-133. When miR-133 is present, the stem cells turn into muscle fibre; when reduced, the stem cells become brown fat.  Dr. Rudnicki's lab showed that adult mice injected with an agent to reduce miR-133, called an antisense oligonucleotide or ASO, produced more brown fat, were protected from obesity and had an improved ability to process glucose. In addition, the local injection into the hind leg muscle led to increased energy production throughout the body—an effect observed after four months.

Using an ASO to treat disease by reducing the levels of specific microRNAs is a method that is already in human clinical trials. However, a potential treatment using miR-133 to combat obesity is still years away.

“While we are very excited by this breakthrough, we acknowledge that it's a first step,” said Dr. Rudnicki.