It’s often said that when very muscular individuals stop training their muscles will turn into fat. What actually happens is their calorie expenditure drops while their calorie consumption is maintained and they put on weight in the form of fat. With this in mind it seems odd to imagine how fat could be tuned into muscle, but two studies reported in Nature suggest that this possibility may exist.

Before looking at these studies it’s worth remembering what fat is and what fat does. There are two types of body fat, brown (Brown Adipose Tissue or BAT) and white (White Adipose Tissue or WAT) which have different structure and functions.

White fat is used to store energy and insulate the body. Receptors on white fat cells respond to hormones and release fatty acids into the blood to be used by muscles for energy. Brown fat is present in newborn babies and then decreases with age.  It generates heat by burning calories and protects infants from the effects of cold.  Brown fat can be found in adults although it only exits in small quantities compared with infants where it can make up to 5 percent of body mass.

Now two studies published in Nature are uncovering new features of fat tissues. One study suggests that brown fat and muscle are more closely linked than previously thought and it may be possible to inter convert them. This means that brown fat could be turned into muscle and vice versa. The other study has shown how the manufacture of brown fat may be promoted.

A team at the Joslin Diabetes Center demonstrated that a bone-inducing protein called BMP-7 drives precursor cells that give rise to mature brown fat cells. This finding follows from earlier studies at the Institute which discovered genes that control the creation of the precursor cells of brown fat. It was also found that obesity resistant mice had clusters of brown fat cells dispersed between bundles of muscle fibers. The latest study used gene therapy to introduce the BMP-7 protein shown to increase the development of brown fat tissue. Mice that developed brown fat tissue gained less weight than those that did not. Dr. Tseng hopes that as more is learned about brown fat development new therapies may offer solutions for “losing weight and preventing the metabolic disorders associated with obesity”,  such as type 2 diabetes. However,  she added that “diet and exercise are still the best approaches for weight loss” for most people.

A second study,  led by  Professor Bruce Spiegelman of the Dana-Farber Cancer Institute, showed how the creation of brown fat from immature muscle cells is regulated by  a molecular switch, PRDM16. They also found that switching off PRDM16 in brown fat cells can convert them into muscle cells.  Effectively this switch turns fat into muscle and muscle into fat although the latter is described by Spiegelman as a lab trick with no practical application. The notable aspects of this study are that muscle precursor cells appear to give rise to brown fat cells under the control of PRDM16 which seems to be a master regulator for the development of brown fat. This follows earlier research findings that inserting PRDM16 into white fat cell precursors would cause them to produce brown fat cells instead. The hope is that PRDM16 can be used to increase metabolism by increasing brown fat in people at risk of becoming obese.

While these research findings may offer possibilites of combating obesity due to metbolic disorders they also raise the usual questions over suitability of medical obesity cures for people who are overweight due to over eating. The comments accompanying the article in Nature show the depth of feeling in the debate over obesity treatments.

Tags: fat, gene therapy, muscle, obesity

This entry was posted on Wednesday, October 1st, 2008 at 1:55 pm and is filed under Research. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.