White fat or brown fat?

A recent study, published in the journal Cell Metabolism, defines a mechanism that controls if a precursor fat cell matures into a brown fat or white fat cell. Why would this matter?

Most people are undergoing a constant battle to get rid of fat. But, fat cells aren't all the same. Two forms of fat cells exist; white fat and brown fat. White fat is the stuff that stores the excess calories and energy that we taken in, making sure we have enough reserves for lean times when food is scarce. White fat accumulates around the mid-section of our body, along the butt and thighs, and elsewhere. Brown fat is quite different. Brown fat generates heat and burns energy. These cells are filled with energy producing iron-filled mitochondria, hence the brown color, and generates heat for the organism. Brown fat, found mostly in infants (along the spine and shoulders of the back) and hibernating mammals. It's main function is to provide heat to avoid hypothermia in mammals that don't shiver. In adult humans, the amount of brown fat is quite low.

Dr Seale and colleagues have now shown that a protein called early B cell factor-2 or Ebf2 acts like a switch during fat cell development that controls which type of fat cell emerges, a brown fat or white fat cell. It turns out that Ebf2 binds to the promoter of genes involved in brown fat development. This results in the recruitment and binding of another protein, PPAR, and the subsequent expression of these genes. This study also showed that overexpression of Ebf2 in white fat cells converts into brown fat cells. Understanding how these cells develop may help develop new ways to control the amount of white fat cells in the body to help fight obesity.

http://www.alnmag.com/news/how-brown-fat-cells-develop-mice?et_cid=3143363&et_rid=454985655&linkid=http%3a%2f%2fwww.alnmag.com%2fnews%2fhow-brown-fat-cells-develop-mice

Bacteria can influence weight

Yet another study has linked the profile of bacteria found in your colon (called the microbiome) to obesity and weight gain. This paper, published in Nature Reviews Endocrinology (7:639-646), reviewed the latest studies to investigate the contribution of bacteria to nutrient metabolism and obesity. Their review has demonstrated that numerous studies have begun to understand the influence of the profile of bacteria in the control of overall weight. Together, all of these studies suggest that the microbiome may be a critical player in metabolism and can influence weight gain or loss.

HDAC4 regulates fasting/feeding states

Many studies have shown that the control of lipid (fat) stores during fasting and feeding states is largely dependent on SIRT1 and FoxO activity. This latest study investigates the role of these proteins in obesity and adds another level of regulation to the mix.

Using a drosophila model, Wang et. al. (Cell 145:596-606) provide evidence that the serine/threonine salt-inducible kinase (SIK) 3 controls lipid storage or lipolysis in a HDAC4/FoxO dependent manner. During feeding, insulin activates SIK3 (its mammalian homolog is SIK2), phosphorylates HDAC4, which prevents its activation and subsequent movement to the nuclear compartment. This inhibits the deacetylation and activation of FoxO and ultimately increases lipid storage. Under fasting conditions, SIK3 activity is inhibited, HDAC4 remains in an active, dephosphorylated state where it can easily translocate to the nucleus. In the nucleus, HDAC4 deacetylates and activates FoxO to increase lipolysis as a mechanism to provide energy to the starving organism. When the organism re-feeds, FoxO is acetylated via the action of p300 and CBP and HDAC4 is re-phosphorylated. Therefore, HDAC4 activity is a critical regulator of fasting or feeding states.

This pathway is not limited to drosophila. Using a mouse hepatocyte cell line, Wang et. al. confirm their findings in mammals, suggesting a universality of this mechanism.

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A new protein that controls obesity

Obesity is on the rise. Our diets aren’t healthy (or low in calories) and we are increasingly sedentary. Many scientists are researching how to control obesity and how to prevent obesity-related diseases including diabetes, cardiovascular disease and cancers. A new study by Zhang et al (Journal of Biological Chemistry 286:28396 August 12, 2011) identifies another player in the regulation of body mass and obesity. This protein, beta-arrestin 1, appears to regulate the expression of genes involved in metabolism and in inflammation. Since both are linked to many obesity-related diseases, these investigators investigated its role in obesity. Elimination of the gene increases body mass and metabolic dysregulation in mice fed a high fat diet. Conversely, overexpression of beta-arrestin 1 reversed these effects and restored normal weight, even in the presence of excess calories. While this is far from a magic pill to control weight and obesity, it does provide insight into how the body regulates weight and its metabolism.

Improving body image may help with weight loss

Want to lose weight? Incorporating sessions to improve body image may improve the amount lost, according to a study published today in the International Journal of Behavioral Nutrition and Physical Activity. Their results demonstrated a significant improvement in overall weight loss amounts when body image was addressed (-7.3% vs -1.7%).


BioMed Central: www.biomedcentral.com
Intl Journal of Behavioral Nutrition and Physical Activity: http://www.ukdistribute.com/links/1310722818976-Body%20image%20change%20and%20improved%20eating%20self_regulation.pdf


Obesity is a growing public health problem in the US and around the world. Current estimates indicate 25-33% of the US population is obese (defined as a body mass index > 25). With increasing lack of physical activity, these numbers are predicted to rise over the coming years. Obesity is linked to many diseases including diabetes, cardiovascular and cancer. Health care costs rise with increased obesity rates. It is not easy to lose weight, but the health and financial benefit of doing, on a personal and societal level, so far exceeds the potential risks.

Over the years, many approaches to weight loss have been published. Some are healthy options that can lead to sustained weight management. Others are fad diets that are both ineffective and unhealthy. This study addressed whether body image could be a significant factor in determining overall outcome of weight management programs. By comparing a program that incorporated sessions on body image with the same program that included general sessions about health, Carraca et. al. demonstrated a significant increase in overall weight loss when body image sessions were included (-7.3% with sessions vs -1.7% without). Body image improved and the preoccupation with societal influence on body image decreased.

There is no magic pill or fad diet that will work. It comes down to effort, desire, and commitment to increased physical activity and a healthy lifestyle. Including methods to improve body image seem to be a key component to add to the mix that may lead to successful and maintained weight loss.

Nicotine suppresses appetite by activation of specific neurons

Many people use smoking as a mechanism to suppresses appetite and control their body weight. Nicotine in cigarettes is the culprit, affecting peripheral energy expenditures, but also affecting the central nervous system to regulate feeding. Mineur et. al. (Science 332: 1330-1332, June 10, 2011) have now uncovered some the of the molecular steps involved in nicotine-suppressed appetite control. In mouse models, nicotine binds to its receptor (the nicotinic acetylcholine receptor or nAChR) in a specific region of the brain called the arcuate nucleus (ARC). Here nicotine activates the pro-opiomelanocortin (POMC) neurons that begin to fire more frequently. This increased neuron stimulation produces more melanocortin that is known to decrease the urge to eat. The hope is that this work can lead to the development of new therapy to treat obesity and other metabolic syndromes.