According to a recent study in the International Journal of Obesity Supplements, the body has the capacity to harness the production of heat by converting white fat cells, the cells that are responsible for storing calories, into beige fat cells, the cells responsible for burning energy. Learning more about this biological process could help fight obesity.
Investigators T.J. Bartness and Vitaly Ryu, in the review titled “Neural control of white, beige and brown adipocytes,” explored the question: “What is the sympathetic nervous system (SNS) innervation of brite/beige adipocytes? That is, is there ‘special’ sympathetic innervation of the subpopulations of brown adipocyte-like fat cells harbored within what are traditionally considered to be the province of white adipocytes only?”
Using a PubMed search, the researchers demonstrated that using heat production and increasing the sympathetic nervous system‘s (SNS) supply of blood vessels to white fat tissue could be a novel strategy to fight obesity.
According to the National Heart, Lung and Blood Institute of the National Institutes of Health, approximately 70% of Americans are obese or overweight. Approaches to fight obesity, such as behavioral or pharmacological strategies involving a reduction of food intake, have been only slightly effective. And while overweight or obese patients who underwent bariatric surgery have experienced some success, the use of weight loss surgery is still considered an extreme measure and advised only in cases of severe obesity with one or more comorbidities.
Researchers believe that increasing the expenditure of energy with brown or brite/beige fat cells could be effective in fighting obesity.
There are two types of fat tissue in the body: white fat tissue and brown fat tissue. White fat is responsible for storing calories and energy. White fat also produces hormones that are secreted into the bloodstream. Brown fat tissue is responsible for heat production and for burning energy. In 2009, it was found that adults have small amounts of brown fat, something that was thought to only exist in babies.
The team of investigators reviewed studies about the neural control of white, beige, and brown fat tissue. Specifically, the researchers studied how the SNS “browns” white fat tissue cells, converting them into “brite” or “beige” fat cells and suggesting a potential strategy for increasing the production of heat.
“Perhaps the most important features of white adipose tissue for the conversion of white fat cells to brite/beige fat cells is the density of the SNS nerves being supplied to white adipose tissue, and the fat cell population surrounding this nerve supply having a genetic ability to brown,” said Dr. Ryu, co-author of the study and senior research scientist II in the Department of Biology and Center for Obesity Reversal at Georgia State University in a recent news release. “SNS drive increases with cold exposure and food deprivation, so that’s when a breakdown of fats and cell ‘browning’ occurs.”
While it remains poorly understood how the SNS supplies white fat tissue with nerves to produce the “brite” cells, based on the studies examined, the investigators discovered the strongest neuroanatomical evidence of the SNS regulating the browning of white fat in mice following exposure to cold for 10 days versus warm acclimated control mice. The results revealed that cold exposure was responsible for increasing the quantity of tyrosine hydroxylase fibers of the marker for SNS nerves, in contact with white fat cells. This fiber contact was linked with triple the quantity of multilocular fat cells, or those cells with many vesicles, in comparison to accumulations of normal white fat tissue. Evidence infers that innervation and stimulation of the SNS regarding the white cells tissue 3-adrenoreceptor is significant in the browning of the white fat tissue.
According to 2011 research by P.T. Chao and others, the only specific brain area that exclusively causes the browning in white fat is the dorsomedial hypothalamic nucleus (DMH). When there is a decrease in the neuropeptide Y (NPY) gene expression with the DMH, the SNS drive to specific subcutaneous white adipose fat depots, or fat just beneath the skin, rises and results in the browning effect.
The investigators concluded that perhaps the most important features of white fat for its production/conversion to brite/beige adipocytes is the density of the sympathetic nerves innervating white fat tissue (and, of course, increases in their activity), as well as the adipocyte cell population surrounding this innervation for its genetic ability to brown. With increases in the SNS drive to white fat tissue, lipolysis is triggered and if the adipocyte population is capable, browning occurs. Whether lipolysis is necessary for browning remains to be demonstrated.
