Adipose – The Misunderstood Tissue

One of the leading health problems in the United States is obesity. As you can see in the graph below, almost 1/3 of all adults in the US are classified as obese. In 12 states, the level of obesity now exceeds 30%. With over 43 million children classified as obese in 2010, most experts predict that the percent of obese adults is expected to grow to over 50% by 2050. While obesity has long been recognized to place demands on the cardiovascular system, we now know that excess weight is related not only to an increased risk of cancer, but also mental health, memory, and reproductive problems.

graph of obesity trends in the US for 2011

While a considerable amount of effort has been directed at programs that establish healthy eating habits, researchers are also taking a closer look at adipose tissue. In the body, fat is stored in primarily stored in adipose tissue. Of all of the tissue types in the body, adipose tissue is probably the least interesting. In fact, adipose tissue isn’t even exciting to look at under the microscope. The adipose cells in this sample are the large white open regions located around the pink-stained tissues (which in this case are of an artery).
Adipose tissue embolus

By Yale Rosen [CC-BY-SA-2.0 (http://creativecommons.org/licenses/by-sa/2.0)], via Wikimedia Commons

In addition to storing fat as a long-term energy reserve, adipose tissue has a number of other functions in the body, including insulating your internal organs  (which is why it is often found around the kidneys, heart and abdomen) and helping to maintain your body temperature (50% of your body fat is located just under your skin).

In general, this is usually as far as the discussions go with regards to adipose tissue. It stores energy as fat, and releases it when needed. But several studies are beginning to take a new look at adipose tissue and how it functions:

Exercise and Adipose Tissue

The first of these studies involves how exercise influences adipose tissue cells. We know that genetics may influence obesity, mainly by altering the body’s view of hunger and calories, and that exercise causes adipose tissue to release a portion of its stored fat as energy. However, recently at Lund University, researchers discovered that even small amounts of exercise influences the expression of genes within the adipose cells.

Gene expression governs how a cell functions. It is the process by which a cell accesses the information within the DNA to perform its specific functions. While historically, gene expression was considered to be predictable (certain cells would express genes in certain ways), we now know that it is possible to alter gene expression by a process called epigenetics.  Epigenetics is the regulation of gene expression due to environmental factors,  and not the internal information within our DNA. The process involves methylation, or the attachment of small, temporary chemical groups to the DNA molecule.

Here is a great tutorial on epigenetics and methylation from Bozeman Biology on YouTube.

The researchers at Lund University discovered that during even small amounts of exercise (less than 2 sessions per week) there were detectable epigenetic changes to over 7,000 genes in an adipose cell! That is a considerable number, since we only have around 25,000 genes in the human genome. Furthermore, some of these genes were related to how the cell stores fat, and are linked to type 2 diabetes and obesity. By studying these changes it may be easier to better understand the relationship between adipose tissue and exercise, and possibly develop compounds that target specific areas of the genome as treatments for obesity-related illnesses.

Fat Cells and Heat

In another study, researchers at Harvard Medical School uncovered an interesting relationship between adipose tissue and heat.

While there are a number of different types of adipose cells in the body, we are going to focus on brown fat versus white fat. To put it simply, scientists believe that the role of brown fat is to burn the energy stored within white fat, specifically when generating body heat. White fat is basically a long-term storage location for energy. But, in many ways, brown fat acts more like a muscle tissue, and in general, most people have a very small percentage of brown fat in their bodies. In fact, a higher the percentage of brown fat has been linked to a reduced risk for many fat-related diseases, such as cardiovascular disease and diabetes.

While we have known for some time that colder temperature causes brown fat cells to release energy as heat to maintain temperature balance, or homeostasis, in the body, the pathway for this process has never been studied in detail in white fat cells. The researchers at Harvard Medical School did just this, and found out that white fat cells contain the same temperature-sensitive energy-releasing pathways as brown fat cells.

While studies still need to be done to understand the differences in how these two cells regulate these pathways, since the pathway basically seems to be off in white fat cells, it does open up a number of possibilities. Can the pathway in the white cell type be activated to release heat? If so, then this may provide a future avenue to reduce the amount of fat stored in white fat cells, and in doing so, the amount of fat in the body.

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