Why does excess fat in the body cause so many different diseases? The problem occurs because as you accumulate more and more fat, your adipose tissue becomes inflamed. Perhaps the main actor in this chronic inflammation is one of your body’s own immune cells called the macrophage. The macrophages in adipose tissue are called adipose tissue macrophages (ATMs).
Hi I’m Dr. Maria Conley and today we’ll talk about adipose tissue macrophages and how these immune cells secrete proteins into the bloodstream that cause chronic inflammation in the body which can lead to cancer, Alzheimer’s dementia and type two diabetes.
Only a few decades ago, we thought that fat cells or adipocytes were merely storage deposits for fat or triglycerides. However we now know that adipocytes are actually endocrine organs, releasing more than 600 different types of proteins or adipocytes into the bloodstream. These adipocytes include hormones and cytokines which regulate appetite and satiety, inflammation, blood pressure, insulin sensitivity and energy expenditure.
When a person becomes obese, their adipocytes enlarge and secrete more pro inflammatory proteins such as TNF alpha and interleukin 6 (IL-6). As the lipid droplet in each adipocyte gets bigger and bigger, the cell expands until it outgrows its blood supply and becomes starved of oxygen. When this occurs, the enlarged fat cell dies.
Certain scavenger cells in your immune system called macrophages migrate through the bloodstream and enter the adipose tissue to get rid of these dead fat cells. These phagocytes (in Greek, “eating cells”) join the resident macrophages already present in adipose tissue. Together, these adipose tissue macrophages surround and gobble up the dying fat cells. These proinflammatory ATMs are the main source of inflammatory cytokines such as TNF alpha and interleukin six. These damaging proteins cause chronic inflammation in the body and promote tumor formation, development of diabetes and Alzheimer’s dementia. TNF alpha also downregulates adiponectin, an adipokine that promotes insulin sensitivity and burning of fat.
Adipose tissue macrophages make up 5% of all the cells in adipose tissue in people of normal weight. But in obese individuals, this percentage jumps to 50% of all cells in adipose tissue.
You need a healthy adipose tissue to serve as a storage site for fat which can be used as an energy source. The problem develops when an individual becomes obese, causing their fat cells to gradually balloon out as more and more fat is deposited inside of each individual cell. These enlarging adipocytes outgrow their blood supply, become starved of oxygen and begin to die off. The macrophages of your immune system sense the presence of these dead cells and they travel to the site to ingest and destroy the dying fat cells. The adipose tissue macrophages are successful in getting rid of dead fat cells but unfortunately they also produce chronic inflammation throughout the body, contributing to insulin resistance, certain cancers and Alzheimer’s dementia.
