It's the calories that matter and too many of any of those will result in body fat - and that is not all equal. The location of where fat is stored in the body can have significant implications for human health, according to a new study which compared fat cells from under the skin and from the harmful fat inside the abdomen, creating the first comprehensive genomic map that reveals unique features, which appear to 'hard-wire' different types of fat early in cell development.
Fat can be harmful or largely benign, depending on where in the body it is located. 'Subcutaneous' fat sits underneath the skin to store energy, and is generally harmless. Meanwhile, accumulation of 'visceral' fat, located in the abdomen, including around the liver, stomach and intestines, promotes inflammation and metabolic disturbances, and is associated with health complications such as type 2 diabetes and heart disease.
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The researchers isolated the fat-storing cells from visceral and subcutaneous fat biopsies from three individuals. The team compared the fat cells' epigenomes, the chemical tags attached to DNA that control how genes are read, and their transcriptomes, the genetic output of the cell.
By creating a comprehensive genomic map, the researchers discovered a number of fundamental epigenetic differences linked to changed genetic output, between the cells in subcutaneous and visceral fat. Further, the team discovered these differences arise early in cell development, and are likely present in the precursor cells from which fat cells arise. This finding indicates that despite the fat cells' similar appearance, fat cells become 'hard-wired' early to be harmful or non-harmful.
"When compared with other cell types in the body, visceral and subcutaneous fat cells are very similar to each other in their function," says lead author Dr Stephen Bradford. "Our analysis revealed epigenetic differences that may control different genes being turned on in subcutaneous and visceral fat cells that could contribute to their different properties and health effects."
"Our findings tell us that a cells' epigenome - the secondary code that controls how genes are read - can give us significant insight into how fat cells develop," says co-senior author Professor Susan Clark, Genomics Research Director at the Garvan Institute. "The study gives us a completely new look at the underlying factors that contribute to the development of cells that can present significant health risks."