|Schematic of the layers of the skin and its associated|
structures. This study found that myofibroblasts near the
hair follicles are able to convert to fat cells.
The skin serves as a protective barrier against the environment. It is composed of three layers: the outermost, waterproof barrier called the epidermis; the middle dermis layer that contains many cell types that make up connective tissue, hair follicles, and sweat glands; and the deepest subcutaneous layer made up of fat and more connective tissue. When this barrier is broken, the body works quickly to repair itself by stopping bleeding, recruiting immune cells to help clean up and prevent infection, growing new cells, and remodeling of the tissue to return to its normal state. Oftentimes, this repair process results in scarring if the repair happens relatively slowly. In the type of healing in which a scar forms, there are no sweat glands, fat, nerves, or hair follicles. Obviously, this presents a huge concern for patients like burn victims that have a large injury resulting in scarring. By better understanding the process of scarring we will hopefully be able to find better ways to treat these patients.
A recent study published in Science was investigating the cell types involved in wound repair in mice. They happened to notice that new fat cells within wounds were being made near hair follicles surrounding the injury. These fat cells looked like normal fat cells and expressed fat-specific proteins. The scientists wanted to know if the hair follicles were necessary for making new fat cells. To test this, they grew cells from the dermal skin layer (made up of many different cells types) of wounds that contained hair follicles or from wounds that didn’t contain follicles. They found that only the cells from wounds that contained hair follicles became fat cells suggesting that the hair follicles were involved in converting these dermal cells into fat cells. They determined that the fat cells specifically came from a cell type called myofibroblasts that are normally present in the dermal skin layer, but only became fat cells if they were right next to hair follicles. When these fibroblasts were grown in culture with scalp hair follicles, they were able to be converted into fat cells. It turns out, these myofibroblasts near the hair follicles specifically turn on expression of proteins called bonemorphogenetic proteins, or BMPs. These proteins have numerous cellular signaling roles, but in this case they activate a specific protein known as ZFP423 which drives cells to become fat cells during development. When the researchers prevented either BMP or ZFP423 from being increased then the myofibroblasts were also prevented from turning into fat cells.
This study has several potential implications, although future studies are necessary to understand the mechanisms that govern the switch from wound myofibroblasts to fat cells. For example, why are the myofibroblasts that are closest to the hair follicles the ones that are converted into fat cells and how does the wound healing process influence the ability of these cells to convert from myofibroblasts to adipocytes? Nevertheless, these findings demonstrate that cells derived from one cell lineage (e.g. the dermis) can convert to another lineage (e.g. fat cells). With future studies, perhaps we can take advantage of this phenomenon to promote regeneration of tissue rather than scarring following an injury. Moreover, the authors suggest that perhaps one day we could treat patients with disorders involving a lack of fat (e.g. lipodystrophies, aging, etc) by converting myofibroblasts from these patients into fat cells.
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