A Fatty, Hairy Secret: How fat, hair, and sweat help heal wounds

A salamander has near superpower-like qualities, able to regenerate limbs and even new organs. (Source: Wikimedia Commons)

Ever noticed how starfish can grow new legs, sponges can split into two organisms, and salamanders can regenerate certain organs? Yet when humans develop a scar, the skin becomes hairless, discolored, and fragile. Although humans possess cognitive and physical advantages over much of the animal kingdom, an immotile organism living at the bottom of the ocean has superpower-like healing qualities that put humans to shame. However, soon humans may make up for these shortcomings with new research on wound healing.

When a small wound is formed, the tissue that replaces the wounded tissue is scar tissue, which is fundamentally different from normal tissue. It lacks hair, sweat glands, and fat. These traits of sweat and fat play fundamental roles in the function of normal skin. Sweat is most important in thermoregulation, keeping bodies at the right temperature for normal bodily function. Thus, people with many burn wounds can have problems with thermoregulation. A bit more surprising are the many roles that fat plays. Perhaps the most perceptible function of fat is the storage of energy. Fats derived from diet pass to fat-storing cells, which are called adipocytes. Fat also plays more unconventional roles in the body. Fat is responsible for maintaining face volume and a wrinkle-free, youthful appearance. Fat even acts in the immune system as part of the first line of defense against bacteria and other pathogens that can potentially invade the body.

It is clear that tissue without these properties would stunt the healing abilities of humans. However, at the center of certain larger wounds, the growth of tissue with hair and fat has been observed. This tissue in the center of the wound is composed of cells that can be molded to different functions. This is a phenomenon known as plasticity, a term often used to describe stem cells. The cells at the center of the wound respond to a signaling molecule called bone morphogenetic protein (BMP) released by nearby hair cells. High levels of BMP cause the plastic cells to form fat-storing adipocytes, which allows scars to heal and form normal skin.

This finding shifts conceptual understanding about possible treatments for wounds. Generally, wound healing aims at removing or killing the scar tissue. However, this research suggests that wound healing should aim to convert these cells to adipocytes, possibly through the use of signaling molecules like BMP. This new way of thinking could lead us to improved wound healing techniques, helping humans catch up to the healing powers of sponges, starfish, and salamanders.