Throughout history, hair has been an important factor in the self-image human beings have of themselves and of the image they present to others. For men a healthy head of hair connotes vigor and virility; for women it represents femininity and beauty. Conversely, the loss of hair can greatly alter those impressions.
Yet today there is increasing hope that the growth of human hair may soon be possible, thanks to some laboratory mice — and a number of researchers who believe in the magic of stem cells.
Dr. Cheng-Ming Chuong, professor of pathology at the Keck School of Medicine of USC, is the senior investigator of a study published by the Stem Cell Laboratory of the University of Southern California at Los Angeles. He and his team of researchers are discovering a means by which hair follicles can be grown from skin cells reproduced in vitro in the lab. The study was funded principally by the National Institutes of Health and published in the Proceedings of the National Academy of Sciences.
In it, researchers outline a step-by-step sequence of events in the production of hair follicles from skin. Specifically, they were able to generate hair by uncovering the major molecular events necessary for the growth of skin and fostering it in adult shaved mice.
"Many aging individuals do not grow hair well, because adult cells lose their regenerative ability. But with our new findings, we are able to make adult mouse cells produce hair again," says Dr. Chuong.
Researchers at the USC lab could not confirm exactly when human trials could begin but were optimistic their findings could inspire a method for treating humans with alopecia and baldness in the near future by using some of the patient's own stem cells to grow skin with hair follicles in a lab, then transplanting it onto balding areas of the scalp.
The science behind the study
Stem cells, by definition, are undifferentiated cells that can be transformed into specialized cells to produce more of their kind. In adults they are used to maintain the normal turnover of regenerative organs, such as blood, bone marrow and skin. Based on findings by scientists at the University of Toronto in the 1960s, stem cell research has increased greatly over the last 50 years.
According to Dr. Mingxing Lei, the first author of the USC study, he and his international team of scientists used progenitor cells, a cell type more differentiated from stem cells. They transplanted the cells into shaved mice and from there witnessed how the cells behaved and recording the hair development that followed.
The team noted that these cells formed skinlike "organoids," 3-D assemblies of cells that gathered themselves into an organlike structure, which in this case was the ability to grow hair. Further, they took hundreds of time-lapse movies to analyze the collective cell behavior.
Next, they observed how the cells combined themselves into polarized cysts, which then coalesced to form layered skin. From it they created skin with hair follicles that were transplanted onto the back of a host mouse. Finally, they observed as the follicles vigorously produced hair. "We used a combination of bioinformatics and molecular screenings" to facilitate their analyses, Dr. Lei explained.
Promising new remedies for hair growth
It is estimated there are between 100,000 to 150,000 hairs on human beings' heads. Of these, 40 to 100 hairs are lost each day, which are replaced by new ones grown from the hair follicles. The causes of hair loss, or alopecia, as it is medically known, are often genetic. But there are other causes, too. Among them are medications and treatments, such as chemotherapy, that altar the body's hormonal balance. Stress, injury to the scalp and physical stretching of the hair can also be factors.
By age 50, pattern baldness affects half the male population and a quarter of the women. Corrective treatments range from the "cure all" patent medicines sold from pitchmen's wagons to corticosteroids to surgery, in which small patches of skin containing hair follicles are removed from the back and sides of the head and transplanted to those areas where hair loss is apparent.
Concurrent with the research being done at USC, a variety of studies into the regeneration of human hair is under way. One is at the Yale University School of Medicine under the guidance of Dr. Valerie Horsley, associate professor of molecular, cellular and developmental biology, who expressed continuing interest in the research being done by Drs. Chuong and Lei. She is, she says, "excited by the work" being done at USC and looks forward to further results.
Another study has been led by Dr. Alexey Terskikh at the Sanford-Burnham Medical Research Institute in La Jolla, California, in which human pluripotent stem cells taken from human embryos and fetal tissue were engineered to become dermal papilla cells, governing the formation of hair follicles and the hair-growth cycle.
