BRUSSELS, Belgium, September 3, 2012 – Skin researchers from the Universitй Libre de Bruxelles, Belgium have discovered a new stem cell population in skin that is responsible for tissue repair.
Our skin protects our bodies from the environment and its toxins, hard knocks, and extremes of temperature, pressure and so on. Consequently, the skin is subject to constant replacement and dead cells are sloughed off and replaced throughout our lifetimes.
However, the number of cells generated by the skin must exactly replace those that are lost. Different theories have been proposed to explain how this delicate balance is maintained.
In this new study, Prof. Cйdric Blanpain and his colleagues have collaborated with Prof. Benjamin Simons at the University of Cambridge, U.K. to show that a new population of stem cells in the skin give rise to a population of progenitor cells that are involved in the daily maintenance of the upper layers of the skin (epidermis). In fact, these stem cells are the major contributor during wound healing.
Blanpain and others used a novel genetic lineage tracing protocol to fluorescently mark two distinct skin cell populations, and follow their survival and contribution to the maintenance of the epidermis over time. These labeling experiments demonstrated the existence of two types of dividing cells. One cell population showed very long-term survival potential while the other population is progressively lost over time.
With Benjamin D. Simons, Blanpain and his lab devised a mathematical model of their lineage tracing analysis. The model suggested that skin, particularly the epidermis, contains a population of stem cells that divide very slowly that give rise to very fast dividing progenitor cells that ensure the daily maintenance of the skin epidermis. Cell proliferation patterns confirmed the existence of slow cycling stem cells. Furthermore, gene profiling experiments showed that the stem and the progenitor cells are characterized by distinct patterns of gene expression.
By assessing the contribution of these two cell populations during wound healing, they showed that only the skin stem cells were capable of extensive tissue regeneration and undergo major expansion during this repair process. The progenitors, on the other hand, did not expand significantly, but provided a short-lived contribution to the wound healing response.
These data resolve a long-standing debate regarding the cell populations that contribute to wound healing in the skin. Apparently, these epidermal stem cells are the main players during wound healing.
“It was amazing to see these long trails of cells coming from a single stem cell located at a very long distance from the wound to repair the epidermis,” said Dr. Blanpain, who was the senior author of the study.
Thus the slow-dividing stem cells promote tissue repair and more the more rapidly dividing progenitors ensure the daily maintenance of the epidermis.
Interestingly, similar populations of slow cycling stem cells that can be rapidly mobilized in case of sudden need have been observed in other tissues, such as the blood, muscle and hair follicle. The division between rapidly cycling progenitors and slow cycling stem cells seems to be relatively conserved across the different tissues.
Of course, these findings may have important implications in regenerative medicine; in particular for skin repair in severely burnt patients or in chronic wounds.