Hair Regrowth as a Pointer to the Role of Immune System Activity in Tissue Regeneration

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The immune system is known to play an important role in regeneration, but the details are still being uncovered. Nonetheless at some point in the near future manipulation of immune cells may prove to be a viable alternative path in regenerative medicine, a different way to achieve faster healing or spur tissue regrowth where it does not normally occur.

Cells from the immune system called macrophages - those in charge of devouring invading pathogens, for example - are also responsible for activating skin stem cells and induce hair growth. The researchers did not investigate the relationship between macrophages and hair for fun. This work emerged more than four years ago from an observation [made] while working on another research project. The mice [at] that time received anti-inflammatory drugs, a treatment that also reactivated hair growth. Convinced that the explanation could reside in the existence of close communication between stem cells and immune cells [the researchers] began to experiment with the different types of cells involved in the body's defense system.
After years of investigation, they discovered that when stem cells are dormant, a fraction of macrophages die, due to a process known as apoptosis. This stimulated the secretion of factors from dying and living macrophages, which in turn activated stem cells, and that is when hairs began to grow again. Macrophages secrete a number of factors including a class of proteins called Wnt. Researchers demonstrated the participation of macrophage-derived Wnts by artificially reproducing the natural process by treating macrophages with a Wnt inhibitor drug encapsulated in liposomes. As expected, when they used this drug, the activation of hair growth was delayed.

From a more fundamental perspective, this research is an effort to understand how modifying the environment that surrounds adult skin stem cells can regulate their regenerative capabilities. "One of the current challenges in the stem cell field is to regulate the activation of endogenous stem cell pools in adult tissues to promote regeneration without the need of transplantation."

Link: http://www.eurekalert.org/pub_releases/2014-12/cndi-cra121914.php