Following damage, many organs regenerate and return to their original state. When regeneration fails, a fibrous scar tissue, often containing scattered fat cells (adipocytes), replaces the functional tissue and interferes with organ function. Preventing this process remains a challenge, and requires identification of the source of the fibrous tissue and characterization of the adult stem cells that are in charge of making the scar.

Dr Fabio Rossi’s team has started to solve the puzzle by identifying a new type of progenitor cell – fibro/adipogenic progenitor (FAP) – that is found in essentially all tissues. These cells are located in close association with blood vessels and they can generate both fibroblasts as well as adipocytes.

So are these progenitors “bad guys”? Not always! These cells are activated by damage even when regeneration proceeds normally and scar is not formed. In this context, these provide support through the production of trophic factors to the stem cells that are actually fixing the tissue. Any attempt to control fibrosis through drugs that block these cells will have to account for the fact that they can be useful too. Finally, the ability of these progenitors to generate new fat cells makes them attractive candidates for use in certain metabolic diseases. For example, when FAPs are transplanted into mice that lack fat and have type 2 diabetes, they generate new fat cells and reduce blood glucose, essentially curing the diabetes.

In conclusion this novel cell type plays a multitude of roles, some beneficial and some damaging, depending on the environment and the specific situation. Further research will hopefully allow one to modulate the function of these cells, thereby improving the response to injury and leading to better treatments for a number of diseases.

Get the whole story in Nature Cell Biotechnology 2010;12:153-163 DOI:10.1038/ncb2015