Fibroblast growth factor (FGF) signaling is involved in a wide range of crucial organical activities with differential actions in several cell types. The activity of FGF is modulated by glycosaminoglycans, found both in the extracellular matrix and on the cell surface.

These molecules are crucial in injury healing. Such a dynamic process is interactive and depends on an adequate regulation of fibroblasts.

Without regulation of these processes, excessive scar tissue develops. Because of impaired healing, keloids and hypertrophic scars often become a problem. These are both serious health conditions that affect people's quality of life, due to high treatment costs and frequent poor results.

A Fibroblast is a type of cell that promotes the production of keratinocytes and the creation of reticular and elastic fibers, and glycoproteins found in the extracellular matrix. The production of fibroblasts enhances the epidermal morphology.

Keratinocytes originate in the basal layer from the mitosis of keratinocyte stem cells. They are rushed through the cells of the epidermis, experiencing gradual specialization until they reach the stratum corneum where they form a layer of enucleated, flattened, highly keratinized cells named squamous cells. This layer forms an effective barrier to the entry of foreign matter and infectious agents in the body and reduces humidity loss.

The Healing Process and Keratinized Cells

Typically occurring during the process of scar removal keratinocytes are eliminated and restored continuously from the stratum corneum. The time of transit from the basal layer to the shedding stage is about one month, although this can be accelerated in conditions of keratinocyte hyperproliferation, such as psoriasis.

The simplest definition of a stem cell in an adult organism is any cell with a high capacity for self-renewal that extends throughout adult life. In addition, stem cells are usually considered to have the potential to originate differentiated progeny.

According to these criteria, the skin has long been recognized as possessing a resident stem cell population. The tissue is made of a stratified squamous epithelium (interfollicular epidermis; IFE) with associated hair follicles and glandular structures (the sebaceous glands and sweat glands).

The IFE undergoes continuous renovation and there is always a need to replace the devitalized, ultimately specialized cells of the outermost cornified layers through the production of cells in the basal layer.

It is now well known that stem cells inside the epidermis are multipotent and able to create daughter cells that specialize along several lineages. Stem cells inside the hair follicle bulge can produce progeny that specialize not only in all the hair follicle descendants, but also in sebocytes and the interfollicular epidermis.

After exposure to adequate mesenchymal signals, cells of the interfollicular epidermis are able of giving rise to hair or sebaceous descendants. There is, nevertheless, evidence for the existence of distinct stem cell populations inside the IFE and sebaceous gland. These findings can be reconciled by afirming that there are separate stem cell populations inside the hair, sebaceous gland and IFE.

Each of these can create daughters that differentiate along any of the epidermal lineages. In steady conditions, however, the stem cells normally originate a more selected repertoire in reaction to signals from the local microenvironment.