Fibroblast growth factor (FGF) signaling is involved in an extensive 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 critical in injury healing. Such a dynamic process is interactive and depends on the proper regulation of fibroblasts.

Without control of these processes, excessive scar tissue develops. Because of inefficient healing, keloids and hypertrophic scars often become a problem. These are both difficult health problems that affect people's quality of life, due to high treatment costs and frequent unsatisfactory results.

A Fibroblast is a type of cell that stimulates the proliferation of keratinocytes and the synthesis of glycosaminoglycans, and glycoproteins found in the extracellular matrix. The proliferation of fibroblasts improves the epidermal morphology.

Keratinocytes appear in the basal layer from the mitosis of keratinocyte stem cells. They are rushed through the cells of the epidermis, experiencing gradual differentiation until they reach the stratum corneum where they form a layer of enucleated, flattened, highly keratinized cells named squamous cells. This layer creates 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

During the natural process of scar removal keratinocytes are eliminated and replaced continuously from the stratum corneum. The time of transit from the basal layer to the shedding stage is about four weeks, although this can be accelerated in conditions of keratinocyte hyperproliferation, like psoriasis.

We can define a stem cell in an adult organism as 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 produce differentiated progeny.

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

The IFE undergoes constant renovation and there is always a need to replace the devitalized, terminally differentiated cells of the outermost cornified layers through the proliferation of cells in the basal layer.

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

Following exposure to adequate mesenchymal signals, cells of the interfollicular epidermis are able of originating hair or sebaceous descendants. There is, nevertheless, evidence for the presence of distinct stem cell populations within the IFE and sebaceous gland. These findings can be reconciled by verifying that there are different stem cell populations within the hair, sebaceous gland and IFE.

Each of these has the capacity to generate daughters that differentiate along any of the epidermal lineages. Under steady conditions, however, the stem cells normally originate a more selected repertoire in response to signals from the local microenvironment.