Fibroblast growth factor (FGF) signaling is involved in a wide range of important organical activities with differential effects in several cell types. The activity of FGF is modulated by glycosaminoglycans, located 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 an adequate regulation of fibroblasts.

With no control of these processes, excessive scar tissue develops. As a result of impaired healing, keloids and hypertrophic scars often become a problem. These are both difficult health conditions that affect people's quality of life, due to high treatment costs and often unsatisfactory results.

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

Keratinocytes originate in the basal layer from the mitosis of keratinocyte stem cells. They are rushed through the layers of the epidermis, experiencing gradual differentiation until they join the stratum corneum where they create a layer of enucleated, flattened, highly keratinized cells called squamous cells. This layer creates an efficient barrier to the entry of foreign matter and infectious agents in the body and minimizes moisture loss.

The Healing Process and Keratinized Cells

Typically occurring during the process of scar removal keratinocytes are shed and restored constantly from the stratum corneum. The time of transit from the basal layer to the elimination stage is approximately four weeks, although this can be sped up in conditions of keratinocyte hyperproliferation, like psoriasis.

The simplest definition of a stem cell in an adult organism is any cell with a high capacity for self-renewal that remains throughout adult life. In addition, stem cells are commonly 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 consists of a stratified squamous epithelium (interfollicular epidermis; IFE) with associated hair follicles and glandular structures (the sebaceous glands and sweat glands).

The IFE supports continuous turnover and there is a never failing need to replace the devitalized, terminally specialized cells of the external cornified layers through the proliferation of cells in the basal layer.

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

After exposure to adequate mesenchymal signals, cells of the interfollicular epidermis are capable of giving rise to hair or sebaceous lineages. There is, nevertheless, evidence for the presence of distinct stem cell populations within the IFE and sebaceous gland. These observations can be reconciled by afirming 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 skin lineages. In steady conditions, however, the stem cells normally give rise to a more selected repertoire in reaction to signals from the local microenvironment.