Fibroblast growth factor (FGF) signaling is part of a wide range of crucial biological activities with differential effects in several cell types. The activity of FGF is modulated by glycosaminoglycans, located both in the extracellular space 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.

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

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

Keratinocytes originate in the basal layer from the mitosis of keratinocyte stem cells. They are pushed up through the layers of the epidermis, experiencing gradual specialization until they join 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 moisture loss.

Keratinized Cells

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

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

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

The IFE undergoes continuous turnover and there is always a need to replace the dead, terminally differentiated cells of the external cornified layers through the proliferation of cells in the basal layer.

It is now well accepted that stem cells inside the epidermis are multipotent and capable of producing daughter cells that differentiate along several lineages. Stem cells within the hair follicle bulge can create progeny that differentiate not only in all the capillary follicle lineages, 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 lineages. There is, however, evidence for the presence of distinct stem cell groups inside the IFE and sebaceous gland. These findings can be reconciled by afirming that there are different stem cell populations inside 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 usually originate a more restricted repertoire in response to signals from the local microenvironment.